研究者データベース

渡辺 豊(ワタナベ ユタカ)
地球環境科学研究院 地球圏科学部門 化学物質循環学分野
准教授

基本情報

所属

  • 地球環境科学研究院 地球圏科学部門 化学物質循環学分野

職名

  • 准教授

学位

  • 博士(水産学)(北海道大学)

J-Global ID

研究キーワード

  • 南大洋   地球環境化学   化学海洋学   地球化学   

研究分野

  • 環境・農学 / 環境動態解析

所属学協会

  • 日本分析化学会   第四紀学会   日本地球化学会   日本海洋学会   日本気象学会   American Geophysical Union   

研究活動情報

論文

  • Keiri Imai, Yutaka W. Watanabe
    JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY 2022年07月 
    We started monitoring the radiocesium released from Fukushima in the North Pacific surface water from May 2011 after the accident soon to June 2016, using the cruise of the Oshoro-maru of Hokkaido University. We found that the reducing rate from the ocean surface of Cs-137 regardless of the distance from Fukushima was almost constant at 0.0033 +/- 0.0005 day(-1). This finding indicated that 96% of Cs-137 in the surface water over the North Pacific were removed by 1000 days after the accident from the surface water to the ocean interior excluding the decrease by radioactive disintegration.
  • Ryosuke Futsuki, Toru Hirawake, Amane Fujiwara, Hisatomo Waga, Takashi Kikuchi, Shigeto Nishino, Tomonori Isada, Koji Suzuki, Yutaka W. Watanabe
    Journal of Oceanography 2022年06月08日 [査読有り]
  • Yusuke Uchiyama, Natsuki Tokunaga, Kohei Aduma, Yuki Kamidaira, Daisuke Tsumune, Toshiki Iwasaki, Masatoshi Yamada, Yutaka Tadeda, Takashi Ishimaru, Yukari Ito, Yutaka W Watanabe, Ken Ikehara, Miho Fukuda, Yuichi Onda
    The Science of the total environment 816 151573 - 151573 2022年04月10日 
    Accidental leakage of radionuclides from the Fukushima Nuclear Power Plant (FNPP1) took place in the aftermath of the catastrophic tsunamis associated with the Great East Japan Earthquake that occurred on March 11, 2011. Significant amount of radionuclides released into the atmosphere were reportedly transported and deposited on land located near FNPP1. The Niida River, Fukushima, Japan, has been recognized as a terrestrial source of highly contaminated suspended radiocesium adhering to sediment particles in the ocean through the river mouth as a result of hydrological processes. Remaining scientific questions include the oceanic dispersal and inventories of the sediments and suspended radiocesium in the ocean floor derived from the Niida River. Complementing limited in situ data, we developed a quadruple nested 3D ocean circulation and sediment transport model in an extremely high-resolution configuration to quantify the transport processes of the suspended radiocesium. Particularly, we investigated the storm and subsequent floods associated with Typhoon 201326 (Wipha) that passed off the Fukushima coast in October 2013, and subsequently promoted precipitation to a considerable extent and associated riverine freshwater discharge along with sediment outfluxes to the ocean. Using in situ bed sediment core data obtained from regions near the river mouth, we conducted a quantitative assessment of the accumulation and erosion of the sediments and explored the resultant suspended radiocesium distribution around the river mouth and nearshore areas along the Fukushima coast. We identified three major accumulative areas, near the river mouth within an area < 1 km, around the breakwaters in the north of the river mouth, and along the southern coastal area, while offshore and northward transports were minor. The present study clearly exhibits substantial retention of the land-derived radiocesium adsorbed to the sediments in the coastal areas, leading to possible long-term influences on the surrounding marine environment.
  • Xianliang L Pan, Bofeng F Li, Yutaka W Watanabe
    Scientific reports 12 1 383 - 383 2022年01月10日 
    With the accelerating mass loss of Antarctic ice sheets, the freshening of the Southern Ocean coastal oceans (SOc, seas around Antarctica) is gradually intensifying, which will reduce the formation of bottom water and weaken the meridional overturning circulation, thus having a significant negative impact on the ocean's role in regulating global climate. Due to the extreme environment of the Southern Ocean and the limitations of observational techniques, our understanding of the glacier-derived freshening of SOc is still vague. We developed a method that first provided us with an expansive understanding of glacier-derived freshening progress over the SOc. Applying this method to the observational data in the SOc from 1926 to 2016, revealed that the rate of glacier-derived freshwater input reached a maximum of 268 ± 134 Gt year-1 during the early twenty-first century. Our results indicate that during the same period, glacier melting accounted for 63%, 28%, and 92% of the total freshening occurred in the Atlantic, Indian, and Pacific sectors of the SOc, respectively. This suggests that the ice shelf basal melt in West Antarctica and the Antarctic Peninsula plays a dominant role in the freshening of the surrounding seas.
  • Hiroshi Ishida, Ryosuke S. Isono, Jun Kita, Yutaka W. Watanabe
    Scientific Reports 11 1 2021年12月 [査読有り]
     
    AbstractThis study examines long-term ocean pH data to evaluate ocean acidification (OA) trends at two coastal research institutions located on the Sea of Japan and the Pacific Ocean. These laboratories are located away from the influences of large rivers and major industrial activity. Measurements were performed daily for the past 30 years (1980s–2010s). The average annual ocean pH for both sites showed generally negative trends. These trends were – 0.0032 and – 0.0068 year–1 (p < 0.001) at the Sea of Japan and Pacific Ocean sites, respectively. The trends were superimposed onto approximately 10-year oscillations, which appear to synchronize with the ocean current periodicity. At the Sea of Japan site, the ocean pH in the summer was higher, and the rate of OA was higher than during other seasons. Our results suggest that seasonality and ocean currents influence OA in the coastal areas of open oceans and can affect the coastal regions of marginal seas.
  • Yutaka W. Watanabe, Yuto Nakano, Jun Nishioka, Masanori Ito
    Progress in Oceanography 102693 - 102693 2021年10月
  • Atsushi Kubo, Kai Tanabe, Yukari Ito, Takashi Ishimaru, Mayumi Otsuki, Hisayuki Arakawa, Yutaka W. Watanabe, Hikaru Miura, Daisuke Tsumune, Jota Kanda
    Marine Pollution Bulletin 161 Pt B 111769 - 111769 2020年12月 [査読有り]
     
    Sedimentary cesium-137 concentrations around the Fukushima Daiichi Nuclear Power Plant (FDNPP) were measured from 2011 to 2017 at eight stations. Although high values were observed until 2013, decreasing trends were observed at the surface sediments of seven stations. We isolated 25 radioactive Cs-bearing microparticles (CsMPs; 1.0-5385 Bq per particle). The contribution ratio of CsMPs to each sample ranged from 4.1% to 99.5% (median 58.8%), with the contribution ratio of the CsMPs in the southern part of the FDNPP was low compared to that from the northern part. In the southern part of the FDNPP, small CsMPs that could not be isolated in this study were present in large quantities immediately after the accident, and gradually diffused away and/or were dissolved over time. In contrast, the CsMPs in the northern part of the FDNPP have most likely accumulated over time, as suggested by the silty nature of the sediments there.
  • Xianliang L. Pan, Bofeng F. Li, Yutaka W. Watanabe
    Scientific Reports 10 1 2020年12月 [査読有り]
  • Coastal transport of sediments and suspended radiocesium in the Fukushima coast due to a typhoon-induced flood event
    Tokunaga N, Uchiyama Y, Tsumune D, Yamada M, Tateda Y, Ishimaru T, ItoY, Watanabe YW, Ikehara K, Fukuda M
    Journal of Japan Society of Civil Engineers Ser 75 667 - 672 2019年06月 [査読有り]
  • Li B. F, Watanabe Y. W, Hosoda S, Sato K, Nakano Y
    GEOPHYSICAL RESEARCH LETTERS 46 9 4836 - 4843 2019年05月16日 [査読有り][通常論文]
  • Watanabe YW, Li BF, Yamasaki R, Yunoki S, Imai K, Hosoda S, Nakano Y
    JOURNAL OF OCEANOGRAPHY 76 2 155 - 167 2019年 [査読有り][通常論文]
     
    We constructed parameterizations for the estimation of dissolved inorganic carbon (DIC) and pH in the western North Pacific, including Japanese coastal regions. Parameterizations, determined as a function of potential temperature (theta) and dissolved oxygen (DO), provided strong correlations with direct measurements for DIC [the coefficient of determination (R-2) = 0.99; the root mean square error (RMSE) = 8.49 mu mol kg(-1)] and pH (R-2 = 0.98, RMSE = 0.030). Predicted DIC and pH values were consistent with previous independent hydrographic observations, generally within 3 mu mol kg(-1) for DIC and 0.010 for pH. By applying these parameterizations to climatological seasonal theta and DO data and time-series theta and DO data from autonomous profiling floats (Argo) in the western North Pacific, large spatiotemporal variations in DIC and pH were demonstrated. Results indicated that the rate of increase in anthropogenic DIC above a depth of 400 m along 30 degrees N in the western North Pacific was + 0.86 +/- 0.11 mu mol kg(-1) year(-1) between 1994 and 2004. This decreased by + 0.58 +/- 0.05 mu mol kg(-1) year(-1) after 2004 partly due to increasing anthropogenic nitrogen input, suggesting that the decrease has induced the slowdown of ocean acidification in the western North Pacific. The declining trend in anthropogenically induced ocean pH was found to be 0.0021 +/- 0.0016 during 1994-2013.
  • Watanabe Y. W, Li B. F, Wakita M
    GEOPHYSICAL RESEARCH LETTERS 45 17 9106 - 9113 2018年09月16日 [査読有り][通常論文]
  • Atsushi Kubo, Kai Tanabe, Genta Suzuki, Yukari Ito, Takashi Ishimaru, Nobue Kasamatsu-Takasawa, Daisuke Tsumune, Takuji Mizuno, Yutaka W. Watanabe, Hisayuki Arakawa, Jota Kanda
    Marine Pollution Bulletin 131 341 - 346 2018年06月01日 [査読有り][通常論文]
     
    Radioactive cesium concentrations in the suspended matter of the coastal waters around the Fukushima Daiichi Nuclear Power Plant (FDNPP) were investigated between January 2014 and August 2015. The concentrations of radioactive cesium in the suspended matter were two orders higher in magnitude than those determined in the sediment. In addition, we discovered highly radioactive Cs particles in the suspended matter using autoradiography. The geometrical average radioactivity of particles was estimated to be 0.6 Bq at maximum and 0.2 Bq on average. The contribution ratio of highly radioactive Cs particles to each sample ranged from 13 to 54%, and was 36% on average. A major part of the radioactive Cs concentration in the suspended matter around the FDNPP was strongly influenced by the highly radioactive particles. The subsequent resuspension of highly radioactive Cs particles has been suggested as a possible reason for the delay in radioactive Cs depuration from benthic biota.
  • Motoyoshi Ikeda, Shinichi S. Tanaka, Yutaka W. Watanabe
    Journal of Oceanography 74 5 1 - 18 2018年04月17日 [査読有り][通常論文]
     
    Climatological water-mass structures were identified in the Arctic Ocean using the geochemical dataset in the Hydrochemical Atlas of the Arctic Ocean (HAAC) as well as data on a geochemically conserved parameter, PO4*, based on phosphate and dissolved oxygen. In the upper ocean above a depth of 500 m, the HAAC was found to reliably depict the boundary between Pacific-Origin Water (P-Water) and Atlantic-Origin Water (A-Water), which is aligned 135°E–45°W near the surface but rotates counterclockwise with depth. Thus, the Arctic and Atlantic oceans exchange high-silicate P-Water and low-silicate A-Water. The PO4* field in the lower ocean below a depth of 1500 m was analyzed statistically, and the results indicated that the Eurasian Basin receives low-PO4* Nordic Seas Deep Water, which flows along the bottom from the Greenland Sea. The routes from the upper ocean to the lower ocean were determined. Only the southern portion of the Canada Basin, which receives water from the Chukchi and Beaufort Seas, has high PO4* levels the rest of the Amerasian Basin receives low-PO4* water from the Laptev Sea and/or the Barents Sea. The Eurasian Basin receives moderate levels of PO4* from the Fram Strait and from the intermediate layer. The intermediate-layer water gradually travels up from the lower ocean and returns to the Atlantic, entraining the subsurface portion. It is likely that high-PO4* water occasionally flows down from the upper ocean along Greenland, making the Eurasian Basin heterogeneous.
  • Toru Hirawake, Shintaro Takao, Koji Suzuki, Jun Nishioka, Yutaka W. Watanabe, Tomonori Isada
    Oceanography in Japan 26 3 65 - 77 2017年05月15日
  • 平譯享, 髙尾信太郎, 鈴木光次, 西岡純, 渡邉豊, 伊佐田智規
    海の研究 26 3 65 - 77 2017年05月 [査読有り][通常論文]
  • Bofeng Li, Yutaka W. Watanabe, Azusa Yamaguchi
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 121 5 3435 - 3449 2016年05月 [査読有り][通常論文]
     
    We provided parameterizations to speculate changes in the vertical distributions of the seawater total alkalinity (TA), dissolved inorganic carbon (DIC), and pH by using all available observations of dissolved oxygen (DO, mmol kg(-1)), water temperature (T, degrees C), and salinity (S) data from previous high quality data sets of ocean hydrographic properties. All data sets were collected in the North Pacific subpolar region during the period of 2000-2010, for 40-400 m depth, and between 40 degrees N and 56 degrees N, 145 degrees E and 130 degrees W). Root mean square errors for the parameterizations with 7.4 mmol kg(-1) for TA, 7.1 mmol kg(-1) for DIC, and 0.02 for pH were obtained with R-2 of more than 0.95. To evaluate the validity of these parameterizations, we compared measured TA, DIC, and pH with predicted values. The differences were almost within 10 mmol kg(-1) for TA and DIC, and 0.05 for pH. Applying our parameterizations to the climatological data sets of DO, T, and S data from World Ocean Atlas 2009, we reconstructed seasonal and monthly vertical distributions of seawater TA, DIC, and pH. Furthermore, by substituting our parameterizations into detailed vertical distributions of DO, T, and S data measured bi-weekly by automatic ocean hydrographic sensors from Argo profiling floats, we described the detailed vertical spatiotemporal distributions of seawater TA, DIC, and pH. In the North Pacific subpolar region, in the case that there is no time-series of ocean carbon species, our parameterizations allowed us to elucidate the dynamics of ocean carbon chemistry from two-week scale to decadal scale.
  • Masanori Ito, Yutaka W. Watanabe, Masahito Shigemitsu, Shinichi S. Tanaka, Jun Nishioka
    JOURNAL OF OCEANOGRAPHY 70 5 415 - 424 2014年10月 [査読有り][通常論文]
     
    To estimate benthic denitrification in a marginal sea, we assessed the usefulness of , a new tracer to measure the excess nitrogen gas (N-2) using dissolved N-2 and argon (Ar) with N* in the intermediate layer (26.6-27.4 sigma (theta) ) of the Okhotsk Sea. The examined parameters capable of affecting are denitrification, air injection and rapid cooling. We investigated the relative proportions of these effects on using multiple linear regression analysis. The best model included two examined parameters of denitrification and air injection based on the Akaike information criterion as a measure of the model fit to data. More than 80 % of was derived from the denitrification, followed by air injection. Denitrification over the Okhotsk Sea shelf region was estimated to be 5.6 +/- A 2.4 mu mol kg(-1). The distribution of was correlated with potential temperature (theta) between 26.6 and 27.4 sigma (theta) (r = -0.55). Therefore, we concluded that and N* can act complementarily as a quasi-conservative tracer of benthic denitrification in the Okhotsk Sea. Our findings suggest that in combination with N* is a useful chemical tracer to estimate benthic denitrification in a marginal sea.
  • Watanabe, Y.W, M. Shigemitsu, T. Ujiie, H. Minami
    Geophysical Research Letters 41 513 - 518 2014年 [査読有り][通常論文]
  • Yutaka W. Watanabe, Masahito Shigemitsu, Takashi Ujiie, Hideki Minami
    GEOPHYSICAL RESEARCH LETTERS 41 2 513 - 518 2014年01月 [査読有り][通常論文]
     
    Time series of biogenic sinking particle flux in the western North Pacific subpolar region over two decades (1989-2008) revealed that the biogenic CaCO3 (CC) flux has shown a significant decreasing trend of 2.7%year(-1) (annual average, -0.880.13mgm(2)day(-1)year(-1)) along with the decreasing particulate organic carbon (POC) flux of 0.7%year(-1), while the biogenic opal (OP) flux had no long-term trend. Comparing these results with the decreasing rate of satellite-derived surface CC with -0.7%year(-1), we concluded that three fourths of the decreasing trend of CC flux was derived from the strengthening of CaCO3 dissolution through seawater column due to the weakening of water ventilation and the rest was from the decline of CaCO3-shelled species, indicating the enhancement of the efficiency in oceanic sequestration of atmospheric CO2 in the sea surface of this region due to the increase of OP/CC ratio. Key Points <list list-type="bulleted" id="grl51305-list-0001"> <list-item id="grl51305-li-0001">CaCO3 and organic carbon sinking fluxes had decreasing trends
  • Masahito Shigemitsu, J. Nishioka, Y. W. Watanabe, Y. Yamanaka, T. Nakatsuka, Y. N. Volkov
    MARINE CHEMISTRY 157 41 - 48 2013年12月 [査読有り][通常論文]
     
    We have found that the ratio of Fe to Al in suspended particulate matter (SPM) in the intermediate layer Of the Okhotsk Sea increases to the open ocean from the dense shelf water on the northwestern continental shelf, which is the source of southward-flowing Okhotsk Sea Intermediate Water (OSIW). The SPM concentration and the Al content of the SPM decrease along the course of the OSIW, whereas the ratios of Ba and Mn to Al increase. The SPM samples on the continental shelf were collected in waters characterized by low N* (the deviation from the stoichiometric relationship between nitrogenous nutrients and phosphate). These low N* values imply that sedimentary denitrification occurs on the continental shelf, and both Fe and Mn are concomitantly reduced in the sediments and diffuse from the sediments to the overlying waters, where they are subsequently oxidized and precipitate. We assume that the SPM in the intermediate layer is influenced mainly by horizontal transport from the continental shelf to the ocean interior and that Ba can be used as a proxy for organic matter. Based on these assumptions, the reults could reflect the following processes: 1) a gradual loss of denser lithogenic matter, evidenced by the decreases of the SPM concentration and of the Al content of the SPM, and 2) a relative increase of the Fe and Mn fractions associated with the organic matter in the SPM, which is derived from the continental shelf. The organic matter-related Fe and Mn could also be affected by the precipitation of both Fe and Mn just above the reduced sediments of the continental shelf. Our results show that the particulate Fe associated with organic matter is preferentially transported from the northwestern continental shelf to the open ocean. (C) 2013 Elsevier B.V. All rights reserved.
  • Yutaka W. Watanabe
    BUNSEKI KAGAKU 62 12 1049 - 1056 2013年12月 [査読有り][通常論文]
     
    In order to describe the spatiotemporal dynamics of ocean biogeochemical cycles in detail, discrete chemical data based on shipboard observations cannot allow us to achieve our goal. By parameterizing biogeochemical parameters based on previous high-precision chemical data set, and applying the observation data derived from satellite and ocean profiling float, it is possible to reconstruct sophisticated pictures of the ocean biogeochemical cycle. With the introduction of some examples for parameterizing ocean carbonate system, the parameterization for the ocean nitrogen system was reported.
  • Jun Nishioka, Takeshi Nakatsuka, Yutaka W. Watanabe, Ichiro Yasuda, Kenshi Kuma, Hiroshi Ogawa, Naoto Ebuchi, Alexey Scherbinin, Yuri N. Volkov, Takayuki Shiraiwa, Masaaki Wakatsuchi
    GLOBAL BIOGEOCHEMICAL CYCLES 27 3 920 - 929 2013年09月 [査読有り][通常論文]
     
    The subarctic Pacific is a high-nutrient low-chlorophyll (HNLC) region in which phytoplankton growth is broadly limited by iron (Fe) availability. However, even with Fe limitation, the western subarctic Pacific (WSP) has significant phytoplankton growth and greater seasonal variability in lower trophic levels than the eastern subarctic Pacific. Therefore, differences in Fe supply must explain the west-to-east decrease in seasonal phytoplankton growth. The Fe flux to the euphotic zone in the WSP occurs at a moderate value, in that it is significantly higher than its value on the eastern side, yet it is not sufficient enough to cause widespread macronutrient depletion, that is, HNLC status is maintained. Although we recognize several Fe supply processes in the WSP, the mechanisms that account for this moderate value of Fe supply have not previously been explained. Here we demonstrate the pivotal role of tidal mixing in the Kuril Islands chain (KIC) for determining the moderate value. A basin-scale meridional Fe section shows that Fe derived from sediments in the Sea of Okhotsk is discharged through the KIC into the intermediate water masses (similar to 800m) of the western North Pacific. The redistribution of this Fe-rich intermediate water by intensive mixing as it crosses the KIC is the predominant process determining the ratio of micronutrient (Fe) to macronutrients (e.g., nitrate) in subsurface waters. This ratio can quantitatively explain the differences in surface macronutrient consumption between the western and eastern subarctic, as well as the general formation and biogeochemistry of HNLC waters of the subarctic North Pacific.
  • Shinichi S. Tanaka, Yutaka W. Watanabe, Tsuneo Ono, Takafumi Aramaki
    MARINE CHEMISTRY 149 85 - 95 2013年02月 [査読有り][通常論文]
     
    Spatial high-resolution estimates of biogenic oxygen were obtained by measuring the concentration of dissolved oxygen, nitrogen and argon during the spring phytoplankton bloom at 21 observation points in the western North Pacific in the area of the Oyashio and Kuroshio Currents off the coast of Hokkaido-Tohoku, Japan. This area extends over approximately 600 km. The test region was divided into 6 mesoscale-vide groups (approximately 20-150 km wide) of observation stations based on variation in the temperature and salinity of the seawater. As suggested by an analysis of the hydrographic data, the area of which water temperature was lower than around the area was found in the Oyashio-Kuroshio mixing area. In the area, vertical water mixing between the warm mixed layer and cold sub-mixed layer occurred. The biogenic oxygen also varied horizontally at mesoscale intervals. The variation was caused by vertical mixing, because the water masses of the mixed layer and sub-mixed layer had positive and negative biogenic oxygen values, respectively. A spatial high-resolution method for estimating the spatial high-resolution net oxygen production rates (NOP) within the mixed layer using a time-stepped model with biogenic oxygen and the physical data was proposed. The estimated NOP varied widely, even within the same water mass group, and ranged from -23.6 +/- 6.0 to 252.7 +/- 68.2 mmol/m(2)/day. Therefore, spatial high-resolution NOP estimates are imperative to analyze biological production in areas with complex water mass structures. (C) 2013 Elsevier B.V. All rights reserved.
  • Yutaka W. Watanabe, Jun Nishioka, Takeshi Nakatsuka
    GEOPHYSICAL RESEARCH LETTERS 40 2 322 - 326 2013年01月 [査読有り][通常論文]
     
    Comparing the data sets of chemical transient tracers (trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), sulfur hexafluoride (SF6)) among three reobservations from 1993 to 2006 in the Okhotsk Sea, we found the remarkable change in the efficiency of oceanic absorption of anthropogenic carbon (EF) based on the observed change of apparent tracer age. EF above 27.0 sigma(theta) increased by 16 % while EF below 27.0 sigma(theta) declined by 27 % during the period from 1993 to 2006. Consequently, EF in the entire water column decreased by 14 %. We concluded that the recent reinforcement of ocean stratification derived from the ocean warming caused the weakening of water ventilation in this region, indicating that the penetration of atmospheric anthropogenic carbon to the deep ocean interior is becoming difficult. Citation: Watanabe, Y. W., J. Nishioka, and T. Nakatsuka (2013), Decadal time evolution of oceanic uptake of anthropogenic carbon in the Okhotsk Sea, Geophys. Res. Lett., 40, 322-326, doi:10.1002/grl.50113.
  • Yutaka W. Watanabe, Takeshi Chiba, Takayuki Tanaka
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 116 2011年02月 [査読有り][通常論文]
     
    Applying the delta C-13 approach to time series of observations in the North Pacific subpolar region (Station KNOT; 44 degrees 00'N, 155 degrees 00'E), we demonstrated time series of vertical distributions of oceanic anthropogenic carbon. We found that the vertical distributions of oceanic anthropogenic carbon during 1999-2006 were almost consistent with those estimated by the other carbon-based quasi-conservative tracer approach (Delta C*). Comparing the oceanic anthropogenic carbon contents and the water-column inventories among 1999, 2000, and 2006, we found the recent oceanic uptake rate of anthropogenic carbon above 27.3 sigma(theta) to be 0.86 +/- 0.12 mu mol kg(-1) yr(-1), which was 1.2 times higher than the expected value derived from oceanic equilibration with increasing atmospheric CO2. Considering the strengthened ocean stratification with a bidecadal oscillation and the recent increase in alkalinity from the Sea of Okhotsk, it was possible to explain the difference in the recent oceanic uptake rate of anthropogenic carbon between our result and the expected one.
  • Takeshi Yoshimura, Jun Nishioka, Koji Suzuki, Hiroshi Hattori, Hiroshi Kiyosawa, Yutaka W. Watanabe
    JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 395 1-2 191 - 198 2010年11月 [査読有り][通常論文]
     
    Increasing CO2 in seawater (i.e. ocean acidification) may have various and potentially adverse effects on phytoplankton dynamics and hence the organic carbon dynamics. We conducted a CO2 manipulation experiment in the Sea of Okhotsk in summer 2006 to investigate the response of the organic carbon dynamics. During the 14-day incubation of nutrient depleted and 200 mu atm in situ pCO(2) surface water with a natural plankton assemblage under 150, 280, 480, and 590 mu atm pCO(2), the amount of net dissolved organic carbon accumulation was significantly lower at >480 mu atm pCO(2) than at 150 mu atm pCO(2), while differences in net particulate organic carbon accumulation between the treatments were small and did not show a clear relationship with the pCO(2). This is the first report to show a decreased net organic carbon production of natural plankton community under elevated pCO(2). Phytoplankton pigment analysis suggests that the relative contribution of fucoxanthin-containing phytoplankton such as diatoms to the phytoplankton biomass was lower at >280 mu atm pCO(2) than at 150 mu atm pCO(2). Different pCO(2) conditions may alter the organic carbon dynamics through changes in plankton processes. We conclude that the continuing increase in atmospheric CO2 in a time scale from the last half century to the end of this century has potential to affect the carbon cycle in nutrient depleted subpolar surface waters. (C) 2010 Elsevier B.V. All rights reserved.
  • Masahito Shigemitsu, Yutaka W. Watanabe, Yasuhiro Yamanaka, Hajime Kawakami, Makio C. Honda
    JOURNAL OF OCEANOGRAPHY 66 5 697 - 708 2010年10月 [査読有り][通常論文]
     
    We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO3, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant mineral in sinking particles, to develop four simple models for settling particles, including the "ballast model". The ballast model is based on the concept that most of the organic matter "rain" in the deep sea is carried by the minerals. These four models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity and reduce the degree of decomposition.
  • Daisuke Tsumune, Jun Nishioka, Akifumi Shimamoto, Yutaka W. Watanabe, Takafumi Aramaki, Yukihiro Nojiri, Shigenobu Takeda, Atsushi Tsuda, Takaki Tsubono
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 26 2948 - 2957 2009年12月 [査読有り][通常論文]
     
    Sulfur hexafluoride (SF(6)) tracer release experiments were carried out to trace the iron-fertilized water mass during the iron-fertilization experiments in the western North Pacific of Subarctic Pacific iron Experiment for Ecosystem Dynamics Study II (SEEDS II) in 2004. A solution of Fe and SF(6) tracer was released into the surface mixed layer over an 8 x 8 km area, and the fertilized patch was traced by onboard SF(6) analysis for 12 days during each experiment. A Lagrangian frame of reference was maintained by the use of a drogued GPS buoy released at the center of the patch to reduce the advection effect on observations. The patch moved along the contour of sea-surface height (SSH) of a clockwise mesoscale eddy for 4 days after release. Then strong easterly winds dragged the patch across the contour of SSH. The patch behavior was affected by both the mesoscale eddy and surface winds. Apparent horizontal diffusivities were determined by the change of the distribution of SF(6) concentrations. The averaged apparent horizontal diffusivity was about 49 m(2) s(-1) during SEEDS II. It was larger than the one in SEEDS. Mixed-layer depth (MLD) was 8.5-18 m during SEEDS, and 12-33 In during SEEDS II. The larger horizontal diffusivity and deeper MLD in SEEDS II were disadvantages to maintain a high iron concentration in the surface layer compared to SEEDS. Temporal change of the MLD corresponded to the temporal change of chlorophyll-a concentration. Temporal change in the surface MLD was also important for the response of phytoplankton by iron fertilization. (C) 2009 Elsevier Ltd. All rights reserved.
  • Yoshimura T., Nishioka J., Suzuki K., Hattori H., Kiyosawa H., Watanabe Y. W.
    Biogeosciences Discussions 6 2 4143 - 4163 Copernicus Publications 2009年04月15日 
    Impacts of the increasing CO2 in seawater (i.e. ocean acidification) on phytoplankton physiology may have various and potentially adverse effects on phytoplankton dynamics and the carbon cycle. We conducted a CO2 manipulation experiment in the Sea of Okhotsk in summer 2006 to investigate the response of the phytoplankton assemblage and dynamics of organic carbon. During the 14-day incubation of nutrient-depleted surface water with a natural phytoplankton assemblage under 150, 280, 480, and 590μatm pCO2, the relative abundance of fucoxanthin-containing phytoplankton such as diatoms and prymnesiophytes decreased with increasing pCO2. The amount of DOC accumulation also decreased with increasing pCO2, while differences in POC accumulation between the treatments were small and did not show a clear trend with the pCO2. Change in the phytoplankton community composition under different pCO2 conditions will alter the organic carbon dynamics as found in the present experiment. Compared to results in the literature from nutrient-replete conditions indicating a potential enhancement of phytoplankton production with elevated pCO2, the present results indicated a different physiological response of phytoplankton under nutrient-depleted conditions. These results indicate that the continuing increase in atmospheric CO2 can significantly affect the structure of marine ecosystems and carbon cycle in nutrient-depleted subpolar surface waters.
  • Masahito Shigemitsu, Yutaka W. Watanabe, Hisashi Narita
    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 9 2008年10月 [査読有り][通常論文]
     
    We present delta(15)N data of organic nitrogen (delta(15)N(ON)) from a deep western subarctic Pacific (WSAP) sediment core over the last 145 ka. To remove the effect of inorganic nitrogen (IN) on bulk nitrogen (BN), we used the contents of IN and BN, and the isotopic ratios of IN (delta(15)N(IN)) and BN (delta(15)N(BN)). The contribution of IN to BN was largest 59% and delta(15)N(IN) had lower values than delta(15)N(BN). However, the large contributions of IN to BN and the distinct isotopic values did not largely change any variability associated with d15 NON in the delta(15)N(BN). Thus, it is possible to use delta(15)N(BN) in carrying out paleoceanographic research with delta(15)N at least in the open WSAP. The d15 NON values have been affected by long-term diagenesis making the values lower with depth in the sediment, but the values during less productive colder periods were generally lower compared to those during neighboring productive warmer periods. The results might indicate that d15 NON during the less productive colder periods (i.e., glacial periods) were lower than that during the productive warmer periods (i.e., interglacial periods). Previous studies have reported that the biological production in WSAP, where it is limited by iron at present, during glacial periods was at more reduced level than during interglacials despite there being more eolian dust supply during glacial periods. This indicates that the increase of biological production with enhanced iron supply derived from eolian dust during the glacial periods did not occur. If this is the case and alternatively the iron input from the subsurface layer to the surface-mixed layer by ventilation process is more important as suggested by recent works, the variations in delta(15)N(ON) would be explained by the variations in the Fe/NO(3)(-) ratio in the upwelled water. Although delta(15)N(ON) has been affected by long-term diagenesis in the sediment, the usage
  • Ai Sakamoto, Yutaka W. Watanabe, Masato Osawa, Kazuo Kido, Shinichiro Noriki
    ESTUARINE COASTAL AND SHELF SCIENCE 79 3 377 - 386 2008年09月 [査読有り][通常論文]
     
    We report several biogeochemical parameters (dissolved inorganic carbon (DIC), total alkalinity (TA), dissolved oxygen (DO), phosphate (PO(4)), nitrate + nitrite (NO(3) + NO(2)), silicate (Si(OH)(4))) in a region off Otaru coast in Hokkaido, Japan on a "weekly" basis during the period of April 2002-May 2003. To better understand the long-term temporal variations of the main factors affecting CO(2) flux in this coastal region and its role as a sink/source of atmospheric CO(2), we constructed an algorithm of DIC and TA using other hydrographic properties. We estimated the CO(2) flux across the air-sea interface by using the classical bulk method. During 1998-2003 in our study region, the estimated fCO(2sea) ranged about 185-335 mu atm. The maximum Of fCO(2sea) in the summer was primarily due to the change of water temperature. The minimum of fCO(2sea) in the early spring can be explained not only by the change of water temperature but also the change of nutrients and chlorophyll-a. To clarify the factors affecting fCO(2sea) (water temperature, salinity, and biological activity), we carried out a sensitivity analysis of these effects on the variation of fCO(2sea). In spring, the biological effect had the largest effect for the minimum of fCO(2sea) (40%). In summer, the water temperature effect had the largest effect for the maximum of fCO(2sea) (25%). In fall, the water temperature effect had the largest effect for the minimum of fCO(2sea) (53%). In winter, the biological effect had the largest effect for the minimum of fCO(2sea) (35%). We found that our study region was a sink region Of CO(2) throughout a year (-0.78 mol/m(2)/yr). Furthermore, we estimated that the increase of fCO(2sea) was about 0.56 mu atm/yr under equilibrium with the atmospheric CO(2) content for the period 1998-2003, with the temporal changes in the variables (T, S, PO(4)) on fCO(2sea), thus as the maximum trend of each variable on fCO(2sea) was 0.22 mu atm/yr, and the trend of residual fCO(2) including gas exchange was 0.34 mu atm/yr. This result suggests that interaction among variables would affect gas exchange between air and sea effects on fCO(2sea). We conclude that this study region as a representative coastal region of marginal seas of the North Pacific is special because it was measured, but there is no particular significance in comparison to any other area. (C) 2008 Elsevier Ltd. All rights reserved.
  • Yutaka W. Watanabe, Masahito Shigemitsu, Kazuaki Tadokoro
    GEOPHYSICAL RESEARCH LETTERS 35 1 2008年01月 [査読有り][通常論文]
     
    Using four pentadecadal hydrographic time series of biogeochemical properties over the North Pacific subpolar region, we found that the linear trends of these properties over this region due to sea surface stratification. Decadal periodicity of 18 years was also found although there were the opposite phases between the eastern and western sides. Despite decreasing trends of DO with an increase of PO(4), N* in the subsurface water showed an increasing trend of 0.18 mu mol kg(-1) y(-1). N* in the surface water had also an increase of 0.12 mu mol kg(-1) y(-1) with a decrease of Si/N. With considering the decease of N/P and increase of Si/N in diatoms under iron-deficient conditions, this finding is evidence that a shift of phytoplankton has already occurred due to the progress in stratification with the depletion of iron derived from deep water, despite being a relatively high primary production region.
  • T Ono, H Kasai, T Midorikawa, Y Takatani, K Saito, M Ishii, YW Watanabe, K Sasaki
    JOURNAL OF OCEANOGRAPHY 61 6 1075 - 1087 2005年12月 [査読有り][通常論文]
     
    Eight-year observation results of DIC from 1996 to 2003 in the Oyashio region have been analyzed to obtain a climatological view of its seasonal variation and interannual variation. Data of DIC obtained by several institutes are synthesized to give a dataset with an uncertainty lower than 5 mu mol/kg. The obtained climatology of NDIC seasonal variation in the Oyashio mixed layer shows a seasonal amplitude of 176 mu mol/kg, with a maximum in January and a minimum in September. These features closely resemble those observed in the southern half of the western subarctic North Pacific (WSNP) including Station KNOT, although the timing of the NDIC maximum is slightly advanced in the case of the Oyashio. Analysis using a quasi-conservative tracer Cp0 (NDIC - 106NP) shows that among 176 mu mol/kg of NDIC seasonal variation, only 16 mu mol/kg is attributed to hydrographic processes while the remaining 160 mu mol/kg is attributed to biological processes. The Cp0 value in the Oyashio mixed layer also resembles that of the WSNP mixed layer during the months May to November, suggesting further resemblance of the Oyashio water mass to that of WSNP in terms of carbon dynamics. The present results also suggest that a single data obtained in Oyashio mixed layer contains 30 mu mol/kg of potential uncertainty for the representativity of this region, which leads to a note about a need to treat with caution results obtained by a single observation in this region.
  • M Wakita, S Watanabe, YW Watanabe, T Ono, N Tsurushima, S Tsunogai
    JOURNAL OF OCEANOGRAPHY 61 1 129 - 139 2005年02月 [査読有り][通常論文]
     
    The dissolved inorganic carbon (DIC) and related chemical species have been measured from 1992 to 2001 at Station KNOT (44degreesN, 155degreesE) in the western North Pacific subpolar region. DIC (1.3similar to2.3 mumol/kg/yr) and apparent oxygen utilization (AOU, 0.7similar to1.8 mumol/kg/yr) have increased while total alkalinity remained constant in the intermediate water (26.9similar to27.3sigma(theta)). The increases of DIC in the upper intermediate water (26.9similar to27.1sigma(theta)) were higher than those in the lower one (27.2similar to27.3sigma(theta)). The temporal change of DIC would be controlled by the increase of anthropogenic CO2, the decomposition of organic matter and the non-anthropogenic CO2 absorbed at the region of intermediate water formation. We estimated the increase of anthropogenic CO, to be only 0.5similar to0.7,mumol/kg/yr under equilibrium with the atmospheric CO2 content. The effect of decomposition was estimated to be 0.8 +/- 0.7 mumol/kg/yr from AOU increase. The remainder of non-anthropogenic CO, had increased by 0.6 +/- 1.1 mumol/kg/yr. We suggest that the non-anthropogenic CO2 increase is controlled by the accumulation of CO2 liberated back to atmosphere at the region of intermediate water formation due to the decrease of difference between DIC in the winter mixed layer and DIC under equilibrium with the atmospheric CO2 content, and the reduction of diapycnal vertical water exchange between mixed layer and pycnocline waters. In future, more accurate and longer time series data will be required to confirm our results.
  • CL Sabine, RA Feely, YW Watanabe, M Lamb
    JOURNAL OF OCEANOGRAPHY 60 1 5 - 15 2004年02月 [査読有り][通常論文]
     
    The recent changes in the North Pacific uptake rate of carbon have been estimated using a number of different techniques over the past decade. Recently, there has been a marked increase in the number of estimates being submitted for publication. Most of these estimates can be grouped into one of five basic techniques: carbon time-series, non-carbon tracers, carbon tracers, empirical relationships, and inverse calculations. Examples of each of these techniques as they have been applied in the North Pacific are given and the estimates summarized. The results are divided into three categories: integrated water column uptake rate estimates, mixed layer increases, and surface pCO(2) increases. Most of the published values fall under the water column integrated uptake rate category. All of the estimates varied by region and depth range of integration, but generally showed consistent patterns of increased uptake from the tropics to the subtropics. The most disagreement between the methods was in the sub-arctic Pacific. Column integrated uptake rates ranged from 0.25 to 1.3 mol m(-2) yr(-1). The mixed layer uptake estimates were much more consistent, with values of 1.0-1.3 mumol kg(-1) yr(-1) based on direct observations and multiple linear regression approaches. Surface pCO(2) changes showed the most obvious regional variability (0.5-2.5 muatm yr(-1)) reflecting the sensitivity of these measurements to differences in the physical and biological forcing. The different techniques used to evaluate the changes in North Pacific carbon distributions do not completely agree on the exact magnitude or spatial and temporal patterns of carbon uptake rate. Additional research is necessary to resolve these issues and better constrain the role of the North Pacific in the global carbon cycle.
  • S Montani, H Obata, T Ono, YW Watanabe, M Yamamoto
    JOURNAL OF OCEANOGRAPHY 59 5 647 - 650 2003年10月 [査読有り][通常論文]
  • YF Xu, YW Watanabe, S Aoki, K Harada
    MARINE CHEMISTRY 72 2-4 221 - 238 2000年12月 [査読有り][通常論文]
     
    There is a large uncertainty of how much anthropogenic CO2 has been and will be taken up by the ocean. The North Pacific is normally considered a small sink of anthropogenic CO2. Recently, some researchers have proposed that the North Pacific may take up more anthropogenic CO2 than thought previously. Here we explore this issue with a basin-wide OGCM of the North Pacific. The sensitivities of ocean circulation and the redistribution of dissolved anthropogenic CO2 in the North Pacific to the values of some mixing parameters are examined. The increase of isopycnal diffusivity generally leads to improvement of distributions of water masses. Larger isopycnal diffusivity produces larger CO2 uptake in the subpolar region but smaller CO2 uptake in the tropical region. Increasing thickness diffusivity reduces CO2 uptake in both the subpolar and subtropical regions, and also reduces the inventory of CO2 in the western subtropical region. Both smaller isopycnal and thickness diffusivities result in a large net transport of CO2 from the North Pacific to the South Pacific. Simulated results show that the North Pacific has taken up about 23 GtC of excess carbon dioxide released by human activities between 1800 and 1997. The averaged uptake rate in the North Pacific during 1990-1997 is 0.40 GtC/year. Our model estimates the largest air-sea fluxes along the western boundary around 42 degreesN, 150 degreesE and in the equatorial Pacific. Our simulated inventories slightly overestimate data-based estimates in the eastern North Pacific, but exhibit less penetration of anthropogenic carbon dioxide in the western North Pacific. (C) 2000 Elsevier Science B.V. All rights reserved.
  • T Ono, YW Watanabe, S Watanabe
    MARINE CHEMISTRY 72 2-4 317 - 328 2000年12月 [査読有り][通常論文]
     
    The temporal variation of the total dissolved inorganic carbon (DIC) content in the western North Pacific is investigated by comparing the DIC distribution obtained from the data sets of three different periods, the GEOSECS data observed in 1973, the CO2 dynamics Cruise data observed in 1982, and recent Japanese data sets observed during the early 1990s. The overall feature of the signal of temporal DIC change during 1973 and early 1990s agreed with that of former studies, and did not significantly change with the calculation scheme (the grid-selection method vs, the multiple regression method). The observed increase in DIC among the different time scales showed a good inner consistency, which also indicates the stability of the method used in the DIC change calculation. The apparent rate of increase of the DIC inventory in the upper 1000 m water column, however, differed significantly by the data set used for the calculation: It was 5.6 +/- 2.4 g C/m(2)/year, based on the data comparison between 1982 and the early 1990s, while it became 7.6 +/- 2.4 g C/m(2)/year when based on the data between 1973 and the early 1990s. This result provides us an information about the data-dependency on the former estimation of temporal DIC change. (C) 2000 Elsevier Science B.V. All rights reserved.
  • YW Watanabe, T Ono, A Shimamoto
    MARINE CHEMISTRY 72 2-4 297 - 315 2000年12月 [査読有り][通常論文]
     
    We propose an approach to estimate the rate of increase of oceanic anthropogenic carbon inventory with CFC11 dating technique. This approach relies on the elapsed time from when the water lost contact with atmosphere as determined by CFC age. Furthermore, the assumption is made that it remains constant over a decadal time scale. Finally, we consider only the increase in anthropogenic carbon from one decade to another and not the entire change from the pre-industrial period to the present. The advantages and disadvantages of our approach are discussed. Using this approach, the spatial distributions of the rate of increase of the anthropogenic carbon inventory and the uptake rate of anthropogenic carbon in the North Pacific were obtained. The western North Pacific subtropical region exhibited a maximum in the rate of increase of the anthropogenic carbon inventory of more than 8 g C m(-2) year(-1) during 1988-1998, which was equivalent to 34% of the total uptake rate in the entire North Pacific. The net total uptake rate of anthropogenic carbon in the whole North Pacific increased with time and was 0.55 +/- 0.09 Pg C year(-1) during 1988-1998 indicating that the North Pacific absorbs 24% of the whole oceanic uptake of anthropogenic carbon. (C) 2000 Elsevier Science B.V. All rights reserved.
  • Y Takahashi, E Matsumoto, YW Watanabe
    MARINE CHEMISTRY 69 3-4 237 - 251 2000年04月 [査読有り][通常論文]
     
    We measured the quantity of delta(13)C in total dissolved inorganic carbon in seawater collected between 48 degrees N and 15 degrees S along 175 degrees E in the central North Pacific during the Northwest Pacific Carbon Cycle Study program (NOPACCS) in 1993 and 1994, focusing on the distribution of delta(13)C on isopycnal surfaces of 25.6, 26.0, 26.4, 26.8 and 27.2 sigma(theta) in the main pycnocline of the North Pacific. The distribution of delta(13)C was controlled largely by biological cycling. Using apparent oxygen utilization as a measure of biological effects on delta(13)C variation, we calculated preformed values of delta(13)C at the time when the water left the surface. The preformed delta(13)C showed a trend of increasing southward in the subtropical region on all the surfaces. Variations in preformed delta(13)C On the surfaces between 25.6 and 26.4 sigma(theta) in the subtropical region most likely reflect the penetration of C-13-depleted anthropogenic CO2, because there was no other effect acting on the preformed delta(13)C. We applied another approach, using dissolved phosphate, to correct for biological effects on delta(13)C distribution. The results of both methods allowed us to determine the changes in delta(13)C due to the penetration of anthropogenic CO2. (C) 2000 Elsevier Science B.V. All rights reserved.
  • T. Ono, Y. W. Watanabe, K. Sasaki
    Journal of Oceanography 56 6 675 - 689 2000年 [査読有り][通常論文]
     
    Vertical distribution of anthropogenic carbon content of the water (exDIC) in the Oyashio area just outside of the Kuroshio/Oyashio Interfrontal Zone (K/O Zone) was estimated by the simple 1-D advection-diffusion model calibrated by the distribution of chlorofluorocarbons (CFCs). The average concentration of exDIC for σθ = 26.60-27.00 is multiplied by the volume transport of Oyashio water into the North Pacific Intermediate Water (NPIW) to estimate the annual transport of exDIC into NPIW through K/O Zone. The estimated transport of exDIC was 0.018-0.020 GtC/y, which corresponds to 15% of the whole total exDIC accumulation in the temperate North Pacific. A simple assessment using the NPIW 1-box model indicates that the current study explains at least 70% of the total annual transport of exDIC into NPIW, and that small exDIC sources for NPIW still exists in addition to K/O Zone.
  • YW Watanabe, A Ishida, M Tamaki, K Okuda, M Fukasawa
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 44 7 1091 - 1104 1997年07月 [査読有り][通常論文]
     
    A cross-section of chlorofluorocarbons (CFCs) in the North Pacific was obtained along 30 degrees N in 1994. Distributions of water column inventories of CFCs in the North Pacific were estimated by interpolating observed concentrations of CFCs to all the North Pacific based on salinity and water temperature. Total amounts of CFC-11 and CFC-12 in the North Pacific were estimated to be 7.92+/-1.17 (x 10(7) moles) and 4.55+/-0.73 (x 10(7) moles), respectively. By introducing the CFCs data into a four-box model for the North Pacific, relations between an exchange coefficient of CFC and a production rate of intermediate water in the North Pacific were estimated. The production rate of intermediate water was calculated to be 24+/-4 Sv by assuming the exchange coefficient of CFC to be large enough due to the surface concentration of CFC to be saturated rapidly. (C) 1997 Elsevier Science Ltd.
  • Yutaka W. Watanabe, Yoshiyuki Takahashi, Takashi Kitao, Koh Harada
    Journal of Oceanography 52 3 301 - 312 1996年05月
  • YW WATANABE, K HARADA, K ISHIKAWA
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 99 C12 25195 - 25213 1994年12月 [査読有り][通常論文]
     
    From August to October 1992, cross sections of chlorofluorocarbons (CFCs) trichlorofluoromethane (CFC-11) and dichlorofluoromethane (CFC-12) were obtained between 48 degrees N and 15 degrees S along 175 degrees E in the central North Pacific. On the basis of the distribution of CFCs, apparent ages of the North Pacific Intermediate Water (NPIW) along 175 degrees E were determined for the isopycnal horizons of 26.40 to 27.40 sigma(theta). The apparent age of NPIW was usually older toward the south and with increase of sigma(theta) along the section. The oldest NPIW on all isopycnal horizons in the North Pacific was located near 10 degrees N. North of 20 degrees N, NPIW on isopycnal horizons less than 26.80 sigma(theta) outcrops in winter in subpolar regions and appears to have formed after 1970. It is suggested that NPIW on isopycnal horizons less than 26.80 sigma(theta) is laterally well mixed between subpolar and subtropical regions on timescales of a few decades. NPIW on isopycnal horizons greater than 26.80 sigma(theta) near 37 degrees N was older than its surrounding. It is suggested that new NPIW formed in the subpolar region is not transported directly southward and that the major current of NPIW is zonal in the central North Pacific, flowing eastward in the subpolar region and then turning more to the south, flowing toward 10 degrees N near the eastern boundary. Thus we also estimated the zonal mean apparent ages of NPIW. The mean ages of NPIW suggested that the apparent southward spreading rates and the apparent southward spreading times of NPIW from the subpolar region to 10 degrees N were approximately 80-170 km yr(-1) and 20-45 years, respectively. It is concluded that the southward spreading time of NPIW is a few decades at most.
  • YW WATANABE, S WATANABE, S TSUNOGAI
    MARINE CHEMISTRY 34 1-2 97 - 108 1991年09月 [査読有り][通常論文]
     
    In 1987 in the Japan Sea, the mean concentration of tritium below 200 m depth was 1.2 T.U. (Tritium Unit = 10(18) times of the molar fraction of tritium in ordinary hydrogen (T/H x 10(18)), which was one third of that in the surface water from 0 to 200 m depth (3.6 T.U.). Tritium was even found near a depth of 2000 m at two stations; 0.5 and 0.9 T.U., values which were outside the analytical error (+/- 0.3 T.U.). These results indicate that vertical mixing is more rapid in the Japan Sea than in the Pacific Ocean where the concentration of tritium decreases steeply with depth and is less than the detection limit for water below 1000 m depth. By introducing these data and the previously obtained Ra-226 data into a three-box model, the turnover time of the Japan Sea deep water and the residence time of the water within the Japan Sea were calculated to be about 100 years and 1000 years, respectively. The exchange coefficient of CO2 at the air-sea interface was also estimated to be 1.4-3.3 m day-1 by coupling these data with the C-14 data in the three-box model. This value which is smaller than the world mean value is probably due to the fact that the region producing the Japan Sea deep water of the northern Japan Sea near the Siberian coast has rather low windspeeds.

その他活動・業績

  • 西岡純, 安田一郎, 小野数也, 中村知裕, 鈴木光次, 渡辺豊, 山下洋平, 平譯享, LIU Hongbin, 藤尾伸三, 柳本大吾, 田中雄大, 原田尚美, 関宰, 岡崎裕典, 長尾誠也, 井上睦夫, 小畑元, 田副博文, 小川浩史, 宗林留美, 三寺史夫, 江淵直人, 若土正暁, VOLKOV Y.N 日本海洋学会大会講演要旨集 2016 107 2016年08月 [査読無し][通常論文]
  • 平譯享, 夫津木亮介, 新明克人, 藤原周, 伊佐田智規, 高尾信太郎, 鈴木光次, 渡邉豊, 野坂裕一 日本海洋学会大会講演要旨集 2016 120 2016年03月 [査読無し][通常論文]
  • 伊佐田智規, 平譯享, 葛西広海, 小埜恒夫, 渡邉豊, 鈴木光次, 齊藤誠一 水産海洋学会研究発表大会講演要旨集 2011 28 2011年 [査読無し][通常論文]
  • Yutaka W. Watanabe, Takeshi Chiba, Takayuki Tanaka Journal of Geophysical Research: Oceans 116 (2) C02006, doi:10.1029/2010JC006199 2011年 [査読無し][通常論文]
     
    Applying the δ13C approach to time series of observations in the North Pacific subpolar region (Station KNOT 44°00′N, 155°00′E), we demonstrated time series of vertical distributions of oceanic anthropogenic carbon. We found that the vertical distributions of oceanic anthropogenic carbon during 1999-2006 were almost consistent with those estimated by the other carbon-based quasi-conservative tracer approach (ΔC*). Comparing the oceanic anthropogenic carbon contents and the water-column inventories among 1999, 2000, and 2006, we found the recent oceanic uptake rate of anthropogenic carbon above 27.3 σθ to be 0.86 ± 0.12 μmol kg-1 yr-1, which was 1.2 times higher than the expected value derived from oceanic equilibration with increasing atmospheric CO2. Considering the strengthened ocean stratification with a bidecadal oscillation and the recent increase in alkalinity from the Sea of Okhotsk, it was possible to explain the difference in the recent oceanic uptake rate of anthropogenic carbon between our result and the expected one. Copyright 2011 by the American Geophysical Union.
  • Sachiko Oguma, Tsuneo Ono, Yutaka W. Watanabe, Hiromi Kasai, Shuichi Watanabe, Daiki Nomura, Humio Mitsudera ESTUARINE COASTAL AND SHELF SCIENCE 91 (1) 24 -32 2011年01月 [査読無し][通常論文]
     
    In this study, we examined the relationship between the low salinity water in the shelf region of the southern Okhotsk Sea which was seasonally sampled (0-200 m), and fluxes of low salinity water from Aniva Bay. To express the source of freshwater mixing in the surface layer, we applied normalized total alkalinity (NTA) and stable isotopes of seawater as chemical tracers. NTA-S diagrams indicate that NTA of low salinity water in the upper 30 m layer just off the Soya Warm Current is clearly higher than in the far offshore region in summer and autumn. Using NTA-S regression lines, we could deduce that the low salinity and high NTA water in the upper layer originates from Aniva Bay. For convenience, we defined this water as the Aniva Surface Water (ASW) with values S < 32, NTA > 2450 umol kg(-1). Formation and transport processes of ASW are discussed using historical data. The interaction between the maximum core of high NTA water on the bottom slope of eastern Aniva Bay and an anticyclonic eddy at the mouth of Aniva Bay are concluded to control ASW formation. Upwelling of the Cold Water Belt water at the tip of Cape Krillion is considered to cause ASW outflow from Aniva Bay. (C) 2010 Elsevier Ltd. All rights reserved.
  • Takeshi Yoshimura, Jun Nishioka, Koji Suzuki, Hiroshi Hattori, Hiroshi Kiyosawa, Yutaka W. Watanabe JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 395 (1-2) 191 -198 2010年11月 [査読無し][通常論文]
     
    Increasing CO2 in seawater (i.e. ocean acidification) may have various and potentially adverse effects on phytoplankton dynamics and hence the organic carbon dynamics. We conducted a CO2 manipulation experiment in the Sea of Okhotsk in summer 2006 to investigate the response of the organic carbon dynamics. During the 14-day incubation of nutrient depleted and 200 mu atm in situ pCO(2) surface water with a natural plankton assemblage under 150, 280, 480, and 590 mu atm pCO(2), the amount of net dissolved organic carbon accumulation was significantly lower at >480 mu atm pCO(2) than at 150 mu atm pCO(2), while differences in net particulate organic carbon accumulation between the treatments were small and did not show a clear relationship with the pCO(2). This is the first report to show a decreased net organic carbon production of natural plankton community under elevated pCO(2). Phytoplankton pigment analysis suggests that the relative contribution of fucoxanthin-containing phytoplankton such as diatoms to the phytoplankton biomass was lower at >280 mu atm pCO(2) than at 150 mu atm pCO(2). Different pCO(2) conditions may alter the organic carbon dynamics through changes in plankton processes. We conclude that the continuing increase in atmospheric CO2 in a time scale from the last half century to the end of this century has potential to affect the carbon cycle in nutrient depleted subpolar surface waters. (C) 2010 Elsevier B.V. All rights reserved.
  • Masahito Shigemitsu, Yasuhiro Yamanaka, Yutaka W. Watanabe, Nobuhiro Maeda, Shinichiro Noriki EARTH AND PLANETARY SCIENCE LETTERS 293 (1-2) 180 -190 2010年04月 [査読無し][通常論文]
     
    We used moored time-series sediment traps to collect settling particles at station KNOT (44 degrees N, 155 degrees E; trap depth 770 m) in the western subarctic Pacific (WSAP) from October 1999 to May 2006. Particulate nitrogen content (PN) and isotope ratios (delta(15)N(PN)) were measured in the samples collected. The general pattern of variation in delta(15)N(PN) results showed lower values during the spring bloom periods and summer, and higher values during winter. To interpret the processes controlling such variations quantitatively and reveal some implications for paleoceanographic use of delta(15)N(PN), we developed an ecosystem model that included nitrogen isotopes. This model was validated with an observed data set and successfully reproduced the seasonal variations of delta(15)N(PN). In simulations, the lower delta(15)N(PN) during the spring bloom period was caused mainly by the highest proportion of dead large phytoplankton (diatom) in PN within a year. the highest f-ratio of the year, and phytoplankton assimilation of nitrate with the lowest delta(15)N of the year. The lower delta(15)N(PN) in summer was due to the high relative proportion of dead non-diatom small phytoplankton and microzooplankton fecal pellet with the lowest delta(15)N values among all the PN components in our model. The higher delta(15)N(PN) in winter was mainly caused by the highest proportion of zooplankton components in PN, with higher delta(15)N values than phytoplankton components, and the enhanced delta(15)N values of ammonium induced by nitrification and its subsequent assimilation by phytoplankton. Our identification of nitrification as one cause of higher delta(15)N(PN) in winter is consistent with previous findings in a proximal marginal sea, the Okhotsk Sea, with an ecosystem model simpler than our model. This might indicate that the cause of higher delta(15)N(PN) in winter is common in the WSAP. In our model, we optimized the isotope effect of each process using our observational data of delta(15)N(PN) and delta(15)N of nitrate published elsewhere as constraints, and investigated the sensitivity of the annual flux-weighted mean of delta(15)N(PN) to the isotopic fractionation effects. As a result, we found that the isotope effects of nitrate assimilation appear to be different for non-diatom small phytoplankton and large diatom, and the annual flux-weighted mean of delta(15)N(PN) can be influenced to some extent by the isotope effect of nitrification. (C) 2010 Elsevier B.V. All rights reserved.
  • Masahito Shigemitsu, Yutaka W. Watanabe, Yasuhiro Yamanaka, Hajime Kawakami, Makio C. Honda Journal of Oceanography 66 (5) 697 -708 2010年 [査読無し][通常論文]
     
    We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO3, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant mineral in sinking particles, to develop four simple models for settling particles, including the "ballast model". The ballast model is based on the concept that most of the organic matter "rain" in the deep sea is carried by the minerals. These four models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity and reduce the degree of decomposition. © 2010 Springer Science+Business Media B.V.
  • Daisuke Tsumune, Jun Nishioka, Akifumi Shimamoto, Yutaka W. Watanabe, Takafumi Aramaki, Yukihiro Nojiri, Shigenobu Takeda, Atsushi Tsuda, Takaki Tsubono DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 (26) 2948 -2957 2009年12月 [査読無し][通常論文]
     
    Sulfur hexafluoride (SF(6)) tracer release experiments were carried out to trace the iron-fertilized water mass during the iron-fertilization experiments in the western North Pacific of Subarctic Pacific iron Experiment for Ecosystem Dynamics Study II (SEEDS II) in 2004. A solution of Fe and SF(6) tracer was released into the surface mixed layer over an 8 x 8 km area, and the fertilized patch was traced by onboard SF(6) analysis for 12 days during each experiment. A Lagrangian frame of reference was maintained by the use of a drogued GPS buoy released at the center of the patch to reduce the advection effect on observations. The patch moved along the contour of sea-surface height (SSH) of a clockwise mesoscale eddy for 4 days after release. Then strong easterly winds dragged the patch across the contour of SSH. The patch behavior was affected by both the mesoscale eddy and surface winds. Apparent horizontal diffusivities were determined by the change of the distribution of SF(6) concentrations. The averaged apparent horizontal diffusivity was about 49 m(2) s(-1) during SEEDS II. It was larger than the one in SEEDS. Mixed-layer depth (MLD) was 8.5-18 m during SEEDS, and 12-33 In during SEEDS II. The larger horizontal diffusivity and deeper MLD in SEEDS II were disadvantages to maintain a high iron concentration in the surface layer compared to SEEDS. Temporal change of the MLD corresponded to the temporal change of chlorophyll-a concentration. Temporal change in the surface MLD was also important for the response of phytoplankton by iron fertilization. (C) 2009 Elsevier Ltd. All rights reserved.
  • Y. W. Watanabe, J. Nishioka, M. Shigemitsu, A. Mimura, T. Nakatsuka GEOPHYSICAL RESEARCH LETTERS 36 (15) L15604 2009年08月 [査読無し][通常論文]
     
    Comparing data set of carbonate species and other hydrographic chemical properties in 1999, 2000 and 2006 in the Okhotsk Sea, we found that salinity-normalized alkalinity in the subsurface water has shown a rate of increase by 2.6 +/- 0.1 mu mol kg(-1) y(-1) while the increase in salinity-normalized dissolved inorganic carbon corrected by AOU was almost half of that in alkalinity. Therefore, pH has increased by 0.013 +/- 0.001 pH unit y(-1) in the subsurface water (26.5 - 27.3 sigma(theta)) which is the origin of the North Pacific intermediate water. This increase in pH could be explained by the increase in alkalinity in the Amur River in the last decade, suggesting a possibility that could mitigate one-fifth of recent ocean acidification in the North Pacific. Citation: Watanabe, Y. W., J. Nishioka, M. Shigemitsu, A. Mimura, and T. Nakatsuka (2009), Influence of riverine alkalinity on carbonate species in the Okhotsk Sea, Geophys. Res. Lett., 36, L15606, doi: 10.1029/2009GL038520.
  • Masahito Shigemitsu, Yutaka W. Watanabe, Hisashi Narita JOURNAL OF OCEANOGRAPHY 65 (4) 541 -548 2009年08月 [査読無し][通常論文]
     
    We have measured inorganic nitrogen (IN) content and the isotope ratio of IN (delta(15)N(IN)) in a sediment core covering the last 145 kyr in the western subarctic Pacific (WSAP). IN content was generally high during glacial periods and shows positive correlations with both eolian dust content and the ratio of organic carbon (C) to organic nitrogen (ON) (C/ON) found in our previous studies. This means that IN was transported from continental areas to the WSAP together with eolian dust and that the IN was not contaminated by volcanic materials, because the eolian dust content was reconstructed using metal components to remove contaminating volcanic materials. Therefore, IN content in the WSAP sediments, the clay fraction of which is not greatly affected by drift deposits seen at the other sites in this region, may potentially be an effective proxy for eolian dust, without the need to consider contamination by volcanic materials. delta(15)N(IN) was generally low during glacial periods and shows negative correlations with IN, eolian dust, and C/ON. The possible causes of the observed variations in delta(15)N(IN) are as follows: (1) authigenic fixation of NH(4)(+) in water-column and pore water of sea-floor sediments to clav minerals; (2) contamination of measured IN by highly resistant organic matter; or (3) variations in the continental source region of the eolian dust supplied to the WSAP and climatically induced changes in delta(15)N of soil organic matter there. The last mechanism shows the potential for delta(15)N(IN) to be used as a proxy for climate change on land, and is consistent with other published explanations of the spatial distribution of delta(15)N(IN) in modern sea-floor sediments.
  • Hiroshi Ishida, Yutaka W. Watanabe, Joji Ishizaka, Toshiya Nakano, Naoki Nagai, Yuji Watanabe, Akifumi Shimamoto, Nobuhiro Maeda, Michimasa Magi JOURNAL OF OCEANOGRAPHY 65 (2) 179 -186 2009年04月 [査読無し][通常論文]
     
    Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a (Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season, as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4 and 2.3% year(-1) in the subtropical area along 137A degrees E (STA(137)) during 1972 to 1997 and in the Kuroshio Extension area along 175A degrees E (KEA(175)) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year(-1) in STA(137) and KEA(175); and (3) decreasing linear trend of larger-size Chl-a (> 3 A mu m) by 0.1 and 2.5% year(-1) in STA(137) and KEA(175), respectively. Water density (sigma (theta) ) at 75 m depth had also decreased by 0.006 and 0.05 year(-1) in STA(137) and KEA(175), respectively. The ratio of biogenic opal to biogenic CaCO(3) in the sinking flux decreased by 0.015 year(-1) in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density of surface water caused by warming in the western North Pacific, especially in the summer.
  • 重光雅仁, 山中康裕, 山中康裕, 山中康裕, 渡辺豊, 岡田直資, 前田亘宏, 乗木新一郎 日本地球化学会年会講演要旨集 56th 353 -337 2009年 [査読無し][通常論文]
     
    西部北太平洋亜寒帯域に位置するStn.KNOT(北緯44度、東経155度)の水深770mに、1999/10/25~2001/6/20及び2002/6/25~2006/5/11の期間にわたってセジメントトラップを設置し、沈降粒子を採取した。セジメントトラップサンプル中に含まれる粒子状有機炭素含量およびその同位体比(δ13C)を測定した。δ13Cの結果は、春季ブルーム時に低くなり、秋季に高くなるという一般的な変動を示した。この変動要因を定量的に調べるため、δ13C計算を組み込んだ生態系モデル(North pacific Ecosystem Model Used for Regional Oceanography)を用いて解析を行った。その結果について報告する。
  • Identifying crucial issues in climate science: drastic change in the earth system during global warmin
    EOS Transactions 90 15 2009年 [査読無し][通常論文]
  • BENTLEY C.D, CARROLL P.M, WATANABE W.O, RIEDEL A.M Journal of the World Aquaculture Society 39 (5) 625 -635 2008年10月 [査読無し][通常論文]
     
    A study was conducted to test the performance of a high-density (> 3000 individuals/mL) continuous recirculating system for rotifers (B. rotundiformis) fed nonviable Nannochloropsis oculata and using sodium hydroxymethanesulfonate to neutralize ammonia. Three different microalgae feed rates (g of N. oculata [68 X 10(9) cells/mL] per million rotifers/d) were tested in successive trials. In Trial 1 (feed rate = 1.5), during a 30-d period, rotifers were harvested daily to 3000 individuals/mL, for an average yield of 178 million/d. Feed efficiency (million rotifers/g/d) was 0.33. In Trial 2 (feed rate = 1.1), during a 32-d period, an average of 106 million rotifers were harvested daily, and feed efficiency was 0.26. In Trial 3 (feed rate = 1.3), during a 30-d period, an average of 107 million rotifers was harvested daily, and feed efficiency was 0.23. An economic analysis based on a feed rate of 1.5 showed that production cost was 40% lower than the traditional batch culture method (US$ 0.29 vs. 0.46 per million rotifers/d). The continuous culture system tested reliably produced large quantities of rotifers on a daily basis without the use of a biofilter and with a lower production cost than a batch culture system.
  • Masahito Shigemitsu, Yutaka W. Watanabe, Hisashi Narita Geochemistry, Geophysics, Geosystems 9 Q10012 2008年10月 [査読無し][通常論文]
     
    We present delta(15)N data of organic nitrogen (delta(15)N(ON)) from a deep western subarctic Pacific (WSAP) sediment core over the last 145 ka. To remove the effect of inorganic nitrogen (IN) on bulk nitrogen (BN), we used the contents of IN and BN, and the isotopic ratios of IN (delta(15)N(IN)) and BN (delta(15)N(BN)). The contribution of IN to BN was largest 59% and delta(15)N(IN) had lower values than delta(15)N(BN). However, the large contributions of IN to BN and the distinct isotopic values did not largely change any variability associated with d15 NON in the delta(15)N(BN). Thus, it is possible to use delta(15)N(BN) in carrying out paleoceanographic research with delta(15)N at least in the open WSAP. The d15 NON values have been affected by long-term diagenesis making the values lower with depth in the sediment, but the values during less productive colder periods were generally lower compared to those during neighboring productive warmer periods. The results might indicate that d15 NON during the less productive colder periods (i.e., glacial periods) were lower than that during the productive warmer periods (i.e., interglacial periods). Previous studies have reported that the biological production in WSAP, where it is limited by iron at present, during glacial periods was at more reduced level than during interglacials despite there being more eolian dust supply during glacial periods. This indicates that the increase of biological production with enhanced iron supply derived from eolian dust during the glacial periods did not occur. If this is the case and alternatively the iron input from the subsurface layer to the surface-mixed layer by ventilation process is more important as suggested by recent works, the variations in delta(15)N(ON) would be explained by the variations in the Fe/NO(3)(-) ratio in the upwelled water. Although delta(15)N(ON) has been affected by long-term diagenesis in the sediment, the usage
  • Yutaka W. Watanabe, Masahito Shigemitsu, Kazuaki Tadokoro GEOPHYSICAL RESEARCH LETTERS 35 (1) L01602, doi:10.1029/2007GL032188 2008年01月 [査読無し][通常論文]
     
    Using four pentadecadal hydrographic time series of biogeochemical properties over the North Pacific subpolar region, we found that the linear trends of these properties over this region due to sea surface stratification. Decadal periodicity of 18 years was also found although there were the opposite phases between the eastern and western sides. Despite decreasing trends of DO with an increase of PO(4), N* in the subsurface water showed an increasing trend of 0.18 mu mol kg(-1) y(-1). N* in the surface water had also an increase of 0.12 mu mol kg(-1) y(-1) with a decrease of Si/N. With considering the decease of N/P and increase of Si/N in diatoms under iron-deficient conditions, this finding is evidence that a shift of phytoplankton has already occurred due to the progress in stratification with the depletion of iron derived from deep water, despite being a relatively high primary production region.
  • Atsushi Tsuda, Shigenobu Takeda, Hiroaki Saito, Jun Nishioka, Isao Kudo, Yukihiro Nojiri, Koji Suzuki, Mitsuo Uematsu, Mark L. Wells, Daisuke Tsumune, Takeshi Yoshimura, Tatsuo Aono, Takafumi Aramaki, William P. Cochlan, Maki Hayakawa, Keiri Imai, Tomoshi Isada, Yoko Iwamoto, William K. Johnson, Sohiko Kameyama, Shungo Kato, Hiroshi Kiyosawa, Yoshiko Kondo, Maurice Levasseur, Ryuji J. Machida, Ippei Nagao, Fumiko Nakagawa, Takahiro Nakanish, Seiji Nakatsuka, Akira Narita, Yoshifumi Noiri, Hajime Obata, Hiroshi Ogawa, Kenji Oguma, Tsuneo Ono, Tomofumi Sakuragi, Motoki Sasakawa, Mitsuhide Sato, Akifumi Shimamoto, Hyoe Takata, Charles G. Trick, Yutaka W. Watanabe, Chi Shing Wong, Naoki Yoshie JOURNAL OF OCEANOGRAPHY 63 (6) 983 -994 2007年12月 [査読無し][通常論文]
     
    mesoscale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in the summer of 2004. The iron patch was traced for 26 days, which included observations of the development and the decline of the bloom by mapping with sulfur hexafluoride. The experiment was conducted at almost the same location and the same season as SEEDS (previous iron-enrichment experiment). However, the results were very different between SEEDS and SEEDS II. A high accumulation of phytoplankton biomass (similar to 18 mg chl m(-3)) was characteristic of SEEDS. In contrast, in SEEDS II, the surface chlorophyll-a accumulation was lower, 0.8 to 2.48 mg m(-3), with no prominent diatom bloom. Photosynthetic competence in terms of F-v/F-m for the total phytoplankton community in the surface waters increased after the iron enrichments and returned to the ambient level by day 20. These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron enrichments and returned to an iron-stressed condition during the declining phase of the bloom. Pico-phytoplankton (< 2 mu m) became dominant in the chlorophyll-a size distribution after the bloom. We observed a nitrate drawdown of 3.8 mu M in the patch (day 21), but there was no difference in silicic acid concentration between inside and outside the patch. Mesozooplankton (copepod) biomass was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS. The copepod biomass increased exponentially. The grazing rate estimation indicates that the copepod grazing prevented the formation of an extensive diatom bloom, which was observed in SEEDS, and led to the change to a pico-phytoplankton dominated community towards the end of the experiment.
  • Shinichi S. Tanaka, Yutaka W. Watanabe MARINE CHEMISTRY 106 (3-4) 516 -529 2007年08月 [査読無し][通常論文]
     
    An improved gas chromatographic system was constructed to analyze oceanic dissolved N-2, Ar and O-2 with a higher accuracy and shorter analytical time. To obtain a higher accuracy of N-2, Ar and O-2 measurements, the following was added to the system: (I) an air trapping system: (II) a N-2-CO2 trapping system after the operation of the air trapping system; (III) an active carbon column system for separating N-2 and CO2 completely and (IV) the introduction of automatic valves controlling most of the system. Compared to previous studies, the precision of the measurements of N-2, Ar and O-2 concentrations was higher at 0.04%, 0.05% and 0.02%, respectively, and our analytical time was shorter at 600 s. Using the improved analytical technique, concentrations of N-2 (C-N2, 561.69-611.81 mu mol/kg) and Ar (C-Ar, 15.126-16.238 mu mol/kg), saturation states of N-2 (Delta N-2, - 5.1-0.9%) and Ar (Delta Ar, - 7.0 to - 1.1%) from 0 in to 3 000 in depth in the western North Pacific were observed during March 2005. Based on these data, we propose a new concept for estimating the amount of bubble injection (B). The total error in calculating B was estimated to be about 20%. We estimated B from 12 to 43 mu mol/kg in this region using the observational values of N-2 and Ar. As each water mass had a significantly different value of B even with an error of 20%, it is possible to use it as an index of sea surface state for when each water mass is produced in the sea surface mixed layer. Moreover, based on our values of B, we estimated preformed dissolved oxygen (DO) (C-preDO, 309-332 mu mol/kg) and the saturation state of C-preDO (Delta preDO, - 7.0 to - 1.2%) in this region. Thus, the difference between C-preDO) and DO content in the ocean interior may be a more useful index for biogenic organic decomposition in the ocean field compared to Apparent Oxygen Utilization (AOU). Until now, the estimation of oceanic uptake of anthropogenic CO2 has used AOU as a major parameter. Therefore, it may be necessary to re-evaluate the oceanic uptake of anthropogenic CO2 based on our new concept of B. (c) 2007 Elsevier B.V. All rights reserved.
  • Masahito Shigemitsu, Hisashi Narita, Yutaka W. Watanabe, Naomi Harada, Shizuo Tsunogai MARINE CHEMISTRY 106 (3-4) 442 -455 2007年08月 [査読無し][通常論文]
     
    A sediment core covering the last 145 kyrs was collected in the western subarctic Pacific (WSAP), and analyzed for Ba, U, Al, Sc, La, Yb, Th, biogenic opal (Opal) and organic carbon (C-org) as well as its isotopic ratio (delta(13) C). This study examined the change of past biological production in WSAP with multiple proxies, together with understanding the relation between Loess from the Asian continent and the biological production. The Loess content was estimated from the metal components, Al, Sc, La, Yb and Th. In this high latitude core (50 degrees N), the Loess content was generally high during the glacial periods, but it was also high even in some interglacial periods. The excess amount of Ba relative to the detrital material composition, Ba-ex, showed the best correlation with the Vostok delta D (r= 0.72, p < 0.001), indicating that the biological production was lower in the glacial periods than in the interglacials. This corroborates the pervasive correlation between Ba-ex in the polar region, WSAP and the Antarctic Sea, and Antarctic temperature, combined with previous research. This correlation might be explained by the stratification caused by cooling. In addition, the time variations of Ba-ex in WSAP were similar to those of Ba-ex in the Okhotsk Sea and of other proxies (C-org, and Opal) in both the Okhotsk and the Bering Sea, indicating the spatial homogeneity of Ba-ex in WSAP including proximal marginal seas. The Opal content was more weakly correlated with the Vostok delta D (r= 0.46, p < 0.001) than Ba-ex, reflecting that Opal in WSAP including proximal marginal seas was spatially heterogeneous compared to Ba-ex. While both the C-org content and U-ex, the excess amount of U relative to the detritus composition, were not positively correlated with the Vostok delta D, they behaved similarly in the sediments. The positive correlation between delta C-13 and the Vostok delta D (r = 0.42, p < 0.001), between 613 C and Ba,x (r= 0.60, p < 0.00 1) and between delta C-13 and Opal (r=0.36, p < 0.01) indicates that 613C in WSAP may give some information on the phytoplankton growth rate. There was not a significant correlation between the spatially homogeneous Ba x in WSAP and Loess (r= - 0. 1 6, p > 0.01), suggesting that the increase of biological production with the increase of Loess supply during the glacial periods did not occur. (c) 2007 Elsevier B.V. All rights reserved.
  • Y. W. Watanabe, H. Yoshinari, A. Sakamoto, Y. Nakano, N. Kasamatsu, T. Midorikawa, T. Ono MARINE CHEMISTRY 103 (3-4) 347 -358 2007年01月 [査読無し][通常論文]
     
    We proposed an empirical equation of sea surface dimethylsulfide (DMS, nM) using sea surface temperature (SST, K), sea surface nitrate (SSN, mu M) and latitude (L, degrees N) to reconstruct the sea surface flux of DMS over the North Pacific between 25 degrees N and 55 degrees N: In DMS= 0.06346 - SST- 0.1210 - SSN-14.11 - cos(L) - 6.278 (R(2) = 0.63, p < 0.0001). Applying our algorithm to climatological hydrographic data in the North Pacific, we reconstructed the climatological distributions of DMS and its flux between 25 degrees N and 55 degrees N. DMS generally increased eastward and northward, and DMS in the northeastern region became to 2-5 times as large as that in the southwestern region. DMS in the later half of the year was 2-4 times as large as that in the first half of the year. Moreover, applying our algorithm to hydrographic time series datasets in the western North Pacific from 1971 to 2000, we found that DMS in the last three decades has shown linear increasing trends of 0.03 +/- 0.01 nM year(-1) in the subpolar region, and 0.01 +/- 0.001 nM year(-1) in the subtropical region, indicating that the annual flux of DMS from sea to air has increased by 1.9-4.8 mu mol m(-2) year(-1). The linear increase was consistent with the annual rate of increase of 1% of the climatological averaged flux in the western North Pacific in the last three decades. (c) 2006 Elsevier B.V All rights reserved.
  • A Sakamoto, T Niki, YW Watanabe ANALYTICAL CHEMISTRY 78 (13) 4593 -4597 2006年07月 [査読無し][通常論文]
     
    Dimethyl sulfide (DMS) derived from marine biological activity affects radiative forcing of the climate. The general analytical technique for DMS in seawater ( purge and trap analytical method, P&T) is complex onboard ship. Thus it is difficult to obtain sufficient data for a comprehensive understanding of the spatiotemporal variability of DMS in the sea surface layer. On the other hand, a new analytical method for DMS using SPME (solid-phase microextraction) has recently been developed as an alternative method to P&T. This method is simpler than P&T because no special or complex apparatus is needed. If it is possible to preserve DMS for an extended period in excess of the duration of the cruise, the SPME method is a promising method for measuring DMS in seawater. We assessed an analytical method which can allow us to preserve DMS on the long-term scale using SPME. In liquid nitrogen (- 196 degrees C), as preserved environment, for a period of 20 days after sampling, we found the preservation rate of DMS to be 94.7 +/- 4.4% (n = 6) in this study. Furthermore, estimating the distribution coefficient with respect to the effect of salinity on SPME, we found that DMS changed by 0.1 nM/%sal, suggesting that salinity has only a minor influence on oceanic DMS measurements in the open ocean because the minimal change of the open ocean salinity is within 2 %. Applying the SPME method to open ocean samples, we found that there were no significant differences in DMS between the unpreserved and preserved samples (r = 0.99, n = 26, SE = 0.01, p < 0.0001), showing the SPME method has potential for use for open ocean surveys.
  • Y Nakano, H Kimoto, S Watanabe, K Harada, YW Watanabe JOURNAL OF OCEANOGRAPHY 62 (1) 71 -81 2006年02月 [査読無し][通常論文]
     
    We have developed new systems capable of profiling to > 1000 m for measuring in situ pH and fugacity of CO2 (fCO(2)) in the ocean using spectrophotometric analysis (pH and CO2 profilers). The in situ pH is determined by detecting the color change of the pH indicator (m-cresol purple). It can withstand ambient pressure to 1000 m depth. The CO2 profiler analyzed in situ fCO(2) by detecting the change of pH in an inner solution, equilibrated with the seawater through a gas permeable membrane. It can be operated to 2500 m depth. We used an amorphous fluoropolymer tubing form of AF-2400 for the gas permeable membrane due to its high gas permeability coefficients. The inner solution was a mixture of 2 mu M bromocresol purple (BCP) and 5 mu M sodium hydroxide. This system gave us a response time of 1 minute, which is twice as fast as previous systems. The precisions of pH and CO2 profilers were within 0.002 and 2.5% respectively. We have used these profilers to study the North Pacific, obtaining good agreement with the difference between the data from profilers and a discrete bottle of 0.002 +/- 0.005 pH (SE, n = 25) and -0.4 +/- 3 mu atm (SE, n = 31).
  • YW Watanabe, H Ishida, T Nakano, N Nagai JOURNAL OF OCEANOGRAPHY 61 (6) 1011 -1016 2005年12月 [査読無し][通常論文]
     
    Using time series of hydrographic data in the wintertime and summertime obtained along 137 degrees E from 1971 to 2000, we found that the average contents of nutrients in the surface mixed layer showed linear decreasing trends of 0.001 similar to 0.004 mu mol-PO4 l(-1) yr(-1) and 0.01 similar to 0.04 mu mol-NO3 l(-1) yr(-1) with the decrease of density. The water column Chl-a (CHL) and the net community production (NCP) had also declined by 0.27 similar to 0.48 mg-Chl m(-2) yr(-1) and 0.08 similar to 0.47 g-C-NCP m(-2) yr(-1) with a clear oscillation of 20.8 similar to 0.8 years. These changes showed a strong negative correlation with the Pacific Decadal Oscillation Index (PDO) with a time lag of 2 years (R = 0.89 +/- 0.02). Considering the recent significant decrease of O-2 over the North Pacific subsurface water, these findings suggest that the long-term decreasing trend of surface-deep water mixing has caused the decrease of marine biological activity in the surface mixed layer with a bidecadal oscillation over the western North Pacific.
  • Y Nakano, YW Watanabe JOURNAL OF OCEANOGRAPHY 61 (4) 673 -680 2005年08月 [査読無し][通常論文]
     
    We found a simple function of pH that relates to sea surface temperature (SST, K) and chlorophyll-a (Chl, mu g 1(-1)) using measured surface seawater pH, SST and Chl data sets over the North Pacific: pH (total hydrogen scale at 25 degrees C) = 0.01325 SST - 0.0253 Chl + 4.150 (R-2 = 0.95, p < 0.0001, n = 483). Moreover, evaluating the seasonal variation of pH based on this algorithm, we compared the measured pH with the predicted pH at the observational time series stations in subpolar and subtropical regions. The average of Delta pH (measured - predicted, n = 52) was 0.006 +/- 0.022 pH. Therefore, the combination of SST and Chl can allow us to determine the spatiotemporal distribution of pH over the North Pacific. Using the climatological data sets of SST and Chl with our pH algorithms, we have described the seasonal distributions of pH at 25 degrees C (pH((25))) and pH in situ temperature (pH(T)) over the North Pacific surface water.
  • Decadal change in dissolved inorganic carbon at Station KNOT in the subarctic western North Pacific
    Journal of Oceanography 61 129-, 129-139.* 2005年 [査読無し][通常論文]
  • Seasonal and interannual variation of DIC in the Oyashio mixed layer: a climatological view
    Journal of Oceanography 61 1059 -1074 2005年 [査読無し][通常論文]
  • Christopher L. Sabine, Richard A. Feely, Yutaka W. Watanabe, Marilyn Lamb Journal of Oceanography 60 (1) 5 -15 2004年02月 [査読無し][通常論文]
     
    The recent changes in the North Pacific uptake rate of carbon have been estimated using a number of different techniques over the past decade. Recently, there has been a marked increase in the number of estimates being submitted for publication. Most of these estimates can be grouped into one of five basic techniques: carbon time-series, non-carbon tracers, carbon tracers, empirical relationships, and inverse calculations. Examples of each of these techniques as they have been applied in the North Pacific are given and the estimates summarized. The results are divided into three categories: integrated water column uptake rate estimates, mixed layer increases, and surface pCO2 increases. Most of the published values fall under the water column integrated uptake rate category. All of the estimates varied by region and depth range of integration, but generally showed consistent patterns of increased uptake from the tropics to the subtropics. The most disagreement between the methods was in the sub-arctic Pacific. Column integrated uptake rates ranged from 0.25 to 1.3 mol m-2yr-1. The mixed layer uptake estimates were much more consistent, with values of 1.0-1.3 μmol kg-1yr-1 based on direct observations and multiple linear regression approaches. Surface pCO2 changes showed the most obvious regional variability (0.5-2.5 μatm yr-1) reflecting the sensitivity of these measurements to differences in the physical and biological forcing. The different techniques used to evaluate the changes in North Pacific carbon distributions do not completely agree on the exact magnitude or spatial and temporal patterns of carbon uptake rate. Additional research is necessary to resolve these issues and better constrain the role of the North Pacific in the global carbon cycle. © The Oceanographic Society of Japan.
  • S Emerson, YW Watanabe, T Ono, S Mecking JOURNAL OF OCEANOGRAPHY 60 (1) 139 -147 2004年02月 [査読無し][通常論文]
     
    We present a compilation of apparent oxygen utilization (AOU) changes observed in the upper pycnocline of the North Pacific Ocean over the last several decades. The goal here is to place previously-published data in a common format, and assess the causes of the observed changes. The general trend along repeat cross sections of the eastern and western subtropical ocean and the subarctic ocean is an increase in AOU from the mid 1980s to the mid 1990s. AOU has also been increasing in a time-series study in the northwest subarctic Ocean off of Japan since the late 1960s. Observed AOU changes south of 35degreesN in the subtropical ocean are 10-20 mumol kg(-1), with much greater changes, reaching 60-80 mumol kg(-1) in isolated areas, in the subtropical/subarctic boundary and the subarctic ocean. Analysis of changes in both AOU and salinity on isopycnals suggests that there are significant salinity-normalized increases that must be due to alteration in the rate of ventilation or organic matter degradation. A common feature in the data is that the maximum increase in AOU is centered near the density horizon sigma(theta) = 26.6. Time series results from the Oyashio Current region near the winter outcrop area of this density horizon indicate that surface waters there have become fresher with time, which may mean this density surface has ceased to outcrop in the latter decades of the 20th century. Whether this is due to natural decadal-scale changes or anthropogenic influences can be decided by determining future trends in AOU on these density surfaces.
  • YW Watanabe, M Wakita, N Maeda, T Ono, T Gamo GEOPHYSICAL RESEARCH LETTERS 30 (24) 2273, doi:10.1029/2003GL018338 2003年12月 [査読無し][通常論文]
     
    From time series of dissolved oxygen ( O-2), phosphate (PO4) and water temperature (T) during the last forty years in the Japan Sea Deep Water and the North Pacific Intermediate Water, we found that O-2, PO4 and T show a clear bidecadal oscillations of about 18 years superimposed on the linear trends of decrease of 0.47 mumol-O-2 kg(-1) yr(-1) and increase of 0.003 mumol-PO4 kg(-1) yr(-1) and 0.005degreesC yr-1 in both two oceanic areas. The changes of O-2, PO4 and T in the two oceanic areas were synchronized despite the water formation systems of each area being independent. Both the linear trends and the oscillations of O-2, PO4 and T in the two oceanic areas also showed a strong correlation with the anomaly of the sea surface level pressure in the North Pacific that possibly affects the change of surface oceanic condition.
  • M Wakita, YW Watanabe, S Watanabe, S Noriki, M Wakatsuchi GEOPHYSICAL RESEARCH LETTERS 30 (24) 2252, doi:10.1029/2003GL018057 2003年12月 [査読無し][通常論文]
     
    We proposed a new simple approach for estimating the oceanic rate of increase of anthropogenic CO2 (U-anth) in a subpolar marginal sea that produces ventilated water with the sea ice formation. This approach was based only on the differences in dissolved inorganic carbon (DIC) and apparent oxygen utilization (AOU) between the ventilated water and the source water. Applying our approach to the Sea of Okhotsk for 1993, 1999 and 2000, we estimated the averaged U-anth transported into the intermediate water (U-I), and in the surface water from spring to fall (U-S(ssimilar tof)) and in the surface water in winter (U-S(W)) to be 1.1 +/- 0.9 mumol kg(-1) yr(-1), 0.70 +/- 0.01 mumol kg(-1) yr(-1) and 1.1 +/- 0.9 mumol kg(-1) yr(-1), respectively, during the past 8 years. The accumulation rate of anthropogenic carbon was estimated as 0.78 x 10(12) g C yr(-1) over the entire Sea of Okhotsk.
  • T Tanaka, YW Watanabe, S Watanabe, S Noriki, N Tsurushima, Y Nojiri GEOPHYSICAL RESEARCH LETTERS 30 (22) 2159, doi:10.1029/2003/GL0108503 2003年11月 [査読無し][通常論文]
     
    [1] We propose a simple approach for estimating the recent oceanic Suess effect of delta(13)C in the subpolar region of the North Pacific, an area which experiences a large seasonal variability of carbonate species, due to the biological activity and vertical water mixing. This approach is based simply on time-series data of delta(13)C from July 1997 to July 2001 and an equation of the Fourier sine expansion. Applying our approach to the fixed sampling location in the western North Pacific, station 'KNOT', we estimated values of -0.012parts per thousand-delta(13)C yr(-1) for the Suess effect of delta(13)C with an amplitude of 1.3parts per thousand-delta(13)C and 1.0 mumol-C kg(-1) yr(-1) for the increase rate of dissolved inorganic carbon with an amplitude of 134 mumol-C kg(-1) in surface water. The Suess effect of delta(13)C in this region was a similar value to that estimated in the Southern Ocean producing the deep water, while it was half as much as values estimated in the subtropical regions which experience a small seasonal variability. The ratio of Suess effect to the increase rate of dissolved inorganic carbon was -0.012parts per thousand (mumol kg(-1))(-1), which was different from the global mean values calculated by recent modeling study. Therefore, we conclude that the Suess effect of delta(13)C in the polar and subpolar regions is generally smaller than found in other regions, suggesting that it is necessary to reevaluate the uptake rate of anthropogenic carbon which has been based on the assumption that the ratio is uniform over the entire ocean.
  • YW Watanabe, A Shimamoto, T Ono JOURNAL OF OCEANOGRAPHY 59 (5) 719 -729 2003年10月 [査読無し][通常論文]
     
    To verify the actual usefulness of time-dependent tracer dating techniques in the ocean, we simultaneously obtained two cross sections of sulfur hexafluoride (SF6) and chlrofluoromethanes (CFC-11, trichlorofluoromethane; CFC-12, dichlorodifluromethane; CFC-113, trichlorotrifluoroethane) in the western North Pacific in 1998. The vertical distribution patterns of SF6 and CFC-113 were similar in shape to those of CFC-11 and CFC-12. Maximum penetration depths of SF6 and CFC-113 remained around 800 m in the subpolar region and 400 m in the tropical region, while the maximum penetration depths of CFC-11 and CFC-12 were still found below 1000 m depth. We also found all maximum contents of these tracers around 26.6-26.8sigma(theta) with a gradual decrease southward. This suggested that a new subsurface water mass in the subpolar region spread out over the entire North Pacific, which agrees closely with previous studies based on the salinity minimum. Moreover, we compared the tracer ages (the elapsed period of a water mass from when the water mass left from the ocean surface) using ten time-dependent tracer dating techniques, CFC-11, CFC-12, CFC-113, SF6, CFC-11/CFC-12, CFC-113/CFC-11, CFC-113/CFC-12, SF6/CFC-11, SF6/CFC-12 and SF6/CFC-113. This quantitative evaluation of multiple tracer dating techniques in the ocean was the first confirmation of its usefulness based on the observational data on the ocean basin-wide scale. We conclude that SF6/CFC-11, SF6/CFC-12, SF6/CFC-113 and SF6 dating techniques would be the most promising tools for determining the age of water mass not only just for the past several decades but for the future, too.
  • MF Lamb, CL Sabine, RA Feely, R Wanninkhof, RM Key, GC Johnson, FJ Millero, K Lee, TH Peng, A Kozyr, JL Bullister, D Greeley, RH Byrne, DW Chipman, AG Dickson, C Goyet, PR Guenther, M Ishii, KM Johnson, CD Keeling, T Ono, K Shitashima, B Tilbrook, T Takahashi, DWR Wallace, YW Watanabe, C Winn, CS Wong DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 49 (1-3) 21 -58 2002年 [査読無し][通常論文]
     
    Between 1991 and 1999, carbon measurements were made on twenty-five WOCE/JGOFS/OACES cruises in the Pacific Ocean. Investigators from 15 different laboratories and four countries analyzed at least two of the four measurable ocean carbon parameters (DIC, TAlk, fCO(2), and pH) on almost all cruises. The goal of this work is to assess the quality of the Pacific carbon survey data and to make recommendations for generating a unified data set that is consistent between cruises. Several different lines of evidence were used to examine the consistency, including comparison of calibration techniques, results from certified reference material analyses, precision of at-sea replicate analyses, agreement between shipboard analyses and replicate shore based analyses, comparison of deep water values at locations where two or more cruises overlapped or crossed, consistency with other hydrographic parameters, and internal consistency with multiple carbon parameter measurements. With the adjustments proposed here, the data can be combined to generate a Pacific Ocean data set., with over 36,000 unique sample locations analyzed for at least two carbon parameters in most cases. The best data coverage was for DIC, which has an estimated overall accuracy of similar to3 mu mol kg(-1). TAlk, the second most common carbon parameter analyzed, had an estimated overall accuracy of similar to 5 mu mol kg(-1). To obtain additional details on this study, including detailed crossover plots and information on the availability of the compiled, adjusted data set, visit the Global Data Analysis Project web site at: http://cdiac.esd.oml.gov/oceans/glodap. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • Y. W. Watanabe, T. Ono, A. Shimamoto, T. Sugimoto, M. Wakita, S. Watanabe Geophysical Research Letters 28 (17) 3289 -3292 2001年09月01日 [査読無し][通常論文]
     
    Comparing the apparent oxygen utilization (AOU) and apparent CFC tracer ages (tau) between extensive decadal reobservation data along 47 degreesN ('85-'99) and 165 degreesE ('87-'00) lines, we found that both AOU and tau markedly increased over the North Pacific between 26.4 - 27.4 sigma (0). The observed AOU increase was almost consistent with the AOU increase calculated from observed change of tau. Based on a linear trend of increasing AOU over 30 years ('68-'98) in the subpolar region [Ono et al., 2001], we concluded that the formation rate of the subsurface water in the North Pacific has continuously reduced at least during the last fifteen years. In the North Pacific, the recent uptake rate of oceanic anthropogenic carbon was also estimated as reduced by as much as 10% from the efficiency of anthropogenic carbon absorption in the middle of 1980s.
  • T Ono, T Midorikawa, YW Watanabe, K Tadokoro, T Saino GEOPHYSICAL RESEARCH LETTERS 28 (17) 3285 -3288 2001年09月 [査読無し][通常論文]
     
    30-years time series of AOU and phosphate in the Oyashio sub-surface domain showed an increasing trend superimposed on bidecadal oscillation. AOU and phosphate trend on isopycnals between 26.7 and 27.2 sigma (0) increased by an average of 0.9 +/-0.5 and 0.005 +/-0.003 mu mol/kg/y, respectively. Salinity on these isopycnals also showed an average linear increase of 0.0008 psu/y. Salinity and density of winter mixed layer, on the other hand, was found to have decreased during the observation period. Observed bidecadal oscillation (average period 20 +/-1 y) in subsurface AOU negatively correlated with that of North Pacific Index (r=-0.88 +/-0.06). As the cause of the linear increase of subsurface phosphate and AOU, we speculated that vertical water exchange in the upper layers of the subarctic North Pacific might have been diminished during this period. A decreasing trend of salinity and density of winter mixed layer in Oyashio that was observed during the same period supported this speculation.
  • Hiroyuki Tsubota, Joji Ishizaka, Akira Nishimura, Yutaka W. Watanabe Journal of Oceanography 55 (6) 645 -653 1999年12月 [査読無し][通常論文]
     
    The Northwest Pacific Carbon Cycle Study (NOPACCS) was a program aimed at investigating the carbon cycle of the North Pacific Ocean, which can be thought of as a large reservoir of carbon dioxide. NOPACCS was also aimed at estimating the North Pacific's capacity as a carbon sink. Project design, scientific results, and data availability, and subsequent projects resulting from this project are also described in this review. Studies of the upper ocean processes focused on the latitudinal differences in the fugacity of carbon dioxide and on the detail of plankton community structures. Intermediate water was studied in relation to the formation of North Pacific Intermediate Water and the amount of accumulated anthropogenic carbon. The sedimentation process, past carbon cycle and coral reefs were also studied during the project. A preliminary, overall view of the carbon cycle of the North Pacific was drawn from the results of the project and compared to global values.
  • Watanabe Y. W. Proc. of the 1994 Sapporo IGBP Symposium 14 393 -399 1995年
  • WATANABE Y. W. Journal of Oceanographic Society of Japan 47 80 -93 1991年

受賞

  • 2003年 2002年度日本海洋学会日高論文賞授賞
  • 1997年 1996年度日本海洋学会岡田賞授賞
  • 1994年 1993年度日本海洋学会日高論文賞授賞

共同研究・競争的資金等の研究課題

  • 次世代南大洋海洋観測に対するパラメタリゼーション技術の開発と展開
    日本学術振興会:科学研究費助成事業 基盤研究(S)
    研究期間 : 2022年04月 -2027年03月 
    代表者 : 渡辺 豊
  • 南大洋縁辺部における準リアルタイムな人為起源二酸化炭素の動態解明
    日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2020年04月 -2022年03月 
    代表者 : 渡辺 豊
     
    全海水の40%を占める南極底層水は熱と物質の巨大な貯留槽であり、この底層水形成域である南大洋でのCO2の取り込み量は全球の気候や生態系変動を大きく支配する。南大洋縁辺部で、南極底層水に大気から取り込まれる人為起源CO2は海洋吸収量の40%にもなると推定されているが、飽和平衡量に到達する前(非平衡)に海洋内部へと沈み込み、その非平衡量は30%までになるとの予測もある。しかし、観測を基盤としてこの非平衡量を確かめるには至っていない。その最大の理由は、海洋のCO2吸収を把握するための炭酸系物質(全炭酸:DIC、アルカリ度:Alk、pH)の測定が他の観測成分に比べて煩雑であること、さらに、海洋観測船を基盤とせざるを得ない制約条件によりデータ数が時空間的に疎であるためである。このため、南極底層水への人為起源CO2取り込み量は正確に未だ分かっておらず、全球的な気候変動予測の大きなボトルネックとなっている。 本申請では「南極底層水に人為起源CO2はどのくらい取り込まれているのか」という最大の問いに答えるために、2020年度は以下の項目を実施した。(1)南大洋縁辺部における炭酸系物質のパラメタリゼーション(炭酸系物質の関数化:DIC, Alk, pH = f (T, S, DO, Pr); T・S・DO・Prによる炭酸系物質の関数化)の開発を行い、高精度なパラメタリゼーションの開発に成功し、これを基盤に南大洋における炭酸系物質の大気海洋間の非平衡量のパラメタリゼーション化も成功した。(2)同海域の既存海洋水理データ群に適用することで、南大洋縁辺域も含めた南緯30度以南の南大洋における全炭酸物質の時空間高解像度なマッピングに成功した。(3)これらを基盤に、南大洋縁辺部に現在展開されている約200個の自動海洋観測ロボットに応用し、南大洋縁辺域の人為起源二酸化炭素濃度の詳細な分布に着手した。
  • 日本沿岸海域における海洋酸性化の動態予測手法の開発
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2019年04月 -2022年03月 
    代表者 : 今井 圭理, 渡辺 豊
  • 海洋炭酸系物質の時空間高解像度マッピング技術の南大洋への展開
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 渡辺 豊, 中野 善之, 脇田 昌英, 野村 大樹
     
    2018年度は以下の項目を実施した。 ●研究項目(1)「南大洋の炭酸系物質(pH, Alk, DIC)のパラメタリゼーションの基本原理の評価のための観測とその展開」:東・南極海をターゲットに、JAMSTEC研究観測船・白鳳丸、水産庁・開洋丸、東京海洋大学・海鷹丸、南極観測船・しらせによって、0m~6000m・36層鉛直採水を広範囲にわたる80観測点海水サンプルを取得し、精度2umol/kg以内で分析を実施した。 ●研究項目(2)「南大洋における炭酸系物質のパラメタリゼーションの開発」:南大洋海域(南緯40度以南)の国際的海洋横断面観測計画CLIVAR・GOSHIPの2万採水層の水深0m~6000mまでに及ぶ高精度・高確度なT・S・DO・Pr・炭酸系物質データ群を用い、炭酸系物質のパラメタリゼーションを行い、同領域における3次元の空間分布の把握を行った。さらに、同領域において、1990年から時間的に離散的ではあるが定点観測が実施されている観測ステーションの時系列高精度データ群(T・S・DO・Pr・炭酸系物質)に上記のパラメタリゼーションを適用し、実データと比較することで、パラメタリゼーションによって得られた炭酸系物質の時系列データの妥当性の評価を実施した。上記のデータ群も基盤に、炭酸系物質を水温・塩分・酸素・圧力の関数とするパラメタリゼーションを実施したところ、予備的であるが、南大洋海域において、0mから海底までの範囲で、pH, Alk, DICのパラメタリゼーションが高精度で実施可能なことを確認した。 ●研究項目(3)「南大洋における準リアルタイムな炭酸系物質のマッピング」:海洋自動観測ロボット(中層プロファイリングフロートならびに水中グライダー)のデータ群に対して、品質管理も含め必要なパラメータ(T, S, DO, Pr)についてデータフォーマットを整備した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 渡辺 豊, 中野 善之, 野村 大樹
     
    迅速で高精度高確度な炭酸系物質測定方法を開発した。これらのデータと北太平洋高緯度海域における15万採水層に及ぶ高精度・高頻度水理データ群も用い炭酸系物質のパラメタリゼーションを行い、同海域における確度と精度ともに0.1%以内で炭酸系物質を復元出来る定式化を可能とした。併せて、人為起源CO2と人間活動起源由来の海水pHを推定する方法の開発にも成功した。 海洋自動観測ロボットデータに適用し、同海域の時空間的に詳細な準リアルタイムの炭酸系物質の動態を把握する観測システムの構築に成功した。その結果、人為起源由来の海洋酸性化はここ数十年にわたり一年に0.002づつ全球的に進んでいることを明らかとした。
  • 日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2012年06月 -2017年03月 
    代表者 : 神田 穣太, 喜多村 稔, 西川 淳, 青野 辰雄, 山口 篤, 高木 省吾, 土屋 光太郎, 立田 穣, 林 敏史, 野田 明, 渡辺 豊, 茂木 正人, 田中 祐志, 守屋 繁春, 小林 卓也, 芳村 毅, 石丸 隆, 五十嵐 敏, 須賀 次郎, 山川 紘, 大津 秀暁, 伊藤 友加里, 高澤 伸江, 内山 香織, 久保 篤史, 今井 圭理
     
    海洋生態系における福島第一原子力発電所事故由来の放射性物質について、以下の研究を行った。1)福島沿岸域において生物と環境の放射性セシウムについて、年に2回の船舶観測による経時的なデータセットを得た。また外洋域の動物プランクトンについても複数の海域で時系列データを得た。2)岩礁性の底生魚に重点を置いて、生態系への移行経路を検討した結果、懸濁・沈降粒子や堆積物の有機物画分等からの移行は小さいことを確認した。3)現場観測データを用い、生態系内の放射性セシウム推移をモデルにより再現し、海洋生物の放射能レベルの今後の推移について検討した。
  • 日本学術振興会:科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2013年04月 -2015年03月 
    代表者 : 渡辺 豊
     
    海水中の窒素とアルゴンの高確度化と同時測定化を図り、一気に海水中の脱窒・窒素過程量を求められる簡便で迅速な方法の開発を本研究の目的とした。このため、既存の分析法の改良を行うとともに、海水中の脱窒・窒素過程量の見積り法を開発した。この方法を用いた結果、オホーツク海においては、窒素固定はほとんど検出されなかったが、7micromole/kg/yearを越える著しい脱窒速度が沿岸部に存在し、これが北太平洋へ流れ出ていく空間分布を明瞭に描きだすことができ、北太平洋への影響を示唆できた。
  • 日本学術振興会:科学研究費助成事業 基盤研究(S)
    研究期間 : 2010年04月 -2015年03月 
    代表者 : 若土 正曉, 三寺 史夫, 西岡 純, 中村 知裕, 江淵 直人, 鈴木 光次, 黒田 寛, 大島 慶一郎, 津旨 大輔, 的場 澄人, 小埜 恒夫
     
    オホーツク海から親潮域の豊かな水産資源を支える“奇跡ともいえる仕組み”を明らかにするため、オホーツク海と北太平洋をつなぐ熱塩/物質循環システムの実態解明を進めた。熱塩循環の強さを決めるオホーツク海北部の高密度水(DSW)の塩濃度は、亜寒帯循環を跨ぐ塩濃度偏差の長距離伝播、海氷生産量変動、降水量変動との「せめぎ合い」により決まる。アムール川河口・オホーツク北部陸棚上に堆積する光合成に必須の栄養物質・鉄は、このDSWに取り込まれ、北太平洋の広範囲に供給される。DSWと潮汐混合を介し強く結合した熱塩循環と物質循環が生物生産を北太平洋規模で規定するという、絶妙なシステムが本研究により明らかとなった。
  • 日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2010年 -2012年 
    代表者 : 渡辺 豊, 西岡 純, 坂岡 桂一郎, 南 秀樹, 小埜 恒夫
     
    海洋の窒素・炭素循環変動とそのフラックスの時空間変動を定量化するための新規見積り法の開発に成功した。同時に、簡易で高頻度に海洋表面溶存気体を採水できるシステムの開発と実証試験を実施し、その開発に成功した。このシステムデータ群と既存のデータ群に、窒素・炭素循環のための新規見積り法を適用し、北太平洋ならびに全球規模の窒素・炭素循環の変動の高時空間分解能な分布を明らかにした。
  • 日本学術振興会:科学研究費助成事業 基盤研究(S)
    研究期間 : 2008年 -2012年 
    代表者 : 安田 一郎, 羽角 博康, 小松 幸生, 西岡 純, 渡辺 豊, 中塚 武, 伊藤 幸彦, 建部 洋晶, 勝又 勝郎, 中村 知裕, 広江 豊, 長船 哲史, 田中 祐希, 池谷 透, 西川 悠, 友定 彰
     
    千島列島やアリューシャン列島海峡域において、中深層に及ぶ通常の数千倍の乱流鉛直混合の存在を、観測によって実証した。この大きな潮汐鉛直混合は、鉄や栄養塩等の物質循環を通じて、親潮など北太平洋亜寒帯海域の海洋生態系に大きな影響を与える。さらにその潮汐混合が18.6年周期で変動することによって生じる海洋変動が、日本東方海面水温とアリューシャン低気圧等の大気海洋相互作用を通じて増幅し、太平洋規模の気候・海洋の約20年変動に影響することが、観測・モデルの両面から明らかとなった。
  • 日本学術振興会:科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2010年 -2011年 
    代表者 : 渡辺 豊
     
    海水中の溶存無機炭素中の炭素安定同位体比(δ^<13> C)を高精度に図り、大気から海水へ取り込まれる人為起源二酸化炭素の吸収速度を高分解能で求める新規見積り法を開発することを研究目的とした。このため、分析法改良や採水手法改良にも取り組み、δ^<13> Cを用いた海洋の人為起源二酸化炭素吸収速度の見積り法を開発した。この方法を用いた結果、北太平洋高緯度海域では、近年、大気中の二酸化炭素分圧で期待されるより1. 2倍高い人為起源二酸化炭素の吸収が行われていたことが明らかとなった。
  • 日本学術振興会:科学研究費助成事業 特定領域研究
    研究期間 : 2006年 -2010年 
    代表者 : 渡辺豊, 安田 一郎, 鶴島修夫
     
    北太平洋の長期変動メカニズム解明のための物理・生物・化学的な総合観測を実施し、大気海洋循環ならびに物質循環長期変動の定量化に成功した。また、海水中の温室効果気体のアルゴリズム化に成功した。さらに、長期変動が海洋環境変動に与える影響を組み込んだ数値モデルを用いて、北太平洋亜寒帯海域での長期変動を復元した。
  • 日本学術振興会:科学研究費助成事業 特定領域研究
    研究期間 : 2006年 -2010年 
    代表者 : 植松 光夫, 横内 陽子, 渡辺 豊, 武田 重信, 山中 康裕, 津田 敦
     
    大気海洋物質循環の全体の取り纏めを行うために4つの研究項目の研究方針を調整し、陸上集中観測や研究航海の企画調整や申請、研究交流のための全体会議、計画研究代表者会議、総括班会議を適宜、開催した。4つのワーキンググループの集会(辺戸岬集中観測WG、台風影響評価WG、生態系長期変動WG、渦相関法検討WG)を企画、開催し、いずれも活発な議論が展開され、新たな研究の連携と発展を見た。成果発表の場として国内外会議でのセッション・Workshop主催件数は、20件を越えた。諸外国の国際会議に特定領域研究の成果を積極的に発表する若手研究者への旅費援助を行った。本研究領域において12名が博士号を取得した。NewsletterやWeb siteを用い、情報を国内外へ公開した。
  • 窒素とアルゴンとラジウムを用いた高確度な海水中の脱窒速度決定法の開発に関する研究
    日本学術振興会:科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2008年 -2009年 
    代表者 : 渡辺 豊
     
    H21年度は、以下の項目を実施した。 実海域における実証試験の実施 生物生産が高く脱窒の起こっている外洋の親潮海域ならびにオホーツク海において、広域範囲にわたる窒素、アルゴンとラジウムの高頻度サンプリングを実施した。H20年度に完成した方法(海水中の窒素の過剰量と、ラジウムによる海水の滞留時間を組み合わせた方法)を用いて、窒素、アルゴンとラジウムに基づく脱窒速度の見積りと、これまでに定性的であるがよく用いられてきた脱窒の指標N^*を比較したところ、外洋域においては時空間的に有意の差がなく、よく一致していることを明らかとした。 さらに、この方法に基づき、親潮域をバックグラウンドとし、オホーツク海との窒素過剰量の差を取るとともに、ラジウムから推定されるオホーツク海の滞留時間を組み合わせて、オホーツク海の全域の脱窒速度の平均場を求めた。その結果、オホーツク海の全脱窒速度は約0.39~1.02T mol/年であり、世界で最も大きな脱窒海域アラビア海の2.92T mol/年に次ぐほどの大きな脱窒海域であることを定量化し、北太平洋の窒素循環に大きな影響を与えていることを明らかとした。このことは、今後の温暖化によって、オホーツク海の窒素変動が北太平洋の窒素循環に多大なインパクトを与える可能性をも示唆した。 この結果は、2010年3月に行われた日本海洋学会で発表し、その内容を査読付英文学術雑誌に投稿するため現在執筆中で、近日中に投稿する予定である。
  • 千島列島・アリューシャン列島付近潮汐混合の実態解明と北太平洋海洋・気候変動
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2008年 -2008年 
    代表者 : 安田 一郎, 小松 幸生, 渡辺 豊, 中塚 武
     
    淡青丸KT-08-7次研究航海(2008年4月23日~5月7日)において、伝導度-水温-水深プロファイラ(CTD)、垂下式超音波流速計(LADCP)、および鉛直微細構造プロファイラ(乱流計)等を用い、房総半島沖合の親潮系低塩分水が貫入した直後の黒潮続流域において2000mまでのグリッド観測を実施した(安田一郎・伊藤幸彦)。この研究航海ではまた、鉛直方向に詳細な硝酸分布が取得できる硝酸塩連続プロファイラをレンタルして使用した。硝酸計データと乱流計データと組み合わせると硝酸の鉛直フラックスが算出でき、これにより本研究における栄養塩・生態系観測研究の基礎が構築されつつある。2009年に予定されている白鳳丸アリューシャン・ベーリング海観測を行うために、5/22-23にシンポジウムを開催し観測計画のとりまとめを行った。2006/2007ロシア船観測によって千島列島海域で得られた観測データの解析を進め、密度逆転からの乱流強度評価手法の開発(院生D1:八木雅宏)、千島列島付近での乱流による栄養塩鉛直輸送の評価(院生D1:金子)を行った。鉄分布観測データの検討(西岡純)、化学トレーサ観測データの解析(渡辺豊)を行った。海洋観測長期データを用いた解析(院生D3:長船哲史)により潮汐18.6年振動がベーリング海にも現れることを明らかにした千島列島付近の潮汐混合を変動させた大気・海洋・海氷結合モデルを開発し、エルニーニョ・南方振動(ENSO)を通じて気候にも影響を与えうることが明らかにされた(羽角・安田・建部)。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2006年 -2008年 
    代表者 : 渡辺 豊, 仁木 拓史, 乗木 新一郎
     
    北太平洋高度海域の沿岸・外洋において、地球温暖化抑制物質であるDMS(ジメチルサルファイド)濃度について、植物プランクトン・クロロフィル・色素データと炭酸物質等とともに、世界で初めての周年規模の時系列観測を試みた。その結果、DMSの北太平洋における月別の詳細な空間分布を描き出すことに成功し、さらに、北太平洋全体でその表層濃度ならびに大気への逃散速度がここ30年で増加して傾向にあることを明らかとした。
  • 窒素とアルゴンを用いた高確度な海水年齢決定法の開発に関する研究
    日本学術振興会:科学研究費助成事業 萌芽研究
    研究期間 : 2006年 -2007年 
    代表者 : 渡辺 豊
     
    H18年度に確立した分析法と以下の計算方法を用いて、H19年度にはその信憑性を明らかにするために北太平洋高緯度海域で季節毎に得た海水試料の分析し、鉛直的な気泡貫入量の見積もりを行った。 A項(真の飽和度)とB項(気泡貫入量)推定式: N_<2(obs)>=A_・N_<2(s)>+0.780・B(1),Ar_<(obs)>=A_・(k_/k_)・Ar_<(s)>+0.009・B(2) A_:窒素の飽和度(%)、N_<2(s)>とAr_<(s)>:現場の水温・塩分・大気組成比から求められるN_2とArのそれぞれの飽和濃度、k_、k_:窒素とアルゴンの気体交換速度、B:気泡が直接溶け込んだ量、0.789及び0.009:N_2とArのそれぞれの大気混合比。 その結果、気泡貫入量は水深1000m以深では変動せず、その上層、表層・中層において季節的に10-50μmol/kgの範囲内で変動することを明らかにした。 さらに、この方法を、年代決定に用いられているCFCsが観測されている南半球40度付近を一周する数十点の観測点試料について、窒素とアルゴンを測定し、気泡貫入の程度を計算した。その結果、年代は5-10年程度補正する必要があることが明らかになった。
  • 千島列島付近潮汐混合の直接観測と北太平洋海洋循環・変動に与える影響の解明
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2005年 -2007年 
    代表者 : 安田 一郎, 日比谷 紀之, 大島 慶一郎, 渡辺 豊
     
    H19年度においては、昨年度に引き続きロシア船を傭船し、約1週間(2007年8月下旬から9月上旬)にわたり千島列島海域の乱流計を用いた乱流直接観測を行うことができた。本年度観測では、昨年度機器の故障により十分な深さまで観測ができなかったブッソル海況西水道において1日連続観測を行うことができた。また、深い混合が予想されたブッソル海況東水道の1点、昨年度オホーツク海側で実施したウルップ海況太平洋側の3点、及び、ムシル海況4点で1日連続観測を行ったほか、重要な観測点で乱流・CTD観測を行うことができた。これらの観測により、千島列島海域には、一般的な中深層での乱流強度の約1万倍にも及ぶ1000cm2/secを越える鉛直拡散が起きていることが実証された。一方、1日の中でも潮汐流に応じて乱流強度は大きく変化すること、また、場所ごとに大きく変化することが明らかとなった。今後、さらに観測を行うとともに、長期観測データやモデルなどを用いてこの海域全体の寄与を明らかにしてゆく必要があることもわかった。また、これら乱流の直接観測データとCTDで取得された密度の鉛直方向の逆転から得られた間接的に乱流強度を比較した結果、乱流強度1桁の誤差範囲で間接的に乱流強度を見積もることができる手法を開発することができた。さらに、木の年輪から得られた長期気候指標北太平洋10年振動指数PDOに有意な18.6年潮汐振動周期を見出し、潮汐振動と気候との位相関係を明らかにした。これにより、日周潮汐の強い時期に、赤道域ではラニーニャ傾向、日本東方海域では高温、アリューシャン低気圧は弱い傾向になることがあきらかとなった。また、千島列島付近の日周潮汐が強い時期に表層の層厚が薄くなり、それが日本南岸まで伝搬することに関連して、本州南岸沿岸海域の栄養塩が上昇する傾向があることが明らかとなった。このように、千島列島付近および亜寒帯海域の潮汐混合は、広く北太平洋に大きな影響を与えていることが示唆された。
  • 北太平洋亜寒帯域の鉄濃度が生物生産と二酸化炭素収支に及ぼす影響に関する観測研究
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2004年 -2006年 
    代表者 : 小埜 恒夫, 葛西 広海, 西岡 純, 渡辺 豊, 芳村 毅
     
    通常のCTDを利用したクリーン採水技術を確立し、親潮域および混合域において年数回の鉄の反復断面観測を実施した。世界で初めて栄養塩と同一の時空間分解能で得られた、鉄濃度周年変動データの解析から、以下の事があきらかになった。 1]親潮域表層における溶存鉄の各月の海域平均濃度は、主要栄養塩と定性的に同じ季節変動パターンを示すだけでなく、硝酸と定量的に一定比(ΔDFe/ΔN=27x10^<-6>[mol/mol])を保って増減している。表層鉄濃度のピークは冬期の最大混合深度期(1-3月)であり、黄砂飛来時期(4月)とは明瞭に異なる。 2]親潮表層の冬期溶存鉄濃度はアラスカ湾より遙かに高いが、両者の亜表層域の鉄濃度も同様に異なる為に、両海域の冬期表層鉄濃度は、亜表層からのエントレインメントと鉛直渦拡散を仮定した同じモデルで再現可能である。親潮表層の溶存鉄:硝酸費も同様にアラスカ湾より高く、北太平洋中層水(NPIW)のそれと同一値をしめす。 3]これらの事から、西部北太平洋表層に存在する鉄は数年-数十年程度の平均滞留時間を持っており、したがって周年-経年変動のスケールでは、鉄の動態は主要栄養塩と同様であることが推定される。つまり大気ダストからの鉄の供給は従来の定説に反してそれほど重要ではなく、生物による取り込みと中層での再分解、そして鉛直混合による表層への回帰という海洋内部での再循環だけで、ほぼ加不足なく溶存鉄の周年変動は説明出来る。 4]春季ブルーム終了時の表層溶存鉄濃度がほぼ0.25nMで一定となる事から、ブルーム形成ケイ藻種の成育限界鉄濃度が0.25nM程度と高く、このためブルーム期には硝酸でなく鉄が主な制限栄養素になっている事が推定される。一方周年を通じた硝酸・溶存鉄プロットは鉄側に切片を持つ事から、鉄も硝酸も低濃度となる夏期には硝酸が親潮表層の制限栄養素となっている。
  • 海洋・大気間の物質相互作用研究計画(IGBP/SOLAS)の準備調査
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2004年 -2004年 
    代表者 : 植松 光夫, 梶井 克純, 津田 敦, 渡辺 豊, 武田 重信, 山中 康裕
     
    本研究では、海洋・大気間の物質相互作用研究計画(IGBP/SOLAS)の特定領域研究申請に向けて、各プロジェクトの具体的な共同研究体制や戦略、国際的な協力体制を確立するため、国内研究立案集会を2004年7月1-2日に東大海洋研にて開催した。 その後、10月6日にDMS関係のデータ、情報交換を含めたSOLAS-Japan DMSワークショップを開催した。ワークショップ終了後、"Dr.Sauveur BELVISO(CEN de Saclay, France)とDr.Dileep KUMAR(National Institute of Oceanography, India)を招待して、それぞれ"Recent progresses of DMS biogeochemistry in the Southern Ocean"と"Dimethylsulphide in the monsoon driven Indian Ocean"というタイトルでセミナーを開催した。 11月15-16日には東大海洋研において「大気・海洋間の生物地球化学的循環過程」について国内SOLASシンポジウムを開催し、30件を越える成果と研究提案の発表があった。 2005年1月20-21日に名古屋大においてSOLAS-Japanワークショップを開催し、来年度の研究計画や長期の航海計画申請について意見を集約した。 国際的な活動として、ノルウェーのベルゲンで開催された国際SOLAS SSC meetingに植松(SSC委員)と武田(SSC委員)が出席し、日本を中心としたアジア域での取り組みについて取りまとめた。2005年には東京で国際SOLAS SSC meetingを開催することに決まった。また、この東京会議に引き続いてAsia SOLAS Workshopの開催を計画した。 2004年10月にカナダ、ハリファックスで開催される国際SOLASシンポジウムに我が国から15名の研究者が発表した。津田がキーノートスピーカーとして招待された。本研究費から4名の発表者に旅費の援助を行った。 この間、特定領域研究申請に向けて作業を行い、2004年11月に「海洋表層・大気下層間の物質循環リンケージ」(大気海洋物質循環)を申請した。

教育活動情報

主要な担当授業

  • 化学海洋学特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 海洋生物地球化学、化学海洋学、物質循環、データ解析、有機物、化学トレーサー、微量元素 Ocean biogeochemistry, Chemical Oceanography, Material cycle, Data analysis, organic matter, chemical tracers
  • 海洋生物地球化学特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : Ocean biogeochemistry, nutrient cycle, trace metal cycle, primary production, non-living organic materials, chemical tracers
  • 環境と人間
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 大気、海洋、生態系、気候変化、地球環境問題、地球温暖化、成層圏オゾン層破壊、大気汚染


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