Researcher Database

Takafumi Hirata
Arctic Research Center
Specially Appointed Associate Professor

Researcher Profile and Settings


  • Arctic Research Center

Job Title

  • Specially Appointed Associate Professor

J-Global ID

Research Interests

  • 衛星リモートセンシング   海洋生態   海洋科学   

Research Areas

  • Environmental science/Agricultural science / Environmental dynamics

Academic & Professional Experience

  • 2019/04 - Today Hokkaido University
  • 2019/12 - 2020/02 ドイツ アルフレッドウェゲナー研究所 ヘルムホルツ極域海洋センター
  • 2009 - 2019/03 Hokkaido University Faculty of Environmental Earth Science
  • 2017/06 - 2017/09 ドイツ ライプニッツ熱帯海洋生態研究センター
  • 2008 - 2009 英国 地球観測センター 研究員(兼任)
  • 2003 - 2009 英国 プリマス海洋研究所 研究員
  • 2003 - 2008 英国 大気海洋フラックス観測センター 研究員 (兼任)


  •        - 2003  デンマーク コペンハーゲン大学

Research Activities

Published Papers

  • Inhibition of competitive exclusion due to phytoplankton dispersion: a contribution for solving Hutchinson's paradox
    YoshioMasuda, YasuhiroYamanaka, Takafumi Hirata, Hideyuki Nakano, Takashi S.Kohyama
    Ecological Modelling 430  2020/08 [Refereed][Not invited]
  • Satellite Ocean Colour: Current Status and Future Perspective
    Steve Groom, Shubha Sathyendranath, Yai Ban, Stewart Bernard, Robert Brewin, Vanda Brotas, Carsten Brockmann, Prakash Chauhan, Jong-kuk Choi, Andrei Chuprin, Stefano Ciavatta, Paolo Cipollini, Craig Donlon, Bryan Franz, Xianqiang He, Takafumi Hirata, Tom Jackson, Milton Kampel, Hajo Krasemann, Samantha Lavender, Silvia Pardo-Martinez, Frédéric Mélin, Trevor Platt, Rosalia Santoleri, Jozef Skakala, Blake Schaeffer, Marie Smith, Francois Steinmetz, Andre Valente, Menghua Wang
    Frontiers in Marine Science 6:485 doi: 10.3389/fmars.2019.00485  2019 [Refereed][Not invited]
  • Biological data assimilation for parameter estimation of a phytoplankton functional type model for the western North Pacific
    Yasuhiro Hoshiba, Takafumi Hirata, Masahito Shigemitsu, Hideyuki Nakano, Taketo Hashioka, Yoshio Masuda, Yasuhiro Yamanaka
    Ocean Science 14 371 - 386 2018 [Refereed][Not invited]
  • Distribution shifts of marine taxa in the Pacific Arctic under contemporary climate changes
    Irene D. Alabia, Jorge García Molinos, Sei-Ichi Saitoh, Toru Hirawake, Takafumi Hirata, Franz J. Muete
    Diversity and Distributions DOI: 10.1111/ddi.12788 2017/11 [Refereed][Not invited]
  • Aiken, J, R.J.W, Brewin, F. Dufois, L. Polimene, N. Hardman-Mountford, T. Jackson, B. Loveday, S. Hoya, G. Dall’Olmo, J. Stephens, T. Hirata
    Progress in Oceanography 158 236 - 254 0079-6611 2017/11 [Refereed][Not invited]
  • Tihomir S. Kostadinov, Anna Cabre, Harish Vedantham, Irina Marinov, Astrid Bracher, Robert J. W. Brewin, Annick Bricaud, Takafumi Hirata, Toru Hirawake, Nick J. Hardman-Mountford, Colleen Mouw, Shovonlal Roy, Julia Uitz
    REMOTE SENSING OF ENVIRONMENT 190 162 - 177 0034-4257 2017/03 [Refereed][Not invited]
    Ocean color remote sensing of chlorophyll concentration has revolutionized our understanding of the biology of the oceans. However, a comprehensive understanding of the structure and function of oceanic ecosystems requires the characterization of the spatio-temporal variability of various phytoplankton functional types (PFTs), which have differing biogeochemical roles. Thus, recent bio-optical algorithm developments have focused on retrieval of various PFTs. It is important to validate and inter-compare the existing PFT algorithms; however direct comparison of retrieved variables is non-trivial because in those algorithms PFTs are defined differently. Thus, it is more plausible and potentially more informative to focus on emergent properties of PFTs, such as phonology. Furthermore, ocean color satellite PFT data sets can play a pivotal role in informing and/or validating the biogeochemical routines of Earth System Models. Here, the phenological characteristics of 10 PFT satellite algorithms and 7 latest-generation climate models from the Coupled Model Inter-comparison Project (CMIPS) are inter compared as part of the International Satellite PFT Algorithm Inter-comparison Project. The comparison is based on monthly satellite data (mostly SeaWiFS) for the 2003-2007 period. The phonological analysis is based on the fraction of microplankton or a similar variable for the satellite algorithms and on the carbon biomass due to diatoms for the climate models. The seasonal cycle is estimated on a per-pixel basis as a sum of sinusoidal harmonics, derived from the Discrete Fourier Transform of the variable time series. Peak analysis is then applied to the estimated seasonal signal and the following phenological parameters are quantified for each satellite algorithm and climate model: seasonal amplitude, percent seasonal variance, month of maximum, and bloom duration. Secondary/double blooms occur in many areas and are also quantified. The algorithms and the models are quantitatively compared based on these emergent phenological parameters. Results indicate that while algorithms agree to a first order on a global scale, large differences among them exist; differences are analyzed in detail for two Longhurst regions in the North Atlantic: North Atlantic Drift Region (NADR) and North Atlantic Subtropical Gyre West (NASW). Seasonal cycles explain the most variance in zonal bands in the seasonally-stratified subtropics at about 30 latitude in the satellite PFT data. The CMIP5 models do not reproduce this pattern, exhibiting higher seasonality in mid and high-latitudes and generally much more spatially homogeneous patterns in phenological indices compared to satellite data. Satellite data indicate a complex structure of double blooms in the Equatorial region and mid-latitudes, and single blooms on the poleward edges of the subtropical gyres. In contrast, the CMIP5 models show single annual blooms over most of the ocean except for the Equatorial band and Arabian Sea. (C) 2016 Elsevier Inc. All rights reserved.
  • Bracher, A, H. Bouman, R. J, W. Brewin, A. Bricaud, V. Brotas, A. M. Ciotti, L. Clementson, E. Devred, A. Di Cicco, S. Dutkiewicz, N. Hardman-Mountford, A. E. Hickman, M. Hieronymi, T. Hirata, S. N. Losa, C. B. Mouw, E. Organelli, D. E. Raitsos, J. Uitz, M. Vogt, A. Wolanin
    Frontiers in Marine Science 2017/03 [Refereed][Not invited]
  • Mouw, C.B, N. J. Hardman-Mountford, S. Alvain, A. Bracher, R. J. W. Brewin, A. Bricaud, A. M. Ciotti, E. Devred, A. Fujiwara, T. Hirata, T. Hirawake, T. S. Kostadinov, S. Roy, J. Uitz
    Frontiers in Marine Science, Ocean Observation 4 2017/02 [Refereed][Not invited]
  • Yoshio Masuda, Yasuhiro Yamanaka, Takafumi Hirata, Hideyuki Nakano
    ECOLOGICAL MODELLING 343 1 - 14 0304-3800 2017/01 [Refereed][Not invited]
    To advance our understanding of competition and coexistence in phytoplankton species within a functional group, such as a diatom group, we developed a numerical model composed of 240 within tropic-level virtual species that can actually or potentially compete. We then explored how the phytoplankton assembly is structured by deterministic or stochastic processes, where the former process is typically represented using the traditional niche theory and the latter process is highlighted using the neutral theory. Because we used eddy-resolving resolution, phytoplankton dispersion and the resultant dispersal limitation were explicitly represented, where the dispersal limitation prevents the most competitive species from using its appropriate niche and subsequently enhances stochastic effects. In the simulation results, all surviving species have an oceanic volume in which the phytoplankton species has the highest specific growth rate in all the 240 species. The abundance in the most competitive space has a strong, positive correlation with the relative species abundance. Moreover, of the phytoplankton types whose abundances in the most competitive space are nearly equal, the survival of a species is affected by its residence time within its habitat; the surviving phytoplankton species tend to have larger residence times compared to the non-persistent species. These results led us to conclude that deterministic processes had significant contributions to a formation of phytoplankton assembly. This was supported by the result that a structure of phytoplankton assembly represented by species rank in abundance was invariant with time and hardly dependent on initial conditions of phytoplankton composition. (C) 2016 The Author(s). Published by Elsevier B.V.
  • Development of models for simulating linkages among physical, ecological, and human systems
    Takahashi K, N Saigusa, T. Oikawa, M. Kawamiya, T. Hajima, Y. Yamanaka, T. Hirata, A. Abe-Ouchi
    地球環境 20 135 - 142 2015 [Refereed][Not invited]
  • C. Laufkoetter, M. Vogt, N. Gruber, M. Aita-Noguchi, O. Aumont, L. Bopp, E. Buitenhuis, S. C. Doney, J. Dunne, T. Hashioka, J. Hauck, T. Hirata, J. John, C. Le Quere, I. D. Lima, H. Nakano, R. Seferian, I. Totterdell, M. Vichi, C. Voelker
    BIOGEOSCIENCES 12 (23) 6955 - 6984 1726-4170 2015 [Refereed][Not invited]
    Past model studies have projected a global decrease in marine net primary production (NPP) over the 21st century, but these studies focused on the multi-model mean rather than on the large inter-model differences. Here, we analyze model-simulated changes in NPP for the 21st century under IPCC's high-emission scenario RCP8.5. We use a suite of nine coupled carbon-climate Earth system models with embedded marine ecosystem models and focus on the spread between the different models and the underlying reasons. Globally, NPP decreases in five out of the nine models over the course of the 21st century, while three show no significant trend and one even simulates an increase. The largest model spread occurs in the low latitudes (between 30 degrees S and 30 degrees N), with individual models simulating relative changes between -25 and +40 %. Of the seven models diagnosing a net decrease in NPP in the low latitudes, only three simulate this to be a consequence of the classical interpretation, i.e., a stronger nutrient limitation due to increased stratification leading to reduced phytoplankton growth. In the other four, warming-induced increases in phytoplankton growth outbalance the stronger nutrient limitation. However, temperature-driven increases in grazing and other loss processes cause a net decrease in phytoplankton biomass and reduce NPP despite higher growth rates. One model projects a strong increase in NPP in the low latitudes, caused by an intensification of the microbial loop, while NPP in the remaining model changes by less than 0.5 %. While models consistently project increases NPP in the Southern Ocean, the regional inter-model range is also very substantial. In most models, this increase in NPP is driven by temperature, but it is also modulated by changes in light, macronutrients and iron as well as grazing. Overall, current projections of future changes in global marine NPP are subject to large uncertainties and necessitate a dedicated and sustained effort to improve the models and the concepts and data that guide their development.
  • Mariana A. Soppa, Takafumi Hirata, Brenner Silva, Tilman Dinter, Ilka Peeken, Sonja Wiegmann, Astrid Bracher
    REMOTE SENSING 6 (10) 10089 - 10106 2072-4292 2014/10 [Refereed][Not invited]
    Diatoms are the major marine primary producers on the global scale and, recently, several methods have been developed to retrieve their abundance or dominance from satellite remote sensing data. In this work, we highlight the importance of the Southern Ocean (SO) in developing a global algorithm for diatom using an Abundance Based Approach (ABA). A large global in situ data set of phytoplankton pigments was compiled, particularly with more samples collected in the SO. We revised the ABA to take account of the information on the penetration depth (Z(pd)) and to improve the relationship between diatoms and total chlorophyll-a (TChla). The results showed that there is a distinct relationship between diatoms and TChla in the SO, and a new global model (ABA(Zpd)) improved the estimation of diatoms abundance by 28% in the SO compared with the original ABA model. In addition, we developed a regional model for the SO which further improved the retrieval of diatoms by 17% compared with the global ABA(Zpd) model. As a result, we found that diatom may be more abundant in the SO than previously thought. Linear trend analysis of diatom abundance using the regional model for the SO showed that there are statistically significant trends, both increasing and decreasing, in diatom abundance over the past eleven years in the region.
  • Shintaro Takao, Takahiro Iida, Tomonori Isada, Sei-Ichi Saitoh, Takafumi Hirata, Koji Suzuki
    PROGRESS IN OCEANOGRAPHY 126 233 - 241 0079-6611 2014/08 [Refereed][Not invited]
    The Sea of Okhotsk is one of the most productive ocean regions in the world. However, the in situ bio-optical properties, which are crucial for satellite ocean-color of the productivity, remain uncertain in this region because little data have been available. We conducted an in situ observation and evaluated the bio-optical properties in terms of chlorophyll a (ChI a) concentration, spectral remote sensing reflectance (R-rs), and the light absorption coefficients of phytoplankton (a(j)), non-algal particles (a(NAP)), and chromophoric dissolved organic matter (a(CDOM)) in the summer of 2006. The data covered a wide range of Chl a levels in surface waters from 0.3 to 8.5 mg m(-3). At 443 nm, a(CDOM) dominated (64% on average) the total non-water absorption (a(t-w)) in this study area. Based on the in situ R-rs data, surface Chl a concentrations that were estimated using the sea-viewing wide field-of-view sensor (SeaWiFS) OC4v6 and the moderate-resolution imaging spectroradiometer (MOD'S) OC3M algorithms were significantly higher than the in situ data by more than 160% and 260%, respectively. In particular, the largest overestimation occurred in the region where a(CDOM) at 443 nm accounted for more than 80% of a(t-w) near the mouth of the Amur River. However, except the CDOM-rich stations, the performance of the OC4v6 and OC3M algorithms became better (i.e., their mean normalized biases were reduced to 50% and 66%, respectively). We conclude that the operational global algorithms were applicable to the summer season in the Sea of Okhotsk except the CDOM-rich region, in which new approaches for ocean-color algorithms (i.e., local algorithms) would be required. (C) 2014 Elsevier Ltd. All rights reserved.
  • Hirata, T, T. Hirawake, F. Sakaida, Yamaguchi, K. Suzuki, H. Murakami, J. Ishizaka, H. Kobayashi, A. Fujiwara, M. Toratani, S. Saitoh
    Journal of the Remote Sensing Society of Japan 34 (4) 278 - 285 2014 [Refereed][Not invited]
  • Werdell,P.J, B.A.Franz, S.W.Bailey, G.C.Feldman, E.Boss, V.E.Brando, M. Dowell, T.Hirata, S.J.Lavender
    Applied Optics 52 (10) 2019 - 2037 2013/04 [Refereed][Not invited]
  • T. Hashioka, M. Vogt, Y. Yamanaka, C. Le Quere, E. T. Buitenhuis, M. N. Aita, S. Alvain, L. Bopp, T. Hirata, I. Lima, S. Sailley, S. C. Doney
    BIOGEOSCIENCES 10 (11) 6833 - 6850 1726-4170 2013 [Refereed][Not invited]
    We investigated the mechanisms of phytoplankton competition during the spring bloom, one of the most dramatic seasonal events in lower-trophic-level ecosystems, in four state-of-the-art plankton functional type (PFT) models: PISCES, NEMURO, PlankTOM5 and CCSM-BEC. In particular, we investigated the relative importance of different ecophysiological processes on the determination of the community structure, focusing both on the bottom-up and the top-down controls. The models reasonably reproduced the observed global distribution and seasonal variation of phytoplankton biomass. The fraction of diatoms with respect to the total phytoplankton biomass increases with the magnitude of the spring bloom in all models. However, the governing mechanisms differ between models, despite the fact that current PFT models represent ecophysiological processes using the same types of parameterizations. The increasing trend in the percentage of diatoms with increasing bloom magnitude is mainly caused by a stronger nutrient dependence of diatom growth compared to nanophytoplankton (bottom-up control). The difference in the maximum growth rate plays an important role in NEMURO and PlankTOM5 and determines the absolute values of the percentage of diatoms during the bloom. In CCSM-BEC, the light dependency of growth plays an important role in the North Atlantic and the Southern Ocean. The grazing pressure by zooplankton (top-down control), however, strongly contributes to the dominance of diatoms in PISCES and CCSM-BEC. The regional differences in the percentage of diatoms in PlankTOM5 are mainly determined by top-down control. These differences in the mechanisms suggest that the response of marine ecosystems to climate change could significantly differ among models, even if the present-day ecosystem is reproduced to a similar degree of confidence. For further understanding of plankton competition and for the prediction of future change in marine ecosystems, it is important to understand the relative differences in each physiological rate and life history rate in the bottom-up and the top-down controls between PFTs.
  • A. P. Palacz, M. A. St John, R. J. W. Brewin, T. Hirata, W. W. Gregg
    BIOGEOSCIENCES 10 (11) 7553 - 7574 1726-4170 2013 [Refereed][Not invited]
    Modeling and monitoring plankton functional types (PFTs) is challenged by the insufficient amount of field measurements of ground truths in both plankton models and bio-optical algorithms. In this study, we combine remote sensing data and a dynamic plankton model to simulate an ecologically sound spatial and temporal distribution of phyto-PFTs. We apply an innovative ecological indicator approach to modeling PFTs and focus on resolving the question of diatom-coccolithophore coexistence in the subpolar high-nitrate and low-chlorophyll regions. We choose an artificial neural network as our modeling framework because it has the potential to interpret complex nonlinear interactions governing complex adaptive systems, of which marine ecosystems are a prime example. Using ecological indicators that fulfill the criteria of measurability, sensitivity and specificity, we demonstrate that our diagnostic model correctly interprets some basic ecological rules similar to ones emerging from dynamic models. Our time series highlight a dynamic phyto-PFT community composition in all high-latitude areas and indicate seasonal coexistence of diatoms and coccolithophores. This observation, though consistent with in situ and remote sensing measurements, has so far not been captured by state-of-the-art dynamic models, which struggle to resolve this "paradox of the plankton". We conclude that an ecological indicator approach is useful for ecological modeling of phytoplankton and potentially higher trophic levels. Finally, we speculate that it could serve as a powerful tool in advancing ecosystem-based management of marine resources.
  • Hardman-Mountford, N.J, L. Polimene, T. Hirata, R.J.W. Brewin, J. Aiken
    Journal of the Royal Sciety Interface 6 (10) 2013 [Refereed][Not invited]
  • Hirata, T, Saux-Picart, S, Hashioka, T, Aita-Noguchi, M, Sumata, H, Shigemitsu, M, Allen, I, Yamanaka, Y
    Journal of Marine Systems 109-110 129 - 137 2013/01 [Refereed][Not invited]
  • Robert J. W. Brewin, Takafumi Hirata, Nick J. Hardman-Mountford, Samantha J. Lavender, Shubha Sathyendranath, Ray Barlow
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 77-80 117 - 127 0967-0645 2012/11 [Refereed][Not invited]
    Using a decade of satellite ocean-colour observations and a model that links chlorophyll-a to the size of the phytoplankton cells, parameterised using pigment data from the Indian Ocean, we examine the implications of the Indian Ocean Dipole (IOD) for phytoplankton size structure. The inferred interannual anomalies in phytoplankton size structure are related to those in sea-surface temperature (SST) and sea-surface height (SSH), derived using satellite radiometry and altimetry, and stratification, derived using the Simple Ocean Data Assimilation (SODA) database. In regions influenced by the Indian Ocean Dipole, we observe a tight correlation between phytoplankton size structure and the physical variables, such that interannual variations in the physical variables accounts for up to 70% of the total variance in phytoplankton size structure. For much of the Indian Ocean, low temperature. low SSH and low stratification (indicative of a turbulent environment) are correlated with larger size classes, consistent with theories on coupling between physical-chemical processes and ecosystem structure. To the extent that phytoplankton function is related to its size structure, changes in physical forcing are likely to influence biogeochemical cycles in the region and the pelagic food web. The limitations of our approach are discussed and we highlight future challenges in satellite ocean-colour monitoring, should climate change lead to any modification in our marine ecosystem. (c) 2012 Elsevier Ltd. All rights reserved.
  • Hirata, T, N. Hardman-Mountford, R.Brewin
    EOS Transactions American Geophysical Union 93 (6) 59 - 60 2012/02 [Refereed][Not invited]
  • Robert J. W. Brewin, Nick J. Hardman-Mountford, Samantha J. Lavender, Dionysios E. Raitsos, Takafumi Hirata, Julia Uitz, Emmanuel Devred, Annick Bricaud, Aurea Ciotti, Bernard Gentili
    REMOTE SENSING OF ENVIRONMENT 115 (2) 325 - 339 0034-4257 2011/02 [Refereed][Not invited]
    Satellite remote sensing of ocean colour is the only method currently available for synoptically measuring wide-area properties of ocean ecosystems, such as phytoplankton chlorophyll biomass. Recently, a variety of bio-optical and ecological methods have been established that use satellite data to identify and differentiate between either phytoplankton functional types (PFTs) or phytoplankton size classes (PSCs). In this study, several of these techniques were evaluated against in situ observations to determine their ability to detect dominant phytoplankton size classes (micro-, nano- and picoplankton). The techniques are applied to a 10-year ocean-colour data series from the SeaWiFS satellite sensor and compared with in situ data (6504 samples) from a variety of locations in the global ocean. Results show that spectral-response, ecological and abundance-based approaches can all perform with similar accuracy. Detection of microplankton and picoplankton were generally better than detection of nanoplankton. Abundance-based approaches were shown to provide better spatial retrieval of PSCs. Individual model performance varied according to PSC, input satellite data sources and in situ validation data types. Uncertainty in the comparison procedure and data sources was considered. Improved availability of in situ observations would aid ongoing research in this field. (C) 2010 Elsevier Inc. All rights reserved.
  • T. Hirata, N. J. Hardman-Mountford, R. J. W. Brewin, J. Aiken, R. Barlow, K. Suzuki, T. Isada, E. Howell, T. Hashioka, M. Noguchi-Aita, Y. Yamanaka
    BIOGEOSCIENCES 8 (2) 311 - 327 1726-4170 2011 [Refereed][Not invited]
    Error-quantified, synoptic-scale relationships between chlorophyll-a (Chl-a) and phytoplankton pigment groups at the sea surface are presented. A total of ten pigment groups were considered to represent three Phytoplankton Size Classes (PSCs, micro-, nano- and picoplankton) and seven Phytoplankton Functional Types (PFTs, i.e. diatoms, dinoflagellates, green algae, prymnesiophytes (haptophytes), pico-eukaryotes, prokaryotes and Prochlorococcus sp.). The observed relationships between Chl-a and PSCs/PFTs were well-defined at the global scale to show that a community shift of phytoplankton at the basin and global scales is reflected by a change in Chl-a of the total community. Thus, Chl-a of the total community can be used as an index of not only phytoplankton biomass but also of their community structure. Within these relationships, we also found nonmonotonic variations with Chl-a for certain pico-sized phytoplankton (pico-eukaryotes, Prokaryotes and Prochlorococcus sp.) and nano-sized phytoplankton (Green algae, prymnesiophytes). The relationships were quantified with a leastsquare fitting approach in order to enable an estimation of the PFTs from Chl-a where PFTs are expressed as a percentage of the total Chl-a. The estimated uncertainty of the relationships depends on both PFT and Chl-a concentration. Maximum uncertainty of 31.8% was found for diatoms at Chla = 0.49 mg m(-3). However, the mean uncertainty of the relationships over all PFTs was 5.9% over the entire Chl-a range observed in situ (0.02< Chl-a < 4.26 mg m(-3)). The relationships were applied to SeaWiFS satellite Chl-a data from 1998 to 2009 to show the global climatological fields of the surface distribution of PFTs. Results show that microplankton are present in the mid and high latitudes, constituting only similar to 10.9% of the entire phytoplankton community in the mean field for 1998-2009, in which diatoms explain similar to 7.5%. Nanoplankton are ubiquitous throughout the global surface oceans, except the subtropical gyres, constituting similar to 45.5%, of which prymnesiophytes (haptophytes) are the major group explaining similar to 31.7% while green algae contribute similar to 13.9%. Picoplankton are dominant in the subtropical gyres, but constitute similar to 43.6% globally, of which prokaryotes are the major group explaining similar to 26.5% (Prochlorococcus sp. explaining 22.8%), while pico-eukaryotes explain similar to 17.2% and are relatively abundant in the South Pacific. These results may be of use to evaluate global marine ecosystem models.
  • Robert J. W. Brewin, Shubha Sathyendranath, Takafumi Hirata, Samantha J. Lavender, Rosa M. Barciela, Nick J. Hardman-Mountford
    ECOLOGICAL MODELLING 221 (11) 1472 - 1483 0304-3800 2010/06 [Refereed][Not invited]
    A three-component model was developed which calculates the fractional contributions of three phytoplankton size classes (micro-, nano- and picoplankton) to the overall chlorophyll-a concentration in the Atlantic Ocean. The model is an extension of the Sathyendranath et al. (2001) approach, based on the assumption that small cells dominate at low chlorophyll-a concentrations and large cells at high chlorophyll-a concentrations. Diagnostic pigments were used to infer cell size using an established technique adapted to account for small picoeukaroytes in ultra-oligotrophic environments. Atlantic Meridional Transect (AMT) pigment data taken between 1997 and 2004 were split into two datasets; 1935 measurements were used to parameterise the model, and a further 241 surface measurements, spatially and temporally matched to chlorophyll-a derived from SeaWiFS satellite data, were set aside to validate the model. Comparison with an independent global pigment dataset (256 measurements) also supports the broader-scale application of the model. The effect of optical depth on the model parameters was also investigated and explicitly incorporated into the model. It is envisaged that future applications would include validating multi-plankton biogeochemical models and improving primary-production estimates by accounting for community composition. (C) 2010 Elsevier B.V. All rights reserved.
  • J. Icarus Allen, James Aiken, Thomas R. Anderson, Erik Buitenhuis, Sarah Cornell, Richard J. Geider, Keith Haines, Takafumi Hirata, Jason Holt, Corinne Le Quere, Nicholas Hardman-Mountford, Oliver N. Ross, Bablu Sinha, James While
    JOURNAL OF MARINE SYSTEMS 81 (1-2) 19 - 33 0924-7963 2010/04 [Refereed][Not invited]
    The MarQUEST (Marine Biogeochemistry and Ecosystem Modelling Initiative in QUEST) project was established to develop improved descriptions of marine biogeochemistry, suited for the next generation of Earth system models. We review progress in these areas providing insight on the advances that have been made as well as identifying remaining key outstanding gaps for the development of the marine component of next generation Earth system models. The following issues are discussed and where appropriate results are presented; the choice of model structure, scaling processes from physiology to functional types, the ecosystem model sensitivity to changes in the physical environment, the role of the coastal ocean and new methods for the evaluation and comparison of ecosystem and biogeochemistry models. We make recommendations as to where future investment in marine ecosystem modelling should be focused, highlighting a generic software framework for model development, improved hydrodynamic models, and better parameterisation of new and existing models, reanalysis tools and ensemble simulations. The final challenge is to ensure that experimental/observational scientists are stakeholders in the models and vice versa. (C) 2010 Elsevier B.V. All rights reserved.
  • Robert J. W. Brewin, Samantha J. Lavender, Nick J. Hardman-Mountford, Takafumi Hirata
    ACTA OCEANOLOGICA SINICA 29 (2) 14 - 32 0253-505X 2010/03 [Refereed][Not invited]
    An important goal in ocean colour remote sensing is to accurately detect different phytoplankton groups with the potential uses including the validation of multi-phytoplankton carbon cycle models; synoptically monitoring the health of our oceans, and improving our understanding of the bio-geochemical interactions between phytoplankton and their environment. In this paper a new algorithm is developed for detecting three dominant phytoplankton size classes based on distinct differences in their optical signatures. The technique is validated against an independent coupled satellite reflectance and in situ pigment dataset and run on the 10-year NASA Sea viewing Wide Field of view Sensor (SeaWiFS) data series. Results indicate that on average 3.6% of the global oceanic surface layer is dominated by microplankton, 18.0% by nanoplankton and 78.4% by picoplankton. Results, however, are seen to vary depending on season and ocean basin.
  • Takafumi Hirata, Nick J. Hardman-Mountford, Ray Barlow, Tarron Lamont, Robert Brewin, Tim Smyth, James Aiken
    PROGRESS IN OCEANOGRAPHY 83 (1-4) 393 - 397 0079-6611 2009/10 [Refereed][Not invited]
    We derived size-specific photosynthetic rates for eastern boundary upwelling regions using satellite ocean colour, by a simple approach that links photosynthetic rate to phytoplankton size classes with the optical absorption of phytoplankton. Comparisons with a conventional chlorophyll-based photosynthetic algorithm and with in situ measurements showed good agreement with our approach (r(2) = 0.728, p < 0.001). Preliminary results from satellite observations for upwelling regions suggest that production in nano phytop lankton-dominated communities may be larger than for those where microphytoplankton is predominant, due to the greater spatial extent of the former. However, photosynthetic rate per unit volume is shown to be larger for microphytoplankton-dominated communities. (C) 2009 Elsevier Ltd. All rights reserved.
  • Takafumi Hirata, Nicholas Hardman-Mountford, James Aiken, James Fishwick
    APPLIED OPTICS 48 (17) 3129 - 3138 1559-128X 2009/06 [Refereed][Not invited]
    The distribution function of the ocean nadir radiance, defined by the upward radiance-to-irradiance ratio, is investigated as functions of the absorption coefficient and the volume scattering function to understand their relationship rather than to develop a numerical algorithm. It is shown for oceanic waters that the distribution function is directly proportional to the volume scattering function normalized by the back-scattering coefficient. The relatively small spectral variation of the distribution function is explained by the small spectral variation of the normalized volume scattering function, as well as by a function that describes the contribution of the backscattering-to-absorption ratio to the distribution function. The interpretation described was verified against in situ data, highlighting factors controlling the distribution function of oceanic waters. (C) 2009 Optical Society of America
  • Nick J. Hardman-Mountford, Takafumi Hirata, Kirsten A. Richardson, Jim Aiken
    REMOTE SENSING OF ENVIRONMENT 112 (8) 3341 - 3352 0034-4257 2008/08 [Refereed][Not invited]
    Based on the view of ecological pattern being steady state, rather than an equilibrium phenomenon, we assert that, if real, ecological biomes and provinces in the ocean should be detectable in surface fields obtained from satellite data as coherent, co-varying spatial regions with a high degree of permanence. Likewise, hierarchy is an important property of ecological systems that should be exhibited by Such patterns if they represent real ecological structure. In this paper, we apply a combination of multivariate statistics and classification techniques to a time series of satellite-derived, surface-ocean chlorophyll data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), (a) to provide an objective characterisation and classification of ecological pattern in the ocean and (b) to investigate the characteristic system Properties (persistence, hierarchy) of the broad-scale patterns observed to test whether they behave as autonomous ecological systems. Comparison of this classification with Longhurst [Longhurst, A. (1998), Ecological Geography of the Sea. San Diego: Academic Press, 398 pp.] suggests the need for equatorial forcing processes to be taken into account to explain observed ecological pattern at the biome level. (C) 2008 Elsevier Inc. All rights reserved.
  • Hirata, T
    Journal of Oceanography 64 (4) 561 - 566 2008/08 [Refereed][Not invited]
  • T. Hirata, J. Aiken, N. Hardman-Mountford, T. J. Smyth, R. G. Barlow
    REMOTE SENSING OF ENVIRONMENT 112 (6) 3153 - 3159 0034-4257 2008/06 [Refereed][Not invited]
    We have developed a model linking phytoplankton absorption to phytoplankton size classes (PSCs) that uses a single variable, the optical absorption by phytoplankton at 443 nm, a(ph)(443), which can be derived from the inversion of ocean colour data. The model is based on the observation that the absolute value of aph(443) co-varies with the spectral slope of phytoplankton absorption in the range of 443-510 nm, which is also a characteristic of phytoplankton size classes. The model when used for analysis of SeaWiFS global data, showed that picoplankton dominated similar to 79.1% of surface waters, nanoplankton similar to 18.5% and microplankton the remainder (2.3%). The N. and S. Atlantic and the N. and S. Pacific Oceans showed seasonal cycles with both micro and nanoplankton increasing in spring and summer in each hemisphere, while picoplankton, dominant in the oligotrophic gyres, decreased in the summer. The PSCs derived from SeaWiFS data were verified by comparing contemporary 8-day composites with PSCs derived from in situ pigment data from quasiconcurrent Atlantic Meridional Transect cruises. (C) 2008 Elsevier Inc. All rights reserved.
  • Takafumi Hirata, Niels K. Hojerslev
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 113 (C3) 0148-0227 2008/03 [Refereed][Not invited]
    A new expression for relationship between the surface irradiance reflectance and Inherent Optical Properties (IOPs) of homogeneous seawater is presented. Physical parameters largely responsible for the relationship are identified. These are the average cosines of the backward volume scattering function and of the downward radiance. Lorenz-Mie computations show that the average cosine of the backward volume scattering function is quasi-constant (0.493 +/- 0.135) for most marine waters, even if the backward volume scattering function itself is considerably variable. As a result, a base magnitude of the proportionality between the irradiance reflectance and IOPs are largely set by the average cosine of the backward volume scattering function and eventually determined by the average cosine of the downward radiance that is primarily driven by the sun angle. Independent numerical simulations of radiative transfer support results of the new expression to show that it gives significant improvement in both physical understanding and numerical prediction of the relationship.
  • Jim Aiken, Nick J. Hardman-Mountford, Ray Barlow, James Fishwick, Takafumi Hirata, Tim Smyth
    JOURNAL OF PLANKTON RESEARCH 30 (2) 165 - 181 0142-7873 2008/02 [Refereed][Not invited]
    We review the concept of phytoplankton functional types (PFTs) in marine ecosystems as a means of advancing bio-mechanistic models that can be coupled to the global carbon cycle and the Earth's climate system. Conventional classification of phytoplankton by size may seem arbitrary, but there appears clear links between size and environmental characteristics (availability of essential nutrients and light) that regulate photosynthesis, phytoplankton selection and succession. Taking a minimalist approach, small phytoplankton (picoplankton) survive in permanently stratified systems with low nutrients, high surface light and low light in deep clines, whereas large phytoplankton (microplankton) thrive in high nutrient, turbulent, high light, near surface systems. Nutrient-light environmental conditions are characteristic properties of globally, latitudinal-dispersed biogeochemical provinces. These contrasting nutrient-light regimes define the extreme ends of the bio-energetic scale of photosynthesis and set the end points of the primary range of phytoplankton functional processes. To determine PFTs from remotely sensed ocean colour data, there must be a specific bio-optical trait (BOT) that can be associated with the phytoplankton species or taxa. We investigate the connection of the bio-energetic scale to phytoplankton types and their BOTs, which is the first, but crucial step for classifying PFTs on the basis of functional processes, from which refinements and further partitioning can be developed.
  • Numerical radiative transfer simulations to examine shape of the phase function of suspended particles on the ocean colour reflectance
    Hirata, T, G. F. Moore
    La Mer 45 91 - 98 2007 [Refereed][Not invited]
  • T. J. Smyth, G. F. Moore, T. Hirata, J. Aiken
    APPLIED OPTICS 46 (3) 429 - 430 1559-128X 2007/01 [Refereed][Not invited]
  • Timothy J. Smyth, Gerald F. Moore, Takafumi Hirata, James Aiken
    APPLIED OPTICS 45 (31) 8116 - 8131 1559-128X 2006/11 [Refereed][Not invited]
    A semianalytical approach to the problem of determining inherent optical properties from satellite and in situ ocean color data is presented. The model uses empirically derived spectral slopes between neighboring wavebands in combination with radiative transfer modeling to determine the spectral absorption (a) and backscatter (b(b)); these values are then further decomposed into absorption due to phytoplankton, detrital, and colored dissolved organic matter components. When compared with over 400 in situ data points the model makes good retrievals of the total absorption and backscatter across the entire spectrum, with regression slopes close to unity, little or no bias, high percentage of variance explained, and low rms errors. (c) 2006 Optical Society of America.
  • T Hirata
    APPLIED OPTICS 42 (9) 1564 - 1573 1559-128X 2003/03 [Refereed][Not invited]
    \An attempt to retrieve the volume scattering function (VSF) of source-free and no-inelastic-scattering ocean water is made from the upwelhng irradiance E-u and downwelling irradiance E-d. It will be shown, from the radiative transfer equation, that the VSF of seawater can be calculated by the planar irradiances when the scattering phase function of the suspended particles in the backward direction and the molecular VSF are known. On the derivation of the hydrosol VSF, several optical properties such as the absorption coefficient a; the scattering coefficients of hydrosol, b, b(f,) b(b) and those of the suspended particles, b(p), b(fp), b(bp); the beam attenuation coefficient c; the average cosines mu, mu(d), and mu(u); and the backscattering shape, factor for the downwelling light stream, r(du), will also be obtained. On the derivation of those optical parameters, classical knowledge related to interrelationships between inherent optical properties and apparent optical properties and obtained with Monte Carlo numerical simulations is analytically verified. The present theory can be applied to surface waters and any wavelengths, except for waters and wavelengths with an extremely low b(b)/a ratio. (C) 2003 Optical Society of America.


Research Grants & Projects

  • Arctic biodiversity change and its consequences: Assessing, monitoring and predicting the effects of ecosystem tipping cascades on marine ecosystem services and dependent human systems
    European Commission (EC):Horizon2020
    Date (from‐to) : 2020/06 -2024/05
  • 海洋植物プランクトンに関する形質空間の概念確立と気候変動に伴う将来予測
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2018/04 -2023/03 
    Author : 山中 康裕, 平田 貴文
  • SGLI/GCOM-C 海色アルゴリズムの改良と海色プロダクトの検証および応用
    JAXA:2nd Research Announcement on the Earth Observations
    Date (from‐to) : 2019 -2021 
    Author : Takafumi Hirata
  • 画像処理技術と生物光学を融合した新型海洋一次生産者別基礎生産算出アルゴリズム
    Japan Society For The Promotion of Science:Grants-in-aid for scientific Research
    Date (from‐to) : 2017 -2019/03 
    Author : Takafumi Hirata
  • Calibration, Validation and Application of the SGLI/GCOM-C ocean algorithms
    Date (from‐to) : 2016/04 -2019/03 
    Author : 平田貴文
  • 画像処理技術と生物光学を融合した新型海洋一次生産者別基礎生産算出アルゴリズム
    Japan Society For The Promotion of Science:Grants-in-aid for scientific Research
    Date (from‐to) : 2016/04 -2018/03 
    Author : Takafumi Hirata
  • Development and calibration of GCOM-C ocean algorithms to derive marine biogeochemical and ecosystem variables towards satellite-model integrated analysis
    Date (from‐to) : 2013/04 -2016/03 
    Author : Takafumi Hirata
  • Ocean Colour Climate Change Initiative
    欧州宇宙機関 (ESA):Climate Change Initiative
    Date (from‐to) : 2014 -2016
  • Development of GCOM-C Ocean algorithm to derive Ecosystem Indicators for a satellite-model integrated analysis of marine ecosystem function and global biogeochemical cycles
    Date (from‐to) : 2009 -2013/03 
    Author : Takafumi Hirata
  • 海色衛星観測と生態系モデルによる一次生産者群集構造と海洋二酸化炭素分圧との関係
    Japan Society For The Promotion of Science:Grants-in-aid for scientific Research
    Date (from‐to) : 2010 -2011 
    Author : Takafumi Hirata

Educational Activities

Teaching Experience

  • Inter-Graduate School Classes(General Subject):Natural and Applied Sciences
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : 北極、地球観測、衛星リモートセンシング

Committee Membership

  • 2020/06 - Today   The North Pacific Marine Science Organization (PICES)   INTEGRATED ECOSYSTEM ASSESSMENT OF THE NORTHERN BERING SEA Working Group Member

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