Research activity information

• Eddy-covariance measurements of turbulent fluxes across the oxygen-depleted benthic layer in a shallow stratified lake
  Yusuke Kawaguchi; Eiji Masunaga; Takao Ouchi; Tatsumi Kitamura; Eun Yae Son
  Limnology, 26, 1, 91, 105, Springer Science and Business Media LLC, 27 Sep. 2024
  Scientific journal, Abstract
  
  Seasonal stratification hinders the ventilation of hypolimnion water, leading to the formation of an anaerobic benthic layer in shallow lakes. This study quantifies the processes of hypoxia formation and recovery in Lake Kasumigaura, Japan, under conditions of developing metalimnion during early summer, specifically from early May to mid-July 2022. We conducted direct observations of vertical turbulent fluxes of dissolved oxygen (DO), as well as heat and momentum fluxes using an eddy-covariance system (ECS), enabling simultaneous measurements of various variables near a sampling volume. Additionally, autonomous acquisition of vertical profiles for DO, temperature, and Chlorophyll a in the lake's vicinity was performed. Our observations revealed that thermal stratification temporarily developed, leading to hypoxia near the bottom when near-surface air temperature exceeded 25 °C. During the metalimnetic period under stable stratification, the ECS demonstrated downward transport of heat and DO, resulting in daily averages of approximately 30–40 W m⁻² and 1–1.5 × 10⁻⁵ mg L⁻¹ m s⁻¹ (equivalent to 1.1–1.7 mmol m⁻² h⁻¹), respectively. Using ECS observations, we estimated a turbulent diffusivity of approximately 5 × 10⁻⁶ m² s⁻¹ during enhanced stratification, consistent with previous reports. Under weak stratification in mid-May, the ECS indicated enhanced vertical fluxes, with occasional upward DO flux. We propose the possibility that phytoplankton acted as oxygen suppliers through photosynthesis activity, promoting vertical DO transfer.
• Multidisciplinary research for sea ice in Saroma-ko Lagoon, Hokkaido, Japan 2023
  Daiki NOMURA; Ryota AKINO; Matthew CORKILL; Keizo HIRANO; Akihide KASAI; Seiji KATAKURA; Yusuke KAWAGUCHI; Tatsuya KAWAKAMI; Riri KIMURA; Delphine LANNUZEL; Ryosuke MAKABE; Mirai MATSUURA; Kohei MATSUNO; Klaus MEINERS; Keizo NAGASAKI; Yuichi NOSAKA; Nana SAMORI; Shinnosuke SAKAYA; Eun Yae SON; Ryotaro SUGA; Yumi SUNAKAWA; Keigo D. TAKAHASHI; Masaharu TAKAHASHI; Yuka TAKEDA; Takenobu TOYOTA; Manami TOZAWA; Pat WONGPAN; Hiroshi YOSHIDA; Kazuhiro YOSHIDA; Masaki YOSHIMURA
  Bulletin of Glaciological Research, 42, 19, 37, Japanese Society of Snow and Ice, 2024
  Scientific journal
• Assessment of Turbulent Mixing Associated With Eddy‐Wave Coupling Based on Autonomous Observations From the Arctic Canada Basin
  E. Y. Son; Y. Kawaguchi; S. T. Cole; J. M. Toole; H. K. Ha
  Journal of Geophysical Research: Oceans, 127, 9, American Geophysical Union (AGU), 13 Sep. 2022
  Scientific journal, Abstract
  
  Interaction between mesoscale eddies and near‐inertial internal waves can contribute to enhanced turbulence mixing but quantitative knowledge from in situ observations is still lacking. This study reveals how eddy/near‐inertial wave interactions (ENIs) can affect the variability of turbulent mixing in the ice‐covered Canada Basin of the Arctic Ocean. We use data from five Ice‐Tethered Profiler with Velocity (ITP‐V) systems that autonomously obtained vertical profiles of horizontal velocity as well as temperature and salinity, which enabled quantification of ENI‐caused turbulent mixing using a fine‐scale parameterization. From the ITP‐V observations in 2013–2015, 67 anticyclones were detected, of which 90% had a deep core at 150–250 m depth. The remaining eddies had a shallow core, typically embedded in the Pacific Summer Water (PSW). Just over one third of the eddies showed evidence of ENI with enhanced near‐inertial internal wave amplitude (NIW) near the eddy cores. For these ENI cases, the parameterized turbulence dissipation rate was O (10⁻¹⁰–10⁻⁸ W kg⁻¹), the larger estimates being several orders of magnitude greater than the background level. For the deep eddies, the ENI process can largely be accounted for by the classical theory, NIWs are trapped inside the negative relative vorticity core of anticyclones. For one shallow eddy, the NIW signal was greatest below the core. We postulate that a vertically elongated system of NIWs cannot be constrained vertically within such small‐cored eddies. It is also interpreted that the wave enhancement below the core was supported by the isopycnal slope near the PSW through its geostrophic shear.
• Atmosphere-sea ice-ocean interaction study in Saroma-ko Lagoon, Hokkaido, Japan 2021
  Daiki NOMURA; Hiroki IKAWA; Yusuke KAWAGUCHI; Naoya KANNA; Tatsuya KAWAKAMI; Yuichi NOSAKA; Sachi UMEZAWA; Manami TOZAWA; Takahito HORIKAWA; Reishi SAHASHI; Taichi NOSHIRO; Ibuki KABA; Makoto OZAKI; Fumiyoshi KONDO; Keisuke ONO; Itsuka S. YABE; Eun Yae SON; Takahiro TOYODA; Sohiko KAMEYAMA; Changqing WANG; Hajime OBATA; Atsushi OOKI; Hiromichi UENO; Akihide KASAI
  Bulletin of Glaciological Research, 40, 1, 17, Japanese Society of Snow and Ice, 2022
  Scientific journal
• Saroma-ko Lagoon Observations for sea ice Physico-chemistry and Ecosystems 2019 (SLOPE2019)
  Daiki NOMURA; Pat WONGPAN; Takenobu TOYOTA; Tomonori TANIKAWA; Yusuke KAWAGUCHI; Takashi ONO; Tomomi ISHINO; Manami TOZAWA; Tetsuya P. TAMURA; Itsuka S. YABE; Eun Yae SON; Frederic VIVIER; Antonio LOURENCO; Marion LEBRUN; Yuichi NOSAKA; Toru HIRAWAKE; Atsushi OOKI; Shigeru AOKI; Brent ELSE; Francois FRIPIAT; Jun INOUE; Martin VANCOPPENOLLE
  Bulletin of Glaciological Research, 38, 1, 12, Japanese Society of Snow and Ice, 2020
  Scientific journal