Japan Geoscience Union Meeting 2023

Presentation information

[J] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-CG Complex & General

[A-CG45] Biogeochemical linkages between the surface ocean and atmosphere

Sun. May 21, 2023 9:00 AM - 10:30 AM 102 (International Conference Hall, Makuhari Messe)

convener:Sohiko Kameyama(Hokkaido University), Yoko Iwamoto(Graduate School of Integrated Sciences for Life, Hiroshima University), Maki Noguchi Aita(Japan Agency for Marine-Earth Science and Technology), Naohiro Kosugi(Meteorological Research Institute), Chairperson:Naohiro Kosugi(Meteorological Research Institute), Maki Noguchi Aita(Japan Agency for Marine-Earth Science and Technology)

9:15 AM - 9:30 AM

[ACG45-02] Distribution and determinants of nutrients and primary production in the eastern Indian sector of the Southern Ocean

*Manami Tozawa1, Daiki Nomura1,2,3, Kaihe Yamazaki4, Masaaki Kiuchi1, Daisuke Hirano4,5, Shigeru Aoki6, Hiroko Sasaki7, Hiroto Murase8 (1.Faculty/Graduate School of Fisheries Sciences, Hokkaido University, 2.Field Science Center for Northern Biosphere, Hokkaido University, 3.Arctic Research Center, Hokkaido University, 4.National Institute of Polar Research, 5.The Graduate University for Advanced Studies, SOKENDAI, 6.Institute of Low Temperature Science, Hokkaido University, 7.Japan Fisheries Research and Education Agency, Yokohama, 8.Tokyo University of Marine Science and Technology)


Keywords:Nutrients, net community production, Southern Ocean Indian Ocean sector, seasonal sea ice zone

To investigate the spatial distributions and determinants of nutrient concentrations, we measured NO3+NO2, PO43−, and Si(OH)4concentrations in the eastern Indian Ocean sector of the Antarctic Ocean (80−150°E, south of 60°S) between December 2018 and February 2019. In the Antarctic Circumpolar Current (ACC) domain, nutrient concentrations were increased by nutrients supplied from the deep layer and by organic matter decomposition and remineralization within the seasonal pycnocline after the development of strong stratification. Strong stratification also enhanced phytoplankton growth and nutrient consumption by photosynthesis. In contrast, in the subpolar region, nutrient concentrations were increased by nutrients supplied by brine discharged during sea ice formation and decreased by dilution with sea ice meltwater. Although high salinity in the surface and subsurface layers corresponded well to upwelling areas around subpolar subgyres, high salinity was not necessarily correlated with nutrient concentrations. We estimated primary production both from in situ nutrient data and from satellite-acquired chlorophyll-a data. According to both estimation methods, primary production was high in the subpolar region, especially around 120−130°E. However, nutrient-based estimation also showed high production in coastal areas where, because of sea ice and cloud cover, estimation based on satellite data was not possible. To understand primary production in seasonal ice areas, the best estimation method should be selected for the research goals or multiple methods should be used in combination.