11:05 〜 11:20
[ACG44-02] 海洋における微量元素・同位体に関する国際研究GEOTRACES計画の現状と将来
★招待講演
キーワード：GEOTRACES、微量元素、同位体
Since trace metals in seawater are essential elements for primary production and important as tracers for tracking ocean processes, research on the biogeochemical cycling of trace metal elements and their isotopes (TEIs) has been actively implemented in recent years by the international GEOTRACES program. GEOTRACES is also recognized as an official activity of the United Nations Decade of Ocean Science starting in 2021. A major research topic of GEOTRACES is to clarify the factors that determine the distribution of TEIs in the ocean and their fluxes, and to elucidate their relationship with global environmental changes. The immediate goal of the GEOTRACES project is to first conduct cross-sectional observations of the ocean on a global scale, and to clarify the distribution of TEIs in seawater from the surface layer to just above the seafloor. So far, the results are published in the Intermediate Data Product (GEOTRACES IDP). The recent GEOTRACES IDP2021 includes datasets from research cruises around the world (https://www.geotraces.org/geotraces-intermediate-data-product-2021/).
In Japan, eight research cruises related to the GEOTRACES project have been conducted using R/V Hakuho-maru in the Indian Ocean, Pacific Ocean, and these adjacent marginal seas. In this presentation, some of the results from the North Pacific will be introduced. So far, Japanese GEOTRACES conducted 5 research cruises mainly in the western subarctic Pacific (KH-11-7, KH-12-4, KH-17-3 and KH-22-7); the distributions of bioactive trace metal elements such as Fe, Mn, Zn, Co, Ni, Cu, and Cd indicated the importance of North Pacific Intermediate Water (NPIW) for their distributions (e.g., Kim et al., 2017; Nishioka and Obata, 2017; Zheng et al., 2021). Various parameters have been also obtained during the cruises, such as Pb and Al, which can be used as indexes of anthropogenic and continental materials, respectively (Minami et al., 2015; Zheng et al., 2019). During these cruises, we not only investigated the distribution of each element concentration, but also studied isotopic ratios and radionuclides (e.g., Otosaka et al., 2014; Takano et al., 2019). Furthermore, obtained samples were not limited to seawater, but also aerosols and sediments. The supply and removal of TEIs occur through the exchange processes at the interfaces; for example, atmosphere-surface ocean, rivers-marginal sea, and seafloor sediment-water column. Therefore, the accumulation of such data is very valuable and contributes to the understanding of marine biogeochemical cycles.
Twelve years have passed since the start of the GEOTRACES research cruise, and the IDP is the most significant achievement of this project. On the other hand, we have not collected the data on spatiotemporal variations since the present dataset is an observational snapshot. How will the distribution of TEIs change in the future as the marine environment undergoes climate change, like global warming? Although this prediction is not easy, it is necessary to elucidate the process of the TEIs cycle in the ocean and evaluate future predictions based on the results. Future oceanographic observations should aim to clarify the various processes that will determine the distribution of TEIs.
In Japan, eight research cruises related to the GEOTRACES project have been conducted using R/V Hakuho-maru in the Indian Ocean, Pacific Ocean, and these adjacent marginal seas. In this presentation, some of the results from the North Pacific will be introduced. So far, Japanese GEOTRACES conducted 5 research cruises mainly in the western subarctic Pacific (KH-11-7, KH-12-4, KH-17-3 and KH-22-7); the distributions of bioactive trace metal elements such as Fe, Mn, Zn, Co, Ni, Cu, and Cd indicated the importance of North Pacific Intermediate Water (NPIW) for their distributions (e.g., Kim et al., 2017; Nishioka and Obata, 2017; Zheng et al., 2021). Various parameters have been also obtained during the cruises, such as Pb and Al, which can be used as indexes of anthropogenic and continental materials, respectively (Minami et al., 2015; Zheng et al., 2019). During these cruises, we not only investigated the distribution of each element concentration, but also studied isotopic ratios and radionuclides (e.g., Otosaka et al., 2014; Takano et al., 2019). Furthermore, obtained samples were not limited to seawater, but also aerosols and sediments. The supply and removal of TEIs occur through the exchange processes at the interfaces; for example, atmosphere-surface ocean, rivers-marginal sea, and seafloor sediment-water column. Therefore, the accumulation of such data is very valuable and contributes to the understanding of marine biogeochemical cycles.
Twelve years have passed since the start of the GEOTRACES research cruise, and the IDP is the most significant achievement of this project. On the other hand, we have not collected the data on spatiotemporal variations since the present dataset is an observational snapshot. How will the distribution of TEIs change in the future as the marine environment undergoes climate change, like global warming? Although this prediction is not easy, it is necessary to elucidate the process of the TEIs cycle in the ocean and evaluate future predictions based on the results. Future oceanographic observations should aim to clarify the various processes that will determine the distribution of TEIs.