Research and Public Dataset Production on the Arctic Marine Environment
Background
The GRENE Arctic Climate Change Research Project (GRENE Arctic) has produced cutting-edge research results focusing on changes in marine ecosystems, particularly in the Pacific Arctic shelf area where sea ice margins retreat significantly during summer. Its successor, the Arctic Challenge for Sustainability (ArCS) project, has been attempting to return the findings to society while making them more attractive through collaboration between the natural sciences and the human and social sciences. At the same time, discussions on the sustainable use of the Arctic Ocean from an economic perspective have been gaining momentum, and it is expected that the latest observation data and numerical simulation results are utilized for social implementation. In the Arctic Ocean, especially in the central basins and marginal ice zones, knowledge on ocean heat transport, ecosystems, and biogeochemical cycles is still insufficient. Changes in the wind pattern and the sea surface heat budget have been cited as factors contributing to the rapid sea ice reduction in recent years, but it is important to conduct a comprehensive assessment that includes the effects of ocean heat on the overlying sea ice. In addition, the ecosystems and biogeochemical cycles in sea ice areas are continuously changing, and understanding the present statuses is an urgent issue for implementing ecosystem-based management of fishery resources, including future projections.
Objective
In the Research Program on Ocean, three Sub Programs (described below) were established for the conservation and sustainable use of the rapidly changing Arctic by elucidating environmental dynamics such as ocean heat transport, ecosystems, and biogeochemical cycles in the central basins and marginal ice zones of the Arctic Ocean. In addition to conventional shipboard and mooring observations, we have developed the advanced observation systems using state-of-the-art portable sensors, profiling floats, wave buoys, automatic water sampling, acoustic and video equipment, etc., in an attempt to approach marginal ice zones and perennial ice areas that have been difficult to access. Despite various constraints such as COVID-19 and the deteriorating situation in Russia and Ukraine, we continued the Arctic cruises by the Research Vessel (R/V) Mirai for five years, and also made the best use of other countries' icebreakers, ice camps, and observation sites. In addition, as a means of promoting intra- and inter-program collaboration and social implementation, several public data sets were constructed and made available on the Arctic Data archive System (ADS) or equivalent websites.
This Research Program has also played an important role in many international joint projects. The R/V Mirai participated in the Synoptic Arctic Survey (SAS) from 2020 to 2022, in which multiple vessels covered the main areas of the Arctic Ocean. The members of this Research Program were also deeply involved in the Multidisciplinary Drifting Observatory for the Study of the Arctic Climate (MOSAiC) from 2019 to 2020, in which the German research icebreaker Polarstern crossed the Arctic Ocean, and many research results were published by analyzing valuable data acquired over a wide area and throughout the year. In addition, some of the members belong to major international frameworks such as the Pacific Arctic Group (PAG), the Ecosystem Studies of Subarctic and Arctic Seas (ESSAS), the Working Group on Integrated Ecosystem Assessment for the Central Arctic Ocean (WGICA), and the Biogeochemical Exchanges Processes at Sea Ice Interfaces (BEPSII) and have served in representative roles. By involving many graduate students and early career researchers in these activities, we have continuously nurtured human resources who will lead future Arctic sea ice and ocean research, and disseminated our achievements and presence to the world.
Summary of Sub Programs
In Sub Program 1, we have developed high-precision data sets by integrating international collaborative cruises and pan-Arctic regional modeling, and have promoted intra- and inter-program collaboration using these data sets in order to clarify in more detail the heat transport and biogeochemical cycles in the ocean from the seasonal and multiyear sea ice areas. We have clarified the transport processes (pathways and modifications) of water masses originating from the North Pacific and North Atlantic, respectively. Utilizing existing mooring equipment and satellite data, we have analyzed the pathways and interannual variations of warm water transport that form sub-surface temperature maxima under sea ice. Furthermore, by expanding the scope of our research to include material supply from the atmosphere, river water, and seafloor sediments to sea ice and the ocean interior, we aimed to understand the seamless biogeochemical cycles from sea ice through the ocean surface to the seafloor. The air–sea CO2 exchange rate, including the statistical data set constructed by ArCS and the experimental results of the pan-Arctic sea ice–ocean model incorporating a carbonate chemistry routine was compared internationally within the framework of the REgional Carbon Cycle Assessment and Processes phase 2 (RECCAP2). In addition, many seafloor sediment samples were collected to reconstruct the paleoenvironment of the past 2,000 years.
In Sub Program 2, we improved an algorithm for accurately estimating primary production of phytoplankton from satellite data and optimized the mapping for the Arctic Ocean. This information is also closely related to the partial pressure of CO2 in the ocean surface layer, and contributes to the high accuracy of the air–sea CO2 exchange analyzed in Sub Program 1. The time-series data obtained from the sediment-trap mooring system revealed phyto- and zooplankton abundance, community composition, and life history. In addition, we established a method for analyzing environmental DNA retained in seawater, including in the central basins and under sea ice where direct collection of organisms by bottom trawling is difficult, and clarified the habitat of Arctic cod and other species based on their genetic information. We also used advanced statistical models to estimate the habitats of potential fishery resources, including future predictions.
In Sub Program 3, we conducted complex observations using a variety of techniques including vessels, drifting buoys, mooring systems, radar, drones, and ice camps to understand the air–sea interaction through sea ice, including wave and gas exchange. Based on these observations, we have accumulated expertise in sea ice observation methods and provided knowledge for safe navigation and highly accurate prediction of sea ice edges. We have analyzed physical, chemical, and biological characteristics (thickness, internal temperature, dissolved gases, nutrients, chlorophyll concentration, etc.) of sea ice and sea water samples collected through time-series observations by mooring systems equipped with ice profiling sonars and through on-ice and shipboard observations, and clarified mechanisms of seasonal and interannual variations. We have also established an international standard protocols for sea ice observation methods, utilizing icebreakers, ice camps, and observation sites in other countries. During the R/V Mirai cruise, we conducted complex observations in the marginal ice zones using the Zodiac boat, portable sensors, wave buoys, stereo cameras, and radars, and accumulated fundamental knowledge on sea ice–ocean–wave interactions.
All of these Sub Programs contribute not only to Strategic Goal 1 "Advanced Observation of Arctic Environmental Change" but also to Strategic Goals 2, 3, and 4, respectively (see figure).
