Research item A01: Reservoir of heat and materials: Southern Ocean and its variations (Short name: Southern Ocean)
The objective of this research is mainly to clarify the process of ice sheet/ocean interactions based on observations of marine physics, chemistry, biology, and geology, as well as sample analysis with the perspective of the Southern Ocean as a reservoir of heat/material; in addition, the objective is to reveal the variations in the ocean/material circulation and ecological dynamics from past to present. This group conducted comprehensive observations in the Southern Ocean by cooperation between research groups via four Japanese research vessels and also conducted various observations and sampling by two foreign research vessels. The research has made progress that contributes to achieving the research targets of elucidating the interactions between the Southern Ocean and the Antarctic ice sheet and their impacts on the global environment. That includes comprehending the mechanisms of warm water intrusion and ice sheet/ice shelf melting in Lützow-Holm Bay where Syowa Station is located, the dynamics of bottom water in the Cape Darnley formation area and the area off Totten Glacier that contains the most decreased ice sheet area, and then the dynamics of the seasonal ecosystem/material transport as well as reconstructing the temperature and salinity of the Southern Ocean in the past.
Research group A01-1: Circulation dynamics of heat, freshwater, and material originating from Antarctic Bottom Water (Bottom Water Group)
This group simultaneously measured chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) in the Cape Darnley Antarctic Bottom Water (AABW) formation area and the outflow destination for the first time (R/V Hakuho-maru), identified the age of the bottom water and the mixing ratio of its source water and obtained data that led to the quantification of dissolved oxygen and nutrients cycle (collaboration with the A01-3 Ecosystem group). This group installed three mooring arrays in a submarine canyon where bottom water is formed, and also installed one mooring array in the polynya (continental shelf) where dense water is formed with the icebreaker Shirase (These mooring arrays were retrieved for data analysis, quantification of the bottom water amount and heat and salt fluxes, elucidation of material transport by bottom water and seasonal variations). This group clarified the three-dimensional distribution of Shirase Glacier meltwater with the Shirase for the first time in the entire Lützow-Holm Bay area. In addition, this group revealed the mechanisms of ice shelf basal melting and warm water intrusion from the open water based on collaborative analyses with ice shelf/sea ice/ocean coupled modeling and detailed mapping of seafloor topography (Cooperation with the A04 Model group /the A03 Exploration group). The cooperation of four research vessels (R/V Hakuho-maru, Kaiyo-maru, Umitaka-maru, and the icebreaker Shirase) enabled effective observations in the Indian section of the Southern Ocean. By sharing observations in the open water areas of the continental slope by R/V Kaiyo-maru and R/V Umitaka-maru, and in the ice covered areas on the continental shelf by the Shirase, this group successfully detected a warm water intrusion in the sea off Totten Glacier. This area contains the most-decreased ice sheet in East Antarctica, a new target area for intensive observation. Mooring arrays were installed in the continental shelf sea ice area off Cape Darnley by the Shirase because R/V Hakuho-maru could not enter that area.
Research group A01-2: Paleoclimate dynamics of the Southern Ocean (Paleo-oceanography group)
This group refined the sample pretreatment and analysis methods, developed paleoenvironmental proxies in the Southern Ocean, and improved their accuracies. This group established a new analysis system and the world’s first device that automates the classification of microfossils by artificial intelligence (AI) and micromanipulator based on microanalysis of biogenic opal (diatom and Radiolaria) to generate a global breakthrough in the paleoenvironmental restoration of Southern Ocean cores that include few foraminifera. This group also dated deep sea sediment cores and began comparative research with ice core dating and sea ice/ocean models. In addition, this group analyzed new and existing data on deep sea sediment cores from various locations in the Southern Ocean and contributed to data accumulation to achieve age integration and paleoenvironmental modeling, such as modeling sea surface temperature on a hemispheric scale over the past millions of years (collaboration with the A02-1 Ice sheet group). Through in situ observation by R/V Hakuho-maru, this group obtained two columns of deep-sea sediment cores, yearly precipitate particles in sediment traps, and strata information under the seafloor via seismic waves (collaboration with the A01-1 Bottom Water Group / A01-3 Ecosystem group). Furthermore, this group improved the accuracy of paleoenvironmental proxies by analyzing the hydrogen/oxygen isotope ratios of surface seawater, planktonic foraminifera, sea ice, and iceberg ice collected at many points on the same meridian and comparing themwith physical oceanographic results (A01-1 Bottom Water Group). Their international collaborative research proceeds with collecting deep sea sediment cores by a French research vessel and analyzing sediment cores obtained from five spots in the Ross Sea by an American research vessel.
Research group A01-3: Ecosystem dynamics in the Antarctic sea ice zone (Ecosystem group)
This group conducted a preliminary observation (January 2018) and a main observation (January 2019) via R/V Umitaka-maru in the Indian sector of the Southern Ocean off Vincennes Bay. In the preliminary observation, this group collected sea ice and organisms with various research devices and obtained biological distribution data and biological samples through mooring arrays in collaboration with the icebreaker Shirase. In the main observation, this group conducted biological sampling with various types of nets, such as a newly introduced large openable plankton net; in addition, this group installed long-term mooring array systems at three observation points on the 110th meridian east (summer ice edge area, circumpolar deep water upwelling area, winter ice edge area) (cooperation with the A01-1 Bottom Water Group /the A01-2 Paleo-oceanography group). The collaborative design process of the mooring arrays with the A01-1 Bottom Water Group contributed to installing many more current profilers and conductivity-temperature-depth sensors (CTDs) than previous (these were retrieved in January 2020, and the subsequent analysis enabled comprehensive discussions on the relationship between seasonal fluctuations of biological pumps and sea ice along with detailed physical fields). Moreover, with the aim of understanding the food web structure of seasonal sea ice areas, this group revealed the relationship between various biological community structures and environmental factors, as well as the contribution to the marine ecosystem by sea ice microorganisms after summer melting and release. This group also proceeded with gastrointestinal analysis of living organisms and stable isotope ratio analysis of carbon and nitrogen. (For the initial life history of Lanternfish, which are located at the top of the food web, larvae most likely eat sedimented particles, and future observations and analyses will aim to clarify the relationship with exported products from the surface layer.) The food habits survey of higher-order predators (short-tailed shearwaters) in the sea area is proceeding as planned, and progress can be expected in the future from both bottom-up and top-down perspectives centered on Lanternfish.
Research item A02: Reservoir of water and heat: Antarctic ice sheet and its variations (Short name: Antarctic ice sheet)
With the perspective of the Antarctic ice sheet as a reservoir of water/heat, this research aims to reveal variations and interactions, such as Antarctic ice sheet mass fluctuations on timescales from the present to millions of years in the past, interactions with the solid Earth, interactions between the global environment and the variability characteristics of the Antarctic climate/carbon reservoirs based on observations of ice sheet flow, surface mass balance, geodesy, and solid Earth geophysics and ice core analyses. Regarding reconstruction of past variations, the A02-1 Ice sheet group developed technology for detailed and accurate paleoenvironmental reconstructions, analyzed various environmental indicators, improved the accuracy of Dome Fuji core dating, and reconstructed CO2concentrations over the past million years via the integrated analysis of ice cores and deep sea sediment cores. As a result, the A02-2 solid Earth group obtained evidence of the ice sheet increases/decreases in the Antarctic continental margin. Concerning in situ observations related to the present ice sheet fluctuations, various in situ investigations of the ice sheet mass balance were carried out from the ice sheet margins to the inland areas. The research has progressed as expected for future collaborative research to elucidate the relationship and interactions between the Antarctic ice sheet, the Southern Ocean, and the global climate.
Research group A02-1: Variations and interactions of climate and the Antarctic Ice Sheet (Ice sheet group)
This group investigated the oxygen/nitrogen ratio, methane concentration, and seven other gas components of Dome Fuji cores up to a depth of 2000 (170,000 years ago) or more with an average resolution of 500 years to significantly improve dating accuracy of the latest super interglacial period with the purpose of precise age integration with deep sea cores during super interglacial periods (the warmest periods and highest sea levels of interglacial periods) that are especially important for ice core analysis. With the obtained data as dating constraints, this group began inversion dating by using ice sheet flow/recharge models. This group also advanced their research schedule and began analyzing the super interglacial at approximately 400,000 years ago. In addition, this group conducted measurements of methane and dust concentrations as indicators that will likely be used for age integration with deep sea cores by a continuous flow analysis system. Furthermore, this group developed an analysis method for CO2concentrations and collected winter fallen snow samples; this research led to the development of paleoenvironmental indicators. This group restored the Dome Fuji air temperature and the Southern Ocean surface sea temperature in the mid-latitudes over the past 720,000 years from oxygen/hydrogen isotope ratios of Dome Fuji ice cores to create model validation data, discussed the relationships with CO2 variations (collaboration with the A04 Model group, Nature Communications), and reconstructed the global average sea water temperature during the last deglaciation from noble gas concentrations in the air (international collaboration research, Nature). Regarding observations, this group observed the Langhovde Glacier ice shelf and the ocean beneath the ice shelf by hot water drilling (collaboration with the A01-1 Bottom Water Group, A02-2 Solid Earth group, and A01-3 Ecosystem group). Analysis of the observation data enabled this group to detect and understand in detail how this warm deep ocean water intruded under the ice shelf, melted massive amounts of ice, floated up to the surface, and moved offshore. On the Antarctic continent, this group conducted surface mass balance observations in a vast area and investigated bed topography under the ice sheet for two consecutive years (cooperation with the A04 Model group and the Group of Publicly offered research), which provided basic data to proceed with expected collaborative research on the ice sheet mass balance.
Research group A02-2: Interaction of the solid Earth and the Antarctic Ice Sheet (Solid Earth group)
This group’s objective is to contribute to research on integrated modeling of the ice sheet/ocean/climate. To achieve this goal, from geodetic, geological, and topographic investigations and bed topographic analyses in the coastal/inland areas of East Antarctica, this group endeavors to improve the accuracy of glacial isostatic adjustment (GIA) models, i.e., the responses of the solid Earth to ice sheet fluctuations and elucidate ice sheet mass balance from past to present. This group analyzed observation data and rock and sediment samples obtained from geodetic/topographic surveys at and around Syowa Station (cooperation with the A03 Exploration group). The success in new absolute gravity measurements taken at the outcrops of the Lützow-Holm Bay area was remarkable. The subsequent analysis indicated the possibility that increased snowfall has affected the gravity gradient in the same area since 2010. This group conducted geodetic investigations at other countries’ Antarctic research stations by utilizing air networks as well. In the topographic investigations, this group successfully obtained lake sediments by their newly developed portable percussion piston corer and elucidated the timing of ice sheet retreat in the southern part of Lützow-Holm Bay resulting from the global climate transition from the last glacial period to the Holocene epoch through surface exposure dating with rock samples at the same time. Calibration of several GIA models and numerical experiments laid the foundation to clarify the period of the East Antarctic ice sheet maximum extent after the last interglacial period.
Research item A03: Challenges for unexplored frontiers (Exploration group)
The A03 Exploration group conducted observations of the ocean under ice and the topography on ice, which are unexplored frontiers, developed the technology required for each group and shared observational equipment and knowledge. At the same time, this group endeavored to analyze topographic data indispensable for ice shelf/ocean models. This group focused on developing an autonomous underwater vehicle (AUV) that could obtain ocean data under sea ice and the ice shelf; this group was involved in each process, which included hearing requests from each group, formulating basic specifications and detailed designs, and completing the entire assembly. This group is currently testing its overall operations on land. The conceptual design and experimental production of a recovery system by remotely operated vehicles (ROVs) have been underway to ensure AUV recovery. This group endeavored to develop a small ROV that can be deployed underwater through a hole opened in the ice in coastal areas that are difficult for AUV deployment. In addition, this group developed a system that can observe the vertical distribution of water temperature and salinity in Antarctic coastal areas (a profiler mooring buoy equipped with software for avoiding sea ice collisions) and installed it off Cape Darnley. These developments are proceeding in collaboration with the A01-1 Bottom Water Group, A02-1 Ice sheet group, A01-3 Ecosystem group, and A02-2 Solid Earth group. For Antarctic land surveys, this group introduced three types of unmanned aerial vehicles (UAVs), such as fixed-wing UAVs, rotor UAVs, and rotor UAVs for laser surveys and conducted topographic surveys (cooperation with the A01-02 Solid Earth group/A02-1 ice sheet group). This group evaluated the accuracy of surface topography based on UAV data (digital surface model: DSM). Moreover, this group derived high-definition topography and snow cover fluctuations, which are indispensable for a model of solid Earth responses to ice sheet fluctuations and evaluated crustal changes and gravity changes due to snow coverage in collaboration with the A02-2 Solid Earth group.
Research item A04: Integrative modeling of the Antarctic ice sheet, ocean, and climate (Model group)
The objective of the A04 Model group is to develop various models, such as ocean/ice sheet interactions, and independently analyze factors affecting changes in the Southern Ocean, material circulation, and Antarctic climate changes by numerical experiments; at the same time, the objective is to pursue integrated research by collaborating closely with the A01 Bottom Water Group and the A02 Paleo-oceanography group. This group utilizes the in situ observations and data analyses from the A01 and A02 groups to discuss and share the results with the other groups. This group improved the accuracy of various models: the Model for Interdisciplinary Research on Climate (MIROC) that creates climate simulations with solar radiation and greenhouse gases as inputs, Simulation Code for Polythermal Ice Sheets (SICOPOLIS) that is a dynamic ice sheet model with atmospheric and ocean temperatures and precipitation amounts as inputs, CCRS Ocean Component Model (COCO), and an ocean material circulation model that uses ocean surface flux as an input. Furthermore, this group investigated theperformance of these models around the Antarctic in detail. This group also started paleoclimatic calculations on different timescales, namely, the past 1000 years, 20000 years, and 3.5 million years, and preliminary calculations of long-term future predictions. After incorporating high-definition seafloor topography and bed topography under the ice sheet obtained by other groups and simulating the past and future situations based on the highly accurate models, this group was ready to advance research that enables comprehension of the tipping point of the Antarctic.
Research item B01: Atmospheric physics and modeling (Group of Publicly offered research)
This research aims to understand the ice sheet mass balance and the predictability and improve the model accuracy in collaboration with the A04 Model group and the A02-2 Ice sheet group. Researchers who use the latest models participate in this research on atmospheric processes from outside the Antarctic research community.
Quantification of the uncertainty in the mid-high latitude atmospheric circulation (Inoue, B01 Group of Publicly offered research)
This group showed that meteorological observation data on the Antarctic region improved the prediction of extreme weather in the mid-latitudes through data assimilation experiments using existing observation data.
Improvement of the surface flux scheme and its impact on the estimation of the surface mass budget of Antarctic ice sheet. (Nishizawa, B01 Group of Publicly offered research)
In the strongly stable field of the Antarctic, estimating surface sublimation, which is significant for estimating increases and decreases inice sheet mass, is difficult. This group improved the relevant scheme by evaluating the defects in the estimation method of ground surface flux that is used for simulations and errors in the estimated flux. This groupverified its effectiveness based on verification tests with large eddy simulation models.
Improving the accuracy of the Antarctic ice sheet surface mass balance estimate (Niwano, B01 Group of Publicly offered research)
This group carried out various adjustment tasks (constructing a setup for the acceptable calculation speed) to perform Antarctic climate calculations via regional polar climate models and performed necessary spin-ups before full-scale calculations. In addition, this group introduced a function for diagnosing the effect of cloud radiation on ice sheet surface mass balance into models.
Research item B02: Various satellite observations (Group of Publicly offered research)
Research on ocean circulation, advection, and sea ice production was conducted and shared data were created mainly in collaboration with the Research item A01 Southern Ocean.
Elucidation of ocean circulation and estimation of the pathway of the Circumpolar Deep Water in the Southern Ocean seasonal sea ice zone by using a satellite radar altimeter (Mizobata, B02 Group of Publicly offered research)
This group created a sea surface dynamic height (SSDH) dataset after January 2011 based on data obtained by satellite radar altimeters and found clockwise circulations on the East Antarctic continental slope. In addition, this group enhanced the knowledge of Antarctic bottom water formation and warm water transport toward polar regions by comparing circulations around 110 degrees east longitude with in situ observation and reanalysis data. Furthermore, this group set up an automatic elevation profiler on one of the mooring arrays (63.5 degrees south latitude) in cooperation with the A01-3 Ecosystem group and A01-1 Bottom Water Group to investigate year-round behaviors of Circumpolar Deep Water. Cons, this project proceeds with collaboration between ocean circulation monitoring via satellite observations and simultaneous observations of Circumpolar Deep Water, the Antarctic Bottom Water, and biological parameters viamooring arrays.
Development of an accurate algorithm to estimate thin ice thickness and creation of a sea ice production dataset based on the estimated thickness (Nihashi, B02 Group of Publicly offered research)
This group developed a thin ice discrimination algorithm using microwave radiometer data to monitor coastal polynyas (open ice / thin ice areas) by satellite observations. Previous algorithms have overestimated thin ice thickness, and consequently, the newly developed algorithm estimated 1.3–1.5 times more sea ice production than previously estimated.
Research item B03: Research using new observation and analysis methods (B03 Group of Publicly offered research)
The objective of this research is to find a new environmental index based on sulfur in ice cores in collaboration mainly with the Ice sheet group.
Construction of an atmospheric chemistry transport model to simulate seasonal variations in sulfuric acid stable isotope compositions in the Antarctic atmosphere (Hattori, B03 Group of Publicly offered research)
Classification of sulfur origin and transport processes through the analysis of sulfate aerosols collected in the Antarctic indicated the possibility that sulfur isotopes in ice cores have origin information. In addition, this group compared the seasonal variations in coastal and inland oxygen isotopes with the global atmospheric chemistry transport model. Furthermore, this group modeled the behaviors of sulfateaerosols and established a method to discern large-scale eruptions that caused global cooling due to fumes reaching the stratosphere and restored the volcanic eruption history for the past 2600 years via sulfuric acid isotope compositions of Antarctic shallow ice cores.