Research results

Research item A01: Reservoir of heat and materials: Southern Ocean and its variations
(Short name: Southern Ocean)

Research group A01-1 (Ohshima/Bottom Water Group):

Observations and modeling of glacier/ocean interactions in the Shirase Glacier area (cooperation with the A04 Model group/A03 Exploration group)

This group conducted oceanographic observations with the icebreaker Shirase for the first time throughout the entire Lützow-Holm Bay area and clarified the three-dimensional distribution of Shirase Glacier meltwater considering isotope ratios. Based on this result and a glacier/ocean combined model, this group revealed detailed interactions between the ocean and glacier: warm circumpolar deep water originating from offshore intrudes along the canyon into the Shirase Glacier terminus area, causes glacier basal melting and flows northward mixed with ice shelf meltwater.

Elucidation of Antarctic bottom water (AABW) and carbon/nutrient circulation by chemical tracers

The A01-1 Bottom Water Group performed several tracer measurements of chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) with R/V Hakuho-maru in the Cape Darnley AABW formation and expansion area for the first time in the Southern Ocean. These measurements determined one possible average age of bottom water and enabled quantification of the bottom water circulation timescale and nutrient cycle. The measurements further enabled estimation of the anthropogenic CO2 concentration in bottom water, which indicated high CO2 concentrations near the seafloor.

Intensive ocean observations in the Totten Glacier sea area (collaboration with the A01-3 Ecosystem group)

The A01-1 Bottom Water Group conducted ocean observations with R/V Kaiyo-maru and ice breaker Shirase in the Totten Glacier sea area, the target area for intensive observations. This area contains the most decreased ice sheet in East Antarctica. This group successfully detected how warm circumpolar deep water originating from the open sea (which causes glacier melting) intrudes along the canyon in the glacier area through observations with these two vessels.

Research group A01-2 (Ikehara/Paleo-oceanography group):

Establishment and application of an automated collection system of single microfossil species via artificial intelligence (AI)

The A01-2 Paleo-oceanography group established an automated collection system comprising a micromanipulator and AI deep learning program (patent application 2018-163981). In addition, this group constructed an AI model based on learning a large amount of microfossil image data. These achievements facilitated automated analysis of the community composition and high-speed automated collection of microfossils and led to practical applications of deep sea sediment cores collected in the Southern Ocean.

Paleo-oceanographic variation analysis of deep-sea sediment cores (collaboration with the A02-1 Paleo-oceanography group)

The A01-2 Paleo-oceanography group integrated new and existing data on the sea surface temperature (SST) restored from sediment cores originating in the Southern Ocean and reconstructed the SST in the entire Southern Ocean over 5 million years. Restoration indicated that SST variations were synchronized with variations in Antarctic air temperature and CO2 levels over the past 3 million years and that the SST during the super interglacial period was approximately one degree higher than the present SST (which supports the possibility of ocean warming causing ice sheet melting). Furthermore, this suggested the possibility that the Southern Ocean drove the development of Northern Hemisphere ice sheets and periodic changes in the glacial cycle through significant SST cooling between 3.5 and 3.3 million years ago and between 2 million and 1.5 million years ago, respectively.

Observations and sampling with R/V Hakuho-maru and foreign research vessels (collaboration with the A01-1 Bottom Water Group/A01-3 Ecosystem group)

The A01-2 Paleo-oceanography group obtained yearly precipitate particle samples from two columns of deep sea sediment cores and sediment traps and information on the sediment wave distribution via reflection surveys. Analysis of 4 long columns of deep sea sediments collected by a French research vessel and deep sea sediment samples at five locations in the Ross Sea by an American research vessel contributed to knowledge accumulation and comprehension concerning the Antarctic environment under warm climate conditions, such as vegetation growth in the West Antarctic during the Pliocene Epoque and climate changes on a thousand-year timescale.

Research group A01-3 (Moteki/Ecosystem group):

Elucidation of horizontal transport of materials and organisms consistent with sea ice flow (collaboration with the A01-1 Bottom Water Group)

Material transport consistent with sea ice flow constitutes a key process in material circulation in the vast seasonal sea ice zone. The A01-3 Ecosystem group revealed the dynamics of microalgae (Takahashi et al.), organic particles, and animals (Hasegawa et al., submitted) to better understand material uptake during sea ice production in coastal areas, material release into the water column in the melting process, and impact on the ecosystem in seasonal sea ice zones.

Observations of the ecosystem to develop paleoenvironmental proxies(collaboration with the A01-2 Paleo-oceanography group)

The A01-3 Ecosystem group determined a new possible environmental indicator proxy through approaches involving both sediment cores and sea ice (Kato and Suto, 2019, Takahashi et al., submitted).

Observations of food web/material circulation under sea ice to comprehend the carbon sequestration process

In the Southern Ocean, the ecosystem structure of the seasonal sea ice zone controls deep sequestration of carbon fixed at the surface. This group has been accumulating observational knowledge and data on the food web comprising various biota and material circulation in the food web.

Research item A02: Reservoir of water and heat: Antarctic ice sheet and its variations

Research group A02-1 (Kawamura/Ice sheet group):

Paleoclimate research by ice core (collaboration with the A04 Model group)

The A02-1 Ice sheet group reconstructed the Antarctic air temperature over the past 7.2 million years and the Southern Ocean SST at mid-latitudes via analysis of oxygen/hydrogen isotope ratios of Dome Fuji ice cores with isotope models (Uemura et al.,2018, nature Comm.). Based on analysis of Antarctic and Greenland ice cores, this group identified climatic links through the atmosphere and ocean between two polar regions (Buizert et al., 2018, Nature). This group also reconstructed the global average sea water temperature during the last deglaciation according to noble gas concentrations. In addition, this group identified a corresponding consistency with Antarctic temperature variations (Bereiter et al.,2018, Nature)

Analysis for precise age integration with deep sea sediment cores

The A02-1 Ice sheet group investigated the oxygen/nitrogen ratio, methane concentration, and seven other gas components with an average resolution of 500 years and obtained data to significantly improve the dating accuracy of Dome Fuji ice cores up to a depth of 2000m (170000 years ago), which includes the latest super interglacial period. This group further investigated the methane concentration and dust via a continuous flow analysis method.

Observational research of ice sheet/ocean interactions through hot water drilling in the Langhovde Glacier (cooperation with the A01-1 Bottom Water Group/A02-2 Solid Earth group/A01-3 Ecosystem group)

The A02-1 Ice sheet group observed the ocean beneath and within the ice shelf through hot water drilling holes and detected and revealed in detail the mechanism of warm deep ocean water intrusion below the ice shelf, thereby melting massive amounts of ice and flowing toward the surface mixed with meltwater.

Observational research of the surface mass balance and ice sheet bed topography in a vast area (cooperation with B01 Publicly offered research/A02-1 Model group/A02-2 Solid Earth group)

The A02-1 Ice sheet group conducted observational research of the surface mass balance and bed topography in the vast area from coastal to inland Dome Fuji. This group analyzed both new and previously obtained data and compiled and developed a chronological database contributing to further collaborative research.

Research group A02-2 (Solid Earth group/Fukuda):

Absolute gravity measurement

The A02-2 Solid Earth group performed absolute gravity measurements at the Syowa Station and surrounding coastal area and calculated the temporal gravity gradient (-0.22 μgal/yr), thereby comparing new data to previous data at the Syowa Station. This group also conducted absolute gravity measurements at two foreign research stations, namely, the Troll Station (Norway) and Maitri Station, and calculated gravity changes at each station.

Topographical surveys

The A02-2 Solid Earth group collected lake and deep sea sediments through drilling with a newly developed portable piston corer (Suganuma et al., patent application, 2019) and rock samples along the Soya coast near the Syowa Station to restore the history of East Antarctic ice sheet melting over the past 20000 years. Analysis of the collected samples revealed precipitous ice sheet retreat from 14000 to 9000 years ago.

Glacial isostatic adjustment (GIA) modeling

TheA02-2 Solid Earth group developed a GIA model facilitating simulation of vertical crustal movement and variation in the gravitational field, calculated the impact of GIA with different viscosity models and compared model results to various observation data, such as absolute gravity measurements, global navigation satellite system (GNSS) observations, and topographical surveys, at and surrounding the Syowa Station. These achievements clearly highlighted the necessity to revise the ice sheet melting history and remove the impact of current load fluctuations (snow cover).

Research item A03: Challenges for unexplored frontiers

Development and installation of a profiler mooring buoy (collaboration with all three research groups in the A01 Southern Ocean)

The profiling buoy system available in the Antarctic coastal area measures vertical profiles of the water temperature/salinity during ascent and transmits observation data at the time of surfacing at the sea surface via satellites. This system is equipped with software to avoid collision with sea ice and was installed offshore of Antarctic Cape Darnley after various tests.

Development of autonomous underwater vehicles (AUVs)

Group A03 developed an AUV to obtain data beneath sea ice and ice shelves. Based on observational items such as the seafloor topography, three-dimensional shape of ice, and water quality, the AUV can be equipped with cameras and comprises split structure flames to be prepared for future technical expansion. The AUV was designed with specifications of a total length of 2.1m, aerial weight 230kg, maximum dive depth 1200m, and the ability to enter 10km at maximum beneath sea ice and the ice shelves. Three action patterns are expected: (A) seafloor tracking (seafloor topography measurement), (B) ice tracking (measurement of sea ice/ice shelf lower shape). The entire assembly was completed, and an operation test on land is underway.

Observations by unmanned aerial vehicles (UAVs) (collaboration with the two research groups of the A02 Antarctic ice sheet)

The A03 Exploration group conducted flight tests of fixed-wing and rotor UAVs at the Syowa Station and coastal outcrops, topographic surveys, and aerial shoot. Based on the collected data, this group created a surface topographic model (digital surface model/DSM) of East Ongle Island and evaluated the accuracy of the DSM with each UAV. The A03 group further derived high-definition topography and snow cover fluctuations, which are indispensable for models of solid Earth responses to ice sheet fluctuations and evaluated crustal and gravity changes in collaboration with the A02-2 Solid Earth group.

Research item A04: Integrative modeling of the Antarctic ice sheet, ocean, and climate (model group/Abe-Ouchi)

Correcting bias in global climate models

Almost all climate models exhibit a common discrepancy with observation data. The A04 model group successfully corrected the warm bias observed near the Antarctic in Japanese climate models by improving the mixing parameter in ocean and cloud microphysics properties (figure on the right). As a result, ocean circulation during glacial periods attained consistency with paleo-oceanographic data.

Reproducing the transition from glacial to interglacial periods via climate modeling

The A04 group successfully obtained the climatic state across the Antarctic region during transition from the glacial period to the Holocene Epoque and the last interglacial period (the super interglacial period) for the first time with a climate model. Figure: Comparing paleoclimate data to simulation results from the deglaciation period to the Holocene Epoque (red) and the last glacial period (blue) (North Atlantic Ocean circulation intensity, Antarctic air temperature, Southern Ocean water temperature). The only difference in configuration for numerical experiments is the history of northern hemispheric ice sheet melting.

Analysis of the factors enabling current Antarctic ice sheet existence

Analysis and discussion of simulation results indicated possible reasons why the current Antarctic ice sheet did not decrease, in contrast to the last interglacial period. The north–south antiphase, the recurrence of cold phenomenon, occurred during the last deglaciation period, and the antiphase entailing the recurrence of cold encompasses a self-excited oscillation in the atmosphere and ocean system induced under the condition that the atmospheric CO2 concentration and the melting rate of northern hemispheric ice sheets remain within certain ranges (Figure: Sea water temperature and distribution of the air temperature maximum gap during the deglaciation period). The red dots indicate the data on ice cores and deep sea sediment samples.

Research item B01: Atmospheric physics and modeling (collaboration with the A04 Model group/A02-1 Ice sheet group)

Weather and climate links between the Antarctic region and mid-latitudes(Inoue/Group of Publicly offered research)

This group enhanced radiosonde observations at the Syowa Station and Dome Fuji. Prior to the enhancement, this group conducted data assimilation experiments considering existing observation data and suggested that meteorological observation data for the polar region contribute to improving the prediction of extreme weather conditions in remote areas such as Australia (Sato et al., 2018, press release).

Improvement of the surface flux scheme in numerical simulation models(Nishizawa/Group of Publicly offered research)

This group clarified problems in the existing surface flux estimation scheme and successfully developed a solution scheme. In addition, this group confirmed the efficiency of the developed scheme in verification experiments with a large-eddy simulation model.

Estimation of the ice sheet recharge amount with a polar regional climate model(Niwano/Group of Publicly offered research)

This group calculated spin-ups at a 6-km horizontal resolution and introduced a new function to evaluate the effect of cloud radiation on the ice sheet surface mass balance.

Research item B02: Various satellite observations (collaboration with all three groups of research item A01 Southern Ocean)

Creating a dataset of sea surface dynamic height (SSDH)(Mizobata/B2 Group of Publicly offered research)

This group created a dataset of sea surface dynamic height (SSDH) after 2011 based on satellite radar altimeter data. In addition, this group found clockwise circulations on the East Antarctic continental slope and indicated poleward transportation of circumpolar deep water (warm water) due to vortices in the same ocean area by comparing circulations approximately 110 degrees east longitude to observation results.

Development of an algorithm to estimate the thin ice thickness and creation of a sea ice production dataset (Nihashi/Group of Publicly offered research)

This group developed a thin ice discrimination algorithm based on satellite microwave radiometer data and calculated the ice thickness according to the type. The new estimations of sea ice production were 1.3–1.5 times greater than previous estimations (Nakata et al., 2019). The figure on the right was used for the cover of the journal to which the article was submitted.

Research item B03: Research involving new observation and analysis methods(collaboration with the A02-1 Ice sheet group)

Restoration of volcanic eruption through analysis on ice cores (Hattori/B03 Group of Publicly offered research)

This group established a method to discern large-scale eruptions causing global cooling upon fume entry into the stratosphere and reconstructed the volcanic eruption history over the past 2600 years via sulfuric acid isotope compositions of Antarctic shallow ice cores (Gautier et al., 2019, press release).