Cosmonaut Sea Research Articles

Factors controlling the phytoplankton crops, taxonomic composition, and particulate organic carbon stocks in the Cosmonaut Sea, East Antarctica

Factors controlling the phytoplankton crops, taxonomic composition, and particulate organic carbon stocks in the Cosmonaut Sea, East Antarctica

Resolution evaluation of the satellite altimetric gravity anomaly models with shipborne gravity data over the Cosmonaut Sea, East Antarctica (44–52° E)

AbstractSeveral satellite gravity anomaly models are freely available to calculate the free‐air gravity anomaly in areas where shipborne gravity measurements are scarce. Two models produced by the Technical University of Denmark (DTU17) and the Scripps Institution of Oceanography (SIOv32.1), respectively, were selected to compute the free‐air anomalies over the Cosmonaut Sea, East Antarctica. A statistical comparison analysis was performed to evaluate the resolution of satellite gravity anomaly models by comparing them with the shipborne surveying date. The radially averaged energy spectra of free‐air anomaly from different sources were calculated and compared over two selected regions to further evaluate the reliability of the data derived from satellite gravity anomaly models. The satellite gravity anomaly models have a better resolution in the ocean basin than in the area near the continental shelf. The comparison analysis revealed that the precision of both DTU17 and SIOv32.1 is close to the shipborne gravity data, but on average, SIOv32.1 is a little bit better than DTU17. The spectral analysis showed that the shipborne measurements may provide higher resolution than the satellite gravity anomaly model at wavelengths shorter than 20 km, and the free‐air data derived from SIOv32.1 have better resolution than the one from DTU17. These shipborne datasets will provide contributions for the updates of the Antarctic gravity anomaly and enable new high‐resolution combined Earth gravity models to be derived in Antarctica.

Stable microbial community diversity across large-scale Antarctic water masses

The distinctive environmental attributes of the Southern Ocean underscore the indispensability of microorganisms in this region. We analyzed 208 samples obtained from four separate layers (Surface, Deep Chlorophyll Maximum, Middle, and Bottom) in the neighboring seas of the Antarctic Peninsula and the Cosmonaut Sea to explore variations in microbial composition, interactions and community assembly processes. The results demonstrated noteworthy distinctions in alpha and beta diversity across diverse communities, with the increase in water depth, a gradual rise in community diversity was observed. In particular, the co-occurrence network analysis exposed pronounced microbial interactions within the same water mass, which are notably stronger than those observed between different water masses. Co-occurrence network complexity was higher in the surface water mass than in the bottom water mass. Yet, the surface water mass exhibited greater network stability. Moreover, in the phylogenetic-based β-nearest taxon distance analyses, deterministic processes were identified as the primary factors influencing community assembly in Antarctic microorganisms. This study contributes to exploring diversity and assembly processes under the complex hydrological conditions of Antarctica.

Biodiversity of Demersal Fish Communities in the Cosmonaut Sea Revealed by DNA Barcoding Analyses.

The Cosmonaut Sea is one of the least accessed regions in the Southern Ocean, and our knowledge about the fish biodiversity in the region is sparse. In this study, we provided a description of demersal fish diversity in the Cosmonaut Sea by analysing cytochrome oxidase I (COI) barcodes of 98 fish samples that were hauled by trawling during the 37th and 38th Chinese National Antarctic Research Expedition (CHINARE) cruises. Twenty-four species representing 19 genera and 11 families, namely, Artedidraconidae, Bathydraconidae, Bathylagidae, Channichthyidae, Liparidae, Macrouridae, Muraenolepididae, Myctophidae, Nototheniidae, Paralepididae and Zoarcidae, were discriminated and identified, which were largely identical to local fish occurrence records and the general pattern of demersal fish communities at high Antarctic shelf areas. The validity of a barcoding gap failed to be detected and confirmed across all species due to the indicative signals of two potential cryptic species. Nevertheless, DNA barcoding still demonstrated to be a very efficient and sound method for the discrimination and classification of Antarctic fishes. In the future, various sampling strategies that cover all geographic sections and depth strata of the Cosmonaut Sea are encouraged to enhance our understanding of local fish communities, within which DNA barcoding can play an important role in either molecular taxonomy or the establishment of a dedicated local reference database for eDNA metabarcoding analyses.

Glacial activity and paleoclimatic evolution records in the Cosmonaut Sea since the last glacial maximum

This research explored the origin and paleoenvironmental significance of sediments from the Cosmonaut Sea, Antarctica, focusing on the period since the Last Glacial Maximum (LGM, 26,000 cal a BP). Sediment samples from core ANT37-C5/6-07 were subjected to AMS14C dating, clay-mineral assemblage analysis, grain size evaluation, and geochemical testing. Results indicated illite as the dominant clay mineral (average 46%), followed by kaolinite (22%) and smectite (21%), with chlorite (11%) being the least abundant. Comparison with previous studies suggested that these sediments are largely derived from weathered material from Prydz Bay and Enderby Land coastal regions. The study of mineral ratios, geochemical elements, and sediment grain size, alongside δ18O values from the East Antarctica EDML ice core, revealed that the ice sheet in the study area retreated around 18600 cal a BP, melted more markedly during 16800-15000 cal a BP, tended to expand during 14800-13500 cal a BP, and then the ice sheet remained in a state of retreat until it expanded again around 5000 cal a BP. It is largely synchronous with the phased changes in the Antarctic climate since the LGM (26ka) of the Cosmonaut Sea. Notably, the sediment record aligns with major paleoclimatic events, including Heinrich Stadial 1 and the Younger Dryas in the northern hemisphere and the Antarctic cold reversal, reflecting a climatic ‘seesaw’ effect. These findings suggest that the sedimentary record in the Cosmonaut Sea is a sensitive indicator of climatic conditions, highlighting a history of glacial movements and revealing East Antarctica’s climatic fluctuations. Additionally, the research indicates that the regional ice sheet is more sensitive to climatic changes than previously believed, underscoring its instability.

Benthic Biodiversity by Baited Camera Observations on the Cosmonaut Sea Shelf of East Antarctica

A free-fall baited camera lander was launched for the first time on the Cosmonaut Sea shelf of East Antarctica at a depth of 694 m during the 38th Chinese National Antarctic Research Expedition (CHINARE) in 2022. We identified 31 unique taxa (23 were invertebrates and eight were fish) belonging to eight phyla from 2403 pictures and 40 videos. The Antarctic jonasfish (Notolepis coatsi) was the most frequently observed fish taxa. Ten species of vulnerable marine ecosystem (VME) taxa were observed, accounting for 32% of all species. The maximum number (MaxN) of Natatolana meridionalis individuals per image frame was ten, and they were attracted to the bait. The macrobenthic community type were sessile suspension feeders with associated fauna (SSFA), which was shaped by the muddy substrata with scattered rocks. Rocks served as the best habitats for sessile fauna. The study reveals the megafauna community and their habitat by image survey in the Cosmonaut Sea for the first time. It helped us obtain Antarctic biodiversity baselines and monitoring data for future ecosystem health assessment and better protection.

Demersal Fish Community in the Near-Shelf Zone of the Cosmonaut Sea, Southern Ocean

Studies on the demersal fish composition of the East Antarctic nearshore region are very scarce due to the harsh physical geography of the East Antarctic region, which is covered in ice and snow year round, leading to a scarcity of scientific surveys. Based on the data from the bottom trawl survey conducted by the 37–38th Chinese National Antarctic Research Expedition (CHINARE) program in the Cosmonaut Sea, East Antarctica, the species of demersal fishes were identified, and the demersal fish composition and the characteristics of depth distribution were examined and analyzed. The basic biological information of highly abundant species was analyzed. The results from 97 individuals sampled within 30–60° E, south of −65° S, indicate that the fishes belong to 5 orders, 11 families, 19 genera, and 23 species. Most of the species are found in Myctophidae and Bathydraconidae, and the most common species is Macrourus whitsoni (Macrouridae). Macrourus whitsoni and Prionodraco evansii have a high abundance in the survey. Macrourus whitsoni has body lengths of 144–662 mm and body weights of 17.3–1425.1 g, and Prionodraco evansii has body lengths of 90.18–134.33 mm and body weights of 4.9–20.7 g. The length–weight relationships for Macrourus whitsoni and Prionodraco evansii are y=0.00002x2.748 and y=0.000006x3.353, respectively. All the Macrourus whitsoni samples were found in waters deeper than 1000 m, with the highest number of individuals captured at depths of 1500–2000 m. Prionodraco evansii was found only at stations less than 250 m deep. These results complement the demersal fish composition and distribution data of the Cosmonaut Sea, East Antarctica. These data can provide valuable basic information for characterizing regional assemblages and delineating zoogeographic boundaries.

Spatial distribution and diversity of the heterotrophic flagellates in the Cosmonaut Sea, Antarctic

As predators of bacteria and viruses and as food sources for microzooplankton, heterotrophic flagellates (HFs) play an important role in the marine micro-food web. Based on the global climate change’s impact on marine ecosystems, particularly sea ice melting, we analyzed the community composition and diversity of heterotrophic flagellates, focusing on the Antarctic Cosmonaut Sea. During the 36th China Antarctic research expedition (2019-2020), we collected seawater samples, subsequently analyzing HFs through IlluminaMiSeq2000 sequencing to assess community composition and diversity. Notable variations in HFs abundance were observed between the western and eastern sectors of the Cosmonaut Sea, with a distinct concentration at a 100-meter water depth. Different zones exhibited diverse indicators and dominants taxa influenced by local ocean currents. Both the northern Antarctic Peninsula and the western Cosmonaut Sea, where the Weddell Eddy and Antarctic Land Slope Current intersect, showcased marine stramenopiles as dominant HFs species. Our findings offer insights into dominant taxa, spatial distribution patterns among heterotrophic flagellates, correlations between taxa distribution and environmental factors, and the exploration of potential indicator taxa.

Species Diversity and Community Structure of Macrobenthos in the Cosmonaut Sea, East Antarctica

The Cosmonaut Sea is an under-studied area and a “white spot” for macrobenthos research. Here, we report on the species diversity and community structure of macrobenthos collected using tringle trawls on the 38th Chinese National Antarctic Research Expedition (CHINARE) in the Cosmonaut Sea, East Antarctica. A total of 11 tringle trawls were deployed at different depths across the shelf, slope and seamount of the Cosmonaut Sea. A total of 275 macrobenthic species were found from 207 to 1994 m. The species richness per station varied from 23 to 89. Echinoderms (100 species), arthropods (48 species) and mollusks (36 species) were the most dominant groups. Echinoderms and arthropods dominated in abundance at seamount stations, and echinoderms, arthropods and polychaetes dominated in abundance at slope stations, while bryozoans, corals, ascidians and sponges were abundant on the Cosmonaut Sea shelf. Depth was the major driving force influencing the distribution of macrobenthos. The main components were two core communities. One was dominated by sessile suspension feeders and associated fauna. Variants of this community include sponges and bryozoans. The other core community was dominated by mobile deposit feeders, infauna and grazers–epifauna, which included arthropods and echinoderms. The results showed that the slope (40–50° E, 65–67° S) of the Cosmonaut Sea may be an important area with complex ecological processes. The results of this study contribute to the knowledge of species diversity and communities of macrobenthos in the Cosmonaut Sea and provide monitoring data for future ecosystem health assessments and better protection.

Paleoproductivity and deep-sea oxygenation in Cosmonaut Sea since the last glacial maximum: impact on atmospheric CO2

The paleoproductivity in the Southern Ocean plays a crucial role in controlling the atmospheric CO2 concentration. Here, we present the sediment record of gravity core ANT37-C5/6-07, which was retrieved from the Cosmonaut Sea (CS), Indian Ocean sector of the Southern Ocean. We found that the change in the oxygen concentration in the CS bottom water is strongly correlated with the atmospheric CO2 fluctuations since the Last Glacial Maximum (LGM). Based on the change in the export production, we reconstructed the evolution history of the deep-water ventilation/upwelling in the study area. During the LGM, a large amount of respiratory carbon was stored in the deep Southern Ocean due to the effect of the low export productivity and restricted ventilation. The oxygen concentration was also low at this time. Despite the increase in paleoproductivity, the biological pump efficiency remained at a low level during the Last Deglaciation. Vast quantities of CO2 were released into the atmosphere through enhanced upwelling. The recovery of ventilation during this period facilitated the supply of oxygen-rich surface water to the deep ocean. Moreover, signals were identified during the transitions between the Heinrich Stage 1 (HS1), Antarctic Cold Reverse (ACR), and Younger Drays (YD) periods. During the Holocene, the productivity increased overall, and the oxygen in the bottom water was consumed but still remained at a high level. This may have been caused by the enhanced ventilation and/or the prevalence of East Cosmonaut Polynya (ECP) near Cape Ann.

First pelagic fish biodiversity assessment of Cosmonaut Sea based on environmental DNA

The Cosmonaut Sea is a typical marginal sea in East Antarctica that has not yet been greatly impacted by climate change. As one of the least explored areas in the Southern Ocean, our knowledge regarding its fish taxonomy and diversity has been sparse. eDNA metabarcoding, as an emerging and promising tool for marine biodiversity research and monitoring, has been widely used across taxa and habitats. During the 38th Chinese Antarctic Research Expedition (CHINARE-38), we collected seawater and surface sediment samples from 38 stations in the Cosmonaut Sea and performed the first, to our knowledge, eDNA analysis of fish biodiversity in the Southern Ocean based on the molecular markers of 12S rRNA and 16S rRNA. There were 48 fish species detected by the two markers in total, with 30 and 34 species detected by the 12S rRNA and 16S rRNA marker, respectively. This was more than the trawling results (19 species) and historical survey records (16 species, “BROKE-West” cruise). With some nonsignificant differences between the Gunnerus Ridge and the Oceanic Area of Enderby Land, the Cosmonaut Sea had a richer fish biodiversity in this research compared with previous studies, and its overall composition and distribution patterns were consistent with what we know in East Antarctica. We also found that the eDNA composition of fish in the Cosmonaut Sea might be related to some environmental factors. Our study demonstrated that the use of the eDNA technique for Antarctic fish biodiversity research is likely to yield more information with less sampling effort than traditional methods. In the context of climate change, the eDNA approach will provide a novel and powerful tool that is complementary to traditional methods for polar ecology research.

Predicted changes in the distribution of Antarctic krill in the Cosmonaut Sea under future climate change scenarios

Antarctic krill (Euphausia superba) are the key species of the ecological system in the Cosmonaut Sea. Long-term habitat alterations in krill due to climate change have been considered in recent decades. However, there is still a lack understanding about krill distribution. The MaxEnt model was used to forecast the suitable distribution area of krill for this study, which is based on data from the Coupled Model Intercomparison Project in its sixth phase (CMIP6) in the near future and far future. A total of 145 occurrence points and 15 environmental factors were selected to build the MaxEnt model. The current suitable habitat regions for krill were mostly detected in the western and central regions of the Cosmonaut Sea, which accounted for 10.07% of the total area. The most important environmental variables that influenced krill distribution were minimum surface solar radiation downward (ssrdmin), the mean temperature (tem) and the mean northward velocity (v). In the near future and far future, the suitable area of krill was seen to decline under all shared socioeconomic pathways (SSPs), with the smallest reduction under SSP1-2.6 and the greatest reduction under SSP5-8.5. The suitable area for krill dropped quicker from the near future to the far future than the present to the near future. Krill habitats were expected to shift to the poles. The tem continued to rise in the future under all SSP scenarios, particularly under the high radiative forcing scenario. The increase in water temperature is the main reason for the decrease in suitable areas for Antarctic krill. Our results show the future distribution of krill in the future and provide a reasonable reference for the ecological protection policy of the Cosmonaut Sea.

Age and growth of Antarctic deep-sea smelt (Bathylagus antarcticus), an important mesopelagic fish in the Southern Ocean

As one of the most abundant mesopelagic fishes, the Antarctic deep-sea smelt Bathylagus antarcticus plays an important role in the Southern Ocean ecosystem. However, because of a lack of studies on this species, there are major gaps in our knowledge of its life history such as age and growth pattern. Fish were collected from the Ross and Amundsen seas in the southern part of the Pacific sector, and from the Cosmonaut Sea in the southwestern part of the Indian sector, in austral summer of 2020. Age determination was made from an analysis of otoliths, and growth curves were estimated through mixed-effects models based on back-calculated length-at-age data. Bathylagus antarcticus shows a positive allometric relationship between total length and wet weight; the results indicate that it can live to age 17 years; and the von Bertalanffy growth function was estimated on the population level with L∞ = 143.83 mm, K = 0.14 year−1, and t0 = −0.64 year. Fish in the Ross and Amundsen seas showed larger mean asymptotic length than that fish in the Cosmonaut Sea, and the K values and otolith growth increments in the first 6 years differed between regions. This work is the first to estimate the age and growth of B. antarcticus, and forms an important basis of forthcoming studies on population dynamics and ecosystems in the Southern Ocean. The long lifespan and slow growth of this species make it a potentially suitable environmental indicator, to be investigated through tools like otolith microchemistry analysis.

Sequential bedform development in mixed turbidite–contourite systems: An example from the Cosmonaut Sea, East Antarctica

Mixed turbidite–contourite depositional systems are commonly found on continental margins, but their bedforms and associated sedimentary processes have not been studied in depth. In this work, we used multibeam echo-sounder, sub-bottom profiling, and multichannel seismic data from the continental rise of the Cosmonaut Sea, East Antarctica, to (1) identify primary bedforms in a combined-current (i.e., turbidity current + contour current) channel–levee system and (2) infer bedform-associated sedimentary processes. Within turbidite channels and on adjacent levees and distal overbank deposits, scours, furrows, and sediment waves of varying dimensions and trends were identified. These bedforms are interpreted to have formed in two steps, which have been likely repeated over and over again through time. First, scours and sediment waves within the channels were formed by turbidity currents, while sediment waves on adjacent levees were likely formed by synchronous interactions between overspilled unconfined turbidity currents and the westward Antarctic Bottom Water (AABW) contour current. Second, after waning of the episodic turbidity currents, AABW flow created a field of erosional furrows on a distal overbank, with these furrows truncating the large field of sediment waves earlier generated by the combined flow of interacting currents. Bedform locations, orientations, and truncating relationships are key for identifying the likely origins of mixed-system bedforms.

Predicting the current habitat suitability and future habitat changes of Antarctic jonasfish Notolepis coatsorum in the Southern Ocean

The Southern Ocean faces many challenges under global climate change. Species distribution models (SDMs) are considered a powerful tool for predicting the potential distributions of species when evaluating the effects of climate change. We employed a partially area-under-the-curve (AUC)-based ensemble model to predict the current habitat suitability and future habitat changes of N. coatsorum in the Southern Ocean. The SDMs developed included six different predictors that contribute to the N. coatsorum distribution: depth accounted for the highest contribution of 33.8%, closely followed by the sea surface temperature (30.3% contribution). The contributions of the sea surface salinity distance from land, sea ice thickness and current velocity were 12.7%, 12.3%, 8.1%, and 2.8%, respectively. N. coatsorum has a suitable distribution area of approximately 5.63 million km2 under current conditions, comprising 29.8% of the Southern Ocean area. A significant expected decrease (43.0%) at the species’ northward edges, especially on the southeast Antarctic coast, may occur in the future as suggested by comparing the current model range to the suitable habitat changes predicted in 2100 under the RCP8.5 scenario, resulting in the formation of three newly gained or remaining climate refugia for N. coatsorum: areas close to the Ronne and Filchner Ice Shelves in the Weddell Sea, the Ross Sea, and along the coast of northeastern Antarctica (including in the Cosmonaut Sea and Prydz Bay). Our ensemble approach for assessing the habitat features of N. coatsorum allows the impacts of climate change on a mesopelagic fish species in the Southern Ocean to be assessed.

Vertical occurrence of copepod carcasses in the Cosmonaut Sea during austral summer

Zooplankton carcasses and their contribution to carbon export are increasingly garnering attention in food web studies of polar oceans. We investigated the occurrence of carcasses of dominant copepod species at four depths (100–200 m, 200–500 m, 500–1000 m, 1000–1500 m) and their potential contribution to particulate organic carbon (POC) concentrations in the Cosmonaut Sea, Antarctica, during summer, 2019/2020. The abundance of small copepods (< 2 mm), either live or dead individuals, was 1-3 orders of magnitude higher than the four dominant large copepod species Calanoides acutus, Calanus propinquus, Metridia gerlachei and Rhincalanus gigas at each depth. Most carcasses were observed at the surface (100–200 m), while the proportions of dead individuals increased with depth, from 22% in the 100–200 m layer to 70% of the 500–1500 m layer. The total number of passive sinkers (carcasses and moults) was dominated by carcasses of small copepods in each depth layer, while the carbon biomass of passive sinkers was dominated by carcasses of large copepods. Both abundance and carbon biomass of passive sinkers decreased with depth. The average contribution of passive sinkers to the POC concentration decreased from 0.27% in the 100–200 m depth stratum to 0.10% in the 500–1500 m layer. This study provides the first report of occurrence and contribution of carcasses from the surface to the mesopelagic layer of the Southern Ocean. This information can improve understanding of the role zooplankton play in downward carbon flux within the ocean’s twilight zone.

The sedimentation, bioturbation and organic matter degradation as revealed by excess 230Th and 210Pb in the Cosmonaut Sea

Sedimentation and bioturbation (the activity of benthic organisms) play an important role in organic matter degradation. The excess 230Th and 210Pb in a sediment core were used to evaluate the sedimentation, bioturbation and organic degradation processes in the Cosmonaut Sea, East Antarctica. Our results show that the sedimentation rate estimated from excess 230Th through the Constant Flux (CF) and Constant Flux and Constant Sedimentation (CFCS) models has changed in the past 200 ka. The mass accumulation and the linear sedimentation rates vary from 0.36 to 0.76 kg m-2 ka-1 and from 0.6 to 1.3 mm ka-1, which are significantly lower than the rates in other Antarctic seas. The stage III (120–202 ka), which corresponds to Marine Isotope Stage (MIS) 6 (glacial period), had the lowest sedimentation rate, indicating less sediment input by sea ice expansion. The bioturbation coefficient estimated by excess 210Pb is as low as 0.023 ± 0.003 cm2 a-1, showing inactive benthic activities. The average C/N ratio of organic matter is 7.2 ± 0.4, which is close to that of fresh organic matter and lower than the typical value of deep-sea sediments, indicating that organic matter is less degraded. The degradation rates of organic carbon and organic nitrogen estimated by the bio-diffusion model are 0.61 ka-1 and 0.29 ka-1, respectively, which are significantly lower than previously reported values for Southern Ocean sites. Despite the low sedimentation rate, low rates of bioturbation and inefficient organic matter degradation are conducive to the preservation of organic matter in sediments of the Cosmonaut Sea.

Distributions of virio- and picoplankton and their relationships with ice-melting and upwelling in the Indian Ocean sector of East Antarctica

Ice melting in the Antarctic summer and upwelling of the Circumpolar Deep Water (CDW) near the Antarctic continent have been suggested to regulate the distributions of microbial communities. However, an understanding of these relationships in the Indian Ocean sector of East Antarctica is lacking. We report on the distribution and relationships of virio- and picoplankton at 77 stations (including 29 stations throughout the entire water column and 48 stations from the epipelagic zone) from 35° to 78°E and 62° to 70°S, covering the Cosmonaut Sea, Cooperation Sea and Prydz Bay. The epipelagic stations were grouped into four clusters based on the virio- and picoplankton composition and abundance. Clusters three and four, which corresponded with areas of upwelling and ice retreat, had high abundances of autotrophic picoeukaryotes; this resulted in subsequent high abundances of heterotrophic prokaryotes and virioplankton. Cluster one and two stations correspond with a high nutrient, low chlorophyll (HNLC) area, where the abundances of autotrophic and heterotrophic picoplankton are low. Viruses were significantly correlated with heterotrophic prokaryotes in the ice-covered areas but more strongly correlated with autotrophic picoeukaryotes in areas associated with ice-edge blooms. Throughout the water column in the Cooperation Sea, nutrient supply from the upwelling of the CDW induced an increased abundance of heterotrophic prokaryotes, particularly in the meso- and bathypelagic zones of stations in the northern part of the area. High viral abundances were detected in the meso- and bathypelagic zones of stations with high abundances of virio- and picoplankton in the epipelagic zone. This study shows that the summer distribution of virio- and picoplankton in the Indian Ocean sector of East Antarctica was mainly controlled by ice-melting and upwelling of the CDW.

The thermodynamic and dynamic control of the sensible heat polynya in the western Cosmonaut Sea

A prominent feature in the west Cosmonaut Sea is the reoccurrence of a sensible heat polynya — the western Cosmonaut Sea Polynya (wCSP), which normally exists in late austral autumn and early winter. The Southern Ocean Sate Estimate (SOSE) reanalysis product is employed to investigate the thermodynamic and dynamic processes controlling the formation and evolution of a real wCSP event in 2009, when the polynya properties revealed from satellite observations are reasonably simulated by SOSE. An oceanic heat budget analysis was conducted for the surface layer above the thermocline, and the results reveal that heat advection is the major term contributing to the surface heat content variation in this area. The precursor of wCSP — an embayment — was formed during cyclonic atmospheric circulations. The negative wind stress curl from a cyclone induced upwelling that brought the warm circumpolar deep water to the surface and presumably melted ice. Meanwhile, the location of the cyclone relative to the wCSP created weaker easterlies over the northern boundary of polynya and stronger easterlies over the southern boundary of polynya. This leads to difference in the meridional oceanic heat transports across the northern and southern boundaries, resulting in net positive meridional oceanic heat transport into the polynya. Both the vertical heat advection and the meridional heat advection contribute significantly to increased heat content in the surface layer of wCSP, causing sea-ice melt and formation of the embayment. The cyclonic wind field promotes convergence of sea ice over the northern area of the embayment and results in the polynya. The formation of wCSP is likely related to the strength and position of Southern Annular Mode on interannual scale, and may potentially affect the biological productivity by controlling the availability of light in the mixed layer.

Diatom based reconstruction of climate evolution through the Last Glacial Maximum to Holocene in the Cosmonaut Sea, East Antarctica

Diatom composition has been studied in two cores retrieved from the Cosmonaut Sea, East Antarctica, during the 36th Chinese Antarctic Research Expedition. The resulting diatom data are compared to other records from the Southern Ocean and the deglaciation history of the Antarctic ice sheet to reveal the climatic response of the ice-proximal environment to the melting of the ice sheet from the Last Glacial Maximum (LGM) to Holocene. The LGM is marked by low productivity and extensive sea ice cover that resulted in poor preservation of diatom frustules. The last deglacial warming process is facilitated by the “bipolar seesaw” effect. The environment in the Cosmonaut Sea is primarily influenced by the melting of the West Antarctic Ice Sheet (WAIS) during the last deglaciation, while the East Antarctic Ice Sheet (EAIS) remained relatively stable. Maximum sea ice retreat and southward intrusion of the warm Circumpolar Deep Water facilitate the melting of the EAIS during the early Holocene. The developing cavity under the WAIS is suggested to be responsible for the mid-late Holocene cooling in the Cosmonaut Sea. This indicates that the deglaciation of the WAIS is a primary control of environmental changes in the Cosmonaut Sea, despite its ice proximal location adjacent to the EAIS.