Chinese Antarctic Research Expedition Research Articles

Relationships among the climate-relevant gases during the Southern Ocean bloom season

The ocean plays an essential role in regulating the sources and sinks of climate-relevant gases, like CO2, N2O and dimethyl sulfide (DMS), thus influencing global climate change. Although the Southern Ocean is known to be a strong carbon sink, a significant DMS source and possibly a large source of N2O, our understanding of the interaction among these climate-relevant gases and their potential impacts on climate change is still insufficient in the Southern Ocean. Herein, we analyzed parameters, including surface water pCO2, dissolved inorganic carbon (DIC), alkalinity (TA), DMS and N2O in the water column, collected during the austral summer of 2015–2016 in the 32nd Chinese Antarctic Research Expedition (CHINARE) at the tip of Antarctic Peninsula. A positive correlation between DMS and pCO2 (indicated by deficit of DIC, ∆DIC, refer to values in 100 m) was observed in waters above 75 m, whereas no correlation between N2O saturation anomaly (SA) and DMS, ∆DIC was found. In the area with stable stratification with phytoplankton bloom, significant DMS source and strong CO2 uptake with weak N2O emission were observed. Conversely, strong mixing or upwelling area was shown to be a strong marine CO2 source and significant N2O release with weak DMS source.

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.

Spatial variations of particulate-bound mercury in the atmosphere along a transect from the mid-Northern Hemisphere to the high southern latitudes

Particulate-bound mercury (PBM) measurements in the boundary layer were performed during the 2015–2016 Chinese Antarctic Research Expedition from the middle Northern Hemisphere (Shanghai, China) to the Antarctic Ice Sheet summit, Dome A. A significant latitudinal gradient in PBM was observed. PBM over the Northern Hemisphere oceans was influenced by both continental and oceanic sources, with elevated PBM levels associated with continental inputs. PBM over this region was significantly higher in November than that in April, which could be related to the continental Hg carried by the strong East Asian winter monsoon. Far away from the continental sources, extremely low PBM was observed over the Southern Ocean (2.6 ± 1.6 pg m−3). Elevated PBM was found across the Antarctic Ice Sheet (79.1 ± 43.4 pg m−3), and the highest PBM observed at Dome A (143.4 ± 27.0 pg m−3) was likely associated with GEM emissions from snow and enhanced oxidation of GEM due to snow photochemistry. Across the Antarctic Ice Sheet, PBM increased significantly with the increasing distance from the coast, which may have resulted from the mixing of air masses from the Antarctic plateau and the ocean. GEM emissions from inland Antarctic snow can influence atmospheric PBM concentrations over the Antarctic coastal seas via the transport by katabatic winds, and thus play an important role in atmospheric Hg cycle in the high southern latitudes.

A Review of Research on Grove Mountains CM-Type Chondrites

CM chondrite is the most important carbonaceous chondrite containing abundant Ca, Al-rich inclusions (CAIs) and other interesting objects, which probably experienced early condensation processes in the Solar Nebula environment and later alteration in parent body surroundings. Thus, it is a vital raw material to explore in the formation and evolution of the early Solar System. Grove Mountains (GRV) CM chondrites have been collected from Antarctica by Chinese Antarctic Research Expedition (CARE) for nearly 20 years. In this paper, we review the study of GRV CM chondrites. In total, there are eight CM chondrites named Grove Mountains officially approved by the Meteoritical Society. Petrology and mineral, matrix, CAIs, metal and sulfide in GRV CM chondrites are carefully reviewed. All the meteorites have similar characteristics with a dominant component of matrix. Phyllosilicate minerals generally developed in the matrix. The different altered mineral assemblages, contents and chemical compositions show that these chondrites underwent varying degrees of aqueous alteration, of which GRV 020005 is the most heavily altered CM chondrite. GRV 020025 is the second heaviest of the CM samples with the most extensive studies among these chondrites. It contains abundant CAIs and amoeboid olivine aggregates (AOAs). The modal content is about 1.0 vol% for CAIs. The findings of some new types of CAIs (such as hibonite-rich and spinel-pyroxene inclusions with forsterite-rich accretionary rims), AOAs and a complex, fine-grained P-bearing sulfide phase enrich the study of GRV 020025.

An Improved Algorithm for the Retrieval of the Antarctic Sea Ice Freeboard and Thickness from ICESat-2 Altimeter Data

ICESat-2 altimeter data could be used to estimate sea ice freeboard and thickness values with a higher measuring accuracy than that achievable with data provided by previous altimeter satellites. This study developed an improved algorithm considering variable lead proportions based on the lowest point method to derive the sea surface height for the retrieval of Antarctic sea ice freeboard and thickness values from ICESat-2 ATL-07 data. We first collocated ICESat-2 tracks to corresponding Sentinel-1 SAR images and calculated lead (seawater) proportions along each track to estimate the sea surface height in the Antarctic Ocean. Then, the Antarctic sea ice freeboard and thickness were estimated based on a local sea surface height reference and a static equilibrium equation. Finally, we assessed the accuracy of our improved algorithm and ICESat-2 data product in the retrieval of the Antarctic sea ice thickness by comparing the calculated values to ship-based observational sea ice thickness values acquired during the 35th Chinese Antarctic Research Expedition (CHINARE-35). The results indicate that the Antarctic sea ice freeboard estimated with the improved lowest point method was slightly larger than that estimated with the ICESat-2 data product algorithm. The root mean squared error (RMSE) of the improved lowest point method was 35 cm with the CHINARE-35 measured sea ice thickness, which was smaller than that determined with the ICESat-2 data product algorithm (65 cm). Our improved algorithm could provide more accurate data on the Antarctic sea ice freeboard and thickness, thus supporting Antarctic sea ice monitoring and the evaluation of its change under global effects.

Restoration of Wintertime Ocean Color Remote Sensing Products for the High-Latitude Oceans of the Southern Hemisphere

Satellite ocean color products have been widely used to monitor spatiotemporal variations in marine ecological environments from regional to global oceans. However, current satellite ocean color products fail to provide effective records during the winter in high–latitude oceans, limiting understanding of the marine ecological environment during the winter season. In this study, we proposed an atmospheric correction model, namely, the Neural Network Atmospheric Correction algorithm for the Southern Hemisphere (NN–AC–SH), and recover winter satellite ocean color products for the high–latitude oceans of the Southern Hemisphere from 2003 to 2020. The accuracy of the NN–AC–SH model was verified based on the in situ data from the Aerosol Robotic Network–Ocean Color (AERONET–OC). The results indicate that the NN–AC–SH model performed better than the traditional near–infrared (NIR) iterative atmospheric correction algorithm, e.g., in the 443, 488 and 531 nm bands, the relative deviations of the NN–AC–SH model were 23.11%, 20.96% and 23.14%, respectively, while the values of the NIR model were 30.72%, 22.85%, and 24.81%, respectively. Under the observation condition of a high solar zenith angle (SZA), the NN–AC–SH model performed better than the NIR model in terms of the amount of effective data (94 vs. 78 data points) and model inversion accuracy (a relative deviation 32.83% vs. 43.60%). Moreover, in situ chlorophyll concentration data from the NASA bio–Optical Marine Algorithm Dataset (NOMAD) and Chinese Antarctic Research Expedition (CHINARE) were used to verify the accuracy of the restored chlorophyll concentration products, and the results reveal that the NN–AC–SH model resulted in more effective records of higher accuracy than those obtained with the NASA–distributed chlorophyll concentration products. Overall, for the first time, this study recovered long time–series (2003–2020) ocean color products for the high–latitude oceans of the Southern Hemisphere (≥50°S) in the winter, which could provide unique satellite products for investigating the marine ecological environment of the Antarctic and sub–Antarctic oceans in the winter.

Impact of Slopes on ICESat-2 Elevation Accuracy Along the CHINARE Route in East Antarctica

As the follow-on study to the assessment of ICESat-2 ice surface elevations, we assessed how they are influenced by the surface slopes, which are derived from the ICESat-2 elevations of the received photons and available in the land-ice surface heights product (ATL06), by using coordinated GNSS observations along a 520 km long traverse of the 36th CHINese Antarctic Research Expedition (CHINARE) route in East Antarctica. We further analyzed the impact of the slopes on the ICESat-2 elevation accuracy, which is important for the studies of the local ice flow dynamics, mass balance, and Antarctic contribution to sea level rise. We found that the along-track surface slopes in the ICESat-2 ATL06 data have a high overall agreement of 0.18° ± 0.16° (1σ) and a correlation of 0.66 (R²) with the GNSS slopes. Furthermore, two waveform related corrections, first-photon and transmit-pulse shape bias corrections, were able to adjust on average a combined elevation bias of ∼1.0 cm. Finally, we found a high linear dependency of elevation errors on slopes, i.e., ∼6.2 cm per 1° slope (R² = 0.57, slope <0.7°). Although significantly smaller than those in ICESat elevation data, these slope-induced elevation errors in ICESat-2 ATL06 data should be carefully considered for studies using high precision elevations, such as the mass balance estimation in sloped areas in Antarctica.

Characteristics of hydrogen/oxygen isotopes in water masses and implications for spatial distribution of freshwater in the Amundsen Sea, Southern Ocean.

Antarctica’s marginal seas are of great importance to atmosphere–ocean–ice interactions and are sensitive to global climate change. Multiple factors account for the freshwater budget in these regions, including glacier melting, seasonal formation/decay of sea ice, and precipitation. Hydrogen (H) and oxygen (O) isotopes represent useful proxies for determining the distribution and migration of water masses. We analyzed the H and O isotopic compositions of 190 seawater samples collected from the Amundsen Sea during the 34th Chinese Antarctic Research Expedition in 2017/2018. The upper-oceanic structure ( 3%) of freshwater generally lie in the upper ~50 m and extend from Antarctica to ~65°S in the meridional direction (anomalously low freshwater proportion occurred between 68°S and 71°S). Winter Water mainly occupied the layer between 50 and 150 m south of 71°S in the western Amundsen Sea. The water structure and spatial distribution of freshwater in the upper Amundsen Sea were found influenced mainly by the rates of basal and surficial melting of ice shelves, seasonal alternation of sea ice melt/formation, wind forcing, and regional bathymetry. Owing to the distance between heavy sea ice boundary (HSIB) and ice shelves is much shorter in the western HSIB than the east HSIB, the western part of the heavy sea ice boundary includes a higher proportion of freshwater than the eastern region. This study, which highlighted the distribution and extent of freshwater derived from ice (ice shelves and sea ice) melt, provides important evidence that the offshore drift pathway of cold and fresh Antarctic continental shelf water is likely interrupted by upwelled UCDW in the Amundsen Sea. Citation : Shao H B, He J F, Luo G F, et al. Characteristics of hydrogen/oxygen isotopes in water masses and implications for spatial distribution of freshwater in the Amundsen Sea, Southern Ocean. Adv Polar Sci, 2021, 32(3): 221-238, doi: 10.13679/j.advps.2021.0037

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.

Assessment of ICESat-2 ice surface elevations over the Chinese Antarctic Research Expedition (CHINARE) route, East Antarctica, based on coordinated multi-sensor observations

Abstract. We present the results of an assessment of ice surface elevation measurements from NASA's Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) along the CHINARE (CHINese Antarctic Research Expedition) route near the Amery Ice Shelf in East Antarctica. The validation campaign was designed and implemented in cooperation with the 36th CHINARE Antarctic expedition from December 2019 to February 2020. The assessment of the ICESat-2 geolocated photon product (ATL03) and land ice elevation product (ATL06) was performed based on coordinated multi-sensor observations using two roof-mounted kinematic global navigation satellite system (GNSS) receivers, two line arrays of corner cube retroreflectors (CCRs), two sets of retroreflective target sheets (RTSs), and two unmanned aerial vehicles (UAVs) with cameras. This systematic validation of the ICESat-2 data covered a variety of Antarctic ice surface conditions along the 520 km traverse from the coastal Zhongshan Station to the inland Taishan Station. This comprehensive investigation is complementary to the 750 km traverse validation of flat inland Antarctica containing a 300 km latitude traverse of 88∘ S by the mission team (Brunt et al., 2021). Overall, the validation results show that the elevation of the ATL06 ice surface points is accurate to 1.5 cm with a precision of 9.1 cm along the 520 km CHINARE route. The elevation of the ATL03 photons has an offset of 2.1 cm from a GNSS-surveyed CCR and is accurate to 2.5 cm with a precision of 2.7 cm as estimated by using RTSs. The validation results demonstrate that the estimated ICESat-2 elevations are accurate to 1.5–2.5 cm in this East Antarctic region, which shows the potential of the data products for eliminating mission biases by overcoming the uncertainties in the estimation of mass balance in East Antarctica. It should be emphasized that the results based on the CCR and RTS techniques can be improved by further aggregation of observation opportunities for a more robust assessment. The developed validation methodology and sensor system can be applied for continuous assessment of ICESat-2 data, especially for calibration against potential degradation of the elevation measurements during the later operation period.

FIELD VALIDATION OF ICESAT-2 DATA ALONG CHINARE ROUTE IN EAST ANTARCTICA

Abstract. A field validation of the ICESat-2 elevation data has been conducted along the CHINARE (CHINese Antarctic Research Expedition) route near the Amery Ice Shelf in East Antarctica from December 2019 to February 2020. The study area covers a 520 km traverse from the coastal Zhongshan Station to the inland Taishan Station. We deployed two roof-mounted GNSS receivers to collect elevation data along the traverse and reduced them to the ice surface height with measured boresight parameters. The comparison of the ICESat-2 data (Release 003) with the high-precision ground-based GNSS along the traverse shows that the elevations of ATL06 ice surface products are accurate to 1.5 cm with 9.1 cm precision, and the elevations of ATL03 photon events are accurate to 4.3 cm with 8.5 cm precision. The validation results indicated high accuracy of 1.5–4.3 cm of ICESat-2 data, which provides the potentials to observe and evaluate the low-level mass changes in East Antarctica. The methodology and hardware system can be improved to execute a continuous assessment of ICESat-2 data in the following mission period.

Shallow-Layers-Detection Ice Sounding Radar for Mapping of Polar Ice Sheets

The accumulation rate is a key parameter in computing the mass balance of glaciers and ice sheets to estimate sea level rise. A shallow-layers-detection ice sounding radar (SLDISR) is developed to measure the accumulation rate and shape of near-surface internal layers with high resolution. With a transmitting frequency from 500 to 2000 MHz, this frequency-modulated continuous wave (FMCW) radar provides a range resolution of about 16 cm in free space by using a Hanning window and a penetrating depth about 150 m under polar ice. The spectral analysis and coherent integration techniques are used to obtain a high processing gain and to improve the signal-to-noise ratio of the system. A phase-locked loop with wideband yttrium iron garnet (YIG) oscillator is applied to generate a sweeping chirp signal as an input source for the transmitter. A stable, low-frequency reference chirp signal is generated with a direct digital synthesizer (DDS) integrated in field-programmable gate array (FPGA). To reduce the high-speed requirement to the analog-to-digital converter (ADC), dechirp technology is adopted at the RF section of the receiver. The implementation of the digital unit is based on an FPGA chip. The designed radar has been successfully deployed in Antarctica during the 31st Chinese Antarctic Research Expedition (CHINARE 31) and CHINARE 33, mainly over the East Antarctic Ice Sheet (EAIS). The echograms indicate the effectiveness of the radar system on detecting clear internal reflecting horizons (IRHs) over ice sheets.

Using stable isotopes to distinguish atmospheric nitrate production and its contribution to the surface ocean across hemispheres

Atmospheric samples and surface seawater collected on a Chinese Antarctic Research Expedition (CHINARE) transect are used to investigate sources and production of nitrate (NO3−) in the atmosphere and its contribution to the surface NO3− pool in the ocean. Most atmospheric NO3− is concentrated on intermediate size particles, and much higher concentrations were observed in the northern hemisphere than in the high southern latitudes. Isotopes of NO3− (δ15N, δ18O and Δ17O) suggest that elevated atmospheric NO3− in coastal areas was associated with human activities, while NO3− in the high southern latitudes tends to be influenced by precursor Antarctic snowpack emissions driven by photolysis. In general, no clear association was found between the isotopes of surface seawater and atmospheric NO3−, suggesting that the ocean is unlikely to be an important direct source of atmospheric NOx on this transect. A significant linear relationship between δ18O and Δ17O of NO3− is used to interpret important pathways for NO3− production. In the tropics, >59% of atmospheric NO3− is produced via OH oxidation of NO2, while the elevated oxygen isotopic ratios (δ18O and Δ17O) in the high southern latitudes suggest increased NO3− production via BrO and/or DMS pathways assuming a minor contribution of the N2O5 channel. In surface seawater, high NO3− concentrations are present in the coastal areas and in the Southern Ocean. In coastal areas of China, positive Δ17O values in seawater NO3− (1.7 ± 1.0‰) provide direct evidence of uncycled atmospheric deposition contribution, with a calculated contribution of at least 2-3% to total surface NO3−. A Δ17O=0 was found everywhere else in seawater, suggesting that atmospheric deposition has a minimal presence in the surface NO3− pool. Near Antarctica, deposition of atmospheric NO3− with extremely low δ15N (<−30‰) could lower δ15N found in sea ice, and this process could be isotopically important to evaluate nitrogen cycling in sea ice.

Legacy and emerging per- and poly-fluoroalkyl substances in surface seawater from northwestern Pacific to Southern Ocean: Evidences of current and historical release

Knowledge on distribution of per- and poly-fluoroalkyl substances (PFASs) in open oceans is limited. By taking part in the 32nd Chinese Antarctic Research Expedition, 41 surface seawater samples were collected in the northwestern Pacific Ocean (NW-PO), eastern Indian Ocean (E-IO) and Southern Ocean (SO), and 23 PFASs comprised of legacy perfluoroalkyl carboxylic acids, perfluoroalkyl sulfonate acids and some new emerging homologs such as 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) were measured. The concentrations of the total PFASs decreased in the order of NW-PO>E-IO>SO. Perfluorooctanoic acid (PFOA) was the most dominant, followed by perfluorooctane sulfonate (PFOS). The PFOA concentration declined exponentially with the offshore distance, while such trend was not obvious for PFOS and other legacy PFASs, suggesting that PFOA was mainly derived from the ongoing land-based emissions, while PFOS was mainly from historical residues. 6:2 Cl-PFESA was identified (<11.1–170 pg/L) in the oceanic waters with relatively high level at the sites near Australia. Multiple receptor models indicated that PFASs in the SO were mainly contributed by atmosphere input, while those in the NW-PO and E-IO were originated from land sources. Isomeric profiles of PFOA showed that telomere-based source became more outstanding than electrochemical fluorinated production in recent years.

Glaciological and Meteorological Conditions at the Chinese Taishan Station, East Antarctica

The glacio-meteorological characteristics of Princess Elizabeth Land in East Antarctica are poorly known due to a lack of measurement. This is problematic given the importance of this area for understanding ice sheet dynamics and climate change. We present a comprehensive approach (including field surveys, reanalysis data, remote sensing, and ice flow models) to investigate the glaciological and meteorological conditions in the vicinity of the new Chinese Taishan Station (73.864°S, 76.974°E) in Princess Elizabeth Land. We collected the datasets of satellite-derived ice surface velocities, surface mass balance, and wind field; mapped the ice thickness and internal layers around the Taishan Station site; and constructed profiles of the surface snow temperature and snow density. Also, we used transient thermodynamical 1-D vertical models to simulate the age of ice and the basal temperature with surface meteorological data and subglacial topography as boundary conditions. These investigations showed that Taishan Station is subject to a relatively high wind velocity, low temperatures (about -36 °C), and simple ice flow. The well-behaved internal layer stratigraphy implies that the ice flow of Taishan Station has been relatively stable, possibly for a long time. The fact that the internal layers are conformal with bed topography, there is a relatively higher basal ice age from ice modelling, and that the site lies over a bed depression filled with ice 1900 m thick, suggests that Taishan Station may be a good location for obtaining undisturbed old ice at depth. The combination of glacio-meteorological parameters suggests that Taishan Station is a potential drill site for the Chinese Antarctic Research Expedition (CHINARE) and an ideal logistical support location for proposed scientific field activities in the East Antarctic ice sheet (e.g. Dome A, Grove Mountains, and Princess Elizabeth Land).

Historical surface mass balance from a frequency-modulated continuous-wave (FMCW) radar survey from Zhongshan station to Dome A

AbstractUsing frequency-modulated continuous wave radar data from the 32nd Chinese Antarctic Research Expedition in 2015/16, subsurface profiles were obtained along an East Antarctic inland traverse from Zhongshan station to Dome A, and four distinct regions were selected to analyze the spatiotemporal variability in historical surface mass balance (SMB). Based on depth, density, and age data from ice cores along the traverse, the radar data were calibrated to yield average SMB data. The zone 49–195 km from the coast has the highest SMB (235 kg m−2a−1). The 780–892 km zone was most affected by the Medieval Warm Period and the Little Ice Age, and the SMB duringad1454–1836 (71 kg m−2a−1) was only one-quarter of that in the 20th century. The SMB in the 1080–1157 km zone fluctuates the most, possibly due to erosion or irregular deposition of snow by katabatic winds in low SMB areas with surface elevation fluctuations. Dome A (1157–1236 km) has the lowest SMB (29 kg m−2a−1) and did not decrease during Little Ice Age. Understanding the spatiotemporal variability of SMB in a larger space can help us understand the complex climate history of Antarctica.

Atmospheric organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in the Antarctic marginal seas: Distribution, sources and transportation

From November 2013 to March 2014, air samples were collected in the Antarctic marginal seas during the 30th Chinese Antarctic research expedition. Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were analyzed in these samples. The mean concentrations were observed for hexachlorobenzene (HCB) >ΣPCBs >Σhexachlorocyclohexanes(HCHs) >Σdichlorodiphenyltrichloroethane(DDTs)>Σchlordanes. High levels of HCB were found near east Antarctica and in the Ross Sea, reflecting the re-emission of HCB from environmental reservoirs of these regions. Parent DDTs (p,p’- and o,p’-DDT) were rarely detected, suggesting that atmospheric DDT was predominantly influencedby weathered DDT from some secondarysources. However, fresh inputs of DDTs could not be excluded because there were still some samples with high proportions of parent DDTs. HCHs only were detected in the South Indian Ocean (near Australia), andthis result might be related to the intense emissions of HCHs from southern Australia. Ratios of trans-chlordane/cis-chlordanein most samples were lower than that in technical chlordane, reflecting the main influence of weathered chlordane. High levels of ΣPCBs were found in the Ross Sea, suggesting an intense re-emission of PCBs. Furthermore, atmospheric PCBs near the Antarctic Peninsula were also relatively high, this finding might be attributed to the emissions of PCBs from nearby Antarctic research stations. Comparing with the Arctic, transport of OCPs and PCBs towards Antarctica is more difficult. The Antarctic marginal seas would act as both barriers and “buffer zones”during the transportation processes.

A Novel Range Processing Method of Surface-Based FMCW Ice-Sounding Radar for Accurately Mapping the Internal Reflecting Horizons in Antarctica

In this article, we establish the nonlinear signal model of the surface-based frequency-modulated continuous wave ice-sounding radar, and propose a novel range processing strategy that aims at removing the frequency ramp nonlinearity effectively. The proposed algorithm takes full consideration of the dependence of nonlinearity on the round-trip delay time while providing certain robustness of noise. The theory analysis and implementation steps of the proposed algorithm are demonstrated. The full-scale simulations with different kinds of nonlinearities and various signal-to-noise ratios verify the effectiveness and robustness of the proposed algorithm. We also apply the proposed method to real dataset collected during the 31st Chinese Antarctic Research Expedition (CHINARE 31) and CHINARE 33. The result shows the effectiveness of our algorithm on illustrating clarified internal reflecting horizons of ice sheets. Compared with the echograms processed by the typical range processing scheme, our algorithm performs better in nonlinearity elimination.

An integrated sampler for shipboard underway measurement of dimethyl sulfide in surface seawater and air

Dimethyl sulfide (DMS), a marine-derived trace gas, can influence atmospheric compositions and has an impact on the global climate. To date, obtaining continuous and coupled shipboard underway measurements of DMS in seawater and air has been challenging. To address this issue, we report a custom-made sampling device based on the purge-and-trap technique. This sampler, in combination with a time-of-flight mass spectrometer (TOF-MS), was successfully utilized to perform coupled shipboard underway measurements of DMS in surface seawater and air around western Antarctica during the 34th Chinese Antarctic Research Expedition from February 2018 to April 2018. The seawater and air streams were continuously introduced into the sampler unit and subsampled every 10 min. The limits of detection (LODs) of DMS in seawater and air were found to be 0.07 nM and 32 pptv, respectively. The variability in the DMS levels in the surface seawater and air can be distinguished and evaluated based on the variations in the DMS peaks. These results demonstrated that the sampling device was effective for consistent, sensitive underway measurements of DMS.

Shock-Induced Olivine-Ringwoodite Transformation in the Shock Vein of Chondrite GRV053584

Shock metamorphism of minerals in meteorites could help to understand the shock history of its parent body and also provide a window into the interior of the Earth. Although shock features in olivine have been well known within and adjacent to shock melt veins and shock melt pockets in meteorites, there are processes that are not yet completely understood. Ringwoodite is formed by crystallization from olivine melts or solid-state phase transformation of olivine. Typically, olivine clasts with a ringwoodite rim around an olivine core have been documented from only a handful of meteorites. Here we report results from GRV053684, a highly shocked L6 chondrite that was collected by Chinese Antarctic Research Expedition in 2006 to Antarctica. The investigations of the shock pressure history and the transformation mechanism of olivine to ringwoodite use optical microscope, electron probe microanalyzer (backscattered electron images, major element quantitative analyses, and quantitative wavelength-dispersive spectrometry elemental X-ray maps), and Raman spectrograph. Ringwoodite in the shock melt vein generally displays as Fe-rich (Fa37-43) polycrystalline rims around Fe-poor (Fa11-20) olivine core and as small individual clasts embedded in shock melt vein matrix. The difference in FeO between ringwoodite rim and olivine core implies that Fe was preferentially partitioned to ringwoodite. The occurrence of maskelynite (An17) indicates a shock pressure ~30 GPa. The FeO and MgO diffusion indicates the transformation process of olivine to ringwoodite is a diffusion-controlled incoherent nucleation and growth. The spatial association between ringwoodite and the shock melt vein matrix suggests that high temperature plays a key role in prompting phase transformation.