Hongmei Ma's research while affiliated with Polar Research Institute of China and other places

Ny-Ålesund, located in Arctic Svalbard, is one of the most sensitive areas on Earth under global warming. Accelerated glacier ablation has become remarkable in Ny-Ålesund in recent years. Glacial meltwaters discharge a significant amount of materials to the ocean, affecting downstream ecosystems and adjacent oceans. In August 2015, various water samples were taken near Ny-Ålesund, including proglacial meltwater, supraglacial meltwater, englacial meltwater, and groundwater. Trace metals (Al, Cr, Mn, Fe, Co, Cu, Zn, Cd, and Pb), major ions, alkalinity, pH, dissolved oxygen, water temperature and electric conductivity were also measured. Major ions were mainly controlled by chemical weathering intensity and reaction types, while trace metals were influenced by both chemical weathering and physicochemical control upon their mobility. Indeed, we found Brøggerbreen was dominated by carbonation of carbonate for carbonate weathering, while Austre Lovénbreen and Pedersonbreen were dominated by sulfide oxidation coupled with carbonate dissolution, with a doubled silicate weathering. The higher enrichment of trace metals in supraglacial meltwater compared to proglacial meltwater suggested anthropogenic pollution from atmospheric deposition. In proglacial meltwater, principal component analysis indicated that trace metals like Cr, Al, Co, Mn and Cd were correlated to chemical weathering. This implies that under the accelerated glacier retreating, glacier derived chemical components are subjected to the future changes in weathering types and intensity.

The study of the fabric and microstructure of ice at the shear margin of the Antarctic ice sheet is of great significance for understanding the ice flow and its contributions to sea level rise. In this study, twenty-three one-meter-long ice cores were drilled from blue ice areas at the shear margin of the Dalk Glacier, Antarctica. The ice fabric and microstructure of these ice cores are analyzed using a G50 fabric analyzer. This study shows that the shallow ice cores in this region present a cluster fabric as a consequence of shear stress. The grain size decreases following the direction of the ice flow towards the exposed bedrock at the end of the glacier, due to the blocking and squeezing by the bedrock. The formation mechanism of the shallow ice layers is that the ice from the original accumulation area flows here, lifted by the bedrock and shaped by the summer ablation and denudation. The basal ice at the shear margin of the Dalk Glacier is strongly rubbed by the bedrock and demonstrates a cluster fabric. The analysis of stable water isotopes shows a weak negative correlation between shallow ice fabric and stable water isotopes with depth. Bedrock topography and shear stress have a greater influence on grain microstructure among different ice cores over long distances at shear margins.

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 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 were 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.

Microbial communities have been identified as the primary inhabitants of Arctic forefields. However, the metabolic potential of microbial communities in these newly exposed soils remains underexplored due to limited access. Here, we sampled the very edge of the glacial forefield in Svalbard and performed the 16S rRNA genes and metagenomic analysis to illustrate the ecosystem characteristics. Burkholderiales and Micrococcales were the dominant bacterial groups at the initial stage of soil development of glacial forefields. 214 metagenome-assembled genomes were recovered from glacier forefield microbiome datasets, including only 2 belonging to archaea. Analysis of these metagenome-assembled genomes revealed that 41% of assembled genomes had the genetic potential to use nitrate and nitrite as electron acceptors. Metabolic pathway reconstruction for these microbes suggested versatility for sulfide and thiosulfate oxidation, H2 and CO utilization, and CO2 fixation. Our results indicate the importance of anaerobic processes in elemental cycling in the glacial forefields. Besides, a range of genes related to adaption to low temperature and other stresses were detected, which revealed the presence of diverse mechanisms of adaption to the extreme environment of Svalbard. This research provides ecological insight into the initial stage of the soil developed during the retreating of glaciers.

Plain Language Summary The atmospheric information contained in polar snow/ice nitrate (NO3⁻) is of great interest in paleoclimate research. The interpretation of NO3⁻ variability recorded in ice cores, however, remains challenging as atmospheric NO3⁻ can be lost from snow prior to ice formation. Here, we present 60‐year records of NO3⁻ and its isotopic composition in snow pits collected from Dome A, an exceptionally low snow accumulation site in central Antarctica. Analysis of our data shows that variations in concentration and isotopic composition of NO3⁻ in the upper snowpack are dominated by photolytic loss, resulting in distinct trends in nitrogen and oxygen isotopes of NO3⁻. In the deeper snowpack, we observe clear trends in both concentration and isotopic composition of NO3⁻, which are closely associated with enhanced snow NO3⁻ UV photolysis due to the decreasing stratospheric ozone during ∼1960–2000. That is, elevated UV doses reaching the snow surface as a result of larger Antarctic ozone holes significantly promoted snow NO3⁻ photolysis. These findings raise the prospect of better understanding of past stratospheric ozone variations using ice core NO3⁻ isotope records.

Antarctica is widely regarded as a sink for persistent organic pollutants (POPs). However, there is a scarcity of data on the occurrence and spatial pattern of POPs in Antarctica, especially in the cold-xeric East Antarctica. Here, organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) in soils from the Larsemann Hills, the second-largest ice-free area along East Antarctica, were investigated. It is shown that the main OCP contaminants were HCB, p,p’-DDD and δ-HCH (3.7–1522.3 pg g⁻¹, 38.2–2276.6 pg g⁻¹ and < LOD–570 pg g⁻¹, respectively). OCPs in soils were primarily caused by long-distance atmospheric transport, but local sources can be found in areas heavily impacted by local human activities. Among DDTs and HCHs, only p,p’-DDD and δ-HCH were detected, indicating that DDTs and HCHs have aged. For PCBs (14.1–993.4 pg g⁻¹), low-chlorinated PCB congeners were found in soil samples far from the station areas (Zhongshan, Progress II, and Progress I), possibly due to long-range atmospheric transport, while high levels of high-chlorinated PCB were found in the soils inside the station area (Law Base) and close to the main road, possibly associated with local station activities. Among the measured PBDEs (81.8–695.5 pg g⁻¹), BDE-209 was the most frequently observed species, and the low-BDE found in soil samples could be from BDE-209 photodegradation. The majority of samples containing high concentrations of BDE-209 are concentrated in the station areas, implying that its source may be related to local station activities.