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Antarctica and the surrounding Southern Ocean act as an important sink in the global mercury cycle; however, corresponding studies of atmospheric mercury species in these regions are still scarce. Here, we report large‐scale observations of atmospheric gaseous elemental mercury (GEM) and gaseous oxidized mercury (GOM) in the Antarctic marine boundary layer (MBL) taken during a summer cruise. There is large variability in the spatial distribution of GOM, which is likely attributable to the diverse land surface types, including coastal Antarctica, sea‐ice region, and oceanic region, along the cruise route. In coastal Antarctica, the highest GOM level (56.23 ± 47.74 pg·m−3) might be attributed to the significant in‐situ oxidation there. Significant in‐situ oxidation of GEM could also occur in the sea‐ice region, causing the significant increase of GOM (up to 87.01 pg·m−3), while the uptake of the high content of sea‐salt aerosols in sea‐ice regions might efficiently eliminate GOM in the air, resulting in generally lower content of GOM (13.10 ± 14.48 pg·m−3) in the sea‐ice region. In the oceanic region, the lowest level of GOM (3.95 ± 4.69 pg·m−3) is due to both the uptake of sea‐salt aerosols and the seasonal melting of first‐year sea‐ice. This study provides insight to understand the mechanisms of the atmospheric mercury cycle in various land surface types in the Antarctic MBL. Key Points: Large spatial variability in gaseous oxidized mercury over different land surface types was observed in the Southern OceanLow gaseous oxidized mercury content in the sea‐ice region would be to some extent attributed to its greater uptake by sea salt aerosolsThe seasonal melting of first‐year sea ice can cause a clear decrease in gaseous oxidized mercury levels [ABSTRACT FROM AUTHOR]

A quantitative assessment of observed and projected environmental changes in the Southern Ocean ( SO) with a potential impact on the marine ecosystem shows: (i) large proportions of the SO are and will be affected by one or more climate change processes; areas projected to be affected in the future are larger than areas that are already under environmental stress, (ii) areas affected by changes in sea-ice in the past and likely in the future are much larger than areas affected by ocean warming. The smallest areas (<1% area of the SO) are affected by glacier retreat and warming in the deeper euphotic layer. In the future, decrease in the sea-ice is expected to be widespread. Changes in iceberg impact resulting from further collapse of ice-shelves can potentially affect large parts of shelf and ephemerally in the off-shore regions. However, aragonite undersaturation (acidification) might become one of the biggest problems for the Antarctic marine ecosystem by affecting almost the entire SO. Direct and indirect impacts of various environmental changes to the three major habitats, sea-ice, pelagic and benthos and their biota are complex. The areas affected by environmental stressors range from 33% of the SO for a single stressor, 11% for two and 2% for three, to <1% for four and five overlapping factors. In the future, areas expected to be affected by 2 and 3 overlapping factors are equally large, including potential iceberg changes, and together cover almost 86% of the SO ecosystem. [ABSTRACT FROM AUTHOR]

A glutathione S-transferase (GST) gene from Antarctic sea-ice bacteria Pseudoalteromonas sp. ANT506 (namely PsGST), was cloned and expressed in Escherichia coli. The open reading frame of PsGST comprised 654bp encoding a protein of 217 amino acids with a calculated molecular size of 24.3kDa. The rPsGST possesses the conserved amino acid defining the binding sites of glutathione (G-site) and substrate binding pocket (H-site) in GST N_3 family. PsGST was expressed in E. coli and the recombinant PsGST (rPsGST) was purified by Ni-affinity chromatography with a high specific activity of 74.21U/mg. The purified rPsGST showed maximum activity at 40°C and exhibited 14.2% activity at 0°C. It was completely inactivated at 50°C for 40min. These results indicated that rPsGST was a typical cold active GST with low thermostability. The enzyme was little affected by H2O2 and Triton X-100, and 50.2% of the remaining activity was detected in the presence of high salt concentrations (2M NaCl). The enzymatic K m values for CDNB and GSH was 0.22mM and 1.01mM, respectively. These specific enzyme properties may be related to the survival environment of Antarctic sea ice bacteria. [ABSTRACT FROM AUTHOR]

Abstract: Antarctic sea-ice plays a primary role in the climate system, potentially modulating interhemispheric millennial-scale climate change and deglacial warming. Recently, microfossil proxy data have provided important insights into this potential forcing. However, additional proxies for glacial sea-ice reconstructions are required, to support the microfossil data and to control for potential preservation issues. We considered highly branched isoprenoids (HBIs) as a sea-ice proxy, building on earlier studies in the Arctic and Antarctic. This study focused on measuring HBIs in glacial deposits in Southern Ocean deep ocean sediment cores. These deep ocean sites provided a study location away from the local sea-ice complexities associated with coastal and shallow water sites and allowed the comparison of HBIs during several phases of glacial sea-ice variability inferred from microfossils. Down-core profiles of di- and tri-unsaturated HBI isomers diene II and triene III were compared with diatom-based reconstructions of Antarctic sea-ice derived in three high resolution sediment cores recovered from a transect across the Scotia Sea, Southwest Atlantic. High quality chronological control was achieved through a combination of abundance stratigraphy, relative geomagnetic palaeointensity data, and down-core magnetic susceptibility/ice core dust correlation. Significant positive correlations, observed between HBI diene II and sea-ice presence, and between HBI triene III and open waters in the Marginal Ice Zone indicated that the two HBIs are both closely related to sea-ice and sea-ice edge dynamics, respectively. Highly significant down-core correlations between the HBIs indicate coeval sedimentation related to the summer breakdown of sea-ice melt-induced stratification. Combined, the two HBIs and diatoms demonstrated their potential as proxies for permanent sea-ice cover and sea-ice seasonality, two parameters poorly resolved in current climate models. The sea-ice reconstructions presented have developed our knowledge regarding HBIs and their relationship with the surface ocean environment and further highlight their potential as an important proxy for glacial Antarctic sea-ice and sea-ice dynamics back to at least ∼60 ka. [Copyright &y& Elsevier]

Abstract: The Australia/New Zealand region of the Southern Ocean is influenced by several of the major global water masses of the oceans and is the prime entry point for cold deep waters into the Pacific basin. During the last glacial there was increased sea-ice extent around Antarctica (as far north as 55°S), as well as increased iceberg presence inferred from ice-rafted debris. Evidence from microfossil assemblages suggests that sea surface temperatures (SST) were up to 7 °C cooler, consistent with recent estimates of cooling for New Zealand derived from glacier modelling and other terrestrial proxies. The Subtropical Front (STF), Subantarctic Front (SAF) and Polar Front (PF) had migrated north, except where the position of the fronts were controlled bathymetrically. Despite the potential for iron fertilisation by increased dust input into the ocean during the glacial, there is limited evidence for higher total biological productivity in the Pacific sector of the Southern Ocean. The altered oceanic circulation during the glacial also decreased nutrients in the surface waters and affected the outgassing of CO2. This contributed to an increased storage of CO2 in the deep waters and lowering of the carbonate lysocline. During the deglaciation, sea-ice retreat and SST increased rapidly at ∼18 ka, roughly synchronous with the reinvigoration of deep water circulation in the Southern Ocean and the release of CO2 stored in the deep waters. The gradient in carbon isotopes (δ13Cbenthic) between Antarctic Intermediate Water (AAIW) and lower Circumpolar Deep Water (LCDW) was greatest at the start of the deglaciation, suggesting that the AAIW ventilation preceded LCDW ventilation, or there was a significant change in air-sea fractionation of δ13C. There was a slight enrichment in δ18Oplanktic, decrease in SSTs and a reduction in intermediate and deep water circulation between ∼14 and 12.5 ka BP during the Antarctic Cold Reversal (ACR), coincident with glacier advances in the New Zealand Southern Alps and other terrestrial records of cooling. Following the ACR, there was a second, more minor, release of deep water CO2, most likely related to reinvigoration of North Atlantic Deep Water (NADW). From 10 ka onwards the modern intermediate and deep water circulation was established. Air temperatures and SSTs reached a maximum in the early Holocene, with the STF located at its most southerly position, and there was a widespread retreat of Antarctic ice sheets to their modern position. A decline to modern SST and air temperatures in the mid to late Holocene followed. While millennial cycles overprinted on the SST and δ18Oplanktic records, may be the result of subtle changes in the position and strength of the westerly winds during the Holocene. [Copyright &y& Elsevier]

Abstract: We report a comprehensive dataset of dissolved iron (Fe) comprising 482 values at 22 complete vertical profiles along a 1° latitudinal section at the Zero meridian. In addition a shorter high resolution (∼00°09′) surface section of the southernmost part of the transect (66°00′–69°35′S) is presented. Within the upper surface mixed layer the concentrations of dissolved Fe vary between 0.1 and 0.3nM. An inverse trend versus fluorescence suggests significant Fe removal by plankton blooms. Vertical mixing and upwelling are the most important supply mechanisms of iron from deep waters to the upper surface mixed layer. At lower latitude (42°S) there is a distinct maximum of 0.6–0.7nM in the 2000–3000m depth range due to inflow of North Atlantic Deep Water. In one region (55°S) elevated dissolved Fe found in the surface mixed layer is ascribed to the recent deposition of aeolian dust originating from South America. Close to the Antarctic continent there is an indication of Fe supply in surface waters from icebergs. In the deep waters there is a strong indication of a hydrothermal plume of dissolved Fe and Mn over the ridge in the Bouvet region (52–56°S). In the Weddell Gyre basin the dissolved Fe in the deep water is 0.47±0.16nM in the eastward flow at ∼56–62°S and is lower with a value of 0.34±0.14nM in the westward flow at high ∼62–69°S latitude. At the edge of the continental ice-sheet on the prime meridian, the continental margin of the Antarctic continent appears to be lesser source of dissolved Fe than in any other place in the world; this is likely because it is unique in being overlain by the extending continental ice-sheet that largely prevents biogeochemical cycling. [Copyright &y& Elsevier]

Abstract: Sea-ice growth and decay in Antarctica is one of the biggest seasonal changes on Earth, expanding ice cover from 4 × 106 km2 to a maximum of 19 × 106 km2 during the austral winter. Analyses of six marine sediment cores from the Scotia Sea, SW Atlantic, yield records of sea-ice migration across the basin since the Lateglacial. The cores span nearly ten degrees of latitude from the modern seasonal sea-ice zone to the modern Polar Front. Surface sediments in the cores comprise predominantly diatomaceous oozes and muddy diatom oozes that reflect Holocene conditions. The cores exhibit similar down-core stratigraphies with decreasing diatom concentrations and increasing magnetic susceptibility from modern through to the Last Glacial Maximum (LGM). Sediments in all cores contain sea-ice diatoms that preserve a signal of changing sea-ice cover and permit reconstruction of past sea-ice dynamics. The sea-ice records presented here are the first to document the position of both the summer and winter sea-ice cover at the Last Glacial Maximum (LGM) in the Scotia Sea. Comparison of the LGM and Holocene sea-ice conditions shows that the average winter sea-ice extent was at least 5° further north at the LGM. Average summer sea-ice extent was south of the most southerly core site at the LGM, and suggests that sea-ice expanded from approximately ∼61°S to ∼52°S each season. Our data also suggest that the average summer sea-ice position at the LGM was not the maximum extent of summer sea-ice during the last glacial. Instead, the sediments contain evidence of a pre-LGM maximum extent of summer sea-ice between ∼30 ka and 22 ka that extended to ∼59°S, close to the modern average winter sea-ice limit. Based on our reconstruction we propose that the timing of the maximum extent of summer sea-ice and subsequent retreat by 22 ka, could be insolation controlled and that the strong links between sea-ice and bottom water formation provide a potential mechanism by which Southern Hemisphere regional sea-ice dynamics at the LGM could have a global impact and promote deglaciation. [Copyright &y& Elsevier]

Abstract: A medium resolution (10–20km around Antarctica) global ocean/sea-ice model is used to evaluate the impact of katabatic winds on sea-ice and hydrography. A correction is developed to compensate for the drastic underestimation of these katabatic winds in the ERA40 reanalysis. This correction derives from a comparison over 1980–1989 between wind stress in ERA40 and those downscaled from ERA40 by the MAR regional atmospheric model. The representation in MAR of the continental orography surrounding the ocean, like the Transantarctic Mountains, and a specific parameterisation of roughness length in the planetary boundary layer yield a major improvement in the representation of katabatic winds along the coast of Antarctica. Wind stress directions at the first ocean point are remarkably similar in ERA40 and MAR, but MAR wind stress amplitudes are much greater. From this comparison, a scale factor constant in time (i.e. no seasonal variation) but spatially varying (decreasing off-shore over a distance of about 150km) is created for the meridional and zonal wind stress components and adapted to the wind vector. The correction thus consists of a local amplification of the amplitude of the 6-hourly ERA40 wind vector components at ocean points near the coast. The impact of katabatic wind correction is investigated in 40-year long twin simulations of a global ocean/sea-ice model. The wind stress over polynyas is increased by a factor of 2, and amplitudes of sensible and latent air–sea heat exchanges are increased by 28% and 18%, respectively. Sea-ice thickness and ice-fraction near the coast of Antarctica show a marked decrease. The amplified katabatic winds also increase the extent of coastal polynyas by 24% (i.e. the total polynya area is augmented by 60,000km3 around Antarctica), and the winter sea-ice production in polynyas is greater by 42%. Outside polynyas, the impact is a reduction of sea-ice production in the Southern Ocean sea-ice pack. Impacts on the ocean circulation are also marked. Katabatic wind amplification strengthens the local overturning in coastal polynyas with a more intense transformation of Antarctic Surface Waters into colder and denser shelf waters (in total over all polynyas around Antarctica, the overturning reaches 4.7Sv in annual mean, an increase of 1.8Sv, and peaks to 6Sv in winter). The modification of shelf water properties and of the zonal surface winds yields an increase of the amplitude of the seasonal cycle of the Antarctic Coastal Current. [Copyright &y& Elsevier]

Abstract: The polar foraminifera Neogloboquadrina pachyderma (sinistral) dominates assemblages from the high latitude Southern Ocean, which plays a key role in determining past climate due to the tight linkage between Antarctic temperature and atmospheric CO2. Here, we use N. pachyderma (s.) harvested from sediment traps off the West Antarctic Peninsula to construct a seasonal time series for the calibration of calcite proxies in a high latitude seasonal sea-ice environment where temperature is decoupled from other environmental parameters. We have used a combination of δ18OCaCO3 and δ 13CCaCO3 to decipher the calcification temperature and salinity, which reflect that N. pachyderma (s.) live in surface waters throughout the year, and at the ice–water interface in austral winter. Further, our results demonstrate that the uptake of trace metals into N. pachyderma (s.) calcite is influenced by secondary environmental conditions in addition to temperature during periods of sea-ice cover. We propose an elevated carbonate ion concentration at the ice–water interface resulting from biological utilisation of CO2 could influence calcification in foraminifera. Our calculations suggest that for N. pachyderma (s.) Mg/Ca, Sr/Ca ratios and Li/Ca ratios are linear functions of calcification temperature and [CO3 2−]. N. pachyderma (s.) Mg/Ca ratios exhibit temperature sensitivity similar to previous studies (~10–20%/°C) and a sensitivity to [CO3 2−] of ~1%/μmol kg−1. Sr/Ca ratios are less sensitive to environmental parameters, exhibiting ~5% increase/°C and ~0.5%/10 μmol kg−1. The relationship between Li/Ca ratios and both temperature and [CO3 2−] is less significant with ~10% increase in Li/Ca ratio/°C and 10 μmol kg−1. We show how a multi-proxy approach could be used to constrain past high latitude surface water temperature and [CO3 2−]. [Copyright &y& Elsevier]

Abstract: Melting icebergs are a mobile source of fresh water as well as a sink of latent heat. In most global climate models, the spatio-temporal redistribution of fresh water and latent heat fluxes related to icebergs is parameterized by an instantaneous more or less arbitrary flux distribution over some parts of the oceans. It is uncertain if such a parameterization provides a realistic representation of the role of icebergs in the coupled climate system. However, icebergs could have a significant climate role, in particular during past abrupt climate change events which have been associated with armada’s of icebergs. We therefore present the interactive coupling of a global climate model to a dynamic thermodynamic iceberg model, leading to a more plausible spatio-temporal redistribution of fresh water and heat fluxes. We show first that our model is able to reproduce a reasonable iceberg distribution in both hemispheres when compared to recent data. Second, in a series of sensitivity experiments we explore cooling and freshening effects of dynamical icebergs on the upper Southern Ocean and we compare these dynamic iceberg results to the effects of an equivalent parameterized iceberg flux. In our model without interactive icebergs, the parameterized fluxes are distributed homogeneously South of 55°S, whereas dynamic icebergs are found to be concentrated closer to shore except for a plume of icebergs floating North–East from the tip of the Antarctic Peninsula. Compared to homogeneous fluxes, the dynamic icebergs lead to a 10% greater net production of Antarctic bottom water (AABW). This increased bottom water production involves open ocean convection, which is enhanced by a less efficient stratification of the ocean when comparing to a homogeneous flux distribution. Icebergs facilitate the formation of sea-ice. In the sensitivity experiments, both the fresh water and the cooling flux lead to a significant increase in sea-ice area of 12% and 6%, respectively, directly affecting the highly coupled and interactive air/sea/ice system. The consequences are most pronounced along the sea-ice edge, where this sea-ice facilitation has the greatest potential to affect ocean stratification, for example by heat insulation and wind shielding, which further amplifies the cooling and freshening of the surface waters. [Copyright &y& Elsevier]

Summer sea surface temperature (SSST) and sea-ice extent, obtained at millennial to centennial resolution, are presented for seven cores recovered in the Atlantic and western Indian Antarctic Zone, from Termination II and the last interglacial s.s., i.e. Marine Isotope Substage (MIS) 5e. The diatom-based SSST estimates show that during the late MIS 6 intensified export of cold waters from the Weddell Sea resulted in SSSTs close to 0°C in the central and eastern Atlantic sector. Due to northward expansion of the winter sea-ice edge by 3–5° latitude the sea-ice seasonality was reduced. Such conditions have great potential for efficient year-round reduction in air–sea gas exchange and glacial CO2 draw down. The warming at Termination II started at 132–131 ka, marked by rapid retreat of the sea-ice edge. The SSST increased within a few thousands of years to reach maximum interglacial summer temperatures ranging between 2.5 and 3.5°C, in the earliest MIS 5e (128–125 ka). Besides a distinct cold reversal around 129.5 ka, the warming was punctuated by short-lived temperature rebounds with amplitudes of 1–1.5°C, occurring at 200–300-yr frequency, thus in the range of the periodicity of solar input. Increased Chaetoceros spp. abundance suggests meltwater events as the primary cause of the coolings. The SSST optimum, characterised by strongly enhanced biogenic sedimentation rates, ended at ca. 125 ka, with the full re-establishment of the global conveyor belt and beginning of the Northern Hemisphere climatic optimum. At this time SSSTs decreased stepwise and stabilised on values slightly warmer than today, showing in the following period of MIS 5e only low amplitude oscillations. During MIS 5d a northward expansion of the sea-ice field took place, but SSSTs only slightly colder than modern ones and a weakened meridional temperature gradient indicate that the Southern Ocean did not fall in a true glacial mode. The tight correlation between Southern Ocean SSST and winter sea-ice records, and Vostok atmospheric temperature and CO2 records support the idea that the Antarctic winter sea-ice and Southern Ocean temperature exert a primary control on the atmospheric–ocean CO2 exchanges and hence on global climate. Reduction of the Antarctic sea-ice field and increase of SSST at the onset of Termination II could have been triggered by precessional changes influencing southern high latitude summer insolation. Positive feedback mechanisms, reduction of surface albedo and release of CO2 into the atmosphere, and changes in global ocean circulation, affected by a collapse or strong reduction in North Atlantic Deep Water (NADW) production, could have induced further reinforcement of the Southern Ocean warming. [Copyright &y& Elsevier]

The snow petrel Pagodroma nivea is an obligate associate of sea-ice and one of the most abundant seabird species of the Southern Ocean. Time- and sex-specific annual variation in adult survival was estimated using capture-mark-recapture of petrels nesting at Pétrels Island, Terre Adélie, 1981–1997. On the basis of a regression analysis, 44% of the variation was linked inversely to the latitudinal extent of sea-ice during winter (June) in the region offshore of the study colony, where this population is likely to spend the non-breeding season. Monthly sea-surface temperature anomalies tended to influence adult survival but the relationship was not statistically significant. Why sea-ice extent should have such a critical effect on this species is yet to be explained, but the relationship, in the context of environmental warming and the consequent potential loss of Antarctic sea-ice, is an important one for this species. [ABSTRACT FROM AUTHOR]