Abstract: Remote Northern Hemisphere (NH) and Southern Hemisphere (SH) lake sediment and peat records of mercury (Hg) deposition have shown a ×3 to ×5 Hg enrichment since pre-industrial times (<1880 AD), leading to the perception that global atmospheric Hg enrichment is moderate and uniform across the hemispheres. Anthropogenic Hg emissions in the NH are, however, approximately 4 times higher than those in the SH. Here, we reconstruct atmospheric Hg deposition in four remote SH peatlands and review sediment and peat Hg records from both hemispheres. We observe a ×4 all-time enrichment in SH Hg deposition from pre-anthropogenic (<1450 AD) to the late 20th-century periods, which is lower than the large ×16 all-time enrichment in NH Hg deposition. We attribute this difference to lower anthropogenic Hg emissions in the SH, and higher natural atmospheric SH Hg concentrations, supported by ×2 higher natural background Hg accumulation in SH peat records. We suggest that the higher SH natural atmospheric Hg deposition reflects the SH land–ocean distribution, and is driven by important SH marine Hg emissions. Our findings indicate that atmospheric Hg background levels and anthropogenic enrichment in both hemispheres are different and should be taken into account in international Hg assessments and environmental policy.

Abstract: The southern westerly winds (SWW) play a major role in climate variability in Southern Hemisphere mid- and high-latitudes, regulating rainfall, ocean circulation, and the Southern Ocean carbon sink. Despite their importance, little is known about millennial scale changes in the SWW and how they have influenced the climate system in the past and interacted with the Earth’s surface elements, such as dust, nutrients and carbon. Here we present a dust record from a 6.6 kyr old peat core in Amsterdam Island (AMS) situated at the northern edge of the SWW (37°S) in the Southern Indian Ocean. Mineral dust flux was used to track atmospheric dust production, long-distance transport and subsequent deposition. Dust provenance was determined from rare earth element (REE) and Nd isotopic signatures (εNd) in the peat core, compared with a reference dataset of Southern Hemisphere dust sources. Using a multi-proxy mixing model, the εNd and REE ratios show a relatively uniform mixture of ca. 40% local, 15% Southern African and 45% Southern South American dust sources since 6.6 cal kyr BP. However, from 1910 AD onwards, there is a doubling in the contribution from Southern Africa (32%). Two mineral dust flux minima occur at 6.2–4.9 cal kyr BP and 3.9–2.7 cal kyr BP, interpreted as periods with equatorward-shifted and/or strengthened SWW at the northern edge of the wind belt. Conversely, periods of higher dust flux at 6.6–6.2 cal kyr BP, 4.9–3.9 cal kyr BP, and 1.4 cal kyr BP onwards are interpreted as poleward-shifted and/or weakened SWW. These interpretations are based on the findings that higher (lower) wind speeds lead to enhanced (less) removal of distal dust on the way to AMS, by wet deposition and turbulence. Published Holocene SWW records at the northern edge of the wind belt (33–41°S) covering South-America, Southern-Africa and Australia, show much variability over the last 6.6 kyr. We suggest this reflects complex regional climate variability in the different SH longitudinal sectors, indicating that SWW are not zonally homogeneous at the northern edge of the wind belt. The recent shift in dust provenance is not accompanied by enhanced total dust deposition at AMS. We therefore suggest that human impact (e.g., land use changes) and drier climate conditions in Southern Africa have led to enhanced dust mobilization.

Abstract: This study is the first synthesis of chemical composition and stable isotopes values for the Kerguelen archipelago waters. The stable isotope values for rainfall and river waters in the Kerguelen archipelago allow a calculation of the Local Meteoric Water Line (δD rainfall = 8.43 x δ18O rainfall + 11) and a summer runoff line (δD river drainage = 7.45 x δ18O river drainage + 6). Surface waters with low- ion concentrations, chlorine facies and stable isotope values infiltrate through fractures and lava flows recharging deeper groundwaters. Thermal groundwater with low- (7 to 50 °C) and high- (50 to 100 °C) temperatures emerges in different localities in the volcanic archipelago. The low-temperature thermal waters might represent a mixture of high-temperature water with rainfall, thermal gradient changes or shallower infiltration compared to that for high-temperature thermal waters. The Rallier du Baty and Val Travers areas contain geothermal fluids with high-temperature springs, fumaroles and a large water flow. In the Rallier du Baty, the major ion chemistry and O, H, C and S stable isotope ratio of low (7 to 50 °C) temperature spring waters in Rallier du Baty area demonstrate a geothermal-system recharged by meteoric water (δD H2O liquid = 7.0 x δ18O H2O liquid + 0.5) rather than sea water. The chemical and isotopic compositions of elevated temperature spring waters (50 to 100 °C) have a long and complex history of meteoric water interacting with cooling magmas (δD H2O liquid = 1.78 x δ18O H2O liquid –  23). Surficial precipitation of aragonite, kaolinite, pyrite, native sulfur attest to a long livied geothermal system. A temperature of the geothermal reservoir has been estimated between 193 and 259 °C by cation geothermometry. The combination of minerals observed, major ion composition of water with thermodynamic modeling and stable isotope data suggest a geothermal system with a series of water/rock interactions from 50 to 250 °C. The conductive cooling of rising of H2O−CO2-rich fluids have produced a H2O−CO2 phase separation with the precipitation of secondary minerals.

Abstract: We argue the need to improve climate change forecasting for ecology, and importantly, how to relate long-term projections to conservation. As an example, we discuss the need for effective management of one species, the emperor penguin, Aptenodytes forsteri. This species is unique amongst birds in that its breeding habit is critically dependent upon seasonal fast ice. Here, we review its vulnerability to ongoing and projected climate change, given that sea ice is susceptible to changes in winds and temperatures. We consider published projections of future emperor penguin population status in response to changing environments. Furthermore, we evaluate the current IUCN Red List status for the species, and recommend that its status be changed to Vulnerable, based on different modelling projections of population decrease of ≥50% over the current century, and the specific traits of the species. We conclude that current conservation measures are inadequate to protect the species under future projected scenarios. Only a reduction in anthropogenic greenhouse gas emissions will reduce threats to the emperor penguin from altered wind regimes, rising temperatures and melting sea ice; until such time, other conservation actions are necessary, including increased spatial protection at breeding sites and foraging locations. The designation of large-scale marine spatial protection across its range would benefit the species, particularly in areas that have a high probability of becoming future climate change refugia. We also recommend that the emperor penguin is listed by the Antarctic Treaty as an Antarctic Specially Protected Species, with development of a species Action Plan.

Abstract: In recent decades, climate change has been faster in various parts of the world. Within species, to counter rapid climate changes shift of geographical area, individuals’ plastic responses or populations’ genetic adaptation might occur. The sub-Antarctic islands are subject to one of the most rapid climate changes on earth, with already visible impacts on native vegetation. Such might be the case of Lyallia kerguelensis a cushion plant strictly endemic to the Kerguelen Islands. In L. kerguelensis, necrotic parts were observed in cushions these last decades and possibly related to water stress. We analysed morphological variability of L. kerguelensis, including necrosis extent, across 19 populations spanning a wide range of environments across the Kerguelen Islands. Inter-population variations in the cushion surface area, shape and compactness were well explained by topography, degree of wind exposure, slope aspect, proportions of coarse sand and bare soil, and geographical distance between populations. All these variables are related to wind intensity and water availability. Moreover, in cushions with less than 10% necrosis in surface area, necrosis extent was positively correlated to soil sodium. Sodium availability might reduce the plant’s capacity for osmotic adjustment in face of other abiotic stresses, such as water stress. We conclude that cushion morphology may have the capacity to adjust to environmental variation, including aspects of climate change, but that cushion necrosis may be accelerated in the driest and most saline environments.