Antarctic Climate Research Articles

Major Artifacts in ERA5 2‐m Air Temperature Trends Over Antarctica Prior to and During the Modern Satellite Era

AbstractGlobal reanalyzes are widely used for investigations of Antarctic climate variability and change. The European Centre for Medium‐Range Weather Forecasts 5th generation reanalysis (ERA5) is well regarded and spans 1940 to today. We investigate whether ERA5 reliably represents the 2‐m air temperature trends across the 1940–2022 (83 years) period at seasonal and annual time scales. We compare ERA5 temperatures with an observation‐based temperature reconstruction for Antarctica (RECON) that has monthly resolution for 1958–2022, the period of reliable observational availability. Results for individual stations are also examined. ERA5 anomalously warms Antarctica in relation RECON especially for the period prior to 1979 when satellite observations over the Southern Ocean were sparse. Trend hotspots that are shown to be artifacts are found at three locations and are present until today. The results demonstrate that ERA5 temperature trends can be questionable even today, but variability is well captured after 1979.

A Bayesian Model for 20th Century Antarctic Sea Ice Extent Reconstruction

AbstractAntarctic sea ice, a key component in the complex Antarctic climate system, is an important driver and indicator of the global climate. In the relatively short satellite‐observed period from 1979 to 2022 the sea ice extent has continuously increased (contrasting a major decrease in Arctic sea ice) up to a dramatic decrease between 2014 and 2017. Recent years have seen record sea ice lows in February 2022–February 2023. We use a statistical ensemble reconstruction of Antarctic sea ice to put the observed changes into the historical context of the entire 20th century. We propose a seasonal Vector Auto‐Regressive Moving Average (VARMA) model fit in a Bayesian framework using regularized horseshoe priors on the regression coefficients to create a stochastic ensemble reconstruction of monthly Antarctic Sea ice extent from 1900 to 1979. This novel model produces a set of 2,500 plausible sea ice extent reconstructions for the sea ice by sector that incorporate the autocorrelation structure of sea ice over time as well as the dependence of sea ice between the sectors. These fully observed reconstructions exhibit plausible month‐to‐month changes in reconstructed sea ice as well as plausible interactions between the sectors and the total. We reconstruct an overall higher sea ice extent earlier in the 20th century with a relatively sharp decline in the 1970s. These trends agree well with previous reconstructions of Antarctic sea ice based on ice core data, whaling locations, and climatological data, as well as early satellite observations in the reconstruction period.

In situ observations of supercooled liquid water clouds over Dome C, Antarctica, by balloon-borne sondes

Abstract. Clouds in Antarctica are key elements that affect radiative forcing and thus Antarctic climate evolution. Although the vast majority of clouds are composed of ice crystals, a non-negligible fraction constitutes supercooled liquid water (SLW; water held in liquid form below 0 °C). Numerical weather prediction models have great difficulty in forecasting SLW clouds over Antarctica, favouring ice at the expense of liquid water and therefore incorrectly estimating the cloud radiative forcing. Remote-sensing observations of SLW clouds have been carried out for several years at Concordia Station (75° S, 123° E; 3233 m above mean sea level), combining active lidar measurements (SLW cloud detection) and passive HAMSTRAD microwave measurements (liquid water path, LWP). The present project aimed at in situ observations of SLW clouds using sondes developed by the company Anasphere, specifically designed for SLW content (SLWC) measurements. These SLWC sondes were coupled to standard meteorological pressure–temperature–humidity sondes from Vaisala and released under meteorological balloons. During the 2021–2022 summer campaign, 15 launches were made, of which 7 were scientifically exploitable above a height of 400 m above ground level, a threshold height imposed by the time the SLWC sonde takes to stabilize after launch. The three main outcomes from our analyses are as follows: (a) the first in situ observations so far of SLW clouds in Antarctica with SLWC sondes; (b) on average, the consistency of SLW cloud heights as observed by in situ sondes and remote-sensing lidar; and (c) the liquid water path (vertically integrated SLWC) deduced by the sondes being generally equal to or greater than the LWP remotely sensed by HAMSTRAD. In general, the SLW clouds were observed in a layer close to saturation (U > 80 %) or saturated (U ∼ 100 %–105 %) just below or at the lowermost part of the entrainment zone, or capping inversion zone, which exists at the top of the planetary boundary layer and is characterized by an inflection point in the potential temperature vertical profile. Our results are consistent with the theoretical view that SLW clouds form and remain at the top of the planetary boundary layer.

Source apportionment of major ions and trace metals in the lacustrine systems of Schirmacher Hills, East Antarctica

The fabric of the Antarctic lacustrine system has a crucial role in assimilating the anthropogenic inputs and mitigating their long time impacts on climate change. Here, we present the changes in the concentrations of major ions and trace metals in the surface water of the lacustrine system to understand the extent of anthropogenic impacts from the adjacent Schirmacher Hills, East Antarctica. The results show that the land-locked lakes (closed-basin lakes surrounded by topographical barriers such as mountains or bedrock formations) in the region have a moderate enrichment in elemental concentrations compared to the pro-glacial lakes (marginal freshwater bodies that form at the terminus of a glacier or ice sheet). The water quality index (WQI: 7.58–12.63) and pollution evaluation index (PEI: 1.36–2.35) remained normal, indicating that the water in these lake are of good quality. However, a significant correlation between lithogenic elements (Al, Fe) and potentially toxic elements (Cd, Cr, and Ba), suggests an increase in the anthropogenic impacts. Based on the principal component analysis (PCA), the source of trace metals to the lacustrine systems appears to be the surrounding environment, followed by aerosol dust particles. Hierarchical cluster analysis (HCA) revealed that regional topography significantly impacts the supply of major ions/trace metals to these lakes. The present study provides baseline data and can be used to estimate and forecast future local and/or global anthropogenic contaminations in the lacustrine system of Schirmacher Hills, East Antarctica. Moreover, the presence of research stations (Maitri and Novolazarevskaya), tourist activities, and the potential for anthropogenic stressors necessitate continued monitoring and impact assessment programs within the Schirmacher Hills lacustrine systems. These programs are crucial for safeguarding this pristine ecosystem from future environmental disturbances under a changing Antarctic climate, as mandated by the Antarctic Treaty System and the Indian Antarctic Act.

Antarstick: Extracting Snow Height From Time‐Lapse Photography

AbstractThe evolution and accumulation of snow cover are among the most important characteristics influencing Antarctica's climate and biotopes. The changes in Antarctica are also substantially impacting global climate change. Therefore, detailed monitoring of snow evolution is key to understanding such changes. One way to conduct this monitoring is by installing trail cameras in a particular region and then processing the captured information. This option is affordable, but has some drawbacks, such as the fully automatic solution for the extraction of snow height from these images is not feasible. Therefore, it still requires human intervention, manually correcting the inaccurately extracted information. In this paper, we present Antarstick, a tool for visual guidance of the user to potentially wrong values extracted from poor‐quality images and support for their interactive correction. This tool allows for much quicker and semi‐automated processing of snow height from time‐lapse photography.

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.

Early Oligocene record of an “iceberg alley” in the Weddell Sea from quartz sand microtextural analysis at ODP Site 696

Abstract The greenhouse to icehouse transition at the Eocene-Oligocene boundary (34 Ma) marked the appearance of continental-scale glaciation in Antarctica. The material recovered from Ocean Drilling Program Site 696 is the only record spanning this major climatic shift in the Weddell Sea region. Using scanning electron microscopy, quartz microtextures in 13 samples across the Eocene-Oligocene transition were analyzed to understand the degree of glacial modification and the transportation history of the >150 µm material. The quartz grains were visually grouped, characterized, and interpreted by grain outline, relief, and surface microtextures. Glacial textures are present throughout the entire interval (34.4–33.2 Ma), with the proportion of iceberg-rafted grains in each sample decreasing into the early Oligocene (33.6 Ma), accompanied by an increase in the frequency of eolian and sea-ice-rafted grains. Mass accumulation rates reveal that the flux of iceberg-rafted debris increased coincident with the flux of eolian and sea-ice-rafted grains following 33.6 Ma, suggesting a strong coupling between land-ice development and high-latitude atmospheric processes. When compared with other Antarctic climate proxy data sets, the intensification of ice rafting at Site 696 occurred after ice-sheet inception in East Antarctica. The prominent influx of terrigenous material after 33.6 Ma points to strengthened glacial conditions accompanied by major changes in the environment of the Weddell Sea region, supporting the idea of a high-latitude role in climate perturbations, in agreement with interpretations of other global proxies.

Understanding the drivers of near-surface winds in Adélie Land, East Antarctica

Abstract. Near-surface winds play a crucial role in the climate of Antarctica, but accurately quantifying and understanding their drivers is complex. They result from the contribution of two distinct families of drivers: the large-scale pressure gradient and surface-induced pressure gradients known as katabatic and thermal wind. The extrapolation of vertical potential temperature above the boundary layer down to the surface enables us to separate and quantify the contribution of these different pressure gradients in the momentum budget equations. Using this method applied to outputs of the regional atmospheric model MAR at a 3-hourly resolution, we find that the seasonal and spatial variability in near-surface winds in Adélie Land is dominated by surface processes. On the other hand, high-frequency temporal variability (3-hourly) is mainly controlled by large-scale variability everywhere in Antarctica, except on the coast. In coastal regions, although the katabatic acceleration surpasses all other accelerations in magnitude, none of the katabatic or large-scale accelerations can be identified as the single primary driver of near-surface wind variability. The angle between the large-scale acceleration and the surface slope is a key factor in explaining strong wind speed events: the highest-wind-speed events happen when the katabatic and large-scale forcing are aligned, although each acceleration, when acting alone, can also cause strong wind speed. This study underlines the complexity of the drivers of Antarctic surface winds and the value of the momentum budget decomposition to identify drivers at different spatial and temporal scales.

Two Ubiquitous Radiative States Observed across the High Latitudes

Abstract Previous studies have shown the Arctic exhibits two preferred radiative states, one that is regarded as “radiatively opaque” and the other as “radiatively clear”; this presents as bimodality in the surface longwave flux distributions. How frequently these two states occur and what causes them to persist has significant implications for the polar climate. Furthermore, in the presence of multimodality, evaluating models based solely on their ability to resolve the mean and variance of a distribution can lead to a poor representation of the physical evolution of our climate. This study takes a holistic view of this bimodal behavior, seeking to understand to what degree the high latitudes of both hemispheres reside in distinct radiative states. Even when separated into climatologically distinct subregions, many polar regions exhibit bimodality in their longwave flux distributions not observed at lower latitudes, suggesting that the existence of these two states is both common in and unique to polar regions. Bimodality arises due to a tendency for the atmosphere to alternate between transmissive or opaque clouds, with surface longwave radiative effects of approximately 0 and 75 W m−2 (relative to clear-sky values), respectively. Clouds need not contain liquid to lead to the opaque state, as is typically assumed. The presence of solely ice clouds can cause bimodality to arise in downwelling longwave flux distributions. While some regions do not explicitly exhibit multimodal surface longwave radiation distributions, it is found that similar cloud states exist but in disproportionate frequencies. Significance Statement Radiation plays an important role in shaping the Arctic and Antarctic climates. Several Arctic expeditions have found that certain regions flip between having a very large energy deficit (“transmissive”) to relatively small energy deficit (“opaque”). The former allows for surface cooling and promotes the formation of ice, while the latter hinders such behavior. This study utilizes satellite observations to understand if this behavior is consistent across the Arctic and Antarctic. Understanding the frequencies of these two states is increasingly important within the context of our rapidly changing climate, and by uncovering the fundamental processes which lead to them, we may be able to model how they will change in the future.

Future Antarctic Climate: Storylines of Midlatitude Jet Strengthening and Shift Emergent from CMIP6

Abstract A main source of regional climate change uncertainty is the large disparity across models in simulating the atmospheric circulation response to global warming. Using the latest suite of global climate models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), a storyline approach is adopted to derive physically plausible scenarios of Antarctic climate change for 2070–99, according to Shared Socioeconomic Pathway SSP5-8.5. These storylines correspond to differences in the simulated amount of seasonal sea ice loss and either (i) the delay in the summertime stratospheric polar vortex (SPV) breakdown or (ii) wintertime SPV strengthening, which together constitute robust drivers of the response pattern to future climate change. Such changes combined are known to exert a strong control over the Southern Hemisphere midlatitude jet stream, which we quantify as collectively explaining up to 70% of the variance in jet response in summer and 35% in winter. For summer, the expected strengthening and displacement of the tropospheric jet stream varies between a ∼1 and 2 m s−1 increase and ∼2°–4° poleward shift, respectively, across storylines. In both seasons, a larger strengthening of the jet is correlated with less Antarctic warming. By contrast, the response in precipitation is more consistent but still strongly attenuated by large-scale dynamics. We find that an increase in high-latitude precipitation around Antarctica is more pronounced for storylines characterized by a greater poleward jet shift, particularly in summer. Our results highlight the usefulness of the storyline approach in illustrating model uncertainty and understanding the processes that determine the spread in projected Antarctic regional climate response. Significance Statement Uncertainty in future climate predictions for the Antarctic is dominated by the unknown response of the large-scale (global) atmospheric circulation. In characterizing such uncertainty, plausible outcomes of climate response (storylines) are generated from the organization of model projections according to the amount of simulated seasonal sea ice loss and the delay in summertime breakdown/winter strengthening of the stratospheric westerly circulation (polar vortex). The intensity and location of the tropospheric jet stream is strongly dependent on both factors, which strongly influences the near-surface climate response over Antarctica. We find that the simulated amount that Antarctic air temperatures increase by in the future (to the end of the century) is intrinsically related to the projected intensification of the Southern Hemisphere tropospheric jet, varying by a factor of 2 or more across storylines for summer. Storylines with greater jet strengthening are associated with less Antarctic warming (reduced poleward advection of air masses from lower latitudes). Similar differences are found for changes in jet position, which we note has a much stronger control on mid- to high-latitude precipitation response. This includes both an enhanced wetting response around Antarctica and drying response farther equatorward, for storylines characterized by a greater poleward jet shift.

Urea amendment decouples nitrification in hydrocarbon contaminated Antarctic soil

Hydrocarbon contaminated soils resulting from human activities pose a risk to the natural environment, including in the Arctic and Antarctic. Engineered biopiles constructed at Casey Station, Antarctica, have proven to be an effective strategy for remediating hydrocarbon contaminated soils, with active ex-situ remediation resulting in significant reductions in hydrocarbons, even in the extreme Antarctic climate. However, the use of urea-based fertilisers, whilst providing a nitrogen source for bioremediation, has also altered the natural soil chemistry leading to increases in pH, ammonium and nitrite. Monitoring of the urea amended biopiles identified rising levels of nitrite to be of particular interest, which misaligns with the long term goal of reducing contaminant levels and returning soil communities to a ‘healthy’ state.Here, we combine amplicon sequencing, microfluidic qPCR on field samples and laboratory soil microcosms to assess the impact of persistent nitrite accumulation (up to 60 months) on nitrifier abundances observed within the Antarctic biopiles. Differential inhibition of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) Nitrobacter and Nitrospira in the cold, urea treated, alkaline soils (pH 8.1) was associated with extensive nitrite accumulation (76 ± 57 mg N/kg at 60 months). When the ratio of Nitrospira:AOB dropped below ∼1:1, Nitrobacter was completely inhibited or absent from the biopiles, and nitrite accumulated. Laboratory soil microcosms (incubated at 7 °C and 15 °C for 9 weeks) reproduced the pattern of nitrite accumulation in urea fertilized soil at the lower temperature, consistent with our longer-term observations from the Antarctic biopiles, and with other temperature-controlled microcosm studies. Diammonium phosphate amended soil did not exhibit nitrite accumulation, and could be a suitable alternative biostimulant to avoid excessive nitrite build-up.

Spatiotemporal Patterns of Polar Low Activity Over the Southern Ocean

AbstractPolar Lows (PLs) are intense maritime meso‐scale cyclones that form over cold ocean regions in high latitudes. They affect the weather and climate of Antarctica and the surrounding ocean by producing storms with near or above gale‐force winds and heavy precipitation. This study investigated PLs in the Southern Ocean (SO) between 60 and 85°S from 2000 to 2020, using a tracking algorithm applied to the ERA5, CCMP, and NCEP/NCAR data sets. The results showed that PLs are most frequent in winter (JJA) and least frequent in summer (DJF), with a maximum in 2018 and a minimum in 2014. The results also show that PLs are concentrated over the Antarctic Circumpolar Current (ACC) region, along the Ross Sea, the Amundsen Sea, and the Bellingshausen Sea from April to October. These regions have strong thermal gradients and orographic forcing that enhance cyclogenesis. Our research reveals that there were 1,073 occurrences of PLs during the study period, with an average 51 cases per year. The study also explored the influence of sea surface temperature anomalies, sea surface currents, and MCAOs Index on PL genesis. The Amundsen‐Bellingshausen Seas Low (ABSL) and Pacific Ocean currents have a considerable effect on PLs developing in the SO. This research provides valuable information on PLs in the SO, which are poorly observed and understood. However, more research is required to understand how these phenomena are evolving in the present, and how they will change in the future.

The Extraordinary March 2022 East Antarctica “Heat” Wave. Part I: Observations and Meteorological Drivers

Abstract Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of −9.4°C on 18 March at Concordia Station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an intense atmospheric river advecting subtropical/midlatitude heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heat wave’s meteorological drivers, impacts, and historical climate context. Here we focus on describing those temperature records along with the intricate meteorological drivers that led to the most intense atmospheric river observed over East Antarctica. These efforts describe the Rossby wave activity forced from intense tropical convection over the Indian Ocean. This led to an atmospheric river and warm conveyor belt intensification near the coastline, which reinforced atmospheric blocking deep into East Antarctica. The resulting moisture flux and upper-level warm-air advection eroded the typical surface temperature inversions over the ice sheet. At the peak of the heat wave, an area of 3.3 million km2 in East Antarctica exceeded previous March monthly temperature records. Despite a temperature anomaly return time of about 100 years, a closer recurrence of such an event is possible under future climate projections. In Part II we describe the various impacts this extreme event had on the East Antarctic cryosphere. Significance Statement In March 2022, a heat wave and atmospheric river caused some of the highest temperature anomalies ever observed globally and captured the attention of the Antarctic science community. Using our diverse collective expertise, we explored the causes of the event and have placed it within a historical climate context. One key takeaway is that Antarctic climate extremes are highly sensitive to perturbations in the midlatitudes and subtropics. This heat wave redefined our expectations of the Antarctic climate. Despite the rare chance of occurrence based on past climate, a future temperature extreme event of similar magnitude is possible, especially given anthropogenic climate change.

The southward migration of the Antarctic Circumpolar Current enhanced oceanic degassing of carbon dioxide during the last two deglaciations

Previous studies suggest that meridional migrations of the Antarctic Circumpolar Current may have altered wind-driven upwelling and carbon dioxide degassing in the Southern Ocean during past climate transitions. Here, we report a quantitative and continuous record of the Antarctic Circumpolar Current latitude over the last glacial-interglacial cycle, using biomarker-based reconstructions of surface layer temperature gradient in the southern Indian Ocean. The results show that the Antarctic Circumpolar Current was more equatorward during the ice ages and shifted ~6° poleward at the end of glacial terminations, consistent with Antarctic Circumpolar Current migration playing a role in glacial-interglacial atmospheric carbon dioxide change. Comparing the temporal evolution of the Antarctic Circumpolar Current mean latitude with other observations provides evidence that Earth’s axial tilt affects the strength and latitude range of Southern Ocean wind-driven upwelling, which may explain previously noted deviations in atmospheric carbon dioxide concentration from a simple correlation with Antarctic climate.

Supercooled liquid water clouds observed over Dome C, Antarctica: temperature sensitivity and cloud radiative forcing

Abstract. Clouds affect the Earth climate with an impact that depends on the cloud nature (solid and/or liquid water). Although the Antarctic climate is changing rapidly, cloud observations are sparse over Antarctica due to few ground stations and satellite observations. The Concordia station is located on the eastern Antarctic Plateau (75∘ S, 123∘ E; 3233 m above mean sea level), one of the driest and coldest places on Earth. We used observations of clouds, temperature, liquid water, and surface irradiance performed at Concordia during four austral summers (December 2018–2021) to analyse the link between liquid water and temperature and its impact on surface irradiance in the presence of supercooled liquid water (liquid water for temperature less than 0 ∘C) clouds (SLWCs). Our analysis shows that, within SLWCs, temperature logarithmically increases from −36.0 to −16.0 ∘C when liquid water path increases from 1.0 to 14.0 g m−2. The SLWC radiative forcing is positive and logarithmically increases from 0.0 to 70.0 W m−2 when liquid water path increases from 1.2 to 3.5 g m−2. This is mainly due to the downward longwave component that logarithmically increases from 0 to 90 W m−2 when liquid water path increases from 1.0 to 3.5 g m−2. The attenuation of shortwave incoming irradiance (that can reach more than 100 W m−2) is almost compensated for by the upward shortwave irradiance because of high values of surface albedo. Based on our study, we can extrapolate that, over the Antarctic continent, SLWCs have a maximum radiative forcing that is rather weak over the eastern Antarctic Plateau (0 to 7 W m−2) but 3 to 5 times larger over West Antarctica (0 to 40 W m−2), maximizing in summer and over the Antarctic Peninsula.

Cirques in the Transantarctic Mountains reveal controls on glacier formation and landscape evolution

In this study, we analyse the morphometry of cirques in the Transantarctic Mountains (TAM) to understand regional glacier formation and landscape evolution since the onset of Cenozoic glaciations. We find that, unlike most glacierised regions worldwide, aspect bias for cirques in the TAM is not particularly strong, indicating that glaciers were able to form and cirques develop on slopes with a variety of aspects. This is perhaps unsurprising, given that Antarctica's climate has been conducive to long-lived and extensive glaciation for many millions of years. Surprisingly, where cirques in the TAM show an aspect bias, this is typically towards the North, NW and/or NE, rather than favouring South-facing slopes where direct solar radiation is comparatively limited. This lack of a poleward aspect bias is unlike most cirque populations globally and indicates that total solar insolation was not a key control on where former glaciers in the TAM were able to initiate. Instead, we argue that prevailing wind directions played a dominant role in controlling the slopes on which past glacier development was favoured. Specifically, South-facing slopes in the TAM are directly exposed to katabatic winds which originate from the interior of the East Antarctic Ice Sheet (EAIS). These slopes are therefore susceptible to wind deflation, with snow and ice being redistributed to lee-side slopes where it can accumulate due to protection from the wind. For this reason, North, NE and/or NW facing slopes may have favoured glacier development, and therefore resulted in a concentration of cirques with these aspects. This evidence suggests that most cirques in the TAM are no older 34 Ma, as outward radiating winds from the continent's interior could only have prevailed when the EAIS was present (in some form). By contrast, the very highest (and likely oldest) cirques in the TAM have more varied aspects, indicating that they may have formed before katabatic winds came to dominate, and by extension, before widespread growth of the EAIS at 34 Ma, and could perhaps have formed as far back as 60 Ma. In general, we find that cirques in the TAM have similar dimensions to those in other regions globally, despite having been occupied by glacial ice for far longer. Thus, our findings support a growing body of evidence which suggests that cirque size and glacier occupation times are not directly coupled, though there is some evidence of spatial variability in cirque size which might relate to the differences in the dynamics of former glaciers.

Early sea ice decline off East Antarctica at the last glacial-interglacial climate transition.

Antarctic climate warming and atmospheric CO2 rise during the last deglaciation may be attributed in part to sea ice reduction in the Southern Ocean. Yet, glacial-interglacial Antarctic sea ice dynamics and underlying mechanisms are poorly constrained, as robust sea ice proxy evidence is sparse. Here, we present a molecular biomarker-based sea ice record that resolves the spring/summer sea ice variability off East Antarctica during the past 40 thousand years (ka). Our results indicate that substantial sea ice reduction culminated rapidly and contemporaneously with upwelling of carbon-enriched waters in the Southern Ocean at the onset of the last deglaciation but began at least ~2 ka earlier probably driven by an increasing local integrated summer insolation. Our findings suggest that sea ice reduction and associated feedbacks facilitated stratification breakup and outgassing of CO2 in the Southern Ocean and warming in Antarctica but may also have played a leading role in initializing these deglacial processes in the Southern Hemisphere.

Decadal Modulation of the Atlantic Meridional Mode on the West Antarctic Climate during Austral Winter

Abstract Based on observations and simplified, comprehensive atmospheric models, we investigate the impact of the tropical Atlantic sea surface temperature (SST) on the West Antarctic temperature and sea ice concentration in austral winter (June–August) on decadal time scales. The tropical gradient SST anomaly (SSTA) associated with the positive phase of the Atlantic meridional mode (AMM) usually leads to cool anomalies over the Antarctic Peninsula (AP) and a dipole-like sea ice distribution, with ice growth in the Amundsen–Bellingshausen Sea and loss in the Ross Sea. When the AMM is in a positive phase, upward motion over the warm region in the North Atlantic and downward motion over the cold region in the South Atlantic strengthen the Southern Hemisphere Hadley cell, resulting in upper-level convergence over the southwestern Atlantic. This convergence induces a Rossby wave, leading to an anticyclone anomaly over the Amundsen–Bellingshausen Sea. Meridional component winds of this anticyclone anomaly are associated with wind-driven sea ice drift, temperature advection, and anomalous turbulence heat fluxes, leading to a dipole-like sea ice distribution and AP cooling. These findings are verified using two types of atmospheric models. Therefore, the AMM plays a vital role in modulating the decadal change in temperature and sea ice distribution in the West Antarctic.

Amplified Interannual Variation of the Summer Sea Ice in the Weddell Sea, Antarctic After the Late 1990s

AbstractThe sea‐ice extent (SIE) in the Weddell Sea plays a crucial role in the Antarctic climate system. Many studies have examined its long‐term trend, however whether its year‐to‐year variation has changed remains unclear. We found an amplified year‐to‐year variance of the Weddell Sea SIE in austral summer since 1998/1999 in observational datasets. Analyses of sea‐ice concentration budget and surface fluxes indicate that it is the thermodynamic process that drives the amplification of SIE variations, rather than the sea‐ice‐drift‐related dynamic process. Compared to 1979–1998, the Southern Annular Mode in the preceding spring shows a closer linkage with the Weddell Sea SIE in 1999–2021 through a stronger and more prolonged impact on sea surface temperature, which thermodynamically modulates local sea ice via changing surface heat and radiation fluxes. Our study helps advance the understanding of extreme low Antarctic‐SIE records occurring in recent decades and improve future projections of the Antarctic sea‐ice variability.

Contrasting impacts of non-native isopods and springtails on ecosystem processes under simulated Antarctic climate conditions

Climate change, coupled with the introduction of non-native organisms, represent major threats to the functioning of ecosystems, especially in species-poor communities such as polar terrestrial ecosystems. In this laboratory study, we quantified the impacts of the non-native springtail Folsomia candida and isopod Porcellio scaber on seed germination and growth of the non-native grass Poa pratensis, and ecosystem respiration. The impacts of invertebrate communities of progressively increasing complexity were assessed, starting with the native springtail Cryptopygus antarcticus alone, followed by C. antarcticus in combination with F. candida or P. scaber and, finally, a community including all three species. The impact of these invertebrate communities were studied in a simulation of contemporary Antarctic soil surface conditions (2 °C) and a +5 °C warming scenario over one growing season.Warming resulted in earlier germination (21 d), 10-fold increased plant biomass, N-content (>5-fold), and higher levels (90%) of ecosystem respiration. Warming also resulted in a 350% increase in C. antarcticus abundance.The presence of the woodlouse P. scaber had the strongest impact on the measured soil and plant variables and this impact was largely irrespective of temperature. Impacts included: delay in seedling emergence (4 d), reduced plant emergence (20%), and higher ecosystem respiration (135%). The presence of both C. antarcticus and P. scaber resulted in 30% higher plant leaf N-content and a reduction in C:N ratio from 21 to 17. The experimental communities containing F. candida showed a 37% reduction in plant biomass under warming. The presence of P. scaber reduced C. antarcticus abundance (94%) but F. candida abundance was unaffected.Our data indicate that non-native invertebrates differ in their ecosystem impacts, with potentially significant consequences for ecosystem functioning and community composition of plants and animals in cold biomes.