Coastal Regions Of Antarctica Research Articles

Local and Remote Atmosphere‐Ocean Coupling During Extreme Warming Events Impacting Subsurface Ocean Temperature in an Antarctic Embayment

AbstractCoastal ocean temperatures can respond to different atmospheric and oceanic processes at local spatial scales or through remote teleconnections. This study focused on subsurface ocean temperatures (subT) at 10 m depth in Maxwell Bay, northern Antarctic Peninsula from February 2017 and January 2022. It investigated extreme warming events during austral summers and their interaction with atmospheric and oceanic conditions regionally and locally. The analysis identified active and extreme Marine Heat Waves (MHWs) in March 2017 and January‐February 2020 associated with a significantly negative Southern Annular Mode index observed 3–4 months before the temperature increase. In March 2017, temperatures exceeded the climatological mean by over 1°C. This anomaly was linked to a strengthened Amundsen Sea Low and a blocking anticyclone moving between the Scotia Sea and the South‐West Atlantic Ocean that deflected westerly winds and facilitated the anomalous transport of warmer northern air masses to the AP. In January‐February 2020, the highest recorded subT was observed (2.97°C), although air‐sea heat fluxes did not show a similar pattern. In February 2020, one of the most intense atmospheric heatwaves ever recorded in West Antarctica was observed. This heatwave corresponded with maximum subT and positive sea surface temperature anomalies extending throughout the western region of the Southern Ocean, related to an extremely negative Southern Annular Mode. This study provides valuable insights into the impact of strong MHWs, a phenomenon that has been less documented in Antarctic coastal regions.

Cross-Shelf Exchange in Prograde Antarctic Troughs Driven by Offshore-Propagating Dense Water Eddies

Abstract This study examines the link between near-bottom outflows of dense water formed in Antarctic coastal polynyas and onshore intrusions of Circumpolar Deep Water (CDW) through prograde troughs cutting across the continental shelf. Numerical simulations show that the dense water outflow is primarily in the form of cyclonic eddies. The trough serves as a topographic guide that organizes the offshore-moving dense water eddies into a chain pattern. The offshore migration speed of the dense water eddies is similar to the velocity of the dense water offshore flow in the trough, which scaling analysis finds to be proportional to the reduced gravity of the dense water and the slope of the trough sidewalls and to be inversely proportional to the Coriolis parameter. Our model simulations indicate that, as these cyclonic dense water eddies move across the trough mouth into the deep ocean, they entrain CDW from offshore and carry CDW clockwise along their periphery into the trough. Subsequent cyclonic dense water eddies then entrain the intruding CDW further toward the coast along the trough. This process of recurring onshore entrainment of CDW by a topographically constrained chain of offshore-flowing dense water eddies is consistent with topographic hotspots of onshore intrusion of CDW around Antarctica identified by other studies. It can bring CDW from offshore to close to the coast and thus impact the heat flux into Antarctic coastal regions, affecting interactions among ocean, sea ice, and ice shelves. Significance Statement Troughs cutting across the Antarctic continental shelf are a major conduit for the transport of dense shelf water from coastal formation regions to the shelf break. This study describes a process in which clockwise-spinning eddies moving offshore in prograde troughs successively entrain filaments of relatively warm Circumpolar Deep Water from offshore across the entire shelf and into the coastal region. This eddy-induced transport provides a new understanding of the shelf edge exchange process identified in previous studies and a mechanism for further onshore intrusion of the warm Circumpolar Deep Water over parts of the Antarctic shelf. The resultant onshore heat flux could potentially bring a substantial amount of heat from offshore into the coastal region and thus affect ice–ocean interactions through melting sea ice and ice shelves.

Investigating halogens and MSA in the Southern Hemisphere: A spatial analysis

Sub-Antarctic islands and Antarctic coastal regions provide valuable sites for investigating environmental processes in the Southern Ocean. The fact that these sites are situated within the sea ice zone underscores their significance in investigating the impact of sea ice on the chemical composition of the boundary layer. In this study we report multi-year average levels of marine aerosols, including bromine, sodium, methanesulphonic acid and iodine, measured in five firn cores collected from sub-Antarctic Islands and coastal Antarctic sites. The records are compared with published Antarctic records to explore the spatial distribution of these species in the Antarctic region and their relationship with sea ice variability. Being mainly sourced from sea-salt aerosols, sodium and bromine exhibit the largest concentrations in the sub-Antarctic region, with progressively reduced deposition from the coast towards the central Antarctic plateau. Due to its gas-phase chemistry, bromine is depleted with respect to sodium in the sub-Antarctic sites. Bromine emitted in the form of sea-salt aerosols undergoes multi-phase recycling in the lower troposphere and, together with gas-phase bromine emitted from sea ice, is likely to be transported away from the source, depositing in enriched concentrations in the plateau compared to the Br/Na sea-water mass ratio. Similarly to bromine and sodium, methanesulphonic acid and iodine are found in higher concentrations in the sub-Antarctic sites, especially where the ocean is sea ice-covered during spring as primary production is stronger than in the ice-free ocean. Sea-salt mediated recycling of gas-phase iodine enhances its atmospheric lifetime, delivering enriched iodine depositions to the Antarctic plateau. Depicting the spatial distribution of these elements is of great importance for understanding the processes delivering these impurities around Antarctica.

Basin-scale tracer replacement timescales in a one-degree global OGCM

This study investigates basin-scale tracer replacement timescales of the two polar oceans and the Atlantic, Indian, and Pacific Oceans using a one-degree global ocean-sea ice model that represents oceans under the largest Antarctic ice shelves, the Filchner-Ronne and Ross Ice Shelf (FRIS and RIS). After a long spin-up with present-day surface boundary conditions, we confirm that the model has a typical representation of wind-driven and thermohaline circulations in one-degree ocean models. We use virtual passive tracers placed in the five oceans and examine the behavior of the passive tracers to estimate the tracer replacement timescales and pathways of the basin-scale ocean waters. Replacement timescales in the polar oceans (114 years for the Southern Ocean and 109 years for the Arctic Ocean) are found to be shorter than those in the three oceans (217 years for the Atlantic Ocean, 163 years for the Indian Ocean, and 338 years for the Pacific Ocean). The Southern Ocean tracer has two clear pathways to the Northern Hemisphere: the surface route in the Atlantic Ocean and the bottom route in the Pacific and Indian Oceans. This surface route is a rapid conduit to transport the Southern Ocean signal to the North Atlantic and Arctic Oceans. The Atlantic Ocean tracer is transported to both polar regions along the North Atlantic Current and the Antarctic Circumpolar Current (ACC). The tracer experiments clearly demonstrate that Atlantic Meridional Overturning Circulation (AMOC) plays a vital role in transporting the water masses in the Atlantic and Arctic Oceans to the Southern Ocean. The southward flow of the AMOC at the intermediate depths carries the northern waters to the ACC region, and then the water spreads over the Southern Ocean along the eastward-flowing ACC. The decay timescales of water in the ice-shelf cavities exposed to the water outside the Southern Ocean are estimated to be approximately 150 years for both the FIRS and RIS. The decay timescales in the Antarctic coastal region are short at the surface and long in the deep layers, with a noticeable reduction in the areas where ACC flows southward toward the Antarctic continent.

Investigating the spatial representativeness of East Antarctic ice cores: a comparison of ice core and radar-derived surface mass balance over coastal ice rises and Dome Fuji

Abstract. Surface mass balance (SMB) of the Antarctic Ice Sheet must be better understood to document the current Antarctic contribution to sea-level rise. In situ point data using snow stakes and ice cores are often used to evaluate the state of the ice sheet's mass balance, as well as to assess SMB derived from regional climate models, which are then used to produce future climate projections. However, spatial representativeness of individual point data remains largely unknown, particularly in the coastal regions of Antarctica with highly variable terrain. Here, we compare ice core data collected at the summit of eight ice rises along the coast of Dronning Maud Land, as well as at the Dome Fuji site, and shallow ice-penetrating radar data over these regions. Shallow radar data have the advantage of being spatially extensive, with a temporal resolution that varies between a yearly and multi-year resolution, from which we can derive a SMB record over the entire radar survey. This comparison therefore allows us to evaluate the spatial variability of SMB and the spatial representativeness of ice-core-derived SMB. We found that ice core mean SMB is very local, and the difference with radar-derived SMB increases in a logarithmic fashion as the surface covered by the radar data increases, with a plateau ∼ 1–2 km away from the ice crest for most ice rises, where there are strong wind–topography interactions, and ∼ 10 km where the ice shelves begin. The relative uncertainty in measuring SMB also increases rapidly as we move away from the ice core sites. Five of our ice rise sites show a strong spatial representativeness in terms of temporal variability, while the other three sites show that it is limited to a surface area between 20–120 km2. The Dome Fuji site, on the other hand, shows a small difference between pointwise and area mean SMB, as well as a strong spatial representativeness in terms of temporal variability. We found no simple parameterization that could represent the spatial variability observed at all the sites. However, these data clearly indicate that local spatial SMB variability must be considered when assessing mass balance, as well as comparing modeled SMB values to point field data, and therefore must be included in the estimate of the uncertainty of the observations.

Simultaneous observations of atmospheric vertical potential gradient from coastal Antarctic stations Bharati and Maitri

Simultaneous observations of the atmospheric electric potential gradient (PG) at Bharati and Maitri stations were studied from 2014 to 2016. A new regional diurnal pattern of fair-weather PG for the coastal Antarctic region, perhaps the ubiquitous characteristics of the PG for the coastal Antarctic region, has been identified. This pattern has a significant broad minimum around noon hours. It is around this time the wind speed is also maximum. The PG data of past years of Syowa, Vostok, and Carnegie Cruise were also used in this study. The surface wind distorts the fair-weather diurnal pattern of PG over Bharati more intensely than at Maitri. The katabatic wind effect on the PG at Bharati appears to be more intense than at Maitri. The topography and katabatic winds associated with the Lambert glacier could be the reason. The observation of Bipolar Air Ion Concentration (BAIC) suggests that the wind speed significantly affects the concentration by accumulation and dispersion. The concentration is maximum when the wind speed is minimum. As the air ion concentration controls the conductivity, the PG is expected to be minimum during these hours to produce an anomalous diurnal pattern in the PG at Bharati. Data quality is improved by measuring the PG with a field monitor at the surface level instead of at an elevated position. This study provides new hope in pursuing globally representative data of the PG for further investigations on the global thunderstorm activity and the solar-terrestrial weather relationship.

Effects of assimilation of YOPP‐SH additional radiosonde observations on analyses and forecasts over Antarctica in austral summer

AbstractRadiosonde observations over Antarctica and the surrounding oceans were enhanced during the Year of Polar Prediction in the Southern Hemisphere (YOPP‐SH) summer Special Observing Period (SOP). Observing System Experiments (OSEs) were conducted in a continuous cycling framework using the Weather Research and Forecasting (WRF) Model and its data assimilation system. Routinely available observations were assimilated in the CTL (control) experiment, and special radiosonde observations from the YOPP‐SH SOP were additionally assimilated in the YOPP experiment. The results were compared to investigate the effects of additional radiosonde observations on analyses and forecasts over and around Antarctica. Verifications against ERA5 re‐analysis, radiosonde observations, and Automatic Weather Station (AWS) observations show overall positive effects of additional radiosonde observations. These positive effects are most noticeable in temperature at lower levels at earlier forecast lead times; afterward, wind forecast improvements at upper levels are the most noticeable. Although routine and special radiosonde observations are concentrated over the eastern and coastal regions of Antarctica (compared to the western and inland regions), the effects of the extra data spread in longitudinal and latitudinal directions; therefore, the effects on the forecasts are not limited to only the areas near the radiosonde observations. A case study reveals how cyclone forecasts are improved through the assimilation of the additional YOPP‐SH SOP radiosonde observations. This study provides insights into future observation strategies in Antarctica, such as horizontal/vertical observation locations, observation variables, and so forth to maximize effects of new observations on forecasts over Antarctica.

Biological Uptake, Water Mass Mixing and Scavenging Limit the Transport of Manganese‐Rich Waters From the East Antarctic Shelf

AbstractManganese (Mn) is an essential element involved in photosynthesis, yet its concentrations in Southern Ocean open waters are very low, arising from biological uptake and limited external inputs. At southern latitudes, waters overlying the Antarctic shelf are expected to have much higher Mn concentrations due to their proximity to external sources. In this study, we investigated the potential export of Mn‐rich Antarctic shelf waters toward depleted open Southern Ocean waters. Our results showed that while high Mn concentrations were observed over the shelf, biological uptake decreased dissolved Mn concentrations in surface waters north of the South Antarctic Circumpolar Current Front (<0.1 nmol kg−1), limiting its export. Conversely, mixing between Mn‐rich Antarctic Bottom Waters and Mn‐depleted Lower Circumpolar Deep Waters combined with oxidative and scavenging processes led to a decrease in dissolved Mn concentrations within bottom waters, with distance from the coast. Particulate Mn concentrations also showed a decreasing trend with distance from the coast. A comparison with other Antarctic coastal regions suggests this bottom water Mn removal may be widespread and that East Antarctica may be characterized by lower Mn concentrations compared to other regions. Still, subsurface dissolved Mn maxima (0.3–0.6 nmol kg−1) represented a potential reservoir for surface waters. We hypothesize that these high subsurface values result from external sources near the shelf. Overall, these results suggest that the moderate lateral export of trace metal‐enriched waters contributes to the extremely low and potentially limiting Mn concentrations previously reported further north in this Southern Ocean region.

Seasonal variation of inorganic carbon parameters and air–sea exchange of CO2 in Marian Cove, King George Island, Western Antarctic Peninsula

Inorganic carbon parameters were observed in Marian Cove, King George Island, Western Antarctic Peninsula, to assess the impact of the Antarctic coastal regions on air–sea CO2 exchange. The variations in total alkalinity (TA) and dissolved inorganic carbon (DIC) were caused by ice melting, formation, and biological activities. The net annual air–sea CO2 flux (5.6 ± 11.8 mmol m−2 d−1) indicated that Marian Cove was a CO2 source in the atmosphere, suggesting the opposite role of the Antarctic coastal regions to the Southern Ocean in CO2 flux estimates. Finally, this study identified the controlling factors of the annual variation of TA and DIC for the first time through direct field observations in King George Island. This study indicated that Antarctic coastal regions can act as a CO2 source to the atmosphere. Thus, further investigations and continuous monitoring are required in the coastal areas to improve our understanding of global carbon cycles.

Change at 85 degrees south: Shackleton Glacier region proglacial lakes from 1960 to 2020

Abstract Over the last two decades, anomalous warming events have been observed in coastal Antarctic regions. While these events have been documented in the Ross Sea sector, the Antarctic interior is believed to have been buffered from warming. In this work, we present data from lakes located near Mt. Heekin and Thanksgiving Valley (~85° S) along the Shackleton Glacier, which are believed to be the southern-most Antarctic dry valley lakes. In 2018, the lakes were characterized, repeat satellite images were examined, and lake water chemistry was measured. Our analysis shows that lake areas recently increased, and the water-soluble ion chemistry indicates a flushing of salts from periglacial soils, likely from increased glacial melt as illustrated by water isotope data. Our results show that high southern latitude ice-free areas have likely been affected by warm pulses over the past 60 years and these pulses may be quasi-synchronous throughout the Transantarctic Mountains.

Source mechanisms and transport patterns of tropospheric bromine monoxide: findings from long-term multi-axis differential optical absorption spectroscopy measurements at two Antarctic stations

Abstract. The presence of reactive bromine in polar regions is a widespread phenomenon that plays an important role in the photochemistry of the Arctic and Antarctic lower troposphere, including the destruction of ozone, the disturbance of radical cycles, and the oxidation of gaseous elemental mercury. The chemical mechanisms leading to the heterogeneous release of gaseous bromine compounds from saline surfaces are in principle well understood. There are, however, substantial uncertainties about the contribution of different potential sources to the release of reactive bromine, such as sea ice, brine, aerosols, and the snow surface, as well as about the seasonal and diurnal variation and the vertical distribution of reactive bromine. Here we use continuous long-term measurements of the vertical distribution of bromine monoxide (BrO) and aerosols at the two Antarctic sites Neumayer (NM) and Arrival Heights (AH), covering the periods of 2003–2021 and 2012–2021, respectively, to investigate how chemical and physical parameters affect the abundance of BrO. We find the strongest correlation between BrO and aerosol extinction (R=0.56 for NM and R=0.28 for AH during spring), suggesting that the heterogeneous release of Br2 from saline airborne particles (blowing snow and aerosols) is a dominant source for reactive bromine. Positive correlations between BrO and contact time of air masses, both with sea ice and the Antarctic ice sheet, suggest that reactive bromine is not only emitted by the sea ice surface but by the snowpack on the ice shelf and in the coastal regions of Antarctica. In addition, the open ocean appears to represent a source for reactive bromine during late summer and autumn when the sea ice extent is at its minimum. A source–receptor analysis based on back trajectories and sea ice maps shows that main source regions for BrO at NM are the Weddell Sea and the Filchner–Ronne Ice Shelf, as well as coastal polynyas where sea ice is newly formed. A strong morning peak in BrO frequently occurring during summer and that is particularly strong during autumn suggests a night-time build-up of Br2 by heterogeneous reaction of ozone on the saline snowpack in the vicinity of the measurement sites. We furthermore show that BrO can be sustained for at least 3 d while travelling across the Antarctic continent in the absence of any saline surfaces that could serve as a source for reactive bromine.

Kelvin‐Helmholtz Billows in the Troposphere and Lower Stratosphere Detected by the PANSY Radar at Syowa Station in the Antarctic

AbstractWe conducted two 10‐day observational campaigns in 2019 targeting turbulence in the troposphere and lower stratosphere by adopting a frequency domain radar interferometric imaging technique using Program of the Antarctic Syowa radar (PANSY radar) and radiosonde observations obtained at Syowa Station in the Antarctic. Seventy three Kelvin‐Helmholtz (K‐H) billows were detected, and two characteristic cases likely excited by the same cyclone were examined in detail. In the first case with the longest observational duration of ∼6.5 hr, the K‐H billows had a thickness of ∼800 m and a horizontal wavelength of ∼2,500 m. According to a numerical simulation, continuously existing gravity waves associated with the cyclone maintained strong vertical wind shear sufficient to cause the K‐H instability. In the second case with the deepest thickness of ∼1,600 m, the K‐H billows had a horizontal wavelength of ∼4,320 m. Numerical simulation suggested that an enhanced upper‐tropospheric jet associated with a well‐developed synoptic‐scale cyclone caused the K‐H instability. Such background conditions, frequently observed in the Antarctic coastal region, are typical mechanisms for K‐H excitation. Linear stability analysis also indicated that the characteristics of the observed K‐H billows were consistent with the most unstable modes. Furthermore, statistical analysis was performed using data of all 73 observed cases. The characteristics of K‐H billows observed at Syowa Station are similar to those observed over Japan. However, the K‐H billows tend to have longer wave periods over Syowa Station than over Japan, likely due to the weaker tropospheric jet in the Antarctic.

Seasonal and interannual variability of the landfast ice mass balance between 2009 and 2018 in Prydz Bay, East Antarctica

Abstract. Landfast ice (LFI) plays a crucial role for both the climate and the ecosystem of the Antarctic coastal regions. We investigate the snow and LFI mass balance in Prydz Bay using observations from 11 sea ice mass balance buoys (IMBs). The buoys were deployed offshore from the Chinese Zhongshan Station (ZS) and Australian Davis Station (DS), with the measurements covering the ice seasons of 2009–2010, 2013–2016, and 2018. The observed annual maximum ice thickness and snow depth were 1.59 ± 0.17 and 0.11–0.76 m off ZS and 1.64 ± 0.08 and 0.11–0.38 m off DS, respectively. Early in the ice growth season (May–September), the LFI basal growth rate near DS (0.6 ± 0.2 cm d−1) was larger than that around ZS (0.5 ± 0.2 cm d−1). This is attributed to cooler air temperature (AT) and lower oceanic heat flux at that time in the DS region. Air temperature anomalies were more important in regulating the LFI growth rate at that time because of thinner sea ice having a weaker thermal inertia relative to thick ice in later seasons. Interannual and local spatial variabilities for the seasonality of LFI mass balance identified at ZS are larger than at DS due to local differences in topography and katabatic wind regime. Snow ice contributed up to 27 % of the LFI total ice thickness at the offshore site close to ground icebergs off ZS because of the substantial snow accumulation. Offshore from ZS, the supercooled water was observed at the sites close to the Dålk Glacier from July to October, which reduced the oceanic heat flux and promoted the LFI growth. During late austral spring and summer, the increased oceanic heat flux led to a reduction of LFI growth at all investigated sites. The variability of LFI properties across the study domain prevailed at interannual timescales, over any trend during the recent decades. Based on the results derived from this study, we argue that an increased understanding of snow (on LFI) processes, local atmospheric and oceanic conditions, as well as coastal morphology and bathymetry, are required to improve the Antarctic LFI modeling.

Spatio-temporal variability of surface turbulent heat flux feedback for mesoscale sea surface temperature anomaly in the global ocean

The surface turbulent heat flux feedback αT plays an important role in the atmosphere–ocean coupling. However, spatio-temporal variability of αT for sea surface temperature anomaly (SSTA) at oceanic mesoscales in the global ocean remains poorly assessed. In this study, we tackle this issue using an advanced statistical model, i.e., the geographically and temporally weighted regression model. The estimated time-mean αT for mesoscale SSTA generally ranges from 10 to 50 W/(m2 K) within 70°S–70°N, except in the Antarctic coastal region where its value drops to zero. The αT is larger in the tropics than in off-tropical regions and locally enhanced in the equatorial cold tongues, western boundary currents, and their extensions. The spatial structure αT is primarily attributed to the non-linearity in the Clausius–Clapeyron relation and inhomogeneity in the background wind speed, whereas adjustment of surface wind speed, air temperature, or moisture to mesoscale SSTA plays an important role in the regional variability. There is an evident seasonal cycle of αT in the tropics and under the northern hemisphere’s storm tracks. The former is due to the seasonally varying response of surface wind speed to mesoscale SSTA, and the latter results from the seasonality of atmospheric and oceanic background states. Our analysis reveals prominent spatio-temporal variability of αT for mesoscale SSTA governed by complicated dynamics.

Dynamical Analysis of Tropopause Folding Events in the Coastal Region of Antarctica

Abstract Tropopause folding events (TFs) are characterized by the rapid and deep descent of the tropopause and are considered to play a significant role in mass exchange between the stratosphere and troposphere. In the present study, TFs occurring in the Antarctic coastal region were examined using the ERA5 dataset. First, the climatological distribution of TF frequency in the extratropics of the Southern Hemisphere was examined. Similar to results from previous studies, TFs were found to often occur along the coast of Antarctica, which is located more than 1000 km south of the maximum of the eddy kinetic energy of synoptic-scale disturbances. This result suggests that the climatological pattern of frequency of TFs in the southern high latitudes cannot be explained only by the geographical distribution of storm tracks. Next, a composite analysis of TFs at Syowa Station was performed. When the negative anomaly of the tropopause height was greatest, strong Q-vector divergence and downwelling were observed in the vicinity of the TF locations. The distribution of Q vectors is related to a local westerly jet and strengthening of the frontal structure associated with meridionally contracted synoptic-scale disturbances. The roles of the topography of the Antarctic Plateau and the radiative cooling on the surface of the continent during the contraction of the disturbances are also discussed based on ray-tracing theory.

Can Ammonium Records in Antarctic Ice Cores be a Proxy for Sea Ice Fluctuations?

Abstract Ammonium (NH4+) accumulation and variability in Antarctic ice cores possess signals of various biological, anthropogenic, and atmospheric processes. However, the use of NH4+ variability in Antarctic ice cores for paleoclimate reconstructions is not well established. Addressing this, we have utilized, published NH4+ ice core records from the Dronning Maud Land (DML), Antarctica to assess the sources of NH4+, its transport, major forcing factors, and their mechanism in controlling the variability of ammonium signals in coastal ice cores. The first principle component (PC1) derived from PC analysis of NH4+ data comprises ~43% of total variability and also depicts a significant spatial correlation with the NSIDC Sea ice concentration (SIC) variability in the Weddell Sea region of the Southern Ocean. In addition, the PC1 shows strong 2-9 year periodicities related to El Niño Southern Oscillation along with two major decadal to centennial periodicities of ~40 and 100 years. The control of sea ice fluctuations and related oceanic processes (ENSO) provide evidence of the marine sources and influence of ocean-related processes as a major controlling factor for the NH4+ variability in DML ice cores. The cumulative accumulation of the NH4+ produced from enhanced biological decomposition, and unutilized ammonium during nitrification under high SIC conditions are possible mechanisms for the increased supply. The correlation of ERA5 surface air temperatures with Nino3.4 suggests that during El Niño conditions, the air temperatures significantly dropped in the Weddell Sea sector, fostering the high SIC conditions. The findings of this study regarding the role of the SIC in the ammonium variability in Antarctic ice cores would help us better interpret the paleo NH4+ records and their applications to deduce the paleoclimate conditions in coastal Antarctic regions.

Chemotaxonomic characterization of the key genera of diatoms in the Northern Antarctic Peninsula.

Diatoms are successful in occupying a wide range of ecological niches and biomes along the global ocean. Although there is a recognized importance of diatoms for the Southern Ocean ecosystems and biogeochemical cycles, the current knowledge on their ecology and distribution along the impacted Antarctic coastal regions remains generalized at best. HPLC-CHEMTAX approaches have been extensively used to this purpose, providing valuable information about the whole phytoplankton community, even for those small-size species which are normally difficult to identify by light microscopy. Despite that, the chemotaxonomic method has reserved minimal focus on great diversity of types associated with diatom genera or species. Here, we show a coupling between the key genera and the corresponding chemotaxonomic subgroup type-A or type-B of diatoms via HPLC-CHEMTAX and microscopic analysis, using chlorophyll-c 1 and chlorophyll-c 3 as biomarker pigments, respectively. The results demonstrated strong correlations for nine of the fifteen most abundant diatom genera observed along the Northern Antarctic Peninsula, from which five (four) were statistically associated with chlorophyll-c 1 (chlorophyll-c 3). Our study highlights the importance to observe diatoms in greater detail, beyond being only one functional group, for a better understanding on their responses under a climate change scenario.

Relationship between meteoric <sup>10</sup>Be and NO<sub>3</sub><sup>−</sup> concentrations in soils along Shackleton Glacier, Antarctica

Abstract. Outlet glaciers that flow through the Transantarctic Mountains (TAM) experienced changes in ice thickness greater than other coastal regions of Antarctica during glacial maxima. As a result, ice-free areas that are currently exposed may have been covered by ice at various points during the Cenozoic, complicating our understanding of ecological succession in TAM soils. Our knowledge of glacial extent on small spatial scales is limited for the TAM, and studies of soil exposure duration and disturbance, in particular, are rare. We collected surface soil samples and, in some places, depth profiles every 5 cm to refusal (up to 30 cm) from 11 ice-free areas along Shackleton Glacier, a major outlet glacier of the East Antarctic Ice Sheet. We explored the relationship between meteoric 10Be and NO3- in these soils as a tool for understanding landscape disturbance and wetting history and as exposure proxies. Concentrations of meteoric 10Be spanned more than an order of magnitude across the region (2.9×108 to 73×108 atoms g−1) and are among the highest measured in polar regions. The concentrations of NO3- were similarly variable and ranged from ∼1 µg g−1 to 15 mg g−1. In examining differences and similarities in the concentrations of 10Be and NO3- with depth, we suggest that much of the southern portion of the Shackleton Glacier region has likely developed under a hyper-arid climate regime with minimal disturbance. Finally, we inferred exposure time using 10Be concentrations. This analysis indicates that the soils we analyzed likely range from recent exposure (following the Last Glacial Maximum) to possibly >6 Myr. We suggest that further testing and interrogation of meteoric 10Be and NO3- concentrations and relationships in soils can provide important information regarding landscape development, soil evolution processes, and inferred exposure durations of surfaces in the TAM.

Total phosphorus records in coastal Antarctic sediments: Burial and evidence of anthropogenic influence on recent input

Total phosphorus (TP) records reflect variations in input and burial of organic matter (OM) in coastal and shelf sediments. At Antarctic regions, TP levels are often derived from natural sources; however, with emergent human pressure at these regions, anthropogenic sources of TP may play an important role. At the Antarctic Peninsula, Admiralty Bay attracts great scientific and touristic interest, especially during austral summer months, thus being vulnerable to human activities. Currently, only scarce spatial distributions of TP are available for this key region, whereas no vertical distributions have been determined. To fill this gap, we investigated short (< 20 cm) sediment cores in ten areas along Admiralty Bay for TP contents. We produced the first TP vertical distributions and established site-specific background values (from 492 ± 13 to 932 ± 17 μg g−1), which are related to hydrodynamics, sedimentology, and natural inputs of P. We observed a gradual surface TP enrichment at all sites, mainly due to input of fresh OM. Benefiting from our background values, we employ the Phosphorus Pollution Index (PPI) to assess possible human impacts. Generally, the increase of PPI suggests natural inputs of P. However, PPI ≥ 1.3 found at the nearby Comandante Ferraz Research Station (Brazil) can be linked to recent (past 2–3 decades) treated sewage inputs in Martel Inlet. We suggest PPI as a proxy for preliminary assessments of anthropogenic impacts in coastal Antarctic regions experiencing increased human pressure.

Exploring the application of TEX86 and the sources of organic matter in the Antarctic coastal region

Isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) are archaeal biomarkers. In many settings, the degree of cyclization of isoGDGTs is correlated with temperature, forming the basis of the TEX86 paleothermometer that is widely used to reconstruct sea surface temperature (SST) across a range of time scales. However, the application of TEX86 to the polar regions is relatively limited and there is currently no consensus on which calibration is best suited for polar environments. In addition, application of TEX86 to the polar regions is complicated by uncertainty regarding the source of organic matter input in coastal polar environments. We tested five different calibrations for TEX86 in marine sediments from the Antarctic coastal region of Admiralty Bay near King George Island, using four short cores that span the second half of the 20th century. We also explored the possible sources of organic matter in these cores using sterol biomarkers. Best results for TEX86 were obtained using a quadratic calibration. The TEX86 signal presented a strong seasonal signal and best matched reanalysis temperatures of the austral spring season (Oct-Nov-Dec). The most abundant compounds observed in the sediments were the sterols cholest-5-en-3β-ol and 24-ethylcholest-5-en-3β-ol, the fatty alcohols C16 and phytol, and isoGDGT-0, indicating a dominant marine origin of the organic matter. Differences in their vertical distributions suggests that some compounds (such as cholest-5-en-3β-ol and phytol) may have had different sources over the evaluated period. Together our results indicate that TEX86 can be used to reconstruct SSTs in the Antarctic coastal region.