Adelaide Island Research Articles

Skeletal magnesium content in Antarctic echinoderms along a latitudinal gradient

Ocean warming and acidification driven by anthropogenic CO2 emissions may impact the mineral composition of marine calcifiers. Species with high skeletal Mg content could be more susceptible in polar regions due to the increased solubility of CO2 at lower temperatures. We aimed to assess the environmental influence on skeletal Mg content of Antarctic echinoderms belonging to Asteroidea, Ophiuroidea, Echinoidea and Holothuroidea classes, along a latitudinal gradient from the South Shetland Islands to Rothera (Adelaide Island). We found that all skeletal structures, except for echinoid spines, exhibited high Mg content, with asteroids showing the highest levels. Our results suggest that asteroids and holothuroids exert a higher biological capacity to regulate Mg incorporation into their skeletons. In contrast, the variability observed in the skeletal Mg content of ophiuroids and echinoids appears to be more influenced by local environmental conditions. Species-specific differences in how environmental factors affect the skeletal Mg content can be thus expected as a response to global climate change.

Prokaryotic diversity in the sponges Mycale (Oxymycale) acerata (Kirkpatrick, 1907) and Dendrilla antarctica (Topsent, 1905) from two distant Antarctic marine areas: South Cove at Rothera Point (Adelaide Island, Western Antarctic Peninsula) and Thetys Bay (Terra Nova Bay, Ross Sea)

The Antarctic environment offers a unique opportunity to study the interactions between Porifera and their microbial symbionts. Reports on the association between prokaryotes and Antarctic sponges are increasing. However, a comparison of the bacterial communities associated to the same sponge species but inhabiting different Antarctic areas has seldom been addressed. This study explored the prokaryotes associated with the sponge species Mycale (Oxymycale) acerata (Kirkpatrick, 1907) and Dendrilla antarctica (Topsent, 1905) collected from South Cove at Rothera Point (Antarctic Peninsula) and Thetys Bay (Ross Sea). In D. antarctica, some groups were equally represented at both sites (e.g., Amylibacter, Cutibacterium, Yoonia-Loktanella), whereas members in the genera Polaribacter and Kistimonas were more abundant in Rothera. Similarly, M. acerata individuals collected from Rothera showed a higher relative abundance of some bacterial genera, such as Polaribacter, Sulfitobacter, and Ulvibacter. The results allowed us to identify some taxa common to sponges belonging to the same species and highlighted the possible influence of site-specific environmental conditions in shaping symbionts.

Revisiting the Past: A comparative study for semantic segmentation of historical images of Adelaide Island using U-nets

The TriMetrogon Aerial (TMA) archive is an archive of historical images of Antarctica taken by the US Navy between 1940 and 2000 with analogue cameras. The analysis of such historic data can give a view of Antarctica's glaciers predating modern satellite imagery and provide unique insights into the long-term impact of changing climate conditions with essential validation data for climate modelling. However, the lack of semantic information for these images presents a challenge for large-scale computer-driven analysis.Such information can be added to the data using semantic segmentation, but traditional algorithms fail on these scanned historical grayscale images, due to varying image quality, lack of colour information and artefacts in the images. To address this, we present a deep-learning-based U-net workflow. Our approach includes creating training data by pre-processing and labelling the raw images. Furthermore, different versions of the U-net are trained to optimize its hyperparameters and augmentation methods. With the optimal hyper-parameters and augmentation methods, a final model has been trained for a use-case to segment 118 images covering Adelaide Island.We tested our approach by segmenting challenging historical images using a U-net model with just 80 training images, achieving an accuracy of 73% for 20 validation images. While no test data is available for our use case, a visual examination of the segmented images shows that our method performs effectively.The comparison of the hyper-parameters and augmentation methods provides directions for training other U-net-based models so that the presented workflow can be used to segment other archives with historical imagery. Additionally, the labelled training data and the segmented images of the test are publicly available at https://github.com/fdahle/antarctic_segmentation.

Carbon and nutrient cycling in Antarctic landfast sea ice from winter to summer

AbstractSeasonal cycling in carbon, alkalinity, and nutrients in landfast sea ice in Hangar Cove, Adelaide Island, West Antarctic Peninsula, were investigated during winter, spring, and summer 2014–2015. Temporal dynamics were driven by changes in the sea‐ice physicochemical conditions, ice‐algal community composition, and organic matter production. Winter sea ice was enriched with dissolved inorganic carbon (DIC) and inorganic nutrients from organic matter remineralization. Variations in alkalinity (Alk) and DIC indicated that abiotic calcium carbonate (ikaite) precipitation had taken place. Relative to other nutrients, low phosphate (PO4) concentrations potentially resulted from co‐precipitation with ikaite. Seawater flooding and meltwater induced variability in the physical and biogeochemical properties in the upper ice in spring where nutrient resupply supported haptophyte productivity and increased particulate organic carbon (POC) in the interstitial layer. Rapid nitrate (NO3) and DIC (< 165 μmol kg−1) uptake occurred alongside substantial build‐up of algal biomass (746 μg chlorophyll a L−1) and POC (6191 μmol L−1) during summer. Silicic acid drawdown followed NO3 depletion by approximately 1 month with a shift to diatom‐dominated communities. Accumulation of PO4 in the lower ice layers in summer likely resulted from PO4 released during ikaite dissolution in the presence of biofilms. Increased Alk : DIC ratios in the lower ice and under‐ice water suggested that ikaite dissolution buffered against meltwater dilution and enhanced the potential for atmospheric CO2 uptake. This study revealed strong seasonality in carbon and nutrient cycling in landfast sea ice and showed the importance of sea ice in biogeochemical cycling in seasonally ice‐covered waters around Antarctica.

Distribution characteristics, sources, and risk assessment of organochlorine pesticides in the Fildes Peninsula and Adelaide Island

This work analyzed the distribution characteristics, sources, and corresponding environmental risks of 10 organochlorine pollutants (OCPs) in soil samples from 13 stations on the Fildes Peninsula and Adelaide Island in Antarctica in 2020. Results showed that the total amount of OCP residues in the study area ranged from N.D. to 2.66 ng·g−1 with an average concentration of 0.90 ng·g−1. Six organochlorine pesticides were detected, and the residue level of DDTs was slightly lower than that of HCHs. The residues of HCHs were mainly γ-HCH and those of DDTs were mainly O, P′-DDT. Source analysis revealed that the residues mainly originated from atmospheric transport and human activities. Environmental risk analysis showed that in the study area, the residues of HCHs and DDTs were present at low levels, and their ecological risk was low.

An innovative ‘flat-pack’ wharf: overcoming construction challenges in Antarctica

A new longer and deeper wharf was completed in 2020 for the UK’s largest Antarctic research station. The £40 million structure replaced the life-expired wharf at Rothera Point on Adelaide Island and enables the station to accommodate British Antarctic Survey’s new polar research and supply vessel RRS Sir David Attenborough. Design and construction at this remote and environmentally extreme location presented many challenges, leading to the development of an innovative ‘flat-pack’ modular solution. This paper describes how the new 74 m long wharf was designed, manufactured, delivered and built in just two short austral summers.

Ocean currents as a potential dispersal pathway for Antarctica\u2019s most persistent non-native terrestrial insect

The non-native midge Eretmoptera murphyi is Antarctica’s most persistent non-native insect and is known to impact the terrestrial ecosystems. It inhabits by considerably increasing litter turnover and availability of soil nutrients. The midge was introduced to Signy Island, South Orkney Islands, from its native South Georgia, and routes of dispersal to date have been aided by human activities, with little known about non-human-assisted methods of dispersal. This study is the first to determine the potential for dispersal of a terrestrial invertebrate species in Antarctica by combining physiological sea water tolerance data with quantitative assessments of ocean current journey times. Fourth instar larvae tolerated sea water submergence for up to 21 days, but submerged egg sacs had significantly reduced hatching success. Using near-surface drifter data, we conclude that ocean current dispersal from Signy Island would not present a risk of species transfer beyond the South Orkney Islands on the tested timescales. However, if E. murphyi were to be introduced to the South Shetlands Islands or Adelaide Island, which are located offshore of the Antarctic Peninsula, there would be a risk of successful oceanic dispersal to neighbouring islands and the Antarctic Peninsula mainland. This study emphasises the need for effective biosecurity measures and demonstrates the role that currently undocumented pathways may have in dispersing non-native species.

Experimental warming of bryophytes increases the population density of the nematode Plectus belgicae in maritime Antarctica

AbstractDespite nematodes routinely being the most frequent soil- and bryophyte-associated animals in maritime Antarctica, there is a lack of clarity about the influence of warming on their populations in the region. Here, we report the results of a field experiment on Adelaide Island that tested the effects of warming with open-top chambers (OTCs) for 37 months on nematodes associated with the bryophytes Cephaloziella varians and Sanionia uncinata. Over the experiment's duration, OTCs increased the population density of the nematode Plectus belgicae in mats of both bryophytes by six-fold, with four- to seven-fold increases in the abundances of male, female and juvenile P. belgicae in warmed mats, and with the largest effects on the abundances of juveniles. Despite C. varians, which is black in colour, warming to a greater extent than S. uncinata during summer, no interactive effects of OTCs and bryophyte species were recorded on the population density of P. belgicae. Our results corroborate a previous study showing that warming increases Plectus population densities in maritime Antarctic soils, with implications for the region's terrestrial food webs.

Juvenile morphology of the large Antarctic canopy-forming brown alga, Desmarestia menziesii J. Agardh

For many types of seaweeds in Polar Regions, open questions remain about how their life cycle contributes to their overall adaptation to the extreme abiotic environment. This applies in particular to the major canopy-forming brown algae in much of the Antarctic Peninsula of the genus Desmarestia, which was investigated here. Diving surveys around Rothera Research Station (Adelaide Island, Antarctica) during December 2017–February 2018 revealed the widespread presence of a hitherto-unknown life form of Desmarestia sp. of a tender, feather-like morphology. Further studies explored whether this could be (1) a new, hitherto undescribed Desmarestia species (2) a new record for the region of a known Desmarestia species previously recorded elsewhere or (3) a so-far unknown life form of a species recorded for the region. Collections enabled the extraction of PCR-friendly DNA and sequencing of ITS1, which unambiguously showed that the samples belonged to Desmarestia menziesii, the only Desmarestia species presently recorded for the Adelaide Island/Marguerite Bay region. The presence of the juvenile morphology was subsequently confirmed throughout much of the natural range of D. menziesii during cruise-based diving surveys along the Western Antarctic Peninsula in 2019 and from collections at Anvers Island in 1989. Our collections thus constitute its juvenile morphology, which is not previously documented in the literature. The wider significance for the Polar seaweeds is discussed in the context of Taxonomy and Ecology.

Snow algae communities in Antarctica: metabolic and taxonomic composition.

Summary Snow algae are found in snowfields across cold regions of the planet, forming highly visible red and green patches below and on the snow surface. In Antarctica, they contribute significantly to terrestrial net primary productivity due to the paucity of land plants, but our knowledge of these communities is limited. Here we provide the first description of the metabolic and species diversity of green and red snow algae communities from four locations in Ryder Bay (Adelaide Island, 68°S), Antarctic Peninsula.During the 2015 austral summer season, we collected samples to measure the metabolic composition of snow algae communities and determined the species composition of these communities using metabarcoding.Green communities were protein‐rich, had a high chlorophyll content and contained many metabolites associated with nitrogen and amino acid metabolism. Red communities had a higher carotenoid content and contained more metabolites associated with carbohydrate and fatty acid metabolism. Chloromonas, Chlamydomonas and Chlorella were found in green blooms but only Chloromonas was detected in red blooms. Both communities also contained bacteria, protists and fungi.These data show the complexity and variation within snow algae communities in Antarctica and provide initial insights into the contribution they make to ecosystem functioning.

Persistent Organic Pollutants in two species of migratory birds from Rothera Point, Adelaide Island, Antarctica

Carcasses of South Polar Skuas (Catharacta maccormicki) and Kelp gulls (Larus dominicanus) were opportunistically collected around of Rothera Research station (67°35′8″S and 68°7′59″W) during the 2016/2017 austral summer. Samples of their tissues (muscle, liver and subcutaneous fat) were analysed for Persistent Organic Pollutants (POPs). Organochlorine pesticides (OCPs) showed the highest concentrations, notably for pp′-DDE and HCB. The Polychlorinated biphenyls (PCBs)-profiles demonstrated a clear dominance of hexa- and hepta-CBs, while concentrations of polybrominated diphenyl ethers (PBDEs) remained low. The concentrations of some POPs (e.g. HCB) were lower than in past studies on similar species, however others were within the previous range (PCBs) or even higher than previous reported values (DDE). Although no major interspecific differences in the absolute concentrations of POPs were detected, their profiles varied, being likely related to feeding and migration patterns of each species. The current study provides important baseline data for future monitoring of POPs in Antarctica.

Inter-decadal variability of phytoplankton biomass along the coastal West Antarctic Peninsula.

The West Antarctic Peninsula (WAP) is a climatically sensitive region where periods of strong warming have caused significant changes in the marine ecosystem and food-web processes. Tight coupling between phytoplankton and higher trophic levels implies that the coastal WAP is a bottom-up controlled system, where changes in phytoplankton dynamics may largely impact other food-web components. Here, we analysed the inter-decadal time series of year-round chlorophyll-a (Chl) collected from three stations along the coastal WAP: Carlini Station at Potter Cove (PC) on King George Island, Palmer Station on Anvers Island and Rothera Station on Adelaide Island. There were trends towards increased phytoplankton biomass at Carlini Station (PC) and Palmer Station, while phytoplankton biomass declined significantly at Rothera Station over the studied period. The impacts of two relevant climate modes to the WAP, the El Niño-Southern Oscillation and the Southern Annular Mode, on winter and spring phytoplankton biomass appear to be different among the three sampling stations, suggesting an important role of local-scale forcing than large-scale forcing on phytoplankton dynamics at each station. The inter-annual variability of seasonal bloom progression derived from considering all three stations together captured ecologically meaningful, seasonally co-occurring bloom patterns which were primarily constrained by water-column stability strength. Our findings highlight a coupled link between phytoplankton and physical and climate dynamics along the coastal WAP, which may improve our understanding of overall WAP food-web responses to climate change and variability.This article is part of the theme issue 'The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change'.

Antarctic Specially Protected Areas (ASPA): a case study at Rothera Point providing tools and perspectives for the implementation of the ASPA network

Antarctica is considered among the world’s last great wildernesses, but its current network of Antarctic Specially Protected Areas (ASPAs) is inadequate, unrepresentative and at risk, needing urgent expansion due to the vulnerability of Antarctica to increasing threats from climate change and human activities. Among the existing ASPAs, no. 129 Rothera Point is unique because its designation related specifically to the monitoring of the impacts associated with the neighbouring Rothera Research Station, operated by the United Kingdom. The station is located on Adelaide Island (Antarctic Peninsula) in Antarctic Conservation Biogeographic Region 3 (ACBR3). We aim here to: (1) provide an improved description of the botanical values of the ASPA, and detailed vegetation mapping as for the establishment of future monitoring, (2) assess the representativeness of the ASPA vegetation within a wider geographical context encompassing Marguerite Bay and Adelaide Island and, (3) use this case study as a contribution to the ongoing discussion within the Antarctic Treaty System on the future development of the continent-wide ASPA network. Even though this specific ASPA was not initially designated for its biodiversity value, a higher species richness was recorded within the ASPA than outside the protected area on Rothera Point. Within the local geographic context, based on the available data, Rothera Point is characterized by high biodiversity and, above all, Leonie Island exhibits the greatest floristic richness within Marguerite Bay and Adelaide Island, being a biodiversity hot-spot of exceptional value. This case study emphasizes the continued existence of significant knowledge gaps relating to Antarctic terrestrial biodiversity, and the urgent need for large-scale assessment of the biological values of Antarctica, as one of the main challenges for the implementation of a robust and representative system of protected areas in terrestrial Antarctica, to protect this global natural heritage in the face of current and predicted future environmental change.

Seasonality of oxygen consumption in five common Antarctic benthic marine invertebrates

The waters of the Southern Ocean exhibit extreme seasonality in primary production, with marine life living below 0 °C for much of the year. The metabolic cold adaptation (MCA) hypothesis suggests that polar species need elevated basal metabolic rates to enable activity in such cold which should result in higher metabolic rates, or at least rates similar to temperate species. This study aimed to test whether any of the five common marine invertebrates around Adelaide Island (Western Antarctic Peninsula) displayed MCA: the suspension-feeding holothurian Heterocucumis steineni, the grazing limpet Nacella concinna, and the omnivorous brittle star, cushion star and sea-urchin Ophionotus victoriae, Odontaster validus and Sterechinus neumayeri, respectively. We also tested a second hypothesis that secondary consumers will exhibit less seasonal variation of metabolic rate than primary consumers. Routine oxygen consumption was measured in both the austral summer and winter using closed circuit respirometry techniques. Metabolic rates for all the species studied were low compared with temperate species, in a fashion consistent with expected temperature effects on biological systems and, therefore, the data do not support MCA. All the species studied showed significant seasonal differences for a standard mass animal except N. concinna. In two species N. concinna and H. steineni, size affected the seasonality of metabolism. There was no difference in seasonality of metabolism between primary and secondary consumers. Thus, for secondary consumers seasonal factors, most likely food availability and quality, vary enough to impact metabolic rates, and produce seasonal metabolic signals at all trophic levels. Other factors such as reproductive status that are linked to seasonal signals may also have contributed to the metabolic variation across trophic levels.

Neogene to Quaternary stratigraphic evolution of the Antarctic Peninsula, Pacific Margin offshore of Adelaide Island: Transitions from a non-glacial, through glacially-influenced to a fully glacial state

A detailed morphologic and seismic stratigraphic analysis of the continental margin offshore of Adelaide Island on the Pacific Margin of the Antarctic Peninsula (PMAP) is described based on the study of a regular network of reflection multichannel seismic profiles and swath bathymetry. We present an integrated study of the margin spanning the shelf to the continental rise, establish novel chronologic constraints and offer new interpretations on tectonic evolution and environmental changes affecting the PMAP. The stratigraphic stacking patterns record major shifts in the depositional style of the margin that outline three intervals in its evolution. The first non-glacial interval (Early Cretaceous to middle Miocene) encompasses a transition from an active to a passive margin (early Miocene). The second glacially-influenced interval (middle to late Miocene) is marked by pronounced aggradational sedimentary stacking and subsidence. Ice sheets advanced over the middle shelf of the margin at the end of this second interval, while the outer shelf experienced rare progradational events. The third, fully glaciated interval shows clear evidence of glacially dominated conditions on the margin. This interval divides into three minor stages. During the first stage (late Miocene to the beginning of the Pliocene), frequent grounded ice advances to the shelf break began, depositing an initial progradational unit. A major truncation surface marked the end of this stage, which coincided with extensive mass transport deposits at the base of the slope. During the second progradational glacial margin stage (early Pliocene to middle Pleistocene), stacking patterns record clearly prograding glacial sequences. The beginning of the third aggradational glacial margin stage (middle Pleistocene to present) corresponded to an important shift in global climate during the Mid-Pleistocene Transition. Morphosedimentary characteristics observed along the margin today began to develop during the latest Miocene but did not become fully established until sometime during the interval between the end of the Pliocene and middle Pleistocene. Between these two time intervals, the northeastward lateral migration of the Marguerite Trough also played a critical role in margin evolution, as it controlled ice sheet drainage pathways across the shelf, which in turn influenced development of slope and rise morphologies. Areas offshore from Adelaide Island differ from other areas of the PMAP due to changes in sedimentary processes that resulted from migration of the trough. This study confirms that the PMAP represents an exceptional locality for decoding, reconstructing and linking past tectonic and climatic changes. The study area specifically records not only the most relevant changes in depositional style, but also the relative importance of persistent along- and down-slope sedimentary processes. Our study approach can be extended to other areas and integrated with additional techniques to understand the evolution and the global linkages of the entire Antarctic continental margin and the ice sheets.

The fate of the non-native Collembolon, Hypogastrura viatica, at the southern extent of its introduced range in Antarctica

Invasive species present a risk to Antarctic ecosystems by altering community structure and function. Reports of non-native invertebrates are increasing at Antarctic sites subject to tourism industry and national operator activity. Furthermore, dispersal of existing non-native species to other Antarctic sites may greatly expand their distributions and increase the spatial scale of potential impacts. Consequently, non-native species occurring near logistical hubs present an enhanced risk. The non-native Collembolon, Hypogastrura viatica, was introduced to Leonie Island, Ryder Bay, near the logistical hub of Rothera Research Station, Rothera Point, Adelaide Island, at some point before 1993, but no attempt had been made to assess the extent of its distribution in the local area. In this study, we surveyed the regularly frequented islands of Ryder Bay and Rothera Point to attempt to assess the continued presence and distribution of this species. Hypogastrura viatica was not identified amongst the 36,796 Collembola specimens extracted from 138 samples taken from the islands and Rothera Point. With no evidence of the continued presence of this non-native Collembolon in the local area, either H. viatica has become extinct or has such a restricted spatial distribution that our monitoring programme failed to detect it. In light of these results, existing local biosecurity measures will be maintained as a precautionary measure to reduce the risk of further anthropogenic dispersal of this potentially invasive Collembolon as well as of any other species imported unintentionally in future.

Planococcus versutus sp. nov., isolated from soil.

A taxonomic study was performed on a novel Gram-stain-positive, coccus-shaped, orange-pigmented motile bacterium, designated as strain L10.15T. The organism was isolated from a soil sample collected in Lagoon Island (close to Adelaide Island, western Antarctic Peninsula) using a quorum-quenching enrichment medium. Growth occurred at 4-30 °C, pH 6-11 and at moderately high salinity (0-15 %, w/v, NaCl), with optimal growth at 26 °C, at pH 7-8 and with 6 % (w/v) NaCl. 16S rRNA gene sequence analysis showed that strain L10.15T belonged to the genus Planococcus and was closely related to Planococcus halocryophilus Or1T (99.3 % similarity), Planococcus donghaensis JH1T (99.0 %), Planococcus antarcticus DSM 14505T (98.3 %), Planococcus plakortidis AS/ASP6 (II)T (97.6 %), Planococcus maritimus TF-9T (97.5 %), Planococcus salinarum ISL-6T (97.5 %) and Planococcus kocurii NCIMB 629T (97.5 %). However, the average nucleotide identity-MUMmer analysis showed low genomic relatedness values of 71.1-81.7 % to the type strains of these closely related species of the genus Planococcus. The principal fatty acids were anteiso-C15 : 0, C16 : 1ω7c and anteiso-C17 : 0, and the major menaquinones of strain L10.15T were MK-5 (48 %), MK-6 (6 %) and MK-7 (44 %). Polar lipid analysis revealed the presence of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and aminophospholipid. The DNA G+C content was 39.4 mol%. The phenotypic and genotypic data indicate that strain L10.15T represents a novel species of the genus Planococcus, for which the name Planococcus versutus sp. nov. is proposed. The type strain is L10.15T (=DSM 101994T=KACC 18918T).

Painful shoulder? Remote clinical management of a Field Guide with shoulder pain and loss of shoulder function in Antarctica

© 2017, Australasian Medical Journal Pty Ltd. All rights reserved. We report the case of a female Field Guide based at the British Antarctic Survey’s Rothera Science Research Station on Adelaide Island, Antarctica who independently contacted a physiotherapist specialising in climbing related injuries (GJ) located in the UK. For a second opinion. The Field Guide was experiencing significant work difficulties due to shoulder pain and subsequent loss of function particularly in overhead activities. The case raises important issues about the medical management of Field Guides operating in extreme environments and remote locations.

Characteristics of the modelled meteoric freshwater budget of the western Antarctic Peninsula

Rapid climatic changes in the western Antarctic Peninsula (WAP) have led to considerable changes in the meteoric freshwater input into the surrounding ocean, with implications for ocean circulation, the marine ecosystem and sea-level rise. In this study, we use the high-resolution Regional Atmospheric Climate Model RACMO2.3, coupled to a firn model, to assess the various contributions to the meteoric freshwater budget of the WAP for 1979–2014: precipitation (snowfall and rainfall), meltwater runoff to the ocean, and glacial discharge. Snowfall is the largest component in the atmospheric contribution to the freshwater budget, and exhibits large spatial and temporal variability. The highest snowfall rates are orographically forced and occur over the coastal regions of the WAP (>2000mm water equivalent (w.e.) y−1) and extend well onto the ocean up to the continental shelf break; a minimum (∼500mmw.e.y−1) is reached over the open ocean. Rainfall is an order of magnitude smaller, and strongly depends on latitude and season, being large in summer, when sea ice extent is at its minimum. For Antarctic standards, WAP surface meltwater production is relatively large (>50mmw.e.y−1), but a large fraction refreezes in the snowpack, limiting runoff. Only at a few more northerly locations is the meltwater predicted to run off into the ocean. In summer, we find a strong relationship of the freshwater fluxes with the Southern Annular Mode (SAM) index. When SAM is positive and occurs simultaneously with a La Niña event there are anomalously strong westerly winds and enhanced snowfall rates over the WAP mountains, Marguerite Bay and the Bellingshausen Sea. When SAM coincides with an El Niño event, winds are more northerly, reducing snowfall and increasing rainfall over the ocean, and enhancing orographic snowfall over the WAP mountains. Assuming balance between snow accumulation (mass gain) and glacial discharge (mass loss), the largest glacial discharge is found for the regions around Adelaide Island (10Gty−1), Anvers Island (8Gty−1) and southern Palmer Land (12Gty−1), while a minimum (<2Gty−1) is found in Marguerite Bay and the northern WAP. Glacial discharge is in the same order of magnitude as the direct freshwater input into the ocean from snowfall, but there are some local differences. The spatial patterns in the meteoric freshwater budget have consequences for local productivity and carbon drawdown in the coastal ocean.

Charles Swithinbank

Charles Swithinbank