Showing papers in "Antarctic Science in 2009"
TL;DR: The Southern Hemisphere climate system varies on timescales from orbital, through millennial to sub-annual, and is closely coupled to other parts of the global climate system as discussed by the authors.
Abstract: The Antarctic climate system varies on timescales from orbital, through millennial to sub-annual, and is closely coupled to other parts of the global climate system. We review these variations from the perspective of the geological and glaciological records and the recent historical period from which we have instrumental data (the last 50 years). We consider their consequences for the biosphere, and show how the latest numerical models project changes into the future, taking into account human actions in the form of the release of greenhouse gases and chlorofluorocarbons into the atmosphere. In doing so, we provide an essential Southern Hemisphere companion to the Arctic Climate Impact Assessment.
559 citations
TL;DR: A review of the scientific literature on the impacts of human activities on the Antarctic environment can be found in this article, where a range of impacts has been identified at a variety of spatial and temporal scales.
Abstract: We review the scientific literature, especially from the past decade, on the impacts of human activities on the Antarctic environment. A range of impacts has been identified at a variety of spatial and temporal scales. Chemical contamination and sewage disposal on the continent have been found to be long-lived. Contemporary sewage management practices at many coastal stations are insufficient to prevent local contamination but no introduction of non-indigenous organisms through this route has yet been demonstrated. Human activities, particularly construction and transport, have led to disturbances of flora and fauna. A small number of non-indigenous plant and animal species has become established, mostly on the northern Antarctic Peninsula and southern archipelagos of the Scotia Arc. There is little indication of recovery of overexploited fish stocks, and ramifications of fishing activity on bycatch species and the ecosystem could also be far-reaching. The Antarctic Treaty System and its instruments, in particular the Convention for the Conservation of Antarctic Marine Living Resources and the Environmental Protocol, provide a framework within which management of human activities take place. In the face of the continuing expansion of human activities in Antarctica, a more effective implementation of a wide range of measures is essential, in order to ensure comprehensive protection of the Antarctic environment, including its intrinsic, wilderness and scientific values which remains a fundamental principle of the Antarctic Treaty System. These measures include effective environmental impact assessments, long-term monitoring, mitigation measures for non-indigenous species, ecosystem-based management of living resources, and increased regulation of National Antarctic Programmes and tourism activities.
411 citations
TL;DR: Experimental studies are needed to evaluate whether there are adequate compensatory mechanisms in these and other calcified Antarctic benthic macroorganisms to cope with anticipated ocean acidification.
Abstract: Antarctic calcified macroorganisms are particularly vulnerable to ocean acidification because many are weakly calcified, the dissolution rates of calcium carbonate are inversely related to temperature, and high latitude seas are predicted to become undersaturated in aragonite by the year 2100. We examined the post-mortem dissolution rates of aragonitic and calcitic shells from four species of Antarctic benthic marine invertebrates (two bivalves, one limpet, one brachiopod) and the thallus of a limpet shell-encrusting coralline alga exposed to acidified pH (7.4) or non-acidified pH (8.2) seawater at a constant temperature of 4°C. Within a period of only 14–35 days, shells of all four species held in pH 7.4 seawater had suffered significant dissolution. Despite calcite being 35% less soluble in seawater than aragonite, there was surprisingly, no consistent pattern of calcitic shells having slower dissolution rates than aragonitic shells. Outer surfaces of shells held in pH 7.4 seawater exhibited deterioration by day 35, and by day 56 there was exposure of aragonitic or calcitic prisms within the shell architecture of three of the macroinvertebrate species. Dissolution of coralline algae was confirmed by differences in weight loss in limpet shells with and without coralline algae. By day 56, thalli of the coralline alga held in pH 7.4 displayed a loss of definition of the conceptacle pores and cracking was evident at the zone of interface with limpet shells. Experimental studies are needed to evaluate whether there are adequate compensatory mechanisms in these and other calcified Antarctic benthic macroorganisms to cope with anticipated ocean acidification. In their absence, these organisms, and the communities they comprise, are likely to be among the first to experience the cascading impacts of ocean acidification.
137 citations
TL;DR: In this paper, the authors used a combination of satellite techniques (interferometric synthetic aperture radar (InSAR), visible-band imagery, and repeat-track laser altimetry) to develop a benchmark map for the Amery============Ice Shelf (AIS) grounding zone (GZ), including its islands and ice rises.
Abstract: We use a combination of satellite techniques (interferometric synthetic aperture radar (InSAR),
visible-band imagery, and repeat-track laser altimetry) to develop a benchmark map for the Amery
Ice Shelf (AIS) grounding zone (GZ), including its islands and ice rises. The break-in-slope, as an indirect
estimate of grounding line location, was mapped for the entire AIS. We have also mapped ,55% of the
landward edge and ,30% of the seaward edge of the ice shelf flexure boundary for the AIS perimeter.
Vertical ice motion from Global Positioning System receivers confirms the location of the satellite-derived
GZ in two regions. Our map redefines the extent of floating ice in the south-western AIS and identifies
several previously unmapped grounded regions, improving our understanding of the stresses supporting the
current dynamical state of the ice shelf. Finally, we identify three along-flow channels in the ice shelf basal
topography, approximately 10 km apart, 1.5 km wide and 300–500m deep, near the southern GZ. These
channels, which form at the suture zones between ice streams, may represent zones of potential weakness in
the ice shelf and may influence sub-ice-shelf ocean circulation.
124 citations
TL;DR: In this paper, the West Antarctic Peninsula region is an important source of Antarctic krill (Euphausia superba) in the Southern Ocean and the abundance and concentration of phytoplankton, krill reproductive and recruitment success and seasonal sea ice extent here were significantly correlated with the atmospheric Southern Oscillation Index and exhibited three- to five-year frequencies characteristic of El Nino - Southern Ocean variability.
Abstract: The West Antarctic Peninsula region is an important source of Antarctic krill (Euphausia superba) in the Southern Ocean. From 1980 - 2004 abundance and concentration of phytoplankton and zooplankton, krill reproductive and recruitment success and seasonal sea ice extent here were significantly correlated with the atmospheric Southern Oscillation Index and exhibited three- to five-year frequencies characteristic of El Nino - Southern Oscillation (ENSO) variability. This linkage was associated with movements of the Southern Antarctic Circumpolar Current Front and Boundary, a changing influence of Antarctic Circumpolar Current and Weddell Sea waters, and eastward versus westward flow and mixing processes that are consistent with forcing by the Antarctic Dipole high-latitude climate mode. Identification of hydrographic processes underlying ecosystem variability presented here were derived primarily from multi- disciplinary data collected during 1990 - 2004, a period with relatively stable year-to-year sea ice conditions. These results differ from the overwhelming importance of seasonal sea ice development previously established using 1980 - 1996 data, a period marked by a major decrease in sea ice from the Antarctic Peninsula region in the late 1980s. These newer results reveal the more subtle consequences of ENSO variability on biological responses. They highlight the necessity of internally consistent long-term multidisciplinary datasets for understanding ecosystem variability and ultimately for establishing well- founded ecosystem management. Furthermore, natural environmental variability associated with interannual- and decadal-scale changes in ENSO forcing must be considered when assessing impacts of climate warming in the Antarctic Peninsula - Weddell Sea region.
106 citations
Abstract: Determining the mass balance of the Greenland and Antarctic ice sheets (GIS and AIS) has long
been a major challenge for polar science. But until recent advances in measurement technology, the
uncertainty in ice sheet mass balance estimates was greater than any net contribution to sea level change.
The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (AR4) was able, for the
first time, to conclude that, taken together, the GIS and AIS have probably been contributing to sea level
rise over the period 1993–2003 at an average rate estimated at 0.4mm yr-1. Since the cut-off date for work
included in AR4, a number of further studies of the mass balance of GIS and AIS have been made using
satellite altimetry, satellite gravity measurements and estimates of mass influx and discharge using a variety
of techniques. Overall, these studies reinforce the conclusion that the ice sheets are contributing to present
sea level rise, and suggest that the rate of loss from GIS has recently increased. The largest unknown in the
projections of sea level rise over the next century is the potential for rapid dynamic collapse of ice sheets.
95 citations
TL;DR: The current list of the austral pycnogonids together with details of their depth range and distribution is presented in this paper, where the benthic insular refuge hypothesis is proposed as an explanation for the southern distribution of the present pycnogenid fauna, with an origin in the Scotia Arc.
Abstract: This study contains the current list of the austral pycnogonids together with details of their depth range and distribution. To date 264 species have been recorded, accounting for 19.6% of the 1344 species recorded worldwide. One hundred and eight species are endemic to Antarctic waters, 62 to the sub- Antarctic, 63 are common in both regions, and 55 are circumpolar. The richest genus is Nymphon, with 67 species and the richest area is the Scotia Sea. Comparing species lists between the years 2000 and 2007 shows that increased expeditions with more sampling has increased the circumpolarity of species and decreased zonal endemicity. The benthic insular refuge hypothesis is proposed as an explanation for the southern distribution of the present pycnogonid fauna, with an origin in the Scotia Arc.
89 citations
TL;DR: In this paper, the authors assess relative weight given to direct, observational evidence of prey taken, as opposed to indirect evidence from scat and biochemical analysis, and conclude that toothfish are important to Weddell seals (Leptonychotes weddellii).
Abstract: Uncertainty exists over the importance of Antarctic toothfish (Dissostichus mawsoni )a s prey of top predators in the Ross Sea. In this paper we assess relative weight given to direct, observational evidence of prey taken, as opposed to indirect evidence from scat and biochemical analysis, and conclude that toothfish are important to Weddell seals (Leptonychotes weddellii). The seals eat only the flesh of large toothfish and therefore they are not detected in scat or stomach samples; biochemical samples have been taken from seal sub-populations where toothfish seldom occur. Using direct observations of non-breeding seals away from breeding haulouts in McMurdo Sound, 0.8-1.3 toothfish were taken per day. Based on these and other data, the non-breeding portion of the McMurdo Sound seal population, during spring and summer, consume about 52 tonnes of toothfish. Too many unknowns exist to estimate the non-trivial amount consumed by breeders. We discuss why reduced toothfish availability to Weddell seals, for energetic reasons, cannot be compensated by as witch to silverf ish (Pleuragramma antarcticum) or squid. The Ross Sea toothfish fishery should be reduced including greater spatial management, with monitoring of Weddell seal populations by CCAMLR. Otherwise, probable cascades will lead to dramatic changes in the populations of charismatic megafauna.
74 citations
TL;DR: In this article, the authors used a combination of theoretical analysis and field observations to show that the recurrence of snow can explain the depth of dry permafrost and the location of ice-cemented ground in Antarctica.
Abstract: Dry permafrost on Earth is unique to the Antarctic and is found in the upper elevations of the McMurdo Dry Valleys. Despite its widespread presence in the Dry Valleys, the factors that control the distribution of dry permafrost and the ice-cemented ground below it are poorly understood. Here I show, by a combination of theoretical analysis and field observations, that the recurrence of snow can explain the depth of dry permafrost and the location of ice-cemented ground in Antarctica. For data from Linnaeus Terrace at 1600–1650 m elevation in Upper Wright Valley a recurrence intervals of about two years explains the presence of ground ice at 25 cm depth, under 12.5 cm of dry permafrost. Snow recurrence periods longer than 10 years would create only dry permafrost at this site. The snow gradient in University Valley resulting from the windblown snow from the polar plateau creates a corresponding gradient in the depth to ice-cemented ground. On the floor of Beacon Valley, the presence of dry permafrost without underlying ice-cemented ground indicates snow recurrence intervals of more than 10 years and implies that the ancient massive ice in this valley is not stable. Snow recurrence may also set the depth to ground ice on Mars.
71 citations
TL;DR: In contrast to the large warming and loss of sea ice in the Arctic in recent decades, Antarctic temperatures and sea ice show little change except for the Antarctic Peninsula as mentioned in this paper, where the signature of greenhouse-driven change is projected to emerge from the natural variability during the present century, the emergence of a statistically significant greenhouse signal may be slower than in other regions.
Abstract: Ongoing climate variations in the Arctic and Antarctic pose an apparent paradox. In contrast to the large warming and loss of sea ice in the Arctic in recent decades, Antarctic temperatures and sea ice show little change except for the Antarctic Peninsula. However, model simulations indicate that the Arctic changes have been shaped largely by low-frequency variations of the atmospheric circulation, superimposed on a greenhouse warming that is apparent in model simulations when ensemble averages smooth out the circulation-driven variability of the late 20th century. By contrast, the Antarctic changes of recent decades appear to be shaped by ozone depletion and an associated strengthening of the southern annular mode of the atmospheric circulation. While the signature of greenhouse-driven change is projected to emerge from the natural variability during the present century, the emergence of a statistically significant greenhouse signal may be slower than in other regions. Models suggest that feedbacks from retreating sea ice will make autumn and winter the seasons of the earliest emergence of the greenhouse signal in both Polar Regions. Priorities for enhanced robustness of the Antarctic climate simulations are the inclusion of ozone chemistry and the realistic simulation of water vapour over the Antarctic Ice Sheet.
59 citations
TL;DR: In order to reconstruct past changes in penguin populations, the authors performed geochemical analyses on a penguin ornithogenic sediment core DG4 retrieved from a lake catchment on Gardner Island, Vestfold Hills.
Abstract: In order to reconstruct past changes in penguin populations we performed geochemical analyses on a penguin ornithogenic sediment core DG4 retrieved from a lake catchment on Gardner Island, Vestfold Hills. P, Se, F, S, As, Sr and Cu in DG4 were identified as the bio-element assemblage by R-clustering analyses on the elemental concentrations and comparisons with those in bedrock and fresh penguin guano. Factor analysis on the levels of these bio-elements in the core permitted a reconstruction of variations in historical penguin populations at Gardner Island spanning the past 8500 years. The penguin population showed significant fluctuations, reaching its highest density between 4700–2400 calibrated years before present. This coincides with evidence for a late Holocene warm period in the Vestfold Hills, similar to that associated with the late Holocene penguin optimum recorded in the Ross Sea and Antarctic Peninsula regions.
TL;DR: In this article, the analysis of seawater samples and gas chromatography with flame ionization and/or mass spectrometric detection was used to analyse individual n-alkanes and PAHs in sediment samples.
Abstract: Admiralty Bay on the King George Island hosts the Brazilian, Polish and Peruvian research stations as well as the American and Ecuadorian field stations. Human activities in this region require the use of fossil fuels as an energy source, thereby placing the region at risk of hydrocarbon contamination. Hydrocarbon monitoring was conducted on water and sediment samples from the bay over 15 years. Fluorescence spectroscopy was used for the analysis of total polycyclic aromatic hydrocarbons (PAHs) in seawater samples and gas chromatography with flame ionization and/or mass spectrometric detection was used to analyse individual n-alkanes and PAHs in sediment samples. The results revealed that most sites contaminated by these compounds are around the Brazilian and Polish research stations due to the intense human activities, mainly during the summer. Moreover, the sediments revealed the presence of hydrocarbons from different sources, suggesting a mixture of the direct input of oil or derivatives and derived from hydrocarbon combustion. A decrease in PAH concentrations occurred following improvement of the sewage treatment facilities at the Brazilian research station, indicating that the contribution from human waste may be significant.
TL;DR: In this article, the authors quantify the propagule pressure associated with the construction of a research station in Antarctica and predict that over 5000 seeds will be entrained during the period of building the station.
Abstract: Although the impacts of biological invasions are widely appreciated, a bias exists in research effort to post dispersal processes because of the difficulties of measuring propagule pressure. Here we quantify the propagule pressure associated with the construction of a research station in Antarctica. Based on quantitative assessment of different classes of cargo, we predict that over 5000 seeds will be entrained during the period of building the station. Seeds from 34 taxa were identified, including known invasive species.
TL;DR: Nearshore marine benthic algal communities along the western Antarctic Peninsula harbour extremely high densities of amphipods that probably play important roles in nutrient and energy flow and Qualitative gut content analyses indicated that 12 of the 38 amphipod species were found with sponge spicules in their guts, however, only one of the amphipodes, Echiniphimedia hodgsoni Walker, had considerable amounts of spiculi in the gut.
Abstract: Nearshore marine benthic algal communities along the western Antarctic Peninsula harbour extremely high densities of amphipods that probably play important roles in nutrient and energy flow. This study extends our evaluation of the importance of amphipods in the nearshore Antarctic Peninsular benthic communities and focuses on sponge associations. We found a mean density of 542 amphipods per litre (L) sponge for twelve species of ecologically dominant sponges. The highest mean density (1295 amphipods per L sponge) occurred with Dendrilla membranosa Pallas. The amphipod community associated with the 12 sponges was diverse (38 species), with mean species richness values ranging from two to eight species. Mean Shannon diversity indices (H') ranged from 0.52 to 1.49. Amphipods did not appear to have obligate host relationships. Qualitative gut content analyses indicated that 12 of the 38 amphipod species were found with sponge spicules in their guts. However, only one of the amphipods, Echiniphimedia hodgsoni Walker, had considerable amounts of spicules in the gut. Organic lipophilic and hydrophilic extracts of the twelve sponges were presented in alginate food disks to a sympatric omnivorous amphipod in feeding bioassays and extracts of only two sponges deterred feeding.
TL;DR: In this article, levels of 25 polycyclic aromatic hydrocarbons (PAHs) were measured in suspended particulate matter (SPM), surface sediment and marine organisms (fish Notothenia coriiceps, bivalve Laternula elliptica and gastropod Nacella concinna) from Potter Cove.
Abstract: In order to establish the environmental status of areas close to Antarctic stations it is necessary to document levels of contaminants present in these sites. Several petrogenic and pyrogenic sources have been reported for polycyclic aromatic hydrocarbons (PAHs) in Antarctica. In this work, levels of 25 PAHs were measured in suspended particulate matter (SPM), surface sediment and marine organisms (fish Notothenia coriiceps, bivalve Laternula elliptica and gastropod Nacella concinna) from Potter Cove. Total PAH levels from SPM were low and similar in all sites studied (30–82 ng g-1 dw), phenanthrene being the dominant compound (68–84%). The exception was an area close to the wharf where significantly higher values of light PAHs such as naphthalene, acenaphthylene, 2,3,5-trimethylnaphthalene and fluorene were detected, indicating the influence of recent fuel spills. PAH concentrations in surface sediments were generally low (37–252 ng g-1 dw) except for two sites (1762 and 1908 ng g-1 dw) which suggested an accumulation process associated with the water circulation pattern. Liver tissue of N coriiceps presented significantly higher PAH levels (257 ng g-1 dw) compared with gonads. The pattern of individual compounds from substrates and organisms suggests a petrogenic and low-temperature combustion origin.
TL;DR: In this article, the authors investigated the effectiveness of current advice relating to travel on foot over Antarctic vegetation-free soils and found that a minimum human presence is sufficient to alter both physical and biological characteristics of Byers Peninsula soils, although at the lowest levels of human activity this difference was not significant in comparison with adjacent undisturbed control areas.
Abstract: Research in extremely delicate environments must be sensitive to the need to minimize impacts caused simply through the presence of research personnel. This study investigates the effectiveness of current advice relating to travel on foot over Antarctic vegetation-free soils. These are based on the concentration of impacts through the creation of properly signed and identified paths. In order to address these impacts, we quantified three factors - resistance to compression, bulk density and free-living terrestrial arthropod abundance - in areas of human activity over five summer field seasons at the Byers Peninsula (Livingston Island, South Shetland Islands). Studies included instances of both experimentally controlled use and natural non-controlled situations. The data demonstrate that a minimum human presence is sufficient to alter both physical and biological characteristics of Byers Peninsula soils, although at the lowest levels of human activity this difference was not significant in comparison with adjacent undisturbed control areas. On the other hand, a limited resilience of physical properties was observed in Antarctic soils, thus it is crucial not to exceed the soil's natural recovery capability.
TL;DR: In this article, the authors investigated nutrient composition and the potential for greenhouse gas production in Antarctic penguin guano, ornithogenic soils and seal colony soils through a laboratory incubation experiment and found that marine animal excreta are an important factor determining storage and composition of nutrients in coastal Antarctica, and that they may considerably affect current and future net fluxes of greenhouse gases.
Abstract: We investigated nutrient composition and the potential for greenhouse gas production in Antarctic penguin guano, ornithogenic soils and seal colony soils through a laboratory incubation experiment. Total organic carbon contents ranged from 0.2–14.7% and total nitrogen contents ranged from 0.05–3.60% across all the samples. Penguin guano and the soils had the δ13Corg values of -28.4‰ to -22.8‰ and highly enriched δ15N values (8.28–35.51‰), indicating a rapid N cycling in local ecosystems. The mean CO2 and CH4 emission rates from penguin guano were significantly higher than those from the soils under aerobic or anaerobic conditions. The CO2-C/TOC rate indicated that the bioavailability of TOC was markedly higher in penguin guano than in the soils. These soils showed higher N2O emission rates under anaerobic conditions, indicating that denitrification may be the major process in N2O emission. The CO2 and CH4 emissions have a significant correlation with TOC in both penguin guano and the soils. Our results show that marine animal excreta are an important factor determining storage and composition of nutrients in coastal Antarctica, and that they may considerably affect current and future net fluxes of greenhouse gases in this region.
TL;DR: In this article, adult male southern elephant seals instrumented in 2000 on King George Island (n = 13), travelled both to the north (n 2) and to the east (n 6) of the Antarctic Peninsula.
Abstract: Adult male southern elephant seals instrumented in 2000 on King George Island (n = 13), travelled both to the north (n = 2) and to the east (n = 6) of the Antarctic Peninsula. Five males remained within 500 km of the island focusing movements in the Bransfield Strait and around the Antarctic Peninsula. Sea surface temperatures encountered by these animals showed little variation. While animal trajectories appeared unaffected by sea ice cover, areas of shallow depths were frequented. Three males moved as far as 75°S to the east of the Peninsula with maximum distances of more than 1500 km from King George Island. They travelled into the Weddell Sea along the western continental shelf break until they reached the region of the Filchner Trough outflow. Here the sea floor consists of canyons and ridges that support intensive mixing between the warm saline waters of the Weddell Gyre, the very cold outflow waters and ice shelf water at the Antarctic Slope Front. The need for re-instrumentation of adult males from King George Island is highlighted to investigate whether males continue to travel to similar areas and to obtain higher resolution data.
Abstract: In situ cosmogenic 10Be exposure dating, radiocarbon determinations, salt and sediment
geochemistry, and rock weathering observations indicate that parts of Larsemann Hills, East Antarctica
have been subaerially exposed throughout much of the last glacial cycle, with the last glaciation occurring
prior to 100 ka BP. Salt-enhanced subaerial weathering, coupled with a paucity of glacial erratics, made
exposure age dating challenging. Rapid subaerial surface lowering in some places means that some
exposure ages may underestimate the true age of deglaciation. Despite this uncertainty, the data are
consistent with the absence of overriding by a thick ice sheet during the Last Glacial Maximum ,20–18 ka BP.
TL;DR: In this article, surface exposure dating using in situ produced cosmogenic nuclides (10 Be and 21 Ne) was used to date the East Antarctic Ice Sheet variations, showing that a major ice advance reaching elevations of about 500 m above present ice levels occurred between 1.125 and 1.375 million years before present.
Abstract: One of the major issues in (palaeo-) climatology is the response of Antarctic ice sheets to global climate changes. Antarctic ice volume has varied in the past but the extent and timing of these fluctuations are not well known. In this study, we address the question of amplitude and timing of past Antarctic ice level changes by surface exposure dating using in situ produced cosmogenic nuclides ( 10 Be and 21 Ne). The study area lies in the Ricker Hills, a nunatak at the boundary of the East Antarctic Ice Sheet in southern Victoria Land. By determining exposure ages of erratic boulders from glacial drifts we directly date East Antarctic Ice Sheet variations. Erosion-corrected neon and beryllium exposure ages indicate that a major ice advance reaching elevations of about 500 m above present ice levels occurred between 1.125 and 1.375 million years before present. Subsequent ice fluctuations were of lesser extent but timing is difficult as all erratic boulders from related deposits show complex exposure histories. Sample-specific erosion rates were on the order of 20- 45 cm Ma -1 for a quartzite and 10- 65 cm Ma -1 for a sandstone boulder and imply that the modern cold, arid climate has persisted since at least the early Pleistocene.
TL;DR: Deception Island is the largest volcano in the actively extending Bransfield Basin, a marginal basin situated behind the extinct South Shetland Islands arc as mentioned in this paper, and its submerged flanks have not been well studied but their bathymetry survey was conducted around the island in 2005.
Abstract: Deception Island is the largest volcano in the actively extending Bransfield Basin, a marginal basin situated behind the extinct South Shetland Islands arc. Deception Island has been well studied but its submerged flanks have not. A multibeam bathymetry survey was conducted around the island in 2005. Data from the flooded caldera show no evidence for recent localized resurgence. The gently-sloped bottom of the caldera basin is consistent with either a broad zone of resurgence on its east side associated with trap door deformation or with higher rates of sediment supply from the east side of the island. Around the island, numerous tectonic and volcanic features on the volcano's east and west flanks are nearly all aligned with the regional strike (~060°) of the Bransfield rift and there is very little evidence for the other fault populations that have been identified on the island. We infer that models that link the ongoing tectonic development of Deception Island to complex regional tectonics are less likely than models in which the dominant regional extension in Bransfield Strait is modulated by the local effects of caldera collapse and possibly a small right-lateral transfer zone offsetting the primary extension axes in the Central and Western Bransfield Basins.
TL;DR: It is demonstrated that mice are having a significant, negative impact at the landscape scale on Marion Island, so adding to the growing list of species and ecosystem-level effects attributable to this invasive rodent.
Abstract: On Southern Ocean islands the effects of the house mouse on plants are not well understood. In particular, its influence at the landscape scale has largely been overlooked. To address this issue, we systematically mapped the distribution of a keystone, cushion plant species, Azorella selago, and mouse damage to it across Marion Island. Mouse damage was observed in a third of the sampled sites from sea level to 548 m a.s.l. Damage to individual cushions ranged from single burrows to the disintegration of entire cushions. Mouse damage was high in sites with low A. selago density, suggesting that in areas of low cushion density the impact of mice may be substantial. Moreover, it is not simply direct impacts on the A. selago population that are ecologically significant. Azorella selago cushions serve as nurse plants for many epiphyte species, so increasing the altitudinal range of a variety of them, and also house high densities of invertebrates especially in fellfield landscapes. In consequence, this study demonstrates that mice are having a significant, negative impact at the landscape scale on Marion Island, so adding to the growing list of species and ecosystem-level effects attributable to this invasive rodent.
TL;DR: In this article, the authors apply the Optimum Multiparameter water mass analysis to the Weddell deep waters in order to investigate their distribution and variability, and identify possible forcing mechanisms for such variability, the water mass temporal anomalies were compared with oceanic and atmospheric modes of variability in that region.
Abstract: The Weddell Sea is one of the key regions of the Southern Ocean with respect to climate as most of the Antarctic Bottom Water (AABW) that occupies the world ocean deepest layers is likely to originate from this region. This study applies the Optimum Multiparameter water mass analysis to the Weddell deep waters in order to investigate their distribution and variability. The dataset used is based on the WOCE repeat sections in the area (SR04 and A12) from 1984 to 1998. The mean water mass distribution is consistent with previous knowledge of the region, along with high interannual variability. Regarding the temporal variability, it seems that the years of maximum Weddell Sea Deep Water (WSDW) contribution correspond to the lowest levels of Weddell Sea Bottom Water (WSBW), and vice versa. In order to identify possible forcing mechanisms for such variability, the water mass temporal anomalies were compared with oceanic and atmospheric modes of variability in that region such as the Southern Annular Mode (SAM). An apparent correlation between the SAM index temporal gradients and WSBW anomalies indicate that the Weddell Sea export of dense waters to the world ocean may be linked to that index on several time scales.
TL;DR: A gridded bathymetric dataset of the shelf and near-shelf sea-floor areas around South Georgia in the Southern Ocean is constructed using a layered hierarchy dependent upon accuracy of each dataset.
Abstract: We introduce a new bathymetric compilation of the area around South Georgia in the Southern Ocean. Using a variety of data sources including multi and single-beam swath bathymetry we have constructed a gridded bathymetric dataset of the shelf and near-shelf sea-floor areas. The grid has been constructed using a layered hierarchy dependent upon accuracy of each dataset. The spikes and errors have been checked both manually and with a novel semi-automated process. We discuss the resulting bathymetry and the potential uses of the new dataset.
TL;DR: In this paper, the first published survey of diatom-environment relationships on sub-Antarctic Macquarie Island was presented, where 208 diatom species from 34 genera were identified.
Abstract: This study is the first published survey of diatom-environment relationships on sub-Antarctic Macquarie Island. Fifty-eight sites in 50 coastal and inland lakes were sampled for benthic diatoms and water chemistry. 208 diatom species from 34 genera were identified. Multivariate analyses indicated that the lakes were distributed along nutrient and conductivity gradients. Conductivity, pH, phosphate (SRP), silicate and temperature all explained independent portions of the variance in the diatom data. Transfer functions provide a quantitative basis for palaeolimnological studies of past climate change and human impacts, and can be used to establish baseline conditions for assessing the impacts of recent climate change and the introduction of non-native plants and animals. Statistically robust diatom transfer functions for conductivity, phosphate and silicate were developed, while pH and temperature transfer functions performed less well. The lower predictive abilities of the pH and temperature transfer functions probably reflect the broad pH tolerance range of diatoms on Macquarie Island and uneven distribution of lakes along the temperature gradient. This study contributes to understanding the current ecological distribution of Macquarie Island diatoms and provides transfer functions that will be applied in studies of diatoms in lake sediment cores to quantitatively reconstruct past environmental changes.
TL;DR: The polydolopid radiation might be related to the expansion of the Nothofagus flora, as both have the same spatial distribution in southern South America and West Antarctica.
Abstract: New polydolopid marsupial specimens have been recovered from the La Meseta Formation, a late early Eocene to probably early Oligocene unit cropping out in the northern third of Seymour (Marambio) Island, at some 100 km off the northern Antarctic Peninsula. Our review of the original materials, as well as the new specimens from the same levels, led us to: 1) revalidate the genus Antarctodolops Woodburne & Zinsmeister 1984, 2) regard Eurydolops seymouriensis Case, Woodburne & Chaney 1988 as a junior synonym of Antarctodolops dailyi Woodburne & Zinsmeister, and 3) recognize a new species of this same genus: A. mesetaense. As previously stated, the polydolopid radiation might be related to the expansion of the Nothofagus flora, as both have the same spatial distribution in southern South America and West Antarctica.
TL;DR: In this paper, the authors presented new whole rock Rb-Sr and zircon U-Pb geochronological data and Sm-Nd isotopic data from the central magmatic arc domain of the Antarctic Peninsula in the area of northwest Palmer Land and southwest Graham Land, showing an age of 169±6 Ma for basement orthogneisses and 132±9 to 71±9 Ma for plutons.
Abstract: New whole rock Rb-Sr and zircon U-Pb geochronological data and Sm-Nd isotopic data are presented from the central magmatic arc domain of the Antarctic Peninsula in the area of northwest Palmer Land and southwest Graham Land, Rb-Sr isochrons indicate an age of 169±6 Ma for basement orthogneisses and 132±9 to 71±9 Ma for plutons. A U-Pb age of 183 ± 2.1 Ma, with no detectable inheritance, on zircons from an orthogneiss from Cape Berteaux provides the first reliable age for the orthogneisses, which are interpreted as metamorphosed silicic volcanic rocks, and Sm-Nd data indicate derivation in a mature volcanic arc. The age indicates they may be correlatives of the Jurassic ‘Chon Aike’ volcanism of the eastern Antarctic Peninsula. A U-Pb zircon age of 107 ± 1.7 Ma on a terrestrial volcanic sequence overlying an uncomformity strongly suggests a mid-Cretaceous age for the extensive volcanic cover of northwest Palmer Land that was previously thought to be Jurassic. The unconformity is interpreted to have been a result of compressional uplift related to the Palmer Land event. This is the first date for the event in the western part of the central magmatic arc terrane of the Antarctic Peninsula.
TL;DR: This paper revisits the phylogenetic relationships of Trematomus using both increased taxon sampling and an expanded dataset which includes DNA sequences from two mitochondrial genes and one single-copy nuclear gene, and demonstrates that the addition of nuclear gene sequence data to mitochondrial data can enhance phylogenetic resolution and increase node support.
Abstract: The biota of Antarctica is amazingly rich and highly endemic. The phylogenetics of notothenioid fishes has been extensively investigated through analyses of morphological characters, DNA sequences from mitochondrial genes, and single copy nuclear genes. These phylogenetic analyses have produced reasonably similar phylogenetic trees of notothenioids, however a number of phylogenetic questions remain. The nototheniid clade Trematomus is an example of a group where phylogenetic relationships remain unresolved. In this paper we revisit the phylogenetic relationships of Trematomus using both increased taxon sampling and an expanded dataset which includes DNA sequences from two mitochondrial genes (ND2 and 16S rRNA) and one single-copy nuclear gene (RPS7). The Bayesian phylogeny resulting from the analysis of the combined mitochondrial and nuclear gene datasets was well resolved and contained more interspecific nodes supported with significant Bayesian posteriors than either the mitochondrial or nuclear gene phylogenies alone. This demonstrates that the addition of nuclear gene sequence data to mitochondrial data can enhance phylogenetic resolution and increase node support. Additionally, the results of the combined mitochondrial and nuclear Bayesian analyses provide further support for the inclusion of species previously classified as Pagothenia and Cryothenia in Trematomus.
TL;DR: The evidence for the continued existence of Abraxas Lake includes a 14 C date that significantly predates the last glacial maximum (though this cannot be considered direct proof of the existence of the lake prior to the Last Glacial Maximum) and the presence of saline porewater throughout the core, including in compacted sediments deposited during the glacial period as mentioned in this paper.
Abstract: Evidence is provided from a sediment core from saline Abraxas Lake, Vestfold Hills, that indicates that the lake existed through the Last Glacial Maximum. It can therefore be concluded that at least part of the Vestfold Hills also remained ice-free through the Last Glacial Maximum, or at most was covered by a thin, non-erosive cold-based ice sheet. The evidence for the continued existence of Abraxas Lake includes a 14 C date that significantly predates the Last Glacial Maximum (though this cannot be considered direct proof of the existence of the lake prior to the Last Glacial Maximum); the presence of saline porewater throughout the core, including in compacted sediments deposited during the glacial period, which implies that the lake obtained its salt prior to any Holocene marine highstand; and the occurrence of marine-derived fauna from the onset of significant biological activity late in the Pleistocene. The occurrence of ice-free land in the Vestfold Hills and similar oases suggests that the margin of the polar ice cap did not reach far beyond its current position at the Last Glacial Maximum, at least in regions now occupied by these oases.
TL;DR: This work examined the power of five microsatellite loci developed for the cosmopolitan moss Ceratodon purpureus to detect genetically distinct clones and infer the distribution of clones within and among populations from the Windmill Islands, East Antarctica, and found surprisingly little contribution of asexual reproduction.
Abstract: The capacity of the polar flora to adapt is of increasing concern given current and predicted environmental change in these regions. Previous genetic studies of Antarctic mosses have been of limited value due to a lack of variation in the markers or non-specificity of the methods used. We examined the power of five microsatellite loci developed for the cosmopolitan moss Ceratodon purpureus to detect genetically distinct clones and infer the distribution of clones within and among populations from the Windmill Islands, East Antarctica. Our microsatellite data suggest that the extraordinarily high levels of variation reported in RAPD studies were artificially elevated by the presence of contaminants. We found surprisingly little contribution of asexual reproduction to the genetic structure of the Windmill Islands populations, but more loci are required to determine the distribution of individual clones within and among populations. It is apparent that Antarctic populations of C. purpureus possess less genetic diversity than temperate populations, and thus have less capacity for adaptive change in response to environmental variation, but more markers are needed to resolve the total genetic diversity in Antarctic C. purpureus and other mosses.