Regions Of Antarctica Research Articles

Evidence for dispersal and habitat controls on pond diatom communities from the McMurdo Sound Region of Antarctica

Microbial life flourishes in the ponds of the McMurdo Sound Region, which includes the McMurdo Dry Valleys (MDV) and the exposed coastal areas of Ross Island, Antarctica. Diatoms live within resident microbial mats, and because of the simplified trophic structure and limited dispersal vectors, the McMurdo Sound Region is an ideal locality to investigate diatom community assembly processes. Wind is hypothesized to transport microbiota between habitats, and following the species-sorting perspective, local conditions should act as an environmental filter. However, the role of spatial scale versus habitat characteristics on diatom community structure has not been investigated. To gain insight into these processes, we sampled microbial mats from 25 ponds and used variation partitioning to assess the spatial scales at which diatoms were influenced by chemistry and physical variables. We found substantial spatial structure in diatom communities, and spatial scale explained more variability than environmental variables. No diatoms were exclusive to Ross Island, but some species were only found in the MDVs. Furthermore, diatom communities were more likely to resemble those from other nearby ponds rather than distant ones, regardless of environmental conditions. Of the environmental variables, bromide and chloride (both indicators of marine influence) were among the most important. These results suggest that geography, dispersal, and historical environmental conditions play a major role in structuring diatom communities at large spatial scales, and chemistry may be more important within regions. These results help explain the biogeography of diatoms here and elsewhere and expand our knowledge of mechanisms influencing microbial metacommunity structure.

Glacial isostatic adjustment in response to changing Late Holocene behaviour of ice streams on the Siple Coast, West Antarctica

The Siple Coast region of Antarctica contains a number of fast-flowing ice streams, which control the dynamics and mass balance of the region. These ice streams are known to undergo stagnation and reactivation cycles, which lead to ice thickness changes that may be sufficient to excite a viscous solid Earth response (glacial isostatic adjustment; GIA). This study aims to quantify Siple Coast ice thickness changes during the last 2000 yr in order to determine the degree to which they might contribute to GIA and associated present-day bedrock uplift rates. This is important because accurate modelling of GIA is necessary to determine the rate of present-day ice-mass change from satellite gravimetry. Recently-published reconstructions of ice-stream variability were used to create a suite of kinematic models for the stagnation-related thickening of Kamb Ice Stream since ∼1850 AD, and a GIA model was used to predict present-day deformation rates in response to this thickening. A number of longer-term loading scenarios, which include the stagnation and reactivation of ice streams across the Siple Coast over the past 2000 yr, were also constructed, and used to investigate the longer term GIA signal in the region. Uplift rates for each of the ice loading histories, based on a range of earth models, were compared with regional GPS-observed uplift rates and an empirical GIA estimate. We estimate Kamb Ice Stream to have thickened by 70–130 m since stagnation ∼165 years ago. Modelled present-day vertical motion in response to this load increase peaks at −17 mm yr–1 (i.e. 17 mm yr–1 subsidence) for the weakest earth models tested here. Comparison of the solid Earth response to ice load changes throughout the last glacial cycle, including ice stream stagnation and reactivation across the Siple Coast during the last 2000 yr, with an empirical GIA estimate suggests that the upper mantle viscosity of the region is greater than 1 × 1020 Pa s. When upper mantle viscosity values of 1 × 1020 Pa s or smaller are combined with our suite of ice-load scenarios we predict uplift rates across Siple Coast that are at least 4 mm yr–1 smaller than those predicted by the empirical GIA estimate. GPS data are unable to further constrain model parameters due to the distance of the GPS sites from the study area. Our results demonstrate that Late Holocene ice load changes related to the stagnation and reactivation of ice streams on the Siple Coast may play a dominant role in defining the present-day uplift signal. However, both the detailed Earth structure and deglacial history of the region need to be better constrained in order to reduce uncertainties associated with the GIA signal of this region.

Taylor's Valley: What the History of Antarctica's 'Heroic Era' Can Contribute to Contemporary Ecological Research in the McMurdo Dry Valleys

Abstract With a particular focus on ecosystem response to climate change, this paper investigates how a study of Griffith Taylor's 1911 expedition into the McMurdo Dry Valleys in East Antarctica might contribute to contemporary ecological research in the region. As the location of a Long Term Ecological Research (LTER) site, the McMurdo Dry Valleys offer an excellent location for thinking about the integration of history and ecology. Following a brief description of the environment of this uniquely ice-free region of Antarctica as it is understood today, this paper presents a three-dimensional model for using historical research to contribute to ecological research. The paper then follows this model to examine what the Taylor expedition did in the Dry Valleys, how its participants sought to make sense of the environment and what the environment was like one hundred years ago. Significant lake-level rise in the McMurdo Dry Valleys since the Taylor expedition suggests quite dramatic environmental change over the course of the twentieth century. The conclusion suggests that a model for integrating history and ecology in the McMurdo Dry Valleys might productively be applied to other parts of the world with more complex ecosystems and much longer human histories.

Crustal and upper-mantle structure beneath ice-covered regions in Antarctica fromS-wave receiver functions and implications for heat flow

Crustal and upper-mantle structure beneath ice-covered regions in Antarctica from<i>S</i>-wave receiver functions and implications for heat flow

Mesoproterozoic Tasmania: Witness to the East Antarctica–Laurentia connection within Nuna: COMMENT

I concur with the finding of Mulder et al. (2015) that the Rocky Cape Group was not sourced from Australia. However, the Rocky Cape Group is but one stratigraphic unit of the micro-continent of VanDieland (Cayley, 2011). For their proposed location for VanDieland to be valid, it must satisfy the constraints imposed by all of the units in the microcontinent, not just one from the period from ca. 1200–1450 Ma. VanDieland also includes the east South Tasman Rise (Cayley, 2011; Mulder et al., 2015). Rocks there include granites with U/Pb zircon ages of 1120 ± 9 Ma (Fioretti et al., 2005) and with U/Th/Pb monazite ages of 1051 ± 8 Ma that were metamorphosed at ca. 1015 Ma and 920–930 Ma (Berry et al., 2008). Mulder et al.’s figure 2 offers two VanDieland positions near the USA-Canadian border, but neither fits these data. While there is evidence of Grenville-age zircon growth in the Belt Supergroup and adjacent rocks (Doughty and Chamberlain, 2008), there is a dearth of similar-aged granites known north of the Grenville Orogen in ‘western’ Laurentia (modern position) and in Victoria Land in East Antarctica, and metamorphism in the region of the Belt Supergroup and the corresponding regions in Antarctica appears to have ceased at ca. 1000 Ma (May et al., 2013; Rocchi et al., 2015). Rather, locating the east South Tasman Rise outboard of the southwestern Grenville Orogen, as suggested by Fioretti et al. (2005) and Moore et al. (2015), provides a more coherent fit than either offered by Mulder et al. Mulder et al. dismiss the 1010 ± 45 Ma detrital zircon ages that Black et al. (2004) obtained from the Jacob Quartzite as resulting from Pb loss. Do they also dismiss results from the Wings Sandstone, another western Tasmanian marginal marine quartzite, where Black et al. (2004) obtained a population of 1022 ± 17 Ma (12 grains), and another as young as 914 ± 44 Ma? Moore et al. (2015, their figure 20) suggested that these come from the erosion of areas near the Grenville Orogen. How do Mulder et al. account for these younger populations? And where is the source for their ca. 1300 Ma upper Rocky Cape Group zircons? None is offered in their figure 4. Mulder et al. describe the Rocky Cape Group as a “marine shelfal package.” Similar modern and ancient packages lie on older cratonic basements (e.g., Jones et al., 2011). Black et al. (2010) found that the Paleozoic western Tasmanian granites had an excess of 1600 Ma zircons when compared to the Rocky Cape Group, implying a basement with excess zircons of that age. Two-stage Nd model ages on granites that intruded the Rocky Cape Group gave ages of 1530 and 1780 Ma, and all other granite model ages in western Tasmania are younger than 2100 Ma (Champion, 2013). Indeed, Mulder et al.’s Hf data suggest a highly juvenile zircon source, difficult to reconcile with their locations. The data imply that the basement under the Rocky Cape Group formed in the middle to late Paleoproterozoic, similar to that of the Cochise Block and the overlying quartzites in southern Arizona, and unlike the Archean to early Paleoproterozoic rocks likely to be outboard of the Belt Basin (Doe et al., 2013; Whitmeyer and Karlstrom, 2007). Leaving VanDieland unrotated, in the position suggested by Moore et al. (2015), would allow these correlations. How do Mulder et al. resolve these issues? Like Mulder et al., I consider that VanDieland was once located outboard of Laurentia. However, they have failed to recognize the significance of the Grenville-age orogenic and sedimentary events and the concealed late Paleoproterozoic basement, constraints outside of the Rocky Cape Group. When these are considered, a Nuna/Rodinia position for VanDieland close to the USA–Mexican border, with the South Tasman Rise aligned with and outboard of the Grenville Orogen, seems more likely than one rotated and up to 1500 km further north.

Twentieth-century sea ice variability in the Weddell Sea and its effect on moisture transport: Evidence from a coastal East Antarctic ice core record

High-resolution study of deuterium excess (d-excess), sea salt sodium (ss-Na+), and methane sulfonic acid (MSA) in an ice core from coastal Dronning Maud Land (cDML), East Antarctica, revealed the history of moisture transport and sea ice extent (SIE) during the last century. Backward wind trajectories show that air parcels were mainly derived from the Weddell Sea region. The d-excess profile shows a dramatic shift from an average value of 8‰ during 1905–1920 to −1‰ during ~1940 and thereafter positive excursion during 1940–1980. The dramatic shift during 1920–1940 has been attributed to the reduced moisture supply from low/mid-latitude to Antarctica associated with shifting of Southern Annular Mode (SAM) from positive to negative mode. The ss-Na+ flux profile shows systematic positive excursion during 1940–1980 which coincide with that of the d-excess profile. The MSA flux shows a negative excursion during 1950–1965, overlapping with the period of positive excursions in ss-Na+ and d-excess profiles. The concomitant increase of ss-Na+ and d-excess values and positive excursions during 1940–1980 indicate higher SIE. Based on significant correlation between the Na+ flux and satellite-derived winter SIE record of the Weddell Sea, ~10% increase in SIE is estimated compared to its average value of the last century. The power spectrum analysis of d-excess and ss-Na+ flux shows a significant periodicity at ~3.5 years, exactly matching with that of the winter SIE in the Weddell Sea. Wavelet analysis of SAM index and Southern Oscillation Index (SOI) shows the highest common power in 4 to 8 year band, overlapping with the periods of higher SIE and opposite phase in 10 to 16 year band, overlapping with the periods of higher d-excess. This study highlights the role of SAM and its teleconnection to El Niño Southern Oscillations (ENSO) in controlling sea ice and moisture source variability in annual to decadal scale in the coastal regions of Antarctica.

Trace element contamination and availability in the Fildes Peninsula, King George Island, Antarctica.

The Ardley Cove area (located on the Maxwell Bay shoreline, Fildes Peninsula, King George Island, Antarctica) is characterized not only by its high biodiversity, but also by a high density of scientific stations, making it potentially one of the most impacted areas of Antarctica. In order to assess the source, contamination levels, distribution and availability of several trace elements (Cr, Ni, Cu, Zn, As, Pb, Cd and Hg) in and around Maxwell Bay, soil and seawater samples were collected. Soil samples were also collected in the study reference site near the Bellingshausen Dome area, as it lies far from centers of human activity and associated infrastructure. Enrichment factors (EFs) and sequential extractions were also used to assess the degree of contamination and availability of the trace elements under investigation. The results obtained in this study pointed to the existence of several contamination hotspots, mainly related to high levels of Zn, Pb, Cd, Cr and Ni. Comparison of the contaminant distribution patterns with data from earlier studies allowed the identification of anthropogenic sources. Use of the EF approach and sequential extractions confirmed these findings. In particular, higher extraction proportions were obtained for Zn and Pb (68 and 71%, respectively), which were also the same elements where the highest EFs were determined. The results obtained in this study clearly point to human impact on the natural environment in this region of Antarctica and we recommend the implementation of appropriate contamination control and remediation methods.

Genetic diversity and biogeography of the south polar water bear Acutuncus antarcticus (Eutardigrada : Hypsibiidae) – evidence that it is a truly pan-Antarctic species

Antarctica is an ice-dominated continent and all its terrestrial and freshwater habitats are fragmented, which leads to genetic divergence and, eventually, speciation. Acutuncus antarcticus is the most common Antarctic tardigrade and its cryptobiotic capabilities, small size and parthenogenetic reproduction present a high potential for dispersal and colonisation. Morphological (light and electron microscopy, karyology) and molecular (18S rRNA and cytochrome c oxidase subunit I (COI) genes) analyses on seven populations of A. antarcticus elucidated the genetic diversity and distribution of this species. All analysed populations were morphologically indistinguishable and made up of diploid females. All specimens presented the same 18S rRNA sequence. In contrast, COI analysis showed higher variability, with most Victoria Land populations presenting up to five different haplotypes. Genetic distances between Victoria Land specimens and those found elsewhere in Antarctica were low, while distances between Dronning Maud Land and specimens from elsewhere were high. Our analyses show that A. antarcticus can still be considered a pan-Antarctic species, although the moderately high genetic diversity within Victoria Land indicates the potential for speciation events. Regions of Victoria Land are considered to have been possible refugia during the last glacial maximum and a current biodiversity hotspot, which the populations of A. antarcticus mirror with a higher diversity than in other regions of Antarctica.

Zealandia’s oldest volutes (Mollusca: Gastropoda: Volutidae) from the early Paleogene of South Island and Chatham Islands: post Gondwana break-up and evolutionary divergence

AbstractThe isolation of Zealandia in the latest Cretaceous and early Paleogene following the final break-up of Gondwana fostered significant provincialism in molluscan faunas, concomitant with the segmentation of oceanic circulation patterns and changing climate nearing the end of the greenhouse phase in the Southwest Pacific. The earliest volutes (Gastropoda: Volutidae) from the Zealandian region reflect this isolation after separation from the Marie Byrd Land region of West Antarctica with several endemic groups being recognized for the first time since collecting first started in the Wangaloa Formation at Mitchells Rocks (Wangaloa), South Island, New Zealand in 1869. Five taxa attributed to the Volutidae are described herein from South Island (Wangaloa Formation and Steel Greensand) and also the Chatham Islands (Red Bluff Tuff) from the early (mid-Danian) to late Paleocene (Thanetian?). These comprise a new mid-Danian fulgorariine? genus and species,Wangaluta henaconstrictan. gen. n. sp.; a new combination also from the Wangaloa Formation,Wangaluta? neozelanica(Finlay and Marwick, 1937); two new zidonine volutes, the mid-DanianAlcithoe. s.l.wangaloaensisn. sp. from the Wangaloa Formation, and alsoTeremelon onouan. sp. from the late Paleocene-early Eocene of the Red Bluff Tuff; and a probable volute, Fulgorariine? gen. indet. sp. indet. from the mid-Danian of the Steel Greensand. All of these taxa are endemic in the early Paleogene of New Zealand and represent a significant boost in our knowledge of post-K-Pg boundary diversification of volutid gastropods in the shrinking Weddellian Biotic Province in the southern rim of the Pacific.

Carga ganadera y capacidad de carga de los pastizales naturales de la Patagonia chilena: estimación a nivel comunal

A study was conducted to determine the Livestock farm intensity coefficient, by the ratio between the stocking and carrying capacity of grazinglands of the Los Rios, Los Lagos, General Carlos Ibanez del Campo (Aysen) and Magallanes and Chilean Antarctica (Chilean Patagonia) regions. The current stocking rate was determined through 2007 Livestock Census information and coverage crosses regarding pastoral rangelands at the county level, and it was compared which the carrying capacity. The latter variable was calculated from the average rangeland DM annual production, which was estimated at regional level through a simple model based on a series of 10-year-MODIS NDVI images with a pixel size of 6.25 ha approximately. Preliminary results of this analysis indicate that the rangelands of the Chilean Patagonia present high spatial variability in terms of their annual DM production. Los Lagos and Los Rios regions are those with higher stocking density, showing them the highest degree of human intervention, which in many cases results in a situation of overgrazing, contrary to what happens in many counties of the Aysen region. In this respect, the Magallanes Region presents degrees of use near the optimum, an aspect that should be taken with caution since the estimates of the model PMSA vs NDVI in shrublands and bunchgrass grassland seem to be less plausible.

Response of Long Lake sediments to Antarctic climate: A perspective gained from sedimentary organic geochemistry and particle size analysis

Sediments from the pristine lakes of ice-free regions of Antarctica are a great source for proxies to reconstruct the effect of past-climate on the lake evolution and its response to Antarctic climate. A 50 cm long sediment core retrieved from Long Lake, a periglacial lake of Schirmacher Oasis in Dronning Maud Land was measured for elemental (C%, N% and C/N), isotopic (δ13C, δ15N) and particle size (sand-silt-clay percent) variation. The radiocarbon dated core spanning the last 48 cal ka BP has been deciphered for the lake's response to Antarctic climate. The C/N ratio (atomic ratio) predominantly indicates that the productivity has been autochthonous for majority of the down-core while the top 0–3 cm indicates that there has been addition of terrestrial organic matter into the lake system owing to longer ice-free conditions. The organic carbon shows significantly lower values (0.2%) throughout the glacial period and major part of the Holocene while the core-top values are consistent with the presence of a microbial mat which is reflected as higher organic carbon (12%). The δ13C and δ15N range from −33 to −9‰ and 2–18‰, respectively. The isotopic signals vary marginally for the entire glacial period (48–8 cal ka BP) suggesting an intense cold period. The gradual increase in C/N ratio, sand content and δ13C and decrease in δ15N beginning at about 6 cal ka BP suggest that the Long Lake experienced longer ice-free conditions owing to sustained warmer Holocene conditions suggesting that the ice-cover over the Long Lake persisted well through early-Holocene. The sand and silt percent shows inverse correlation likely reflecting the warmer and colder conditions. The Holocene is characterised by higher sand content owing to melting of ice due to warmer conditions. The Long Lake's response to Antarctic climate is reflected in its response to the ice-cover conditions which regulates the productivity and sedimentation in the lake system.

Elevation change around Dome A region of Antarctica from EnviSat satellite radar altimetry during 2002–2012

The expected responses of ice sheets to climate warming are growth in the thickness of the inland ice areas and thinning near the margins. In recent decades, researchers have identified glacier acceleration along Antarctic ice sheet coastal margins. However, the study of ice sheet interiors where seasonal accumulation eventually balances ice wastage at the lower elevation is poorly understood. In this paper, the ice sheet elevation change around Dome A region is analyzed from 2002 to 2012 using two million elevation change measurements from EnviSat satellite radar altimeter data covering an area of about 7000 km2. A declining trend of 0.572 ± 1.31 mm/year which means that the Dome A region was in balance during the last decade can be captured. In addition, two obvious changes in accumulation which divide elevation change time series into three independent equilibration stages are also extracted. In order to explain this phenomenon, two speculations related to snowfall and firn compaction are proposed in this paper.

Malaysia Strategies in Sustaining its Antarctic Endeavours

This article evaluates the ways Malaysia strategies its Antarctic's path in assuring the sustainability of its scientific works, as well as its diplomatic linkages with the Governors of Antarctica Region. The main concerns for Malaysia is to be able to maintain the efforts to tackle the human capital shortage in order to compete and maintain constantly scientific activities in the cold region as evident that Malaysia qualifies to be the Consultative Member State‘s status. This paper clarifies the strategies activated by Malaysia at local level and at international endeavours in sustaining its interests in the Antarctica Science.

Observed platelet ice distributions in Antarctic sea ice: An index for ocean‐ice shelf heat flux

AbstractAntarctic sea ice that has been affected by supercooled Ice Shelf Water (ISW) has a unique crystallographic structure and is called platelet ice. In this paper we synthesize platelet ice observations to construct a continent‐wide map of the winter presence of ISW at the ocean surface. The observations demonstrate that, in some regions of coastal Antarctica, supercooled ISW drives a negative oceanic heat flux of −30 Wm−2 that persists for several months during winter, significantly affecting sea ice thickness. In other regions, particularly where the thinning of ice shelves is believed to be greatest, platelet ice is not observed. Our new data set includes the longest ice‐ocean record for Antarctica, which dates back to 1902 near the McMurdo Ice Shelf. These historical data indicate that, over the past 100 years, any change in the volume of very cold surface outflow from this ice shelf is less than the uncertainties in the measurements.

Seamount biodiversity: high variability both within and between seamounts in the Ross Sea region of Antarctica

Seamounts in the Ross Sea were surveyed during the New Zealand IPY-CAML research voyage in 2008. Admiralty seamount, and seamounts of the Scott Island Seamount chain (Scott Island, Scott A, Scott B, Scott South) were sampled to examine variability in benthic faunal communities of seamounts. Multivariate analysis of video and still image data showed that benthic community composition was highly variable both within and between seamounts. The distribution patterns of benthic communities varied considerably, with very high densities of certain taxa in some places, sparse fauna in many others, and highly patchy distributions for others. Dissimilarities between seamounts were influenced by differences in population densities of taxa, the proportions of transects in which taxa were present, and by taxa being restricted to only one seamount or group of seamounts. Scott Island seamount was less similar to the others, despite the greater distances between Admiralty and Scott A and B seamounts. The observed variability in community composition was mainly associated with differences in depth, chlorophyll concentration, and seabed rugosity. Results support an earlier hypothesis that the location of seamounts relative to the Ross Sea gyre could be an important factor determining the composition and abundance of benthic invertebrate communities.

Winter use of sea ice and ocean water mass habitat by southern elephant seals: The length and breadth of the mystery

Understanding the responses of animals to the environment is crucial for identifying critical foraging habitat. Elephant seals (Mirounga leonina) from the Kerguelen Islands (49°20′S, 70°20′E) have several different foraging strategies. Why some individuals undertake long trips to the Antarctic continent while others utilize the relatively close frontal zones is poorly understood. Here, we investigate how physical properties within the sea ice zone are linked to foraging activities of southern elephant seals (SES). To do this, we first developed a new approach using indices of foraging derived from high temporal resolution dive and accelerometry data to predict foraging behaviour in an extensive, low resolution dataset from CTD-Satellite Relay Data Loggers (CTD-SRDLs). A sample of 37 post-breeding SES females were used to construct a predictive model applied to demersal and pelagic dive strategies relating prey encounter events (PEE) to dive parameters (dive duration, bottom duration, hunting-time, maximum depth, ascent speed, descent speed, sinuosity, and horizontal speed) for each strategy. We applied these models to a second sample of 35 seals, 20 males and 15 females, during the post-moult foraging trip to the Antarctic continental shelf between 2004 and 2013, which did not have fine-scale behavioural data. The females were widely distributed with important foraging activity south of the Southern Boundary Front, while males predominately travelled to the south-eastern part of the East Antarctica region. Combining our predictions of PEE with environmental features (sea ice concentration, water masses at the bottom phase of dives, bathymetry and slope index) we found higher foraging activity for females over shallower seabed depths and at the boundary between the overlying Antarctic Surface Water (AASW) and the underlying Modified Circumpolar Deep Water (MCDW). Increased biological activity associated with the upper boundary of MCDW, may provide overwintering areas for SES prey. Male foraging activity was strongly associated with pelagic dives within the Antarctic Slope Front where upwelling of nutrient rich Circumpolar Deep Water onto surface water may enhance and concentrate resources. A positive association between sea ice and foraging activity was found for both sexes where increased biological activity may sustain an under-ice ecosystem. Variability of the East Antarctic sea ice season duration is likely a crucial element to allow air-breathing predators to benefit from profitable prey patches within the pack ice habitat.

A influência dos modos de variabilidade climática na temperatura em superfície na Antártica

Este trabalho analisa a variação sazonal da temperatura do ar à superfície (Tar) na Antártica, e sua relação com os modos de variabilidade climática El Niño-Oscilação Sul (ENOS) e Oscilação Antártica (OA). Os resultados indicam que para os 4 períodos sazonais as Tar nas estações localizadas no setor oriental da Antártica apresentaram significativas correlações negativas (nível de significância de 1% na maioria das estações) com a OA. Todavia o único período sazonal, em que o setor continental (Amundsen-Scott, Dome C) apresentou forte correlação negativa com a OA, foi durante o inverno (significativa a 1%). Correlações positivas foram encontradas (significâncias entre 1% e 5%) entre as Tar da Península Antártica e Shetland do Sul com a OA para os períodos de outono, inverno e primavera. Os resultados demonstram a influência que a OA exerce sobre a climatologia da Tar na Antártica. É importante notar um dipolo entre as regiões oriental da Antártica e da Península Antártica, no que concerne as influências da OA. O modo de variabilidade ENOS apresentou correlação negativa significativa com as três estações da Península Antártica somente durante a primavera, enquanto que para a estação Rothera, à oeste da Península, a correlação foi significativa também para o outono e inverno. A correlação entre ENOS e Tar foi positiva e significativa no setor do Mar de Ross durante a primavera, e com o setor oriental da Antártica durante o verão, com nível de significância chegando a 5%.

A System for the Automatic Classification of Ice Sheet Subsurface Targets in Radar Sounder Data

Exhaustive investigations of the ice sheet subsurface can be carried out by analyzing the information contained in the huge archives of radargrams acquired by dedicated radar sounder (RS) instruments. The analysis can be done by using properly designed automatic techniques for a quantitative, objective, and reliable extraction of information from radargrams. Unfortunately, the definition and development of such automatic techniques have only been marginally addressed in the literature. In this paper, we propose a novel and efficient system for the automatic classification of ice subsurface targets present in radargrams. The core of the system is represented by the extraction of a set of features for target discrimination. The features are based on both the specific statistical properties of the RS signal and the spatial distribution of the ice subsurface targets. Such features are then provided as input to an automatic classifier based on support vector machine. Experimental results obtained on two real-world data sets acquired by airborne-mounted RSs in large regions of Antarctica confirm the robustness and effectiveness of the proposed classification system.

'Stable' region of Antarctica is melting

'Stable' region of Antarctica is melting

Charles Swithinbank

Charles Swithinbank