Patriot Hills Research Articles

Sedimentary evidence of glacial entrainment at Patriot Hills and Union Glacier moraines, Ellsworth Mountains, West Antarctica.

This work aims to analyze and compare the sedimentological data of Ellsworth Mountains, West Antarctica: Patriot/Independence Hills and Union Glacier, and how sedimentological data can be used to infer sediment entrainment. Particular attention was concentrated on morainic deposits. Remote sensing data was used in the identification of deposits and the ice flow; granulometric, morphoscopic, and geochemical analyses were applied to investigate the sedimentary origin and transport history. Sediment rich in Si Al, Fe, and Ca predominate in Independence Hills and Rossman Cove but Ca prevails in Elephant Head. CIA indicated low values, which depict low chemical weathering processes. X-ray diffraction reveals the presence of minerals that constitute the local rocks in the Union Glacier area, and from the unexposed basement rocks in Independence Hills. Principal Component Analysis and Cluster Analysis results suggest the sediment is related to the local rocks in the Union Glacier and distinct exotic sources in Independence Hills, associated with far-traveled sediment. It is also observed the influence of distinct processes of entrainment sediment on its granulometric and morphoscopic characteristics.

Contextualizing the 1997 warm event observed at Patriot Hills in the interior of West Antarctica

Between 5 and 8 December 1997, the surface air temperature increased up to 3°C in the interior of West Antarctica, at Patriot Hills (PH), located at about 80°08’S, 81°16ʹ W, at an elevation of 855 m a.s.l. This was about 15°C warmer than the mean air temperature (−12°C) for this location at this time of the year. The ice surface field along the hills used as a runway for large aircraft melted, forming small ponds at the foot of the slope. This warm event was associated with a passing mid-tropospheric ridge that reached the interior of West Antarctica, whose anticyclonic circulation advected warm air towards the PH area. The foehn effect of the descending airflow on the northern slope of PH did not significantly contribute to the warming. The El Niño–Southern Oscillation (ENSO) was reaching its mature phase during the last quarter of 1997 and the warming/melting episode may be related to large-scale circulation associated with ENSO occurrence. However, warm events in the interior of West Antarctica may occur during any phase of ENSO. In contrast, the negative phase of the Antarctic Oscillation seems to support the development of the mid-tropospheric ridges that can advect warm maritime air towards the interior of West Antarctica. The 3°C registered at PH may be one of the highest near-surface air temperatures measured below 2500 m a.s.l. in the far interior coastal area of West Antarctica. This suggests a new subregion for determining air temperature records in Antarctica may need to be considered.

Interannual surface evolution of an Antarctic blue-ice moraine using multi-temporal DEMs

Abstract. Multi-temporal and fine-resolution topographic data products are increasingly used to quantify surface elevation change in glacial environments. In this study, we employ 3-D digital elevation model (DEM) differencing to quantify the topographic evolution of a blue-ice moraine complex in front of Patriot Hills, Heritage Range, Antarctica. Terrestrial laser scanning (TLS) was used to acquire multiple topographic datasets of the moraine surface at the beginning and end of the austral summer season in 2012/2013 and during a resurvey field campaign in 2014. A complementary topographic dataset was acquired at the end of season 1 through the application of structure from motion with multi-view stereo (SfM-MVS) photogrammetry to a set of aerial photographs acquired from an unmanned aerial vehicle (UAV). Three-dimensional cloud-to-cloud differencing was undertaken using the Multiscale Model to Model Cloud Comparison (M3C2) algorithm. DEM differencing revealed net uplift and lateral movement of the moraine crests within season 1 (mean uplift ~ 0.10 m) and surface lowering of a similar magnitude in some inter-moraine depressions and close to the current ice margin, although we are unable to validate the latter. Our results indicate net uplift across the site between seasons 1 and 2 (mean 0.07 m). This research demonstrates that it is possible to detect dynamic surface topographical change across glacial moraines over short (annual to intra-annual) timescales through the acquisition and differencing of fine-resolution topographic datasets. Such data offer new opportunities to understand the process linkages between surface ablation, ice flow and debris supply within moraine ice.

Assessing the continuity of the blue ice climate record at Patriot Hills, Horseshoe Valley, West Antarctica

AbstractWe use high‐resolution ground‐penetrating radar (GPR) to assess the continuity of the Blue Ice Area (BIA) horizontal climate record at Patriot Hills, Horseshoe Valley, West Antarctica. The sequence contains three pronounced changes in deuterium isotopic values at ~18 cal ka, ~12 cal ka, and ~8 cal ka. GPR surveys along the climate sequence reveal continuous, conformable dipping isochrones, separated by two unconformities in the isochrone layers, which correlate with the two older deuterium shifts. We interpret these unconformities as discontinuities in the sequence, rather than direct measures of climate change. Ice sheet models and Internal Layer Continuity Index plots suggest that the unconformities represent periods of erosion occurring, as the former ice surface was scoured by katabatic winds in front of mountains at the head of Horseshoe Valley. This study demonstrates the importance of high‐resolution GPR surveys for investigating both paleoflow dynamics and interpreting BIA climate records.

Variabilidade do conteúdo iônico da neve e do firn ao longo de um transecto antártico

Com o objetivo de interpretar a variabilidade no conteúdo iônico da neve e do firn entre Patriot Hills (80º18’S, 81º21’W) e o Polo Sul Geográfico, foram determinadas as concentrações dos íons majoritários e as razões isotópicas das 200 primeiras frações de cinco testemunhos de neve e firn (com profundidades de até 46 m), durante a travessia chileno-brasileira ocorrida no verão de 2004–2005. Após as amostras serem limpas (em câmara fria) e derretidas (em sala limpa classe 100), os íons Na+ , K+ , Mg2+, Ca2+, MS- (CH3 SO3 - ), Cl- , NO3 - e SO4 2- foram analisados por cromatografia iônica, com limites de detecção entre 0,3 e 1,8 µg L-1, dependendo do íon. A razão isotópica deutério/hidrogênio (δD) foi determinada com precisão de 0,5‰. Dataram-se as amostras, com precisão anual e exatidão de ±2 anos, a partir da contagem anual de camadas de neve e de firn dos perfis de Na+ , nssSO4 2- (sulfato não proveniente do sal marinho, do inglês non-sea-salt sulfate) e δD. A partir da datação obteve-se as taxas médias de acumulação líquida de neve para os sítios de cada testemunho de neve e firn, as quais apresentaram uma correlação negativa (r > 0,4, em módulo) à medida que se aumentavam a elevação e a distância da costa, respondendo, ainda, às feições superficiais locais e à ocorrência de ventos catabáticos. Constataram-se aerossóis do sal marinho com alteração na razão Na+ /Cl- no registro dos cinco testemunhos de neve e firn, mas a presença de aerossóis produzidos na formação do gelo marinho só foi identificada nos sítios mais próximos à costa. Os registros de NO3 - , assim como os de MS- , indicam a provável ocorrência de processos pós- -deposicionais, ligados tanto a eventos vulcânicos, como a reações fotoquímicas acentuadas por superfícies com formação de esmalte de gelo.

Charles Swithinbank

Charles Swithinbank

Variações na composição isotópica de oxigênio na neve superficial ao longo de uma travessia antártica

Este trabalho apresenta a variabilidade das razões de isótopos de oxigênio na neve superficial ao longo de uma travessia do manto de gelo da Antártida ocidental realizada no verão austral de 2004/2005 por uma expedição conjunta entre pesquisadores chilenos e brasileiros. A travessia foi realizada entre a estação chilena Tenente Parodi, em Patriot Hills (80°18’S, 081°21’W) e o Polo Sul geográfico, cobrindo uma distância de mais de 1.205 km. Foram coletadas amostras de neve superficial (entre 0,05 a 0,2 m de profundidade) aproximadamente a cada 10 km (total de 104 amostras). A temperatura média anual foi obtida em seis pontos espaçados aproximadamente 220 km entre si, a uma profundidade entre 10 e 15 m. A razão isotópica do oxigênio (δ 18O) de cada amostra foi determinada por espectrometria de massas com fonte de gás (GSMS - Gas Source Mass Spectrometry) com precisão de 0,05 ‰. Os resultados indicam forte correlação entre δ 18O e temperatura local, latitude, altitude e distância da costa, sendo a primeira positiva e as outras negativas. Valores isotópicos relativamente altos são encontrados entre 87°30’S e 86°44’S, resultantes de processos pós-deposicionais devido à formação de glaze ice (esmalte de gelo) identificadas em campo. O gradiente δ18O/Elevação encontrado foi de -0,08‰ /100 m e o gradiente δ 18O/Temperatura de 0,743 ‰/°C. Com exceção das anomalias citadas, os resultados são concordantes com os encontrados por outros pesquisadores no manto de gelo antártico.

Late Pleistocene and early Holocene change in the Weddell Sea: a new climate record from the Patriot Hills, Ellsworth Mountains, West Antarctica

ABSTRACTThe transition from the late Pleistocene to the Holocene (30 000–5000 years ago) was a period of considerable climate variability, which has been associated with changes in deep water formation and the intensity of the Meridional Overturning Circulation. Although numerous records exist across the North Atlantic region, few Antarctic ice core records have been obtained from the south. Here we exploit the potential of upwelling ancient ice – so‐called blue ice areas (BIAs) – from the Patriot Hills in the Ellsworth Mountains to derive the first deuterium isotope record (δD) from continental Antarctica south of the Weddell Sea. Gas analysis and glaciological considerations provide a first relative chronology. Inferred temperature trends from the Patriot Hills BIA and snow pit suggest changing climate influences during the transition between the last glacial period and Holocene. Under modern conditions, the interplay between the Antarctic high‐pressure system and the Southern Annular Mode appears to play a significant role in controlling katabatic wind flow over the site while the BIA record suggests that greater sea ice extent during the last glacial period was a major control. Our results demonstrate the considerable potential of the Patriot Hills site for reconstructing past climate change in the south Atlantic region.

Periglacial features in Patriot Hills, Ellsworth Mountains, Antarctica

This work describes periglacial features identified at Patriot Hills, at the southernmost part of Ellsworth Mountains, Antarctica, during the 2008/2009 Brazilian Antarctic Expedition, and discusses their morphogenetic environment. Identified periglacial features were classified into: (a) rock glacier-like landform; (b) slightly creeping debris-mantled slopes; (c) steep debris-mantled slopes; and (d) rock falls. Results obtained from sediment sample analysis suggest activity and passive movement of a rock glacier-like landform, albeit minimal. Wind seems to play an important role in Patriot Hills local geomorphology. Periglacial features such as slightly creeping debris-mantled slope appear to have preferred slope orientation. They are commonly found onto slopes where the katabatic wind flows down. Slopewash and groundwater movement processes may be limited or non-existent since most snow disappears through sublimation

Sub-ice topography in Patriot Hills, West Antarctica: first results of a newly developed high-resolution FM-CW radar system

AbstractWe present a newly developed high-resolution frequency-modulated continuous-wave (FMCW) radar system for sounding the sub-ice topography. The system, working in the frequency range from 200 to 400 MHz, was developed to measure thickness and internal layers in cold ice with a resolution better than 1 m. This system has the potential to measure accumulation rates, an important input for improved knowledge of the mass balance of polar ice sheets. First measurements for the test, calibration and optimization of the new ice sounder were made in December 2005 near the Ellsworth Mountains, specifically in Patriot Hills, West Antarctica, at 80°18′ S, 81°22′ W. The complete radar system was installed on a ski-mounted support frame, and towed by hand across the ice surface. The measurement results show the capability of this system to measure ice thickness up to 1000 m and to define internal layers within the ice body.

Reassessment of ice mass balance at Horseshoe Valley, Antarctica

AbstractHorseshoe Valley (80°18′S, 81°22′W) is a 30 km wide glaciated valley at the south-eastern end of Ellsworth Mountains draining into the Hercules inlet, Ronne Ice Shelf. The ice at Horseshoe Valley has been considered stable; now we use Global Positioning System (GPS) measurements obtained between 1996 and 2006 to investigate ice elevation change and mass balance. Comparison of surface heights on a profile across Horseshoe Valley reveals a slight but significant elevation increase of 0.04 m a-1 ± 0.002 m a-1. The blue ice area of Patriot Hills (∼13 km2) at the mount of Horseshoe Valley shows large interannual variability in area, with a maximum extent in 1997, an exceptionally warm summer, but no clear multi-year trend, and an elevation increase of 0.05 m a-1 in eight years, which agrees with the result from Horseshoe Valley.

Elevation change and ice flow at Horseshoe Valley, Patriot Hills, West Antarctica

AbstractPatriot Hills is located at 80˚18’ S, 81˚22’W, at the southernmost end of the Heritage Range, Ellsworth Mountains, West Antarctica. A comparison of glacier elevation data and ice velocities obtained by the differential global positioning system in the period 1996–97 is presented. Ablation/accumulation rates measured at a network of stakes in Horseshoe Valley show average accumulation of 70 kg m–2 a–1 in the central part of the valley, and a maximum ablation of ∼170 kg m–2 a–1 at the edge of the blue-ice area, close to Patriot Hills. Changes in the surface elevation of the glacier measured at 81 stakes in the period 1995–97 show a mean thickening of +0.43±0.42ma–1, which, considering the uncertainties, indicates that the ice sheet around Patriot Hills is in near steady state. Surface velocities, in combination with ice thicknesses obtained by ground-based radio-echo sounding, are used to compute the ice flux across the Horseshoe Valley transect. A total outflow of 0.44 ±0.08km3 a–1 is obtained. Considering a catchment area for Horseshoe Valley of 1087 km2 upstream from the flow transect, and a net accumulation rate of 100 kg m–2 a–1, a total input of 0.11 ±0.04km3 a–1 by snow accumulation is obtained. Accepting a near-equilibrium condition for the ice sheet, the flux difference, i.e. 0.33 km3 a–1, must be supplied by flow from the inland ice sheet through ice cliffs located in mountain gaps in the Heritage Range. If Horseshoe Valley is not in steady state but is thickening, the positive mass balance could be due to increased snow accumulation or enhanced ice flow from the interior of the ice sheet. New data are needed to elucidate this.

Qualitative evaluation of computer vision algorithms in polar terrains

We address the issue of Computer Vision in Antarctica for robot navigation by analysing images collected at Patriot Hills, Antarctica in the Fall of 1998. Conditions produced by polar weather and terrain are unique and challenging for perception equipment and computer vision algorithms. The later aspect will be studied here through the evaluation of a colour segmentation algorithm, a stereo vision algorithm and a feature points detector and tracker algorithm.

Temperature distribution around polar habitation modules buried in ice: numerical modelling

This work presents a numerical model based on the finite volume approach to predict the ice temperature distribution around buried habitation modules in cold regions, such as Patriot Hills in the Antarctic continent. The model allows for the prediction of the possible melting of the ice surrounding the module, which stems from the heat load generated inside it to ensure the specified comfort conditions. Analytical equations for the atmospheric temperature variation, T ∞ (t), and for the ice temperature distribution without the habitation module, T(x,t), based on monthly averaged experimental data, are obtained and used in the present work to specify the boundary conditions and the initial condition required for the numerical solution of the governing energy equation. Such equations are, respectively, T ∞ (t)=−22.37+8.83 cos(0.524 t)+3.92 sin(0.524 t) and T(x,t)=−22.37+ e −0.296 x [8.73 cos(0.524 t−0.296 x)+3.96 sin(0.524 t−0.296 x)]. The convection heat transfer coefficient, h, between the ice surface and the atmosphere is h=38.6 W/m 2K. The model is applied to the ice volume surrounding a cylindrical module ( r=2 m, H=2 m), with the walls composed of two layers: a 4-cm thick layer of insulation (polyurethane) and 1 cm of a structural reinforcement layer (glass fibre). The results show that for the conditions simulated herein, that is, for the heat load required to ensure a comfort temperature of 15°C inside the module, the ice temperature everywhere is kept far below its melting point.

Mass balance of the Antarctic ice sheet at Patriot Hills

Glaciological data collected at Patriot Hills, Antarctica (80°18'S, 81°22'W), are used to assess the local mass balance of the ice sheet. The data were collected during two field campaigns conducted by the Instituto Antartico Chileno in January and November 1995. Measurements included surveying of stakes, and ice thickness derived from discrete radar soundings with a ground-based high-frequency impulse system. Ablation occurred on the bare-ice field at the base of Patriot Hills, with a maximum value of 7g cm −2a−1. Net accumulation was detected away from the mountains, over the firn-covered area of the glacier, with a maximum rate of 10 g cm 2 a−1 Ice thickens rapidly away from the mountains, reaching a thickness of 383 m, the maximum range of the radar system, near the center of the blue-ice field. No significant difference in surface elevation of the ice was detected over the 305 d period, which indicates that the ice is in near-equilibrium at Patriot Hills.

Ionic Constituents in Surface Snow Samples Obtained by ANTARCTIC WALK EXPEDITION, Summer of 1992/93.

Surface snows were daily sampled by a traverse team of Antarctic Walk Expedition from Patriot Hills (80°21'S, 81°36'W) west Antarctica, to South Pole (ca. 1,080 km away) between November 1992 and January 1993. To study spatial- and temporal-variations in snow chemistry, surface and fallen snow samples were also taken daily at a base camp near Patriot Hills for the same period of the traverse trip. Sea-salts components (Na + , Cl - and Mg 2+ ) showed constantly lower concentration levels in higher inland and southern locations. Spatial variations of methanesulfonate (MSA) and SO 4 2- concentration levels showed nearly parallel and similar variations to sea-salts profiles but were still variable at inland locations. A comparison between the base camp and the traverse data set suggested an unique sourcetransportation process for NO 3 - in higher inland of Antarctica.