International Trans-Antarctic Scientific Expedition Research Articles

A PPP kinematic application on historical GPS data: the reprocessing of the ITASE98-99 Antarctica mission height profiles

The analysis of altimetric profiles in Antarctica and their evolution over the years is a sensitive topic for the scientific community since it helps understand the effects of climate change that the continent undergoes. Different geomatic techniques, including the GNSS technology, can be employed to obtain altimetric profiles. However, the GNSS differenced approaches, such as the Post Processing Kinematic, are hardly usable to define long profiles in Antarctica because of the low number of CORS stations. In these conditions, the Precise Point Positioning (PPP) approach is a valid alternative to avoid processing very long baselines. The aim of this article is to define a standard procedure for the processing of historical GPS data, thanks to the availability of a dataset from the International Trans-Antarctic Scientific Expedition, which took place between 1998 and 1999 (ITASE98-99). This expedition focused on mapping the Antarctic territory, subdividing it by nations of influence, using geophysical and geodetic technologies, including GPS. The altimetric profiles had already been calculated in 2002 by the Geomatics group of the University of Bologna using the Gipsy-OASIS II software. In this work, the new version of the JPL software, GipsyX, is used to apply the newly implemented models and reprocessed products. The calibration of the processing parameters leading to the final PPP solution is described in the paper, including details on the implementation of a post-processing filtering procedure. The average a posteriori elevation error is 4.6 cm, while 99% of them are within 27 cm. The comparison of the new results to both the previous processing and the REMA elevation model shown that about double the number of solutions are now available, meter-level elevation spikes have been avoided, and a half meter bias is now reduced to a few centimeters. Given the almost 15 years difference between the 1999.0 expedition epoch and the REMA reference epoch, the obtained results can be used to study accumulation/erosion effects on the Antarctica ice sheet.

Megadunes in Antarctica: migration and characterization from remote and in situ observations

Abstract. Megadunes are peculiar features formed by the interaction between the atmosphere and cryosphere and are known to be present only on the East Antarctic Plateau and other planets (Mars and Pluto). In this study, we have analysed the glaciological dynamic of megadunes, their spectral properties and morphology on two sample areas of the East Antarctic Plateau where in the past international field activities were carried out (EAIIST, East Antarctic International Ice Sheet Traverse; It-ITASE, Italian International Trans-Antarctic Scientific Expedition). Using satellite images spanning 7 years, we analysed the spatial and temporal variability in megadune surface characteristics, i.e. near-infrared (NIR) albedo, thermal brightness temperature (BT) and slope along the prevailing wind direction (SPWD), useful for mapping them. These parameters allowed us to characterize and perform an automated detection of the glazed surfaces, and we determined the influence of the SPWD by evaluating different combinations of these parameters. The inclusion of the SPWD significantly increased the accuracy of the method, doubling it in certain analysed scenes. Using remote and field observations, for the first time we surveyed all the components of upwind migration (absolute, sedimentological and ice flow), finding an absolute value of about 10 m a−1. The analysis shows that the migration is driven by the snow accumulation on the crest and trough prograding upwind on the previous windward flanks characterized by glazed surface. Our results present significant implications for the surface mass balance estimation, paleo-climate reconstruction using ice cores, and the measurements using optical and radar images/data in the megadune areas.

Seasonal climate information preserved in West Antarctic ice core water isotopes: relationships to temperature, large-scale circulation, and sea ice

As part of the United States' contribution to the International Trans-Antarctic Scientific Expedition (ITASE), a network of precisely dated and highly resolved ice cores was retrieved from West Antarctica. The ITASE dataset provides a unique record of spatial and temporal variations of stable water isotopes (d 18 O and dD) across West Antarctica. We demonstrate that, after accounting for water vapor diffusion, seasonal information can be suc- cessfully extracted from the ITASE cores. We use meteo- rological reanalysis, weather station, and sea ice data to assess the role of temperature, sea ice, and the state of the large-scale atmospheric circulation in controlling seasonal average water isotope variations in West Antarctica. The strongest relationships for all variables are found in the cores on and west of the West Antarctic Ice Sheet Divide and during austral fall. During this season positive isotope anomalies in the westernmost ITASE cores are strongly related to a positive pressure anomaly over West Antarctica, low sea ice concentrations in the Ross and Amundsen Seas, and above normal temperatures. Analyses suggest that this seasonally distinct climate signal is due to the pronounced meridional oriented circulation and its linkage to enhanced sea ice variations in the adjacent Southern Ocean during fall, both of which also influence local to regional temperatures.

An emerging technique: multi-ice-core multi-parameter correlations with Antarctic sea-ice extent

AbstractUsing results stemming from the International Trans-Antarctic Scientific Expedition (ITASE) ice-core array plus data from ice cores from the South Pole and Siple Dome we investigate the use of sodium (Na+), non-sea-salt sulfate (nssSO42–) and methylsulfonate (MS–) as proxies for Antarctic sea-ice extent (SIE). Maximum and mean annual chemistry concentrations for these three species correlate significantly with maximum, mean and minimum annual SIE, offering more information and clarification than single ice-core and single species approaches. Significant correlations greater than 90% exist between Na+ and maximum SIE; nssSO42– with minimum and mean SIE; and MS– with mean SIE. Correlations with SIE within large geographic regions are in the same direction for all ice-core sites for Na+ and nssSO42– but not MS–. All ice cores display an SIE correlation with nssSO42– and MS–, but not all correlate with Na+. This multi-core multi-parameter study provides the initial step in determining which chemical species can be used reliably and in which regions as a building block for embedding other ice-core records. Once established, the resulting temporal and spatial matrix can be used to relate ice extents, atmospheric patterns, biological productivity and site conditions.

Advanced microstructural characterization of four East Antarctic firn/ice cores

AbstractThe microstructures and microchemistry of four US International Trans-Antarctic Scientific Expedition ice cores were examined, at three depths (30, 60, 90 m) each, using scanning electron microscopy, including electron backscattered patterns and energy-dispersive spectroscopy (EDS), in order to assess the relationship between chemical and physical properties. The physical characteristics (grain size, porosity, density, internal surface volume, and crystallographic orientation) at the four sites were inhomogeneous, as expected on the basis of differences in the moisture content of deposited snow and the accumulation rate at their respective locations. Evidence of shallow subgrain boundary formation and trends in internal surface volume, having implications for the study of firn densification and ice-sheet modeling, were also found. Chemical characterization revealed that site-specific variations in particulate concentration and source could accurately be determined using EDS analysis. It was also found that the combination of elements predominant within the sample controls the morphology and microstructural location of the impurities.

GPR and GPS data integration: examples of application in Antarctica

Ground Penetrating Radar (GPR) and Global Positioning System (GPS) techniques were employed in snow accumulation studies during the Italian leg of the International Trans-Antarctic Scientific Expedition (ITASE). The acquired data were useful both for glaciological and climatological studies. This paper presents some results obtained by GPR and GPS data integration employed to determine accumulation/ablation processes along the profile of the traverse that show how the snow-sublayer thickness can vary quickly in just a few kilometres. Some examples of data integration employed in detection and characterisation of buried crevasses are also presented.

Variability in the teleconnection between the El Niño–Southern Oscillation and West Antarctic climate deduced from West Antarctic ice core isotope records

The U.S. contribution to the International Trans‐Antarctic Scientific Expedition (ITASE) program obtained several ice cores from the West Antarctic Ice Sheet. Because of proximity to the Pacific Ocean, the West Antarctic ice cores are expected to have an El Niño–Southern Oscillation (ENSO) signature. The ITASE 2001‐5 core δ18O isotope was selected for detailed analysis here because its location, high annual accumulation, and record length make it an ideal candidate for capturing the effects of regional circulation anomalies in the isotopic composition. The 2001‐5 core is compared to two other cores, the 2001‐2 and 2001‐3 cores, which are further west and therefore capture some spatial variability of the regional circulation on various time scales. Analysis shows that several phenomena, including ENSO, leave a signature in the ice cores. Evidence suggests that ENSO signals in the ice cores are significantly modulated by low‐frequency variability. Correlation with the Southern Annular Mode (SAM), global temperature, Pacific Decadal Oscillation, and ENSO shows that temperature and ENSO generally appear to have the strongest influence on the 2001‐5 isotope signal while there is no clearly dominant single influence in the other cores. Results suggest that the teleconnection between ENSO and the 2001‐5 core is quite dependent on the state of the SAM. Specifically, when the Southern Oscillation Index (SOI) and SAM are in phase, there is an ENSO related pressure anomaly west of the Antarctic Peninsula, in the vicinity of the ice cores studied. This extends previous findings to span the entire 20th century.

An up‐to‐date quality‐controlled surface mass balance data set for the 90°–180°E Antarctica sector and 1950–2005 period

On the basis of thousands of surface mass balance (SMB) field measurements over the entire Antarctic ice sheet it is currently estimated that more than 2 Gt of ice accumulate each year at the surface of Antarctica. However, these estimates suffer from large uncertainties. Various problems affect Antarctic SMB measurements, in particular, limited or unwarranted spatial and temporal representativeness, measurement inaccuracy, and lack of quality control. We define quality criteria on the basis of (1) an up‐to‐date review and quality rating of the various SMB measurement methods and (2) essential information (location, dates of measurements, time period covered by the SMB values, and primary data sources) related to each SMB data. We apply these criteria to available SMB values from Queen Mary to Victoria lands (90°–180°E Antarctic sector) from the early 1950s to present. This results in a new set of observed SMB values for the 1950–2005 time period with strong reduction in density and coverage but also expectedly reduced inaccuracies and uncertainties compared to other compilations. The quality‐controlled SMB data set also contains new results from recent field campaigns (International Trans‐Antarctic Scientific Expedition (ITASE), Russian Antarctic Expedition (RAE), and Australian National Antarctic Research Expeditions (ANARE) projects) which comply with the defined quality criteria. A comparative evaluation of climate model results against the quality‐controlled updated SMB data set and other widely used ones illustrates that such Antarctic SMB studies are significantly affected by the quality of field SMB values used as reference.

Volatile chlorinated hydrocarbons in antarctic superficial snow sampled during Italian ITASE expeditions

In order to detect the presence of some volatile chlorinated hydrocarbons (VCHCs) and to understand their transport and deposition mechanism, superficial snow was sampled during two Italian ITASE (International Trans Antarctic Scientific Expedition) expeditions: the first traverse was carried out in 1998/1999 from Terra Nova Bay to Dome Concordia; the second traverse was carried out in 2001/2002 through Adélie, George V, Oates and Northern Victoria Lands. Some VCHCs (chloroform; 1,1,1-trichloroethane; tetrachloromethane; 1,1,2-trichloroethylene; tetrachloroethylene) were analysed using a highly sensitive and selective hyphenated technique composed of a purge-and-trap injector coupled to a gas chromatograph with a mass spectrometric detector (PTI-GC-MS) operating in SIM mode. Investigated VCHCs were present in all analysed snow samples with concentration levels of several units, tens, or sometimes hundreds of ng kg(-1). VCHC snow concentration levels remained approximately constant with changing distance from the coast and the comparison between fresh and aged snow did not show any substantial differences; on the basis of this evidence marine aerosol and dry deposition may be rejected as principal VCHC transport and deposition mechanism hypotheses. VCHC concentration levels in Antarctic snow samples were comparable to or greater than those found in snow from temperate zones.

The International Trans-Antarctic Scientific Expedition (ITASE): an overview

AbstractFrom its original formulation in 1990 the International Trans-Antarctic Scientific Expedition (ITASE) has had as its primary aim the collection and interpretation of a continent-wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations. ITASE offers the ground-based opportunities of traditional-style traverse travel coupled with the modern technology of GPS, crevasse detecting radar, satellite communications and multidisciplinary research. By operating predominantly in the mode of an oversnow traverse, ITASE offers scientists the opportunity to experience the dynamic range of the Antarctic environment. ITASE also offers an important interactive venue for research similar to that afforded by oceanographic research vessels and large polar field camps, without the cost of the former or the lack of mobility of the latter. More importantly, the combination of disciplines represented by ITASE provides a unique, multidimensional (space and time) view of the ice sheet and its history. ITASE has now collected >20 000km of snow radar, recovered more than 240 firn/ice cores (total length 7000 m), remotely penetrated to ~4000m into the ice sheet, and sampled the atmosphere to heights of >20 km.

Snow chemistry across Antarctica

AbstractAn updated compilation of published and new data of major-ion (Ca, Cl, K, Mg, Na, NO3, SO4) and methylsulfonate (MS) concentrations in snow from 520 Antarctic sites is provided by the national ITASE (International Trans-Antarctic Scientific Expedition) programmes of Australia, Brazil, China, Germany, Italy, Japan, Korea, New Zealand, Norway, the United Kingdom, the United States and the national Antarctic programme of Finland. The comparison shows that snow chemistry concentrations vary by up to four orders of magnitude across Antarctica and exhibit distinct geographical patterns. The Antarctic-wide comparison of glaciochemical records provides a unique opportunity to improve our understanding of the fundamental factors that ultimately control the chemistry of snow or ice samples. This paper aims to initiate data compilation and administration in order to provide a framework for facilitation of Antarctic-wide snow chemistry discussions across all ITASE nations and other contributing groups. The data are made available through the ITASE web page (http://www2.umaine.edu/itase/content/syngroups/snowchem.html) and will be updated with new data as they are provided. In addition, recommendations for future research efforts are summarized.

A 200 year sulfate record from 16 Antarctic ice cores and associations with Southern Ocean sea-ice extent

AbstractChemistry data from 16, 50–115m deep, sub-annually dated ice cores are used to investigate spatial and temporal concentration variability of sea-salt (ss) SO42– and excess (xs) SO42– over West Antarctica and the South Pole for the last 200 years. Low-elevation ice-core sites in western West Antarctica contain higher concentrations of SO42– as a result of cyclogenesis over the Ross Ice Shelf and proximity to the Ross Sea Polynya. Linear correlation analysis of 15 West Antarctic ice-core SO42– time series demonstrates that at several sites concentrations of ssSO42– are higher when sea-ice extent (SIE) is greater, and the inverse for xsSO42–. Concentrations of xsSO42– from the South Pole site (East Antarctica) are associated with SIE from the Weddell region, and West Antarctic xsSO42– concentrations are associated with SIE from the Bellingshausen–Amundsen–Ross region. The only notable rise of the last 200 years in xsSO42–, around 1940, is not related to SIE fluctuations and is most likely a result of increased xsSO42– production in the mid–low latitudes and/or an increase in transport efficiency from the mid–low latitudes to central West Antarctica. These high-resolution records show that the source types and source areas of ssSO42– and xsSO42– delivered to eastern and western West Antarctica and the South Pole differ from site to site but can best be resolved using records from spatial ice-core arrays such as the International Trans-Antarctic Scientific Expedition (ITASE).

Solar forcing of the polar atmosphere

AbstractWe present highly resolved, annually dated, calibrated proxies for atmospheric circulation from several Antarctic ice cores (ITASE (International Trans-Antarctic Scientific Expedition), Siple Dome, Law Dome) that reveal decadal-scale associations with a South Pole ice-core 10Be proxy for solar variability over the last 600 years and annual-scale associations with solar variability since AD 1720. We show that increased (decreased) solar irradiance is associated with increased (decreased) zonal wind strength near the edge of the Antarctic polar vortex. The association is particularly strong in the Indian and Pacific Oceans and as such may contribute to understanding climate forcing that controls drought in Australia and other Southern Hemisphere climate events. We also include evidence suggestive of solar forcing of atmospheric circulation near the edge of the Arctic polar vortex based on ice-core records from Mount Logan, Yukon Territory, Canada, and both central and south Greenland as enticement for future investigations. Our identification of solar forcing of the polar atmosphere and its impact on lower latitudes offers a mechanism for better understanding modern climate variability and potentially the initiation of abrupt climate-change events that operate on decadal and faster scales.

Bedrock topography and wind erosion sites in East Antarctica: observations from the 2002 US-ITASE traverse

AbstractIce stratigraphy from deep-penetrating radar data collected during the 2002 US International Trans-Antarctic Scientific Expedition (US-ITASE) traverse shows evidence of a significant erosion surface and drift-filled basin related to a previously undiscovered 1400m subglacial mountain between Hercules Dome (87˚420 S, 108˚ W) and South Pole. The 3MHz radar profile crosses three subglacial mountains at approximately 458 to the ice-flow direction. Cross-cutting reflectors in the top 500m of ice stratigraphy are interpreted as angular unconformities resulting from wind erosion as the ice deforms over the mountain tops. The unconformities correlate locally with zones of high RADARSAT reflectivity. Several nearby sites with similar relatively high RADARSAT reflectivity adjacent to the traverse indicate that active wind erosion may be taking place at these locations as well. Based on the local correlation between surface wind scour and subglacial topography, we interpret the nearby cluster of bright RADARSAT reflectivity to indicate the presence of a small range of subglacial mountains. The ability to trace isochronal stratigraphy, associated with scour sites using shallow and deep radar, to nearby dated ice cores presents the possibility of exploiting wind-scour zones to access well-dated older ice with shallow-coring equipment.

Simulation of the net snow accumulation along the Wilkes Land transect, Antarctica, with a regional climate model

AbstractRegional climate modelling in conjunction with accumulation measurements collected on Antarctic traverses of the International Trans-Antarctic Scientific Expedition (ITASE) is presented as a tool for extending the spatial coverage of field measurements. The modelling of part of East Antarctica spanned the 7 year epoch 1980–86 where data covering the same period are available. The agreement between simulation and observation is improved when a parameterization of the snow surface redistribution processes, such as wind erosion, is included in the regional climate model. The modelled spatial distribution of the net snow mass transported in the boundary layer over coastal East Antarctica indicates that this mass is a significant component of the surface mass balance.

Sources and transport pathways of marine aerosol species into West Antarctica

AbstractSixteen high-resolution marine aerosol (Na+, SO42–) records from spatially distributed International Trans-Antarctic Scientific Expedition (ITASE) ice cores spanning the last ~200 years from the Pine Island–Thwaites and Ross drainage systems and the South Pole are used to examine sources (sea spray and frost flowers) and transport pathways of marine aerosols into West Antarctica. Factors contributing to the amount of marine aerosols transported inland include sea-ice extent, the presence of open-water features (polynyas, leads), wind strength and direction, and the strength and positioning of low-pressure systems. Analysis of SO42–/Na+ ratios indicates that frost flowers can contribute significantly (40%) to the Na+ budget of Antarctic ice cores. Higher Na+ concentrations in the Ross drainage system may result from greater production of marine aerosols related to frost flowers in the Ross Sea region in association with greater sea-ice extent and larger open-water areas. Significant positive correlations of sea-ice extent and the Na+ time series exist in some regions of West Antarctica. Higher wind speeds in winter and higher Na+ concentrations when sea-level pressure is lower indicate that intensified atmospheric circulation enhances transport and production of marine aerosols.

A time marker at 17.5 kyr BP detected throughout West Antarctica

AbstractDeep radar soundings as part of the International Trans-Antarctic Scientific Expedition (US-ITASE) traverses in West Antarctica have revealed a bright internal reflector that we have imaged throughout widespread locations across the ice sheet. The layer is seen in traverses emanating from Byrd Station in four directions and has been traced continuously for distances of 535km toward the Weddell Sea drainage, 500km toward South Pole, 150km toward the Executive Committee Range and 160km toward Kamb Ice Stream (former Ice Stream C). The approximate area encompassed by the layer identified in these studies is 250 000km2. If the layer identification can also be extended to Siple Dome where we have additional radar soundings (Jacobel and others, 2000), the approximate area covered would increase by 50%. In many locations echo strength from the layer rivals the bed echo in amplitude even though it generally lies at a depth greater than half the ice thickness. At Byrd Station, where the layer depth is 1260 m, an age of ~17.5 kyr BP has been assigned based on the Blunier and Brook (2001) chronology. Hammer and others (1997) note that the acidity at this depth is >20 times the amplitude of any other part of the core. The depiction of this strong and widespread dated isochrone provides a unique time marker for much of the ice in West Antarctica. We apply a layer-tracing technique to infer the depth–time scale at the inland West Antarctic ice sheet divide and use this in a simple model to estimate the average accumulation rate.

High-resolution ice cores from US ITASE (West Antarctica): development and validation of chronologies and determination of precision and accuracy

AbstractShallow ice cores were obtained from widely distributed sites across the West Antarctic ice sheet, as part of the United States portion of the International Trans-Antarctic Scientific Expedition (US ITASE) program. The US ITASE cores have been dated by annual-layer counting, primarily through the identification of summer peaks in non-sea-salt sulfate (nssSO42–) concentration. Absolute dating accuracy of better than 2 years and relative dating accuracy better than 1 year is demonstrated by the identification of multiple volcanic marker horizons in each of the cores, Tambora, Indonesia (1815), being the most prominent. Independent validation is provided by the tracing of isochronal layers from site to site using high-frequency ice-penetrating radar observations, and by the timing of mid-winter warming events in stable-isotope ratios, which demonstrate significantly better than 1 year accuracy in the last 20 years. Dating precision to ±1 month is demonstrated by the occurrence of summer nitrate peaks and stable-isotope ratios in phase with nssSO42–, and winter-time sea-salt peaks out of phase, with phase variation of <1 month. Dating precision and accuracy are uniform with depth, for at least the last 100 years.

High-resolution ice-core stable-isotopic records from Antarctica: towards interannual climate reconstruction

AbstractIce-core records are a key resource for reconstructing Antarctic climate. However, a number of physical processes preclude the simple interpretation of ice-core properties such as oxygen isotopic ratios in terms of climate variables like temperature or sea-level pressure. We show that well-dated, sub-annually resolved stable-isotopic records from the United States International Trans-Antarctic Scientific Expedition (US-ITASE) traverses and other sources have a high correlation with local seasonal temperature variation. However, this temporal relationship cannot be simply extended to quantitative interannual resolution reconstructions of site temperature. We suggest that a consistent and important target for ice-core calibrations is a composite of annual mean temperature records from Antarctic weather stations, which covaries strongly with the dominant mode (from principal component analysis) of temperature variability in the Antarctic. Significant correlations with this temperature index are found with individual ice-core records, with a composite of the ice cores, and through a multiple linear regression model with the ice cores as predictors. These results imply that isotopic signals, like the instrumental temperature mode itself, have a strong response to large-scale atmospheric circulation variability, which in the Antarctic region is dominated by the Southern Annular Mode.

PAGES: Always bottom up

In a recent article titled “Back to the Future” (Eos, 16 March, p. 107), L. C. Witton lays out the goals of IGBP‐PAGES for the next few years, noting that, “PAGES is aiming to become a truly bottom‐up organization that is driven by the insights of individual scientists…”In fact, PAGES has always been a truly bottom‐up organization, and this statement unfortunately fosters the view that it has been otherwise. Those who promote such a view choose to overlook the countless workshops that PAGES has organized, largely at the suggestion of those “at the bottom,” and the numerous publications that have resulted from these meetings. These include reports and recommendations on inter alia: IDEAL—An International Decade for the East African Lakes, the PAGES/CLIVAR Intersection, High Resolution Records of Past Climate from Monsoon Asia, Paleomonsoons in Africa, IMAGES—International Marine Global Change Study, PANASH‐Paleoclimates of the Northern and Southern Hemispheres, GNIP—Global Network for Isotopes in Precipitation, Continental Drilling for Paleoclimate Records, Climate Impact of Explosive Volcanism, International Trans‐Antarctic Scientific Expedition (ITASE), ARTS—Annual Records of Tropical Systems and the Paleoclimate Modelling Intercomparison Project (PMIP) (see http://www.pages.unibe.ch).