The broad aim of the International Trans-Antarctic Scientific Expedition (ITASE) is to establish how the modern atmospheric environment (climate and atmospheric composition) is represented in the upper layers of the Antarctic ice sheet. Primary emphasis is placed on the last ~200 years of the record, although some ITASE records encompass the last 1000 years. A ~200 year time period was chosen for study because it is relatively simple to recover many ice cores covering this interval using oversnow traverse logistics, and also to develop a spatial network of cores valuable in understanding geographically constrained differences in climate over Antarctica. Further, this time period covers the onset of major anthropogenic involvement in the atmosphere and the immediate pre-anthropogenic atmosphere.
ITASE was conceived in 1990 and endorsed by the Scientific Committee on Antarctic Research (SCAR) Working Group on Glaciology and approved by the XXII SCAR Delegates at Bariloche, Argentina, in 1992. ITASE was endorsed as a core program of SCAR-GLOCHANT (Global Change and the Antarctic) in 1996. It was formally approved and adopted by the IGBP PAGES (International Geosphere– Biosphere Program Past Global Changes) as a core project within Focus II on Antarctic Paleoenvironments. It also forms a contribution to the IGBP International Global Atmospheric Chemistry (IGAC) core project under their focus on Polar Air Snow Chemistry (PASC). As of XXVII SCAR in Shanghai, China, in 2002, 19 nations are involved in ITASE (Argentina, Australia, Belgium, Brazil, Canada, China, France, Germany, India, Italy, Japan, Netherlands, New Zealand, Norway, Russia, South Korea, Sweden, United Kingdom, United States).
For details concerning national programs, the ITASE Science and Implementation Plan (Reference Liu, Jezek and LiMayewski, 1996) and other ITASE information, refer to the SCAR Project Office maintained at the Climate Change Institute, University of Maine (http://www2.umaine.edu/itase/).
Antarctica plays a critical role in the dynamic linkages that couple the spatially and temporally complex components of the Earth system (atmosphere, biosphere, anthrosphere, hydrosphere, cryosphere, lithosphere and cosmogenic input). However, our knowledge of the functioning of Antarctica within the global system and the spatial and temporal complexity of Antarctic climate is poor, largely due to the limitations and the short period (typically 30–50 years) of observational and instrumental data on Antarctic climatic variables. Further, Antarctica exhibits significant regional contrasts, including decoupling of climate change on decadal scales between different parts of the continent. Large areas of the interior of the ice sheet are influenced by the continental temperature inversion, while other portions of the interior and the coastal regions are influenced by the incursion of cyclonic systems that circle the continent. As a consequence, these coastal regions are mainly connected with lower-tropospheric transport, whereas high-altitude regions in the interior are more likely influenced by vertical transport from the upper troposphere and stratosphere. As a result, the coastal regions experience higher climatic variability than regions in the interior. Further, high-frequency climatic changes impact both Antarctica and the surrounding Southern Ocean. Some may be related to the El Niño– Southern Oscillation (ENSO) and other local- to regional- to global-scale climate features such as atmospheric blocking, sea-ice variations and volcanic-event-induced atmospheric shielding. Over time periods longer than the instrumental era, ice-core studies demonstrate that Antarctica experienced millennial- to decadal-scale climatic variability which is associated with significant changes in temperature, snow accumulation, wind-blown dust, sea-salt loading and methane composition.
ITASE is focused to address two key scientific objectives:
What is the spatial and temporal variability of Antarctic climate (e.g. extreme events, regional to global atmospheric phenomena, and snow accumulation variations) over the last 200–1000 years?
What are the environmental changes (e.g. sea-ice variation, ocean productivity, anthropogenic activity, volcanic activity) impacting Antarctica over the last 200–1000 years?
ITASE has, since its inception in 1990, sampled an extensive portion of the Antarctic ice sheet, including many of the proposed deep ice-core drilling sites and much of the topography and climate of the Antarctic ice sheet (Fig. 1). To date, ITASE research has resulted in the collection of more than 240 cores (for a total length of ~7000 m), greatly expanding the pre-ITASE ice-core inventory over Antarctica (Fig. 2), and >20 000km of associated ground-penetrating radar (GPR) coverage. Several properties were identified as part of the original ITASE sampling program, notably: isotopes, major anions and cations, trace elements, hydrogen peroxide (H2O2), formaldehyde (HCHO), organic acids, 10m temperatures, stratigraphy, and GPR–GPS (global positioning system). Additionally, traverses have provided opportunities for the installation of automatic weather stations, and the measurement of, for example, atmospheric chemistry, ice dielectric and ice-core microparticles plus the deployment of experiments valuable for ground truth in remote-sensing missions and geophysical measurements for crustal investigation (Ferracioli and others, 2001). In sum, ITASE has developed into a highly multi- and interdisciplinary activity (Fig. 3).
To fulfill its objectives, ITASE is producing local- to regional- to continental-scale maps of past climate and environment, elucidating transfer functions between atmosphere/snow/ice, providing observational data for climate models, and both utilizing and validating satellite and ground-based remote sensing.
Overview Of Itase Results
Although full-scale reconstructions of past climate over Antarctica have yet to be finalized, ITASE has pioneered calibration tools and reconstruction of climate indices and evidence for climate forcing using single sites through to multiple arrays of sites. Initial syntheses of combined ITASE and deep ice-core records demonstrate that inclusion of instrumentally calibrated ITASE ice-core records allows previously unavailable reconstruction of past regional- to continental-scale variability in atmospheric circulation and temperature (Reference Magand, Frezzotti, Pourchet, Stenni, Genoni and FilyMayewski and others, 2004). Emerging results demonstrate the utilization of ITASE records in testing meteorological re-analysis products. Connections are now noted between ITASE climate proxies and global-scale climate indices such as ENSO (Reference MayewskiMeyerson and others, 2002; Reference Bertler, Barrett, Mayewski, Fogt, Kreutz and ShulmeisterBertler and others, 2004) in addition to major atmospheric circulation features over the Southern Hemisphere such as the Amundsen Sea low, East Antarctic high and Antarctic Oscillation (Reference Kaspari, Mayewski, Dixon, Sneed and HandleyKreutz and others, 2000; Reference Meyerson, Mayewski, Kreutz, Meeker, Whitlow and TwicklerProposito and others, 2002; Reference Schneider, Steig and van OmmenSouney and others, 2002; Reference Goodwin, De Angelis, Pook and YoungGoodwin and others, 2003b; Reference BecagliBecagli and others, 2004; Reference Ekaykin, Lipenkov, Kuz’mina, Petit, Masson-Delmotte and JohnsenEkaykin and others, 2004; Reference WhillansXiao and others, 2004; Reference JezekKaspari and others, 2005; Reference Wolff and BalesYan and others, 2005; Reference Schneider and SteigShulmeister and others, 2006). Ice-core nitrate concentrations have been used to reconstruct regional climate patterns associated with high-pressure ridging over Wilkes Land, East Antarctica (Reference Goodwin, De Angelis, Pook and YoungGoodwin and others, 2003b). Large-scale calibrations between satellite-deduced surface temperature and ITASE ice-core proxies for temperature are also now available (Reference Rotschky, Eisen, Wilhelms, Nixdorf and OerterSchneider and others, 2005). ITASE is developing proxies for sea ice, a critical component in the climate system, through studies of sulfur compounds such as sulfate and methanesulfonate (MSA) (Reference Van Ommen and MorganWelch and others, 1993; Reference Curran, van Ommen, Morgan, Phillips and PalmerCurran and others, 2003; Reference DixonDixon and others, 2005). ENSO–sea-ice connections are noted utilizing ice-core MSA and sulfate series over the Ross Sea embayment region (Reference MayewskiMeyerson and others, 2002; Reference BecagliBecagli and others, 2005). Partitioning of the sources of sulfate is being undertaken through the examination of sulfur isotopes as an aid to further refining air-mass trajectory fingerprinting and the sulfur cycle over Antarctica (Reference Oerter, Graf, Wilhelms, Minikin and MillerPruett and others, 2004). ITASE research is also focused on understanding the factors that control climate variability over Antarctica and the Southern Ocean, through, for example, the documentation of the impact of solar forcing (via ultraviolet-induced changes in stratospheric ozone concentration) on zonal westerlies at the edge of the polar vortex (Reference Van den BroekeVan Ommen and Morgan, 2004; Reference MayewskiMayewski and others, 2005).
The greatest unknown in the determination of the mass balance of the Antarctic ice sheet, and its potential role in sea level and ice dynamics, is the surface mass balance (snow accumulation which is precipitation minus sublimation and wind-blown snow). This is the input term in the ice-sheet mass-balance equation. Understanding the distribution of snow precipitation over the Antarctic continent, and the surface processes on different spatial and temporal scales (dependent on wind and surface slope) that redistribute that precipitation (Reference Gow and RowlandGow and Rowland, 1965; Reference VittuariWhillans, 1975; Reference Ekaykin, Lipenkov, Barkov, Petit and Masson-DelmotteEkaykin and others, 2002; Reference Frezzotti, Gandolfi and UrbiniFrezzotti and others, 2002), is the area of greatest common interest between ITASE and another SCAR activity ISMASS (Ice Sheet Mass Balance and Sea Level program; see ISMASS Committee (2004) for a description of the rationale behind ISMASS and of areas of research in greatest need of attention). ITASE research reveals high variability in surface mass balance, and that single cores, stakes and snow pits do not represent the geographical and environmental characteristics of a local region (Reference PropositoRichardson and Holmlund, 1999; Reference FrezzottiFrezzotti and others, 2004b; Reference ShulmeisterSpikes and others, 2004). Field observations show that the interaction of surface wind and subtle variations of surface slope have a considerable impact on the spatial distribution of snow at short and long spatial scales (Reference Urbini, Gandolfi and VittuariVan den Broeke and others, 1999; Reference AlbertAlbert, 2002) and that spatial variability of surface mass balance at the km scale is one order of magnitude higher than its temporal variability (20–30%) at the centennial timescale (Reference FrezzottiFrezzotti and others, 2004a). Data collected in the ITASE framework and by associated projects (EPICA DC (Dome Concordia) and DML (Dronning Maud Land), Siple Dome, Law Dome, Dome Fuji) also reveal systematic biases compared to previous compilations (Reference MayewskiOerter and others, 1999; Reference FrezzottiFrezzotti and others, 2004a; Reference Legrand and MayewskiMagand and others, 2004; Reference Pruett, Kreutz, Wadleigh, Mayewski and KurbatovRotschky and others, 2004).
The extensive use, along ITASE traverses, of new techniques like GPR and GPS, integrated with core data, provides detailed information on surface mass balance (Reference PropositoRichardson and Holmlund, 1999; Reference Spikes, Hamilton, Arcone, Kaspari and MayewskiUrbini and others, 2001; Reference Arcone, Spikes, Hamilton and MayewskiArcone and others, 2004; Reference Pruett, Kreutz, Wadleigh, Mayewski and KurbatovRotschky and others, 2004). At many sites, stake-farm and ice-core accumulation rates are observed to differ significantly, but isochronal layers in firn, detected with GPR, correlate well with ice-core chronologies (Reference FrezzottiFrezzotti and others, 2004a). Some GPR layers have been surveyed extensively throughout Antarctica and they can be used as historical benchmarks to study past accumulation rates (Reference ShulmeisterV.B. Spikes and others, unpublished information). In addition, coupling ground survey data with satellite-based observations provides new tools for measuring, for example, ice surface velocity (Reference Van den BroekeVittuari and others, 2004) and ice-sheet surface temperature (Reference Richardson and HolmlundSchneider and Steig, 2002).
Atmosphere–snow chemical exchange processes play a key role in the quantitative interpretation (inversion) of ice-core records (Reference Welch, Mayewski and WhitlowWolff and Bales, 1996) as well as in tropospheric photochemistry of the polar latitudes (e.g. Reference Dominé and ShepsonDominé and Shepson, 2002; Jacobi and others, 2002). Century-scale records, from West Antarctica, of hydrogen peroxide, a potential proxy of past atmospheric oxidation capacity, are reported from ITASE cores, and changes in firn concentrations are linked to trends in accumulation variability across large spatial scales (Reference Frey, McConnell, Hanna and BalesFrey and others, 2004). Continuous multi-day gas-phase measurements of peroxides, formaldehyde and ozone were conducted during three field seasons, for the first time on a ground traverse. Results include the first quantitative data from the interior of Antarctica of methylhydroperoxide (MHP), a higher organic peroxide acting as a radical reservoir, the detection of significant latitudinal gradients of atmospheric peroxides, as well as data on gaseous HCHO and O3 in a wide range of different depositional environments, such as up to a five-fold change in accumulation rate and a 30 K difference in mean annual temperature (Reference Frey, McConnell, Hutterli, Belle-Oudry and BalesFrey and others, 2003). Atmospheric measurements at ITASE sites are being compared to predictions of the NASA Goddard Space Flight Center (GSFC) point photochemical model and used, together with data from pit and core measurements, to validate existing atmosphere transfer models for H2O2 and HCHO. On-site meteorology data and balloon soundings yielding vertical profiles of ozone, temperature and moisture provide further constraints in the ongoing modeling efforts of which the ultimate goal is a quantitative reconstruction of past change in atmospheric composition and oxidation potential.
Meteorological observations and ITASE field data coupled with mesoscale atmospheric model results (e.g. Reference SteigVan den Broeke, 1997; Reference Gallée, Guyomarc’h and BrunGallée and others, 2001; Reference Genthon and KrinnerGenthon and Krinner 2001) provide significant improvements to our understanding of post-depositional processes resulting from the interaction between surface layers of the atmosphere and snow (blowing snow and surface and blowing sublimation).
The growing ITASE database has the potential to explore temporal variability and recent evolution of Antarctic climate utilizing an unprecedented spatio-temporal array. Data extraction and validation activities are an essential preliminary (e.g. Reference Souney, Mayewski, Goodwin, Morgan and van OmmenSteig and others, 2005) to the synthesis task. Such activities, together with development of instrumental calibration techniques, have been a significant component of ITASE studies. Maps of surface distribution of chemical species (Reference Bertler, Barrett, Mayewski, Fogt, Kreutz and ShulmeisterBertler and others, 2005) indicate the unprecedented scope for exploring climate variability as extended time series become available over broad regions through ITASE and deep drilling projects. An updated compilation of published and new data of major-ion and MSA concentrations from 522 Antarctic sites is provided by the national ITASE programs of Australia, Brazil, China, Germany, Italy, Japan, New Zealand, Norway, South Korea, the United Kingdom, the United States and the national Antarctic program of Finland. The concentrations of aerosol species 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 achieve an understanding of the fundamental factors that ultimately control the chemistry of a snow or ice sample. The ability to determine individual sources and pathways of aerosols, as well as mechanisms that rule precipitation efficiency and post-depositional effects (Reference Kreutz, Mayewski, Pittalwala, Meeker, Twickler and WhitlowLegrand and Mayewski, 1997), will allow exceptionally detailed and accurate interpretation of glaciochemical records, necessary for reconstructing past climate conditions with near-instrumental quality.
Antarctica is Earth’s largest storehouse of buried climate archives (ice cores) and ITASE has already changed this continent from the most poorly sampled of continents, with respect to climate, to the most highly resolved for periods extending beyond the instrumented record of climate. This remarkable accomplishment is essential to unraveling the role of Antarctica in the global climate system. Future ITASE traverses (Fig. 1) will be essential in completing this goal.