Workshop Report on Recent Change in the
Climate and Atmospheric Chemistry over
Antarctica
Mayewski, P and Goodwin, I
Glaciologists, geophysicists, remote sensing specialists and meteorologists from fifteen countries met at the Climate Change Research Center, University of New Hampshire from 19-23 April to discuss the International Trans Antarctic Scientific Expedition (ITASE). ITASE is investigating the last ~200 years of change in climate and atmospheric chemistry over the Antarctic ice sheet (Mayewski and Goodwin, 1997). It is jointly sponsored by the Group of Specialists on Global Change and the Antarctic (GLOCHANT) of the Scientific Committee on Antarctic Research (SCAR) and the Past Global Changes (PAGES) project of the International Geosphere Biosphere Program (IGBP).
The available Antarctic meteorological data (re-analysis fields, in-situ observations, operational model fields) provide approximate descriptions of spatial and temporal variability of Antarctic accumulation and associated atmospheric circulation from approximately 1980 to date. Progress has been made in describing the impact of the seasonal cycle, semi-annual oscillation and ENSO cycle on Antarctic accumulation over this time period. Difficulties still remain in explaining fully the history and forcing of Antarctic climate and the links between tropical forcing and high latitude response. These difficulties arise largely because of the relatively short duration and sparse spatial coverage of Antarctic meteorological data.
By combining available meteorological data from the Antarctic and Southern Ocean with ice core proxies for a variety of climate parameters (eg., moisture balance, atmospheric circulation and temperature) ITASE plans to extend the Antarctic climate record back ~200 years. This coverage offers the temporal perspective needed to assess the multi-decadal state of natural climate variability in Antarctic climate. In the process ITASE will be able to contribute to understanding the impact of global change on the Antarctic continent and the influence of Antarctica on global change. Examples of some of the issues treated at the meeting follow:
(1) Annual layer dating of ice cores and absolute dating through unique stratigraphic markers.
Development of annually resolved ice core series is recognized as an essential component of the ITASE program because of the fidelity needed for comparison and calibration with instrumental series. Several dating tools are used in dating ITASE cores. These include: annual layer counting of stable isotope, chemistry and particle series. These annual layering counting tools are calibrated to volcanic and nuclear fall-out markers. As an example, sulfate from a variety of well documented volcanic emissions, covering the last ~200 years, is potentially documented in Antarctic ice cores. These events include: Lascar, Chile (1993), Pinatubo, Philippines and Cerro Hudson, Chile (1991), El Chichon, Mexico (1982), Deception Island, South Shetlands (1972, 1969, 1967), Agung, Indonesia (1963), Cerro Azul, Argentina (1932), Santa Maria, Gautemala (1902), Tarawera, New Zealand (1886), Krakatau, Indonesia (1883), Coseguina, Nicaragua (1835), Babuyan, Philippines (1831), Galunggung, Indonesia (1822), Tambora, Indonesia (1815) and Unknown (1809).
(2) Ice core proxies for Antarctic moisture flux.
A selection of twenty three ice core derived accumulation rate time series, distributed around the continent, were compared during the workshop. Empirical orthogonal analysis (EOF) of the series demonstrates that within regions the series share significant common variance. Investigation into associations between regions may provide evidence of the history of moisture bearing atmospheric circulation systems potentially associated with features in the ENSO system and the Antarctic Circumpolar Wave.
(3) Ice core proxies for major Antarctic atmospheric circulation patterns.
Recent instrumental linkages between the tropical ENSO system and the high southern latitudes demonstrate the existence of an ENSO-Antarctic climatic teleconnection. These investigations reveal that annual temperatures at South Pole are positively correlated to annual values of the Southern Oscillation Index (SOI) of the previous year (Savage et al., 1988). The ENSO signal has been interpreted at South Pole in an ice core covering the time period 1922-1984 AD, and also in a core from Dronning Maud Land. They clearly show increases in methylsulfonic acid (MSA) concentration during El Ni_o events identified in the Quinn et al. (1987) historical El Ni_o chronology. MSA is produced from the oxidation of atmospheric dimethylsulfide (DMS), a major emission of marine phytoplankton. A new record from South Pole was presented at the meeting. This core extends the South Pole ice core proxy for ENSO back to 1500 AD and also identifies a sea ice MSA association previously observed at a site to the north on the Newall Glacier, southern Victoria Land. Background values of MSA in the South Pole core are associated with sea ice extent anomalies (185Á-245ÁE) and outliers in MSA are associated with warm events (El Ni_o events) allowing investigation of ENSO-sea ice associations. A seasalt proxy for the strength of the Amundsen Sea Low developed from the Siple Dome ice core was also presented at the meeting.
(4) Ice core proxies for temperature and borehole temperature.
Stable isotope measurements of ice (dD, d18O and deuterium excess) have classically been employed as a proxy for temperature in Antarctica and more recently borehole measurements have been undertaken to provide direct measures of snow surface temperature times series. An overview of results from these studies which was presented at the meeting, combined with instrumental observations, reveals an ~1oC warming in the Antarctic Peninsula and Dronning Maud Land over the past few decades. High resolution ice cores on Law Dome, Wilkes Land have enabled the discrimination of seasonal stable isotope signals which are being calibrated to the instrumental meteorological record. This calibration is being used to resolve major precipitation events and temperature fluctuations.
(5) Examination of the ice sheet record in between ice core sites.
Ice cores can provide annually resolved records of environmental change but they are based on centimeter scale diameter samples. Snow and ice radar systems on the other hand provide detailed information that can be tuned to investigate snow layering in the upper several tens of meters of the Antarctic ice sheet and down to thousands of meters in depth to detect ice thickness and bedrock configuration. Radar measurements between and around ice core sites add information that is extremely valuable in assessing the representativeness of ice core sites and in the determination of decadally averaged snow layer thicknesses between core sites. Detailed examination of changes in topography and ice dynamics that exert controls on accumulation rate are being conducted through GPS surveys along ITASE traverse routes in order to remove the influence of these factors and more clearly assess the influence of climate change on accumulation.
(6) Ground truth for satellite remote sensing of the Antarctic ice sheet.
Recent advances in remote sensing technology and availability of images has vastly improved traverse route selections, core site selection and spatial interpolation of ice core time series. As an example temporal changes in snow surface elevation and velocity can be mapped using laser altimetry and interferometric methods. ITASE traverses provide unique opportunities for developing ground truthing for remote sensing experiments that are geared toward characterizing and interpreting changes in surface topography, surface temperature, surface velocity and various other surface characteristics of ice sheets (roughness, grain size, albedo).
The workshop also provided a venue for discussing the coordination of sample collection, sample handling, data exchange, data interpretation and future ITASE oversnow traverse plans for the next decade. ITASE efforts over the next decade are widely dispersed over the continent (Figure 1). Themes to be investigated by current and future ITASE investigations include:
(1) Relationship between Antarctic precipitation variability with ENSO associated climate, particularly, precipitation variability in Southern Australia and perhaps South America.
(2) Variations in cyclogenesis, storm tracks, moisture flux and the strength of the low pressure cells that surround Antarctica.
(3) Interannual and decadal variability in sea ice extent and concentration, persistence and maintenance of coastal 'latent heat' polynyas.
(4) Changes in the chemistry of the atmosphere over Antarctica and differentiation of natural versus anthropogenic controls on such change.
References:
Mayewski, P.A. and Goodwin, I.D., 1997, International Trans Antarctic Scientific Expedition (ITASE) "200 Years of Past Antarctic Climate and Environmental Change", Science and Implementation Plan, 1996. PAGES Workshop Report Series 97-1, 48p.
Quinn, W.H., Neal, V.T. and Antunez de Mayolo, S.E., 1987, El Nino occurrences over the past four and a half centuries, Jour. Geophys. Res. 92, C13, 14,449-14,461.
Savage, M.L., Stearns, C.R. and Weidner, G.A., 1988, The Southern Oscillation signal in Antarctica, Second Conference on Polar Meteorology and Oceanography, 141-144.
Author address list:
1. Paul Mayewski
Climate Change Institute
320 Edward Bryand Global Science Center
University of Maine
Orono, Maine 04469
USA
2. Ian Goodwin
Faculty of Science & Mathematics University Drive, Callaghan
The University of Newcastle
NSW 2308
Australia