Draft Proposal 2004 - page 4
Introduction - Antarctica’s Role in Global Change
The Antarctic ice sheet plays a significant role in the global system. Encircled by the world’s most biologically productive oceans, Antarctica is the largest reservoir of fresh water on the planet, a major site for the production of the cold deep water that drives ocean circulation, a major player in Earth’s albedo dynamics, and an important driving component for atmospheric circulation. Thus, Antarctica plays a critical role in the dynamic linkages that couple the spatially and temporally complex components of the Earth’s system (atmosphere, biosphere, anthrosphere, hydrosphere, cryosphere and lithosphere). While the existence of a complex global climate system is now recognized, the details of its functioning are still poorly understood. In the Northern Hemisphere and portions of the Southern Hemisphere, direct observational and instrumental records exist only for the last ~2000 and ~100 years, respectively, and, except at isolated sites, observational and instrumental records in Antarctica cover only the last 30-40 years.
Spatial Complexity - Antarctica exhibits significant regional contrasts in present-day climate regime (accumulation rate, temperature, atmospheric circulation). 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 cyclonic systems circulating around the continent. As a consequence, these peripheral areas are mainly connected with lower tropospheric transport, whereas high altitude areas in the interior are more likely influenced by vertical transport from the upper troposphere and stratosphere.
A recent example of spatial complexity is a slight cooling of the entire Antarctic ice sheet, as observed from in situ and satellite temperature measurements during the period 1979-1998 (Comiso, 2000). Over the same period, the Antarctic Peninsula has experienced a gradual warming (Jacobs and Comiso, 1997). Both changes are linked to variations in sea ice extent. Alternating warm and cold anomalies in the sea ice region surrounding the continent may be related to eastward propagating temperature patterns consistent with effects of the Antarctic Circumpolar Wave reported by White and Peterson (1996). As suggested by Comiso (2000) the explanation behind the variability in sea ice and temperature requires longer time series.
Ice core records further illustrate the spatial complexity of climate over the past few centuries. Surveys of the distribution of glaciochemical proxies for atmospheric circulation reveal changes in atmospheric circulation influence as a function of distance inland from the coast, and elevation (e.g., Kreutz and Mayewski, 1999). Variability in accumulation rate on scales of tens of meters to many kilometers and complexities in accumulation rate distribution have been demonstrated to result from changes in topography (e.g., Whillans, 1975) and the interaction of several moisture-bearing circulation systems (e.g., Reusch et al., 1999).
Temporal Complexity - Deep ice coring programs in central Greenland (GISP2 and GRIP), East Antarctica (Taylor Dome), and West Antarctica (Siple Dome) demonstrate that the polar regions have experienced large, rapid, climate oscillations, on a scale that industrial age humans have not yet faced (e.g., Alley et al., 1993; Mayewski et al, 1993). These changes include temperature increases of many oC, twofold changes in snow accumulation, order-of-magnitude changes in wind-blown dust and sea-salt loading in the atmosphere and large changes in methane concentration. Changes during these events, equal to most of the glacial-interglacial difference, commonly occurred over decades or less. These abrupt changes in climate have not been restricted to the Holocene. While significantly more subdued in the Holocene they have still been sufficient to cause major disruptions to civilizations and ecosystems (Mayewski et al., in press 2004a, b). Several of these Holocene climate events may be synchronous from the Arctic to the Antarctic (Domack and Mayewski, 1999), and the most recent of these events, the Little Ice Age, appears prominently in many of these records, notably the Antarctic (e.g., Kreutz et al., 1997).
High frequency complexity in Antarctic climate is also manifested through inter-annual variability in synoptic systems such as the global scale El Niño Southern Oscillation (ENSO). Regional scale factors such as the Amundsen Sea Low and East Antarctic High (Kreutz et al., 2000; Souney et al., 2002) also have an effect, as do atmospheric blocking and sea ice variations (White and Peterson, 1996; Cullather et al., 1996).