BIOGEOCHEMICAL PROCESSES IN A POLAR DESERT: EXAMPLES FROM THE MCMURDO DRY VALLEYS, ANTARCTICA

The McMurdo Dry Valleys (MCM) represent the largest of the ice-free areas on the Antarctic continent. They are among the coldest and driest terrestrial environments on earth. The dry valley landscape is a mosaic of perennially ice-covered lakes, ephemeral streams, soils and glaciers. Despite the extreme conditions, biological communities exist within this landscape. Although this region has been investigated since IGY in 1958, only since the establishment of a Long-Term Ecological Research (LTER) program in 1993 have the valleys been studied as an integrated ecosystem. The presence of liquid water remains the primary limiting condition for life in Antarctica. The biogeochemistry of MCM is sensitively linked to very small variations in climate. In this presentation I will review the findings of MCM-LTER research on the biogeochemical cycling of nutrients within the aquatic portion of the MCM ecosystem, relate chemical evolution of meltwater as it flows from the glaciers to the closed-basin lakes, and speculate on the connection between the terrestrial and aquatic environments in terms of carbon, nitrogen, phosphorus and silica dynamics. What would be considered subtle changes in temperature, cloud cover and albedo have a profound impact on nutrient fluxes in the aquatic portion of the ecosystem. These flux variations, in turn, impact species diversity within the system. The influence of past climatic changes on present day ecosystem structure and function will be demonstrated. This concept of legacy, the influence or memory of past climatic events on the current biogeochemical system, appears to be extremely important in Antarctic systems such as MCM. The biogeochemistry of the lake ecosystems was once thought to be relatively stable, but MCM-LTER data indicate that they are extremely dynamic in nature.