PHYSICAL AND GEOCHEMICAL CHANGES IN TWO ANTARCTIC FRESHWATER LAKES THROUGH TIME

The McMurdo Dry Valleys are the largest ice-free area on the Antarctic continent, and they contain a number of perennially ice-covered lakes. These valleys and the lakes within them have been investigated since the 1957 IGY, due in part to the unique climate history that data from them reveal, and their close proximity to both US and New Zealand permanent scientific stations. Most of these lakes are closed-basin ones, and their variations in depth, ice-cover thicknesses, and chemical constituents have been used to understand climate variability on scales from seasonal to millennial. Lake Hoare, the freshest of the closed-basin lakes, in Taylor Valley, has been closely monitored on an annual basis since the establishment of the McMurdo Dry Valleys Long-Term Ecological Research site (MCM-LTER) program in 1993. The only flow-through lake, Lake Miers, in Miers Valley, has been sampled periodically since 1964, and has only recently become part of the MCM-LTER monitoring program. In this presentation, we address both the physical and geochemical time-series data from both these lakes, and discuss their trends over time. These lakes are sentinels of subtle changes in climate within the Dry Valleys, but because of their difference in basin type (i.e closed vs flow through) some of the responses to changing climatic variables are similar, but some are different. We review how each lake has responded to variations in water balance, which is driven in most part by changes in austral summer temperatures. These changes in water input in turn directly affect the geochemistry of the upper water column of the lakes. We will discuss how the difference between closed-basin vs flow through impacts the physical and geochemical characteristics of the lakes. Finally we speculate on future changes in these two lakes based on climate warming scenarios.