Hydrological and Biogeochemical Modeling of Taylor Valley Lakes, East Antarctica

This research is focused on better understanding of past and present hydrological and biological sensitivity of perennially ice-covered lakes in Taylor Valley, McMurdo Dry Valleys, East Antarctica, with respect to changes in climate, summarized in three distinct chapters.;Glacial Lake Washburn was present in Taylor Valley during the Last Glacial Maximum (LGM), despite a significantly cooler climate. Contemporary anomalous warm summer westerly winds are responsible for generating a large volume of melt water during the short austral summers by increasing the degree days above freezing. The high frequency of westerly winds during the LGM was responsible for the formation of large glacial lakes during the LGM. Data from a nearby Taylor Dome ice core record supports windier conditions and a link between Taylor Dome and Taylor Valley was established. However, the surface air temperature increase due to the westerly winds is not preserved in the annually averaged ice core record. Yet, it was the seasonal warming due to increased frequency of anomalous summer winds that contributed to the GLW formation. This analysis suggests that summer air temperature during the LGM were as warm as today.;An autonomous underwater vehicle was deployed under the thick ice cover of West Lobe of Lake Bonney, generating a high-resolution, spatially distributed biogeochemical and physical dataset. Ice thickness varied depending on shading from nearby mountains and sediment accumulation on the surface of the ice. Spatial ice thickness variations controlled available underwater photosynthetically active radiation (PAR) and chlorophyll-a distribution. PAR was negatively correlated with chlorophyll-a, which was attributed to short-term photoadaptation of phytoplanktonic communities.;Ice thicknesses of perennially ice-covered lakes in Taylor Valley were modeled utilizing a one-dimensioned heat equation coupled with the atmosphere and the underlying water column. The long-term ice thickness trends are strongly controlled by the heat content of a lake. Deep lakes with deep-water temperature maximum will either hinder or facilitate ice thickness growth or decay due to the heat flux from below. Shallow lakes are more responsive to climatic changes. Future ice thickness predictions suggest that ice covers of perennially ice-covered lakes can become seasonally ice-free within couple decades.