Impact of Episodic Warming Events on the Physical, Chemical and Biological Relationships of Lakes in the McMurdo Dry Valleys, Antarctica

Lakes in the Taylor Valley, Antarctica were investigated to determine the impact of a significant air temperature warming event that occurred during the austral summer of 2001–2002. The warming in the valleys caused an increase in glacial run-off, record stream discharge, an increase in lake levels, and thinning of the permanent ice covers. These changes in the physical environment drove subsequent changes in the biogeochemistry of the lakes. Primary production in West Lake Bonney during the flood was reduced 23% as a consequence of stream induced water column turbidity. Increased nutrient levels within the lakes occurred in the year following the temperature induced high flow year. For example, soluble reactive phosphorus loading to Lake Fryxell was four-fold greater than the long-term average loading rates. These high nutrient levels corresponded to an increase in primary production in the upper water columns of Lakes Bonney and Fryxell. Depth integrated chlorophyll-a values increased 149% in East Lake Bonney, 48% in West Lake Bonney, and showed little change in Lake Fryxell; chlorophyll-a in Lake Hoare decreased 18% compared to long-term averages recorded as part of our ten year monitoring program, presumably from a reduction in under-ice PAR caused by increased sediment loads on the ice cover. Overall the warming event served to ‘‘recharge’’ the ecosystem with liquid water and associated nutrients. Such ‘‘floods’’ may play an important role in the long-term maintenance of liquid water in these dry valley lakes.