0 1998, by the American Soc~ty at Limnology and Oceanography. Inc Evidence of deep circulation in two perennially ice-covered Antarctic lakes

• Main Authors: Scott W. Tyler, Peter G. Cook, Anya Z. Butt, James M. Thomas, Peter T. Doran, W. Berry Lyons
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Antarctic; Fryxell; Hoare; Lake Fryxell; Lake Hoare; The Antarctic; Antarc*
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.570.1514; http://www.aslo.org/lo/toc/vol_43/issue_4/0625.pdf

The perennial ice covers found on many of the lakes in the McMurdo Dry Valley region of the Antarctic have been postulated to severely limit mixing and convective turnover of these unique lakes. In this work, we utilize chlorofluorocarbon (CFC) concentration profiles from Lakes Hoare and Fryxell in the McMurdo Dry Valley to determine the extent of deep vertical mixing occurring over the last 50 years. Near the ice-water interface, CFC concentrations in both lakes were well above saturation, in accordance with atmospheric gas supersaturations re-sulting from freezing under the perennial ice covers. Evidence of mixing throughout he water column at Lake Hoare was confirmed by the presence of CFCs throughout he water column and suggests vertical mixing times of 20-30 years. In Lake Fryxell, CFC-11, CFC- 12, and CFC- 113 were found in the upper water column; however, degradation f CFC- 11 and CFC- 12 in the anoxic bottom waters appears to be occurring with CFC- 113 only present in these bottom waters. The presence of CFC-113 in the bottom waters, in conjunction with previous work detecting tritium in these waters, strongly argues for the presence of convective mixing in Lake Fryxell. The evidence for deep mixing in these lakes may be an important, yet overlooked, phenomenon in the limnology of perennially ice-covered lakes. The McMurdo Dry Valley region of the Antarctic (77”S