Millennial-Scale Surface-Level Changes of Closed-Basin Antarctic Lakes

B L Hall (University of Maine, Orono, ME 04469-5790; ph. 207-581-2191; fax 207-581-1203; Internet: brendah@maine.maine.edu); G H Denton (University of Maine, Orono, ME 04469-5790; ph. 207-581-2190; fax 207-581-1203; Internet: debbies@maine.maine.edu)

Millennial-scale oscillations are believed to be the building blocks of abrupt climate change. Yet the cause of such oscillations is problematic because orbital forcing cannot account for the rapidity and frequency of observed climate changes. One step toward determining the origin of millennial-scale events is to discover their geographic extent and timing. Are these events global and synchronous? What is their timing relative to known internal and external forcing factors? Do they occur in the present interglacial period?

Here we present evidence of millennial-scale surface-level changes of closed-basin, amplifier lakes in the Dry Valleys (77-78 S) region of Antarctica. Using over 200 radiocarbon dates of lacustrine algae within relict deltas and shorelines, we have constructed preliminary surface-level curves for lakes in Taylor, Wright, and Victoria Valleys. Peaks in lake-level are generally synchronous among the valleys. In Taylor Valley, high lake levels (up to 300 m above the present lake) occurred at about 18,600, 18,100, 17,200, 16,300, 15,600, 14,900, 13,900, 13,300, 12,800, 12,300, 11,700, 10,500, 9300, 8900, and 6000 C-14 yr B.P. In Wright Valley, high lake levels (up to 470 m above present-day Lake Vanda) occurred at about 25,700, 19,900, 19,000, 14,500-15,400, 12,700, 11,900, 10,800, 7900-8400, 6000, and 2700 C-14 yr B.P. Farther north in Victoria Valley, we recorded high lake levels (up to 160 m above present-day Lake Vida) at 18,900, 13,800, 12,900, 12,200, 10,600, 9000, and 5700 C-14 yr B.P.

The importance of these lake-level data is that they are one of only a few records from the Antarctic that show evidence of millennial-scale climate change. Moreover, they suggest that millennial-scale climate change was not limited to the glacial period, but has occurred in the present interglacial period. The cause of such large and abrupt variations in lake level is not well-known, but is believed to relate to climatically induced changes in meltwater production.