DISSOLVED-GASES IN PERENNIALLY ICE-COVERED LAKES OF THE MCMURDO DRY VALLEYS, ANTARCTICA

Measurements of dissolved N-2, O-2, Ar, CO2, and CH4 were made in pere nnially ice-covered Lake Hoare. Results confirm previous reports that O-2 concentrations in the upper water column exceed atmospheric equili brium and that N-2 and Ar are supersaturated throughout the water colu mn. The mean supersaturation of N-2 was found to be 2.0 (+/-0.37) and Ar was 3.8 (+/-1.1). The ratios of N-2/Ar (20.3 +/- 3.8), and O-2/Ar ( 22.5 +/- 4.0) at the ice-water interface are consistent with those pre viously measured, suggesting that bubble formation is the main process for removing gas from the lake. However, the saturations of N-2 and A r greatly exceed those previously predicted for degassing by bubble fo rmation only at the ice-water interface. The data support the hypothes is that removal of gas by bubbles occurs in the water column to a dept h of 11 m in Lake Hoare. CO2 concentration increases from near zero at the ice-water interface to 80-100 times saturation at and below the c hemocline at c. 28 m. There is considerable variability in the gas con centrations throughout the water column; samples separated in depth by one metre may vary by more than 50% in gas content. It is likely that this phenomenon results from the lack of turbulent mixing in the wate r column. Methane (c. 2 mu g 1(-1)) was detected below the chemocline and immediately above the sediment/water interface at a depth of 30 m. Samples from lakes Vanda, Joyce, and Miers, also show supersaturation s of O-2, N-2, and Ar at levels similar to levels found in Lake Hoare.