Water column and sediment characteristics of Lake Fryxell, Taylor Valley, Antarctica

Abstract

Abstract Lake Fryxell is a permanently icecovered 19 m deep lake in the lower Taylor Valley, Antarctica (75°35'S, 163°35'E). The lake is thermally and chemically stratified and has a euphotic (aerobic) zone above 9 m depth and an anaerobic (anoxic) zone below. Lake waters are derived from glacial melt into which upward diffusion of brines or redissolved salts from the basin has formed a diffusion cell of about 1000 years age. Lake sediment cores contain five recognised units, three of which are calcareous. The uppermost unit (E) has, at the top of the sediment column, calcite flakes precipitated as a result of biological CO2 fixation in the euphotic zone. The calcite is either deposited as stromatolites, where the lake bed is within the euphotic zone, or from suspension over deeper parts of the lake. Unit D is a varve-like aragonite deposit dated at about 10 000 years RP. and was deposited as a result of evaporative concentration of lake waters following the retreat of the Ross Sea I expanded ice sheet from the Taylor Valley. Unit C is transitional between units Band D. Unit B is a calcareous mud of mixed aragonitecalcite mineralogy dated at about 20 000 years B.P. This date coincides with the maximum extent of advance ofthe Ross Ice Sheet up the Taylor Valley, and its associated glacial lake Washburn. Thus, unit B was deposited in a deep lake but in a similar manner, chemically, to that of the present CaC03H 2O-C02 system. Unit A is probably an outwash fan of the Ross Sea ice.