The evolution of Ace Lake, Antarctica, determined from sedimentary diatom assemblages

The sediments in Ace Lake in the Vestfold Hills, East Antarctica, contain a continuous sequence of diatom frustules that record the lake's history since its formation during the retreat of continental ice more than 9200 years ago. Frustules from six indicator groups; Pinnularia microstauron, Nitzschia cylindrus, Nitzschia curta, Eucampia antarctica, a freshwater Stauroneis species and several centric species in a sediment core were used to determine the sequence of the lake's evolution. The history of the lake falls into five stages. Ace Lake began as a marine inlet influenced by dynamic mixing of ocean and meltwater inputs. As the ice sheet retreated, isostatic uplift isolated the lake allowing it to be flushed by meltwater input from the retreating ice sheet. Over the course of 800 years (similar to 9200-8400 C-14 yr B.P.) the lake became meromictic supporting a freshwater diatom assemblage. Approximately 6700 years ago, coinciding with Antarctic sea level maxima, diatom assemblages indicate that seawater flooded over the sill into Ace Lake disturbing the freshwater meromixis. The sediments in this period were laminated and contained elemental sulphur suggesting that the marine input was limited in extent and energy. Approximately 5500 years ago this marine input ceased and the lake again became a meromictic basin which stabilised over 1700 years to become the lake that it is today and has been with little change for about the past 4000 years.