Vestfold Hills

Location The Vestfold Hills lie along the coast of Princess Elizabeth Land (68°25'-68°40' S, 77°50'-77°35' E) and occupy an area of —410 km2. The region and several outlying islands are typically snow free and contain —150 freshwater and saline lakes, which account for 8% and 2% of the total area, respectively.

Formation and diversity Following the retreat of the continental ice sheet after the last glacial maximum —12 000 years ago, isostatic rebound occurred at a faster rate than sea level rise. As the land rose, it cut off fjords and trapped pockets of seawater, creating lakes. The freshwater lakes include supraglacial and proglacial lakes, while the saline lakes range from brackish to hypersaline (6x seawater) and include both permanently stratified and seasonally mixed lakes. The lakes closest to the ice sheet are typically fresh, while those closer to the coast tend to be saline or hypersaline. The stratified lakes can be divided into different geographical regions: Long Peninsula, Broad Peninsula, Ellis Fjord, and Mule Peninsula.

Ace Lake, lying in the northern portion of the Vestfold Hills on Long Peninsula, 10 km from the ice sheet and 150 m from the sea, went through a complicated evolution, beginning as freshwater, which was then inundated by seawater, dried down and refilled by glacial melt water. The bottom saline waters and the upper fresh waters do not mix and the lake is permanently stratified. The lake is oligotrophic with a depth of 25 m, an area of 0.16 km2 and a 1.5-2 m thick ice cover. The water below 12 m is permanently anoxic and contains sulfate reducing and methanogenic bacteria. Extensive studies have been carried out on Ace Lake and have shown that there are significant interannual variations in biological activity related to the ice cover and local meteorology.

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