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Report on Victoria University of Wellington Antarctic Expedition 1961-62: VUWAE 5

AN INTERESTING ECOLOGICAL SITUATION IN AN ANTARCTIC LAKE

AN INTERESTING ECOLOGICAL SITUATION IN AN ANTARCTIC LAKE

During a recent study of the chemistry and heat balance of Lake Vanda, Antarctica, Phormidium and other blue-green algae were accidentally collected on a nylon line. The algae were collected only in a strongly convective layer. We wish to report this interesting ecological situation and also the novel manner by which these algae were collected.

Lake Vanda (Lat. 77° 35′S., Long. 161° 39′E) is permanently covered with about 12 ft of ice and is five miles long and a mile wide. It occupies the lowest part of Wright Valley, a dry valley in Victoria Land, Antarctica. Armitage and House (1), during a liminological survey in the summer of 1960/61, found that the water at the bottom of the lake was at 22°C and strongly saline. They obtained only one organism, a chlorella-like alga, from the filtration of more than 100 gallons of lake water.

Our work in the summer of 1961/62 (2) made it likely that the bottom water is warmed by solar radiation. The bottom water is prevented from convecting by its strong density stratification.

The main layers in the lake are shown by Fig. 1. The top layer is the 12 ft of ice. The waters from 12 ft to 55 ft and from 125 ft to 160 ft have a salt gradient and are weakly density stratified. From 55 ft to 125 ft the temperature and chemical composition are uniform and this part is considered to be most strongly convective.

(Fig. 1)

While making measurements on the heat balance of the lake, equipment was frequently suspended from nylon monofilaments. If these lines were allowed to remain in position for 24 hours a red material was found to accumulate on that part of the line that had been between 55 ft and 125 ft. This material froze as it came into the air and accumulated at the eyelet of the winding reel. A sample of this material was examined by the biological staff at Mcllurdo base and was identified as being principally Phormidlum with a few Chroocuccus. and a few Anabaena. One live rotifer was present.

It appears that these algae live in a strongly convective layer isolated from the surface of the lake (mean annual temperature −20°C) by 50 ft of colder less saline water and by 12 ft of ice. Their environment is an almost uniform 7.8°C, their nutrient medium almost isotonic, with 600 ppm Cl', 120 ppm Na+, 37 ppm K+, 14 meq/l Ca++, 3 Meq/l Mg++ and 1.3 meq/l HCO3; its available energy from sunlight is about 1000 cal/cm2/yr, mostly in the blue part of the spectrum and all during the summer months.

The authors wish to thank David Mason, John Bunt and Dr C. R. Goldman for identifying the micro-organisms and the United States Navy and U.S.A.R.P. personnel, without whose cooperation the expedition would not have been possible.