McMurdo Dry Valleys
There are very rare locations in Antarctica which are not covered with ice and are flat and wast enough to have streams and lakes.
The largest ice-free region in Antarctica is McMurdo Dry Valleys. Area of this region is some 4,800 km² and it is one of the driest places on Earth. Katabatic winds which "fall down" from the vast ice plains of Antarctica are working like a giant haidryer and as a result the valleys have almost no life – just dry gravel and cliffs. In a way this landscape is similar to a landscape of other, lifeless planets.
These extreme conditions have created unusual natural landmarks, such as lakes with unique chemical composition.
Description of lake
History of exploration
Lake was first reached during the British Antarctic Expedition of 1901-1904 (Discovery Expedition). Later, during the next expedition it was named after geology professor at the University College London, Thomas George Bonney.
Long-term research of the lakes in McMurdo Valleys started in 1993 (Long-Term Ecosystem Research Programme) and has provided rich material about these exotic ecosystems.
In 2008 and 2009 the lake was explored by submersible robot ENDURANCE – this project is financed by NASA in order to prepare for the exploration of objects elsewhere in the space, for example – in the ocean on Jupiter’s moon Europa. This robot is able to map the lake in three dimensions, explore biology and geochemistry.
Size and location
The lake is fairly large – it is some 7 km long and up to 0.9 km wide. Lake is located 57 – 60 m above the sea level.
Thanks to the harsh Antartic climate lake is permanently covered with 3.7 – 4.5 m thick ice. Less than 5% of sunlight is passing through the ice – thus the lake is in eternal darkness or… almost darkness. Only in summer there may open a narrow moat in the ice.
As the lake is permanently covered with ice, the water here is not mixed by wind. Streams in the lake are very weak as well. Calculations show that retention time (full water exchange time) exceeds 50 thousand years.
With a narrow, approximately 50 m wide and 12 – 13 m deep chasm the lake is divided into two parts: the western and the eastern lobes. Each of the lobes is up to 40 m deep and they have very distinct chemical and biological properties.
The lake water is deprived of nutrients – there is extreme phosphorus deficiency. Nevertheless the deeper parts of the lake contain microbial life – cyanobacteria, proteobacteria, algae, also ciliates.
Level of the lake is changing. Thus, in the time period between 1903 and 1970 it rised per 12 m. It means that at some times the lake was divided into two parts, each evolving separately and having different geochemical and biological properties. Later, when upper layer of the water was added, it did not mix with the "original" lakes – thus in principle we have here two separate lakes which by occasion have been united by a top layer of "fresh" water which one day again may disappear.
The western part of the lake is smaller (1 – 2.1 km² – subject to change due to the movements of Taylor Glacier) and is located at the end of Taylor Glacier.
Here the lake is reached by another very unusual natural landmark: orange colored icefall or spring – Blood Falls. This spring is an opening into unusual ecosystem below Taylor Glacier, which has developed for more than million years without contact to the outside world.
Chemocline (border between the less mineralised upper layer of the lake and hypersaline deeper part of the lake) here is at the depth of some 15 m. Below the chemocline the water is not only very salty: it contains also dissolved dimethylsulfide ((CH3)2S). This substance is fairly common in the world: for example, it causes the smell of decaying algae at the sea. Nevertheless the extremely high concentration of dimethylsulfide in the western lobe of Lake Bonney is nearly unique in the world.
Eastern lobe is larger than the western: it is 3.3 – 3.8 km² large. Here the chemocline is located deeper, at the depth of some 20 meters.
This part of the lake is oversaturated with N2O – nitrous oxide known also as "laughing gas". Concentration of this gas in the lobe below the chemocline exceeds the normal concentration of N2O 5,800 times – nowhere on Earth it has been found in such amount.
Even above the ice of the lake the concentration of N2O is per 45% higher than usual – gas seeps through the ice in the atmosphere. Sudden release of this gas in large amounts can put us in danger – it has good ability to eliminate the layer of stratospheric ozone.
This lobe contains also record-high concentration of dimethylsulfoxide ((CH3)2S0) which creates garlic taste on the skin but is not toxic.
- John C. Priscu, Malcolm T. Downes, Christopher P. McKay, Extreme Supersaturation of Nitrous Oxide in a Poorly Ventilated Antarctic Lake.Limnology and Oceanography, 1996, 1544-1551
|Coordinates:||77.7169 S 162.3998 E|
|Categories:||Lakes and streams, Rare natural materials, Ecosystems|
|Address:||Antarctic and Sub-antarctic region, Antarctica, East Antarctica, Victoria Land, McMurdo Dry Valleys, at the end of Taylor Glacier|
|Area:||˜ 500 ha|
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