lundi 24 janvier 2011

The secrets of the lakes in Yuboku Valley

As I have told you, on the 7th January, Gigi and myself have discovered a lake in a valley, that was not yet explored. The Yuboku valley was exposed to the North, and well protected against the winds. We could sample cyanobacterial mats under the ice, and it was clear that there was life in this lake. It was already quite late, and therefore, we had to leave the Valley without going to a second lake that we had spotted. But, we planned to come back and take the equipment for drilling.
Thus, this Saturday, we went back there with a whole party and the drilling equipment (including the BP-1, the hand-made corer by Bernard and Paul. The weather was bad, it was cloudy, there was drifting snow and gusts of katabatic winds. Therefore, it took us 2H30 instead of 1H to arrive there.
Stefan, Alain, me (with the yellow helmet), René, Joachim (German geologist, just a hand)
It was decided to name the first lake, Zorigto's lake, whereas the second one was called Gigi's lake.
This time, Zorigto's lake was completely frozen, the pH was 9.2 and the water had a temperature of 0°C. We could easily drill a hole in the ice in the middle of the lake and measured a depth of 1,8 meter. We could not find any sediment, but only rocks at the bottom that were covered by cyanobacterial biofilms.

Gigi's lake
Gigi's lake was located deeper in the valley and was L shaped. It was just at the foot of the moraine with a quite steep slope. Probably the lake was formed during the retreat of the glacier on the southern side of the lake.
On the surface of ice, we have found dried pieces of mats frozen in the ice. I have collected these pieces near the southern shore and some wet sand on the western shore. 
We have started to drill at the center of the lake but we couldn't reach more than 1.5 m due to the hard ice and problems with the engine of the drill. Then, we moved closer to the southern side of the lake where the ice was thinner. We have manually drilled 3 holes in the ice, close to each others. There, the ice thickness was 58 cm,  and the total lake depth  was 84 cm. The pH was again quite high, 9.0, the oxygen was 10 mg/l and the temperature was 0°C.
Unfortunately, we could not find any sediments, but the size of the rocks on the bottom was smaller than on the southern shore of the lake. Probably,  there was a fractionation of rock material from south to north, with a finer fraction closer to the northern side of the lake. Therefore, on the basis of this hypothesis, we have moved 30 m NNW (to the north where the sediments are finer, but closer to the western shore where the ice is thinner). We have drilled 2 holes. The ice thickness and the lake depth were about 80 cm. During the first drilling on this spot,  the drill has hit the bottom and brought the mixture of yellowish clay, sand and gravel to the surface! WOW, we had sediments at least!

Before the last drilling, we have applied some silicon grease on the surface of the plunger and changed the rubber. Finally, we managed to collect a 4 cm length sediment core with wet ice on top of the sediments. It was placed in a plastic film and kept in the half of the plastic tube, marked top and bottom, as you can see. 
After coming back to PES, I have immediately put it in the freezer at -60 °C. One conclusion for the future is that a long drill with a good engine should be used to drill in the center of the lake. Moreover, if there is an expedition here in future, it would be practical to bring the drilling equipment in a camp and let it stand for the duration of the expedition. The team could spend hte day in Yukobu and come back to the Station for the night (1-1H30 travel). On the way between Yuboku and the Station, there are small crevasses of 20-50 cm that can easily be crossed by skidoos. There is also a long area with sastrugis (ice ridges made by the wind) that are not very high, but a bit boring to go through. Moreover, we have to cross the Gunnestadbreen glacier on the way to Yuboku valley, and the weather there is always worse than near the PES. The valley itself is quite protected, but there are occasional gusts of katabatic northwards winds.
Anyway, we have only a small idea of the secrets of the lakes in Yuboku Valley, especially for the third lake that we had no time to look at.
Cheers, Zorigto

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