7 FEBRUARY UPDATE: Valery Lukin, director of the Russian Antarctic programme, says drilling at Lake Vostok stopped on 5 February at a depth of 3720.47 metres – 29.53 metres short. The drilling team left by aircraft on 6 February. Drilling resumes in December 2011.

1 February post: A Russian drilling team hoping to reach the surface of Lake Vostok, a vast freshwater lake 3,750 metres under Antarctica’s ice-sheet, appears to have run out of time as the region’s summer drilling season draws to a close.

The ambitious project, launched more than 20 years ago, has been repeatedly delayed by technical glitches and funding problems (See ‘Race against time for raiders of the lost lake’). But the team had hoped to reach the lake’s surface by 6 February, when the last aircraft of the summer research season is due to leave the Vostok research station, about 1,300 kilometres from the South Pole.

It looks like they will end up 20 metres short this time. Valery Lukin, director of the Russian Antarctic programme, toldNature via email today that, after reaching 3,709 metres, drilling stopped from 26 to 30 January, while scientists measured the densities of drilling fluids, widened the hole’s diameter in upper layers, removed slime, added Freon where needed, and prepared to upgrade their electrico-mechanical drill pump.

“On the morning of 31 January, drilling in the borehole was continued by the electrico-mechanical drill. For the latest day, 2.2 m of the new ice core was extracted. So the borehole depth in the morning of 1 February was 3711.2 metres. Drilling will be continued until the last day of the Antarctic summer operations at Vostok – 6 February 2011. We plan to reach a depth of 3720 m – 3730 m,” Lukin writes.