Lake El´gygytgyn is a 3.6 million year old impact crater lake with a diameter of 12 km and a water depth of 170 m, located in central Chukotka, NE Siberia (detailed map). During the last 10 years the sedimentary record of the lake has become a major focus of multi-disciplinary multi-national paleoclimatic research. Futhermore, the meteorite impact event shall be reconstructed from the breccia and brecciated volcanic bedrock expected to occur beneath the lake sediments. To address these objectives, the International Continental Scientific Drilling Program (ICDP) and national funding agencies have provided funding for deep drilling operations on the lake and in its permafrost catchment in autumn 2008 and spring 2009.

Background

A pre-site survey conducted at Lake El´gygytgyn has evidenced that a full-length sediment core would yield a complete record of Arctic climate evolution, back one million years prior to the first major glaciation of the Northern Hemisphere. This makes Lake El´gygytgyn unique in the terrestrial Arctic, especially since geomorphological evidence from the catchment suggests that the crater was never glaciated during the entire Late Cenozoic.

Two sediment cores retrieved from the deepest part of the lake in 1998 and 2003 revealed basal ages of approx. 250 ka and 340 ka respectively, and thus, represent the longest continuous climate records as yet available from the Arctic continent. Their continuous sedimentation confirmed the lack of glacial erosion, and the sediment composition underlined the sensitivity of this lacustrine environment to reflect high-resolution climatic change on Milankovitch and sub-Milankovitch time scales.

Four sediment units were distinguished, reflecting relatively warm, peak warm, cold and dry, and cold but more moist climates (sketch of climate modes). Additional cores from the western lake have shown that the formation of debris flows is associated with partial erosion of the underlying sediments at the slope, but also with the deposition of ´pelagic rain´ in the central part of the lake without erosion.

Seismic investigation carried out during expeditions in 2000 and 2003 revealed a depth-velocity model of brecciated bedrock overlain by a suevite layer, in turn overlain by two lacustrine sedimentary units up to 350 m in thickness. The upper well-stratified sediment unit appears undisturbed apart from intercalation with the debris flows near the slopes. Based on extrapolation of sedimentation rates the entire Quaternary and possibly parts of the late Tertiary record are reflected by the 170 m thick upper unit, whilst the earliest history of the lake is presumably represented with a higher sedimentation rate by the lower unit. There is no evidence for glacial erosion or complete lake drying in the entire sedimentary record.

Currently finished

The drilling campaigns in autumn 2008 and winter/spring 2009 have been finished successful:

At the end of the last year, permafrost drilings were performed by a Russian construction company from the 260 km distant Pevek. It yielded impressive results: the team reached a drilling depth of 142 metres despite heavy snowstorms and low temperatures. The cores contain information on the permafrost history and its influence on lake sedimentation.

The lake drillings which have just been completed were no less successful: lake sediments were drilled 315 meters below the lake bottom; the upper 110 meters overlapped to close the remaining gap of the first drilling in the archive. First results indicate that the climate and environment history of the last 3.6 Mio years is largely documented. Measurements of the magnetic properties in the upper part of the sediment layers show numerous warm and glacial periods with different intensities and characteristics.

An important goal of the lake drilling was the drilling of the impact breccias. This clastic rock created by a meteorite impact was found 315 meters below the lake bottom. The cores drawn by drilling 200 meters into the breccias are invaluable.