El´gygytgyn Drilling Project, Russian Arctic
Coordination of the international project as Principal Investigator
Summary
Lake El´gygytgyn is located in a 3.6 million year old meteorite impact crater in central Chukotka, northeastern Russian Arctic. Within the scope of the International Continental Scientific Drilling Program (ICDP) a drilling operation was carried out in the El´gygytgyn Crater in winter 2008/09. Driling comprised three holes in the centre of the 170 m deep lake, utilizing the lake-ice cover as a platform, plus one hole close to the shore in the western lake catchment. Because of its unusual origin and high-latitude setting, scientific drilling at Lake El´gygytgyn offered unique opportunities across three geoscientific disciplines, namely:
- paleoclimate research, for the first time allowing the time-continuous reconstruction of the climatic and environmental history of the terrestrial Arctic back into the mid-Pliocene;
- permafrost research, promising a better understanding of the history and present behavior of the Arctic´s frozen surficial materials;
- impact science, providing new insights into planetary cratering processes and the response of volcanic target rocks.
Pre-Site Surveys
Site surveys carried out in 1998, 2000, and 2003 confirmed the potential the sedimentary record of Lake El´gygytgyn has for multi-disciplinary paleoclimatological research. First 13 m and 16 m long sediment cores from the central part of the lake yielded basal ages of ~250 kyr and 340 kyr before present (BP), respectively, evidencing that this lake has neither been desiccated nor inundated by continental ice sheets during the past glacial/interglacial cycles. Moreover, the lake sediment characteristics underscored the sensitivity of this lacustrine system to regional climatic and environmental change. Complementary shallow cores taken at the lake slopes demonstrated that gravitational mass movement had little impact on the sedimentation in the lake center. A seismic survey on the lake floor detected more than 300 meters of lacustrine sediments above an impact breccia and brecciated volcanic bedrock. These results confirmed the assumption that the basin had collected sediments continuously since the time of the impact.
Drilling operations
Drilling in remote northeastern Russia was a massive logistical undertaking. In summer 2008, the majority of technical equipment and field supplies was transported from the U.S. and Germany to Pevek, Russia, by way of Vladivostok and the Bering Strait.
In Pevek, the combined cargo was loaded onto trucks driven with bulldozer assistance more than 350 km over winter roads and cross-country to Lake El´gygytgyn. There, the operation was supported by a temporary winter camp on the western lake shore that was designed for up to 36 people. In the camp, a laboratory container for whole-core measurements of magnetic susceptibility stood next to a reefer in which the sediment cores were kept from freezing.
Permafrost drilling at Site 5011-3 in the western lake catchment was conducted in Nov./Dec. 2008 using a mining rig (SIF-650M) employed by a local drilling company (Chaun Mining Corp., Pevek). The crew reached a depth of 141.5 m with 91 % recovery.
After drilling, the borehole was permanently instrumented with a thermistor chain for ground temperature monitoring as part of the Global Terrestrial Network for Permafrost (GTN-P) of the International Permafrost Association (IPA), thus contributing to our understanding of future permafrost behavior in the light of contemporary rapid change.
In January/February 2009 an ice road was established between the camp and Site 5011-1 on central Lake El´gygytgyn. There, an ice pad of 100 m diameter was first cleared of snow and then artificially flooded with lake water to thicken and strengthen the ice to about 2 m thickness. This was necessary to allow for drilling operations with the 100-ton drilling system “Russian GLAD 800”, which was developed for extreme cold weather and operated by the U.S. consortium DOSECC. The system consists of a modified Christensen CS-14 diamond coring rig positioned on a mobile platform that is weather-protected by insulated walls and a tent on top of the 20 m high derrick. Lake drilling at Site 5011-1 was conducted from February to April 2009. It included the use of casing through the 170 m thick water column into the uppermost sediments. Holes 1A and 1B had to be abandoned after twist-offs at 147 and 112 meters below lake floor (mblf), respectively. Drilling by Hydraulic Piston Corer (HPC) and Extended Nose Corer (EXC) resulted in recoveries of 92 % in Hole 1A and 98 % in Hole 1B. In Hole 1C, continuous drilling started in 100 mblf with an Alien Bit Corer (ALN), followed by a Hard rock Bit Corer (HBC) from 265 mblf on. With these tools, recoveries of only 52 % in the lake sediments and 76 % in the impact rocks were obtained.
Core Processing
Initial processing of the drill cores recovered from the El´gygytgyn Crater, including basic descriptions, photographical documentations, and partial measurements of magnetic susceptibilities, took place already on site. Following core export to Germany in Sept. 2009, the permafrost cores were further processed at the Alfred Wegener Institute (AWI) in Bremerhaven. The impact rock cores were characterized in detail at the Natural History Museum in Berlin, before a sampling party took place there in May 2010. The lake sediment cores were fully processed at the University of Cologne by the end of 2012. This involved core opening and description, MSCL logging, XRF scanning and X-radiography, as well as continuous subsampling of one core half in 2 cm thick increments. The ca. 9000 subsamples from the lake sediment composite were subdivided into 9 alliquots for a variety of analyses to be carried out on the laboratories collaborating in the El´gygytgyn Project. In early 2013, the archive halves of the lake sediment cores were shipped to the U.S. National Lacustrine Core Repository (LacCore) at the University of Minnesota for long-term storage.
Results and Publications
First major results obtained from the El´gygytgyn lake sediment record were published by Melles et al. (2012, Science 337: 315-320) and Brigham-Grette et al. (2013, Science 340: 1421-1427). Whilst the latter paper discusses the long-term climate development from the protracted warmth of the middle Pliocene into the earliest glacial cycles of the Quaternary, showing stepped cooling events during the Pliocene-Pleistocene transition, the former paper focuses on exceptionally warm interglacials („super interglacials“), which irregularly occurred at Lake El´gygytgyn throughout the Quaternary and are to be explained by feedback mechanisms with Antarctica rather than variations in global greenhouse gas concentrations or orbital parameters.
Many details of both the lake sediment record and the permafrost core were published in 2013 and 2014 in about 30 papers that are combined into a special issue of the journal Climate of the Past (guest edited by Brigham-Grette et al.). Selected findings from the impact rocks, on the other hand, were published in 12 papers in a special issue of the journal Meteoritics and Planetary Science (2013, 48(7): 1107-1358).