Research at Lake El'gygtygn

About 3.6 million years ago, a meteorite landed in north-eastern Siberia, creating an 18 kilometer-wide crater that since filled with 170 m of water and 350 m sediments. We believe that these sediments hold a 3.6 million climate record of the Arctic -- the longest continuous terrestrial arctic climate record by far. In fact, our previous shallow cores (about 12 m deep) from there are already the oldest at 250,000 years. The project team consists of Russians, Germans, Americans, Austrians, and Canadians. We have recently been funded through a consortium of national and international funding agencies to extract a core throughout the entire sediment thickness and into the shattered bedrock beneath. This drilling project is scheduled to occur in spring of 2008. This project is part of the endorsed IPY project called BIPOMAC.

Most of my research here has been to understand the modern hydrological and limnological environment so that we can better constain the paleoclimate interpretations. I've done this through a combination of field work (trips in 1998 and 2000) and remote sensing of the lake ice, though I am now getting into modeling interactions between lake ice and lake water circulation. As part of our outreach work, I've created a number of 3D visualizations of this remote crater-lake. Recently I was funded by NSF to return to the lake during the drilling project to investigate winter water circulation within the lake and to model sublimation rates of lake ice to help us determine whether the lake may have dried up in the past. I am facilitating some data exchange on this page.

I have written two papers about my research here thus far, and there are another dozen or so by the project team, many of them in a recent special issue in the Journal of Paleolimnology dedicated to our project.

Nolan, Matt and Julie Brigham-Grette, 2007. Basic hydrology, limnology, and meteorology of modern Lake El’gygytgyn, Siberia. J. of Paleolimnology, 37:17-35.

Nolan, Matt, Glen Liston, Peter Prokein, Julie Brigham-Grette, Virgil Sharpton, and Rachel Huntzinger, 2003. Analysis of Lake Ice Dynamics and Morphology on Lake El'gygytgyn, Siberia, using SAR and Landsat. J. Geophys. Research, 108 (D2) 8062, doi:10.1029/2001JD000934.

Our Study Area: A Lake with the Oldest Terrestrial Climate Record of the Arctic, Inside One of the Best Preserved Meteorite Impact Craters on Earth
The El’gygytgyn depression in northeastern Siberia is the best preserved meteorite impact crater on earth for both its size and its location in igneous target rocks. Soon after the impact 3.6 million years ago, the crater partially filled with a large lake. The streams draining the crater watershed carry with them sediments that contain proxy indicators of climate at the time of deposition. In 1998 we retrieved a 300,000 year old sediment core from the lake. We have since analyzed the sediments, creating the longest terrestrial climate record of the Arctic. A longer core retrieval is planned, which will hopefully yield a climate record more than 3 million years old. At right is a mosaic of Ikonos satellite images of the crater.

Lake Ice is the Dominant Control on Lake Biogeochemistry and the Sediment Core Proxies
The 1998 core reveals distinct transitions in most of the proxies, including sedimentation rate, laminations, diatoms, pollen, magnetic susceptibility, and other biogeochemical markers on millenial time-scale. These studies indicate that duration of lake ice cover – particularly whether it melts in summer or not – is the dominant control on lake biogeochemistry, because of the way it affects both mixing dynamics and dissolved oxygen content. Knowledge of paleo lake ice cover duration is also a valuable clue towards understanding paleo-climate. Understanding the modern hydrological, limnological, and energy balance processes is necessary to fully interpret the core record, because such observations provide our best opportunity to link climate and proxy dynamics.

Satellite SAR is an Excellent Tool for Studying Modern Lake Ice Dynamics
Based on over 400 SAR scenes, we have determined the average dates of snow melt onset, ice melt onset and completion of both over the past four years. Shown below is snow melt onset in two springs. SAR microwaves penetrate through the dry winter snow and the dominant backscatter signal comes from bubbles in the ice. Once the upper few centimeters of snow begin to melt, however, the penetration depth is reduced to less than the snow thickness (roughly 1 m), and the backscatter changes considerably. During subsequent freezing events, the ice backscatter signal briefly returns, validating our interpretation. From this strong signal response we can determine snow-melt onset to within a single day in some years.

SAR is also an excellent tool for observing the dynamics of lake ice break up. Seen here are scenes of moat formation, lead formation, and wind-blown ice floes; a Landsat 7 scene is shown for comparison. We have compared these data to modeled predictions of snow and lake ice dynamics with reasonable success (above right). We can now use this model to hindcast the conditions necessary to keep the lake ice from melting during the summer as part of the core-proxy interpretations. Our observations from the past four years are summarized in the table below.

Variations in Ice Backscatter Indicate Regions of Increased Biologic Production
We also observed an interesting distribution of bubble scatterers within the lake ice. Below is a time-series of SAR scenes showing the evolution of this pattern. As the ice thickens (from below), more bubbles are entrained. The shallow shelves have the warmest sediments due to solar radiation, and therefore the highest biological productivity. This productivity increases bubble formation due to increased respiration and decomposition, indicating new uses for SAR in studying lake biota dynamics.

These Variations in SAR Backscatter May Also Indicate the Location of the Central Peak of the Impact Crater, 500 Meters Below the Surface, Which Has Important Implications for the Next Sediment Coring Location
Two mechanisms may explain the central bright spot seen in the ice backscatter: density-driven currents from the shelves and groundwater/gas upwelling. Because the shelf water is about 4ºC and the bulk of the lake is near 3ºC, a density-driven current carries warm shelf water (and its inhabitants) to the bottom (below left), causing increased respiration and decomposition there. Because the lake is surrounded by permafrost but not underlain by it, the highly shattered bedrock is likely a conduit for groundwater and gas upwelling. Seismic evidence suggests that piping structures exist within the sediments above the central peak. Long-term, consistent upwelling there has consolidated the sediments, possibly correlating the deepest part of the lake basin with the central peak over time – this has important implications for future coring projects. The blue cross at lower right indicates the 1998 coring location; note that it is not within the bright spot, possibly indicating it is in a different biogeochemical regime, particularly during glacial times when these density driven currents may have been established under the ice. The darker area surrounding this bright spot varies yearly, possibly due to the varying strength of the density-driven current from year to year.