Data from an impact crater
Laura Nielsen for Frontier Scientists –
There's a place in Northeast Russia where, 3.6 million years ago, a meteorite slammed into Earth. A lake filled the crater. Today, the sediment that has settled at the bottom of Lake El-gygytgyn provides a rare preserved climate record: the longest sediment core record ever collected on land in the Arctic. The secrets at the bottom of the lake are being uncovered.
The international Lake El’gygytgyn Drilling Project undertook the complex mission of extracting sediment cores (long cylinders of mud containing ancient fossils of organic matter, pollen, algae, minerals and ash) from the frozen Siberian lake located 60 miles [100 kilometers] north of the Arctic Circle. The lake is in a great position to give insight into the Arctic's climate past because, unlike much of the land in the northern hemisphere, it was not long-covered by the continental glaciers which dominated during the ice ages. Principle investigator Julie Brigham-Grette of the University of Massachusetts Amherst was the the lead U.S. scientist on the project.
Numbers much like ours
The unprecedented knowledge gained from the Lake El'gygytgyn sediment core about Earth's climate 2.2 to 3.6 million years ago has “Major implications for understanding the pacing and context of how the Arctic transitioned from a forested landscape without ice sheets to the ice- and snow-covered land we know today,” says Brigham-Grette. The record shows segments in Earth's history when atmospheric carbon dioxide (CO2) levels were similar to today (estimated at about 400 parts per million), yet conditions were different. The Arctic was dominated by forests instead of tundra and permafrost. The Greenland ice sheet probably melted entirely.
The discrepancy suggests that we're still catching up: our climate is changing so quickly that there is essentially lag time as Earth's systems adjust. Plants are already shifting their ranges north; perhaps we too will see a forested Arctic.
By reconstructing ancient paleo-temperatures, the scientists are working to understand what led to the warm Arctic conditions... what was the tipping point? Their research suggests that commonly accepted estimations of future sea-level rise may be overly conservative.
Geologist Julie Brigham-Grette explains: "The value of our record is looking at the fact that the Arctic can become very quickly very warm and that warmer environment is reaching a point where increasing melt of places like Greenland and the West Antarctic ice sheet are almost inevitable."
Ice age patterns
Ancient climate conditions recorded by Lake El'gygytgyn sediment cores alternated between glacial periods, times during ice ages when glaciers and ice sheets advanced over the continents, and interglacials when warmer climate dominated. These periods lasted thousands of years. When temperatures rose during the warm interglacials the rate of change was slow, whereas the hike in CO2 and temperature levels we are experiencing in modern times is happening very quickly over the course of mere centuries.
Julie Brigham-Grette's team delved into the sediment record to locate warm interglacial periods, especially super-interglacial periods when summer temperatures rose in excess of 6 or 7 degrees warmer than present – these are "Intervals in the Arctic back through the last few million years that are much much warmer than anyone expected," Brigham-Grette notes.
The team coordinated with scientists who have drilled ocean-sediment cores from Antarctica to see what was happening on the opposite side of the world around the same time periods as the Arctic super-interglacials.
They found evidence of a connection. When the West Antarctic ice sheet disappeared in the southern hemisphere, there was a slight delay and then northern hemisphere Arctic conditions became warmer and wetter. Brigham-Grette: "We were able to determine that during many times when the West Antarctic ice sheet disappeared, we see a corresponding warm period following very quickly in the Arctic. Arctic warm periods cluster with periods when the Western Antarctic ice sheet is gone.” And during the most intense of those Arctic warm periods, it is vastly unlikely that the Greenland ice sheet survived at all.
Diatoms, pollen, and ash
What is there in lake sediment that tells us what past climate conditions were like?
The bodies of ancient Diatoms, microscopic organisms which are a type of algae, can be tested to reconstruct past climate conditions. PolarTREC teacher Tim Martin who accompanied the Lake El'gygytgyn expedition explains: "The number and kind of diatoms in the sediment is a good indicator of the past climate history of the lake. In times when the lake was warm with more nutrients, there were more diatoms, in times when the lake was frozen year-around, there are fewer."
We know from studying Arctic snow and water tracks that nutrients move in complex ways through the far-north environment. Vital elements like nitrogen which are necessary for life cycle more slowly in ice bound environments, but can be carried more fluidly by liquid water. The chemical composition of organisms like diatoms help scientists infer past climate data.
Other plants help tell the story of climate history too. Layers of pollen trapped in Lake El'gygytgyn sediment cores also serve as proxy data. We can use knowledge about modern plant species' habitats to understand what habitats their ancestors thrived in, which allows scientists to determine seasonal temperature ranges and precipitation rates in years long past. It's intriguing to look at images of the cores because the color of the sediment fluctuates along with past climate conditions.
Sediment can contain evidence of wildfires, volcanic ash, and soil particles that once reached the atmosphere due to meteorite impacts. Volcanic eruptions which eject ash high into the atmosphere leave airborne minuscule particles that can linger aloft for a long time. Enough of those tiny black particles together can reduce the amount of sunlight which reaches the ground, and affect growing conditions for plants.
We can't go back in time and use modern-day temperature sensors, and so gaining evidence from these clues hidden in lake sediment is an important part of the scientific process, providing the context for understanding warm interglacials. Lake El'gygytgyn work represents the art of rescuing climate clues from mud.
Frontier Scientists will take a closer look at what Julie Brigham-Grette's team discovered in the Lake El'gygytgyn sediment record, and what it can teach us about Earth's climate cycles.
Want to delve deeper right away? Watch: Julie Brigham-Grette presents Lake El'gygytgyn Research on FrontierScientists' Youtube channel
Find Lake El'gygytgyn papers in Science
2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia
Martin Melles, Julie Brigham-Grette, Pavel S. Minyuk, Norbert R. Nowaczyk, Volker Wennrich, Robert M. DeConto, Patricia M. Anderson, Andrei A. Andreev, Anthony Coletti, Timothy L. Cook, Eeva Haltia-Hovi, Maaret Kukkonen, Anatoli V. Lozhkin, Peter Rosén, Pavel Tarasov, Hendrik Vogel, and Bernd Wagner
Science 20 July 2012: 337 (6092), 315-320.Published online 21 June 2012 [DOI:10.1126/science.1222135]
Pliocene Warmth, Polar Amplification, and Stepped Pleistocene Cooling Recorded in NE Arctic Russia
Julie Brigham-Grette, Martin Melles, Pavel Minyuk, Andrei Andreev, Pavel Tarasov, Robert DeConto, Sebastian Koenig, Norbert Nowaczyk, Volker Wennrich, Peter Rosén, Eeva Haltia, Tim Cook, Catalina Gebhardt, Carsten Meyer-Jacob, Jeff Snyder, and Ulrike Herzschuh
Science 21 June 2013: 340 (6139), 1421-1427.Published online 9 May 2013 [DOI:10.1126/science.1233137]
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
- 'El'gygytgyn Crater, Russian Far East' Michon Scott, NASA Earth Observatory image of the day (Dec14, 2008)
- Geologic Climate Research in Siberia expedition journal 'April 16, 2009 In the lab and a hike with Wildlife' PolarTREC teacher Tim Martin, Lake El'gygytgyn Drilling Project (April16, 2009)
- 'Ice-Free Arctic May be in Our Future, Say UMass Amherst, International Researchers' Janet Lathrop for UMassAmherst News & Media Relations (May9, 2013)
- 'Scientists’ Concerns Challenge Conservative Sea-Level Rise Projections' Yale Forum ‘This Is Not Cool’ video series, Yale Project on Climate Change Communication (Dec5, 2013)
- 'UMass Amherst Researchers, International Team, Say Past Periodic Warmth in Arctic May Be Related to Melting Antarctic Ice Sheets' Janet Lathrop for UMassAmherst News & Media Relations (June21, 2012)