If you thought Iceland’s volcano that erupted in 2010—Eyjafjallajökull—was hard to pronounce, avert your eyes. A unique new record of arctic climate has just been published from Russia’s Lake El’gygytgyn— or as many researchers despairingly call it, “Lake E.”
The 550 ft deep lake fills an impact crater that formed nearly 3.6 million years ago. Since then, the lake has dutifully collected sediment that washed in from the small basin surrounding it. The area has been spared the abuse of ice sheets, as well, which tend to disturb accumulated sediments and sometimes scrape them away altogether.
Since the lake is nutrient-poor and covered with ice for much of the year, the water is clear and oxygen-rich. But conditions change along with climate, and that’s what makes the lake appealing to paleoclimate researchers. Such lengthy records of climate are incredibly rare above sea level. Ice cores from Greenland only go back around 125,000 years, and the longest Antarctic ice core completed records around 800,000 years.
At great expense and effort, a large group of collaborators collected several sediment cores from the lake bottom, including a 517 meter long one that went straight down to the bedrock at the bottom of the crater. (They also recorded some videos in the field). In the first of many papers to be published, the researchers describe a record of the last 2.8 million years of climate in the Siberian Arctic.
A host of methods were used to interrogate the core and extract the stories it tells. Changes in magnetic properties helped determine the age along the core (using the frequent oscillations of Earth’s magnetic field) and indicate how much oxygen was in the water. When lakes stay stratified all year instead of mixing in the spring and fall, or when a surplus of organic matter sits decaying at the bottom, oxygen in the deep lake water becomes depleted and magnetite (an iron oxide) dissolves. The ratio of manganese to iron provides another measure of oxygenation.
The researchers also measured organic carbon, which tracks the preservation or decay of organic matter, and the ratio of silicon to titanium, which shows the productivity of photosynthetic diatoms. In addition, pollen assemblages were painstakingly collected to record shifts in the plant ecosystems around the lake. And you can figure out a lot just using your eyeballs and some good old-fashioned sedimentology.
The researchers identified three distinct “facies,” or characteristic packages of sediment. The first included thin gray and black layers of sediment that were deposited during the coldest periods, when ice on the lake stayed year-round. Without periods of wind-driven mixing, the bottom water became oxygen-poor. The gray sediment is indicative of reduced iron (rather than oxidized), and the black color signifies organic matter that accumulated rather than decaying completely.
Another facies containing browner sediment with less distinct layers is the most common in the core. This corresponds, roughly, to modern conditions. The ice thaws off in summer, allowing photosynthetic activity and oxygenation.
The third facies, a rusty-red due to the prevalence of oxidized iron (in contrast to the gray sediment), appears to be associated with particularly warm episodes between “ice ages” (or glaciations). Photosynthetic activity was especially high during these “super interglacials."
These time periods are identified by their ocean sediment core monikers—Marine Isotope Stages (MIS). MIS 5e, which occurred around 130,000 years ago, came at a peak in arctic summer solar radiation. Sea level likely hit a high point a few meters higher than it is today. MIS 11c, a little over 400,000 years ago, was an unusually long interglacial, though it doesn’t look as warm as MIS 5e in Antarctic ice core records.
Surprisingly, the Lake El’gygytgyn region seems to have been considerably warmer during MIS 11c than it was during MIS 5e. This is despite the fact that summer solar radiation was less intense (though the season was longer) and greenhouse gas concentrations were similar. The authors write, “Consequently, the distinctly higher observed [temperature and precipitation] at MIS 11c cannot readily be explained by the local summer orbital forcing or GHG concentrations alone, and suggest that other processes and feedbacks contributed to the extraordinary warmth at this interglacial, and the relatively muted response to the strongest forcing at MIS 5e.”
The Arctic is especially sensitive to climate changes (through the loss of reflective snow and ice, for example), and what happens there affects the rest of the planet as well. Figuring out which feedbacks could account for the warm temperatures during MIS 11c could be useful.
Seeing how climate responds to many different situations helps researchers obtain a deeper understanding of the climate system. And therein lies the value in climate records from disparate regions. As the authors put it, “The observed response of the region’s climate and terrestrial ecosystems to a range of interglacial forcing provides a challenge for modeling and important constraints on climate sensitivity and polar amplification.”
Science, 2012. DOI: 10.1126/science.1222135 (About DOIs).
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