Inter-hemispheric climate coupling
Laura Nielsen for Frontier Scientists –
Paleoclimatology is the study of past climates. One of the many ways to study paleoclimatology is to collect a 2.5 inch [6.6 centimeter] wide tube of mud from a well-situated site. It’s amazing how much we can learn of Earth’s climate past – and what those findings teach us about the future.
A series of sediment cores were collected at Lake E’gygytgyn in Siberia. The bedrock beneath the lake was formed 3.6 million years ago when a meteorite slammed into Earth, an event that helps scientists assign time frames to all the sediment that has since collected at the site of the collision. Martin Melles, Institute of Geology and Mineralogy at Cologne University, was the project manager for the Germany-based researchers who took part in the international Lake El’gygytgyn Drilling Project. He states that the project goal was to collect sediment cores representing “A high resolution and uninterrupted reconstruction of the Arctic's climatic history,” because “We can derive from this how the Arctic will react to future climactic change and what impact these changes will have.”
The record chronicles a variable climate, with temperatures cycling slowly over many thousands of years through cold glacial periods when ice sheets crawled overland to warm interglacial periods when the Arctic became so warm that the far north hosted forests instead of tundra and permafrost.
“We're seeing intervals in the Arctic back through the last few million years that are much much warmer than anyone expected,” geologist Julie Brigham-Grette says. Those warm periods show Siberian regional summer temperatures north of the Arctic Circle of about 59 to 61 degrees Farenheit [about 15 to 16 degrees Celcius], which is 14.4 degrees Farenheit [8 degrees Celcius] warmer than modern trends. The warmer and wetter (with a precipitation rate three times higher than present) region even hosted forests.
Looking at the times leading up to those warm periods, as well as when the warm changed back to cold, helps us examine our own climate future. What happens when sea ice and ice caps melt? When permafrost thaws? How variable is our climate, and what are its tipping points? What led up to glacial or interglacial periods? The mud of the sediment cores provides a kind of fingerprint: layers filled with climate data.
Some of the powerful differences in temperature in Earth’s past can be explained by orbital cycles: the Earth’s orbit can be more circular or more oblong, which slightly changes how near to the Sun we approach, while the tilt of the planet’s axis can slightly increas or decrease, which alters how much sunlight reaches different lattitudes during the seasons. This causes slight climate variability over the span of many tens of thousands of years.
University of Massachusetts Amherst reports that “Simulations using a state-of-the-art climate model show that the high temperature and precipitation during the ‘super interglacials’ cannot be explained by Earth’s orbital parameters or variations in atmospheric greenhouse gases alone, which geologists typically see driving the glacial/interglacial pattern during ice ages. This suggests additional climate feedbacks are at work.”
Antarctica and the Arctic
Climate at the North and South pole are connected. Sediment records from Antarctica show that the West Antarctic ice sheet melted at various times in history. Following many of those events, the Arctic warmed. These recurring intervals of paired warming show that climate in the two hemispheres is linked – it’s called inter-hemispheric climate coupling.
“When the West Antarctic ice sheet pulls back we see a corresponding warmth in the high lattitudes again, probably affecting the size of the Greenland ice sheet with major implications for changes in sea level,” says Julie Brigham-Grette. “Our results mesh with what glaciologists are seeing today. Seven of the 12 major ice shelves around the Antarctic are melting or are gone. We suspect the tipping point for the gradual de-glaciation of Greenland and the Arctic may be lower than glaciologists once thought.”
Earth is a complicated place. We can’t explain past warming using only orbital dynamics or levels of Carbon Dioxide. Scientists affiliated with the project outlined some past events that might explain the rapid warming the sediment records show occurred in both Antarctica and the Arctic around similar times.
When you imagine Antarctica, the picture includes large ice shelves that hang off the rocky edge of the ice-covered continent. Normally that ice keeps nearby ocean water very cold. The cold water travels along currents toward the north Pacific where it wells up to the surface. Ocean circulation can be affected, though. If Antarctic ice sheets disintegrate or melt away, they no longer enforce cold water currents that journey to the Arctic. Instead, surface ocean waters in the Arctic become warmer.
When Antarctica’s ice sheets disintegrate the ocean gains more water and sea levels rise globally. The Bering Strait usually restricts how much warm surface water approaches the Arctic from the south, but higher sea levels would mean warm surface water didn’t have to squeeze through such a narrow space, letting more warm water past the Bering Strait into the Arctic Ocean.
Either way, a warmer ocean means higher temperatures and more rainfall for the Arctic, which impacts paleoclimatology and sea ice history. Grasping the climate connections between the hemispheres gives us insight into our near future.
Lake El’gygytgyn researchers aren’t only looking at how knowledge of paleoclimates can inform us about present-day climate change, they’re also making the science behind sediment coring more accessible. The University of Massachusetts Amherst and U.S. Project lead Julie Brigham-Grette hosted middle and high school teachers, leading them through a workshop on coring in local lakes, and working together to develop curriculum which the teachers could take back to their classrooms. Bolstering student interest in STEM fields (science, technology, engineering, and mathematics) is so important for our future. Students can look at local lacustrine (lake) records to understand how projects like the one at Lake El’gygytgyn collect proxy records to study Earth’s climate.
Watch: Lake El'Gygytgyn Teacher Training Workshop2013 Building System Science into the Classroom on FrontierScientists' Youtube channel
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
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] (abstract link)
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] (abstract link)
Watch: Julie Brigham-Grette presents Lake El'gygytgyn Research on FrontierScientists' Youtube channel
- 'Geologic Climate Research in Siberia expedition journal' PolarTREC teacher Tim Martin, Lake El'gygytgyn Drilling Project (2009)
- 'Ice-Free Arctic May be in Our Future, Say UMass Amherst, International Researchers' Janet Lathrop for UMassAmherst News & Media Relations (May9, 2013)
- 'Polar Archive' video, DFG Science TV (June15, 2009)
- 'UMass Amherst Geo Sci Newsletter' (2013)
- 'UMass Amherst Researchers, International Team, Say Past Periodic Warmth in Arctic May Be Related to Melting Antarctic Ice Sheets' Janet Lathrop for UMass Amherst News & Media Relations (June21, 2012)