14 December 2016
By Aylin Woodward
Sediment layers from a lake in the western Canadian Arctic may hold the key to predicting sea-ice loss and warming Arctic temperatures, new research finds.
In a new study presented at the 2016 American Geophysical Union Fall Meeting, researchers found that sediment cores from the deepest part of a lake in Nunavut, Canada can reveal a detailed history of fluctuating ocean temperatures and precipitation levels for at least the past 700 years.
According to the researchers, layers of the lake’s sediment offers clues to a 20-30 year recurring fluctuation in sea surface temperature called the Pacific Decadal Oscillation, or PDO. Like a long-lived El Niño, the PDO affects temperature and precipitation in areas surrounding the Pacific Ocean. Research has shown that sea-ice loss during the negative phase of the PDO—when there are colder-than-normal ocean temperatures along the western American coast—is linked to increased Arctic warming.
“Our big challenge is to predict future PDO changes, so we have a reliable way of knowing what’s coming in terms of future Arctic warming,” said François Lapointe, a paleoclimatologist at the National Institute of Scientific Research at the University of Quebec in Quebec City, Canada and lead author of the new study. “With our records we have a better potential in projecting the PDO in the future.”
The PDO record has typically been reconstructed using tree rings from temperature and precipitation-sensitive trees that would have been affected by the climate variability associated with the PDO. But according to Lapointe, such reconstructions aren’t always the most reliable. “The literature shows that different PDO reconstructions from trees in different geographic areas don’t always agree,” he said. Lapointe suggested certain trees might respond to PDO conditions in different ways, which could explain these inconsistencies.
Lapointe suspected lake sediments might also capture changes in the PDO. For the new study, he journeyed to Cape Bounty off the coast of Melville Island to collect lake sediment layers known as varves. Each annual varve consists of a layer of coarse silts deposited in spring when snow melts and a layer of clay deposited in winter. Thicker varves indicate an increased level of snowmelt or large amount of rainfall for that year.
Lapointe’s team looked at a 4.36-meter (14.3-foot) section of lake sediment to examine over 2,000 years of the varve record. They found varve thickness variation correlated with the PDO: thicker sediments appeared in years with more precipitation, when the PDO phase was negative.
The new analysis of lake sediments demonstrates a less polluted signal at Cape Bounty, East Lake: varves can consistently map PDO fluctuations, which can inform PDO projections into the future, according to the researchers.
“Lapointe has created a brand new paleo-record of the Pacific Decadal Oscillation,” said Mathias Vuille, a climate dynamics scientist at the State University of New York, Albany and co-author of the new study, published in Climate of the Past Discussions. “There are a few that exist, but they’re mostly based on tree-rings. Now we have one that’s based on annual varves.”
“You’ve got no trees up there [near Cape Bounty], so this is one of the only paleoclimate reconstructions of this region,” said Jean-Philippe Jenny, a biogeoscientist at the Max Planck Institute for Biogeochemistry in Jena, Germany and co-author of the study.
Jaclyn Cockburn, professor of geography at the University of Guelph in Ontario, Canada is impressed by Lapointe’s ability to “see the forest for the trees.” Cockburn, who judged Lapointe’s poster but was not involved in the study, said that he “has that ability to go from the field into the lab and still have that sense of the big picture.”
—Aylin Woodward is a graduate student in the UC Santa Cruz Science Communication Program. Follow her on Twitter @AylinWoodward.