Glacier’s size runs hot and cold

U. BUFFALO (US) — Calving glaciers are particularly sensitive to climate change, shrinking rapidly in response to global warming and growing at a similar pace during periods of cooling.

An analysis of Jakobshavn Isbrae, a tongue of ice extending out to sea from Greenland’s west coast, and adjacent lake sediments and plant fossils  show the glacier that retreated about 40 kilometers inland between 1850 and 2010, expanded outward at a similar pace about 200 years ago, during a time of cooler temperatures known as the Little Ice Age.

Shanna Losee measures sediment properties in the Glacial Lake Morten lake basin, Greenland. (Credit: Jason Briner)

“We know that Jakobshavn Isbrae has retreated at this incredible rate in recent years, and our study suggests that it advanced that fast also,” says Jason Briner, associate professor of geology at University at Buffalo.

Jakobshavn Isbrae is one of the world’s fastest-flowing glaciers, releasing enormous quantities of Greenland’s ice into the ocean. Changes in the rate at which icebergs calve off from the glacier could influence global sea level rise.

The research is published online in the journal Quaternary Science Reviews.

The decline of Jakobshavn Isbrae between 1850 and 2010 has been well-documented through aerial photographs and satellite photographs which show the ice shrinking rapidly from west to east along a narrow fjord.

To reconstruct the glacier’s advance from east to west during earlier, cooler years, Briner examined sediment samples from Glacial Lake Morten and Iceboom Lake, two glacier-fed lakes that sit along the glacier’s path of expansion.

As Jakobshavn Isbrae expanded seaward, it reached Glacial Lake Morten first, damming one side of the lake with ice and filling the basin, previously a tundra-covered valley, with meltwater.

To pinpoint the time in history when this happened, researchers counted annual layers of overlying glacial sediments and used radiocarbon dating to analyze plant fossils at the lake bottom (the last vestiges of the old tundra). The team’s conclusion: Glacial Lake Morten formed between 1795 and 1800.

Sediment layers show that Jakobshavn Isbrae reached Iceboom Lake about 20 or 25 years later, around 1820.

Jakobshavn Isbrae’s rate of expansion from Glacial Lake Morten to Iceboom Lake matched the glacier’s rate of retreat between those two points. Aerial imagery shows Iceboom Lake draining around 1965 and Glacial Lake Morten draining between 1986 and 1991.

Jakobshavn Isbrae (Credit: Bea Csatho)

Researchers from Brown University contributed to the study.

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