Monday, February 4, 2013

New paper finds Greenland Istorvet icecap was smaller than the present 1000 years ago

A paper published today in Quaternary Science Reviews examines fossilized plants at the edge of the Istorvet ice cap in East Greenland and determines the ice cap "was smaller than the present from AD 200 to AD 1025." The ice cap subsequently grew during the Little Ice Age [LIA] and then retreated to the present size significantly larger than was present during the Medieval & Roman warming periods. 

Aerial photo of the Istorvet ice cap today, retreated positions shown by dots above from AD 600-1000, and lower limit during the LIA shown by "LIA Limit"

Late Holocene expansion of Istorvet ice cap, Liverpool Land, east Greenland

  • a Department of Geology, University of Cincinnati, Cincinnati, OH 45226, USA
  • b School of Earth and Climate Sciences and the Climate Change Institute, University of Maine, Orono, ME 04469, USA
  • c Department of Earth Sciences, Dartmouth College, Hanover, NH 03755, USA
  • d Geological Survey of Denmark and Greenland, Oster Voldgade 10, Copenhagen, Denmark
  • e GCI, 41086 Tiller Road, Soldiers Grove, WI 54655, USA

Abstract

The Greenland Ice Sheet is undergoing dynamic changes that will have global implications if they continue into the future. In this regard, an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior. Small, independent ice caps adjacent to the Greenland Ice Sheet (hereinafter called “local ice caps”) are sensitive indicators of the response of Greenland ice-marginal zones to climate change. Therefore, we reconstructed late Holocene ice-marginal fluctuations of the local Istorvet ice cap in east Greenland, using radiocarbon dates of subfossil plants, 10Be dates of surface boulders, and analyses of sediment cores from both threshold and control lakes. During the last termination, the Istorvet ice cap had retreated close to its maximum Holocene position by ∼11,730 cal yr BP. Radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the Istorvet cap was smaller than at present from AD 200 to AD 1025. Sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its Holocene maximum position by ∼AD 1150. Thereafter the ice cap remained at or close to this position until at least AD 1660. The timing of this, the most extensive of the Holocene, expansion is similar to that recorded at some glaciers in the Alps and in southern Alaska. However, in contrast to these other regions, the expansion in east Greenland at AD 1150 appears to have been very close to, if not at, a maximum Holocene value. Comparison of the Istorvet ice-cap fluctuations with Holocene glacier extents in Southern Hemisphere middle-to-high latitude locations on the Antarctic Peninsula and in the Andes and the Southern Alps suggests an out-of-phase relationship. If correct, this pattern supports the hypothesis that a bipolar see-saw of oceanic and/or atmospheric circulation during the Holocene produced asynchronous glacier response at some localities in the two polar hemispheres.

Highlights

► Deglaciation to the present extent of local ice cap completed by 11,730 cal yr BP. ► Relic plant remains indicate former restricted extent of ice caps in East Greenland. ► Ice cap extents were smaller than present until about AD 1025. ► Local independent Greenland glaciers reached Holocene maximum by AD 1150. ► The Greenland ice sheet may mirror the Holocene growth and decay of local ice caps.

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