Retreating glaciers in East Greenland reveal plant remains dating from the 16th and 17th centuries

Retreating glaciers in East Greenland reveal plant remains dating from the 16th and 17th centuries
Retreating glaciers in East Greenland reveal plant remains dating from the 16th and 17th centuries
Anonim

Discovered mosses and willow shrubs buried under modern retreating glaciers in East Greenland can be dated to 400-500 years ago, suggesting that this period (the beginning of the Little Ice Age) was just as warm or warmer than it is today.

It is widely accepted that the surface temperature of Greenland has been several degrees warmer, and the volume and area of ​​ice has been significantly less for almost all of the last 8,000-10,000 years.

What may not yet be widely accepted is the conclusion that present-day temperatures and ice area are still in the "cold stage" range of the Holocene, rather than the warm stage.

New research documents a warmer than today early and middle Holocene in East Greenland - a time when ice caps were "absent" or were much less extensive than they are now. Plant remains buried under retreating glaciers in East Greenland confirm that these places were not covered by glaciers 400-500 years ago.

But the authors also report that there were intermittent short "cold spells" during the Holocene, when the extent of Greenland's glaciers reached today's levels.

"… The Renland Ice Cap briefly reached a size during cold phases that could be similar to today's."

This suggests that current temperatures and volumes of ice also fall within the "cold stage" range.

Brief conclusions of the study:

Holocene glacial history of the Renland Ice Cap, East Greenland, reconstructed from lacustrine sediments

Basic moments

- Precipitation from glacier-fed lakes limits the Holocene history of the Renland Ice Cap.

- By ∼10,000 BC the ice area was the same or less than it is now.

- Oscillations of glaciers on a millennial scale occurred throughout the Holocene.

- To fully understand the changes in the ice sheet in the region, several geographic conditions need to be studied.

Shrinking glaciers, melting permafrost and shrinking sea ice indicate a rapid shrinking of the Arctic cryosphere in response to current climate warming, and this trend is expected to continue, if not accelerate.

The response of the Arctic cryosphere to past periods of climate change can provide insight into its current and future behavior. Here we explore the ∼12,000-year history of glacier and meltwater fluctuations associated with the Renland Ice Cap, East Greenland, which extends from an early Holocene thermal optimum through the cooling of the Little Ice Age to the present.

Sediments from glacier-fed lakes indicate rapid Early Holocene deglaciation, with the ice area likely to have been somewhat smaller than it is today by ∼9500 BC. Glacial activity led to the periodic deposition of rock chips in the studied lakes in the early Holocene, at least until ∼7500 BC.

Stone chips are absent for most of the period ∼7000-4000 BC, indicating that the extent of the glaciers was generally shorter than at present.

However, thin layers of bluish-gray clay during this period may indicate a millennial expansion of the ice sheet, with the Renland Ice Cap briefly reaching such dimensions during cold phases that it may were similar to modern ones.

Glacial deposition occurred again in the Late Holocene at ∼3200-3400 BP, followed by a short glacial episode of ∼1340 BP, followed by a major event beginning shortly after ∼1050 BP.

We assume that the deposition of rock chips in the lakes in the past millennium was consistent with the advancement of the Renland glaciers towards their Little Ice Age positions, marked by a fresh, gray demolition boundary.

Radiocarbon dates of in situ plant residues adjacent to the current ice cap indicate a short relatively warm period ∼500 years ago, when the ice was within the 2011 boundary, after which the glaciers recovered.

The overall pattern of ice fluctuations in Renland is similar to that of other ice caps in the region, but with important differences, including the retention of a possible Middle Holocene record at a time when ice caps at lower altitudes in the Scorsby Sound region may have been absent.

This finding supports the concept that several geographic and geomorphological conditions need to be studied in order to fully understand ice variations in the region.

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