Greenland ice sheet collapse, 400,000 years ago

New evidence suggest that the longest interglacial (the time in […]

Post Author:

Chris Machens

Date Posted:

July 19, 2014

New evidence suggest that the longest interglacial (the time in between ice ages) – a warming period, called Marine Isotope Stage 11, more than 400,000 years ago, created nearly complete deglaciation of southern Greenland, thus contributed 4-6 meters to global sea level rise at that period. Overall se alevel rose about 6-13 meters above present levels. The estimated attribution from Greenland has been scarce so far, the new study helps to close a gap. The new study also hints to our situation today, offers clues what we should expect.

Bedrock terrane boundaries (black dashed lines) and sampling sites for Greenland stream sediments (filled circles; multiple sites per symbol); KMB, Ketilidian Mobile Belt (grey); AB, Archaean Block (red); NMB, Nagssugtoqidian
Bedrock terrane boundaries (black dashed lines) and sampling sites for Greenland stream sediments (filled circles; multiple sites per symbol); KMB, Ketilidian Mobile Belt (grey); AB, Archaean Block (red); NMB, Nagssugtoqidian

Reporting Climate Science, has more: The study is one of the first to zero in on how the vast Greenland ice sheet responded to warmer temperatures during that period, which were caused by changes in the Earth’s orbit around the sun.“The climate 400,000 years ago was not that much different than what we see today, or at least what is predicted for the end of the century,” said Anders Carlson, an associate professor at Oregon State University and co-author on the study. “The forcing was different, but what is important is that the region crossed the threshold allowing the southern portion of the ice sheet to all but disappear.

“This may give us a better sense of what may happen in the future as temperatures continue rising,” Carlson added.

The researchers examined sediment cores collected off the coast of Greenland from what is called the Eirik Drift. During several years of research, they sampled the chemistry of the glacial stream sediment on the island and discovered that different parts of Greenland have unique chemical features. During the presence of ice sheets, the sediments are scraped off and carried into the water where they are deposited in the Eirik Drift.

“Each terrain has a distinct fingerprint,” Carlson noted. “They also have different tectonic histories and so changes between the terrains allow us to predict how old the sediments are, as well as where they came from. The sediments are only deposited when there is significant ice to erode the terrain. The absence of terrestrial deposits in the sediment suggests the absence of ice.

“Not only can we estimate how much ice there was,” he added, “but the isotopic signature can tell us where ice was present, or from where it was missing.”

This first “ice sheet tracer” utilizes strontium, lead and neodymium isotopes to track the terrestrial chemistry.

Carlson said the ice sheet loss likely went beyond the southern edges of Greenland, though not all the way to the center, which has not been ice-free for at least one million years.

The Ilulissat Fjord toward the terminus where Jakobshavn Isbrae (Greenland’s fastest glacier) rapidly discharges ice into the ocean

South Greenland ice-sheet collapse during Marine Isotope Stage 11

Nature 510, 525–528 (26 June 2014) doi:10.1038/nature13456

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Varying levels of boreal summer insolation and associated Earth system feedbacks led to differing climate and ice-sheet states during late-Quaternary interglaciations. In particular, Marine Isotope Stage (MIS) 11 was an exceptionally long interglaciation and potentially had a global mean sea level 6 to 13 metres above the present level around 410,000 to 400,000 years ago, implying substantial mass loss from the Greenland ice sheet (GIS).

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here are, however, no model simulations and only limited proxy data to constrain the magnitude of the GIS response to climate change during this ‘super interglacial’, thus confounding efforts to assess climate/ice-sheet threshold behaviour and associated sea-level rise. Here we show that the south GIS was drastically smaller during MIS 11 than it is now, with only a small residual ice dome over southernmost Greenland.

We use the strontium–neodymium–lead isotopic composition of proglacial sediment discharged from south Greenland to constrain the provenance of terrigenous silt deposited on the Eirik Drift, a sedimentary deposit off the south Greenland margin. We identify a major reduction in sediment input derived from south Greenland’s Precambrian bedrock terranes, probably reflecting the cessation of subglacial erosion and sediment transport as a result of near-complete deglaciation of south Greenland.

Comparison with ice-sheet configurations from numerical models suggests that the GIS lost about 4.5 to 6 metres of sea-level-equivalent volume during MIS 11. This is evidence for late-Quaternary GIS collapse after it crossed a climate/ice-sheet stability threshold that may have been no more than several degrees above pre-industrial temperatures.

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Another analogous period was MIS5,

High rates of sea-level rise during the last interglacial period

Marine Isotope Stage (MIS) 5e (around 123,000 years ago), was the last interglacial period before the present (Holocene), and compared global mean surface temperatures were at least 2 °C warmer. Mean sea level was 4–6 m higher than at present, following reductions of the Greenland ice sheet. Fossil reef proxies indicate sea level fluctuations of up to 10 m around the mean. Based on the data obtained from stable oxygen isotopes of planktonic foraminifera and age constraints from corals, estimates suggest average rates of sea-level rise of 1.6 m per century. The findings are important to understand current climate change, because global mean temperatures during MIS-5e were similar to the projected climate change today.

The teaser image shows the Sermilik fjord (Sermilik Station), a place where hundreds of icebergs calve from Greenland’s vast ice sheets.
Study shows Antarctica’s impact on sea – A massive melt from the Antarctic ice sheet 14,600 years helped increase global sea levels by 16 metres
Under the Ice: A closer look at recent Antarctica and Greenland Ice Melt

About the Author: Chris Machens

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Covering the climate for Climate State since 2011. Peter Sinclair noted in 2017, "Climate State has been doing an absolutely amazing job of providing a useful historical archive of important experts warning on climate issues through past decades."

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