The Global Last Glacial Maximum

Around 27,000 years ago, ice sheets reached their maximum across the world, after a period of global cooling caused by variations in the Earth’s orbit around the sun. There was a massive ice sheet in North America (the Laurentide Ice Sheet)[1, 2], a large Eurasian Ice Sheet covering Britain, Ireland and Scandinavia as well as northern Europe[3], an ice sheet in Antarctica[4], the Himalaya and Patagonia[5, 6]. Land near the ice sheets that escaped glaciation was cold, with tundra vegetation. Northern Europe was frequented by ice-age animals such as mammoth, reindeer and arctic hare. There was a landbridge betweeb Britain and Europe, and animals could walk freely across it. Numerous human artefacts from this time are scattered across the landscape.

Ice sheets at the Last Glacial Maximum worldwide, around 27,000 to 21,000 years ago. From data in Ehlers et al., 2011.

The term ‘Last Glacial Maximum’ (LGM) has no formal stratigraphic status in Geological time, however, because each ice sheet reached its maximum extent at different times[7]. The Global Last Glacial Maximum can also be defined by the global sea level low-stand; when all the ice was locked up in the ice sheets, global sea levels reached as much as 125 m below present. The timing of this, 26,000 to 21,000 years before present, could therefore delimit the timing of maximum ice volume worldwide [8]. The timing of the global Last Glacial Maximum could also be defined by the minimum in the marine isotope record. The status of the global ‘Last Glacial Maximum’ is therefore debated.

In Britain, the Last Glacial Maximum was reached around 27-21 ka[3], but different parts reached their maximums at different times. Like many ice sheets at their maximum, it was constrained at its northern limits by the steep drop in the sea floor at the continental shelf edge. Likewise in Patagonia, the ice sheet reached the continental shelf edge and could go no further on its Pacific, western margin[6]. In the Antarctic Peninsula, the Antarctic Ice Sheet reached the continental shelf edge at around 25,000 years ago[9].

A recent publication, Quaternary Glaciations – Extent and chronology, a closer look, edited by Ehlers, Gibbard and Hughes[10], provides detailed information on each of these ice sheets at their maxima.  It even provides GIS shapefiles that you can download to examine the LGM of each ice sheet yourself:

http://booksite.elsevier.com/9780444534477/digital_maps.php

In the map above, you can see the extent of the world’s ice sheets outlined in blue. Mountain glaciers are shown as green dots. The continental shelf edges around the world are visible in paler blue, and in many places would have been dry land due to the global sea level lowering at the Last Glacial Maximum, but close to the ice it would depend on how much each individual landmass was lowered by the weight of the overlying ice sheets.

References

  1. Stokes, C.R. and L. Tarasov, 2010, Ice streaming in the Laurentide Ice Sheet: A first comparison between data-calibrated numerical model output and geological evidence. Geophysical Research Letters 37(1): p. L01501.
  2. Winsborrow, M., C.D. Clark, and C.R. Stokes, 2004, Ice streams of the Laurentide ice sheet. Geographie Physique Et Quaternaire 58(2-3): p. 269-280.
  3. Hughes, A.L., R. Gyllencreutz, Ø.S. Lohne, J. Mangerud, and J.I. Svendsen, 2016, The last Eurasian ice sheets–a chronological database and time‐slice reconstruction, DATED‐1. Boreas 45(1): p. 1-45.
  4. Bentley, M.J., et al., 2014, A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum. Quaternary Science Reviews 100(0): p. 1-9.
  5. Martínez, O., A. Coronato, and J. Rabassa, Chapter 52 – Pleistocene Glaciations in Northern Patagonia, Argentina: An Updated Review, in Developments in Quaternary Sciences, P.L.G. Jürgen Ehlers and D.H. Philip, Editors. 2011, Elsevier. p. 729-734.
  6. Coronato, A. and J. Rabassa, Chapter 51 – Pleistocene Glaciations in Southern Patagonia and Tierra del Fuego, in Developments in Quaternary Sciences, P.L.G. Jürgen Ehlers and D.H. Philip, Editors. 2011, Elsevier. p. 715-727.
  7. Clark, P.U., A.S. Dyke, J.D. Shakun, A.E. Carlson, J. Clark, B. Wohlfarth, J.X. Mitrovica, S.W. Hostetler, and A.M. McCabe, 2009, The Last Glacial Maximum. Science 325(5941): p. 710-714.
  8. Hughes, P.D., P.L. Gibbard, and J. Ehlers, 2013, Timing of glaciation during the last glacial cycle: evaluating the concept of a global ‘Last Glacial Maximum’ (LGM). Earth-Science Reviews 125(0): p. 171-198.
  9. Ó Cofaigh, C., et al., 2014, Reconstruction of ice-sheet changes in the Antarctic Peninsula since the Last Glacial Maximum. Quaternary Science Reviews 100(0): p. 87-110.
  10. Jurgen Ehlers, P.L. Gibbard, and D.H. Philip, eds. Index. Quaternary Glaciations – extent and chronology, a closer look. Vol. Volume 15. 2011, Elsevier: Amsterdam.

 

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