Deglacial rapid sea level rises caused by ice-sheet saddle collapses

• Published in: Nature (London) Vol. 487; no. 7406; pp. 219 - 222
• Main Authors: Gregoire, Lauren J., Payne, Antony J., Valdes, Paul J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 12.07.2012; Nature Publishing Group
• Subjects: 704/106/413; 704/2151/213; Climate change; Computer Simulation; Deglaciation; Earth sciences; Earth, ocean, space; Environmental aspects; Exact sciences and technology; Global Warming; Humanities and Social Sciences; Ice; Ice Cover; Ice sheets; letter; Marine; Marine and continental quaternary; Marine geology; Measurement; Melting; Meltwater; multidisciplinary; North America; Oceans and Seas; Science; Science (multidisciplinary); Sea level; Sea level rise; Surface-ice melting; Surficial geology; Time Factors; Canada; North American Cordillera; Atlantic Ocean; North American Atlantic; North Atlantic; Newfoundland; Hudson Bay; Laurentide ice sheet; Northwest Atlantic; Eastern Canada; Labrador; North America; United Kingdom; ANW, Canada, Newfoundland and Labrador, Labrador; PNW, Canada, Hudson Bay; models; changes of level; Quaternary; domes; simulation; climate warming; ice; deglaciation; upper Quaternary; North America; lower Holocene; paleoclimate; meltwater; upper Pleistocene; ice sheets; Cenozoic; Phanerozoic; mechanism; Holocene; shrinkage; collapse; sea level; Pleistocene; climate change
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature11257

A simulation of ice sheet retreat reveals two meltwater pulses coinciding with MWP-1A and the ‘8,200-year’ event, caused by saddle collapses between ice domes. Cooling events linked to saddle-zone degradation During the last deglaciation, the retreating ice sheets occasionally released massive amounts of fresh water. These 'meltwater pulses' are often implicated as important influences on abrupt climate change, but the underlying triggering mechanisms are not clear. Here Lauren Gregoire et al . show that 'saddle zones' that connect adjacent high domes on ice sheets can be lowered by ongoing warming to an elevation at which they rapidly degrade, leading to separate domes and a meltwater pulse that is consistent with geological observations. Although the mechanism itself is not novel, the authors establish that two important sudden-cooling events — meltwater pulse 1A and the '8,200-year' event — were probably caused by saddle separation. The last deglaciation (21 to 7 thousand years ago) was punctuated by several abrupt meltwater pulses, which sometimes caused noticeable climate change 1 , 2 . Around 14 thousand years ago, meltwater pulse 1A (MWP-1A), the largest of these events, produced a sea level rise of 14–18 metres over 350 years 3 . Although this enormous surge of water certainly originated from retreating ice sheets, there is no consensus on the geographical source or underlying physical mechanisms governing the rapid sea level rise 4 , 5 , 6 . Here we present an ice-sheet modelling simulation in which the separation of the Laurentide and Cordilleran ice sheets in North America produces a meltwater pulse corresponding to MWP-1A. Another meltwater pulse is produced when the Labrador and Baffin ice domes around Hudson Bay separate, which could be associated with the ‘8,200-year’ event, the most pronounced abrupt climate event of the past nine thousand years 7 . For both modelled pulses, the saddle between the two ice domes becomes subject to surface melting because of a general surface lowering caused by climate warming. The melting then rapidly accelerates as the saddle between the two domes gets lower, producing nine metres of sea level rise over 500 years. This mechanism of an ice ‘saddle collapse’ probably explains MWP-1A and the 8,200-year event and sheds light on the consequences of these events on climate.