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


The last deglaciation (21 to 7 thousand years ago) was punctuated by several abrupt meltwater pulses, which sometimes caused noticeable climate change1,2. 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 years3. 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 rise4,5,6. 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 years7. 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.

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Figure 1: The deglaciation of North America.
Figure 2: MWP-1A in model and data.
Figure 3: Mechanism of saddle collapse.
Figure 4: The 8,200-year event in our model.


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This work was supported by the Marie Curie Research Training Network NICE (MRTN-CT-2006-036127) and the NERC QUEST (NE/D001846/1) and ORMEN (NE/C509558/1) projects. Glimmer was developed within the NERC National Centre for Earth Observation. We thank R. Kahana for providing part of the input climate data and for comments on the manuscript. We also thank members of the BRIDGE group, the NICE network and PALSEA, a PAGES/INQUA/WUN network, for discussions and suggestions. The numerical simulations were carried out using the computational facilities of the BRIDGE group and those of the Advanced Computing Research Centre, University of Bristol (

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Authors and Affiliations



L.J.G. performed the experiments, the analysis and wrote the manuscript. P.J.V. provided the input climate. All authors contributed to designing the experiments, discussed the results and implications and commented on the manuscript at all stages.

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Correspondence to Lauren J. Gregoire.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Table 1, Supplementary Figures 1-5, Supplementary References and a Supplementary Discussion, which provides a comparison of the modelled North American deglaciation with data and describes additional experiments referred to in the main text. (PDF 820 kb)

Supplementary Movie 1

This movie shows the evolution of ice elevation, surface mass balance and meltwater flux of the North American ice sheet through the last deglaciation. The two meltwater pulses happen when ice domes separate. The pulses are associated with an extension of the ablation area (area where melting is higher than snow accumulation) in the saddle between multiple ice domes. (MOV 5679 kb)

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Gregoire, L., Payne, A. & Valdes, P. Deglacial rapid sea level rises caused by ice-sheet saddle collapses. Nature 487, 219–222 (2012).

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