Holocene lowering of the Laurentide ice sheet affects North Atlantic gyre circulation and climate

Abstract

The Laurentide ice sheet, which covered Canada during glacial periods, had a major influence on atmospheric circulation and surface climate, but its role in climate during the early Holocene (9-7 ka), when it was thinner and confined around Hudson Bay, is unclear. It has been suggested that the demise of the ice sheet played a role in the 8.2 ka event (an abrupt 1-3 °C Northern Hemisphere cooling lasting ~ 160 years) through the influence of changing topography on atmospheric circulation. To test this hypothesis, and to investigate the broader implications of changing ice sheet topography for climate, we analyse a set of equilibrium climate simulations with ice sheet topographies taken at 500 year intervals from 9.5 to 8.0 ka. Between 9.5 and 8.0 ka, our simulations show a 2 °C cooling south of Iceland and a 1 °C warming between 40° and 50°N in the North Atlantic. These surface temperature changes are associated with a weakening of the subtropical and subpolar gyres caused by a decreasing wind stress curl over the mid-North Atlantic as the ice sheet lowers. The climate response is strongest during the period of peak ice volume change (9.5-8.5 ka), but becomes negligible after 8.5 ka. The climatic effects of the Laurentide ice sheet lowering during the Holocene are restricted to the North Atlantic sector. Thus, topographic forcing is unlikely to have played a major role in the 8.2 ka event and had only a small effect on Holocene climate change compared to the effects of changes in greenhouse gases, insolation and ice sheet meltwater.

The penultimate deglaciation: protocol for Paleoclimate Modelling Intercomparison Project (PMIP) phase 4 transient numerical simulations between 140 and 127 ka, version 1.0

“…Changes in continental ice sheets during the deglaciation will significantly impact the climate system through their albedo, which will directly affect the radiative balance (e.g. He et al, 2013). Changes in continental ice-sheet geometry can also significantly impact atmospheric dynamics (e.g.…”

“…Their simulations highlight the potential and feasibility of transient simulations of the PDG. In addition, as a proof of concept, transient experiments of the last deglaciation have been successfully performed with AOGCMs and Earth system models (Liu et al, 2009;Menviel et al, 2011;Roche et al, 2011;Gregoire et al, 2012;He et al, 2013;Otto-Bliesner et al, 2014). As detailed in the previous sections, the proposed transient simulation of the PDG will use boundary forcings consistent with the ones used for the last deglaciation (Ivanovic et al, 2016): i.e.…”

“…Transient numerical simulations have already been performed for the last deglaciation (Liu et al, 2009;Menviel et al, 2011;Roche et al, 2011;Gregoire et al, 2012;He et al, 2013;Otto-Bliesner et al, 2014) and provide a dynamical framework to further our understanding of the climatechange drivers, teleconnections and feedbacks inherent in the Earth system. Currently, no three-dimensional transient simulations were run across the full time interval covered by the penultimate deglaciation (∼ 140-127 ka).…”

The penultimate deglaciation: protocol for PMIP4 transient numerical simulations between 140 and 127 ka, version 1.0

“…(e.g. Löfverström et al, 2014;Gong et al, 2015;Roberts and Valdes, 2017;Gregoire et al, 2018). Therefore, the impact of ice-sheet extent and topography on MIS 6, across the PDG and during MIS 5e, should be studied in detail through sensitivity experiments.…”

Simulating the Early Holocene demise of the Laurentide Ice Sheet with BISICLES (public trunk revision 3298)

“…It is important to constrain the evolution of the saddle collapse in order to better understand the major forcing of the 8.2 ka event, as both the modelled regional climate responses and the ocean circulation are sensitive to the duration and magnitude of the meltwater pulse (Matero et al, 2017). Changes in topography may play a secondary role, for example by modifying atmospheric circulation and thereby influencing North Atlantic Gyre circulation, but in this instance they are likely to be a much weaker forcing for climate change than freshwater released by the melting ice (Gregoire et al, 2018). Accurately representing the dynamical processes at marine margins of ice sheets has previously been challenging for studies of deglaciation of continental-scale ice sheets, which takes place over several millennia, due to the high computational cost of the models.…”