Collapse of the North American ice saddle 14,500 years ago caused widespread cooling and reduced ocean overturning circulation

Ruza F Ivanovic,Paul J Valdes,Lauren J Gregoire,Andrew D Wickert,Andrea Burke

doi:10.1002/2016gl071849

Abstract

AbstractCollapse of ice sheets can cause significant sea level rise and widespread climate change. We examine the climatic response to meltwater generated by the collapse of the Cordilleran‐Laurentide ice saddle (North America) ~14.5 thousand years ago (ka) using a high‐resolution drainage model coupled to an ocean‐atmosphere‐vegetation general circulation model. Equivalent to 7.26 m global mean sea level rise in 340 years, the meltwater caused a 6 sverdrup weakening of Atlantic Meridional Overturning Circulation (AMOC) and widespread Northern Hemisphere cooling of 1–5°C. The greatest cooling is in the Atlantic sector high latitudes during Boreal winter (by 5–10°C), but there is also strong summer warming of 1–3°C over eastern North America. Following recent suggestions that the saddle collapse was triggered by the Bølling warming event at ~14.7–14.5 ka, we conclude that this robust submillennial mechanism may have initiated the end of the warming and/or the Older Dryas cooling through a forced AMOC weakening.

Highlights

During the Last Glacial Maximum 26–19 thousand years ago, a vast ice sheet stretched over North America [Clark et al, 2009]
In SC_east, the Mississippi-bound meltwater is reduced to ~30% of the total saddle collapse pulse, with ~20% of the flux heading to the North American East Coast
To assess the effect of the North American ice saddle collapse, we developed a physically consistent numerical approach whereby a transient general circulation model (GCM) climate simulation was used to drive a dynamical ice sheet model, which in turn drove a high-resolution drainage model, providing freshwater forcing scenarios to plug back into a GCM

Summary

Introduction

During the Last Glacial Maximum 26–19 thousand years ago (ka), a vast ice sheet stretched over North America [Clark et al, 2009]. As climate warmed and this ice sheet decayed, large volumes of meltwater flooded to the oceans [Tarasov and Peltier, 2006; Wickert, 2016]. This period, known as the “last deglaciation,” included episodes of abrupt climate change, such as the Bølling warming, when Northern Hemisphere temperatures increased by 4–5°C in just a few decades [Lea et al, 2003; Buizert et al, 2014], coinciding with a 12–22 m sea level rise in less than 340 years (Meltwater Pulse 1a (MWP1a)) [Deschamps et al, 2012]. It has been suggested that an Antarctic source of MWP1a could have caused the Bølling warming [Weaver et al, 2003], though possibly only if the total flux is

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