Abrupt cold events in the North Atlantic Ocean in a transient Holocene simulation

Abstract

Abstract. Abrupt cold events have been detected in numerous North Atlantic climate records from the Holocene. Several mechanisms have been discussed as possible triggers for these climate shifts persisting decades to centuries. Here, we describe two abrupt cold events that occurred during an orbitally forced transient Holocene simulation using the Community Climate System Model version 3. Both events occurred during the late Holocene (4305-4267 BP and 3046-3018 BP for event 1 and event 2, respectively). They were characterized by substantial surface cooling (−2.3 and −1.8 • C, respectively) and freshening (−0.6 and −0.5 PSU, respectively) as well as severe sea ice advance east of Newfoundland and south of Greenland, reaching as far as the Iceland Basin in the northeastern Atlantic at the climaxes of the cold events. Convection and deep-water formation in the northwestern Atlantic collapsed during the events, while the Atlantic Meridional Overturning Circulation was not substantially affected (weakening by only about 10 % and 5 %, respectively). The events were triggered by prolonged phases of a positive North Atlantic Oscillation that caused substantial changes in the subpolar ocean circulation and associated freshwater transports, resulting in a weakening of the subpolar gyre. Our results suggest a possible mechanism by which abrupt cold events in the North Atlantic region may be triggered by internal climate variability without the need of an external (e.g., solar or volcanic) forcing.

North Atlantic Ice‐Rafting, Ocean and Atmospheric Circulation During the Holocene: Insights From Western Mediterranean Speleothems

“…Correspondence to: Y. Ait Brahim, aitbrahim@xjtu.edu.cn Citation: Ait Brahim, Y., Wassenburg, J. A., Sha, L., Cruz, F. W., Deininger, M., Sifeddine, A., et al (2019 might have played a major role in triggering or amplifying these abrupt cooling episodes of the Holocene (e.g., Deininger et al, 2017;Goslin et al, 2018;Klus et al, 2018;Yang et al, 2016). However, the linkage between the atmospheric circulation and the ice-rafting events is still a matter of debate (e.g., Darby et al, 2012;Sorrel et al, 2012).…”

“…Although Bond et al (2001) indicate that North Atlantic land and sea surface temperature patterns are not in favor of a NAO-like forcing of the Bond events, modeling and other proxy data support that NAO-like conditions might have intervened in the enhancement of ice-rafting through a slowdown of the Atlantic Meridional Overturning Circulation (AMOC). However, contradictory mechanisms have been proposed, involving either northward or southward shifts of the westerly winds belt (akin to positive and negative NAO-like conditions; e.g., Yang et al, 2016;Deininger et al, 2017;Klus et al, 2018;Goslin et al, 2018). In this context, new high-resolution paleoclimate records from key NAO regions are crucial to improve our understanding of the North Atlantic hydroclimate variability, as well as to study the forcing mechanisms and the coupling between atmospheric and oceanic processes.…”

“…However, we propose that enhanced ice-rafting might have taken place in the northern North Atlantic during periods with predominant positive NAO-like patterns as well (Bond events 2, 3, and 4 and around 7.5 ka BP). Indeed, north shifts of the westerly winds belt have also been proposed as a potential amplifier of the pluricentennial ice-rafting events (Goslin et al, 2018;Klus et al, 2018). Strong northerly winds were suggested as a potential trigger of ice drifting by strengthening the polar vortex and cooling at polar and suppolar latitudes (Bond et al, 2001).…”

Climate Change and Social Unrest: A 6,000‐Year Chronicle From the Eastern Mediterranean

“…(d) Sea surface temperature from Northern Iceland (Sicre et al, 2008). (e) Sea surface temperature (°C) in the Northwest Atlantic (Klus et al, 2018). (f) Sea‐ice concentration (%) in the Northwest Atlantic (Klus et al, 2018).…”

“…(e) Sea surface temperature (°C) in the Northwest Atlantic (Klus et al, 2018). (f) Sea‐ice concentration (%) in the Northwest Atlantic (Klus et al, 2018). The cold periods are shaded in blue and denoted by a number ( Cp 1 to Cp 5 ).…”