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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 8 | Copyright
Clim. Past, 14, 1165-1178, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Aug 2018

Research article | 14 Aug 2018

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

Andrea Klus1, Matthias Prange1, Vidya Varma2, Louis Bruno Tremblay3, and Michael Schulz1 Andrea Klus et al.
  • 1MARUM – Center for Marine Environmental Sciences and Faculty of Geosciences, University of Bremen, Bremen, Germany
  • 2National Institute of Water and Atmospheric Research, Wellington, New Zealand
  • 3Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Canada

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 3046–3018BP 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 −0.5PSU, 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.

Publications Copernicus
Short summary
Numerous proxy records from the northern North Atlantic suggest substantial climate variability including the occurrence of multi-decadal-to-centennial cold events during the Holocene. We analyzed two abrupt cold events in a Holocene simulation using a comprehensive climate model. It is shown that the events were ultimately triggered by prolonged phases of positive North Atlantic Oscillation causing changes in ocean circulation followed by severe cooling, freshening, and expansion of sea ice.
Numerous proxy records from the northern North Atlantic suggest substantial climate variability...