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Climate of the Past An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/cp-2017-106
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
25 Sep 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).
Abrupt cold events in the North Atlantic in a transient Holocene simulation
Andrea Klus1, Matthias Prange1, Vidya Varma2, Louis Bruno Tremblay3, and Michael Schulz1 1MARUM – Center for Marine Environmental Sciences and Faculty of Geosciences, University of 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 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 (event 1 referring to 4305–4267 BP and event 2 referring to 3046–3018 BP) and were characterized by substantial surface cooling (−2.7 and −2.2 °C, respectively) and freshening (−0.7 and −0.6 PSU, respectively) as well as severe sea ice advance east of Newfoundland and south of Greenland. Sea ice even reached 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 significantly affected. The events were triggered by prolonged phases of a positive North Atlantic Oscillation which, through changes in surface winds, caused substantial changes in the sub-polar ocean circulation and associated freshwater transports, resulting in a weakening of the sub-polar 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.

Citation: Klus, A., Prange, M., Varma, V., Tremblay, L. B., and Schulz, M.: Abrupt cold events in the North Atlantic in a transient Holocene simulation, Clim. Past Discuss., https://doi.org/10.5194/cp-2017-106, in review, 2017.
Andrea Klus et al.
Andrea Klus et al.
Andrea Klus et al.

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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...
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