1. Department of Geology and Geochemistry,
2. Department of Meteorology, Stockholm University, SE-106 91 Stockholm, Sweden
3. Finnish Institute for Marine Research, F-00561 Helsinki, Finland
4. Leibniz Institute of Marine Sciences at the University of Kiel (IFM-GEOMAR), DE-24148 Kiel, Germany
5. Center for Coastal and Ocean Mapping, University of New Hampshire, Durham, New Hampshire 03824, USA
6. Alfred Wegener Institute for Polar Research, DE-27570 Bremerhaven, Germany
7. Laboratory of Palaeobotany and Palynology, Utrecht University, NL-3584 Utrecht, The Netherlands
8. Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882, USA

Correspondence to: Martin Jakobsson¹ Correspondence and requests for materials should be addressed to M.J. (Email: martin.jakobsson@geo.su.se).

Abstract

Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate¹. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic's deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean². Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ('ventilated') conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygen-poor 'lake stage', to a transitional 'estuarine sea' phase with variable ventilation, and finally to the fully ventilated 'ocean' phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum³, although it remains unclear if there is a causal relationship between these two events.

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