Episodic fresh surface waters in the Eocene Arctic Ocean


Henk Brinkhuis, Universiteit Utrecht
Stefan Schouten, Royal Netherlands Institute for Sea Research
Margaret E. Collinson, Royal Holloway, University of London
Appy Sluijs, Universiteit Utrecht
Jaap S. Sinninghe Damsté, Royal Netherlands Institute for Sea Research
Gerald R. Dickens, Rice University
Matthew Huber, College of Science
Thomas M. Cronin, United States Geological Survey
Jonaotaro Onodera, Kyushu University
Kozo Takahashi, Kyushu University
Jonathan P. Bujak, Bujak Research International
Ruediger Stein, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung
Johan Van Der Burgh, Universiteit Utrecht
James S. Eldrett, Shell UK Exploration and Production
Ian C. Harding, University of Southampton
André F. Lotter, Universiteit Utrecht
Francesca Sangiorgi, Universiteit Utrecht
Han Van Konijnenburg Van Cittert, Universiteit Utrecht
Jan W. De Leeuw, Universiteit Utrecht
Jens Matthiessen, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung
Jan Backman, Stockholms universitet
Kathryn Moran, University of Rhode Island
S. Clemens, Brown University
F. Eynaud, Université de Bordeaux
J. Gattacceca, Centre Européen de Recherche et d’Enseignement de Géosciences de l’Environnement
M. Jakobsson, Stockholms universitet
R. Jordan, Yamagata University
M. Kaminski, University College London
J. King, University of Rhode Island
N. Koc, Norsk Polarinstitutt
N. C. Martinez, Boston University
D. Mcinroy, British Geological Survey
T. C. Moore, University of Michigan, Ann Arbor
M. O'Regan, University of Rhode Island
H. Pâlike, University of Southampton
B. Rea, University of Aberdeen

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It has been suggested, on the basis of modern hydrology and fully coupled palaeoclimate simulations, that the warm greenhouse conditions that characterized the early Palaeogene period (55-45 Myr ago) probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes. Little field evidence, however, has been available to constrain oceanic conditions in the Arctic during this period. Here we analyse Palaeogene sediments obtained during the Arctic Coring Expedition, showing that large quantities of the free-floating fern Azolla grew and reproduced in the Arctic Ocean by the onset of the middle Eocene epoch (∼50 Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an ∼800,000-year interval. The abundant remains of Azolla that characterize basal middle Eocene marine deposits of all Nordic seas probably represent transported assemblages resulting from freshwater spills from the Arctic Ocean that reached as far south as the North Sea. The termination of the Azolla phase in the Arctic coincides with a local sea surface temperature rise from ∼10°C to 13°C, pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans. We suggest that onset and termination of the Azolla phase depended on the degree of oceanic exchange between Arctic Ocean and adjacent seas. © 2006 Nature Publishing Group.

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