title: Episodic fresh surface waters in the Eocene Arctic Ocean.
abstract: 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 (approximately 50 Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an approximately 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 approximately 10 degrees C to 13 degrees 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.
authors.affiliation: Palaeoecology, Institute of Environmental Biology, Utrecht University, Laboratory of Palaeobotany and Palynology, Budapestlaan 4, 3584 CD Utrecht, The Netherlands. H.Brinkhuis@bio.uu.nl
authors.forename: Henk
authors.initials: H
authors.lastname: Brinkhuis
authors.forename: Stefan
authors.initials: S
authors.lastname: Schouten
authors.forename: Margaret E
authors.initials: ME
authors.lastname: Collinson
authors.forename: Appy
authors.initials: A
authors.lastname: Sluijs
authors.forename: Jaap S
authors.initials: JS
authors.lastname: Sinninghe Damsté
authors.forename: Gerald R
authors.initials: GR
authors.lastname: Dickens
authors.forename: Matthew
authors.initials: M
authors.lastname: Huber
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Cronin
authors.forename: Jonaotaro
authors.initials: J
authors.lastname: Onodera
authors.forename: Kozo
authors.initials: K
authors.lastname: Takahashi
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Bujak
authors.forename: Ruediger
authors.initials: R
authors.lastname: Stein
authors.forename: Johan
authors.initials: J
authors.lastname: van der Burgh
authors.forename: James S
authors.initials: JS
authors.lastname: Eldrett
authors.forename: Ian C
authors.initials: IC
authors.lastname: Harding
authors.forename: André F
authors.initials: AF
authors.lastname: Lotter
authors.forename: Francesca
authors.initials: F
authors.lastname: Sangiorgi
authors.forename: Han
authors.initials: H
authors.lastname: van Konijnenburg-van Cittert
authors.forename: Jan W
authors.initials: JW
authors.lastname: de Leeuw
authors.forename: Jens
authors.initials: J
authors.lastname: Matthiessen
authors.forename: Jan
authors.initials: J
authors.lastname: Backman
authors.forename: Kathryn
authors.initials: K
authors.lastname: Moran
mesh_terms: D001110:Arctic Regions; D029624:Ferns / Q000166:cytology / Q000254:growth & development*; D005580:Fossils; D019015:Geologic Sediments / Q000032:analysis*; D017752:Greenhouse Effect; D049690:History, Ancient; D046448:Ice Cover; D009792:Oceans and Seas; D011891:Rain; D012623:Seawater / Q000032:analysis*; D013170:Spores / Q000302:isolation & purification; D013997:Time Factors