Episodic fresh surface waters in the Eocene Arctic Ocean.
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.
Brinkhuis
Henk
H
Palaeoecology, Institute of Environmental Biology, Utrecht University, Laboratory of Palaeobotany and Palynology, Budapestlaan 4, 3584 CD Utrecht, The Netherlands. H.Brinkhuis@bio.uu.nl
Schouten
Stefan
S
Collinson
Margaret E
ME
Sluijs
Appy
A
Sinninghe Damsté
Jaap S
JS
Dickens
Gerald R
GR
Huber
Matthew
M
Cronin
Thomas M
TM
Onodera
Jonaotaro
J
Takahashi
Kozo
K
Bujak
Jonathan P
JP
Stein
Ruediger
R
van der Burgh
Johan
J
Eldrett
James S
JS
Harding
Ian C
IC
Lotter
André F
AF
Sangiorgi
Francesca
F
van Konijnenburg-van Cittert
Han
H
de Leeuw
Jan W
JW
Matthiessen
Jens
J
Backman
Jan
J
Moran
Kathryn
K
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