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*Are coccolithophores major contributors to the production and sedimentation of biogenic carbonates in the Nordic Seas : a paleo(Holocene) perspective.

Author

Garcia Jennifer1, Giraudeau Jacques1, Dylmer Christian Vademar1, Husum Katrine2

Author affiliation

1 Université Bordeaux 1 / CNRS - UMR EPOC, France

2 University of Tromsø, Norway

 

Conference

41th Arctic Workshop

Montreal, Canada

March 2-4, 2011

 

TALK


Abstract

Common views on the community structure of phytoplankton suggest that blooms in the Sub-Arctic/Nordic Seas are dominated by diatoms which are readily grazed by euphausiids and copepods which in turn provide the main food source for higher trophic levels. Satellite mappings of ocean color however indicate increased instances of coccolithophore blooms in this high latitude setting over the last 20 years (e.g. Smyth et al., 2004- Barents Sea -; Olafsson et al., 2000 –Iceland Sea -). Coccolithophores are minute flagellates of ca 8 µm that carries plates (“coccoliths”) composed of calcium carbonate. The recent biogeographic shift of coccolithophore blooms, as depicted by satellite imagery, is thought to reflect freshening (from meltwater and increased precipitations) and warming (from inflow of Atlantic waters –AW-) of the sub-polar seas, triggered by the present global warming. The few available data on coccolithophore standing stocks in surface waters, though suggesting a general affinity for Atlantic-derived waters, indicate maximum stocks in close vicinity to the Arctic front.

Synoptic maps of calcium carbonate contents  in surface sediments of the Nordic  Seas indicate that high concentrations of calcite (>40%) are observed beneath the present path of warm AW (Taylor et al., 2002). Past wt% CaCO3 variations in marine sediments cores from the Greenland, Iceland, Norwegian and Barents Sea are therefore likely to highlight the paleo dynamics of AW flow. We investigated the Holocene patterns of bulk and coccolith-derived carbonates in Holocene sediment cores located beneath the main and secondary branches of AW flow through Fram Strait, NW Iceland and SW Barents Sea, in close vicinity to the present winter sea-ice boundary. While discussing the potential biases linked to dissolution/dilution effects, as well as the exceptionally high contribution of primary producers (coccolithophores) to the calcium carbonate sedimentation in high latitude settings, we will show that such datasets provide invaluable, first order, semi-quantitative estimates of AW dynamics in critical areas of the Nordic Seas.

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