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Séminaire


Southern Ocean Nitrogen and Silicon dynamics during the last deglaciation

Date
le 20-06-2011 à 10:45

Lieu
Salle Stendhal, DGO, Bâtiment B18

Intervenant(s)
Rebecca ROBINSON, Graduate School of Oceanography, University of Rhode Island

Résumé
The reinvigoration of overturning in the Southern Ocean is hypothesized to have returned CO2 from the deep ocean to the atmosphere at the end of the last ice age. Large peaks in opal accumulation have been put forward as evidence for an increase in wind driven upwelling between 10 and 15 kyr BP (Anderson et al., 2009). Coupled diatom-based nitrogen and silicon isotope records, used alongside opal accumulation rates, provide quasi-quantitative estimates of Southern Ocean nutrient supply, by upwelling, and nutrient utilization across this interval. Significant changes in the consumption of N and Si across the two opal accumulation peaks indicate major changes in both upwelling and nutrient demand. We find N and Si consumption to be relatively incomplete during peak opal accumulation at the onset of the deglaciation. Nutrient supply must have been significantly enhanced. The second deglacial peak in opal accumulation is associated with more complete Si consumption and variable N consumption. We suggest that this peak represents strong upwelling and more complete utilization of the available silicic acid pool. Differences between the Si and N responses during opal peaks may stem from decreasing iron availability across the glacial termination.
In my talk, I will introduce new culture-based constraints on the diatom-bound N isotope proxy used in this study and the potential affect of diatom assemblage changes on interpreting nutrient utilization in the past.
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