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Abstract(s)
Coccolithophores contribute significantly to marine
primary productivity and play a unique role in ocean biogeochemistry
by using carbon for photosynthesis (soft-tissue
pump) and for calcification (carbonate counter pump). Despite
the importance of including coccolithophores in Earth
system models to allow better predictions of the climate system’s
responses to planetary change, the reconstruction of
coccolithophore productivity mostly relied on proxies dependent
on accumulation and sedimentation rates and preservation
conditions. In this study we used an independent proxy,
based on the coccolith fraction (CF) Sr=Ca ratio, to reconstruct
coccolithophore productivity. We studied the marine
sediment core MD03-2699 from the western Iberian margin
(IbM), concentrating on glacial–interglacial cycles of Marine
Isotopic Stage (MIS) 12 to MIS 9. We found that IbM coccolithophore
productivity was controlled by changes in the
oceanographic conditions, such as in sea surface temperature
(SST) and nutrient availability, and by competition with
other phytoplankton groups. Long-term coccolithophore productivity
was primarily affected by variations in the dominant
surface water mass. Polar and subpolar surface waters
during glacial substages were associated with decreased
coccolithophore productivity, with the strongest productivity
minima concomitant with Heinrich-type events (HtEs). Subtropical, nutrient-poorer waters, increased terrigenous input,
and moderate to strong upwelling during the deglaciation
and early MIS11 are hypothesized to have attributed a
competitive advantage to diatoms to the detriment of coccolithophores,
resulting in intermediate coccolithophore productivity
levels. During the progression towards full glacial
conditions an increasing presence of nutrient-richer waters,
related to the growing influence of transitional surface waters
and/or intensified upwelling, probably stimulated coccolithophore
productivity to maxima following the rapid depletion
of silica by diatoms. We present conceptual models
of the carbon and carbonate cycle components for the IbM
in different time slices that might serve as a basis for further
investigation and modelling experiments.
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European Geosciences Union