22.05.2014: FB1-Seminar

15:00 h, Gr. Konferenzraum, Düsternbrooker Weg 20

Abstract:

Physical regulation of ecosystems on multi-decadal time-scales is presently receiving much attention in the literature, while the equally marked sub-decadal fluctuations in climate and ecosystems in the North Atlantic are receiving less attention. We here show that the mixed layer depths in the Irminger Seas determines the biomass of dominant zooplankton species on the south Iceland shelf – Calanus finmarchicus. Deep mixed layers are associated with a large on-shelf biomass, a large volume of Labrador Sea Water, a large subpolar gyre and a large oceanic overwintering C. finmarchicus stock (subarctic state). We suggest that advection of zooplankton onto the Iceland shelf is the causal mechanism. This variable food resource is also demonstrated to regulate the hatching success of kittiwakes in the Faroe Islands, which has its winter feeding grounds over the subpolar gyre. Furthermore, we show that subarctic states result in higher oceanic, pre-bloom, nutrient concentrations, and this might reinforce the oceanic regulation of the shelf ecosystems by stimulation of the on-shelf primary production. The on-shelf zooplankton biomass variability consists mainly of clear sub-decadal pulses, without a trend. The oceanic signal consists both of this sub-decadal variability, which mostly are associated with deep-water formation and inter-decadal variability associated with the horizontal gyre circulation. The pulses are probably predictable by at least half a year (winter convection to subsequent summer production), while the gyre dynamics might be predictable by several years – especially during periods like after the mid-1990s when the subpolar gyre suddenly started to decline. The longer-term trend might have started to disrupt the oceanic regulation of the pulses, as the silicate levels in the subpolar North Atlantic are approaching critically low values. We suggest this as the main reason for the persistent decline in several seabird populations during the last couple of decades.

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