Interannual variability of deep water particle flux in relation to production and lateral sources in the northeast Atlantic

Results of particle flux studies using sediment traps in the northeast Atlantic Ocean at 33oN, 22oW, a time-series station (L1/K276) operated within the German contribution to the international Joint Global Ocean Flux Study (JGOFS) between summer 1993 and summer 2001, are presented. The particle flux at 2000 m depth is highly seasonal with only one main peak in February and March and is characterized by strong interannual variability. The comparison of the particle flux time series with the measurements of chlorophyll and phaeopigments in the sediment trap material, and chlorophyll-a concentrations at surface from SeaWiFS together with the similarity of the pattern observed in the alkenone flux, particulate organic carbon (POC) and calcium carbonate (CaCO3) leads to the conclusion that the particle flux at this position is fast and directly coupled to the phytoplankton development and decay in the overlying euphotic zone. SeaWiFS chlorophyll-a data (1997-2001) and characteristics of the upper water column (mixed layer depth, depth of nitracline, primary production) as predicted by an eddy-permitting model of the North Atlantic coupled with a simple nitrate-phytoplankton-zooplankton-detritus (NPZD) pelagic-ecosystem model are used to understand the observed interannual differences in particle flux at 2000 m. Our results suggest that the interannual differences in the observed particle flux are a direct consequence of the variability of phytoplankton biomass and primary production in the euphotic zone in this region.