Seasonal variability of amino acid flux and composition of particulate matter in the Northeast Atlantic at 47°N–20°W

Abstract

Sediment trap data is presented from two moorings deployed at a German JGOFS station in the North Atlantic (47°N–20°W) between March 1992 and May 1993 using `Kiel Sediment Traps'. Both particulates and supernatant solutions in the sample bottles were analysed chemically. The supernatant-dissolved fraction was included in the calculation of fluxes and particulate contents. The paper concentrates on three major aspects. Firstly, the fluxes of particulate mass and amino acids at 1000, 2000 and 3500 m depth are discussed. A different source region is deduced for the particles trapped at 2000 m. Secondly, the particulate contents of calcium carbonate, biogenic opal, chlorophyll and amino acids at 1000 m depth are discussed, revealing a seasonal change in particle composition, mainly from phytoplankton to zooplankton matter. Particle flux is closely related to particle composition, phytoplankton matter dominating in high flux periods and zooplankton matter in low flux periods. The amino acid content reacts sensitively to the shift in plankton distribution from phytoplanktic to zooplanktic material. Differences between two neighbouring moorings show that plankton productivity at the surface was patchy. Thirdly, the amino acid composition spectra of the 1000 m trap samples are presented. Four different groups of samples can be delineated on the basis of their different amino acid compositions. The grouping is closely related to the seasonal changes in other chemical properties and gives additional evidence for the deduced shift in plankton distribution at the surface.