A sediment trap investigation of sinking coccolithophorids in the North Atlantic

Coccolith fluxes were studied in two vertically arranged and synchronized time series sediment traps at 700 m and 1025 m depth at JGOFS Station 47°N/20°W over a period of 3 weeks during May and June, 1990. A short but distinct pulse of the coccolithophorid Syracosphaera pulchra (Lohmann) was used to trace the vertical transport of coccoliths. For the bulk material the settling velocity was estimated to range from 137.8 m day−1 to 162.5 m day−1. Maximum fluxes were 3.6 × 109 coccoliths m−2 day−1 in the upper and 2.3 × 109 coccoliths m−2 day−1 in the lower trap, or coccolith calcite fluxes of 42.6 mg m−2 day−1 and 28.7 mg m−2 day−1. Prior to the pulse the average flux was 7.5 × 107 coccoliths m−2 day−1 (0.6 mg coccolith carbonate m−2 day−1) at 700 m and 1.4 × 108 coccoliths m−2 day−1 (1.3 mg coccolith calcite m−2 day−1) at 1025 m. Detailed studies of the fecal pellet content at 1025 m in five size fractions from < 32 μm to > 500 μm showed that during the S. pulchra pulse most coccoliths were transported in fecal strings larger than 500 μm but that prior to this event a mixed coccolith and diatom flora was carried by several types of fecal pellet. Coccoliths in the fecal pellets showed no signs of dissolution. Mechanical breakage of coccoliths by zooplankton grazing, however, was severe. Profiles of suspended matter from the same time and location suggest that coccoliths, which were released into the water by coprorhexy and microbial degradation of the settling fecal matter, account for the 33% decline of coccolith calcite between the two traps. It is concluded that the export is characterized by a large variability in the flux of the different settling components, which is intimately related to day to day fluctuations in fecal pellet production by migrating zooplankton and nekton in the overlying mesopelagic zone.