A SEDIMENT TRAP INVESTIGATION OF SINKING COCCOLITHOPHORIDS IN THE NORTH-ATLANTIC

Coccolith fluxes were studied in two vertically arranged and synchroni zed time series sediment traps at 700 m and 1025 m depth at JGOFS Stat ion 47 degrees N/20 degrees W over a period of 3 weeks during May and June, 1990. A short but distinct pulse of the coccolithophorid Syracos phaera pulchra (Lohmann) was used to trace the vertical transport of c occoliths. For the bulk material the settling velocity was estimated t o range from 137.8 m day(-1) to 162.5 m day(-1). Maximum fluxes were 3 .6 x 10(9) coccoliths m(-2) day(-1) in the upper and 2.3 x 10(9) cocco liths m(-2) day(-1) in the lower trap, or coccolith calcite fluxes of 42.6 mg m(-2) day(-2) and 28.7 mg m(-2) day(-1). Prior to the pulse th e average flux was 7.5 x 10(7) coccoliths m(-2) day(-1) (0.6 mg coccol ith carbonate m(-2) day(-1)) at 700 m and 1.4 x 10(8) 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 f rom < 32 mu m to > 500 mu m showed that during the S. pulchra pulse mo st coccoliths were transported in fecal strings larger than 500 mu m b ut that prior to this event a mixed coccolith and diatom flora was car ried 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 r eleased into the water by coprorhexy and microbial degradation of the settling fecal matter, account for the 33% decline of coccolith calcit e between the two traps. It is concluded that the export is characteri zed by a large variability in the flux of the different settling compo nents, which is intimately related to day to day fluctuations in fecal pellet production by migrating zooplankton and nekton in the overlyin g mesopelagic zone.