Coccolithophore (CaCO3) flux in the Sea of Okhotsk: seasonality, settling and alteration processes.

Coccolithophore fluxes were determined in the Sea of Okhotsk using samples from a 1 year experiment (12 August 1990 to 12 August 1991) with sediment traps at 258 and 1061 m depth. A special study was made on Coccolithus pelagicus, using fragmentation and the degree of etching, as indicators of transport mechanisms. A Corrosion Index for C. pelagicus is developed. The coccolithophore flux pattern at 258 m depth was characterised by a strong seasonality, with flux peaks during autumn 1990 (late November to early December) and spring 1991 (March). The assemblage consisted almost entirely of the two species C. pelagicus and Emiliania huxleyi. During autumn, coccolithophore transportation to 258 m depth mainly occurred within cylindrical fecal pellets and marine snow aggregates of silicoflagellates, and through agglutination on tintinnids. Grazing caused severe fragmentation of coccoliths and disintegration of coccospheres. Marine snow aggregates contained many intact coccospheres of C. pelagicus. During spring, coccolithophores were probably removed from the euphotic zone by the ballast effect of sinking diatoms. The coccolithophore flux peak in spring occurred immediately after the ice had retreated from the trap station, and the trapped assemblage included coccoliths of subtropical species. These features indicate drifting from an ice-free location to the south or east. The coccolith and coccosphere flux at 1061 m was respectively 7 and 12 times lower than at 258 m depth, and maximum fluxes were recorded 2 months later. Increasing carbonate dissolution from 258 to 1061 m depth is expressed in the coccolithophore-CaCO