Coccolithophore (-CaCO3) flux in the Sea of Okhotsk: seasonality, settlingand 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 t raps at 258 and 1061 m depth. A special study was made on Coccolithus pelag icus, using fragmentation and the degree of etching, as indicators of trans port mechanisms. A Corrosion Index for C. pelagicus is developed. The cocco lithophore flux pattern at 258 m depth was characterised by a strong season ality, with flux peaks during autumn 1990 (late November to early December) and spring 1991 (March). The assemblage consisted almost entirely of the t wo species C. pelagicus and Emiliania huxleyi. During autumn, coccolithopho re transportation to 258 m depth mainly occurred within cylindrical fecal p ellets and marine snow aggregates of silicoflagellates, and through aggluti nation on tintinnids. Crazing caused severe fragmentation of coccoliths and disintegration of coccospheres. Marine snow aggregates contained many inta ct coccospheres of C. pelagicus. During spring, coccolithophores were proba bly removed from the euphotic zone by the ballast effect of sinking diatoms . The coccolithophore flux peak in spring occurred immediately after the ic e 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 time s lower than at 258 m depth, and maximum fluxes were recorded 2 months late r. Increasing carbonate dissolution from 258 to 1061 m depth is expressed i n the coccolithophore-CaCO3 flux reduction of 82%, and in the increasing pe rcentage of etched coccoliths of Coccolithus pelagicus from 32 to >90%. (C) 2000 Elsevier Science B.V. All rights reserved.