Seasonal occurrence of coccoliths in sediment traps from West Caroline Basin, equatorial West Pacific Ocean

Coccolith fluxes were investigated by sediment trap studies in the West Car oline Basin, which is located in the equatorial western Pacific. The invest igation was conducted from June 1991 to March 1992 at two water depths, 159 2 and 3902 m, as part of the Northwest Pacific Carbon Cycle Study (NOPACCS) program. Two seasonal maxima of coccolith fluxes were observed during Sept ember-early October and late December-January. The average coccolith and co ccosphere fluxes at the depth of the shallow trap were 1800 X 10(6) coccoli ths m(-2) day(-1) and 1.9 X 10(6) coccospheres m(-2) day(-1), respectively. The flux of coccoliths followed the same trend as the total flux, and was closely correlated with the flux of organic matter flux. Florisphaera profu nda, Gladiolithus flabellatus, Gephyrocapsa oceanica, Umbilicosphaera sibog ae var. sibogae, Emiliania huxleyi, and Oolithotus fragilis were the most a bundant species together comprising more than 85% of the total flora. Obser ved seasonal changes of the species composition of coccolith flora, as well as analysis of the R-mode cluster, revealed that during the summer, the as semblage was marked by the dominance of G. oceanica and U. sibogae. However , during the winter, the assemblage was dominated by E. huxleyi and O. frag ilis. These assemblage changes were influenced by monsoonal events, which w ere observed off the New Guinea coast. F. profunda dominated the community in the shallow trap throughout most of the year; peak values of this specie s were recorded during the winter. The coccosphere assemblage was dominated by G. oceanica at both water depths. In the deep trap, the sedimentation p attern was similar to that observed at the shallow depth. Mean coccolith an d coccosphere fluxes at the deep trap were 2000 X 10(6) coccolith m-2 day ( -1) and 0.08 X 10(6) coccospheres m(-2) day (-1), respectively. The increas e in coccolith flux with water depth suggests a lateral influx. The estimat ed average daily mass of CaCO3 flux in coccoliths and coccospheres was 16.6 mg m(-2) day(-1) at the 1592 m trap and 17.9 mg m(-2) day(-1) at the 3902 m trap, respectively. These calculated values contributed only 23.3% to the total CaCO3 flux at the shallow trap and 27.9% at the deep trap. (C) 2001 Elsevier Science B.V. All rights reserved.