Coccolithophore export production, species composition, and coccolith-CaCO 3 fluxes in the NE Atlantic ( [formula omitted] and [formula omitted

Abstract

Coccolithophores were examined in two sediment traps, deployed for one year (April 1989 to April 1990) at approximately 1 km water depth, in the subtropical NE Atlantic at 34° N 21° W (station NABE-34) and in the temperate NE Atlantic 48° N 21° W (station NABE-48) as part of the JGOFS North Atlantic Bloom Experiment (NABE). At both stations, maximum coccolith and coccosphere fluxes were recorded during local spring bloom periods. The average coccolith and coccosphere fluxes at NABE-34 were 1.12×10 9 m −2 d −1 and 4.90×10 6 m −2 d −1 , respectively. At this station coccoliths from 51 taxa were identified. A marked seasonal change was noticed in relative abundances of Emiliania huxleyi and deep photic zone species: E. huxleyi dominated during spring, while in late autumn the coccolith assemblage was dominated by Florisphaera profunda and the coccosphere assemblage by G. flabellatus and Algirosphaera spp.. Emiliania huxleyi was the most abundant species in the overall coccolith and coccosphere assemblages with 69% and 64%, respectively. At NABE-48, the average daily fluxes were significantly lower, with 3.88×10 8 coccoliths m −2 d −1 and 8.45×10 5 coccospheres m −2 d −1 , and only 36 taxa were recorded in the trap samples. Emiliania huxleyi was the dominant species in the coccolith assemblage throughout the year with 72%, and showed maximum fluxes during spring 1990. Coccolithus pelagicus exhibited a distinct seasonal pattern, with maximum fluxes in early June 1989, probably related to the development of a mesoscale cyclonic eddy in the vicinity of the trap site. Holococcolithophore fluxes were highest during maximum sea surface temperatures in summer. The coccosphere assemblage was dominated by Gephyrocapsa spp., Syracosphaera spp., and E. huxleyi. Estimated CaCO 3 fluxes of coccoliths, coccospheres, and calcareous dinophytes were compared with the CaCO 3 content in the fine (<32 μm) fraction. The annual mass estimated CaCO 3 flux of coccoliths and coccospheres was 5.1 g m 2 yr at NABE-34 and 2.7 g m 2 yr at NABE-48, and that of calcareous dinophytes 0.9 and 0.1 g m 2 yr , respectively. These summed mass estimated values contributed on average only 55% at NABE-34 and 60% at NABE-48 to the fine fraction CaCO 3.