Calcareous nannoplankton biocoenosis : sediment trap studies in the equatorial Atlantic, central Pacific, and Panama Basin
Steinmetz, John C.
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Sediment traps deployed on three moored vertical arrays collected particles at various depths in the equatorial Atlantic (Station E), central Pacific (Station P1), and in the Panama Basin (Station PB1). The calcareous nannoplankton from the <63 μm size fraction were studied in order to characterize the flux of coccospheres and coccoliths, the taxa present, and their condition of preservation throughout the water column. The average calculated flux of coccospheres ranged from a low value of 24 coccospheres/m2/day in the central Pacific, to an intermediate value of 4725 in the equatorial Atlantic, to a high of 8030 in the Panama Basin. In general, the coccosphere flux decreased with depth at all three sites. Coccolith fluxes and flux profiles were significantly different at each of the three sites. At Station E, the flux decreased regularly with depth but increased sharply at the lowermost trap (724 m above the bottom). The average flux for the entire column was 316 x 106 coccoliths/m2/day. At Station P1, the flux was low in the shallowest two traps and increased markedly in the three deepest traps. This increase is due mainly to a suspected Umbilcosphaera sibogae bloom which occurred shortly before the traps were deployed in September 1978. The highest coccolith flux was recorded in the Station PB1 traps averaging 910 x 10 6 coccoliths/m2/day. The flux profile at this station was essentially constant in the shallowest four traps and decreased almost 59% in the lowermost two traps. The average coccolith carbonate fluxes for the entire columns for the Stations E, P1, and PB1 are, respectively, 2.53, 2.68, and 7.28 mg/m2/day. These fluxes represent minimum values, since coccospheres and coccoliths were also contained in fecal pellets and other particles larger than the size fraction studied (<63 μm). Scanning electron microscopic examination of the trap samples revealed 56 species belonging to 33 genera of calcareous nannoplankton. Three new species are described and illustrated: Alsphaera spatula n. sp., Umbilcosphaera calvata n. sp., ari;d Umbilcosphaera scituloma n. sp. A census of taxa present, including their relative frequency and state of preservation, is presented together with a photographic atlas of the taxa. Station E is the most diverse with 50 species, and is the best preserved of the three sites. Station PBi the least diverse with 26 more poorly preserved species. In general, the best preserved specimens were observed in the shallowest sample at each of the three sites; diversity and state of preservation diminished with increasing depth.