Seasonal variations in the flux of microplankton and radiolarian assemblage compositions in the northeastern tropical Atlantic at 2195 m.

BOLTOVSKOY DEMETRIO; ULIANA ELEONORA; WEFER GEROLD

LIMNOLOGY AND OCEANOGRAPHY

AMER SOC LIMNOLOGY OCEANOGRAPHY

Lugar: New ; Año: 1996 vol. 41 p. 615 - 635

0024-3590

Fluxes of silicoflagellates, the dinoflagellate Actiniscus sp., polycystine and phaeodarian radiolarians, tintinnids, ciliate (?) cysts, and pelagic molluscs were estimated in 13 sediment trap samples retrieved in the northeastern tropical Atlantic (20°55.3´N, 19°44.5´W) at 2,195 m between 22 March 1988 and 8 March 1989 (CB1 site). Each sample integrated the flux over 27 d. In addition, polycystines were identified to species in all samples. Highest fluxes were recorded for the polycystines, followed by the tintinnids, silicoflagellates, cysts, phaeodarians, Actiniscus, and molluscs. For phytoplankters our estimates are lower than most previously reported data, while for polycystines (up to 162,133 ind. m‑2 d‑1) and tintinnids (up to 201,064 ind. m‑2 d‑1) the values found are among the highest ever recorded in the World Ocean. Temporal variations in the fluxes of the heterotrophic organisms counted were generally in good agreement with total mass flux, suggesting fairly tight couplings with primary production at the surface. Fluxes of tintinnids were more variable through time and were better associated with variations in total mass flux than those of the slower-reproducing radiolarians. In total, 145 polycystine taxa were identified. Species compositions changed very little throughout the year and did not vary with changes in total mass flux. Close comparison of the present data set with a similar survey based on a yearly series of sediment trap samples retrieved between 1 March 1989 and 16 March 1990 from 853 m at a nearby location (GBN3 site) showed significant differences, both in the fluxes of the groups surveyed, and in the percentages of many polycystine species. All groups (except silicoflagellates) had noticeably higher output rates at CB1, and proportions of several polycystines associated with colder or more productive environments were higher at CB1 than at GBN3. Conversely, GBN3 yielded higher proportions of various radiolarians characteristic of warmer and more oligotrophic waters. Because temperatures below ca. 70 m are higher at CB1 than at GBN3, it is suggested that different productivity levels, rather than different surface temperatures are important in structuring the specific differences recorded. Several other contrasting traits between these two sites are also explored as sources for the differences recorded.