RUTHERFORD, Scott, rutherfo@deschutes.gso.uri.edu,

D'HONDT, Steven, Graduate School of Oceanography, URI, Narragansett, RI 02882.

Preliminary analysis of foraminiferal data from CLIMAP core tops suggests that Recent planktic foraminiferal diversity does not monotonically decrease from a maximum in the tropics to a minimum at the poles (contra Stehli et al., 1969). Species richness and evenness indices were calculated for core tops from the North Atlantic and Indian Oceans. In both oceans, richness is greater in the mid-latitude gyre than at the equator and is lowest at high latitudes. Species richness in the North Atlantic peaks along the northern perimeter of the central gyre. Factor analysis suggests that the high species richness in this region results from mixing of assemblages from different water masses. Evenness peaks in the center of the gyres and decreases toward upwelling areas and with increasing latitude. In general, assemblages with high diversity also exhibit high evenness. To assess what may control these diversity patterns, the indices were compared to sea-surface chlorophyll-a concentrations as measured by the coastal zone color scanner (CZCS). A logarithmic regression between the CZCS data and each ecological index suggests that the chlorophyll-a concentration explains approximately 50% of the variance in species richness and evenness. Other factors that may influence species richness and evenness include sea-surface temperature, mixed-layer thickness, and seasonality of oceanic conditions. Stehli, F. G., R. G. Douglas and N. D. Newell. (1969). Generation and maintenance of gradients in taxonomic diversity. Science. 164: 947-949.

1996,Geological Society of America, Abstracts with Programs, 28 (7): A297