CURRENT AND PRODUCTIVITY PATTERNS IN THE EQUATORIAL PACIFIC ACROSS THE LAST GLACIAL MAXIMUM BASED ON RADIOLARIAN EAST-WEST AND DOWNCORE FAUNAL GRADIENTS

Radiolarians were studied in 11 box-cores (142 samples in total, obtained at 3cm intervals) retrieved in the western (160-degrees-E), central (135-degrees-W) and eastern (90-degrees-W) equatorial Pacific. The western and central cores span the last ca. 40,000 years, while the eastern core is estimated to reach approx. 12,000-17,000 years. Time-averaged data show very sharp assemblage composition differences between the three locales. Species dominant at the westernmost sites are indicative of warm, oligotrophic conditions; thanatocoenoses from 135-degrees-W suggest strong input of California Current radiolarians; while the easternmost core hosts assemblages which point to a significant influence of the Peru Current. Downcore changes in the proportions of these three characteristic groups of species are inconclusive in the westernmost cores. In the central area the steady upcore increase in shells presumably advected from the northeastern Pacific, and the concomitant decrease of warmer-water radiolarians, indicate a growing influence of advection from the California Current. In the easternmost core colder-water indicators decrease from bottom to top, while those indicative of warmer waters increase, suggesting a gradual waning of advection from the Peru Current. It is concluded that, in the central and eastern parts of the equatorial Pacific belt, radiolarian distributional patterns in the sediments and their shifts during the last millennia respond chiefly to environmental conditions at depths in excess of 50m (rather than to sea surface temperature), and to subsurface and deep lateral advection of shells from eastern boundary current areas.