RADIOLARIAN VERTICAL-DISTRIBUTION PATTERNS ACROSS THE SOUTHERN CALIFORNIA CURRENT

Polycystine radiolarians were identified in 36 plankton samples collec ted at depths ranging from 0 to 2000 m at four stations extending west from about the U.S.-Mexico border (approx. 32-degrees-N, 117-degrees- W to 124-degrees-W), in November-December 1977. In total, 136 radiolar ian taxa were recorded, but 90% of all individuals were accounted for by only 40 of these. Highest abundances were found either at the surfa ce, or at 25-50 m. Based on maxima in the vertical profiles of the mos t abundant radiolarians, three major depth-intervals were defined in t he upper 300 m: 0-50 m, 100 m and 200-300 m. Between-station-similarit ies in the specific makeups of these layers, however, were low. Thirty -nine taxa had peak abundances below 300 m at one or more stations; 11 of these are probably deep-water forms. Although in terms of individu als per liter of water filtered, upper-layer taxa are noticeably more abundant than deep species, the latter have much more extended depth-r anges, which might significantly enhance their sedimentary output. The inshore and oceanic stations shared very similar, warmer-water radiol arian assemblages in the uppermost 25 m, whereas the intermediate stat ion was dominated by colder-water forms at those depths. Below 50 m, h owever, the inshore station had enhanced proportions of deeper- and co lder-water species, differing strongly from the oceanic site. We sugge st that this pattern results from circulation of the Southern Californ ia Eddy, which transports Central Water from the oceanic station on th e western edge of the California Current around the intermediate stati ons to the inshore stations. The cold-water signal at subsurface layer s of the inshore station could be reinforced by coastal upwelling and southward transport by the California Current, thus further enhancing the abundances of deeper-water radiolarians at this site. Analyses of the effect of such vertical patterns on paleoceanographic interpretati ons stress the importance of the signal of ''environmentally neutral'' deep-living species, as well as that of shells produced in the near-s urface layers of distant areas and transported at depth to the region of the study.