Spatial distribution pattern of living polycystine radiolarian taxa - Baseline study for paleoenvironmental reconstructions in the Southern Ocean (Atlantic sector)

The horizontal and vertical distribution of living polycystine radiolarian taxa was investigated at seven locations on a N-S transect between the Antarctic Zone (54 degrees S) in the Southern Ocean and the Subtropical zone (30 degrees S) in the southeastern South Atlantic during austral autumn. Four to five depth intervals from 0 to 1000 m depth were sampled with 55 mu m mesh opening/closing nets in combination with a hydrographic CTD survey. A factor analysis for the delineation of specific assemblages and the relation between different taxa and taxa groups resulted in eight factors, of which five represent surface and subsurface factors and three deep water factors. The spatial distribution pattern of the factors shows that distinct radiolarian assemblages are closely related to water depth, distribution of water masses, hydrographic boundaries such as frontal systems, and nutrients. This documents that the distribution of individual radiolarian assemblages is controlled by specific hydrographic conditions and water depth, and allows the definition and consolidation of the autecological demands. These data are crucial for the paleoenvironmental interpretation of fossil polycystine radiolarian assemblages. The comparison of living polycystine radiolarian taxa with those preserved in surface sediments shows general similarities, This study includes the first documentation on the distribution of living Cycladophora davisiana in Circumpolar Deep Water and supports previous studies stating that C. davisiana also lives in deep-water masses.