The calcareous nannoplankton assemblages of surface sediments in the Tasman and Coral Seas

Abstract

The species composition of calcareous nannoplankton in 53 core-top samples collected from the Tasman and Coral Seas was investigated. The material originated from sediment preserved inside the spherical tests of the planktic foraminifer Orbulina universa . A comparative study of calcareous nannoplankton from inside foraminifers and in adjacent bulk sediment from the same samples shows good similarity between both assemblages. Based on the results from the core tops, distribution maps of each calcareous nannoplankton species are presented for the Tasman and Coral Seas. The geographic distribution of individual species indicates that their composition is strongly controlled by sea-surface temperature (SST). Correlation with summer temperatures were used because it is assumed that plankton productivity is best during that season. The percentage abundance of each species versus SST are determined, and the relationships between floral composition and positions of oceanic fronts such as the Subtropical Convergence, Tasman Front and (southern) Tropical Convergence, are discussed. The nannoplankton assemblages are also discussed in line with the effects of dissolution, and in particular for samples obtained from the deep-ocean floor.