Radiolarians In Surface Sediments Of The Northern Okinawa Trough And Their Paleoceanographic Implications

Radiolarian is one of the dominant microfossil groups found in marine sediments. The ecological distributions of recent radiolarians are closely related to physical, chemical and hydrological properties of the water masses and controlled mainly by ocean circulation. The radiolarians in sediments can provide lots of infonnation on paleoceanographical environments and paleoclimate variations, which have a capacity of providing invaluable data for the global environmental changes and climatic processes. The fossil record of radiolarians in marine sediments is essential for accurate estimation of ocean paleoenvironments. Based on a quantitative analysis of radiolarian in 80 surface-sediment samples from the northern area of Okinawa Trough, this paper reported the species composition and faunal assemblages characteristic of radiolarian, expounded the distribution pattern of radiolarian abundance and diversity in surface sediments from this area. In this paper, a preliminary study on the relation of the distribution and abundance of radiolarian to environmental factors, such as chemical and physical properties of the overlying masses (sea-surface temperature, salinity, nutrients and primary productivity) and the type and composition of sea-bed sediments was made. The radiolarian data was evaluated using a Q-mode factor analysis to identify different faunal assemblages and their geographic distributions, then the relationship between radiolarian assemblages and distribution of water masses, hydrographic boundaries such as frontal systems was analyzed. A new radiolarian-based transfer function to estimate mean-annual sea surface temperature (SST) and seasonal range were examined to test its success in the study area. The results obtained in this study are as follows: (1) The result of species analysis shows that Spumellaria was dominant in the more than 190 species identified, and the radiolarian assemblage of the northern area of Okinawa Trough belong to warm-water fauna compared to their available ecology knowledge. The distribution of radiolarians in surface sediments shows that their abundance and diversity markedly increase from northwest to southeast, and can be divided into three provinces. (2) The distribution of radiolarian is closely related to sea-surface temperature, salinity and hydrographic boundaries such as the Kuroshio front, the Tsushima Warm Current front. While it exhibit a negative relationship with nutrients and primary productivity of the surface water. The distribution pattern also indicate radiolarian concentrations are strongly affected by the sediment type, radiolarian abundance and diversity is higher in the clay or mud than in fine sand, silt or coarse sand and decrease with the increase of terrigenous material. There is direct correlation between the radiolarian preservation and the amount of volcanic glass, the numerous volcanic ash shards have a significant influence on the radiolarian distribution pattern. (3) A Q-mode factor analysis of the samples identified three factors or assemblages, which account for 90.2% of the variance in the radiolarian data. These factors have their areas of dominance in the following regions: the Tsushima Current water, the Kuroshio water and the shelf water. The spatial distribution pattern of the factors shows that distinct radiolarian assemblages are closely related to water mass, ocean current and hydrographic conditions. (4) The test of a new radiolarian-based transfer function to estimate mean-annual sea surface temperature (SST) and se...