Tien-Nan Yang

Distribution of coccolithophorids and coccoliths in surface ocean off northeastern Taiwan

This study depicts quantitatively the distribution of coccolithophorids and coccoliths during one summer season in the area off northeastern Taiwan where the Kuroshio flows northward and interacts with the shelf waters of the East China Sea. To minimize the influence of diurnal variation of coccolithophorids, only samples taken at sunrise were analyzed. Sea-surface water (2m in depth) samples were obtained at six stations during the summer of 1996. Forty-one species were identified with Emiliania huxleyi (Lohmann) Hay et Mohier, Palusphaera vandelii Lecal emend. R. E. Norris, Umbellosphaera Paasche spp. and Syracosphaera Lohmann spp. being the predominant forms. Three coccolithophorid communities were recognized: (1) the continental shelf community, dominated by Emiliania huxleyi, Gephyrocapsa ocean ica Kamptner and Calciosolenia murrayi Gran, which showed intermediate biodiversity and species evenness; (2) the Kuroshio community, which showed the highest diversity and evenness, with a flora dominated by genus Umbellosphaera Paasche; and (3) the Western North Pacific Central Water community, which had the lowest diversity and evenness, with dominant species Calicasphaera Kleijne and Palusphaera vandelii. The absolute abundance of loose coccoliths ranged from 10.2 x l0^(4) individual coccoliths 1^(-1) to 22.9 x l0^(4) individual coccoliths 1^(-1), while those of coccospheres were much less, ranging from 11.5 x l0^(3) cells 1^(-1) to 19.7 x 10 cells 1^(-1) The largest absolute abundance of coccoliths and coccospheres was found in the Kuroshio path.

Glacial-Holocene calcareous nannofossils and paleoceanography in the northern South China Sea

Abstract Last glacial to Holocene paleoceanography of the northern South China Sea was inferred from nannofossil variations and several hydrographic proxies from a piston core, SCS90-36 (17°59.70′N, 111°29.64′E, water depth 2050 m). The upper part of the sedimentary sequence (dated 15.5 to 1.2 ka) provided a high-resolution record whereas part of the sediments older than 15.5 ka was lost due to erosion. A correspondence analysis of the nannofossil succession suggests that the paleoceanography developed in four stages. The first stage (26−13.3 ka) has a fairly well-preserved diverse nannoflora dominated by Gephyrocapsa and Florisphaera profunda. The floral composition together with high concentration of ketones (C37) and organic carbon indicates high surface-water fertility. The second stage, the deglacial period (13.3−10.7 ka), had an increased surface-water turbidity and a stronger influence of Pacific open-ocean waters as evidenced by the decrease of Florisphaera profunda and increase of Emiliania huxleyi, respectively. A preservation peak of calcareous microfossils centered at 12 ka correlates to the global preservation event of Termination I. The third stage, early Holocene (10.7−4.4 ka), is marked by a gradual increase of F. profunda and small placolith taxa at the expense of E. huxleyi. The floral composition indicates that conditions were more oligotrophic compared to the pre-Holocene. The preservation of nannofossils became progressively worse, indicating a rise of the nannofossil lysocline. In sediments deposited at 5.5 and 4 ka, nannofossil preservation improves, probably reflecting a local cooling event. During the last stage, from 4.4 to 1.2 ka, E. huxleyi, Umbilicosphaera and large Reticulofenestra increased their relative abundance to replace small placoliths. Further stratification of the surface water column may have been responsible for this floral succession.