Dinoflagellate Cyst Assemblages in a Sediment Core from the Northern East China Sea and Their Implications

In order to study palaeoceanographic changes in the northern East China Sea since the last glacial period, a sediment core from the northern shelf of the East China Sea have been investigated in the aspect of dinoflagellate cyst. A total of 14 genera and 24 dinoflagellate cyst taxa have been identified from the sediment core and classified into four groups; gonyaulacoid (5 genera and 13 species), gymnodinioid (1 genus and 2 species), tuberculoidinioid (1 genus and 1 species), protoperidinioid (7 genera and 8 species). Throughout the core, dinoflagellate cyst assemblages are dominated by gonyaulacoid group (mainly Genus Spiniferites). A considerable difference in dinoflagellate cyst concentrations between the bottom-and the upper part of the sediment core can be explained by the post-glacial sea-level rise. In particular, a major transition to a full-oceanic environment suitable for colonization by dinoflagellates is inferred by a marked increase in total dinoflagellate cyst concentrations at 360 cm core depth. It also suggests that the dinoflagellate productivity during the Holocene period may have been associated with East Asian monsoon development, which would have regulated fresh-water discharges and thus nutrient inputs from the adjacent rivers. An infrequent occurrence of protoperidinioid group might be attributed to a less favourable environment for these species, or tentatively linked to a species-selective aerobic degradation.