Coccolith assemblages and their response to climate and surface hydrography in the Yellow Sea, Northwest Pacific, AD 1780–2011

Abstract

A study of coccolith assemblages from a box core from the central South Yellow Sea (SYS) was performed revealing fluctuations on their relative abundance (%) that can be related to climatic and hydrographic changes over the last 230 years (1780–2011). Total coccolith abundances ranged from 7.0 to 55.1×106 coccoliths·g-1 sediment. Although the abundance of different species varied widely throughout the core, seven taxa dominated the assemblage. Among these species, Gephyrocapsa oceanica was the most dominant species, and it showed an average percentage of 50.1%. The pattern of G. oceanica (eutrophic species) was opposite to that of the combined percentage of Braarudosphaera bigelowii and Umbilicosphaera sibogae (both oligotrophic species), indicating that in the Yellow Sea (YS), the distribution pattern of G. oceanica might be characteristic of nutrient availability. Similar patterns between G. oceanica and the Siberian High were observed on an inter-decadal time scale, indicating that the East Asian Winter Monsoon (EAWM) may be an important driver of ecological changes in the YS. When the EAWM prevails, both the Yellow Sea Coastal Current (YSCC) and Yellow Sea Warm Current (YSWC) strengthen, and the increasing nutrient availability and warmer water brought by the strengthened YSWC favor eutrophic and warm-water coccolithophore species, such as G. oceanica. This likely mechanism demonstrates that coccolith assemblages can be used as benign and reliable proxy for climate change and surface oceanography.