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

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 55.1×10^6 coccoliths·g^-1sediment. 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.

Organic carbon isotopes of the Sinian and Early Cambrian black shales on Yangtze Platform,China

Organic matter of the Sinian and early Cambrian black shales on the Yangtze Platform belongs to the light carbon group of isotopes with the δ13C values from - 27 % to -35 % , which are lower than those of the contemporaneously deposited carbonates and phosphorites. A carbon isotope-stratified paleooceanographic model caused by upwelling is proposed, which can be used not only to interpret the characteristics of organic carbon isotopic compositions of the black shales, but also to interpret the paleogeographic difference in the organic carbon isotope compositions of various types of sedimentary rocks.

Carbon isotope composition and its implications of Lower Cretaceous Aptian-Albian shallow water carbonates in the Cuoqin Basin, North Tibet

The d 13C values of Lower Cretaceous Aptian-Albian platform-type carbonates in the Cuoqin Basin, North Tibet vary between 2.48 and 5.46. The mean value is 3.93. The values are not only provided with positive excursion, but also 1.17 higher than those of con-temporaneous pelagic carbonates which possess pretty high d 13C values. The origin is ap-proached. During the oceanic anoxic events, a great number of organisms were rapidly buried, causing the increase of the d 13C value of oceanic total dissolved carbon (TDC) and generally promoting the values of marine carbonates. After that, owing to the organisms undergoing dif-ferent isotopic fractionation in the paleo-ocean with stratified structure, d 13C values of shallow sea carbonate were obviously higher than those of pelagic carbonates.

Shifts of the Kuroshio axis over the last 20 000 years

Core 255 from the southern Okinawa Trough was selected to monitor the shift of the Kuroshio axis over the last 20 000 years. During the last glacial maximum the Kuroshio axis had ever shifted outside the Okinawa Trough. It entered the Okinawa Trough again at about 6 500 a BP, leading to abrupt increase of sedimentation rate, distinctly coarser sediment and remarkably increased abundance of foraminiferal indicators of the Kuroshio in the core. But, during about 4 000-3 000 a BP the abundance of the Kuroshio indicator Pulleniatina obliquiloculata sharply decreased again, indicating that the Kuroshio axis had ever shifted easterly for a short period or the Kuroshio was weakened and that moment.