Keywords:Asian Monsoon, East China Sea, Millennial-scale climate variability, oxygen isotope, Mg/Ca, IODP Exp.346
Abrupt millennial-scale climate changes during the late Quaternary were widely recognized in the East Asian monsoon region from deep-sea sediments in the Japan Sea and more recently from oxygen isotope (δ18O) variability in Chinese speleothems (δ18Osp). The finely 230Th-dating method on the speleothems enables comparison to climate records from other regions on millennial scale, and there is little doubt that the variability of these δ18Osp records is synchronized with climate perturbation in the North Atlantic high latitude, known as Heinrich events and with Dansgaard-Oeschger (D-O) oscillations in Greenland. However, mechanisms of the climate response in East Asia remain unclear due to the lack of fundamental agreement on what the δ18Osp climate signal represents. A primary impediment to interpreting the variability in δ18Osp is the lack of the means to decompose δ18Osp into constituent components. By contrast, the δ18O of calcite planktic foraminifers (δ18Op) from nearshore marine sediments can be quantitatively partitioned into sea surface temperature (SST) and δ18Ow of seawater (δ18Ow), a function of sea surface salinity (SSS). In this study, millennial-scale climate variability in East Asia is investigated using 400,000-yr records of SST, δ18Op, and δ18Ow from the East China Sea (IODP Site U1429). δ18Ow can be interpreted as reflecting SSS, hence rainfall, as the monsoonal runoff from the Yangtze River determines summer SSS in the northern East China Sea. As a result, SST and δ18Ow variability accounts for 58% and 35% of the total variability of δ18Op and the rest (6%) is the ice volume component or noise; the primary contributor to δ18Op variations is SST, and the secondary is δ18Ow. Foraminiferal δ18Op shows the strongest similarly with Chinese δ18Osp, indicating that δ18Osp is best interpreted as the combination of changes in surface temperature and monsoon rainfall; it is not indicative of summer monsoon rainfall alone. Partitioning of variance between temperature and rainfall does not change on glacial-interglacial timescales indicating that the hemispheric teleconnection mechanism between the Atlantic and East Asia does not depend on the global climate background status (CO2, ice volume). In comparison with the millennial scale Greenland temperature, the East China Sea SST decreases and δ18Ow increases (rainfall deceases) in most of the North Atlantic cold events (e.g., Heinrichs). However, SST and δ18Ow exhibit overall poor coherence, revealing that these climate parameters fundamentally behave differently on the millennial scale, but tend to respond in the manner described above (decrease in temperature and rainfall) once a severe cold event occurs in the North Atlantic.