East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the south China Sea

Based on the study of 10 sediment cores and 40 core-top samples from the So uth China Sea (SCS) we obtained proxy records of past changes in East Asian monsoon climate on millennial to bidecadal time scales over the last 220,0 00 years. Climate proxies such as global sea level, estimates of paleotempe rature, salinity, and nutrients in surface water, ventilation of deep water , paleowind strength, freshwater lids, fluvial and/or eolian sediment suppl y, and sediment winnowing on the sea floor were derived from planktonic and benthic stable-isotope records, the distribution of siliciclastic grain si zes, planktonic foraminifera species, and the U-37(K) biomarker index. Four cores were AMS-C-14-dated. Two different regimes of monsoon circulation do minated the SCS over the last two glacial cycles, being linked to the minim a and maxima of Northern Hemisphere solar insolation. (1) Glacial stages le d to a stable estuarine circulation and a strong O-2-minimum layer via a cl osure of the Borneo sea strait. Strong northeast monsoon and cool surface w ater occurred during winter, in part fed by an inflow from the north tip of Luzon. In contrast, summer temperatures were as high as during interglacia ls, hence the seasonality was strong. Low wetness in subtropical South Chin a was opposed to large river input from the emerged Sunda shelf, serving as glacial refuge for tropical forest. (2) Interglacials were marked by a str ong inflow of warm water via the Borneo sea strait, intense upwelling south east of Vietnam and continental wetness in China during summer, weaker nort heast monsoon and high sea-surface temperatures during winter, i.e, low sea sonality. On top of the long-term variations we found millennial- to centen nial-scale cold and dry, warm and humid spells during the Holocene, glacial Terminations I and II, and Stage 3. The spells were coeval with published variations in the Indian monsoon and probably, with the cold Heinrich and w arm Dansgaard-Oeschger events recorded in Greenland ice cores, thus suggest ing global climatic teleconnections. Holocene oscillations in the runoff fr om South China centered around periodicities of 775 years, ascribed to subh armonics of the 1500-year cycle in oceanic thermohaline circulation. 102/84 -year cycles are tentatively assigned to the Gleissberg period of solar act ivity. Phase relationships among various monsoon proxies near the onset of Termination IA suggest that summer-monsoon rains and fluvial runoff from So uth China had already intensified right after the last glacial maximum (LGM ) insolation minimum, coeval with the start of Antarctic ice melt prior to the delta(18)O signals of global sea-level rise. Vice versa, the strength o f winter-monsoon winds decreased in short centennial steps only 3000-4000 y ears later, along with the melt of glacial ice sheets in the Northern Hemis phere. (C) 1999 Elsevier Science B.V. All rights reserved.