IODP Exp 346: Onset and evolution of millennial-scale variability of the Asian monsoon (sailing participation)

点击翻译按钮获取中文摘要

The Asian monsoon is the most convectively active atmospheric circulation system on Earth, and its seasonal rains impact about half the world's people. The timing and distribution of modern monsoon rainfall is relatively well documented, but past spatio-temporal patterns of changes in the Asian monsoon are poorly constrained. Recent evidence suggests the East Asian and Indian summer monsoons have varied significantly in concert with Dansgaard-Oescgher (D-O) cycles. These cycles have global resonance as they appear to be coupled between northern and southern hemispheres via complex interactions between the atmosphere, ocean, cyrosphere and biosphere. During a typical D-O cycle, slow cooling in the North Atlantic is terminated abruptly by rapid warming that recurs at a millennial-scale pacing. Assembling a comprehensive picture of Earth's climate response during D-O cycles is essential to understanding how abrupt warming events are amplified and propagated through the climate system. Ultimately this is important because the rate of temperature increase during a D-O cycle in northern high latitudes is comparable to rates of warming projected for the coming decades. The Himalaya and Tibetan Plateau (HTP), one of the most topographically imposing features on Earth, plays a key role in determining the strength of the Asian monsoon. In addition, the size of the HTP forms an obstacle that blocks low-level Westerly Jet circulation (WJC). Geological records have implicated the uplift of the Tibetan Plateau, starting c. 50 Myr ago, in enhanced continental aridity, late Cenozoic cooling, intensification of the Asian summer and winter monsoon, and even perhaps causing increased weathering and drawdown of atmospheric CO2. Furthermore, it has been proposed that the renewed uplift and extension of the HTP at c. 3.6 Ma acted as a trigger for the onset of D-O-type climatic variability. The coherence between monsoon variability and D-O cycles is therefore thought to be a consequence of renewed HTP uplift during the Plio-Pleistocene, creating two discrete modes of WSC. The emergence of these two modes of atmospheric circulation also provides a potential teleconnection to D-O events documented in the North Atlantic. Integrated Ocean Drilling Program (IODP) expedition 346 proposes to core and log seven sites covering a wide latitudinal range from the Japan Sea to the northern East China Sea to test the hypothesis that Plio-Pleistocene uplift of the HTP, and the consequent emergence of two discrete modes of WJC, caused the amplification of millennial-scale variability in the East Asian summer (EASM) and winter (EAWM) monsoons. IODP 346 aims to recover cores that will provide the geological evidence that (1) monitors past behaviours in the WJC, EASM, EAWM and the Tsushima Warm Current; (2) reconstructs the behaviour of the sub-Polar Front and ice-rafted debris, and (3) understands the ventilation history of the Japan Sea and its link to the influx of freshwater through the Tsushima Strait and winter cooling.