East Asian hydroclimate modulated by the position of the westerlies during Termination I

Abstract

Speleothem oxygen isotope records have revolutionized our understanding of the paleo East Asian monsoon, yet there is fundamental disagreement on what they represent in terms of the hydroclimate changes. We report a multiproxy speleothem record of monsoon evolution during the last deglaciation from the middle Yangtze region, which indicates a wetter central eastern China during North Atlantic cooling episodes, despite the oxygen isotopic record suggesting a weaker monsoon. We show that this apparent contradiction can be resolved if the changes are interpreted as a lengthening of the Meiyu rains and shortened post-Meiyu stage, in accordance with a recent hypothesis. Model simulations support this interpretation and further reveal the role of the westerlies in communicating the North Atlantic influence to the East Asian climate.

Deciphering Oxygen Isotope Records From Chinese Speleothems With an Isotope‐Enabled Climate Model

“…While our results are based on the numerical experiments, comparing speleothem δ 18 O with other proxy data can provide additional clues to interpret speleothem δ 18 O. For example, Zhang et al () compared a speleothem δ 18 O record with a speleothem trace metal record, which is believed to represent local precipitation and revealed the decoupling of precipitation and speleothem δ 18 O signals. Also, a recent finding of marine sediments in the East China Sea (Clemens et al, , Site U1429 of the International Ocean Discovery Program) representing the monsoon runoff showed that it did not feature the 23‐kyr cycles present in speleothem records.…”

“…This pattern is similar to the leading mode of interannual precipitation variability in East Asia (Day et al, ). Speleothem trace element ratios also suggest that low values of speleothem δ 18 O in central China can coincide with dryness instead of wetness in that region (Zhang et al, ). This, however, is not enough to reach a conclusion regarding central China receiving less precipitation in P min , since similar simulations with other models like EC‐Earth and GFDL‐CM2.1 do not clearly show less precipitation in central China (Bosmans et al, ).…”

“…Any description of the East Asian monsoon should include both rainfall and circulation systems: The prominent feature of the East Asian monsoon rainfall is the rainbelt from mid‐June to mid‐July, which is called mei‐yu, extending from central eastern China to Japan (where the caves of Sanbao and Hulu are located, Figure ); the circulation of the East Asian monsoon features westerly winds over the northern Indian Ocean and southerly winds over the South China Sea and Eastern China. Modern observations reveal a tripole pattern of the East Asian precipitation at interannual scales (Figure 1 in Zhang et al, ) (Day et al, ). In this mode, strong monsoon winds are associated with low precipitation in central China.…”

Late Quaternary East Asian Summer Monsoon Variability Deduced From Lacustrine Mineral Magnetic Records of Dahu Swamp, Southern China

“…(e) Hopanoid mass accumulation rates (blue) (Xie et al, ) and mean annual precipitation reconstructed by the pollen‐transfer function method (blue) (Xiao et al, ) from Dajiuhu peatland. (f) Stalagmite ARM/SIRM record from Heshang cave (blue) (Xie et al, ), and the leading principal component (PC1) of six trace element ratio time series (Sr/Ca, Ba/Ca, and Mg/Ca) from Haozhu cave (red) (Zhang et al, ). (g) Paleoprecipitation record based pollen assemblages from Gonghai lake (blue) (Chen et al, ) and magnetic susceptibility record from Lantian loess section (red) (Liu et al, ).…”

“…Speleothem δ 18 O records in southern and central China have been regarded as yielding the most significant and reliable information about EASM changes on various timescales (Cheng et al, ; Wang et al, ). However, the climatic interpretation of speleothem δ 18 O remains highly controversial in terms of large‐scale shifts in Asian summer circulation, and more “local‐scale” changes in precipitation (Caley et al, ; Maher & Thompson, ; Zhang et al, ). The traditional paradigm links the cave δ 18 O signals as a proxy for regional rainfall of the EASM, with higher EASM rainfall corresponding to more depleted δ 18 O (Cheng et al, ; Wang et al, ).…”