Precession-band variance missing from East Asian monsoon runoff

Speleothem CaCO(3) δ(18)O is a commonly employed paleomonsoon proxy. However, inferring local rainfall amount from speleothem δ(18)O can be complicated due to changing source water δ(18)O, temperature effects, and rainout over the moisture transport path. These complications are addressed using δ(18)O of planktonic foraminiferal CaCO(3), offshore from the Yangtze River Valley (YRV). The advantage is that the effects of global seawater δ(18)O and local temperature changes can be quantitatively removed, yielding a record of local seawater δ(18)O, a proxy that responds primarily to dilution by local precipitation and runoff. Whereas YRV speleothem δ(18)O is dominated by precession-band (23 ky) cyclicity, local seawater δ(18)O is dominated by eccentricity (100 ky) and obliquity (41 ky) cycles, with almost no precession-scale variance. These results, consistent with records outside the YRV, suggest that East Asian monsoon rainfall is more sensitive to greenhouse gas and high-latitude ice sheet forcing than to direct insolation forcing.