Precession-band variance missing from East Asian monsoon runoff

Speleothem CaCO3 delta O-18 is a commonly employed paleomonsoon proxy. However, inferring local rainfall amount from speleothem delta O-18 can be complicated due to changing source water delta O-18, temperature effects, and rainout over the moisture transport path. These complications are addressed using delta O-18 of planktonic foraminiferal CaCO3, offshore from the Yangtze River Valley (YRV). The advantage is that the effects of global seawater delta O-18 and local temperature changes can be quantitatively removed, yielding a record of local seawater delta O-18, a proxy that responds primarily to dilution by local precipitation and runoff. Whereas YRV speleothem delta O-18 is dominated by precession-band (23 ky) cyclicity, local seawater delta O-18 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.