Direct correlation of Chinese speleothem δ 18 O and South China Sea planktonic δ 18 O: Transferring a speleothem chronology to the benthic marine chronology

Orbital tuning of benthic δ 18 O is a common approach for assigning ages to ocean sediment records. Similar environmental forcing of the northern South China Sea and the southeast Asian cave regions allows for transfer of the speleothem δ 18 O radiometric chronology to the planktonic and benthic δ 18 O records from Ocean Drilling Program Site 1146, yielding a new chronology with 41 radiometrically calibrated datums, spanning the past 350 kyr. This approach also provides for an independent assessment of the accuracy of the orbitally tuned benthic δ 18 O chronology for the last 350 kyr. The largest differences relative to the latest chronology occur in marine isotope stages (MIS) 5.4, 5.5, 6, 7, and 9.3. Prominent suborbital‐scale structure believed to be global in nature is identified within MIS 5.4 and MIS 7.2. On the basis of the radiometrically calibrated chronology, the time constant of the ice sheet is found to be 5.4 kyr at the precession band (light δ 18 O lags precession minima by −55.4°) and 10.4 kyr at the obliquity band (light δ 18 O lags obliquity maxima by 57.4°). These values are significantly shorter than the single 17 kyr time constant originally estimated by Imbrie et al. (1984), based primarily on the timing of terminations I and II and the 15 kyr time constant used by Lisiecki and Raymo (2005).