NOAA/WDS Paleoclimatology - South China Sea 350KYr Radiometric Marine Chronology

Orbital tuning of benthic d18O 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 d18O radiometric chronology to the planktonic and benthic d18O 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 d18O 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 d18O lags precession minima by -55.4°) and 10.4 kyr at the obliquity band (light d18O 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).

底栖δ¹⁸O（benthic d18O）的轨道调谐，是为海洋沉积物记录定年的常用方法。南海北部与东南亚洞穴区域受到相似的环境强迫，因此可将石笋δ¹⁸O（speleothem d18O）的放射性测年年表，迁移至大洋钻探计划（Ocean Drilling Program, ODP）1146站位的浮游与底栖δ¹⁸O记录中，由此得到一套涵盖过去350千年（kyr）的全新年表，包含41个经放射性校准的基准点。该方法还可独立评估过去350千年内，经轨道调谐的底栖δ¹⁸O年表的准确性。相较于最新年表，最大的偏差出现在海洋同位素阶段（marine isotope stages, MIS）5.4、5.5、6、7及9.3中。在MIS 5.4与MIS 7.2中，识别出了被认为具有全球性特征的显著亚轨道尺度结构。基于经放射性校准的年表，冰盖的时间常数在岁差波段为5.4千年：轻δ¹⁸O较岁差极小值滞后-55.4°；在黄赤交角波段为10.4千年：轻δ¹⁸O较黄赤交角极大值滞后57.4°。该数值远小于Imbrie等人1984年最初估算的单一17千年时间常数——其估算主要基于终止带I与II的时间，同时也小于Lisiecki与Raymo 2005年所采用的15千年时间常数。