Last Glacial Maximum carbon isotopic composition@en

We present Holocene and last glacial maximum (LGM) oxygen and carbon isotope measurements on Planulina wuellerstorfi in six southeast Pacific cores. Sedimentation rates are low in this part of the ocean, and measurements were made on individual foraminiferal shells in order to identify the Holocene and glacial individuals on the basis of their extreme d18O. The new d13C data were combined with previous P. wuellerstorfi data for interpretation of global thermohaline circulation. Data from the Southern Ocean were examined closely for regional coherency and a few anomalous d13C values suspected of having productivity overprint were removed. The resulting global d13C distributions and gradients indicate that the deep water circulation was similar during the Holocene and LGM. This interpretation brings d13C data to a better agreement with Cd/Ca data and marks a sharp contrast with a widely held view based on d13C measurements that the glacial Southern Ocean was the terminus of the thermohaline circulation. The proposed presence of glacial North Atlantic Deep Water does not necessarily contradict the postulated presence of Glacial North Atlantic Intermediate Water.本研究报道了东南太平洋6个岩芯中武氏平旋虫（Planulina wuellerstorfi）的全新世（Holocene）与末次冰盛期（last glacial maximum, LGM）氧、碳同位素测试数据。该海域沉积速率较低，故本研究对单个有孔虫壳体开展测试，以通过其极端的δ¹⁸O值区分全新世与冰期个体。本研究将新获取的δ¹³C数据与已发表的武氏平旋虫（P. wuellerstorfi）数据相结合，用于全球温盐环流（thermohaline circulation）的解译。本研究对南大洋（Southern Ocean）的相关数据进行了细致的区域一致性检验，并剔除了若干疑似受生产力叠加信号改造的异常δ¹³C值。最终得到的全球δ¹³C分布与梯度特征表明，全新世与末次冰盛期的深水环流模式基本一致。该解译使得δ¹³C数据与镉钙比（Cd/Ca）数据的一致性得到显著提升，同时与此前基于δ¹³C测试提出的"冰期南大洋为温盐环流终端"的主流学术观点形成鲜明反差。冰期北大西洋深层水（glacial North Atlantic Deep Water）的存在假说，与冰期北大西洋中层水（Glacial North Atlantic Intermediate Water）的存在假说并不必然矛盾。