A reconstruction of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the glacial inception

The reconstruction of the stable carbon isotope evolution in atmospheric CO2 (d13Catm ), as archived in Antarctic ice cores, bears the potential to disentangle the contributions of the different carbon cycle fluxes causing past CO2 variations. Here we present a new record of d13Catm before, during and after the Marine Isotope Stage 5.5 (155 000 to 105 000 years BP). The record was derived with a well established sublimation method using ice from the EPICA Dome C (EDC) and the Talos Dome ice cores in East Antarctica. We find a 0.4 permil shift to heavier values between the mean d13Catm level in the Penultimate (~ 140 000 years BP) and Last Glacial Maximum (~ 22 000 years BP), which can be explained by either (i) changes in the isotopic composition or (ii) intensity of the carbon input fluxes to the combined ocean/atmosphere carbon reservoir or (iii) by long-term peat buildup. Our isotopic data suggest that the carbon cycle evolution along Termination II and the subsequent interglacial was controlled by essentially the same processes as during the last 24 000 years, but with different phasing and magnitudes. Furthermore, a 5000 years lag in the CO2 decline relative to EDC temperatures is confirmed during the glacial inception at the end of MIS 5.5 (120 000 years BP). Based on our isotopic data this lag can be explained by terrestrial carbon release and carbonate compensation.

对南极冰芯中记录的大气CO₂稳定碳同位素演化（d13Catm）进行重建，有望厘清驱动过去CO₂浓度变化的各类碳循环通量的贡献。本文报道了海洋同位素阶段5.5（Marine Isotope Stage 5.5，距今155000至105000年）前后的d13Catm新记录。该记录依托南极东部欧洲南极冰芯钻探计划Dome C（EDC）与塔洛斯穹顶的冰芯样品，采用成熟的升华法获取。研究发现，在倒数第二次冰期（约140000年前）与末次冰盛期（约22000年前）的平均d13Catm水平之间，存在0.4‰的偏重值偏移。该偏移可通过以下三种机制解释：（i）输入至海洋-大气联合碳库的碳通量的同位素组成变化；（ii）该碳通量的强度变化；或（iii）长期泥炭堆积过程。本研究的同位素数据表明，终止事件II及随后间冰期的碳循环演化过程，本质上与过去24000年的调控机制一致，但相位与幅度存在差异。此外，本研究证实，在海洋同位素阶段5.5末期（约120000年前）的冰期起始阶段，CO₂浓度下降较EDC温度记录存在5000年的滞后。基于本研究的同位素数据，该滞后现象可通过陆地碳释放与碳酸盐补偿效应予以解释。