Age determination of Vostock Ice Core

The object of the present study is to introduce a means of comparing the Vostok and marine chronologies. Our strategy has been to use the delta18O of atmospheric O2 (denoted delta18Oatm) from the Vostok ice core as a proxy for the delta18O of seawater (denoted delta18Osw). Our underlying premise in using delta18Oatm as a proxy for delta18Osw is that past variations in delta18Osw (an indicator of continental ice volume) have been transmitted to the atmospheric O2 reservoir by photosynthesizing organisms in the surface waters of the world's oceans. We compare our record of delta18Oatm to the delta18Osw record which has been developed from studies of the isotopic composition of biogenic calcite (delta18Oforam) in deep-sea cores. We have tied our delta18Oatm record from Vostok to the SPECMAP timescale throughout the last 135 kyr by correlating delta18Oatm with a delta18Osw record from V19-30. Results of the correlation indicate that 77% of the variance is shared between these two records. We observed differences between the delta18Oatm and the delta18Osw records during the coldest periods, which indicate that there have been subtle changes in the factors which regulate delta18Oatm other than delta18Osw. Our use of delta18Oatm as a proxy for delta18Osw must therefore be considered tentative, especially during these periods. By correlating delta18Oatm with delta18Osw, we provide a common temporal framework for comparing phase relationships between atmospheric records (from ice cores) and oceanographic records constructed from deep-sea cores. Our correlated age-depth relation for the Vostok core should not be considered an absolute Vostok timescale. We consider it to be the preferred timescale for comparing Vostok climate records with marine climate records which have been placed on the SPECMAP timescale. We have examined the fidelity of this common temporal framework by comparing sea surface temperature (SST) records from sediment cores with an Antarctic temperature record from the Vostok ice core. We have demonstrated that when the southern ocean SST and Antarctic temperature records are compared on this common temporal framework, they show a high degree of similarity. We interpret this result as supporting our use of the common temporal framework for comparing other climate records from the Vostok ice core with any climate record that has been correlated into the SPECMAP chronology.

本研究旨在提出一种对比沃斯托克冰芯（Vostok ice core）与海洋年代序列的方法。我们的研究策略是以沃斯托克冰芯的大气氧δ¹⁸O（记作δ¹⁸Oatm）作为海水δ¹⁸O（记作δ¹⁸Osw）的代用指标。我们采用δ¹⁸Oatm作为δ¹⁸Osw代用指标的核心前提为：过去海水δ¹⁸Osw（大陆冰量的指示指标）的变化，可通过全球海洋表层水体中的光合生物，传递至大气氧储库。我们将δ¹⁸Oatm记录与基于深海岩芯（deep-sea cores）中生物成因方解石氧同位素δ¹⁸O（记作δ¹⁸Oforam）构建的δ¹⁸Osw记录进行对比。通过将δ¹⁸Oatm与来自站位V19-30的δ¹⁸Osw记录进行关联，我们将沃斯托克冰芯的δ¹⁸Oatm记录绑定至过去13.5万年以来的SPECMAP年代标尺（SPECMAP timescale）。相关性分析结果显示，两条记录共享77%的方差。我们在最冷期观测到δ¹⁸Oatm与δ¹⁸Osw记录存在差异，这表明除δ¹⁸Osw外，尚有其他因素会对δ¹⁸Oatm的调控产生细微影响。因此，我们将δ¹⁸Oatm作为δ¹⁸Osw代用指标的做法需审慎对待，尤其在上述冷期。通过将δ¹⁸Oatm与δ¹⁸Osw关联，我们为对比冰芯来源的大气记录与深海岩芯构建的海洋学记录之间的相位关系，提供了统一的时间框架。我们为沃斯托克冰芯建立的关联年龄-深度关系，不应被视为沃斯托克绝对年代标尺。我们认为，该标尺是将沃斯托克气候记录与已锚定SPECMAP年代标尺的海洋气候记录进行对比的优选标尺。我们通过对比沉积岩芯的海表温度（SST，sea surface temperature）记录与沃斯托克冰芯的南极温度记录，检验了该统一时间框架的保真度。研究证实，在该统一时间框架下，南大洋海表温度与南极温度记录呈现高度相似性。我们将这一结果解读为，支持采用该统一时间框架，对比沃斯托克冰芯的其他气候记录与任何已锚定SPECMAP年代序列的气候记录。