Southern Ocean and atmospheric CO2 in a warm world - unravelling CO2 sinks in the Southern Ocean during the last interglacial climate state (Project acronym: SOCO)

对过去温暖气候间隔期间大气CO2变率的原因进行了讨论。人们普遍认为，在过去的100万年里，深海，特别是南大洋中碳封存的变化调节了大气中二氧化碳的变化。然而，间冰期气候期间控制深海碳储存过程的最基本性质和时间尚不清楚。我们建议量化南大洋深海碳固存的变化，并解决其在最后一个温暖气候状态（海洋同位素阶段5）期间的生物和物理控制。最后一次间冰期提供了一个理想的试验平台，用于研究在“有时比今天更温暖”的气候中与全球碳循环相关的气候反馈和阈值。首先，我们将重建末次间冰期深海碳含量的千年尺度变化，其次，将这些估计与出口生产重建相结合，以估计生物生产力和非生物（即物理/动力）过程对深海碳水平的影响，从而对大气CO2的影响。第三，我们将直接量化海洋表层和深海pH值的变化，以明确确定海洋和大气之间二氧化碳分配的效率。这将提供关于在温暖和比现在更温暖的气候中主导大气碳储量的过程和区域的关键信息，以及最终导致大气二氧化碳减少和间冰期消亡的原因。该项目将为与当前全新世间冰期碳循环动力学的比较提供重要的基准。

The causes of atmospheric CO2 variability during past warm climate intervals are debated. It is widely accepted that changes in carbon sequestration in the deep ocean, in particular in the Southern Ocean, have regulated the atmospheric CO2 variability over as much as the last million years. However, the most basic nature and timing of processes controlling deep-ocean carbon storage during interglacial climates are not understood. We propose to quantify changes in deep-ocean carbon sequestration and to resolve its biological and physical controls during the last warm climate state (Marine Isotope Stage 5) throughout the Southern Ocean. The last interglacial offers an ideal test bed for studying climate feedbacks and -thresholds associated with the global carbon cycle during an 'at times warmer than today' climate. First, we will reconstruct millennial-scale variations in last interglacial deep-ocean carbon content and second, combine these estimates with export production reconstructions to estimate the influence of biological productivity and non-biological (i.e. physical/dynamical) processes on deep-ocean carbon levels, and thus on atmospheric CO2. Third, we will directly quantify changes in surface- and deep-ocean pH to unequivocally determine the efficiency of the partitioning of CO2 between the ocean and the atmosphere. This will provide critical information on the processes and regions that dominate the atmospheric carbon inventory in a warm and warmer-than-present climate, and what eventually leads to a decline of atmospheric CO2 and the demise of an interglacial. This project will provide important benchmarks for a comparison with carbon cycle dynamics of the current Holocene interglacial.