Impact of carbon cycle changes in the Pacific Southern Ocean on climate shifts during the past 3.5 million years (IMPAC3.5T)

南大洋的物理、动力和生物过程对深海碳储存、南极冰盖的稳定性、海洋生产力和全球气候有很大影响。这些众多的过程，特别是在南大洋太平洋部分，对长期气候变化和比现在更温暖的气候条件的驱动因素和影响，对于地质过去和未来都没有足够的了解。在这个项目中，我们调查了太平洋南部海洋深层碳储存和海洋-大气CO2交换之间的性质和相互作用，这两个过去的气候状态提供了该海洋地区如何影响全球气候和大气CO2水平的极端情况：首先，间冰期气候和比现在更温暖的气候（即，上新世中期温暖期（MPWP），海洋同位素阶段（MIS）11和31）和第二，过去170万年的冰川气候条件和冰川加剧与中更新世气候转变（MPT）。该项目的主要目标是：（a）量化南太平洋在这些关键时间段内作为大气CO2变化驱动因素的CO2释气（或吸收）变化;（B）估计南太平洋深海海洋碳储存过去的变化，并将其与该区域相关的海洋-大气CO2交换联系起来;（c）评估驱动这两种变化的可能机制。我们的古重建的基础是特殊的（时间上高分辨率和碳酸盐丰富）的沉积记录钻在IODP网站U1541在南太平洋中部。该项目旨在通过参照现有和新出现的大气CO2记录，以浮游有孔虫B同位素分析为基础，高分辨率重建海洋表层pCO 2水平，从而实现其目标。这些研究结合了对深海碳储存（通过有孔虫铀/钙水平和（Cibicidoides）孔隙密度）、表层海洋水文（通过有孔虫镁/钙比率和稳定氧同位素）、深海碳酸盐系统和海冰范围（均通过沉积普查计数）的伴随变化的多替代评估。该项目提供了非常需要的海洋机制，管理过去的大气CO2变化，正在重建从冰芯和海洋沉积物一样。此外，它大大扩展了我们目前对长期（可能不可逆转）气候变化和比现在更温暖的气候中过去海洋碳循环动态的理解，特别是在我们地球未来的高二氧化碳世界中。

Physical, dynamical and biological processes in the Southern Ocean have a strong leverage on deep-ocean carbon storage, the stability of the Antarctic ice sheet, marine productivity and global climate. The drivers and impact of these numerous processes, particularly in the Pacific sector of the Southern Ocean, on long-term climate shifts and warmer-than-present climate conditions are insufficiently known for both the geological past and the future. In this project, we investigate the nature and interplay between deep carbon storage and ocean-atmosphere CO2 exchange in the Pacific Southern Ocean for two past climate states that provide extremes of how this ocean region might have impacted global climate and atmospheric CO2 levels: first, interglacial climates and warmer-than-present climates (i.e., the Mid-Pliocene Warm Period (MPWP), Marine Isotope Stage (MIS) 11 and 31) and second, glacial climate conditions of the last 1.7 million years and glacial intensification associated with the Mid-Pleistocene Climate Transition (MPT). The main objectives of the project are to a) quantify changes in Pacific Southern Ocean outgassing (or uptake) of CO2 as driver of atmospheric CO2 changes during these key intervals, b) estimate past changes in the ocean carbon storage in the deep Pacific Southern Ocean and link them with associated ocean-atmosphere CO2 exchange in that region, and c) assess possible mechanisms driving both. The basis of our paleo-reconstructions is the exceptional (temporally highly resolved and carbonate-rich) sedimentary record drilled at IODP Site U1541 in the central South Pacific Ocean. The project aims at achieving its goals through high-resolution reconstructions of surface ocean pCO2 levels based on planktonic foraminiferal B isotope analyses that are referenced against existing and emerging atmospheric CO2 records. These are combined with a multi-proxy assessment of concomitant variations in deep-ocean carbon storage (via foraminiferal U/Ca levels and (Cibicidoides) pore densities), surface ocean hydrography (via foraminiferal Mg/Ca ratios and stable oxygen isotopes), the deep-ocean carbonate system and sea ice extent (both via sedimentary census counts). The project provides much needed constraints on the oceanic mechanisms governing past atmospheric CO2 variations that are being reconstructed from ice cores and marine sediments alike. In addition, it significantly expands our current understanding of past marine carbon cycle dynamics during long-term (possibly irreversible) climate shifts and warmer-than present climates, specifically during the high-CO2 world foreseen for the future of our planet.