The Southern Ocean's role in CO2 change

冰川-间冰期二氧化碳变化的原因被描述为古气候的圣杯。几十年的研究已经将焦点缩小到南大洋作为冰川间冰期CO2变化的最重要驱动力（Sigman等人，2010年），由于其与深海的密切联系，（Rae & Broecker，2018）及其独特的地球化学：作为一个高营养低叶绿素的区域，从深层上升流带到表面的CO2不能被生物生产力有效地捕获，并且可能释放到大气中。已经提出了几种机制来解释南大洋如何在冰川期间捕获更多的CO2，包括铁肥化、海洋分层和海冰增加。然而，虽然这些过程的各种示踪剂存在，直到最近，还不可能定量评估其对CO2储存和释放的影响。本项目的目的是量化南大洋在最后一个冰河时代的CO2变化中的作用，包括冰川-间冰期CO2变化，有助于推动冰河时代本身，以及与快速气候变化相关的CO2漂移。为此，我们将使用化石碳酸盐的硼同位素组成（Foster & Rae，2016，Rae 2018）来重建南大洋pH值和CO2在冰川周期中的变化。学生将使用新的分析方法来克服小样本量，从南大洋南极区首次高分辨率重建pH值和CO2。这些数据将与最后一次冰期循环中南大洋深处CO2储存和释放的新记录相结合，通过将这些数据与生物泵效率、海冰和海洋环流的多代理记录进行比较，以及与地球系统模型的实验，我们将计算出这些过程在冰川-间冰期到百年时间尺度上CO2变化的相对重要性。

The cause of glacial-interglacial CO2 change has been described as the âceholy grailâc of palaeoclimate. Several decades of research have narrowed focus onto the Southern Ocean as the most important driver of glacial interglacial CO2 change (Sigman et al., 2010), due its intimate link to the deep ocean (Rae & Broecker, 2018) and its unique biogeochemistry: as a high nutrient low-chlorophyll region, CO2 brought to the surface from deep upwelling cannot be efficiently captured by biological productivity and may outgas to the atmosphere.Several mechanisms have been proposed to explain how the Southern Ocean may have trapped more CO2 during glacials, including iron fertilisation, ocean stratification, and a âcelidâc of increased sea ice. However, while various tracers of these processes exist it has, until recently, not been possible to quantitatively assess their impact on CO2 storage and release.The aim of this project is to quantify the role of the Southern Ocean in CO2 change over the last ice age, including the glacial-interglacial CO2 changes that help drive the ice ages themselves, and the CO2 excursions associated with rapid climate change. To do this we will use the boron isotope composition of fossil carbonates (Foster & Rae, 2016, Rae 2018) to reconstruct how Southern Ocean pH and CO2 changed over glacial cycles.The student will make the first high-resolution pH and CO2 reconstructions from the Antarctic Zone of the Southern Ocean, using novel analytical approaches to overcome small sample sizes. These will be coupled with new records of CO2 storage and release in the deep Southern Ocean over the last glacial cycle.By comparing these data to multi-proxy records of biological pump efficiency, sea ice, and ocean circulation, alongside experiments with an Earth system model, we will work out the relative importance of these processes in CO2 change on glacial-interglacial to centennial timescales.