The Southern Ocean's role in CO2 change

冰期-间冰期CO2变化的成因被描述为古气候的<s:1>均匀颗粒<e:1>。几十年的研究已经将焦点缩小到南大洋作为冰期间冰期二氧化碳变化的最重要驱动因素（Sigman等，2010），由于其与深海的密切联系（Rae & Broecker, 2018）及其独特的生物地球化学：作为一个高营养低叶绿素区域，从深层上升流带到地表的二氧化碳不能被生物生产力有效捕获，并可能释放到大气中。已经提出了几种机制来解释南大洋如何在冰期捕获更多的二氧化碳，包括铁肥料、海洋分层和海冰增加的<s:1> celidc <e:1>。然而，尽管存在这些过程的各种示踪剂，但直到最近还无法定量评估它们对二氧化碳储存和释放的影响。该项目的目的是量化南大洋在上一个冰期二氧化碳变化中的作用，包括帮助驱动冰期本身的冰期-间冰期二氧化碳变化，以及与快速气候变化相关的二氧化碳漂移。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值和二氧化碳在冰川循环中的变化。该学生将利用新颖的分析方法克服小样本量的问题，首次从南大洋的南极区进行高分辨率的pH和CO2重建。这些将与上一个冰期循环期间南大洋深处二氧化碳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，并结合地球系统模型的实验，我们将计算出这些过程在冰期-间冰期到百年时间尺度上对二氧化碳变化的相对重要性。

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.