UKIODP Moratorium Award - IODP Expedition 361, Southern African Climates - Ian Hall

南非气候（SAFARI）361号考察队将调查上新世/更新世期间气候与阿古拉斯洋流之间的相互作用。在南印度洋和莫桑比克海峡的六个钻探地点将确定（1）厄古拉斯海流的敏感性，（2）印度-大西洋门户环流的动力学，以及（3）过去5 Ma主要海洋和气候重组期间厄古拉斯泄漏与大西洋经向翻转环流（AMOC）变化之间的联系。阿古拉斯海流是南半球最强的西边界海流，从热带印度洋沿着东非边缘向非洲尖端输送约70 Sv的温暖和含盐表面沃茨。与大气的热量和水分交换影响南部非洲的气候，包括个别天气系统，如该区域的热带气旋形成和降雨模式。最近的海洋模型和古海洋学数据进一步指出，在晚更新世的强度和模式的AMOC控制的厄古拉斯电流的潜在作用。溢出的盐水Agulhas水到南大西洋刺激浮力异常，作为一个控制机制，对全流域的AMOC，在北大西洋和北方半球气候的对流活动的影响。第361次考察的目的是将这项工作扩展到上新世/更新世期间主要的海洋和气候重组时期，以评估厄古拉斯海流和随后的（海洋间）海洋热量和盐的输送在塑造区域和全球规模的海洋和气候发展方面发挥了作用。在这项暂停建议中，一个具体的重点将是中更新世过渡期（MPT），距今约1250 - 70万年，代表了更新世气候历史的一个关键时期。在这段时间里，冰川-间冰期循环的周期性从40 kyr的节奏变成了频率较低、强度更大、不对称的100 kyr模式。这种转变发生在轨道强迫没有显著变化的情况下，表明气候系统的内部反馈在实现这一重大气候重组中发挥了相当大的作用。大多数关于MPT起源的假设都是对长期冷却的响应，由大气pCO 2下降驱动。冰芯记录显示，在过去的800 kyr冰川间冰期pCO 2波动约100 ppm。过去三十年来，提出了各种固碳和深海储存机制。这些机制之一调用的效率增加，预制的营养物质的利用在南大洋亚南极带的结果，增加灰尘通量。在这一高营养、低叶绿素（HNLC）地区的铁有限条件下，冰川尘埃施肥可能推动了初级生产力的提高，并增加了海洋表层的碳出口。考虑到这种机制作为晚更新世pCO 2变化驱动因素的潜力，可以想象，在MPT可能存在类似的过程。我将使用来自Agulhas高原上Exp 361现场的材料，重建MPT上亚南极带的出口生产。这将使我能够研究软组织生物泵对MPT发作期间观察到的铁沉积增加的反应，并最终有助于我们理解导致MPT后世界冰川pCO 2降低的过程。

The South African Climates (SAFARI) Expedition 361 will investigate the interaction between climate and the Agulhas Current during the Pliocene/Pleistocene. Six drill sites in the southern Indian Ocean and Mozambique Channel will determine (1) the sensitivity of the Agulhas Current, (2) the dynamics of Indian-Atlantic gateway circulation, and (3) the connection between Agulhas Leakage and shifts of the Atlantic Meridional Overturning Circulation (AMOC) during major ocean and climate reorganizations of the past 5 Ma. The Agulhas Current is the strongest western boundary current in the Southern Hemisphere, transporting some 70 Sv of warm and saline surface waters from the tropical Indian Ocean along the East African margin to the tip of Africa. Exchanges of heat and moisture with the atmosphere influence southern African climates, including individual weather systems such as extratropical cyclone formation in the region and rain-fall patterns. Recent ocean models and paleoceanographic data further point at a potential role of the Agulhas Current in controlling the strength and mode of the AMOC during the Late Pleistocene. Spillage of saline Agulhas water into the South Atlantic stimulates buoyancy anomalies that act as a control mechanism on the basin-wide AMOC, with implications for convective activity in the North Atlantic and Northern Hemisphere climate. Expedition 361 aims to extend this work to periods of major ocean and climate restructuring during the Pliocene/Pleistocene to assess the role that the Agulhas Current and ensuing (interocean) marine heat and salt transports have played in shaping the regional- and global-scale ocean and climate development.Within this moratorium proposal a specific focus will be on the The Middle Pleistocene Transition (MPT), circa 1250 and 700 thousand years (kyr) before present (BP) which represents a key interval of Pleistocene climate history. During this time the periodicity of glacial-interglacial cycles altered from a 40 kyr rhythm to a less frequent, more intense and asymmetric 100 kyr pattern. This shift occurred in the absence of significant changes in orbital forcing, suggesting that internal feedbacks in the climate system played a considerable role in bringing about this major climatic reorganisation. Most hypotheses for the origin of the MPT invoke a response to a long-term cooling, driven by decreasing atmospheric pCO2. Ice core records extending over the past 800 kyr indicate glacial-interglacial pCO2 fluctuations of ~100 ppm. Various mechanisms of carbon sequestration and deep ocean storage have been proposed over the past three decades. One of these mechanisms invokes an increase in the efficiency of preformed nutrients utilisation in the Subantarctic Zone of Southern Ocean as a result of increased dust flux. Glacial dust fertilisation in the iron-limited conditions of this High Nutrient, Low Chlorophyl (HNLC) region, could have driven an increase in primary productivity and increased export of carbon from the surface ocean. Given the potential of this mechanism as a driver of Late Pleistocene pCO2 variability, it is conceivable that a similar process may have operated across the MPT. I will use use material from Exp 361 Site on the Agulhas Plateau to reconstruct export production in the Subantarctic Zone across the MPT. This will allow me to investigate the response of the soft-tissue biological pump to the increased iron deposition observed during the onset of the MPT and will ultimately contribute to our understanding of the processes that resulted in lower glacial pCO2 in the post-MPT world.