Pleistocene Open Ocean Antarctic Intermediate Water Variability

作为全球温盐环流的一部分，南极中层水（AAIW）不仅重新分配热量和盐，而且还通风中间深度和运输营养物质从南大洋（SO）到营养物质匮乏的热带地区。因此，AAIW对海洋生物地球化学和碳循环具有全球重要性。AAIW的形成与SO中的绕极深水（CDW）的上涌有着内在的联系，并受到西风和与海冰出口和融化有关的季节性清新的调制。虽然很明显，AAIW的传输和组成发挥了重要作用的海洋和气候变化在最后一次冰消期有很少的AAIW的变化较长的记录。虽然仍有争议，一个持久的共识，如果稍弱的AAIW流量在末次冰期最大已经开始出现从代理数据大西洋。新大陆同位素记录表明，更大和更快的变化已被证明是有偏见的沉积叠印，这是一个固有的问题，大陆架的设置，大多数AAIW深度岩心回收。为了避免这种叠印，并制定一个长期AAIW的变化的理解，我们提出了一个新的研究，利用中间水深钻芯从公海位置在南大西洋（DSDP网站516），东南太平洋（ODP网站1236）和塔斯曼海（DSDP网站592和IODP网站U1510）。虽然在这些地点的沉积率低，第一个初步结果表明，完整的幅度冰川/间冰期底栖氧同位素变异预期的中间沃茨已被记录，因此，其他参数也将是有效的，没有显着的生物扰动的影响。从这些含氧沉积物中获得的稀土元素模式将补充底栖有孔虫稳定的C & O同位素和温度（Mg/Ca，Li/Mg）和营养物含量（Cd/Ca，Ba/Ca）的微量金属代用品，以及混合有孔虫涂层Nd同位素作为中间深度水团混合的代用品。这些工具将允许重建的水团来源，有助于AAIW，其营养成分和温度演变，跨越约150万年，并涵盖重要的中更新世过渡（MPT）。在每个地点建立高分辨率海底同位素地层学之后，将对中期计划之前、期间和之后跨越关键冰期和间冰期的样本进行所有代用指标分析。总之，这些记录从不同的盆地将提供重要的新的见解AAIW在塑造冰川终端的演变的潜在作用，AAIW直接连接南大洋与低纬度海洋盆地。还将获得新的见解，了解海洋环流如何在更新世期间对轨道和不断增加的冰盖作用力作出反应。

As part of the global thermohaline circulation Antarctic Intermediate Water (AAIW) not only redistributes heat and salt but also ventilates intermediate depths and transports nutrients from the Southern Ocean (SO) to the nutrient deprived tropics. AAIW is therefore of global importance to marine biogeochemistry and carbon cycling. AAIW formation has been intrinsically tied to the upwelling of Circumpolar Deep Water (CDW) in the SO and has been modulated by westerly winds and a seasonal freshening related to sea ice export and melt. Although it is clear that AAIW transport and composition played an important role for the oceanographic and climatic changes during the last deglaciation there are very few longer records of AAIW variability. Although still debated, a consensus on a persistent, if slightly weaker AAIW flow during the last glacial maximum has started to emerge from proxy data for the Atlantic. Neodymium isotope records that suggested greater and more rapid variability have been shown to be biased by sedimentary overprinting, which is a problem inherent to the continental shelf settings where most AAIW depth cores were recovered. To avoid such overprinting and to develop an understanding of longer term AAIW variability we propose a new study utilising intermediate water depth drill cores from open ocean locations in the South Atlantic (DSDP Site 516), the SE Pacific (ODP Site 1236) and the Tasman Sea (DSDP Site 592 and IODP Site U1510). Although the sedimentation rates at these locations are low, first preliminary results indicate that the full amplitude of glacial/interglacial benthic oxygen isotope variability expected for intermediate waters has been recorded and thus also other parameters will be valid without significant effects of bioturbation. Rare earth element patterns obtained from these oxic sediments will complement benthic foraminiferal stable C & O isotopes and trace metal proxies for temperature (Mg/Ca, Li/Mg) and nutrient content (Cd/Ca, Ba/Ca), as well as mixed foraminiferal coating Nd isotopes as proxy for intermediate depth water mass mixing. These tools will allow the reconstruction of the water mass sources contributing to AAIW, its nutrient content and its temperature evolution, spanning approximately the last 1.5 million years and covering the important mid Pleistocene transition (MPT). After the establishment of a high resolution benthic isotope stratigraphy at each site, samples spanning key glacial and interglacial intervals from before, during and after the MTP will be analysed for all proxies. Taken together, these records from different basins will provide important new insights into the potential role of AAIW in shaping the evolution of glacial terminations given that AAIW directly connects the Southern Ocean with the low latitude ocean basins. New insights will also be gained into how ocean circulation responded to orbital and increasing ice sheet forcing during the Pleistocene.