Unlocking the potential of IODP site U1534 to reveal the sensitivity of Atlantic Overturning Circulation to "cold water route" variability.

大西洋纬向翻转环流（AMOC）在调节地球气候方面起着重要作用。过去这种翻转环流强度的减弱与北方的急剧冷却有关。最近大西洋副极地的冷却和墨西哥湾流区域的变暖趋势表明AMOC的减弱。大气环流模式通常偏向于一个稳定的AMOC，无法复制观测到的AMOC对气候强迫的敏感性。AMOC稳定性的模型偏差表明，某些参数的表示不准确，损害了我们预测未来AMOC变化的能力。对AMOC的一个要素仍然知之甚少的是南极中层水（AAIW）的作用。AAIW是AMOC北向流的主要水团之一。与北大西洋深水向南流动的平衡，AAIW目前在北大西洋渗透到北纬20度。尽管最近的研究工作激增，但尚未就AAIW在促成AMOC变异性方面的作用达成共识。今天，AAIW主要形成于东南太平洋和西南大西洋。AAIW和它的前身，亚季风模式水，平流向东通过德雷克海峡沿着亚季风锋（SAF）。这种注入冷，低盐度的太平洋水进入南大西洋通常被称为“冷水路线”。太平洋和大西洋之间的连通性通过这个冷水路线的变化可能会修改AAIW形成在西南大西洋的物理特性，反过来影响的热量和盐度预算的AMOC。它已经表明，在末次冰期，SAF可能是在一个更偏北的位置相对于今天。由于被南美洲截断，SAF无法将太平洋来源的亚南极模式水输送到南大西洋，从而有效地关闭了冷水路线。在冰消期，SAF向南迁移，一旦在德雷克海峡内建立，路线是开放的，太平洋水源被注入南大西洋。冷水航线的开通和AMOC的复兴的巧合需要进一步的调查，以限制AMOC通过德雷克海峡的太平洋-大西洋连通性的敏感性。海洋沉积物回收IODP网站U1534远征382目前的第一次机会，以限制变化的端元物理和地球化学性质的AAIW，因为它进入了多个冰川间冰期循环的上肢的AMOC。该提案将为U1534生成一个确定的年龄模型，并将为未来NERC拨款奠定基础，以解决冷水路线对AMOC的影响问题。此外，这里提出的进展将使许多与国家和国际合作者以及潜在学生的相关项目受益，并优化英国领导的海洋钻探工作的产出。

The Atlantic meridional overturning circulation (AMOC) plays a fundamental role in regulating the Earth's climate. Past reductions in the strength of this overturning circulation have been associated with dramatic cooling in the northern hemisphere. A recent trend of cooling in the subpolar Atlantic Ocean and warming in the Gulf Stream region is indicative of a weakening of the AMOC. General Circulation Models are typically biased toward a stable AMOC and unable to replicate the observed sensitivity of the AMOC to climate forcing. This model bias in AMOC stability suggests that certain parameters are inaccurately represented, compromising our ability to predict future AMOC change. One element of the AMOC that remains poorly understood is the role of Antarctic Intermediate Water (AAIW). AAIW is one of the primary water masses characterizing the northward-flowing upper limb of the AMOC. Counter-balancing the southward flow of North Atlantic Deep Water, AAIW currently penetrates as far as 20 deg N in the North Atlantic. Despite a recent surge in research effort a consensus on the role of AAIW in contributing to AMOC variability has not been achieved. Today, AAIW is primarily formed in the SE Pacific and SW Atlantic Oceans. AAIW and its precursor, Subantarctic Mode Water, are advected eastward through Drake Passage along the Subantarctic Front (SAF). This injection of cold, low salinity Pacific water into the South Atlantic Ocean is commonly referred to as the 'cold water route. Variability in the connectivity between the Pacific and Atlantic Oceans via this cold water route may modify the physical properties of AAIW forming in the SW Atlantic Ocean, in turn affecting the heat and salinity budget of the AMOC. It has been shown that during the last glacial period the SAF was likely in a more northerly position relative to today. Truncated by South America, the SAF would not have transported Pacific-sourced Subantarctic Mode Water into the South Atlantic effectively closing the cold water route. During the deglaciation the SAF migrated south and once established within Drake Passage the route was open and Pacific-sourced water was injected into the South Atlantic. The coincidence of this opening of the cold water route and reinvigoration of the AMOC demands further investigation to constrain the sensitivity of AMOC to Pacific-Atlantic connectivity through Drake Passage. Marine sediments recovered at IODP Site U1534 on Expedition 382 present the first opportunity to constrain variability in endmember physical and geochemical properties of AAIW as it enters the upper limb of the AMOC over multiple glacial-interglacial cycles. This proposal will generate a definitive age model for U1534 and will form the foundation for a future NERC grant to address the question of the cold water route influence on AMOC. In addition, the advances proposed here will benefit numerous associated projects with national and international collaborators and potential studentships and optimise the outputs of this UK-lead ocean drilling effort.