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

大西洋经向翻转环流（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半球的急剧降温有关。最近大西洋亚极区变冷和墨西哥湾流区变暖的趋势表明AMOC正在减弱。一般环流模式倾向于稳定的AMOC，无法复制观测到的AMOC对气候强迫的敏感性。AMOC稳定性中的这种模型偏差表明，某些参数被不准确地表示，影响了我们预测未来AMOC变化的能力。AMOC的一个要素仍然知之甚少，那就是南极中间水（AAIW）的作用。AAIW是AMOC上肢向北流动的主要水团之一。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AMOC变异性中的作用达成共识。今天，AAIW主要形成于太平洋东南部和大西洋西南部。AAIW及其前体亚南极模态水沿亚南极锋（SAF）通过德雷克通道向东平流。这种将寒冷、低盐度的太平洋水注入南大西洋的做法通常被称为“冷水路线”。通过这条冷水路线，太平洋和大西洋之间连通性的变化可能会改变西南大西洋AAIW形成的物理性质，进而影响AMOC的热量和盐度收支。研究表明，在末次冰期，南亚冰架的位置可能比今天更偏北。由于被南美洲截断，SAF无法将源自太平洋的亚南极模态水输送到南大西洋，从而有效地关闭了冷水路线。在冰川消融期间，SAF向南迁移，一旦在德雷克海峡建立，路线就开放了，太平洋的水被注入南大西洋。这条冷水航线的开通和AMOC的复兴的巧合需要进一步的调查，以限制AMOC对通过德雷克海峡的太平洋-大西洋连接的敏感性。382考察队在IODP站点U1534回收的海洋沉积物首次提供了限制AAIW末端物理和地球化学性质变化的机会，因为它在多个冰期-间冰期旋回中进入AMOC上肢。该提案将生成U1534的确定年龄模型，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内和国际合作者和潜在学生相关的项目受益，并优化英国主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.