Antarctic Intermediate Water Formation in the Southeast Pacific

0327544/TalleyIntellectual Merit：该项目旨在描述东南太平洋南极中间水（AAIW）形成的过程。计划研究(1)南极环极流表层水穿过南亚海区向北的Ekman平流；(2)局地海气通量驱动的对流；(3)靠近深层混合区的AAIW穿过北部锋向北俯冲。南极中间水（AAIW）是一种低盐度、高氧和低位势涡度（厚）的水团，几乎覆盖了整个南半球和热带海洋，深度约为800至1000米。作为最密集的环极亚南极模态水域（SAMW）， AAIW是在亚南极锋（SAF）以北的东南太平洋形成的一个厚的、裸露的混合层。SAMW和AAIW的形成对人为CO2的海洋汇有主要影响，其最大的不确定性在中深度。AAIW在南半球淡水运输中发挥着重要作用，因此可以影响全球范围的海洋倾覆过程。AAIW是唯一一个没有在其冬季源头进行研究的中深度、大规模水体，尽管几十年来人们对其源头区域的位置有了普遍的了解。该项目包括对AAIW露头区和锋面的冬季水文调查，以及在冬季调查之后的夏季调查，以研究前一个冬季水域的演变、重新冻结和分散。该区域的结果将与其他区域的亚南极模态水（SAMW）形成有关。更广泛的影响：本项目收集的冬季和夏季全面覆盖的高质量数据集将填补影响长期气候变化的物理过程的全球海洋观测中一个重要而巨大的空白。将为研究生和博士后提供培训。这项工作将加强美国和智利科学家之间的合作。研究人员将继续与智利和欧盟的研究生合作，不需要国家科学基金会支付任何费用。

0327544/TalleyIntellectual Merit: This project aims at characterizing the processes responsible for the formation of Antarctic Intermediate water (AAIW) in the southeast Pacific. The plan is to study (1) northward Ekman advection of Antarctic Circumpolar Current surface waters across the SAF, (2) convection driven by local air-sea fluxes, and (3) northward subduction of AAIW across the northern front bounding the deep mixing region. Antarctic Intermediate Water (AAIW) is a low salinity, high oxygen and low potential vorticity (thick) water mass that fills almost all of the southern hemisphere and the tropical oceans at about 800 to 1000 m depth. As the densest of the circumpolar Subantarctic Mode Waters (SAMW), AAIW is formed as a thick, outcropping mixed layer in the southeastern Pacific just north of the Subantarctic Front (SAF). SAMW and AAIW formation have a major impact on the oceanic sink for anthropogenic CO2, whose largest uncertainty is at intermediate depths. AAIW has a major role in southern hemisphere freshwater transport and as such, can impact global-scale ocean overturning processes. AAIW is the only intermediate-depth, large-scale water mass that has not been studied at its winter source, despite general knowledge of the location of the source region for several decades. The project consists of a winter hydrographic survey of the AAIW outcropping region and the fronts that bound and a summer survey following the winter survey to study the evolution, restratification, and dispersal of the previous winter's waters. Results from this region will be relevant to Subantarctic Mode Waters (SAMW) formation in other regions. Broader Impacts: The high-quality data set collected under this project with a comprehensive coverage in winter and summer will fill an important and large gap in global ocean observations for physical processes that impact long-term climate change. Training will be provided for a graduate student and a post-doc. The proposed work will strengthen collaboration between U.S. and Chilean scientists. The investigators will continue working with Chilean and European Union graduate students, at no cost to NSF.