Dynamics of the Orkney Passage Outflow (DynOPO)

在过去的三十年中，填充全球海洋深渊的南极底水（AABW）在世界大部分海洋，特别是大西洋盆地表现出显著的变暖和体积收缩。虽然这些变化的原因尚不清楚，但现有证据表明，在大西洋，AABW的变暖和收缩可能是由威德尔海北部的风的变化引起的，那里产生了大量的AABW。这一假说认为，这些风通过改变AABW与通道上的温暖海水之间湍流混合的强度，调节了AABW通过奥克尼通道（威德尔海的主要AABW出口路线）向北出口的体积和温度。在本提案中，我们开始测试并在必要时重新定义这一假设：(1)对AABW如何通过奥克尼通道进行首次系统测量，其特性如何在途中变化，以及哪些过程对决定AABW在通道中的流动和转变至关重要；(2)在长达数年的时间尺度上确定奥克尼海峡AABW的通量和特性如何以及为什么对风强迫作出响应。为了解决上面的任务(1)，我们将测量AABW的速度和性质以及通道中几个关键位置的湍流混合强度。观测结果将通过从船上降到海底的仪器和一种新型的自主水下航行器来获得，这种水下航行器在测量海底附近发生的一系列潜在的关键过程方面特别有效。为了完成任务(2)，我们将加强英国南极调查局最近在奥克尼海峡部署的一系列系泊设施，以监测AABW的通量和特性。我们将在系泊处配备足够的海洋仪器，以确定决定AABW对风强迫反应的过程，这些过程目前的阵列无法解决。我们将使用任务(1)和(2)的发现来定义通过奥克尼通道逃离威德尔海的AABW的体积和性质如何以及为什么会对风的变化做出反应。有了这一新的认识，我们将重新审视近几十年来观测到的广泛的AABW增温和收缩，并为监测AABW环流未来变化的国际战略提供信息。

During the last three decades, the Antarctic Botttom Water (AABW) filling the bulk of the global ocean abyss has exhibited a striking warming and contraction in volume over much of the world ocean, particularly in the Atlantic basin. While the causes of these changes are unknown, available evidence suggests that, in the Atlantic Ocean, the warming and contraction of AABW may be caused by changes in winds over the northern Weddell Sea, where much AABW is produced. This hypothesis asserts that those winds regulate the volume and temperature of the AABW exported northward via the Orkney Passage (a major AABW exit route from the Weddell Sea) by altering the intensity of the turbulent mixing between AABW and overlying warmer waters in the passage.In this proposal, we set out to test and, if necessary, redefine this hypothesis by:(1) carrying out the first systematic measurements of how AABW flows through the Orkney Passage, how its properties change along the way, and what processes are important in determining the AABW flow and transformation in the passage;(2) determining how and why the flux and properties of AABW in the Orkney Passage respond to wind forcing on time scales of up to several years.To address task (1) above, we will measure the velocity and properties of AABW and the intensity of turbulent mixing at several key locations in the passage. The observations will be obtained both with instruments lowered to the seabed from a ship and with a novel autonomous underwater vehicle, which is particularly effective at measuring a range of potentially crucial processes occurring near the ocean floor. To address task (2), we will enhance an array of moorings recently deployed in the Orkney Passage by the British Antarctic Survey to monitor the flux and properties of AABW. We will equip the moorings with sufficient oceanographic instrumentation to identify the processes determining the AABW's response to wind forcing, which are not resolved by the present array.We will use our findings from tasks (1) and (2) to define how and why the volume and properties of the AABW escaping the Weddell Sea through the Orkney Passage react to changes in winds. Armed with this new understanding, we will revisit the widespread AABW warming and contraction observed over recent decades, and inform the international strategy to monitor future changes in AABW circulation.