Collaborative Research: Transport, Internal Waves and Mixing in the Samoan Passage

知识价值：大部分南极底部的水向北流入北太平洋的深海，经过萨摩亚通道，使其成为太平洋翻转环流的关键阻塞点。详细的测流仪和水文观测证实了6.0 Sverdrups的强劲北流。此外，测量结果表明，混合和水力控制非常强。然而，许多重要的问题仍未得到解答，包括流量的水力控制程度、混合强度和导致混合的过程、潮汐和近惯性流在调节流量和混合中的作用，以及输运的时间变异性。更好地了解这些因素对于我们理解太平洋的大规模环流，以及我们对深海通道流动的总体理解都至关重要。该项目需要一个协调的观测和建模计划，以测量和了解萨摩亚航道的流动和混合，其中包括以下要素：1)两次巡航，每次巡航包括25天的集中系泊阵列和剖面仪器，以及船舶调查，降低ADCP/CTD和微观结构剖面仪，以解决时间和空间上的水流和混合。这两次巡航将相隔18个月，以便长期监测时间序列，并在对第一次巡航数据的分析基础上，在第二次巡航中更加集中注意力。2)在巡航之间的同一位置部署一个18个月的监测系泊阵列，与20年前的位置相同，以获得另一种直接估计的属性和通过通道的运输。3)不同复杂性和真实感的模型层次，从用于内波和交换流问题的二维MIT gcm配置到用于评估下游溢流演化、旋转效应和远程内波源影响的区域三维运行。总之，这些模型将为观察带来更大范围的背景，并允许测试假设和参数依赖性。4)详细的航道多波束测深图。更广泛的影响：深海环流预计将在最长的时间尺度上影响海洋对气候变化和大气二氧化碳增加的反应，而萨摩亚通道显然是大多数大尺度海洋模型中的一个弱点。这项工作直接解决了这些模型需要模拟的过程，以提高它们的预测能力。此外，国际社会认识到需要象目前在大西洋（W线，RAPID）进行的努力一样，扩大对萨摩亚航道的监测，以便评估太平洋翻转环流的年代际变化。所提出的测量和建模旨在确定这种监测阵列的最有效配置。各种各样的外展活动计划与游轮相结合，包括纪录片拍摄和在当地科学中心的展览。该项目将在美国培养1名博士后和研究生，以及4名暑期本科生。此外，加拿大和澳大利亚的科学家和学生参与这项工作将支持国际合作。

Intellectual Merit:The bulk of Antarctic Bottom Water flowing northward into the abyssal North Pacific goes through the Samoan Passage, making it a key choke point in the overturning circulation of the Pacific. Detailed current meter and hydrographic observations confirm a strong northward flow of 6.0 Sverdrups. In addition, measurements are suggestive of extremely strong mixing and hydraulic control. However, many important questions remain unanswered, including the degree of hydraulic control of the flow, the strength of the mixing and the processes leading to it, the role of tidal and near-inertial flows in modulating the flow and the mixing, and the temporal variability of the transport. A better understanding of each of these is vital to our understanding of the large-scale circulation in the Pacific, as well as to our general understanding of flow through deep passages. This project entails a coordinated observational and modeling program to measure and understand flow and mixing through the Samoan Passage, which includes the following elements: 1) Two cruises, each including a 25-day focused mooring array with profiling instrumentation and a ship survey with lowered ADCP/CTD and microstructure profilers to resolve the currents and mixing in time and space. The cruises will be separated by 18 months to enable a long monitoring time-series and a sharper focus in the second cruise based on the analysis of data from the first. 2) An 18-month monitoring mooring array deployed between the cruises at the same location as that done 20 years prior in order to obtain another direct estimate of the properties and transport through the passage. 3) A hierarchy of models of differing complexity and realism, ranging from a 2-D MIT gcm configuration used for internal wave and exchange flow problems through regional 3-D runs to evaluate downstream overflow evolution, rotational effects and the influence of remote internal wave sources. Together, the models will bring a larger-scale context to the observations and allow testing of hypotheses and parameter dependencies. 4) Detailed multi-beam bathymetric mapping of the passage.Broader Impacts:The abyssal circulation is expected to influence the ocean's response to climate change and atmospheric carbon dioxide increases on the longest timescales, and the Samoan Passage is clearly a weak point in most large scale ocean models. This work directly addresses the processes that these models will need to simulate in order to improve their predictive capability. In addition, the community recognizes a need for extended monitoring of the Samoan Passage, in like manner to ongoing efforts in the Atlantic (Line W, RAPID), in order to assess decadal changes to the Pacific overturning circulation. The proposed measurements and modeling are intended to determine the most efficient configuration for such a monitoring array. A variety of outreach activities are planned in conjunction with the cruises, including documentary filming and exhibits at local science centers. The project will educate a postdoc and graduate student in the US, as well as 4 summer undergraduate fellows. In addition, the inclusion of Canadian and Australian scientists and students in the work will support international collaboration.