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

学术贡献：南极底层水的大部分向北流入深海北太平洋，经过萨摩亚海峡，使其成为太平洋翻转环流的关键瓶颈。详细的海流计和水文观测证实了6.0 Sverdrups的强烈北流。 此外，测量结果表明，极强的混合和水力控制。 然而，许多重要的问题仍然没有答案，包括水力控制的流动程度，强度的混合和导致它的过程，潮汐和近惯性流的作用，在调制的流量和混合，以及运输的时间变化。 更好地了解这些都是至关重要的，我们在太平洋的大规模环流的理解，以及我们通过深通道流的一般理解。 该项目需要一个协调的观测和建模计划，以测量和了解通过萨摩亚海峡的水流和混合，其中包括以下内容：1）两次航行，每次航行包括一个为期25天的带剖面测量仪器的集中系泊阵列，以及一次使用降低的ADCP/CTD和微结构剖面仪的船舶调查，以解决水流和混合的时间和空间问题。这两次航行将间隔18个月，以便能够在第二次航行中根据对第一次航行数据的分析进行长时间的监测，并使重点更加突出。 2)在两次巡航之间的同一地点部署了一个为期18个月的监测系泊阵列，与20年前部署的系泊阵列相同，以便对通过该通道的特性和运输情况进行另一次直接估计。 3)不同复杂性和现实主义的模型层次，从2-D麻省理工学院gcm配置用于内波和交换流问题，通过区域3-D运行，以评估下游溢流演变，旋转效应和远程内波源的影响。总之，这些模型将为观察带来更大规模的背景，并允许测试假设和参数依赖性。4)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，萨摩亚海峡显然是大多数大型海洋模型的一个弱点。这项工作直接解决了这些模型需要模拟的过程，以提高其预测能力。此外，共同体认识到有必要扩大对萨摩亚海峡的监测，以类似于目前在大西洋进行的监测（W线，RAPID），以评估太平洋翻转环流的十年变化。建议的测量和建模的目的是确定最有效的配置，这样的监测阵列。 计划与游轮一起开展各种外联活动，包括拍摄纪录片和在当地科学中心举办展览。该项目将在美国培养一名博士后和研究生，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.