Collaborative Research: Hydraulic Control and Mixing of the Deep Ocean Flow through the Samoan Passage

海洋的大规模环流也被称为经向翻转环流（MOC），由一系列浅水和深水洋流组成，这些洋流在地球仪周围输送物质、热量、碳和营养物质。萨摩亚海峡是太平洋环流系统的一个重要组成部分，其向北深处的分支承担了大部分的输送。最近的观测得到了美国国家科学基金会以前资助的一个项目的支持，发现了一个以前未知的分裂之间的流动更深的东部通道和多个较浅，西部通道内的萨摩亚通道复杂。在过去的二十年里，还观察到了其他变化，如通过通道的气流变暖和减弱，这支持了长期观测的必要性。 该项目将使用观测、理论和数值模型相结合的方法详细研究通过萨摩亚海峡的水流动力学。目前，太平洋海洋观测中心没有部署深海监测系统，该项目有可能帮助开发一个观测系统，以补充目前部署在大西洋的观测系统。气候模型预测全球翻转环流将减弱，这些观测系统可以证实或反驳这一点。从拟议的工作中获得的知识可能适用于世界各地类似的深通道和断裂带。两名早期职业科学家，暑期本科生，一名研究生和一名博士后研究员将通过该项目获得海洋学现代方法的宝贵培训。 通过与一家现代舞蹈公司、桦树水族馆和圣地亚哥一所高中的合作，计划开展各种外展活动，让公众了解从该项目中获得的成果和知识。在以前的NSF资助下收集的大量测量数据，包括系泊时间序列和深拖测量的组合，将用于研究萨摩亚海峡水流的水力效应。强烈的湍流混合被观察到的流量通过和各种收缩和窗台，从而大大改变了它的水质量特性。最近的测量结果表明，至少在一个主要的窗台，通过萨摩亚通道的流量的水力临界。该项目的三个具体目标包括：调查水力过程对各种底坎的混合和摩擦的影响，研究水力临界性和对通过萨摩亚通道和周围的水流的运输和分配的影响，并为通过萨摩亚通道的水流提供有效的监测战略。由于这一项目，水力理论将得到改进，并通过观测得到验证，使其适用于其他通道的密集溢流和被认为是深海涌升重要驱动力的众多断裂带的水流。

The large-scale circulation of the ocean also known as the Meridional Overturning Circulation (MOC) comprises a series of shallow and deep water currents that transport mass, heat, carbon, and nutrients around the globe. The Samoan Passage, which carries the majority of the transport in its deep northward branch, is an important element of the Pacific Ocean circulation system. Recent observations supported by a previously funded NSF project have identified a previously unknown split of the flow between a deeper eastern channel and multiple shallower, western pathways within the Samoan Passage complex. Additional changes such as a warming and weakening of the flow through the passage have also been observed over the past twenty years, which supports the need for long-term observations. This project will examine the dynamics of the flow through the Samoan Passage in detail using a combination of observations, theory and numerical models. Currently, there are no deep ocean monitoring system deployed in the Pacific MOC and this project has the potential to aid in the development of an observing system that can complement the one currently deployed in the Atlantic. Climate models predict a weakening of the global overturning circulation, which could be confirmed or refuted with these observing systems. The knowledge gained from the proposed work can likely be applied to similar deep passages and fracture zones around the world. Two early career scientists, summer undergraduates, a graduate student and a post-doctoral researcher will gain valuable training in modern methods used in oceanography through this project. Diverse outreach activities are planned to engage the public with the results and knowledge gained from this project through collaborations with a modern dance company, and the Birch Aquarium and a high school in San Diego.Extensive measurements collected under previous NSF funding, including a combination of moored time series and deep towed measurements will be used to study hydraulic effects on the flow in the Samoan Passage. Strong turbulent mixing was observed as the flow passes through and over various constrictions and sills, thereby substantially altering its water mass characteristics. The recent measurements indicate hydraulic criticality of the flow through the Samoan Passage, at least at one major sill. The three specific objectives of this project include: investigating the influence of hydraulic processes on mixing and friction at various sills, studying hydraulic criticality and implications for transport and partition of the flow through and around the Samoan Passage, and informing an efficient monitoring strategy for the flow through the Samoan Passage. As a result of this project, hydraulic theory will be improved and observationally validated, making it applicable to dense overflows in other passages and to the flow in the multitude of fracture zones that are believed to be important drivers for abyssal upwelling.