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

海洋的大规模环流也称为经向翻转环流 (MOC)，由一系列浅水和深水流组成，这些水流在全球范围内输送质量、热量、碳和营养物质。萨摩亚航道在其向北的深支中承载着大部分运输，是太平洋环流系统的重要组成部分。最近由美国国家科学基金会资助的一个项目支持的最新观察发现，萨摩亚航道复合体内较深的东部航道和多个较浅的西部航道之间存在以前未知的水流分裂。在过去的二十年里，还观察到了其他变化，例如通过通道的水流变暖和减弱，这支持了长期观测的必要性。 该项目将结合观测、理论和数值模型，详细研究萨摩亚海峡的水流动力学。目前，太平洋海洋中心尚未部署深海监测系统，该项目有可能帮助开发一种观测系统，以补充目前在大西洋部署的观测系统。气候模型预测全球翻转环流减弱，这些观测系统可以证实或反驳这一点。从拟议工作中获得的知识可能会应用于世界各地类似的深层通道和断裂带。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、伯奇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，让公众了解该项目的成果和知识。在之前的国家科学基金会资助下收集的广泛测量数据，包括系泊时间序列和深拖测量相结合，将用于研究萨摩亚航道水流的水力效应。当水流穿过并越过各种狭窄处和窗台时，观察到强烈的湍流混合，从而显着改变其水团特性。最近的测量表明，流经萨摩亚航道的水流处于水力临界状态，至少在一个主要基台处如此。该项目的三个具体目标包括：研究水力过程对各种基台混合和摩擦的影响，研究水力临界性以及对流经萨摩亚航道及其周围的水流输送和分隔的影响，并为通过萨摩亚航道的水流提供有效的监测策略。该项目的结果是，水力理论将得到改进和观测验证，使其适用于其他通道中的密集溢流以及众多裂缝带中的流动，这些裂缝带被认为是深海上涌的重要驱动因素。

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.