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子午线翻转环流(MOC)，由一系列浅水和深水水流组成，在全球范围内输送质量、热量、碳和营养物质。萨摩亚航道是太平洋环流系统的一个重要组成部分，承担着其向北纵深支流的大部分运输。最近的观测发现，在之前资助的一个国家科学基金会项目的支持下，在萨摩亚航道综合体内较深的东部航道和多条较浅的西部航道之间存在着一种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，如通过该通道的气流变暖和减弱，这支持了长期观测的必要性。该项目将采用观测、理论和数值模型相结合的方法，详细研究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。气候模型预测了全球翻转环流的减弱，这可以用这些观测系统来证实或驳斥。从拟议的工作中获得的知识很可能应用于世界各地类似的深部通道和断裂带。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在海洋学中使用的现代方法方面的宝贵培训。通过与一家现代舞公司、桦树水族馆和圣迭戈的一所高中合作，计划开展不同的外展活动，让公众了解该项目的成果和知识。在以前的NSF资助下收集的广泛测量，包括系泊时间序列和深度拖曳测量的组合，将用于研究水力对萨摩亚航道水流的影响。当水流通过和越过各种狭窄和底座时，观察到了强烈的湍流混合，从而显著改变了其水团特征。最近的测量表明，通过萨摩亚航道的水流至少有一个主堤处于水力临界状态。该项目的三个具体目标包括：调查水力过程对不同门槛的混合和摩擦的影响；研究水力临界性及其对萨摩亚航道及其周围水流输送和分配的影响；以及制定有效的萨摩亚航道水流监测战略。作为这项工程的结果，水力理论将得到改进和观测验证，使其适用于其他航道的密集溢流，以及被认为是深海上升流的重要驱动因素的大量裂隙带中的水流。

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.