Collaborative Research: Benthic Exhange Events and Near-Boundary Mixing on the Continental Shelf

将在蒙特利湾进行一项创新的实地研究，检查蒙特利湾大陆架上边界-内部交换事件的动力学。主要的焦点是边界层侵入，通常以从大陆边缘分离的中间nepheloid层（inl）的形式出现。该项目的目标是：(1)确定中、外大陆架底栖生物物质再悬浮的过程；(2)提高我们对入侵形成机制的理解；(3)调查入侵中物质运输的命运；(4)调查入侵动力学的事件尺度和季节变化。驱动假说认为，内波强迫混合后的引力坍缩驱动入侵；然而，该实验旨在解决底栖生物交换的一般问题，包括平流机制，如漩涡、陆架流或收敛的底部埃克曼通量。测量将包括一个中央底栖站、一个近海系泊剖面站和跨越固定站的跨架自主水下航行器（AUV）测量。观测策略是直接观察底栖生物交换：从海底界面穿过分层的外边界层，穿过整个水柱，然后进入跨大陆架维度。新的“混合”湍流包设计，通过标量耗散和涡流相关技术来测量湍流，将部署在每个测量平台上。高分辨率的边界层测量，包括底部剪切应力、湍流耗散率、悬浮颗粒和侵蚀事件，将通过底栖三脚架和系泊进行。在该平台的近海，系泊剖面仪将连续测量整个水柱的CTD、光学和湍流。这两个固定站都将包括全水柱速度剖面，由此我们将量化内波能量密度通量，并估计侵入/ inl的横向输送。由PI Bellingham新开发的远程AUV将绘制跨大陆架区域的湍流和侵入图，解决异流和等流运输过程。两个部署，一个在春末上升流季节，另一个在分层的秋季条件下，将在事件和季节尺度上提供前所未有的全水柱混合、内波能、底栖生物响应和inl的时间覆盖。固定仪器将部署一个月，在此期间AUV将连续运行两周。知识价值。关于边界-内部交换动态的基本问题激发了这个项目。在较深的大陆斜坡上，这一过程对全球深海混合有重要影响。在大陆架上，特别是东部边界上涌海岸的大陆架上，底栖生物交换通过向内部和上层水柱提供底栖铁（一种限制性微量营养素）和潜在的底栖栖息囊，在生态系统功能中起着至关重要的作用。底栖生物交换事件可以在事件水平上解释上升流和海岸水华之间的一些矛盾的脱钩。入侵/ inl是经常观察到的，但对它们的时间变异性、扩散速率和持续时间或强迫知之甚少。有充分的证据表明，内波与地形的相互作用与内波之间存在关联。然而，到目前为止，还没有研究直接测试混合和大陆边缘的边界入侵分散之间的关系。这项研究的重点是大陆架，但研究结果将转移到更深的大陆边缘。更好地了解这些动力学可以改善全球环流模式中边界混合的参数化。更广泛的影响。作为这项合作工作的一部分，将开发一项有价值的创新技术，即将湍流仪器整合到蒙特利湾研究所（MBARI）远程自主水下航行器（AUV）的有效载荷中。将这项技术转移到一个尖端的、常规操作的AUV系统，意味着它将在未来几年用于研究精细分辨率的通量和沿海生物系统的运输。未获资助的合作者约翰·瑞安将调查地表水华的潜在联系。该项目将包括培训和指导一名博士后研究员和两名研究生，研究成果将纳入莫斯兰丁海洋实验室（MLML）和海军研究生院的研究生课程。公众宣传和教育将受益于MLML教师提升计划和MBARI的暑期实习计划。

An innovative field study examining the dynamics of boundary-interior exchange events on the Monterey Bay shelf will be conducted in Monterey Bay. The main focus is on boundary layer intrusions, often seen in the form of intermediate nepheloid layers (INLs) detaching from the continental margin. The objectives of the project are to (1) identify processes responsible for resuspension of benthic material on the mid- to outer-shelf, (2) improve our understanding of intrusion formation mechanisms, (3) investigate the fate of material transported in intrusions, and (4) investigate event-scale and seasonal variability in intrusion dynamics. The driving hypothesis is that gravitational collapse after internal-wave-forced mixing drives intrusions; however, the experiment is designed to resolve benthic exchange generally, including advective mechanisms such as eddies, shelf currents, or convergent bottom Ekman fluxes.Measurements will include a central benthic station, an offshore moored profiler station and cross-shelf autonomous underwater vehicle (AUV) surveys spanning the fixed stations. The observational strategy is to directly observe benthic exchange: from the seafloor interface through the stratified outer boundary layer, across the entire water column, and then into the cross-shelf dimension. New "hybrid" turbulence packages designed to measure turbulence via both scalar dissipation and eddy correlation techniques will be deployed on each of the measurement platforms. High-resolution boundary layer measurements, including bottom shear stress, turbulent dissipation rate, suspended particulates, and erosion events, will be made from a benthic tripod and mooring. Offshore of this platform, a moored profiler will continuously measure, over the entire water column, CTD, optics, and turbulence. Both fixed stations will include full-water-column velocity profiles, from which we will quantify internal wave energy density flux and estimate lateral transport of intrusions/INLs. A long-ranging AUV, newly developed by PI Bellingham, will map both turbulence and intrusions in cross-shelf sections, resolving diapycnal and isopycnal transport processes. Two deployments, one in the late spring upwelling season and the other during stratified fall conditions, will provide unprecedented temporal coverage of full-water-column mixing, internal wave energy, benthic response, and INLs at both event and seasonal scales. The fixed instrumentation will be deployed for one-month-long periods during which the AUV will operate continuously for two weeks.Intellectual Merit. Fundamental questions about the dynamics of boundary-interior exchange motivate this project. On deeper continental slopes this process has important consequences for global abyssal mixing. On continental shelves, particularly those of eastern boundary upwelling coasts, benthic exchange plays a crucial role in ecosystem functioning by providing benthic iron (a limiting micronutrient) and, potentially, benthic resting cysts to the interior and upper water column. Benthic exchange events may explain some of the paradoxical decoupling between upwelling and coastal blooms at the event level. Intrusions/INLs are commonly observed, yet very little is known about their temporal variability, dispersal rates and duration, or forcing. There is ample evidence for an association between INLs and internal wave interaction with topography. Yet, to date there has been no study directly testing the relationship between mixing and boundary intrusion dispersal on a continental margin. This study is focused on the shelf but the findings will be transferrable to deeper continental margins. Better understanding of these dynamics may improve parameterization of boundary mixing in global circulation models.Broader Impacts. A valuable, innovative technique that will be developed as part of this collaborative work is the incorporation of turbulence instrumentation into the payload of the Monterey Bay Research Institute (MBARI) long-range Autonomous Underwater Vehicle (AUV). The transfer of this technology to a cutting-edge, and routinely operated, AUV system means it will be used in years to come in investigations of fine-resolution fluxes and transports of coastal biological systems. Un-funded collaborator John Ryan will investigate potential links to surface blooms. The project will include training and mentoring of a postdoctoral researcher and two graduate students, and the research findings will be incorporated into the graduate curricula at Moss Landing Marine Laboratory (MLML) and the Naval Postgraduate School. Public outreach and education will benefit from the established MLML Teacher Enhancement Program and MBARI's summer internship program.