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

合作研究：大陆架底栖交换事件和近边界混合

• 批准号: 0961810
• 负责人: Erika McPhee-Shaw
• 金额: $ 48.93万
• 依托单位: San Jose State University Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-01 至 2015-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0961810&HistoricalAwards=false
• 关键词: Collaborative; Research; Benthic; Exhange; Events

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.

将在蒙特利湾进行一项创新性的实地研究，研究蒙特利湾大陆架边界-内部交换事件的动态。主要的焦点是边界层侵入，通常以从大陆边缘分离的中间类云层(INL)的形式出现。该项目的目标是：(1)确定导致底栖生物物质在中陆架到外陆架上再悬浮的过程；(2)增进我们对入侵形成机制的理解；(3)调查在入侵中运输的物质的去向；(4)调查入侵动力学中的事件尺度和季节变化。驱动假设是内波强迫混合后的重力塌陷驱动入侵；然而，该实验旨在解决一般的海底交换，包括涡流、陆架流或收敛的底部Ekman通量等平流机制。测量将包括一个中心海底站、一个近海系泊剖面站和跨越固定站的跨陆架自主水下机器人(AUV)调查。观测战略是直接观察海底交换：从海底界面穿过分层的外边界层，跨越整个水柱，然后进入跨陆架维度。将在每个测量平台上部署旨在通过标量耗散和涡旋相关技术测量湍流的新的“混合”湍流组件。高分辨率边界层测量，包括底部剪切力、湍流耗散率、悬浮颗粒和侵蚀事件，将由海底三脚架和系泊设备进行。在该平台的近海，一台停泊的剖面仪将在整个水柱上连续测量CTD、光学元件和湍流。这两个固定测站都将包括全水柱速度剖面，我们将根据这些剖面来量化内波能量密度通量，并估计侵入/INL的横向传输。由Pi Bellingham最新开发的远程AUV将绘制出跨陆架部分的湍流和侵入情况图，解决双周期和等周期输送过程。两次部署，一次在晚春上升流季节，另一次在分层秋季条件下，将在事件和季节尺度上提供前所未有的全水柱混合、内波能量、海底响应和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。关于边界-内部交换动态的基本问题推动了这个项目。在更深的大陆斜坡上，这一过程对全球深海混合具有重要影响。在大陆架上，特别是东部边界上升海岸的大陆架上，底栖生物交换通过向内部和上层水柱提供底栖铁(一种有限的微量营养素)，并有可能提供底栖性休眠包囊，在生态系统运行中发挥关键作用。海底交换事件可能在事件层面上解释了上升流和沿海水华之间的一些矛盾的脱钩现象。入侵/INL通常被观察到，但对它们的时间变异性、扩散速度和持续时间或强迫作用知之甚少。有充分的证据表明INL和内波与地形的相互作用之间存在联系。然而，到目前为止，还没有直接测试混合与大陆边缘边界入侵扩散之间的关系的研究。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。更好地理解这些动力学可能会改进全球环流模式中边界混合的参数化。作为这项合作工作的一部分，将开发的一项有价值的创新技术是将湍流仪器纳入蒙特利湾研究所(MBARI)远程自主水下机器人(AUV)的有效载荷。将这项技术转移到尖端的、常规操作的AUV系统意味着，它将在未来几年内用于研究高分辨率的通量和沿海生物系统的传输。联合国资助的合作者约翰·瑞安将调查地表水华的潜在联系。该项目将包括一名博士后研究员和两名研究生的培训和指导，研究成果将被纳入莫斯登陆海洋实验室(MLML)和海军研究生院的研究生课程。公共宣传和教育将受益于已建立的MLML教师增强计划和MBARI的暑期实习计划。