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: 0962391
• 负责人: James Bellingham
• 金额: $ 15.01万
• 依托单位: Monterey Bay Aquarium Research Institute
• 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 2014-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0962391&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.

将在蒙特雷湾进行一项创新的实地研究，审查蒙特雷湾大陆架边界-内部交换事件的动态。主要重点是边界层侵入体，通常以从大陆边缘分离的中间云状层的形式出现。该项目的目标是：（1）查明造成中陆架至外陆架海底物质再悬浮的过程;（2）增进我们对侵入形成机制的了解;（3）调查侵入物中搬运的物质的命运;（4）调查侵入动态中的事件规模和季节变化。驱动假说是内波强迫混合后的重力坍缩驱动入侵;然而，实验的目的是解决底栖交换一般，包括平流机制，如涡流，陆架流，或收敛的底部Ekman通量，测量将包括一个中央底栖站，一个离岸停泊的剖面站和跨大陆架自主水下航行器（AUV）的调查跨越固定站。观测战略是直接观测海底交换：从海底界面通过分层外边界层，跨越整个水柱，然后进入跨大陆架层面。新的“混合”湍流包设计通过标量耗散和涡流相关技术测量湍流将部署在每个测量平台。高分辨率的边界层测量，包括底部剪切应力，湍流耗散率，悬浮颗粒物，和侵蚀事件，将从一个底栖三脚架和系泊。在该平台的海上，系泊的剖面仪将在整个水柱上连续测量CTD、光学和湍流。这两个固定站将包括全水柱速度剖面，从中我们将量化内波能量密度通量和估计入侵/INLs的横向运输。PI贝灵汉新开发的远程自主式潜水器将绘制跨大陆架部分的湍流和侵入图，解决纵贯和等密度的运输过程。两个部署，一个在晚春上升流季节，另一个在分层秋季条件下，将提供前所未有的时间范围内的全水柱混合，内波能量，底栖生物的反应，并在事件和季节尺度的INLs。固定仪器将部署一个月，在此期间，自主式潜水器将连续运行两周。关于边界内部交换动力学的基本问题激发了这个项目。在较深的大陆坡，这一过程对全球深海混合有重要影响。在大陆架上，特别是在东部边界上升流海岸，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）和潜在的底栖休眠孢囊，在生态系统功能中发挥着至关重要的作用。底栖生物交换事件可以解释上升流和沿海水华在事件层面上的矛盾脱钩。入侵/INLs是经常观察到的，但很少有人知道他们的时间变化，传播率和持续时间，或强迫。有充分的证据表明INLs和内波与地形的相互作用之间存在联系。然而，到目前为止，还没有研究直接测试混合和边界入侵扩散之间的关系在大陆边缘。这项研究的重点是大陆架，但研究结果也可用于更深的大陆边。更好地理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。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，即在蒙特雷湾研究所（MBARI）远程自主水下航行器（AUV）的有效载荷中加入湍流仪器。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调查沿海生物系统的精细分辨率通量和运输。联合国资助的合作者约翰·瑞安将调查与表面水华的潜在联系。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和海军研究生院的研究生课程。公共宣传和教育将受益于既定的MLML教师增强计划和MBARI的暑期实习计划。