Continental Shelf Benthic Oxygen Fluxes Determined by Eddy Correlation in the Presence of Wave Motions

在过去的十年中，位于加利福尼亚州北部洋流系统的俄勒冈州-华盛顿州大陆架的大片区域在夏季上升流季节受到严重缺氧的影响。陆架上溶解氧的质量平衡表明，沉积物的摄氧量大于使用传统底栖室和微剖面测量海底通量的估计值。这种失衡的最有可能的解释是，主要物理和生物过程中的时间和空间变异性尚未确定，这些过程有助于机架上的氧气利用。俄勒冈州立大学(OSU)的一位科学家计划利用涡旋相关(EC)技术来确定俄勒冈大陆架内部和中部海底氧气通量的大小和变异性，以及波浪诱导的运动对这些通量的贡献。这项技术假定，通过测量氧气波动和海床上方垂直速度波动之间的协方差，可以获得直接的垂直通量估计。为了实现这一目标，将进行波浪水槽实验和使用EC着陆器的现场测量。最初，高能波存在下的EC测量将在俄亥俄州立大学欣斯代尔波浪研究设施的大波浪水槽中进行研究，这是北美最大的同类波浪通道。波浪水槽实验的目的是通过实验验证在波浪和沙床存在的情况下进行数据收集、平均和坐标旋转以获得无偏通量的最佳方法。此外，将采用波浪-湍流分解方法来量化波浪对海底氧气交换的贡献，并记录随着波高的逐步增加和减少而演变的河床形态和孔隙水剖面序列。一旦波浪水槽实验完成，将进行四次为期8天的研究巡航，在3年内的春季、夏季和秋季在俄勒冈州的大陆架上进行测量。目标地点的特点是水深25至85米的渗透性沙子，可能会出现涟漪。辅助测量将包括底水溶解氧、营养物质、色素浓度、温度和盐度，而沉积物岩心将被分采样进行整体渗透率测量和210Pb、有机碳、氮、颗粒尺寸和颜料的剖面。至于更广泛的影响，这位科学家计划与参与康塞普西翁和俄勒冈州外低氧水域微生物倡议(MI-Loco)项目的美国和智利科学家合作。作为该项目的一部分，一名研究生将得到支持和培训。

Within the last decade, broad sections of the Oregon-Washington continental shelf located in the northern California Current System have been affected by severe hypoxia during the summer upwelling season. Mass balances of dissolved oxygen on the shelf indicate oxygen uptake of sediments is greater than estimated from benthic flux measurements using traditional benthic chambers and microprofiles. The most probable explanation for this inbalance is uncharacterized temporal and spatial variability in the major physical and biological processes contributing to on-shelf oxygen utilization. A scientist from Oregon State University (OSU) plans to determine the magnitude and variability of benthic oxygen fluxes on the inner and middle Oregon shelf and the contribution of wave-induced motions to these fluxes using the eddy correlation (EC) technique. This technique assumes that a direct vertical flux estimate can be obtained by measuring the covariance between fluctuations of oxygen and fluctuations of vertical velocity above the seabed. To attain the goal, both wave flume experiments and field measurements using the EC lander will be carried out. Initially, EC measurements in the presence of energetic waves will be studied in the large wave flume at OSU's Hinsdale Wave Research Facility which is the largest wave channel of its type in North America. The purpose of the wave flume experiments is to experimentally verify the best approaches to data collection, averaging, and coordinate rotation to derive unbiased fluxes in the presence of waves and a sandy bed. In addition, the wave-turbulence decomposition method will be applied to quantify wave contributions to seafloor oxygen exchange and to document the sequence of bedforms and pore water profiles that evolve in response to stepwise increases and decreases in wave height. Once the wave flume experiments have been completed, four 8-day research cruises will be carried out to make measurements on the Oregon shelf over 3 years during spring, summer and fall conditions. The sites to be targeted are characterized by permeable sands at 25 to 85 m water depth and can exhibit ripples. Ancillary measurements will include bottom water dissolved oxygen, nutrients, pigment concentration, temperature and salinity, whereas sediment cores will be subsampled for bulk permeability measurements and profiles of 210Pb, organic carbon, nitrogen, grain size, and pigments.As regards broader impacts, the scientist plans to collaborate with U.S. and Chilean scientists involved in the Microbial Initiative in Low Oxygen waters off Concepcion and Oregon (MI-LOCO) project. One graduate student would be supported and trained as part of this project.