The project is a comprehensive observational and analytical program to examine the dynamics and source waters of the relaxation flows in a coastal upwelling system on the central California coast. Autonomous vehicles, high-frequency radars, moorings, and drifters, will be used to acquire pressure, density, and velocity data relevant to the relaxation flows. The data will be used to determine spatial scales of the flows, cross-shore density structure, cross-shore and alongshore velocity fields, pressure gradients, and the region of contact with the sea floor. Aspects of the research include: 1) to evaluate the roles of barotropic and baroclinic pressure gradient forcing, 2) to identify regions where ageostrophic flows dominate the cross-shore and alongshore momentum balances, 3) to determine source waters for the relaxation flows, and 4) to examine the inner shelf circulation response to wind relaxations over an extensive coastal region (the northern part of the Southern California Bight) by analyzing extensive regional data sets collected over many years.
Wind relaxations are common features of coastal upwelling systems worldwide, and have impacts on alongshore and cross-shore transport of water-borne materials such as larvae, nutrients, terrestrial runoff, and buoyant pollutants like oil. This study will clarify the role of relaxation flows in the recruitment of intertidal and sub-tidal organisms by revealing details of the near-shore flow structure. The observational plan advances capabilities of state-of-the-art autonomous and Lagrangian platforms and sensors.
A post-doc and undergraduate students will be trained. Opportunities will be created for marine ecology graduate students to conduct field experiments focused on the ecological consequences of relaxation flows. This research will build on, and leverage, existing regional ocean observing infrastructure and it will increase the capacity for oceanographic studies at two universities.
The major goal of the project is to examine the response of the mid- and inner-shelf circulation to changes in the wind field in our study are north of Pt. Conception California. In particular we are interested in how propagating poleward currents are generated and evolve in response to changes regional wind relaxations. Major activities during 2013 were a summer field experiment to further collect primary data and extensive analysis of data collected during our 2012 field season. The field deployments were similar to those during 2013: five oceanographic moorings were installed (south to north) at Alegria, Pt. Arguello, Pt. Purisima, and two at Pt. Sal, one in 15 m water depth and another in 26 m. Instrumentation on the moorings collected depth-resolved time series of current velocity, temperature, salinity (from the gliders and a mooring at Pt. Purisima), and bottom pressure across the mid-shelf and inner shelf. These results will provide insight into the physical oceangraphy of this important region. One important impact of our work on other disciplines, specifically marine ecology, is evaluating the effects of changing wind fields on along-shore transport of larvae and other water-borne materials such as nutrients and other biogenic particles. Additionally, our work is examining how wind relaxations and cross-shore transport of waters contribute to settlement across putative range boundaries, such as at Pt. Conception, CA. Another important impact of this project on other disciplines, specifically marine conservation and policy, is an improved understanding of the coastal currents that deliver larvae to near-shore habitats. The functioning of Marine Protected Areas (MPAs), a critical tool for managing coastal resources, depends upon larval delivery from remote sources. Poleward relaxation flows, such as studied in this research, are a principal larval delivery mechanism for MPAs in the California Current Large Marine Ecosystem. Therefore an improved understanding of these flows will contribute to ongoing efforts to assess the functioning of MPAs.
