Dynamical and Material Connectivity Across Continental Shelves

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

Inside the surf zone, the water is typically well mixed because wave action dominates dynamics and creates strong turbulence. Further offshore on the continental shelf, the water is stratified by density and circulation is primarily driven by wind and by pressure gradients. These two regimes are typically studied separately because of the drastic differences in the dynamics and scales of variability. However, exchange processes at the Surf-Shelf Transition Zone (SSTZ) are critical for a number of important concerns ranging from larval transport to pollution. This study will develop and use modeling approaches that handle both sets of dynamics and scales gracefully and lead to a better understanding of this important transition zone. The primary hypotheses are (1) the SSTZ has high intrinsic variability beyond the wind-, tide- and wave-forced flows; (2) surf eddies and submesoscale shelf eddies have intermittent strong interactions; and (3) the eddies play a dominant role in setting the rates of material transport across and along bathymetric gradients, as well as vertically through the pycnocline. This research program is a necessary precursor to addressing the many important fluxes of biogeochemical, ecological, pollutant, and sedimentary fluxes within the SSTZ. The approach is to use a multiply-nested circulation model (Regional Oceanic Modeling System, ROMS) that includes the wave-averaged Stokes drift vortex force and material advection and wave-augmented mixing processes, coupled to a surface gravity wave model that includes Doppler-shift refraction by the current. It will be used for a set of idealized SSTZ process studies to assess the competing influences of bathymetric shape; stratification; surface waves; prevailing alongshore currents and their instability; surf eddies; shelf eddies and coastally-trapped waves; tides; and storm-water inflows. In addition, realistic ROMS simulations, with full physics and aggressive down-scale grid nesting, will be made for extensive periods at several SSTZ sites in Southern California, and existing measurements will provide model validation tests. Realistic SSTZ modeling and validation studies will be extended to other sites through unpaid collaborations with Japanese and Santa Barbara colleagues. Intellectual Merit : Both surf eddies and submesoscale shelf eddies are relatively unexplored phenomena, and the proposed comprehensive theoretical and computational examination of their nature, dynamics, and material transport effects in the SSTZ will lead to new phenomenological discoveries, future field experiments for validation, and reassessments of the material fluxes in this front-line human-ocean interface. Broader Impacts : The nearshore region is the primary intersection of human activities with the ocean, and progress in understanding and modeling its behavior for currents, pollutants, ecosystems, inundation, and beach morphology will empower better management and protection. The knowledge gained will be disseminated through professional and public lectures and publications; by consultation with National Weather Service beach safety forecasters and Orange County, CA, wastewater managers; and by inclusion into the undergraduate and graduate ocean curriculum at UCLA. It will provide research training for a minority STEM graduate student. Its research collaborations will strengthen both an international scientific cooperation with Japan and the physical oceanographic underpinnings of the Long Term Ecological Research program on the giant kelp forest ecosystem in the Santa Barbara Channel.