Quantifying the relative importance of various physical mechanisms for plankton and nutrient transport between the shore and the shelf waters
Nirnimesh Kumar, University of Washington, Department of Civil & Environmental Engineering, Seattle, WA, United States, James M Pringle, University of New Hampshire Main Campus, Durham, NH, United States, Melissa Moulton, Applied Physics Laboratory University of Washington, Seattle, WA, United States, Sutara Suanda, University of Otago, Dunedin, New Zealand and Melanie R Fewings, Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States
Abstract:
The transition region from land to the ocean, the “nearshore”, extends a few kilometers from the shoreline and includes a surf zone, dominated by surface gravity waves, and an inner shelf where mixing, stratification, nonlinear internal waves, submesoscale dynamics, cross- and alongshore winds are all important for driving circulation. The dynamics in these two regions control the interactions between the deeper ocean and the coast. Understanding the circulation within and between these regions is critical for societal and ecological issues. Intertidal and nearshore benthic organisms must cross these regions to disperse and recruit. The concentration of pathogens, human viruses, and excessive nutrients from terrestrial runoff, and thus their malign effects, are controlled by the exchanges across these regions to the deeper ocean.
In the past decade, significant progress has been made in investigating mechanisms responsible for cross-shore exchange in the nearshore. Yet the relative importance of these mechanisms in moving water and organisms across the nearshore, and regional differences in the importance of the processes is not known. Existing coastal numerical models focused on understanding exchange dynamics usually lack the resolution and physics to accurately represent nearshore processes.
Here, we present a review of dominant cross-shore exchange mechanisms identified through long-term field measurements, remote sensing and numerical modeling. The relative importance of individual physical transport mechanisms from the surf zone to the mid-shelf is compared by estimating an exchange velocity expressed as a depth-integrated Lagrangian velocity. Additional complexity in exchange dynamics associated with swimming behaviors is also discussed. A goal of this work is to guide other researchers in determining what physical features of their area must be known to understand which processes are locally important.
