Ship Based and HIgh Resolution Array Measurements of the Inner Shelf
Abstract
ONR DRI “The Inner Shelf - Connecting the Coastal Ocean & the Surf Zone” Project Summary: Ship-Based & High-Resolution Array Measurements of the Inner Shelf John A. Barth and James A. Lerczak, CEOAS, Oregon State University The inner shelf, with water depths between 5 and 50 m, is the region between the deeper continental shelf, where wind-driven processes dominate, and the surfzone, where wave-driven motions dominate. While some modeling and sparse observations give us an idea about the mechanisms responsible for exchanging water and tracers (e.g. plankton, contaminants, pathogens, swimmers, sediment) across the inner shelf, we still do not have a quantitative understanding of these processes. We propose to measure and understand two key processes that contribute to exchange across the inner shelf. The first is three-dimensional circulation features that act to exchange fluid and the material it contains across the inner shelf. From the offshore side of the inner shelf, instabilities of wind-driven currents and fronts create cross-shelf meanders and eddies. On the shoreward side, instabilities of surface wave-driven alongshore currents create intense eddies that move offshore. The second key process is the shoreward transport of material by nonlinear internal waves and bores. These waves originate offshore, span time scales from semi-diurnal to minutes, and can radically alter inner-shelf stratification and currents as they propagate shoreward. Each of these processes, eddy-driven exchange and transport by nonlinear internal waves is strongly modified by changes in the background stratification and velocity fields set up through wind forcing. Therefore, in addition to studying the details of the eddies and waves, it is key to adequately sample the time-dependent hydrographic and velocity structure spanning the mid to inner shelf. Objectives: 1) Repeatedly measure the cross-shelf and vertical distribution of hydrographic and velocity fields across the mid to inner shelf and relate them to wind forcing; 2) Understand how these distributions relate to the creation and propagation of eddies that exchange water and tracers across the inner shelf; 3) Sample highly nonlinear internal motions as they transit from the mid shelf to the surfzone and understand how they contribute to cross-shelf exchange and how they alter inner-shelf hydrographic and velocity fields; and 4) Repeatedly sample along the coast in the inner shelf to quantify cross-shelf exchange and the dominant temporal and alongshore spatial scales driving the exchange. Approach: We propose to exploit the synergies between two high spatial resolution measurement techniques: A) Ship-based sampling will yield high spatial resolution measurements both across and along the inner shelf, with sampling intervals set by both boat speed and the duration of ship-based sampling. Measurements across the mid to inner shelf are critical to setting the background conditions upon which inner-shelf processes act and will be needed for any numerical modeling of this region. B) Water-column moorings arranged in a spatially-lagged array, primarily in the along-shelf direction in the inner shelf, but including some cross-shelf elements, will sample fast enough to capture both eddies and internal waves. Combining these two approaches will yield more information than possible from either on its own. Collaboration: We propose to collaborate with colleagues to create a sampling design that captures the range of anticipated time-dependent, three-dimensional features contributing to cross-shelf exchange across the inner shelf. These include measurements made in the nearshore region, remote sensing, additional moored array elements and measurements from small personal water craft. We also will work closely with numerical modelers interested in this region.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512617
Entities
People
- John A. Barth
Organizations
- Office of Naval Research
- Oregon State University
- United States Navy