Coastal Currents

Excerpt

Coastal currents are coherent water masses in motion that are found in the region between the coastline and the edge of the continental shelf. Coastal currents are important because the coastal zone is the place where most nutrients, pollutants, and sediments are introduced into the ocean, and where most larvae are generated and dispersed. Coastal currents are responsible for the transport and dispersal of these biological, chemical, and geological tracers in the water. For example, predictions of the advection and diffusion of spilled oil is dependent upon knowledge of the currents near the coast. Coastal currents often are considered as being made up of two components, alongshore, or parallel to the coast, and cross-shore, or perpendicular to the coast. Away from the influence of inlets or river mouths, cross-shore flows are typically weaker than alongshore flows, yet the larger gradients in crossshore properties make the cross-shore flows better at redistributing those tracers. In addition, if a current is periodic, such as a tidal current, even though it may be quite strong, it may not result in significant net transport. A non-periodic event-driven current such as from a storm may result in a significant net transport. Some currents that are persistent and result in significant transport of water are named after an adjacent landmass, such as the California Current and the Kuroshio Current. In general, currents are classified by the processes that form them (Wright, 1995). Some of the most important currents that exist near the coast outside of the surf zone include (1) wave-driven currents, (2) tidal currents, (3) wind-driven currents, and (4) buoyant plumes. …