surface manifestation of a front along the shoal/channel interface in South San Francisco Bay, February 2008
Fronts are regions where two differing water masses converge resulting in strong gradients often visible at the water surface. Convergent circulations often associated with fronts lead to accumulation of materials along fronts thus gaining the nickname “trash lines” from fisherman. In addition to trash however, the convergence also leads to accumulation of phytoplankton and larvae, the base of the aquatic food chain, which propagates up the food chain leading to an accumulation of fish, sea mammals, and even sea birds feeding along these highly productive interfaces. Fronts often form in estuaries due to interactions between shoals (shallow regions) and channels. Shoals are important regions in estuaries as they experience enhanced productivity and enhanced sediment resuspension. Thus shoal/channel interactions and fronts can mitigate transport of waterborne constituents between the shoals and channels and influence the overall estuarine dynamics.
Field work in the Snohomish River Estuary, Everett, WA and South San Francisco Bay, San Francisco, CA has been conducted to examine shoal/channel interactions and fronts in more detail including frontogenesis (frontal formation), frontal propagation, and frontal influence on vertical mixing and longitudinal dispersion.