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Monterey Bay Studies

Monterey Bay Studies


Monterey Bay National Marine Sanctuary Project, 1999

Rippled Scour Depressions of the Southern Monterey Bay Shelf

by Stephen L. Eittreim, Kaye Kinoshita, George B. Tate, and David A. Cacchione


Similar to many other continental shelves of the world, the southeast Monterey Bay inner shelf contains distinct depressions floored with rippled sand in which the dominantly coarse material of the depressed floor moves as bedload. These 1-m-deep features occur in the offshore former Fort Ord region, the site of impingement of very large storm waves from the northwest, and have been ascribed to rip-current and alongshore flow associated with these large waves. Recently-acquired EM-1000 multibeam bathymetric data now show that two types of these features exist on the southeast Monterey Bay shelf: the dominantly shore-parallel type in 10-30m water-depth and the shore-normal type at greater water depths, to 60m. Both types tend to have thin pinch-outs that point offshore. The shore-normal, deep-water type is concentrated in one area that has been called a nodal zone for alongshore sediment transport separating the consistently southerly flow off northern Fort Ord from the variable and northerly flow off southern Fort Ord. The inter-trough areas of the shore-normal troughs are flat featureless plains with small ripples populated with abundant short seapens. No large crecentic dunes exist in the inter-trough areas as is the case on the shelf off north-central California. Repeated measurements show that, whereas the shallow shore parallel troughs are extremely dynamic, with major changes in shape over periods of months, the deep shore-normal trough system shows no change whatsoever, within the accuracies of differential GPS navigation.

This abstract is from Monterey Bay National Marine Sanctuary Symposium, Sanctuary Currents '97, Facets of Biodiversity, Poster Session, 1997.

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