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Joint Meeting Pacific Section, AAPG & Cordilleran Section GSA April 29–May 1, 2005, San José, California

Characterizing Bedform Habitat Based on High-Resolution Multibeam Bathymetry, Backscatter and Video Imagery in the Georgia Basin, British Columbia and Northwest Straits, Washington, USA

Holly L. Lopez and H. Gary Greene
Moss Landing Marine Lab, 98272 Moss Landing Road, Moss Landing, CA 95039
[email protected] and [email protected]

The Georgia Basin and Northwest Straits have undergone tectonic and glacial processes which produced metamorphic, plutonic and sedimentary rocks and diverse marine benthic habitats that vary from dynamic bedforms, to glacially-scoured moraines, to fractured and faulted bedrock outcrops. Based on multibeam bathymetric, backscatter and other geophysical data sets, bedforms of differing sizes have been identified in Haro Strait, San Juan Channel, the Strait of Juan de Fuca, and the Boundary Pass region, British Columbia. Bedforms are features of relief created on the bed of a fluid flow as a result of an unstable interaction between the flow and the bed material. The bed may be composed of loose grains, cohesive mud or rock. Variables which influence the creation of bedforms in the marine environment include current velocity, water viscosity, water depth, seafloor slope, sediment concentration, and sediment grain size. These influence the size and shape of bedforms which range from small ripples to large dune fields. It is possible that currents in the Georgia Basin and Northwest Straits region contribute to bedform construction and are evidence that sediments are actively migrating. Coarse-grained bedforms were identified using an ROV in San Juan Channel where sand lance (Ammodytes spp.) were observed emerging from the sediment waves. Sand lance are commonly found over sandy substrates where sand is used as a place of refuge. Similar conditions exist in San Francisco Bay. There have been numerous studies regarding the relationship between fish and highly rugose substrate; however, the potential relationship between fish and bedforms as habitat, specifically, in the Pacific Northwest, is not known.

The goals of this study are: 1) to identify and characterize bedforms as habitat which occur in the Georgia Basin and Northwest Straits; 2) to map their distribution based on remote sensing data according to the deep-water classification scheme for marine benthic habitats used at the Center for Habitat Studies at Moss Landing Marine Laboratories; and, 3) to gain a better understanding of the physical and biological characteristics of the region and compare with other similar settings.

Posted with permission of The Geological Society of America; abstract also online ( © Copyright 2005 The Geological Society of America (GSA).