Seafloor Acoustic Map of the Southern Monterey Bay Shelf

Abstract

The southern Monterey Bay continental shelf was recently swath-mapped with the Simrad EM-1000 system. This system produces 96-channel bathymetric and acoustic backscatter information along swath widths up to 5 times the water depth. The shelf was surveyed from the 20-m to the 95-m isobath, over an area centered on the former Restricted Zone offshore of Fort Ord, from Moss Landing on the north, to Cypress Pt. on the south. Some of the notable findings that will be displayed at this symposium are:

1. A prominent north-south ridge, tentatively called the Fort Ord ridge, of very high backscatter and 6-m relief, composed of westward-dipping (5-degree slope) sandstone ledges, down-faulted on the east.
2. A series of flat-floored troughs, with coarse sand bottoms are strung out northward from Monterey along the coast between about 15 m and 30 m and culiminate in a large trough off Ft. Ord that extends to 58 m depth. These features may be caused by fresh-water seeps or acquifer outcrops. An alternate explanation is that these troughs are the locus of rip-current offshore transport of coarse sands.
3. The north Monterey County outfall pipe, which delivers storm-drainage and treated wastewater to a location about 1 mile offshore Marina, is prominently displayed as a high-backscatter, 2-m-high lineament. The pipe has caused sediment to pile up on its north side.

This abstract (MCS# 96-26) is from Monterey Bay National Marine Sanctuary Symposium, Sanctuary Currents '96, Building Community Connections in Science, Education and Conservation, Poster Session, 1996.