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Survey of Offshore Hazards in Southern California
The USGS scientists conducting this survey benefited from early, close consultation with cooperating scientists at the University of California, Santa Barbara, and at Moss Landing Marine Laboratories. Data collected during the survey will be interpreted in collaboration with academic colleagues to support several National Science Foundation proposals.
The Auriga and its crew enjoyed splendid weather during the early-morning departure past the glittering cityscape of downtown San Francisco, then ran headlong into full-gale conditions in southern California. On the way south, the 150-ft-long ship was crowded with crew and equipment. The tools of the marine geologist's trade jammed the rear deck: four bright-yellow "fish" housed the sidescan-sonar, the Huntec, the chirp profiler, and the 12-kHz bathymetric-profiler systems. Also on deck were the multichannel seismic streamer, the air compressor, and various winches. Much of the deck space was occupied by four large shipping containers, which housed facilities for data recording and archiving, and tools and repair space for all USGS equipment. The vessel was staffed by six members of the ship's crew, six USGS geologists, three technicians from the USGS' Marine Facility in Redwood City, CA, one technician under contract, and five biologists from Cascadia Research, a nonprofit research organization based in Olympia, WA. These 21 people shared 14 first names, as well as tight quarters. "Mike" was the go-to guy, as there were five of them.
The first part of the survey involved 4 days of collecting sidescan-sonar data near Point Conception for the MMS. Sidescan-sonar data provide a photograph-like view of the sea-floor surface. These data will help the MMS update its map of natural oil and gas seeps in this area. The main issue is that long stretches of beach are befouled by tarballs, and iridescent oil sheens are evident offshore, much to the dismay of the local populace. Scientists and managers in MMS are working with USGS scientists to assess the extent of natural sea-floor seepage of tar and heavy oils. USGS geochemists are also "fingerprinting" the natural oils, which will help MMS distinguish them from produced oils spilled during human activities. Previous surveys showed numerous sea-floor pockmarks and both acoustic and methane anomalies in the water column. Fortunately, this work in the typically windiest area was completed before the gales struck.
The scientists also investigated the Goleta submarine landslide, which is famous among marine researchers, in part because of its clear expression in bathymetric maps created from multibeam-sonar data. To foster research into the mechanics of slide generation and emplacement, the USGS scientists obtained both high-resolution and airgun seismic-reflection data over this feature. The high-resolution data provide a detailed look at sediment layers as much as 75 m below the sea floor. The airgun data provide less detail but give scientists a look at features as much as 1 km below the sea floor. Surveying had to be suspended whenever marine mammals got too close to the vessel, which occurred several times each day and occasionally lasted for more than half an hour. Starting in the mid-1990s, marine researchers planning to use sound energy to probe beneath the sea floor were required to obtain permits specifying the conditions under which they could operate seismic sound sources, such as airguns. The permit requirement was established to protect marine mammals that use sound themselves for various purposes, including communication, navigation, and locating prey. Once a bureaucratic quagmire, acquiring permits to conduct seismic surveys near marine mammals has become routine. A new twist is that endangered marine turtles have been added to the list of protected species. For last June's Auriga cruise, the USGS scientists obtained permits from the California Coastal Commission, the California State Lands Commission, and the National Marine Fisheries Service. The Channel Islands National Marine Sanctuary also advised them.
Other cooperative work was conducted with Cascadia Research biologists who are investigating the effects of airgun signals on large whales. Their ship, the research vessel Robert Gordon Sproul from the Scripps Institution of Oceanography, and the Auriga converged at Santa Rosa Island, where, by chance, 20 to 30 large whales loitered. Biologists on both ships and in an inflatable boat observed whale behavior as the Auriga fired its airgun along several tracklines. Initial reports from the biologists are that the whales first made room as the Auriga approached them and then returned to the original area once the vessel departed. Apparently, the airgun caused neither hurried dispersal nor long-term interruption of whale activities. Eventually, such investigations will provide answers to outstanding controversies about whether sound sources used for marine research actually harm ocean animals. Commonly, seismic data are collected with the ship headed parallel to the troughs of offshore waves. This direction is good for data but stressful for people. To atone for long seasick hours, we celebrated the end of the cruise with a swim call. Many participants, faces in frozen shock, spent as much as 30 seconds in the 52°F water.
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in this issue:
Parasites as Indicators of Coastal-Ecosystem Health Climate-Change Effects Lecture usSEABED - Seabed Characteristics von Huene Receives Prestigious Award |
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U. S. Department of the Interior | U.S. Geological Survey
cover story:
