Investigation of the Nature, Extent and Fate of Natural Oil Seepage Off Southern California

Abstract

Abstract Natural oil and gas seeps in the Santa Barbara Channel and in Santa Monica Bay have been investigated using aerial, surface, and underwater survey techniques. These studies have provided an insight to the nature and extent of natural submarine seepage and have resulted in the development of procedures and equipment for investigating oily material in the marine environment. Ten separate zones of offshore seepage have been investigated and extensive bottom surveys at some of these sites have revealed ocean floor conditions, modes of oil release, and seepage flow rates. Oil is released from these seeps at a total rate approaching 100 barrels per day, and the resulting oil slicks contaminate several square miles of surface water. Standardized methods have been developed for sampling, classifying, and characterizing oil-tar beach pollutants; these techniques have been field-tested and have provided baseline pollution levels along several miles of coastline. Introduction A natural oil or gas seep is a place on the earth's surface where liquid and/or gaseous hydrocarbons have migrated from buried oil-bearing strata. Although not commonplace, numerous areas of natural seepage have been reported worldwide (Link, 1952; Johnson, 1971). They are most often found in the vicinity of major petroleum provinces and, historically, were used as indicators of promising areas for exploratory drilling. Natural seepage can occur either on land or beneath an overlying body of water. The terres trail seeps tend to be localized with regard to their effects on the neighboring environment. Submerged (or offshore) seeps, however, may have a much broader range of influence. Depending upon its buoyancy, a released oil globule will either stay in the water column which in some cases results in the formation of tar mounds (Vernon and Slater, 1963) - or it will rise to the surface and form an oil slick. These oil slicks may then contaminate a large extent of the neighboring water and shoreline. On the North American continent, natural submarine oil seeps are known to exist off the coasts of Alaska and California, and in the Gulf of Mexico (Emery, 1960; Johnson, 1971; Link, 1952; Vedder, 1969). What little knowledge currently exists about the nature and effects of oil seepage has been obtained from studies of the seeps off southern California. The first quantitative investigations were concerned primarily with the problem of beach contamination (Ludwig, 1960; Merz, 1959; Rosen, 1959). It was not until the 1969 Santa Barbara oil spill, however, that serious efforts were made to study their in situ behavior. These later studies were focused on the seeps off Coal Oil Point in the Santa Barbara Channel and in the Santa Monica Bay (Allen, et al., 1969, 1971; Mikolaj, 1971). The locations of these seep areas are shown in Figure 1. Although natural submarine oil seeps have an environmental impact on relatively small and localized geographical areas, their study has more than a parochial interest.