Carbon isotopic comparisons of oil products used in the developmental history of Alaska

Studies of the fate of oil released into Prince William Sound, AK, as a result of the 1989 Exxon Valdez oil spill, have led to an unexpected discovery. In addition to oil-like residues attributed to the spill, the ubiquitous presence of flattened tar balls, the carbon isotopic compositions of which fall within a surprisingly narrow range [δ13CPDB=−23.7±0.3‰ (n=65)], were observed on the shorelines of the northern and western parts of the sound. These compositions are similar to those of some oil products [−23.7±0.7‰ (n=35)] that were shipped from California and used in Alaska for fuel, lubrication, construction, and paving before ∼1970. These products include fuel oil, asphalt, and lubricants [−23.8±0.5‰ (n=11)], caulking, sealants, and roofing tar [−23.7±0.7‰ (n=16)], and road pavements and airport runways [−23.5±0.9‰ (n=8)]. Fuel oil and asphalt [−23.5±0.1‰ (n=3)], stored at the old Valdez town site and spilled during the 1964 Alaskan earthquake, appear to be the source of most of the beached tar balls. Oil products with lighter carbon isotopic compositions, between −25 and −30‰ (n=18), appear to have been used more recently in Alaska, that is, after ∼1970. The source of some of the products used for modern pavement and runways [−29.3±0.2‰ (n=6)] is likely Alaskan North Slope crude oil, an example of which was spilled in the 1989 oil spill [−29.2‰ (n=1)].