PRELIMINARY ASSESSMENT OF BEACH TAR SOURCES ALONG THE SANTA BARBARA COUNTY COASTLINE

A multi-faceted tarball study is currently underway as a collaborative effort between the U.S Geological Survey, University of California, Santa Barbara, Minerals Management Service, and the county of Santa Barbara, California. The goal of the study is to understand the relationship between source and flux of oil and tar from offshore seeps to deposition on the coastline.

Collection, counting, and weighing of tarballs from 10 beaches spanning the coastline of Santa Barbara county occurred monthly between May 2002 and August 2003. Tarball samples were extracted in the laboratory with methylene chloride and compound classes isolated by column chromatography using alumina/silica gels. Both aliphatic and aromatic fractions were collected and analyzed by gas chromatography/mass spectrometry (GC/MS) for identification and quantification of specific organic biomarkers. Cluster and principal component analysis of the data used specific oil-source biomarker parameters and excluded maturity and biodegradation parameters because they confound the source signature. Correlation between the limited seep samples and beach tar is not statistically robust, but preliminary analysis using eight source parameters shows good correlation in a few sample sets. The largest correlative sample set had eleven samples, including two offshore tar samples that originated from a seep likely located near Point Conception and nine from northern and southern beaches of Santa Barbara County and on San Miguel Island.

Work is currently underway to locate and directly sample more offshore seeps, providing additional samples for comparison with the beach tars. Upon completion of chemical analysis of the tarballs and seep samples, a regional assessment to link tar source with tar deposition will be made in order to understand the fate of natural seepage.