OVERVIEW OF NATURAL OIL S EEPAGE IN THE S ANTA BARBARA CHANNEL AND S OUTHERN S ANTA MARIA BAS IN, S OUTHERN CALIFORNIA US A

Thomas D. Lorenson1, Frances D. Hostettler1, Jennifer A. Dougherty1, Robert J. Rosenbauer1, Kenneth E. Peters1, and Mary Elaine Helix2

s c ienc e for a c hanging world

Abstract

1US Geological Survey, 345 Middlefield Road MS-999, Menlo Park, CA 94025 tlorenson@usgs.gov

2Minerals Management Service, 770 Paseo Camarillo, 2nd Floor Camarillo, CA  93010

A five year study of tars and oils in southern California waters and beaches is underway as part of a joint U.S. Geological Survey-Minerals Management Service (USGS/MMS) program to identify natural and anthropogenic sources. Natural sources for these petroleum hydrocarbons include ubiquitous onshore and offshore shallow oil seeps, especially prominent along the southern California coast. Anthropogenic sources include accidental oil spills from vessels and sunken wrecks, from offshore drilling rigs and pipelines, and from ships involved in the processing and transport of oil.

We have collected and analyzed about 650 tars and oils from along the California coast including selected oils from offshore platforms to differentiate them from natural seep oil and tarballs. A chemical fingerprint for each sample was determined by a combination of thirty-two measured parameters. We partitioned the oils into genetic families based on a statistical method using only source related biomarkers. The distributions of samples in each family can be mapped, thus revealing information about their origins and seasonal patterns of tar deposition on local beaches.

An extensive area of active seeps has been located by sidescan imagery and sampled by a remotely operated vehicle (ROV) in the area near Point Conception where about 150,000 barrels of tar up to 5-m thick cover the seafloor over an estimated 5 km2 area.

In cooperation with the University of California, Santa Barbara, we sampled six offshore seeps around Coal Oil Point, near Santa Barbara. This seep oil is lighter and geochemically distinct from that near Point Conception and occurs as far west as offshore Gaviota. Our results demonstrate that tar accumulations on California beaches can be related to natural sources and that there is extensive offshore seepage. Future work will focus on fingerprinting platform-produced oils, monitoring unusual beach tar deposition events, and perhaps making flux measurements of selected seeps.

Results

MMS

An automated, multi-tiered chemometric decision tree allows identification of genetically distinct oil groups offshore California. For example, samples in Family 2, Group 1, Subgroup 2 can be described as Group 212. A similar approach was used to classify seep, crude oil, and source-rock extracts in the Circum-Arctic area (Peters et al., 2005b). KNN = K-nearest neighbor, SIMCA = soft independent modeling of class analogy.

http://www.bubbleology.com/seeps/

Un-processed multibeam bathymetry of the shelf offshore Coal Oil Point, July 2006. The outcropping Monterey Formation is clearly visible. The exposed section is a breached antiform whose southern flank is host to the prolific La Goleta seeps. Anomolous seafloor features resembling pockmarks and grooves are present.

La Goleta seeps

Direction of perspective view

Breached antiform

Who am I ?..

Where do I come from?...

How did I here?

Life's great mystery is universal......

Sidescan image of the seafloor southwest of Point Conception, California shows several tar mounds ranging in diameter from about 10 to 100 m. Tar mounds such as these are confined to the area near Point Conception. They cover at least 5 km2 and contain about 150,000 barrels of oil. Red flag symbols indicate ROV dive sites.

Remotely operated vehicle (ROV) video image shows a crab near the top of extruding tar on a tar mound like those show in the sidescan images. Lack of colonizing sessile organisms suggests that this mound is quite young.

Remotely operated vehicle (ROV) video image of a colonized tar mound likely older than than the bare tar mound. Sea anemones and other sessile organisms are covering the tar.

Location Point Conception

Chemometrics

Biomarkers

Coal Oil Point

N-S cross section from Carpinteria to SCI

Biomarkers are molecular fossilsComplex Organic Compounds

Linked to Precursors in Living OrganismsUbiquitous in Crude Oils and Source Rocks

We have used biomarker to characterize seep oil and tars, and beached tars in an effort to link common sources and distinguish between natural

05-95_Holl

O_99-101_Coa

O_00-68_Cmoh

O_04-7_Val

04-272_Jk

Family211212213

PCA Plot

Chemometrics reduces the data into principal components:

Sorts out the biomarker ratios to define groups of samplesTests for correlations between and within the sample groups

Relates the tar residues to possible local sources

Life of a "tarwhip"Seafloor to beach

KNN model

2

1 2

KNN

1

1 2 3 4

SIMCA

3

1 2 3 4 5

SIMCA

SIMCA SIMCA

1 2 3 4

SIMCA

Subg

roup

Grou

p

Fami

ly

New Sample

Seep sample group 22

Huntec data over coalescing tar mounds S. of Pt.Conception