Time Evolution Of Beach Tar, Oil Slicks, And Seeps In The Coal Oil Point Seep Field, Santa Barbara Channel, California

Abstract

Linking beach tar with sources in a complex natural marine seepage area presents numerous challenges. Efforts at Coal Oil Point (COP), CA included beach tar distribution surveys, oil slick tracking, sampling, and chemical analysis, underwater scuba surveys, aerial surveys, and numerical modeling. Despite a wind from the east and current to the west, a slick was tracked initially north from its source, presumably due to spreading, then it drifted east, ending in a kelp bed off COP. Sample chromatograms showed mixing with another oil slick by the appearance of a heavier series of n-alkane peaks where the trajectory changed direction. Trajectory simulations suggested that interface currents were poorly described by parameterizations of wind and surface currents, and/or the existence of small-scale circulations not resolved by CODAR or the drift buoy. Detailed tar accumulation surveys covered 175-m (4400 m2) of COP beach where tar accumulation generally is greatest. Maximum total beach tar observed was 1.5 kg, with significant variability. Modeling suggested a similar source location for the three analyzed surveys. Analysis also suggested kelp canopies can play a significant roll in the arrival time and location of beach tar by blocking onshore transport. However, wind, current, and kelp conditions were such that much of the variability in tar accumulation for these surveys probably was from source emission variability.

Tracking an oil slick from multiple natural sources, Coal Oil Point, California

“…Oil in the convergence zone is thick, which causes outward motion due to gravitational spreading of the oil against the outflow from the bubble flow, and inflow to the downwelling by continuity. Spreading was identified in Leifer et al (2004c) as the most likely explanation for an initial northward slick trajectory, perpendicular to winds and currents during a different slick tracking study. At the slick convergence zone (60 min, Fig.…”

“…However, it also meets oil slicks advected by currents and winds. The interaction of the two often forms an eye-shaped convergence zone (or ring), visible from the air (Leifer et al, 2004c). Thick oil slicks, including brown mousse and tar balls are commonly found in the convergence zone, which often is thickest at the upcurrent point.…”

“…This may be due to oil trapping in the kelp where it could have degraded for longer, or mixed with tar trapped in the kelp. Tar trapping in kelp has been proposed to affect tar distributions on the beaches off COP (Leifer et al, 2004c) and oil slicks on beaches off Summerland, CA (Leifer et al, 2004b). Also shown is a chromatogram for the Seep Tent Seep oil slick (Fig.…”

A Synthesis Review of Emissions and Fates for the Coal Oil Point Marine Hydrocarbon Seep Field and California Marine Seepage

“…Generally, oil is presumed to drift at the vector sum of the currents and wind speed after applying a windage factor of~2-3% [153], which assumes the interface drifts at the current velocity. Leifer et al [154] tracked an oil slick in the COP seep field and found that for a 3% windage factor, there should be a current factor (i.e., not 100%).…”

Measuring Floating Thick Seep Oil from the Coal Oil Point Marine Hydrocarbon Seep Field by Quantitative Thermal Oil Slick Remote Sensing

“…These fractions are termed the windage factor, W F , typically 2%-3% [29] and a current factor, C F . In a COP study, Leifer, et al [30] found that oil drift could be explained by W F = 12% and C F = 0 or a W F = 3% and C F > 0.…”