Vol. 53 - Alaska Resources Library and Information Services

increase in water-borne oil concentrations within a water layer sandwiched by lower
concentrations of more highly weathered oil.
The persistence of low molecular weight
saturates (C[subscript]
6-C[subscript]
10 alkanes) and alkylated benzenes and naphthalenes in the plume in
similar proportion to the total petroleum in the neat oil was unexpected. Surely the
subsurface release of dispersed oil accounted for this. A surface release followed by
application of chemical dispersants would have allowed some loss of light aromatics to
occur by evaporation.
The very striking similarity between the BIOS dispersed oil plume behavior and
that observed in the Ixtoc I spill
(Boehm, Barak, Fiest and Elskus 1982) is of
no small importance. A subsurface release of oil that creates small oil
droplets either through shear (Ixtoc) or through stabilization through
chemical dispersion (BIOS) with resulting droplets advected by strong
currents, results in subsurface coherent plumes of unweathered
fresh oil with
a full contingent of toxic aromatics. The similarities between the two events
are also striking given the 25°C water column temperature differential
between Gulf of Mexico and Arctic waters. Of course these initial high levels
of oil (roughly 10 ppm in the Ixtoc I and 10 ppm and greater in the BIOS
scenarios) will eventually be reduced through dilution and diffusion even if the
coherent subsurface plume persists as it did for 20 km or so in the Ixtoc I
spill.
During and after the dispersed oil experiment, there was little evidence for
either the large-scale beaching of dispersed oil or the surfacing, in the water column, of
dispersed oil. However, both phenomena did occur to minor extents and resulted in some
important information. Oil that was found adhering to the Bay 9 beach was present at low
levels (5-10 ppm).
molecular weight components.
The oil had weathered significantly, due mainly to losses of low
Both the concentration of oil on the beach and its
composition were nearly identical to those found in the offshore benthic sediments
implying a detectable, but low sorptive affinity of dispersed oil. Oil which did appear to
have coalesced at the sea surface was highly weathered through loss of low boiling
saturates and aromatics.
The state of weathering of this surface oil sampled several
hours after initial dispersed oil discharge was equivalent to that of nine-day-old beached
surface oil (Bay 11).
Thus it appears that the coalesced oil formed after solubles were
stripped from the oil in the water column with the coalesced oil forming from a
weathered residue.
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