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OIL POLLUTION IN THE WESTERN ENGLISH CHANNEL (APRIL 1978)
One month after the wreck, sediments were collected during an
oceanographic cruise (R/V SUROIT) to assess sea bottom contamination of
the western English Channel. The sampled sediments were coarse- to
medium-grained calcareous sands (more than 70% CaCo,) . In the Bays of
Morlaix and Lannion and near the Aber zone, the content of calcium
carbonate in the sands was somewhat lower (50-70% CaCO-) . Organic
carbon content was generally low, from 0.02 to 0.6 percent (m = 0.18%
+ 0.13%). The oil concentrations in the sediment ranged from 10 to
1,100 ppm (nonpurified organic extracts) (Marchand and Caprais, 1981).
Generally, the zone of contaminated sediments reflected offshore and
coastal areas impacted by the drifting slicks (Fig. 4). The pollution
of the sea bottom was a result of the diffusion of oil into the water
column. Off Sept-Iles, a gradient was observed from the coast to the
open sea (210, 52, 42, 34 ppm). At the 49°N parallel, from west to
east, one could observe an increasing and decreasing gradient (21, 19,
48, 102, 54, 52, 24 ppm). The highest petroleum accumulation in marine
sediments were located in the coastal and sheltered zone of the Abers
(100 to more than 10,000 ppm) and in the Bays of Morlaix and Lannion (10
to more than 1,500 ppm) (Fig. 5).
FIGURE 4. Oil pollution in marine sediments (April 1978)
Concentrations expressed in ppm.
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