Perhaps the most interesting results from the pelagial study were 

 obtained from the sediment traps. During the first period of sediment 

 trapping (Nov. 1-9), very high amounts of oil (up to 0.7%) were recorded 

 in the sedimented matter. This was also true for station IV situated 

 about 2.5 km windward of the tanker. Unfortunately, no traps were 

 positioned before November 1st, which leaves the period just after the 

 spill, with potentially high sedimentation of oil, uncovered. This is 

 likely to be a larger source of uncertainty in the following calcula- 

 tions, than the methodological uncertainties inherent in all attempts at 

 measuring sedimentation. Between Nov. 9 and Nov. 17 there was still a 

 substantial oil content in sedimented matter at stations II and V, 

 whereas at station IV practically no oil was found. From Nov. 17 on- 

 ward, oil was still found in sedimented matter from station V, probably 

 as a consequence of release from the shores due to waves and cleaning 

 operations . 



Several mechanisms can facilitate sedimentation of oil, e.g., 

 weathering of the oil leading to increased density, adsorption of oil to 

 particles, or ingestion by zooplankton. Conover (1971) found oil incorpor- 

 ated in zooplankton fecal pellets, a mechanism which, through the rela- 

 tively high sinking rates of fecal pellets, will accelerate sedimenta- 

 tion. In the present case it is, however, unlikely that zooplankton 

 itself or the production of fecal pellets significantly contributed to 

 the sedimentation of oil. At this time of year zooplankton biomasses 

 are low, near the yearly minimum. A more probable path is sedimentation 

 through adsorption to detritus particles, since seston levels in the 

 area are normally high in the autumn, due to wind-induced re-suspension 

 of bottom sediment. Only two days before grounding, the area was sub- 

 ject to fairly strong southwest winds. Wind speeds of up to 10-14 m/s 

 also occurred several times during the acute phase of the spill. 



The sediment trap data make it possible to estimate roughly the 

 amount of oil leaving the water phase through sedimentation. The af- 

 fected area has been estimated as the area inside a line connecting the 



outermost points where oil has been found, either through visual observa- 



2 

 tion (Fig. 4.9) or by direct measurements of oil. A total area of 42 km 



75 



