OVERVIEW OF THE BIOGENIC AND ANTHROPOGENIC HYDROCARBON 

 DISTRIBUTIONS IN SEDIMENTS ALONG 

 THE NORTH ATLANTIC MARGIN 



Paul D. Boehm 

 Technical Director 



Battel le Ocean Sciences 

 Duxbury, MA 



Georges Bank and the adjacent, slope, rise and submarine canyon areas are 

 characterized by highly dynamic sediment transport, deposition and 

 resuspension cycles. Pollutant and biogenic hydrocarbon distributions follow 

 the general trends of those for fine sediments. Saturated and polycyclic 

 aromatic hydrocarbons are found at very low levels in the central bank area 

 where sediments are coarse and are found at elevated levels in the 

 depositional areas of the "mud patch" , at canyon heads, and in fine grained 

 sediment areas further offshore. 



Hydrocarbons of a biogenic, terrigenous nature appear to be in overall 

 steady state, while marine biogenic hydrocarbon distributions are deposited 

 and then eroded from the surface sediments, eventually being deposited in 

 depositional areas to the southwest and west. Indirect evidence suggests that 

 anthropogenic hydrocarbons are associated with the easily resuspended fine 

 sediment fraction, while the biogenics associate with the coarser fractions. 

 It has been estimated that 40-50% of the organic matter is resuspended and 

 transported to the slope from the shelf. 



Both the saturates and the PAH compounds are strongly associated with 

 total organic carbon in the sediments. Saturated hydrocarbons of a terrigenous 

 plant wax origin dominate the overall hydrocarbon assemblage. While the 

 absolute concentration of total hydrocarbons range from 0.2 to 20ppm, and PAH 

 compounds range from about 0.01 to 1.0 ppm, the respective ratios to TOC are 

 relatively constant, suggesting a well mixed geochemical area. The PAH/TOC 

 ratios are very similar to those found in sediments from other geographical 

 areas, well removed from the North Atlantic OCS. The PAH distributions are 

 similar to those originating in the combustion of fossil fuels, with 

 distributions dominated by the higher molecular weight PAH (i.e. 4- and 5-ring 

 compounds) rather than petrol eum-sourced PAH. 



The distributions of hydrocarbons in the shelf and slope areas have 

 important implications for predictions of the fate of pollutants which may 

 originate through outer continental shelf (OCS) development. Sedimented 

 hydrocarbons associated with fine grained sediments will be redistributed from 

 their point of origin rapidly (weeks to months) and will be transported to 

 depositional areas which include canyon heads, deeper slope areas and basins 

 such as the mud patch area. Data suggest that although introduced pollutants 

 may be deposited at these canyon heads and be transported down the canyons, 

 the data also suggest the possibility of up-canyon transport and deposition of 

 pollutants at canyon heads, as well. 



B-10 



