Georges Bank  monitoring program: hydrocarbons in bottom sediments and hydrocarbons and trace metal in tissues

Abstract

Hydrocarbons in sediments and hydrocarbons attd trace metals in tissues from Georges Bank were analyzed to evaluate potential changes to the benthic environment resulting from exploratory drilling operations. Sediment hydrocarbon concentrations varied with grain size: concentrations up to 2.5 ug/g dry weight total aromatic equivalents occurred in the fine-grained sediments of Lydonia Canyon and the "Mud Patch' area south of Martha's Vineyard, whereas concentrations were less than ug/g dry weight in sediments from the shallow areas of Georges Bank, at a regional control site, and at the site of drilling operations. Increases in total aromatic equivalents from approximately 0.1 ug/g dry weight to 0.4 ug/g dry weight were measured in sediments from a site 0.25 km from the drill rig concurrent with drilling operations. Petrogenic hydrocarbons were detected in both drilling fluid extracts and in sediments collected during drilling operations, suggesting short-term deposition of drilling discharges in near-rig sediments. Drilling discharge residues were not observed in the near-rig sediments one month after drilling operations were terminated. Furthermore, hydrocarbon residues from drilling discharges were not observed in sediments from stations located at distances greater than 6 kin from the drill site either during or subsequent to the drilling operations.