Hydrocarbons in cores of northwestern Atlantic coastal and continental margin sediments

Abstract

The concentrations and composition of hydrocarbons in sections from a 210Pb dated core from Buzzards Bay, Massachusetts are reported. Terrigenous n-alkane concentrations remain constant throughout the 62 cm and 195 years sampled. Gas Chromatographic analysis on SCOT columns revealed an unresolved complex mixture of alkanes and cycloalkanes which decreases in concentration with increasing depth. Phenanthrene and C 1 and C 2 substituted phenanthrene concentrations also decreased with increasing depth and the relative abundance of C 1 and C 2 homologs compared to phenanthrene suggest a pyrolytic origin for these aromatic hydrocarbons. The various sources of hydrocarbons in surface sediments and the processes which could govern their distribution are discussed. The most likely source of the phenanthrenes and the unresolved complex mixture of alkanes and cycloalkanes in the upper core sections circa 1900 to the present seems to be urban air fallout. A depth distribution of alkanes and cycloalkanes similar to the Buzzards Bay core was found for a second area of Buzzards Bay and for cores from sediments of the Gulf of Maine and Hudson Canyon. Two C 25 cycloalkenes were identified as major hydrocarbons in the sediments. Their concentrations decrease with increasing depth in the cores. Mass spectra of these compounds and their hydrogenation products are reported.