Distribution of hydrocarbons in recent marine sediments off the coast of Baja California

Abstract

Concentrations of linear or n-hydrocarbons, polycyclic aromatic hydrocarbons (PAHs) and unresolved complex mixture (UCM), were measured in recent marine sediments in 24 stations off the coastal region at the Mexico-USA border. The average concentration found for n-hydrocarbons was 15 μg g −1, with a maximum of 70.6 μg g −1 and minimum of 0.8 μg g −1. The average concentration for UCM was 37 μg g −1 with a maximum of 220.5 μg g −1 and a minimum below detection levels. For the PAHs, the average concentration was 0.4 μg g −1, with a maximum of 1.93 μg g −1. Maxima and minima are consistent with previous studies in northern stations. A North to South gradient distribution is reported. Cluster analysis supports the hypothesis of a North to South transport. The sources of hydrocarbons appeared to be mainly anthropogenic. No significant correlation was found between particle size and hydrocarbon content, PAHs or UCM. Deposition of the n-hydrocarbons and UCM was apparently dictated by closeness to point sources as a poor correlation was found with organic content ( r = 0.27–0.32 α = 0.05) and with grain size of sediments ( r = 0.019–0.079 α = 0.05). Distribution of PAHs was found to decrease toward the coast. Possible sources of these materials are discussed. Grain size distribution suggest the general direction of main flow of material for the area studied.