Effects of offshore oil exploration and development in the Alaskan Beaufort Sea: Long-term patterns of hydrocarbons in sediments.

The United States Bureau of Ocean Energy Management (BOEM) has sponsored 4 major monitoring projects in the oil and gas development area of the Alaskan Beaufort Sea since the 1980s, the last being the Arctic Nearshore Impact Monitoring in the Development Area III (ANIMIDA III) Project (2014-2017). These studies were conducted to better understand the physical, chemical, and biological environments and how oil and gas activities may impact them. This paper focuses on monitoring sediment hydrocarbon chemistry. The projects included measuring polycyclic aromatic hydrocarbons (PAHs), n-alkanes and isoprenoids (SHCs), and sterane/triterpene (S/T) geochemical biomarkers and determining their distribution, possible sources, and environmental significance in the sediments of the Beaufort Sea and rivers emptying into it. Concentrations of hydrocarbons in sediments were variable on both spatial and temporal scales; surface sediment concentrations of total PAHs (TPAHs), the class of hydrocarbons of greatest environmental interest, averaged between 300 and 700 μg/kg in different years of monitoring between 1985 and 2015. The concentrations were similar to those measured in other marine regions of Alaska where oil activities have not occurred. Sediment TPAH concentrations were below sediment quality guidelines values, indicating a low risk of harm to benthic marine communities. The hydrocarbons in the Beaufort Sea sediments are primarily from non-oil petrogenic and biogenic sources, with small amounts of pyrogenic hydrocarbons. Most of the hydrocarbons are carried to the Beaufort Sea in coastal erosion and river inputs of hydrocarbon-rich materials, such as peat and shale. The majority of the Beaufort Sea Development Area, including near production facilities, contains uncontaminated sediments with only a few small areas near (<100 m) some exploratory wells where petroleum hydrocarbon concentrations are above regional background. Integr Environ Assess Manag 2019;15:224-236. © 2019 SETAC.