Discriminating between natural and anthropogenic features of the sedimentary record in the coastal Beaufort Sea

The coastal Beaufort Sea is at a crossroads with respect to the impacts of human activities. Accurate discrimination of regional and global anthropogenic impacts, versus those due to natural physical and biogeochemical processes, is an important tool for managing environmental issues in the Arctic. We have investigated several natural and anthropogenic features in age-dated sediment cores from the coastal Beaufort Sea. For example, Hg enrichment (by 20 to >50% or +20 to 40 ng/g) was identified in some surface sediments using Hg/Al ratios in cores from nearshore, outer shelf and slope environments. Nearshore Hg anomalies, although quite limited in number, have been linked to drilling fluids deposited during oil and gas exploration in the 1980s. In contrast, similar offshore Hg anomalies are likely due to natural sediment diagenesis as previously noted by others in the deeper Arctic Ocean. We also found Ba enrichment in surface sediments that can be best explained by the deposition of natural, Ba-rich suspended particles from the Colville River; yet, Ba enrichment can sometimes be explained by the presence of drilling fluids in sediments near historic drilling sites. Human induced diagenetic changes are likely to follow current increases in river runoff and coastal erosion. Higher deposition rates for sediment and organic carbon in the coastal Beaufort Sea may create future anomalies for As, Cd and other metals. For example, metal anomalies can presently be found in older subsurface sediments where a layer of carbon-rich sediment was previously deposited. Correct identification of natural versus anthropogenic forcing factors that lead to distinct diagenetic features in the sedimentary record will help us to identify problem areas and make informed regulatory decisions.