Organic Matter Analysis of Sediments from Simpson Bay, Alaska using Elemental, Stable Isotopic, and Molecular Signatures

Abstract

Sediment samples from Simpson Bay, Alaska were analyzed to determine the influence of earthquake events on the accumulated organic matter. Radiochemical analysis of 210Pb activity in the sediment dated the cores and determined the depths of the layers from 1964 and 1974, two years where large earthquakes affected this region. Organic carbon (OC) to total nitrogen ratio (C/N) variation suggests a change in the source of organic matter in the targeted earthquake layers. However, the stable profiles for lignin-derived biomarkers and stable carbon isotopes imply that the earthquake events did not disrupt the drainage basin of Simpson Bay enough to change the signatures of the organic matter deposited shortly after these occurrences. The OC, C/N and biomarker signatures were then used to determine the geographic distribution of sediments and organic matter throughout the bay. Organic carbon and lignin biomarker concentrations suggest sources of organic matter to the system from the East Bay and from the North Bay. Biomarker analysis also implies that the source from the East Bay has a higher terrestrial organic matter input than the source in the North Bay. Stable carbon isotopic data imply that the dominant source of organic carbon in the open portions of the bay has a marine source, due to the fact that terrigenous material is deposited at the mouths of the rivers and creeks that feed the system.