Characterization of sedimentary organic matter in recent marine sediments from Hudson Bay, Canada, by Rock-Eval pyrolysis

Abstract

A combination of Rock-Eval pyrolysis and isotopic analyses is used to characterize the sources and distribution of organic matter in modern marine sediments from the subarctic Hudson Bay (including Hudson Strait and Foxe Basin), Canada. This approach reveals organic matter contributions from both marine and terrigenous sources, with spatial patterns and varying degrees of degradation that are consistent with inferences from traditional geochemical tracers for modern organic matter. Rock-Eval parameters characterize Hudson Bay organic matter with low hydrogen index, high oxygen index and a high degree of residual carbon that suggests heavily reworked materials. Locations of higher primary productivity in Hudson Strait, Foxe Basin, the northeast and far west of Hudson Bay, and the concentration of watershed runoff in the southern part of Hudson Bay can be delineated using the ratios between hydrogen and oxygen indices and from the distribution of labile organic carbon. Relatively high temperatures of peak hydrocarbon yield identify an advanced state of OM degradation or humic substances as important classes of organic carbon compounds in the majority of the sediment. Such highly degraded and oxygenated organic matter is unusual compared to that typically observed in other Arctic shelf seas and is consistent with a strong role for sediment and organic matter recycling in Hudson Bay. In the offshore region, the source of highly oxidized and labile organic matter identified by Rock-Eval parameters is resolved with δ13C and biomarker information that also permit examination of the sediment biogeochemical regime. This approach suggests that a distinct association with Mn enriched sediment contributes to the oxidization signal by abiotic or biological Mn related processes. These interpretations extend the limited information available on using Rock-Eval analyses to characterize organic matter in recently deposited marine sediments and describe an important consideration to using this method in Mn enriched environments.