New radiocarbon estimation method for carbonate-poor sediments: A case study of ramped pyrolysis 14C dating of postglacial deposits from the Alaskan margin, Arctic Ocean

Abstract Sediments up to about 50 ka old can be dated by radiocarbon (14C), and typically biogenic carbonate minerals formed by organisms like foraminifera or mollusks are the primary choice for dating. However, carbonate-poor environments, typical for polar seas, limit the possibilities for 14C dating to bulk organic matter (OM), which is typically biased by the old carbon. In this study, ramped pyrolysis-oxidation (RPO) 14C dating of bulk OM was applied to two Arctic Ocean sediment cores with independent age constraints from prior studies in order to assess its applicability in this environment. Application of RPO to Arctic sediment samples yielded a series of progressively older ages with increasing pyrolysis temperatures and with sediment depth, similar to previous applications in Antarctica. The difference between the independently dated carbonate ages and the RPO-derived ages was proportional to the gradient of 14C ages of the released carbon vs. the pyrolysis temperature. Using this empirical relationship, we propose a new method to estimate sediment age based on RPO 14C data. Ages derived by this method in our data set show offsets from the independent age controls mostly under ~700 years. These results are much closer to the actual ages than the bulk OM data. This simple method may have a broad application to sediments with biogenic carbonate deficiency whereby dating is reliant on bulk OM.