[MIS19-P22] Application of the ramped pyrolysis 14C dating to postglacial sediments from the Alaskan margin, Arctic Ocean
Samples were taken from two sediment cores collected on the 2005 HOTRAX expedition and comprising Holocene marine and older glaciomarine strata (Darby et al., 2009a). Several 14C ages have been generated on the Holocene biogenic carbonates (Darby et al., 2009b). New samples from both the Holocene and older sediments were pyrolyzed from room temperature to 900 °C, and the released, purified CO2 fractions were sealed in borosilicate glass ampoules at the University of South Florida. Measurement ofΔ14C was conducted at the University of Tokyo.
Pyrolysis followed by oxidation generated three peaks of CO2 at ~300 °C, ~400 °C and ~540 °C, which were deconvolved into three Gaussian peaks (G1 to G3). These peaks were interpreted to reflect the consecutive degradation of oxygen-containing OM functional groups, cleavage of carbon-carbon bonds, and cleavage of aromatic ring carbon, respectively. In this scenario G1 contains most of the autochthonous carbon from the sediment. We found that the slopes of the G1-G3 14C ages plotted against temperature of the Gaussian centroid are proportional to the offset between 14C ages of G1 and earlier analyzed biogenic carbonates from the same core levels. Assuming that this relationship is a constant function of the overall measured age spectra, we propose to use it for estimating sediment ages from the ramped pyrolysis 14C data. The estimated G1 age offsets range from 800 to 3,000 years in the Holocene and from 4,000 to possibly as high as 5,000 years in the older glaciomarine sediments.