Ramped PyrOx 14C With a Twist: Improving Radiocarbon Chronologies on Highly Detrital Marginal Antarctic Sediments
Cristina Subt1, Hoil Yoon2, Kyu-Cheul Yoo2, Jae IL Lee3, Eugene W Domack1 and Brad E Rosenheim4, (1)University of South Florida, Marine Science, St Petersburg, FL, United States, (2)KOPRI Korea Polar Research Institute, Incheon, Korea, Republic of (South), (3)Korea Polar Research Institute, Incheon, Korea, Republic of (South), (4)University of South Florida St. Petersburg, College of Marine Science, St Petersburg, FL, United States
Abstract:
Highly detrital sediments can be difficult to date when the detritus includes material similar to that from which dates are sought. For radiocarbon dating, samples with a high degree of pre-aged detrital carbon contamination necessitate measurement of a very small portion of the sample to remove that contamination from the targeted component, even when using advanced techniques such as Ramped PyrOx (RP)
14C dating. Here we present three case studies of alternative RP approaches, producing accurate and precise chronologies for highly detrital sediments near the Larsen C ice shelf, near the Drygalski Ice Tongue in Ross Sea, and in Lapeyrère Bay, Anvers Island. For sediments where the proportion of organic carbon that was modern at the time of deposition is too small for a traditional AMS analysis after RP treatment, we have developed an innovative multiple RP analyses approach to minimize the cost in precision from using smaller temperature intervals, while maximizing the benefit in accuracy.
Resulting sub ice-shelf chronologies show vastly improved dates down-core, significantly younger than the equivalent 14C chronology from the bulk acid insoluble organic (AIO) carbon with increasing ages down-core. By comparison, bulk AIO 14C dates in the study areas are not only older, but are subject to age reversals and nearly constant ages that make sedimentation rates impossible to resolve. Using our new approaches, we can reduce pre-aged carbon contamination in Lapeyrère Bay, and date sediments within layers of siliceous mud and ooze in the Ross Sea, and near the Larsen C ice shelf. Improved accuracy for 14C dates of highly detrital sediments can sometimes require the incorporation of a larger blank correction to account for multiple analyses, decreasing the precision. Application of this method refines ages of hard-to-date sediments, removing limits on what to include in a regional approach to chronicle ice shelf collapse.
