Sediment chronology in Antarctic deglacial sediments: Reconciling organic carbon 14 C ages to carbonate 14 C ages using Ramped PyrOx

• Published in: The Holocene
• Main Authors: Subt, Cristina, Fangman, Kimberly A, Wellner, Julia S, Rosenheim, Brad E
• Format: Article in Journal/Newspaper
• Language: English
• Published: SAGE Publications 2015
• Subjects: Antarctic; Antarc*
• Online Access: http://dx.doi.org/10.1177/0959683615608688; http://journals.sagepub.com/doi/pdf/10.1177/0959683615608688; http://journals.sagepub.com/doi/full-xml/10.1177/0959683615608688

We present the first study which directly compares carbonate radiocarbon ( 14 C) dates with the Ramped PyrOx (RP) radiocarbon dating technique within a single sediment core, and we confirm the utility for the latter constructing chronologies of high latitude, Holocene marine margin sediment successions. Historically, the heavily detrital nature of Antarctic margin sedimentary organic material and lack of carbonate preservation have made these sediments difficult to date accurately. Here, we use archived cores with existing foraminiferal ages to compare with RP dates at equal or similar depth intervals. The lowest temperature RP splits were integrated over narrower intervals than in previous studies to reduce the amount of mixing with older, more thermochemically stable end-members during pyrolytic decomposition. Ages of the low-temperature RP splits coincide with their corresponding carbonate counterparts, suggesting that the RP 14 C dating method is a reliable alternative to carbonate dates in sediments where carbonates are absent or not sufficiently preserved for 14 C dating. The rarity of calcareous material in most Antarctic sediments often obligates the use of the bulk acid insoluble organic (AIO) fraction of the sediment, which can be problematic because of contamination by older carbon. The bulk AIO 14 C ages, which are calculated using the weighted arithmetic mean of all RP splits of individual samples, show that age reversals and biases can occur using bulk AIO dates for age models because of variable proportions of pre-aged organic matter down-core. The application of the RP dating method can reduce these effects to produce a more reliable chronology that is statistically identical to the foraminiferal dating chronology.