Atlantic Radiocarbon Calibration using framework forming cold water corals

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Radiocarbon calibration is a major tool for paleoclimatology and paleoceanography. Calibrating marine radiocarbon ages is thus of crucial importance. However, the presently available marine calibration curve MarCal13 is thought to be a hypothetical calibration curve relying on only few measurements from varved sediments, tropical corals and partly foraminifera. This calibration curve requires significant improvement. Coupled U-Th and 14C dating of cold-water corals (or deep sea corals) is mostly used to trace and quantify changes in deep water circulation and carbon cycling. Through our preliminary work on fossil corals from the Moroccan coral reefs we demonstrate that glacial corals reveal solely minor deviation from the atmospheric evolution. The origin of such damped oceanic radiocarbon variability at mid-depth (500 - 900m) is related to the interaction of generally well-ventilated water masses and the downward mixing of carbon within the subtropical Atlantic. Numerous sediment cores from the cold-water coral province have been collected providing fossil coral fragments which span 14 to 60 kyrs in age, thus spanning the entire radiocarbon calibration period. Consequently, we dispose a unique archive to trace radiocarbon variations in the near surface ocean back in time. Through mass spectrometric U-Th dating changes of the subtropical Atlantics radiocarbon balance can be achieved at yet unprecedented age precision and absolute timing. Hence, this project aims to advance our understanding of the marine radiocarbon variability through time and if successful this project will deliver a significantly improved MarCal13 record, which will serve as a benchmark for chronological studies of marine sediments and carbon cycling.