WG1: Chronology

Dating and Chronological Modeling

Precise correlation between high precision palaeoclimate archives over the last 60,000 years is critical to gain a better understanding of the exact timing and, hence, mechanisms of past climate change. The abrupt climatic changes in this time-frame occur at millennial to centennial scales and developing and integrating independent chronologies with this level of resolution is a core goal of IMTIMATE. The INTIMATE approach is the key here, as only by detailed comparison of different chronologies can we assess the reliability of comparison between records. INTIMATE scientists have been at the forefront of developing key protocols for developing this research over a number of years, and have pioneered high precision comparison of ice core and radiocarbon chronologies (e.g. Lowe et al, 1995; Blockley et al., 2004). One key issue is building on the improvements in radiocarbon dating and radiocarbon calibration. Although considerable effort has been expended in developing continuous ‘comparison’ curves to encompass the entire dating range of 14C (e.g. Hughen et al., 2007), an internationally accepted calibration record based on absolutely dated tree ring records only spans the last 12,400 years ago (IntCal04; Reimer et al., 2004). To most effectively compare datasets through this period this Action will exploit the latest radiocarbon datasets such as the developing Lake Suigetsu terrestrial calibration curve. Key to the INTIMATE approach, however, has been the integration of several dating methods to underpin radiocarbon-based chronologies and to set up an event stratigraphical approach to compare records (Lowe et al., 2008). Chronological control will thus be augmented by new varved sequences in Europe and Asia, time-parallel marker horizons in the form of pan-European tephra, Greenland ice core reconstructions and geomagnetic excursions (e.g. Rasmussen et al., 2006; Blockley et al., 2007; Turney et al., 2008). Protocols for the development and application of these methods and their interpretation (including Bayesian modelling using the software programme OxCal) will be developed, and the outcomes of this will be used to help INTIMATE members develop precise and accurate chronological models during COST workshops and other meetings.