Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 4 3 2008 10.5194/cpd-4-791-2008 http://www.clim-past-discuss.net/4/791/2008/ http://www.clim-past-discuss.net/4/791/2008/cpd-4-791-2008.html http://www.clim-past-discuss.net/4/791/2008/cpd-4-791-2008.pdf 791 807 2008-06-25 Revisiting the absolute calibration of the Greenland ice-core age-scales L. Skinner luke00@esc.cam.ac.uk Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK Recently, an absolute "calibration" was proposed for the GRIP and GISP2 Greenland ice-core time scales (Shackleton et al., 2004). This calibration attempted to reconcile the stratigraphic integration of ice-core, marine and speleothem archives with the absolute age constraints that marine and speleothem records incorporate. Here we revisit this calibration in light of the new layer-counted chronology of the NGRIP ice-core (GICC05). The GICC05 age-scale differs from the proposed absolute calibration by up to 1200 years late in the last glaciation, with implications both for radiocarbon cycling and the inferred timing of North Atlantic climate events relative to absolutely dated archives (e.g. relative sea-level). By precisely aligning the stratigraphy of Iberian Margin marine cores with that of the Greenland ice-cores, it appears that either: 1) the radiocarbon content of mid-latitude Atlantic surface-waters was extremely depleted (resulting in average surface reservoir ages up to 1700 years prior to ~22 ka BP); or 2) the GICC05 age-scale includes too few years (is up to 1200 years too young). It is shown here that both of these possibilities are in fact correct to some degree. Northeast Atlantic surface reservoir ages should be revised upward by ~350 years, while the NGRIP age-scale appears to be "missing" time. 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