Summary
Ice core records from Antarctic and Greenland have revealed that the last deglaciation (ca. 19,000 to 11,000 years before present) was accompanied by a ca. 80 ppmv increase in atmospheric CO2 and a sequence of large, hemispheric climate variations. Precise information on the relative timing of these north-south climate variations and their relation with the rise in CO2 is a key to resolving questions concerning the mechanisms which force and couple climate changes between the hemispheres. Here we present a series of records for the deglaciation: a proxy for regional Antarctic temperature derived from a composite of four high-dating-precision Antarctic ice cores (Law Dome, Siple Dome, Byrd, EPICA Dronning Maud Land); a proxy for regional Greenland temperature constructed from the North-Greenland ice core; and two ice core records of atmospheric CO2 (from Byrd and Siple Dome). All records are synchronised to the common Greenland Ice Core 2005 Chronology (GICC05), using dating ties provided by fast variations in global methane gas concentrations. Warming (and cooling) trends in Antarctica closely match cold (and warm) periods in Greenland on both millennial and sub-millennial timescales, and there is little to no time lag between trend changes in Antarctica and abrupt climate transitions in Greenland. This pattern may be explained by shifts in the balance of meridional ocean heat flux between the hemispheres, consistent with the bipolar seesaw hypothesis. The deglacial CO2 rise is highly correlated with Antarctic temperature (r2 = 0.95 with Byrd CO2, r2 = 0.96 with Siple CO2). Detailed lag-correlation analysis, suggests that the deglacial CO2 rise trailed the Antarctic temperature rise by between 0-400 yr. This lag is substantially shorter and more tightly constrained than the most often cited previous estimate of 200-1400 y. The observed timing constraints provide important new criteria for testing theoretical and numerical models which seek to explain the pattern of climate evolution during the deglaciation.