Bipolar volcanic ice-core synchronization of the last glacial cycle

Precise synchronization of climate records is essential for deducing the dynamics of the climate system. Ice cores from the Greenland and Antarctic ice sheets have previously been synchronized by the use of cosmogenic isotopes, gas concentrations, and traces of large volcanic eruptions. Identification of identical sequences of volcanic sulfate depositions at both poles have been applied to synchronize ice cores in the Holocene, in the last deglaciation, in Marine Isotope Stage 3 (MIS3) and around the Indonesian Toba eruption occurring close to 74 ka. We now extend this inter-hemispheric volcanic synchronization approach to also cover MIS2 (16.5-24.5 ka BP), MIS4 and part of MIS5 (60-110 ka BP) allowing for a precise bipolar synchronization of the entire last glacial period. The synchronization is based on some 250 volcanic eruptions that are identified as acidity spikes in both Greenland and Antarctica. Similar to previous work, the identification of volcanic sequences at the two poles is supported by annual layer counting in both Greenland and Antarctica, although the identification of annual layers becomes increasingly difficult with depth. To support the synchronization we investigate the deduced annual layer thicknesses (not requiring layer counting) and the inferred depth-depth relation between synchronized ice cores. The precise bipolar synchronization allows to determine the exact inter-hemispheric phasing of abrupt climate change during the last glacial, and to investigate a possible relation between abrupt climate change and volcanism. Furthermore, the frequency and magnitude of large volcanic eruptions of the last glacial can be established.