Bipolar volcanic synchronization of abrupt climate change in Greenland and Antarctic ice cores during the last glacial period

The last glacial period is characterized by a number of abrupt climate events that have been identified in both Greenland and Antarctic ice cores. The mechanisms governing this climate variability remain a puzzle that requires a precise synchronization of ice cores from the two Hemispheres to be resolved. Previously, Greenland and Antarctic ice cores have been synchronized primarily via their common records of gas concentrations or isotopes from the trapped air and via cosmogenic isotopes measured on the ice. In this work, we apply ice-core volcanic proxies and annual layer counting to identify large volcanic eruptions that have left a signature in both Greenland and Antarctica. Generally, no tephra is associated with those eruptions in the ice cores, so the source of the eruptions cannot be identified. Instead, we identify and match sequences of volcanic eruptions with bipolar distribution of sulfate, i.e. unique patterns of volcanic events separated by the same number of years at the two poles. Using this approach, we pinpoint 80 large bipolar volcanic eruptions throughout the second half of the last glacial period (12–60 ka before present). This improved ice-core synchronization is applied to determine the bipolar phasing of abrupt climate change events at decadal-scale precision. During abrupt transitions, we find more coherent Antarctic water isotopic signals (δ18O and deuterium excess) than was obtained from previous gas-based synchronizations, providing additional support for our volcanic framework. On average, the Antarctic bipolar seesaw climate response lags the midpoint of Greenland abrupt δ18O transitions by 122 ± 24 years. The time difference between Antarctic signals in deuterium excess and δ18O, which is less sensitive to synchronization errors, suggests an Antarctic δ18O lag of 152 ± 37 years. These estimates are shorter than the 200 years suggested by earlier gas-based synchronizations. As before, we find variations in the timing and duration between the response at different sites and for different events suggesting an interaction of oceanic and atmospheric teleconnection patterns as well as internal climate variability.