Bipolar ice core constraints on the variability of the Brewer-Dobson Circulation during climate transitions

The Brewer-Dobson circulation is the global atmospheric overturning circulation and regulates global mass and energy redistributions in the stratosphere as well as mass exchange between the troposphere and the stratosphere. Through transporting O₃ to the troposphere and redistributing O₃ in the stratosphere that influence surface UV-B radiation, the Brewer-Dobson circulation also plays an critical role in atmospheric oxidation capacity which matters for air quality, greenhouse gas removal and climate change. While many studies have assessed changes in the Brewer-Dobson circulation in the past few decades and in the future in response to greenhouse gas warming, that how Brewer-Dobson circulation has changed in the past climate is poorly constrained and limited modelling studies reached opposite results on the strength of the Brewer-Dobson circulation in the last glacial maximum (LGM). Atmospheric nitrate O-17 excess signal is sensitive to O₃ abundance, and the latter is influenced by the strength of the Brewer-Dobson circulation especially during climate transitions (e.g., the glacial-interglacial cycle and the abrupt climate events). By comparing the nitrate O-17 excess records from the GISP2 and WAIS divide ice cores, we find a coherent changes in the O-17 excess signal from the LGM to the Holocene, suggesting a stronger Brewer-Dobson circulation in the LGM. In addition, during abrupt climate changes (i.e., the D-O events in Greenland and the corresponding AIM events in Antarctica), there is an apparent difference in the changes of O-17 excess in response to temperature in Greenland and Antarctica, a result implies that the Brewer-Dobson circulation should be enhanced when Greenland cools. These results are consistent with earlier model studies, but are in conflict with recent model work which predicts a weakened Brewer-Dobson circulation in the LGM. Specific mechanisms driving the response of the Brewer-Dobson circulation to past climate changes remains to be explored.