ORBITAL TO MILLENNIAL-SCALE DRIVERS OF SOUTHERN HEMISPHERE MID-LATITUDE CLIMATE OVER THE PAST 50KA

The climate of the mid-latitudes is dominated by the westerlies, which are an important component of the climate system - transmitting heat and energy between the low and high latitudes. In the Southern Hemisphere, the position of the westerlies may also influence Southern Ocean carbon storage through ventilation, acting as a critical feedback mechanism for driving changes in atmospheric CO₂ and global climate. However, there remain few long, high-resolution climate records from the Southern Hemisphere mid-latitudes capable of reconstructing these changes, particularly on millennial timescales. Here, we use measurements of leaf wax hydrogen isotopes and the MBT5ME’ paleotemperature index to reconstruct climate variability in the southern mid-latitudes over the past 50 ka from the Pupuke maar lake system on the North Island of New Zealand. We use an analysis of modern precipitation isotopes to demonstrate that leaf wax hydrogen isotope values reflect the position of the westerlies through seasonal changes in moisture source. The Lake Pupuke record shows that the westerlies shifted in phase with the Intertropical Convergence Zone on a range of timescales (e.g., glacial, millennial, Holocene) throughout the record, reflecting the dominant role of interhemispheric temperature gradients in driving global atmospheric circulation responses to climate forcing. In contrast, temperature variations at Lake Pupuke show a signal more consistent with changes in Antarctica, suggesting that high latitude millennial-scale warming and cooling events propagated at least into the Southern Hemisphere midlatitudes, with differences in the magnitudes of these events potentially indicating changes in heat transport and delivery across the Southern Ocean. The decoupling of local temperature and isotope-inferred precipitation suggests an important role for remote forcings in driving the climate and atmospheric circulation of the mid-latitudes.