MILLENNIAL-SCALE AND DEGLACIAL CHANGES IN THE SOUTHERN HEMISPHERE WESTERLIES DRIVEN BY NORTHERN HEMISPHERE CLIMATE

The Southern Hemisphere westerly wind belt (SHWW) is one of the major features of the Earth’s atmospheric circulation and has been predicted to play a major role in Southern Hemisphere climate changes in the future. Despite the importance of this system, the processes that control the long-term behavior of the SHWW are not well understood. Here, we present compound-specific hydrogen isotope (δD_wax) and branched GDGT-derived temperature from Lake Pupuke, New Zealand (36°78.30’S, 174°76.70’E) to independently reconstruct the mid-latitude hydroclimate and temperature variations spanning the last 45,000 years. We argue that Lake Pupuke δD_wax, as a proxy for the isotopic composition of rainfall, reflects changes in the moisture sources driven by the changes in the northern edge of the SHWW in the southwestern Pacific, based on our investigation of the hydrogen isotope variability in the modern rainfall. We find that Lake Pupuke temperature changes are synchronous and coherent with Antarctic temperature variability on orbital to millennial timescales – suggesting coherent, hemisphere-wide temperature variations over the past 45,000 years. However, dD_wax data show that changes in the SHWW occurred synchronously with Northern Hemisphere climate changes. This implies that Northern Hemisphere climate exerts a dominant control on the response of the SHWW, irrespective of changes in the Southern Hemisphere mid and high latitude climate conditions. We propose that reconstructed changes in the position of the SHWW are driven by the changes in the Hadley circulation as it responds to the perturbations in the northward, cross-equatorial heat transport of the Atlantic Ocean, through its influence on the position and strength of the westerly jet modulated by the strength of the South Pacific subtropical jet.