Progressive declines in Pacific Antarctic Zone upwelling intensity during each glaciation of the last 460 ka

The long 100,000-year glacial-interglacial cycles are key features of climate evolution since the Mid-Pleistocene Transition, and changes in the Southern Ocean are proposed to have played an important role in the generation of these cycles. Data from the Indian and Pacific sectors of the Antarctic Zone over the last 150 ka show that during the glacial intervals, export production decreased, and surface nitrate concentration, as reflected by d¹⁵N of organic matter bound in diatom frustules (d¹⁵N_db), decreased. Together these findings suggest that upwelling was weaker in the Antarctic Zone during the ice ages. Here we report ~2-kyr resolution d¹⁵N_db measurements from the Pacific sector of the Antarctic Zone extending to the past 460 ka, with chronology supported by TEX₈₆^L-paleotemperature proxy correlation with air temperature reconstructed from Antarctic ice cores. The results show continuously increasing Antarctic Zone d¹⁵N_db during peak glacial periods. This suggests progressive declines in surface nitrate concentration and, thus, in upwelling and/or vertical mixing intensity as land ice sheets grew, even though Antarctic ice core temperature and atmospheric CO₂ appear to have stabilized at their minima earlier in each ice age. This correlation points to an interhemispheric mechanism that links southern high-latitude conditions to northern high-latitude ice buildup during peak glacial intervals. We will discuss the implications for the saw-tooth pattern of the 100,000-year glacial-interglacial cycles and for carbon cycle feedbacks within these 100,000-year cycles.