146 / 2024-09-10 00:41:34

Global Ocean Circulation Reorganization Intensified Glacial Cycles during the Mid-Pleistocene Transition

Ocean Circulation,Glacial Cycles,Mid-Pleistocene Transition

The Mid-Pleistocene Transition (MPT, 1300–600 ka) is a crucial period for understanding the mystery of glacial cycles, when it intensified and became asymmetric despite the relatively stable orbital forcing. Previous research has suggested that alterations in ocean circulation may have played a role in the intricate interactions among climate systems during the MPT. However, a worldwide perspective on this circulation reorganization, encompassing its underlying causes, extent, and consequences, has remained elusive. To attain a global understanding of the ocean circulation, we acquired three high-resolution, precisely dated Neodymium isotope (εNd) records across the MPT, along the path of the Deep West Boundary Current of the Pacific Ocean. Results revealed that, substantial circulation reorganization occurred during every glacial period since the first ~100ka glacial cycle (MIS 25-21). The expansion of southern sourced deep water into the Pacific Basin was the dominant feature of glacial periods after the MPT, as shown by the significant εNd negative excursions of Pacific sites, ODP 807 and 1208. In addition, an decreased propotion of North Atlantic Deep Water into the Southern Ocean has also been seen, evidenced by the positive excursions of south Pacific site ODP 1123. Subsequently, we compared model results with compiled global εNd datasets, the result hints that salinity increase of Southern Ocean deep water was the cause of its expansion. Through enhancing ocean carbon storage and decreasing atmospheric CO2, the circulation reorganization might contributing to global cooling and intensification of glaciation. Since this pattern of reorganization has never been seen prior to the first ~100kyr glacial cycle, but recurred during each subsequent glacial period, we propose that the predominance of Southern Ocean deep water among global deep oceans was a determinative feature of the ~100kyr glacial cycles.