Southward displacement of the glacial westerly jet over Asia driven by enhanced Arctic amplification after the Mid-Brunhes Event

Abstract

The climate and paleoenvironmental evolution of the East Asian continent and adjacent Northwest Pacific Ocean is governed by the interplay of the region's dominant features in oceanic and atmospheric circulation, which control the redistribution of heat and moisture. In the atmospheric realm, the subtropical westerly jet stream and East Asian monsoon are crucial components of climate evolution over East Asia, an area that is inhabited by almost half of the world's population. Reconstruction of long-term changes in atmospheric circulation in this region is to date scarce, especially on timescales predating the last glacial-interglacial cycle. Here, we reconstruct dust fluxes, marine productivity and water temperatures in the Northwest Pacific Ocean using lipid biomarkers both from terrestrial and marine organisms and elemental scanning data. Land-plant derived wax lipids in the studied sediments were used as indicators for dust fluxes and hence are representative of past changes in wind strength and pathways. We evaluate changes both in the zonal westerlies and monsoonal winds over the past 1 Ma and across major climatic events. Prior to the Mid-Brunhes Event (MBE; ~ 430 ka ago), concentrations of these compounds showed a distinct glacial-interglacial pattern, which we relate to past changes in the position of the westerly jet stream. We demonstrate substantial changes in wind patterns across the MBE, resulting in reduced dust fluxes to the Northwest Pacific in ensuing glacials. We propose that the westerly jet was permanently located south of the Himalaya-Tibetan Plateau through peak glacials, fostered by amplified Arctic cooling.