East Asian winter monsoon variability during the last 500 thousand years recorded by environmental magnetism of sediments in the Japan Sea

Abstract

The East Asian Winter Monsoon (EAWM) is driven by the dry and cold north-westerly winds blowing from central Asia towards the Western Pacific Ocean as atmospheric high-pressure cell develops over Siberia and Mongolia due to low continental temperatures during boreal winter. Today, the EAWM surface winds together with the prevailing mid-latitude upper troposphere westerly jet (WJ) winds transport hundreds of millions of tons of dust every year across East Asia and/or to the North Pacific and further. Various records of past EAWM and/or WJ variability are available but well-resolved records with (sub)orbital resolution to investigate the dynamics of and relationships between EAWM and WJ are rare. The Japan Sea, as the largest marginal sea located in mid-latitude East Asia, is significantly under the influence of the EAWM and WJ. Previous studies suggest that the composition, concentration, and size of magnetic particles in sediments are sensitive to changes in aeolian dust input. Here, we study the magnetic mineralogy and reconstruct high-resolution continuous environmental magnetic records spanning the last 500 kyrs using sediments cored during Integrated Ocean Drilling Program (IODP) Expedition 346 (Asian Monsoon) at Site U1424 in the Japan Sea. Our results suggest that magnetite is the dominant magnetic phase at Site U1424 and there is a significantly increased contribution of high-coercivity magnetic phase, presumably hematite transported through aeolian dust, in samples from glacial periods. Magnetic grain size proxy (kARM/k) of Site U1424 sediments appears to covary with the population of coarse particles (> ~14 μm) that are dominated by aeolian dust, and shows a striking similarity to published EAWM records, especially during the interglacials and glacial inceptions. During the glacial maxima, largely enhanced EAWM indicated by published records are, however, not shown in the Site U1424 kARM/k record. We suggest that Site U1424 kARM/k is a proxy for dust transportation to the Japan Sea modulated by EAWM intensity as well as interactions between EAWM and the WJ. During the interglacials and glacial inceptions when the main axis of WJ frequently reaches Northern China close to the dust source region of the EAWM, interactions between the EAWM and WJ during winter/spring at mid-level troposphere enable long-distance transportation of coarse dust particles (mainly modulated by EAWM) to the Japan Sea. During the glacial maxima, when the WJ main axis no longer frequently reaches the EAWM source regions, reduced interaction between WJ and EAWM prevented long-distance transportation of coarse dust particles. A conceptual model is also presented to summarise the consequences of changes in EAWM and WJ and their interactions over glacial and interglacial cycles at different locations along the Asian dust transportation pathway.