Mechanism for enhanced eolian dust flux recorded in North Pacific Ocean sediments since 4.0 Ma: Aridity or humidity at dust source areas in the Asian interior?

Eolian material within pelagic North Pacific Ocean (NPO) sediments contains considerable information about paleoclimate evolution in Asian dust source areas. Eolian signals preserved in NPO sediments have been used as indices for enhanced Asian interior aridity. We here report a detailed eolian dust record, with chemical index of alteration (CIA) and Rb/Sr variations, for NPO sediments from Ocean Drilling Program Hole 885A over the past 4.0 m.y. CIA and Rb/Sr co-vary with the dust signal carried by combined eolian hematite and goethite concentrations. Changes in CIA around the intensification of Northern Hemisphere glaciation (iNHG) event at ca. 2.75 Ma indicate that dust production in source areas was associated mostly with physical and chemical weathering before and after the iNHG event, respectively. We here attribute the eolian flux increase into the NPO across the iNHG event mainly to increased availability of wind-erodible sediment in dust source areas derived from snow and glacial meltwater runoff, which resulted from glacial expansion and enhanced snowfall in the mountains surrounding the Tarim region in response to global cooling. Our results provide a deeper understanding of Asian interior environmental changes in response to global paleoclimate changes, where dust source areas became intermittently moister rather than more arid in response to global cooling.
This study was supported by the National Key R&D Program of China (2016YFA0601903); the National Natural Science Foundation of China (NSFC 41430962); the NSFC-Shandong Joint Fund for Marine Science Research Centers (U1606401); the National Program on Global Change and Air-Sea Interaction (GASI-GEOGE-03); the Australia-New Zealand International Ocean Discovery Program Consortium (ANZIC), which provided Legacy/Special Analytical Funding (ANZIC is supported by the Australian government through the Australian Research Council's LIEF funding scheme [LE140100047], the Australian and New Zealand consortium of universities and government agencies); and the Ocean Drilling Program, which was sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc.