Abstract
Abstract 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.
Highlights
Asian interior dust source areas provide large quantities of eolian dust that is carried by westerlies to the North Pacific Ocean (NPO; Maher, 2011; Prospero et al, 2002; Ziegler and Murray, 2007)
RelHm+Gt (Fig. 2E) and operationally defined eolian dust (ODED) content (Fig. 2F) variations have strong similarities, especially around the intensification of Northern Hemisphere glaciation (iNHG) event, where they increase synchronously at 2.75 Ma and subsequently enter a high-eolian-input period, which further confirms that RelHm+Gt is a reliable eolian proxy
Pre-iNHG data lie below the threshold for chemical weathering, and corresponding chemical index of alteration (CIA) values are less than that of the upper continental crust (UCC; Taylor and McLennan, 1985), which indicates that eolian materials are physical weathering products with no significant chemical alteration before 2.75 Ma
Summary
Asian interior dust source areas provide large quantities of eolian dust that is carried by westerlies to the North Pacific Ocean (NPO; Maher, 2011; Prospero et al, 2002; Ziegler and Murray, 2007). Eolian dust archived in pelagic NPO sediments provides valuable insights into paleoclimate changes over different time scales (Rea, 1994). Ocean Drilling Program (ODP) Hole 885A is located downwind of Asia and is sufficiently far from the continent to preclude riverine inputs and ice-rafted debris influences (Snoeckx et al, 1995). Sediments from this hole are sourced from the Tarim Basin and adjacent deserts (Pettke et al, 2000). Interpretation of eolian proxies remains controversial (Pye, 1989; Prospero et al, 2002), and it is necessary to assess how eolian materials are produced within dust source areas in response to paleoclimate changes
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