Intensified glacial conditions drove the long-term decrease of the hematite content of Asian dust in an icehouse world

Abstract

Hematite is one of the most stable and common iron oxides in rocks and soils worldwide. Hematite-contained atmospheric dust can affect the global climate by modulating radiative forcing and supplying iron to oceanic ecosystems. The Asian arid and semi-arid regions are one of the most important sources of atmospheric mineral dust in the Northern Hemisphere. Elucidating the spatial and temporal variations of the hematite content of Asian dust in the geological past can provide insights into ancient environments and climates. We conducted detailed diffuse reflectance spectroscopy analyses of the Pleistocene Tajikistan loess, combined with a synthesis of published hematite data for contemporaneous dust sequences in NW China. The results showed a consistent decrease in the hematite content of Asian dust encompassing both glacial and interglacial conditions throughout the Pleistocene. We conclude that intensified glacial conditions led to the decrease in the hematite content of Asian dust, via two dominant pathways: increasing sediment supply and decreasing land surface temperature. This decreasing hematite content of Asian dust may have important influences on the global climate by modulating radiative forcing and carbon cycle on geological time scales.