Properties and impact of South Pacific dust over the last four million years

Atmospheric mineral dust is an important component of the global climate system. It influences the Earth’s radiative budget and supplies (micro)nutrients like iron (Fe) to the ocean. The Southern Ocean is a critical region where dust-Fe input enhances primary productivity and thus oceanic uptake of atmospheric CO₂. The climate impact of dust-Fe depends on its total amount and partial solubility of the dust particles releasing Fe to the surface ocean, and the latter critically depends on the rock composition and environmental conditions in the source regions. However, these dust properties are particularly poorly constrained for the Pliocene and Pleistocene time period. Here we present radiogenic neodymium, strontium and lead isotope compositions paired with element concentration data of the dust fraction extracted from marine sediments of IODP Expedition 383 Sites U1540 and U1541 in the subantarctic South Pacific to trace dust provenance and chemical maturity. Our data reveal systematic shifts in the origin and chemical maturity of dust particles from orbital to millennial time scales during major climate transitions of the last four million years. Notably, there is an increase in South American dust contributions from ~40% to 60% across the Northern Hemisphere Glaciation, and from ~30% to 65% during the Mid-Pleistocene Transition. These pronounced changes in dust provenance correspond with shifts toward more pristine mineral compositions of the dust fraction reaching the South Pacific. Tracers of export production such as opal flux indicate a high sensitivity of South Pacific carbon export to the chemical maturity of the dust particles rather than the total dust-Fe input, amplifying export production during the Mid-Pleistocene Transition and across Northern Hemisphere Glaciation.