Systematic changes in circumpolar dust transport to the Subantarctic Pacific Ocean over the last two glacial cycles

The input of the soluble micronutrients iron (Fe) and/or manganese (Mn) by mineral dust stimulates net primary productivity in the Fe/Mn-deficient Southern Ocean. This mechanism is thought to increase carbon export, thus reducing atmospheric CO2 during the Pleistocene glacial cycles. Yet, relatively little is known about changes in the sources and transport pathways of Southern Hemisphere dust over glacial cycles. Here, we use the geochemical fingerprint of the dust fraction in marine sediments and multiisotope mixture modeling to identify changes in dust transport to the South Pacific Subantarctic Zone (SAZ). Our data show that dust from South America dominated the South Pacific SAZ during most of the last 260,000 a with maximum contributions of up to similar to 70% in the early part of the glacial cycles. The enhanced dust-Fe fluxes of the latter parts of the glacial cycles show increased contributions from Australia and New Zealand, but South American dust remains the dominant component. The systematic changes in dust provenance correspond with grain size variations, consistent with the circumpolar transport of dust by the westerly winds. Maximum contributions of dust from more proximal sources in Australia and New Zealand (up to similar to 63%) paired with a finer dust grain size indicate reduced westerly wind speeds over the South Pacific SAZ during deglacial and peak interglacial intervals. These quantitative dust provenance changes provide source-specific dust-Fe fluxes in the South Pacific SAZ and show how their systematic changes in magnitude and timing influence the Southern Ocean dust-Fe feedback on glacial-interglacial to millennial time scales.

Automated summary

The input of soluble micronutrients iron and manganese through mineral dust in the Southern Ocean can stimulate primary productivity and reduce atmospheric CO2 during glacial cycles. Changes in dust sources and transport pathways in the Southern Hemisphere over these cycles remain poorly understood. This study used geochemical fingerprinting and isotopic mixture modeling to identify changes in dust transport to the South Pacific Subantarctic Zone. Results showed that dust from South America dominated the region during glacial cycles, with increased contributions from Australia and New Zealand in later parts of the cycles. These changes in dust provenance corresponded with variations in grain size, indicating the influence of circumpolar transport by westerly winds.