Patagonian dust, Agulhas Current, and Antarctic ice-rafted debris contributions to the South Atlantic Ocean over the past 150,000 years

Disentangling inputs of aeolian dust, ice-rafted debris (IRD), and eroded continental detritus delivered by ocean currents to marine sediments provide important insights into Earth System processes and climate. This study uses Sr-Nd-Pb isotope ratios of the continent-derived (lithogenic) fraction in deep-sea core TN057-6 from the subantarctic Southern Ocean southwest of Africa over the past 150,000 y to identify source regions and quantify their relative contributions and fluxes utilizing a mixing model set in a Bayesian framework. The data are compared with proxies from parallel core Ocean Drilling Program Site 1090 and newly presented data from potential South America aeolian dust source areas (PSAs), allowing for an integrated investigation into atmospheric, oceanic, and cryospheric dynamics. PSA inputs varied on glacial/interglacial timescales, with southern South American sources dominating up to 88% of the lithogenic fraction (mainly Patagonia, which provided up to 68%) during cold periods, while southern African sources were more important during interglacials. During the warmer Marine Isotope Stage (MIS) 3 of the last glacial period, lithogenic fluxes were twice that of colder MIS2 and MIS4 at times, and showed unique isotope ratios best explained by Antarctic-derived IRD, likely from the Weddell Sea. The IRD intrusions contributed up to 41% at times and followed Antarctic millennial warming events that raised temperatures, causing instability of icesheet margins. High IRD was synchronous with increased bioavailable iron, nutrient utilization, high biological productivity, and decreased atmospheric CO2. Overall, TN057-6 sediments record systematic Southern Hemisphere climate shifts and cryospheric changes that impacted biogeochemical cycling on both glacial/interglacial and subglacial timescales.

Impact/Purpose

This manuscript was entirely completed at my former institution, Lamont-Doherty Earth Observatory of Columbia University.  The research deconvolves the sources of sediment to a marine sediment core during the full last glacial cycle (150,000 years ago to present). It utilizes different isotopes (strontium, neodymium, and lead) to create a geochemical fingerprint that is then compared to the geochemical fingerprint of source regions. The most significant finding is that ice rafted debris (IRD), from sediment-laden icebergs, contributed material to the South Atlantic Ocean during marine isotope stage (MIS) 3 (55-35,000 years ago), possibly due to millennial-scale shifts in Southern Hemisphere temperature. This IRD contained highly bioavailable iron, which influenced the biological pump and may be responsible for millennial-scale shifts of 20 ppm in atmospheric carbon dioxide during MIS3. 

Citation

Barkley, A., G. Winckler, C. Recasens, M. Kaplan, B. Koffman, F. Calabozo, J. Middleton, R. Anderson, Y. Cai, L. Bolger, J. Longman, AND S. Goldstein. Patagonian dust, Agulhas Current, and Antarctic ice-rafted debris contributions to the South Atlantic Ocean over the past 150,000 years. National Academy of Sciences, WASHINGTON, DC, 121:e2402120121, (2024). [DOI: 10.1073/pnas.2402120121]

DOI: Patagonian dust, Agulhas Current, and Antarctic ice-rafted debris contributions to the South Atlantic Ocean over the past 150,000 years