Glacial – Interglacial Changes in Dust Supply to the Pacific Southern Ocean
Final Report Abstract
This project was designed to unravel the role of changes in South Pacific dust provenance during past glacial-interglacial climate variations. It has been hypothesized that the glacial increase in dust supply to the iron-limited Southern Ocean Subantarctic Zone (SAZ) fostered enhanced primary productivity resulting in a net drawdown of atmospheric CO2. This important feedback mechanism was suggested to have forced the climate system towards full glacial states relying on the assumption that glacial-interglacial changes in the Southern Ocean dust input were related to largely synchronized emissions from the three major continental sources in Australia, South America and Africa. However, previous work on South Pacific sediments from late Holocene and the Last Glacial Maximum (LGM) indicate a heterogeneous depositional pattern in the South Pacific with South American contributions dominating in particular in the SAZ. Identifying dust sources and transport routes is important for the understanding of the dust-climate feedback in the Southern Ocean as changes in dust mineralogy (source region) and transport conditions (e.g., length, altitude) affect the solubility of important micronutrients including Fe, thereby affecting the primary productivity in the Southern Ocean. During this project, such reconstructions were carried out by analyzing the geochemical fingerprint of the dust fraction (<5 µm) extracted from South Pacific SAZ sediment core PS75/056-1. The geochemical data were used to quantify the contributions from the individual source regions. Our results show that the dust provenance changed systematically in the South Pacific SAZ over the last 260 ka (ka = kiloanni) in conjunction with previously published independent dust input proxies. The data provide evidence for an overall high contribution of South American dust to the South Pacific over the entire investigated time interval, with increasing proportions of Australian dust towards peak glacial and early deglacial intervals. In contrast, complementary work on sediment core PS58/270-5 shows that dust input alone is insufficient to explain the maxima in lithogenic input fluxes during peak interglacial and early deglacial times in the Southeast Pacific Antarctic Zone (AZ). Instead, the lithogenic input was probably linked with drifting ice. Importantly, the maxima in lithogenic input in the AZ correspond with shifts in sediment geochemistry over the last four glacial cycles, suggesting that reduced Fe solubility of the lithogenic input muted the primary productivity in the Southeast Pacific AZ.
Publications
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Systematic changes in circumpolar dust transport to the Subantarctic Pacific Ocean over the last two glacial cycles. Proceedings of the National Academy of Sciences, 119(47).
Struve, Torben; Longman, Jack; Zander, Martin; Lamy, Frank; Winckler, Gisela & Pahnke, Katharina
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Systematic changes in dust transport to the Subantarctic Pacific Ocean over the last two glacial cycles. International Conference on Paleoceanography 14. Bergen, Norway
Torben Struve; Jack Longman; Martin Zander; Frank Lamy; Gisela Winckler & Katharina Pahnke
