Astronomically-Paced Changes in Paleoproductivity, Winnowing, and Mineral Flux Over Broken Ridge (Indian Ocean) Since the Early Miocene

Lyu, J.; Auer, G.; Bialik, O.M.; Christensen, B.; Yamaoka, R.; De Vleeschouwer, D.

Zusammenfassung

A significant shift in Earth's climate characterizes the Neogene, transitioning from a single-ice-sheet planet to the current bipolar configuration. This climate evolution is closely linked to changing ocean currents, but globally-distributed continuous high-resolution sedimentary records are needed to fully capture this interaction. The Ocean Drilling Program (ODP) Site 752, located on Broken Ridge in the Indian Ocean, provides such a Miocene-to-recent archive. We use X-ray fluorescence (XRF) core scanning to build an eccentricity-tuned age-depth model and reconstruct paleoceanographic changes since 23 Ma. We find two intervals of enhanced productivity, during the early and middle Miocene (18.5–13.7 Ma) and late Pliocene/early Pleistocene (3–1 Ma). We also report a mixed eccentricity-obliquity imprint in the XRF-derived paleoproductivity proxy. In terms of grain size, three coarsening steps occur between 19.2–16 Ma, 10.8–8 Ma, and since 2.6 Ma. The steps respectively indicate stronger current winnowing in response to vigorous Antarctic Intermediate Water flow over Broken Ridge in the early Miocene, the first transient onset of Tasman Leakage in the Late Miocene, and the intensification of global oceanic circulation at the Plio-Pleistocene transition. High-resolution iron and manganese series provide a detailed Neogene dust record. This study utilized a single hole from an ODP legacy-site. Nevertheless, we managed to provide novel perspectives on past Indian Ocean responses to astronomical forcing. We conclude that Neogene sediments from Broken Ridge harbor the potential for even more comprehensive reconstructions. Realizing this potential necessitates re-drilling of these sedimentary archives utilizing modern drilling strategies.