Late Miocene‐Pliocene Vigorous Deep‐Sea Circulation in the Southeast Indian Ocean: Paleoceanographic and Tectonic Implications

Deep ocean circulation in the Southern Hemisphere plays a central role in global ocean overturning circulation and determines ocean carbon sink variability on multimillion‐year timescales. For this reason, it is important to understand how deep currents that originate in the Southern Ocean responded to past climate fluctuations and changing temperature patterns in the Southern Hemisphere oceans. To investigate this feedback mechanism, we analyze deep‐sea sediment cores formed under the influence of bottom currents from the Mentelle Basin (International Ocean Discovery Program Sites U1513, U1514, and U1516), in the Southeastern Indian Ocean. We show that bottom current activity intensified in the Australian‐Antarctic Basin during the cooling intervals of the late Miocene (ca. 7.8–4.8 Ma) and late Pliocene (ca. 3.59–3.2 Ma). At those intervals, bulk grain‐sizes and terrigenous input increased, via current winnowing. Ferromanganese nodules and stratigraphic hiatuses are also observed within these periods, indicative of intense sediment erosion at the seafloor. Sediment accumulation and preservation in the basin was particularly low at the deep Site U1514 (3,838 m water depth), suggesting that enhanced current transport and sediment erosion occurred preferentially within the deepest parts of the basin. We suggest that bottom water fluxes in the Australian‐Antarctic Basin intensified during late Miocene and Pliocene cooling intervals, likely boosted by renewed Australian‐Antarctic Discordance spreading since the Miocene. Key Points Deep‐water transport in the Australian–Antarctic Basin intensified during Neogene cooling intervals Intervals of winnowing favored the preservation of coarser terrigenous packages, the formation of hiatuses and ferromanganese nodules Renewed rifting in the Australian–Antarctic Discordance in the Miocene may have boosted bottom water fluxes into the Mentelle Basin