Tracing Tasman Leakage since the middle Miocene

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The southern hemisphere oceans are strongly coupled. The exchange of water and heat between the South Pacific, Indian and South Atlantic oceans is fundamental to the global thermohaline circulation. However, the relevance of interocean exchange at intermediate water depths between the Pacific and Indian oceans has only recently been established for the present-day. Different contemporary oceanographic models identify significant transport from the Pacific into the Indian Ocean at ~1000 m water depth, originating in the Tasman Sea. The so-called Tasman Leakage has however never been identified in a paleoceanographic context. This proposal aims to evaluate the onset of this pathway of interocean exchange, and is designed to constrain Tasman Leakage variability in response to climatic (north-south migration of climate belts) as well as to tectonic processes (northward movement of the Australian continent). Ocean Drilling Program (ODP) Sites 752 and 754 on Broken Ridge (eastern Indian Ocean) provide well-suited sedimentary archives to address these questions: Both sites are situated within the Tasman Leakage flow path, at a present-day intermediate water depth of ~1070 m. Their late Oligocene to recent intervals consist of sub-horizontal pelagic carbonate-rich sequences that allow for the use of different isotopic and elemental proxies. When compared to a series of existing sedimentary archives in the southern Indian Ocean and southwest Pacific, the newly-generated proxy records for Site 752 and 754 will provide a unique opportunity to evaluate the role of Tasman Leakage in regulating Pacific-Indian Ocean exchange since the late Oligocene.