Preprints
https://doi.org/10.5194/cp-2021-151
https://doi.org/10.5194/cp-2021-151

  24 Nov 2021

24 Nov 2021

Review status: this preprint is currently under review for the journal CP.

Plio-Pleistocene Perth Basin water temperatures and Leeuwin Current dynamics (Indian Ocean) derived from oxygen and clumped isotope paleothermometry

David De Vleeschouwer1, Marion Peral2, Marta Marchegiano2, Angelina Füllberg1, Niklas Meinicke1, Heiko Pälike1, Gerald Auer3, Benjamin Petrick4, Christophe Snoeck2,5, Steven Goderis2, and Philippe Claeys2 David De Vleeschouwer et al.
  • 1MARUM - Center for Marine Environmental Sciences, University of Bremen, Klagenfurterstr. 2-3, 28359 Bremen, Germany
  • 2Analytical, Environmental, and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
  • 3Institute of Earth Sciences (Geology and Paleontology), University of Graz, Heinrichstraße 26, 8010 Graz, Austria
  • 4Paleontology and Historical Geology, Kiel University, Ludewig-Meyn-Str. 14 R.12, 24118 Kiel, Germany
  • 5Maritime Cultures Research Institute, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium

Abstract. The Pliocene sedimentary record provides a window into Earth’s climate dynamics under warmer-than-present boundary conditions. However, the Pliocene cannot be considered a stable warm climate that constitutes a solid baseline for middle-road future climate projections. Indeed, the increasing availability of time-continuous sedimentary archives (e.g., marine sediment cores) reveals complex temporal and spatial patterns of Pliocene ocean and climate variability on astronomical timescales. The Perth Basin is particularly interesting in that respect because it remains unclear if and how the Leeuwin Current sustained the comparably wet Pliocene climate in West-Australia, as well as how it influenced Southern Hemisphere paleoclimate variability. To constrain Leeuwin Current dynamics in time and space, this project constructed a new orbitally-resolved planktonic foraminifera (Trilobatus sacculifer) stable isotope record (δ18O and clumped isotopes Δ47) for the Plio-Pleistocene (4–2 Ma) interval of International Ocean Discovery Program (IODP) Site U1459. It complements an existing TEX86 record from the same site and similar planktonic isotope records from the Northern Carnarvon Basin (ODP Site 763 and IODP Site U1463). The comparison of TEX86 and Δ47 paleothermometers reveals that TEX86 likely reflects sea surface temperatures (SST, 23.8–28.9 °C), whereas T. sacculifer Δ47 calcification temperatures probably echo the state of the lower mixed layer and upper thermocline at the studied Site U1459 (18.2–20.8 °C). The isotopic δ18O gradient along a 19° S–29° S latitudinal transect, between 3.9–2.2 Ma, displays large variability, ranging between 0.5 and 2.0 ‰, whereby a low latitudinal gradient is indicative of a strong Leeuwin Current and vice versa. These results challenge the interpretation that suggested a tectonic event in the Indonesian Throughflow as the cause for the rapid steepening of the isotopic gradient (0.9 to 1.5 ‰) around 3.7 Ma. The tectonic interpretation appears obsolete as it is now clear that the 3.7 Ma steepening of the isotopic gradient is intermittent, with flat latitudinal gradients (~0.5 ‰) restored in the latest Pliocene (2.9–2.6 Ma). Still, the new analysis affirms that a combination of astronomical forcing of wind patterns and eustatic sea level controlled Leeuwin Current intensity. A period of relatively weak Leeuwin Current between 3.7 and 3.1 Ma is advocated; a time interval also marked by cooler conditions throughout the Southern Hemisphere. In conclusion, the intensity of the Leeuwin Current and the latitudinal position of the subtropical front are rooted in the same forcing: Heat transport through the Indonesian Throughflow (ITF) valve propagated to the temperate zone through Indian Ocean poleward heat transport. The common ITF forcing explains the observed coherence of Southern Hemisphere ocean and climate records.

David De Vleeschouwer et al.

Status: open (until 19 Jan 2022)

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David De Vleeschouwer et al.

David De Vleeschouwer et al.

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Short summary
The Leeuwin Current transports warm water along the western coast of Australia: from the tropics to the Southern Hemisphere mid-latitudes. Therewith, the current influences climate in two ways: First, as a moisture source for precipitation in southwest Australia. Second, as a vehicle for equator-to-pole heat transport. In this study, we study sediment cores along the Leeuwin Current pathway to understand its ocean-climate interactions between 4–2 Ma.