07 Apr 2022
07 Apr 2022
Status: this preprint is currently under review for the journal CP.

Leeuwin Current dynamics over the last 60 kyrs – relation to Australian extinction and Southern Ocean change

Dirk Nürnberg1, Akintunde Kayode1, Karl J. F. Meier2, and Cyrus Karas3 Dirk Nürnberg et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, D-24148 Kiel, Germany
  • 2Institute of Earth Science, Heidelberg University, Im Neuenheimer Feld 234, Heidelberg D-69120, Germany
  • 3Universidad de Santiago de Chile, Av. Bernardo O’Higgins 3363, Santiago, Chile

Abstract. The Leeuwin Current flowing southward along West Australia is an important conduit for the poleward heat transport and interocean water exchange between the tropical and the subantarctic ocean areas. Its past development, and its relationship to Southern Ocean change and to Australian ecosystem response, however is largely unknown. We here reconstruct sea surface and thermocline temperatures and salinities from foraminiferal-based Mg/Ca and stable oxygen isotopes from offshore southwest and southeast Australia reflecting the Leeuwin Current dynamics over the last 60 kyrs. Its variability resembles the biomass burning development in Australasia from ~60–20 ka BP implying that climate-modulated changes related to the Leeuwin Current most likely affected Australian vegetational and fire regimes. In particular during ~60–43 ka BP, warmest thermocline temperatures point to a strongly developed Leeuwin Current during Antarctic cool periods when the Antarctic Circumpolar Current weakened. The pronounced centennial-scale variations in Leeuwin Current strength appear in line with the migrations of the Southern Hemisphere frontal system and are captured by prominent changes in the Australian megafauna biomass. We argue that the concerted action of a rapidly changing Leeuwin Current, the ecosystem response in Australia, and human interference since ~50 BP enhanced the ecological stress on the Australian megafauna until a tipping point was reached at ~43 ka BP, after which faunal recuperation no longer took place. While being weakest during the last glacial maximum, the deglacial Leeuwin Current intensified at times of poleward migrations of the Subtropical Front. During the Holocene, the thermocline off South Australia was considerably shallower compared to the short-term glacial and deglacial periods of Leeuwin Current intensification.

Dirk Nürnberg et al.

Status: open (until 10 Jun 2022)

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Dirk Nürnberg et al.

Dirk Nürnberg et al.


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Short summary
Did climate or humans caused glacial/interglacial vegetational re-constellations in Australia, and the extinction of the exotic megafauna at ~43 ka BP? We highlight the role of the rapidly varying Leeuwin Current for the Australian ecosystem change. We note that the concerted action of a weakening Leeuwin Current, the ecological response, and human interference enhanced the ecological stress on the megafauna until a tipping point was reached, after which faunal recuperation no longer took place.