Heat export from the tropics drives mid to late Holocene palaeoceanographic changes offshore southern Australia

• Published in: Quaternary Science Reviews
• Main Authors: Perner, Kerstin, Moros, Matthias, De Deckker, Patrick, Blanz, Thomas, Wacker, Lukas, Telford, Richard J., Siegel, Herbert, Schneider, Ralph, Jansen, Eystein
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon-Elsevier Ltd
• Subjects: Planktic foraminifer; Sea surface temperature; Palaeoceanography; ENSO; Holocene; Southern Ocean; Australia; Pacific; North Atlantic
• Online Access: http://hdl.handle.net/1885/232672; https://doi.org/10.1016/j.quascirev.2017.11.033; https://openresearch-repository.anu.edu.au/bitstream/1885/232672/3/01_Perner_Heat_export_from_the_tropics_2018.pdf.jpg

The Leeuwin Current (LC), an eastern boundary current, transports tropical waters from the Indo-Pacific Warm Pool (IPWP) towards southern latitudes and modulates oceanic conditions offshore southern Australia. New, high-resolution planktic foraminifer assemblage data and alkenone-derived sea surface temperatures (SST) provide an in-depth view on LC variability and mechanisms driving the current's properties during the mid to late Holocene (last c. 7.4 ka BP). Our marine reconstructions highlight a longer-term mid to late Holocene reduction of tropical heat export from the IPWP area into the LC. Mid Holocene (c. 7.4 to 3.5 ka BP) occurrence of high SSTs (>19.5 °C), tropical planktic foraminifera and a well-stratified water column document an enhanced heat export from the tropics. From c. 3.5 ka BP onwards, a weaker LC and a notably reduced tropical heat export cause oceanic cooling offshore southern Australia. The observed mid to late Holocene trends likely result from large-scale changes in the IPWP's heat storage linked to the El Niño-Southern Oscillation (ENSO) phenomenon. We propose that a strong and warm LC occurs in response to a La Niña-like state of ENSO during the mid Holocene. The late Holocene LC cooling, however, results from a shift towards an El Niño-like state and a more variable ENSO system that causes cooling of the IPWP. Superimposed on these longer-term trends we find evidence of distinct late Holocene millennial-scale phases of enhanced El Niño/La Niña development, which appear synchronous with northern hemispheric climatic variability. Phases of dominant El Niño-like states occur parallel to North Atlantic cold phases: the ‘2800 years BP cooling event’, the ‘Dark Ages’ and the ‘Little Ice Age’, whereas the ‘Roman Warm Period’ and the ‘Medieval Climate Anomaly’ parallel periods of a predominant La Niña-like state. Our findings provide further evidence of coherent interhemispheric climatic and oceanic conditions during the mid to late Holocene, suggesting ENSO as a potential mediator. This ...