[M-IS06] Evolution and variability of the Tropical Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS06-01] Western Pacific Warm Pool view of prolonged El Niño-like conditions during the Late Miocene

★Invited Papers

*Anna Joy Drury^1,2,3, Thomas Westerhold³, Nina Rohlfs³, Ze Tao², Ana-Christina Ravelo⁴, Bridget Wade² (1.School of Geography, Geology and the Environment, University of Leicester, 2.Department of Earth Sciences, University College London, UK, 3.MARUM, University of Bremen, Germany, 4.Ocean Sciences Department, University of California, USA)

Keywords:Late Miocene, Permanent El Niño, Foraminifera , Stable isotope geochemistry

The Late Miocene is characterised by warmer-than-present conditions with temperatures comparable to those predicted for 2100. It is important to understand how equatorial Pacific climate systems such as the El Niño Southern Oscillation (ENSO) were impacted during past global warmth. The presence of long-term El Niño-like conditions in the equatorial Pacific remains ambiguous, with several studies proposing either 1) a permanent Late Miocene El Niño-like state (e.g., Ravelo et al., 2014), 2) alternating El Niño-like (9.6-6.5 Ma) and La Niña-like (6.5-6.1 Ma) conditions (e.g., Nathan and Leckie, 2009; Drury et al., 2018), or 3) modern thermal gradients since ~12 Ma (e.g., Zhang et al., 2014). As the modern ENSO system causes significant global precipitation and temperature anomalies, reconciling these disparate views of prolonged El Niño-like conditions during the Late Miocene is a key step towards understanding the potential global impacts of long-term warming in the equatorial Pacific.

The scarcity of suitable archives coupled with low-resolution data in the Western Pacific Warm Pool (WPWP) hindered clarification of the Late Miocene permanent El Niño status. The recovery of International Ocean Discovery Program (IODP) Site U1488 during IODP Expedition 363 to the WPWP provided key material to resolve this issue. We generated high-resolution (2.5 kyr) mixed layer, thermocline and benthic foraminiferal stable oxygen (δ¹⁸O) and carbon (δ¹³C) isotope stratigraphies to reconstruct the evolution of water column structure in the WPWP between ~10 and 6 Ma. We integrate our new WPWP records with high-resolution foraminiferal data from the eastern equatorial Pacific. Our initial findings provide insight into the extent of prolonged El Niño-like conditions during the Late Miocene, and how these conditions may have impacted heat transport and carbon cycling in the equatorial Pacific Ocean.