Plio-Pleistocene Indian Ocean Dipole dynamics and their impact on paleoclimate

The Indian Ocean Dipole (IOD) is a distinct east-west temperature gradient in the Indian Ocean, similar to the El Niño Southern Oscillation in the Pacific. Here, positive IOD (+IOD) events bring warm eastern and cool western sea surface temperatures, and vice versa for negative IOD (-IOD). This temperature seesaw brings increased seasonal rainfall to northeastern Africa while western Australia faces severe droughts during +IOD events. Conversely, -IOD states result in more droughts in Africa and increased precipitation in Australia. In addition to these immediate climatic impacts, possible IOD-driven teleconnections may impact the Australasian Monsoon system, as they (appear to) modulate summer monsoon precipitation over India, Southeast Asia, and possibly Australia.

However, despite its nature as a key climate driver in the Indian Ocean today, little data exists on changes in large-scale IOD patterns in the geologic past, especially in our past understanding of its role in ENSO dynamics. For instance, on glacial-interglacial timescales, sea level-driven exposure of the West Australian Shelf affects Pacific heat transport into the western region of the IOD. These changes were further exacerbated by the ongoing restriction and reorganization of the Indonesian Gateway since 5 Ma ago and the related changes in Pliocene to recent ENSO dynamics.

To disentangle the impact of IOD patterns in the Plio-Pleistocene climatic patterns in the Indo-Pacific region, we present new X-ray fluorescence core scanning data from Ocean Drilling Project (ODP) Site 763 between 2 – 5 Ma ago. These data provide new insights into Australian climate dynamics, which we could then relate to Indo-Pacific Warm Pool (IPWP) changes and the establishment of Late Pliocene to Pleistocene pIOD mean states. Changes in IOD and IPWP sea surface temperature patterns were constructed using a selected set of latitudinal temperature gradients through the equatorial Indo-Pacific. Temperature gradients were calculated using published SST reconstructions based on mixed layer planktonic foraminifer (Trilobatus sacculifer) Mg/Ca records from ODP Site 806 (West Pacific Warm Pool), ODP Site 763 (eastern Indian Ocean) and ODP Site 709 (western Indian Ocean).

Comparison of these data for the first time, reveals the close interconnectivity of tropical climate and oceanographic changes over the study interval. These include Plio-Pleistocene Australian and African hydroclimate trajectories and the contemporary monsoonal precipitation over Southeast Asia. We further pinpoint shifts in the Indian Ocean climate system corresponding to the tectonic restriction of the Indonesian Gateway (3.6 Ma), the Pliocene M2 glacial event (3.3 Ma), and the intensification of Northern Hemisphere glaciation (2.9- 2.7 Ma).

Our results provide insight into the importance of permanent shifts in the Indian Ocean Walker Circulation mean states for near-future climate scenarios. Our recorded IOD mean state shifts highlight the need for further detailed studies to better understand past IOD changes and their associated paleoclimatic impact in the region.