A series of studies conducted as part of this project point to the role of Indo-Pacific climate variability beyond the well-known El Nino-Southern Oscillation as key driver of tropical hydroclimate across a range of time scales. The project outcomes are built on a synthesis of state-of-the-art climate model simulations with paleo proxy records from a variety of different environmental archives, such as stalagmites, tree-rings, corals, and sediments. In particular, we highlight synchronicity between the Australian and Asian summer monsoon systems in the late Holocene: we used new highly-resolved stalagmite records from Northern Australia to demonstrate that the tropical rain belt has expanded and contracted on multidecadal to centennial time scales throughout the past 3,000 years. Furthermore, the width of the tropical rain belt over the Austral-Asian sector is modulated throughout the Last Millennium on multidecadal time scales by the Interdecadal Pacific Oscillation, a climate phenomenon in the Pacific that affects the climate across the tropics. A tree-ring based reconstruction of the Interdecadal Pacific Oscillation reveals that this climate phenomenon has been actively influencing tropical hydroclimate across the Indo-Pacific for at least 700 years, with more than a dozen positive and negative phases going back to 1350 C.E.

The Interdecadal Pacific Oscillation has also been determined to be a major player in the expansion of the tropics over the past few decades, especially for the Northern Hemisphere; in contrast, the Southern Hemisphere expansion of the tropical belt since the 1970s appears to have a robust anthropogenic component. These results are consistent across a variety of different metrics related to the global zonal atmospheric circulation, both near-surface and at height, as well as measures related to the tropical and subtropical surface water balance. The highly-resolved Northern Australian stalagmite records provide a crucial long-term context of the southern edge of the tropics, which is much less defined from proxy reconstructions than its Northern Hemisphere counterpart.

The Interdecadal Pacific Oscillation furthermore plays a key role for changes in the frequency of the dominant climate mode in the Indian Ocean, the Indian Ocean Dipole, as seen in clustering of these events on multidecadal time scales from coral reconstructions extending back to 1240 C.E. More recently, robust signals in heat and freshwater changes seen in observations and proxy records across the Indo-Pacific warm pool and into the Indian Ocean since the 1990s, can largely be associated with multidecadal variability associated with the Interdecadal Pacific Oscillation.

Research findings are of importance for adjacent disciplines in hydrology, water resource management, seasonal forecasting, and decadal predictions in regions affected by Indo-Pacific climate variability associated with the Indian Ocean Dipole, the El Nino-Southern Oscillation, and the Interdecadal Pacific Oscillation.

The project so far led to a series of peer-reviewed publications and conference presentations (12 papers, 1 book chapter, 17 conference talks/posters), many of which with involvement of students and early-career researchers. Specifically, this project allowed for educational opportunities for undergraduate students to gain valuable hands-on experiences in interdisciplinary research in the field of paleoclimate, atmospheric science, oceanography, climate dynamics, and climate modeling at WHOI. Two undergraduate students conducted research related to this project at WHOI, including topically-related honors theses at their home institutions, and both of them are now enrolled in PhD programs.

Last Modified: 09/29/2020
Modified by: Caroline C Ummenhofer