Low-frequency coupling of the Indian and Pacific Walker circulation modulated by volcanic forcing

Climate variability in the Indian and Pacific Oceans exhibits strong coupling on interannual to decadal timescales. Since the early 2000s, however, synchronization of decadal climate modes between the two basins has decreased due to enhanced greenhouse gas forcing and anthropogenically driven warming of the Indian Ocean. Understanding mechanisms of decoupling is crucial for properly characterizing and predicting low-frequency (decadal-multidecadal) climate variations which have a large impact on regional water resources around the Indian Ocean rim and marine ecosystems.

Here we contextualize the recent inter-basin decoupling by reconstructing Indo-Pacific basin interactions over the past four centuries (1630-2000 CE) through leveraging a compilation of tropical paleoclimate archives and two reconstruction methods. Specifically, we employ a network of coral proxy records from the Indian Ocean, Maritime Continent, and Pacific Ocean, alongside select hydroclimatically-sensitive stalagmite and tree-ring records from the Indian Ocean rim to reconstruct the Indian and Pacific Walker circulations, as well as the Indian Ocean Basin Mode over the past four centuries.

Our results confirm that Indo-Pacific coupling was present throughout the preindustrial era, and was disrupted only by a series of strong tropical volcanic eruptions during the early 19th century. We find, based on last millennium climate model simulations and hemispheric temperature reconstructions, that the interhemispheric asymmetry of cooling in response to volcanic forcing as well as the Indian Ocean’s strong sensitivity to external forcings caused this anomalous decoupling of Indo-Pacific climate. Additionally, the mechanisms of past decoupling associated with volcanism provide insights into the source of inter-model spread on the magnitude of future Indo-Pacific trends.