Asian-Australian monsoon evolution over the last millennium linked to ENSO in composite stalagmite δ18O records

The Asian-Australian monsoon (AAM) system distinctly influences global climate. However, the linkage between ENSO (El Niño–Southern Oscillation) and AAM is still poorly understood over the last millennium. Here, we combined stalagmite δ18O (δ18Os) records with exceptionally high-resolution and high-precision chronologies to demonstrate a tight remote coupling between AAM and tropical ocean hydrology on the multi-year, decadal, and centennial timescales. Our results reveal that (1) There is a significant negative correlation between the multi-year weighted average precipitation δ18O (δ18Oaw) from the AAM and Southern Oscillation Index (SOI), providing a modern analogous coupling for linking stalagmite δ18O (δ18Os) and ENSO over the past 100 years. (2) Over the last millennium, the integrated δ18Os record exhibit positive excursions during the Little Ice Age (LIA), marked by a tendency for more El Niño-like state conditions in the tropical Pacific, which is consistent in SST-gradient ENSO reconstruction but different to precipitation reconstruction. (3) Wavelet and power spectrum analysis for the integrated δ18Os record in the AAM region show that there is a significant multi-year periodicity (2.2, 2.8, 3.5, 4.6 yr), conceding with the ENSO cycle (2–7 yr), whereas, some multi-decadal and centennial cycles (10.1, 17, 28.6, 52.7, 143 yr) are significant too. We provide evidence from instrumental and paleocliamte datasets (GNIP and NOAA) and propose a possible “circulation effect” mechanism responsible for variations of δ18Os in the East Asian Monsoon (EAM) and Australian Monsoon (AM) region over the last millennium.