Intensified NAO-South Asian Monsoon teleconnection during the Little Ice Age: Insights from speleothem records

The North Atlantic Oscillation (NAO) exerts a dominant influence on atmospheric circulation in Northern Hemisphere, yet its impact exhibits substantially nonstationary across decadal to centennial timescales, particularly in its interaction with the South Asian Summer Monsoon (SASM) at its downstream terminus. Here, we present a high-resolution (1.2-year) speleothem δ¹⁸O record from the northern boundary of Sichuan Basin, southwest China. When combined with high-resolution speleothem records from the broader SASM domain, it reveals a marked intensification of the positive coherence between the NAO and SASM during the Little Ice Age (1580–1880 CE). In contrast to the solar-driven dynamics of the Medieval Warm Anomaly, the positive NAO–SASM coupling appears to persist into the contemporary period of anthropogenic global warming. It indicates a distinct response of the NAO-SASM coherence to the warming climates. These findings offer novel insights into the complex, coupled dynamics between the NAO and monsoon systems, and highlight the important role of the internal variability in the SASM in the context of future climate scenarios.