Rapid climatic response to the Hudson Bay Ice Saddle collapse (~8.6 ka) recorded in Ireland

The Atlantic Meridional Overturning Circulation (AMOC) has shown signs of decline over the last two decades. Climate models project that a continued slowdown of the AMOC will increase precipitation over parts of northern Europe, particularly in the Irish-British Isles¹, with potential impacts on agriculture and related systems. However, the ability of climate models to predict when such changes might occur remains limited, calling for the use of paleoclimate archives. Here, we present a stalagmite‑based paleoclimate record from the west coast of Ireland spanning 11.1–7.7 ka (b2k). Combined Sr/Ca and stable isotope data indicate a sudden increase in precipitation at ~8.6 ka, coincident with the collapse of the Hudson Bay Ice Saddle (HBIS)² and a reduction in eastern North Atlantic bottom and surface currents^3,4. We interpret this hydroclimatic shift as a response to the slowdown of the AMOC caused by the HBIS freshwater discharge, indicating a minimum time lag (of decadal scale) between ocean circulation disruption and atmospheric response. Due to enhanced thermal and pressure gradients over the North Atlantic, a weakened AMOC can favour positive North Atlantic Oscillation (NAO+) conditions, which typically bring wetter and stormier weather over northern Europe. We therefore associate the ~8.6 ka precipitation increase with the development of NAO+ conditions in the region, which aligns with existing work⁵. In addition, our record evidences sustained precipitation throughout the '8.2 ka' cooling anomaly, suggesting that, regardless of temperature direction, heightened precipitation is a persistent consequence of AMOC reduction in northwest Europe.

1: Jackson et al. (2015) Climate Dynamics, 45. 2: Lochte et al. (2019) Nature Communications, 10, 586. 3: Ellison et al. (2006) Science, 312. 4: Thornalley et al. (2009) Nature, 457. 5: Smith et al. (2016) Scientific Reports, 6, 24745.