Interplay of North Atlantic freshening and deep convection during the last deglaciation constrained by Iberian speleothems

Abstract

The last deglaciation featured abrupt climate shifts driven by interactions among Earth system components, notably retreating ice sheets and meltwater input. While globally detected, the magnitude, timing, and sequence of North Atlantic meltwater events remain uncertain. We present a Uranium-Thorium-dated stalagmite from northwestern Iberia spanning 24–12 kaBP, capturing both the impact of North Atlantic meltwater on surface ocean chemistry and regional air temperature changes. Our record reveals primarily gradual meltwater inflow during the Last Glacial Maximum and early deglaciation (about 20.8–18.2 kaBP), followed by abrupt increases during Heinrich Stadial 1. The first abrupt cooling is decoupled from the first meltwater pulse, appearing around 810 years later – unlike the timing observed for later pulses. This evolving relationship between meltwater and cooling provides new constraints on the changing sensitivity of deep Atlantic convection to meltwater input throughout the deglaciation.