A speleothem record of glacial (25–11.6 kyr BP) rapid climatic changes from northern Iberian Peninsula

Low and high frequency climatic fluctuations in northern Iberian Peninsula during the last glacial maximum (LGM) and deglaciation are documented in a stalagmite using δ18O and δ13C and hydrologically sensitive trace metal ratios Mg/Ca and Ba/Ca. U/Th dating indicates speleothem growth commenced at 25 kyr BP (Present = year 1950) and extended to 11.6 kyr BP making this one of few European speleothem growing during the last glacial period. Rapid climatic fluctuations as Heinrich event 2 (H2) and Greenland Interstadial (GI-) 2 are well characterized in this record by more arid and cold conditions and by more humid conditions, respectively. Speleothem growth ceased from 18.2 to 15.4 kyr BP (the so-called Mystery Interval) likely reflecting the driest and potentially coldest conditions of this record, coincident with the 2 kyr duration shutdown of the North Atlantic Meridional Overturning Circulation (MOC). A major gradual increase in humidity and possibly in temperature occurred from 15.5 to 13.5 kyr BP, beginning in the Bølling and culminating in the Allerød period. This gradual humidity change contrasts with more abrupt humidity shifts in the Mediterranean, suggesting a different climate threshold for Mediterranean vs. Atlantic margin precipitation.