Orbital-to-millennial scale climate variability during Marine Isotope Stages 5 to 3 in northeast Iberia

The climate during the last glacial cycle was characterized by abrupt millennial-scale changes superimposed on long-term orbital control. This study examines this climate variability for northeast Iberia for the time interval 118.9 to 36.9 kyr using a multi-proxy approach (δ¹⁸O, δ¹³C and Mg/Ca) applied to a stalagmite that covers this period continuously. During Marine Isotope Stage (MIS) 5 and 4, δ¹⁸O is controlled by orbital pacing, whereby more humid conditions prevailed during minima in boreal summer precession. In contrast, during MIS 3 δ¹⁸O lags precession and co-varies with δ¹³C (ρ = 0.53, p-value < 0.001, n = 500), suggesting a common control of both isotopes by reduced precipitation during dry periods. δ¹³C shows a positive correlation with Mg/Ca, reflecting water availability, vegetation productivity and microbial activity in the catchment of the cave's drip water. The δ¹³C values exhibit a response to Heinrich Stadials (HS) and other cold marine events (e.g. C26 to C23), as well as Dansgaard-Oeschger oscillations (D-O). The Last Interglacial ended at 108.6 ± 0.3 kyr at this site. Two periods with a marked “W-shape” pattern in δ¹³C can be recognized between 70 and 50 kyr (hereafter multi-event). The older multi-event (including HS-6 and D-O 18) is characterized in the North Atlantic by high IRD discharges and cold sea-surface temperatures, while the two phases attending to the hydrology in the study area suggest dry conditions prior to HS-6. A dry climate prevailed during the younger multi-event (including HS-5a and D-O 15), coincident with an increase in productivity-related foraminifera species at lower latitudes, suggesting a reinforcement of the trade winds associated with a stronger Hadley Cell.