Radiometric, isotopic, and petrographic evidence of changing interglacials over the past 550,000 years from six stalagmites from the Serra do Courel in the Cordillera Cantábrica of northwestern Spain

Seventy U-Th ages from six stalagmites from the Cordillera Cantábrica in northwestern Spain indicate deposition during interglacial, but not glacial, stages over the last 550 kyr. Stable isotope data and petrographic observations suggest that, within each interglacial, conditions typically progressed from drier to wetter. Consideration of the most precise U-Th ages suggests that stalagmite deposition occurred in times more predictable from European pollen records than from the global marine isotope record. For example, during the last interglacial, ages suggest deposition in an interval better characterized as the Eemian, as opposed to MIS 5e, and during the St. Germain I or MIS 5c interval. The same holds for MIS 7, where ages suggest deposition during MIS 7a and MIS 7c but not MIS 7e. These age ranges for interglacials, consistently later than those suggested by the benthic marine record, are compatible with warm conditions maintained by thermohaline circulation that simultaneously supplied the moisture for growing ice sheets of the subsequent glaciation. Trends both within and across these six stalagmites suggest that cooler temperatures were associated with wetter conditions, both during interglacials and in conditions intermediate between interglacials and glacials in northern Spain. In contrast, other researchers’ results from a stalagmite from the Last Glacial Maximum and subsequent deglaciation suggest colder temperatures were associated with drier conditions. The two trends combine to suggest wettest conditions in times intermediate between interglacials and glacials, compatible with a model in which modern climatic belts from dry Arctic to wet European to dry marginal Saharan have moved over northern Spain in the cycle from glacial to interglacial times. Extrapolation to a warmer future would suggest drier conditions in the northern Iberian Peninsula than those of today.