A STALAGMITE RECORD OF MILLENNIAL-SCALE CONTINENTAL CLIMATE DURING THE LAST GLACIAL CYCLE FROM WESTERN IBERIA
Oxygen isotopic values shift by 1.0-1.5‰ during MIS 3-4 with lower values defining D/O interstadials and showing the same characteristic asymmetry of these structures in the Greenland ice records. Although temperature effects on oxygen isotopic ratios of meteoric precipitation as recorded at the GNIP station of Porto, 179 km north of Buraca Gloriosa, are statistically significant, the slope is shallow; hence the stalagmite record from this region likely reflects precipitation dynamics rather than temperature changes. At this location, amount effects impart a prominent influence on modern isotopic ratios of precipitation. Thus amount effects, as well as the strong seasonality of precipitation in this Mediterranean climate, are thought to be the primary drivers of oxygen isotopic variability in Buraca Gloriosa stalagmites.
Carbon isotopic values shift by 3.5-4‰ between D/O events, with lower values defining D/O interstadials. These changes likely reflect increased vegetation density and reduced prior calcite precipitation during the warmer, wetter climates of D/O interstadials. Hiatuses in stalagmite growth during Heinrich stadials likely also reflect these cold and dry conditions. Future measurements of temperature, humidity and barometric pressure in Buraca Gloriosa will provide additional insight into seasonal changes in cave conditions that could influence these isotopic fluctuations.