A HIGH-RESOLUTION RECORD OF CONTINENTAL CLIMATE VARIABILITY OVER THE LAST 90,000 YEARS FROM BURACA GLORIOSA CAVE, WESTERN PORTUGAL

Many studies of climate variability over the last glacial cycle have been developed for continental and marine margin western Europe, but a prominent gap in climate data exists in continental western Iberia. Here we present a stalagmite record spanning much of the last glacial cycle from Buraca Gloriosa Cave, western Portugal. Chronologies are based upon 51 high-precision ²³⁰Th dates that show intermittent growth over the last 90 ka.

Both the oxygen and carbon isotope records contain millennial-scale variability similar to those observed in Greenland stadial-interstadial events in both structure and timing. Oxygen isotope ratios vary by 1.0 to 1.5‰ during MIS 3 and 4 with isotopically higher values occurring during Greenland stadials. Modern temperature effects on oxygen isotope values of precipitation collected from the closest GNIP station (Porto, Portugal), 180 km north of the cave location, suggest that while temperature may be responsible for a portion of the isotopic variation, changes in precipitation seasonality cause a majority of the observed stalagmite isotopic variability.

Carbon isotopic data exhibit fluctuations of 3.5 to 4.0‰ during D/O events, with higher values corresponding to D/O stadials, likely due to decreases in vegetation density as a result of reduced precipitation. Similarly, growth ceased during most Heinrich stadials including H1, H2, H4, H5, H6 and H7, which we interpret as a decrease in the amount of precipitation and/or a lessened amount of infiltration. However, our record preserves the Younger Dryas interval, suggesting this period was neither as cold nor arid as the other recorded Heinrich events in western Iberia.

In the Holocene, oxygen isotope values exhibited increased high frequency variability from 11.4 to 1.2 ka, with values fluctuating between -4.4‰ and -2.4‰. Carbon isotope values ranged from -10.9‰ to -3.5‰. Although evaporative controls on stalagmite isotopic values may have been more prominent during this period, measurements of modern cave conditions showed that humidity remained at or near 100% and atmospheric pressure variations inside the cave changed minimally from summer to winter. This study provides vital climate data spanning the last glacial cycle from western Iberia, helping fill a geographic gap in western European terrestrial climate records.