DEVELOPING A DECADAL-SCALE STALAGMITE RECORD OF HYDROCLIMATE AND ATMOSPHERIC VARIABILITY FOR WESTERN IBERIA (PORTUGAL) DURING THE LATE HOLOCENE

The Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) was a time of substantial climate variability in Europe. Changes in precipitation patterns and amounts between these two periods are evident in stalagmites and other precipitation proxy records. For example, a multiproxy record developed by Trouet et al. (2009) from Scotland and Morocco suggests that there was a major reorganization in the winter North Atlantic Oscillation (wNAO) around AD 1420, roughly coincident with the transition from the MCA into the LIA. The wNAO, defined as the sea level pressure difference between Iceland and Lisbon for the months of December through March, is the primary mode of atmospheric variability in the North Atlantic sector. The climatic effects in Europe and the North Atlantic region associated with the wNAO mode include modulation of precipitation patterns, storm tracks, air temperatures, and regional ocean circulation. Trouet et al. (2009) also concluded that the wNAO was in a persistently positive mode during Medieval times. Hence, some regions in Europe, including the Iberian Peninsula, may have experienced persistently dry conditions during the MCA.

This project utilizes multiple actively growing, precipitation-sensitive stalagmites collected from Buraca Gloriosa, a cave in central Portugal, which is located within the high-pressure belt of the wNAO system (~100 km from Lisbon). This provides the opportunity to further evaluate the hydroclimate during the MCA and the LIA intervals. These new records will complement other proxy data and allow us to develop a more robust understanding of the wNAO system during the late Holocene.

The Buraca Gloriosa cave is instrumented inside and out yielding relative humidity, temperature, and pressure data. Additionally, a dripcounter was installed to quantify infiltration rates. Inside the cave, temperature, pressure, and relative humidity (at or near 100%) change very little throughout the year. Uranium-Thorium disequilibrium methods provide a precise age model for the stalagmites. Stable oxygen and carbon isotopic ratios from microsampled stalagmite carbonate suggest that a large shift in hydroclimate occurred within the early MCA (ca. AD 1000) at this location, which was followed by a less pronounced change in hydroclimate around AD 1400 possibly related to the wNAO.