Climatic conditions between 19 and 12 ka in the eastern Pyrenees, and wider implications for atmospheric circulation patterns in Europe. (15th May 2021) - Reixach, Theo
Abstract: The chronology of the most extensive Late Pleistocene glaciation in the eastern Pyrenees is now well established, but climatic variations during the subsequent Last Glacial-to-Interglacial Transition (LGIT) are much less well documented. The aim of this research is to fill that gap. We present a new series of 22 10 Be exposure ages from a sequence of moraines in the upper Ariège catchment, and update 64 previously published exposure ages from seven other valleys. Based on (i) geomorphological maps of successive generations of ice-marginal deposits and (ii) their age distributions, followed by (iii) glaciological modeling to infer corresponding mass-balance gradients and equilibrium line altitudes (ELAs), we reconstruct glacier behaviour in the eastern Pyrenees during the LGIT and retrieve paleoclimatic parameters for each glacial stillstand. Results document rapid deglaciation involving four relative stillstands, with an ELA rise of ∼410 m and increases in temperature and precipitation of ∼4 °C and ∼40%, respectively, between ∼18 ka (Greenland Stadial GS-2.1b) and ∼14.5 ka (Greenland Interstadial GI-1). A cold and dry environment prevailed from ∼18 ka onward, and deglaciation was almost complete by GI-1. Only small glaciers persisted as late as ∼12.3 ka in cirques where local conditions allowed it. These patterns are compatible with a transient Polar Front Jet Stream repositioning to latitudes of 40–42°N between 18 and 16 ka, with Westerlies-dominated circulation not yet feeding precipitation to the mountain belt abundantly from the northwest, and outbursts of polar air meeting with cool sea waters in the western Mediterranean mostly suppressing precipitation from Mediterranean sources. Highlights: Pyrenean paleoclimates are inferred from cosmogenic dating and glaciological modeling. Full deglaciation in the eastern Pyrenees occurred between 19.2 ± 0.7 and 14.5 ± 0.6 ka. Small cirque glaciers persisted until ∼12 ka in a few sheltered, elevated valleys. The earlier period (∼20–14 ka) was colder and drier than all subsequent intervals. A cool Mediterranean and cold Atlantic (Polar Front ∼42°N) impeded precipitation.