Unprecedented recent regional increase in organic carbon and lithogenic fluxes in high altitude Pyrenean lakes.

We have conducted a monitoring survey and paleolimnological study of a W-E transect of six high altitude lakes (1870-2630 m asl) in the western and central Pyrenees (Spain) to evaluate the regional response to current global change in high altitude Mediterranean mountains. The reconstructed Total Organic Carbon (TOC) and lithogenic (L) fluxes during the last 1200 years show the expected variability as lakes differ in altitude, geological and climate settings, limnological properties and human impact history. However, all show unique patterns after 1850 CE, particularly during the Great Acceleration (after 1950 CE). Recent L increase could be related to higher erodibility by rainfall and run-off during the longer snow-free season in the Pyrenees. In all sites, higher TOC and geochemical (lower δC, lower C/N) and biological (diatom assemblages) signatures since 1950 CE suggest an increase in algal productivity, likely favored by warmer temperatures and higher nutrient deposition. These recent, unprecedented L and TOC increases, in spite of their diverse history and limnological properties of the lakes, demonstrate the regional impact of the Great Acceleration not only in the ecological dynamics of alpine lakes but also in the hydrological cycle in high altitude mountain watersheds.