The Medieval Climate Anomaly and the Little Ice Age in the Eastern Ecuadorian Andes
1IRD, UMR226, Institut des Sciences de l'Evolution de Montpellier (ISEM), UM2, CNRS, IRD, Place Eugène Bataillon cc 061, 34095 Montpellier cedex, France
2CNRS Université Paris 1, Laboratoire de Géographie, 92195 Meudon, France
3IRD, UMR163, Université Blaise Pascal, CNRS, IRD, Laboratoire Magmas et Volcans, 5 rue Kessler, 63038 Clermont-Ferrand, France
4Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, NY, USA
5Instituto Geofísico, Escuela Politécnica Nacional, A. P. 17-2759, Quito, Ecuador
6Dpto. Botanica Universidad Centrale del Ecuador (UCE), Quito, Ecuador
Abstract. To better characterize the climate variability of the last millennium in the high Andes, we analysed the pollen content of a 1100-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the Eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined to distinguish the atmospheric moisture from the soil moisture content of the páramo. Results showed that between 900 AD and 1230 AD, the Medieval Climate Anomaly interval was warm and moist with high T/P index linked to a high ENSO variability and a weak South American Summer Monsoon (SASM) activity. Between 1230 and 1650 AD, a dry climate prevailed characterized by an abrupt decrease in the T/P index related to lower ENSO variability with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed, first a wet phase between 1650 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic SSTs favored the return of a wet páramo, and a cold and dry phase between 1750 and 1810 AD associated with low ENSO variability and weak SASM activity resulting in drying of the páramo. The Current Warm Period marks the beginning of a climate characterized by high convective activity, the highest in the last millennium, and weaker SASM activity modifying the water stock of the páramo. Our results show that the páramo is progressively loosing its capacity for water storage and that the variability of both tropical Pacific and Atlantic SSTs matters for Andean climate patterns although many teleconnection mechanisms are still poorly understood.