Chironomid-based reconstruction of Lateglacial summer temperatures from the Ech palaeolake record (French western Pyrenees)

Chironomid head capsules were extracted and identified in 52 samples along a sediment core retrieved from the Ech palaeololake, (710 m a.s.l. in the west-central Pyrenees). The pollen stratigraphy together with radiocarbon dates provided the basis for the chronology of the record. Since temperature changes were identified as one of the major determining factors for shifts in the Ech chironomid assemblages during the Lateglacial, July air temperatures were tentatively inferred from the chironomid record using a transfer function based on a combined Swiss and Norwegian calibration dataset. The model reconstructed July air temperatures between 10 and 13 degrees C during the Oldest Dryas, a two step increase in temperatures to 16 and 17.5 degrees C during the first part of the Interstadial followed by a decrease to 16.5 degrees C at the end of the Interstadial. The Ech record features three centennial-scale 1.5 degrees C coolings during the Interstadial. Inferred temperatures decreased to 15-15.5 degrees C during the Younger Dryas, and reached ca. 17 degrees C at the beginning of the Holocene. The applicability of the combined Swiss-Norwegian transfer function to the Pyrenean fossil record was substantiated by the good statistics of the inference and the similar distribution of taxa with respect to temperature in the Alps and the Pyrenees. The reliability of the Ech record, including its chronology, was supported by its good concordance with other previously published chironomid-based lateglacial temperature reconstructions from Europe and the NGRIP delta O-18 record.