Lateglacial and early Holocene summer temperatures in the southern Swiss Alps reconstructed using fossil chironomids

We present a Lateglacial and early Holocene chironomid-based July air temperature reconstruction from Foppe (1470m a.s.l.) in the Swiss Southern Alps. Our analysis suggests that chironomid assemblages have responded to major and minor climatic fluctuations during the past 17 000 years, such as the Oldest Dryas, the Younger Dryas and the Bolling/Allerod events in the Lateglacial and the Preboreal Oscillation at the beginning of the Holocene. Quantitative July air temperature estimates were produced by applying a combined Norwegian and Swiss temperature inference model consisting of 274 lakes to the fossil chironomid assemblages. The Foppe record infers average July air temperatures of ca. 9.9 degrees C during the Oldest Dryas, 12.2 degrees C during most of the Bolling/Allerod and 11.1 degrees C for the Younger Dryas. Mean July air temperatures during the Preboreal were 14 degrees C. Major temperature changes were observed at the Oldest Dryas/Bolling (+2.7 degrees C), the Allerod/Younger Dryas (-2 degrees C) and the Younger Dryas/Holocene transitions (+3.9 degrees C). The temperature reconstruction also shows centennial-scale coolings of ca. 0.8-1.4 degrees C, which may be synchronous with the Aegelsee (Greenland Interstadial 1d) and the Preboreal Oscillations. A comparison of our results with other palaeoclimate records suggests noticeable temperature gradients across the Alps during the Lateglacial and early Holocene.