Lateglacial and early Holocene summer temperatures in the southern Swiss Alps reconstructed using fossil chironomids STE ´ PHANIE SAMARTIN, 1 * OLIVER HEIRI, 1,2 ELISA VESCOVI, 1 STEPHEN J. BROOKS 3 and WILLY TINNER 1 1 Oeschger Centre for Climate Change Research and Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland 2 Palaeoecology, Institute of Environmental Biology, Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, CD 3584 Utrecht, The Netherlands 3 Department of Entomology, Natural History Museum, Cromwell Road, London SW7 5BD, UK Received 4 April 2011; Revised 24 August 2011; Accepted 28 August 2011 ABSTRACT: We present a Lateglacial and early Holocene chironomid-based July air temperature reconstruction from Foppe (1470 m 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 Bølling/Allerød 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 8C during the Oldest Dryas, 12.2 8C during most of the Bølling/Allerød and 11.1 8C for the Younger Dryas. Mean July air temperatures during the Preboreal were 14 8C. Major temperature changes were observed at the Oldest Dryas/Bølling (þ2.7 8C), the Allerød/Younger Dryas (2 8C) and the Younger Dryas/Holocene transitions (þ3.9 8C). The temperature reconstruction also shows centennial-scale coolings of ca. 0.8–1.4 8C, 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. Copyright # 2011 John Wiley & Sons, Ltd. KEYWORDS: chironomids; climate; southern Europe; Bølling/Allerød; Younger Dryas. Introduction Most available quantitative reconstructions of Lateglacial and Holocene climates in Europe originate from northern and central sectors of the continent. In the Alpine region (Northern, Western, Central Alps and the Jura mountains) they are mainly based on fossil pollen and chironomid assemblages preserved in lake sediments (e.g. Heiri and Lotter, 2003; Heiri et al., 2003b; Ilyashuk et al., 2009). In Southern Europe and, as part of it, the Italian peninsula with the Southern Alps, only a few quantitative palaeoclimatic reconstructions are available (e.g. Heiri et al., 2007; Larocque and Finsinger, 2008; Finsinger et al., 2010). Palaeoclimatological studies in this area can therefore contribute to our understanding of climatic patterns and of biotic responses to temperature changes throughout Europe and the Mediterranean region. Furthermore, quantitat- ive temperature reconstructions from Southern Europe are important as they can help to improve our understanding of the long-term dynamics of Mediterranean climate (Tzedakis, 2007) and are necessary to evaluate the performance of climate models when inferring climatic changes in the southern sector of the European continent (Renssen et al., 2009). Here we present a new Lateglacial and early Holocene chironomid-based temperature reconstruction from a lake sediment sequence from Foppe (1470 m a.s.l.) in the Southern Alps of Italian Switzerland (Canton Ticino). The strongly sclerotized headcapsules of Chironomidae larvae preserve well in lake sediments for thousands of years. In the majority of cases fossil headcapsules can be identified to generic or species group level, and sometimes even to species. The particular composition of the fossil assemblage can therefore be used to reconstruct the past chironomid fauna of a lake and, indirectly, to infer past environmental conditions. Detailed knowledge of chironomid distribution, together with the development of transfer functions, has allowed chironomid-based palaeotem- perature records to be produed (e.g. Brooks, 2006). With these transfer functions, estimates of past July air temperatures, with a prediction error typically in the range 1–1.5 8C, can be reconstructed from fossil chironomid assemblages. The main aim of this study was to quantitatively reconstruct past temperatures for the Foppe area and to assess the amplitude of summer temperature changes in the Southern Alps. In addition, the results are compared with the Foppe vegetation history record (E. Vescovi, C. Jacquat and W. Tinner, unpublished data) to discuss possible linkages between vegetation and climate. The chironomid-inferred temperatures are also compared with other palaeoclimatic records to assess whether the climatic history at Foppe is consistent with the patterns of climatic change observed in the Alps and the surrounding areas during the Lateglacial and the early Holocene. Material and methods Site description Foppe is a small-sedge mire (1470 m a.s.l., 46827 0 35 00 N, 8847 0 40 00 E), growing on acidic soil and located in the Lepontine Alps of the Ticino (southern Switzerland, Fig. 1). The mire covers an area of about 3 ha and is situated on a plateau facing south-east. The Quaternary landscape was shaped by the Ticino glacier and the study area was completely ice-covered during the Last Glacial Maximum (Bini et al., 2009). The underlying bedrock is composed of pre-Mesozoic meta- morphic rocks, mainly gneiss and mica schist. The climate at present is cool-temperate with considerable precipitation in the summer months. Monthly mean air temperature and precipi- tation for the period 1960–2006, interpolated to a 1-ha grid using a DAYMET model (Thornton et al., 1997), indicate mean JOURNAL OF QUATERNARY SCIENCE (2012) 27(3) 279–289 ISSN 0267-8179. DOI: 10.1002/jqs.1542 Copyright ß 2011 John Wiley & Sons, Ltd. *Correspondence: S. Samartin, as above. E-mail: stephanie.samartin@ips.unibe.ch