COS 118-2 - Chironomid-based environmental reconstructions in Italy and southern Switzerland using subfossil chironomid assemblages

Thursday, August 11, 2011: 1:50 PM
18B, Austin Convention Center
St├ęphanie Samartin1, Oliver Heiri1 and Willy Tinner2, (1)Oeschger Centre for Climate Change Research and Institute of Plant Sciences, University of Bern, Bern, Switzerland, (2)Institute of Plant Sciences and Oeschger Centre for Climate Change Research, University of Bern, 3013 Bern, Switzerland
Background/Question/Methods

South of the European Alps, in Italy and in southern Switzerland few quantitative palaeoclimatic reconstructions are available. Paleoclimatic studies in southern Europe can help to elucidate the main features of regional climatic dynamics, assess the degree of synchroneity with corresponding developments in other parts of Europe and improve our understanding of biotic responses to temperature changes. Here we present Late-Glacial and Holocene chironomid-based summer temperature reconstructions from the Southern Alps, the Po-Plain and the Northern Apennines.

Results/Conclusions

Our analyses suggest that midge assemblages responded to climatic events during the past 17’000 years, such as the Bølling warming, the Younger Dryas, the Preboreal Oscillation and the Holocene Thermal Optimum. At Foppe (1470 m a.s.l.) chironomid-reconstructed July air temperature estimates are about 9.9°C during the Oldest Dryas, and 12.2°C during most of the Bølling/Allerød. Lower temperatures of about 10.1°C are inferred during the Younger Dryas. The Holocene starts with an abrupt warming of 4°C, temperatures during the earliest Holocene (~11’600 – 10’000 cal BP) were on average 14°C. Our results imply that early Holocene temperatures were higher in the Southern Alps than in the Northern Alps, as it is still today (+1.5 – 2°C at 1470m a.s.l.) and that today’s temperatures were reached at the onset of the Holocene. Paleobotanical evidence shows that afforestation in the lowlands south of the Alps started before the Bølling onset. Our temperature reconstruction from Origlio (416 m a.s.l.) suggests that a “Pre-Bølling” warming which started around 16’200 cal BP triggered these very early forest expansions. For the first time we can reproduce a chironomid-inferred Holocene temperature reconstruction at two neighboring sites in Southern Europe. The Holocene and Late Glacial temperature reconstructions from Lago Gemini (1349 m a.s.l.) and Lago Verdarolo (1390 m a.s.l.) show prominent common features: low temperatures during the Oldest and Younger Dryas (8.4° - 9.2°C and 8.6° - 10.7°C, respectively), warmer temperatures during the Bølling/Allerød (10.3° - 11.9°C) and a relatively warm early Holocene (13.3° - 14°C). The most notable feature of the Holocene climate is the pronounced middle Holocene Thermal Optimum (HTM) at around 7’000 cal BP, when chironomid-inferred July-air temperatures were 15° - 15.6° C, i.e. up to 0.3° - 0.9°C warmer than at present. Mid-Holocene temperatures were rather stable and on average 13.6° - 14.4°C, late Holocene temperatures were slightly cooler ranging from 12.8° - 13.8°C.

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