High-resolution chironomid-inferred temperature history since ad 1580 from varved Lake Silvaplana, Switzerland: comparison with local and regional reconstructions

Abstract

Chironomids were used to reconstruct mean July air temperatures between c. AD 1580 and 2001 at Lake Silvaplana, a varved lake located in the Engadine, eastern Swiss Alps. The goal of this study was to reconstruct temperature changes at near-annual resolution, and validate the reconstruction by comparison with records based on early instrumental data, documentary proxy evidence, dendrochronology, geochemical (biogenic silica (BSi)) and mineralogical data (quartz/mica ratios) at local and regional scales. Warmer than-the-climate-normal (AD 1961—1990) mean July air temperatures were inferred between c. AD 1610 and 1662, AD 1710 and 1740, AD 1790 and 1866, AD 1940 and 1960 and AD 1990 and 2001. Colder-than-the-climate-normal July air temperatures were reconstructed between c. AD 1662 and 1710, AD 1740 and 1790, AD 1866 and 1919, and AD 1970 and 1990. The 420-year chironomid-inferred mean July air temperature record was significantly ( p < 0.01) related to June—September (JJAS) temperatures reconstructed from early instrumental and documentary data at regional scale, JJA temperature inferred from documentary proxy evidence at local scale and summer temperatures based on early instrumental data in central Europe. When the Z-scores of warm/cold periods were compared between records, only one period ( c. AD 1740—1790) did not show significant correlations between the chironomid record and any of the eight other records considered here, probably because of increased precipitation and changes in the sediment composition which influenced the chironomid assemblages. 75% of the periods considered had significant correlations between the chironomid records, and both the reconstruction based on quartz/mica ratios and the inferred JJAS early instrumental and documentary proxy evidence, while 60% of the periods showed significant correlations between the chironomid-based record and the reconstruction based on early instrumental data of Central Europe. These results suggest that chironomids in the sediment of Lake Silvaplana yield valid temperature reconstructions at regional scales for the last 420 years.