Mathias Trachsel

Mineralogy‐based quantitative precipitation and temperature reconstructions from annually laminated lake sediments (Swiss Alps) since AD 1580

[1] We present quantitative autumn, summer and annual precipitation and summer temperature reconstructions from proglacial annually laminated Lake Silvaplana, eastern Swiss Alps back to AD 1580. We used X-ray diffraction peak intensity ratios of minerals in the sediment layers (quartz qz, plagioclase pl, amphibole am, mica mi) that are diagnostic for different source areas and hydrometeorological transport processes in the catchment. XRD data were calibrated with meteorological data (AD 1800/ 1864–1950) and revealed significant correlations: mi/pl with SON precipitation (r = 0.56, p < 0.05) and MJJAS precipitation (r = 0.66, p < 0.01); qz/mi with MJJAS temperature (r = � 0.72, p < 0.01)and qz/am with annual precipitation (r = � 0.54, p < 0.05). Geological catchment settings and hydro-meteorological processes provide deterministic explanations for the correlations. Our summer temperature reconstruction reproduces the typical features of past climate variability known from independent data sets. The precipitation reconstructions show a LIA climate moister than today. Exceptionally wet periods in our reconstruction coincide with regional glacier advances. Citation: Trachsel, M., U. Eggenberger, M. Grosjean, A. Blass, and M. Sturm (2008), Mineralogy-based quantitative precipitation and temperature reconstructions from annually laminated lake sediments (Swiss Alps) since AD 1580, Geophys. Res. Lett., 35, L13707, doi:10.1029/2008GL034121.

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

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.

High-resolution summer temperature reconstruction from Lake Silvaplana based on in-situ reflectance spectroscopy

Annually laminated (varved) sediments of proglacial Lake Silvaplana (46 27’N, 9 48’E, 1791 m a.s.l., Engadine, eastern Swiss Alps) provide an excellent archive for quantitative high-resolution (seasonal – annual) reconstruction of high- and lowfrequency climate signals back to AD 1580. The chronology of the core is based on varve counting, Cs-137, Pb-210 and event stratigraphy. In this study we present a reconstruction based on in-situ reflectance spectroscopy. In situ reflectance spectroscopy is known as a cost- and time-effective non destructtive method for semi-quantitative analysis of pigments (e.g., chlorines and carotenoids) and of lithoclastic sediment fractions. Reflectance-dependent absorption (RDA) was measured with a Gretac Macbeth spectrolino at 2 mm resolution. The spectral coverage ranges from 380 nm to 730 nm at 10 nm band resolution. In proglacial Lake Silvaplana, 99% of the sediment is lithoclastic prior to AD 1950. Therefore, we concentrate on absorption features that are characteristic for lithoclastic sediment fractions. In Lake Silvaplana, two significant correlations that are stable in time were found between RDA typical for lithoclastics and meteorological data: (1) the time series R 570 /R 630 (ratio between RDA at 570 nm and 630 nm) of varves in Lake Silvaplana and May to October temperatures at nearby station of Sils correlate highly significantly (calibration period AD 1864 – 1951, r = 0.74, p < 0.01 for 5ptsmoothed series; RMSE is 0.28 C, RE = 0.41 and CE = 0.38), and (2) the minimum reflectance within the 690nm band (min690) data correlate with May to October (calibration period AD 1864 – 1951, r = 0.68, p < 0.01 for 5pt-smoothed series; RMSE = 0.22 C, RE = 0.5, CE = 0.31). Both proxy series (min690nm and R 570 /R 630 values) are internally highly consistent (r = 0.8, p < 0.001). In proglacial Lake Silvaplana the largest amount of sediment is transported by glacial meltwater. The melting season spans approximately from May to October, which gives us a good understanding of the geophysical processes explaining the correlations between lithoclastic proxies and the meteorological data. The reconstructions were extended back to AD 1580 and show a broad corresponddence with fully independent reconstructions from tree rings and documentary data.