Thousand years of climate change reconstructed from chironomid subfossils preserved in varved lake Silvaplana, Engadine, Switzerland

摘要

Fossil chironomids (non-biting midges) from varved Lake Silvaplana, Switzerland, were used to reconstruct climate (mean July air temperatures) during the last millennium. At the beginning of the record, corresponding to the last part of the " Medieval Climate Anomaly" (MCA) (here the period between ca 1032 and 1262 AD), the chironomid-inferred mean July air temperatures were 1 °C warmer (p < 0.01) than the climate reference period (1961-1990). The " Little Ice Age" seems to have been separated into three phases: significantly colder (-1.1 °C in average, p < 0.001) temperatures were inferred between ca 1262 and 1481 AD, between ca 1514 and 1718 AD (-1.2 °C in average, p < 0.001) and between ca 1734 and 1782 AD (-0.6 °C in average, p < 0.1). Although the average temperature changes inferred by chironomids were within the error of prediction (1.5 °C) of the chironomid-temperature inference model used for reconstruction, the pattern of temperature changes corresponds well with records of the past millennium in Switzerland, in Europe and in the Northern Hemisphere. The average inferred July temperatures between ca 1900 and 2001 AD were significantly warmer (p < 0.05) than the climate reference period (1961-1990) by 1 °C which is in agreement with the instrumental data. The inferred July temperatures were in the same range as the inferred temperatures during the last part of the MCA suggesting that during the 20th century, at Lake Silvaplana, the chironomid-inferred temperatures do not exceed the natural climate variability of the past millennium.