High-resolution diatom δ~(18)O records, from the last 150 years, reflecting changes in amount of winter precipitation in two sub-Arctic high-altitude lakes in the Swedish Scandes

摘要

Waters from high-altitude alpine lakes are mainly recharged by meteoric water. Because of seasonal variations in precipitation and temperature and relatively short hydraulic residence times, most high-altitude lakes have lake water isotopic compositions (δ~(18)O_(lake)) that fluctuate due to seasonality in water balance processes. Input from snowmelt, in particular, has a significant role in determining lake water δ~(18)O. Here we compare two high-resolution δ~(18)O_(diatom) records from lake sediments in the Swedish Scandes with instrumental data from the last century obtained from nearby meteorological stations. The time period AD 1900-1990 is characterised by an increase in winter precipitation and high winter/summer precipitation ratios and this is recorded in δ~(18)O_(diatom) as decreasing trends. Lowest δ~(18)O_(diatom) values and highest amount of winter precipitation are found around AD 1990 when the winter North Atlantic Oscillation index was above +2. We conclude that for the last 150 a the main factor affecting the δ~(18)O_(diatom) signal in these sub-Arctic high-altitude lakes with short residence times has been changes in amount of winter precipitation and that δ~(18)O_(diatom) derived from high-altitude lakes in the Swedish Scandes can be used as a winter precipitation proxy.