Chrysophyte resting stages: a tool for reconstructing winter/spring climate from Alpine lake sediments

Chrysophyte algae produce siliceous resting stages (stomatocysts) that are indicators of past environmental conditions. The objective of this study was to assess their strength for climate reconstructions. Stomatocysts were collected using sediment traps exposed in 45 mountain lakes (1502-2309 m a.s.l., Austrian Alps). Bi-hourly water-temperature measurements were used to determine dates of freezing and break-up, spring and autumn mixing. Canonical correspondence analyses revealed that the stomatocyst assemblages were related to the dates of ice break-up and spring mixing. The two dates are controlled by winter/spring air temperature. We developed a weighted averaging-partial least squares (WA-PLS) stomatocyst/date-of-spring-mixing regression and calibration model (R² _boot=0.85), and reconstructed 'dates of spring mixing' for Jezero v Ledvici (1824 m a.s.l., Slovenian Alps) from AD 1842 to 1996. Sample-specific standard errors of prediction corresponded to 0.6°C - 1.0°C. Despite dating uncertainties and poor fits of fossil assemblages with the training set, reconstructed 'dates of spring mixing' were significantly correlated with the mean March-April air temperature, which is known to drive break-up dates. Furthermore, the record was in agreement with glacier advances during the Little Ice Age.