A 700-year record of climate change based on geochemical and palynological data from varved sediments (Lac Pavin, France)

The Fe-flux budget of the meromictic crater Lac Pavin (French Massif Central) is re-evaluated in the light of new results from detailed sediment investigations (geochemistry, sedimentology, pollen, varve counting). Sedimentation of Lac Pavin during the last 700 years is characterised by high net accumulation of biogenic silica (100-500 g m(-2) yr(-1) SiO2) and autochthonous Fe-precipitates (F-Fe-exe=2-200 g m(-2) yr(-1) Fe) at overall high sediment accurnulation (e.g. AD 1530-1890: 3.7 mm yr(-1)). High net accumulation of biogenic silica and Fe-exe is sustained by nutrient and Fe-influx via sub-lacustrine springs. The feeding of the groundwater inflow is closely correlated with the seepage of meteoric waters which declines in winter due to freezing of the ground. In the context of the derived local vegetation dynamics, balanced Fe-exe-flux is interpreted as a proxy for rainfall during the growing season. Meteorological monitoring data document a significant inverse correlation between monthly temperature and rainfall between May and October which reflects enhanced cloudiness for precipitation above average. Beech, growing under suboptimal conditions at the high altitude of the study site, represents a major tree component in the catchment of Lac Pavin. Minor temperature decrease in the growing season can explain reduced flowering of beech in the following year. Distinct short term variability of beech characterised by an inverse Correlation with the balanced F-Fe-exc supports the data interpretation. Two periods with prevailing of overall wetter and cooler conditions in the growing season were derived: ca. AD 1525-1600, and AD 1630-1660. Climate change to drier and warmer conditions is implied around AD 1450 and AD 1620. The Late Maunder Minimum (AD 1675-1715) is characterised by distinct short term variability of the palaeo-hydrological conditions at the study site. (c) 2007 Elsevier B.V All rights reserved.