Lipid biomarker (brGDGT)- and pollen-based reconstruction of temperature change during the Middle to Late Holocene transition in the Carpathians

Abstract

To reconstruct changes in vegetation, temperature, and sediment geochemistry through the last 6.5 cal ka BP, in the Subcarpathian belt of the Eastern Carpathians (Romania), pollen, branched glycerol dialkyl glycerol tetraethers (brGDGTs) and X-ray fluorescence analyses have been integrated. Pollen and brGDGTs (a bacterial lipid biomarker proxy) are used as paleothermometers for reconstructing the mean annual air temperature (MAAT) and mean temperature above freezing (MAF), respectively. Both proxies show roughly consistent records. The highest MAAT and MAF occurs during the oldest part of the record (from 6.5 to 4.2 cal ka BP), and the Middle to the Late Holocene shift is marked by a prominent decrease in temperature between 5.4 and 4.2 cal ka BP, coinciding with Bond event 4 and 3. This transition is coeval with a decrease in summer insolation, shift from consistent NAO- conditions to a predominance of NAO+ phase and coincides with the beginning of the Neoglacial cooling in northern latitudes. The warm bias in the MAF reconstruction during the Late Holocene is explained as a change in the lipid provenance or in the composition of the brGDGT producers after 4.2 cal ka BP.