Coupling Between Atmospheric [CO2] and Temperature During the last Millennium

The Little Ice Age climate deterioration is the most recent cool pulse of a series of recurrent climate fluctuations throughout the Holocene. Within the ongoing discussion on the coupling of CO₂ and temperature, documentation of both parameters on a high temporal resolution is needed. Recent Northern Hemisphere temperature reconstructions based on tree-ring chronologies reveal a higher amplitude for temperature fluctuations during the last millennium than proposed so far. Ice core atmospheric [CO₂] records already demonstrate low amplitude fluctuations associated with the Little Ice Age. In this study an alternative high resolution CO₂ record is obtained by means of stomatal frequency analysis of (sub-) fossil oak (Quercus robur) leaves. The leaf material is derived from a four meter long sediment core consisting of laminated clayey gyttja taken in an oxbow lake in the southern Netherlands. The derived CO₂ reconstructions show a series of distinct shifts of higher amplitude than documented in Antarctic ice core records. The stomatal frequency based CO₂ record for the last millennium suggests a dynamic atmospheric CO₂ regime parallelling the temperature deviations during the last millenium referred to as the Little Ice Age and the late Medieval Warm Period.