Stomatal evidence for a decline in atmospheric CO₂ concentration during the Younger Dryas stadial: A comparison with Antarctic ice core records.

J. C. MCELWAIN¹*, F. E. MAYLE² and D. J. BEERLING¹

1Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, England. ²Department of Geography, University of Leicester, Leicester LE1 7RH, England.*Present address: J.C. McElwain, Department of Geology, Field Museum of Natural History, 1400 S. Lake Shore Drive, Chicago, IL 60605, USA.

ABSTRACT: A recent high-resolution record of Lateglacial CO₂ change from Dome Concordia in Antarctica reveals a trend of increasing CO₂ across the Younger Dryas stadial (GS-1) (Monnin et al., 2001). These results are in good agreement with previous Antarctic ice core records, however they contrast markedly with a proxy CO₂ record based on the stomatal approach to CO₂ reconstruction, which records a ~ 70 ppm mean CO₂ decline at the onset of GS-1 (Beerling et al., 1995). To address these apparent discrepancies we tested the validity of these stomatal-based CO₂ reconstructions from Kråkenes (Beerling et al., 1995) by obtaining further proxy-CO₂ records based on a similar approach using fossil leaves from two independent lakes in Atlantic Canada. Our Lateglacial CO₂ reconstruction reveal an abrupt ~ 77 ppm decrease in atmospheric CO₂ at the onset of the Younger Dryas stadial (GS-1), which lagged climatic cooling by ~ 130 years. Furthermore, the trends recorded in the most accurate high-resolution ice core record of CO₂, from Dome Concordia (Monnin et al., 2001), can be reproduced from our stomatal-based CO₂ records, when time averaged by the mean age distribution of air contained within Dome C ice (200 to 550 years). If correct, our results indicate an abrupt drawdown of atmospheric CO₂ within two centuries at the onset of GS-1, suggesting some re-evaluation of the behaviour of atmospheric CO₂ sinks and sources during times of rapid climatic change such as the Lateglacial may be required.