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CO2 radiative forcing during the Holocene Thermal Maximum revealed by stomatal frequency of Iberian oak leaves

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Author: García-Amorena, I. · Wagner-Cremer, F. · Gomez Manzaneque, F. · Hoof, T.B. van · García Álvarez, S. · Visscher, H.
Type:article
Date:2008
Institution: TNO Bouw en Ondergrond
Source:Biogeosciences Discussions, 5, 5, 3945-3964
Identifier: 241011
Keywords: Geosciences · air temperature · atmospheric chemistry · carbon dioxide · deciduous tree · Hypsithermal · Neoglacial · Northern Hemisphere · orbital forcing · paleotemperature · radiative forcing · radiocarbon dating · reconstruction · stomata · trace gas · Eurasia · Europe · Southern Europe · Spain · Quercus

Abstract

Here we analyse radiocarbon-dated Quercus leaf assemblages from northern Spain to obtain past atmospheric CO2 mixing ratios for the time period 9000ĝ€"1100 cal BP by means of stomatal frequency analysis. Normalized, stomata based CO2 records show fluctuations of 20 ppmv during the Holocene that parallel Northern Hemisphere palaeotemperature reconstructions. The calculated radiative forcing of CO2 indicates a CO2 contribution of +0.1°C to the Holocene Thermal Maximum from 7 to 5 kyr BP, and −0.05°C to the Neoglacial cooling around 4 kyr BP. Derived northern hemispheric air-temperature anomalies forced by atmospheric CO2 variation suggest an active role of this trace gas as an amplifier of initial orbital forcing of Holocene climate.