TY - JOUR
T1 - Reconstructing ice-age palaeoclimates
T2 - quantifying low-CO₂ effects on plants
AU - Prentice, I. C.
AU - Cleator, S. F.
AU - Huang, Y. H.
AU - Harrison, S. P.
AU - Roulstone, I.
PY - 2017/2
Y1 - 2017/2
N2 - We present a novel method to quantify the ecophysiological effects of changes in CO₂ concentration during the reconstruction of climate changes from fossil pollen assemblages. The method does not depend on any particular vegetation model. Instead, it makes use of general equations from ecophysiology and hydrology that link moisture index (MI) to transpiration and the ratio of leaf-internal to ambient CO₂ (χ). Statistically reconstructed MI values are corrected post facto for effects of CO₂ concentration. The correction is based on the principle that e, the rate of water loss per unit carbon gain, should be inversely related to effective moisture availability as sensed by plants. The method involves solving a non-linear equation that relates e to MI, temperature and CO₂ concentration via the Fu-Zhang relation between evapotranspiration and MI, Monteith's empirical relationship between vapour pressure deficit and evapotranspiration, and recently developed theory that predicts the response of χ to vapour pressure deficit and temperature. The solution to this equation provides a correction term for MI. The numerical value of the correction depends on the reconstructed MI. It is slightly sensitive to temperature, but primarily sensitive to CO₂ concentration. Under low LGM CO₂ concentration the correction is always positive, implying that LGM climate was wetter than it would seem from vegetation composition. A statistical reconstruction of last glacial maximum (LGM, 21±1 kyr BP) palaeoclimates, based on a new compilation of modern and LGM pollen assemblage data from Australia, is used to illustrate the method in practice. Applying the correction brings pollen-reconstructed LGM moisture availability in southeastern Australia better into line with palaeohydrological estimates of LGM climate.
AB - We present a novel method to quantify the ecophysiological effects of changes in CO₂ concentration during the reconstruction of climate changes from fossil pollen assemblages. The method does not depend on any particular vegetation model. Instead, it makes use of general equations from ecophysiology and hydrology that link moisture index (MI) to transpiration and the ratio of leaf-internal to ambient CO₂ (χ). Statistically reconstructed MI values are corrected post facto for effects of CO₂ concentration. The correction is based on the principle that e, the rate of water loss per unit carbon gain, should be inversely related to effective moisture availability as sensed by plants. The method involves solving a non-linear equation that relates e to MI, temperature and CO₂ concentration via the Fu-Zhang relation between evapotranspiration and MI, Monteith's empirical relationship between vapour pressure deficit and evapotranspiration, and recently developed theory that predicts the response of χ to vapour pressure deficit and temperature. The solution to this equation provides a correction term for MI. The numerical value of the correction depends on the reconstructed MI. It is slightly sensitive to temperature, but primarily sensitive to CO₂ concentration. Under low LGM CO₂ concentration the correction is always positive, implying that LGM climate was wetter than it would seem from vegetation composition. A statistical reconstruction of last glacial maximum (LGM, 21±1 kyr BP) palaeoclimates, based on a new compilation of modern and LGM pollen assemblage data from Australia, is used to illustrate the method in practice. Applying the correction brings pollen-reconstructed LGM moisture availability in southeastern Australia better into line with palaeohydrological estimates of LGM climate.
KW - last glacial maximum
KW - palaeoclimate reconstruction
KW - moisture index
KW - water-use efficiency
KW - plant available moisture
UR - http://www.scopus.com/inward/record.url?scp=85010871811&partnerID=8YFLogxK
UR - http://purl.org/au-research/grants/arc/DP1201100343
U2 - 10.1016/j.gloplacha.2016.12.012
DO - 10.1016/j.gloplacha.2016.12.012
M3 - Article
AN - SCOPUS:85010871811
SN - 0921-8181
VL - 149
SP - 166
EP - 176
JO - Global and Planetary Change
JF - Global and Planetary Change
ER -