Publications des scientifiques de l'IRD

Alexandre A., Landais A., Vallet-Coulomb C., Piel C., Devidal S., Pauchet S., Sonzogni C., Couapel Martine, Pasturel M., Cornuault P., Xin J. M., Mazur J. C., Prie F., Bentaleb I., Webb E., Chalie F., Roy J. (2018). The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity : insights from climate chamber and climate transect calibrations. Biogeosciences, 15 (10), p. 3223-3241. ISSN 1726-4170.

Titre du document
The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity : insights from climate chamber and climate transect calibrations
Année de publication
2018
Type de document
Article référencé dans le Web of Science WOS:000433556900001
Auteurs
Alexandre A., Landais A., Vallet-Coulomb C., Piel C., Devidal S., Pauchet S., Sonzogni C., Couapel Martine, Pasturel M., Cornuault P., Xin J. M., Mazur J. C., Prie F., Bentaleb I., Webb E., Chalie F., Roy J.
Source
Biogeosciences, 2018, 15 (10), p. 3223-3241 ISSN 1726-4170
Continental atmospheric relative humidity (RH) is a key climate parameter. Combined with atmospheric temperature, it allows us to estimate the concentration of atmospheric water vapor, which is one of the main components of the global water cycle and the most important gas contributing to the natural greenhouse effect. However, there is a lack of proxies suitable for reconstructing, in a quantitative way, past changes of continental atmospheric humidity. This reduces the possibility of making model-data comparisons necessary for the implementation of climate models. Over the past 10 years, analytical developments have enabled a few laboratories to reach sufficient precision for measuring the triple oxygen isotopes, expressed by the O-17-excess (O-17-excess = ln (delta O-17+1)-0.528 x ln (delta O-18+1)), in water, water vapor and minerals. The O-17-excess represents an alternative to deuterium-excess for investigating relative humidity conditions that prevail during water evaporation. Phytoliths are micrometric amorphous silica particles that form continuously in living plants. Phytolith morphological assemblages from soils and sediments are commonly used as past vegetation and hydrous stress indicators. In the present study, we examine whether changes in atmospheric RH imprint the O-17-excess of phytoliths in a measurable way and whether this imprint offers a potential for reconstructing past RH. For that purpose, we first monitored the O-17-excess evolution of soil water, grass leaf water and grass phytoliths in response to changes in RH (from 40 to 100 %) in a growth chamber experiment where transpiration reached a steady state. Decreasing RH from 80 to 40% decreases the O-17-excess of phytoliths by 4.1 per meg/% as a result of kinetic fractionation of the leaf water subject to evaporation. In order to model with accuracy the triple oxygen isotope fractionation in play in plant water and in phytoliths we recommend direct and continuous measurements of the triple isotope composition of water vapor. Then, we measured the O-17-excess of 57 phytolith assemblages collected from top soils along a RH and vegetation transect in inter-tropical West and Central Africa. Although scattered, the O-17-excess of phytoliths decreases with RH by 3.4 per meg/%. The similarity of the trends observed in the growth chamber and nature supports that RH is an important control of O-17-excess of phytoliths in the natural environment. However, other parameters such as changes in the triple isotope composition of the soil water or phytolith origin in the plant may come into play. Assessment of these parameters through additional growth chambers experiments and field campaigns will bring us closer to an accurate proxy of changes in relative humidity.
Plan de classement
Sciences fondamentales / Techniques d'analyse et de recherche [020] ; Sciences du milieu [021] ; Pédologie [068] ; Bioclimatologie [072]
Description Géographique
MAURITANIE ; SÉNÉGAL ; GABON ; CONGO ; ZONE SAHARIENNE ; ZONE SOUDANOSAHELIENNE ; ZONE TROPICALE ; ZONE GUINÉENNE ; ZONE EQUATORIALE
Localisation
Fonds IRD [F B010073057]
Identifiant IRD
fdi:010073057
Contact