17O-excess of grass leaf phytoliths across the North American prairies records late-growing season daytime relative humidity

17O-excess of grass leaf phytoliths across the North American prairies records late-growing season daytime relative humidity Guo M. E. auteur aut IRD Alexandre A. auteur aut IRD Longstaffe F. J. auteur aut IRD Peugeot Christophe auteur aut IRD Webb E. A. auteur aut IRD text journalArticle eng text/pdf reformatted digital access Because it is an important climate parameter, an accurate proxy is required for the reconstruction of past Relative Humidity (RH). Triple oxygen isotopes of grass-leaf phytoliths have a high potential for this purpose. A strong correlation between RH and O-17-excess of grass leaf phytoliths has been previously demonstrated from calibration experiments in growth chambers and at natural Sub-Saharan African and Mediterranean sites. Here we focus on the potential of 17 O-excess of grass leaf phytoliths as a proxy of RH across the North American Great Plains. We tested the relationship between the O-17-excess of naturally grown Calamovilfa longifolia phytoliths and RH for different periods of the grass growing season. The results show that O-17-excess of leaf phytoliths has a strong correlation with late-growing season (July-August) daytime RH, which varies from 29 to 72 % across North America. The correlation can be expressed as: O-17-excess leaf phytoliths = 4.14(+0.47) x RH (%) - 497(+26) (R-2 = 0.85, p-value<0.0001). To use the O-17-excess of bulk phytoliths buried in soils and sediments as a quantitative proxy of past RH, future calibration studies on soil phytoliths are needed to evaluate the contribution of non-transpiring phytoliths. The(17)O-excess of stem water, which was determined by O-17-excess of stem phytoliths, shows similar values to the O-17-excess of precipitation in North America without evaporation, which therefore does not affect the O-17-excess of leaf phytoliths in North America. These results demonstrate that the O-17-excess of phytoliths is a promising proxy for regional growing season RH. specialized Phytoliths Relative Humidity Transpiration North American prairies O-17-excess AMERIQUE DU NORD 021 020 076 068 Chemical Geology 671 122484 [11 p.] 2025 0009-2541 https://www.documentation.ird.fr/hor/fdi:010092600 10.1016/j.chemgeo.2024.122484 0009-2541 [F B010092600] https://www.documentation.ird.fr/hor/fdi:010092600 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2025-02/010092600.pdf IRD - Base Horizon / Pleins textes 2025-02-07 2025-11-04 fdi:010092600 fre