Liliane Merlivat

Bio: Liliane Merlivat is an academic researcher. The author has contributed to research in topics: Water vapor & Condensation. The author has an hindex of 1, co-authored 1 publications receiving 397 citations.

Molecular diffusivities of H2 16O,HD16O, and H2 18O in gases

Abstract: Isotopic effects on the molecular diffusion coefficients of H2 16O, HD16O, and H2 18O have been determined by two independent methods. In the first one, the evaporation of liquid water under controlled laminar flow conditions was investigated. In the second one, the transport of water vapor through a diffusion tube was measured. The molecular diffusion coefficient of natural water vapor in nitrogen was redetermined. At 21 °C and P=760 Hg mm, D=0.244±0.004 cm2/sec. For the isotopic molecules we have DHD16O/DH216O=0.9757±0.0009 and DH218O/DH216O=0.9727±0.0007. Agreement between the data obtained in the pure gas phase experiment and the two‐phase experiment shows that the condensation coefficients of the isotopically substituted molecules are identical. Interpretation of the isotopic effects on molecule diffusivities indicates that the relative mass differences between H2 16O, HD16O, and H2 18O alone cannot account for the experimental results. This is more important for the D–H substitution in which the asy...

Oxygen and hydrogen isotopes in the hydrologic cycle

Abstract: Changes of the isotopic composition of water within the water cycle provide a recognizable signature, relating such water to the different phases of the cycle. The isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes. As a result, meteoric waters are depleted in the heavy isotopic species of H and O relative to ocean waters, whereas waters in evaporative systems such as lakes, plants, and soilwaters are relatively enriched. During the passage through the aquifers, the isotope composition of water is essentially a conservative property at ambient temperatures, but at elevated temperatures, interaction with the rock matrix may perturb the isotope composition. These changes of the isotope composition in atmospheric waters, surface water, soil, and groundwaters, as well as in the biosphere, are applied in the characterization of hydrological system as well as indicators of paleo-climatological conditions in proxy materials in climatic archives, such as ice, lake sediments, or organic materials.

Global climatic interpretation of the deuterium‐oxygen 18 relationship for precipitation

Abstract: A theoretical model is derived to account for the deuterium-oxygen 18 relationship measured in meteoric waters. A steady state regime is assumed for the evaporation of water at the ocean surface and the subsequent formation of precipitation. The calculations show that the deuterium and oxygen 18 content in precipitation can be taken as linearly related. From the slope and the intercept (known as the deuterium excess) of the δD-δ18O linear relationship for precipitation we compute the mean values on a global scale of the evaporating ocean surface temperature and the relative humidity of the air masses overlying the oceans. The deuterium excess is primarly dependent on the mean relative humidity of the air masses formed above the ocean surface. Paleoclimatic data may be obtained by this isotopic method from the analysis of old water and ice samples. A moisture deficit of the air over the ocean, equal to only 10%, in comparison to 20% for modern conditions, is deduced from the deuterium-oxygen 18 distribution measured in groundwater samples older than 20,000 years.

Deuterium and oxygen 18 in precipitation: Modeling of the isotopic effects during snow formation

Abstract: The classical Rayleigh model assuming isotopic equilibrium fails to explain the deuterium and oxygen 18 contents of polar snow. This model leads to too high temperature-isotope gradients (both for δD and δ18O), to too low δD - δ18O slopes, and consequently to an excessively large range of deuterium excess values (d = δD - 8δ18O). We present a new model that takes into account the existence of an isotopic kinetic effect at snow formation as a result of the fact that vapor deposition occurs in an environment supersaturated over ice. This kinetic effect is thoroughly discussed from a microphysical point of view and tested against experimental data and field observations. This new formulation reconciles predicted and observed values both for the temperature-isotope and δD - δD18O relationships for reasonable values of supersaturation over ice.

Carbon Isotope Fractionation and Plant Water-Use Efficiency

Abstract: In order for plants to grow, they must fix carbon. Carbon usually enters the leaves as carbon dioxide, diffusing through pores in the epidermis called stomata. Increased stomatal conductance, g, of leaves causes an increase in the partial pressure of CO2 inside the leaves, p i . This usually causes an increase in the rate of CO2 assimilation, A, but also allows a greater rate of transpirational water loss, E. Such an action by a plant is a gamble, because while it increases the likelihood of growth and reproductive success, it also increases the probability of desiccation and death (Cowan 1986).