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Global trends in the δ²H-δ18O enrichment slope of continental lakes and shallow soil water undergoing natural evaporation are predicted on the basis of a steady state isotope balance model using basic monthly climate data (i.e., temperature and humidity), isotopes in precipitation data, and a simple equilibrium liquid-vapor model to estimate isotopes in atmospheric moisture. The approach, which demonstrates the extension of well-known conceptual models in stable isotope hydrology to the global scale, is intended to serve as a baseline reference for evaluating field-based isotope measurements of vapor, surface water, and soil water and as a diagnostic tool for more complex ecosystem models, including isotope-equipped climate models. Our simulations reproduce the observed local evaporation line slopes (4-5 range for lakes and 2-3 range for soil water) for South America, Africa, Australia, and Europe. A systematic increase in slopes (5-8 range for lakes) toward the high latitudes is also predicted for lakes and soil water in northern North America, Asia, and Antarctica illustrating a latitudinal (mainly seasonality-related) control on the evaporation signals that has not been widely reported. The over-riding control on the poleward steepening of the local evaporation lines is found to be the isotopic separation between evaporation-flux-weighted atmospheric moisture and annual precipitation, and to lesser extents temperature and humidity, all of which are influenced by enhanced seasonality in cold regions. [ABSTRACT FROM AUTHOR]

Information about the paper on new tool for paleoclimate reconstructions on continents that was discussed at the European Society for Isotope Research (ESIR) meeting is presented. The δ18Oxygen of the cellulose organic fraction provides an insight into changes of the δ18Oxygen of lake water. The changes in lake water were caused by the change of the oxygen abundance of the local precipitation and in the evaporative enrichment of the lake water.

The vertical distributions of 18O and 2H in porewater of a glaciolacustrine clay were simulated to explore the potential conservation of signals deriving from changes in the isotopic composition of Holocene precipitation in low-permeability deposits. The simulations used a groundwater velocity of zero, assuming that transport was solely by diffusion. As expected, distributions were highlysensitive to the timing of Holocene events, with recent events having the greatest preservation potential. Simulations show that these signals are confined to the area immediately below the weathered zone, where infiltration of modern water via fractures or fluctuations in the water table could threaten signal preservation in the field. Century-scale events with magnitudes of 6 thousandths or less in delta18O have little effect on the isotopic profiles if they occur more than 1000 years ago. Longer duration events occurring more than 1000 years ago are preserved as slight alterations in the shape of the isotopic profiles. Differences in the effective diffusion coefficients for 1H2H16O and 1H2 18O result in alteration of the original d-excess (d = delta2H-8delta18O). Hence this parameter is not conservative in groundwater environments where transport is dominantly by diffusion. On the other hand, simulated vertical profiles of d-excess amplify fluctuations in the isotopic composition of precipitation that are subdued in the individual profiles of delta18O and delta2H. Simulations that include Holocene events with timings, durations and magnitudes estimated for the Hypsithermal, Medieval Warm Period and Little Ice Age result in distributions that differ from the baseline by ~=076 thousandths in delta18O (~-=5 thousandths in delta2H). That these events are preservedas a measurable offset in the isotopic profile suggests that some aqui [ABSTRACT FROM AUTHOR]