I n chapter 2 the isotopic fractionation of water in some simple condensation-evaporation processes are considered quantitatively on the basis of the fractionation factors given in section 1.2. The condensation temperature is an important parameter, which has got some glaciological applications. The temperature effect (the 6's decreasing with temperature) together with varying evaporation and exchange appear in the "amount effect" as high 6's in sparse rain. The relative deuterium-oxygen-18 fractionation is not quite simple. If the relative deviations from the standard water (S.M.O.W.) are called 6, and 6,,, the best linear approximation is 6, = 8 6,,. Chapter 3 gives some qualitative considerations on non-equilibrium (fast) processes. Kinetic effects have heavy bearings upon the effective fractionation factors. Such effects have only been demonstrated clearly in evaporation processes, hut may also influence condensation processes. The quantity d = 6, -8 is used as an index for non-equilibrium conditions. The stable isotope data from the world wide 1.A.E.A.-W.M.O. precipitation survey are discussed in chapter 4. The unweighted mean annual composition of rain at tropical island stations fits the line 6, = 4.6 6,, indicating a first stage equilibrium condensation from vapour evaporated in a non-equilibrium process. Regional characteristics appear in the weighted means. The Northern hemisphere continental stations, except African and Near East, f i t the line 6 , = 8.0 a,, + 10 as far as the weighted means are concerned (6, = 8.1 a, , + 11 for the unweighted) corresponding to an equilibrium Rayleigh condensation from vapour, evaporated in a non-equilibrium process from S.M.O.W. The departure from equilibrium vapour seems even higher in the rest of the investigated part of the world.At most stations the 6, and varies linearily with a, , with a slope close to 8, only at two stations higher than 8, at several lower than 8 (mainly connected with relatively dry climates). Considerable variations in the isotopic composition of monthly precipitation occur at most stations. At low latitudes the amount effect accounts for the variations, whereas seasonal variation at high latitudes is ascribed to the temperature effect. Tokyo is an example of a mid latitude station influenced by both effects.Some possible hydrological applications are outlined in chapter 5. (FRIEDMAN, 1953).(4) The heavy isotope content in precipitation decreases with the condensation temperature, which is reflected b y ( a ) variation of t h e composition of precipitation from individual atmospheric cooling processes-in simple cases in accordance with the Rayleigh condit,ions ( DANSGAARD, 1953),the heavy isotope concentrations in fresh water decreasing with increasing 1at.it u d e and altitude (DANSGAARD, 1954), and Tellus XVI (1964), 4 & 0.2 x0 on 6,, for OI8. For details of the measuring technique reference is made to DANSGAARD (1961).If a sample composition is given by d' relative to a secondary standard, which deviates 6,%, from SMOW, the 6 for the samp...

In chapter 2 the isotopic fractionation of water in some simple condensation‐evaporation processes are considered quantitatively on the basis of the fractionation factors given in section 1.2. The condensation temperature is an important parameter, which has got some glaciological applications. The temperature effect (the δ's decreasing with temperature) together with varying evaporation and exchange appear in the “amount effect” as high δ's in sparse rain. The relative deuterium‐oxygen‐18 fractionation is not quite simple. If the relative deviations from the standard water (S.M.O.W.) are called δD and δ18, the best linear approximation is δD = 8 δ18. Chapter 3 gives some qualitative considerations on non‐equilibrium (fast) processes. Kinetic effects have heavy bearings upon the effective fractionation factors. Such effects have only been demonstrated clearly in evaporation processes, but may also influence condensation processes. The quantity d = δD −8 δ18 is used as an index for non‐equilibrium conditions. The stable isotope data from the world wide I.A.E.A.‐W.M.O. precipitation survey are discussed in chapter 4. The unweighted mean annual composition of rain at tropical island stations fits the line δD = 4.6 δ18 indicating a first stage equilibrium condensation from vapour evaporated in a non‐equilibrium process. Regional characteristics appear in the weighted means. The Northern hemisphere continental stations, except African and Near East, fit the line δD = 8.0 δ18 + 10 as far as the weighted means are concerned (δD = 8.1 δ18 + 11 for the unweighted) corresponding to an equilibrium Rayleigh condensation from vapour, evaporated in a non‐equilibrium process from S.M.O.W. The departure from equilibrium vapour seems even higher in the rest of the investigated part of the world. At most stations the δD and varies linearily with δ18 with a slope close to 8, only at two stations higher than 8, at several lower than 8 (mainly connected with relatively dry climates). Considerable variations in the isotopic composition of monthly precipitation occur at most stations. At low latitudes the amount effect accounts for the variations, whereas seasonal variation at high latitudes is ascribed to the temperature effect. Tokyo is an example of a mid latitude station influenced by both effects. Some possible hydrological applications are outlined in chapter 5.

No abstract

No abstract

Abstract. Well-documented present-day distributions of stable water isotopes (HDO and H2180) show the existence, in middle and high latitudes, of a linear relationship between the mean annual isotope content of precipitation (/SD and/5•SO) and the mean annual temperature at the precipitation site. Paleoclimatologists have used this relationship, which is particularly well obeyed over Greenland and Antarctica, to infer paleotemperatures from ice core data. There is, however, growing evidence that spatial and temporal isotope/ surface temperature slopes differ, thus complicating the use of stable water isotopes as paleothermometers. In this paper we review empirical estimates of temporal slopes in polar regions and relevant information that can be inferred from isotope models: simple, Rayleigh-type distillation models and (particularly over Greenland) general circulation models (GCMs) fitted with isotope tracer diagnostics. Empirical estimates of temporal slopes appear consistently lower than present-day spatial slopes and are dependent on the timescale considered. This difference is most probably due to changes in the evaporative origins of moisture, changes in the seasonality of the precipitation, changes in the strength of the inversion layer, or some combination of these changes. Isotope models have not yet been used to evaluate the relative influences of these different factors. The apparent disagreement in the temporal and spatial slopes clearly makes calibrating the isotope paleothermometer difficult. Nevertheless, the use of a (calibrated) isotope paleothermometer appears justified; empirical estimates and most (though not all) GCM results support the practice of interpreting ice core isotope records in terms of local temperature changes. •

No abstract

No abstract

No abstract