Isotopic composition seasonal variations

In the last decades, several ice cores over 1,000 m depth have been recovered from Greenland and Antarctica. In these cores, seasonal variations are generally observed only for the uppermost portions. After a certain depth, which depends on accumulation rates, seasonal variations disappear completely and isotopic changes reflect long-term climatic variations. No matter how thin a sample one cuts from the ice core, its isotope composition will represent a mean value of several years of snow deposition. 

Application of Isotopic Methods to Non-Steady-State Groundwater-Lake Systems. Isotopic compositions of lakes whose hydraulic-residence times are relatively short (about 2 years or less) vary seasonally (32). Seasonal response occurs whenever a significant mass of water of a different isotopic composition is either added to or removed from the lake. Seasonal variations in P, E, G, 8P, 8a, and 8 are the principal driving forces behind observed variations in 8j for isotopically non-steady-state systems. In northern Wisconsin, many lakes are isotopically non-steady-state. 

Rivers and streams not only integrate the precipitation amount weighted hypsometric mean elevation of the drainage basin above the sampling site, but also the seasonal variation in the isotopic composition of the precipitation falling on that watershed. This will be most... 

Fricke HC, Clyde WC, O Neil JR (1998) Intra-tooth variations in 8180(P04) of mammalian tooth enamel as a record of seasonal variations in continental climate variables. Geochim Cosmochim Acta 62 1839-1850 Fricke HC, O Neil JR (1996) Inter-and intra-tooth variation in the oxygen isotope composition of mammalian... 

Chanton, J.P., and Martens, C.S. (1988) Seasonal variations in ebulhtive flux and carbon isotopic composition of methane in a tidal freshwater estuary. Global Biogeochem. Cycles 2, 289-298. 

The amount of monthly rain varies during the year, causing a seasonal variation in the isotopic composition. This point is demonstrated in a case study from northeastern Brazil (Fig. 9.13). 

In the previous sections the many factors that determine the isotopic composition of groundwater have been described. Many of these, especially the temperature, vary seasonally, while others, such as the intensity of rain, vary from one rain event to another. As a result, single samples may be nonrepresentative. Table 9.5 gives examples for the variations between daily precipitation events for a single station. 

Further studies followed the annual variation in O and Deuterium content of precipitation and of stream water. It was found that the isotopic composition of the rainwater varied with season of the year, but this was not reflected by changes in the drainage water, su esting a mixing of waters and a high soil water storage. 

Hemming N. G., Guilderson T. P., and Fairbanks R. G. (1998a) Seasonal variations in the boron isotopic composition of coral a productivity signal Global Biogeochem. Cycles 12(4), 581-586. 

However, the isotopic composition of seepage water at some localities is observed to be distinctly different from the annual average precipitation at the cave site, where cave drip waters may exhibit either a seasonal bias away from annual average rainfall, or large variations within individual cave systems or within local karst areas (Table 4)... 

Expected foraminiferal oxygen isotopic composition. We calculate 8 0 offsets between foraminiferal calcite and the 8 0 values predicted for calcite in equihhrium with culture system 8 0(water) at the average culture temperature (7 °C). The observed variation in the culture system 8 0(water) values during each experiment (Fig. 1) is much smaller than the seasonal cycle in S C(DIC) values (Figs 4 and 6b), and most of the 2002 8 0(water) shift occurred early in the experiment, before we expect significant foraminiferal calcification to have taken place (Fig. 1). We therefore used the average 8 0(water) value for each experiment (8 0(water) = —4.32%c in 2001 and — 3.39%o in 2002) to calculate the equilibrium calcite 8 0. 

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