Isotopic water composition continental effect

Fig. 9. Continued) and Ab O values (this study, and McCorkle et al 1997). The carbon isotopic offsets are calculated relative to bottom water DIC, and the oxygen isotopic offsets are calculated relative to calcite in equilibrium with bottom water using the expressions of McCorkle et al (1997) (solid diamonds) and Shackleton (1974) (open circles). The vertical line shows the trend in isotopic offsets predicted by a pore water b C effect only. The observed b C depletions of pore water DIC in the 0-0.5 cm depth interval range from — 1 to — 2.2%o at the nearby sites discussed by McCorkle et al (1997) (white hexagons, dotted line). Because pore water carbonate ion concentration is likely to be lower than bottom water values at these relatively shallow continental margin sites, a carbonate ion influence on shell composition would tend to cause Ab O values greater than zero (ellipse).

We determined the shell C and O isotopic composition of the cultured foraminifera, and compared these isotopic values with the water chemistry of the culture chambers, and also with the shell chemistry of field specimens collected from sites on the North Carolina and South Carolina (USA) continental margin. The culmred foraminifera showed substantial offsets from the 8 C of system water dissolved inorganic carbon (—0.5 to —2.5%c, depending on species) and smaller offsets (0 to — 0.5%o) from the predicted 8 0 of calcite in equilibrium with the culture system water at the growth temperature. These offsets reflect at least three factors species-dependent vital effects ontogenetic variations in shell chemistry and the aqueous carbonate chemistry ([COJ] or pH) of the experimental system. 

Continental glaciation exerts effects on the isotopic composition of the oceans arising from isotopic fractionation in the meteoric cycle. High-latitudinal precipitation is depleted in the heavy stable isotopes relative to ocean water so that when continental glaciers grow, the light... 

The effect of early diagenesis on the Fe isotope compositions of pore waters and authigenic minerals in continental margin sediments. Geochim. Cosmochim. Acta, 70 (8), 2006-2022. 

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