Ontogenetic isotopic variation in foraminifera - Implications for palaeo proxy

Abstract

The oxygen isotopic composition (delta(18)O) of Marginopora kudakajimaensis (Foraminiferida) is found to differ by 0.5parts per thousand among the individuals living under similar physico-chemical conditions. The delta(18)O variation along the growth direction (ontogeny) is much higher, ranging between 1.5,and 2.5parts per thousand. In comparison, the ontogenetic variation in carbon isotopes (delta(13)C) is relatively small. The range and standard deviation of ontogenetic delta(18)O decrease progressively for deeper water species. There is no such systematic change in oft values. The study suggests that as palaeo proxy, the isotopic data not only require correct species discrimination but also a good understanding of the palaeobiology of the species.