9315645 MIX This study has two primary goals: 1) To test two recent hypotheses that seek to explain the apparent disequilibrium of Delta-13C (and possibly Delta-18 O) in calcitic shells of symbiotic and asymbiotic planktic foraminifers. The first of these theories arises from laboratory culture work on Orbulina universa and states that photosynthesis by algal symbionts creates a light-dependent, but temperature-independent, Delta-13C enrichment in the shells of symbiotic species such as O. universa, G. sacculifer, and G. ruber, which issuperimposed on the combined host-symbiont respiratory Delta 13C depletion. The second theory, based on coral data and abiotic laboratory studies but which may apply to planktic foraminifers, postulates a linked kinetic disequilibrium in both Delta-13C and Delta-18 O that depends on calcification rate. 2) To evaluate the importance of deep calcification on the isotopic composition of foraminiferal tests. There is considerable evidence from sediment trap and plankton two studies to suggest that much of the isotopic composition of planktic foraminifers arises from equilibrium calcification at depths well below the euphotic zone - between 100m and 1000m depending on the species in question. It is important to consider both these research topics when attempting to evaluate the factors that control the isotopic composition of planktic foraminifers. It is possible for example, that the apparent observations of deep equilibrium calcification noted above are in fact due to disequilibrium calcification in the euphotic zone. Alternatively, deep equilibrium calcification superimposed on euphotic zone disequilibrium calcification could greatly obscure climatic information recorded in the foraminiferal test. Answers to these questions will have a profound effect on the climatic interpretation we place on isotopic results from planktic foraminifers.
