The thesis aims to describe developments in the uses of planktonic foraminiferal calcite for oceanographic applications, specifically Mg/Ca ratios and foraminiferal shell weights as proxies for calcification temperature and paleo-pCO2 respectively.

Sample preparation for the analysis of Mg/Ca and Sr/Ca ratios in foraminiferal calcite is investigated with the aim of defining a method that will give reproducible results and minimize signal contamination. Each step of the cleaning procedure is scrutinized in order to gauge which are most important and which may be omitted as unnecessary and potentially detrimental to the elemental measurements being made.

Success in the application of Mg/Ca-thermometry depends on the ability to quantify and compensate for any alteration of the primary signal after deposition. Compositional variations in foraminiferal calcite may be associated with partial dissolution at the seafloor. Investigation is made into the excessive scatter observed within a latitudinal transect of core-top Mg/Ca and Sr/Ca ratios and attributed to partial dissolution. Possible means of correcting for or minimizing the effects of such alteration are investigated and assessed.

Recent interest in planktonic foraminiferal shell weight loss as a proxy for dissolution, and, as such, a potential means of quantifying compositional variability, demands investigation into the possibility that initial shell weight may not be constant. It is demonstrated that considerable variability does occur in the shell weights of several species of planktonic foraminifera in the modern surface ocean. It is proposed that initial shell weight is a function of calcification rate and controlled ultimately by the carbonate ion concentration, [CO3=], of ambient seawater during calcification. A first attempt is made to calibrate the effects of [CO3=] on shell weight in the modern ocean. The potential effects of anthropogenic atmospheric CO2 increases on marine calcification are then synthesized using the empirical relations between [CO3=] and calcification rate.

The development and application of planktonic foraminiferal shell weight as a potential new proxy for paleo-pCO2 reconstruction is described. A down-core record of shell weight for a single species, Globigerina bulloides, is interpreted in terms of surface water [CO3=] variability over the last 50ka. By combining the calculated values of [CO3=] with thermodynamic constraints attained via Mg/Ca thermometry and paleosalinity estimation, it is shown that a realistic record of surface-ocean pCO2 may be constructed.