Research Student 2011
Climate Change and Earth-Ocean-Atmosphere Systems
Project Title: Glacial-interglacial variation in ocean pH and the response of deep ocean carbonate cycles
Project Supervisor: Harry Elderfield
Project Description: Seawater boron isotopic composition reflected in foraminifera tests is strongly influenced by changes in pH and hence atmopsheric carbon dioxide concentration - a critical control over Earth's climate. The use of boron isotopes as a proxy for paleo-pH therefore has the potential to help reconstruct changes in the oceanic carbonate system and climate over millions of years. However, analytical difficulties currently prevent full realisation of the potential of boron isotopes as a measure of ancient seawater pH. Extremely well constrained pH values are of paramount importance, as a slight overestimation of the decrease in oceanic pH by as little as 0.2 can infer a doubling of atmopsheric carbon dioxide concentrations compared to present levels. We are currently developing existing ICP-MS methods for measuring boron isotopes and trace elements at low concentrations in foraminifera, whilst maintaining low procedural blanks and high precision.
The primary aim of my project is to determine how the accumulation of calcium carbonate deposits on the ocean floor is linked to surface and deep ocean pH on glacial-interglacial timescales. A simple view of the oceanic carbonate system is that it acts as a buffer, such that when concentrations of carbonate ion in the ocean increase, atmopsheric carbon dioxide concentrations and hence pH decrease, and vice versa. Carbonate ion concentrations also control whether or not calcium carbonate is preserved in sediments, however, at certain times carbonate accumulation is seemingly not linked to climate. I aim to reconstruct past ocean pH to investigate the relationship between surface and deep ocean pH and calcite preservation. This will help to improve understanding of the controls of atmopsheric carbon dioxide by deep-ocean carbonate storage.