New constraints on CO2 using the boron isotope proxy - NERC GW4+ DTP project

This project is one of a number that are in competition for funding from the NERC GW4+ DTP. The GW4+ DTP consists of the Great Western Four alliance of the University of Bath, University of Bristol, Cardiff University and the University of Exeter plus six Research Organisation partners. The partnership aims to provide a broad training in earth and environmental sciences, designed to train tomorrow’s leaders in earth and environmental science. For further details about the programme, please see http://nercgw4plus.ac.uk/

Background
The boron-isotope proxy for seawater pH provides important constraints on past variations in ocean acidification and pCO2 (Hemming and Hönisch, 2007) – both of outstanding importance for understanding the evolution of Earth’s climate system.

To date, the proxy has been used most extensively in foraminifera microfossils (e.g., Foster et al., 2012). However, the foraminiferal boron isotope proxy is extremely sensitive to changes in seawater chemistry which remain poorly constrained for intervals older than ~10 Myr. This presents a real challenge for reconstructions of absolute pCO2 in deep time.

Organisms that exert a pH control on an internal calcification pool provide a novel opportunity to constrain past changes in the boron isotopic composition of seawater. This project will reconstruct changes in the boron isotopic composition of seawater through time, and use these new reconstructions to quantify pCO2 in past warm climates..

Project Aims and Methods
The project aims are:
1) to reconstruct changes in the boron isotopic composition of seawater through time
2) use this record to determine absolute pCO2 concentrations in past warm climates.
The project will explore the sensitivity to seawater pH and boron isotope composition in a range of biogenic calcite, including molluscs and fish otoliths.

Modern samples from a range of seawater pH conditions will be analysed for their boron isotope composition. The method will be validated using Pleistocene samples before being applied to deep time samples. Fossil samples could be collected during fieldwork or drawn solely from collections, for example National Museum Wales, University of Copenhagen, Natural History Museum of Copenhagen or other national/international archives.

Samples will be prepared in Cardiff University’s clean lab facility, and analysed using their Nu Plasma 2 multi-collector ICP-MS. Samples will be analysed as solutions and by using the laser ablation facility at Cardiff University. Fossil samples will be screened using the Cathodoluminescence Microscope at Exeter University.