Boron has two naturally occuring stable isotopes - 10B and 11B. The 11B/10B ratio in marine carbonate (such as the shells of foraminifer) is set by the pH of the water in which the carbonate grew. Whilst the pH proxy is growing in popularity we continue its ground truthing and pursue analytical developments that exploit the latest technologies.
It was recognised in the early 1990's that the boron isotopic composition of marine carbonates, such as foraminifera and coral, was determined largely by ocean pH (Hemming and Hanson, 1992).
The development of the boron isotope-pH proxy rapidly followed and has occured hand-in-hand with advances in analytical techniques.
Because boron has only two isotopes, getting the required analytical precision is therefore difficult.
Gavin and his group has been at the forefront of using the latest generation of mass spectrometers (multi-collector inductively coupled plasma mass spectrometers, MC-ICPMS for short) to make the tricky boron isotope measurements for the past decade (e.g. see Foster, 2008 and Foster et al., 2013).
We continue to make analytical developments and are currently exploring a number of novel systems to aid in the measurement and preparation of samples (e.g. ESI's prepFAST).
Along side these analyitical efforts, we are also exploring the groundtruthing of the proxy with culture experiments (growing coral and foraminifera at different pH) and laboratory experiments with inorganic calcite/aragonite.
Our ultimate aim is to make boron isotope measurements routine and strengthen the theoretical and experimental basis of the d11B-pH proxy.
Foster, G.L., and Rae, J.W.B (2016) Reconstructing ocean pH with boron isotopes in foraminifera. Annual Review of Earth and Planetary Sciences, 44, 207-237 (doi:10.1146/annurev-earth-060115-012226)
Martin, P., Goodkin, N. F., Stewart, J.A., Foster, G.L., Sikes, E.L., White, H.K., Hennige, S., Roberts, J.M. (2016) Deep-sea coral d13C: A tool to reconstruct the difference between seawater pH and d11B-derived calcification site pH. Geophysical Research Letters, 43, 299-308 (doi:10.1002/2015GL066494).
Edgar, Kirsty M., Anagnostou, Eleni, Pearson, Paul N. and Foster, Gavin L. (2015) Assessing the impact of diagenesis on δ11B, δ13C, δ18O, Sr/Ca and B/Ca values in fossil planktic foraminiferal calcite. Geochimica et Cosmochimica Acta (doi:10.1016/j.gca.2015.06.018).
Foster, Gavin L., Hönisch, Bärbel, Paris, Guillaume, Dwyer, Gary S., Rae, James W.B., Elliott, Tim, Gaillardet, Jérôme, Hemming, N. Gary, Louvat, Pascale and Vengosh, Avner (2013) Interlaboratory comparison of boron isotope analyses of boric acid, seawater and marine CaCO3 by MC-ICPMS and NTIMS. Chemical Geology, 358, 1-14. (doi:10.1016/j.chemgeo.2013.08.027).
Henehan, Michael J., Rae, James W. B., Foster, Gavin L., Erez, Jonathan, Prentice, Katherine C., Kucera, Michal, Bostock, Helen C., Martínez-Botí, M.A., Milton, J.A., Wilson, P.A., Marshall, Brittney J. and Elliott, Timothy (2013) Calibration of the boron isotope proxy in the planktonic foraminifera Globigerinoides ruber for use in palaeo-CO2 reconstruction. Earth and Planetary Science Letters, 364, 111-122. (doi:10.1016/j.epsl.2012.12.029).