The Acid Test: revolutionizing the record of abrupt changes in ocean pH through novel laser analysis of marine microfossils

Gavin Foster, Dr Christopher Standish, Dr Andy Milton, Prof James Zachos (UCSC, California)
Rationale: 

Changes in the amount of carbon in the ocean are a prime controller of long and short trends in atmospheric CO2, and hence play a key role in the evolution of climate on all timescales in the geological past. As recent trends in ocean acidification show, ocean pH is intimately related to the amount of carbon in the atmosphere-ocean system. Records of past pH derived from the boron isotopic composition of foraminifera can therefore play a vital role in reconstructing not only the amount of CO2 in the atmosphere but also in understanding why atmospheric CO2 changed in the past (e.g., Gutjahr et al., 2017). In this project, you will exploit new analytical developments using laser ablation methods that allow for the rapid, accurate and precise analysis of the boron isotopic composition of single fossil specimens of foraminifera (Standish et al., 2019). There are no analogues to modern and future climate change, but scattered through the geological record are events of relatively rapid change called “hyperthermals”. We will use this method to determine the true magnitude of ocean acidification that accompanied the Paleocene-Eocene Thermal Maximum (PETM; ~56 million years ago) and other Eocene hyperthermals (e.g. Harper et al., 2020) to better constrain the sources of carbon during these enigmatic but important events (http://www.thefosterlab.org/blog/2018/9/4/hyperthermals-insights-into-our-warm-future-from-past-rapid-changes-in-climate).  

Methodology: 

Determination of the boron isotopic composition of single foraminifera by laser ablation has the potential to revolutionise our understanding of past oceanographic pH change. Thanks to >x10 higher sensitivity and quick sample preparation time, compared to traditional bulk methods, laser ablation permits a fast sample throughput facilitating the development of records at unprecedented temporal resolution, even where sample material is scarce (Standish et al., 2019). The initial stages of the project will be focused on developing the method, in particular focusing on exploiting recent mass spectrometric advances available at Southampton (e.g. our new ThermoScientific Neoma multicollector inductively coupled plasma mass spectrometer, MC-ICPMS, and our unique Nu Plasma Vitesse Time of Flight ICPMS) to combine boron isotopes with information on trace element composition (e.g. Mg/Ca, B/Ca, Al/Ca). The residual shell material left over from ablation will then be measured for oxygen and carbon stable isotope composition, and there is an option with young material, to explore linking single shelled radiocarbon dates with these other proxy systems (through collaboration with Dr Bryan Loughead, Uppsala University, Sweden). This multiproxy tool-kit will be capable of tracing a wide range of palaeo-environmental variables (e.g. temperature, pH, carbon system), and, once developed, it will be ground-truthed in more modern samples to explore the wealth of information locked up in single foraminiferal shells. It will then be applied to determine the evolution of ocean carbon content in unprecedented detail across the PETM and Eocene Thermal Maximum-2 events on the New Jersey margin (e.g., Bass River) and at several pelagic deep-sea sites (e.g. ODP 1210 in the North Pacific and Site 1265 in SE Atlantic; Harper et al. 2020, in addition to the soon to be drilled sites from the IODP Expedition 392 Agulhas Plateau).

 

Location: 
University of Southampton
Training: 

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted in the School of Ocean and Earth Science, which cohabits the National Oceanography Centre Southampton. Specific training willinclude:

·         Boron isotopic composition of foraminifera by laser ablation MC-ICPMS on our newly purchased Neoma MC-ICPMS with its collision cell and MS/MS option.

·         The analysis of the chemical composition of foraminifera using our novel time of flight ICPMS method.

·         Methods of sample preparation, foram taxonomy, and foraminiferal cleaning

·         Oxygen and carbon stable isotope analysis of foraminifera

·         Correlation, integration, and interpretation of multi-proxy datasets from marine drill cores.

·         Foraminiferal taxonomy and physiology

 

The student will spend at least 3 months of the studentship at the University of California, Santa Cruz, with Zachos preparing samples from the PETM and other Eocene hyperthermals. In addition, there will be opportunities to travel to International Ocean Discovery Program core repositories, participate in IODP-related workshops and summer schools, and to attend international scientific meetings to present project results

Eligibility & Funding Details: 

Please see https://inspire-dtp.ac.uk/how-apply for details.

Background Reading: 

Gutjahr, M., Ridgwell, A., Sexton, P. F., Anagnostou, E., Pearson, P. N., Pälike, H., ... Foster, G. L. (2017). Very large release of mostly volcanic carbon during the Paleocene-Eocene Thermal Maximum. Nature, 548, 573-577. DOI: 10.1038/nature23646.

 

Standish, C.D., Chalk, T.B., Babila, T.L., Milton, J.A., Palmer, M.R., Foster, G.L. (2019) The effect of matrix interferences in situ boron isotope analysis by laser ablation MC-ICP-MS, Rapid Communications in Mass Spectrometry,  33, 959-968, https://doi.org/10.1002/rcm.8432. 

 

Harper, D.T., Honisch, B., Zeebe, R.E., Schaffer, G., Haynes, L.L., Thomas, E., Zachos, J.C. (2020) The magnitude of surface ocean acidification and carbon release during Eocene Thermal Maximum 2 (ETM-2) and the Paleocene-Eocene Thermal Maximum (PETM), Paleoceanography and Paleoclimatology, 35, e2019PA003699, https://doi.org/10.1029/2019PA003699.