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


Project Description

Project 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 benthic foraminifera (Standish et al., 2019). We will use this method to: (i) examine the role of ocean pH (and hence atmospheric CO2) change in ushering in the world of large polar ice sheets by generating records of deep ocean pH during the onset of Antarctic glaciation at the Eocene-Oligocene Transition (EOT; ~34 million years ago) [e.g., Coxall et al., 2005]; and (ii) determine the true magnitude of ocean acidification that accompanied the Paleocene-Eocene Thermal Maximum (PETM; ~56 million years ago) and other Eocene hyperthermals 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 benthic foraminifera by laser ablation has the potential to revolutionise the boron isotope technique for reconstructing the pH of past oceans. This arises because the sensitivity of the method is >10x higher than traditional bulk methods, and little or no sample preparation is required permitting fast sample throughput and development of records at unprecedented temporal resolution and in samples where material is scarce (Standish et al., 2019). The initial stages of the project will be focused on developing the method, in particular in using split-stream methods to simultaneously determine boron isotopes on multicollector inductively coupled plasma mass spectrometer (MC-ICPMS) and trace element composition (e.g. Mg/Ca, B/Ca, Al/Ca) on quadrapole ICPMS. Development will also be required to accurately measure the foram shells post-ablation for oxygen and carbon stable isotope ratios. This new method will then be applied to determine the evolution of ocean carbon content in unprecedented detail: (i) through the EOT from a global perspective, but focusing on North Atlantic drift sites from IODP Expedition 342 on the Newfoundland margin; and (ii) across the PETM and Eocene Thermal Maximam-2 events at New Jersey margin sites (e.g., Bass River) and at pelagic deep-sea sites.

Training:

All doctoral candidates will enroll in the Graduate School of NOCS (GSNOCS), where they will receive specialist training in oral and written presentation skills, have the opportunity to participate in teaching activities, and have access to a full range of research and generic training opportunities. GSNOCS attracts students from all over the world and from all science and engineering backgrounds. There are currently around 200 full- and part-time PhD students enrolled (~60% UK and 40% EU & overseas). The student will be part of the vibrant Geochemistry Group and Paleoceanography & Palaeoclimate groups in the School of Ocean and Earth Science, and a member of http://www.thefosterlab.org. Specific training will include the following techniques:

• Boron isotopic composition of foraminifera by laser ablation MC-ICPMS
• The trace element composition of foraminifera using laser ablation ICPMS
• 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 drillcores

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, and to international scientific meetings to present project results.

References

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

Coxall, H.K., Wilson, P.A., Pälike, H., Lear, C.H., and Backman, J., 2005. Rapid stepwise onset of Antarctic glaciation and deeper calcite compensation in the Pacific Ocean. Nature, 433: 53-57, doi:10.1038/nature03135

How good is research at University of Southampton in Earth Systems and Environmental Sciences?

FTE Category A staff submitted: 68.62

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