CO2 change and climate sensitivity in warmer worlds

CO2 exerts a major control on Earth’s environment, including ocean acidity and global climate. Human carbon emissions have elevated CO2 levels to 420 ppm, substantially higher than at any time in the 800,000 year ice core record. If we want to understand how Earth’s environment and climate will respond to a high CO2 world, we need to look deeper into the geological past (e.g. Tierney et al., 2020).

This project will use boron isotopes in marine carbonates to reconstruct atmospheric CO2 in key warmer-than-present intervals of the last 100 Million years. By examining the relationship between CO2 and global climate, we will constrain climate sensitivity, providing critical bounds on this crucial parameter for future climate predictions (e.g. Sherwood et al., 2020). These data will also allow us to better examine key CO2 thresholds for major ice growth and retreat, and to better understand the processes governing CO2 change on a range of timescales.

CO2 reconstructions will be based on the boron isotope composition (11B) of foraminifera (Foster & Rae 2016), which reflects water pH – and thus CO2 chemistry. This method has provided several high profile reconstructions during this time period (e.g. Gutjahr et al., 2017), yet few high-resolution records currently exist (see Rae et al., 2021). The aim of this project is to transform this with detailed new boron isotope reconstructions of atmospheric CO2.

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Image Captions

CO2 and climate change over the last 66 million years (Rae et al., 2021)


Marine carbonate samples are made available from the IODP and may also be collected during dedicated fieldwork. These will be analysed for boron isotopes and trace elements in the St Andrews Isotope Geochemistry (STAiG) labs, following techniques recently developed to improve precision on small samples. Trace elements will be measured on a new state-of-the-art triple quadrupole ICPMS.

We will also take advantage of – and continue to develop – new protocols for sample preparation (including automation), that will allow faster throughput of samples and thus higher resolution records to be generated. Depending on student interest, Earth system modelling may also be used to help understand the implications of and controls on changes in CO2.

The project is designed to be flexible, with the opportunity to focus on approaches, time intervals, and techniques of particular interest to the student.

Project Timeline

Year 1

Sediment core sampling, training in clean laboratory methods and mass spectrometry, initial measurements and training, literature review

Year 2

Generate long-term records. First manuscript.

Year 3

Finalize data sets including higher resolution intervals, apply numerical techniques, prepare written manuscripts and write thesis.

Year 3.5

Finalize data sets including higher resolution intervals, apply numerical techniques, prepare written manuscripts and write thesis.

& Skills

The student will gain specific training in mass spectrometry, clean lab chemistry, and geochemical modelling, as well as broader education in geochemistry, oceanography, and climate science. Over the course of the PhD the student will gain transferable skills such as scientific writing, statistics and data analysis, and problem-solving, as well as time management and working towards a long-term goal.

References & further reading

Foster & Rae (2016), AnnRev, 44, (207-237)
Gutjahr et al. (2017), Nature 548.7669 (2017): 573
Rae, et al., (2021). AnnRev, 49.
Tierney, et al. (2020). Science, 370(6517), p.eaay3701.

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