IAP2-22-453

Constraining the climatic impact of mystery volcanic eruptions

Large explosive volcanic eruptions are the most important natural drivers of climate variability and have led to major societal impacts in the past via the global cooling they exert. In an evolving climate, it is vital that we understand all drivers of climate change, including those from natural sources. However, the climatic impact of eruptions that occurred before the satellite era is highly uncertain. Sulfate aerosol produced from eruptions can be transported throughout the atmosphere and is eventually deposited on the surface, including on the Greenland and Antarctic ice sheets, where it is incorporated into ice. Sulfate spikes in ice cores are an excellent record of past volcanic eruptions (e.g. Sigl et al., 2015) but most of the signals are from mystery eruptions, and could be attributable to a wide range of eruptions with different properties including the SO2 emission, latitude and emission altitude (e.g. Marshall et al., 2021). This is problematic because eruptions with different properties have different climate impacts (e.g. Marshall et al., 2019) and consequently there is a large uncertainty associated with estimating the climatic impact of eruptions using ice core sulfate deposition records.

Measurements of sulfur isotopes in ice cores can provide critical additional information. These measurements can be used to identify whether sulfate produced after an eruption was present in the stratosphere above the ozone layer due to exposure to UV radiation that produces a specific and time-evolving isotopic signature (Burke et al., 2019). These signals can be used to better constrain the amount of sulfate formed in the troposphere vs the stratosphere (which is most relevant for the climatic impact), the emission altitude (Lin et al., 2018; Crick et al., 2021), as well as making inferences on whether the sulfate signal came from a tropical or an extratropical eruption (Burke et al., 2019).

In this project, the candidate will use aerosol-climate modelling to further constrain some of the properties of past eruptions, and consequently their climatic impact. The candidate will investigate how sulfate deposition depends on eruption properties, with a focus on the role of the SO2 emission altitude and the depth of the plume, and how these factors might be reflected in sulfur isotopes. Depending on the interest of the candidate, the project will also afford opportunities to explore other records of the climatic impact of eruptions to compare with model simulations, such as from tree-rings and speleothems. Constraining the climatic impact of past eruptions is crucial to improving simulations of historical climate to enable the detection and attribution of climate change and in quantifying the efficacy of volcanic forcing of climate.

Methodology

The project will involve running and analysing climate simulations using the UK Earth System Model (UKESM). Although the project is predominantly model-based, the candidate will have the opportunity to learn how sulfur isotope measurements are made during a research visit to St Andrews and sulfur isotope data will be used to inform the climate modelling. Specific tasks include:

1) Running idealized UKESM simulations of eruptions. The project will initially focus on exploring the role of emission altitude and plume depth on ice sheet sulfate deposition, including the timing, total amount deposited, and the deposition pathways. Scenarios include a high-latitude eruption vs. a low-latitude eruption with emissions spanning the upper troposphere and lower-stratosphere, and entirely in the stratosphere.

2) Modelling sulfur isotope signatures using a photochemical model and developing the UKESM to simulate changes in sulfur isotopes that could be used to predict the isotopic signature following large eruptions to compare with measurements.

3) Running simulations of large unidentified eruptions such as those that occurred in 1452, 1458 and 1809.

4) Collating and analysing proxy records of volcanism and eruption properties to compare with model simulations.

The project will also involve collaboration with Prof Anja Schmidt enabling the candidate to benefit from expertise at the interface between Volcanology and climate modelling.

Project Timeline

Year 1

Conducting a literature review, learning to run the UKESM, sensitivity simulations. Research visits to the University of St. Andrews.

Year 2

Running UKESM for chosen eruptions and analysing output. Attendance at national conference (e.g. VMSG, RMetS).

Year 3

Evaluation of climate model simulations against proxy records and comparison to sulfur isotope measurements, and constraining eruption properties and climatic impact of past eruptions. Attendance at international conference (e.g. EGU, AGU). Drafting publication.

Year 3.5

Thesis writing and paper submission.

Training
& Skills

This project will ideally suit a candidate with a background in atmospheric and environmental sciences, physics, mathematics, or geology. Previous experience with computer programming (e.g. Python or MATLAB) is advantageous but not essential. The candidate will gain expertise in climate science, climate modelling, and volcanology, and gain a wide range of skills in data analysis and computer programming, scientific writing, and research presentations, relevant for employment in both academia and industry. The candidate will have the opportunity to attend the National Centre for Atmospheric Science (NCAS) introductory training courses in Atmospheric Science and Scientific Computing as well as model specific training courses in the Unified Model and the UK Chemistry and Aerosol Scheme that are core components of the UK Earth System Model. The candidate may also have the opportunity to attend a climate modelling summer school and will present their work at national and international conferences.

References & further reading

Burke, A., Moore, K. A., Sigl, M., Nita, D. C., McConnell, J. R., & Adkins, J. F. (2019). Stratospheric eruptions from tropical and extra-tropical volcanoes constrained using high-resolution sulfur isotopes in ice cores. Earth and Planetary Science Letters, 521, 113-119.

Crick, L., Burke, A., Hutchison, W., Kohno, M., Moore, K. A., Savarino, J., … & Wolff, E. W. (2021). New insights into the ∼ 74 ka Toba eruption from sulfur isotopes of polar ice cores, Climate of the Past, 17, 2119–2137.

Lin, M., Zhang, X., Li, M., Xu, Y., Zhang, Z., Tao, J., … & Thiemens, M.H. (2018). Five-S-isotope evidence of two distinct mass-independent sulfur isotope effects and implications for the modern and Archean atmospheres. Proceedings of the National Academy of Sciences, 115(34), 8541-8546.

Marshall, L., Johnson, J. S., Mann, G. W., Lee, L., Dhomse, S. S., Regayre, L., … & Schmidt, A. (2019). Exploring how eruption source parameters affect volcanic radiative forcing using statistical emulation. Journal of Geophysical Research: Atmospheres, 124(2), 964-985.

Marshall, L. R., Schmidt, A., Johnson, J. S., Mann, G. W., Lee, L. A., Rigby, R., & Carslaw, K. S. (2021). Unknown eruption source parameters cause large uncertainty in historical volcanic radiative forcing reconstructions. Journal of Geophysical Research: Atmospheres, 126, e2020JD033578.

Robock, A. (2000). Volcanic eruptions and climate. Reviews of Geophysics, 38(2), 191-219.

Schmidt, A., Thordarson, T., Oman, L.D., Robock, A. & Self, S. (2012). Climatic impact of the long‐lasting 1783 Laki eruption: Inapplicability of mass‐independent sulfur isotopic composition measurements. Journal of Geophysical Research: Atmospheres, 117, D23116.

Sigl, M., Winstrup, M., McConnell, J. R., Welten, K. C., Plunkett, G., Ludlow, F., … & Woodruff, T. E. (2015). Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature, 523(7562), 543-549.

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