Project highlights

  • Conduct fieldwork in Iceland to investigate aerosols generated by geysers and bubbling geothermal springs
  • Become an expert in the analysis of natural bioaerosols, combining molecular biology and geochemistry with advanced flow cytometry techniques to identify traces of extremophiles dispersed in geothermal aerosols
  • Pioneer a fundamental understanding of geothermal aerosols applicable to many environments on Earth and elsewhere in the Solar System.


Geothermal springs in Iceland host unique microbial communities adapted for life under multiple extreme conditions, including high temperatures, extreme pH and nutrient limitation. The mechanisms controlling how these highly specialised extremophiles are dispersed and come to colonise fresh geothermal habitats are not well understood. This project will combine state-of-the-art bioaerosol sampling and monitoring approaches in the field with lab-based microbiology and geochemistry techniques to investigate the role of aerosols as a repository and transport mechanism for geothermal extremophiles.

In marine settings, bubble bursting through wave action is well documented to loft aerosols, including microorganisms and microscopic droplets of seawater, into the atmosphere, where they can be transported over significant distances. Geothermal springs, particularly those which experience vigorous bubbling or geyser eruptions, can also produce high numbers of aerosols, but the abundance and diversity of geothermal microorganisms ejected within these aerosols, and how they are transported with distance, remain unexplored.  Major differences between the oceans and geothermal springs, such as fluid chemistry, temperature, bubbling rates and the presence or absence of surface microlayers, have the potential to drive significant differences between marine aerosols and geothermal aerosols, with unknown implications for how extremophiles are with unknown implications for how extremophiles are transported.

The student will use state-of-the-art aerosol sampling and monitoring equipment to study aerosol flux, composition and microbiology at active bubbling geothermal springs and geysers in Iceland. This work will involve: (1) studying the flux and spatio-temporal dynamics of aerosols at geothermal settings and how these vary with physical conditions such as spring chemistry, geothermal gas activity and temperature; (2) using advanced flow cytometry techniques to quantify and identify microbial biomass transferred from springs into the aerosol phase; and (3) building a detailed picture of microbiology and geochemistry of geothermal aerosols to identify what traces of the extremophile communities can be transported to colonise fresh habitats.

The successful candidate will contribute to a fundamental knowledge of geothermal bioaerosol production that is relevant both for understanding microbial dispersal on Earth, and to understanding the potential for detecting life at environments beyond Earth where aerosols form, such as the plumes of Saturn’s moon Enceladus.

A photo shows a plume of water vapour erupting from a hot spring. Diagrams illustrate bubbles bursting at a liquid surface to produce airborne droplets (aerosols).
Figure 1: Left: Actively erupting geothermal geyser in Iceland. Middle and right: schematic representation of aerosol formation at geothermal environments.

CENTA Flagship

This is a CENTA Flagship Project


The Open University


  • Organisms and Ecosystems


Project investigator

Mark Fox-Powell, The Open University ([email protected])


How to apply


The student will begin by working with existing aerosol samples taken in summer 2022 to optimise techniques before conducting their own sampling campaign in Iceland. The following methods will be used:

  1. Field sampling and monitoring of aerosols using cyclonic impaction and aerosol photometry, alongside monitoring of in situ environmental conditions.
  2. Low-biomass and trace geochemistry handling of aerosol samples.
  3. Advanced cell counting and sorting techniques using fluorescent labelling and flow cytometry.
  4. DNA extraction, amplification and sequence analysis.
  5. Cultivation-based microbial assays.
  6. Analytical geochemistry of spring and aerosol samples, including ion chromatography and inductively-coupled plasma optical emission spectroscopy.

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.

The student will receive training in in situ aerosol sampling, the clean handling of samples for low biomass and trace geochemical analyses, culture-independent and -dependent microbiological techniques, analysis of water geochemistry, and in the geomicrobiology of geothermal environments. Through visits to CEH Wallingford, the student will also receive training in cell enumeration and cell sorting with flow cytometry. Fieldwork will provide training in sample prioritisation and hypothesis testing, logistics and planning. The student will gain experience managing interdisciplinary collaborative work and will benefit from training in scientific writing, grant proposal writing, time management, presentation skills, and networking.

Partners and collaboration

This project will be in partnership with Tim Goodall, CEH. Tim is an expert in flow cytometry techniques for cell counting and cell sorting, and will host the student for short visits at CEH Wallingford to facilitate detailed quantification of microbial biomass within aerosol and spring samples. Sorting of microorganisms for targeted DNA sequencing based on cell size and activity will also be pursued (time permitting).

Further details

The successful candidate will join AstrobiologyOU, a vibrant, multi-disciplinary group of researchers investigating the scientific, technical, social and ethical challenges associated with understanding the limits of life on Earth and beyond.

If you wish to apply to the project, applications should include:

  • A CV with the names of at least two referees (preferably three and who can comment on your academic abilities)

Applications to be received by the end of the day on Wednesday 11th January 2023.

Possible timeline

Year 1

Literature review and familiarisation with geothermal environments, aerosol formation, and sampling techniques. Initial analyses of existing aerosol samples. Plan and conduct field campaign (summer 2024). Write report and begin analyses of new field samples.

Year 2

Process field samples for analysis. Set up cultures. Conducted analysis of aqueous geochemistry of spring and aerosol samples. Visit CEH and receive training in flow cytometry; collect cell abundance data. Present results at national conference and begin preparing manuscript for publication.

Year 3

Conduct detailed analysis of microbial communities in aerosol and spring samples, and associated cultures. Correlate with aerosol flux data and geochemical analyses. Prepare second manuscript for publication. Present results at a major international conference. Write up and submit thesis.

Further reading

Alsante, A. N., Thornton, D., C., O., & Brooks, S. D. (2021) Ocean Aerobiology. Frontiers in Microbiology, 12,

Christiansen, S., Salter, M. E., Gorokhova, E., Nguyen, Q. T. & Bilde, M. (2019) Sea Spray Aerosol Formation: Laboratory Results on the Role of Air Entrainment, Water Temperature, and Phytoplankton Biomass. Environmental Science and Technology 53, pp. 13107-13116, doi: 10.1021/acs.est.9b04078

Fox-Powell, M. G., Channing, A., Applin, D., Cloutis, E., Preston, L. J. & Cousins, C. R. (2018) Cryogenic silicification of microorganisms in hydrothermal fluids. Earth and Planetary Science Letters 498, pp 1-8,

Moreras-Marti, A., Fox-Powell, M., Zerkle, A., Stueeken, E., Gazquez, F., Brand, H., Galloway, T., Purkamo, L. & Cousins, C. R. (2021) Volcanic controls on the microbial habitability of Mars-analogue hydrothermal environments. Geobiology 19 (5) pp 489-509,

Porco, C.C., Dones, L. and Mitchell, C., (2017). Could it be snowing microbes on Enceladus? Assessing conditions in its plume and implications for future missions. Astrobiology, 17(9), pp.876-901

Rastelli, E., Corinaldesi, C., Dell’Anno, A., Martire, M.L., Greco, S., Facchini, M.C., Rinaldi, M., O’Dowd, C., Ceburnis, D. & Danovaro, R. (2017). Transfer of labile organic matter and microbes from the ocean surface to the marine aerosol: an experimental approach. Scientific Reports 7, 11475,


Samples of geothermal aerosols are already in hand at the Open University, meaning that analyses can proceed immediately. If field sampling of geothermal aerosols cannot occur, the student will use bespoke experimental equipment at the Open University to simulate geothermal aerosol formation in the laboratory.