Joshua Shea

Postdoctoral researcher in igneous geochemistry

Department of Earth Sciences · University of Cambridge

I work on how the deep Earth carries and releases volatiles — carbon, in particular — and what that means for the long-term carbon cycle and the conditions that made the planet habitable. My approach combines high-precision SIMS measurements on natural melt inclusions with piston-cylinder and multi-anvil experiments, backed by fairly heavy data analysis in Python.

Right now I am working with Oliver Shorttle at Cambridge, on three threads:

• Carbon in the upper mantle. Using olivine- and plagioclase-hosted melt inclusions from mid-ocean ridges to constrain the carbon isotope composition of MORB-source mantle and how spreading-ridge cumulates redistribute volatiles.
• Hydrothermal vents and the origin of life. Experimental petrology connecting volcanism and deep volatile cycles to prebiotic chemistry.
• Mars. Mantle melting on Mars and what InSight, NWA samples, and an upcoming return mission can tell us.

If any of this overlaps with what you do — or what you’d like to do — get in touch.

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Recent

Heavy carbon in Earth’s early mantle (in prep, Nature Geoscience)
Olivine-hosted melt inclusions from Iceland record δ¹³C values heavier than the convecting upper mantle, pointing to a distinct deep primordial carbon reservoir. → explainer

A revised carbon isotope composition of the convecting upper mantle
Geochemical Perspectives Letters, 2026. New SIMS-derived estimate for MORB-source δ¹³C, with downstream consequences for the long-term carbon cycle. → publications

Mars Forum, JPL — invited talk
March 2025. Mantle melting on Mars with applications for sample return.

A. H. Voisey Medal (2024)
Awarded by the NSW Division of the Geological Society of Australia for early-career contribution to the Earth Sciences.