I am a geochemist who studies the exchange of carbon between the atmosphere and rocks, and how these carbon transfers respond to and drive climate change.
Our research quantifies how erosion and weathering processes act as CO2 sinks, and CO2 sources, and transfer CO2 between the atmosphere, hydrosphere and oceans, and long-term, geological storage in sedimentary deposits. To do this, we’ve developed several geochemical approaches, which include trace element proxies of weathering and their isotopes (e.g. rhenium), while also tracking carbon as CO2, dissolved and particulate organic carbon, and their radiocarbon and stable C isotope composition. I mostly work on modern river catchments to constrain fluxes and their controls, including work on small catchments in the European Alps, New Zealand (East Cape and Southern Alps), Taiwan, Sichuan, Andes, alongside over a decade of work in the Mackenzie River basin.
My research currently tackles four main themes:
1. Environmental controls on CO2 emissions from weathering of sedimentary rocks:
Oxidation of organic carbon in sedimentary rocks is a major, natural CO2 emission to the atmosphere and O2 sink, thought to emit between 40 – 100 x1012 g C yr-1, and has been greatly accelerated by burning fossil fuels. Despite this recognition, the natural flux is poorly constrained by measurements and the environmental controls on this major CO2 emission are not well known.
This topic forms the theme of the ERC Starting Grant – ROC-CO2 (http://roc-co2.weebly.com/) to develop novel tracers of oxidative weathering (rhenium) and new ways to directly measure CO2 emissions. Our research has demonstrated for the first time a link between temperature and CO2 release from sedimentary rock weathering (Soulet et al., 2021).We now seek to understand how this relates to microbial activity in the shallow weathering zone, and whether a temperature-feedback operates more widely
2. Oxidative weathering in the geological past:
We lack information on how this CO2 source has changed in the past. This research will address this knowledge gap with the trace element rhenium (Re) and its isotope system. Rhenium concentrations in river waters have been used to quantify rock-organic carbon oxidation in the modern day. The isotopic composition of Re could record global changes in oxidative weathering fluxes in the geological record, due to the potential for changes in the Re isotopic composition of seawater driven by inputs of Re from rivers. We’ve made the first measurements of the Re isotope composition of rivers, showing fractionation that could help trace oxidative weathering (Dellinger et al., 2021). This theme is associated with an ongoing NERC Standard Grant (Dec 2019 – Dec 2022) (in collaboration with Dr. Alex Dickson, Dr. Mathieu Dellinger and Dr. Julie Prytulak).
3. Extreme geomorphic events for carbon export from the terrestrial biosphere:
High magnitude geomorphic events are capable of eroding large amounts of carbon at the same time as large volumes of sediment, exporting materials quickly through river systems. Past research has used modern-day rivers to show the potential importance of infrequent, but widespread landsliding associated with earthquakes for this carbon flux. A NERC Standard Grant has funded research using New Zealand lake records, whose sediments record multiple earthquake events and associated widespread landsliding events (Wang et al., 2020). These new empirical data will inform process based models that can be used to explore erosion and carbon cycling over longer-timescales, while providing numerical experiments of how different climatic and tectonic settings influence carbon export by erosion.
4. Greenhouses gases release from Arctic Rivers in a warming world:
Rivers around the world emit large quantities of greenhouse gas, with an estimated 1.8 – 2.9 PgC yr-1 released as CO2, and ~20-25 TgC yr-1 as methane (CH4). The river CO2 and CH4 emissions act to counter the net transfer of greenhouse gases from the atmosphere to the land, estimated to be 1.6 ± 0.5 PgC yr-1. Despite this recognition, the age and source of the CO2 and CH4 that is degassed from rivers is poorly constrained. Only with knowledge of these key features can we constrain how riverine CO2 and CH4 emissions will change with ongoing and future warming, unmasking potential feedbacks to warming by the natural carbon cycle. This research theme will be tackled by RIV-ESACPE, an ERC Consolidator Grant which will start in June 2022, which aims to address these significant gaps in our knowledge of how lateral transfers of carbon in sediments and water of Arctic catchments impact the carbon cycle.
View Selected Publications
- Soulet, G, R. G. Hilton, M. H. Garnett, T. Roylands, S. Klotz, T. Croissant, M. Dellinger, & C. Le Bouteiller (2021) Temperature control on CO2 emissions from the weathering of sedimentary rocks, Nature Geoscience, 665–671, https://doi.org/10.1038/s41561-021-00805-1
- Dellinger, M., R. G. Hilton, & G. M. Nowell (2021) Fractionation of rhenium isotopes in the Mackenzie River basin and insights on oxidative weathering, Earth & Planetary Science Letters, 573, 117131, https://doi.org/10.1016/j.epsl.2021.117131
- Schwab, M., R. G. Hilton, P.A. Raymond, N. Haghipour, E. Amos, S.E. Tank, R. M. Holmes, E.T. Tipper, & T. I. Eglinton (2020) An abrupt aging of dissolved organic carbon in Arctic Rivers, Geophysical Research Letters, 47, e2020GL088823, https://doi.org/10.1029/2020GL088823
- Hilton, R. G., & A. J. West (2020) Mountains, erosion and the carbon cycle, Nature Reviews Earth & Environment, 1, 284-299, https://doi.org/10.1038/s43017-020-0058-6
- Wang, J., J. D. Howarth, E. L. McClymont, A. L. Densmore, S. J. Fitzsimons, T. Croissant†, D. R. Gröcke, M. D. West, E. L. Harvey, N. V. Frith, M. Garnett & R. G. Hilton (2020) Long-term patterns of hillslope erosion by earthquake-induced landslides shape mountain landscapes, Science Advances, 6, eaaz6446, https://doi.org/10.1126/sciadv.aaz6446
- Horan, K., R. G. Hilton, M. Dellinger, E. Tipper, V. Galy, D. Calmels, D. Selby, J. Gaillardet, C. J. Ottley, D. Parsons, & K. W. Burton (2019) Carbon dioxide emissions by rock organic carbon oxidation and the net geochemical carbon budget of the Mackenzie River Basin, American Journal of Science, 319, 473-499, https://doi.org/10.2475/06.2019.02
- Frith, N., R. G. Hilton, J. D. Howarth, D. Gröcke, S. J. Fitzsimons, T. Croissant, J. Wang, E. L. McClymont, J. Dahl, & A. L. Densmore (2018) Carbon export from mountain forests enhanced by earthquake-triggered landslides over millennia, Nature Geoscience, 11, 772-776, https://doi.org/10.1038/s41561-018-0216-3
- Soulet, G., R. G. Hilton, M. H. Garnett, M. Dellinger, T. Croissant, M. Ogrič, & S. Klotz (2018) Technical note: in situ measurement of flux and isotopic composition of CO2 released during oxidative weathering of sedimentary rocks, Biogeosciences, 15, 1–16, https://doi.org/10.5194/bg-15-1-2018
- Hemingway, J. D., R. G. Hilton, N. Hovius, T. I. Eglinton, N. Haghipour, L. Wacker, M. C. Chen, V. Galy (2018) Microbial oxidation of lithospheric organic carbon in rapidly eroding tropical mountain soils, Science, 360, 209-212, https://doi.org/10.1126/science.aao6463
- Horan, K., R. G. Hilton, D. Selby, C. Ottley, D. Grocke, M. Hicks & K. Burton (2017) Mountain glaciation drives rapid oxidation of rock-bound organic carbon, Science Advances, 3, e1701107, https://doi.org/10.1126/sciadv.1701107
- Hilton, R. G., (2017) Climate regulates the erosional carbon export from the terrestrial biosphere, Geomorphology, 277, 118-132, https://doi.org/10.1016/j.geomorph.2016.03.028