IAP2-23-021

The impact of abrupt global warming on soil erosion and the carbon cycle – lessons from the past for the future

Anthropogenic climate change is driving imbalances between soil erosion and soil formation rates (Li and Fang, 2016). This perturbation will have biogeochemical consequences that impact terrestrial and marine ecosystems and that may underpin carbon cycle feedbacks dictating the long-term evolution of the climate. This project aims to constrain the expected magnitude, longevity, and biogeochemical consequences of this perturbation by studying abrupt climate change events in the geological record.

Studies in modern river catchments show that soil erosion rates are much more sensitive to changes in rainfall compared to soil formation by chemical weathering (Gislason et al., 2006). Soil stocks and their associated nutrient stores are therefore predicted to decline over the coming centuries in response to anthropogenic climate change (Quinton et al., 2010). Conversely, this perturbation is expected to increase the supply of eroded soil material towards the ocean, acting to shuttle nutrients and carbon from terrestrial to marine environments. The longer-term outcomes of this perturbation and its role in carbon cycle-climate feedbacks, however, is poorly constrained. In this context, this project seeks to answer the following questions; how long will it take for soil erosion and formation rates to reach a new steady state and what are the longer-term biogeochemical consequences?

The geological record can be used to test hypotheses regarding the long-term (>1000 years) response of the earth system to climate change, by coupling empirical constraints from paleo-proxy reconstructions with Earth System modelling (e.g. Adloff et al., 2021). The central hypothesis of this project is that transient imbalances in soil erosion vs formation rates accompanying abrupt global warming events play a major role in long-term carbon cycle feedbacks. This hypothesis will be tested using novel proxy reconstructions of soil erosion vs formation balances using barium isotopes. The development and application of this proxy will be the first of its kind, capitalizing on recent research advances (Bridgestock et al. 2019, 2021 and unpublished). These proxy reconstructions will be coupled with Earth System modelling using cGENIE to investigate the carbon cycle implications of the constrained perturbations. These include soil erosion driving; (1) terrestrial organic carbon burial, and (2) marine organic carbon burial via soil nutrient inputs to the ocean. The relative importance of these 2 pathways will be constrained through the generation of marine sediment biomarker records. The targeted time periods will be the Paleocene-Eocene Thermal Maximum (PETM) and other Eocene hyperthermals, representing abrupt climate change events of different magnitude (e.g. Gutjahr et al., 2017). Together these activities will advance our mechanistic understanding for the role of terrestrial – marine couplings in carbon cycle feedbacks relevant for predicting the longer-term outcomes of anthropogenic climate change.

Methodology

Records of bulk marine sediment barium isotope compositions spanning the PETM and other hyperthermal events will be produced at from multiple sites. Sample preparation will involve acid digestions and Ba separation by ion exchange chromatography in the St Andrews isotope Geochemistry (STAiG) laboratories, followed by Ba isotope analyses by MC-ICP-MS (see Bridgestock et al., 2019). Changes to terrestrial and marine organic carbon inputs will be assessed using specific organic compounds (biomarkers e.g. Inglis et al., 2022). To characterise biomarker distributions, samples will be prepared by solvent extraction and separation, with analysis by GC-MS (see McClymont & Mackay et al., 2023). Samples are either already available at the host institution or will be sourced from external collaborators and the International Ocean Discovery Program.

These records will be interpreted with the aid of the Earth System model cGENIE. A representation of the Ba isotope cycle, and its links to erosion-chemical weathering balances and other key processes will be implemented in cGENIE (see Adloff et al., 2021). The marine sediment Ba isotope and biomarker records will then be used to constrain cGENIE model experiments, investigating the couplings between climate change, soil erosion-formation balances and organic carbon burial.

This work is envisaged to lead to the following outputs (as PhD chapters/journal articles):
1. Modelling development for the implementation of the Ba cycle in cGENIE, model calibration to modern data and experiments to explore the controls of this new proxy.
2. Findings from applying this data-model approach to the PETM.
3. Findings from other hyperthermal events to evaluate the response of these feedbacks to different magnitudes of climate change and background climate conditions.

Project Timeline

Year 1

Literature review. Initial training in required analytical chemistry and numerical modelling methods. Implementation of a representation of the Ba cycle in the earth-system model cGENIE. Selection of target sample sites.

Year 2

Generation of bulk marine sediment Ba isotope records spanning the PETM and other Eocene hyperthermals. Generation of new biomarker distribution data at the Organic Geochemistry Lab Durham. Presentation of initial results at a national conference (e.g. The Geochemistry Groups Research in Progress Meeting), and writing of results into paper(s)/chapters(s).

Year 3

cGENIE model experiments to investigate the role of climate driven soil erosion for driving terrestrial and marine organic carbon burial, constrained by the barium isotope and biomarker records. Presentation of findings at an international conference (e.g. Goldschmidt), and writing of results into paper(s)/chapter(s).

Year 3.5

Finish writing, submit and defend PhD thesis

Training
& Skills

Training in Earth System modelling, coding in the fortran language and data analysis in Python.

Training in analytical chemistry techniques for the measurement of trace metal concentrations, metal isotope systems and biomarkers: triple quadrupole inductively coupled plasma mass spectrometry (QQQ-ICP-MS), multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and associated sample preparation.

Training in analytical chemistry techniques for the measurement of trace organic molecules (biomarkers): gas chromatography mass spectrometry.

Training in the handling and interpretation of paleo-proxy data

References & further reading

Adloff M., Ridgwell A., Monteiro F. M., Parkinson I. J., Dickson A. J., Pogge von Strandmann, P. A. E., Fantle, M. S. and Greene S. E., 2021, Inclusion of a suite of weathering tracers in the cGENIE Earth system model – muffin release v.0.9.23, Geoscientific Model Development, 14, 4187-4223, doi:10.5194/gmd-14-4187-2021

Bridgestock L., Y-T. Hsieh, D. Porceilli & G. M. Henderson, 2019, Increased export production during recovery from the Paleocene-Eocene thermal maximum constrained by sedimentary Ba isotopes, Earth and Planetary Science Letters, 510, 52-63

Bridgestock L., Nathan, J., Paver, R., Hsieh, Y-T. Porcelli, D., Tanzil, J., Holdship, P., Carrasco, G., Annammala, K. V., Swarzenski,, P. W., and Henderson, G. M., 2021, Estuarine processes modify the isotope composition of dissolved riverine barium fluxes to the ocean, Chemical Geology, 579, doi:10.1016/j.chemgeo.2021.120340

Gislason S. R., Oelkers E. H. and Snorrason, A., 2006, Role of river-suspended material in the global carbon cycle, Geology, 34, 49-52, doi:10.1130/G22045.1

Gutjahr M., Ridgwell A., Sexton P. F., Anagnostou E., Pearson P. N., Pälike H., Norris R. D., Thomas E. and Foster G. L., 2017, Very large release of mostly volcanic carbon during the Palaeocene-Eocene Thermal Maximum, Nature, 548, doi:10.1038/nature23646

Inglis et al., 2022, Biomarker approaches for reconstructing terrestrial environmental change Annual Review of Earth and Planetary Sciences , 50 , 369—394, DOI: 10.1146/annurev-earth-032320-095943

Li Z. and Fang H., 2016, Impacts of climate change on water erosion: A review, Earth-Science Reviews, 163, 94-117, doi:10.1016/j.earscirev.2016.10.004

McClymont & Mackay et al., 2023, Biomarker proxies for reconstructing Quaternary climate and environmental change. Journal of Quaternary Science, https://doi.org/10.1002/jqs.3559.

Quinton J N., Govers G., Van Oost K. & Bardgett R. D., 2010, The impact of agricultural soil erosion on biogeochemical cycling, Nature Geoscience, 3, 311-314, doi:10.1038/ngeo838

Apply Now