Capturing the short-term variability of carbon dioxide emissions from sedimentary rock weathering in a remote mountainous catchment, New Zealand

Type Article
Date 2022-10
Language English
Author(s) Roylands Tobias1, Hilton Robert G.1, 2, Garnett Mark H.3, Soulet GuillaumeORCID1, 4, Newton Josephine-Anne3, Peterkin Joanne L.5, Hancock Peter6
Affiliation(s) 1 : Department of Geography, Durham University, South Road, Durham DH1 3LE, United Kingdom
2 : Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, United Kingdom
3 : NEIF Radiocarbon Laboratory, Rankine Avenue, East Kilbride, Glasgow G75 0QF, United Kingdom
4 : Geo-Ocean, Brest University, CNRS, Ifremer, F-29280 Plouzané, France
5 : Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, United Kingdom
6 : Gisborne District Council, 15 Fitzherbert Street, PO Box 747, Gisborne 4010, New Zealand
Source Chemical Geology (0009-2541) (Elsevier BV), 2022-10 , Vol. 608 , P. 121024 15p.)
DOI 10.1016/j.chemgeo.2022.121024
WOS© Times Cited 3
Keyword(s) Oxidative weathering, Petrogenic organic carbon, Carbon dioxide, Carbon isotopes, Microbial respiration, Silicate weathering
Abstract

Weathering of organic carbon contained in sedimentary rocks (petrogenic OC, OCpetro) is an important control on the concentrations of carbon dioxide (CO2) and oxygen in the atmosphere. Of particular significance are steep mountainous catchments, where high rates of physical erosion introduce OCpetro to the surface, where oxygen in air and water can help drive oxidative weathering reactions, yet measurements of CO2 emissions from OCpetro oxidation are still scarce. Here, we use in situ gas accumulation chambers and show that CO2 fluxes, and their environmental controls, can be determined during a stand-alone, short-term (8 days) field campaign, applied to a remote setting. In the rapidly eroding Waiapu River catchment, New Zealand, dominated by mudstones, we measured high rates of CO2 release (222–1590 mgC m−2 d−1) in five accumulation chambers in the near-surface of naturally fractured and bedded rock outcrops. The corresponding CO2 concentrations are very high (pCO2 ~4700–27,100 ppmv), and such values could influence acid-hydrolysis reactions during chemical weathering of co-occurring silicate minerals. The CO2 is radiocarbon depleted (fraction modern, F14C = 0.0122–0.0547), confirming it is petrogenic in origin. Stable carbon isotopes suggest a source from OCpetro, but δ13C values of the CO2 are lower by ~3.5–3.7 ± 0.1 ‰ from those of OCpetro (−25.9 ± 0.1 ‰), consistent with isotope fractionation associated with microbial respiration of OCpetro. Over 6 days of measurement, we find that CO2 fluxes respond quickly to changes in temperature and humidity, indicating an environmental regulation that is captured by our short-term installation. The approaches applied here mean that future research can now seek to constrain the climatic, lithological and biological controls on OCpetro oxidation across regional to global scales.

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Roylands Tobias, Hilton Robert G., Garnett Mark H., Soulet Guillaume, Newton Josephine-Anne, Peterkin Joanne L., Hancock Peter (2022). Capturing the short-term variability of carbon dioxide emissions from sedimentary rock weathering in a remote mountainous catchment, New Zealand. Chemical Geology, 608, 121024 15p.). Publisher's official version : https://doi.org/10.1016/j.chemgeo.2022.121024 , Open Access version : https://archimer.ifremer.fr/doc/00786/89751/