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Capturing the short-term variability of carbon dioxide emissions from sedimentary rock weathering in a remote mountainous catchment, New Zealand
Chemical Geology ( IF 3.6 ) Pub Date : 2022-07-21 , DOI: 10.1016/j.chemgeo.2022.121024
Tobias Roylands , Robert G. Hilton , Mark H. Garnett , Guillaume Soulet , Josephine-Anne Newton , Joanne L. Peterkin , Peter Hancock

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.



中文翻译:

捕捉新西兰偏远山区流域沉积岩风化造成的二氧化碳排放的短期变化

沉积岩中所含有机碳(成岩OC、OC petro)的风化作用是对大气中二氧化碳(CO 2)和氧气浓度的重要控制。特别重要的是陡峭的山区集水区,高速率的物理侵蚀将 OC petro引入地表,空气和水中的氧气可以帮助驱动氧化风化反应,但对OC petro氧化产生的 CO 2排放的测量仍然很少。在这里,我们使用原位气体聚集室并表明 CO 2通量及其环境控制可以在独立的短期(8 天)野外活动中确定,并应用于远程设置。在快速侵蚀的新西兰怀阿普河流域,以泥岩为主,我们测量了天然裂缝和层状岩石近地表的五个聚集室中的高 CO 2释放率(222-1590 mgC m -2 d -1 )露头。相应的 CO 2浓度非常高(p CO 2  ~4700–27,100 ppmv),这些值可能会影响共生硅酸盐矿物化学风化过程中的酸水解反应。CO 2是放射性碳耗尽的(现代馏分,F14 C = 0.0122–0.0547),证实它是成岩性的。稳定的碳同位素表明来自 OC petro ,但 CO 2的δ 13 C 值比OC petro ( -25.9 ± 0.1 ‰)低约 3.5–3.7 ± 0.1 ‰,这与与微生物呼吸相关的同位素分馏一致OC石油。经过 6 天的测量,我们发现 CO 2通量对温度和湿度的变化反应迅速,这表明我们的短期安装已经捕捉到了环境调节。这里应用的方法意味着未来的研究现在可以寻求限制对 OC petro的气候、岩性和生物控制跨区域到全球范围的氧化。

更新日期:2022-07-21
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