Atmospheric turbulence triggers pronounced diel pattern in karst carbonate geochemistry
CO<sub>2</sub> exchange between terrestrial ecosystems and the atmosphere is key to understanding the feedbacks between climate change and the land surface. In regions with carbonaceous parent material, CO<sub>2</sub> exchange patterns occur that cannot be explained by biolog...
| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-07-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/10/5009/2013/bg-10-5009-2013.pdf |
| Summary: | CO<sub>2</sub> exchange between terrestrial ecosystems and the atmosphere is key to understanding the feedbacks between climate change and the land surface. In regions with carbonaceous parent material, CO<sub>2</sub> exchange patterns occur that cannot be explained by biological processes, such as disproportionate outgassing during the daytime or nighttime CO<sub>2</sub> uptake during periods when all vegetation is senescent. Neither of these phenomena can be attributed to carbonate weathering reactions, since their CO<sub>2</sub> exchange rates are too small. Soil ventilation induced by high atmospheric turbulence is found to explain atypical CO<sub>2</sub> exchange between carbonaceous systems and the atmosphere. However, by strongly altering subsurface CO<sub>2</sub> concentrations, ventilation can be expected to influence carbonate weathering rates. By imposing ventilation-driven CO<sub>2</sub> outgassing in a carbonate weathering model, we show here that carbonate geochemistry is accelerated and does play a surprisingly large role in the observed CO<sub>2</sub> exchange pattern of a semi-arid ecosystem. We found that by rapidly depleting soil CO<sub>2</sub> during the daytime, ventilation disturbs soil carbonate equilibria and therefore strongly magnifies daytime carbonate precipitation and associated CO<sub>2</sub> production. At night, ventilation ceases and the depleted CO<sub>2</sub> concentrations increase steadily. Dissolution of carbonate is now enhanced, which consumes CO<sub>2</sub> and largely compensates for the enhanced daytime carbonate precipitation. This is why only a relatively small effect on global carbonate weathering rates is to be expected. On the short term, however, ventilation has a drastic effect on synoptic carbonate weathering rates, resulting in a pronounced diel pattern that exacerbates the non-biological behavior of soil–atmosphere CO<sub>2</sub> exchanges in dry regions mbox{with carbonate soils}. |
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| ISSN: | 1726-4170 1726-4189 |