The sources and sinks of CO2 in caves under mixed woodland and grassland vegetation

Breecker, Daniel O.; Payne, Ashley E.; Quade, Jay; Banner, Jay L.; Ball, Carolyn E.; Meyer, Kyle W.; Cowan, Brian

doi:10.1016/j.gca.2012.08.023

Cited by 117 publications

(79 citation statements)

References 51 publications

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“…All other records showed a dominance of the flux of CO 2 derived from organic carbon with a t > 100 yr. The minimum age of soil CO 2 predicted by the all successful model runs is consistently on the order of decades or centuries, which contrasts starkly with observations of soil gas in temperate and tropical sites (Trumbore, 2000) as well as the single published measurement of soil CO 2 in karst soil (Breecker et al, 2012).…”

Section: Geochemical Box Modelcontrasting

confidence: 86%

“…Peyraube et al (2013) Benavente et al (2010). Additionally a study of the sources of cave CO 2 by Breecker et al (2012) also hypothesized that the majority of cave CO 2 is advected from a deep biogenic source, and numerous studies have suggested that generation of subterranean CO 2 is an important, and possibly necessary, driver of carbonate dissolution and karst development (e.g. Wood, 1985;Atkinson, 1977;Gabrovsek et al, 2000;and Gulley et al, 2014).…”

Section: The Sources Of Speleothem Carbonmentioning

confidence: 99%

“…These predictions are at odds with observations of soil CO 2 ages in nonkarst sites, which are typically on the order of years, with CO 2 derived from root respiration and decomposition of organic matter with a turnover time of <1 yr comprising 50e60% of soil CO 2 in boreal and temperate sites and >80% in tropical sites (Trumbore, 2000). To date there is only one published measurement of soil a 14 CO 2 in karst terrain, from Cave of the Bells, Arizona, which was indistinguishable from contemporaneous atmospheric a 14 CO 2 (Breecker et al, 2012). This discrepancy between observed soil CO 2 ages and the predicted mean age of soil CO 2 in karst settings based on the shape of the bomb peak in speleothems suggests that:…”

Section: Introductionmentioning

confidence: 99%

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Radiocarbon evidence for decomposition of aged organic matter in the vadose zone as the main source of speleothem carbon

Noronha

Johnson

Southon

et al. 2015

Quaternary Science Reviews

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a b s t r a c tSeveral recent studies have used records of the radiocarbon ( 14 C) bomb peak in speleothems to inversely model the soil a 14 CO 2 and the age distribution of soil organic material (SOM) above caves, in part to investigate the potential of speleothems as sensitive records of past SOM dynamics. The results of these modeling studies have suggested that soil CO 2 at karst sites is derived primarily from the decomposition of SOM with turnover times on the order of decades to centuries. This result is in stark contrast with observations of soil a 14 CO 2 at non-karst sites, which indicate that soil CO 2 is derived primarily from root respiration and decomposition of SOM with much shorter turnover times. This discrepancy suggests that SOM in karst settings may have a very different age distribution than sites that have been studied previously and/or that soil CO 2 is not the main source of speleothem carbon. To help resolve this discrepancy, we present an improved inverse model which we use to estimate the age of CO 2 above several caves. We also present results from a detailed case study of soil carbon dynamics at Heshang Cave, China. This work demonstrates that SOM in karst sites may be much older than SOM in non-karst soils that have been studied previously, but that CO 2 produced in the shallow soil zone is unlikely to be the main source of speleothem carbon. A review of the literature suggests that the most likely explanation for the aforementioned discrepancy is that decomposition of down-washed SOM in the vadose zone is the dominant source of speleothem carbon.

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Section: Geochemical Box Modelcontrasting

confidence: 86%

Section: The Sources Of Speleothem Carbonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Radiocarbon evidence for decomposition of aged organic matter in the vadose zone as the main source of speleothem carbon

Noronha

Johnson

Southon

et al. 2015

Quaternary Science Reviews

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“…Throughout the outgassing stage the connexion between the underground and the outdoor atmosphere is active and the gas interchange is allowed. This means that a ventilation process (temperature-driven air flow) is responsible for the CO2 removal from the cavity (Breecker et al, 2012). On the contrary, in the isolation stage the gas interchange is limited.…”

Section: Study Sitesmentioning

confidence: 99%

Role of soil pore structure in water infiltration and CO2 exchange between the atmosphere and underground air in the vadose zone: A combined laboratory and field approach

Pla

Cuezva

Martı́nez-Martı́nez

et al. 2017

CATENA

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The soils above caves represent a membrane that regulates the connection between the underground environment and the outside atmosphere. In this study, soils from two different field sites (Cueva de Altamira and Cueva del Rull in Spain) are investigated. Field results are analysed and linked to laboratory tests. Several laboratory experiments are performed to quantify CO2 diffusion coefficients and water infiltration rates in these soils under different degrees of soil water saturation and compaction.Tests confirm that the grain size distribution, organic matter content, mineral composition and water content of soils affect gas transport through the soil pore network. Both field and lab results reveal that Altamira soil has a coarser texture and therefore has higher CO 2 diffusion coefficients, infiltration rates and hydraulic conductivity values than Rull soil. Rull soil contains a higher proportion of fine particles and organic matter, which explains the lower fluid transport coefficients.When soils are near saturation, fluid transport does not depend on the physical properties of soil but depends on the soil water content. In this state, liquid transport regulates the available space within the soil pores, which leads to a reduction in the gaseous diffusion coefficient of the soil. After rainfall episodes, the connection between the exterior atmosphere and underground cavities is hindered due to a rise in the soil water content, which is responsible for the closure of the overlying membrane. This study demonstrates that soil-produced CO2 reaches the underground atmosphere through diffusion processes that are controlled by the intrinsic properties of soil (porosity, grain size distribution, texture, mineralogy and organic matter content) and soil water content.

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“…Both gases, 222 Rn and CO2 follow the same pattern even when the source is different. These annual cycles are characterized by two outstanding moments related with the thermal relationship between outdoor and indoor air temperatures and responsible for the intensity of cave ventilation (Bourges et al, 2006;Frisia et al, 2011;Breecker et al, 2012). The cave is governed by a dynamic model, which combines diffusive and adevctive fluxes.…”

Section: Gaseous Recharge Of Rull Cavementioning

confidence: 99%

Changes in the CO2 dynamics in near-surface cavities under a future warming scenario: Factors and evidence from the field and experimental findings

Pla

Cuezva

Garcia-Anton

et al. 2016

Science of The Total Environment

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This study is based in a field monitoring of a cave-soil-atmosphere system validated with laboratory experimentation. CO2 and 222 Rn dynamics in the cavity demonstrate the dependence on the climatic parameters, mainly on the differences between outdoor and indoor temperatures. Within the cave, the annual cycles are characterized by two outstanding moments: cave gaseous recharge and ventilation when cave acts as gaseous sink or source respectively. Relationship with soil above the cave exists permanently. Soil temperature and moisture are responsible for CO2 production at different time scales.Soil CO2 in Rull site reaches values higher than 3000 ppm in April-May, which falls to nearly 1000 ppm during the summer time. Due to CO 2 diffusion, maximum values in the cave are reached in the warmest months and are in accordance to soil CO2 values. Within the cave, maximum CO2 concentration is, in average, 3470 ppm while minimum is 623 ppm. Cave temperature and relative humidity remain quite stable with mean values of 16.1 ºC and 97.9% respectively. To describe field findings, CO2 production and diffusion experiments are developed related to soil behaviour. Results show that soil CO2 production increases as soil temperature and moisture increase according to a calculated logarithmic equation until water content in soil exceeds the saturation values. In addition, CO2 diffusion in Rull soil is reduced around 60% when water content in soil increases from 0 to 30%. Soil-produced CO2 reaches Rull cave, by diffusion. We estimate 57 kg of emitted CO2 from the cave to the atmosphere in an annual cycle, considering a volume of 9915 m 3 . Finally, projections of future climate in the study site confirm a general tendency for annual-mean conditions to be warmer and drier, which will directly affect soil CO2 production. Under this situation, Rull cave will experience changes in the stored and then exchanged annual amount of CO2.

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The sources and sinks of CO2 in caves under mixed woodland and grassland vegetation

Cited by 117 publications

References 51 publications

Radiocarbon evidence for decomposition of aged organic matter in the vadose zone as the main source of speleothem carbon

Radiocarbon evidence for decomposition of aged organic matter in the vadose zone as the main source of speleothem carbon

Role of soil pore structure in water infiltration and CO2 exchange between the atmosphere and underground air in the vadose zone: A combined laboratory and field approach

Changes in the CO2 dynamics in near-surface cavities under a future warming scenario: Factors and evidence from the field and experimental findings

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