TY - JOUR
T1 - The CO2 consumption potential during gray shale weathering
T2 - Insights from the evolution of carbon isotopes in the Susquehanna Shale Hills critical zone observatory
AU - Jin, Lixin
AU - Ogrinc, Nives
AU - Yesavage, Tiffany
AU - Hasenmueller, Elizabeth A.
AU - Ma, Lin
AU - Sullivan, Pamela L.
AU - Kaye, Jason
AU - Duffy, Christopher
AU - Brantley, Susan L.
N1 - Funding Information:
Special thanks go to Stojan Zigon from the Department of Environmental Sciences at Jozef Stefan Institute in Slovenia for his help with carbon stable isotope analyses of soil, soil gas and DIC samples. Emmanuel Sosa helped with alkalinity titration. Financial support to L. Jin includes a University Research Initiative grant from University of Texas at El Paso and a seed grant from the National Science Foundation through Pennsylvania State University as part of the SSHO. Financial Support was also provided by National Science Foundation Grant EAR – 0725019 (to C. Duffy), EAR – 1239285 (to S. Brantley), and EAR – 1331726 (to S. Brantley) for the Susquehanna Shale Hills Critical Zone Observatory. Logistical support and data from the Observatory are acknowledged. We conducted this research at the Penn State Stone Valley Forest which is funded by the Penn State College of Agriculture Sciences, Department of Ecosystem Science and Management and managed by the staff of the Forestlands Management Office.
Publisher Copyright:
© 2014 Elsevier Ltd.
PY - 2014/10/1
Y1 - 2014/10/1
N2 - Shale covers about 25% of the land surface, and is therefore an important rock type that consumes CO2 during weathering. We evaluated the potential of gray shale to take up CO2 from the atmosphere by investigating the evolution of dissolved inorganic carbon (DIC) concentrations and its carbon isotopic ratio (δ13CDIC) along water flow paths in a well-characterized critical zone observatory (Susquehanna Shale Hills catchment). In this catchment, chemical weathering in shallow soils is dominated by clay transformation as no carbonates are present, and soil pore waters are characterized by low DIC and pH. In shallow soil porewaters, the DIC, dominated by dissolved CO2, is in chemical and isotopic equilibrium with CO2 in the soil atmosphere where pCO2 varies seasonally to as high as 40 times that of the atmosphere. The degradation of ancient organic matter is negligible in contributing to soil CO2. The chemistry of groundwater varies along different flowpaths as soil pore water recharges to the water table and then dissolves ankerite or secondary calcite under the valley floor. Weathering of carbonate leads to much higher concentrations of DIC (~2500μmol/L) and divalent cations (Ca2+ and Mg2+) in groundwaters than soil waters. The depth to the ankerite weathering front is hypothesized to be roughly coincident with the water table but it varies due to heterogeneities in the protolith composition. Groundwater chemistry therefore shows different saturation indices with respect to ankerite depending upon location along the valley. The δ13CDIC values of these groundwaters document mixing between the ankerite and soil CO2. The major element concentrations, DIC, and δ13CDIC in the first-order stream incising the valley of the catchment are derived from groundwater and soil waters in proportions that vary both spatially and temporally. The CO2 degassed slightly in the stream but little evidence of C isotopic equilibration with the atmosphere is observed, due to the short length of the stream and short contact time with air.The ankerite reaction front also lies close to the pyrite dissolution front. Pyrite oxidation in bedrock likely released sulfuric acid and played a minor role in the ankerite dissolution, shifting groundwater δ13CDIC slightly above the expected mixing values. At the catchment scale, the stream SO42- is also dominantly derived from wet deposition, as stream has δ34SSO4 values around 3‰, well within the range of acid deposition.
AB - Shale covers about 25% of the land surface, and is therefore an important rock type that consumes CO2 during weathering. We evaluated the potential of gray shale to take up CO2 from the atmosphere by investigating the evolution of dissolved inorganic carbon (DIC) concentrations and its carbon isotopic ratio (δ13CDIC) along water flow paths in a well-characterized critical zone observatory (Susquehanna Shale Hills catchment). In this catchment, chemical weathering in shallow soils is dominated by clay transformation as no carbonates are present, and soil pore waters are characterized by low DIC and pH. In shallow soil porewaters, the DIC, dominated by dissolved CO2, is in chemical and isotopic equilibrium with CO2 in the soil atmosphere where pCO2 varies seasonally to as high as 40 times that of the atmosphere. The degradation of ancient organic matter is negligible in contributing to soil CO2. The chemistry of groundwater varies along different flowpaths as soil pore water recharges to the water table and then dissolves ankerite or secondary calcite under the valley floor. Weathering of carbonate leads to much higher concentrations of DIC (~2500μmol/L) and divalent cations (Ca2+ and Mg2+) in groundwaters than soil waters. The depth to the ankerite weathering front is hypothesized to be roughly coincident with the water table but it varies due to heterogeneities in the protolith composition. Groundwater chemistry therefore shows different saturation indices with respect to ankerite depending upon location along the valley. The δ13CDIC values of these groundwaters document mixing between the ankerite and soil CO2. The major element concentrations, DIC, and δ13CDIC in the first-order stream incising the valley of the catchment are derived from groundwater and soil waters in proportions that vary both spatially and temporally. The CO2 degassed slightly in the stream but little evidence of C isotopic equilibration with the atmosphere is observed, due to the short length of the stream and short contact time with air.The ankerite reaction front also lies close to the pyrite dissolution front. Pyrite oxidation in bedrock likely released sulfuric acid and played a minor role in the ankerite dissolution, shifting groundwater δ13CDIC slightly above the expected mixing values. At the catchment scale, the stream SO42- is also dominantly derived from wet deposition, as stream has δ34SSO4 values around 3‰, well within the range of acid deposition.
UR - http://www.scopus.com/inward/record.url?scp=84908046488&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84908046488&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2014.07.006
DO - 10.1016/j.gca.2014.07.006
M3 - Article
AN - SCOPUS:84908046488
SN - 0016-7037
VL - 142
SP - 260
EP - 280
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -