| 其他摘要 | To understand the roles of carbonate rocks in carbon cycle, four carbonate profiles in Guizhou Province were selected and compared with silicate profiles in CO2 consumption calculated based on elemental changes in the profiles. The carbon and oxgen isotopic value in the carbonate profiles was also studied and related to the local climate. The major elemental results demonstrate that the chemical weathering reaction of carbonate rocks mainly happened at the rock-regolith interface, with quick dissolution of carbonate minerals and great leaching of active elements (Ca, Mg, Na, K). During this process, the CO2 consumption per volume of carbonate rocks was about 4 times larger than that of silicate profiles. During the further weathering process of the insoluble residuas on carbonate rocks, the CO2 consumption per volume of silicate regolith was about tens to hundreds times larger than that of carbonate regolith because most active elements had been lost in the carbonate regolith. However, it implies that chemical weathering of carbonate rocks can produce net carbon sink as well as silicate rocks. To understand the roles of carbonate rocks in carbon cycle, four weathering profiles devoloped on carbonate rocks in Guizhou Province were selected and compared with that on silicate rocks.The CO2 consumption were calculated based on elemental changes in the profiles. The carbon and oxgen isotopic values in the carbonate weathering profiles were also studied and related to the local climate. The major elemental results demonstrate that the chemical weathering reaction of carbonate rocks mainly happened at the rock-regolith interface, with quick dissolution of carbonate minerals and great leaching of active elements (Ca, Mg, Na, K). During this process, the CO2 consumption per volume of carbonate rocks was about 4 times larger than that of silicate weathering profiles. During the further weathering process of the insoluble residuas on carbonate rocks, the CO2 consumption per volume of carbonate regolith was about tens to thousands times smaller than that of silicate regolith because most active elements had been lost in the carbonate regolith. However, it implies that chemical weathering of carbonate rocks can produce net carbon sink as well as silicate rocks. At carbonate weathering profiles, the δ13C values of soil organic matter (δ13CSOM) reflect a coexistence of C3 and C4 plants. The soil SEM observation and the δ13C value of soil disseminated carbonate (δ13CSC) demonstrate that the soil carbonate is dominant by pedogenic carbonate, and its formation is closely associated with root activities. The estimated δ13C value of pedogenic carbonate (δ13CPC) based on δ13CSOM is higher than δ13CSC, suggests that the C3 plant take a larger percent when carbonate precipitated. The different climate conditions in the west compared with that in the middle of Guizhou Province are shorter rainy season, less rainfall, more nonuniform precipitation and lower temperature, which resulted in a higher stable carbon and oxygen isotopic value of soil carbonate (δ13CSC and δ18OSC) and higher positive correlation coefficients of them in the west in carbonate weathering profiles. However, the climate factor can't explain the difference of δ13CSC and δ18OSC between silicate weathering profiles, demonstrate that the δ13CSC and δ18OSC are possiblely affected by other factors including the rock and vegetation type. This paper also find a negative correlation between δ13CSC and CIA (chemical index of alteration), which is related to the formation process of pedogenic carbonate. It demonstrates that δ13CSC can be an index that indicates weathering intensity, but it's also affected by other factors besides weathering. The radioactive carbon isotopes of the soil organic matter show that the average residence time of organic matter increase with soil depth, and the CO2 flux produced by decomposition of soil organic matter is higher in the upper layer |
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