CARBON-DIOXIDE IN THE ATMOSPHERE - EVIDENCE FROM CENOZOIC AND MESOZOIC PALEOSOLS
CARBON-DIOXIDE IN THE ATMOSPHERE - EVIDENCE FROM CENOZOIC AND MESOZOIC PALEOSOLS
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DOI：
10.2475/ajs.291.4.377
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发表时间：
1991-04-01
影响因子：
2.9
通讯作者：
CERLING, TE
中科院分区：
文献类型：
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作者：
CERLING, TE
土壤CO2和土壤碳酸盐的同位素组成的扩散反应模型进行了评估。说明了在不同条件下哪些变量是重要的，并表明在一定条件下，土壤碳酸盐的碳同位素组成可用于估算晚古生代至今大气中的P（CO2）。在均匀条件下产生的土壤碳酸盐的同位素组成在大多数土壤中在20 cm以下基本上是恒定的。土壤有机质的同位素组成是决定土壤碳酸盐碳同位素组成的重要因素。然而，在C4植物出现之前，可能在第三纪，构成生物量的重要部分，大气中的CO2浓度可以估计，因为大气中的CO2与土壤中产生的CO2混合。扩散-反应模型还表明，在高等陆地植物出现之前，大多数土壤碳酸盐的δ C-13值受大气的强烈影响，这是由于非维管植物的根深较浅。在始新世和晚中新世以来，由于土壤碳酸盐的极限碳同位素组成介于-相对于PDB为11.5至-12.5 permil。然而，早白垩世和早侏罗纪古土壤的δ C-13值在-6.5和-8.5 permil之间，表明P（CO2）明显高于今天，可能在1500到3000 ppmV的数量级。
A diffusion-reaction model for the isotopic composition of soil CO2 and soil carbonate is evaluated. It shows which variables are important under different conditions and shows that under certain circumstances the carbon isotopic composition of soil carbonate can be used to estimate P(CO2) of the atmosphere from late Paleozoic to the present. The isotopic compositon of soil carbonate produced under uniform conditions is essentially constant below about 20 cm in most soils. Today, the isotopic composition of soil organic matter, which is most important factor in determining the carbon isotopic composition of soil carbonate. However, prior to the advent of C4 plants making up a significant fraction of the biomass, probably in the Tertiary, the concentration of CO2 in the atmosphere can be estimated because of mixing of atmospheric CO2 with CO2 produced in the soil. The diffusion-reaction model also suggests that before the advent of higher land plants most soil carbonate should have delta C-13 values that are strongly influenced by the atmosphere due to the shallow rooting depth of non-vascular plants.Preliminary results reported here suggest that P(CO2) was less than about 700 ppmV during the Eocene and since late Miocene because the limiting carbon isotopic composition of soil carbonate was between -11.5 to -12.5 permil relative to PDB. However, early Cretaceous and early Jurassic paleosols have delta-C-13 values between -6.5 and -8.5 permil suggesting that P(CO2) was significantly higher than today, probably on the order of 1500 to 3000 ppmV.