TEMPERATURE RECONSTRUCTION USING THE CLUMPED ISOTOPE FOR THE HOLOCENE SOIL CARBONATES ON THE CHINESE LOESS PLATEAU
Abundant soil carbonates are preserved in the loess-paleosol sequences,which are invaluable archive for the carbonate clumped isotope(Δ47)analysis to quantitatively reconstruct paleotemperature and environmental changes.However,no systematic studies were conducted to investigate the Δ47 compositions of the Holocene soil carbonates and their climatic implications on the Chinese Loess Plateau(CLP).Thus,this study analyzed the stable and clumped isotopes of the Holocene soil carbonates obtained from the upper 3 meters in Weinan(34.5°N,109.6°E)and Luochuan(35.7°N,109.4° E)sections,which are located on the southern and middle part of the CLP,respectively.Meanwhile,the soil temperature was monitored at different depths(0.5 m,1 m,2 m and 4 m)for the upper 4 meters.The results show that the soil carbonate formation temperature(T47)reconstructed from Δ47 values is approaching warm season temperature,and the mean T47 is 25 ℃ for Weinan and 18℃ for Luochuan,which are 8～10℃ higher than mean annual temperature in the studied region.Furthermore,the soil water oxygen isotope compositions(δ18O)were reconstructed from T47 and soil carbonate δ18O,which are consistent with the monitored warm season precipitation δ18O.Altogether,these data suggest that the soil carbonates were precipitated during the warm-wet season on the CLP.Notably,the T47 in the two sections are similar with the measured soil temperatures at the soil carbonates formation depths.This indicates the important role of the carbonate's formation depth,because the T47 of soil carbonates reflected the soil temperature which is further strongly related to the soil depth.In other word,the deeper formation depth of soil carbonates will correspond to lower/mean annual temperature.This inference is supported by the recent study on the Lingtai section in central part of CLP,which show that the mean T47 of the soil carbonates formed in the last interglacial is 5℃ lower than those for the Holocene.Besides,the published results also imply the influences of formation depth of soil carbonates on their carbon and oxygen isotopes.Therefore,it is pivotal to constraint the formation depth of soil carbonates as well as their formation season in future studies.
万方数据
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