Miocene soil respiration history in Longzhong Basin and its response to East Asian summer monsoon

Soil respiration is an important link in the study of soil carbon cycle, for which understanding the soil respired carbon dioxide concentration, soil respiration rate, and the influencing factors is important. Most present studies focus on modern soil respiration and few concerned that in geological history. Taking the Miocene Lianhua Section, Longzhong Basin in Tianshui, Gansu, NW China as a case of an ancient analogue and as a reference point for predicting future climate change under high carbon dioxide concentration, we studied and compared the δ¹³C values of the organic matter in carbonate nodules (δ¹³C_om) and that of the inorganic matter in pedogenic carbonate nodules (δ¹³C_pc) from the section, from which the soil respiration rate and soil respired carbon dioxide concentration during the Miocene were reconstructed. Results show that the soil respiration rate ranged 150～400 gC·m⁻²·a⁻¹ and the carbon dioxide released from soil respiration ranged (700～2400)×10⁻⁶. Both soil respired CO₂ and soil respiration rate were shown increased during the Middle Miocene warm period, and the soil respired CO₂ and soil respiration rate decreased before and after the Middle Miocene. This change is consistent with the East Asian summer precipitation, indicating that warm-wet climate enhanced soil respiration.