季节温度变化及土壤pH差异对土壤bGDGTs温度指标的影响

Influence of Seasonal Temperature Variation and pH Disparity on bGDGTs Thermometers in Soils

为深入了解bGDGTs化合物对温度的响应是否受季节性变化和pH差异的影响,我们对中国多个偏碱性土壤bGDGTs化合物进行为期一年的观测.研究结果表明:在一年内,bGDGTs的组成对温度的响应是长期积累的结果,并不能反映短期(季节)的温度变化.寒冷的青藏高原高海拔地区b GDGTs指标可能反映了春季/夏季过渡阶段的温度;而其他区域bGDGTs的分布和指标均未呈现明显的季节性特征.土壤pH是造成不同校正公式斜率差异的最主要原因,不同pH条件下,MBT指标对温度的响应存在显著差异.在中国中性-偏碱性土壤中,MBT指标与年均大气温度MAAT(5~25?C)的关系为:MAAT=20.78×MBT+5.92(R2=0.88, p <0.001).该校正公式在中性-偏碱性土壤环境中比之前的MBT-MAAT校正公式更精确,为反演中国区域古温度提供理论依据.

To better understand the seasonal variation of b GDGTs in soils, we collected samples time-serially from several Chinese alkaline soils over 1 year. On the seasonal scale, the composition of b GDGTs is the result of a long-time adaption to temperature variation rather than a short-time adjustment. bGDGTs-derived temperatures in soils from cold and high altitude of Tibet Plateau are likely to reflect the temperature of spring/summer transition period. However, in other sites, the distribution and proxies of bGDGTs don＇t show significant seasonal variation or bias. Furthermore,soil pH appears to be the main reason for discrepancy in slopes of different calibrations, which can result in distinct calibration formulas in soils.Combining with the previously published datasets, our results demonstrate that the responses of MBT index to temperature are different in alkaline and acidic soils. Here, we propose an MBT-MAAT calibration in neutral to alkaline soils： MAAT = 20.78 × MBT ＋ 5.92（R2 = 0.88, p 0.001）（5-25℃）. This calibration partially amends the impact of soil pH on MBT-MAAT relationship, which provides more accurate calibration for paleotemperature reconstruction in specific regions of China.