恢复地史时期大气CO_2浓度的新指标:苔藓植物化石

New Proxy for Atmospheric Paleo-CO_2 Level During Phanerozoic:Carbon Isotope Discrimination of Fossil Liverworts

在中国已知最好的苔藓植物化石产地之一河北蔚县,采集了大量中侏罗世的苔藓植物化石,选取了3种保存较好的数十块苔类植物化石进行实验室分析处理,测定了它们的碳同位素组成,并计算出Δ13C,运用国际学术界古大气CO2浓度的最新研究成果,即通过地质学、植物学、植物生理学、地球化学和概率统计学的多学科交叉研究,利用苔藓植物化石有机碳同位素判别这一全新指标和重建古大气二氧化碳的模型——BRYOCARB,恢复出中侏罗世的古大气CO2浓度约为705(BRYO-CARBNP)或566(BRYOCARBP)μmol/mol,结果表明苔藓植物化石是恢复地质历史时期大气CO2浓度变化的有效新指标.

This paper summarizes the latest approaches and results of reconstructed paleo-CO2 level for the pre-Quaternary period.With the link and response between the carbon isotope composition of the fossil liverworts and the paleo-CO2 level,the carbon isotope discrimination（Δ13C） of fossil liverwort is introduced as a new proxy for paleo-CO2 level.It is an interdisciplinary research concerning the relevant domains such as geology,botany,phytophysiology,geochemistry,probability and statistics.The theory and process of the new proxy are clarified and its corresponding mathematical model,BRYOCARB,is introduced.Furthermore,in order to test the result of the new method,a case study has been carried out.Three species fossil liverworts of the Middle Jurassic were collected from Yuxian County,Hebei Province,which is one of the best known fossil sites of bryophytes in China.After a series of experiments and analyses,their carbon isotope compositions were measured and then their Δ13C were calculated.With the Δ13C values and some other environmental parameters running in BRYOCARB,the paleo-CO2 level was calculated,which is ~705（BRYOCARBNP for with no pores liverworts） μmol/mol or ~566（BRYOCARBP for with pores liverworts） μmol/mol.The results show a good agreement with other proxies and the long term geochemical models,which proves the carbon isotope discrimination of fossil liverwort is an effective proxy.