利用颗石藻生理作用来校正烯酮古CO2气压计中的b值

烯酮的碳同位素是古大气CO2重建的重要方法之一。此方法的理论基础为浮游植物对碳吸收的“被动扩散模型”，可表达为：εp =εf -b/[CO2]。其中[CO2]为海水溶解CO2浓度；εf为光合固碳酶RubisCO对碳同位素的最大分馏值为25‰；εp为光合固碳过程中有机碳与CO2之间碳同位素的分馏值；b值则代表颗石藻的生理作用。颗石藻是一种海洋单细胞、可钙化的浮游藻类，也是大洋长链烯酮的生产者。在应用中，先由现代海水磷酸盐浓度估算出b值，且假定在地质历史期间b值不发生变化，事实上这种情形很难发生。因此需要一种新的方法来校正b值。项目拟直接利用颗石藻的生理作用来校正b值。颗石藻生理作用包括钙化与光合作用，可由颗石形态、同位素反映。通过测定颗石形态以及同位素，使其作为参数可用来直接限定b值，这样便能使这个方法更为可靠。为探索CO2变化在古气候演变中起的作用提供强有力的工具。

The alkenone δ13C is one of the important tools for paleo-CO2 reconstruction. This CO2 paleobarometer plays important roles in coevolution of green-house gases and climate. This CO2 reconstruction tool is based on the “passive diffusion” model, and it can be described as: εp =εf -b/[CO2], in which [CO2] is sea water CO2 concentration; εf is 25‰, the fractionation of carbon isotope for carbon fixation enzyme RubisCO; εp is the actual carbon fractionation during phytoplankton photosynthesis; and b value represents coccolithophore total physiology. In practical use, the b value is calculated from modern ocean phosphate concentration, and is assumed to be constant during the geological past. In this project, we try to introduce a new method, using coccolithophore physiology to calibrate the b value. Coccolithophore is a kind of marine unicellular calcified phytoplankton, and is also the alkenone producer in oceans. Coccolithophore physiology (calcification and photosynthesis) can be represented by coccolith isotopes and morphology, which can be used to constrain b value directly. This new method can make the CO2 paleobarometer tool more reliable, and provide powerful proofs in exploring the CO2 variation and its importance in climate change in the geological past.