Controls on Carbon Isotopic Fractionation in Emiliania Huxleyi

尽管实验室和实地研究表明，烯酮的同位素分析显示出作为二氧化碳代用物的巨大潜力，因为细胞的几何形状可以估计，但在自然样品中，特定生长速率与碳同位素分馏之间的关系尚未得到很好的定义。为此，主要研究人员将开发和评估一种基于13C标记和同位素比率监测气相色谱-质谱相结合的新方法，以确定赫胥黎Emiliania huxleyi和Gephyrocapsa oceanica在海洋中的原位生长速率。本研究的目的是确定生长条件的范围，其中13c -烯酮标记技术给出了生长速率的可靠估计，并确定在什么条件下可能会出现偏差。此外，主要研究人员将评估营养和光照限制对碳同位素分馏的影响，探索培养技术如何影响13C标记，以及碳同位素分馏、生长速度和水CO2浓度之间的关系，采用稀批培养与连续培养实验。最后，在一系列精选的实验中，13C与烯酮的结合率将与赫克斯黎蛤和大洋蛤的其他脂质进行比较，以深入了解烯酮的生理功能和生物合成途径。将进行现场试验，直接比较天然产烯烃藻类的分馏关系与实验室实验中得出的分馏关系。这项研究的结果将有助于校准和验证烯酮碳同位素作为二氧化碳代用物的使用，如果古海洋学界要使用这种代用物来更好地理解气候变化的机制，这是必不可少的知识。

Although laboratory and field studies suggest that isotopic analyses of alkenones show great potential as a CO2 proxy because cell geometry may be estimated, the relationship between specific growth rate and carbon isotopic fractionation in natural samples has not been well defined. For this reason, the principal investigators will develop and evaluate a novel method based on combining 13C labeling and isotope-ratio-monitoring gas chromatography-mass spectrometry to determine in situ growth rates of Emiliania huxleyi and Gephyrocapsa oceanica in the ocean. The objectives of this research are to define the range of growth conditions where the 13C-alkenone-labeling technique gives reliable estimates of growth rate and to identify under what conditions bias may be anticipated. In additions, the principal investigators will evaluate the effects of nutrient and light limitation on carbon isotopic fractionation and explore how culture techniques affect 13C labeling and the relationship between carbon isotopic fractionation, growth rate and aqueous CO2 concentrations using dilute batch versus continuous culturing experiments. Lastly, in a select suite of experiments, the rate of incorporation of 13C into alkenones will be compared with other lipids for E. huxleyi and G. oceanica to provide insight into the physiological function(s) and biosynthetic pathway(s) of alkenones. A field component will be carried out to compare directly the fractionation relationship in natural alkenone-producing algae with those developed in laboratory experiments. Results from this study will help calibrate and validate the use of carbon isotopes in alkenones as a CO2 proxy, essential knowledge if the paleoceanographic community is to use this proxy to better understand mechanisms of climate change.