Controls on Carbon Isotopic Fractionation in Emiliania Huxleyi

虽然实验室和实地研究表明，烯酮的同位素分析显示出巨大的潜力，作为一个CO2的代理，因为细胞的几何形状可以估计，特定的生长速率和碳同位素分馏在天然样品之间的关系还没有得到很好的定义。 因此，主要研究人员将开发和评估一种新的方法，该方法基于结合13 C标记和同位素比监测气相色谱-质谱法，以确定海洋中Emiliania huxleyi和Gephyrocapsa oceanica的原位生长速率。 本研究的目的是确定13 C-烯酮标记技术提供可靠的增长率估计的生长条件的范围，并确定在什么条件下可能会出现偏倚。 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，并探索培养技术如何影响13 C标记以及使用稀释批次与连续培养实验的碳同位素分馏，生长速率和含水CO2浓度之间的关系。 最后，在一组选定的实验中，将13 C掺入烯酮的速率与E. huxleyi和G. oceanica，以提供对烯酮的生理功能和生物合成途径的深入了解。 将进行一个现场部分，直接比较天然产生烯酮的藻类与实验室实验中开发的分馏关系。 这项研究的结果将有助于校准和验证烯酮中碳同位素作为CO2代用品的使用，如果古海洋学界要使用这种代用品来更好地了解气候变化的机制，这是必要的知识。

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.