Experiment: The effect of temperature, salinity and growth rate on the stable hydrogen isotopic composition of long chain alkenones produced by Emiliania huxleyi and Gephyrocapsa oceanica

Two haptophyte algae, Emiliania huxleyi and Gephyrocapsa oceanica, were cultured at different temperatures and salinities to investigate the impact of these factors on the hydrogen isotopic composition of long chain alkenones synthesized by these algae. Results showed that alkenones synthesized by G. oceanica were on average depleted in D by 30 compared to those of E. huxleyi when grown under similar temperature and salinity conditions. The fractionation factor, alpha alkenones-H2O, ranged from 0.760 to 0.815 for E. huxleyi and from 0.741 to 0.788 for G. oceanica. There was no significant correlation of alpha alkenones-H2O with temperature but a positive linear correlation was observed between alpha alkenones-H2O and salinity with ~3 change in fractionation per salinity unit and a negative correlation between alpha alkenones-H2O and growth rate. This suggests that both salinity and growth rate can have a substantial impact on the stable hydrogen isotopic composition of long chain alkenones in natural environments.

本研究选取两株定鞭金藻（haptophyte algae）——赫氏艾密里藻（Emiliania huxleyi）与大洋桥石藻（Gephyrocapsa oceanica），在不同温度与盐度条件下开展培养实验，以探究这两个环境因子对该类藻类合成的长链烯酮（long chain alkenones）氢同位素组成的影响。结果表明，在温度与盐度一致的培养环境中，大洋桥石藻合成的长链烯酮的氘（D）相对丰度平均较赫氏艾密里藻贫化30。同位素分馏系数（fractionation factor）α_alkenones-H2O在赫氏艾密里藻中的取值区间为0.760~0.815，在大洋桥石藻中则为0.741~0.788。相关性分析显示，该分馏系数与温度无显著相关性，但与盐度呈显著正线性相关——盐度每变动1个单位，分馏系数约变化3；同时该分馏系数与藻类生长速率呈负相关。上述结果表明，在自然环境中，盐度与藻类生长速率均可对长链烯酮的稳定氢同位素组成产生显著影响。