Are Carotenol-Chlorin Esters Diatom Biomarkers?

最近，研究人员在阿曼和秘鲁边缘、南加州海湾和蒙特利湾的沉积物中发现了新的胡萝卜素和氯化物酯(胡萝卜素-氯-酯，CCES)。与CCES相关的绿素是叶绿素a的降解产物脱镁叶绿酸a和焦脱镁叶绿酸a。硅藻生物标志物、岩藻黄质的降解产物异果黄质-脱水和异果珊瑚醇-脱水是唯一与CCES相关的胡萝卜素。PI还在硅藻占优势区域的水柱样品中发现了CCE，在实验室摄食硅藻的桡足类动物的粪便颗粒中也发现了CCE。结果表明，CCES是在摄食硅藻的桡足类动物体内通过酶促的酯交换反应产生的。因此，沉积CCE可以作为硅藻新产物的标志，有机碳和氮同位素特征将反映硅藻对碳通量做出贡献的特征。一系列实验室实验将进一步证实这一假设。最初的实验将在加州近海常年存在的桡足类动物--太平洋哲水蚤身上进行。来自圣巴巴拉盆地和蒙特利湾的匹配水柱和沉积物捕集器样本覆盖所有季节，将用于将CCES的产生与浮游植物群落结构和其他环境因素联系起来。

Novel esters of carotenols and chlorins (Carotenol-Chlorin-Esters, CCEs) were recently discovered by the investigator in sediments from the Oman and Peru margin, the Southern California Bight, and Monterey Bay. The chlorins associated with CCEs were pheophorbide a and pyropheophorbide a, degradation products of chlorophyll a (Chl a). Isofucoxanthin-dehydrate and isofucoxanthinol-dehydrate, degradation products of fucoxanthin and a biomarker for diatoms, were the only carotenols associated with CCEs. The PI also found CCEs in water column samples in regions dominated by diatoms and CCEs were found in the fecal pellets of a copepod fed diatoms in the laboratory. It is suggested that CCEs are produced by enzymatically mediated transesterifications in copepods grazing on diatoms. Thus, sedimentary CCEs could be markers for new production derived from diatoms and the organic carbon and nitrogen isotopic signature would reflect that of the diatoms that contributed to the flux of carbon to the sediments. A set of laboratory experiments will further corroborate this hypothesis. Initially experiments will be performed with the copepod, Calanus pacificus, that is present year-round off California. Matched water column and sediment trap samples from the Santa Barbara Basin and Monterey Bay, covering all seasons, will be used to relate the production of CCEs to phytoplankton community structure and other environmental factors.