SGER: Improving the Utility of Paleoproxies from Coccolith Chemistry: Calibration and Analytical Advances

根据球石方解石的元素(锶/钙)化学，SGER请求提供资金以开发一种新的球石藻类古生产力指标。对一个物种的培养研究，以及对两个横跨上升流地区的沉积物岩芯顶部的球石的分析表明，球石的锶/钙比率随着营养刺激的球石生长率的变化而变化。然而，目前尚不清楚这些反应是否在海洋中广泛存在，球藻中的锶/钙变化是由营养物质浓度或营养物质对生长速度的影响引发的，是否特定的营养物质对这种影响负责，或者是否一般的营养限制状态驱动了这种反应，以及这些反应对不同物种是否相同。定标研究将通过对另外三个物种(石斑鱼、远缘瓢虫和大洋藻)的营养限制培养以及在营养物质刺激的水华事件之前、期间和之后的时间序列浮游生物和沉积物陷阱样本的分析来进行。在浮游生物样本和一些沉积物圈闭中收集的极少量物质只能通过开发一种新的离子探针(SIMS)技术来分析，该技术能够精确地测量单个或小群10-20个拾取的球石的锶/钙比。除了改进指示剂的校准外，SIMS离子探针技术还将有利于对岩心下部沉积物进行锶/钙分析，以确定古生产力，因为它将消除非碳酸盐相的元素贡献，并允许对给定物种或属的纯样品进行锶/钙测定。

This SGER request funding to develop a new indicator of paleo-productivity of coccolithophorid algae, based on elemental (Sr/Ca) chemistry of coccolith calcite. Culture studies of a single species, Emiliania huxleyi, and analysis of coccoliths from sediment core tops in two transects across upwelling areas, suggest that coccolith Sr/Ca ratios vary with nutrient-stimulated changes in coccolithophorid growth rates. However, it is unclear whether these responses are widespread in the ocean, whether Sr/Ca variations in coccoliths are triggered by nutrient concentrations or the effect of nutrients on growth rate, whether a particular nutrient is responsible for this effect or if the state of nutrient limitation in general drives the response, and whether these responses are the same for different species. Calibration studies will be conducted through nutrient-limited culture of three additional species (Calcidiscus leptoporus, Coccolithus pelagicus, and Gephyrocapsa oceanica) and by analysis of time series plankton and sediment trap samples before, during, and after nutrient-stimulated bloom events. The very small amount of material collected in plankton samples and some sediment traps can be analyzed only through the development of a new ion probe (SIMS) technique capable of precise Sr/Ca measurements of individual or small groups of 10-20 picked coccoliths. In addition to improving calibration of the indicator, the SIMS ion probe technique will also benefit Sr/Ca analysis of downcore sediments for paleoproductivity determinations because it would eliminate elemental contributions from noncarbonate phases and permit determinations of Sr/Ca on pure samples of a given species or genera.