Developing bottom water temperature (BWT) calibrations using elemental ratios in benthic foraminifera

来自冰芯、珊瑚、树木年轮、海洋和湖泊沉积物等地质档案的数据揭示了过去大气和海洋条件的变化，这些变化超出了仪器时代观察到的变化范围，但过去变化的精确机制往往不为人所知。次表层海洋的温度是许多海洋过程的关键指标，准确的估计将有助于检验过去海洋和气候变化的许多假设。过去，次表层温度通常是根据底栖有孔虫的元素比率，特别是镁/钙（Mg/Ca）来估计的，但有许多证据表明，镁（和其他金属）结合到底栖有孔虫的壳中受到壳构造（生物矿化）过程的影响。本研究探讨了底栖有孔虫中Mg/Ca和其他元素比值的控制因素，旨在为过去估计地下温度提供新的校准方法。改进的校准将使地下温度估计能够用于测试过去气候变化的假设，并测试用于预测未来气候变化的相同数值模型重现过去地下温度估计的能力。该项目得益于古海洋学家和地球化学家之间的合作。一名博士后科学家将参与这项研究，其中还包括社区参与数据合成。这些数据综合将通过诺阿的古气候学世界数据服务公开提供，并将在参与者的网页上向一般受众介绍结果，该小组将从各种海洋环境中产生新的海底元素数据，目的是分离温度和碳酸盐化学对元素比例，特别是镁/钙和锂/钙（Li/Ca）的控制。生物矿化模型将为控制元素比例的环境因素提供统一的框架和更多的定量约束，并为新的多元素（例如，Mg/Li）校准。新的校准将用来自校准中省略的区域的沉积物岩心顶部样本的数据进行测试，并评估冰川和冰退海洋的垂直和水平温度趋势是否合理。过去的温度估计将与气候模型模拟的预测进行比较。将通过一个古气候名录服务器要求社区参与数据综合和数据模型比较。虽然模型数据合成将集中在过去的22,000年，结果将提供更好的校准，以估计地下温度在一个更长的时间尺度。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

Data from geological archives such as ice cores, corals, tree rings, and marine and lake sediments reveal past changes in atmosphere and ocean conditions that exceed the range of variability observed during the instrumental era, but the precise mechanisms of past changes are often not well known. Temperature of the subsurface ocean is a key indicator of many ocean processes and accurate estimates would help test many hypotheses of past ocean and climate change. Subsurface temperature in the past is generally estimated from elemental ratios, especially magnesium/calcium (Mg/Ca) of benthic foraminifera but there are many lines of evidence that the incorporation of Mg (and other metals) into the shells of benthic foraminifera is influenced in the process of shell construction (biomineralization). This research investigates the controls on Mg/Ca and other elemental ratios in benthic foraminifera with the goal of providing new calibrations to estimate subsurface temperature in the past. Improved calibrations will enable subsurface temperature estimates that can be used to test hypothesis of past climate change, as well as test the ability of the same numerical models that are used to predict future climate change to reproduce estimates of subsurface temperature in the past. The project benefits from a collaboration between a paleoceanographer and a geochemist. A postdoctoral scientist will participate in the research, which also includes community participation in data syntheses. These data syntheses will be made publicly available through NOAA's World Data Services for Paleoclimatology, and results will be described for general audiences on participants' web pages.The team will generate new benthic elemental data from a wide range of ocean environments, with the goal of isolating the control of temperature and carbonate chemistry on elemental ratios, especially Mg/Ca and lithium/calcium (Li/Ca). A biomineralization model will provide a unifying framework and more quantitative constraints on the environmental factors controlling the elemental ratios, and context for new multi-element (e.g., Mg/Li) calibrations. New calibrations will be tested with data from sediment core-top samples from regions omitted from the calibrations, and by assessing whether vertical and horizontal temperature trends in the glacial and deglacial ocean are reasonable. Past temperature estimates will be compared to predictions from climate model simulations. Community participation in both the data synthesis and data-model comparisons will be requested through a paleoclimate listserv. While model-data synthesis will focus on the last 22,000 years, the results will provide improved calibrations to estimate subsurface temperature over a much longer time scale.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.