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测到的变率范围，但过去变化的确切机制往往不为人所知。地下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。过去的地下温度一般是根据底栖有孔虫的元素比来估计的，特别是镁/钙（Mg/Ca），但有许多证据表明，镁（和其他金属）在底栖有孔虫壳中的结合在壳构建过程中受到影响（生物矿化）。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，旨在为估算过去的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，以及测试用于预测未来气候变化的相同数值模式再现过去地下温度估计的能力。这个项目得益于一位古海洋学家和一位地球化学家的合作。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。这些综合数据将通过美国国家海洋和大气管理局的世界古气候学数据服务向公众提供，结果将在参与者的网页上向公众介绍。该团队将从广泛的海洋环境中生成新的底栖生物元素数据，其目标是分离温度和碳酸盐化学对元素比例的控制，特别是Mg/Ca和锂/钙（Li/Ca）。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）校准提供背景。新的校准将使用来自校准中省略的地区的沉积物岩心顶部样本的数据进行测试，并通过评估冰川和去冰川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式模拟的预测进行比较。将通过古气候列表服务请求社区参与数据综合和数据模型比较。虽然模型数据综合将集中在过去22000年，但结果将提供改进的校准，以估计更长的时间尺度下的地下温度。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.