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

点击翻译按钮获取中文摘要

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.