Collaborative Research: Deep ocean temperature and continental ice volume from benthic foraminiferal test composition, 77Ma to Present

University Of Rochester, Rochester NY

Investigators

Abstract

Sea floor sediments record the natural variability of the Earth’s climate system. Studying sediment records can improve our ability to predict how the climate system will respond to human activities. This project will produce records of deep-sea temperatures, continental ice volume, and atmospheric carbon dioxide. The records will document changes in the climate system over the last 77 million years. Those data will improve our understanding of processes such as polar amplification and the ability of the Earth’s system to adjust to different atmospheric carbon dioxide concentrations. This study will also improve our knowledge of long-term changes in deep ocean temperatures and ice-sheet volume variability and their connection to changes in atmospheric carbon dioxide. The project will be carried out by two female scientists, one of whom is an early career researcher. Several undergraduate and graduate students will participate to the proposed research activities. The outreach program will involve Earth/Environmental Science teachers from middle and high schools. Benthic foraminifera are excellent recorders of past environmental conditions. In particular, the benthic foraminiferal (bf) magnesium/calcium ratio (Mg/Ca) is used as a temperature proxy, making it possible to separate temperature from ice volume effects on the widely used bf oxygen isotope proxy (d18O). However, the bf Mg/Ca signal is complicated by a dependency on carbonate saturation state (“omega”) in addition to temperature. Benthic foraminiferal lithium, boron and strontium to calcium ratios (Li-B-Sr/Ca) show promise in separating the temperature and omega contributions to bf Mg/Ca. The proposed research will: 1) construct robust temperature and ice volume histories during the late Cretaceous and Cenozoic (~77-0 Ma) using bf d18O in conjunction with bf Mg-Li-B-Sr/Ca; and 2) calibrate offsets in bf Mg-Li-B-Sr/Ca for multiple species across paleodepth transects to encompass a range of omega. Different species’ physiological response to variations in temperature, omega, and seawater element/Ca ratios will be addressed using a multivariate model. One-Myr sample spacing will be used for the calibrations, whereas a new higher-resolution (~200 Kyr) record will provide a robust dataset of bf Mg/Ca variations since 77 Ma. This dataset will be used, together with bf d18O data, to test the hypothesis that deep ocean temperature and continental ice volume covary from the Late Cretaceous to the Cenozoic. The connections among changes in deep ocean temperature (and chemistry), continental ice volume, and atmospheric carbon dioxide concentration will be investigated using a numerical box model of the ocean carbon cycle. 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.