From local to global: deciphering oceanic oxygenation responses through the Penultimate Glacial Cycle

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Recent records suggest that oxygen levels in the ocean are decreasing. As a result, oxygen minimum zones (OMZs) have intensified and expanded. Yet, measurements of ocean dissolved oxygen have been limited in time (since ~1950s) preventing observations of longer term ocean oxygen trends. Better knowledge of ocean oxygen in the past will be valuable to understand future impacts due to climate change. This project will extend ocean oxygen records beyond the 20th century into the geologic past. The project will target the transition between warm and cool climate periods to test ocean oxygen response to climate change. Past oxygen levels will be reconstructed using two different proxies. The porosity of foraminifera shells is a proxy for oxygen locally in an OMZ, and thallium isotopes reflect global oxygen content. Therefore, this study will compare global versus local ocean oxygen changes within two different OMZs that will be studied. The project will support two female early-career scientists and undergraduate students. Additional outreach programs will use the Woods Hole Science and Technology Education Partnership to work with teachers to develop science curriculum for K-12 schools. This project will investigate both local and global oxygen responses to millennial climate change through the Penultimate Glacial cycle, using benthic foraminiferal surface porosity and thallium isotopes. Surface porosity of benthic foraminifera has recently been developed as a quantitative proxy of bottom water dissolved oxygen concentrations in the oxygen minimum zones, whereas seawater thallium isotopic compositions have proved to track global ocean oxygen content through Mn oxide burial flux variations. Combination of the two analyses would thus allow a simultaneous understanding of oxygen minimum zone and global ocean oxygen responses to the changes of climate states (glacial and interglacial periods) and to high-resolution transient climate oscillations during the (de)glaciation. The goal will be achieved with sediment cores from the Arabian Sea and the Southern California margin oxygen minimum zones. The study will test the hypotheses of (1) weaker Arabian Sea and California oxygen minimum zones in the glacial periods compared to the Last Interglacial; (2) lower global ocean oxygen inventory in the glacial periods; and (3) a close correlation between the global oxygen content and atmospheric CO2. This study thus allows evaluation of global versus local ocean oxygenation perturbations in the two oxygen minimum zones and potential implications on marine respired carbon storage. This project will support two female early-career scientists and undergraduate students. Outreach programs in collaboration with Woods Hole Science and Technology Education Partnership will include class visits and annual tours and research talks at Woods Hole Oceanographic Institution to help local school teachers develop science curriculum and improve climate literacy. 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.