The Atlantic's role in ice age inception and termination: Assessing carbon storage and release with new Brazil Margin profiles from MIS 2 to MIS 6

University Of Connecticut, Storrs CT

Investigators

Abstract

The driver of glacial-interglacial carbon dioxide (CO2) cycles remains one of the most important unresolved questions in the field of paleoclimatology. Lower atmospheric CO2 levels correspond to ice sheet expansion, while rising CO2 levels are a primary driver of ice sheet retreat. Although it has long been assumed that ocean-atmosphere exchange mediates CO2 levels, the underlying mechanisms have remained elusive. During the Last Glacial Maximum (LGM; ~20,000 years ago), the deep Atlantic was more stratified than today, which likely enhanced carbon storage in the abyss. If earlier glacial intervals were characterized by a similar pattern, it would suggest that stratification is fundamental to deep ocean carbon storage and therefore glaciations. Recent studies also suggest the deep Atlantic circulation slowed during the last deglaciation, which may result in carbon accumulation in the surface ocean and atmosphere. If this mechanism is a key driver of ice sheet retreat, then evidence for a weaker deep Atlantic circulation should exist during each deglaciation of the last 140,000 years. The primary goal of this project is to use data from multiple cores in the Southwest Atlantic to assess changes in ocean circulation and carbon storage during the last full glacial cycle. Using sediment cores from approximately 1500 m to 4000 m water depth, the research will assess: 1) the strength of the Atlantic's meridional overturning circulation (AMOC), 2) water column stratification in the South Atlantic, and 3) their relation to oceanic carbon storage. AMOC strength and water column stratification will be reconstructed by analyzing carbon and oxygen isotopic ratios in the shells of benthic (bottom dwelling) foraminifera. Carbon storage will be assessed by analyzing the boron to calcium ratio (B/Ca) in benthic foraminifera during key glacial and interglacial intervals of the last 140,000 years. Each core will be dated using oxygen isotope stratigraphy, a well-known tool in the field of paleoclimatology. The proposed work could transform our understanding of the climate system by creating the first integrated picture of deep Atlantic circulation and carbon storage spanning the last full glacial cycle. The results will therefore provide a unique framework for understanding the source of atmospheric CO2 variability over long timescales. The results should also be useful to the broader paleoclimate community by providing an internally consistent depth transect of cores that can be studied using analyses beyond the scope of the current project. The educational impact of the proposed work includes the participation of a graduate student and two undergraduate students at the University of Connecticut. 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.