Magnetofossils and Benthic Foraminifera Record Changes in Food Supply and Deoxygenation of the Coastal Marine Seafloor During the Paleocene‐Eocene Thermal Maximum

Abstract

AbstractContinental shelf sediments along the northeast continental margin of North America contain a magnetofossil‐rich interval deposited during the Paleocene‐Eocene Thermal Maximum (PETM), an abrupt global warming event that occurred ∼56 Ma. These magnetofossils were produced by magnetotactic bacteria and unidentified, iron‐biomineralizing organisms. Previous work shows three distinct magnetofossil endmembers identified from principal component analysis of first‐order reversal curves (FORC‐PCA). The relative proportions of these magnetofossil endmembers varied over time during the PETM. Benthic foraminiferal species associations from the same sediments also vary during the PETM. Here, we compare the variability in magnetofossils and benthic foraminifera and statistically test, for the first time, whether they are significantly correlated. We find that changes in the type of magnetofossils present within the sediment correspond to changes in benthic foraminiferal assemblages, thus reflecting syndepositional conditions such as changes in oxygen, nutrients, and organic carbon concentrations, rather than diagenetic processes. We also find that magnetofossil‐producing organisms may respond to specific environmental pressures differently than benthic foraminifera, and in some cases, may better record these environmental signals. Therefore, FORC‐PCA on magnetofossil‐rich sediments can be used to understand discrete changes in ocean and/or early sediment chemistry over episodes of climate change. These environmental responses are inferred from non‐destructive, reproducible magnetic measurements, adding an independent environmental proxy to more commonly studied microfossil and geochemical proxies. Notably, these measurements only require small bulk sediment samples and do not need to contain calcium carbonate, making this approach ideal where sample material is limited and the record is affected by ocean acidification.