Diversification of Iron-Biomineralizing Organisms During the Paleocene-Eocene Thermal Maximum: Evidence From Quantitative Unmixing of Magnetic Signatures of Conventional and Giant Magnetofossils

摘要

Conventional magnetofossils represent magnetic mineral remains of magnetotactic bacteria. Giant magnetofossils have no known modern analog. Both conventional and giant magnetofossil assemblages can record paleoenvironmental information through changes in magnetotactic bacteria diversity driven by nutrient supply and oxygenation. We use marine sediments that record a rapid global warming event, the Paleocene-Eocene Thermal Maximum (~56 Ma), to assess how abundant wellpreserved magnetofossils with high morphological disparity record paleoenvironmental information. We find that conventional magnetofossils can be distinguished from giant, needle-shaped magnetofossils using principal component analysis of first-order reversal curves (FORC-PCA); moreover, FORC-PCA may be able to distinguish between well-preserved magnetically soft and magnetically hard magnetofossils. FORC-PCA is a robust, nondestructive technique that can be applied to other marine archives to understand how these ecosystems respond to rapid environmental change. We hypothesize that the sudden appearance of giant magnetofossils represents a natural response to niche expansion within the water column (a thicker oxic-anoxic interface) and eutrophication (via iron supply) by protists that biomineralize giant magnetofossils. This application has potential as a proxy for changes in marine oxygen and iron concentrations stimulated by rapid planetary change. Plain Language Summary Magnetofossils are fossilized magnetic particles produced by magnetotactic bacteria and other microorganisms. They are geologically significant because they record environmental and ecological information including bacterial diversity and marine oxygen levels. Here, we test if high-field magnetic measurements can discriminate between different sizes and shapes of magnetofossils within bulk samples of marine sediments that record rapid global warming 56 million years ago, the largest global warming event in the past ~80 million years.