UC San Diego

A partial analog for modern global change is the Paleocene-Eocene Thermal Maximum (PETM)--a transient episode of warming and acidification at ~55.5 Ma that triggered extinctions in deep sea biotas, extensive biogeographic shifts, and the appearance of `excursion biotas' (common occurrences of taxa restricted to the PETM interval). We analyzed the impact of the PETM on fish production and biodiversity using three deep sea sites in the Pacific and tropical Atlantic. Fossil fish teeth (ichthyoliths) mass accumulation rates show transient increases in fish production at all sites coincident with early stages of the PETM and exhibit little variation before and after the PETM. Fish tooth morphological diversity changes little across the PETM in both the equatorial Pacific and North Pacific gyre with larger changes at the equatorial Atlantic site. There is no evidence for the appearance of distinctive "excursion taxa" during the PETM, suggesting that fish experienced fewer

geographic range shifts than calcareous and organic-walled plankton. The increase in ichthyolith accumulation, interpreted as export production at the PETM broadly matches published estimates of PETM export production from biogenic barium fluxes. Our findings contrast with model predictions for the next century, which suggest that increased global temperatures will lead to reduced subtropical fish production. Disparities between future Earth models and PETM data may reflect the different timescales of observation.