66-9 Reconstructing the prehistoric shark community across the Early Eocene Climate Optimum at IODP Site U1553 and DSDP Site 596 using fossil dermal denticles

Session: Environmental Instability During Greenhouse Periods: Impact on Terrestrial and Marine Ecosystems (Posters)

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Abstract:

The fossil record is an excellent archive to explore how ecosystems respond to environmental change. The Early Eocene Climate Optimum (EECO, 53-49 million years ago) is the hottest interval in the last 100 million years, with average global surface temperatures of 27 ℃. Future atmospheric CO2 predictions indicate the possibility of an Eocene-like climate in the near future. Here, we use isolated fossil shark dermal denticles and fish teeth to expand our understanding of how fish and sharks responded to the extreme global warmth during the EECO. We compare these trends using two deep-sea sediment cores: IODP Site U1553 from south of New Zealand and DSDP Site 596 from the center of the Pacific gyre.  Given its location near the Southern Ocean and the Antarctic Circumpolar Current, we hypothesize that these oceanographic conditions would expose IODP Site U1553 to higher temperatures compared to DSDP Site 596 as warm surface waters were circulated around the globe. DSDP Site 596 is located in deeper waters and near no major currents within the Pacific gyre. Deep sea shark communities at DSDP Site 596 may have been able to escape being exposed to the extreme warmth of the EECO. At IODP Site U1553, we found similar trends in denticle and fish teeth accumulation through the Eocene, indicating a potential predator-prey abundance relationship, with shark populations tracking fish populations across the warming interval. IODP Site U1553 denticle assemblages were significantly different from modern, with >70% of fossil denticles exhibiting geometric morphology compared to <1% today, suggesting that the EECO open-ocean shark community was dominated by very different sharks than those that thrive in the oceans today. Denticle morphological diversity was not strongly impacted by the EECO, with most denticle morphotypes persisting throughout the study interval. Shark communities at both sites were relatively resilient to the extreme conditions of the EECO, however the precise timing and magnitude of denticle community changes differed between the sites, indicating a geographic or environmental constraint on shark community dynamics. As we grapple with the impacts of increasing carbon emissions, ecosystems across geologic time allow us to better understand how our own ocean ecosystems may respond to our future climate.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7859

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