Guest essay by Eric Worrall
The Paleocene-Eocene Thermal Maximum (PETM), a period of extremely rapid global warming which occurred 10 million years after the demise of the dinosaurs, was supposed to have been an ocean catastrophe. Instead, even temperate climate fish treated the warmth like a tropical food buffet.
Ancient Fish Thrived During a Period of Rapid Global Warming
Teeth and scales preserved in marine sediments suggest that fish thrived during one of Earth’s fastest-warming periods.
By Elyse DeFranco 14 December 2021
About 55 million years ago, Earth’s climate underwent a rapid and intense period of warming, both on land and at sea. Temperatures soared more than 5°C, and even Arctic seas turned tropical. Reconstructing this warm era, the Paleocene-Eocene Thermal Maximum (PETM), provides a glimpse into Earth’s possible future. “One of the best tools we have to understand how the [ocean] system responds is to look at past instances of global change,” said Elizabeth Sibert, a paleoceanographer and paleoecologist at the Yale Institute for Biospheric Studies.
By examining fossil evidence from the PETM preserved in marine sediment cores, Sibert and her colleagues sought to understand how fish might respond to warming oceans. Contrary to the predictions of many models, they found that fish actually grew more abundant as temperatures soared. Sibert and her team will present their research on 14 December at AGU’s Fall Meeting 2021.
Sibert and her team examined sediment records in three different cores collected by the Ocean Drilling Program. The drill sites spanned tropical reaches of the north central Pacific, eastern equatorial Pacific, and Atlantic Oceans. The researchers filtered microscopic fish scales and teeth from varying depths of the sediment core, counting and sorting them for a window into past ocean life during the PETM.
“This is the first time we have an idea of what mid to upper trophic level groups were doing during this warming event,” said team member Richard Norris, a paleobiologist at the Scripps Institution of Oceanography. “Previously, almost all studies of the PETM have been based upon unicellular plankton or microzooplankton.”
The results paint a consistent picture of the past across all three samples: Fish became more abundant as temperatures climbed, then gradually decreased again as the warming waned. Plus, the various fish types didn’t change much during this temperature flux. “It’s really surprising,” said Norris. “You’d think that as things warm up that you might get a really different community of fishes.”
Still, Sibert urges caution when comparing fish outcomes during the PETM and what might happen this century—and beyond. “The rate of warming…can have dramatic and differential impacts on marine ecosystems,” she noted.
The abstract of the study;
PP23A-02 – Enhanced open-ocean fish production and community resilience across the Paleocene-Eocene thermal maximum
Elizabeth C Sibert Yale University
Douglas W Tomczik Scripps Institution of Oceanography
Daniel Gaskell Yale University
Gregory L. Britten Massachusetts Institute of Technology
Richard D Norris Scripps Institution of Oceanography
Marine ecosystem models predict that anthropogenic warming will likely result in decreased marine fish production in the coming centuries, although the magnitude of this effect is poorly constrained. By contrast, preliminary work on the early Paleogene (62-48 Ma) has suggested that warmer climate periods were associated with long-term increases in open-ocean fish production. The historical response of fish communities to rapid-scale warming events closer in rate to anthropogenic warming remains unknown. The Paleocene-Eocene Thermal Maximum (PETM) was a transient and rapid interval of global warming approximately 56 million years ago (Ma) and is a partial analog to modern climate change. To test how fish populations responded to past rapid ocean warming, we compiled records of fish abundance and diversity across the PETM, using isolated microfossil fish teeth and shark scales (ichthyoliths) preserved in three deep-sea sediment cores: Ocean Drilling Program (ODP) Site 1209 in the North Pacific Ocean, ODP Site 1220 in the Equatorial Pacific, and ODP Site 1260 in the Equatorial North Atlantic Ocean. We find that, in contrast to future projections, ichthyolith accumulation rates (IARs) from all sites show significant increases in fish production coincident with early stages of the PETM, before returning to pre-PETM levels as the hyperthermal conditions waned. Furthermore, the morphological diversity and composition of PETM ichthyolith assemblages remain largely constant across the event, with no evidence of excursion or disaster biotas. These findings suggest that on millennial timescales fishes may be more resilient to rapid global climate change than previously thought. Further, the temperature sensitivity of fish production across the rapid warming of the PETM can be quantitatively compared to the temperature sensitivity of fish production throughout the Early Paleogene, providing a means to interrogate the sensitivity of fish populations to changes in ocean temperature throughout Earth’s past and across different time scales.
Good on the authors for having the courage to report and present their findings.
I would have loved to be at the AGU meeting where Elizabeth and the other authors presented their study, her evidence that all their carefully crafted alarmist ocean biome global warming models could be totally wrong.
via Watts Up With That?
December 15, 2021 at 08:41PM