| Autor: |
Behrooz, L., Monteiro, F. M., Naafs, B. D. A., Taylor, K. W. R., Dickson, A. J., Graham, O. A., Pearson, A., Pancost, R. D. |
| Zdroj: |
Paleoceanography & Paleoclimatology; Nov2024, Vol. 39 Issue 11, p1-20, 20p |
| Abstrakt: |
The Paleocene–Eocene Thermal Maximum (PETM) is associated with climatic change and biological turnover. It shares features with the Oceanic Anoxic Events (OAEs) of the Mesozoic, such as transient global warming and biogeochemical perturbations. However, the PETM experienced a more muted expansion of marine anoxia compared to the Mesozoic OAEs (especially OAE2), with geographically limited evidence for photic zone euxinia (PZE). We explore the extent and drivers of marine deoxygenation during the PETM using biomarkers for water column euxinia and anoxia as well as an intermediate complexity Earth system model (cGEnIE). These reveal that the water column in the North‐East Peri‐Tethys became anoxic, with euxinic conditions reaching the photic zone (PZE) during the PETM. Our model shows that euxinia developed due to a global increase in the ocean nutrient inventory with concomitant oxygen consumption, similar to findings for OAE2. The particularly strong regional response in the NE Peri‐Tethys appears to arise from a combination of global CO2‐weathering forcing, regionally restricted circulation and upwelling of sulphidic thermocline waters. Unlike OAE2, anoxia and PZE do not become widespread in our PETM simulations, consistent with new and existing geochemical and biological proxy data. This globally muted response could result from reduced biogeochemical feedbacks to climate forcing relative to the mid‐Cretaceous climate. Our observations suggest that similar mechanisms operated in response to disparate Cenozoic (PETM) and Mesozoic (OAEs) transient global warming events, while also highlighting that background conditions are crucial in modulating the sensitivity of Earth's system to them. Plain Language Summary: Ancient global warming events can help us understand the impact(s) of current global warming. A response to many past global warming events has been the expansion of oxygen deficient waters in the ocean. This is also true for the Paleocene‐Eocene Thermal Maximum that occurred about 56 million years ago. Here we show that this decrease in oxygen was so dramatic in the Peri‐Tethys (a precursor to the Mediterranean Sea of today) that it extended into the photic zone and stimulated the growth of unusual bacteria that require both light and hydrogen sulfide. This did not appear to be a direct result of warming but rather an indirect result ‐ warming caused the delivery of nutrients that stimulated the production of organic matter, which consumed oxygen in the underlying waters when it sank and degraded. This has potential analogs throughout Earth history and potentially for the future, but our work also shows that the magnitude of this response will be governed by other factors, such as the restriction of circulation, biogeochemical feedbacks and location of upwelling zones. Key Points: Photic zone euxinia (PZE) occurred in the NE Peri‐Tethys during the Paleocene–Eocene Thermal MaximumPhotic zone euxinia was likely stimulated by an increase in the nutrient inventory rather than as a direct response to ocean warmingThe restriction of PZE to specific regions is governed by geography [ABSTRACT FROM AUTHOR] |
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