HKU paleontologists discovered collapse and recovery of shallow marine ecosystem during historic hyperthermic event

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About 56 million years ago, the Paleocene-Eocene Thermal Maximum (PETM), one of the most famous historical hyperthermic events, drove our planet into a super greenhouse state. It is very important for us to understand how this happened and how it affected the environment, as studying past climate events of extreme global heat can be one of the best ways for us to understand and predict. future environmental and ecological changes in response to ongoing anthropogenic factors. warming up.

Ms Skye Yunshu TIAN, PhD student at the School of Biological Sciences and Swire Institute of Marine Science (SWIMS) at the University of Hong Kong (HKU), conducted a research project on PETM in collaboration with Dr Moriaki YASUHARA from same affiliation, Huai-Hsuan M HUANG of the Smithsonian Institution, Fabien L CONDAMINE of the National Center for Scientific Research (CNRS), and Marci M. ROBINSON of the US Geological Survey. Ms Tian presented a clear scenario of recovery-disturbance of shallow marine ecosystems caused by extreme warming and deoxygenation of the oceans during the PETM, which may be the best natural analogue of the ongoing anthropogenic warming. This discovery was recently published in the famous journal Global and Planetary Change.

Apply an innovative method to assess the local dynamics of diversity

PETM was triggered by a massive injection of carbon into the atmosphere, a sudden rise in global temperature of 5 to 8 ℃ has been associated with profound changes in ocean chemistry and biotic response. It is of crucial importance for scientists to study how a transient hyperthermic event like PETM can cause the extinction, origin and renewal of fauna in different marine ecosystems that ultimately punctuate long-term evolution. However, not all marine biota have responded to anomalous paleo-oceanographic and paleoclimatic conditions in the same way, and a synthetic understanding is lacking, especially in the less well-studied shallow marine ecosystem. Ms. Tian, ​​Dr. Yasuhara and their collaborators applied innovative modeling of birth and death to quantitatively assess the dynamics of local diversity across PETM in Maryland, eastern United States, and found strong peaks of local extinction and origin before and after PETM, respectively. The great disturbance of the shallow marine ecosystem at the start of the PETM was likely induced by extreme warming of surface waters and oxygen deficiency of deeper waters, known as the minimum oxygen zone, which, together, vertically compressed suitable shallow marine habitats above the minimum oxygen zone. . The shallow, heat-sensitive species that made up 46.2% of the pre-PETM assemblage became extinct regionally at least without cooler refuge. The recovery of the shallow marine ecosystem towards the end of PETM was surprisingly strong with 50% of species newly present in the post-PETM assemblage. Yet the impacts of the PETM climate anomaly were irreversible and the faunal composition of the local assemblage was permanently altered.

The research group used fossil ostracods preserved in a marine sediment core as a model organism to fully understand the collapse-recovery model of shallow benthic and marine diversity in Salisbury Bay of the Mid-Atlantic Coastal Plain, because this small (generally

All ostracode shells in the samples were taken and identified under a microscope, then the census dataset was constructed for statistical analyzes. The application of birth-death modeling made possible an explicit and quantitative local diversity trajectory by overcoming common problems in microfossil research, for example low fossil abundance, ghost lineage and preservation biases.

We must be aware of the strong possibility of future loss of biodiversity in marine ecosystems due to oceanographic and climatic changes associated with global warming. As the deoxygenation of seawater and the high heat during PETM sharply decreased species diversity, altered the composition of fauna, and disrupted the shallow marine ecosystem as a whole, the results of this research imply that we can expect similar circumstances to occur in the future and cause socio-economic problems. loss if the emission of greenhouse gases continues as is currently the case.

“We call this event the PETM using its acronym. Climate change during this extreme event itself is increasingly understood, but its impact on marine ecosystems, especially shallow marine ecosystems, remains poorly understood. However, it is important, since now we are worried about the warming of our planet and its consequences. PETM cannot be a perfect analogue of the past for the future, as human-induced carbon dioxide emissions are much faster even compared to this extreme weather event. But still, PETM is one of the best partial analogues for thinking about future scenarios of what will happen to marine ecosystems and biodiversity through anthropogenic warming, ”said Dr Yasuhara.

“We are now concerned that the current and future warming will cause the expansion of the ‘minimum oxygen zone’, the zone with minimum oxygen content in the average depths to about a few hundred to a thousand meters deep. This is because oxygen is less soluble in warmer waters. This enlarged minimum oxygen zone at shallower depths makes the habitable shallow marine area above it narrower. Thus, animals that live there may be at a higher risk of extinction, as they are stuck in a narrower habitat and exposed to extremely high temperatures. Indeed, this has already happened in distant times, when the Earth was warmer than today and caused substantial extinction, as our study showed. It is therefore very likely that future warming with the status quo CO2 emissions could lead to serious circumstances such as extinction or substantial disappearance, ”Ms. Tian concluded.

About the research paper

Journal: Global and Planetary Changes

Title: Collapse and Restoration of the Shallow Marine Ecosystem during the Paleocene-Eocene Thermal Maximum

Authors: Skye Yunshu Tian (The University of Hong Kong), Moriaki Yasuhara (The University of Hong Kong), Huai-Hsuan M. Huang (National Museum of Natural History, Smithsonian Institution), Fabien L. Condamine (University of Montpellier), Marci M. Robinson (Florence Bascom Geoscience Center, US Geological Survey).

The research paper can be viewed from here: https://doi.org/10.1016/j.gloplacha.2021.103649

Download images and captions: https://www.scifac.hku.hk/press


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