Contrasting Environmental Responses to Early Eocene hyperthermal events on the Southern Tethyan Shelf

Past extreme warming events on Earth, such as those that occurred during the early Eocene epoch (~56–48 million years ago), were triggered by massive amounts of carbon release; however, their environmental impacts differed dramatically. By studying multiple geochemical indicators, such as organic carbon isotope, total organic carbon (TOC) content, and elemental compositions, in shallow marine sediments along Southern Tethyan Shelf<b> </b>(Egypt), we found that the magnitude of carbon emissions influences the degree of environmental disruption. For instance, the Paleocene-Eocene Thermal Maximum involved significant carbon emissions, which triggered a dangerous chain reaction, including intense global warming, accelerated silicate weathering, and the activation of phosphorus into the oceans. This resulted in high productivity under anoxic conditions, and enhanced organic matter burial. In contrast, the smaller Eocene Thermal Maximum 2 release caused moderate warming under persistent ocean oxygenation, with no runaway nutrient feedback, resulting in lower productivity. Our findings demonstrate that the severity of such extreme climate events depends directly on the magnitude of the carbon release. Therefore, studying these past events helps us predict how modern carbon emissions might push Earth’s systems past dangerous tipping points, thereby reshaping the climate and ecosystems.