An international drilling expedition led by researchers from the GEOMAR Helmholtz Centre for Ocean Research in Kiel and the University of Oslo has provided compelling evidence that hydrothermal vents were a key driver of global warming about 55 million years ago. Published in the journal Nature Geoscience, the study reveals that these vents were active in very shallow water depths or even above sea level, allowing significantly larger quantities of methane to enter the atmosphere than previously believed.
The research delves into the period when the Atlantic Ocean was formed as continents started to separate, releasing magma and leading to the creation of large igneous provinces (LIPs). One such LIP formed between Greenland and Europe and lies beneath the ocean surface. The international drilling campaign collected extensive sample material from this province, leading to the latest findings. The study highlights that hydrothermal vents were active at shallow depths or even above sea level around the Paleocene-Eocene boundary, contributing to greenhouse gas emissions that had a significant impact on the climate. This period witnessed intense volcanic eruptions, leading to a warming of the world's climate by at least five degrees Celsius and a mass extinction event known as the Paleocene-Eocene Thermal Maximum (PETM).
Contrary to the conventional notion that volcanic eruptions cool the climate by releasing aerosols into the stratosphere, the researchers propose that large quantities of greenhouse gases, including methane, entered the atmosphere through hydrothermal venting. This hypothesis gained traction after the discovery of hydrothermal vent systems associated with magmatic intrusions in sedimentary basins. An expedition involving around 30 scientists from 12 nations embarked on an International Ocean Discovery Program (IODP) research cruise to the Vøring Plateau off the Norwegian coast. They drilled directly into hydrothermal vents, obtaining cores that offered insights into Earth's history.
The study reveals that a vent was active just before the Paleocene-Eocene Thermal Maximum and that the resulting crater was filled as global warming began. Surprisingly, the vent was active at a shallow water depth, likely less than 100 meters, suggesting that other vents were also located in similar conditions. This, in turn, would have enabled significantly larger amounts of greenhouse gases to enter the atmosphere. The research offers valuable lessons for today's climate concerns. It dismisses the notion that the ancient warming was caused by the dissolution of gas hydrates, a recent topic of discussion. Moreover, it shows that the Earth's climate system took millennia to cool down, highlighting the intricate regulatory mechanisms within the Earth system. As scientists continue to delve into Earth's past to understand climate dynamics, these findings shed light on the role of hydrothermal vents in shaping ancient climates and provide insights into the complex interplay between geologic processes and global temperatures.
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