Volcanic eruptions have a significant impact on the climate due to their ash, smoke and gases. But how strongly such eruptions have shaped the climate of past earth age is not always clear. An example of this is the end of the Cretaceous period around 66 million years ago. For this mass extinction, it is controversial what proportion the massive eruptions of the deckan trapps in India had in the climate changes of this change of upheaval. A research team has now decoded the time sequence of events.
Geological deposits show that in the course of the earth’s history there have been several outbreaks of so -called large magmatic provinces – huge volcanic areas, the eruptions of which have left miles -thick deposits of volcanic material. For some of these eruptions, it is already known that they played a key role for large extinction events because their volcanic outgosses massively changed the global climate.
However, the role of volcanism is controversial for the most famous mass extinction, the end of the dinosaur era around 66 million years ago. The reason: “The mass extinction at the end of the Cretaceous period meets the outbreak of a Magmatic large province and with an asteroid attack,” explain Thomas Westerhold from Marum – Center for Marine Environmental Sciences at the University of Bremen and his colleagues. It is therefore difficult to separate whether the massive volcanic Vulcan of Dekkan Trapps in India or the impact of the Chicxulub-Sanoid in Yucatan were the main cause of the drastic climate changes at the end of the chalk.
Synchronization of geological climate archives
In order to create more clarity, Westerhold and his team have deciphered the time sequence of events during the last million years before extinction of the dinosaurs. The aim was to find a direct time connection between the climate changes and the volcanic outbreak phases of the Dekkan trapps. “We use the rhythmic changes in the solar radiation that are recorded in geological data, like a metronome to synchronize the climate archives,” explains Westerhold. In the first step, the researchers examined fossil foraminifers from drilling nuclei from the bottom of the South Atlantic and Northwest Pacific. The shells of these small marine organisms provided information about the sea temperatures and living environment in the ocean 66 to 67 million years ago via their isotope conditions.
“When we dated the geological archives perfectly, we could see that two large climate and living world changes took place in both oceans at the same time,” explains Westerhold, explaining the first find. “Now we had to find a way to check whether these changes are in connection with the Trapps Dekkan in India.” For this purpose, the team examined the Osmium isotope composition in the South Atlantic and Northwest Pacific Depacific: “The formation of flood bastes and their subsequent weathering leave a fingerprint in the chemistry of the oceans. The deposits should have the same osmium fingerprint at the same time, ”explains co-author Junichiro Kuroda from the University of Tokyo.
Changes in two stages
The researchers identified two stages of change in the Osmium isotope data. The first occurred around 66.49 million years ago, the second followed 66.28 million years ago. These two steps not only occurred in both oceans at the same time, but also at the same time as the main interdication phases of the Dekkan Trapps at the end of the chalk season. “But it was even more surprising that the two steps had different effects on the environment, documented by fossil residues in the drilling nuclei,” says Westerhold. Accordingly, the early eruption phase of the Dekkan trapps initially only led to an increase in the basic sea temperatures by around one degree. For the second stage, however, the isotope data suggests an increase of four to five degrees.
As a reason for these differences, the research team based on geochemical modeling assumes that the amount of flood basalt in the early phase of the Dekkan Trapp volcanism must have been larger than assumed. However, because a lot of sulfur -containing, rather climate -cooling gases were released, the warming was less strong. “It seems plausible that this first eruption phase with a high sulfur content followed a second eruption period around 66.28 million years ago, which was characterized by high carbon dioxide exemption or basalt intrusion in carbon-rich host rocks,” explain the researchers. This second phase caused stronger global warming and at the same time acidilization of the ocean.
Source: Thomas Westerhold (Marum – Center for Marine Environmental Sciences at the University of Bremen) et al., Science Advance, DOI: 10.1126/Sciadv.adr8584