Whales were not always such massive creatures. Millions of years ago, they were much smaller. So what caused them to evolve into the largest animals on the planet?

ATLAS associate research professor Pedro DiNezio helped an interdisciplinary team of researchers using Earth system models to investigate this question.

This line of research was spearheaded by��, Professor, Department of Geosciences, University of Arizona, after the discovery of remarkable whale fossils at Cerro Ballena, Chile, a region she had been conducting research in.��

DiNezio played an instrumental role in bringing together the different disciplinary perspectives in the project, using Earth system models not simply as computational tools, but as a framework to test and connect the team’s hypotheses into a mechanistic explanation.

We cannot directly experiment with Earth’s past, so this kind of research requires combining geological evidence with Earth system models to test possible explanations for what happened.

The Late Miocene Epoch (roughly 11.6 million to 5.3 million years ago) was marked by heavy volcanic activity in South America. “My colleagues have this evidence that there was a lot of volcanism in the tropical Andes in the Altiplano—the region between Peru, Bolivia and northern Argentina—back in the Miocene,” DiNezio explained. “They saw the sediments, the ash layers, that those volcanoes left, and they could measure how big those eruptions were by measuring the thickness of these deposits. And they knew that whales had changed a lot around that time.”��

Scientists were also aware that during the Late Miocene, the Earth cooled rapidly in geological time scales. The team wondered how they could connect all these pieces of evidence into a larger narrative grounded in data.

Source: Nature.com

DiNezio, who has spent decades using Earth system models developed at�� (NCAR) to study past and future climates, recognized that these tools could help test whether ancient volcanism reshaped ocean ecosystems and climate.

“The essential concept in these models is that they represent the Earth as an interconnected global system—different components of the planet and how they interact. That gives us a way to test ambitious scientific questions that would otherwise be impossible to study directly.”

For this project, that meant focusing on oceanic food chains—whales would only grow in size if they had an abundance of food over long periods of time.��

“These models have been developed over decades by generations of scientists to represent the Earth as an interconnected system—atmosphere, ocean, ecosystems, and the carbon cycle,” DiNezio said. “That allows us to test mechanistic hypotheses about how changes in one part of the Earth system can cascade through the rest.” DiNezio said.��

But the idea raised a critical question: If volcanoes in the Andes released nutrients into the atmosphere, where would they go, and how would ocean ecosystems respond?��

They started by analyzing how ash from volcanic eruptions in the Andes would travel through the atmosphere and settle in the southern oceans. This ash contains silica, a key nutrient for diatoms, microscope algae that underpin the entire oceanic food web. “Our simulations showed that a single point in the Andes in South America can have an influence on the entire Southern Ocean,” DiNezio said. “Our modeling results show that the volcanoes can essentially reshape [it] into a highly productive ecosystem.”

The team then tested whether this process could have a long-term effect on the carbon cycle. As ocean productivity increased, the models showed that some of this newly generated organic carbon was transported into the deep ocean, where long-term storage could contribute to climate cooling.

The team proposes that this increased abundance may also have created ecological conditions favorable for larger marine mammals.

“What’s exciting is that we now have a mechanistic hypothesis that connects these different lines of evidence,” DiNezio said. “Other scientists can now test, refine or challenge this explanation with new data.”

Next, the team hopes to reconstruct whale migration patterns during this period to further test the hypothesis.