Andes volcanoes – the missing link between algae blooms, whales and climate millions of years ago

Researchers work in the field at Cerro Ballena near Caldera, Chile, as part of a study showing that an increase in volcanic activity in the Andes in the Late Miocene Epoch likely resulted in a cooling of the Earth between 5.4 million and 7 million years ago. From left are team members Carolina Gutstein, Mark Clementz, Barbara Carrapa, Whitney Worrell, Priscilla Martinez and Fabían Muñoz.
Photo Credit: Carolina Gutstein

Scientific Frontline: Extended "At a Glance" Summary: Andes Volcanoes and the Late Miocene Marine-Climate Link

The Core Concept: During the Late Miocene epoch, massive volcanic eruptions in the Andes deposited nutrient-rich ash into the Southern Ocean, triggering widespread marine algae blooms that simultaneously fueled the evolution of gigantic whales, caused localized mass mortality events, and significantly cooled the Earth by drawing atmospheric carbon dioxide into the sea.

Key Distinction/Mechanism: While volcanic activity is traditionally understood as a driver of global warming through the emission of carbon dioxide, this mechanism demonstrates the opposite effect. The volcanic ash delivered vital nutrients (iron, phosphorus, and silicon) to the ocean, hyper-fertilizing primary producers like diatoms. This biological explosion sequestered vast amounts of carbon dioxide from the atmosphere, creating a cooling feedback loop, while simultaneously producing neurotoxins in certain localized blooms that proved fatal to marine mammals.

Major Frameworks/Components: 

• Ocean Geochemistry & Fertilization: The role of volcanic ash in altering ocean chemistry by distributing trace elements like iron, which act as a critical limiting nutrient for marine primary producers.
• The Biological Pump: The process by which photosynthetic phytoplankton (such as diatoms) absorb atmospheric carbon dioxide and sequester it in the deep ocean, driving global temperature reductions.
• Paleoclimatic Modeling: The integration of fossil evidence, geologic geochronology, and computer simulations to test how oceanic biology responds to deliberate volcanic nutrient input.
• Evolutionary Gigantism: The correlation between highly productive, nutrient-rich marine environments and the evolutionary trend toward immense body sizes in baleen whales.

Branch of Science: Geosciences, Paleontology, Paleoclimatology, Ocean Geochemistry, Marine Biology

Future Application: Understanding the deep-time relationship between atmospheric aerosols, ocean productivity, and carbon drawdown provides critical baseline data for modern climate models. It offers insights into how the Earth’s natural systems regulate carbon dioxide and evaluates the long-term viability of theorized climate mitigation strategies, such as artificial iron fertilization of the oceans.

Why It Matters: This research solves a long-standing paleoclimatic mystery regarding the Late Miocene cooling event by proving that the biological response of the ocean to geological events is a powerful regulator of global climate. It fundamentally shifts the understanding of volcanoes from being mere climate-warmers to complex catalysts that can, under the right conditions, trigger global cooling and drive massive ecological shifts.

Now extinct, Cerro Aconcagua in northwestern Argentina was an active stratovolcano until the Miocene epoch, when it was part of the Altiplano-Puna Volcanic Complex in the Central Andes, the largest active silicic magma system on Earth.
Photo Credit: Barbara Carrapa

In 2010, construction workers on the Panamerican Highway traversing Chile's Atacama Desert stumbled upon a nearly perfectly preserved fossilized whale – and once paleontologists rushed to the site to document the ancient treasures in a race against time while the road project was on hold, more were unearthed in quick succession. 

Totaling more than 40 specimens – whales, porpoises and other marine mammals – dating from about 6 to 9 million years ago, the site known as Cerro Ballena, or "Whale Hill," is now famously recognized as the world's largest concentration of whale fossils. Paleontologists soon realized the animals perished quickly and in a relatively small area. But why?

As if one mystery wasn't enough, around the same time marine life experienced important changes, whales became bigger and climate data reveal a dramatic shift toward cooler sea surface temperatures. Geologic records from that time, known as the late Miocene, bear witness to intense volcanic eruptions in the wake of tectonic upheaval that led to the building of the Andes mountain range along the western edge of South America. 

Now, a study led by researchers at the University of Arizona provides a previously unrecognized piece of the puzzle: The vast amounts of volcanic ashes released into the atmosphere ended up in the ocean, particularly in the Southern Ocean, where they provided a smorgasbord for marine algae to feast on. Volcanic ash is known to contain important nutrients, including phosphorus, iron and silicon. A significant increase in volcanic activity in the Andes peaking between eight and four million years ago, therefore, likely delivered a significant pulse of nutrients – especially iron – to the Southern Ocean.

Two of the study's co-authors, Mark Clementz and Carolina Gutstein, are pictured with an outcrop bearing whale fossils.
Photo Credit: Barbara Carrapa

This induced a chain reaction driving environmental changes by increasing productivity among primary producers – organisms that consume carbon dioxide and use sunlight to create their own food and energy. Increased productivity also supported larger body size in whales. However, in some localities, like Cerro Ballena, nutrients from Andes volcanoes lead to widespread algal blooms, which released toxins that proved detrimental to any whales in the affected areas. The same algal blooms also would have removed large amounts of carbon dioxide, a powerful greenhouse gas, from the atmosphere, which would have helped cool the planet. 

Volcanic eruptions have long been recognized as major sources of carbon dioxide in the atmosphere before humans began burning fossil fuels on an industrial scale, thus driving warming. But the role of volcanism in doing the opposite – cooling down the Earth system – has gone largely unrecognized, said Barbara Carrapa, a professor of geosciences in the University of Arizona College of Science and first author of this study, which is published in the journal Nature Communications Earth & Environment.

"Once you put a lot of very important nutrients coming from volcanoes into the ocean, then your primary producers are going to go crazy, because all of a sudden they have a lot of nutrients available to them, and that, in turn, is going to affect the entire marine ecosystem," she said. 

Among those primary producers, some of the globally most abundant are diatoms, single-celled algae that build intricate silicate shells. 

Bringing together experts from a variety of fields, including climate modeling, ocean geochemistry, geology and paleobiology, the study showed that Andean volcanoes provide the missing link between changes in ocean geochemistry and marine ecosystems and ultimately resulted in carbon sequestration and global cooling via biological processes in the ocean. Surprisingly, the geochronology of volcanic ashes in the region and the relationships between volcanism, ocean productivity and ultimately climate had been largely unexplored. 

By combining paleoclimate records, fossil evidence and geologic data with computer climate modeling simulations, the study shows a potential link between sustained, large-scale volcanism in the Altiplano-Puna Volcanic Complex in the Central Andes, the largest active silicic magma system on Earth, and global climatic and ecological change.

The Miocene witnessed a major transition in both geography and climate, continuing a cooling trend that had begun around 60 million years ago, at the end of Mesozoic era, also known as the "Age of the Dinosaurs." The continents had taken their present-day positions for the most part, only Antarctica was covered by ice, extensive forests were replaced by grasslands in many places of the world, and mammals were diversifying. 

According to co-author Kaustubh Thirumalai, an associate professor in the U of A's Department of Geosciences, the Miocene was a time of profound change, establishing the ecosystems we see today. Giant mammals roamed the continents, including ground sloths, mammoths and whales, which had set out as moderately sized creatures, embarked on an evolutionary trend toward the gigantic sizes they are known for.

Not surprisingly, the cooling trend, particularly during the late Miocene, was accompanied by declining carbon dioxide levels in the atmosphere, but the exact cause was a mystery, Thirumalai said. Was the change caused by a decrease in volcanic activity releasing less carbon dioxide, or by an increase in chemical weathering, which takes carbon dioxide out of the atmosphere? 

To find answers, the team took advantage of climate simulation models to test various scenarios, Thirumalai explained. 

"To illustrate our approach, we'd say, 'Let's start erupting the Andes on purpose and see what happens,'" he said. "And what we found is that there is another component that wasn't really appreciated – the biology of the ocean responds, with feedback effects on climate worldwide."

These feedback mechanisms can help store carbon in the deep ocean resulting in global cooling, Carrapa explained.

"Once you take the biological effects of volcanoes fertilizing the ocean into consideration, we could see a beautiful correlation between Andean volcanism and all those changes that are happening in the ocean, specifically those looking at the late Miocene cooling event," she said. "Together with the Humbold Current, which serves to distribute nutrients along the Pacific coast of South America, everything together created the perfect storm where, if you put the ash in the right place, and you ignite primary production, you eventually affect marine ecosystems as a whole, including whales."

"This work improves our understanding of how natural processes can regulate Earth's climate, which is directly relevant to anticipating future climate change and its impacts on society," said co-author and whale expert Mark Clementz, a professor of geology and geophysics at the University of Wyoming and co-author of this study. "By identifying links between volcanism, ocean productivity, and carbon dioxide drawdown, it provides insight into mechanisms that can influence global climate over long timescales."

Published in journal: Communications Earth & Environment

Title: Andean volcanism, ocean fertilization, marine ecosystem turnover, and global cooling in the Late Miocene

Authors: Barbara Carrapa, Mark T. Clementz, Nicolás J. Cosentino, Pedro DiNezio, Pam Vervoort, Kaustubh Thirumalai, Jordan T. Abell, Dominik Hülse, Priscilla R. Martinez, and Carolina S. Gutstein

Source/Credit: University of Arizona | Daniel Stolte

Reference Number: es041826_01

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