Volcanic activity in the Andes may have played a crucial role in cooling the Earth, particularly during the Late Miocene period. This theory, supported by a new study led by Barbara Carrapa from the University of Arizona, suggests that the explosive volcanism in the Andes, which built the longest active volcanic arc on Earth, had a significant impact on ocean life and the planet's climate. The research, published in the journal Nature Communications, highlights the intricate relationship between volcanic ash, ocean ecosystems, and global cooling.
The Andes, especially the Altiplano-Puna Volcanic Complex, experienced repeated supereruptions between 8 and 4 million years ago. These eruptions released vast amounts of fine ash, carrying essential nutrients like iron, phosphorus, and silicon into the open ocean. Diatoms, which require silica to build their shells, benefited significantly from this volcanic fertilization. As a result, diatom populations soared, leading to a surge in primary producers and a cascade of effects throughout the marine ecosystem.
Geographical factors played a pivotal role in this process. Westerly winds carried the ash eastward across the South Atlantic and into the Southern Ocean, with some settling locally in the Pacific. Fossil evidence from the Southern Ocean sediments shows a sharp increase in diatom numbers during the Late Miocene, coinciding with major volcanic eruptions in the Andes. This period also witnessed a significant growth in whale sizes, with baleen whales increasing from an average of 16 feet to around 39 feet.
However, the Pacific coast of Peru and Chile tells a different story. The Pisco Formation in Peru and similar deposits in Chile contain whale graveyards, indicating repeated harmful algal blooms. Layers of volcanic ash from Andean eruptions are found throughout these sites, suggesting a correlation between volcanic activity and marine mammal mortality.
Computer models, such as HYSPLIT and the Community Earth System Model, were used to test the hypothesis. These models demonstrated that ash from the Altiplano Puna region primarily travels east into the South Atlantic and further. Simulations showed that diatom growth at the ocean surface more than doubled within two years of volcanic eruptions, leading to increased carbon dioxide absorption by the ocean.
Longer-term studies using the cGENIE model revealed that repeated eruptions every 75 years reduced atmospheric carbon dioxide by about nine parts per million over 2,000 years. More frequent eruptions, larger events, and higher dust input increased this reduction to about 15 parts per million over 20,000 years. While this may seem insignificant, it likely influenced the climate, especially when combined with other feedback effects.
The study's findings have significant implications for our understanding of Earth's climate regulation. By fertilizing the ocean with nutrients, volcanoes can trigger primary production and impact entire marine ecosystems, including whales. This natural process may have played a crucial role in cooling the planet during the Late Miocene, a period of peak volcanic activity in the Andes.
In conclusion, the Andes' volcanic activity, particularly during the Late Miocene, had a profound impact on ocean life and the Earth's climate. This study highlights the importance of considering biological effects in our understanding of climate regulation, which is essential for anticipating future climate change and its societal impacts.
