Some of the most important players in Earth’s climate system are nearly invisible. Calcifying plankton, microscopic organisms that form hard shells, help regulate the planet’s temperature by capturing carbon and moving it through the ocean. A new review published in Science finds that these organisms are not fully represented in the climate models used to predict Earth’s future. The research was led by an international team from the Institute of Environmental Science and Technology at the Universitat Autònoma de Barcelona (ICTA-UAB) (Spain).
The study focuses on three major groups of calcifying plankton: coccolithophores, foraminifers, and pteropods. According to the authors, climate models often simplify or exclude these organisms, which can lead to an incomplete picture of how the ocean responds to climate change.
How Calcifying Plankton Shape the Carbon Cycle
When climate models leave out calcifying plankton, they may miss key steps in the global carbon cycle. These organisms build tiny shells made of calcium carbonate (CaCO3), a substance that plays a central role in ocean chemistry. As plankton grow and die, they help move carbon from the atmosphere into deeper layers of the ocean.
This process, known as the ocean carbon pump, helps stabilize Earth’s climate over long periods of time. It also affects seawater chemistry and contributes to the formation of sediments that scientists use to study past climates.
“Plankton shells are tiny, but together they shape the chemistry of our oceans and the climate of our planet,” said Patrizia Ziveri, ICREA research professor at ICTA-UAB and lead author of the study. “By leaving them out of climate models, we risk overlooking fundamental processes that determine how the Earth system responds to climate change.”
The Missing Process of Shallow Dissolution
The researchers point out that much of the calcium carbonate produced by plankton does not sink all the way to the ocean floor. Instead, a significant portion dissolves in the upper ocean, a process known as “shallow dissolution.” This breakdown is driven by biological activity, including predation, clumping of particles, and microbial respiration.
Shallow dissolution changes ocean chemistry in important ways, yet it is largely missing from major Earth System Models (e.g. CMIP6) used in global climate assessments. Without accounting for this process, models may misjudge how carbon moves through the ocean and how the system responds to environmental stress.
Different Plankton Face Different Climate Threats
The study also emphasizes that not all calcifying plankton behave the same way. Each group has unique characteristics that influence where it lives, how it functions in marine ecosystems, and how vulnerable it is to climate change.
Coccolithophores are the largest producers of CaCO3, but they are especially sensitive to ocean acidification because they lack specialized mechanisms to remove excess acidity from their cells. Foraminifers and pteropods do have such mechanisms, but they face other risks, including declining oxygen levels and rising ocean temperatures. Together, these organisms determine how carbon is stored and recycled in the ocean, and treating them as a single group can oversimplify the ocean’s response to climate pressures.
Improving Climate Models With Better Ocean Biology
The authors call for urgent efforts to measure how much calcium carbonate each plankton group produces, dissolves, and exports to deeper waters. They argue that incorporating these details into climate models would improve predictions of ocean and atmosphere interactions, long-term carbon storage, and the interpretation of sediment records used to reconstruct Earth’s climate history.
“If we ignore the ocean’s smallest organisms, we might miss important climate dynamics,” says Dr. Ziveri. “Integrating calcifying plankton into climate models could offer sharper predictions and deeper insights into how ecosystems and societies may be affected.”
The researchers conclude that closing these knowledge gaps is essential for building the next generation of climate models, ones that more accurately reflect the biological complexity of the oceans.
