A new review in Science highlights how calcifying plankton, tiny marine organisms that form calcium carbonate shells, are underrepresented in climate models. These plankton play a crucial role in the ocean carbon pump, pulling carbon from the atmosphere and storing it in deep waters. The omission could lead to underestimating the ocean's response to climate change.
Calcifying plankton, including coccolithophores, foraminifers, and pteropods, are microscopic builders of calcium carbonate shells that influence Earth's climate. An international team led by Patrizia Ziveri, an ICREA research professor at the Institute of Environmental Science and Technology at Universitat Autònoma de Barcelona in Spain, published a review in Science examining their role.
These organisms contribute to the global carbon cycle by capturing atmospheric carbon and transporting it through the ocean via the carbon pump. This process stabilizes the planet's temperature over time and affects seawater chemistry, aiding in sediment formation for paleoclimate studies. However, major climate models, such as those in CMIP6 used for global assessments, often simplify or exclude these plankton, leading to incomplete predictions of ocean responses to environmental changes.
A key overlooked aspect is shallow dissolution, where much of the calcium carbonate dissolves in the upper ocean due to biological activities like predation and microbial respiration. This alters ocean chemistry but is not accounted for in current models, potentially misjudging carbon movement and system resilience.
The review notes varying vulnerabilities among the groups. Coccolithophores, major producers of calcium carbonate, are highly sensitive to ocean acidification without mechanisms to handle excess acidity. Foraminifers and pteropods possess such adaptations but face threats from declining oxygen and rising temperatures.
"Plankton shells are tiny, but together they shape the chemistry of our oceans and the climate of our planet," Ziveri said. "By leaving them out of climate models, we risk overlooking fundamental processes that determine how the Earth system responds to climate change."
The authors urge better measurements of production, dissolution, and export of calcium carbonate by each group to refine models. "If we ignore the ocean's smallest organisms, we might miss important climate dynamics," Ziveri added. Integrating these details could enhance forecasts of carbon storage and ecosystem impacts, improving sediment-based climate reconstructions.