Earth’s climate system is governed not only by atmospheric processes and large-scale ocean circulation, but also by the quiet, persistent activity of microscopic life. Among the most influential of these organisms are marine plankton that build shells of calcium carbonate, such as coccolithophores and foraminifera. Though invisible to the naked eye, these tiny organisms play a disproportionately large role in regulating atmospheric carbon dioxide and stabilizing the global climate. Recent research, however, suggests that many climate models fail to fully account for their influence, raising concerns that future climate projections may underestimate how the oceans respond to a warming world.
Marine plankton occupy the base of the oceanic food web and are essential to biogeochemical cycles. Photosynthetic phytoplankton absorb carbon dioxide from the atmosphere and convert it into organic matter using sunlight, forming the foundation of marine ecosystems. Calcifying plankton take this process a step further. In addition to photosynthesis, they extract dissolved carbon and calcium ions from seawater to construct intricate shells made of calcium carbonate. This dual role links biological activity directly to both the carbon cycle and ocean chemistry.
One of the most important climate-related functions of calcifying plankton is their contribution to the ocean’s “biological carbon pump.” When these organisms die or are consumed, their calcium carbonate shells often sink through the water column. As they descend, they transport carbon from surface waters into the deep ocean, where it can remain sequestered for hundreds to thousands of years. This process effectively removes carbon dioxide from the atmosphere, moderating global temperatures and slowing the pace of climate change. Over geological time scales, the accumulation of these shells has even contributed to the formation of limestone and chalk deposits, permanently locking away vast amounts of carbon.
Despite their significance, calcifying plankton are surprisingly underrepresented in many climate models. Traditional Earth system models tend to emphasize physical processes such as ocean circulation, heat exchange, and atmospheric dynamics, while simplifying or aggregating biological processes. When marine biology is included, it often focuses on broad categories of plankton rather than the distinct roles played by specific groups like calcium carbonate–producing organisms. As a result, the feedbacks between plankton activity, ocean chemistry, and atmospheric carbon dioxide may be inadequately captured.
New research highlights the consequences of this omission. Studies using advanced observations and improved biogeochemical modeling show that calcifying plankton respond sensitively to changes in temperature, acidity, and nutrient availability. Ocean warming can alter their geographic distribution, pushing populations toward higher latitudes. At the same time, increasing ocean acidification—caused by the absorption of excess atmospheric carbon dioxide—makes it more difficult for these organisms to form and maintain their shells. These changes can weaken the biological carbon pump, reducing the ocean’s capacity to absorb carbon and amplifying climate change.
The problem is not simply that calcifying plankton may decline in the future, but that their responses can trigger complex feedback loops. For example, if shell production decreases, less carbon sinks to the deep ocean, leaving more carbon dioxide in surface waters and the atmosphere. This can accelerate warming, further stressing marine ecosystems. Conversely, in some regions, certain calcifying plankton may temporarily thrive under higher carbon dioxide conditions, potentially increasing shell production and altering local carbon cycling. Capturing these nuanced, region-specific responses requires models that explicitly represent calcifying organisms and their interactions with ocean chemistry.
Another critical aspect often overlooked is the influence of calcium carbonate shells on seawater alkalinity. The formation and dissolution of these shells affect the ocean’s ability to buffer changes in acidity. When shells dissolve at depth, they increase alkalinity, which can enhance the ocean’s long-term capacity to absorb carbon dioxide from the atmosphere. Ignoring this process may lead models to underestimate the resilience of the ocean carbon sink under certain conditions, or misjudge the timing and magnitude of future changes.
Improving climate models to include calcifying plankton is not merely a technical refinement; it has profound implications for climate policy and adaptation strategies. Accurate projections of ocean carbon uptake are essential for estimating remaining carbon budgets and evaluating the effectiveness of emissions reductions. If models underestimate the ocean’s response to climate change, policymakers may be working with incomplete information, potentially misjudging the urgency or scale of action required.
Incorporating these microscopic engineers into climate models also underscores a broader lesson about the Earth system: small organisms can have planetary-scale impacts. The climate is not shaped solely by volcanoes, ice sheets, or industrial emissions, but also by the cumulative activity of countless tiny lives drifting through the sunlit surface of the sea. Recognizing this challenges traditional distinctions between biology and climate science and highlights the need for truly interdisciplinary approaches.
Advances in satellite observations, laboratory experiments, and field studies are now making it possible to better quantify the role of calcifying plankton. High-resolution imaging can track blooms across ocean basins, while chemical analyses reveal how shell formation responds to changing conditions. Coupling these data with next-generation Earth system models offers a pathway toward more accurate and reliable climate forecasts.
In conclusion, tiny marine plankton that build calcium carbonate shells are silent regulators of Earth’s climate, drawing carbon from the atmosphere and locking it away in the deep ocean. Their absence from many climate models represents a significant gap in our understanding of how the planet responds to climate change. As research continues to reveal the complexity and importance of these organisms, it becomes increasingly clear that predicting Earth’s future climate requires paying close attention to its smallest inhabitants. By integrating calcifying plankton into climate models, scientists can better capture the delicate balance between biology, chemistry, and physics that governs our planet’s climate system.
Source: Universitat Autonoma de Barcelona
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