Marine plankton are key players in carbon cycle regulation

We are dependent on oxygen that is generated by miniscule planktonic creatures that live in the oceans. Scientists estimate that over 50% of the Earth’s oxygen is produced by these tiny, drifting protists, plants and algae.

It is these microscopic oceanic organisms, even more than the tall tree outside your window, that are the unsung heroes of our planet. Marine plankton drive the Earth’s carbon cycle and regulate the climate.

Plankton drifts with the ocean’s currents and has a dual role in producing oxygen and storing carbon dioxide (CO₂). This makes these organisms indispensable in maintaining the planet’s delicate balance.

A recent discovery has shed light on the intricate relationship between these planktonic life forms and one of the greatest challenges of our time – increasing atmospheric CO₂.

Marine plankton and carbon storage

Buried deep within the ocean’s waters resides a near-invisible, yet vital organism – Trilobatus trilobus, a species of plankton that belongs to the group known as the formainifera.

These tiny heroes sequester and store CO₂ in their calcium carbonate shells through a process known as calcification.

This is the process whereby living organisms, like plankton, build hard, shell-like structures using calcium, carbon and oxygen from their surroundings. The protective “suits of armor” are made of a material similar to chalk or limestone.

Once the plankton expire, their shells sink to the seafloor, becoming long-term carbon storage facilities. This means that the huge task of CO₂ storage is undertaken partially by these microscopic life forms.

Now, scientists from the University of Oxford have explored this phenomenon in more detail and uncovered some fascinating insights.

Initially, research focused on how changes in ocean chemistry and acidification influence calcification. However, this study revealed that physical properties of the ocean, such as density, also play a crucial role in this complex process.

The artful adaptations of marine plankton

What makes T. trilobus so remarkable? This planktonic species demonstrates an extraordinary ability to adapt its calcification process in response to environmental fluctuations, particularly to changes in ocean density and salinity.

These survival strategies ensure that the plankton can maintain buoyancy and thrive in varying conditions.

For example, when ocean density decreases due to freshwater influx from melting ice caps, T. trilobus reduces the calcification rate, thus forming lighter shells that help to keep the individuals buoyant.

This adjustment not only supports the survival of the microorganisms, but also affects ocean chemistry by leaving surface waters more alkaline.

The increase in alkalinity enhances the ocean’s ability to absorb even more CO₂, illustrating the intricate relationship between these microscopic organisms and the planet’s carbon cycle.

The unseen impact on climate change

The adaptive behavior of T. trilobus has far-reaching implications for climate regulation.

By modifying calcification in response to environmental changes, these plankton indirectly boost the ocean’s capacity to absorb CO₂ and act as a natural mitigator of atmospheric carbon.

This dynamic process highlights the vital role of marine ecosystems in buffering the effects of climate change.

“Our findings demonstrate how planktonic foraminifera adapt their shell architecture to changes in seawater density. This natural adjustment, potentially regulating atmospheric chemistry for millions of years, underscores the complex interplay between marine life and the global climate system,” explained Dr. Stergios Zarkogiannis, the study’s lead scientist.

The role of plankton in ocean calcification

Dr. Zarkogiannis and his team explored the intricacies of T. trilobus shells, collected from deep-sea sediments along the Mid-Atlantic Ridge.

Using advanced techniques like X-ray microcomputed tomography and shell trace element geochemistry, they linked variations in calcification to environmental changes, including salinity, density, and carbonate chemistry.

Their findings revealed that plankton produce lighter, thinner shells in equatorial waters and thicker, heavier shells in denser subtropical regions, illustrating how these tiny organisms adapt to their surroundings.

“Although planktonic organisms may passively float in the water column, they are far from passive participants in the carbon cycle. By actively adjusting their calcification to control buoyancy and ensure survival, these organisms also regulate the ocean’s ability to absorb CO₂,” said Dr. Zarkogiannis.

This dual role underscores their profound importance in understanding and addressing climate challenges.”

The future of plankton research

While this study illuminates the adaptive capabilities of T. trilobus, further research is needed to determine whether buoyancy regulation influences calcification in other marine organisms.

By continuing to unravel the intricate ways in which plankton interact with their environment, scientists can better understand – and perhaps leverage – their role in mitigating climate change.

The full study was published in the journal Royal Society Open Science.

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