Rising temperatures may flip plankton into carbon emitters

Scientists at Duke University and the University of California, Santa Barbara have identified a climate feedback loop involving widely distributed yet underappreciated microbes like plankton that could quicken the pace of climate change. 

However, this discovery comes with a silver lining: a potential early warning sign that might help us brace for the tipping point.

The researchers have been studying microscopic organisms called mixotrophs. These versatile organisms have two metabolic modes, allowing them to photosynthesize like plants or consume food like animals, depending on their environment. Daniel Wieczynski, a postdoctoral associate at Duke and the first author of the study, calls them the “Venus fly traps of the microbial world.”

Using a computer model to predict behavior

A computer model was used by the team to demonstrate the potential impact of these tiny organisms on the global climate. The researchers discovered that rising temperatures can cause these creatures to shift from absorbing carbon dioxide – a potent greenhouse gas – to emitting it. This shift results from the effects of global warming on their metabolism.

The release of carbon dioxide could potentially lead to increased temperatures, creating a dangerous positive feedback loop. In this scenario, minor degrees of warming could result in a disproportionate impact, accelerating climate change.

Jean P. Gibert, a senior author of the study from Duke, emphasized the role mixotrophs play in regulating the climate, despite their absence in most climate change models. Mixotrophs are abundant in oceans, lakes, and damp soils, forming a significant part of plankton communities and peatlands ecosystems.

“Mixotrophs can both capture and emit carbon dioxide, they’re like ‘switches’ that could either help reduce climate change or make it worse,” explained study co-author Holly Moeller, assistant professor at UC Santa Barbara.

How the study was conducted

To examine how these effects could escalate, a mathematical model was developed. This model predicted how mixotrophs might shift between different modes of metabolism as global warming continues. 

The model was run under a temperature range of 19 to 23 degrees Celsius (66-73 degrees Fahrenheit), in line with projected global temperature surges of 1.5 degrees Celsius above pre-industrial levels within the next five years, with the potential to exceed 2 to 4 degrees by century’s end.

The model revealed that as temperatures increase, mixotrophs are more likely to consume food rather than rely on photosynthesis, leading to an imbalance in carbon absorption and emission. This could eventually push the microbes past a tipping point, shifting from carbon sink to carbon source and thereby contributing to global warming rather than mitigating it.

The scientists warned that reverting from this tipping point would require a significant decrease in temperatures, more than one degree Celsius, a challenge that highlights the seriousness of the situation.

The research team found a ray of hope amidst the gloom

However, there’s a glimmer of hope. The study suggests that by carefully observing mixotroph abundance, scientists may be able to anticipate this crucial tipping point. 

“Right before a tipping point, their abundances suddenly start to fluctuate wildly,” Wieczynski said. “If you went out in nature and you saw a sudden change from relatively steady abundances to rapid fluctuations, you would know it’s coming.”

An additional factor identified by the study is nutrient pollution. The researchers found that increased levels of nutrients, like nitrate and phosphate, released from wastewater treatment facilities, farms, and lawns could cause the warning signs of rapid fluctuations to disappear, allowing the tipping point to arrive unannounced.

Investing in early detection is crucial

While these model predictions require validation through real-world observations, they underscore the importance of investing in early detection. 

“Tipping points can be short-lived, and thus hard to catch,” Gibert said. “This paper provides us with a search image, something to look out for, and makes those tipping points — as fleeting as they may be – more likely to be found.”

The research team is hopeful that these findings can contribute to the broader climate science community and help focus efforts on preventative measures. By understanding the role these tiny mixotrophs play in our climate and detecting these fluctuations early, we may be able to implement solutions before reaching these potentially irreversible tipping points.

The research paper, published in the journal Functional Ecology, combines a fascinating look into the world of microbial activity with critical insights into climate change. The researchers’ efforts underline the complexity and interconnectedness of our ecosystem and the urgency of monitoring even the tiniest contributors to our climate.

This important work was made possible through the support of the Simons Foundation (grant number 689265), the National Science Foundation (grant number 1851194), and the U.S. Department of Energy (grant number DE-SC0020362). As the world continues to grapple with climate change, studies like this remind us of the importance of research and the potentially game-changing insights it can provide.

More about plankton

Plankton is a broad term used to describe the wide range of tiny organisms that drift within oceans, seas, and other bodies of water. The term “plankton” comes from the Greek for “drifter” or “wanderer.” They can’t swim against the current, but some can move up and down in the water column.

There are two main types of plankton: phytoplankton and zooplankton.

Phytoplankton

These are the plant-like members of the plankton community, and they’re photosynthetic. They’re mostly single-celled organisms like cyanobacteria (formerly called blue-green algae) and diatoms but can also form colonies. 

Phytoplankton serve as the base of the aquatic food web, providing an essential ecological function for all aquatic life. In addition, phytoplankton is responsible for producing approximately half of the oxygen on Earth through photosynthesis.

Zooplankton

These are the animal-like members of the plankton community, which range from tiny protozoans to large jellyfish. Zooplankton are generally larger than phytoplankton, and they often feed on phytoplankton. There are many types of zooplankton, including single-celled dinoflagellates, tiny crustaceans like copepods and krill, and the larvae of larger animals such as fish and crabs.

It’s also important to mention mixotrophs, organisms that can switch between photosynthesis (like phytoplankton) and predation (like zooplankton) depending on their environment. Some dinoflagellates and other types of plankton fall into this category.

Plankton play an essential role in the carbon cycle. Through photosynthesis, phytoplankton absorb carbon dioxide from the atmosphere and use it to produce carbohydrates for growth. When they die, some of their organic matter sinks to the deep ocean, effectively transferring carbon from the atmosphere to the ocean floor. This process is known as the “biological carbon pump.”

Influence of plankton on the environment

Plankton populations can greatly influence weather patterns and climate. For example, phytoplankton blooms can influence cloud formation, because the particles they release can form nuclei around which water droplets condense to make clouds. In addition, because of their role in the carbon cycle, changes in plankton populations can impact atmospheric carbon dioxide levels, influencing global temperatures and climate.

Plankton populations can also serve as an indicator of environmental changes or disruptions. For example, changes in sea temperature, nutrient availability, or water acidity can all impact plankton populations. Scientists often monitor these populations to understand more about current conditions or future trends in the Earth’s climate system.

Image Credit: Daniel J. Wieczynski, Duke University

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