Arctic heatwaves have complex effects on phytoplankton

The response of Arctic phytoplankton to heatwaves differs significantly from their response to constantly elevated temperatures. The findings from new research broaden our understanding of the complex effects of temperature fluctuations on these crucial marine organisms.

Fascinating world of Arctic phytoplankton

Arctic phytoplankton are microscopic algae that form the foundation of the Arctic marine food web. These tiny organisms thrive in the cold, nutrient-rich waters of the Arctic Ocean and play a crucial role in the ecosystem’s health and productivity.

Crucial role in the Arctic ecosystem

Arctic phytoplankton are the primary producers of the Arctic Ocean. They harness the energy of the sun through photosynthesis, converting carbon dioxide and water into organic compounds.

This process forms the basis of the entire marine food chain, supporting a wide range of organisms, from tiny zooplankton to massive whales.

In addition to their role in the food web, Arctic phytoplankton also contribute to the global carbon cycle. As they photosynthesize, they absorb significant amounts of carbon dioxide from the atmosphere, helping to regulate the Earth’s climate.

When phytoplankton die, some of this carbon sinks to the ocean floor, where it can remain sequestered for hundreds or even thousands of years.

Phytoplankton adaptations to the Arctic environment

Arctic phytoplankton have evolved unique adaptations to survive in the harsh conditions of the Arctic Ocean. They can thrive in water temperatures near the freezing point of seawater.

They have evolved special enzymes and cellular mechanisms that allow them to maintain their metabolic processes in these extreme conditions.

The Arctic experiences dramatic seasonal changes in light availability, from the 24-hour darkness of the polar night to the constant daylight of the midnight sun.

Arctic phytoplankton have developed strategies to optimize their light-harvesting abilities, such as adjusting their pigment composition and cellular structures to capture as much light as possible.

Finally, nutrients in the Arctic Ocean are limited, particularly in terms of nitrogen and iron. Arctic phytoplankton have evolved efficient nutrient uptake mechanisms, such as specialized transport proteins and symbiotic relationships with bacteria, to maximize their access to these essential elements.

Phytoplankton paradox: Heatwaves vs. constant warming

The study was conducted by a team led by Dr Klara Wolf from the Universities of Hamburg and Konstanz, and Dr Björn Rost from the Alfred Wegener Institute (AWI). The experiments took place at the Alfred Wegener Institute’s AWIPEV Station in Svalbard.

One of the key findings of the study is that the phytoplankton’s behavior primarily depends on the cooling phases after or between heatwaves.

“Under stable temperatures, even an extreme increase of +7° C led to accelerated growth and higher productivity, with surprisingly small changes in the composition of species, even over weeks,” explains Klara Wolf.

“In contrast, the effects of heatwaves are considerably more complex and don’t follow the same pattern. This implies that our knowledge about constant temperature increases cannot readily be applied to these short-term warm phases, which normally only last a few days,” Wolf continued.

The team emphasizes that not just the exposure to increased temperatures has a major impact on productivity, but also and especially the cooling phases after or between heatwaves. However, very little is known about these effects.

Complex puzzle for scientists

Björn Rost, an AWI biologist, highlights the importance of gaining a better understanding of how heatwaves impact the polar regions.

“Our study represents an important first step and shows which aspects of heatwaves and which phytoplankton-related processes we need to take a closer look at,” Rost explained.

“In addition, our study shows that what we know about the processes and effects of constantly higher temperatures can’t simply be applied one-to-one,” he concluded.

The study reveals that scenarios involving fluctuating temperatures can produce a broad range of effects, making it more challenging to predict their implications compared to continuous warming.

Maintaining the food web

Phytoplankton form the basis of the marine food web in the Arctic, and changes in their behavior could have far-reaching consequences for the entire ecosystem.

To develop better projections and models regarding how primary production and the Arctic ecosystem will change in response to climate change, researchers need to investigate not only the effects of mean temperatures but also the effects of temperature fluctuations.

“While stable warming up to a certain temperature increases productivity, some heatwaves can decrease it, while others increase it,” the researchers explain.

A better grasp of the effects of variable temperatures, especially the cooling phases, is therefore essential to improving forecasts on potential biodiversity changes.

Climate change lessons from Arctic phytoplankton

The study emphasizes the crucial role of phytoplankton research in understanding the potential impacts of climate change on the Arctic ecosystem. Changes at the basis of the food web can impact all higher trophic levels, all the way up to fisheries.

As heatwaves become more common in the Arctic due to climate change, it is essential to continue investigating their effects on phytoplankton and the broader ecosystem.

By gaining a better understanding of these complex processes, researchers can develop more accurate models and projections, helping to inform conservation efforts and sustainable management practices in the face of a changing climate.

The full study was published in the journal Science Advances.

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