Palaeoclimatology: New study shows that polar and subpolar foraminifera respond differently to temperature changes

They are barely visible to the naked eye, yet planktonic foraminifera play an important role in our understanding of Earth's climate history. These microscopic organisms drift through the ocean and build calcium carbonate shells that eventually sink to the seafloor. Preserved in marine sediments, their shells provide scientists with valuable information about past ocean conditions.

But there is a catch: the chemistry of these shells can be influenced not only by the surrounding environment, but also by the biology of the organisms themselves.

A new study, co-authored by Mohamed Ezat, Adele Westgård and Freya Sykes from the iC3 Polar Research Hub, investigates how environmental conditions affect respiration in three polar and subpolar foraminifera species. Led by Diane Armitage and Audrey Morley, it focusses on the effects of temperature, salinity, oxygen, carbonate chemistry and nutrients.

Figure: Scaling of individual planktonic respiration rates as a function of estimated biovolume with respiration normalised either using species-specific Q10s established in this study or a uniform Q10 of 3.18 from Lombard et al. (2009). Panels show normalisation to (a) 4 °C, (b) 15 °C and (c) 24 °C. Grey shaded regions represent the 95 % confidence intervals of the regression models. Credit: Armitage et al. (2026), Biogeosciences.

How does a microscopic organism respond to its environment?

Respiration is fundamental to life. As foraminifera respire, they consume oxygen and release carbon dioxide, changing the chemistry of the tiny layer of seawater surrounding their shells. This can potentially influence the chemical signals that scientists later use to reconstruct past climates.

Until now, however, little was known about respiration in foraminifera living in the cold waters of the polar and subpolar oceans, partially because of the technical difficulties of measuring respiration from such small organisms.

The researchers measured respiration in 158 individual foraminifera collected during two research campaigns in the Nordic Seas. They studied the polar species Neogloboquadrina pachyderma alongside the subpolar Neogloboquadrina incompta and Turborotalita quinqueloba. Advanced oxygen microsensors allowed the team to measure the respiration of individual organisms, while micro-CT imaging was used to accurately estimate their internal volume.

“Working with individual living foraminifera allows us to see physiological responses that would otherwise be hidden when we look only at populations or sediment samples,” says Adele Westgård, iC3 postdoc and co-author of the study. 

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One species stands out

The results reveal a striking difference between the species.

Neogloboquadrina pachyderma, the dominant planktonic foraminifera in polar waters, showed remarkably stable respiration across large environmental gradients. Its respiration had a relatively low temperature sensitivity.

The other two studied species responded much more strongly to temperature. 

“This difference between species tells us that there is no single physiological response we can apply to all polar and subpolar foraminifera,” says Adele. “Their ability to cope with environmental change is closely linked to the conditions they have evolved to live in.”

The study also found a consistent relationship between the size of the organisms and their respiration rates. Larger foraminifera generally respired more, highlighting the importance of accounting for organism size when comparing metabolic activity.

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What does this mean for reconstructing the past?

The findings have implications beyond understanding modern Arctic ecosystems.

Because N. pachyderma dominates many cold polar environments, its relatively stable respiration is encouraging for palaeoclimate scientists. The researchers conclude that respiration is unlikely to significantly influence geochemical proxies derived from this species.

For N. incompta and T. quinqueloba, however, the stronger temperature response suggests that physiological effects may need to be considered when interpreting their shell chemistry and reconstructing past environmental conditions.

“As the Arctic changes, we need to understand not only how the environment changes, but also how the organisms living there respond,” explains Mohamed Ezat, co-author of the study. “That biological perspective is essential for interpreting both the future of polar ecosystems and the climate information preserved in their fossil remains.”

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Find out more

The study, “The impact of essential climate variables on respiration rates in subpolar and polar planktonic foraminifera”, is available open access in the journal Biogeosciences.

Lead authors Diane Armitage and Audrey Morley works at the University of Galway, Ireland.

Co-author Mohamed Ezat is an iC3 researcher at the UiT Arctic University of Norway. He runs the Foraminifera Culturing Lab. He is the assistant lead of the iC3 research unit investigating how past changes in ice sheets affect the global carbon cycle and marine ecosystems, the PI of the ARCLIM project, Co-PI of the Into The Blue (i2B) project and an Associate Professor at the Department of Geosciences in Tromsø. His research focuses on past climate variability and ocean circulation. 

Co-author Adele Westgård is an iC3 afiliated postdoc working in the Into The Blue (i2B) project and the ARCLIM project, based in the Department of Geosciences at the UiT Arctic University of Norway, Tromsø. To find out more about her work, check out this blog and her list of publications, or contact her by email or on LinkedIn.

Co-author Freya Sykes is an iC3 affiliated PhD student working in the ARCLIM project, based in the Department of Geosciences at the UiT Arctic University of Norway, Tromsø. To find out more about her work, please check out this blog and her list of publications, or contact her by email or on LinkedIn.