Tiny plankton shells have long served as invaluable archives of Earth’s climatic past, especially in polar regions where direct measurements are sparse. Yet a groundbreaking study by researchers at the iC3 Polar Research Hub at UiT The Arctic University of Norway reveals a previously overlooked complexity within these microscopic recorders. The species Neogloboquadrina pachyderma, a pivotal planktonic foraminifera used extensively to reconstruct ancient ocean temperatures, constructs its shell in two distinct chemical layers. This discovery challenges longstanding assumptions and promises to refine and perhaps revolutionize paleotemperature estimates in Earth’s coldest oceans.
Neogloboquadrina pachyderma constructs its shell primarily from calcium carbonate, using elements dissolved in the surrounding seawater. For decades, the magnesium-to-calcium (Mg/Ca) ratio embedded in these shells has served as a reliable proxy for past seawater temperatures: higher magnesium content typically signals warmer conditions, while lower magnesium suggests colder ones. However, the new findings demonstrate that the outer shell crust, formed by the same organism under identical environmental conditions as the inner shell, exhibits a markedly different chemical signature. Specifically, the crust contains lower concentrations of magnesium, sodium, and boron than the shell’s interior.
This dual chemical signature implies that the Mg/Ca ratio, which is central to paleotemperature reconstructions, may have been underestimated when measurements incorporated both shell layers indiscriminately. Since a thicker, low-magnesium crust skews the average composition lower, temperature readings derived from whole-shell analyses could inadvertently reflect artificially cooler conditions than the organism actually experienced. This effect is especially critical in polar regions, where the thermal gradients are subtle and precision essential for understanding climate dynamics.
The researchers conducted their experiments by cultivating living N. pachyderma in highly controlled laboratory settings within the Foraminiferal Culturing Laboratory at UiT. This approach allowed them to isolate biological factors from environmental variables with unprecedented accuracy. By growing individual specimens under known and stable temperature and chemical conditions, the team ensured that any observed differences in shell chemistry stemmed from biological processes rather than external fluctuations. Laser ablation techniques then permitted high-resolution chemical analyses of specific shell layers instead of bulk dissolution methods.
Utilizing laser-based elemental mapping, the scientists were able to precisely differentiate between the outer crust and the internal shell material. The strikingly distinct compositions suggested that these layers form via different biomineralization pathways or mechanisms. This insight opens new avenues for understanding how foraminifera regulate ion uptake during shell construction, a process previously thought to reflect seawater chemistry passively. The dual-layer chemistry essentially encodes a biological signal superimposed upon the environmental one, complicating—but also enriching—our interpretations of fossil shells.
Lead author Adele Westgård emphasizes the importance of this finding: “The shell is not a monolithic recorder of its environment. Different parts of the same organism’s shell carry divergent geochemical stories. To accurately reconstruct past ocean conditions, we must decipher and separate these biological signatures from the climatic ones.” This nuanced perspective challenges climate scientists to refine their proxy analyses by targeting specific parts of the shell or developing algorithms that mathematically disentangle the composite chemical signals.
This revelation also intersects with broader questions in paleoceanography regarding the reliability and resolution of fossil-based climate reconstructions amid biological variability. Previously, differences in shell chemistry across samples were often attributed solely to environmental heterogeneity or diagenetic alteration after burial. The new study shows that inherent biological variation within individual shells can contribute substantially to observed geochemical disparities, complicating the interpretation of sediment core data spanning thousands of years.
By integrating advanced laboratory culturing methods with sophisticated analytical chemistry techniques, the study pioneers a path forward for enhancing paleoclimate accuracy. Future research can adopt similar methodologies to analyze individual shell components in both living and fossil specimens, potentially recalibrating temperature proxies and sharpening temporal climate reconstructions. This approach is particularly vital in regions undergoing rapid transformation, such as the Arctic, where precise baseline data are critical for forecasting future changes.
Moreover, the findings underscore the interdependence between biology and geochemistry in Earth’s climate archives. The biological processes governing shell formation are themselves responsive to environmental cues, yet they impose their own signature onto the sedimentary record. Distinguishing these overlapping signals is essential for interpreting past ocean temperature records correctly, with significant implications for models of ice sheet dynamics, ocean circulation, and global climate feedback loops.
In a time of accelerating polar warming, understanding the mechanisms behind climate proxies is more urgent than ever. Reliable historical baselines enable scientists to gauge the magnitude and speed of current changes against natural variability and to project future scenarios with greater confidence. The study, published in Geochimica et Cosmochimica Acta, offers a significant leap towards such reliability by revealing the biological intricacies embedded within the very shells that encode Earth’s climate history.
Ongoing work at iC3 and its associated laboratories promises to build on these findings by extending culturing studies to other foraminiferal species and environmental settings. Combining microscopy, molecular biology, and geochemistry, researchers aim to develop comprehensive models of biomineralization under changing oceanic and climatic regimes. These integrated approaches exemplify the frontier of paleoclimate science, where interdisciplinary collaboration unlocks deeper insights into Earth’s complex environmental past.
Ultimately, better paleoclimate reconstructions depend on better biological understanding. This study highlights the critical need to bridge the disciplines of marine ecology, geochemistry, and climate science to accurately interpret the signals preserved in marine sediments. As Adele Westgård notes, the challenge lies in unweaving the biological imprints from the environmental records to read the past oceans with clarity and precision. Such efforts illuminate not just Earth’s history but also its unfolding climatic future.
Subject of Research: Cells
Article Title: Laboratory-grown crust in planktic foraminifera Neogloboquadrina pachyderma; insights into resolving inaccuracies in polar palaeotemperature estimates
News Publication Date: 26-Apr-2026
Web References:
- https://ic3.uit.no/news/interview-a-significant-challenge-is-the-need-for-further-culturing-of-foraminifera
- https://uit.no/project/arclim/culturing-lab
- https://ic3.uit.no/news/plasmalab-isotopes-trace-nutrients-geochemistry-climate-charlie-compton-jones
- https://ic3.uit.no/news/foraminifera-paleoclimatology
- https://ic3.uit.no/news/plasmalab-geochemical-proxies-foraminifera-paleo-arclim-ocean-temperature
- https://ic3.uit.no/news/freya-sykes-foraminifera
- https://ic3.uit.no/ru4-how-did-past-changes-in-ice-sheets-affect-the-global-carbon-cycle-and-marine-ecosystems
- https://en.uit.no/enhet/ig
References:
Westgård, A., Ezat, M., & Sykes, F. (2026). Laboratory-grown crust in planktic foraminifera Neogloboquadrina pachyderma; insights into resolving inaccuracies in polar palaeotemperature estimates. Geochimica et Cosmochimica Acta. DOI: 10.1016/j.gca.2026.04.027
Image Credits: Geochimica et Cosmochimica Acta
Keywords: Neogloboquadrina pachyderma, foraminifera, paleotemperature estimates, polar oceans, magnesium/calcium ratio, biomineralization, paleoclimate proxies, marine geochemistry, Arctic climate history, laboratory culturing, shell chemistry
