A study by iC3 researchers found that the polar plankton species Neogloboquadrina pachyderma can grow an outer shell crust with a different chemical composition than the inner shell, even when both form under identical conditions.
The Research
Led by Adele Westgård at the iC3 Polar Research Hub, the study focuses on N. pachyderma—the only polar plankton species in the foraminifera group. These organisms build a calcium carbonate shell.
Key Discovery
Fossil shells of this species are commonly used to reconstruct past ocean temperatures by analyzing magnesium-to-calcium ratios. Higher magnesium levels typically indicate warmer water. The study, however, revealed a critical complication:
- The outer crust of the shell contained lower levels of magnesium, sodium, and boron compared to the inner shell.
- This chemical difference could lead to underestimating past temperatures if the entire shell is measured together.
How the Study Was Done
The team cultured N. pachyderma in controlled laboratory conditions and used laser-based analysis to measure trace elements in individual shell layers. They also developed code to identify and separate the two shell layers based on their distinct chemical composition.
Implications for Climate Science
The finding suggests that biological processes, not just environmental conditions, influence shell chemistry.
- Separating or avoiding crust material in analyses could improve the accuracy of past ocean temperature reconstructions.
- The study is published in Geochimica et Cosmochimica Acta.