Diatom culturing experiments reveal the mystery of barium isotopes in pelagic barite
- Alan Hsieh
- Mar 20
- 2 min read
Have you ever wondered how tiny ocean organisms influence the chemistry of seawater? Our recent study explores this question by examining barium (Ba) isotopes, which serve as valuable tracers for understanding past and present ocean productivity and carbon export. Specifically, we investigated how diatoms may impact Ba isotope fractionation during the formation of pelagic barite.
In the ocean, Ba forms a mineral called barite (BaSO₄) in pelagic particulate microenvironments as organic particles decay and sink into the deep ocean. Scientists analyze barite and its chemical records to reconstruct past ocean productivity and marine chemistry. However, one mystery remains: why does pelagic barite show more negative Ba isotope fractionation than lab-precipitated barite?
To solve this puzzle, we turned to diatoms, a type of phytoplankton that plays a key role in the marine carbon cycle. These microscopic organisms take up Ba while they grow, but their influence on Ba isotopes has remained unclear—until now.
We conducted a series of culturing experiments using the model marine diatom Thalassiosira weissflogii to explore how diatoms take up Ba from seawater and how this process affects its isotopic composition. Our study revealed that:
Diatoms passively take up Ba through Ca transporters, with uptake rates influenced by growth conditions.
Ba/C ratios in cultured diatoms are significantly lower than those in marine particles, suggesting that biological uptake alone cannot explain the observed particulate Ba sinking flux, requiring additional sources such as microbial processes.
Diatoms preferentially take up isotopically lighter Ba, providing the first direct evidence of Ba isotope fractionation in organic-associated Ba before the formation of pelagic barite. This may explain why pelagic barite shows more negative Ba isotope fractionation than lab-precipitated barite.
This research sheds new light on how marine life interacts with chemical elements and their isotope compositions in the ocean, which is crucial for future studies using Ba isotopes to reconstruct past ocean productivity and marine chemistry.
If you’re interested in learning more, check out our full paper here:
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