Primary vitamin B12 limitation and widespread stress in Antarctic phytoplankton

In an Amundsen Sea nutrient enrichment experiment, a diatom–prasinophyte phytoplankton community was limited primarily by cobalamin, with iron acting secondarily.

• Why it matters: Iron is often assumed to limit Southern Ocean phytoplankton, but microbial competition and limited B12 biosynthesis may create conditions for widespread cobalamin limitation and stress.
• What they did: The team ran nutrient enrichment in the Amundsen Sea and measured protein biomarkers across a broad Southern Ocean area to assess cobalamin stress in diatoms and Phaeocystis.
• The result: Biomarkers indicate widespread cobalamin stress in diatoms and Phaeocystis, implying that warming-driven ice-shelf melting could shift limitation toward cobalamin and favor mixotrophic flagellates with low cobalamin requirements.

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