Schanke, N. L. | bioRxiv Science

bioRxiv2026

Primary vitamin B12 limitation and widespread stress in Antarctic phytoplankton

Iron is considered the dominant limiting or colimiting nutrient for phytoplankton growth in the Southern Ocean. However, strong competition and limited biosynthesis capabilities for vitamin B12 (cobalamin) within the microbial community creates conditions suitable for cobalamin limitation. Through a nutrient enrichment experiment in the Amundsen Sea, we show that growth in a phytoplankton community comprising diatoms and prasinophytes was limited primarily by cobalamin and secondarily by iron. Protein biomarkers across a broad area of the Southern Ocean further indicate widespread cobalamin stress within diatoms and Phaeocystis. As warming-induced melting of ice-shelves increases iron supplies in the coastal Southern Ocean, shifts from iron to cobalamin limitation favor mixotrophic flagellates with low cobalamin requirements, altering community composition and function.

ecology↗

bioRxiv2023

Zinc stimulation of coastal productivity in low carbon dioxide environments

The ocean acts as a carbon sink, absorbing carbon from the atmosphere and resulting in substantial uptake of anthropogenic CO2 emissions. As biological processes in the oceans such as net primary production (NPP) contribute significantly to this sink, understanding how they will shift in response to increasing atmospheric CO2 is necessary to project future ocean carbon storage capacity. Macronutrient and micronutrient resource limitation within the oceans regulates NPP, and while some micronutrients such as zinc (Zn) are present at very low concentrations, their ability to limit NPP has remained unclear. Zn is a key micronutrient used by phytoplankton for a multitude of metabolic functions, yet there have been few observations of its influence on natural oceanic phytoplankton populations. In this study, we observed Zn limitation of growth in the natural phytoplankton community of Terra Nova Bay, Antarctica, in addition to primary iron (Fe) limitation. Shipboard incubation experiments amended with Zn and Fe resulted in significantly higher chlorophyll a content and dissolved inorganic carbon drawdown compared to Fe addition alone. Zn and Fe stress response proteins detected in incubation and environmental biomass provided independent verification of algal co-stress for these micronutrients. We consider total biomass and low surface ocean pCO2 as potential drivers of environmental Zn stress. This study definitively establishes that Zn limitation can occur in the modern oceans, opening up new possibility space in our understanding of nutrient regulation of NPP through geologic time, and we consider the future of oceanic Zn limitation in the face of climate change.

biochemistry↗