In the vast expanse of the Southern Ocean, two microscopic architects help shape the planet’s climate: the diatom Pseudo-nitzschia subcurvata and the prymnesiophyte Phaeocystis antarctica. The study “Individual and interactive effects of warming and CO2 on Pseudo-nitzschia subcurvata and Phaeocystis antarctica, two dominant phytoplankton from the Ross Sea, Antarctica”.
The researchers cultivated both species under tightly controlled laboratory conditions, adjusting temperature from freezing levels up to 14 °C and exposing the cultures to CO2 concentrations spanning past, present, and future atmospheric scenarios. Critically, they used UIC Inc. carbon analyzers to precisely measure dissolved inorganic carbon and ensure accurate CO2 system calibration. These high-resolution measurements allowed the team to link growth responses directly to verified carbonate chemistry.
The results paint a picture of ecological rebalancing. P. subcurvata showed strong acceleration in growth as temperatures rose toward 8 °C, displaying a wider thermal tolerance and a higher optimal temperature than P. antarctica. In contrast, P. antarctica increased growth only slightly with warming and reached its upper temperature limit more quickly. When the two species were grown together, the diatom gained dominance much faster at 6 °C than at 0 °C, suggesting that future warming could tilt community composition toward diatoms.
CO2 told a different story. Both species increased growth up to about 425 ppm, but further CO2 enrichment produced little additional benefit. In fact, extremely high CO2 levels slightly inhibited P. antarctica, likely because of the associated low pH. Changes in cellular carbon, nitrogen, phosphorus, and silica ratios were modest compared with the effects of temperature. The precise DIC data generated with UIC Inc. instrumentation were essential for determining that CO2 levels above ~425 ppm offered minimal physiological advantage.
The larger implication is clear: warming is likely to be the dominant driver reshaping Ross Sea phytoplankton communities, favoring diatoms and altering nutrient export patterns. CO2 increases alone appear to play a secondary role. As climate change advances, these shifts could influence carbon cycling, food web structure, and the biogeochemistry of one of Earth’s most productive marine ecosystems.
Reference: Zhu, Z., Qu, P., Gale, J., Fu, F., & Hutchins, D. A. (2017). Individual and interactive effects of warming and CO₂ on Pseudo-nitzschia subcurvata and Phaeocystis antarctica, two dominant phytoplankton from the Ross Sea, Antarctica. Biogeosciences, 14(22), 5281–5295. https://doi.org/10.5194/bg-14-5281-2017
