Future ocean warming may cause large reductions in Prochlorococcus biomass and productivity

Area of Science:

• Marine Biology
• Oceanography
• Climate Science

Background:

• Prochlorococcus is Earth's most abundant photosynthetic organism, vital for oceanic ecosystems.
• Its sensitivity to climate change, particularly rising ocean temperatures, is not well understood.

Purpose of the Study:

• To quantify the temperature dependence of Prochlorococcus cell division rates.
• To project the impact of future ocean warming on Prochlorococcus production.

Main Methods:

• Analysis of decade-long field measurements using continuous-flow cytometry (SeaFlow instrument).
• Collection of per-cell chlorophyll fluorescence and size data for approximately 800 billion phytoplankton cells.
• Utilized a global ocean ecosystem model to simulate future production scenarios.

Main Results:

• Prochlorococcus division rates increase exponentially with temperature up to 28°C, then sharply decline.
• Future ocean temperatures under moderate and high warming scenarios are projected to exceed this optimal range.
• A 17-51% reduction in Prochlorococcus production in tropical oceans is predicted under future warming.

Conclusions:

• Prochlorococcus division rates are primarily temperature-dependent, with a critical upper threshold.
• Future warming may significantly reduce Prochlorococcus production, impacting marine ecosystems.
• Thermal adaptation may not be sufficient to mitigate the negative effects of warming on Prochlorococcus.