Eukaryotic phytoplankton drive a decrease in primary production in response to elevated CO₂ in the tropical and...

Area of Science:

• Marine biology
• Oceanography
• Climate change science

Background:

• Anthropogenic carbon dioxide (CO2) emissions are driving ocean acidification.
• The impact of ocean acidification on marine phytoplankton productivity remains uncertain.
• Phytoplankton are crucial primary producers in marine ecosystems.

Purpose of the Study:

• To investigate the effects of ocean acidification on phytoplankton community composition and productivity.
• To assess regional variations in phytoplankton response to elevated CO2 levels in the western North Pacific.
• To project potential global impacts on primary production in vulnerable ocean regions.

Main Methods:

• Field studies were conducted across the western North Pacific, including the North Pacific Subtropical Gyre and the northern South China Sea.
• Phytoplankton community composition and primary production rates were measured under ambient and acidified conditions.
• Data were extrapolated to predict global impacts on oligotrophic ocean regions.

Main Results:

• Ocean acidification led to consistent reductions in primary production in the North Pacific Subtropical Gyre and northern South China Sea.
• Prokaryotic phytoplankton showed neutral to positive responses to high CO2.
• Small eukaryotic phytoplankton (<20 µm), nitrogen-limited, were primarily responsible for the observed decrease in community primary production.

Conclusions:

• Ocean acidification negatively impacts primary production in specific subtropical and tropical regions.
• Small eukaryotic phytoplankton are particularly vulnerable to ocean acidification.
• Global primary production in low chlorophyll-a, oligotrophic regions may decrease by approximately 5 Pg C y-1 due to acidification and stratification.