Counterintuitive carbon-to-nutrient coupling in an Arctic pelagic ecosystem.

Area of Science:

• Marine biogeochemistry
• Microbial ecology
• Ocean carbon cycle

Background:

• Predicting the ocean's carbon cycle role needs understanding stoichiometric coupling in biogeochemical processes.
• A high-CO(2) world may increase dissolved organic matter's carbon/nitrogen ratio, but its impact depends on mineralization.
• The fate of organic carbon in marine ecosystems is linked to microbial food web dynamics.

Purpose of the Study:

• To investigate how degradable organic carbon affects Arctic pelagic ecosystems.
• To determine the influence of microbial food web state on organic carbon fate and accumulation.
• To understand the stoichiometric coupling between carbon and mineral nutrients in autotrophic and heterotrophic processes.

Main Methods:

• Field study in an Arctic pelagic ecosystem.
• Manipulation of degradable organic carbon levels.
• Monitoring of microbial food web states, bacterial growth rates, and nutrient limitation.

Main Results:

• When bacteria were mineral nutrient-limited, added organic carbon accumulated.
• When bacteria were organic carbon-limited, added organic carbon decreased phytoplankton biomass and activity.
• This led to reduced total organic carbon accumulation, a counterintuitive 'more carbon yields less carbon' effect, especially in diatom-rich systems.

Conclusions:

• The microbial food web state critically controls the fate of organic carbon in marine systems.
• Bacterial competition for mineral nutrients can counteract organic carbon accumulation, even in high-CO(2) scenarios.
• Accurate ocean carbon cycle modeling requires detailed knowledge of stoichiometric coupling in both microbial and phytoplankton processes.