Warming and CO₂ Enhance Arctic Heterotrophic Microbial Activity

Area of Science:

• Marine microbial ecology
• Climate change science
• Arctic Oceanography

Background:

• Ocean acidification and warming are key climate change impacts on marine ecosystems.
• The Arctic Ocean is warming faster than other regions globally.
• Marine planktonic microorganisms are crucial for ocean biogeochemical cycles.

Purpose of the Study:

• To investigate the combined effects of warming and elevated CO2 on Arctic microbial communities.
• To assess changes in phototrophic and heterotrophic microbial abundances and processes.
• To examine viral activity (lytic and lysogenic) under simulated future Arctic conditions.

Main Methods:

• Experimental microcosms simulating Arctic fjord conditions (Svalbard).
• Controlled temperature treatments (1°C, 6°C, 10°C) with elevated CO2 concentrations (135–2,318 μatm).
• Measurements of chlorophyll a, bacterial production (BP), bacterial mortality, and viral lytic/lysogenic activity.

Main Results:

• Chlorophyll a decreased with increasing temperature.
• Bacterial production significantly increased with pCO2 at 6°C and 10°C.
• Lysogeny increased with pCO2, especially at 10°C, and protistan grazing showed a positive interaction with temperature.

Conclusions:

• Future Arctic warming and CO2 increase will reduce phytoplankton biomass.
• Bacterial production will be enhanced, altering microbial food web carbon fluxes.
• The Arctic plankton community's capacity to act as a CO2 sink will likely diminish.