Small but mighty: The invisible yet serious impacts of microbial communities in a warming Arctic Ocean

Climate-related changes in the Arctic Ocean have already resulted in a shift in microbial communities that has the potential to significantly alter the delicate and interconnected Arctic ecosystem. As ARTHI RAMACHANDRAN writes, microbes are notoriously quick to adapt to changing conditions—and rapid changes in the composition of their communities could have unknown consequences, not only for the marine food web but even for greenhouse gas emissions.

The Arctic Ocean is a unique and fragile ecosystem that is particularly vulnerable to the impacts of climate change. If the Arctic region experiences a temperature increase of 1.5°C or more, warmer sea surface temperatures and unprecedented melting of sea ice will alter the ocean’s water masses, circulation patterns and more, including the communities of bacteria at the base of the food web.

In terms of total biomass, most life in the Arctic Ocean is microbial—and these microbes are essential to the health and stability of Arctic marine ecosystems. They provide critical ecosystem services     , such as nutrient cycling, carbon sequestration, decomposition, primary production, water purification and climate regulation. Yet the consequences of climate warming on the microbial food web—and, in turn, the Earth’s biogeochemical cycles—are not yet well understood.

One thing we do know is that the climate crisis has significant implications for these microbial communities. Rising temperatures have already led to observable shifts in their composition and abundance, and these shifts have the potential to alter the entire Arctic food web.

As the Arctic continues to warm, there will be a continued increase in sea ice melt and an influx of freshwater, which will decrease the salinity of the Arctic Ocean’s upper waters. This means that previously dominant bacterial groups may decline, while others that are better adapted to less saline environments will thrive. We do not yet know what the downstream effects of this might be, including whether these will be positive or negative.

Tiny organisms, global impacts

Changes in microbial communities may even affect greenhouse gas emissions. For example, certain bacterial species are known to consume methane and carbon dioxide. Changes in their composition and abundance in response to climate warming might alter the rates at which these greenhouse gases are consumed.

An increase in the presence of bacteria that consume greenhouse gases, like methane, could be positive in the short term—but there could be long-term consequences because this could mean a decrease in other types of bacteria, and it’s unclear how the ecosystem services they provide might shift. We’re still trying to figure out if and how shifts in microbial communities due to climate change will have negative effects on the ecosystem as a whole.

Furthermore, shifts in the composition and abundance of microbial communities may have cascading effects on fish and marine mammals because these species rely on microbial communities for their food.

The rapidly changing environmental conditions in the Arctic Ocean have led to questions about whether there will be an increase in adaptation, evolution and/or migration of microbial organisms. The Arctic Ocean’s microbial communities can be seen as both sentinels and amplifiers of global change. Their responses to climate warming can provide important insights into the overall health and functioning of Arctic marine ecosystems as well as the potential of these systems to influence global biogeochemical cycles.

These invisible changes may have drastic and irreversible impacts on Arctic and global ecosystems, especially if we continue on the current pathway to a future where the global temperature rise exceeds 1.5°C.