The Arctic Ocean, a remote and often harsh environment, teems with an immense population of microscopic, plant-like organisms known as phytoplankton. These tiny drifters, though unseen by the naked eye, exist throughout the frigid waters. Their presence in this extreme northern habitat plays a role in the Arctic’s unique ecosystem.
Understanding Arctic Phytoplankton
Phytoplankton are self-feeding, photosynthesizing microorganisms, akin to plants on land, that inhabit the sunlit surface layers of oceans and lakes. In the Arctic, these organisms have developed adaptations to challenging conditions, including very cold temperatures, limited light, and the presence of sea ice. Some species can even photosynthesize using weak light during the Arctic winter.
Many Arctic phytoplankton species can be found living within or beneath sea ice, adapting to low-light environments by maximizing light absorption. Diatoms are a common group of Arctic phytoplankton, known for their ability to adapt to various light conditions, from light-limited under-ice environments to intensely illuminated melt layers. Dinoflagellates are another important type, with some species, like Polarella glacialis, capable of driving blooms even in sea ice.
Foundation of Arctic Life
Arctic phytoplankton serve as primary producers, forming the base of the Arctic marine food web. Through photosynthesis, they convert sunlight and dissolved inorganic carbon into organic matter, making energy available to higher trophic levels. This process depends on light and nutrient availability, leading to strong seasonality in their production.
The energy captured by phytoplankton is then transferred to zooplankton, such as copepods and krill, which graze on these microscopic plants. These zooplankton, in turn, become a food source for larger animals like fish, seals, whales, and seabirds. For instance, ringed seals feed on small crustaceans like shrimp and krill, while harp seals consume small fish. The entire Arctic ecosystem relies on phytoplankton productivity.
Global Climate Regulators
Beyond their local ecosystem role, Arctic phytoplankton play a role in regulating the global climate. They absorb substantial carbon dioxide (CO2) from the atmosphere during photosynthesis, similar to how terrestrial plants remove CO2. This absorption helps to mitigate the increase of atmospheric CO2, a major greenhouse gas.
The “biological pump” further enhances their role in carbon sequestration. When phytoplankton die, the carbon incorporated into their organic matter sinks to the deep ocean, removing it from the surface waters and atmosphere for long periods. Additionally, phytoplankton contribute to global oxygen production, accounting for at least half of the oxygen produced on Earth.
Responding to a Warming Arctic
Climate change is impacting Arctic phytoplankton, with cascading effects throughout the ecosystem. Melting sea ice, a direct consequence of rising temperatures, alters their habitat and changes light exposure. Thinner ice allows more light to penetrate, potentially leading to earlier and larger phytoplankton blooms, but also exposes under-ice algae to harmful excessive sunlight.
Rising ocean temperatures affect phytoplankton growth rates and shift species composition, as warmer waters may favor certain species. This may lead to non-Arctic species replacing Arctic species, with unknown nutritional consequences for the food web. Ocean acidification, caused by excess CO2 absorption, also poses a threat, making it harder for some phytoplankton to form protective shells or affecting their nutrient uptake. These changes in phytoplankton communities can disrupt the Arctic food web and alter their climate regulation capacity.