Oceans Absorb More Emissions Than Expected, Driven by Huge Plankton Blooms

The ocean is a vital component of the global carbon cycle, as it absorbs almost 30% of the carbon dioxide (CO₂) emissions from human activities.

This helps to mitigate the effects of climate change by reducing the amount of CO₂ in the atmosphere.

However, the ocean carbon cycle is complex and dynamic, and it involves various physical, chemical and biological processes that are not fully understood or modeled.

The biological carbon pump: how zooplankton move carbon

(Photo : JOAO LAET/AFP via Getty Images)

The biological carbon pump is a process that transfers organic carbon from the surface ocean to the deep ocean, where it can be stored for long periods of time, as per Phys.org.

The biological carbon pump starts with phytoplankton, microscopic plants that use sunlight and CO₂ to produce organic matter through photosynthesis.

Phytoplankton are the primary producers of organic carbon in the ocean, and they support the marine food web.

Zooplankton are tiny animals that feed on phytoplankton and other organic matter in the ocean. Zooplankton include various groups of organisms, such as copepods, krill, jellyfish and salps.

These organisms play a crucial role in the biological carbon pump, as they consume, transform and transport organic carbon in different ways:

They can directly export organic carbon to the deep ocean by sinking after they die or produce fecal pellets.

Moreover, zooplankton can indirectly export organic carbon to the deep ocean by feeding at the surface and excreting or respiring at depth, creating a vertical flux of dissolved organic carbon or CO₂.

Zooplankton can enhance the export of organic carbon to the deep ocean by aggregating phytoplankton or other particles into larger and faster-sinking units, such as marine snow or fecal pellets, and can also affect the efficiency of the biological carbon pump by recycling organic carbon in the surface or intermediate layers of the ocean, reducing the amount of carbon that reaches the deep ocean.

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The zooplankton uncertainty: how zooplankton affect climate models

Zooplankton are highly diverse and variable in their abundance, distribution, behavior and physiology, as per Nature.

They respond to various environmental factors, such as temperature, light, nutrients and predators.

They also interact with other components of the ocean carbon cycle, such as phytoplankton, bacteria and dissolved inorganic carbon. These factors make zooplankton difficult to observe, measure and model.

In a new study published in the journal Communications Earth & Environment, Tyler Rohr and colleagues from Australia and Canada show that zooplankton are likely to be the biggest source of uncertainty in how we model the marine carbon cycle and its feedbacks to climate change.

The researchers used a global earth system model that includes a detailed representation of zooplankton diversity and dynamics. They performed a series of simulations with different levels of CO₂ emissions and different assumptions about zooplankton behavior and physiology.

The researchers found that:

•  Zooplankton can have a large impact on the ocean carbon cycle by altering the amount of CO₂ uptake by phytoplankton, the amount of organic carbon export to the deep ocean, and the amount of CO₂ outgassing from the ocean to the atmosphere.
•  Zooplankton can also have a large impact on climate change by affecting the global temperature, sea level rise, ocean acidification and oxygen levels.
•  Zooplankton can account for up to 50% of the uncertainty in projecting future changes in ocean carbon storage and climate feedbacks under different emission scenarios.

The researchers suggested that improving our understanding and modeling of zooplankton diversity and dynamics is essential for reducing uncertainty and increasing confidence in predicting future changes in the ocean carbon cycle and climate.

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