Oceans’ ‘biological pump’ harvesting twice as much carbon as previously thought

The 'biological carbon pump' (BCP) in the Earth’s oceans are capturing twice as much carbon dioxide (CO2) from the atmosphere as previously thought, scientists have said, which could help to improve future climate models.

The BCP effectively takes CO2 from the atmosphere and deposits it into the ocean interior and sediments on the seafloor.

The cycle is primarily led by phytoplankton, a catch-all term for microscopic lifeforms that live in the ocean and encompassing photosynthesising bacteria, green algae and other forms of life.

Phytoplankton is thought to be responsible for around one per cent of the world’s biomass and is a key component of marine ecosystems. They use sunlight to create food and energy, absorbing CO2 in the process and releasing oxygen as a bi-product.

Once these creatures die, they sink to the bottom of the ocean floor, in effect creating a store of carbon-based material in solid form.

A team of researchers tried to figure out exactly how much carbon was being sequestered from the atmosphere during this process. The ability of phytoplankton to absorb CO2 is partly based on how much sunlight pierces the upper layer of the ocean waters.

They measured the depth of the ocean’s sunlit surface area, the euphotic zone, using a technique known as chlorophyll fluorescence detection that looks for the presence of photosynthetic phytoplankton in the deeper layers of the ocean.

This zone, home to most ocean-based life, varies significantly throughout the world, but is thought to be home to around 90 per cent of ocean-dwelling life.

The team used previous findings about the BCP in combination with their own research to estimate how fast the carbon particles are sinking. They found that about twice as much carbon sinks into the ocean per year than previously estimated.

Study leader Dr Ken Buesseler, a geochemist with the Woods Hole Oceanographic Institution, said: “If you look at the same data in a new way, you get a very different view of the ocean’s role in processing carbon, hence its role in regulating climate.

“Using the new metrics, we will be able to refine the models to not just tell us how the ocean looks today, but how it will look in the future. Is the amount of carbon sinking in the ocean going up or down? That number affects the climate of the world we live in.”

The research should help to provide more accurate forecasts about the carbon concentration in the atmosphere in the future.

In November 2019, researchers at the University of Exeter called for the creation of a “robust network” of satellites to help monitor the levels of carbon in the ocean.

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