The ocean right now is acting as a big ‘carbon toilet’. An essential natural system that removes carbon dioxide from the atmosphere and locks him in the deep sea, helping regulate global climate. However, the recent heat waves we have experienced at sea are altering this critical process, which could have serious consequences for the climate of the entire planet.
The ‘carbon toilet’. On the surface of the ocean we can now find organisms called phytoplanktonwhich have the ability to absorb CO₂ and produce oxygen through a simple photosynthesis mechanism with the help of sunlight. The problem is that we live in a life cycle that constantly advances, and that is why these organisms are food for small marine animals. called zooplanktonwhich generate feces in the form of small pellets that they sink to the seabed.
This phenomenon, called the “biological carbon pump,” transports carbon from the atmosphere to the bottom of the sea, where it can remain isolated for centuries. In this way, the seabed can be seen as a large ‘cemetery’ of CO₂ stored in the feces of these animals. Something that in the long term is helping us clean the atmosphere and mitigate global warming.
Heat waves. In the Pacific Northwest, two major episodes of marine heat waves that occurred in the periods 2013-2015 and 2019-2020 are changing everything. Temperature increases drastically altered the composition of phytoplankton and zooplankton, generating a “clogging” effect on the carbon toilet we have in the ocean.
The lack of deep mixing and nutrients, caused by warming and stratification of the water, favored smaller species that produce feces that tend to float rather than sink, slowing the transport of carbon to the depths.
A new layer. If the feces float, this simply means that the organic carbon now accumulates in the superficial layers of the water instead of reaching the deep areas where it was sequestered. This is also added to a greater bacterial proliferation in warm waters that decomposed more organic matter, releasing CO₂ again into the water and subsequently into the atmosphere itself. This is something that weakens the role of ‘buffer’ to try to compensate for the concentration of CO₂ in our atmosphere.
Consequences. These changes not only affect the carbon cycle, but also the very base of the marine food chain. The decline in large phytoplankton reduces oxygen production and limits the feeding of larger marine species, including whales and commercial fish relevant to humanity. Zooplanktons are also responding to warming with changes in size and distribution, further impacting the efficiency of the carbon cycle since the smaller their size, the less CO2 they will capture and the less O2 they will produce.
How it was done. In order to draw these conclusions, the research was based on a decade of data that was obtained through Argo biogeochemical floats. These are autonomous devices that have the ability to explore the ocean layers by measuring chemical and biological parameters without the need for constant human presence.
This has allowed changes in marine ecosystems to be monitored in detail during extreme events, revealing hitherto invisible patterns and providing an essential tool for future studies and mitigation strategies.
The future. These episodes of marine heat waves are increasingly frequent in our oceans due to global warming, as we are also experiencing in Spain. This means that if greenhouse gas emissions are not quickly reduced, the ocean could lose much of its ability to absorb atmospheric carbon.
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