By Femi Akinola
A new study by a Massachusetts Institute of Technology (MIT) researcher published in the Nature Communications finds that scientists may have to rethink the relationship between the oceans circulation and its long term capacity to store carbon.
Scientists have noted that as climate change advances, the ocean overturning circulation is predicted to weaken substantially. With such a slowdown, they estimate the ocean will pull down less carbon-dioxide from the atmosphere.
However, they said a slower circulation should also dredge up less carbon from the deep ocean that would otherwise be released back into the atmosphere. On balance, they said the ocean should maintain its role in reducing carbon emissions from the atmosphere, if at a slower pace.
The reason, according to Jennifer Chu, Massachusetts Institute of Technology, USA, has to do with previously uncharacterized feedback between the ocean available iron, upwelling carbon and nutrients, surface microorganisms, and a little-known class of molecules known generally as ”ligands.”
When the ocean circulates more slowly, scientists noted, all these players interact in a self-perpetuating cycle that ultimately increases the amount of carbon the ocean outgases back to the atmosphere.
”By isolating the impact of this feedback, we see a fundamentally different relationship between ocean circulation and atmospheric carbon levels, with implications for the climate,” says study author, Jonathan Lauderdale, a research scientist in MIT’s Department of Earth, Atmospheric, and Planetary Sciences. ”What we thought is going on in the ocean is completely overturned.”
Lauderdale says the findings shows that ”we can’t count on the ocean to store carbon in the deep ocean in response to future changes in circulation. We must be proactive in cutting emissions now, rather than relying on these natural processes to buy us time to mitigate climate change.”
In 2020, Lauderdale led a study that explores ocean nutrients, marine organisms, and iron, and how their interactions influences the growth of phytoplankton around the world.
Phytoplankton are microscopic, plant-like organisms that live on the ocean surface and consume a diet of carbon and nutrients that upwell from the deep ocean and iron that drifts in from desert dust.
The more phytoplankton that can grow, Lauderdale explained, the more carbon-dioxide they can absorb from the atmosphere via photosynthesis, and ” this play a large role in the ocean’s ability to sequester carbon,” he said.
From the 2020 study, Lauderdale team developed a simple ”box” model, representing conditions in different parts of the ocean as general boxes, each with a different balance of nutrients, iron, and ligands-organic molecules that are thought to be byproducts of phytoplankton.
Lauderdale team found out that adding iron to one ocean region to consume additional nutrients robs other regions of nutrients that phytoplankton need to grow.
This lower the production of ligands and the supply of iron back to the original ocean region, limiting the amount of extra- carbon that would be taken up from the atmosphere.
