Poor Ocean Circulation Leads to More Carbon Dioxide in the Air?

As the ocean gets weaker, it could release more carbon from the deep ocean into the atmosphere - rather than less, as some have predicted
Despite long-held beliefs, poor ocean circulation can actually result in more carbon dioxide in the air rather than less. Credit: MIT News / iStock / CC BY-NC-ND 3.0

A recent study suggests that the long-held understanding of the affect of ocean circulation on carbon storage may need revision. As ocean circulation weakens, there is concern it could in fact release more—rather than less—carbon dioxide from its depths into the air.

This significant shift is tied to a newly identified interaction involving the ocean’s iron availability, the movement of carbon and nutrients, surface microorganisms, and molecules broadly known as “ligands.”

Surprising revelations about ocean circulation

Jonathan Lauderdale, a research scientist at MIT’s Department of Earth, Atmospheric, and Planetary Sciences and author of the study, explains a crucial new interaction. “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.”

“What we thought is going on in the ocean [has been] completely overturned,” he said. This discovery points to a reversal of what scientists previously believed about the ocean’s role in carbon sequestration.

Insights from the box model

In 2020, Lauderdale led a study using a straightforward “box” model to simulate conditions in various ocean regions, capturing the interactions among ocean nutrients, marine life, and iron.

This model demonstrated that introducing more iron into the ocean—a proposed method to boost phytoplankton growth and carbon dioxide (CO2) capture—would not be as effective as anticipated due to ligand constraints.

The research highlighted a critical insight: ligands, which are essential for making iron soluble and accessible to phytoplankton, vary significantly across different ocean areas. This variability can lead to an unexpected increase in atmospheric CO2 when ocean circulation weakens, contrary to previous models that suggested the opposite.

Challenging previous models

During further model refinements, Lauderdale incorporated interactions of carbon between the ocean and the atmosphere, exploring different levels of ocean circulation.

The updated model revealed a surprising outcome. Weaker ocean circulation correlates with higher atmospheric CO2 levels. This contradicts previous assumptions and indicates that ligand concentrations indeed vary between ocean regions, confirming the initial unexpected findings.

Implications for climate policy

Lauderdale’s work necessitates a reconsideration of how oceanic processes are represented in climate models.

“This huge slowdown in overturning circulation could actually be a big problem: In addition to a host of other climate issues, not only would the ocean take up less anthropogenic CO2 from the atmosphere, but that could be amplified by a net outgassing of deep ocean carbon, leading to an unanticipated increase in atmospheric CO2 and unexpected further climate warming,” Lauderdale warns.

He emphasizes the urgency of proactive emission reductions, as relying on the ocean’s natural processes might not suffice to mitigate climate change effectively.

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