New research shows that rain helps the ocean sequester more carbon than previously thought!

Calculations of how the ocean traps carbon from the atmosphere have not taken into account the role of rain in this process. Today, extensive research concludes that this role is entirely relevant. Image: CC

Enzo Campetella Meteored Argentine 31/10/2024 10:00 8 min

This story is similar to the one that happens when you’re low on funds on your credit card and the bank informs you that they’re extending your credit limit a little further. The debts continue, but you now have a little more time. Let’s see how we can translate this daily story into the atmosphere in which we live. It turns out that precipitation has so far been ignored in calculations of the carbon absorption capacity of the oceans, but a new estimate shows they increase the ocean sink by 5-7%. Give us a little more credit!

Most measurements of gas concentrations in the ocean are made by ships, which take water samples at a depth of 5 to 7 meters. But because rain hits the surface, its effects are invisible at these depths. This phenomenon was ignored due to lack of data.

Now let’s see what it is in reality. As reported Live ScienceThirty years ago, David Ho installed two pink dinosaur-themed swimming pools in the parking lot of a NOAA building in Miami, where afternoon storms were common. He was 22 years old, had just graduated from college, and was working as a technician at NOAA. What did David do? He filled both pools with water, added a tracer gas and placed a canopy over one of them as a control.

He then gave himself time to wait, and then for several months he watched the rain fall and accumulate as it soaked in. During this process, he took samples from each pool using glass syringes. The following are David Ho’s words, not ours: “ It was pretty miserable. But I got some interesting results. David’s Pelopincho would then have helped science! Let’s continue to go through its history to find out the results.

How rain contributes to the process

These first experiments carried out by David Ho demonstrated that rain increases the rate of transfer of carbon dioxide (CO2), that is, how efficiently it is transferred from air to water. Ho, now an oceanographer at the University of Hawaii at Manoa, has continued his research on the subject since then, analyzing the effect in a NASA rain simulator and on research trips to the Pacific. With more resources than his swimming pools pulled by dinosaurs thirty years ago, his observations have made it possible to understand the role of rain in the absorption of CO2.

The graphs show the changes in salinity at the ocean-atmosphere interface that produce precipitation. Image: David Ho.
The graphs show the changes in salinity at the ocean-atmosphere interface that produce precipitation. Image: David Ho.

Their latest study, published in Nature Geoscience, is the culmination of this work and provides the first comprehensive global estimate of what happens to CO2 fluxes when rain reaches the ocean. Other researchers from the Institut Polytechnique de also participated in the study. It shows that the global ocean absorbs about a quarter of CO2 emissions from human activities and that precipitation increases this absorption by 140 to 190 million metric tons, or 5 to 7 percent, per year.

Given the seriousness of research of this magnitude, Mr. Ho believes that “ It may be surprising that it has taken so long to quantify this process, but this is partly because it is a difficult problem to examine “. The work is now subject to peer review to be truly recognized by the scientific community, but there is every reason to believe that its contribution will be very revealing in improving the understanding of the interaction between the atmosphere and the oceans in the context of this complex process.

Data that helps understand reality

It is important to understand that the uptake of carbon dioxide in the ocean is not uniform. Some regions act as sinks, drawing gas downward, while other regions release it. The study summary states that precipitation modifies local physical and biogeochemical properties of the sea surface, but its spatio-temporal variability has meant that it has been neglected in studies of carbon uptake by seas. oceans on a global scale.

Spatial distribution of rain-induced CO2 concentration changes. Image David Ho.
Spatial distribution of rain-induced CO2 concentration changes. Image David Ho.

This entire process demonstrates the importance of improving the quality and collection of data for each variable in order to better understand the processes at play. This task takes time, sometimes a lot of time for specialists to reach definitive conclusions. And sometimes they need minds like that of Ho who, even with few resources like his two dinosaur pools, was able to embark on a path that today provides invaluable data for science in a world that shows that the oceans are warming.

Different physical and chemical processes in the gas and liquid phases of water control the transfer of CO2 between the atmosphere and the ocean. Rain influences interfacial flow by increasing turbulence in the ocean and modulating the CO2 concentration gradient between air and sea. At the same time, raindrops inject CO2 absorbed during their fall into the ocean. through wet deposition. This study presents a comprehensive estimate of these effects on ocean carbon uptake over the period 2008-2018, based on satellite and in situ observation products and reanalyses.

Article reference:

Parc, L., Bellenger, H., Bopp, L. et al. Global ocean carbon uptake enhanced by rainfall. Nat. Geosci. 17, 851–857 (2024). https://doi.org/10.1038/s41561-024-01517-y

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