Climate science: a source of "greenhouse gases" hidden in marsh mud

TThe smell that emanates from the ocean is immediately recognizable: it sometimes feels fresh and clean, but sometimes it's a little moist, brackish or sulfuric. This smell actually indicates an abundant source of what some scientists call an "anti-greenhouse gas".

The ocean already plays an important role in carbon capture, which can help offset the amount of carbon remaining in the atmosphere. But the sea also has another effect on temperature regulation. This sea scent is partly the odor of dimethyl sulphide (DMS), which is released when marine microorganisms break down another marine nutrient called dimethylsulfoniopropionate (DMSP).

The DMS has sometimes been called a "greenhouse gas" because, once in the atmosphere, it decomposes rapidly into aerosols that allow the formation of clouds. These clouds can help disperse UV rays in the space, creating a cooling effect.

In an article published Monday in Microbiology of nature Jonathan Todd, Ph.D., and a team from the University of East Anglia have shown that the bacteria hidden in the bottom of the swamp mud can make DMSP, the key ingredient needed to make DMS.

"Previously, DMSP was widely regarded as a molecule of eukaryotic algae in the ocean's surface ocean," says Todd Reverse. "However, we show that the concentration of DMSP, DMSP and DMS synthesis rates are much higher in all tested coastal mud samples than in surface waters."

It is interesting to note that these bacteria seem to be scattered in the underwater mud of the world. Todd and his team took mud samples from several estuaries and salt marshes scattered throughout eastern England and found that nearly a quarter of the bacteria living in these samples were able to produce DMSP. He also found traces of it in the Mariana Trench – the deepest of the natural ocean trenches, which runs for nearly 11 km. These bacteria were thriving up to 4 kilometers deep.

In terms of climate, we can consider the DMSP as a fuel that can be transformed one day into a greenhouse gas, the DMS. And these muddy stores seem to be a particularly rich source. This team estimates that "there could be 100 million DMSP-producing bacteria in one gram of swamp mud, suggesting that these coastal areas could play a much larger role in the global production of DMS than in other areas of the world." we did not think so before.

Can we really use the "greenhouse gas"?

These results lend themselves to a somewhat controversial idea: we may be able to manipulate these marine ecosystems to produce more DMS and try to compensate for climate change in this way.

This idea dates back to 1987, when James Lovelock (the author of "Gaia's Hypothesis") proposed using DMS-producing plankton to offset global warming. In 2007, he wrote a letter proposing an "emergency treatment for the pathology of global warming": the creation of pipes 100 to 200 meters long that can bring ocean nutrients to the surface, reviving the production of DMS .

In this letter, Lovelock admitted that a project like this "could fail for technical or economic reasons". And since then, he has been criticized because it could also cause dangerous blooms of algae or other unintended consequences. But the idea has never totally disappeared. In 2015, another article published in Scientific reports used two climate models to show that the increase in DMS production would actually offset some of the changes in warming.

Personally, I do not think that there is a geo-engineering angle in the work, others may not be in agreement. "

Nevertheless, even this document recognized that there would likely be an "excessive mix of positive and negative climate impacts" to attempt such an aggressive geoengineering program.

Todd, in the context of this new document, does not see the work of his team this way.

"We believe our study provides important insights needed to understand the global production and cycle of DMSP and DMS," he said. "Personally, I do not think there is a geo-engineering angle in the work, others may not agree."

However, as we continue to look for a solution, some might be inspired to know that our salt marshes and estuaries could be much richer sources of the "greenhouse gas" we once thought.

Abstract:

Dimethylsulfoniopropionate (DMSP) and its dimethylsulfide catabolite (DMS) are essential marine nutrients1,2 that play a role in the global sulfur cycle2, atmospheric chemistry3, signaling4,5 and, potentially, regulation climate6,7. It was previously thought that the production of DMSP was a photographic and oxic process mainly confined to the surface oceans. However, we show here that DMSP concentrations and DMSP and DMS synthesis rates are higher in surface sediments, for example in salt ponds, estuaries and deep oceans than in the above-mentioned seawater. underlying. A quarter of the bacterial strains isolated from saline sediments produced DMSP (up to 73 mM), and we identified several previously unknown DMSP producers. Most DMSP-producing isolates contained dsyB8, but some alphaproteobacteria, gammaproteobacteria, and actinobacteria used a DsyB-independent methionine methylation pathway that was previously uniquely associated with higher plants. These bacteria contained a methionine methyltransferase (mmtN) gene, a marker for the bacterial synthesis of DMSP by this route. DMSP-producing bacteria and their dsyB and / or mmtN transcripts were present in all tested seawater samples and Tara Oceans bacterioplankton datasets, but were much more abundant in marine surface sediments. Approximately 1 × 108 g – 1 bacteria from surface marine sediments would produce DMSP, and their contribution to this process should be included in future global DMSP production models. We propose that coastal and marine sediments, which cover a large part of the Earth's surface, are environments with high levels of productivity in DMSP and DMS, and that bacteria are important producers of DMSP and DMS in these areas. environments.