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Anoxic ocean basins are among the best candidates for deep-sea carbon sequestration, scientists say

A review of the potential consequences of sequestered organic carbon in oxic and anoxic regions of the seafloor. Red arrows indicate potential pathways for different biomass transformations in the atmosphere: respiration into dissolved inorganic carbon (DIC), fermentation into DIC and methane (CH).4), or breakdown into dissolved organic matter (DOM). Credit: AGU Advances (2024). DOI: 10.1029/2023AV000950

Anoxic ocean basins may be among the most viable locations for large-scale carbon sequestration in the deep ocean, while minimizing negative impacts on marine life. UC Santa Barbara researchers say in a paper published in Journal AGU Advances.

They suggest that as we look for ways to actively reduce carbon levels in the atmosphere, sending plant biomass to these arid, oxygen-free zones on the seafloor becomes a viable option.

“The big picture here is that all the best models we have say we’re going to have to do some form of net negative CO.2 Remove to kill ” said geochemist, geobiologist and lead author Morgan Raven, referring to the limiting objective. 1.5°C above pre-industrial levels established by the International Panel on Climate Change.

There are different ways to store carbon. One method that shows promise is to sink carbon to the seafloor in the form of plant biomass, so plants cannot emit CO.2 And methane falls into the air. Ideally, the carbon would be locked away for hundreds, if not thousands, of years.

While not a new idea, it is one that is still surrounded by a lot of uncertainty. How does the introduction of loads of plant material affect the chemistry and ecology of the areas where it will be dumped? How can we ensure that decomposition products don’t end up in sensitive habitats, or that the carbon doesn’t make its way back up the water column after being released to the surface? These are some of the unintended consequences that could further damage already fragile marine ecosystems, or prevent the reduction of carbon sequestration targets.

“And so a lot of this project came out of the original question, what is the least bad version of this idea that we can imagine?” said Raven, assistant professor of earth science.

Anoxic ocean basins emerged as the most likely candidate. Not only are they deep, but they are largely isolated from their geologically important, oxygen-providing currents. They cannot support animal life, and are populated primarily by microbes and some very specialized fungi that have a different metabolism than organisms in oxygen-rich environments. Importantly, these conditions are ideal for the preservation of plant matter — primarily pickles —.

Not all anoxic ocean basins are the same. The researchers chose three to test—basins with different characteristics—to determine where the best biomass storage sites could be found: the Black Sea in eastern Europe, the Cariaco Basin near Venezuela, and the Gulf of Mexico. Orca Basin in Mexico (USA).

“What’s great about the Black Sea is that it’s so confined that it’s pretty much isolated from the rest of the ocean,” Raven said. “And so it’s been slowly becoming more and more non-toxic, especially recently, since humans have put a bunch of fertilizer into it over the last century.”

They also examined the Cariaco Basin, which has similar chemical properties to Black, but has a faster water turnover. The third site was the “wildly strange” Orca Basin, a hypersaline mini-basin located on the continental slope. The salt concentration in the basin is so high that it creates a dramatic difference in density from the overlying waters.

“The interface where it goes from normal seawater to saltwater, if you try to get a submarine there, you’re going to bounce off that layer,” Raven said. Once it passes through the interface of the two densities, the material can be hypothetically trapped in a hypersaline layer.

Ultimately, for its size and isolation, the Black Sea basin emerged as the best option of the three. With a depth of 2,300 m (7,500 ft) and an area of ​​322,367 sq km (124,467 sq mi), this anoxic basin has the potential to contain biomass on a scale relevant to the global climate.

“The Black Sea is really where it’s going to make a dent in the climate,” Raven said. “And its deep water is so isolated from the rest of the ocean.”

The concept of sinking plant biomass has attracted the attention of private investment, which has increased funding levels in recent years for projects exploring the potential of deep-sea carbon sequestration. Several organizations have stepped up to the challenge of submerging plant material. Collecting biomass from a variety of sources including cultivated or fast-growing seaweeds such as giant kelp or sargassum, or terrestrial plants such as agricultural or forestry waste.

Each strategy has advantages and potential pitfalls that require further investigation, said Raven, who serves as a science consultant to SeaFields (sea plant biomass) and Carboniferous (terrestrial) companies. ). This study is a step in that direction.

“Given the situation we’re in and the commitments we’ve made to the Paris Agreement and California’s climate goals,” he said, “every year Seizure strategies become more important.”

More information:
MR Raven et al., Biomass storage in anoxic marine basins: preliminary estimates of geochemical effects and CO2 sequestration potential, AGU Advances (2024). DOI: 10.1029/2023AV000950

Reference: Anoxic marine basins among best candidates for deep-sea carbon sequestration, scientists say (2024, February 19) February 20, 2024 https://phys.org/news/2024-02-anoxic-marine Retrieved from -basins-candidates -deep.html

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