A startup named Carboniferous is getting ready to dump 20 burlap sacks of sugarcane residue into one of the world’s most oxygen-starved areas of the Gulf of Mexico, about 300 kilometers off the coast of Louisiana. For a plan with significant planetary aspirations, it sounds almost comically modest. However, the U.S. Environmental Protection Agency discreetly granted a research permit for precisely this experiment in March. Despite its modest scope, this decision represents something truly uncommon: federal approval for ocean biomass sinking, a carbon removal method that has been on the periphery of climate science for years without much institutional support.
The timing is not coincidental. There have been setbacks in the carbon removal sector. Microsoft recently informed partners that it is halting contracted carbon removal purchases, which together account for about 80% of all such purchases to date. That is a significant setback for a sector that was already having trouble demonstrating its commercial viability. Therefore, it felt less like a policy statement and more like a lifeline thrown to an industry that was holding its breath when the EPA quietly moved in the opposite direction and approved a permit under the Marine Protection, Research, and Sanctuaries Act.
Fundamentally, the idea behind Carboniferous’s work is a sort of geological shortcut. Throughout their lives, land plants absorb carbon dioxide; however, when vegetation burns, dies, or decomposes, the majority of that carbon is released back into the atmosphere in a matter of months or years. The plan is to stop that process by gathering the plant residue, submerging it in deep, anoxic ocean environments where there is no oxygen and the temperature is close to freezing, and letting the darkness take care of the rest. Decomposition slows to a crawl under those circumstances. Instead of returning to the atmosphere within a season, carbon may remain buried for centuries or more. The Orca Basin is regarded as a promising candidate due to its exceptionally high salinity and almost complete lack of oxygen.
There is a good scientific reason to investigate this. In comparison to terrestrial forests, the world’s oceans already store about 50 times more carbon than the entire atmosphere. Furthermore, if global temperature targets are to be met, carbon dioxide removal is practically inevitable, according to the IPCC, which is hardly prone to alarmism. Pursuing ocean-based carbon storage was never really the question. The issue is whether it is ethical to sink sugarcane bales into the ocean floor.
Under the correct circumstances, the answer might be yes. There is also a chance that it isn’t, which is where the scientific unease starts. According to studies, ocean biomass storage has the potential to permanently store between 0.1 and 1 gigatons of carbon dioxide per year. When you compare that range to estimates that suggest humanity may need to remove 7 to 9 gigatons annually by the middle of the century, possibly increasing to 20 gigatons by the year 2100, it becomes clear how important that range is. The math is difficult to close.
There are also more profound concerns. Anaerobic bacteria that produce methane, a greenhouse gas far more potent than carbon dioxide over shorter timescales, could be stimulated by flooding deep-ocean environments with organic matter. Stratified ocean layers, according to supporters, would keep any methane from rising to the surface. Perhaps. However, there may be a lot of work involved in that sentence.
A crucial link in the ocean’s food chain, the mesopelagic zone—that twilight band of ocean between about 200 and 1,000 meters deep—is a remarkably active area that may be home to a million undiscovered species. Before sinking biomass reaches the floor, it passes through this zone, releasing organic matter and particulates in the process. It’s really unclear how that affects oxygen levels, microbial activity, and the tiny organisms that commercial fisheries ultimately rely on. A sudden influx of biomass may cause the seafloor communities themselves—bacteria, fungi, and organisms that science has hardly cataloged—to react in ways that are challenging to simulate and more difficult to undo.
Carboniferous is not the only company following this course. With the goal of producing a million tons of biomass residue per year by 2030, Israel’s Rewind is burying agricultural waste in anoxic areas of the Mediterranean and Black Sea. BlueGreen Water Technologies uses hydrogen peroxide to sink harmful algal blooms, which is an even more bizarre approach. The goals are high, the data is still sparse, and the experimentation is worldwide.
Observing all of this, it seems like the climate crisis is forcing scientists and policymakers to make choices that would have seemed unthinkable ten years ago. Just 20 burlap sacks are covered by the EPA permit for Carboniferous; this is a research study rather than a deployment. However, the path it suggests merits greater public attention than it is currently receiving. The oceans are not voids. Before the scale of the answer becomes difficult to reverse, it is worthwhile to carefully consider what happens when we begin to treat them as one.
