Marine life in the high seas soak up an amount of carbon equivalent to 30 percent of the US’s annual emissions. This carbon-sequestering service is worth about $148 billion a year, according a new study from the Global Ocean Commission.

At the same time, increased fishing activity threatens the whole process, according to the researchers.

The high seas are the deep water, unclaimed oceans beyond each nation’s 200-mile exclusive economic zone (EEZ). As such, they make up the majority of the world’s oceans, and sit outside the local regulation of individual countries.

The high seas also happen to be hugely productive carbon sinks. Plankton are the carbon-eating plants of the seas, which then makes it way up the food chain; dissolved carbon dioxide in the world’s oceans thus gets locked up in all marine life.

When organisms die in the deep seas, pretty much everybody ends up on the bottom of the ocean, which makes for an effective, natural sequestration process. (It’s also the phenomenon driving ocean fertilization schemes.) The authors estimate that in the high seas, this amounts to taking more than 1.6 billion tonnes of CO2 out of the atmosphere and burying it in the seabed every year.

The thing is, with fisheries impacted worldwide, more governments are subsidizing fishing operations on the high seas. More fishing activity could put a dent in the ocean’s sequestration effect, co-author Rashid Sumaila of the University of British Columbia’s Fisheries Center said.

Here’s the kicker: The dollar value of all the fish caught way out there is actually negative when costs of fishing like fuel and subsidies are subtracted. A 2009 analysis of 12 nations’ bottom-trawling fleets on the high seas by Sumaila found that fleets received $152 million a year in government subsidies—some 25 percent of the value of their catch.

“Most would not be fishing the high seas without subsidies,” Sumaila told me.

Bottom trawling is a particularly destructive method of fishing, in which entire swathes of the ocean bottom are bulldozed and every living thing scooped up. While it’s long been known to be harmful to reefs and other bottom-dwelling life, recent studies suggest bottom trawling is also leading to “long-term biological desertification.”

In the new report, the authors argue that a ban on fishing in the high seas, which represent 58 percent of the world’s oceans, would be valuable just for protecting and enhancing their role as a carbon sponge, Sumaila said. But that is just one of 14 other valuable services the high seas provide humanity, according to the study.

The study was commissioned by the Global Ocean Commission, an 18-month-old organization comprised of former senior politicians and business leaders concerned about threats to the oceans. The High Seas And Us report will be officially launched at a meeting in New York City on June 24 along with the Commission’s short- and medium-term solutions.

Last May scientists writing in the journal Science called for an end to “the frontier mentality of exploitation” of the high seas, and recommended a ban on trawling to protect the carbon-removal service and halt the decline in the productivity of the oceans. The amount of wild fish caught peaked 25 years ago.

About 70 percent of fish caught inside EEZs spend some time in the high seas. If the high seas are protected from fishing, those fish are likely to grow larger and become more numerous, benefiting near-shore fisheries, Sumaila said. A number of studies of marine protected zones where fishing is banned or very limited show that these become baby-fish incubators that increase the numbers of fish outside of the protected areas.

If fishing was banned in the high seas, fisheries’ profits would soar more than 100 percent, the amount of fish caught would exceed 30 percent and ocean fish stocks would increase 150 percent, according to estimates published in a study in PLOS Biology last March.

It’s important to note that the $148 billion value of carbon removal is an estimate, Sumaila said. It is based on estimates of the future economic cost of carbon to global society, and uses a median carbon cost of $90 a ton, as derived from data provided by the US Federal Government Interagency Working Group.

“There is a lot of uncertainty, so there is a wide range of $74 billion to $222 billion,” he said.

Given the reality that fishing the high seas is a money loser, even a low carbon price could make a fishing ban valuable, not to mention the other potential benefits of regulating international fisheries.

Of course, it’s a rather contentious issue. Fishing and trawling bans have been proposed before, but some fishing nations object. “We need wide public understanding of the vital importance of the high seas to all of us,” concluded Sumaila.