The Deep Brief #25 | 17 January 2026
Your end of week ocean intelligence, built to inform, agitate, and equip you
The ocean story this week is about a treaty that finally has teeth, and a price tag we have been ignoring.
Today, the High Seas Treaty enters into force. For the first time, nearly half of our planet will be governed by a legally binding framework for conservation. It took two decades of negotiations and 60 ratifications to get here. The institutions to make it work do not yet exist.
New research reveals $2 trillion in annual ocean damages that economists have been ignoring. When ocean impacts are included in the social cost of carbon, the figure nearly doubles. A major review of climate intervention methods warns that marine geoengineering is being commercialised faster than science can assess its risks. The ocean is being positioned as a fix for problems we created, without adequate understanding of what we might break.
In other news, ocean acidification may be corroding shark teeth, potentially compromising the hunting efficiency of apex predators that have survived 400 million years. Researchers are deploying underwater robots in Antarctica to study internal tsunamis triggered by calving glaciers, a phenomenon that may rival wind-driven mixing in redistributing ocean heat but is not factored into climate models.
Three deep dives. Three quick hits. One hard truth from the sea.
Deep Dives
Today the ocean gets its constitution
After two decades of negotiations, the High Seas Treaty enters into force today.
For the first time, the high seas will be governed by a comprehensive, legally binding framework. The high seas are the parts of the ocean that belong to no country, covering more than 60% of the ocean and nearly half the planet. Until today, they were largely unregulated.
The treaty, formally called the BBNJ Agreement (Biodiversity Beyond National Jurisdiction), creates the legal tools to establish marine protected areas in international waters, require environmental assessments before activities like deep-sea mining can proceed, and ensure that benefits from marine genetic resources are shared fairly between rich and poor nations.
Palau became the first country to ratify in early 2024. Morocco and Sierra Leone triggered the 60-ratification threshold last September, starting the 120-day countdown to today. The first meeting of member countries must happen within a year to agree on how the treaty will actually work.
That is when the real work begins: setting up the offices, the scientific advisors, and the systems that will actually enforce the rules. Without them, this is just words on paper.
The High Seas Alliance put it directly: achieving 60 ratifications is not the finish line, it is the starting block.
Several sites are already being proposed for protection once the machinery is operational: the Salas y Gómez and Nazca Ridges off South America, the Lord Howe Rise and South Tasman Sea near Australia, the Sargasso Sea in the Atlantic, the Eastern Pacific Thermal Dome. These are biodiversity hotspots currently exposed to fishing pressure, pollution, and the looming prospect of deep-sea mining.
UN Secretary-General António Guterres called it historic. IUCN Director General Grethel Aguilar called it a defining moment. The pressures are mounting: shipping, overfishing, pollution, warming. The high seas regulate climate, store carbon, produce oxygen. Their degradation would be felt everywhere.
The question now is whether ambition survives contact with implementation.
Read more via High Seas Alliance
The ocean’s $2 trillion bill
Economists have been miscounting climate damage.
There is a number governments use to measure how much harm each tonne of carbon emissions causes. It is called the social cost of carbon. Policymakers use it to decide whether climate regulations are worth the cost. Corporations use it for risk planning. It shapes decisions worth trillions of dollars.
The ocean has never been included in that calculation. Until now.
A study published this week in Nature Climate Change by researchers at Scripps Institution of Oceanography is the first to put a price tag on climate damage to the ocean. The result: the social cost of carbon nearly doubles. From $51 to $97.2 per tonne of CO2. A 91% increase.
The study accounts for impacts on coral reefs, mangroves, fisheries, fish farms, and seaports. It includes obvious costs like decreased fishing revenue and damaged ports. It includes less obvious costs like reduced nutrition when fish populations decline. It includes what the researchers call existence value: the worth humans derive simply from knowing these ecosystems exist.
Global carbon dioxide emissions in 2024 were estimated at 41.6 billion tonnes, according to the Global Carbon Budget. At the new blue social cost of carbon, that implies roughly $2 trillion in ocean-related damages from a single year of emissions. Damages that have been invisible in standard climate cost estimates.
The burden falls unevenly. Island nations and small economies are hit hardest. Their dependence on seafood for nutrition means climate damage translates directly into health impacts: less calcium, fewer omega-3 fatty acids, less protein and iron in diets, leading to increased disease risk and deaths.
Lead author Bernardo Bastien-Olvera described the ocean as the big missing piece in climate impact models. The hope is that policymakers will use this framework for better decisions. The fear is that they will continue to ignore what cannot be easily priced.
Read the study in Nature Climate Change
Geoengineering the ocean: the risks we do not know
What happens to the ocean when we try to engineer the climate? A comprehensive review in Reviews of Geophysics suggests the answer is: we do not know enough to find out safely.
Twenty-six researchers from institutions across the world analysed eight climate intervention methods and their potential impacts on marine ecosystems. The findings are a comprehensive catalogue of uncertainty.
Climate interventions fall into two categories. Carbon dioxide removal tries to fix the root problem by pulling CO2 out of the atmosphere. Solar radiation modification tries to cool the planet by reflecting sunlight back into space, without reducing the CO2 that is causing the problem. Both could affect the ocean. All of them carry risks.
Adding minerals to make seawater less acidic appears relatively low-risk but remains poorly studied. Growing seaweed to capture carbon works while the seaweed is alive, but releases the carbon again when it dies and decomposes. The net benefit depends entirely on where the seaweed grows and where it ends up. Adding iron to the ocean stimulates the growth of tiny plants called phytoplankton, which absorb carbon, but this can disrupt nutrient cycles elsewhere. Spraying particles into the upper atmosphere could lower temperatures but might also change rainfall patterns, ocean currents, and marine productivity in ways we cannot yet predict.
The review makes clear that current computer models cannot capture many of these effects. They do not account for contaminants in the minerals being added, how ecosystems might reorganise around new seaweed farms, or how impacts cascade through marine food webs.
This matters because commercialisation is already underway. Marine carbon removal startups are selling carbon credits while emissions continue to rise and some countries step back from reduction pledges. The researchers argue that impact assessments are essential to identify and shut down scaling efforts that carry unacceptable risks.
Some scientists argue that geoengineering research is a dangerous distraction from cutting emissions. The review’s authors disagree. The distraction is already here. The question is whether we understand what we are doing before we do more of it.
I’ll be looking more closely at who is commercialising marine carbon removal and what accountability frameworks exist. Expect more on this in the coming weeks.
Read the paper in Reviews of Geophysics
Quick Hits
Shark teeth are dissolving
Ocean acidification may be corroding the teeth of apex predators.
Researchers at Heinrich Heine University Düsseldorf collected naturally shed teeth from blacktip reef sharks and soaked them in seawater at different acidity levels: one matching current ocean conditions (pH 8.1) and one matching projections for the year 2300 (pH 7.3). After eight weeks, teeth in the more acidic water showed visible damage: corrosion on the surface, degraded roots, and loss of the fine serrations sharks use to cut through prey.
Sharks like hammerheads, tiger sharks, and bull sharks swim with their mouths open, constantly exposing their teeth to seawater. Shark skin is also covered in tiny tooth-like scales called dermal denticles, which help them move efficiently through water. Because denticles are made of similar material to teeth, they may be similarly vulnerable to acid damage.
The researchers acknowledge caveats: results may differ in living sharks, and some species can strengthen their teeth by adding fluoride. The implications for shark survival remain unknown. What is known: sharks have been around for 400 million years. Whether they can adapt to an ocean acidifying faster than at any point in their evolutionary history is an open question.
Read more via Frontiers in Marine Science
Antarctica’s hidden tsunamis
When icebergs break off from Antarctic glaciers, they trigger underwater tsunamis that researchers suggest may rival wind in mixing the ocean and redistributing heat.
British Antarctic Survey researchers are at Rothera Research Station this week to study a phenomenon discovered by chance in 2020. Scientists aboard the research ship RRS James Clark Ross were collecting ocean data near William Glacier when the glacier front collapsed. Their instruments recorded internal tsunamis several metres high, invisible from the surface but powerful enough to churn different layers of seawater together.
This kind of mixing was previously thought to be driven mainly by wind, tides, and temperature differences at the surface. The £3.7 million POLOMINTS project, involving the University of Exeter and other institutions, will use underwater robots, drones, and machine learning to understand how these hidden waves work. The stakes are high: internal tsunamis could pull warm water up from the deep, accelerating the melting of ice sheets and raising sea levels faster than current models predict.
Read more via University of Exeter
Marine carbon removal is not ready to scale safely
Recent assessments caution that marine carbon dioxide removal approaches are not ready to scale safely. The systems needed to monitor what is actually happening and verify that carbon is being stored, not just moved around, are not yet in place.
The ocean may play a role in carbon removal in the future. Emissions cuts remain the priority. Removal without proper oversight creates new risks while offering false comfort.
Find out more via The Lab
Hard Truth from the Sea
Today marks a genuine achievement. Twenty years of negotiation. Sixty ratifications. A legal framework where there was none. The High Seas Treaty deserves recognition.
It is also a beginning, not an end.
This week we learned that economists have been underpricing ocean damage by half. We learned that climate interventions are being commercialised without adequate understanding of their risks. We learned that ocean mixing processes remain invisible to the models we rely on for predictions.
The ocean does not wait for institutions to be established. It does not wait for models to be refined. It does not wait for policymakers to factor in what they have been ignoring.
The treaty is the framework. Implementation is the test. The gap between them is where I'll be watching.
That’s the Deep Brief for this week. If you found it useful, share it with someone who needs to know what is happening below the surface.
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See you next week.
- Luke
The devil is always in the details. Fascinating factoid on the sharks teeth. Another comprehensive and compelling update. Thank you.
Great updates. It’ll be interesting to see how effectively the High Seas Treaty is enforced. There are large parts of the world where trawlers operate with impunity, and another piece of paper is not going to stop them.