Fixes to the ocean climate could make the oxygen crisis worse.
A geochemical alternative with fewer hazards
Scientists are looking to the ocean to slow down global warming. About 25% of CO2 emissions caused by humans are absorbed by the sea, which is the greatest carbon sink on Earth. Potential ways to lower atmospheric carbon and perhaps restore diminishing oxygen levels are provided by this enormous system.
However, recent studies indicate that not all remedies benefit the ocean itself. Deoxygenation is one of the ocean's most pressing issues, and some of the most talked-about marine carbon dioxide removal (mCDR) methods may make it worse.
The rate at which oceans are losing oxygen is shocking. About 2% of the oxygen in the world's oceans has been lost since the 1960s. There is more to this trend than just statistics. It manifests itself in declining marine ecosystems, increased fish mortality, and biodiversity loss.
The ocean's ability to move oxygen to deeper layers is diminished by global warming, which results in warmer water and more robust layering. However, what if this loss is exacerbated by the very strategies intended to halt warming?
Unexpected consequences of carbon removal
This subject is addressed in a recent study that was published in the journal Environmental Research Letters. The research team examined several mCDR techniques under the direction of Dr. Andreas Oschlies of the GEOMAR Helmholtz Centre for Ocean Research.
Among these were artificial upwelling, ocean fertilisation, macroalgae farming, and improving the alkalinity of the ocean. They investigated the direct and indirect impacts of these methods on ocean oxygen using fictitious worldwide models.
"What benefits the climate does not necessarily benefit the ocean," Oschlies stated. In order to compare how each approach strikes a compromise between the objective of carbon removal and its unintentional oxygen implications, his team worked with the UNESCO Global Ocean Oxygen Network (GO2NE).
The work demonstrates that significant oxygen losses can result from a variety of biotic mCDR techniques, particularly those that include sinking and biomass production.
The severe disadvantages of ocean fertilisation
Ocean fertilisation is one of the earliest mCDR techniques that has been suggested. It entails supplementing the ocean surface with nutrients, mostly iron, to promote the growth of phytoplankton.
After absorbing CO₂, these small plants sink, transferring carbon to deeper seas. However, they also use up oxygen when the phytoplankton decompose.
According to model projections, a century of constant fertilisation of the Southern Ocean would result in a worldwide oxygen depletion of roughly 3%. That is over twice as much oxygen loss as warming alone.
Oxygen levels may decrease by more than 50 micromoles in some places beneath the fertilised zones. The deoxygenation observed in high-emission climatic scenarios is mirrored or surpassed by these changes.
Simulations show that all oxygen increases due to reduced global warming are placed in the shade thanks to this carbon removal due to biomass losses.
"Our model simulations show that such an approach can lead to a reduction in dissolved oxygen. This is times higher than oxygen gain, which is expected from a reduction in global warming," Oschlies said.
Setang Solutions and Its Boundary
Macroalgae have gained popularity as a promising MCDR strategy. Algae grow rapidly, do not require fresh water, and absorb large amounts of carbon. However, what happens after growth determines its environmental impact.
When macroalgae submerge into the deep sea, they will eventually decompose as fertilized plankton. Complete remineralization of submerged macroalgae can reduce the world's marine oxygen cloud by more than 10% within a century.
The oxygen impact is strong, even if only a part of it decomposes. Projects that suggest large-scale open-ocean kelp sinking as a climate remedy should be wary of these findings.
One variation of this technique, however, does not degrade oxygen levels. Oxygen is preserved when seaweed is harvested and removed, either for use in goods or for safe storage. The removal of nutrients even lowers oxygen use elsewhere, and there is no breakdown in the water.
According to model calculations, harvesting might increase ocean oxygen levels by more than 2% worldwide. The benefit of less heat alone is 10 times smaller than this gain.
Cooler surfaces, lower damage
artificial rise is another MCDR idea. It involves pumping deep, cold, nutrient-rich water onto the surface to stimulate photosynthesis.
This helps to absorb CO2, but also increases the production of organic matter. This biomass consumes oxygen as soon as it sinks and collapses.
The simulation shows that artificial rise can reduce oxygen by about 1.5 pmol. This effect is particularly focused on tropical and subtropical zones, and is already susceptible to waste of depletion.
Some areas may be reduced by 10%. Worse, when used next to macroalgae breeding, oxygen drainage can be further increased.
The cooling effect from the upward direction provides a small benefit of oxygen solubility. However, these benefits are compensated for by biomass loss. As mentioned in this study, if upward trends are not managed carefully, they can lead to higher warming in the long run.
Daily oxygen cycles in the ocean
include the falling of land biomass, such as marine wood and plant waste. In this case, the ocean acts not as a carbon producer, but as a storage space. Depending on the biomass composition, oxygen consumption can be slower than that of marine materials.
However, when nutrients reach the surface from this disintegration, they can fertilize surface water and cause the same oxygen consumption cycle as seen during marine fertilization.
mCDR techniques also focus on Blue Carbon Ecosystems, like seagrass beds, salt marshes, and mangroves. They store CO₂ in sediments after absorbing it. The effects of oxygen in these areas are complicated. While respiration lowers oxygen at night, photosynthesis increases it during the day.
Both oxygen-rich and oxygen-poor stages of marine life may be stressed by these systems' capacity to produce strong daily oxygen cycles. Despite their limited global size, their local oxygen dynamics are worth closely observing.
A geochemical alternative with fewer hazards
Not every mCDR technique exacerbates oxygen loss. One notable feature of ocean alkalinity enhancement (OAE) is its low oxygen impact. Using this technique, seawater is treated with alkaline materials such as pulverised limestone. Without promoting the creation of biomass, it alters the chemistry of the ocean to absorb more CO₂.
Large-scale OAE may marginally raise ocean oxygen levels worldwide, according to model studies. The increase is steady but modest, roughly 0.5 Pmol.
OAE does not introduce nutrients that could promote oxygen-consuming degradation, in contrast to biotic approaches. From an oxygen perspective, this makes it one of the safer marine carbon methods for the time being.
Monitoring oxygen and removing carbon from the ocean
The study ends with a compelling suggestion. Oxygen must be measured throughout the whole mCDR project, regardless of its size, from a small-scale trial to a full deployment.
"The ocean is a complex system that is already under pressure," Oschlies said. "If we intervene in large-scale measures, no matter how good our intentions are, we need to ensure that marine environmental conditions are no longer threatened.
Oxygen is one of six important climate variables already followed for marine health. It directly connects to biological diversity, ecosystem services, and carbon storage. However, when it comes to carbon removal, it is often overlooked.
Oxygen monitors aren't just for it. In some cases, oxygen, such as macroalgae harvesting, can signal the cosystem. Otherwise, it could reveal unintended risks in endangered areas. In both cases, oxygen provides important feedback on whether our climate options will help or harm the ocean.
Carbon removal must protect marine oxygen.
Carbon Dioxide Removal is no longer an option. Even the most ambitious emissions rule out unavoidable emissions. To achieve the net-zero goal, carbon must be drawn out of the air. The ocean, with its scale and its buffering power, seems to be an obvious partner. However,
should assess the solution more than its climate impact. It needs to protect the ocean's lifespan, support biological diversity, and prevent further damage.
This study reveals that biotype MCDR strategies must be treated with caution. Without oxygen, it is an ocean-collapsing ecosystem. And climate protection solutions that empty the ocean of life are not the solution at all.
About the Creator
Keep reading
More stories from Francis Dami and writers in Earth and other communities.
By the end of the century, Antarctic atmospheric rivers are expected to triple.
Meteorologists refer to these features as atmospheric rivers. Picture a tiny, invisible firehouse that stretches thousands of miles through the sky, carrying more water than the Amazon. They originate over warm seas, move poleward, and then release their load as snow or heavy rain.
By Francis Dami7 months ago in Earth
US Balks as UK and France Pledge Troops to Postwar Ukraine
As the war in Ukraine grinds on with no clear end in sight, the debate over what comes after the fighting has taken a sharper turn. The United States has signalled reluctance about committing troops to Ukraine once the war ends, even as the United Kingdom and France openly pledge to consider deploying forces in a postwar security role. The divergence has exposed differing strategic priorities among Western allies and raised new questions about how Ukraine’s future security will be guaranteed. While all three nations remain united in their support for Kyiv during the war, the emerging split over postwar troop commitments highlights the complexity of planning for peace in a conflict that continues to reshape Europe’s security landscape. What the UK and France Are Proposing British and French leaders have increasingly spoken about the need for long-term security arrangements for Ukraine once active hostilities end. Their position reflects a growing concern that any ceasefire or peace agreement could be fragile, leaving Ukraine vulnerable to renewed aggression. The idea under discussion is not a combat deployment in an active war zone, but rather a stabilisation or reassurance force. Such troops could help train Ukrainian forces, protect critical infrastructure, and serve as a visible deterrent against future attacks. Supporters argue that a limited but credible international presence would help ensure that any peace settlement is respected. For London and Paris, this approach fits within a broader European push to take more responsibility for continental security. Both governments see Ukraine not only as a partner but as a frontline state whose stability directly affects Europe as a whole. Why Washington Is Hesitant The United States, while remaining Ukraine’s most significant military backer during the war, has taken a more cautious stance on postwar troop deployments. American officials have stressed that there are no plans to send US forces into Ukraine, even after a potential peace agreement. This hesitation is rooted in several factors. First, Washington remains wary of any move that could risk a direct confrontation with Russia. Even in a postwar scenario, the presence of US troops on Ukrainian soil could be portrayed by Moscow as a provocation, escalating tensions rather than reducing them. Second, domestic considerations play a major role. After years of overseas military engagements, there is limited appetite among the American public and political class for new long-term deployments abroad, particularly in a region where risks remain high and outcomes uncertain. Finally, US strategy has increasingly emphasised supporting allies through funding, training, and equipment rather than large-scale troop commitments. From Washington’s perspective, enabling Ukraine to defend itself may be preferable to stationing American forces on the ground. A Question of Deterrence At the heart of the debate lies a fundamental question: what will actually deter future aggression against Ukraine? The UK and France appear to believe that a physical presence, however limited, would send a powerful signal of commitment. Troops on the ground would demonstrate that Ukraine’s security is directly tied to that of major European powers, raising the cost of any future attack. The US, by contrast, seems to place greater faith in alternative mechanisms such as long-term military aid, security guarantees, and sanctions frameworks. American officials argue that deterrence does not necessarily require boots on the ground, especially if Ukraine emerges from the war better armed and more integrated with Western institutions. This difference reflects broader strategic cultures. European powers, facing the immediate proximity of the conflict, may feel a stronger need for visible reassurance measures, while the US assesses risks from a more global perspective. Implications for NATO Unity Although Ukraine is not a NATO member, the discussion has clear implications for the alliance. Any deployment of UK or French troops would be closely scrutinised for what it means for NATO’s role and credibility. NATO operates on consensus, and the absence of US support for a postwar troop presence could complicate coordination. Even if London and Paris act independently or as part of a smaller coalition, questions would remain about command structures, rules of engagement, and the political backing required for such a mission. At the same time, the situation underscores a broader shift within NATO, with European members increasingly expected to shoulder more responsibility. If the UK and France proceed with their plans, it could mark a significant step toward a more autonomous European security posture. Ukraine’s Perspective For Kyiv, the debate is both encouraging and frustrating. On one hand, the willingness of major European powers to consider troop deployments signals long-term commitment and recognition of Ukraine’s security concerns. On the other hand, uncertainty from the US—Ukraine’s most powerful ally—adds another layer of unpredictability. Ukrainian leaders have consistently argued that security guarantees must be concrete, not symbolic. From their perspective, any postwar arrangement must ensure that Russia cannot simply regroup and strike again. Whether this is achieved through foreign troops, binding treaties, or accelerated integration with Western institutions remains an open question. What is clear is that Ukraine wants assurances that go beyond promises and declarations. The Risk of Mixed Signals One potential danger of the current divergence is the message it sends to Moscow. Differing positions among Western allies could be interpreted as hesitation or lack of unity, potentially weakening deterrence rather than strengthening it. At the same time, open debate is not necessarily a sign of weakness. Allies often disagree on tactics while remaining aligned on broader goals. The challenge will be ensuring that these differences do not undermine the core objective of securing a stable and sovereign Ukraine. Diplomats on both sides of the Atlantic are likely to continue working behind the scenes to narrow the gap, even if public statements suggest a clear divide. Looking Ahead The question of postwar Ukraine remains largely theoretical while fighting continues. Yet the discussion itself reveals how seriously Western governments are taking the long-term consequences of the conflict. The UK and France’s willingness to pledge troops reflects a belief that peace must be actively protected. The US reluctance highlights concerns about escalation, sustainability, and domestic support. Reconciling these approaches will be one of the most important diplomatic challenges once the guns eventually fall silent. For now, the disagreement does not signal a breakdown in alliance unity, but it does expose the difficult choices ahead. As the war continues, planning for peace is proving almost as complex—and politically sensitive—as managing the conflict itself.
By Muhammad Hassan6 days ago in Earth
US Lawmakers Arrive in Copenhagen to Counter Trump’s Greenland Threats
In a high-stakes diplomatic maneuver, a delegation of U.S. lawmakers recently arrived in Copenhagen to discuss Greenland’s future, aiming to counteract the aggressive rhetoric and territorial ambitions expressed by former President Donald Trump. The visit comes amid rising concerns over Greenland’s strategic importance in the Arctic and the implications of any unilateral moves by the United States. For Denmark, Greenland’s autonomous territory, the presence of U.S. lawmakers underscores both Washington’s interest in Arctic security and the need to maintain strong transatlantic ties. For the United States, the visit signals a delicate recalibration of policy following Trump’s controversial proposals regarding Greenland, including his infamous attempt to buy the island outright during his presidency. Why Greenland Matters Geopolitically Greenland is more than a frozen expanse of ice; it is a geopolitical prize. Strategically located between North America and Europe, Greenland is key to: Arctic shipping routes that are becoming increasingly navigable due to melting ice Natural resources, including rare earth minerals, oil, and gas reserves Military and surveillance installations, notably the Thule Air Base, which is critical to U.S. missile warning systems and space surveillance The Arctic region is warming faster than any other part of the planet, making Greenland both a resource hub and a potential flashpoint for international competition. Trump’s proposals had alarmed Denmark and other NATO allies, raising questions about the United States’ long-term commitment to respecting international norms and allied sovereignty. The Lawmakers’ Mission The delegation, composed of senators and representatives from both political parties, is tasked with: Reassuring Denmark that the U.S. government respects Greenland’s autonomy Discussing security cooperation, particularly regarding Arctic defense and NATO commitments Exploring economic partnerships that benefit Greenland while maintaining regional stability Officials emphasize that this visit is not about reversing Trump’s statements retroactively, but about ensuring that future U.S. policy reflects diplomatic consensus rather than unilateral ambition. Denmark’s Response Denmark has maintained a firm stance on Greenland’s sovereignty, consistently stating that the island is not for sale. Danish leaders have welcomed the U.S. delegation as a positive step toward strengthening trust and clarifying intentions. Copenhagen also hopes to use the opportunity to reinforce cooperative approaches to Arctic security, particularly in light of growing Russian and Chinese interest in the region. For Denmark, maintaining strong relations with the United States — while safeguarding Greenland’s autonomy — is a balancing act that requires careful diplomacy. Greenland’s Perspective Greenlanders themselves are increasingly vocal in the debate over their future. Many support greater economic independence and political autonomy, and local leaders insist that Greenlanders should have the final say over any decisions affecting their land and resources. The U.S. delegation’s visit highlights the need to consult Greenlandic authorities directly, rather than negotiating solely with Denmark. This approach is seen as a step toward more inclusive, respectful diplomacy, which acknowledges Greenland’s status as more than just a strategic asset. The Role of NATO and Transatlantic Relations Trump’s proposals regarding Greenland strained transatlantic relations, raising concerns among NATO members about the reliability of U.S. commitments. The arrival of bipartisan lawmakers in Copenhagen aims to reaffirm NATO solidarity and demonstrate that U.S. policy is consistent with alliance obligations. By engaging Denmark directly, Congress seeks to prevent miscommunication and maintain stability in a region that is increasingly vital for global security. Analysts note that Greenland’s location provides the United States with a critical vantage point for Arctic monitoring and missile defense, making cooperative relations essential. Global Implications The Greenland issue has broader consequences for international geopolitics and Arctic governance. Key points include: Resource security: Greenland’s rare earth minerals are essential for electronics, renewable energy, and defense technologies, making control and access highly strategic. Climate change and navigation: Melting ice is opening new shipping lanes, which could shift global trade patterns and increase competition for influence. Power dynamics in the Arctic: Russia and China have also shown growing interest in the Arctic, prompting the United States and Europe to strengthen alliances and prevent unilateral exploitation. The lawmakers’ visit signals to the international community that the U.S. is committed to diplomatic solutions rather than transactional or coercive strategies. Challenges Ahead Despite the visit’s diplomatic intent, challenges remain: Political polarization in the U.S.: Future administrations may have different approaches to Greenland, raising uncertainty about long-term commitments. Geopolitical competition: Russia and China continue to advance their presence in the Arctic, complicating cooperative efforts. Local autonomy: Greenlandic voices must be prioritized, or any policy may face resistance at the local level. Successfully navigating these challenges will require transparent dialogue, careful planning, and sustained international cooperation. The Path Forward The visit of U.S. lawmakers to Copenhagen is a cautionary and corrective measure. It signals that while Greenland is strategically important, it is not a bargaining chip. Future cooperation will likely focus on: Strengthening Arctic security frameworks Promoting economic development for Greenlanders Maintaining stability in U.S.-European relations Ensuring that Greenlandic voices remain central to decision-making This proactive approach reflects a broader understanding that diplomacy, not unilateral action, is essential in regions of high strategic value. Final Thoughts Greenland has moved from the margins of global attention to the forefront of geopolitical strategy and climate concern. The arrival of U.S. lawmakers in Copenhagen underscores the importance of measured, inclusive diplomacy in the Arctic, contrasting sharply with the impulsive rhetoric that characterized Trump’s Greenland proposals. As nations navigate the Arctic’s emerging opportunities and challenges, Greenland’s sovereignty and the voices of its people will remain central to regional stability, global security, and international cooperation. The lawmakers’ visit represents a step toward rebuilding trust, reinforcing alliances, and charting a sustainable path forward for one of the planet’s most strategically vital territories.
By Muhammad Hassanabout 21 hours ago in Earth
Comments (1)
The ocean's role in absorbing CO2 is crucial, but some mCDR methods might worsen deoxygenation. It's a complex issue, and we need to find solutions that balance carbon removal and ocean health. We've seen how warming affects oxygen movement. These new findings show we gotta be careful with mCDR techniques to avoid making the ocean's oxygen problem even worse.