When we picture the effects of melting glaciers, many of us think of rising seas and retreating ice streams. But along Greenland’s coastline, a quieter transformation is underway, one that is affecting how the ocean breathes and how it reacts to and buffers itself against change.

In Young Sound, a fjord carved into Greenland’s remote northeastern coast, decades of monitoring have revealed that glacial meltwater does not simply dilute the salt in seawater. As fresh water enters the ocean, it weakens the ocean’s natural chemical resistance to swings in acidity. This so-called buffering capacity keeps seawater pH in balance. The loss of buffering due to freshwater runoff leaves these coastal waters unusually sensitive to even small biological and environmental shifts.

Atmospheric warming is accelerating fastest in the Arctic, and with it come longer glacial melt seasons and increased freshwater runoff. The result is a coastal ocean that is both a frontline witness to climate change and a laboratory for understanding how the chemistry of the seas can change in unexpected ways.

The Ocean’s Chemical Safety Net

Globally, the ocean absorbs about a quarter of carbon dioxide (CO₂) emissions each year. That uptake helps to slow climate change, but at a cost. The more CO₂ that water absorbs, the more acidic it becomes. Thankfully, seawater chemistry is naturally buffered by dissolved ions—particularly carbonate, bicarbonate, and hydroxide—that act as chemical shock absorbers. These negatively charged ions, collectively called alkalinity, bind to the positive hydrogen ions released when carbonic acid forms, keeping the ocean’s pH relatively stable compared with the more variable conditions in freshwater rivers and lakes.

The polar oceans play a special role in this balance and in the global carbon cycle because cold waters at high latitudes take up carbon from the atmosphere faster than warm tropical waters. Yet these regions are also changing the most rapidly.

When Meltwater Meets the Sea

For 20 years, our team at Aarhus University has measured salinity, temperature, and carbon chemistry in Young Sound. Each August, we make the 2-day journey to northeast Greenland, where we spend the month sailing down the 90-kilometer-long fjord to capture these valuable measurements (Figure 1).

During the time we have monitored this ecosystem, the melt season has lengthened, with sea ice–free conditions now lasting 8 days longer than 20 years ago. Glaciers feeding the fjord are also thinning and retreating, discharging about 5.5 million cubic meters more water into the fjord each year. These changes have freshened the coastal ocean and subtly, but significantly, altered its chemistry.

Fjords like these have long been known as major CO₂ sinks. Surface waters near glaciers often have very low CO₂ concentrations, creating a disequilibrium between CO₂ levels in the surface ocean and the atmosphere that draws carbon out of the air. But how or why these glacial ecosystems act as carbon sinks and what mechanisms are at play haven’t been thoroughly described. We have also been deeply curious about what else happens when fresh water enters the sea. What are the hidden consequences of this change?

To find out, we paired our long-term field observations with controlled lab experiments in which we mixed glacial meltwater with seawater. Controlled experiments allow us to dig into the nuances of chemical changes that are impossible to measure in the field. We also ran mixing models that allowed us to estimate how the chemistry of those mixed waters responds to small shifts in biological activity or mineral interactions.

The results were striking. When meltwater mixes with seawater, it not only reduces salinity but also dilutes alkalinity, the measure of how well water can neutralize acid and buffer against pH change. This weakening of buffering capacity means that even small changes in photosynthesis or respiration can drive much larger swings in CO₂ uptake and acidity than they would in more saline waters.

We found that in the freshened waters of Young Sound, these processes have 2–3 times the influence on carbon uptake that they do farther out at sea. In effect, meltwater primes the coastal ocean to overreact, amplifying any ecosystem changes that might occur.

Measurements from around Greenland show that this is not just a theoretical risk. Surface waters are measurably more acidic where meltwater inputs are high. The biological consequences of this trend are still uncertain, but species living at the edge of their tolerance, such as shell-forming plankton and Arctic cod larvae, could face growing stress as the chemistry of their habitat fluctuates more widely.

A Fragile Balance in the Freshening Arctic

Our study adds nuance to conventional perceptions of carbon cycling in fjords, long seen as places where atmospheric CO₂ is drawn down. The findings confirm that fjords absorb carbon as a result of biological activity and glacial input but indicate that they do so in a fragile, easily tipped state. Slight shifts in the processes that pull CO₂ out of the air could tip the scales in either direction: toward even more uptake and the accompanying acidification or toward a release of CO₂ to the atmosphere.

This chemical sensitivity explains why Arctic fjords can show such strong seasonal and spatial swings in carbon chemistry and why predicting their long-term role in the carbon cycle is difficult. As glaciers retreat and meltwater inputs grow, those sensitivities are likely to intensify.

At first glance, changes in how seawater in the narrow, remote fjords of Greenland reacts to glacial melt might sound like a local concern. But the chemical processes at play have global resonance.

The Arctic Ocean as a whole is freshening, driven by accelerating ice melt as well as by increasing river discharge and changing weather bringing more precipitation to the region. Although river water, which arrives from the six great Arctic rivers of North America and Eurasia, is more alkaline than glacial melt, its alkalinity is only about half that of seawater. In other words, river runoff also increases the ocean’s chemical sensitivity. Fresh water also delivers organic matter from permafrost, fine sediments from glaciers, and tannin-rich runoff from tundra soils, each of which can influence carbon cycling and further compound changes already underway.

Similar patterns of increased rainfall and runoff reducing surface salinity are emerging around the Antarctic Peninsula, the Gulf of Alaska, and the North Atlantic. Almost everywhere that fresh water enters the ocean, it lowers alkalinity and limits the ocean’s ability to buffer change.

A Window into Climate Intervention

Our results also carry lessons for researchers and companies contemplating ocean chemistry interventions as ways to remove CO₂ from the atmosphere. One proposed approach, ocean alkalinity enhancement, involves adding crushed minerals such as lime, olivine, and basalt to seawater to both counteract acidification and increase the ocean’s capacity to take up CO₂.

Glacial systems already perform a natural version of this experiment by grinding rock into fine sediment and discharging it into the ocean. Minerals in this sediment react with seawater and shape its carbon chemistry.

Our study suggests that such reactions are especially potent in freshwater-influenced coastal regions, where reduced buffering capacity may amplify chemical responses not only from natural biological processes but also from potential human attempts to alter seawater chemistry. Thus, understanding the balance between carbon uptake and chemical vulnerability will be essential before any large-scale interventions are attempted.

Consequences Locally and Globally

Coastal communities from Greenland to Alaska to northern Eurasia depend on Arctic waters as part of their cultural identity and, by way of fisheries and tourism, for their economic and food security. As chemical buffering capacity declines, coastal ecosystems may become more susceptible to acidification and other environmental stresses. Small changes in temperature, ecosystem metabolism, or nutrient inputs could then have outsized effects on the marine life that supports these communities.

At the same time, changing conditions in coastal Arctic ocean regions complicate scientific modeling of carbon cycling and climate feedbacks, which typically relies on averaged estimates of the ocean’s chemical reactivity. With meltwater making the coastal ocean more reactive, these seas may absorb or release CO₂ more variably than how global predictions would suggest. In addition to the real effects on local ecosystems, seawater chemical variability could also affect the accuracy of modeled global carbon budgets, which we use to inform future climate projections and guide international policy goals.

As coastal glaciers retreat and meltwater rivers carve new paths to the sea, they are doing more than raising sea level and reshaping coastlines. They are rewiring ocean chemistry, leaving it fresher and more easily disturbed.

The chemical sensitivity we see in Greenland’s fjords today may be a preview of what is to come in many coastal regions. If so, then we must be concerned with not only how much CO₂ the ocean can absorb but also how stably it can hold that CO₂ in a rapidly changing world.

Author Information

Henry C. Henson (hch@ecos.au.dk), Aarhus University, Denmark

Citation: Henson, H. C. (2026), Melting glaciers make the coastal ocean more sensitive, Eos, 107, https://doi.org/10.1029/2026EO260116. Published on 16 April 2026.

Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

China said on Monday that strengthening its military is beneficial to world peace, slamming a think tank report that warned the threat of a direct strike by Beijing on Australia was increasing.

A Lowy Institute report said on Sunday that China is capable of a direct missile strike on Australia and the threat of such a move is growing as Beijing amasses long-range and hypersonic weapons and builds islands in the South China Sea.

China’s capacity to strike Australia would grow over the next decade as “the DF-27 intermediate-range ballistic missile, and potentially a conventionally armed intercontinental ballistic missile, grow in service numbers”, the Sydney-based group said.

China condemned the report’s “serious strategic misjudgement” on Monday, saying it was committed to “a path of peaceful development”.

“The growth of China’s military strength represents an increase in the forces for world peace,” foreign ministry spokesperson Lin Jian told reporters at a news briefing.

“China’s development of military strength is intended to safeguard national sovereignty, security and development interests and is not directed at any specific country,” he added.

The report found the main threat to Australia was from Chinese missiles fired from ships, submarines and a new intermediate-range ballistic missile that could reach the island continent from China.

The DF-27 missile has a range of 5,000 to 8,000 kilometres (3,100 to 5,000 miles), the US military said in December.

The report said it was assessing Beijing’s capability and not its intentions.

Lin urged the “relevant institutions” on Monday to “stop hyping up the so-called China threat” and to view the country’s development in an objective, fair and rational manner.

Australia reshaped its military strategy three years ago in response to China’s rapid navy build-up and rising friction between Beijing and Washington, focusing on deterring an adversary from its northern approaches.

Jan Erik Waider has a knack for capturing shorelines, volcanic eruptions, and glaciers at their most mesmerizing—shrouded in mist, glowing in the darkness, or illuminated by pale northern light. His atmospheric photographs of icy seas and rugged landscapes from Iceland to the Antarctic, focus on dramatic forms and cast remote places into a dreamy ethereality.

Most recently, Waider captured a striking phenomenon in the Baltic Sea, just off the coast of northern Germany. Fresh ice formed a thin layer on the rolling surface, creating faceted, polygon-like shapes that moved gently and rhythmically with the waves without breaking apart.

Waider’s aerial drone perspective creates an otherworldly, almost totally abstract effect. At first glance, it appears as though it could be a minimalist animation highlighting the interactions between water, light, and motion. “Soft evening light, fine crack lines, and shifting tones from warm gold to deep green turned this fleeting moment into a study of structure, depth, and calm,” Waider says.

See more on Waider’s YouTube channel, Instagram, and Behance.

Do stories and artists like this matter to you? Become a Colossal Member today and support independent arts publishing for as little as $7 per month. The article Meditate to the Undulations of Baltic Sea Ice in Jan Erik Waider’s Hypnotic Videos appeared first on Colossal.

Spikes, fans, florets, waves, and other characteristics of marine creatures continue to shape the work of Lisa Stevens. The Bristol-based artist’s vibrant practice revolves around ceramic sculptures inspired by sea urchins, coral, nudibranchs, and other underwater organisms. Each piece is unique, with numerous colorful glazes and textures, and they often take on a fantastical quality, incorporating hybrid features that conjure associations with celestial objects, anatomy, and other facets of nature.

Find more on Stevens’ Instagram, plus watch clay sculpting tutorials on YouTube.

Do stories and artists like this matter to you? Become a Colossal Member today and support independent arts publishing for as little as $7 per month. The article Vibrant Sea Creatures Spring to Life in Lisa Stevens’ Textured Sculptures appeared first on Colossal.

The Philippines defence minister was defiant on Friday after Beijing sanctioned him for what it termed “irresponsible remarks” as the two nations grapple over the disputed South China Sea.

Gilberto Teodoro as well as his spouse and child will be banned from entering China’s mainland, Hong Kong and Macau, an unnamed foreign ministry spokesperson said in an online statement on Thursday.

It added that “organisations and individuals in China” will not be allowed to “engage in any transaction, cooperation or other activities with him and his spouse and child”.

The two countries have in recent years regularly dealt with flare-ups in tensions over the disputed South China Sea.

Beijing claims the strategic waterway nearly in its entirety, despite an international ruling that said its assertions are baseless.

In a statement early Friday, Teodoro said he had been sanctioned for “speaking truth”.

“Their own countrymen and the others under their control suffer far worse,” he said. “I will just keep doing my duty and uphold our nation in the face of the wickedness they are committing here and even in our seas.”

Manila reacted to the sanctions late Thursday by saying that “the Philippines views it as an unfriendly act that further complicates the bilateral relations”.

China regularly deploys navy and coast guard vessels to bar the Philippines from important reefs and islands in the area.

The Chinese statement said Teodoro’s rhetoric “undermines China’s legitimate interests and sabotages China-Philippines relations”, without specifying to which remarks it referred.

At a summit in Singapore last month, Teodoro criticised Beijing’s activities in the disputed waters, saying Manila “will not sacrifice our territorial integrity and sovereignty”.

Asked last week about Teodoro’s remarks at the summit, Beijing’s foreign ministry spokeswoman Mao Ning said that he “is known to vilify China”.

“All he cares is selfish personal gains to the point that he would perform political theatrics even when people’s well-being is at stake,” Mao said.

Taiwan’s coast guard said Sunday it has deployed vessels “to respond appropriately” to a Chinese operation in waters east of the island democracy, which it said “violates international law”.

It comes after Chinese state media reported Saturday that the “law enforcement operation” was in response to talks between Japan and the Philippines to draw a boundary in the affected waters.

China, which asserts Taiwan is part of its territory, called the talks “illegal” and has claimed exclusive control over the waters.

The Chinese ships have been monitored “throughout the entire process” and Taiwan “has deployed the necessary vessels to respond appropriately,” the Taiwanese coast guard said in a statement.

Taiwan said it had detected four Chinese government vessels departing from Xiamen port which had sailed outside Taiwanese restricted waters southwest of the island.

Taiwan’s coast guard dispatched more than five vessels “to assist with surveillance”.

The Chinese vessels were expected to arrive “in the relevant waters” on Sunday, the statement said, adding that “China does not enjoy any sovereign rights in the waters east of Taiwan”.

Tokyo and Manila said last month they would start formal talks “to delimit the maritime boundary” of an economic zone and continental shelf between them, angering Beijing.

On Saturday, Beijing’s transport ministry organised maritime police from coastal provinces Fujian and Guangdong to “conduct a special maritime traffic law enforcement operation in waters east of Taiwan Island”, state news agency Xinhua said.

The report did not give details on the operation, including how long it lasted or whether it was still ongoing, and it did not say whether maritime police dispatched ships to the area.

The operation was “a necessary action taken against Japan and the Philippines’ unilateral announcement they would start ‘negotiations on delimiting a maritime boundary'” near Taiwan, Xinhua added.

Taiwan said Wednesday it should be consulted on the Japan-Philippines talks.

Manila and Tokyo’s shared grievances over Chinese maritime territorial claims have seen them draw increasingly close in recent years.

Japan and China are in territorial and economic disputes in the East China Sea, where coast guard ships from both sides routinely stage tense standoffs.

Beijing has meanwhile deployed navy and coast guard vessels in the South China Sea, in a bid to bar the Philippines from strategically important reefs and islands, leading to a string of confrontations.

Taiwan’s coast guard said Saturday that a Chinese survey vessel had joined a coast guard ship in waters around Pratas Island in the northern part of the South China Sea.

The Taiwanese coast guard said it was “the first observed instance of Chinese coast guard and survey vessels acting in coordination to provoke Taiwan”.

Taiwan controls Pratas but Beijing also claims the island, along with most of the strategic waterway.

SANAA, June 9 — Yemen’s Iran-aligned Houthis said yesterday that they would ban ships linked to Israel from the Red Sea after Israel renewed its military attacks on Iran, adding to concerns about global ‌shipping and energy flows.

This is why it matters and what it means for the Iran war and the global energy crisis:

How big is the risk to global energy markets?

Iran’s closure of the Strait of Hormuz since Israel and the United States attacked it on February 28 has disrupted most oil and other energy exports from the Gulf, raising prices and causing a major energy shock.

Saudi ‌Arabia has responded by diverting more than 70 per cent of its normal daily crude exports to the Red Sea port of Yanbu.

That has been a lifeline for the energy market, helping to keep down global oil prices.

Any sustained Houthi disruption to Red Sea shipping including potential attacks on shipping or ports could be a big problem.

When the Houthis launched attacks on Red Sea shipping in November 2023, Gulf oil exports were flowing freely, meaning cargoes were diverted to avoid the Red Sea, but not halted. This time, they are being loaded there.

A Houthi source told Reuters preventing Israeli ships from transiting the Red Sea was “a first step” but that if escalation continued, the group would stop any ships heading to Israel as well as other measures.

When the group attacked shipping during the Gaza war its stated target of Israel-linked vessels included any vessel belonging to any company that used Israeli ports and its attacks on those ships dissuaded most companies from using the route.

Who are the Houthis?

The Houthis emerged as a military, political and religious movement in north Yemen in the 1990s, fighting guerrilla wars against the government in Sanaa.

They adhere to the Zaydi sect of Shi’a Islam, and after the 2011 Arab Spring they strengthened ties with ‌Iran and seized on instability to capture the capital in 2014, derailing a Gulf-backed political transition plan.

Saudi Arabia and Arab allies launched a military intervention months later to restore the ⁠ousted government and dislodge a group it saw as a proxy for Iran, Riyadh’s arch regional ⁠rival.

As Yemen’s civil war ground to a stalemate, the Houthis attacked oil installations and other infrastructure in Saudi Arabia and the ⁠United Arab Emirates with missiles and drones.

However, a ⁠2022 truce between Yemen’s warring sides has largely ⁠held.

Are the Houthis an Iranian proxy?

Iran champions the Houthis as part of its regional “Axis of Resistance”, which includes Lebanon’s Hezbollah and Iraqi Shi’ite militias, though its ties with the Yemeni movement are less clear than with those other groups.

The Houthis do not recognise Iran’s supreme leader as their ultimate religious authority in the same way Hezbollah and the Iraqi groups do. Its ⁠motivations are mainly domestic, though it is ideologically aligned with Iran.

The US says Iran has armed, funded and trained the Houthis with help from Hezbollah. The Houthis deny being an Iranian proxy and say they develop their own weapons.

Houthi military helicopter flies over the Galaxy Leader cargo ship in the Red Sea in this photo released November 20, 2023. — Houthi Military Media handout pic via Reuters

What happened when the Houthis attacked Red Sea ships before?

After the October 7, 2023, Hamas attack on Israel, and Israel’s devastating campaign in Gaza, the Houthis began firing at Israel and on international shipping in the Red Sea, saying they were doing so in support of Palestinians.

The Houthi attacks in the Red Sea severely disrupted global shipping, prompting Maersk, Hapag-Lloyd and other major companies to divert around Africa — a far longer, more expensive route.

A US-led mission to restore free navigation in ⁠the Red Sea involved repeated strikes on Houthi targets and a defensive campaign that shot down hundreds of drones and missiles.

But some Houthi attacks continued until last summer, only ending completely with the Gaza ceasefire in October.

What have they done during the latest Iran war?

While Hezbollah and the Iraqi groups joined ⁠the war early with rocket and drone fire after the first US and Israeli strikes on Iran, the Houthis have been comparatively quiet.

The group’s leader Abdul Malik al-Houthi said on ⁠March 5: “Our fingers are ⁠on the trigger at any moment should developments warrant it”.

Iranian military commanders have repeatedly warned the Houthis could join the war, with Revolutionary Guards Quds Force commander Esmaeil Qaani saying on June 1 they could choke off the Red Sea.

But before this week, the group’s only involvement was a few missile and drone attacks on Israel in late March and early April.

Why the Houthis have been relatively quiet so ‌far is not entirely clear.

They and Iran may have wanted to use the threat of another major energy route closure to warn Israel and the United States off further escalations.

The Houthis may also feel less committed to Iran’s security than do Tehran’s other regional allies.

And the group may not want to antagonise its powerful, wealthy neighbour Saudi Arabia and risk reigniting the conflict at home. — Reuters