The Ocean’s Menopause: More Acidic, with Hot Flashes and Shortness of Breath

“The ocean is the world’s largest storage of mobile natural carbon s. It has long served us well by absorbing a third of our CO₂ emissions,” says oceanresearcher Melissa Chierici.

The ocean has absorbed some of our emissions from holiday trips to Thailand, car rides to work, taco Fridays, and most importantly: from fossil fuels.

And it is the CO₂ from all our human activities that is now causing our largest carbon sink to approach its limit. The climate is changing, and the ice is melting. The Arctic Ocean is becoming more acidic (i.e less basic).

“We see that the ocean is changing.”

Years of Monitoring

Melissa has been researching the marine environment for many years. She is a chemical oceanographer and studies complex biological, physical, and chemical processes in the ocean.

She does this to understand how the marine environment functions and how it is affected by climate change and human activity.

“It’s not so easy to explain, but we take various samples to measure the ocean’s health. Almost like a doctor takes blood samples from a patient. While a doctor checks oxygen levels and acidity in the blood, we examine the ocean’s acidity, oxygen, and CO₂ uptake,” explains Melissa.

Together with physical oceanographers who study ocean currents, temperature, and salinity through the water column, Melissa explores how the marine environment is interconnected.

“The oceanographer’s job is to understand both how the ocean itself affects the climate and how climate change affects the ocean. But also, to find out what consequences changes in the marine environment have for the animals living in the ocean and the ecosystem they are part of,” she says.

A bitter experience

But it can be too much. Even for the ocean.

“The northern seas are particularly vulnerable because cold Arctic water can absorb more CO₂ than warmer seas. The Barents Sea, especially the northern part, absorbs more CO₂ than other seas. We are already seeing the consequences of this, as the marine environment is changing faster here,” says Chierici.

This is new knowledge. Through the research program Arven etter Nansen / The Nansen Legacy, researchers have studied 20-year-long time series of surface water observations. Many of these samples have been collected and analysed by the Institute of Marine Research (IMR).

The result is maps that depict changes in the environment at the top of the water column. Not only can you see how much ice is gone, but you can also see that the ocean is becoming more acidic (i.e. less basic).

“We place CO₂ level measurements as separate layers on maps of the Barents Sea. This allows us to see changes in the marine environment over time. Where they happen, how quickly they happen, and where they happen the fastest. When we then add more layers, with measurements of ice and temperature, we find the connections. In the Barents Sea and surrounding areas, CO₂ levels have increased significantly in recent decades,” says Chierici.

So, the Barents Sea absorbs CO₂ at faster rates than the global surface ocean mean rates, and it is becoming more acidic. Acidification here is happening faster than elsewhere.

“We can say this with certainty because we conduct annual ‘health checks.’ We measure the same things, in the same place, and at the same depth every year. This enables us to document these changes,” she says.

Overload and Vicious Circles

Climate change is not disputed among oceanographers. There is no doubt that the ocean has become warmer. And the ice-covered areas in the Arctic are shrinking.

“We know that the ocean is warmer, more acidic, and that oxygen levels are changing. We are already outside the norm,” says Chierici.

The ocean’s ability to absorb and “process” CO₂ is essentially about the balance between acid and base.

Simply put: Acid is a substance that makes water taste sour. Base is a substance that removes the sour taste. In the case of the ocean, it is CO₂ that makes the ocean acidic, while salty seawater contains bases that remove the acidity. This is what scientists call a buffer.

But when the ice melts, it affects the ocean’s ability to absorb CO₂ on several levels and in several ways. Ocean acidification happens faster, while the effect of the acidity (lower pH) becomes greater. Because:

1.  Ice cover limits the ocean’s direct uptake of CO₂. Larger open areas mean the ocean absorbs more CO₂.
2.  When the ice melts, the freshwater is at the surface of the water column. Cold freshwater absorbs more CO₂ than saltwater.
3.  Meltwater from ice weakens the bases, i.e., the buffering capacity of the ocean, because freshwater does not neutralize CO₂ as well as saltwater.

As if that weren’t enough, Atlantic water is brought in by ocean currents. It already contains a lot of anthropogenic CO₂s, contributing to further weakening.

“Together, all this leads to a kind of overload. The ocean becomes acidic faster while its resistance to acidification weakens,” says Chierici.

Maps showing both CO₂ levels and ice cover show clear connections between less ice, higher CO₂ uptake, and more acidic oceans.

“The surface of the Barents Sea has become more acidic. When acidification propagates down the water column, it will have even greater consequences for marine life. And that is what we need to study now, what happens further down in the deep sea,” explains the oceanographer.

Calcium for Growth and Strength

When the marine environment becomes more acidic, conditions for forming solid structures made of calcium carbonate is limited. Simply because calcium carbonate (CaCO3) dissolves in less basic environment.

Something you might remember from childhood is the mantra about drinking milk. Because children need calcium carbonate to grow big and strong. The same applies to many species in the ocean.

“Many species depend on calcium carbonate. Snails build shells, shrimp and lobsters use CaCO3 to bind their joints, fish larvae need to build skeletons and grow. When the ocean becomes more acidic, animals must use more energy to produce this mineral . We don’t know how they will adapt over time, but shells and skeletons will become weaker,” says Chierici.

This means more challenging conditions for various plankton species, shrimp, lobsters, snails, mussels, starfish, sea urchins, and corals. In the worst case, species may become extinct or be outcompeted by other species that tolerate acidification better.

“For example, sea butterflies are food for many fish species, seabirds, and marine mammals. If they disappear, the entire food chain is affected – and the ecosystem will change. Coral reefs serve as nurseries for many different species, and they need calcium carbonate to become hard and resilient. If they become weaker, smaller, and fewer, it will affect many different species,” explains Chierici.

Hope for the Ocean?

A few decades ago, the ozone layer was the topic of discussion. The layer in the atmosphere that protects the Earth, and those of us living here, from being fried by the sun. In the 1970s, holes in the ozone layer were discovered, and measures were taken to protect it. Today, the ozone layer is on the mend. But can we also succeed in reversing the changes in the ocean?

“Unfortunately, the changes in the ocean cannot be reversed. What has already happened, we must deal with. But if we manage to stop CO₂ emissions, we can slow down and perhaps ensure that acidification levels off. The question is whether we can do it in time, because it must happen now,” urges Chierici.

The ocean’s uptake of CO₂ is essentially a natural process, just like menopause. But some transitions can be quite intense, and that’s where we are with the ocean.

The doctor has already made the diagnosis, but much remains uncertain. Both regarding the symptoms and how much time we have left.