Ocean Acidification

Wei-Jun Cai, an expert in marine chemistry at the University of Delaware, is sounding new alarm bells about the changing chemistry of the western region of the Arctic Ocean, where he and an international team of collaborators have found acidity levels increasing three to four times faster than ocean waters elsewhere.

They also identified a strong correlation between the accelerated rate of melting ice in the region and the rate of ocean acidification, a perilous combination that threatens the survival of plants, shellfish, coral reefs and other marine life and biological processes throughout the planet’s ecosystem.

The new study, published on Thursday, Sept. 30 in Science, the flagship journal of the American Association for the Advancement of Science, is the first analysis of Arctic acidification that includes data from more than two decades, spanning the period from 1994 to 2020.

Scientists have predicted that by 2050 — if not sooner — Arctic sea ice in this region will no longer survive the increasingly warm summer seasons. As a result of this sea-ice retreat each summer, the ocean’s chemistry will grow more acidic, with no persistent ice cover to slow or otherwise mitigate the advance.

That creates life-threatening problems for the enormously diverse population of sea creatures, plants and other living things that depend on a healthy ocean for survival. Crabs, for example, live in a crusty shell built from the calcium carbonate prevalent in ocean water. Polar bears rely on healthy fish populations for food, fish and sea birds rely on plankton and plants, and seafood is a key element of many humans’ diets.

That makes acidification of these distant waters a big deal for many of the planet’s inhabitants.

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The oceans take up around 10% more of humanity’s carbon emissions than previously thought. This uptake slows global warming but worsens problems such as ocean acidification.

Researchers think the oceans absorb roughly one-quarter of CO₂ emissions from human activities. But estimates of the precise size of this ‘carbon sink’ vary.

Jens Terhaar at the University of Bern in Switzerland and his colleagues analysed models and observations of carbon flowing in and out of the ocean. They found three factors that influence the size of the carbon sink.

One is how salty the waters are in a particular zone in the Southern Ocean around Antarctica. A second is the strength of an ocean-current pattern in the North Atlantic Ocean. The third is a measure of how much CO₂ seawater can absorb in given atmospheric conditions. By focusing on how these three factors feed into climate models, the scientists were able to match the models to observations more accurately, thus reducing uncertainties in the size of the carbon sink.

The extra uptake would balance out only two to four years of global CO₂ emissions at current rates.

Copepods are among the most important organisms in the ocean. The millimeter-small animals are food for many fish species and are therefore of central importance for life in the sea. Marine biologists fear that climate change could affect the small crustaceans in the future – and that this could decimate the most important food source for fish and many other marine animals. A team from GEOMAR Helmholtz Centre for Ocean Research Kiel, the University of Connecticut, and the University of Vermont has therefore investigated for the first time in more detail whether copepods can genetically adapt to changing living conditions over the course of evolution. In doing so, they have taken into account both the effect of higher water temperatures and ocean acidification. The work of the U.S.-German group is special because it was one of the first to expose marine animals to multiple stressors in the lab.

The results, recently published in the scientific journal Proceedings of the National Academy of Sciences, are cautiously optimistic. The team, led by Professor Dr. Reid Brennan, marine ecologist at GEOMAR, and Professor Dr. Melissa Pespeni of the University of Vermont, found through detailed genetic analysis that the small crustaceans can indeed adapt to the new conditions over the course of about 25 generations – which corresponds to a period of just over one year, since several generations of crustaceans can mature in a year at moderate water temperatures. The researchers found that as water temperatures rise and conditions become more acidic, gene variants become prevalent in the copepods’ genome that result in the animals being better able to withstand environmental stress. “These mechanisms help, among other things, to ensure that copepod eggs develop properly despite unfavorable environmental conditions and that important metabolic processes continue,” says Reid Brennan.

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Overreliance on fossil fuels has led to a buildup of greenhouse gasses like carbon dioxide (CO₂) in the atmosphere. But CO₂ doesn’t only stay in the air; it also dissolves into the ocean, where it decreases the pH of the water and leads to ocean acidification. Corals are especially vulnerable to damage from ocean acidification, and rising CO₂ levels jeopardize the future of coral reefs globally. However, a new study from researchers at the University of Pennsylvania and Australia’s University of Queensland, reports certain corals may do better than others at withstanding ocean acidification.

The study was published in Proceedings of the Royal Society B. Using samples from the Great Barrier Reef, the researchers studied how coral from environments with greater CO₂ variability respond to increasing acidification.

Ocean acidification threatens coral because it breaks down the rocky, calcified skeletons that give coral its distinctive structure, says Katie Barott, an assistant professor of biology in Penn’s School of Arts & Sciences and senior author on the study. When water CO₂ levels surge, corals can no longer grow or maintain their skeletons.

While ocean acidification is a consequence of climate change, there are also regular fluctuations in water pH that occur regardless of greenhouse gas emission levels. These fluctuations are driven by respiration from the coral and photosynthesis from the coral’s symbiotic algae.

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A new study led by the Institut de Ciències del Mar (ICM-CSIC) in Barcelona has revealed that plastic degradation contributes to ocean acidification via the release of dissolved organic carbon compounds from both the plastic itself and its additives.

“Thanks to this study we have been able to prove that in highly plastic-polluted ocean surface areas, plastic degradation will lead to a drop of up to 0.5 pH units, which is comparable to the pH drop estimated in the worst anthropogenic emissions scenarios for the end of the 21st century,” points out Cristina Romera-Castillo, ICM-CSIC researcher and first author of the study, which has been published this week in the journal Science of the Total Environment.

Acidification and plastic pollution are two of the major problems facing the ocean today. Since the industrial revolution, the increase in ocean acidity has made it more difficult for some calcifying organisms, such as corals, to maintain their skeletons. Every year up to 13 million tons of plastic reach the sea.

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What is measured

Ocean acidification describes the long-term decrease in the pH of our oceans and coastal waters. This indicator measures:

• change in pH, acidity, and pCO₂ (partial pressure CO_2, which is a measure of dissolved carbon dioxide) in New Zealand’s subantarctic surface waters (Munida Transect) from 1998 to 2020
• pH at selected coastal sites (New Zealand Ocean Acidification Observing Network, NZOA-ON) from 2015 to 2021.

Why it is important

The oceans are a large carbon sink and have very likely absorbed 20–30 percent of the carbon dioxide (CO₂) emitted by human activities in the last two decades (Bindoff et al., 2019). CO₂ absorption reduces atmospheric greenhouse gas concentrations. However, when seawater absorbs CO₂ from the atmosphere, chemical reactions produce hydrogen ions that acidify the seawater and decrease its pH.

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The ocean plays a key role in mitigating climate change by absorbing about 25 percent of the carbon dioxide gas (CO2) released into the atmosphere each year by human activities. However, this comes at a cost to ocean health because the uptake of this human-released carbon causes changes in ocean chemistry, called ocean acidification (OA), that can be detrimental to marine ecosystems. 

A University of California – Santa Cruz (UCSC) and NOAA led research team set out to understand how OA metrics, such as pH and the partial pressure of CO2 (pCO2), have changed below the surface waters of the open North Pacific Ocean and coastal California Current System since industrialization (~1750). The California Current Large Marine Ecosystem along the US West Coast is a highly productive coastal ecosystem fueled by seasonal upwelling of cold, nutrient-rich water that supports important fisheries, tourism, and cultural heritage. 

This new research, led by Mar Arroyo, graduate student at UCSC, used observational data from research cruises as part of the GO-SHIP and West Coast Ocean Acidification surveys as well as output from a regional ocean model. The findings were published in the journal Geophysical Research Letters. 

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It’s not just the land that is groaning under the heat – the ocean is also suffering from heatwaves. In the Mediterranean Sea along the Italian and Spanish coasts, for example, water temperatures are currently up to 5 °C higher than the long-term average at this time of year. Scientists have investigated marine heatwaves for a few years now – for example at the University of Bern. However, relatively little is known about how marine heatwaves co-occur with other extreme events in the ocean. Such events are known as compound events and considered to be a major risk of climate change. While the processes that lead to extreme events on land, such as floods, forest fires, heatwaves, or droughts and how they interact with each other have been intensively studied in the past, the finding that ocean weather and climate extreme events can also occur in combination is relatively new.

A group of researchers at the Oeschger Center for Climate Change Research, led by Thomas Frölicher, has now investigated whether marine heatwaves co-occur in combination with extreme events in other potential marine ecosystem stressors. In addition to heat, potential stressors also include high acidity levels in the ocean. “For the first time, we have quantified the frequency of compound events in which marine heatwaves happen together with extreme acidity”, says Friedrich Burger, postdoctoral researcher and first author of the study just published in the journal Nature Communications. Extreme events of high ocean acidity are occurrences where the proton concentration in seawater is higher than normal.

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For the generations who grew up watching Finding Nemo, it might not come as a surprise that the North American West Coast has its own version of the underwater ocean highway – the California Current marine ecosystem (CCME). The CCME extends from the southernmost tip of California up through Washington. Seasonal upward currents of cold, nutrient-rich water are the backbone to a larger food web of krill, squid, fish, seabirds and marine mammals. However, climate change and subsequent changes in ocean pH, temperature and oxygen levels are altering the CCME — and not in a good way.

New research led by McGill University Biology professor Jennifer Sunday and Professor Terrie Klinger from the Washington Ocean Acidification Center within EarthLab at the University of Washington warns that climate impacts will significantly affect twelve economically and culturally important species make their home in the CCME over the next 80 years. The northern part of this region and areas that are closer to shore will have strongest responses within this setting to changing ocean conditions. The region can expect to see substantial loss in canopy-forming kelp, declining survival rates of red urchins, Dungeness crab and razor clams, as well as a loss of aerobic habitat for anchovy and pink shrimp.

Effects of changing climate are complex

Evaluating the biological effects of several environmental variables at once shows the complexities in climate sensitivity research. For example, while some anticipated environmental changes will boost metabolism and increase consumption and growth, accompanying changes in other variables, or even the same ones, could potentially decrease survival rates. Notably, physiological increases (such as in size, consumption or motility) are not always beneficial, especially when resources – such as food and oxygenated water – are limited.

Of all the climate effects modeled, ocean acidification was associated with the largest decreases in individual biological rates in some species, but the largest increases in others. This result emphasizes the need for continued research and monitoring to provide accurate, actionable information.

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Climate change is threatening marine species and ecosystems with rising temperatures and extreme weather. Now scientists from Cambridge and the Royal Belgian Institute of Natural Science have observed how sea snails living on rocky shores are coping with climate change, through studying 130 years of data from dog whelk shells.

As the level of carbon dioxide in the atmosphere rises it is absorbed by the oceans — causing pH levels to fall. This process, known as ocean acidification, is potentially disastrous for shellfish because they find it increasingly difficult to build the shells that protect them from predators.

The new study, published in Nature Communications Earth and Environment, has matched climate driven changes over the last century to changing shell characteristics of dog whelks from museum collections.

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An international team of experts has produced a list of 15 issues they believe are likely to have a significant impact on marine and coastal biodiversity over the next five to ten years.

Their “horizon scanning” technique focuses on identifying issues that are not currently receiving widespread attention, but are likely to become important over the next decade. The aim is to raise awareness and encourage investment into full assessment of these issues now, and potentially drive policy change, before the issues have a major impact on biodiversity.

The issues include the impacts of wildfires on coastal ecosystems, the effects of new biodegradable materials on the marine environment, and an ’empty’ zone at the equator as species move away from this warming region of the ocean.

“Marine and coastal ecosystems face a wide range of emerging issues that are poorly recognized or understood, each having the potential to impact biodiversity,” said Dr. James Herbert-Read in the University of Cambridge’s Department of Zoology, joint first author of the paper.

He added: “By highlighting future issues, we’re pointing to where changes must be made today—both in monitoring and policy—to protect our marine and coastal environments.”

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While there are many well-known issues facing ocean biodiversity including climate change, ocean acidification and pollution, this study focused on lesser-known emerging issues that could soon have significant impacts on marine and coastal ecosystems.

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Marine biologists have found that black sea urchins in the Mediterranean Sea are remarkably tolerant of warm, acidic water. As a colonising species, the urchins’ adaptability could lead to an ecological disaster in our climate change-impacted seas.

In bubbling vents off the coast of Ischia, a volcanic island in the Gulf of Naples, lives a curious population of black sea urchins. For at least 30 years, they have lived in these low pH, carbon dioxide-rich environments – a proxy for climate change-induced acidic oceans.

Now, University of Sydney researchers have determined they can also tolerate unprecedentedly warm sea temperatures – another climate change by-product. This means that these urchins, already one of the most abundant animals in the Mediterranean Sea, will likely plunder further afield as oceans continue to warm and become more acidic.

The researchers have described their findings in Biology Letters, a publication of the Royal Society.

The Mediterranean Sea is warming 20 percent faster than the global average, with predicted warming of up to 5.8°C by 2100.

“Given their ability to withstand a large temperature range, these sea urchins are likely to continue spreading throughout the Mediterranean Sea, with serious consequences for coastal habitats,” said lead researcher, University of Sydney marine biologist Dr Shawna Foo.

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A blueprint for measuring calcium carbonate on the ocean floor could help marine scientists monitor coral reef health around the globe.

Climate change and pollution from human activities are irreversibly changing many marine habitats, particularly coral reefs. To assess and mitigate future impacts, ecologists must understand how these ecosystems are functioning right now.

One indicator of coral reef health is how much calcium carbonate is produced over time as shells and skeletons of marine animals accumulate on the ocean floor. Researchers often use special tiles on the seabed, which gradually become home to settling pioneering plants and animals. After a year, the researchers retrieve the tiles to see how much calcium carbonate has accumulated on them and which living species are present.

“To understand how marine ecosystems are changing over space and time we need to be able to compare data collected from different habitats,” says marine scientist Maggie Johnson. “But researchers employ a range of approaches or measure different variables, meaning that the data might not be directly comparable,” she adds. This makes it tricky to create a global picture of marine ecosystem health.

Johnson and her colleagues have developed a standardized method for making and deploying calcification accretion units (CAUs), which are similar to settlement tiles but more specifically are used for measuring calcium carbonate. The comprehensive “how to” guide provides detailed instructions for tile construction and CAU assembly, from material suppliers to measurements, as well as how to place them and retrieve them, all of which will enable researchers to collect comparable data from coral and oyster reefs worldwide.

“Coral reefs cover less than one percent of the seafloor, yet provide more than 25 percent of the ocean’s biodiversity,” says Johnson. “Much of this diversity comes from tiny critters living in the unseen cracks and crevices,” she adds. These hidden species, or “cryptic taxa,” cannot be captured by visual surveys, but the CAUs include a small space for these tiny taxa to occupy. “During collection, the tiles must be placed in zipped bags to keep the community of cryptic critters intact all the way to the lab,” says Johnson.

The guide advises immediate processing of the samples, while the animals and plants are still alive. This involves taking high resolution photographs that are later used for spotting species and microscope observations to count baby coral. The calcium carbonate is then removed by a weak acid.

“By weighing the tiles before and after decalcifying them, researchers can calculate how much calcium carbonate was deposited on that tile over a year,” says Johnson. “This figure can help compare reef conditions in different parts of the world or how the health of one reef is changing over time.”

Understanding the impacts of human activities on marine habitats will help researchers and governments find ways to mitigate the negative impacts. “This standardized and accessible approach will help promote collaboration and informed decision-making even when using data from all over the world,” concludes Johnson.

JOURNAL: Methods in Ecology and Evolution

DOI: 10.1111/2041-210X.13867 

ARTICLE TITLE: Calcification accretion units (CAUs): A standardized approach for quantifying recruitment and calcium carbonate accretion in marine habitats

A new report from the Scientific Committee on Antarctic Research (SCAR) reveals how climate change is significantly impacting Antarctica’s ice sheets, climate and ecosystems, with far-reaching global consequences. 

The report, released May 24 at the Antarctic Treaty Consultative Meeting in Berlin, shows that Antarctic ice sheets are melting, the continent’s climate is changing, and the Southern Ocean is warming, becoming more acidic and losing oxygen. Locally, changing climates are already affecting the region’s iconic whales, seals, penguins, and the krill they rely on for food. Emperor penguins may be all but gone by the end of the century unless urgent action is taken, the report concludes.

But while seemingly isolated from the rest of the world, Antarctica’s changes also have impacts on all other continents. 

“What happens in Antarctica, does not stay in Antarctica,” said Cassandra Brooks, assistant professor of environmental studies and contributor to the report, specifically on marine elements of the region. 

Melting ice sheets mean that global average sea level rise will put nearly a billion people at risk from coastal flooding over the next several decades, a number that could increase by the end of the century. The Antarctic has also played a profound role in regulating the world’s climate, in part by absorbing heat and carbon dioxide emissions resulting from human activity. 

The report also states that: “Global impacts influenced by Antarctic change include extreme climate and weather events, droughts, wildfires and floods, and ocean acidification.”

For example, current levels of global warming have already committed the planet to about 16 inches (40 cm) of global sea level rise, which turns what was considered a one in 100-year coastal flood event into an annual one. 

“Antarctica’s changes have profound consequences for all of us,” said Monash University Professor Steven Chown, who led the report and is SCAR’s immediate past president. Chown is also Director of Securing Antarctica’s Environmental Future (SAEF), of which Brooks is a Partner Investigator, through CU Boulder’s status as a Participating Organization. 

The report makes clear that adhering to, and preferably exceeding, the Paris Climate Agreement greenhouse gas emissions reductions targets will substantially lessen changes to the Antarctic and their implications for society.

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The autumn may be a time when Great Bay Estuary — and the oysters, seagrass and fish that inhabit it — is particularly vulnerable to the effects of ocean and coastal acidification caused by climate change, according to new research from UNH.

For three and a half years, scientists have been monitoring the buffering capacity of the saltwater and freshwater mingling at the mouth of the Piscataqua River. Buffering is the chemical ability of a water body to counteract the effects of acidification. This long time series of data has provided a clearer picture of how the buffering varies throughout the year, and will inform efforts to combat acidification impacts on shellfish, seaweed, and other species growing in the estuary and along the Seacoast.

Chris Hunt, a research associate professor in the UNH Ocean Process Analysis Laboratory, is the first author on a new study published in the journal Limnology and Oceanography that focuses on the chemical and biological dynamics that determine the pH of New Hampshire’s coastal waters. Ocean acidification (OA) has come into focus in the last decade, as ocean water is absorbing some of the increased carbon dioxide in the atmosphere, which then decreases the pH of the water and makes it more acidic. This has led to impacts on shellfish and coral reefs that are then challenged to form their hard calcified shells in the acidic environment. However, little is known about coastal acidification (CA), which is influenced by numerous factors that all interact with one another.

“Coastal acidification is a developing concept, and we don’t really know how much OA will in turn affect CA,” Hunt says. “We do know that it has implications for our fisheries, coastal and estuarine health, and carbon sequestration. We’re trying to learn more in order to tease apart the individual effects of OA and CA.” He worked closely with UNH research professors Joe Salisbury and Doug Vandemark to study this phenomenon.

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New research from Te Herenga Waka—Victoria University of Wellington shows that tropical ocean-dwelling sponges may have a good chance of survival even as Earth’s oceans are impacted by climate change.

The research, led by Professor James Bell from the School of Biological Sciences and Dr. Riccardo Rodolfo-Metalpa from the Institute for Research Development, was recently published in Global Change Biology.

Professor Bell and his colleagues traveled to Papua New Guinea in 2019 to study sponges in coral reefs surrounding shallow water carbon dioxide seeps—places where carbon dioxide bubbles from the sea floor

“Sponges are very abundant near these seeps in the ocean floor,” Professor Bell says. “The carbon dioxide from the seeps makes the ocean more acidic in this area, which is something that will happen to all of Earth’s oceans due to climate change. That means we can use this area as a proxy to see how sponges might cope with more acidic oceans.”

Previous research has suggested that sponges are well-suited to surviving in acidic ocean conditions because of their higher tolerance for both acidic conditions and warmer temperatures. Many sponges also contain photosymbionts which could potentially thrive in more acidic oceans due to greater access to carbon dioxide for photosynthesis.

“We were able to show that sponges that contain photosymbionts in this area can offset the metabolic costs of dealing with ocean acidification,” Professor Bell says. “This means while the sponges might not thrive under climate change conditions, they will survive.”

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“Sponges are really important on current coral reefs and our research continues to support the hypothesis that sponges will still be found on future reefs, even if corals were to completely disappear,” Professor Bell says. “These changed ecosystems will have major consequences for the resources people take from corals reefs. Sponge-dominated reefs will not be able to provide as many resources as coral-dominated reefs, but it will be better than no resources at all.

“While our understanding of the impacts of climate change on marine organisms is increasing, we still have limited ability to manage these impacts. A global concerted effort to rapidly eliminate carbon emissions is the only way in which we will keep ocean acidification and warming to a level that won’t fundamentally alter marine ecosystems forever.”

The Gulf of Maine is growing warmer and saltier, and those changes have led to a substantial decrease in the productivity of phytoplankton that are the center of the marine food web. Specifically, phytoplankton in the gulf are now about 65 percent less productive than they were two decades ago, scientists from Bigelow Laboratory for Ocean Sciences reported in research published on June 7, 2022.

The Gulf of Maine helps fuel New England’s marine ecosystems and maritime economy. Like plants on land, phytoplankton absorb carbon dioxide from the atmosphere and use sunlight to grow via photosynthesis; they then become food for other organisms. Disruptions to the productivity of these microscopic organisms can lead to adverse effects on the region’s fisheries and the communities that depend on them.

Research published in 2021 showed that the Gulf of Maine has been warming faster than most ocean basins. In the new effort from Bigelow, funded in part by NASA, scientists showed how that warming has affected the phytoplankton.

The natural-color image above shows the northwest Atlantic Ocean blooming with phytoplankton on June 5, 2022, as observed by the Moderate Resolution Imaging Spectroradiometer on NASA’s Aqua satellite.

“Phytoplankton are at the base of the marine food web on which all of life in the ocean depends, so it’s incredibly significant that its productivity has decreased,” said William Balch, a Bigelow Laboratory scientist who co-led the study. “A drop of 65 percent will undoubtedly have an effect on the carbon flowing through the marine food web, through phytoplankton-eating zooplankton, and up to fish and apex predators.”

The findings are the result of an analysis of the Gulf of Maine North Atlantic Time Series (GNATS), a 23-year sampling program that has measured the temperature, salinity, and other chemical, biological, and optical properties of the gulf. Balch says the changes that they are recording show an intricate connection between the gulf and the greater Atlantic Ocean.

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• A new study warns that cold-water corals, also known as deep-water corals, could be most impacted by a decrease in food supply as climate change shifts the dynamics of the planet’s oceans.
• The authors came to this conclusion by examining how cold-water corals survived the last major period of global warming that occurred at the end of the last glacial period and the start of the current interglacial period, which is somewhat analogous to how the Earth is projected to warm by the end of this century.
• However, experts point out that cold-water corals today are subjected to a number of additional stressors, including ocean acidification, destructive fishing practices, and pollution, and that the climate is changing far more rapidly than it did in the past.
• Cold-water corals are considered to be equally important — or perhaps even more important — than tropical corals, which makes understanding their chances of survival of the utmost importance, researchers say.

Between 1869 and 1870, the H.M.S. Porcupine sailed into the North Atlantic Ocean and scraped a dredge along the seafloor. When the sailors pulled the dredge back to the surface, it held pieces of stony coral that lived in the cold, sunless depths of the sea.

Examining the coral back on land, English paleontologist Peter Martin Duncan noted in a report, with some wonder, that these corals could live as easily in the deep, cold ocean as well as other organisms could in the warmer, shallower parts of the sea. “It suggests that a great number of the Invertebrata are not much affected by temperature,” he said, “and that the supply of food is the most important matter in their economy.”

Today, the ocean is a very different place than what it was when the H.M.S. Porcupine set sail. Climate change is causing global ocean temperatures to rapidly rise, while lowering oxygen levels and acidifying the water. The seas are also being damaged by overfishing, pollution, and other human activities like transportation. But according to a new study published in PLOS Biology, the biggest threat to cold-water corals, like the ones scooped up by the H.M.S. Porcupine all those years ago, is a lack of food. As it turns out, Duncan’s observations appeared to be correct.

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New study shows that these tiny algae are not the winners of the acidification game, after all.

Diatoms – single-celled algae which occupy much of the world’s water – were thought to be more resistant to acidification than some of their aquatic counterparts, with their silicon-containing shells more impervious to acid than the carbonates in shellfish and corals.

But according to research published in Nature, acidification threatens diatoms as well.

“With an overarching analysis of field experiments and observational data, we wanted to find out how ocean acidification affects diatoms on a global scale,” says first author Dr Jan Taucher, a marine biologist at the Helmholtz Centre for Ocean Research Kiel, Germany.

“Our current understanding of ecological effects of ocean change is largely based on small-scale experiments – that is, from a particular place at a particular time. These findings can be deceptive if the complexity of the Earth system is not taken into account.”

The researchers examined five experiments done in different ocean waters, from 2010 to 2014. They then designed five similar experiments, simulating ocean water from 2100.

More acidic water, the researchers found, causes the silicon shells of diatoms to thicken. This makes them sink and dissolve, meaning their silicon falls to the bottom of the ocean and becomes silica, where it can’t get into new diatoms. This causes an overall decline.

“Our study uses diatoms as an example to show how small-scale effects can lead to ocean-wide changes with unforeseen and far-reaching consequences for marine ecosystems and matter cycles,” says Taucher.

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This research sits in contrast with previous studies, which assumed the main risk of ocean acidification was calcium-dependent, not silicon-dependent, organisms.

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Ellen Phiddian, COSMOS, 28 May 2022. Press release.