By the end of this century, coral reefs in Australia and around the world could be slower to recover, structurally simpler, and increasingly dominated by fleshy algae as rising carbon dioxide reshapes ocean chemistry.
These are the predictions that new international research – published this week in Communications Biology – is warning against, as scientists present a volley of stark new findings about the current and long-term impact of a process known as ocean acidification.
As the oceans absorb more carbon dioxide from the atmosphere, they are becoming increasingly acidic – eroding the very calcium carbonate skeletons that build coral reefs. Yet despite decades of laboratory studies and ecosystem models, scientists have lacked real-world systems that reflect how entire reef communities respond to these long-term chemical shifts.
Researchers from the Australian Institute of Marine Science (AIMS) have now filled that gap by studying shallow-water reefs naturally bathed in volcanic CO₂. These reefs, located near remote submarine vents in Papua New Guinea’s Milne Bay Province, experience chronic exposure to elevated carbon dioxide, offering scientists a rare preview of the seascapes expected under future emissions scenarios.
The sea along the Basque coast is changing quietly. An analysis of more than 21,700 measurements collected between 2002 and 2022 shows that the pH of seawater is steadily decreasing—clear evidence of ocean acidification driven by rising atmospheric carbon dioxide.
According to the study, published in Continental Shelf Research, the pH of waters from the surface down to 100 meters is declining by 0.022 to 0.041 units per decade. “If this trend continues at the same pace, the impacts on the health of marine ecosystems could be significant,” explains Ernesto Villarino, AZTI researcher and lead author of the study.
Conducted by AZTI with the support of the Naturklima Foundation, as part of the Gipuzkoa Marine Climate Change Observatory, and in collaboration with the Institute of Marine Sciences of Andalusia (ICMAN-CSIC), this research analyzes the longest continuous pH monitoring series ever recorded along the Basque coast. The data, provided by the Basque Water Agency (URA), confirm that the Bay of Biscay is also affected by ocean acidification, underlining the need to strengthen mitigation and climate-adaptation strategies.
When scientists raised baby reef-building corals in acidic seawater pushed toward about pH 7.6, the youngsters still built skeletons.
The tiny skeletons were denser yet less stable, so the corals were more likely to snap when waves or animals pushed on them.
Across tropical oceans, reefs depend on countless such skeletons growing, thickening, and locking together.
As ocean acidification deepens, scientists are racing to understand whether coral skeletons can keep pace.
Inside a coral’s first skeleton
The work was led by Dr. Federica Scucchia, a postdoctoral associate at the University of Rhode Island (URI). Her research focuses on biomineralization, the way living organisms build hard mineral structures, in young reef building corals.
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The team combined three-dimensional X-ray scanning with short growth intervals. They also used electron microscopes to see features smaller than a micrometer and to trace tiny crystals.
These tools let them map mineral density, crystal size, and growth zone shapes in Stylophora pistillata, a common Red Sea stony coral.
Under normal pH, the thickening deposits made up most of the skeleton and wrapped around a web of rapid accretion deposits.
Inside those fibers, much of the mineral turned out to be amorphous calcium carbonate, a disordered mineral form that later transforms into crystals. Only a smaller share had already organized into dense calcium carbonate crystals that pack tightly together.
In more acidic water, the pattern shifted in several important ways. Both growth zones became denser overall, and the crystals inside them grew larger, even though the total skeleton volume shrank.
Ocean acidification and nutrient loading present significant threats to marine ecosystems, particularly to critical species like Sargassum hemiphyllum var. chinense. A groundbreaking study led by Chen et al., published in BMC Genomics, investigates how these stressors affect the physiological and transcriptomic responses of this seaweed. Researchers are gaining new insights into how climate change and nutrient enrichment may disrupt marine life, offering a glimpse into the resilience of Sargassum hemiphyllum and highlighting its ecological importance.
The study reveals intricate details about the adaptability of Sargassum hemiphyllum var. chinense in response to increasing temperatures and acidification levels. As global temperatures rise and CO2 emissions lead to ocean acidification, understanding how marine organisms react to these conditions becomes crucial. The researchers conducted a series of experiments simulating these stressors, measuring physiological changes in the algae over time. The findings suggest that while Sargassum hemiphyllum endures these challenges, the responses are profound and affect growth and survival.
Moreover, the meticulous transcriptomic analysis conducted by the researchers provides a robust framework for interpreting the complex changes triggered by environmental stressors. The team utilized RNA sequencing technology to evaluate gene expression profiles, revealing key pathways that the algae activate in response to both acidification and nitrogen enrichment. This revelation underscores the adaptability of marine flora and suggests potential avenues for increasing resilience against climate changes.
The physiological changes noted in Sargassum hemiphyllum are equally fascinating. The team observed variations in biomass, muscle integrity, and reproduction rates, providing concrete evidence that environmental conditions directly influence the survival and proliferation of this species. The implications are staggering, considering Sargassum hemiphyllum‘s role as a critical habitat for various marine organisms. The study calls attention to the interconnectivity within marine ecosystems and the potential cascading effects that might distress entire food webs.
The waters bordering North America could soon be inhospitable to critical marine creatures if the Northeastern Pacific Ocean continues to acidify at the current rate, a new study shows.
Earth’s oceans have become approximately 30% more acidic since the industrial revolution began more than 200 years ago. Acidification changes marine chemistry and depletes key minerals that calcifying organisms, such as corals and clams, need to build their skeletons and shells. The Northeastern Pacific is naturally more acidic than other oceans, fueling debate about how much its chemistry will change in the coming decades.
The study, published Nov. 13 in Nature Communications, shows that high baseline acidity makes the water more sensitive to additional carbon dioxide from human activities. Analyses of coral skeletons from the past century revealed that CO2 has been accumulating in North American waters faster than in the atmosphere, driving rapid acidification.
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“The findings implicate not only marine ecosystems, but all of the people who depend on them as well,” added lead author Mary Margaret Stoll, a UW doctoral student of oceanography.
The ocean becomes more acidified when carbon dioxide dissolves to form an acid that releases hydrogen and bicarbonate ions, lowering the water’s pH level. In North America, a powerful current system — the California Current — transports cool water south along the coast. The combination of current flow and wind creates optimal conditions for upwelling, a process that cycles deep water to the surface.
Organic matter — dead plants and animals — sinks to the bottom of the ocean, where it decomposes and releases carbon dioxide back into the water. Upwelling surfaces this CO2 rich water, increasing the acidity of subsurface and surface zones. These natural fluctuations complicate researchers’ efforts to predict how much acidification will occur from human activities.
This study helps resolve these questions with records kept by centuries old corals.
New research from the university of St Andrews has found that some coastal areas will become much more acidic than previously anticipated.
Because atmospheric CO2 and ocean pH (acidity) are tightly coupled, the more CO2 that is released into the atmosphere, the more is absorbed by seawater, making the ocean progressively more acidic. However, in a paper published in Nature Communications, researchers, using the California Current as an example, show that oceanic upwelling systems actually amplify ocean acidification.
Upwelling is where nutrient- rich and already acidic waters from deep in the oceans rise along the coast. When organic matter from the surface ocean sinks to the deep ocean, microbes gradually break it down in a chemical reaction that releases CO2 and increases seawater acidity. When this deep water upwells, it brings the acidity to the surface, where it further reacts with the atmospheric CO2, which makes these water masses even more acidic.
The researchers used historic coral samples and boron isotope signatures recorded in their skeletons to reconstruct how acidity changed over the 20th century, and then applied a regional ocean model to predict how acidity will change during the 21st century. The study showed that in these upwelling regions of the ocean, ocean acidification outpaces the level “expected” from rising atmospheric CO2alone. This is because the upwelled water masses are acidic to start with and anthropogenically rising CO2 exacerbates the acidity.
Upwelling systems are among the most productive systems on our planet and support much of the world’s fisheries. Understanding how they respond to rising CO2₂ is therefore not only critical for ocean science, but also carries major implications for fisheries and their potential vulnerabilities.
Co Author Dr Hana Jurikova, Senior Research Fellow in from the School of Earth and Environmental Science, said: “Predicting how upwelling systems will respond to climate change is highly complex, as anthropogenic influences interact with natural sources of ocean acidification. Our research shows that such interactions can amplify environmental change in the California Current System, highlighting the need for similar studies in other regions to better anticipate future change.”
The California Current can be used as an example of other upwelling systems. Other important areas of coastal upwelling around the world include the Humbold Current off the coast of Peru or the Benguela and Canary Currents off the coast of west Africa.
Co Author Dr James Rae, Reader in the School of Earth and Environmental Science, said: “the ocean becoming more acidic poses major risks to marine ecosystems and the communities and economies they support. The solutions we now have for climate change, like heat pumps and electric vehicles, also fix ocean acidification, so it’s critical that we support them”.
Human greenhouse gas emissions are raising temperatures and sea levels, collapsing ice sheets and acidifying oceans. Now, research maps out the range of emissions pathways that can limit these changes.
How much greenhouse gas can be emitted before the Earth changes beyond the natural world’s ability to adapt? One approach to answer this involves looking at the characteristics of the world humans evolved in and establish limits to preserving these ecosystems1. There are many of these ‘planetary boundaries’ proposed, and previous work has mapped out how to stay within them2. However, in reality, many of the targets interact in complex ways — for instance, the amount of carbon dioxide that can be released while staying below a temperature target can be increased if more cooling sulfates are emitted3, but these sulfates can increase acid rain. Now, writing in Nature Climate Change, Gasser and colleagues4 propose a framework to address these interconnections that assesses a range of climate targets and produces a set of compatible emissions pathways with different degrees of climate uncertainty.
The ocean’s smallest engineers, calcifying plankton, quietly regulate the Earth’s thermostat by capturing and cycling carbon. However, a new review published this week in Science by an international team led by the Institute of Environmental Science and Technology at the Universitat Autònoma de Barcelona (ICTA-UAB) (Spain) finds that these organisms, coccolithophores, foraminifers, and pteropods, are oversimplified in the climate models used to predict our planet’s future.
By omitting these plankton, current models may underestimate key processes in the global carbon cycle and the ocean’s capacity to respond to climate change. Calcifying plankton build minute shells of calcium carbonate (CaCO₃), a critical component of the ocean’s carbon cycle. These organisms influence seawater chemistry and facilitate the transfer of carbon from the atmosphere to the deep ocean. This “carbon pump” helps regulate Earth’s climate and influences everything from ocean chemistry to the fossil record.
“Plankton shells are tiny, but together they shape the chemistry of our oceans and the climate of our planet,” said Patrizia Ziveri, ICREA research professor at ICTA-UAB and lead author of the study. “By leaving them out of climate models, we risk overlooking fundamental processes that determine how the Earth system responds to climate change.”
The Deep Acoustic Lander recorded sound at the Challenger Deep, nearly 11,000 meters below sea level, in 2021. David Barclay
The ocean is a noisy place. Ship propellers and whale songs reverberate at the lowest pitches, while at higher tones dolphins click and shrimp snap their claws. Between these frequencies are the sounds of the churning sea itself, generated as waves, wind, and rain roil its surface. Researchers have now used this ambient noise to probe the rising acidity of the ocean. The acoustic technique, published last week in the Journal of Geophysical Research: Oceans, could make it easier to measure this key parameter of ocean health across vast distances rather than relying on point measurements.
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The carbon emissions that are warming the globe also acidify seawater. The ocean naturally absorbs about one-third of annual carbon dioxide emissions; as this gas dissolves and reacts, it creates bicarbonate and hydrogen ions. The hydrogen lowers the pH of seawater, increasing ocean acidity, which can harm sea life and slow future carbon uptake. Ship-based measurements in shallow parts of the ocean have found that, since 1985, pH has already dropped from 8.11 to 8.04.
The waters of the ocean are layered, however, and measurements at one depth may not apply to others. Adding pH sensors to the thousands of robotic Argo floats that patrol the seas, diving as deep as 2000 meters, is one way to get a broader picture of acidity. But David Barclay, an acoustical oceanographer at Dalhousie University, and his co-authors found a way to measure average pH across even greater depth ranges, by taking advantage of the intrinsic physics of sound.
The Gulf of Maine is warming faster than 99% of the world’s oceans, raising concerns for its $2 billion-a-year American lobster fishery. Scientists at William & Mary’s Batten School & VIMS have been studying the impacts of ocean acidification and warming on lobster reproduction, and the results of their most recent research suggest the rising temperatures pose the greatest risk.
Utilizing a purpose-built experimental facility designed by Professor Emily Rivest and housed in the Batten School of Coastal & Marine Sciences & VIMS’ Seawater Research Laboratory, the researchers exposed egg-bearing lobsters from the Gulf of Maine to water temperature and pH conditions that mimic those predicted for 2060. Published in the journal Marine Ecology Progress Series, the results revealed that the embryos can handle ocean acidification surprisingly well, but increased temperatures led to distinct stress responses that ultimately resulted in smaller larvae.
“American lobsters are dynamic creatures that have been shown to tolerate highly variable conditions as they move from coastal waters to the deeper ocean,” said the study’s lead author Brittany Jellison, who conducted the research as a postdoctoral scholar at the Batten School & VIMS. “However, as we observe rising ocean temperatures, increased acidification and more frequent marine heat waves, it’s important to understand how future environmental changes might impact this economically and culturally important species.”
Some reef-building corals seem to keep making sturdy skeletons even as the ocean grows more acidic. New evidence from long-lived corals suggests they can tweak the chemistry at the site where their skeleton forms, helping them push through conditions that should, in theory, slow them down.
The work, led by CU Boulder researchers and collaborators, looks back over roughly two centuries of rising acidity and finds corals adjusting their internal calcification engine to stay in the game.
Corals adapt to harsh chemistry
“We found that corals were able to regulate the mechanism they use to build and maintain their skeletons despite the ocean becoming more acidic,” said Jessica Hankins, the paper’s first author and a Ph.D. student in the Department of Geological Sciences.
“It’s an unexpected and hopeful signal; however, we need more long-term data to know what it really means.”
In the vast and intricate ecosystems of coral reefs, a hidden danger lurks, posing threats not just to the colorful corals themselves but to entire marine environments. Recent research spearheaded by Liu, PY., Chiu, WC., Lim, S.L., and their collaborators has shed light on the mysterious and pervasive sponge known as Terpios hoshinota. This sponge, infamous for its destruction of coral reefs, exhibits a remarkable ability to thrive under extreme environmental stressors, raising crucial questions about the future of coral ecosystems worldwide.
The study culminated from a comprehensive genomic analysis that aimed to unravel the underlying mechanisms behind the resilience and adaptability of T. hoshinota. As climate change continues to push marine environments to their limits, understanding how this sponge flourishes in conditions that would otherwise be detrimental to many marine organisms is not just interesting—it’s essential.
The research focuses on the genetic underpinnings that allow T. hoshinota to prosper in the face of rising sea temperatures, ocean acidification, and various pollutants. It is now well established that climate change has dire implications for marine biodiversity. The stressors these ecosystems endure can catalyze shifts that drastically alter their composition. As corals struggle, T. hoshinota capitalizes, spreading across coral reefs and frequently leading to mass coral die-offs.
One of the surprising findings of the research was that T. hoshinota possesses a unique set of genes that facilitate the breakdown of harmful substances in its environment. These genes effectively enable the sponge to withstand conditions that would typically weaken or kill other marine organisms. The genomic data indicates that this sponge has evolved sophisticated biochemical pathways, granting it a metabolic edge in nutrient acquisition even when resources are scarce.
Perhaps more alarming is the sponge’s ability to adapt rapidly to changing environmental conditions. The study highlights the sponge’s remarkable genomic plasticity, allowing for quick responses to stress. While many coral species take years or decades to make adaptations, T. hoshinota seems to have a genetic toolkit that allows for swift modifications. This adaptability could mean that the sponge will remain a dominant presence within marine ecosystems, further complicating conservation efforts targeting coral health.
Quantifying the threat of ocean acidification to predict its impact on shellfish larvae
1. Key Points
As ocean acidification worsens, concerns over its effects on calcifying organisms※1, including shellfish and coral, are increasing. To date, research has been unable to quantify the impact of ocean acidification on calcifying organisms, largely because of their incredibly small shells.
In the present study, mollusk larvae with tiny shells measuring approximately 0.1 mm were raised in an environment designed to simulate severe ocean acidification. Subsequently, a high-resolution microfocus X-ray computed tomography (MXCT)※2 scanner was used to obtain three-dimensional measurements of the shells. For the first time, globally, changes in shell morphology, in terms of reduced shell thickness, size, and density, were quantified precisely.
In addition, gene expression in genomic domains involved in shell formation was reduced significantly, which marks a significant step toward comprehensive understanding of the effects of ocean acidification on organisms, with respect to biological responses and the impact on shells.
The methodology employed in the present study could also be applied to other organisms with calcified shells or skeletons, such as bivalves and corals. Such studies could facilitate environmental impact assessment, marine conservation, and fisheries resource management in future.
Fig. 1. Predicting the future using a technique to measure the shell density of shellfish larvae.
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2. Overview
As global warming intensifies, so does ocean acidification. Such ocean acidification poses a serious threat to marine ecosystems. It not only lowers the pH of seawater but also reduces the “aragonite saturation state (Ωaragonaite)※3, ※4 ”. Aragonite is a crystalline form of calcium carbonate. When the “aragonite saturation state” is 1 or higher, it indicates a supersaturated state; conversely, values below 1 indicate an unsaturated state. The value is as an indicator of how easily organisms can form aragonite-based shells or skeletons. When the aragonite saturation state decreases, it is more difficult for organisms to form aragonite shells or skeletons. However, evaluating the effects of ocean acidification on early developmental stages of organisms such as plankton and mollusk larvae with aragonite shells, has proven challenging. Their shells are exceptionally small (approximately 0.1 mm in diameter and only a few micrometers※5 thick), which makes precise quantitative assessment more challenging than with mature specimens.
To address the challenges above, Keisuke Shimizu (Associate Researcher) and Katsunori Kimoto (Acting Group Leader) from the Japan Agency for Marine-Earth Science and Technology Research Institute for Global Change Earth Surface System Research Center, alongside Masahide Wakita (Associate Researcher, Mutsu Research Institute), carried out joint research with Takenori Sasaki (Associate Professor, University Museum at the University of Tokyo). The team analyzed the morphology of the shells of shellfish larvae, using high-resolution MXCT and scanning electron microscopy (SEM)※6, as well as gene expression. Globally, the research team is the first to successfully visualize and quantify the effects of decreased aragonite saturation on the growth and structure of extremely small shells (approximately 0.1 mm) composed of aragonite crystals, using shell density (which is analogous to human bone density) as a novel growth marker. In addition, the findings suggest that a decrease in aragonite saturation may both directly impact shells and influence gene expression domains involved in shell formation in shellfish larvae. The findings could facilitate prediction of the effects of environmental change (such as global warming and acidification) on calcifying organisms such as shellfish and corals.
These results have been published in the Journal of Molluscan Studies on September 18 (Japan time). The research was conducted with the support of a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (KAKENHI; JP23H02299).
Une nouvelle limite planétaire a été franchie pour la première fois en 2025: l’acidification des océans. Ce processus, directement lié à nos émissions de CO2, est délétère pour les écosystèmes marins.
L’acidité des océans perturbe la reproduction, la croissance et les fonctions métaboliques de nombreuses espèces. WIKIMEDIA COMMONS
Après celle sur le cycle de l’eau en 2023, une nouvelle limite planétaire a été franchie pour la première fois en 2025: l’acidification des océans. Provoquée par nos émissions de CO2, elle vient de dépasser un seuil alarmant. C’est la conclusion centrale du rapport sur les limites planétaires publié le 24 septembre par le Planetary Boundaries Science Lab, un laboratoire allemand dépendant de l’Institut de recherche de Potsdam sur les effets du changement climatique.
La notion de limites planétaires est développée depuis 2009 par plusieurs scientifiques à la pointe des sciences du «système Terre», autour notamment du chercheur suédois Johan Rockström. Ils définissent ces limites comme autant de seuils dans des processus planétaires à ne pas franchir, au risque de déstabiliser l’ensemble du système de manière irréversible, avec des effets majeurs pour le vivant. L’humanité, entre autres, dépend depuis 12 000 ans de cette stabilité pour «vivre, grandir et prospérer en toute sécurité», répète avec insistance le rapport.
7 limites dépassées sur 9
Les signaux rouges clignotent de toutes parts. Sur neuf limites planétaires identifiées par les chercheurs, l’acidification des océans est la septième à être franchie. Les six premières (changement climatique, cycle de l’eau, biodiversité, perturbations du cycle de l’azote et du phosphore, déforestation et changement d’utilisation des sols, pollution terrestre par des milliers de substances synthétiques) sont non seulement déjà dépassées, mais leur situation continue de s’aggraver.
Seules deux limites sont respectées et ne se détériorent pas: la pollution aux aérosols atmosphériques et le maintien de la couche d’ozone.
L’acidité de l’eau à la surface de l’océan a augmenté de 30 à 40% depuis l’ère préindustrielle, alertent les auteurs du rapport. Un processus directement lié à nos émissions de gaz à effet de serre puisque l’océan a la capacité de dissoudre une partie du CO2 atmosphérique. Il est même un puits de carbone essentiel, qui absorbe environ le quart de l’ensemble des émissions anthropiques.
Revers de la médaille: ce CO2 dissout dans l’eau conduit, par une suite de réactions chimiques, à augmenter l’acidité de l’océan. Un phénomène extrêmement délétère pour les organismes marins. Beaucoup d’espèces – coraux, mollusques et certains crustacés notamment – ont de plus en plus de difficulté à fabriquer leur coquille et leur squelette lorsque l’acidité augmente.
Working from a dock on St. Helena Island, S.C., on a sweltering day this summer, Ed Atkins pulled in a five-foot cast net from the water and dumped out a few glossy white shrimp from the salt marsh.
Mr. Atkins, a Gullah Geechee fisherman, sells live bait to anglers in a shop his parents opened in 1957. “When they passed, they made sure I tapped into it and keep it going,” he said. “I’ve been doing it myself now for 40 years.”
These marshes, which underpin Mr. Atkins’s way of life, are where the line between land and sea blurs. They provide a crucial nursery habitat for many marine species, including commercial and recreational fisheries.
But these vast, seemingly timeless seascapes have become some of the world’s most vulnerable marine habitats, according to a new study published on Thursday in the journal Science that adds up and maps the ways human activity is profoundly reshaping oceans and coastlines around the world.
Soon, many of Earth’s marine ecosystems could be fundamentally and forever altered if pressures like climate change, overfishing, ocean acidification and coastal development continue unabated, according to the authors.
Temperatures in the Mediterranean are currently rising to record levels. Instead of a refreshing dip, holidaymakers in places like Greece, Italy, and Spain, among other places, are now facing water temperatures up to 28° C or even higher. With an average water temperature of 26.9° C, July 2025 was the warmest since records began for the Mediterranean Sea, according to the Copernicus Earth Observation Service.
Warming caused by climate change is considered—alongside stressors such as overfishing, pollution, and habitat destruction—a major factor threatening marine and coastal habitats.
“The consequences of warming are not only projections for the future, but very real damages we are witnessing now. The continuing rise in temperatures, sea level and ocean acidification cause severe risks for the environment in and around the Mediterranean Sea,” says Dr. Abed El Rahman Hassoun, Biogeochemical Oceanographer at the Helmholtz Center for Ocean Research Kiel.
Meta-study on climate change scenarios
Dr. Hassoun and Prof. Dr. Meryem Mojtahid, Professor of Paleo-Oceanography at the University of Angers and at the Laboratory of Planetology and Geosciences (France), working with colleagues, have investigated the effects of climate change on marine and coastal ecosystems in the Mediterranean region. Their paper is published in the journal Scientific Reports.
The projections of the meta-study are based on recognized climate scenarios of the IPCC (Intergovernmental Panel on Climate Change). The research team analyzed 131 scientific studies on the Mediterranean published up to August 2023. For the first time, this resulted in a so-called “burning ember” diagram for Mediterranean marine and coastal ecosystems—a risk assessment tool originally developed by the IPCC.
“The diagram clearly shows how strongly climate change threatens key ecosystems. I hope our results will help raise awareness and inspire real action to protect these unique ecosystems,” says Mojtahid. The study also draws on the Research Initiative on Climate Change and Environmental Degradation in the Mediterranean Region (MedECC). In 2020, the initiative published the first Mediterranean Assessment Report under the name MAR1, thus playing a key role in consolidating knowledge on climate and environmental changes in the Mediterranean area.
Each year, billions upon billions of tons of CO2 are pumped into the atmosphere. A significant proportion of this ends up in Earth’s oceans, where it can react with water to form carbonic acid, which causes ocean acidification.
While a lot of research has focused on how this process occurs deep inside the liquid, less attention has been paid to how this reaction proceeds at aqueous interfaces, where water meets another substance, for example, at the ocean surface.
In a new study published in PNAS, Cambridge and University College London researchers have found that CO₂ can react within the very top layer of water, through a new so-called ‘In and Out’ mechanism. In this process, instead of fully dissolving into the water, CO₂ briefly dips into the surface layer, reacts, and then reemerges. This happens in a very thin layer, just a few molecules thick.
“It is like, instead of diving deep into the water to react, CO₂ does a quick dip in the water, partially dissolving in the topmost layer of water where it can react to form carbonic acid. This acid species then returns to the surface and pops back out,” said Samuel Brookes, first author of the paper and a PhD student at Cambridge’s Yusuf Hamied Department of Chemistry and Cavendish Laboratory.
The ‘In and Out’ mechanism challenges previous assumptions about where and how CO₂ can turn into carbonic acid and shows that reactions can happen right at the water’s surface, not just deep within it.
Sharks without teeth might sound like the stuff of dreams to swimmers and surfers. Now a new study has found that ocean acidification could leave the apex predators without their critical survival weapon.
Shark jaws carry several rows of teeth and new ones quickly push forward to replace losses. However, rapidly acidifying oceans are damaging shark teeth and could speed losses past replacement rates. Sharks with bad teeth could struggle to feed themselves efficiently, “potentially affecting shark populations and marine ecosystem stability”, the study said.
Ocean acidification is caused by rapid carbon dioxide absorption creating a chain reaction that lowers pH levels. Projections suggest oceans could be far more acidic by the year 2300, falling from a current average pH of about 8.1 to 7.3, a change that will have “profound implications for marine organisms”, the study said.
To test acidification effects, researchers kept 60 freshly fallen shark teeth in artificial seawater tanks, one matching the current ocean average pH of 8.1, another with the projected 7.3 pH. The teeth, safely collected from a German aquarium, had already been naturally discarded by six male and four female blacktip reef sharks.
Maximilian Baum, who conducted the study, with a blacktip reef shark jaw. He found increased root corrosion and altered serration. Photograph: Roman Müller-Böhm
Carbon dioxide in the atmosphere enters the ocean at the surface and has been increasing the acidity of Pacific waters since the beginning of the industrial revolution over 200 years ago. A new study, led by University of Hawai‘i at Mānoa oceanographers, revealed that the ocean is acidifying even more rapidly below the surface in the open waters of the North Pacific near Hawai‘i. Their discovery was published recently in theJournal of Geophysical Research: Oceans.
“Ocean acidification has far‐reaching consequences for ocean biology and the global climate,” said Lucie Knor, lead author of the study and postdoctoral researcher in the UH Mānoa School of Ocean and Earth Science and Technology (SOEST). “We expected some indicators of ocean acidification to be changing more rapidly below the surface, because that was what some global studies have previously discovered, but we were very surprised that this was true for every single ocean acidification indicator.”
Knor and co-authors analyzed a 35‐year record of ocean carbon measurements made by the Hawai’i Ocean Time-series program throughout the entire water column–from the surface to nearly three miles deep–at the open ocean field site 60 miles north of O‘ahu, Hawai‘i, Station ALOHA.
Tully Rohrer, Lucie Knor, Fernando Pacheco, Daniel Fitzgerald with the CTD Rosette that collects Hawai’i Ocean Time-series water samples. Credit: Carolina Funkey.
They found that in all layers, there are increases of carbon from natural decomposition of sinking organisms. In some layers, accelerated acidification is associated with fresher and colder waters.
“Deeper waters are already naturally quite acidic in the North Pacific, so quickly increasing acidity could negatively impact plankton species and other organisms that live below the surface,” said Knor. “In the long run, these changes in ocean chemistry also make it harder for the ocean to keep taking up more CO₂ from the atmosphere.”
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“We illustrate that regional-scale changes in source water chemistry and circulation are substantial drivers of the subsurface intensification of ocean acidification around Hawaii,” said Christopher Sabine, co-author of the article and Oceanography professor in SOEST.
Currently, the research team is investigating the carbon specifically from human-made sources in the water column at Station ALOHA and how that is changing over time in different layers.
A combination of three phenomena is increasingly threatening ecosystems in the southern and equatorial regions of the Atlantic ocean—marine heat waves, high acidification, and low chlorophyll concentration.
Before 2016, it was unusual for these factors to converge. Since then, they have been observed simultaneously every year. All three phenomena stem from the current climate emergency.
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The increased occurrence of these three drivers makes it impossible for ecosystems to recover, as a minimum amount of time is required for regeneration to take place.
The study
The study was published in the journal Nature Communications and was carried out by researchers from the Federal University of Santa Catarina (UFSC) and the National Institute for Ocean Research (INPO).
The data cover 1999 through 2018 and were collected using research satellites. Six regions of the South Atlantic were evaluated, considering their high biodiversity and biological productivity.
The locations studied are the Western Equatorial Atlantic (near the coast of the Brazilian Northeast), the Western Subtropical Atlantic, the Brazil-Malvinas Confluence, the Gulf of Guinea, the Angola Front, and the Agulhas Current (which connects the Atlantic and Indian Oceans).
