Shellfish aquaculture is a vital industry in the US, but one which faces mounting challenges threatening both productivity and business viability. Research often fails to align with growers’ immediate needs, so researchers set out to help close this gap in a new study published in Aquaculture Reports, interviewing over 30 commercial shellfish growers across the US Pacific region.
Funded as part of NOAA’s Ocean Acidification Program, former Research Scientist at the University of Washington School of Aquatic and Fishery Sciences (UW SAFS) and now a Fisheries Resource Management Specialist with NOAA Fisheries, Connor Lewis-Smith led the research to document how industry participants perceive ocean acidification threats and evaluate emerging adaptation strategies that are actively being researched: parental priming and native species portfolio diversification.
The research team included scientists from NOAA Northwest Fisheries Science Center (NWFSC), Puget Sound Restoration Fund, UW SAFS, and the University of the Virgin Islands. They interviewed owners, field managers, hatchery managers, and other staff from operations across five states on the Pacific Ocean: Washington, Oregon, California, Alaska, and Hawaii. “Operations ranged in scale and included hatchery, nursery, and growout components. We also included tribally managed and tribally affiliated businesses,” Lewis-Smith said.
Bird’s-eye view of an oyster farm (Connor Lewis-Smith).
Ocean acidification has been identified in the Planetary Boundary Framework as a planetary process approaching a boundary that could lead to unacceptable environmental change. Using revised estimates of pre-industrial aragonite saturation state, state-of-the-art data-model products, including uncertainties and assessing impact on ecological indicators, we improve upon the ocean acidification planetary boundary assessment and demonstrate that by 2020, the average global ocean conditions had already crossed into the uncertainty range of the ocean acidification boundary. This analysis was further extended to the subsurface ocean, revealing that up to 60% of the global subsurface ocean (down to 200 m) had crossed that boundary, compared to over 40% of the global surface ocean. These changes result in significant declines in suitable habitats for important calcifying species, including 43% reduction in habitat for tropical and subtropical coral reefs, up to 61% for polar pteropods, and 13% for coastal bivalves. By including these additional considerations, we suggest a revised boundary of 10% reduction from pre-industrial conditions more adequately prevents risk to marine ecosystems and their services; a benchmark which was surpassed by year 2000 across the entire surface ocean.
L’impact de l’acidification de la mer Méditerranée sur la biodiversité marine est un sujet d’actualité préoccupant… Mais, certains êtres vivants semblent tirer leur épingle du jeu face à cette acidification : les herbiers marins de posidonie ! Mais jusqu’à quand ? La classe des 5e 2 du collège Albert Camus vous invite à découvrir ce trésor de la méditerranée, peu connu du grand public à travers leur émission « Radio Camus 06 s’exprime ! » Crédits : Remerciement à M. Gattuso (IMEV) pour cette entrevue enrichissante, Mme Hansson (IAEA) pour la documentation, à Mme Dargent pour son écoute et ses conseils, aux professeurs et à la classe de 5e2 pour la mise en œuvre du projet mené finalisé et à toutes les personnes qui ont participé au podcast : Emma, Iloé, Sophie, Camille, Nichita, Francesco, Amy, Manon, Sacha, Carla, Nolhan, Hadrien, Mme Cali, M. Sanchez, Mme Heams-Nérac, M. Lombardo.
The pH of the world’s oceans has decreased since the Industrial Revolution due to the oceanic uptake of increased atmospheric CO2 in a process called ocean acidification. Low pH has been linked to negative impacts on the calcification, growth, and survival of calcifying invertebrates. Along the Western Antarctic Peninsula, dominant brown macroalgae often shelter large numbers of diverse invertebrate mesograzers, many of which are calcified. Mesograzer assemblages in this region are often composed of large numbers of amphipods which have key roles in Antarctic macroalgal communities. Understanding the impacts of acidification on amphipods is vital for understanding how these communities will be impacted by climate change. To assess how long-term acidification may influence the survival of different members in these assemblages, mesograzers, particularly amphipods, associated with the brown alga Desmarestia menziesii were collected from the immediate vicinity of Palmer Station, Antarctica (S64°46′, W64°03′) in January 2020 and maintained under three different pH treatments simulating ambient conditions (approximately pH 8.1), near-future conditions for 2100 (pH 7.7), and distant future conditions (pH 7.3) for 52 days then enumerated. Total assemblage number and the relative proportion of each species in the assemblage were found to be similar across the pH treatments. These results suggest that amphipod assemblages associated with D. menziesii may be resistant to long-term exposure to decreased pH.
The ocean and the atmosphere are constantly seeking balance.
Gases like oxygen, nitrogen, and carbon move between the ocean’s surface and the atmosphere by billions of metric tons every year.
A higher concentration of one gas in the atmosphere leads to more of that gas being taken up by the ocean as the two try to reach a state of balance – or equilibrium. However higher concentrations of carbon, emitted by human activities predominantly through the burning of fossil fuels, have been observed in the atmosphere since the Industrial Revolution.
This has consequently led to an increase in the ocean’s accumulation of carbon globally. This increase in ocean carbon has caused a chain of chemical reactions driving one of the primary environmental threats to marine ecosystems, fisheries and coastal communities – ocean acidification.
Carbon dioxide absorbed at the ocean’s surface binds with water molecules to produce an acid known as carbonic acid (H2CO3), which dissociates into bicarbonate ions (HCO3–) and a free-floating hydrogen ion (H+).
A rise in hydrogen ions is what changes the pH of any liquid, lowering the pH and making it more acidic.
Ocean water is turning ever so slightly more acidic, and that small shift has now pushed the chemistry of the sea past a point that scientists once marked as the global “do not cross” line.
A new assessment shows that by 2020 the average concentration of calcium carbonate, a building block for shells and reefs, had fallen more than 20 percent from pre‑industrial levels in many regions.
This results in a thinning of nature’s protective shield for corals, oysters, other mollusks, and countless plankton.
“Ocean acidification isn’t just an environmental crisis, it’s a ticking timebomb for marine ecosystems and coastal economies,” said Professor Steve Widdicombe of Plymouth Marine Laboratory, after reviewing the study.
How carbon drives ocean acidity
One extra molecule of carbon dioxide in the air means another will slip into the sea, combine with water, and release a hydrogen ion.
Sargassum hemiphyllum is a major brown macroalga and has important ecological and economic significance. Ocean acidification and nitrogen enrichment are serious threats to marine ecosystems primarily by altering the physiology of organisms. However, the response of S. hemiphyllum to the combined effects of ocean acidification and elevated nitrogen levels remains unclear. This study conducted a 7-day dual-factor experiment to investigate the physiological and transcriptional responses of S. hemiphyllum under two CO2 levels (400 μatm and 1000 μatm) and two NO3⁻ levels (50 μmol/L and 300 μmol/L). The results showed that high CO2 and NO3- concentrations promoted the synthesis of photosynthetic pigments including qN and NPQ. Physiological results showed that high CO2 and the combined high NO3- and CO2 treatments enhanced growth rate and NO3- uptake rate, but NR activity was significantly decreased. Transcriptome analysis identified differentially expressed genes involved in oxidative phosphorylation, carbon metabolism, the TCA cycle, and nitrogen metabolic pathways. Notably, genes related to oxidative phosphorylation and TCA cycle were significantly up-regulated under high NO3- and dual-factor treatments, suggesting that carbohydrate metabolism and energy metabolism of S. hemiphyllum were significantly enhanced. The qRT-PCR analysis revealed that the expression levels of key genes involved in carbon fixation and nitrogen metabolism, including PFK, PRK, GAPDH, Rubisco, NR, and MDH, were significantly downregulated. These findings elucidate the molecular mechanisms by which S. hemiphyllum adapts to ocean acidification and nitrogen enrichment, offering valuable insights for understanding its capacity to withstand changing marine environments.
The carbonate system in Mediterranean coastal zones remains inadequately quantified, exhibiting substantial discrepancies in research on CO2 partial pressure (pCO2), particularly in the insufficiently studied Algero-Provencal sub-basin. This study addresses a critical knowledge gap by providing the first characterization of carbonate chemistry parameters along the Algerian coast, a region previously lacking published data. The findings contribute to enhancing the accuracy of regional and global ocean biogeochemical models, particularly for the southern Mediterranean.The Algiers coastline comprises three bays: Bou-Ismail Bay (BB) to the west, Algiers Bay (BA) at the center, and Zemmouri Bay (BZ) to the east. A detailed dataset was assembled from direct and indirect measurements of carbonate system parameters in the surface waters of the three bays collected during spring and summer campaigns from 2011 to 2017. The carbonate system exhibited significant heterogeneity.During the June 2014 campaign, pCO2levels exhibited considerable variation among the three bays. BA exhibited the lowest pCO2 at 284.6 µatm, whereas BB and BZ recorded markedly elevated values of approximately 516 µatm. The extensive spatial range of approximately 250 µatm was predominantly influenced by biological processes, with BA exhibiting greater photosynthetic activity and dissolved oxygen (DO) levels compared to BB and BZ. Sampling campaigns were conducted in BA and BB from 2011 to 2017. pCO2 and DO levels in BA and BB demonstrated considerable temporal variability. In BA, pCO2 fluctuated between a minimum of 227 µatm during a phytoplankton bloom in July 2013 (with DO supersaturation at 180 %) and a maximum of 466 µatm in April 2011, attributed to rainfall and respiratory processes(with DO undersaturation at 76 %). In BB, spring campaigns (March 2015 and 2017) exhibited DO saturation levels (102–112 %) and lower pCO2 values (392 µatm), while summer campaigns demonstrated pCO2 supersaturation (up to 541 µatm) and DO undersaturation (70 %) attributable to thermal and respiratory processes.
Sea temperature and pH are key environmental factors affecting krill habitats.
Krill habitat suitability shows spatiotemporal heterogeneity across regions.
Under low emission scenario, krill habitat suitability will recover by 2100.
Under high emission scenario, highly suitable habitat may be lost by 2100.
Abstract
Antarctic krill plays a crucial role in the Southern Ocean ecosystem. However, data limitations leave a significant gap in understanding the changes in krill habitat suitability. This study integrated data from Chinese Antarctic research expeditions and KRILLBASE database, using Maxent model to assess spatiotemporal shifts in krill suitable habitat from 1991 to 2100 across the eastern and western Antarctic under SSP-RCP scenarios. The results reveal regional differences in climate and environmental impacts on krill habitats. Sea temperature and pH are dominant environmental factors affecting habitat suitability. With climate changes, the suitable habitats are shifting toward higher latitudes, and the latitudinal shift of habitats in CCAMLR Areas 48 and 58 is in the opposite direction. Under high-emission scenarios, krill habitats face severe contraction and loss, whereas low-emission scenarios suggest partial recovery by 2100. Coordinated global action to protect krill habitats is essential to address the biodiversity crisis in the Southern Ocean.
Until now, ocean acidification has not been deemed to have crossed its ‘planetary boundary’, but a major new study led by the UK’s Plymouth Marine Laboratory and the US-based NOAA – also launched this week – found the safety limit was reached five years ago.
Marking a significant milestone in Indigenous-led environmental stewardship, the Makah Tribe of Noah Bay in Washington has detailed the launch of their Ocean Acidification Action Plan during the 2025 United Nations Ocean Conference in Nice, France this week.
The announcement was made during a special side event hosted by the International Alliance to Combat Ocean Acidification in recognition of the gathering political momentum surrounding action on ocean acidification.
An alarming report was issued this week to coincide with the UN Ocean Conference in which scientists warned that ocean acidification was a ‘ticking time bomb’ and far worse than first feared.
Until now, ocean acidification has not been deemed to have crossed its ‘planetary boundary’, but a major new study led by the UK’s Plymouth Marine Laboratory and the US-based NOAA has found this safety limit was reached five years ago.
It’s a crisis that is contributing to the pressures being faced by coral reef ecosystems, the loss of habitats, and a threat to the survival for shell-building marine creatures by reducing the availability of calcium carbonate – a crucial building block that many of these marine organisms need to form shells and skeletons.
For Millennia, the Makah People’s culture, well-being, and economy have been intrinsically linked to the ocean’s bounty, with fish, shellfish, and other marine resources playing a role in food security, livelihoods, and cultural practices and traditions.
But today, many of the marine species on which the Makah tribe’s livelihood and traditions depend are at risk from ocean acidification.
It occurs when the ocean absorbs excess carbon dioxide from the atmosphere, setting off chemical reactions that acidifies seawater. This chemical alteration threatens marine organisms that rely on carbonate-based shells and skeletons, creating cascading effects that can knock entire marine ecosystems out of balance.
The Makah tribe is located in a region that was the first in the world to observe the impacts of changing ocean chemistry on traditional foods, including shellfish. Their Action Plan is a decisive step towards addressing this critical issue with Indigenous perspectives and priorities, combined with scientific research.
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While here at the UN Ocean Conference, Makah Tribe Natural Resource Policy lead, Mr Anthony Bitegeko was joined by the Portuguese Secretary of State of Fisheries and Maritime Affairs, Salvador Malheiro as well as Ms Mette Westergaard Bech, team leader on Ocean Acidification, Ministry of Environment and Gender Equality for Denmark to release the Ocean Acidification Action Plans.
They join countries such as Greece, Mexico, Fiji, Palau, Canada, and the UK in creating an action plan.
Key components of the action plan include integrating ocean acidification across mainstream climate, ocean, and coastal management plans; establishing cross-sector partnerships to ensure regional ocean acidification science is being applied to local decision making; developing educational initiatives; and advocating for policy changes at local, state, and federal levels.
“It’s clear that governments can no longer afford to overlook acidification in mainstream policy agendas,” said Ocean Acidification Alliance execrative director, Jessie Turner.
“That’s why we are so proud and encouraged by members of the National Ocean Acidification Action Planning Leadership Circle as they do the hard work to ensure that action on ocean acidification and climate change is a critical part of domestic and multilateral agendas.”
The Makah Tribe’s story is just one of many, with coastal communities around the world already concerned about the impact of ocean acidification.
Professor Steve Widdicombe, co-chair of the Global Ocean Acidification Observing Network and the co-focal point for the UN’s Sustainable Development Goal 14 target 3 – aiming to minimise and address the impacts of ocean acidification.
After a week of deliberation and discussion, the United Nations Ocean Conference today by consensus adopted a political declaration titled “Our ocean, our future: united for urgent action”, stressing that the ocean plays an essential role in mitigating the adverse effects of climate change.
“The ocean is fundamental to life on our planet and to our future, and we remain deeply alarmed by the global emergency it faces”, the Conference’s outcome document (A/CONF.230/2025/L.1) said, adding also: “Action is not advancing at the speed or scale required to meet Goal 14 and realize the 2030 Agenda [for Sustainable Development]”.
The declaration, also known as the “Nice Ocean Action Plan”, expressed deep concern that the ability of the ocean and its ecosystems to act as a climate regulator and to support adaptation has been “weakened”.
Underlining the importance of interlinkages between the ocean, climate and biodiversity, the declaration called for enhanced global action to minimize the impact of climate change and ocean acidification. It emphasized the particular importance of implementing various UN agreements and frameworks, recognizing that it would significantly reduce the risks and impacts of climate change and help to ensure the health, sustainable use and resilience of the ocean.
Further emphasizing the need to adapt to the “unavoidable effects” of climate change, the declaration affirmed the importance of the full and effective implementation of the Convention on Biological Diversity and its Protocols, as well as the Kunming-Montreal Global Biodiversity Framework.
Bivalves play a key role in coastal ecosystems and provide society with many ecosystem services. Anthropogenic activities produce a multitude of interacting stressors which can cause unexpected responses in the physiology, behaviour, condition, development, reproduction and survival of bivalves. Responses can be (1) additive: the response is the sum of the effect of individual stressors, (2) synergistic: the combined effect is greater than the sum of individual stressors or, (3) antagonistic: the combined effect is smaller than the sum of individual stressors. There has been a proliferation of research on the effects of multiple stressors on marine bivalves but an evaluation of the literature in the context of management and restoration has not been undertaken. This review and meta-analysis aimed to determine bivalves’ responses to stressor interactions and identify research trends and gaps. The meta-analysis highlights a prevalence of antagonistic and additive responses to stressors and an overall antagonistic effect. The observed antagonistic responses may be associated with how multiple stressor studies are being conducted. The literature demonstrates a bias towards individual-level laboratory experiments that focus on responses of adult bivalves to climate-change related ‘global’ stressors. Suggestions for future research include an emphasis on (1) ‘local’ stressors, (2) earlier life stages, and (3) field-based studies incorporating stressor gradients and spatiotemporal variability. These investigations will complement the existing knowledge base and ultimately provide a more complete picture of the impacts of multiple stressors on bivalves– information that is vital for management decision-making and restoration of bivalve populations.
Researchers have found that ocean acidification entered a “danger zone” in 2020, suggesting increased carbon dioxide levels have caused Earth to breach another planetary boundary.
The new study suggests our planet’s oceans are becoming too acidic to remain healthy. (Image credit: Philip Thurston via Getty Images).
Earth’s oceans are in worse condition than scientists thought, with acidity levels so high that our seas may have entered a “danger zone” five years ago, according to a new study.
Humans are inadvertently making the oceans more acidic by releasing carbon dioxide (CO2) through industrial activities such as the burning of fossil fuels. This ocean acidification damages marine ecosystems and threatens human coastal communities that depend on healthy waters for their livelihoods.
Previous research suggested that Earth’s oceans were approaching a planetary boundary, or “danger zone,” for ocean acidification. Now, in a new study published Monday (June 9) in the journal Global Change Biology, researchers have found that the acidification is even more advanced than previously thought and that our oceans may have entered the danger zone in 2020.
The researchers concluded that by 2020, the average condition of our global oceans was in an uncertainty range of the ocean acidification boundary, so the safety limit may have already been breached. Conditions also appear to be worsening faster in deeper waters than at the surface, according to the study.
“Ocean acidification isn’t just an environmental crisis — it’s a ticking time bomb for marine ecosystems and coastal economies,” Steve Widdicombe, director of science and deputy chief executive at Plymouth Marine Laboratory, a marine research organization involved in the new study, said in a statement. “As our seas increase in acidity, we’re witnessing the loss of critical habitats that countless marine species depend on and this, in turn, has major societal and economic implications.”
In 2009, researchers proposed nine planetary boundaries that we must avoid breaching to keep Earth healthy. These boundaries set limits for large-scale processes that affect the stability and resilience of our planet. For example, there are boundaries for dangerous levels of climate change, chemical pollution and ocean acidification, among others.
A 2023 study found that we had crossed six of the nine boundaries. The authors of that study didn’t think the ocean acidification boundary had been breached at the time, but they noted it was at the margin of its boundary and worsening.
Katherine Richardson, a professor at the Globe Institute at the University of Copenhagen in Denmark who led the 2023 study and was not involved in the new study, told Live Science that she was “not at all surprised” by the new findings.
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What causes ocean acidification?
Ocean acidification is mostly caused by the ocean absorbing CO2. The ocean takes up around 30% of CO2 in the atmosphere, so as human activities pump out CO2, they are forcing more of it into the oceans. CO2 dissolves in the ocean, creating carbonic acid and releasing hydrogen ions. Acidity levels are based on the number of hydrogen ions dissolved in water, so as the ocean absorbs more CO2, it becomes more acidic.
Marine phytoplankton are facing increasing dissolved CO2 concentrations and ocean acidification caused by anthropogenic CO2 emissions. Mixotrophic organisms are capable of both photosynthesis and phagotrophy of prey and are found across almost all phytoplankton taxa and diverse environments. Yet, we know very little about how mixotrophs respond to ocean acidification. Therefore, we studied responses to simulated ocean acidification in three strains of the mixotrophic chrysophyte Ochromonas (CCMP1391, CCMP2951, and CCMP1393). After acclimatization of the strains to treatment with high-CO2 (1000 ppm, pH 7.9) and low-CO2 concentrations (350 ppm, pH 8.3), strains CCMP1393 and CCMP2951 both exhibited higher growth rates in response to the high-CO2 treatment. In terms of the balance between phototrophic and heterotrophic metabolism, diverse responses were observed. In response to the high-CO2 treatment, strain CCMP1393 showed increased photosynthetic carbon fixation rates, while CCMP1391 exhibited higher grazing rates, and CCMP2951 did not show significant alteration of either rate. Hence, all three Ochromonas strains responded to ocean acidification, but in different ways. The variability in their responses highlights the need for better understanding of the functional diversity among mixotrophs in order to enhance predictive understanding of their contributions to global carbon cycling in the future.
First investigation limpet populations collected from the naturally acidified site.
Increased dimension and energy endpoints in Patella caerulea from very low pH (<7.4).
Induction of antioxidant systems and neurotoxicity in Patella rustica exposed to OA.
Transplant of Patella caerulea activated oxidative stress and neurotoxicity endpoints.
Abstract
Ocean acidification (OA) is reported to entail a detrimental impact on calcifying organisms. Nevertheless, patellid limpets – P. caerulea, P. rustica, and P. ulyssiponensis – are able to persist in extremely low pH conditions inside the Castello Aragonese CO2 vent systems (Ischia Island), suggesting that they may have developed tolerance to OA, through plasticity and/or adaptive mechanisms. The aim of this study is to evaluate the long-term strategies adopted by limpets that spent their entire life cycle in naturally acidified conditions and the short-term ones induced by a 30-day in situ transplant experiment.
Regarding native limpet populations, P. caerulea exhibited increasing size and higher energy resources in the extremely acidified site, potentially related to different food availability or to reduction in competition and/or predatory pressure; furthermore, no effects on oxidative stress, biomineralization and neurotoxicity occurred. Similarly, P. ulyssiponensis didn’t exhibit any significant effects among different pH conditions regarding biochemical endpoints. Conversely, P. rustica displayed a significant modulation of almost all biochemical parameters, possibly due to its different position on the rocky shore. The short-term exposure of P. caerulea produced a decrease in protein content and an increase in glycogen content in the extreme acidified site, with an induction of superoxide dismutase and glutathione-S-transferases activities in the intermediate pH site.
Overall, our study revealed that different species of the same genus may have developed distinct responses to OA and suggested different mechanisms to cope with short and long-term exposure to low pH conditions.
As the largest active carbon reservoir on Earth, the ocean is a cornerstone of the global carbon cycle, playing a pivotal role in modulating ocean health and regulating climate. Understanding these crucial roles requires access to a broad array of data products documenting the changing chemistry of the global ocean as a vast and interconnected system. This review article provides a comprehensive overview of 60 existing ocean carbonate chemistry data products, encompassing compilations of cruise datasets, derived gap-filled data products, model simulations, and compilations thereof. It is intended to help researchers identify and access data products that best align with their research objectives, thereby advancing our understanding of the ocean’s evolving carbonate chemistry.
The response of marine organisms to ocean acidification depends on their adaptive capacity, which can be partially understood by evaluating the amount of existing variability in CO2 sensitivity within a species. The process of local adaptation is a mechanism that can drive variability in CO2 sensitivity. In this study, we measured the survival and molt rate of Dungeness crab Metacarcinus magister zoeae that were produced by gravid crabs collected from 3 locations in waters off of Washington State, USA, and reared in a common laboratory in ambient, medium, and high CO2 treatments. The 3 locations from which crabs were collected have different carbonate chemistry dynamics, and Dungeness crabs in these locations are to some extent genetically distinct. We hypothesized that these conditions may favor local adaptation. We did not find evidence of local adaptation, but did see different levels of CO2 sensitivity associated with the mother. This variation in CO2 sensitivity suggests an adaptive capacity that is likely to influence Dungeness crab response to future acidification.
Projected increases in ocean temperature and partial pressure of carbon dioxide (pCO2) due to anthropogenic carbon emissions are expected to significantly alter coastal marine ecosystems, particularly within the Southern California Bight and Northwest Atlantic Ecoregion. These changes may disrupt food web stability through alterations in abiotic conditions. To assess the impacts of elevated temperature and pCO2 on embryonic development in the superorder Decapodiformes, I investigated two mid-trophic squid species, Doryteuthis opalescens and Doryteuthis pealeii, during their paralarval stage. Specifically, I examined metabolic and morphological responses in squid reared in four seawater treatments: combinations of present-day and projected levels of temperature and pCO2 by the end of the century. The results revealed species-specific responses. D. opalescens paralarvae exhibited generally negative responses, including reduced morphological development, under elevated temperature and pCO2 conditions. In contrast, D. pealeii paralarvae demonstrated positive responses, with increased morphological dimensions under the same conditions. Additionally, D. pealeii paralarvae showed elevated O2 consumption rates, while D. opalescens paralarvae exhibited a more subdued metabolic response to temperature increases. These findings highlight significant interspecific variability in responses to future ocean conditions, despite the similarity in life history traits between the two species. This study underscores the complexity of climate change impacts on Decapodiformes and emphasizes the necessity of species-specific assessments to predict ecological consequences for marine organisms.
The aragonite saturation state (Ωarag) was determined for surface waters of the western Arctic Ocean over 3 years, from 2020 to 2022, to investigate the current state of ocean acidification and to assess the interannual variation in surface Ωarag. In the Chukchi marginal area (CMA), surface Ωarag ranged from 0.97 to 1.86 over 3 years, with an average value of 1.20, indicating near-saturated conditions with respect to aragonite. In the East Siberian marginal area (ESMA), surface Ωarag varied from 0.88 to 1.47, with an average value of 1.12, which was slightly lower than levels in the CMA. The ESMA experienced significant changes in environmental conditions and seawater carbonate chemistry during 2020–2022 compared to 2016–2018. These notable changes in the ESMA during 2020–2022 were attributed to the influence of the Beaufort Gyre. In contrast, the CMA showed little interannual variation in environmental conditions and seawater carbonate chemistry from 2016 to 2022. In the ESMA, the progression of ocean acidification depends on the Arctic Oscillation (AO) state; ocean acidification improves with a positive AO state and worsens when the AO state is negative.
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