Although net negative emissions of carbon dioxide (CO2) are essential to meet climate targets, little is known about how declining atmospheric CO2 levels will affect ocean acidification. Here, by analysing the acidity ([H+]) and corrosivity to aragonite (ΩArag) in eight Earth system models that made simulations under rising then falling CO2 levels, we identify the Arctic as a hotspot for delayed reversibility of ocean acidification. Under falling CO2, Arctic surface waters remain comparatively more acidic, and aragonite-corrosive conditions (ΩArag < 1) persist until atmospheric CO2 drops ~120 ppm below the threshold at which they first appeared under rising CO2. This hysteresis arises from the erosion of the natural surface-layer deficit in dissolved inorganic carbon, initially maintained by sea ice limiting air–sea gas exchange and not fully restored as sea ice recovers during CO2 decline. Thus, the Arctic Ocean experiences not only the greatest acidification but also the most delayed benefits from negative emissions.
Continue reading ‘Persistence of Arctic Ocean acidification under negative emissions’Archive for the 'Science' Category
Persistence of Arctic Ocean acidification under negative emissions
Published 14 August 2026 Science Leave a CommentTags: Arctic, biogeochemistry, chemistry, globalmodeling, modeling
Method for correcting the temperature dependence of field-type glass electrode pH sensors
Published 14 August 2026 Science Leave a CommentTags: chemistry, field, methods, modeling, North Pacific, sensor
Seawater pH measurement is essential for monitoring ocean acidification and its biogeochemical impacts. Glass electrode pH sensors are widely used for in situ applications due to their ease of operation, low power consumption, and no reagent requirements. However, their accuracy can be affected by temperature-dependent effects, particularly those associated with the internal reference solution. Conventional calibration methods based on the Nernst response do not explicitly account for temperature-induced variations in the internal solution, which may lead to systematic bias under conditions with large temperature gradients. In this study, a correction method is proposed to address temperature-dependent errors by modeling the internal pH (pHin). The model incorporates two primary temperature-dependent contributions: the intrinsic temperature dependence of the phosphate buffer and potential shifts caused by activity changes in saturated KCl. These effects are combined through the electrode response factor (fR), defined as the ratio of the observed electrode slope to the theoretical Nernst slope, to estimate pHin as a function of temperature and correct measured pH values to a reference temperature of 25 °C. Application of the method to vertical seawater profiles demonstrated a reduction in deviation from colorimetric reference measurements. The corrected results showed reduced temperature-dependent bias across depth. This approach provides a practical framework for improving the reliability of in situ glass electrode pH measurements under varying thermal conditions. The proposed method addresses equilibrium temperature-dependent effects of the internal solution but does not explicitly account for transient hysteresis, pressure effects, or long-term sensor drift.
Deep dive: evaluating students’ use of Toulmin’s argumentation pattern in chemistry classrooms for constructing scientific arguments about ocean acidification
Published 14 August 2026 Science Leave a CommentTags: chemistry, education
Science education plays a key role in helping students to become responsible citizens, capable of making appropriate decisions based on scientific information, participating in discussions on socio-scientific issues (SSIs), and taking action in the context of climate change. Thus, achieving scientific literacy in general and practising scientific argumentation skills – as part of scientific literacy – in particular, are essential. Therefore, the pilot study presented here focusses on improving upper secondary students’ (ISCED 3) scientific argumentation skills by implementing Toulmin’s Argumentation Pattern (TAP) in the chemistry classroom. We focus on chemistry education to better understand subject-specific argumentation in chemistry classrooms. This pilot study is part of an interventional study that aims to implement TAP as a construction mechanism to improve students’ scientific argumentation skills. Our study is embedded in the SSI of human-induced ocean acidification. In order to gain insight into students’ scientific argumentation patterns and develop adequate teaching materials, we asked 29 upper secondary students to write well-founded arguments to confirm a claim about calcification of coral skeletons made in a newspaper headline. Students’ arguments were constructed prior to and following the provision of support material based on TAP. These arguments were analysed with regards to their formal quality using qualitative content analysis. Our findings indicate that TAP aligned well with our participants’ intuitive arguments. We discuss our findings and propose how using TAP can contribute to teaching and learning chemistry-specific argumentation skills.
Continue reading ‘Deep dive: evaluating students’ use of Toulmin’s argumentation pattern in chemistry classrooms for constructing scientific arguments about ocean acidification’From climate data to regulatory decisions: integrating climate AI into marine EIAs
Published 13 August 2026 Science Leave a CommentTags: policy
Climate change is increasingly reshaping the sustainable development of the ocean through ocean warming, deoxygenation, acidification, and other compounding stressors. Against this backdrop, environmental impact assessment (EIA) has become a pivotal governance instrument for anticipating and reducing the climate-related impacts of human activities at sea. From the United Nations Convention on the Law of the Sea (UNCLOS) to the Agreement on Biodiversity Beyond National Jurisdiction (the BBNJ Agreement), regulatory expectations for marine EIAs are moving toward more structured thresholds, procedural workflows, and reporting obligations. At the same time, rapid advances in climate artificial intelligence (climate AI), such as machine-learning forecasting, deep-learning nowcasting, and agentic AI workflows, are expanding the ability to produce timely, high-resolution, and probabilistic climate information from heterogeneous climate data streams. These capabilities can strengthen climate-related EIAs by combining short-term forecasting and nowcasting for early warning, long-term observation and monitoring for dynamic baselines, and scenario-based climate modelling for impact estimation and decision support. Climate AI can therefore be integrated throughout the EIA workflow rather than appended as an auxiliary layer, translating climate data into regulatory evidence under changing marine-climate conditions. To ensure regulatory robustness and accountability, implementation should be grounded in evidence standards and quality assurance, transparent and auditable documentation, human oversight, responsibility allocation, and formal mechanisms for cross-institutional data sharing. We argue that a standards-driven, AI-enabled EIA framework can improve the relevance, reviewability, and robustness of marine EIA decisions, supporting long-term ocean sustainability under accelerating climate risks.
Continue reading ‘From climate data to regulatory decisions: integrating climate AI into marine EIAs’Pressures on coastal biodiversity in South Africa: a cross-realm review
Published 13 August 2026 Science Leave a CommentTags: review, socio-economy
South Africa’s coastal zone comprises diverse ecosystems and species, and provides important benefits to people. It is also under significant pressure from numerous activities that take place on land, in estuaries, and in the sea, and that are rarely considered together. Here, we review the pressures on coastal biodiversity in South Africa, taking a cross-realm perspective. The pressures are reviewed under 10 themes: biological resource use; energy production and mining; pollution; coastal development; transportation and service corridors; natural systems modifications (sand-flow disruptions, estuarine hydrological regime change, livestock grazing and browsing); human intrusions and disturbance; aquaculture, agriculture and plantation forestry; invasive and other problematic species and diseases; and climate change, severe weather and ocean acidification. Many of these are intense or pervasive cross-realm pressures, often with cumulative, synergistic impacts that are collectively causing habitat fragmentation and loss, declines in species richness and abundance, altered animal behaviour, reduced ecosystem resilience, and declines in capacity to provide ecosystem services. However, the inter-connected nature of these pressures also means that integrated coastal management provides opportunities to address multiple pressures and impacts cross-realm. Sustainable development that is mindful of long-term climate projections is imperative in the coastal zone to safeguard this national asset into the future.
Continue reading ‘Pressures on coastal biodiversity in South Africa: a cross-realm review’Giant kelp-associated variation in coastal seawater chemistry across contrasting sites in Chile and Tasmania
Published 13 August 2026 Science Leave a CommentTags: algae, chemistry, field, Indian, South Pacific
Background and Aims
Widespread shifts in seawater chemistry are occurring across spatial and temporal scales, with important consequences for coastal ecosystems. Giant kelp (Macrocystis pyrifera) forests elevate seawater pH and dissolved oxygen (DO) through photosynthesis, potentially providing short-term refugia from ocean acidification and deoxygenation. However, whether these effects persist across contrasting environmental settings remains unclear. Here, we assess how biological and oceanographic conditions regulate giant kelp-mediated modification of seawater chemistry across multiple sites.
Methodology
Hourly measurements of seawater pH, DO and temperature were collected during spring–summer 2022–23 using paired deployments inside and outside giant kelp forests at one site in central Chile and four sites in Tasmania, Australia. The influence of giant kelp density was also evaluated at two sites in southern Chile and three sites in Tasmania. An upwelling index was calculated for the central Chile site to assess the influence of regional oceanographic forcing on kelp-associated seawater chemistry patterns.
Key Results
Hourly pH and DO were higher inside giant kelp forests than outside at the central Chile site and at one Tasmanian site. At these locations, stronger daytime pH–DO relationships indicated that photosynthetic carbon uptake exceeded night-time respiration, generating a net positive metabolic signal. In Tasmania, giant kelp density was positively associated with hourly pH and DO, whereas no such relationship was detected in southern Chile. At the central Chile site, kelp-associated effects intensified during a strong upwelling event, reducing the severity of low pH and DO conditions.
Conclusions
Giant kelp forests can locally buffer short-term fluctuations in seawater pH and DO, but this capacity is highly site-dependent and influenced by giant kelp density and environmental conditions. Overall, our findings suggest that continued loss of giant kelp forests in Tasmania may reduce their potential to provide short-term refugia, while in Chile the strength of kelp-mediated seawater chemistry modification is likely to remain strongly influenced by variability in upwelling and freshwater inputs.
Continue reading ‘Giant kelp-associated variation in coastal seawater chemistry across contrasting sites in Chile and Tasmania’CARIMED (CARbon, tracers, and ancillary data In the MEDiterranean Sea): a ship-based data synthesis product – overview and quality control procedures
Published 12 August 2026 Science Leave a CommentTags: chemistry, field, Mediterranean
The Mediterranean Sea (MedSea) is highly sensitive to climate-driven changes in temperature, oxygen, and pH, among other variables. To better assess these long-term trends, we developed CARIMED (CARbon, tracers, and ancillary data In the MEDiterranean Sea), the first comprehensive, harmonised data synthesis product for the MedSea. CARIMED integrates hydrographic, inorganic carbon, transient tracer, and ancillary measurements from 46 research cruises spanning the period from 1976 to 2018, containing observations for the entire water column across all MedSea sub-basins. A substantial component of the data was retrieved from fragmented or locally archived historical records, thus consolidating previously inaccessible measurements. Following global synthesis approaches, CARIMED applies a quality-controlled, and bias-adjusted framework. A key adaptation was the secondary quality control (2QC) procedure, specifically tailored to the MedSea’s unique hydrography, utilising sub-basin divisions and supplementary checks (including statistical consistency assessments) to resolve complex, often contradictory, inter-cruise offsets. This rigorous process minimised systematic biases, yielding a dataset with improved consistency, and highlights the urgent need for adapted standard operating procedures and reference materials to address the MedSea biogeochemical particularities. CARIMED delivers two complementary, freely available products: the aggregated original cruise data product (https://doi.org/10.20350/digitalCSIC/17785, García-Ibáñez et al., 2025) and the final bias-adjusted data synthesis product (https://doi.org/10.25921/cp5b-zq67, Álvarez et al., 2025; hosted at https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/oceans/CARIMED/, last access: 26 June 2026). This essential resource establishes a new benchmark for assessing long-term biogeochemical trends, validating regional ocean models, and supporting climate-change mitigation and adaptation strategies in this rapidly changing semi-enclosed basin.
Continue reading ‘CARIMED (CARbon, tracers, and ancillary data In the MEDiterranean Sea): a ship-based data synthesis product – overview and quality control procedures’Preferential impairment of later mating stages and sex-dependent metabolic shifts in Japanese medaka exposed to acute acidification
Published 12 August 2026 Science Leave a CommentTags: biological response, fish, laboratory, performance, physiology, reproduction
Highlights
- Acute acid stress (pH 4.5) preferentially impairs later mating stages in medaka, rather than causing a generalized reproductive collapse.
- Early initiation phases (following and courtship) are relatively less affected, whereas progression to the crossing stage and spawning is strongly suppressed.
- General locomotion and territorial aggression show no detectable change under acute acidification.
- Females exhibit increased ammonia excretion and oxygen consumption, indicating sex-specific physiological strain under acid stress.
- The behavioral impairment is consistent with an energy reallocation toward acid–base homeostasis, reducing investment in energetically costly terminal mating behaviors.
Abstract
Environmental acidification poses a significant threat to aquatic organisms, yet the underlying mechanisms of how acid stress disrupts complex social and reproductive behaviors remain incompletely understood. In the present study, we investigated the behavioral and physiological responses of adult Japanese medaka (Oryzias latipes) under acute acid exposure (pH 4.5, 24 h). Our results showed that acute acid stress reduced mating success, with a stronger impairment observed in the transition to the crossing stage and subsequent spawning, while the earlier, male-driven stages of following and courtship were relatively less affected under the present experimental conditions. This reproductive impairment did not coincide with detectable changes in generalized emotional-like behavior. Fish showed normal performance in the novel tank test and maintained territorial aggression. Physiologically, we observed a clear sexual dimorphism. Under acid stress, males maintained relatively stable MO₂ and JAmm, whereas females showed elevated MO₂ and JAmm. These findings suggest that reproductive impairment may be more pronounced in energetically demanding mating stages and may be associated with sex-dependent physiological strain. We further propose that the increased metabolic cost of acid-base regulation in females could shift energy allocation, and that high-cost coordination behaviors may be reduced in order to maintain short-term survival. This study provides evidence linking bioenergetics, acid-base regulation, and reproductive behavior in a teleost model under acidification.
RETRACTION: Ocean acidification disrupts the innate ability of fish to detect predator olfactory cues
Published 12 August 2026 Science Leave a CommentTags: biological response, fish, physiology
Retraction: D.L. Dixson, P.L. Munday, G.P. Jones, “ Ocean Acidification Disrupts the Innate Ability of Fish to Detect Predator Olfactory Cues,” Ecology Letters 13 no. 1, (2010): 68–75, https://doi.org/10.1111/j.1461-0248.2009.01400.x.
The above article, published online on 21 December 2009 in Wiley Online Library (onlinelibrary.wiley.com), has been retracted by agreement between the Editor-in-Chief, Peter H. Thrall; and John Wiley & Sons Ltd. A third-party complainant alerted the publisher to their observation of a statistically implausible variance in the data. The authors were contacted regarding the concerns raised. After evaluating the full dataset provided by the authors, an investigation by members of the journal’s editorial team determined that the data provided contained substantial errors, including repeated blocks, missing data, and structural errors. The authors acknowledged the inconsistencies with the data and provided an explanation, which included carelessness during manuscript reorganization, and they also asserted that the reported data anomalies did not affect the overall published results. The authors maintain that the errors were not a result of intentional data fabrication, but rather, poor standards of data handling and quality control. However, neither the publisher nor the editor has confidence in the article, primarily because the data provided during the investigation were not consistent with the observation methods described in the article. Therefore, because the journal has no basis on which to affirm confidence in the published results, the article must be retracted. The authors have been informed of the retraction.
Continue reading ‘RETRACTION: Ocean acidification disrupts the innate ability of fish to detect predator olfactory cues’Invasive macroalgae exert stronger effects than elevated CO₂ on seagrass (Posidonia oceanica) seedling performance and associated microbiomes
Published 11 August 2026 Science Leave a CommentTags: algae, biological response, laboratory, Mediterranean, mesocosms, multiple factors, oxygen, phanerogams, physiology, primary production, reproduction, respiration
Highlights
- Invasive macroalgae reduced P. oceanica seedling biomass and leaf development.
- Macroalgal invasion depleted carbohydrate reserves in seedling roots and rhizomes.
- Elevated CO2 increased rhizome starch but did not mitigate invasion impacts.
- Root microbiome diversity declined markedly under macroalgal invasion.
- Future CO2 enrichment unlikely to buffer invasion stress at recruitment stage.
Abstract
Seagrass seedlings are key to meadow recovery under global change, as they enable recolonization of degraded areas and provide genetic variability needed for adaptation. While invasive macroalgae increasingly threaten seagrass communities, elevated CO2 has been proposed to enhance seagrass performance and potentially buffer other stressors. Here, we conducted a mesocosm experiment to test the combined effects of two invasive macroalgae (Lophocladia trichoclados and Caulerpa cylindracea) and elevated CO2 on Posidonia oceanica seedlings. CO2 enrichment increased carbohydrate reserves in rhizomes and induced subtle shifts in root-associated microbiomes. In contrast, invasive macroalgae had consistently negative effects on seedling development and physiology and strongly altered both above- and belowground microbial communities. Despite its potential to stimulate seagrass productivity, elevated CO2 did not mitigate the detrimental impacts of invasive macroalgae. These findings indicate that future CO2 conditions may not offset invasion-driven stress at the recruitment stage, highlighting the need for targeted management efforts to limit macroalgal proliferation and support seagrass meadow regeneration.
Continue reading ‘Invasive macroalgae exert stronger effects than elevated CO₂ on seagrass (Posidonia oceanica) seedling performance and associated microbiomes’Crustose coralline algae buffer shallow reef environments from dissolution
Published 11 August 2026 Science Leave a CommentTags: algae, biological response, chemistry, dissolution, field
Ocean acidification threatens coral reefs by reducing seawater pH and carbonate saturation state. Crustose coralline algae are particularly vulnerable because their high-magnesium calcite skeletons dissolve more readily than coral aragonite skeletons. However, this dissolution may increase alkalinity and buffer reef-water chemistry. Here we show, using repeated low-tide observations and in situ incubations in a shallow reef system in the southern Great Barrier Reef, that reef-water pH varies by more than one unit over the day (7.47 – 8.61), reaching levels comparable to those projected for the end of this century. Nighttime respiration promotes dissolution of high-magnesium calcite produced by crustose coralline algae, increasing alkalinity and helping maintain seawater supersaturated with respect to aragonite. At the same time, isolated coral incubations experience a greater decline in pH and aragonite saturation state in the absence of this buffering effect. These findings suggest that high-magnesium calcite-producing communities may help partially buffer reefs against future acidification.
Continue reading ‘Crustose coralline algae buffer shallow reef environments from dissolution’Tracing the imprints of dual stressors: eco-physiological and genotoxic insights from Mystus gulio under acidification and warming scenario
Published 10 August 2026 Science Leave a CommentTags: biological response, fish, Indian, individualmodeling, laboratory, modeling, molecular biology, physiology, reproduction
Global warming has caused a rise in ocean temperature and acidification, which collectively wreak havoc on marine animals. However, the combined ramifications of these stressors on energy metabolism, oxidative balance, and DNA integrity remain inadequately studied in teleosts. The present study aims to unravel the combined effects of warming (34°C) and acidification (pH 7.7) on energetic balance, antioxidant defense, and DNA stability in Mystus gulio at two intervals (15th and 45th day). Furthermore, the Effect Addition model was used to disentangle potential additive or non-additive effects of the combined stressors. Elevated temperature and acidification induced a marked energetic imbalance, as mirrored by suppressed ingestion and absorption rates, reduced scope for growth, and elevated excretion. Oxidative stress biomarkers revealed significant upregulation of SOD, CAT, and GST under combined treatment, which ultimately led to augmented lipid peroxidation. Genotoxic assessment delineated progressive upsurges in tail DNA (%) and olive tail moment, indicating compromised genomic stability. The integrated biomarker response consisted of six parameters, RR, ER, SOD, CAT, GST, and LPO, further corroborating that elevated temperature, alone and in combination with acidification, posed the highest cumulative physiological burden. Furthermore, the model assessment indicated that the interaction between warming and acidification varied among different biomarkers. Collectively, these findings corroborate that concurrent thermal and low pH perturbations destabilise physiological processes, oxidative instability, and DNA damage, which may undermine growth potential and jeopardise population structure and destabilise trophic relationships. The present study provides a mechanistic understanding of the impacts of multiple stressors and offers a robust integrative framework to predict fish vulnerability under future climate-driven oceanic vicissitudes.
Warming and acidification shape zooplankton community dynamics in Jiaozhou Bay: evidence from an Acid-Heat Vector Intensity Index
Published 10 August 2026 Science Leave a CommentTags: biological response, community composition, field, laboratory, North Pacific, otherprocess, zooplankton
Highlights
- Warming and coastal acidification shape Jiaozhou Bay zooplankton dynamics.
- AHIvec summarizes monitoring-oriented surface temperature-pH departure.
- GAMs showed nonlinear, zone-specific zooplankton response patterns.
Abstract
Ocean warming and coastal acidification often co-occur in nearshore embayments, yet their joint associations with zooplankton remain difficult to characterize because responses are frequently nonlinear and spatially heterogeneous. In this study, we developed an integrated quantitative framework for characterizing joint warming-acidification exposure in Jiaozhou Bay. Based on six cruises conducted at nine stations in May (spring) and August (summer) from 2022 to 2024, we characterized zooplankton communities using abundance, biomass, Shannon-Wiener diversity (H′), and Pielou’s evenness (J). We further introduced a joint-exposure indicator, the Acid-Heat Vector Intensity Index (AHIvec), which summarizes joint temperature-pH departure based on standardized anomalies of temperature and pH. Generalized additive models (GAMs) were then applied to examine nonlinear response patterns and zone-specific associations between environmental gradients and zooplankton community attributes. Within the 2022–2024 observation window, sea surface temperature was generally higher in 2024 than in 2022, whereas surface pH was generally lower; however, these patterns should be interpreted as short-term observations rather than formal long-term trend estimates. Zooplankton also showed pronounced spring-summer and spatial variability. Notably, abundance showed pronounced temporal variation and generally increased with temperature, whereas biomass peaked at intermediate temperatures (∼20–22 °C) and declined thereafter, indicating a mismatch between abundance and biomass. Although pH-related associations were weaker than temperature-related associations, they became more evident at the lower end of the observed pH range (approximately 7.7–7.9). The AHIvec gradient was associated with contrasting zone-specific patterns in zooplankton community attributes. Overall, recent temperature-pH variations were associated with changes in zooplankton abundance, biomass, and diversity in Jiaozhou Bay. The AHIvec + GAM framework provides a monitoring-oriented complement to direct temperature-pH analyses for characterizing joint exposure in coastal ecosystems.
Global genome-wide patterns of genetic diversity and population structure in Coryphaena hippurus
Published 10 August 2026 Science Leave a CommentTags: biological response, fish, Indian, laboratory, Mediterranean, molecular biology, North Atlantic, North Pacific, physiology
Highlights
- Genome-wide SNPs reveal four discrete populations across ocean basins.
- Mediterranean population forms a deeply divergent and isolated lineage.
- Nuclear SNPs detect Pacific–Atlantic.
- Environmental gradients (salinity, phosphate, pH, light) shape genomic structure.
- Genetic connectivity varies within basins, revealing hidden substructure.
Abstract
The origin and maintenance of marine biodiversity remain poorly understood, particularly in highly connected oceanic environments where extensive dispersal is expected to limit population differentiation. Evolutionary processes driving population divergence or speciation frequently depend on a proper knowledge of species’ life history and its interaction with major environmental variables. Using a genome-wide approach, we investigated the global population structure of the cosmopolitan pelagic fish Coryphaena hippurus Linnaeus, 1758, generating a dataset of 8.7 million SNPs and complete mitochondrial genomes.
Our results reveal, for the first time, four genetically differentiated populations, corresponding to major oceanic basins: Atlantic, Pacific, Indian and Mediterranean Sea. The Mediterranean population exhibited a distinct genomic signature, likely resulting from historical isolation and restricted contemporary exchange through the strait of Gibraltar. Despite this structure, genome-wide analyses uncovered extensive signals of historical connectivity among basins. D-statistics and f4-ratio tests detected significant excess allele sharing, particularly between Indo-Pacific and Atlantic populations, while phylogenetic network reconstruction in TreeMix supported multiple migration events, highlighting the role of ancestral gene flow in shaping global genetic patterns.
At finer scales, a limited but significant intra-oceanic structure was detected within both Atlantic and Pacific basins. Seascape genomic analyses revealed that environmental gradients such as salinity, phosphate concentration, light availability (PAR, Kd), and pH are significantly associated with genomic variation, suggesting that ecological factors contribute to population differentiation across heterogeneous marine environments.
Annual variations of seawater carbonate system in the surface layer of the South-Eastern Mediterranean Sea
Published 7 August 2026 Science Leave a CommentTags: chemistry, Mediterranean
Seawater carbonate system measurements in the Mediterranean Sea are relatively scarce, especially in its eastern basin. This study describes the monthly variations of carbonate system parameters in the open sea and coastal water column of the eastern Mediterranean Sea during the period February 2018 to January 2019. Water samples were collected for analysis of Total Alkalinity and pHT at the shallow coastal THEMO1 and the deeper open-water THEMO2 (1,500 m bottom depth) stations off the Mediterranean coast of Israel. In the surface layer (<25 m), TA increased with salinity at a rate of +72 μmol·kg−1 and the pCO2(SW) was strongly and positively correlated with temperature. During summertime, surface waters were highly super-saturated with respect to atmospheric pCO2 (pCO2(SW) ∼ 600 μatm), while during winter they were only slightly super-saturated. The estimated net annual CO2 flux from the surface of the eastern Mediterranean Sea to the atmosphere during the study period was +2.8 Tg C·y−1, which is three times greater than a previous estimate made for this region (0.9 Tg C·y−1), and is attributed to the smaller volume of Atlantic water input in the present study compared to the previous one as well as the substantially shallower total dissolved inorganic carbon enriched core of the Levantine Intermediate Water in this study. Based on these results, it is still expected that future warming and salinization, reduced Atlantic Water influx to the eastern Mediterranean Sea, and increased stratification will increase the flux of CO2 to the atmosphere in this region.
Plain Language Summary
This study investigated annual variations in atmospheric CO2 flux from the surface of the eastern Mediterranean Sea based on monthly seawater sampling and carbon chemistry analyses conducted at two locations off the Mediterranean coast of Israel from February 2018 to January 2019. The results indicate that the southeastern Mediterranean Sea was a net source of CO2 to the atmosphere. This behavior was largely driven by seasonal changes in seawater temperature, which controls the saturation concentration of dissolved CO2 in seawater. During summer months, warm surface waters were a strong source of CO2 to the atmosphere, while during winter they were a weak sink. The study estimates that approximately 2.8 million tons of carbon were released annually from the sea to the atmosphere during the study period. This revised and more comprehensive estimate is ∼3 times higher than previous estimates reported for the same region. The increase is suggested to result from recent changes in regional circulation, particularly a reduced inflow of Atlantic Ocean waters into the eastern Mediterranean Sea. Based on these findings, continued warming, increasing salinity, and enhanced stratification of the eastern Mediterranean Sea are expected to further intensify CO2 release to the atmosphere in the future.
Continue reading ‘Annual variations of seawater carbonate system in the surface layer of the South-Eastern Mediterranean Sea’Vulnerability to low salinity but compensatory responses to low pH in an intertidal limpet
Published 7 August 2026 Science Leave a CommentTags: biological response, BRcommunity, laboratory, molecular biology, mollusks, mortality, multiple factors, North Pacific, physiology, salinity
Highlights
- Low salinity linked to warming may intensify coastal pH reduction.
- Low salinity reduced righting and emergence in the limpet Patelloida pygmaea.
- Low salinity reduces Mg/Ca ratios in newly formed shell layers.
- Low pH increases shell thickness and Mg/Ca ratios despite dissolution.
- CHS2 upregulation suggests compensatory resistance to low pH.
Abstract
Rising anthropogenic carbon dioxide emissions have driven ongoing ocean warming and associated climate changes. In the Yellow Sea, this warming is associated with enhanced monsoonal rainfall, which increases freshwater inputs and lowers coastal salinity. Increased freshwater input can weaken seawater buffering capacity, thereby leading to lower pH conditions in coastal environments. Here, we examined the effects of low pH and low salinity on the intertidal limpet Patelloida pygmaea. Adult limpets were exposed for 31 days to four experimental artificial seawater conditions combining two pH levels (8.0 and 7.5) and two salinity levels (30 and 21 psu). Survival and condition factor were not influenced by pH or salinity. However, low salinity reduced righting and emergence behavior. In addition, the Mg/Ca ratio in the M + 1 layer was lower at 21 psu than at 30 psu. Low pH resulted in a thicker M + 2 layer with higher Mg/Ca ratios despite shell dissolution, potentially helping to maintain shell integrity. While there was no change in heat shock protein (HSP70) expression, these shell modifications were accompanied by an upregulation of chitin synthase (CHS2) genes under low pH. These findings suggest that P. pygmaea is negatively influenced by low pH and low salinity, but also demonstrate compensatory mechanisms that enhance resistance to low pH.
Trends and persistence in ocean acidification as measured by station ALOHA
Published 6 August 2026 Science Leave a CommentTags: chemistry, modeling, review
Ocean acidification, largely driven by the uptake of anthropogenic carbon dioxide, is reflected in a sustained decline in seawater pH. This paper examines the dynamics of surface-ocean pH at Station ALOHA over the period 1985–2024 using fractional integration methods, which allow for a flexible characterisation of persistence and trend behaviour. The differencing parameter is estimated under alternative assumptions concerning the error term, namely white-noise and autocorrelated Bloomfield disturbances, and recursive estimation is used to assess the evolution of the relevant parameters over time. The results show a negative and statistically significant time trend in both the original and logged pH series. The estimates of the differencing parameter are positive and significantly different from zero in all cases, providing evidence of long-memory behaviour. Under white-noise errors, the estimate of the differencing parameter is 0.89 and the unit-root hypothesis cannot be rejected, whereas allowing for autocorrelation yields an estimate of approximately 0.55, implying mean reversion with long-lasting but transitory effects of shocks. Recursive estimates further indicate that both persistence and the magnitude of the negative pH trend have increased over time. These findings suggest that pH dynamics at Station ALOHA are characterised by a persistent decline and slow adjustment following disturbances, highlighting the importance of long-term ocean monitoring and modelling approaches that account for fractional dependence. Nevertheless, the results should be interpreted with caution because the analysis is based on a single long-term record combining observational and reconstructed data.
Continue reading ‘Trends and persistence in ocean acidification as measured by station ALOHA’Multilevel impacts of ocean acidification on vision: retinal damage, optic tectum hyperexcitability, and behavioral dysfunction in marine medaka
Published 6 August 2026 Science Leave a CommentTags: biological response, fish, laboratory, performance, physiology, reproduction
Ocean acidification (OA), driven by atmospheric carbon dioxide (CO2) emissions, significantly impacts marine organism. This study investigated OA effects on retinal structure and function in marine medaka (Oryzias melastigma) across life stages under controlled CO2 exposures (450 × 10−6, 1 000 × 10−6, and 1 800 × 10−6). Quantitative analyses revealed concentration-dependent retinal pathology, with larval incidence rising from 16.7% (450 × 10−6) to 50.0% (1 800 × 10−6). Significant structural alterations include progressive pigment epithelium thickening and concurrent atrophy in inner plexiform and ganglion cell layers. Electrophysiological recording demonstrated severe neural hyperexcitability, with larval and adult fish showing 91.3% and 154.9% increased firing counts respectively at 1 800 × 10−6. Behavioral analyses revealed significant CO2-induced locomotor dysfunction with distinct light-dependent patterns. Under illumination, larvae exhibited hyperactivity at 1 800 × 10−6, while adults showed progressive impairment (high-performance swimmers declining from 60% to 37.5%). Conversely, dark conditions intensified activity across concentrations, with adults displaying dose-dependent increases in swimming speed (23.5% to 68.8%). These results demonstrated that OA induces significant visual disruption and behavioral changes. The differential responses across life stages and light conditions suggest complex neurophysiological impacts that may have cascading ecological consequences for marine fish in acidifying ocean.
Continue reading ‘Multilevel impacts of ocean acidification on vision: retinal damage, optic tectum hyperexcitability, and behavioral dysfunction in marine medaka’Ocean acidification influence on Cymodocea nodosa seedling development
Published 5 August 2026 Science Leave a CommentTags: biological response, laboratory, Mediterranean, phanerogams, physiology, vents
Ocean acidification may positively affect seagrasses, although the response of the early life stages remains generally unknown. This study investigated the effect of OA and seed origin on the viability, morphometry, and chemical content of Cymodocea nodosa seedlings, using a field experiment along a natural-low pH gradient created by submarine vents in Vulcano Island, Italy. After four months of exposure, seedlings under increased pCO2 showed a reduction in the viability but a higher development exhibiting a lower C leaf content, independently of their origin. Results indicate compensating responses which may favour the plant acclimation in early life stages to future acidification scenarios.
Continue reading ‘Ocean acidification influence on Cymodocea nodosa seedling development’Ocean acidification as a planetary signal linking Earth system memory to deep-time lithosphere–ocean geochemical interactions
Published 5 August 2026 Science Leave a CommentTags: chemistry, globalmodeling, modeling
Highlights
- First ever reinterpretation of ocean acidification as a planetary-scale signal encoding Earth system disequilibrium.
- Links rapid surface pH decline to deep-ocean, sedimentary, and lithospheric memory.
- Reveals a rate mismatch that overwhelms geological buffering despite modest pH magnitude.
- Identifies CCD shoaling as the key integrator of short-term forcing and deep-time response.
- Synthesis elevates ocean acidification to a diagnostic of long-term carbon cycle stability.
Abstract
Ocean acidification (OA) is widely recognized as a defining chemical signature of the Anthropocene ocean, yet it is still predominantly framed as a near-surface ecological stressor. Here, we advance a planetary-scale reinterpretation of OA as an information-bearing signal that links rapid anthropogenic carbon forcing to deep-time lithosphere–ocean geochemical interactions and long-lived Earth system memory. Observations since the late 20th century document a persistent, spatially heterogeneous decline in global surface-ocean pH, corresponding to a ∼30–35% increase in hydrogen ion concentration, driven by sustained air–sea CO2 uptake. Projected pH declines of 0.3–0.4 units by 2100 under high-emission scenarios imply rates of change at least an order of magnitude faster than most natural variations recorded in the geological archive. We synthesize carbonate system thermodynamics, carbonate compensation depth dynamics, sedimentary proxy evidence, and Earth system modeling to demonstrate how small, rapid surface perturbations propagate vertically, trigger widespread carbonate undersaturation, and imprint durable stratigraphic and geochemical signatures through sediment dissolution, altered burial fluxes, and delayed alkalinity restoration. Comparison with hyperthermal events, particularly the Paleocene–Eocene Thermal Maximum, reveals that the uniqueness of modern OA lies not in magnitude alone but in an unprecedented rate mismatch that overwhelms geological buffering mechanisms. Furthermore, we identify critical knowledge gaps regarding irreversibility, sedimentary signal emergence, and threshold behavior under rapid forcing. Overall, this study reframes OA as a planetary-scale diagnostic of whole-Earth system disequilibrium, revealing its fundamental significance for evaluating long-term carbon cycle stability, Earth system resilience, and the enduring geological legacy of anthropogenic emissions beyond human timescales.
Continue reading ‘Ocean acidification as a planetary signal linking Earth system memory to deep-time lithosphere–ocean geochemical interactions’
