Seaweed cultivation has been proposed as an active biogeochemical intervention to elevate seawater pH and create localized refugia from ocean acidification. To date, most studies have relied on autonomous sensors to contrast seawater pH inside and outside of seaweed cultivation plots. These studies provide important temporal observations but lack information about the spatial capacity for seaweed cultivation to provide pH refugia for surrounding habitats. This study investigated the spatiotemporal variability of seawater pH and CO₂ chemistry across the Onna-son reef, Okinawa, Japan, during the fall, winter, and spring seasons, with spring surveys coinciding with the peak extent of Mozuku (Cladosiphon okamuranus) cultivation. Relative to open-ocean conditions, seawater pH was elevated during 77–100% of afternoon observations in fall (up to + 0.10), 53% in winter (up to + 0.02), and 75–92% in spring (up to + 0.13). The greatest drawdown in dissolved inorganic carbon (DIC; − 44 µmol kg⁻1) and highest spatial pH variability (0.19) were observed during spring, the period of maximum seaweed cultivation, but coincided with reduced current velocities, small wave heights, and low mean sea level, conditions conducive to enhanced biogeochemical modification. Comparable pH elevations were observed during fall under similar temperature regimes, but higher current velocities, which suggest that seaweed cultivation may not be more effective than natural macroalgal habitats in elevating local seawater pH at this site. Future assessments of seaweed aquaculture as a mitigation strategy should explicitly incorporate local hydrodynamics and natural macroalgal influences, as these will impact the variability across both space and time.
Continue reading ‘Seasonal reef-scale variability in seawater CO₂ chemistry in the presence and absence of seaweed cultivation in Onna, Okinawa, Japan’Archive for the 'Science' Category
Seasonal reef-scale variability in seawater CO₂ chemistry in the presence and absence of seaweed cultivation in Onna, Okinawa, Japan
Published 26 August 2026 Science Leave a CommentTags: algae, chemistry, fisheries, North Pacific
Elucidating impact of ocean acidification on coral exoskeletons using an in-situ (S)TEM platform
Published 25 August 2026 Science Leave a CommentTags: biological response, corals, field, methods, mitigation, mortality, physiology
Scleractinian (stony) corals can build highly ordered aragonite (CaCO3) exoskeletons, which are vital for marine ecosystems, coastal stability, and of cultural and economic importance through supporting fisheries and tourism. However, they face multiple challenges through global climate change, unsustainable human activity, and coral-specific diseases. In the latter category, Stony Coral Tissue Loss Disease (SCTLD) has recently emerged as one of the most destructive coral diseases, spreading rapidly and causing widespread tissue mortality across many marine species [1]. We have recently started exploring remnant effects of this disease on Montastraea cavernosa exoskeletons, abundant throughout the Caribbean Sea, Gulf of Mexico, and Atlantic Ocean. Indeed, through use of multi-scale electron diffraction characterization techniques, we find that their skeletogenisis is impacted by this disease from the micro- through atomic scale [2]. Notably, at the nanoscale we observe pockets of more soluble amorphous calcium carbonate (ACC) within centers of calcification (CoCs; i.e. the center of the three-dimensional fans containing arranged elongated aragonite crystals) for healthy corals, which appear absent in STCLD-afflicted corals. At the atomic level, we reveal planar defects in diseased coral, which are much lower in density in healthy corals, presumably inflicted through dysregulation processes after tissue death.
Yet, the most severe threat to global coral reefs and their exoskeletons is climate change. As oceans increase the uptake of anthropogenic CO2 primarily from burning fossil fuels, ocean acidity has increased. The reduction in pH because of this Ocean Acidification (OA) not only reduces the rate of net ecosystem calcification, but also increases net dissolution of skeletons. At current trends, most coral exoskeletons are expected to dissolve starting in 2050 [3]. Currently, it is unclear how exactly (the onset of) dissolution proceeds and affects their aragonitic framework. Given our expertise in characterization of coral skeletons, herein we discuss a developed in-situ platform to investigate OA effects at the nanoscale.
As proof of concept, we sandwiched crushed geological aragonite nanoparticles between own fabricated SiNx-based chips, compatible with a Protochips Atmosphere gas cell holder [4]. Thereafter, we introduced water vapor at 14 Torr at room temperature (∼60% relative humidity) for 10 minutes to create a hydrated environment for the particles (Fig. 1b). In a third step, we introduced gaseous CO2 at a pressure of 1 atm (Fig. 1c). The formed unstable carbonic acid produces HCO3– and H+, which increases acidity (i.e. lowers pH). Indeed, we observe rapid dissolution of aragonite particles after CO2. While we expect roughly a pH ∼4 in this system, this experimental observation matches theoretical expectations that aragonite would dissolve under these conditions (Fig 1c-f). We further observe nucleation and growth of new particles in a dendritic fashion in the vicinity of the dissolved particles (Fig 1c-f). Likely, this is crystallization of calcite, the most stable crystalline polymorph of CaCO3, induced by local dissolution of aragonite [5]. Although pCO2 in the oceans is expected to be much lower (∼400 – 500 µatm) and thus dissolution timescales are expected to shift, this illustrates our platform can capture aragonite dissolution.
To expand our platform methodology, using conventional Ga+ FIB-methods, we prepared a lamella of geological aragonite with a thinned region (∼100 nm), which was then transferred on top of a SiNx-based chip, and attached this in one of the corners between the Si support and the SiNx layer (Fig. 2a). We were able to sandwich the lamella between both chips when observing the cell in the TEM (Fig 2b,c). Next, we will target healthy and STCLD-afflicted coral sections to investigate how nanoscale dissolution proceeds at/near more soluble areas including defects due to the devastating OA process. This understanding may allow for more accurate forecasting of marine ecosystem collapse, enabling targeted mitigation strategies, protecting food supplies, and predicting climate feedback loops [6].
Fig. 1. In-situ OA platform experiment showing TEM snapshots of: a) Initial geological aragonite nanoparticles. Inset: selected area diffraction pattern indicating aragonite spots. b) Introduction of water vapor (14 Torr) after 10 min. The white arrow indicates an apparent hydration layer surrounding the large particle. c) Introduction of CO2 at 1 atm pressure after 10 s. d) 60s e) 90s and f) 150s. White arrows in c-f) mark the outer layer of the large particle dissolving in time, red arrows illustrate growth of new crystals.
Fig. 2. a) SEM image of geological aragonite lamella attached to SiNx chip. b) TEM image of lamella after cell assembly (top and bottom chip). c) In-situ selected area diffraction pattern of the lamella.
Continue reading ‘Elucidating impact of ocean acidification on coral exoskeletons using an in-situ (S)TEM platform’Comparing ocean acidification communication strategies and effectiveness in marine education centers
Published 25 August 2026 Science Leave a CommentTags: education
Ocean acidification (OA), one of the most impactful aspects of our changing oceans, significantly threatens ecosystems, industries, and communities reliant on at-risk species, such as corals and shellfish. Washington state, with its notable reliance on such species for both its economy and culture and its naturally acidified waters, is especially vulnerable. However, OA remains an under-discussed and misunderstood phenomenon, especially among the public. While many informal marine education centers such as aquariums, science centers, and marine reserves do provide communication on OA, the prevalence, type, and quality of this communication varies drastically, meaning that the public’s ability to receive effective OA education varies as well. Thus, I conducted staff interviews to catalogue the prevalence of OA communication efforts at marine education centers and address barriers to effective OA outreach. I found that while 88% of participating marine education centers discuss OA in some capacity, 81% feel restricted in their ability to talk about OA or ocean change, citing issues such as audience interest and politics. I also conducted visitor surveys at Point Defiance Zoo & Aquarium to determine how attendees’ preconceived knowledge of OA’s causes, impacts, and mitigation strategies changed based on provided communication and what gaps remain. While visitor knowledge of OA increased by a statistically significant amount (from 63% of visitors knowing essentially nothing about OA before the visit to 44% after; p < 0.001), only 49% of visitors correctly identified fossil fuel emissions as a primary cause of OA. Despite this, 97% of visitors indicated willingness to take action against OA, and nearly equivalent amounts of visitors supported individual-level vs societal-level action. Together, this research lays the groundwork for improving OA communication to the public by highlighting the importance of uplifting meaningful action, intentionally connecting with visitors through community-level and place-based impacts, and addressing staff hesitancy to discuss ocean change issues. Going forward, these recommendations will be critical in driving tangible action to address OA and protect at-risk communities and ecosystems.
Continue reading ‘Comparing ocean acidification communication strategies and effectiveness in marine education centers’Recent history of surface ocean acidification extremes that compound marine heatwaves
Published 25 August 2026 Science Leave a CommentTags: field, methods, modeling
Compound extremes are of concern for ocean health, such as when ocean acidification extremes (OAX) and marine heatwaves (MHW) co-occur. These compound events (OAX∩MHW) may amplify stress beyond the impact of each driver alone, yet their historical distribution remains poorly quantified. We used an observation-based product (OceanSODA-ETHZ) to investigate surface ocean OAX∩MHW from 1982 to 2024. OAX and MHW are defined when detrended surface hydrogen ion concentration and sea surface temperature exceed their 95th percentiles. Events show distinct spatial and temporal patterns: they occur roughly four times more often than by chance in the low- to mid-latitudes, but are rare in the eastern tropical Pacific and the high latitudes. They occur primarily in summer and show strong variability associated with the El Niño-Southern Oscillation. Most events are small ( <106 km2) and brief (1 month), but several are exceptional, including: the Blob (2015) in the northeastern Pacific (12.6 ×106 km2), the North Atlantic marine heatwave lasting nearly a year (2023–2024), and the most intense event off the Western Australian coast (2011). Mechanistically, OAX∩MHW occur when warming-induced increases in [H+] are not offset by a reduction in dissolved inorganic carbon that typically accompanies MHW. This is typical of the permanently stratified low-to-mid latitude oceans, where the seasonal cycle of [H+] is controlled by temperature. By characterizing past compound extremes and improving our understanding of individual events, we highlight conditions that may lead to future ecosystems being at risk.
Plain Language Summary
This study examines the recent history of “compound extremes” in the ocean, where marine heatwaves and ocean acidification extremes occur simultaneously. Using observational data from 1982 to 2024, we find that these compound events are happening more frequently than would be expected by chance, particularly in the low- to mid-latitudes. Conversely, they are rare in the eastern equatorial Pacific and polar regions. These compound events are most prevalent during summer and are influenced primarily by the El Niño/Southern Oscillation. While most of these events are relatively small and short-lived, there have been a few exceptionally large, long, and intense occurrences. Some of the most notable events include: “The Blob,” in the northeastern Pacific in 2015; the longest-lasting event that occurred in the Atlantic Ocean from 2023 to 2024; and the most intense event that occurred off Western Australia in 2011. These compound extremes happen in areas where the warming from a marine heatwave also leads to an increase in ocean acidity. This phenomenon is most common in regions of the ocean that are permanently stratified, meaning they have distinct layers of water that do not mix well.
Continue reading ‘Recent history of surface ocean acidification extremes that compound marine heatwaves’Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways
Published 24 August 2026 Science ClosedTags: algae, biological response, BRcommunity, community composition, otherprocess, photosynthesis, physiology, review
Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways
Highlights
- Focused on a novel inorganic carbon sequestration pathway of non-calcifying macroalgae.
- Clarified algae-bacteria synergistic driving mechanism for calcium carbonate precipitation.
- Systematically sorted out potential mineralizing microbial taxa within the phycosphere and their core metabolic pathways.
Abstract
Macroalgae are dominant primary producers that drive carbon sequestration in coastal ecosystems. Macroalgal carbon sequestration primarily refers to the long-term storage of macroalgae-derived organic carbon in the ocean. However, calcium carbonate (CaCO3) formation is frequently observed in non-calcifying macroalgal environments, suggesting the existence of an overlooked inorganic carbon process in macroalgal ecosystems. Here, we introduce multiple pathways that may drive CaCO3 formation in macroalgal ecosystems. These include the effects of macroalgal photosynthesis and carbon-concentrating mechanisms on the seawater carbonate system, the role of phycosphere interfacial properties in facilitating CaCO3 nucleation, and the macroalgae-bacteria synergy that promotes CaCO3 formation. We identified several current knowledge gaps—the unclear carbon sequestration or source effect of CaCO3 formation in macroalgal ecosystems and the stability of CaCO3 minerals in macroalgal ecosystems—that require further investigation. This review advances the understanding of macroalgal carbon cycling beyond organic pathways and emphasizes the importance of a comprehensive assessment of macroalgal carbon sequestration, including that of inorganic carbon.
ISO 18191:2026 – Water quality — Determination of pHT in seawater — Method using the purple indicator of m-cresol
Published 24 August 2026 Science ClosedTags: chemistry, methods, policy
This document specifies a spectrophotometric determination of the pHT of seawater on the total hydrogen ion concentration pH scale. The total hydrogen ion concentration, [H+]T, is expressed as moles per kilogram of seawater. The method is suitable for assaying oceanic levels of pHT from 7.4 to 8.2 for normal seawater of practical salinity ranging from 20 to 40.
Continue reading ‘ISO 18191:2026 – Water quality — Determination of pHT in seawater — Method using the purple indicator of m-cresol’Lobsters and acidic seas: can shellfish help neutralise one of the greatest threats to the ocean?
Published 24 August 2026 Science , Web sites and blogs Closed
A lobster in St George, Maine. The crustacean is a tricky test subject, disliking warm seawater and ‘unfortunately, they eat each other.’ Photograph: D Grill/Tetra
Crustaceans are the subject of tests to see if alkalis added to seawater, so it absorbs more CO2, harm marine life. But Trump’s halt to funding threatens to scupper the research
For many in the US region of New England, the lobster roll is synonymous with summertime. Loaded into a toasted bun, chunks of the sweet meat are served hot and soaked in butter, or chilled and slathered in mayonnaise with celery and herbs.
The only thing more debated than the recipe is the price: the once-humble roll now routinely fetches $30 (£22), or even $50, in a sign of the changing times – and seas.
A third-generation lobster fisherman, Scott Lord spends his days hauling traps on the Gulf of Maine, which is warming faster than 99% of the world’s oceans. “Whether you agree with who says why it’s happening, it is happening,” he says.
Bycatch that was once plentiful, such as sea urchins, sand dollars or starfish, are increasingly rare. And, most concerning, Lord has noticed the number of inshore lobsters dropping dramatically over the past 15 years, pushing fishers farther and farther offshore.
Motivated to find a remedy, Lord joined a regional shellfish committee. “Why are there not clams where there used to be clams? Why are they not coming back, no matter what we do?” he asks.
Hundreds of miles to the south in Massachusetts, on a sandy crook of land that spins out to form Cape Cod, Adam Subhas, a scientist at the Woods Hole Oceanographic Institution, is trying to find the answers.
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Subhas heads LOC-NESS (Locking Ocean Carbon in the North-east Shelf and Slope, an initiative researching how to decarbonise the ocean, also known as marine carbon dioxide removal (mCDR). Scientists working in this field are trying to discover whether the ocean, which is estimated to absorb about 31% of atmospheric carbon, could be manipulated to soak up even more.
Proponents say ocean carbon removal could help stop the world from passing the 2C (3.6F) tipping point outlined in the 2016 Paris Agreement, if used in conjunction with the reduction of fossil fuels.
What was once a small-scale idea is rapidly gaining traction. A database newly launched by the Pulitzer Center, Ocean Carbon Removal Watch, which tracks mCDR investments, field trials and research, shows that more than £370m has been invested in the sector over the past five years.
This was initially driven by the private sector but, thanks to a spate of US federal investments in 2023 – totalling at least £44m, according to a Guardian analysis of the database – scientific field trials began to catch up. Until, that is, President Trump announced sweeping cuts to all federally funded ocean sciences.
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“The funding cuts are affecting everyone,” says Subhas.
Continue reading ‘Lobsters and acidic seas: can shellfish help neutralise one of the greatest threats to the ocean?’REMINDER: Registration open for the 6th International Symposium on the Ocean in a High-CO₂ World
Published 24 August 2026 Events , Science Closed
Registration for the 6th International Symposium on the Ocean in a High-CO₂ World , 13-16 October 2026, Wellington, New Zealand, is still open.
Following previous editions in Paris, Monaco, Monterey Bay, Hobart, and Lima, the 6th Symposium will still retain its core focus on ocean acidification – but the themes for this edition are broadened to include many related emerging topics such as ocean solutions and mCDR, deoxygenation, multiple drivers, co-design of research, and the integration of different knowledge systems.
This edition also offers a new dynamic format. In addition to scientific oral presentations and poster sessions, more than 20 topical workshops and trainings will be offered throughout the conference.
Don’t miss this unique opportunity, taking place only every four years, to discuss your research with the global scientific and user communities active on ocean change and help shape future research and coordination initiatives on ocean acidification and beyond.
Continue reading ‘REMINDER: Registration open for the 6th International Symposium on the Ocean in a High-CO₂ World’‘Acid rain’ changes the chemistry of soils and waters, causes damage to materials, and threatens wildlife and human health. Most important anthropogenic sources of acidifying compounds emitted to the air are fuel combustion and agriculture. Sulfur dioxide and nitrogen oxides in the atmosphere act as strong acids increasing the natural acidity of rainwater. Ammonia emissions from agriculture and the subsequent deposition of reduced nitrogen compounds trigger acidification processes in soils. Besides those external hydrogen ion (H+) sources, ecosystem internal turnover processes linked to nutrient cation uptake by vegetation, the nitrogen cycle, and biomass export from ecosystems are also of major importance. Several H+ sinks in soil, bedrock, and waters can compensate for H+ release (e.g., carbonate dissolution or silicate weathering). Land-use changes and fossil fuel use have led to dramatically increasing atmospheric carbon dioxide (CO2) concentrations worldwide. CO2 is absorbed by oceans and reacts with seawater to form carbonic acid. Acidification of oceans could have adverse effects on marine organisms using calcium carbonate in seawater to construct their shells and skeletons. Acidification is the result of a sensitive (un-)balance between ecosystem internal and external H+ sources and internal H+ sinks of different capacities and reaction rates.
Continue reading ‘Acidification’Aquatic acidification is a global change phenomenon driven by ever increasing anthropogenic carbon dioxide (CO2) emissions. This drives changes to the carbonate chemistry equilibrium in natural water, resulting in an increase in acidity, which has been shown to influence aquatic organisms. There is substantial evidence that acidification has consequences on marine, coastal, and freshwater ecosystems. The response of organisms varies among species and some biological processes are more sensitive than others, resulting in a complex biological response to acidification. Calcifying organisms, the larval and juvenile stages of many species, and coral reefs ecosystems are considered particularly vulnerable to acidification. The negative impacts of acidification may have eventual downstream consequences on species diversity and ecosystem resilience in the future if CO2 emissions continue unabated. Immediate global and local action is needed to limit the negative ecological and socioeconomic effects of this phenomenon.
The diagram illustrates the variability of p H across freshwater, coastal, and marine environments, the biological responses to acidification, and strategies for mitigation and adaptation. At the top, a landscape cross-section shows p H ranges: freshwater with less than 7.2 to 12 and high variability, multiple drivers, and uncertain responses; coastal waters with 7.5 to 8.5, high variability, multiple drivers, and complex responses; and marine waters with 7.9 to 8.1, more stable, gradual acidification, and high organism sensitivity. On the right, complex biological responses are described, including autotrophic activity raising p H, locally variable conditions, and potential refugia. Sensitive biological processes listed are behavior, calcification, metabolism and energy budgets, and larval development. Sensitive ecosystems include coral reefs, deep-sea ecosystems, and areas of high anthropogenic activity. At the bottom, two interconnected cycles are shown. The “Mitigate Impacts” cycle features reducing global emissions, carbon capture through seaweed and algae, and deacidification via calcium carbonate. The “Local Adaptation” cycle emphasizes managing multiple stressors, conserving refuge habitats with increased p H, and supporting sustainable fisheries and aquaculture.
Continue reading ‘Acidification in aquatic systems’Witness to ocean acidification
Published 20 August 2026 Science ClosedTags: biological response, laboratory, mortality, paleo, physiology, protists
Foraminifera inhabit coastal and deep-sea marine environments. These microscopic, single-celled organisms are widely used as proxies for relative age determination and reconstructing past climates. The ratio of calcium isotopes (44Ca/40Ca) in their calcium carbonate shells depends on the amount of carbon dioxide (CO2) and carbonate saturation in seawater at the time of the shells’ formation. On page 527 of this issue, Chen et al. (1) report geochemical evidence that a rise in atmospheric CO2 concentration and ocean acidification at the end of the Aptian Stage [~113 million years ago (Ma)] may have caused the largest extinction of planktic foraminifera of the Cretaceous Period (146 to 66 Ma) (2–4), which is second only to the extinction event at the end of the Cretaceous Period (66 Ma) (5–7). The findings could be important for understanding potential effects of present-day increases in atmospheric CO2 levels on marine organisms.
Paraticinella rohri collected from the South Atlantic is a species of planktic foraminifera that went extinct at the Aptian–Albian boundary. IMAGE: HUBER AND LECKIE (3)
Seafloor-dwelling benthic foraminifera appeared more than 500 million years ago. It took at least 350 million years for them to evolve into planktic species that float in the upper ocean (8–10). The earliest species of planktic foraminifera lacked morphological diversity and were minor constituents of marine sediments. The first major morphological diversification of planktic foraminifera occurred (2, 11) during the Aptian Stage (125 to 113 Ma) of the mid-Cretaceous Period. New species of planktic foraminifera arose, with elongated chambers (Leupoldina) and larger, more heavily calcified shells (Globigerinelloides and Hedbergella), and the first species with a peripheral keel (Pseudoplanomalina cheniourensis) appeared by the late Aptian. Large increases in atmospheric CO2 concentration caused by massive volcanic eruptions triggered substantial depletion of oxygen in the oceans, including Oceanic Anoxic Event 1a and other similar events. Atmospheric CO2 likely drove warming of the atmosphere and water; warmer waters hold less dissolved oxygen compared to cooler water.
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Continue reading ‘Witness to ocean acidification’Field-deployable full-range underwater pH sensor using a polyprotic SERS probe
Published 20 August 2026 Science ClosedTags: chemistry, modeling, sensor
Accurate measurement of pH in underwater environments is essential for oceanographic research, environmental monitoring and subsurface exploration. However, conventional electrode-based sensors are limited by drift, corrosion and narrow operational ranges, particularly under extreme pH and high-salinity conditions. Here we present a fibre-optic surface-enhanced Raman scattering platform that enables full-range (pH 0–14) underwater pH sensing using the polyprotic molecular probe 2-amino-5-mercapto-1,3,4-thiadiazole. This probe exhibits 6 pH-dependent conformations, generating distinct surface-enhanced Raman scattering fingerprints that are decoded via machine learning for accurate, drift-resistant pH prediction with errors below 0.2 pH units. The sensor demonstrates high salt tolerance (up to 1 M NaCl), rapid reversibility and robust photostability, and can be deployed remotely at depths of up to 10 m in seawater and groundwater. By establishing a versatile optical strategy based on polyprotic molecular fingerprints, this work expands the capabilities of environmental monitoring and subsurface exploration in challenging aquatic environments.
Continue reading ‘Field-deployable full-range underwater pH sensor using a polyprotic SERS probe’Calcium isotopes link ocean acidification to Aptian–Albian foraminiferal extinctions
Published 19 August 2026 Science ClosedTags: biological response, laboratory, mortality, paleo, physiology, protists
Editor’s summary
About three quarters of planktic foraminifera species disappeared in the Aptian-Albian extinction event. What role might ocean acidification (OA) have played in this die-out? Chen et al. measured calcium isotope ratios in foraminifera, using them as a proxy for biocalcification and carbonate saturation (see the Perspective by Leckie). Their data reveal a dramatic reduction in calcification rates accompanied by decreases in the size, abundance, and diversity of planktic foraminifera. These results are consistent with the hypothesis that ocean acidification drove the extinctions of these organisms at the Aptian-Albian boundary. —Jesse Smith
Abstract
The second-largest extinction event in the evolutionary history of planktic foraminifera occurred at the Aptian–Albian boundary. This extinction may reflect ocean acidification (OA) associated with Oceanic Anoxic Event 1b. As calcium isotope ratios (δ44/40Ca) can track how biocalcification rates respond to OA, we measured δ44/40Ca records for planktic and benthic foraminifera, bulk carbonates, and authigenic calcite across the Aptian–Albian boundary in the South Atlantic. Benthic and bulk δ44/40Ca data display a distinct sequence of negative and positive excursions, similar to δ44/40Ca variations across other OA events. Planktic δ44/40Ca values increase markedly, tracking a reduction in calcification rates coincident with decreases in the size, diversity, and shell thickness of planktic foraminifera. These results suggest that OA drove extinctions of planktic foraminifera at the Aptian–Albian boundary.
Continue reading ‘Calcium isotopes link ocean acidification to Aptian–Albian foraminiferal extinctions’A hidden driver of the greenhouse effect: production mechanisms and climate implications of N2O derived from marine planktonic ammonia-oxidizing archaea
Published 18 August 2026 Science ClosedTags: biogeochemistry, phytoplankton, review
Nitrous oxide (N2O) is a potent and long-lived greenhouse gas, and the ocean represents its primary natural source. An accurate understanding of the emission intensity and driving mechanisms of oceanic N2O directly affects the estimation of atmospheric N2O budget and the projection of climate change. Recent studies have demonstrated that ammonia-oxidizing archaea (AOA) dominate nitrification in marine environments and are thus recognized as an important biological source of marine N2O production. However, their specific metabolic pathways, regulatory mechanisms, and environmental response patterns remain poorly understood. This paper systematically reviews the spatial distribution characteristics of marine N2O and its major biogeochemical sources, with a particular focus on the potential metabolic pathways and key intermediates involved in AOA-derived N2O production. We further synthesize the current understanding of how environmental factors—including dissolved oxygen, pH, temperature, substrate availability, and organic carbon—regulate AOA nitrogen metabolism and N2O generation. In addition, we discuss the potential mechanisms underlying the shift in AOA metabolic strategies and variations in N2O yield under multifactorial coupling scenarios the scenario of multifactorial coupling. On this basis, we identify the major knowledge gaps in existing research, particularly regarding culture systems, mechanistic elucidation, in situ validation, and global-scale quantification. Finally, we proposed future research directions for AOA-derived N2O emissions under ongoing oceanic changes. This review aims to advance the understanding of the biogeochemical mechanisms governing marine N2O production and to provide a theoretical basis for improving the parameterization of marine nitrogen cycle and climate models.
Continue reading ‘A hidden driver of the greenhouse effect: production mechanisms and climate implications of N2O derived from marine planktonic ammonia-oxidizing archaea’Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean
Published 17 August 2026 Science ClosedTags: biological response, community composition, Indian, laboratory, otherprocess, photosynthesis, physiology, phytoplankton
Phytoplankton and microzooplankton (MZP) are key components of marine food webs, driving carbon transfer through the microbial loop. Short-term laboratory microcosm bottle incubations using seawater from the Bay of Bengal (BoB) and Arabian Sea (AS) in 2022 examined the effects of reduced pH. Phytoplankton biomass (Chl-a) remained stable or increased by up to 12% under low pH, suggesting reduced grazing or improved prey quality. MZP diversity (Shannon index, H′) showed basin-specific responses. In the BoB (Exps. 1–2), H′ ranged 2.00–3.70 with high evenness (J′ = 0.93–1.00) and slight declines under medium acidification (ΔpH = 0.2). In contrast, the AS (Exps. 3–4) showed wider variability (H′ = 0.00–3.63) and greater sensitivity, with sharp diversity losses under stronger acidification (ΔpH = 0.4). AS assemblages showed pronounced richness declines (D′ = 2.85–0.00), whereas BoB communities remained stable. Regional and pH-related differences were linked to shifts in ciliates and dinoflagellates. Autotrophic bacteria sustained under low pH, while heterotrophic bacteria increased later, indicating altered microbial-loop functioning. Overall, pH, chlorophyll-a, and heterotrophic bacteria structured the community, accounting for > 65% of the variation. Thus, short-term acidification reshapes MZP assemblages and may modify trophic interactions across the northern Indian Ocean.
Continue reading ‘Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean’Biological modulation of shell δ13C in Mytilus galloprovincialis and Phorcus sp.: divergent responses between CO2 vents and laboratory mesocosms
Published 17 August 2026 Science ClosedTags: biological response, BRcommunity, field, laboratory, Mediterranean, mesocosms, mollusks, physiology, vents
table isotopes are fundamental proxies for deciphering past environmental conditions and carbon cycle perturbations. However, applying these geochemical tools with a forward-looking perspective can also help predict the resilience of marine biota in future acidified oceans. This study investigates carbon uptake and biomineralization pathways under reduced pH in two ecologically keystone calcifying species: the bivalve Mytilus galloprovincialis and the gastropod Phorcus sp. To unravel these mechanisms, we adopted a dual approach, comparing isotopic trajectories (δ13C) under strictly controlled laboratory mesocosms with observations from natural CO2 vent systems in Ischia, Italy. Our results reveal a striking discrepancy between settings. Under laboratory conditions, both species exhibited a significant depletion in shell δ13C as pH decreased, directly tracking seawater carbonate chemistry. Conversely, specimens from the volcanic vents displayed a paradoxical δ13C enrichment at low-pH sites (pH ~7.4). These divergent trajectories indicate that in complex natural environments, the geochemical signal of ocean acidification can be overridden by metabolic overprints and trophically driven vital processes. Consequently, while laboratory experiments are essential to isolate kinetic fractionation, natural analogues remain crucial to capture the biological resilience and complex ecological feedback of future oceans. Future research combining these geochemical trends with direct, in vivo physiological assessments will be essential to precisely constrain the underlying metabolic kinetics and refine predictive metabolic models.
Continue reading ‘Biological modulation of shell δ13C in Mytilus galloprovincialis and Phorcus sp.: divergent responses between CO2 vents and laboratory mesocosms’Persistence of Arctic Ocean acidification under negative emissions
Published 14 August 2026 Science ClosedTags: Arctic, biogeochemistry, chemistry, globalmodeling, modeling
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’Method for correcting the temperature dependence of field-type glass electrode pH sensors
Published 14 August 2026 Science ClosedTags: 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 ClosedTags: 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 ClosedTags: 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’
