Applications open: Sixth International Symposium on the Ocean in a High-CO2 World

Published 28 July 2026 Events Closed

The IAEA’s Ocean Acidification International Coordination Centre (OA-ICC) (https://www.iaea.org/ocean-acidification) is cooperating on the organization of this event and has limited funds at its disposal to help meet the costs of the attendance of selected participants from eligible IAEA Member States to present their work and foster international collaboration at the conference.

The deadline to apply is Friday September 4th. To apply, applicants will need to submit their application through their national authority to the IAEA – in most cases, this will be your country’s permanent mission to the IAEA.

If you have questions on the application procedure, please contact Ms Lina Hansson (L.Hansson(at)iaea.org) or Ms Carolina Galdino (C.Galdino(at)iaea.org).

Dates: 13–16 October 2026

Location: Tākina Convention & Exhibition Centre, Wellington, New Zealand

Form A and Form C

Introduction
Held every four years, the International Symposium on the Ocean in a High-CO2 World is the largest global gathering on ocean acidification. The Symposium brings together scientists, communities, policymakers, and stakeholders from sectors such as fisheries and aquaculture to share and discuss the latest research on the impacts of ocean acidification on marine life and potential solutions to counter its effects. The Sixth edition will maintain a focus on ocean acidification but will also expand to consider other ocean climate impacts, such as ocean warming and deoxygenation, particularly in a multiple-driver context. Research on marine carbon dioxide removal interventions, which have been suggested to mitigate climate change and ocean acidification, will also be a key part of the conference. More information on the seven key themes of the conference, its 22 workshops, and the detailed programme can be found on the Symposium website (https://highco2-vi.org/).

Objectives
The purpose of the event is to provide a space for scientists from the ocean acidification (OA) research community to disseminate the results of their research, discuss joint projects with peers and engage with stakeholders. The event, held every four years, is the world’s largest conference on OA and related stressors.

Target Audience
Scientists from developing IAEA Member States. Priority will be given to early-career scientists actively working on ocean acidification, multiple stressors or marine carbon dioxide removal (mCDR). Applicants should hold a university degree in marine biology, oceanography or a related scientific field. Female scientists are encouraged to apply.

Working Language
English

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Participation and Registration
All persons wishing to participate in the event through the IAEA have to be designated by an IAEA Member State.

In order to be designated by an IAEA Member State, participants are requested to send the Participation Form (Form A) and Grant Application Form (Form C – if applicable) to their competent national authority (e.g. Ministry of Foreign Affairs, Permanent Mission to the IAEA or National Atomic Energy Authority) for onward transmission to the IAEA by 4 September.

Selected participants will be informed in due course on the procedures to be followed with regard to administrative and financial matters.

Participants are hereby informed that the personal data they submit will be processed in line with the Agency’s Personal Data and Privacy Policy and is collected solely for the purpose(s) of reviewing and assessing the application and to complete logistical arrangements where required. The IAEA may also use the contact details of Applicants to inform them of the IAEA’s scientific and technical publications, or the latest employment opportunities and current open vacancies at the IAEA. These secondary purposes are consistent with the IAEA’s mandate.

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Additional Requirements
The participants should have a university degree in marine chemistry, biology, oceanography, or a related scientific field, and must be active researchers in the ocean acidification /mCDR field or should have already received technical training on ocean acidification / mCDR by the IAEA or through other efforts.

Selection will be based on merit and motivation. Applications must include, in addition to Form A and C, if applicable:

  •  A motivation letter with a short description of research interests, motivation to participate, and plans regarding present and future research on OA and/or mCDR (max one A4 page)
  •   CV with publication list
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Coral reef community structure and photophysiology differ between upwelling and non-upwelling locations on the Pacific Coast of Costa Rica

Published 28 August 2026 Science Leave a Comment
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Reef-building corals and coralline algae form the calcium carbonate frameworks that underpin tropical coral reefs, yet in some locations, coral cover has declined by ~50% in recent decades due to marine heatwaves and other stressors. Identifying refugia environments, such as upwelling systems, that may buffer stress, promote recovery, and could enhance resilience by promoting physiological plasticity that supports thermotolerance is therefore critical. Here, we compared benthic community composition, coral percent cover, and photophysiology between an upwelling location in the Gulf of Papagayo and a non-upwelling location in Sámara on the Pacific coast of Costa Rica. Waters in Papagayo were cooler, more acidic, and had higher chlorophyll-a concentrations. Reefs at this location exhibited higher crustose coralline algae, higher sea urchin abundance, and lower macroalgae cover, compared to Sámara. Papagayo also showed higher stony coral cover, driven by Pocillopora spp., while Sámara was dominated by massive, heat-tolerant Porites spp. Photophysiological parameters were significantly different between locations. Specifically, photosynthetic efficiency (Fv′/Fm′) was 10–45% higher, and maximum photosynthetic rate (Pmax) was 20–40% lower in corals from Papagayo than in those from Sámara. These results reveal that two locations differing in environmental regime within a relatively small geographic area also differ in coral community composition and photophysiological features. Although further research is needed to resolve whether these environmental contrasts shape the observed biological differences, the observed patterns are consistent with the hypothesis that such regimes may support reef persistence or refugia, providing a basis for future work to test this hypothesis directly.

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New tool could predict ocean acidity in Bering Sea

Published 28 August 2026 Press releases Leave a Comment

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Disaster declarations have been declared for both the Bering Sea snow crab and Bristol Bay red king crab fisheries in recent years. Corey Arnold/Alaska Bering Sea Crabbers

Crab populations in the Bering Sea are struggling. And researchers say climate change is a big cause. A new tool described in a study published Aug. 3 in the Journal of Geophysical Research Oceans will help researchers predict one of climate change’s biggest threats to crabs: ocean acidity. The study’s authors hope their work can help crabbers and fishery managers.

“I’m excited with this new model and study,” said Jamie Goen, the executive director of the nonprofit trade association Alaska Bering Sea Crabbers. “It will help us better understand what could be happening and how that might impact fisheries.”

Darren Pilcher, the study’s lead author and an oceanographer at the University of Washington, said he started the study because of requests from fisheries stakeholders.

The ocean absorbs a quarter of our carbon emissions, which make the water more acidic when the two mix. Acidic conditions are harmful for many different animals. This is especially true for shellfish, like crabs.

“They can eat more, and that helps a little bit, only to a certain point,” Pilcher said. “In fact, in some of the previous experiments with red king crab, if you lower the pH to a value of 7.5, the crab just die.”

Scientists have pointed to factors from climate change, like ocean acidification, as the reason the number of Bristol Bay red king crabs has plummeted in recent years. Goen said that other species, like snow crab, have also tanked.

“When I started this job eight years ago, we had 60 vessels in the fleet,” she said. “But obviously with the collapse of snow crab and the closure of red king crab, we’re down to 40 active vessels right now.”

Pilcher and his team wanted to help the fishery by creating a tool that could forecast acidity in the Bering Sea. Ocean acidity doesn’t exist in a vacuum, so the first step was to make a computer model of the entire Bering Sea, recreating the water conditions at any given time. They put a lot of existing data into their model on ocean conditions over time, measuring things like temperature, currents, and distribution of phytoplankton.

Then they added in ocean acidity data collected from the region, and tested their new tool by having it forecast the acidity of the Bering Sea over a roughly 40 year period. They compared that forecast to what actually happened each year.

Pilcher said they also compared their new tool to a simple baseline model, which predicts that conditions at the beginning of the year will stay the same throughout the year.

“It’s actually a really good forecast for the ocean because the ocean doesn’t really change that quickly,” he said.

They tested both models for both the bottom and surface of the ocean. Pilcher found that they were both equally good at predicting acidity at the bottom of the ocean. But he said their new model did a lot better at predicting surface temperatures than the baseline model.

“It kind of makes sense because the bottom waters, especially during the summer, are more cut off from the atmosphere,” he said. “Whereas of course the surface is still very connected to the atmosphere and is responding to it on a quicker time frame.”

Pilcher hopes the information from their experiment, and his new model, can inform future management.

“We could say, ‘Hey, this is what we’re predicting for the upcoming summer,’ so that we can give everybody a little bit advance notice if there are, say, worse acidification conditions,” he said.

He said they’ve also discussed partnering with a new king crab mariculture project happening on St. Paul Island. The plan is to raise larval Bristol Bay red king crabs in a lab, and release them back into Bristol Bay when they reach a certain size. But because juvenile crabs are more vulnerable to ocean acidity than adults, Goen said Pilcher’s model could provide important data.

“Where I could see an immediate benefit is knowing if those waters are going to be unusually acidic or higher in temperature in a given year,” she said. “Then maybe that’s not the best year to put some brood stock back into Bristol Bay.”

Goen said she hopes for more research on the changing ocean chemistry in the Bering Sea, so fishermen can make informed decisions. But for now, she said Pilcher’s results are very promising.

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Seasonal forecasts of pH and aragonite saturation for the Bering Sea shelf

Published 28 August 2026 Science Leave a Comment
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The number of numerical model forecasts of ocean environmental conditions has greatly expanded in recent years, including biogeochemical variables. Forecasts can provide marine resource managers with advance warning of extreme events such as heatwaves and hypoxia, though forecast products are scarcer in high-latitude environments. The Bering Sea shelf is a large marine ecosystem that supports critical commercial, cultural, and subsistence ecosystem services that are vulnerable to extreme events and anthropogenic stressors such as ocean acidification (OA). Here, we use a regional oceanographic model of the Bering Sea to assess model forecast skill in predicting bottom water pH and aragonite saturation state (Ωarag) on lead times from 1 to 9 months. We simulate 28 years (1982–2010) of 3-member ensemble retrospective forecasts, initialized both in April and May following the retreat of winter sea ice and several months in advance of early fall when the most acidic bottom water conditions occur. The results suggest that the model is skillful (anomaly correlation coefficients > 0.5) in forecasting shelf-wide anomalies in bottom water pH and Ωarag, on lead times up to 9 months owing primarily to strong persistence. However, predictive skill for finer scale spatial anomalies is more limited and variable. Model forecast skill is also strong in Bristol Bay, home to the red king crab fishery that has faced recent closures and is threatened by OA. The model forecasts presented here can provide several months advanced notice for acidified water conditions and bolster a suite of products used to support evidence-based fisheries management.

Plain Language Summary

Similar to weather forecasts for the atmosphere, numerical models can also be used to forecast ocean conditions. The skill of these forecasts can be high up to several months in advance because the ocean has a relatively long memory and changes occur more slowly, particularly below the surface. The Bering Sea sustains substantial marine fisheries, which are threatened by changing ocean conditions such as increasing water acidity. Here we used an ocean model to test how well the model can forecast acidified bottom water conditions several months in advance. We did this by running a suite of reforecasts (i.e., we retroactively forecast years that have already occurred) and comparing to the model simulation of the conditions that did occur. Our results suggest that the model can generate skillful forecasts with lead times of up to 9 months, mainly because the conditions that occur at the start of our forecast tend to persist through the summer and into the fall. These forecasts can provide Bering Sea resource managers with advance warnings of water conditions that are harmful to marine species, such as Bristol Bay red king crab.

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Climate change drivers of harmful algal blooms in marine and coastal ecosystems

Published 27 August 2026 Science Leave a Comment
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Climate change is widely recognized to contribute to marine warming, acidification, and deoxygenation, while the frequency of harmful algal blooms (HABs) is increasing, causing severe ecological disruptions. Eutrophic regions are increasingly exposed to thermal extremes, hypoxic conditions, and low pH levels and may therefore serve as sensitive indicators of ecosystem responses to climate forcing. HAB occurrence reflects interactions among nutrient availability, temperature variability, and hydrodynamic conditions. Future work should aim to quantify the relative contributions of interacting environmental drivers to improve the robustness of predictive models of HAB dynamics under future climate scenarios. Climate change is likely to amplify HAB intensity and spatial distribution, although regional outcomes depend on interacting environmental drivers. These findings have implications for fisheries management, aquaculture sustainability, public health issues and long-term monitoring. Monitoring strategies should ideally prioritize ecosystem functional responses and early-warning indicators of climatic variability.

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Aragonite saturation horizon variability along North Pacific seamounts and implications for deep-sea coral reefs

Published 27 August 2026 Science Leave a Comment
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The 2014 discovery of living deep-sea coral reefs along the Northwest Hawaiian Islands (NWHI) and lower Emperor Seamount Chain (ESC), despite the North Pacific’s shallow aragonite saturation horizon (ASH) and high CaCO3 dissolution rates, underscores the need to understand the local seawater chemistry where these reefs persist. We investigated seawater carbonate chemistry using discrete samples along NWHI and ESC from two cruises ∼1 year apart (08/26/21–09/26/21, 09/09/22–10/24/22). Across the two cruises, ASH depth difference ranged from 15 to 77 m. Since the Pacific ASH shoals by 1–2 m yr−1, this long-term trend cannot explain the magnitude of ASH change observed. Potential contributions from anthropogenic CO2 and examining intermediate water mass changes from temperature-salinity plots did not provide an explanation for the observed changes. Instead, ASH depth variability was primarily governed by localized biogeochemical processes, namely changes in intermediate water respiration and CaCO3 dissolution. Indicators for dissolution (TA*) and respiration (AOU) suggest changes in ASH depth were driven by changes in dissolution at the northern- and southern-most sites, whereas respiration exerted stronger control at central sites. Combining 2021 and 2022 data with data from 2014 to 2019 revealed high interannual ASH variability, by as much as >200 m. Deep-sea coral reefs across the NWHI and ESC currently reside close to the ASH depth and likely experience interannual shifts between under- and supersaturation. As ocean acidification induced shoaling occurs alongside these interannual fluctuations, the frequency of undersaturation will be an important consideration for deep-sea coral reef longevity.

Plain Language Summary

In 2014, thriving deep-sea coral reefs were found in the Pacific near Hawaii and the Emperor Seamounts, where conditions were thought too acidic for reef development. To understand how these reefs persist, we studied the carbonate chemistry of this region during two research cruises (2021 and 2022). We found that the depth at which seawater becomes corrosive for coral skeletons (aragonite saturation horizon, ASH) changed far more from year to year than the gradual Pacific trend of 1–2 m yr−1. Human sourced carbon dioxide and natural shifts in ocean water masses do not explain the observed large changes. Instead, local biological and chemical processes, respiration and the dissolution of calcium carbonate, played a major role. When comparing seawater chemistry from 2014 to 2022, the ASH fluctuated even more dramatically than the predicted trend of 1–2 m yr−1. While climate change continues to drive corrosive deep waters closer to the surface, processes that occur on shorter timescales, local respiration and dissolution, can similarly expose deep sea coral reefs to corrosive conditions that can impact their longevity. Therefore, short term and local scale processes can affect long term acidification trends, making gradual shoaling harder to observe in short term data.

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Early detection of coral reef acidification micro-hotspots driven by offshore energy development

Published 26 August 2026 Science Leave a Comment
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Offshore energy development is a key measure to safeguard global energy security. At present, offshore oil and gas, wind power, tidal power and other offshore energy industries are expanding rapidly worldwide. However, large-scale energy activities have become a non-negligible driver of coastal ocean acidification. Carbon emissions generated throughout the full lifecycle of energy facilities locally alter seawater chemistry. This triggers ocean acidification of varying degrees and accelerates the corrosion and degradation of surrounding coral reefs.1,2,3 If population-averaged datasets are adopted to conduct environmental assessments of ocean acidification impacts, it will inevitably fail to identify fine-scale ecological risks to coral reefs induced by energy-related activities.4,5 Undoubtedly, this will become one of the critical bottlenecks restricting the green and sustainable development of offshore energy.

This study targets corals from the South China Sea. We adopt large-view macro-lens infrared thermal imaging. The technique reveals inherent microscale heterogeneity in coral skeletal corrosion susceptibility. The findings provide new technical references for ecological impact assessment, layout optimization and environmental risk control of offshore energy facilities. It also helps promote coordinated development between offshore energy exploitation and marine ecological conservation.

HIGH-PURITY PRIMARY ARAGONITE SKELETON OF GONIOPORA FROM THE SOUTH CHINA SEA

The coral sample used in this study was collected from Wuzhizhou Island, Sanya, South China Sea (Figure 1A). Whole-rock X-ray diffraction (XRD) analysis shows that aragonite is the dominant mineral phase, with a content of 88.5%. This matches the typical mineral composition of pristine coral skeletons. Minor impurities including halite (2.3%), clay minerals (2.3%), dolomite (1.9%), quartz (1.2%), K-feldspar (1.1%), calcite (1.1%), plagioclase (0.9%), and gypsum (0.7%) are also detected in the sample (Figure 1B). Plane-polarized and cross-polarized light micrographs show that the images display regular skeletal frameworks and unevenly distributed pore networks, which lay a structural basis for the spatial differentiation of lattice defects (Figure 1C & D).

Figure 1.  Early detection of coral reef acidification micro-hotspots driven by offshore energy development.(A) Photograph of the intact coral sample collected from the South China Sea; (B) X-ray diffraction pattern, showing dominant primary aragonite with a content of 88.5%, and some minor impurities; (C, D) Plane-polarized and cross-polarized light micrographs; (E) Large-view macro-lens infrared thermal image, with a measured temperature range of 23.60~25.60 °C. The color changes from red for high EBT to purple for low EBT. Dark green areas correspond to the coral pore system, including large corallite cavities, dendritic connected pores and scattered micro-pores. Orange areas represent skeletal matrix with high EBT, which features weak corrosion susceptibility. Bright yellow and light green areas represent matrix with low EBT, acting as acidification micro-hotspots with strong corrosion susceptibility. Sporadic blue spots are residual bubbles formed during thin section preparation, not native skeletal structures.

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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 Comment
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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.

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Elucidating impact of ocean acidification on coral exoskeletons using an in-situ (S)TEM platform

Published 25 August 2026 Science Leave a Comment
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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.

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Comparing ocean acidification communication strategies and effectiveness in marine education centers

Published 25 August 2026 Science Leave a Comment
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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.

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Why marine heat waves and acidification strike together

Published 25 August 2026 Press releases Leave a Comment

A chemistry tug-of-war between ocean acidity and carbon in warming oceans determines when and where these damaging events strike.

This data visualization shows an intense marine heat wave in the Atlantic Ocean and Mediterranean Sea on 13 August 2026. New research examines the relationship between marine heat waves and ocean acidification. Credit: European Union, Copernicus Marine Service Data

Marine heat waves and extreme ocean acidification events are each damaging on their own. But when both stressors hit simultaneously, their individual effects can be exacerbated.

That threat may be best exemplified by “the Blob” of 2013–2015, during which both a marine heat wave and an ocean acidification extreme event hit the northeastern Pacific. Fisheries were closed, marine mammals were stranded, seabirds died, and sea creatures either changed their distribution or perished.

But our understanding of these compound heat-acidity ocean extreme events is limited, with more research focused on the marine heat wave component than on the acidification aspect.

Gregor and Gruber used 43 years of monthly data (1982–2024) on surface ocean temperatures and acidity to determine when, where, and why compound heat-acidity extreme events have occurred. They defined extreme events as those situations when detrended acidity and temperature exceed their 95th percentiles.

Compound ocean heat-acidity events happen more often than would be expected by chance, the authors found. In the low to midlatitudes, they occur roughly 4 times more often than compared to chance, mostly in places with permanent stratification. In these places, heat waves drive waters to be more acidic. The compound events were least common in the eastern equatorial Pacific and around the poles, where deep waters upwell to the surface. When marine heat waves strike in these upwelling regions, a warm lens (top layer of water) prevents the surfacing of the deep acidic waters, leading to unusually low acidity for the region.

A majority (73%) of compound heat-acidity extreme events in the study period were smaller than 500,000 square kilometers (193,000 square miles, roughly the size of Spain) and lasted for about a month. But a few events, like the Blob in 2015, lasted for more than a year, sometimes with long-lasting consequences.

El Niño and La Niña events are important drivers of these compound events, but the events seldom happen at the weather events’ epicenter in the equatorial Pacific. During El Niño, warmer waters create a lens that prevents upwelling, thus reducing the typical acidity of the region. And during La Niña, cold, deep waters with higher acidity upwell, resulting in only an acidification extreme. However, it is in the neighboring regions where the knock-on effect of this warming or acidity causes compound extremes to occur.

The new findings are in line with several key facets of earlier work and offer more insights into temporal patterns and drivers. (AGU Advances, https://doi.org/10.1029/2025AV002112, 2026)

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Recent history of surface ocean acidification extremes that compound marine heatwaves

Published 25 August 2026 Science Leave a Comment
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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 ( <1⁢06 km2) and brief (1 month), but several are exceptional, including: the Blob (2015) in the northeastern Pacific (12.6 ×1⁢06 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.

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Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways

Published 24 August 2026 Science Leave a Comment
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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.

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ISO 18191:2026 – Water quality — Determination of pHT in seawater — Method using the purple indicator of m-cresol

Published 24 August 2026 Science Leave a Comment
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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.

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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 Leave a Comment

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.

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REMINDER: Registration open for the 6th International Symposium on the Ocean in a High-CO₂ World

Published 24 August 2026 Events , Science Leave a Comment

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.

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Acidification

Published 21 August 2026 Science Leave a Comment
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‘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.

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Acidification in aquatic systems

Published 21 August 2026 Science Leave a Comment
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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.

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Witness to ocean acidification

Published 20 August 2026 Science Leave a Comment
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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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Field-deployable full-range underwater pH sensor using a polyprotic SERS probe

Published 20 August 2026 Science Leave a Comment
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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.

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Tiny fossils crack a cretaceous cold case

Published 19 August 2026 Press releases Leave a Comment

Ancient ocean acidification triggered one of the ocean’s most severe extinctions

New research examining hundreds of microscope fossils offers one of the clearest examples yet of how rising CO2 can alter ocean chemistry and harm marine life. Above, Jonathan Chen, the study’s lead author, uses a fine-tipped brush to separate tiny fossils from surrounding sediment.

A 113-million-year-old marine murder mystery may finally be solved.

Using chemical clues locked inside microscopic fossils, Northwestern University scientists found evidence that ocean acidification drove one of the largest extinction events in the history of planktic foraminifera — tiny shell-building organisms that help regulate Earth’s carbon cycle.

The scientists attribute the acidification to the eruption of the Kerguelen Plateau, a massive volcanic province in the southern Indian Ocean. During the Early Cretaceous period, the volcanic province spewed vast quantities of carbon dioxide (CO2) into the atmosphere. As the oceans absorbed that CO2, seawater became more acidic, making it more difficult for marine organisms to build and maintain their shells.

The new study, published in Science, marks the fifth Northwestern-led investigation to link widespread volcanic eruptions to ocean acidification and extinction, strengthening evidence for a recurring pattern that played out across more than 60 million years.

The findings also provide one of the clearest examples yet of how rising CO2 can alter ocean chemistry and harm marine life. As current-day oceans absorb human-generated CO2, the ancient events offer a natural experiment for understanding how modern ocean acidification might affect shell-building organisms and the ecosystems that depend on them.

“By examining fossils, scientists already knew surface plankton were getting smaller and building thinner shells, which suggested they were under stress,” said Northwestern’s Jonathan Chen, who led the study. “But we didn’t know that ocean acidification was responsible. By measuring the fossils’ calcium isotopes, we finally provided that missing evidence. We found a giant increase in calcium isotope ratios right as the extinction unfolded, indicating the organisms’ shells were calcifying at a much slower rate. That was the smoking gun linking ocean acidification to the severe biocalcification stress that ultimately led to their extinction.”

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