With the United States withdrawing from the Paris Agreement, there is a lot of uncertainty about what U.S. climate diplomacy will look like under the current administration. But despite challenges at the national level, many state governments are poised to continue making progress on global climate action. This new dynamic is already playing out in response to ocean acidification. Daniel and Alison sat down with Jessie Turner, executive director of the International Alliance to Combat Ocean Acidification (OA Alliance), to explore the landscape—or seascape—of subnational climate diplomacy.
Continue reading ‘Keeping U.S. climate action afloat: subnational diplomacy on ocean acidification (podcast)’Archive Page 45
Keeping U.S. climate action afloat: subnational diplomacy on ocean acidification (podcast)
Published 31 March 2025 Web sites and blogs ClosedMetabolomic and physiological analyses of two picochlorophytes from distinct oceanic latitudes under future ocean acidification and warming
Published 28 March 2025 Science ClosedTags: adaptation, biological response, growth, laboratory, morphology, multiple factors, photosynthesis, physiology, phytoplankton, temperature
Highlights
- Ocean acidification and warming impacted picochlorophytes’ metabolome and physiology
- High CO2 significantly altered Chlorella‘s metabolome, with fewer changes in Parachlorella.
- High temperature enhanced Chlorella photosynthesis, while high CO2 benefited Parachlorella.
Abstract
Phytoplankton are cosmopolitan marine photosynthetic organisms that are vital to biogeochemical cycles and marine ecosystems. The current rise in atmospheric CO2 and surface ocean temperatures are poised to disrupt the ecological niches of phytoplankton. Picochlorophytes, a broad taxon of small green eukaryotic phytoplankton, have been shown to perform well under future rising oceanic CO2 and temperature scenarios. This study investigates the acclimation responses of cosmopolitan picochlorophytes from the Chlorella-lineage under high CO2 (1000 p.p.m.) and a rise of 4˚C (8˚C – polar picochlorophyte; 32 ˚C, tropical picochlorophyte). In order to determine how the future ocean warming and acidification might affect picochlorophytes, a polar strain of Chlorella and a tropical Parachlorella were selected, and their physiology and GCMS-based metabolomics were investigated. Growth rate and cellular dimensions (diameter, volume, and surface area) of Chlorella significantly increased in all environmental future scenarios compared to Parachlorella. Photosynthetic parameters of the picochlorophytes studied showed acclimation, with high temperature and high CO2 triggering the adaptation of Fv/Fm , NPQmax, and Ek of Chlorella and Parachlorella, respectively. High CO2 induced the most changes in the Chlorella metabolome, altering the levels of metabolites related to amino acids and their derivatives, glutathione production, carbohydrates, and photochemical quenching. Combined high CO2/temperature altered Parachlorella’s metabolome, though with a small number of biomarkers detected. This study provided evidence to support the hypothesis that picochlorophytes could thrive in a more acidified and warmer ocean.
Continue reading ‘Metabolomic and physiological analyses of two picochlorophytes from distinct oceanic latitudes under future ocean acidification and warming’Safeguarding South-East Asia’s marine ecosystems from ocean acidification threats
Published 28 March 2025 Newsletters and reports ClosedTags: Indian, policy, South Pacific
The increasing carbon dioxide emissions from human activities are being absorbed by the oceans, leading to a decrease in seawater pH levels worldwide. South-East Asia is particularly vulnerable to this problem, as the projected trend of ocean acidification severely threatens marine life in the region, as well as marine industry productivity and food safety. Urgent action must be taken by the Association of Southeast Asian Nations (ASEAN) Secretariat and its Member States to sustain coastal populations’ livelihoods and economic prosperity.
Recommendations:
- Improve marine protected areas (MPAs) by applying science-based design and grass-roots community participation
- Establish a regional task force and collaborative funding
- Increase public awareness and implement marine educational programmes through curriculum integration
Multi-endmember mixing and primary productivity drive carbonate system variability on a highly heterogeneous, shallow productive bank
Published 27 March 2025 Science ClosedTags: chemistry, field, North Atlantic
This study presents the first high-resolution spatial analysis of carbonate chemistry on Georges Bank, a highly productive shallow bank located at the southeastern edge of the Gulf of Maine. Despite numerous studies on the hydrography, nutrient chemistry, and biology, regional carbonate chemistry remains unexplored, in particular for near-bottom conditions. Observations from cruises in May and October 2021 were used to identify multi-endmember mixing, and a Bayesian mixing model was applied to temperature and salinity to separate water mass mixing from non-conservative drivers such as net community production, air–sea exchange, and other biogeochemical processes/errors. Major findings from this study indicate that carbonate chemistry is highly heterogeneous and driven by multi-endmember mixing, although biological production and respiration were notable while air–sea CO2 exchange was minimal. Five water masses with unique carbonate chemistry were observed that varied by season and with depth, showing complexity that is uncommon in other regions along the US Atlantic coast. In both cruises, a Warm Slope Water intrusion was identified at depth that contained a strong signal of CaCO3 dissolution during the October cruise, observed in situ for the first time in this region. Under a high emissions scenario, our results suggest that much of the bank’s bottom waters may become undersaturated with respect to aragonite by 2100. Together, these findings suggest that the in situ dissolution observed may only worsen with future ocean acidification, with potentially significant implications for ecologically and economically important shellfish species on Georges Bank.
Continue reading ‘Multi-endmember mixing and primary productivity drive carbonate system variability on a highly heterogeneous, shallow productive bank’Chapter 12 – Development of multiparametric standard seawater (MSSW) for CO2 parameters, dissolved oxygen, and density of seawater
Published 27 March 2025 Science ClosedTags: methods
Multiparametric Standard Seawater (MSSW) is being developed based on the technology used to manufacture the reference material for nutrients in seawater (RMNS), without adding mercuric chloride to sterilize it, but by adopting aluminum bottles and plastic inner caps with high impermeability to gas and water vapor. The history, current status, and future plans for the development of MSSW for measurements of Practical Salinity, density, dissolved inorganic carbon, total alkalinity, pH, dissolved oxygen (DO), and dissolved organic matter are discussed. Substances that interfere with the Winkler method for DO determination (nitrite, iodate, and hydrogen peroxide) were evaluated for MSSW. The values of the parameters of interest were relatively homogeneous, but the concentrations of dissolved organic carbon depended on the serial number in the lot tested. Long-term stabilities were good in most cases, but DO concentrations began to gradually decrease immediately after production and appeared to stabilize a few years later. The Practical Salinity also tended to decrease (–0.00015 year–1), and the cause of the decreasing trend urgently needs to be clarified. One possibility is an increasing trend (about +0.00015 year–1) of the Practical Salinity of IAPSO standard seawater for salinity measurements.
Continue reading ‘Chapter 12 – Development of multiparametric standard seawater (MSSW) for CO2 parameters, dissolved oxygen, and density of seawater’The University of Delaware’s School of Marine Science seeks two doctoral students to join a research group investigating ocean uptake of carbon, ocean acidification and marine carbon dioxide removal. Funding is available for two to three students, each of whom may select one of the following projects:
- Inorganic carbon chemistry and ocean acidification along the North American East Coast;
- Using stable carbon isotopes of dissolved inorganic carbon (δ13C-DIC) to constrain the ocean uptake of CO2 in ocean basins globally. New research cruises are scheduled for the Pacific Ocean in 2026 and 2027;
- Assessing coastal wetland carbon export and evaluating its potential for marine carbon dioxide removal;
- Inorganic carbon chemistry and ocean acidification in the Arctic Ocean. A trans-Arctic cruise from Norway to Alaska is anticipated for summer 2026.
Interested students are encouraged to contact Dr. Wei-Jun Cai directly at wcai@udel.edu.
Visit Dr. Cai’s University of Delaware webpage for more information on the Cai Lab’s research.
NOAA Ocean Acidification Program, 25 March 2025. More information.
Effects of feed satiation on energy metabolism in the mussel Mytilus coruscus under ocean acidification and warming and possible hormonal regulation
Published 26 March 2025 Science ClosedTags: biological response, laboratory, mollusks, multiple factors, North Pacific, physiology, temperature
Highlights
- Mussels possibly control their metabolism through hormone regulation
- The energy metabolism of mussels is influenced more by food availability than by ocean acidification and warming
- The interactive effects of environmental stressors differ from their individual effects
- Adequate food supply enhances mussels adaptation and resilience to environmental stressors
- Mytilus coruscus has high potential to adapt to environmental stressors
Abstract
Over the past several decades, it is thought that human activities have been a significant factor in bringing about increased atmospheric carbon dioxide concentrations, thereby contributing to elevated ocean acidification and warming. Due to their sessile nature, marine bivalves are considered to be particularly vulnerable to such alterations of the marine environment. Much remains unknown concerning the underlying strategies by which marine bivalves modify energy demand under such conditions. In addition, whether feed availability has an effect and plays a role in this respect is unclear. In the present study, we attempted to address these questions by investigating metabolism and energy pathways in the mussel Mytilus coruscus. Warming, acidification, and food shortage have significantly impacted metabolism, energy pathways, circadian rhythms, hormone activity, and gene expression related to metabolism and circadian rhythms in mussels, leading to energy limitations. Thermal tolerance data indicate that M. coruscus has substantial adaptive capacity to environmental stressors. Bivalves can regulate energy production pathways by modulating serotonin and triiodothyronine hormones, and adequate food availability enhances this regulation. Our findings suggest that ocean warming and acidification synergistically alter energy metabolism in mussels, causing energy limitations, and that food availability is crucial for maintaining mussel condition.
Continue reading ‘Effects of feed satiation on energy metabolism in the mussel Mytilus coruscus under ocean acidification and warming and possible hormonal regulation’State of the global climate 2024
Published 26 March 2025 Newsletters and reports , Press releases , Science ClosedTags: chemistry, video/audio
Key messages
- Key climate change indicators again reach record levels
- Long-term warming (averaged over decades) remains below 1.5°C
- Sea-level rise and ocean warming irreversible for hundreds of years
- Record greenhouse gas concentrations combined with El Niño and other factors to drive 2024 record heat
- Early warnings and climate services are vital to protect communities and economies
The annually averaged global mean near-surface temperature in 2024 was 1.55 °C ± 0.13 °C above the 1850–1900 average. This is the warmest year in the 175-year observational record, beating the previous record set only the year before. While a single year above 1.5 °C of warming does not indicate that the long-term temperature goals of the Paris Agreement are out of reach, it is a wake-up call that we are increasing the risks to our lives, economies and the planet.
Over the course of 2024, our oceans continued to warm, sea levels continued to rise, and acidification increased. The frozen parts of Earth’s surface, known as the cryosphere, are melting at an alarming rate: glaciers continue to retreat, and Antarctic sea ice reached the second-lowest extent ever recorded. Meanwhile, extreme weather continues to have devastating consequences around the world.
In response, WMO and the global community are intensifying efforts to strengthen early warning systems and climate services to help decision-makers and society at large be more resilient to extreme weather and climate. We are making progress but need to go further and need to go faster. Only half of all countries worldwide have adequate multi-hazard early warning systems. This must change.
Investment in National Meteorological and Hydrological Services is more important than ever to meet the challenges and build safer, more resilient communities. Authoritative scientific information and knowledge is necessary to inform decision-making in our rapidly changing world, and this report provides the latest science-based update on the state of our knowledge of key climate indicators
“A stark reminder”: record-breaking CO2 levels recorded for Earth’s polar regions
Published 26 March 2025 Web sites and blogs ClosedDaily average atmospheric carbon dioxide (CO2) levels have exceeded 430ppm for the first time since records began, and likely for the first time in at least 3 million years, “raising a red flag that today’s fossil fuel emissions are pushing the climate into greater and more deadly extremes” according to the International Cryosphere Climate Initiative (ICCI), a network of senior policy experts and researchers working with governments and organizations to preserve as much of the Earth’s cryosphere (the frozen parts of the Earth system) as possible.
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The milestone is particularly concerning for polar and temperate ocean regions where marine life is already experiencing the detrimental effects of changing ocean chemistry. Approximately 25% of carbon emissions are absorbed by the Ocean, leading to increasing acidification as CO2 dissolves in seawater to form carbonic acid. This chemical change makes it increasingly difficult for shell-building marine organisms to build and maintain their calcium carbonate structures, threatening the foundation of marine food webs.
“The news that the 430ppm CO2 concentration in the atmosphere has been reached is extremely disappointing and worrying,” said PML’s Professor Helen Findlay, who is a science expert member of the ICCI High Urgency Group.
“We’re still emitting an alarming amount of CO2, given the climate crises, and this should be a stark reminder to the world that we need to get on track with emissions reductions and the energy transition. A quarter of that carbon is going into our oceans and continuing to cause acidification, as we showed in our recent report on Ocean Acidification status around the UK and Ireland.”
“Acidification will take thousands of years to recover from, so the more CO2 going in, the more we are committing to another impact on our ocean’s health.”
Continue reading ‘“A stark reminder”: record-breaking CO2 levels recorded for Earth’s polar regions’Molecular evidence for the intermediate disturbance hypothesis in an acidified marine system
Published 25 March 2025 Science ClosedTags: biological response, echinoderms, field, molecular biology, North Atlantic, vents
The Intermediate Disturbance Hypothesis (IDH), postulated by Connell (1978), suggests that ecosystems exhibit higher species diversity when disturbances occur at intermediate scales. In this study, the applicability of the IDH at the intraspecific scales (organismal) was investigated using molecular data. As an experimental perturbation framework, a naturally acidified system located in La Palma Island, Canary Island (Spain) with a sharp fluctuating pH gradient was sampled. Molecular data were obtained from sequences of a fragment of the mitochondrial Cytochrome C Oxidase subunit I gene in two sea urchin species (Arbacia lixula and Paracentrotus lividus) to explore genetic diversity at the organism level. These data were compared with previous metabarcoding results of taxonomic benthic diversity at the community level. Both sea urchin species showed the highest levels of haplotype and nucleotide diversity at the intermediate pH fluctuation zone, mirroring metabarcoding data that revealed the highest levels of taxonomic diversity at the same zone. The results support the validity of the IDH in marine ecosystems affected by strong pH fluctuations and across different levels of biological organization (from organisms to communities).
Continue reading ‘Molecular evidence for the intermediate disturbance hypothesis in an acidified marine system’Alabama School of Math and Science students research ocean acidification’s effect on local oysters
Published 25 March 2025 Media coverage ClosedSix high school students at the Alabama School of Math and Science are taking science to the sea. They are students from all over the state of Alabama doing college-level research projects that deal with our coastal ecosystems.
Students and instructors at working on research projects in one of the ASMS labs
All of these projects deal with ocean acidification, which occurs when excess carbon dioxide in the atmosphere reacts with water and creates carbonic acid. Lillian Abernathy, a student researcher at ASMS, explains, “Carbonic acid takes away the necessary nutrients that oysters need to grow their shells.”
Here are the six projects these students are researching:
- Calcium-binding proteins in Crassostrea virginica as indicators of in situ pH stress (Lillian Abernathy, a senior from Geneva County).
- Evaluating the impact of phytochemicals on reducing pathogenicity in Crassostrea virginica under ocean acidification (Naria Khristoforova, a senior from Shelby County).
- Effect of ocean acidification, Perkinsus marinus, submerged aquatic vegetation on apoptosis of hemocytes in Crassostrea virginica (BoKyeong Kim, a junior from Autauga County).
- Ocean acidification’s impact on the susceptibility of Perkinsus marinus in Crassostrea virginica (Hyerin Park, a junior from Autauga County)
- Effects of ocean acidification on Pif gene expression in Crassostrea virginica (Kayty Phan, a junior from Mobile County).
- Lower pH levels decrease the productivity of the nitrogen cycle in Crassostrea virginica pallial fluid (Emma Kate South, a junior from Baldwin County)
“I’m looking at gene expression and what’s called the extra pallial fluid cavity in the eastern oyster,” said Emma Kate South, another student researcher.
Ocean acidification can also affect the oyster’s immune system. Hyerin Park notes that this makes oysters more susceptible to Parkinsus marinas, which eats away at the oyster’s tissue. “It’s a really common pathogen down here and it really affects a lot of the oysters,” Park said.
Protecting oysters is very important for conserving our local habitats and preserving a way of life for many along the Gulf Coast. Abernathy stated, “Maintaining those populations is something I’m really passionate about because people need to make money.”
The Alabama School of Math and Science is able to provide these students with these research opportunities thanks to university level labs. This research helps students decide their future.
“Funding from NOAA from the education grant gives us the ability to do this class…and a skillset that is transferable from high school on to college,” said Dr. Rebecca Domangue.
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Continue reading ‘Alabama School of Math and Science students research ocean acidification’s effect on local oysters’Salinity-dependent effects of seawater acidification on growth, photosynthetic physiology and biochemistry of the invasive macroalga Codium fragile
Published 25 March 2025 Science ClosedTags: algae, biological response, growth, laboratory, multiple factors, North Pacific, physiology, salinity
Highlights
- Decreased and increased salinity adversely affect the growth and photosynthetic physiology of Codium fragile under ambient pCO2 conditions.
- Ocean acidification could help Codium fragile to encounter moderate salinity stress by up-regulating photosynthetic ability.
- The deleterious effect of progressively decreased salinity on growth of Codium fragile was magnified when pCO2 increased.
Abstract
Ocean acidification (OA) and seawater salinity are two major environmental factors that influence the growth and distribution of macroalgae in coastal ecosystems. To investigate the effects of OA and salinity on the invasive macroalga Codium fragile, the growth, Chlorophyll a fluorescence, and biochemical compositions (pigment and soluble carbohydrate contents, the superoxide dismutase (SOD) activity, and malondialdehyde (MDA) contents) were studied after exposure to two pCO2 levels (400 ppmv, LC; and 1000 ppmv, HC) and four salinity regimes (high salinity, 40 psu; control salinity, 30 psu; medium salinity, 20 psu; low salinity, 10 psu). The results showed that, except for SOD activity at 20 psu, the growth, maximum and effective quantum yield of PSII, and maximum relative electron transport, pigment and soluble carbohydrate contents, SOD activity, and the MDA content were adversely impacted by both hypo- and hypersaline under LC conditions. Similarly, under HC conditions, the growth, photosynthetic physiology and biochemistry were negatively impacted by low salinity, while high salinity enhanced pigment contents and chlorophyll fluorescence parameters but inhibited SOD activity and MDA contents. Furthermore, higher pCO2 significantly promoted growth, pigment contents, and photosynthetic performance at 20 and 40 psu, while it amplified the depression in growth at 10 psu. These findings suggest that OA may enhance the potential invasive ability and salinity tolerance of C. fragile under medium hyposaline and hypersaline conditions by alleviating the negative effects of salinity stress on growth, photosynthesis, and pigments synthesis. However, it may also synergistically reduce algal growth at further reduced salinity. These data collected herein are valuable for understanding C. fragile cultivation and predicting its future distribution in response to changing ocean conditions.
Continue reading ‘Salinity-dependent effects of seawater acidification on growth, photosynthetic physiology and biochemistry of the invasive macroalga Codium fragile’Detrital source diversity moderates decomposition and nutrient release in current and future ocean conditions
Published 25 March 2025 Science ClosedTags: algae, biological response, BRcommunity, laboratory, multiple factors, South Pacific, temperature
Highlights
- The decomposition of mixed and single detrital sources was assessed in current and future ocean conditions.
- The identity of detrital sources significantly influenced decomposition rates, and carbon and nutrient release.
- Detrital mixing significantly decreased variation in mass loss and nitrogen release.
- Ocean warming sometimes increased rates of decomposition of macrophyte detritus.
- Ocean acidification did not significantly influence detrital mass loss or nutrient release.
Abstract
The complex interactions between detrital diversity and ocean climate change are not well understood. Here, we used sixteen outdoor raceways to test the hypothesis that ocean warming, and acidification would increase rates of decomposition and nutrient release from detritus of common macroalgae, but the magnitude of change would vary for single detrital sources compared to mixed sources. Our litter-bag experiment to test this hypothesis had six types of macroalgal detritus: (i) Ecklonia radiata, (ii) Sargassum vestitum, (iii) Caulerpa filiformis, (iv) Ecklonia and Sargassum mix, (v) Ecklonia and Caulerpa mix, and (vi) Sargassum and Caulerpa mix. The experimental design also had an orthogonal set of treatments testing effects of ocean warming and acidification, individually and combined, based on the RCP 8.5 climate model for 2081–2100. The identity of detrital sources significantly influenced decomposition rates, carbon liberation and nutrient release. The treatments with two detrital sources did not have increased rates of decomposition and nutrient release compared to single sources. However, detrital source mixing significantly moderated variation in decomposition and nutrient release rates. While ocean acidification had little effect on the decomposition of macroalgal detritus, ocean warming tended to increase rates of decomposition. Given that excessive decomposition can lead to severe anoxia, the results suggest the risk of this occurring will be greater in the warmer oceans of coming decades. In such circumstances, the moderating force of detrital diversity may become increasingly important in maintaining benthic oxygen concentrations and detritus-based production.
Continue reading ‘Detrital source diversity moderates decomposition and nutrient release in current and future ocean conditions’Food availability, but not tidal emersion, influences the combined effects of ocean acidification and warming on oyster physiological performance
Published 25 March 2025 Science ClosedTags: biological response, growth, laboratory, mollusks, multiple factors, North Atlantic, physiology, reproduction, respiration, temperature
Highlights
- Effects of pH/temperature conditions, tidal treatments, and food levels are studied.
- Ocean acidification and warming enhance the physiological performance of oysters.
- Food level impacts responses to future conditions and disease susceptibility.
- Intertidal oysters increase food intake to compensate for limits during emersion.
Abstract
Many studies on the effects of ocean acidification and warming (OAW) in intertidal mollusks overlook critical factors like tidal emersion and food availability, both of which can shape organisms’ responses. Experiments on intertidal bivalves often use constant immersion and abundant food, which likely underestimate global change impacts and underscore the need for more realistic experiments mimicking natural ecosystems. This study investigated the physiological responses of juvenile Pacific oyster Crassostrea gigas exposed for 81 days to current and OAW conditions (+3 °C, −0.3 pH units) under two tidal treatments (0 vs. 30 % emersion) and two food levels (ad libitum vs. limited). We measured growth, reproduction, food ingestion, respiration, and biochemical traits like energy reserves and membrane fatty acids. At the experiment’s end, oysters were challenged with a viral disease to assess the physiological cost of acclimation and potential trade-offs. Results showed improved oyster physiological performance under OAW with high food level. Nevertheless, food availability emerged as the predominant factor in oyster performance, limiting growth, reproduction, and energy reserves, while increasing oxygen consumption and disease susceptibility. Food deprivation attenuated the beneficial effects of OAW through antagonistic interaction, suggesting physiologically weakened oysters may struggle to adapt to environmental hazards. Finally, tidal treatment had no significant effect, implying that oysters possess physiological compensatory mechanisms, particularly in food acquisition, enabling them to meet nutritional needs during immersion periods. This study provides valuable insights for designing global climate change experiments that align with ecological realism and improves our understanding of the acclimation potential in bivalves facing rapid ocean changes.
Continue reading ‘Food availability, but not tidal emersion, influences the combined effects of ocean acidification and warming on oyster physiological performance’Physical and biogeochemical controls of sea surface pCO2 along the North American Atlantic coastal ocean margins on different time scales
Published 24 March 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Atlantic, regionalmodeling
Coastal ocean margins play a crucial role in the global carbon cycle, acting as significant carbon sinks and highly productive ecosystems while being particularly vulnerable to climate change and ocean acidification. Despite their importance, there remains a critical knowledge gap in understanding the complex carbon dynamics and acidification processes in these regions, especially in the North American Atlantic Coastal Ocean Margin (NAACOM), which encompasses diverse and economically vital coastal ecosystems. This dissertation aims to investigate the complex physical and biogeochemical processes controlling inorganic carbon chemistry and ocean acidification processes along the NAACOM on different spatial and temporal scales. Through a series of studies, I address critical gaps in understanding the spatial and temporal variability of surface ocean partial pressure of CO2 (pCO2) and air-sea CO2 fluxes in these regions.
I first evaluate the reliability of multiple pCO2 products in the Gulf of Mexico (GoMx). Our analysis reveals significant spatial and seasonal variations in pCO2 due to complex local non-thermal dynamics, particularly in the Louisiana Shelf and Western Florida Shelf. I find that the GoMx is CO2-neutral overall, but with notable spatial differences in pCO2 trends. However, despite the fact that all the reconstructed data products are capable of providing a reasonable estimated annual mean pCO2 climatology for the GoMx, they are unable to simulate the long-term trend of pCO2 within the GoMx.
To address the limitations in existing pCO2 products, I develop a new regional reconstructed pCO2 product (ReCAD-NAACOM-pCO2) for the entire NAACOM. This product uses a novel two-step approach combining random forest and linear regression. Trained on Surface Ocean CO2 Atlas (SOCAT) observations and various environmental variables, ReCAD-NAACOM-pCO2 demonstrates high accuracy and robustness in capturing regional-scale variations, seasonal cycles, and decadal trends of pCO2 from 1993 to 2021.
Utilizing this new product, I investigate the spatial and seasonal variability of pCO2 and air-sea fluxes across the NAACOM. I reveal a south-to-north decreasing gradient in pCO2, primarily driven by the meridional temperature gradient and modulated by regional processes. In southern areas, seasonal thermal cycles dominate pCO2 seasonality, while in northern areas, biological processes play a more significant role. Our analysis identifies the NAACOM as a CO2 sink, with a mean flux of -0.63 ± 0.19 mol C m-2 yr-1 (-10.14 ± 3.00 Tg C yr-1) in the narrow margin (depth < 200m) and -0.60 ± 0.21 mol C m-2 yr-1 (-24.24 ± 8.31 Tg C yr-1) in the wide margin (distance from coast < 400km). This wide-margin CO2 uptake is around 60% lower than previously reported values, emphasizing the importance of accurate regional assessments.
Finally, I explore the impact of Gulf Stream variability on coastal acidification along the U.S. East Coast. Our findings show unexpectedly rapid acidification, with pCO2 increasing faster than atmospheric CO2 in both the Mid and South Atlantic Bights (MAB and SAB) during 2002-2021, accompanied by a rapid decline in the dissolution saturation of pH and calcium carbonate saturation state (Ω). Specifically, during this period, the sea surface pCO2 of the SAB shelf grew 60% faster than the atmosphere pCO2 and 28% faster than the MAB. I attribute this acceleration to an overall extraordinary regional warming background, and additionally to reduced biological carbon removal and decreased buffer capacity on the SAB shelf — all linked to Gulf Stream dynamics. By incorporating Gulf Stream dynamic parameters into a multiple linear regression model and Earth System Models, I provide revised estimates for past and future pCO2 levels in these regions. I show that the rapid pCO2 contrast between SAB and MAB can be traced back to the 1990s and will continue to be larger in the future due to a weakening Gulf Stream.
This dissertation significantly advances our understanding of carbon dynamics in the NAACOM, providing crucial insights for improved coastal carbon cycle modeling. Our findings highlight the complex interplay of physical, biological, and chemical processes in shaping coastal carbon dynamics and acidification patterns. The development of the ReCAD-NAACOM-pCO2 product offers a valuable tool for future research in this area.
Furthermore, our research underscores the urgent need for enhanced ocean acidification monitoring in Gulf Stream-influenced areas and other Western Boundary Current regions. The rapid coastal acidification observed along the U.S. East Coast has important implications for marine ecosystem management and policy-making. As coastal regions face increasing pressures from climate change, our work provides critical information to support informed decision-making and adaptation strategies.
Continue reading ‘Physical and biogeochemical controls of sea surface pCO2 along the North American Atlantic coastal ocean margins on different time scales’Beyond climate change obligations: which lessons from the ITLOS advisory opinion on climate change and ocean acidification for the progressive development of the law of the sea?
Published 24 March 2025 Science ClosedTags: policy
Although scholars largely agree that the United Nations Convention on the Law of the Sea (UNCLOS) is a “living instrument”, the case law shows UNCLOS tribunals’ reluctance to fully engage with questions other than those strictly speaking regulated under the Convention. Amongst these are questions relating to the protection of marine biodiversity and human rights, which have frequently arisen in the context of UNCLOS disputes but received considerably little attention. This is particularly surprising, given the interconnected nature of the marine environment with biodiversity and ecosystems, and with the rights of the communities thriving on them.
Against this background, the present paper unpacks the principle of systemic integration as discussed by the International Tribunal for the Law of the Sea in its 2024 Advisory Opinion, investigating two mechanisms regulating the relationship between UNCLOS and other international instruments, namely the rule of reference technique and Article 237 UNCLOS. Then, it shifts the focus onto international biodiversity law and international human rights law, critically assessing to what extent the Tribunal’s cautious approach to these two regimes was justified in the light of systemic integration. Finally, it offers some remarks on the prospects of litigating the conservation of marine biodiversity and the protection of human rights before UNCLOS international dispute settlement mechanisms.
Continue reading ‘Beyond climate change obligations: which lessons from the ITLOS advisory opinion on climate change and ocean acidification for the progressive development of the law of the sea?’Spatiotemporal dynamics of marine heatwaves and ocean acidification affecting coral environments in the Philippines
Published 21 March 2025 Science ClosedTags: biological response, BRcommunity, chemistry, corals, modeling, North Pacific, regionalmodeling
The coral reefs in the Philippines are facing an unprecedented crisis. This study, based on a comprehensive analysis of marine heatwaves (MHWs), degree heating weeks (DHWs), and ocean acidification (OA) indices derived from satellite observations and reanalysis data, reveals how thermal stress and OA have progressively eroded coral ecosystems from 1985 to 2022. This study analyzed 12 critical coral habitats adjacent to the Philippines. The monthly average sea surface temperature (SST) in the study area ranged from 26.6 °C to 29.3 °C. The coast of Lingayen Gulf was identified as the most vulnerable coral reef site in the Philippines, followed by Davao Oriental and Polillo Island. The coast of Lingayen Gulf recorded the highest total MHW days in 2022, amounting to 293 days. The coast of Lingayen Gulf also reached the highest DHW values in July and August 2022, with 8.94 °C weeks, while Davao Oriental experienced the most extended average duration of MHWs in 2020, lasting 90.5 days per event. Large-scale climate features such as the El Niño–Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) significantly influenced the study area’s SST anomalies and MHW events. High-risk coral bleaching periods, such as 1988–1989, 1998–1999, 2007–2008, and 2009–2010, were characterized by transitions from El Niño and positive PDO phases, to La Niña and negative PDO phases. However, since 2015, global warming has led to high cumulative heat stress without specific climate background patterns. We propose a Coral Marine Environmental Vulnerability Index (CoralVI) to integrate the spatiotemporal dynamics of warming and acidification and their impacts on coral habitats. The data show a rapid increase in the marine environmental vulnerability of coral habitats in the Philippines in recent years, extending to almost the entire coastline, posing significant threats to coral survival.
Continue reading ‘Spatiotemporal dynamics of marine heatwaves and ocean acidification affecting coral environments in the Philippines’An updated synthesis of ocean total alkalinity and dissolved inorganic carbon measurements from 1993 to 2023: the SNAPO-CO2-v2 dataset
Published 21 March 2025 Science ClosedTags: chemistry, field, review
Total alkalinity (AT) and dissolved inorganic carbon (CT) in the oceans are important properties to understand the ocean carbon cycle and its link with global change (ocean carbon sinks and sources, ocean acidification) and ultimately to find carbon-based solutions or mitigation procedures (marine carbon removal). We present an extended database (SNAPO-CO2; Metzl et al., 2024c) with 24 700 new additional data for the period 2002 to 2023. The full database now includes more than 67 000 AT and CT observations along with basic ancillary data (time and space location, depth, temperature, and salinity) in various oceanic regions obtained since 1993 mainly in the framework of French research projects. This includes both surface and water columns data acquired in open oceans, coastal zones, rivers, the Mediterranean Sea, and either from time series stations or punctual cruises. Most AT and CT data in this synthesis were measured from discrete samples using the same closed-cell potentiometric titration calibrated with certified reference material, with an overall accuracy of ±4 µmol kg−1 for both AT and CT. The same technique was used on board for underway measurements during cruises conducted in the southern Indian and Southern oceans. The AT and CT data from these cruises are also added to this synthesis. The data are provided in one dataset for the global ocean (https://doi.org/10.17882/102337, Metzl et al., 2024c) that offers a direct use for regional or global purposes, e.g., AT–salinity relationships, long-term CT estimates, constraint and validation of diagnostics CT and AT reconstructed fields, ocean carbon and coupled climate–carbon models simulations, and data derived from Biogeochemical Argo (BGC-Argo) floats. These data can also be used to calculate pH, fugacity of CO2 (fCO2), and other carbon system properties to derive ocean acidification rates or air–sea CO2 fluxes.
Continue reading ‘An updated synthesis of ocean total alkalinity and dissolved inorganic carbon measurements from 1993 to 2023: the SNAPO-CO2-v2 dataset’Regression-based characterization of the marine carbonate system across shelf and nearshore waters of Queen Charlotte Sound
Published 21 March 2025 Science ClosedTags: chemistry, modeling, North Pacific, regionalmodeling
Highlights
- Carbonate system parameters were predicted by linear regressions in coastal waters.
- Oxygen concentrations were key predictive variables in most linear regressions.
- Regression uncertainty was always greater in coastal waters than in offshore waters.
- The aragonite saturation horizon initially shoaled at the onset of winter winds.
- Persistent downwelling favourable winds subsequently deepened the saturation horizon.
Abstract
Marine carbonate system measurements are essential for understanding ocean acidification and CaCO3 saturation states, and their response to oceanographic and anthropogenic processes. Acquiring such measurements in remote coastal areas is limited by challenges in the development and deployment of autonomous sensors for these parameters, and by the complexity and costs of directly measuring them. We address this challenge by extending an established method of estimating carbonate system parameters through proxy variables to the remote waters of Queen Charlotte Sound, British Columbia. Paired regressions are developed from bottle samples and common hydrographic measurements for both offshore and coastal waters that intersect in this region but retain distinct relationships between total alkalinity and salinity. Application of these regression models to regional autonomous glider data demonstrates that established features of this shelf system can be characterized from a carbonate system perspective along a contiguous transect from land to the shelf break, despite greater regression uncertainties in coastal water. These results also provide new insight into the dynamics of aragonite saturation on the shelf in relation to regional winds. This approach extends a tool to gain knowledge of the marine carbonate system to a coastal region of the northeast Pacific Ocean where hydrographic data used as proxies are more commonly available.
Continue reading ‘Regression-based characterization of the marine carbonate system across shelf and nearshore waters of Queen Charlotte Sound’
