The Pacific Small Island Developing States (Pacific SIDS) are at the forefront of climate change impacts, yet these effects remain understudied and therefore poorly understood. Ocean acidification (OA) research in Samoa is in its infancy, with a new OA project established to monitor seawater carbon chemistry in coastal ecosystems. The study measured seawater carbon chemistry—including pH, dissolved carbon dioxide and total alkalinity—within the marine protected area (MPA) of Savaia, Lefaga, on Upolu Island, Samoa. Sampling was conducted over twelve months at four locations within the MPA (Site 1, Site 2, Site 3, Site 4), focusing on spatio-temporal variability in pH, temperature and total alkalinity. Measurements were obtained using water samples and an iSAMI pH sensor. The mean pH recorded was 8.06 ± 0.07, while the mean total alkalinity was 1955.1 ± 25 µmol∙kg−1, which is lower than the typical value of 2305 µmol∙kg−1 observed in tropical environments. This decline in total alkalinity and the corresponding low pH could be a potential source of acidification to downstream coastal ecosystems with potential implications for coral reefs, biodiversity and fishery livelihoods.
Continue reading ‘Variability of carbon chemistry at the marine protected area of Savaia Village, Upolu Island, Samoa’Posts Tagged 'sensor'
Variability of carbon chemistry at the marine protected area of Savaia Village, Upolu Island, Samoa
Published 10 September 2026 Science ClosedTags: chemistry, field, sensor, South Pacific
Field-deployable full-range underwater pH sensor using a polyprotic SERS probe
Published 20 August 2026 Science ClosedTags: chemistry, modeling, sensor
Accurate measurement of pH in underwater environments is essential for oceanographic research, environmental monitoring and subsurface exploration. However, conventional electrode-based sensors are limited by drift, corrosion and narrow operational ranges, particularly under extreme pH and high-salinity conditions. Here we present a fibre-optic surface-enhanced Raman scattering platform that enables full-range (pH 0–14) underwater pH sensing using the polyprotic molecular probe 2-amino-5-mercapto-1,3,4-thiadiazole. This probe exhibits 6 pH-dependent conformations, generating distinct surface-enhanced Raman scattering fingerprints that are decoded via machine learning for accurate, drift-resistant pH prediction with errors below 0.2 pH units. The sensor demonstrates high salt tolerance (up to 1 M NaCl), rapid reversibility and robust photostability, and can be deployed remotely at depths of up to 10 m in seawater and groundwater. By establishing a versatile optical strategy based on polyprotic molecular fingerprints, this work expands the capabilities of environmental monitoring and subsurface exploration in challenging aquatic environments.
Continue reading ‘Field-deployable full-range underwater pH sensor using a polyprotic SERS probe’Method for correcting the temperature dependence of field-type glass electrode pH sensors
Published 14 August 2026 Science ClosedTags: chemistry, field, methods, modeling, North Pacific, sensor
Seawater pH measurement is essential for monitoring ocean acidification and its biogeochemical impacts. Glass electrode pH sensors are widely used for in situ applications due to their ease of operation, low power consumption, and no reagent requirements. However, their accuracy can be affected by temperature-dependent effects, particularly those associated with the internal reference solution. Conventional calibration methods based on the Nernst response do not explicitly account for temperature-induced variations in the internal solution, which may lead to systematic bias under conditions with large temperature gradients. In this study, a correction method is proposed to address temperature-dependent errors by modeling the internal pH (pHin). The model incorporates two primary temperature-dependent contributions: the intrinsic temperature dependence of the phosphate buffer and potential shifts caused by activity changes in saturated KCl. These effects are combined through the electrode response factor (fR), defined as the ratio of the observed electrode slope to the theoretical Nernst slope, to estimate pHin as a function of temperature and correct measured pH values to a reference temperature of 25 °C. Application of the method to vertical seawater profiles demonstrated a reduction in deviation from colorimetric reference measurements. The corrected results showed reduced temperature-dependent bias across depth. This approach provides a practical framework for improving the reliability of in situ glass electrode pH measurements under varying thermal conditions. The proposed method addresses equilibrium temperature-dependent effects of the internal solution but does not explicitly account for transient hysteresis, pressure effects, or long-term sensor drift.
Mechanically flexible pH sensor demonstrating high sensitivity in seawater and long-term operational stability for ocean environmental applications
Published 23 July 2026 Science ClosedTags: sensor
The development of robust and flexible pH sensors is critical for accurate in-situ monitoring of marine environments, particularly for applications such as ocean acidification research and underwater vehicle-based sensing. In this study, we present a highly stable and flexible pH sensor based on iridium oxide (IrOx) electrodes with potential for reliable operation in complex marine settings, based on its performance in laboratory-simulated conditions and long-term stability in real seawater. The sensor exhibits a near-Nernstian response with an average sensitivity of −65.07 mV/pH in aqueous solutions (pH 3–10), demonstrating excellent stability after 4000 bending cycles with minimal hysteresis. A rapid response time of 9.29 s and negligible potential drift (±5 mV over 5 min) highlight its precision and repeatability. While cation interference, particularly from Mg²⁺, induces slight potential shifts (4–5 mV), the sensor maintains its Nernstian behavior across all tested interferents including Na⁺, K⁺, Ca²⁺, and Mg²⁺. High-resolution measurements within the marine-relevant pH range (7.9–8.4) confirm excellent sensor performance with sensitivities exceeding −64.5 mV/pH. This targeted validation, combined with the sensor’s exceptional mechanical flexibility, underscores its suitability for real-time pH monitoring in dynamic marine systems. These findings demonstrate the sensor’s potential for advancing marine chemistry research and environmental monitoring applications.
Development of hypoxia and acidification during harmful algal blooms: dynamic multi-stressor conditions in NY, USA, estuaries
Published 14 July 2026 Science ClosedTags: algae, biological response, chemistry, field, multiple factors, North Atlantic, sensor, toxicants
Highlights
- Alexandrium blooms occurred with normoxic conditions and moderate pH (7.5-8.0).
- Alexandrium blooms occurred with moderate pCO2 (400 – 1,000 µatm) and saturating conditions for aragonite.
- Dinophysis blooms co-occurred nocturnal acidification (8.71 to 13.6 hr d−1) and hypoxia (0.52 to 3.88 hr d−1).
- Dinophysis blooms co-occurred with high pCO2 (1,000 – 3,500 µatm) and undersaturated aragonite (Ωar < 1).
- The co-occurrence of nocturnal hypoxia, acidification, Ωar undersaturation, and HABs coupled is a significant threat for marine life.
Abstract
While harmful algal blooms (HABs), hypoxia, and ocean acidification are common occurrences in coastal zones, research investigating the co-occurrence and interactions between these processes has been lacking. Here, we documented the initiation, peak, and demise of eight distinct HAB events caused by Alexandrium catenella and Dinophysis acuminata over a two-year period in two estuaries (Northport Harbor and Cold Spring Harbor, NY, USA). We concurrently characterized the dynamics of carbonate chemistry, including pCO2 and the saturation state of aragonite (Ωar), pH, dissolved oxygen (DO), and general environmental conditions in space and time. HABs occurred in succession and reached high densities with A. catenella blooms exceeding 104 cells L−1 being succeeded by D. acuminata blooms exceeding 106 cells L−1. A. catenella blooms occurred during spring months under generally normoxic conditions with moderate levels of pCO2 (400 – 1,000 µatm), only brief periods of acidification (pH < 7.5), mostly saturating conditions for aragonite, and an absence of hypoxia. In contrast, D. acuminata blooms, which occurred in summer, consistently co-occurred with bouts of extended nocturnal acidification (8.71 to 13.6 hr d−1) and hypoxia (0.52 to 3.88 hr d−1) coupled with higher levels of pCO2 (1,000 – 3,500 µatm), and undersaturating conditions for aragonite (Ωar < 1). During both blooms, nearshore locations hosted higher cell densities, lower pH and DO, and higher pCO2 compared to open water regions. The co-occurrence of multiple stressors including nocturnal hypoxia, acidification, Ωar undersaturation, and HABs, coupled with strong diel cycling of DO, pH, and pCO2, especially during D. acuminata blooms, represents a significant and previously unrecognized threat for marine life.
Continue reading ‘Development of hypoxia and acidification during harmful algal blooms: dynamic multi-stressor conditions in NY, USA, estuaries’High-precision performance of a full-ocean-depth pH sensor: calibration and assessment under simulated hadal pressure conditions
Published 23 June 2026 Science ClosedTags: chemistry, methods, sensor
Real-time in situ pH monitoring in the hadal zone is essential for resolving deep-sea carbon dynamics but is severely challenged by extreme hydrostatic pressures and complex biochemical environments. Current sensors often lack the necessary robustness and calibration protocols for full-ocean-depth applications. To address these challenges, we developed a solid-state electrochemical pH sensor system comprising a fouling-resistant sulfonated poly(ether ether ketone)/ionic liquid composite IrOx (SP/IL-IrOx) working electrode and a pressure-tolerant silica-stabilized ionic liquid (Si-StabIL) reference electrode. Using Tris-artificial seawater (Tris-AS) buffers, we established a standardized high-pressure calibration protocol and systematically evaluated sensor performance over the full-ocean-depth pressure range (0.1−120 MPa) under simulated hadal pressure conditions. The sensor exhibited near-Nernstian sensitivity with high reversibility and repeatability, with potential deviations of no more than 1.6 mV, corresponding to less than 0.03 pH units across the investigated pressure range. Long-term reliability was demonstrated by a minimal drift of only 0.01 pH units during continuous operation in the Tris-AS buffer at 120 MPa for 65 h. Crucially, the sensor captured the nonlinear, pressure-driven acidification of simulated hadal-zone seawater during a 7 day pressurization experiment while maintaining stable response in calibration buffers. These results demonstrate the robustness of the sensor system and provide an experimental basis for calibration and pH assessment under simulated full-ocean-depth pressure conditions.
Continue reading ‘High-precision performance of a full-ocean-depth pH sensor: calibration and assessment under simulated hadal pressure conditions’Present and future seawater CO2 chemistry across multiple coral reef habitats and scales at Dongsha Atoll and Taiping Island in the South China Sea
Published 22 May 2026 Science ClosedTags: biogeochemistry, chemistry, corals, field, laboratory, North Pacific, sensor
Coral reefs consist of diverse benthic habitats that influence seawater CO2 chemistry variability on multiple spatial and temporal scales. Understanding the present-day seawater CO2 chemistry variability across both habitat-specific and reef-wide scales is critical to accurately predict the effects of future environmental change. Here, we utilize autonomous sensors and discrete seawater samples across diverse habitats at multiple scales ranging from habitat-specific (inner lagoon, patch reefs and seagrass beds; 0.02–0.72km2) to reef-wide scales at Dongsha Atoll (250km2) and Taiping Island (20km2) to characterize seawater chemistry. Across all habitats, daily mean pH ranged from 7.79–8.60 with mean diel variability ranging from 0.19–0.91. Spatially, pH variability ranged from 0.08 (patch reef) to 1.29 (inner lagoon). Biogeochemical modification of seawater chemistry was dominated by organic carbon cycling at individual habitat scales, whereas inorganic carbon cycling dominated at the scale of Dongsha Atoll. The largest alkalinity depletion (net calcification) was associated with patch reef habitats, whereas the highest alkalinity repletion was associated with a semi-enclosed lagoon. Under two climate change scenarios (linear dissolved inorganic carbon increase derived from historical observations and the CMIP6 SSP5-8.5 pathway), pH and/or aragonite saturation state (ΩAr) observations across all habitats in this study are projected to be below proposed thresholds for net reef accretion (pH < 7.7: inner lagoon ~ 10–13%; seagrass beds ~ 21–44%; patch reefs ~ 0–100%; atoll-wide ~ 4–98% of observations) or net dissolution (ΩAr < 2.92: inner lagoon ~ 10–18%; seagrass beds ~ 44–75%; patch reefs ~ 77–100%; atoll-wide ~ 94–100% of observations) by the year 2100. The results highlight the importance of habitat-specific and scale-conscious assessments of future coral reef environmental conditions.
Continue reading ‘Present and future seawater CO2 chemistry across multiple coral reef habitats and scales at Dongsha Atoll and Taiping Island in the South China Sea’Acidification in coastal waters of Adélie Land, Antarctica (1985–2025)
Published 29 April 2026 Science ClosedTags: Antarctic, chemistry, field, modeling, regionalmodeling, sensor
Ocean acidification is expected to be particularly severe in Antarctic continental shelves due to enhanced anthropogenic carbon uptake in cold waters in response to rising atmospheric CO2, sea-ice retreat, freshening and climate-change feedbacks. Models suggest that undersaturated conditions with respect to aragonite (Ωar), a major form of calcium carbonate formed by marine species, could be reached as soon as 2052 for austral winter. Here we present new ocean carbonate system observations from cruises conducted since 2010 in the Adélie Land coastal region in East Antarctica, along with data from a BCG-Argo float and results from a neural network model for the period 1985–2025. The region is a permanent CO2 sink and was most pronounced since 2006. The CO2 sink leads to a positive increase of surface water total CO2 concentrations (CT) (+0.44 ± 0.01 µmol.kg-1.yr-1) and to a progressive decrease of pH (-0.013 per decade) and Ωar (-0.035 per decade) for the winter season. The lowest surface Ωar of 1.2 was observed in winter 2024 from the float data, a critical limit for some marine species such as pteropod. A projection of the CT concentrations in the future, based on observed anthropogenic CO2 concentrations and emissions scenarios, suggests that aragonite saturation state (Ωar = 1) will occur in surface waters as soon as 2055 in the Adélie Land region, which is part of a larger area of East Antarctica proposed as a Marine Protected Area by the Commission for the Conservation of Antarctic Marine Living Resources since the early 2010s.
Continue reading ‘Acidification in coastal waters of Adélie Land, Antarctica (1985–2025)’Sea-Bird Scientific introduces deep SeapHOx V2 moored system
Published 23 December 2024 Educational Materials , Resources , Web sites and blogs ClosedTags: resource, sensor
Sea-Bird Scientific has introduced the Deep SeapHOx™ V2. Designed for long-term deployments in diverse environments, from shallow regions to the deep ocean, this state-of-the-art multiparameter moored system integrates the Deep SeaFET™ V2 pH sensor with the tried-and-true SBE 37 SMP-ODO MicroCAT CTD+DO sensor. The result? A powerful tool for monitoring ocean acidification and other critical physical and biological processes.
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Applications and Case Studies
The Deep SeapHOx V2 is designed to support a wide range of oceanographic research and monitoring applications:
- Carbon cycle analysis – track the movement and storage of carbon in the ocean to better understand the global carbon cycle.
- Climate science – collect data on ocean temperature and salinity to contribute to climate models and predict future climate change scenarios.
- Coral reef monitoring – investigate the conditions that support deep-sea coral ecosystems and assess their vulnerability to environmental changes.
- Deoxygenation and hypoxia monitoring – measure dissolved oxygen levels to identify and study hypoxic zones, which can have significant impacts on marine life.
- Fisheries and aquaculture – early warning and monitoring for critical marine resources that are sensitive to changing pH.
- Case study – Experimental kelp farming with Saccharina latissima
- Food web studies – analyze the interactions between different species in the marine food web and how they are affected by environmental factors.
- Marine biology – Study the health and behavior of marine organisms in response to changing environmental conditions.
- Ocean acidification – monitor changes in ocean pH levels to understand the impacts of increased carbon dioxide on marine ecosystems.
- Case study – Inductive modem technology for use in measuring pH
Recent developments in ionophore-based potentiometric electrochemical sensors for oceanic carbonate detection
Published 18 March 2024 Science ClosedTags: chemistry, field, multiple factors, review, salinity, sensor, temperature
The increasing level of atmospheric carbon dioxide (CO2) driven by human activities contributes to the global concern of climate change. A consequence of these circumstances is ocean acidification, which reduces seawater pH. The increasing absorption of atmospheric CO2 into the ocean decreases the concentration of carbonate ions and causes the sea to become more acidic, severely harming marine species. This harm to marine life has created the need for in situ carbonate sensing and monitoring to understand how marine ecosystems respond to pH reduction. Over the past few decades, many sensors with different compositions and structures have been developed to detect carbonate in seawater and other aquatic environments to simulate oceanic conditions. This review summarizes the recent developments in carbonate ionophores, a key component in carbonate electrochemical sensors, and compares the reported performance of these sensors through various parameters (e.g., sensitivity, response time, lifetime, testing media, and measuring range). Current challenges within the development of carbonate ionophores and sensors and possibilities for future research are also discussed.
Continue reading ‘Recent developments in ionophore-based potentiometric electrochemical sensors for oceanic carbonate detection’Total dissolved inorganic carbon sensor based on amperometric CO2 microsensor and local acidification
Published 26 July 2021 Science ClosedTags: laboratory, methods, resource, sensor
We present a dipping probe total dissolved inorganic carbon (DIC) microsensor based on a localized acidic microenvironment in front of an amperometric CO2 microsensor. The acidic milieu facilitates conversion of bicarbonate and carbonate to CO2, which in turn is reduced at a silver cathode. Interfering oxygen is removed by an acidic CrCl2 oxygen trap. Theoretical simulations of microsensor functioning were performed to find a suitable compromise between response time and near-complete conversion of bicarbonate to CO2. The sensor exhibited a linear response over a wide range of 0–8 mM DIC, with a calculated LOD of 5 μM and a 90% response time of 150 s. The sensor was successfully tested in measuring DIC in bottled mineral water and seawater. This DIC microsensor holds the potential to become an important tool in environmental sensing and beyond for measurements of DIC at high spatial and temporal resolution.
Continue reading ‘Total dissolved inorganic carbon sensor based on amperometric CO2 microsensor and local acidification’
