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To elucidate the seawater biological and physicochemical factors driving differences in organic composition between supermicron and submicron sea spray aerosol (SSA

Ion-sensitive field effect transistor-based pH sensors have been shown to perform well in high frequency and long-term ocean sampling regimes. The Honeywell Durafet is widely used due to its stability, fast response, and characterization over a large range of oceanic conditions. However, potentiometric pH monitoring is inherently complicated by the fact that the sensors require careful calibration. Offsets in calibration coefficients have been observed when comparing laboratory to field-based calibrations and prior work has led to the recommendation that an in situ calibration be performed based on comparison to discrete samples. Here, we describe our work toward a self-calibration apparatus integrated into a SeapHOx pH, dissolved oxygen, and CTD sensor package. This Self-Calibrating SeapHOx is capable of autonomously recording calibration values from a high quality, traceable, primary reference standard: equimolar tris buffer. The Self-Calibrating SeapHOx's functionality was demonstrated in a 6-d test in a seawater tank at Scripps Institution of Oceanography (La Jolla, California, U.S.A.) and was successfully deployed for 2 weeks on a shallow, coral reef flat (Lizard Island, Australia). During the latter deployment, the tris-based self-calibration using 15 on-board samples exhibited superior reproducibility to the standard spectrophotometric pH-based calibration using > 100 discrete samples. Standard deviations of calibration pH using tris ranged from 0.002 to 0.005 whereas they ranged from 0.006 to 0.009 for the standard spectrophotometric pH-based method; the two independent calibration methods resulted in a mean pH difference of 0.008. We anticipate that the Self-Calibrating SeapHOx will be capable of autonomously providing climate quality pH data, directly linked to a primary seawater pH standard, and with improvements over standard calibration techniques.

Marine aerosols strongly influence climate through their interactions with solar radiation and clouds. However, significant questions remain regarding the influences of biological activity and seawater chemistry on the flux, chemical composition, and climate-relevant properties of marine aerosols and gases. Wave channels, a traditional tool of physical oceanography, have been adapted for large-scale ocean-atmosphere mesocosm experiments in the laboratory. These experiments enable the study of aerosols under controlled conditions which isolate the marine system from atmospheric anthropogenic and terrestrial influences. Here, we present an overview of the 2019 Sea Spray Chemistry and Particle Evolution (SeaSCAPE) study, which was conducted in an 11 800 L wave channel which was modified to facilitate atmospheric measurements. The SeaSCAPE campaign sought to determine the influence of biological activity in seawater on the production of primary sea spray aerosols, volatile organic compounds (VOCs), and secondary marine aerosols. Notably, the SeaSCAPE experiment also focused on understanding how photooxidative aging processes transform the composition of marine aerosols. In addition to a broad range of aerosol, gas, and seawater measurements, we present key results which highlight the experimental capabilities during the campaign, including the phytoplankton bloom dynamics, VOC production, and the effects of photochemical aging on aerosol production, morphology, and chemical composition. Additionally, we discuss the modifications made to the wave channel to improve aerosol production and reduce background contamination, as well as subsequent characterization experiments. The SeaSCAPE experiment provides unique insight into the connections between marine biology, atmospheric chemistry, and climate-relevant aerosol properties, and demonstrates how an ocean-atmosphere-interaction facility can be used to isolate and study reactions in the marine atmosphere in the laboratory under more controlled conditions. This journal is

Here we present first of its kind high frequency Total Alkalinity (AT) and pH data from a single solid-state autonomous sensor collected during a 6-day deployment at a barrier reef in Kāneʻohe Bay on the CRIMP-2 buoy. This dual parameter sensor is capable of rapid (

Author(s): Lilly, LE; Send, U; Lankhorst, M; Martz, TR; Feely, RA; Sutton, AJ; Ohman, MD | Abstract: We analyzed impacts of the 2014–2015 Pacific Warm Anomaly and 2015–2016 El Nino on physical and biogeochemical variables at two southern California Current System moorings (CCE2, nearshore upwelling off Point Conception; CCE1, offshore California Current). Nitrate and Chl-a fluorescence were l1 μM and l1 Standardized Fluorescence Unit, respectively, at CCE2 for the entire durations of the Warm Anomaly and El Nino, the two longest periods of such low values in our time series. Negative nitrate and Chl-a anomalies at CCE2 were interrupted briefly by upwelling conditions in spring 2015. Near-surface temperature anomalies appeared simultaneously at both moorings in spring 2014, indicating region-wide onset of Warm Anomaly temperatures, although sustained negative nitrate and Chl-a anomalies only occurred offshore at CCE1 during El Nino (summer 2015 to spring 2016). Warm Anomaly temperature changes were expressed more strongly in near-surface (l40 m) than subsurface (75 m) waters at both moorings, while El Nino produced comparable temperature anomalies at near-surface and subsurface depths. Nearshore Ωaragonite at 76 m showed notably fewer undersaturation events during both warm periods, suggesting an environment more conducive to calcifying organisms. Planktonic calcifying molluscs (pteropods and heteropods) increased markedly in springs 2014 and 2016 and remained modestly elevated in spring 2015. Moorings provide high-frequency measurements essential for resolving the onset timing of anomalous conditions and frequency and duration of short-term (days-to-weeks) perturbations (reduced nitrate and aragonite undersaturation events) that can affect marine organisms.

Equimolal tris (2-amino-2-hydroxymethyl-propane-1,3-diol) buffer in artificial seawater is a well characterized and commonly used standard for oceanographic pH measurements. We evaluated the stability of tris pH when stored in purportedly gas-impermeable bags across a variety of experimental conditions, including bag type and storage in air vs. seawater over 300 d. Bench-top spectrophotometric pH analysis revealed that the pH of tris stored in bags decreased at a rate of 0.0058±0.0011 yr−1 (mean slope ±95 % confidence interval of slope). The upper and lower bounds of expected pH change at t=365 d, calculated using the averages and confidence intervals of slope and intercept of measured pH change vs. time data, were −0.0042 and −0.0076 from initial pH. Analyses of total dissolved inorganic carbon confirmed that a combination of CO2 infiltration and/or microbial respiration led to the observed decrease in pH. Eliminating the change in pH of bagged tris remains a goal, yet the rate of pH change is lower than many processes of interest and demonstrates the potential of bagged tris for sensor calibration and validation of autonomous in situ pH measurements.

Significance Sea spray aerosol, produced through breaking waves, is one of the largest sources of environmental particles. Once in the atmosphere, sea spray aerosol influences cloud formation, serves as microenvironments for multiphase atmospheric chemical reactions, and impacts human health. All of these impacts are affected by aerosol acidity. Here we show that freshly emitted sea spray aerosol particles become highly acidic within minutes as they are transferred across the ocean−air interface. These results have important implications for atmospheric chemistry and climate, including aerosol/gas partitioning, heterogeneous reactions, and chemical speciation at the surface and within sea spray aerosol., Aerosols impact climate, human health, and the chemistry of the atmosphere, and aerosol pH plays a major role in the physicochemical properties of the aerosol. However, there remains uncertainty as to whether aerosols are acidic, neutral, or basic. In this research, we show that the pH of freshly emitted (nascent) sea spray aerosols is significantly lower than that of sea water (approximately four pH units, with pH being a log scale value) and that smaller aerosol particles below 1 μm in diameter have pH values that are even lower. These measurements of nascent sea spray aerosol pH, performed in a unique ocean−atmosphere facility, provide convincing data to show that acidification occurs “across the interface” within minutes, when aerosols formed from ocean surface waters become airborne. We also show there is a correlation between aerosol acidity and dissolved carbon dioxide but no correlation with marine biology within the seawater. We discuss the mechanisms and contributing factors to this acidity and its implications on atmospheric chemistry.

Coral reefs are facing intensifying stressors, largely due to global increases in seawater temperature and decreases in pH. However, there is extensive environmental variability within coral reef ecosystems, which can impact how organisms respond to global trends. We deployed spatial arrays of autonomous sensors across distinct shallow coral reef habitats to determine patterns of spatiotemporal variability in seawater physicochemical parameters. Temperature and pH were positively correlated over the course of a day due to solar heating and light‐driven metabolism. The mean temporal and spatial ranges of temperature and pH were positively correlated across all sites, with different regimes of variability observed in different reef types. Ultimately, depth was a reliable predictor of the average diel ranges in both seawater temperature and pH. These results demonstrate that there is widespread environmental variability on diel timescales within coral reefs related to water column depth, which needs to be included in assessments of how global change will locally affect reef ecosystems.

Variable gas diffusion cell geometries were tested for the extraction of dissolved inorganic carbon (DIC) from a microfluidic (tens to hundreds of microliters) seawater sample. With a focus on optimization of diffusion cell geometry, we compare five unique diffusion cell designs. Using 3-D printing technology to streamline the prototyping and testing process, we were able to conceive, design, fabricate, and thoroughly evaluate each design over the course of about one month. In total, 1043 DIC measurements were carried out in 109 experiments for the five working manifolds. We find that a small diameter, cylindrical diffusion cell design offers several advantages over its planar counterparts and a larger diameter cylindrical cell, most notably the ability to increase the ratio of the exchange membrane’s contact surface area to solution volume (the “aspect ratio”) without sacrificing channel integrity. Multiple designs approached short-term repeatability of $\mu \text{L}$ of sample.

Ocean acidification may shift coral reefs from a state of net ecosystem calcification (+NEC) to net ecosystem dissolution (–NEC). Changes in NEC are typically inferred from either measured or calculated total alkalinity (TA) or the dissolved calcium (Ca) to salinity ratio relative to a reference value. The alkalinity anomaly technique has historically been the primary method to estimate NEC due to the greater analytical challenges and uncertainty associated with dissolved Ca measurements in seawater. However, this method assumes that changes in salinity-normalized TA are exclusively the result of calcification and dissolution processes. In many cases, this assumption is valid, but in some environments additional processes can significantly influence seawater TA (e.g., nutrient fluxes, redox processes). Seawater Ca is unaffected or less sensitive to these processes, and therefore, Ca and TA anomalies can be used to estimate absolute or relative changes in NEC with greater confidence. Here, we present a two-year time series of monthly seawater Ca and TA measurements across the Bermuda carbonate platform and the nearby Bermuda Atlantic Time-series Study (BATS) location offshore. High precision Ca measurements (±6 μmol kg−1) were conducted using an improved spectrophotometric titration system and showed mostly good agreement with changes in TA over the same spatial and temporal scales. Ca and TA measurements across the Bermuda platform showed seasonal fluctuations relative to offshore waters, with +NEC during summer months and near-zero or possible –NEC (net dissolution) during winter months. These seasonal patterns were most pronounced at the inshore locations with the longest residence times (10+ days), which allow stronger biogeochemical signals to develop relative to the offshore source water. Although obtaining high accuracy and precision Ca measurements remains challenging, parallel measurements of Ca and TA from both inshore and offshore waters over a multi-annual timescale strengthen the validity of predictions for when, where, and why a reef system, such as the Bermuda platform, may shift from +NEC to –NEC.

The suitability of the Honeywell Durafet to the measurement of pH in productive, high-fouling, and highly-turbid estuarine environments was investigated at the confluence of the Murderkill Estuary and Delaware Bay (Delaware, USA). Three different flow configurations of the SeapHOx sensor equipped with a Honeywell Durafet and its integrated internal (Ag/AgCl reference electrode containing a 4.5 M KCl gel liquid junction) and external (solid-state chloride ion selective electrode, Cl-ISE) reference electrodes were deployed for four periods between April 2015 and September 2016. In this environment, the Honeywell Durafet proved capable of making high-resolution and high-frequency pH measurements on the total scale between pH 6.8 and 8.4. Natural pH fluctuations of >1 pH unit were routinely captured over a range of timescales. The sensor pH collected between May and August 2016 using the most refined SeapHOx configuration exhibited good agreement with multiple sets of independently measured reference pH values. When deployed in conjunction with rigorous discrete sampling and calibration schemes, the sensor pH had a root-mean squared error ranging between 0.011 and 0.036 pH units across a wide range of salinity relative to both pH T calculated from measured dissolved inorganic carbon and total alkalinity and pH NBS measured with a glass electrode corrected to pH T at in situ conditions. The present work demonstrates the viability of the Honeywell Durafet to the measurement of pH to within the weather-level precision defined by the Global Ocean Acidification Observing Network (GOA-ON, ≤ 0.02 pH units) as a part of future estuarine CO2 chemistry studies undertaken in dynamic environments.

The accuracy and precision of ion sensitive field effect transistor (ISFET) pH sensors have been well documented, but primarily by ocean chemistry specialists employing the technology at single locations. Here we examine their performance in a network context through comparison to discrete measurements of pH, using different configurations of the Honeywell DuraFET pH sensor deployed in six coastal settings by operators with a range of experience. Experience of the operator had the largest effect on performance. The average difference between discrete and ISFET pH was 0.005 pH units, but ranged from −0.030 to 0.083 among operators, with more experienced operators within ± 0.02 pH units of the discrete measurement. In addition, experienced operators achieved a narrower range of variance in difference between discrete bottle measurements and ISFET sensor readings compared to novice operators and novice operators had a higher proportion of data failing quality control screening. There were no statistically significant differences in data uncertainty associated with sensor manufacturer or deployment environment (pier-mounted, flowthrough system, and buoy-mounted). The variation we observed among operators highlights the necessity of best practices and training when instruments are to be used in a network where comparison across data streams is desired. However, while opportunities remain for improving the performance of the ISFET sensors when deployed by less experienced operators, the uncertainty associated with their deployment and validation was several-fold less than the observed natural temporal variability in pH, demonstrating the utility of these sensors in tracking local changes in acidification.

Equimolar Tris (2-amino-2-hydroxymethyl-propane-1,3-diol) buffer prepared in artificial seawater media is a widely accepted pH standard for oceanographic pH measurements, though its change in pH over pressure is largely unknown. The change in volume (Δ V ) of dissociation reactions can be used to estimate the effects of pressure on the dissociation constant of weak acid and bases. The Δ V of Tris in seawater media of salinity 35 (Δ V Tris ⁎ ) was determined between 10 and 30 °C using potentiometry. The potentiometric cell consisted of a modified high pressure tolerant Ion Sensitive Field Effect Transistor pH sensor and a Chloride-Ion Selective Electrode directly exposed to solution. The effects of pressure on the potentiometric cell were quantified in aqueous HCl solution prior to measurements in Tris buffer. The experimentally determined Δ V Tris ⁎ were fitted to the equation Δ V Tris ⁎ = 4.528 + 0.04912 t where t is temperature in Celsius; the resultant fit agreed to experimental data within uncertainty of the measurements, which was estimated to be 0.9 cm − 3 mol − 1 . Using the results presented here, change in pH of Tris buffer due to pressure can be constrained to better than 0.003 at 200 bar, and can be expressed as: ∆ pH Tris = − 4.528 + 0.04912 t P ln 10 RT . where T is temperature in Kelvin, R is the universal gas constant (83.145 cm 3 bar K − 1 mol − 1 ), and P is gauge pressure in bar. On average, pH of Tris buffer changes by approximately − 0.02 at 200 bar.

A novel chemical sensor package named “WavepHOx” was developed in order to facilitate measurement of surface ocean pH, dissolved oxygen, and temperature from mobile platforms. The system comprises a Honeywell Durafet pH sensor, Aanderaa optode oxygen sensor, and chloride ion selective electrode, packaged into a hydrodynamic, lightweight housing. The WavepHOx has been deployed on a stand-up paddleboard and a Liquid Robotics Wave Glider in multiple near-shore settings in the Southern California Bight. Integration of the WavepHOx into these mobile platforms has enabled high spatiotemporal resolution pH and dissolved oxygen data collection. It is a particularly valuable tool for mapping shallow, fragile, or densely vegetated ecosystems which cannot be easily accessed by other platforms. Results from three surveys in San Diego, California, are reported. We show pH and dissolved oxygen variability >0.3 and >50% saturation, respectively, over tens to hundreds of meters to highlight the degree of natural spatial variability in these vegetated ecosystems. When deployed during an extensive discrete sampling program, the WavepHOx pH had a root mean squared error of 0.028 relative to pH calculated from fifty six measurements of total alkalinity and dissolved inorganic carbon, confirming its capacity for accurate, high spatiotemporal resolution data collection.

Coral reefs are threatened worldwide, and there is a need to develop new approaches to monitor reef health under natural conditions. Because simultaneous measurements of net community production (NCP) and net community calcification (NCC) are used as important indicators of reef health, tools are needed to assess them in situ. Here we present the Benthic Ecosystem and Acidification Measurement System (BEAMS) to provide the first fully autonomous approach capable of sustained, simultaneous measurements of reef NCP and NCC under undisturbed, natural conditions on time scales ranging from tens of minutes to weeks. BEAMS combines the chemical and velocity gradient in the benthic boundary layer to quantify flux from the benthos for a variety of parameters to measure NCP and NCC. Here BEAMS was used to measure these rates from two different sites with different benthic communities on the western reef terrace at Palmyra Atoll for 2 weeks in September 2014. Measurements were made every ∼15 min. The trends in metabolic rates were consistent with the benthic communities between the two sites with one dominated by fleshy organisms and the other dominated by calcifiers (degraded and healthy reefs, respectively). This demonstrates the potential utility of BEAMS as a reef health monitoring tool. NCP and NCC were tightly coupled on time scales of minutes to days, and light was the primary driver for the variability of daily integrated metabolic rates. No correlation between CO2 levels and daily integrated NCC was observed, indicating that NCC at these sites were not significantly affected by CO2.

The surface of the ocean has absorbed one-third of the CO2gas that has been released by anthropogenic activities, which has resulted in a reduction in pH and the aragonite saturation state (Ωara) with potential negative impacts in calcifying organisms, such as corals. To evaluate these effects, the natural variability present must first be understood, including that of processes that operate at diurnal, seasonal, and interannual frequencies. The objective of this study was to determine the influence of physical and biogeochemical processes on the seasonal variability of the CO2-system in a fringe coral reef of the Eastern Tropical Pacific (ETP). To achieve this, a SeapHOx sensor was installed to measure temperature, salinity, dissolved oxygen, and pHTot at 30-min intervals from November 2013 (early winter) to July 2014 (early summer). The recorded temperature and salinity data fed a mixing model to identify the water masses present in the reef. We show how physical and biogeochemical oceanic processes influence and control the variability of the carbonate system. The presence of water masses with different carbon chemistries responded to two scenarios: (1) seasonal circulation on the order of months and (2) an intermittence between water masses related to mesoscale structures (eddies) on the order of weeks. A low-pH and Ωara condition was detected during summer, which was related to the presence of warm and respired Tropical Surface Water. The broadest changes in Ωara were the result of physical processes (winter ΔΩara = 0.14 and summer ΔΩara = 0.34 units) and corresponded to the transition between water masses with different carbon-biogeochemistry signals. Our results suggest that the Cabo Pulmo coral community develops in an environment with a wide range of pH and Ωara conditions and that seasonal changes are controlled by open ocean carbon biogeochemistry.

Ocean acidification, the decrease in seawater pH as a result of increasing carbon dioxide, has been shown to be an important driver of oyster mortality in West Coast shellfisheries [1]. Yet carbon chemistry is only sparsely measured, especially relative to its high variability in coastal ecosystems, due to the complexity and cost of appropriate sensors and their maintenance. Worse, data are rarely communicated in real time to water quality or aquacultural managers. In the Agua Hedionda Lagoon (AHL) in Carlsbad, CA, researchers from Scripps Institution of Oceanography and industry representatives from the Carlsbad Aquafarm have come together through a NOAA-facilitated project to alleviate this data shortage using a combination of cutting-edge research technology alongside off-the-shelf and easy-to-implement IoT communications packages. Keywords: Water quality, Internet of things, Ocean acidification, Aquaculture

Assessing the impacts of anthropogenic ocean acidification requires knowledge of present-day and future environmental conditions. Here, we present a simple model for upwelling margins that projects anthropogenic acidification trajectories by combining high-temporal-resolution sensor data, hydrographic surveys for source water characterization, empirical relationships of the CO2 system, and the atmospheric CO2 record. This model characterizes CO2 variability on timescales ranging from hours (e.g., tidal) to months (e.g., seasonal), bridging a critical knowledge gap in ocean acidification research. The amount of anthropogenic carbon in a given water mass is dependent on the age; therefore a density–age relationship was derived for the study region and then combined with the 2013 Intergovernmental Panel on Climate Change CO2 emission scenarios to add density-dependent anthropogenic carbon to the sensor time series. The model was applied to time series from autonomous pH sensors deployed in the surf zone, kelp forest, submarine canyon edge, and shelf break in the upper 100 m of the Southern California Bight. All habitats were within 5 km of one another, and exhibited unique, habitat-specific CO2 variability signatures and acidification trajectories, demonstrating the importance of making projections in the context of habitat-specific CO2 signatures. In general, both the mean and range of pCO2 increase in the future, with the greatest increase in both magnitude and range occurring in the deeper habitats due to reduced buffering capacity. On the other hand, the saturation state of aragonite (ΩAr) decreased in both magnitude and range. This approach can be applied to the entire California Current System, and upwelling margins in general, where sensor and complementary hydrographic data are available.

Chemical properties of the California Undercurrent (CU) have been changing over the past several decades, yet the mechanisms responsible for the trend are still not fully understood. We present a survey of temperature, salinity, O2, pH, and currents at intermediate depths (defined here as 50–500 m) in the summer (30 June to 10 July) and winter (8–15 December) of 2012 in the southern region of the Southern California Bight. Observations of temperature, salinity, and currents reveal that local bathymetry and small gyres play an important role in the flow path of the California Undercurrent (CU). Using spiciness (π) as a tracer, we observe a 10% increase of Pacific Equatorial Water (PEW) in the core of the CU during the summer versus the winter. This is associated with an increase in π of 0.2, and a decrease in O2 and pH of 30 μmol kg−1 and 0.022, respectively; the change in pH is driven by increased CO2, while total alkalinity remains unchanged. The high-π, low-O2, and low-pH waters during the summer are not distributed uniformly in the study region. Moreover, mooring observations at the edge of the continental shelf reveal intermittent intrusions of PEW onto the shelf with concomitant decreases in O2 and pH. We estimate that increased advection of PEW in the CU could account for approximately 50% of the observed decrease in O2, and between 49 and 73% of the decrease in pH, over the past three decades.

The photosynthetic quantum yield (Φ), defined as carbon fixed or oxygen evolved per unit of light absorbed, is a fundamental but rarely determined biophysical parameter. A method to estimate Φ for both net carbon uptake and net oxygen evolution simultaneously can provide important insights into energy and mass fluxes. Here we present details for a novel system that allows quantification of carbon fluxes using pH oscillation and simultaneous oxygen fluxes by integration with a membrane inlet mass spectrometer. The pHOS system was validated using Phaeodactylum tricornutum cultured with continuous illumination of 110 μmole quanta m-2 s-1 at 25°C. Furthermore, simultaneous measurements of carbon and oxygen flux using the pHOS-MIMS and photon flux based on spectral absorption were carried out to explore the kinetics of Φ in P. tricornutum during its acclimation from low to high light (110 to 750 μmole quanta m-2 s-1). Comparing results at 0 and 24 hours, we observed strong decreases in cellular chlorophyll a (0.58 to 0.21 pg cell-1), Fv/Fm (0.71 to 0.59) and maximum ΦCO2 (0.019 to 0.004) and ΦO2 (0.028 to 0.007), confirming the transition toward high light acclimation. The Φ time-series indicated a non-synchronized acclimation response between carbon uptake and oxygen evolution, which has been previously inferred based on transcriptomic changes for a similar experimental design with the same diatom that lacked physiological data. The integrated pHOS-MIMS system can provide simultaneous carbon and oxygen measurements accurately, and at the time-resolution required to resolve high-resolution carbon and oxygen physiological dynamics.

International audience; Research assessing the biological impacts of global ocean change often requires a burdensome characterization of seawater carbonate chemistry. For laboratory-based ocean acidification research, this impedes the scope of experimental design. Honeywell Durafet ® III pH electrodes provide precise and continuous seawater pH measurements. In addition to use in oceanographic sensor packages, Durafets can also be used in the laboratory to track and control seawater treatments via Honeywell Universal Dual Analyzers (UDAs). Here we provide performance data, instructions, and step-by-step recommendations for use of multiple UDA-Durafets. Durafet pH measurements were within ±0.005 units pH T of spectrophotometric measurements and agreement among eight Durafets was better than ±0.005 units pH T. These results indicate equal performance to Durafets in oceanographic sensor packages, but methods for calibration and quality control differ. Use of UDA-Durafets vastly improves time-course documentation of experimental conditions and reduces person-hours dedicated to this activity. Due to the versatility of integrating Durafets in laboratory seawater systems, this technology opens the door to advance the scale of questions that the ocean acidification research community aims to address.

Characterization of several potentiometric cells without a liquid junction has been carried out in universal buffer, aqueous HCl, and artificial seawater media. The electrodes studied include Ion Sensitive Field Effect Transistor (ISFET) pH electrodes, and Chloride-Ion Selective Electrodes (Cl-ISE) directly exposed to the solution. These electrodes were compared directly to the conventional hydrogen electrode and silver-silver chloride electrode in order to report the degree to which they obey ideal Nernstian laws. These data provide a foundation for operating the ISFET|Cl-ISE pair in seawater as a pH sensor. In order to obtain the highest quality pH measurements from this sensor, its response to changes in pH and salinity must be properly characterized. Our results indicate near-ideal Nernstian response for both electrodes over a wide range of pH (2-12) and Cl(-) molality (0.01-1). We conclude that the error due to sub-Nernstian response of the cell ISFET|seawater|Cl-ISE over the range of seawater pH and salinity is negligible (0.0001 pH). The cross sensitivity of the Cl-ISE to Br(-) does not seem to be a significant source of error (0.003 pH) in seawater media in the salinity range 20-35.

We use autonomous nitrate (NO3−), oxygen (O2), and dissolved inorganic carbon (DIC) observations to examine the relationship between ratios of C:N:O at an upwelling site in the Southern California Current System. Mean ratios and 95% confidence intervals observed by sensors over 8 months were NO3−:O2 = −0.11 ± 0.002, NO3−:DIC = 0.14 ± 0.001, and DIC:O2 = −0.83 ± 0.01, in good agreement with Redfield ratios. Variability in the ratios on the weekly time scale is attributable to shifts in biological demand and nutrient availability and shown to exhibit a spectrum of values ranging from near 100% New Production to 100% Regenerated Production.

Performance of autonomous pH sensors is evaluated by comparing in situ data to independent bench-top measurements of pH and to co-located pH, O2, and p CO 2 sensors. While the best practice is always to deploy a properly calibrated sensor, the lengthy time period required for sensor conditioning and calibration often results in sensor deployment without comprehensive calibration. Quality control (QC) procedures are examined to determine the errors associated with different in situ calibration approaches and lay a framework for best practices. Sensor packages employing the Honeywell Durafet remained stable across multiple deployments for over nine months. However, sensor performance was often limited by biofouling. Regional empirical relationships for estimating carbonate system parameters are shown to enable identification of otherwise indistinguishable sensor offset and drift when multiple sensor types are co-located. Uncertainty is determined by calibration approach and must be quantified on a case-by-case basis. Our results indicate that the Durafet is capable of accuracy, relative to a chosen reference, of better than 0.03 pH units over multiple months. Accuracy is improved when a robust shore-side calibration is performed, an independent means of QC is available throughout a deployment, and effective biofouling prevention measures are taken.

Predicting consequences of ocean deoxygenation and ocean acidification for nearshore marine ecosystems requires baseline dissolved oxygen (DO) and carbonate chemistry data that are both high-frequency and high-quality. Such data allow accurate assessment of environmental variability and present-day organism exposure regimes. In this study, scales of DO and pH variability were characterized over one year in a nearshore kelp forest ecosystem in the Southern California Bight. DO and pH were strongly, positively correlated, revealing that organisms on this upwelling shelf are not only exposed to low pH but also to low DO. The dominant scale of temporal DO and pH variability occurred on semidiurnal, diurnal and event (days–weeks) time scales. Daily ranges in DO and pH at 7 m water depth (13 mab) could be as large as 220 μmol kg−1 and 0.36 units, respectively. Sources of pH and DO variation include photosynthesis within the kelp forest ecosystem, which can elevate DO and pH by up to 60 μmol kg−1 and 0.1 units over one week following the intrusion of high-density, nutrient-rich water. Accordingly, highly productive macrophyte-based ecosystems could serve as deoxygenation and acidification refugia by acting to elevate DO and pH relative to surrounding waters. DO and pH exhibited greater spatial variation over a 10 m increase in water depth (from 7 to 17 m) than along a 5 km stretch of shelf in a cross-shore or alongshore direction. Over a three-month time period, mean DO and pH at 17 m water depth were 168 μmol kg−1 and 7.87, respectively. These values represent a 35% decrease in mean DO and 37% increase in [H+] relative to near-surface waters. High-frequency variation was also reduced at depth. The mean daily range in DO and pH was 39% and 37% less, respectively, at 17 m water depth relative to 7 m. As a consequence, the exposure history of an organism is largely a function of its depth of occurrence within the kelp forest. With knowledge of local alkalinity conditions and high-frequency temperature, salinity, and pH data, we estimated pCO2 and calcium carbonate saturation states with respect to calcite and aragonite (Ωcalc and Ωarag) for the La Jolla kelp forest at 7 m and 17 m water depth. pCO2 ranged from 246 to 1016 μatm, Ωcalc was always supersaturated, and Ωarag was undersaturated at the beginning of March for five days when pH was less than 7.75 and DO was less than 115 μmol kg−1. These findings raise the possibility that the benthic communities along eastern boundary current systems are currently acclimatized and adapted to natural, variable, and low DO and pH. Still, future exposure of coastal California populations to even lower DO and pH may increase as upwelling intensifies and hypoxic boundaries shoal, compressing habitats and challenging the physiological capacity of intolerant species.

Titrations, while primarily known as the chemical rite of passage for fledgling science students, are still widely used for chemical analysis. With its many years of existence and improvement, the method would seem an unlikely candidate for innovation, yet it is desirable, in this age of autonomous sensing where analyzers may be sent into space or to the bottom of the ocean, to have a simplified titrimetric method that does not rely upon volumetric or gravimetric measurement of sample and titrant. In previous work on the measurement of seawater alkalinity, we found that use of a tracer in the titrant eliminates the need to measure mass or volume. Here, we show the versatility of the method for diverse types of titrations and tracers. The results suggest that tracers may be employed in all types of titrations, opening the door for greatly simplified laboratory and field-based chemical analysis.

Although predictions suggest that ocean acidification will significantly impact polar oceans within 20–30 years, there is limited information regarding present-day pH dynamics of the Southern Ocean. Here, we present novel high-frequency observations of pH collected during spring of 2010 using SeaFET pH sensors at three locations under fast sea ice in the southern Ross Sea. During these deployments in McMurdo Sound, baseline pH ranged between 8.019–8.045, with low to moderate overall variation (0.043–0.114 units) on the scale of hours to days. The variation was predominantly in the direction of increased pH relative to baseline observations. Estimates of aragonite saturation state (ΩAr) were > 1 with no observations of subsaturation. Time series records such as these are significant to the Antarctic science community; this information can be leveraged towards framing more environmentally relevant laboratory experiments aimed at assessing the vulnerability of Antarctic species to ocean acidification. In addition, increased spatial and temporal coverage of pH datasets may reveal ecologically significant patterns. Specifically, whether such variation in natural ocean pH dynamics may drive local adaptation to pH variation or provide refugia for populations of marine calcifiers in a future, acidifying ocean.

This study examines the utility of combining pH measurements with other inorganic carbon parameters for autonomous mooring-based carbon cycle research. Determination of the full suite of inorganic carbon species in the oceans has previously been restricted to ship-based studies. Now with the availability of autonomous sensors for pH and the partial pressure of CO 2 ( p CO 2 ), it is possible to characterize the inorganic carbon system on moorings and other unmanned platforms. The indicator-based pH instrument, SAMI-pH, was deployed with an autonomous equilibrator-infrared p CO 2 system in Monterey Bay, California USA from June to August 2007. The two-month time-series show a high degree of short-term variability, with pH and p CO 2 changing by as much as 0.32 pH units and 240 μatm, respectively, during upwelling periods. The pH and salinity-derived alkalinity (A Tsalin ) were used to calculate the other inorganic carbon parameters, including p CO 2 , total dissolved inorganic carbon (DIC) and CaCO 3 saturation states. The calculated p CO 2 was within 2 μatm of the measured p CO 2 during the first day of the deployment and within 8 μatm over the first month. The DIC calculated from pH–A Tsalin and p CO 2 –A Tsalin were within 5 μmol kg −1 of each other during the first month. However, DIC calculated from pH– p CO 2 differed by ~ 50 μmol kg −1 from the other estimates over the same period, reflecting the sensitivity of the pH– p CO 2 calculation to measurement error. The data continued to diverge during the final month and this difference was likely driven by extensive biofouling. Because of the relative insensitivity of CO 3 2− concentration to these errors, aragonite saturation calculated from the pH– p CO 2 pair was within 0.15 of the pH–A Tsalin values over the entire deployment. These results show that in situ pH, when combined with other CO 2 parameters, can provide valuable insights into both data quality and inorganic carbon cycling.

Variation in ocean pH is a dynamic process occurring naturally in the upwelling zone of the California Current Large Marine Ecosystem. The nearshore carbonate chemistry is under-characterized and the physiology of local organisms may be under constant challenge from cyclical changes in pH and carbonate ion concentration of unexpectedly high magnitude. We looked to environmental pH conditions of coastal upwelling and used those values to examine effects of low pH on 4-arm larvae of purple sea urchin Strongylocentrotus purpuratus . We deployed a pH sensor at a nearshore shallow benthic site for 3 weeks during summer 2010 to assess the changes in pH in the Santa Barbara Channel, a region considered to have relatively less intense upwelling along the US Pacific Coast. Large fluctuations in pH of up to 0.67 pH units were observed over short time scales of several days. Daily pH fluctuations on a tidal pattern followed temperature fluctuations over short time scales, but not over scales greater than a day. The lowest pH values recorded (~ 7.70) are lower than some of those pH values predicted to occur in surface oceans at the end of the century. In the context of this dynamic pH exposure, larvae were raised at elevated pCO 2 levels of 1000 ppm and 1450 ppm CO 2 (pH 7.7 and 7.5 respectively) and measured for total larval length (from the spicule tip of the postoral arm to the spicule tip of the aboral point) along the spicules, to assess effects of low pH upwelling water on morphology. Larvae in all treatments maintained normal development and developmental schedule to day 6, and did not exhibit significant differences in larval asymmetry between treatments. At day 3 and day 6, larvae in the 1450 ppm CO 2 treatment were significantly smaller (p 2 has an as yet undetermined physiological mechanism, but has implications for locomotion and feeding. These effects of small magnitude in these urchin larvae are indicative of a potential resilience to near-future levels of ocean acidification. Using environmental monitoring of pH to inform experimental parameters provides a means to improve our understanding of acclimatization of organisms in a dynamic ecosystem.

We report on the first seawater tests at 1 atm of the Honeywell Durafet® pH sensor, a commercially available ion sensitive field effect transistor (ISFET). Performance of this sensor was evaluated in a number of different situations including a temperature-controlled calibration vessel, the MBARI test tank, shipboard underway mapping, and a surface mooring. Many of these tests included a secondary reference electrode in addition to the internal reference supplied with the stock Durafet sensor. We present a theoretical overview of sensor response using both types of reference electrode. The Durafet sensor operates with a short term precision of ± 0.0005 pH over periods of several hours and exhibits stability of better than 0.005 pH over periods of weeks to months. Our tests indicate that the Durafet pH sensor operates at a level of performance satisfactory for many types of biogeochemical studies at low pressure.

We describe a novel method for determination of carbonate ion concentration in seawater by acidimetric titration with UV detection. Because CO 3 2− absorbs light at wavelengths of less than ~ 250 nm, it is feasible to titrate most carbonate-containing natural waters with acid and observe an increase in %Transmittance. The observed signal is proportional to the concentration of carbonate ion in the original sample. Present technology permits a theoretical precision in the determination of [CO 3 2− ] in natural seawater background of ~ 0.5% (at 10 cm pathlength, 200 μM CO 3 2− , ± 0.0001 AU). The procedure has been tested at 1 and 10 cm pathlengths using single and multipoint titration methods, respectively. Results using natural seawater test solutions indicate a resolution in [CO 3 2− ] of 3.6% in a standard 1 cm cuvette using a very simple manual method, and 0.7% using a custom-built 10 cm closed titration cell. Estimates of the relative distribution of CO 3 2− between inner and outer sphere complexes with Mg 2+ and Na + were also determined and the equilibrium constants agree with published values. This method provides a new tool for studies of several fundamental aspects CO 2 chemistry, including the second dissociation constant of carbonic acid, CO 3 2− ion pairing, and can be used to directly measure the distribution of carbonate ion in seawater and many other types of natural waters.

We estimated rates of production and export in the South Pacific (80uW to 180uW in a zonal band between 35uS and 50uS) using 1.5 yr of oxygen measurements from profiling floats. Export production, calculated from oxygen utilization rates below the compensation depth from December to April, was 10.7 6 2 mmol C m22 d21 (n 5 36, 95% CI). The corresponding satellite net primary production was 46 6 4 mmol C m22 d21, yielding a regional e-ratio of 0.23 6 0.05. Averaging oxygen utilization rates resulted in a net cancellation of most water mass changes related to advection and float migration. The composite vertical profile of remineralization rates, obtained by binning 36 rate profiles, agreed with published measurements based on oxygen utilization rates in hydrographic surveys and fits the classic form of a particulate organic carbon (POC) attenuation function. However, the disagreement between oxygen-based remineralization rates and those obtained by sediment traps suggests fundamental differences between these two methods. Using float data to constrain a one-dimensional mixed-layer model, the annual net community production at 45uS, 144uW was ,2.5 mol C m22 yr21. Spatial

Increasing atmospheric carbon dioxide is driving a long-term decrease in ocean pH which is superimposed on daily to seasonal variability. These changes impact ecosystem processes, and they serve as a record of ecosystem metabolism. However, the temporal variability in pH is observed at only a few locations in the ocean because a ship is required to support pH observations of sufficient precision and accuracy. This paper describes a pressure tolerant Ion Sensitive Field Effect Transistor pH sensor that is based on the Honeywell Durafet ISFET die. When combined with a AgCl pseudoreference sensor that is immersed directly in seawater, the system is capable of operating for years at a time on platforms that cycle from depths of several km to the surface. The paper also describes the calibration scheme developed to allow calibrated pH measurements to be derived from the activity of HCl reported by the sensor system over the range of ocean pressure and temperature. Deployments on vertical profiling platforms enable self-calibration in deep waters where pH values are stable. Measurements with the sensor indicate that it is capable of reporting pH with an accuracy of 0.01 or better on the total proton scale and a precision over multiyear periods of 0.005. This system enables a global ocean observing system for ocean pH.

Understanding how declining seawater pH caused by anthropogenic carbon emissions, or ocean acidification, impacts Southern Ocean biota is limited by a paucity of pH time-series. Here, we present the first high-frequency in-situ pH time-series in near-shore Antarctica from spring to winter under annual sea ice. Observations from autonomous pH sensors revealed a seasonal increase of 0.3 pH units. The summer season was marked by an increase in temporal pH variability relative to spring and early winter, matching coastal pH variability observed at lower latitudes. Using our data, simulations of ocean acidification show a future period of deleterious wintertime pH levels potentially expanding to 7–11 months annually by 2100. Given the presence of (sub)seasonal pH variability, Antarctica marine species have an existing physiological tolerance of temporal pH change that may influence adaptation to future acidification. Yet, pH-induced ecosystem changes remain difficult to characterize in the absence of sufficient physiological data on present-day tolerances. It is therefore essential to incorporate natural and projected temporal pH variability in the design of experiments intended to study ocean acidification biology.

Understanding how declining seawater pH caused by anthropogenic carbon emissions, or oceanacidification, impacts Southern Ocean biota is limited by a paucity of pH time-series. Here,we present the first high-frequency in-situ pH time-series in near-shore Antarctica fromspring to winter under annual sea ice. Observations from autonomous pH sensors revealed aseasonal increase of 0.3 pH units. The summer season was marked by an increase in temporalpH variability relative to spring and early winter, matching coastal pH variability observedat lower latitudes. Using our data, simulations of ocean acidification show a future periodof deleterious wintertime pH levels potentially expanding to 7–11 months annually by 2100.Given the presence of (sub)seasonal pH variability, Antarctica marine species have anexisting physiological tolerance of temporal pH change that may influence adaptation tofuture acidification. Yet, pH-induced ecosystem changes remain difficult to characterize inthe absence of sufficient physiological data on present-day tolerances. It is thereforeessential to incorporate natural and projected temporal pH variability in the design ofexperiments intended to study ocean acidification biology.

An autonomous sensor for long-term in situ measurements of the pH of natural waters is described. The system is based upon spectrophotometric measurements of a mixture of sample and sulfonephthalein indicator. A simple plumbing design, using a small, low-power solenoid pump and valve, avoids the need for quantitative addition of indicator. A approximately 50-microL slug of indicator is pulled into the sample stream by the pump, and subsequent pumping and mixing results in a section of indicator and sample where absorbance measurements can be made. The design also permits direct determination of the indicator pH perturbation. Absorbances are recorded at three wavelengths (439, 579, and 735 nm) using a custom-built 1.7-cm path length fiber-optic flow cell. Solution blanks are obtained by periodically flushing the cell with sample. Field tests were performed in a local river over an 8-day period. The in situ accuracy, based on comparison with laboratory spectrophotometric pH measurements, was -0.003 pH unit (n = 16), similar to the measurement precision. No drift was observed during the 8-day period. The absorbance ratio used to calculate pH, in combination with a simple and robust optical design, imparts an inherent stability not achievable with conventional potentiometric methods, making the design feasible for long-term autonomous pH measurements.

Iglesias-Prieto et al. (1) present 24 h of continuous temperature, conductivity, and sea-level data recorded at a submarine spring in Mexico and argue that Crook et al. (2) attribute changes in coral calcification only to changes in aragonite saturation (Ωarag) while ignoring these other parameters and their variability. On the contrary, Crook et al. (2, 3) conducted extensive monitoring of all these parameters over a 3-y period at both the spring (low pH) and control (high pH) sites (Fig. 1). Furthermore, corals were collected for the calcification study only from sites where mean temperature and salinity were closest to that of the control sites, while pH and aragonite saturation state were substantially different. These …

Community structure and assembly are determined in part by environmental heterogeneity. While reef-building corals respond negatively to warming (i.e. bleaching events) and ocean acidification (OA), the extent of present-day natural variability in pH on shallow reefs and ecological consequences for benthic assemblages is unknown. We documented high resolution temporal patterns in temperature and pH from three reefs in the central Pacific and examined how these data relate to community development and net accretion rates of early successional benthic organisms. These reefs experienced substantial diel fluctuations in temperature (0.78°C) and pH (>0.2) similar to the magnitude of 'warming' and 'acidification' expected over the next century. Where daily pH within the benthic boundary layer failed to exceed pelagic climatological seasonal lows, net accretion was slower and fleshy, non-calcifying benthic organisms dominated space. Thus, key aspects of coral reef ecosystem structure and function are presently related to natural diurnal variability in pH.

The tracer monitored titration (TMT) technique is evaluated for measurement of dissolved oxygen. The TMT developed in this work uses a simple apparatus consisting of a low-precision pump for titrant delivery and an optical detector based on a white LED and two photodiodes with interference filters. It is shown that the classic Winkler method can be made free of routine volumetric and gravimetric measurements by application of TMT theory, which allows tracking the amounts of titrant and sample using a chemical tracer. The measurement precision of the prototype setup was 0.3% RSD.