Gene expression studies of marine phytoplankton under ocean acidification conditions are frequently based on relative measurements, with actin commonly used as a reference gene. Evidence from other organisms suggests that actin gene expression may be regulated by environmental conditions, compromising the role of actin as a reference gene. In this work the reliability of actin as a reference gene for ocean acidification experimental conditions (high CO2 vs low CO2) in two different metabolic states (acclimated metabolism vs perturbed metabolism) for the coccolithophore Emiliania huxleyi was tested. The transcriptional response of the actin (act) is compared with the expression of specific target genes associated with inorganic carbon uptake (α-carbonic anhydrase: αca1) and assimilation (RuBisCO: rbcL), which was regulated under the experimental conditions. Our results showed act expression instability in experimental conditions, evidencing that act is not a reliable reference gene for studies assessing the effect of ocean acidification on Emiliania huxleyi. Furthermore, when the act-based normalization was quantitatively tested, rbcL and αca1 expression were compromised, leading us to conclude that absolute gene expression quantification should be considered as a potentially reliable alternative for studying gene expression under ocean acidification conditions
Continue reading ‘Evaluation of actin as a reference for quantitative gene expression studies in Emiliania huxleyi (Prymnesiophyceae) under ocean acidification conditions’Posts Tagged 'methods'
Evaluation of actin as a reference for quantitative gene expression studies in Emiliania huxleyi (Prymnesiophyceae) under ocean acidification conditions
Published 24 February 2021 Science ClosedTags: biological response, laboratory, methods, molecular biology, physiology, phytoplankton
Spectrophotometric determination of the bicarbonate dissociation constant in seawater
Published 15 February 2021 Science ClosedTags: chemistry, methods
Highlights
- K1K2 values were obtained via spectrophotometric pH measurements.
- New method improved precision in CO2 system dissociation constants.
- New K2 parameterization improves internal consistency of CO2 system calculations.
Abstract
The aqueous carbon dioxide (CO2) system stoichiometric dissociation constants K1 and K2 express the relative concentrations of CO2, HCO3− (bicarbonate), and CO32− (carbonate) in terms of pH. These constants are critical in the study of seawater and the oceans because any mathematical expression that relates the four major CO2 system parameters (pH, here expressed on the total hydrogen ion concentration scale, pHT; total dissolved inorganic carbon, CT; total alkalinity, AT; and CO2 fugacity, fCO2) requires the use of K1 and K2. Uncertainties associated with current characterizations of pK1 and pK2 (where pK = −log K), on the order of 0.01 and 0.02, limit the accuracy of marine CO2 system calculations. This work reports the results of a spectrophotometric method to experimentally determine the product K1K2 over environmentally relevant ranges of temperature (288.15 ≤ T ≤ 308.15 K) and salinity (19.6 ≤ Sp ≤ 41) where Sp denotes the practical salinity scale. Using previously published parameterizations of K1, values of pK2 could then be calculated from the new K1K2 values. The resulting set of pK2 values was fitted as a function of Sp and T to obtain a new pK2 parameterization (denoted as SWpK2) calculated with the K1 of Waters and Millero (2013) as revised by Waters et al. (2014): SWpK2 = 116.8067 – 3655.02 T−1 – 16.45817 ln T + 0.04523 Sp – 0.615 Sp0.5 – 0.0002799 Sp2 + 4.969 (Sp/T)
The average root mean square deviation between the equation and the observed data is 0.003. Residuals of this pK2 fitting function (i.e., measured pK2 minus parameterized pK2) are substantially smaller than the residuals obtained in previous works. Similarly, the total standard uncertainty in pK2 is reduced from 0.015 (previous characterizations) to 0.010 (this work). Internal consistency assessments (comparisons of measured versus calculated values of AT, CT, pHT, and fCO2) were used to evaluate the computational utility of the new K2 parameterization. Assessments from both laboratory and shipboard data indicate that the internal consistency of CO2 system calculations is improved using the K2 parameterization of this work. This new K2 parameterization provides the most precise, and potentially the most accurate, bicarbonate dissociation constant characterization presently available for open ocean conditions.
Continue reading ‘Spectrophotometric determination of the bicarbonate dissociation constant in seawater’Synoptic assessment of coastal total alkalinity through community science
Published 10 February 2021 Science ClosedTags: chemistry, field, methods, North Atlantic
Comprehensive sampling of the carbonate system in estuaries and coastal waters can be difficult and expensive because of the complex and heterogeneous nature of near-shore environments. We show that sample collection by community science programs is a viable strategy for expanding estuarine carbonate system monitoring and prioritizing regions for more targeted assessment. ‘Shell Day’ was a single-day regional water monitoring event coordinating coastal carbonate chemistry observations by 59 community science programs and seven research institutions in the northeastern United States, in which 410 total alkalinity (TA) samples from 86 stations were collected. Field replicates collected at both low and high tides had a mean standard deviation between replicates of 3.6 ± 0.3 µmol kg−1 (σmean ± SE, n = 145) or 0.20 ± 0.02%. This level of precision demonstrates that with adequate protocols for sample collection, handling, storage, and analysis, community science programs are able to collect TA samples leading to high-quality analyses and data. Despite correlations between salinity, temperature, and TA observed at multiple spatial scales, empirical predictions of TA had relatively high root mean square error >48 µmol kg−1. Additionally, ten stations displayed tidal variability in TA that was not likely driven by low TA freshwater inputs. As such, TA cannot be predicted accurately from salinity using a single relationship across the northeastern US region, though predictions may be viable at more localized scales where consistent freshwater and seawater endmembers can be defined. There was a high degree of geographic heterogeneity in both mean and tidal variability in TA, and this single-day snapshot sampling identified three patterns driving variation in TA, with certain locations exhibiting increased risk of acidification. The success of Shell Day implies that similar community science based events could be conducted in other regions to not only expand understanding of the coastal carbonate system, but also provide a way to inventory monitoring assets, build partnerships with stakeholders, and expand education and outreach to a broader constituency.
Continue reading ‘Synoptic assessment of coastal total alkalinity through community science’A system for the determination of surface water pCO2 in a highly variable environment, exemplified in the southern Baltic Sea
Published 4 February 2021 Science ClosedTags: Baltic, chemistry, field, methods
Highlights
- The system for pCO2 measurements, data storage and ship-to-shore transmission is presented.
- In the open Baltic Sea waters the pCO2 measurements obtained an accuracy of ±1.3 µatm met the state-of-the-art requirements (±2.0 µatm).
- We discuss redefining requirements for quality control and assurance for pCO2 measurements in the coastal zone.
Abstract
Measurement of pCO2 in highly dynamic coastal zones such as the southern Baltic Sea presents many challenges. In this study, we designed a system to measure pCO2 and then validated it in a series of laboratory and seagoing tests. The fast response time of the system was shown to provide a better resolution of CO2 system gradients. In the open waters of the Baltic Sea, the accuracy of the pCO2 measurements (±1.3 µatm) met the requirements of the ICOS (±2.0 µatm). In the coastal zone, there was less consistency between pCO2, DIC and pH measurements, suggesting the need to redefine the quality assurance and control requirements for the measurement of pCO2 in dynamic regions.
Continue reading ‘A system for the determination of surface water pCO2 in a highly variable environment, exemplified in the southern Baltic Sea’Assimilating synthetic Biogeochemical-Argo and ocean colour observations into a global ocean model to inform observing system design
Published 27 January 2021 Media coverage , Science ClosedTags: biogeochemistry, globalmodeling, methods, modeling
A set of observing system simulation experiments was performed. This assessed the impact on global ocean biogeochemical reanalyses of assimilating chlorophyll from remotely sensed ocean colour and in situ observations of chlorophyll, nitrate, oxygen, and pH from a proposed array of Biogeochemical-Argo (BGC-Argo) floats. Two potential BGC-Argo array distributions were tested: one for which biogeochemical sensors are placed on all current Argo floats and one for which biogeochemical sensors are placed on a quarter of current Argo floats. Assimilating BGC-Argo data greatly improved model results throughout the water column. This included surface partial pressure of carbon dioxide (pCO2), which is an important output of reanalyses. In terms of surface chlorophyll, assimilating ocean colour effectively constrained the model, with BGC-Argo providing no added benefit at the global scale. The vertical distribution of chlorophyll was improved by assimilating BGC-Argo data. Both BGC-Argo array distributions gave benefits, with greater improvements seen with more observations. From the point of view of ocean reanalysis, it is recommended to proceed with development of BGC-Argo as a priority. The proposed array of 1000 floats will lead to clear improvements in reanalyses, with a larger array likely to bring further benefits. The ocean colour satellite observing system should also be maintained, as ocean colour and BGC-Argo will provide complementary benefits.
Continue reading ‘Assimilating synthetic Biogeochemical-Argo and ocean colour observations into a global ocean model to inform observing system design’Seasonality and biological forcing modify the diel frequency of nearshore pH extremes in a subarctic Alaskan estuary
Published 27 January 2021 Science ClosedTags: chemistry, methods, North Pacific
Acidification in nearshore waters is influenced by a multitude of drivers that shape the dynamics of pH and carbonate chemistry variability on diurnal, seasonal, and yearly time scales. Monitoring efforts aimed at characterizing high temporal variability are lacking in many nearshore systems, particularly in high‐latitude regions such as Alaska. To rectify this, a nearshore acidification sensor array was established in the Fall of 2017 within Kachemak Bay, Alaska. Presented here are the results from the first year of these deployments, and the first record of a year‐long high‐frequency pH time series for nearshore Alaska. SeaFET™ pH and O2 sensors deployed in Jakolof Bay and Bear Cove reveal a seasonally dynamic system in which nearshore waters in these two enclosed bays transition to being predominantly net autotrophic systems for a period of 60‐plus days. High rates and durations of primary production in late spring and early summer create high pH conditions and extreme variability. Observed pH values in Jakolof Bay and Bear Cove tracked hourly rates of change on the order of 0.18 and 0.10 units, respectively. In Jakolof Bay nondirectional variability within a 12‐h period was > 1 pH unit, exposing organisms to unstable, nonstatic pH conditions on tidal and diurnal cycles. Consistent frequency patterns detailing the magnitude of pH variability was correlated to tidal and O2 signatures, elucidating the dynamics and drivers of pH variability. This first year of observations is the first step in quantifying the anthropogenic contribution to acidification for Kachemak Bay in the forthcoming years.
Continue reading ‘Seasonality and biological forcing modify the diel frequency of nearshore pH extremes in a subarctic Alaskan estuary’Mind your methods: acidification degrades total nitrogen and stable isotopic values within calcified marine macroalgae
Published 26 January 2021 Science ClosedTags: algae, biological response, laboratory, methods, physiology
Nitrogen and carbon are commonly used to determine nutrient regimes and trophic structures within marine ecosystems. Macroalgae are convenient for assessing nutrient conditions via stable isotopes and tissue nutrient levels because of their ability to absorb and integrate ambient nutrients over extended time periods. Calcified macroalgae, such as Halimeda and Udotea spp, are common constituents of tropical marine ecosystems, making them ideal candidates for nutrient-based and food web analyses. However, calcified genera require acidification to remove calcium carbonate to accurately determine δ13C and percentage of N (by weight); the overall effect of acidification on the tissue nutrients and stable isotopes of calcified genera is unresolved. Individuals of Halimeda kanaloana (n = 10) and Udotea geppiorum (n = 9) were collected from Maui, O‘ahu, and Lāna‘i. Each specimen was split into two samples and either decalcified using liquid-phase HCl (acidified) or left unaltered (control). We found that liquid-phase HCl acidification resulted in significantly lower percentage of N in both Halimeda kanaloana and Udotea geppiorum. Whereas δ13C values in acidified samples of both species were predictably lowered, the δ15N in acidified U. geppiorum was significantly increased. Acidification may have unpredictable consequences on both the percentage of nutrients in calcified algal tissue and their δ15N, suggesting that the use of acidification in calcified algal nutrient studies may produce erroneous conclusions. Analysing two sets of samples as calcified (for δ15N) and acidified (for δ13C) would eliminate these errors. However, the use of calcified macroalgae to assess percentage of N should be avoided.
Continue reading ‘Mind your methods: acidification degrades total nitrogen and stable isotopic values within calcified marine macroalgae’Coastal Ocean Data Analysis Product in North America (CODAP-NA) – An internally consistent data product for discrete inorganic carbon, oxygen, and nutrients on the U.S. North American ocean margins
Published 26 January 2021 Projects , Science ClosedTags: biogeochemistry, chemistry, methods, North Atlantic, North Pacific
Internally-consistent, quality-controlled data products play a very important role in promoting regional to global research efforts to understand societal vulnerabilities to ocean acidification (OA). However, there are currently no such data products for the coastal ocean where most of the OA-susceptible commercial and recreational fisheries and aquaculture industries are located. In this collaborative effort, we compiled, quality controlled (QC), and synthesized two decades of discrete measurements of inorganic carbon system parameters, oxygen, and nutrient chemistry data from the U.S. North American continental shelves, to generate a data product called the Coastal Ocean Data Analysis Product for North America (CODAP-NA). There are few deep-water (> 1500 m) sampling locations in the current data product. As a result, cross-over analyses, which rely on comparisons between measurements on different cruises in the stable deep ocean, could not form the basis for cruise-to-cruise adjustments. For this reason, care was taken in the selection of data sets to include in this initial release of CODAP-NA, and only data sets from laboratories with known quality assurance practices were included. New consistency checks and outlier detections were used to QC the data. Future releases of this CODAP-NA product will use this core data product as the basis for secondary QC. We worked closely with the investigators who collected and measured these data during the QC process. This version of the CODAP-NA is comprised of 3,292 oceanographic profiles from 61 research cruises covering all continental shelves of North America, from Alaska to Mexico in the west and from Canada to the Caribbean in the east. Data for 14 variables (temperature; salinity; dissolved oxygen concentration; dissolved inorganic carbon concentration; total alkalinity; pH on the Total Scale; carbonate ion concentration; fugacity of carbon dioxide; and concentrations of silicate, phosphate, nitrate, nitrite, nitrate plus nitrite, and ammonium) have been subjected to extensive QC. CODAP-NA is available as a merged data product (Excel, CSV, MATLAB, and NetCDF, https://doi.org/10.25921/531n-c230, https://www.ncei.noaa.gov/data/oceans/ncei/ocads/metadata/0219960.html) (Jiang et al., 2020). The original cruise data have also been updated with data providers’ consent and summarized in a table with links to NOAA’s National Centers for Environmental Information (NCEI) archives (https://www.ncei.noaa.gov/access/ocean-acidification-data-stewardship-oads/synthesis/NAcruises.html).
Continue reading ‘Coastal Ocean Data Analysis Product in North America (CODAP-NA) – An internally consistent data product for discrete inorganic carbon, oxygen, and nutrients on the U.S. North American ocean margins’Coccolithophore calcification studied by single-cell impedance cytometry: towards single-cell PIC:POC measurements
Published 22 January 2021 Science ClosedTags: dissolution, laboratory, methods, phytoplankton
Since the industrial revolution 30% of the anthropogenic CO2 is absorbed by oceans, resulting in ocean acidification, which is a threat to calcifying algae. As a result, there has been profound interest in the study of calcifying algae, because of their important role in the global carbon cycle. The coccolithophore Emiliania huxleyi is considered to be globally the most dominant calcifying algal species, which creates a unique exoskeleton from inorganic calcium carbonate platelets. The PIC (particulate inorganic carbon): POC (particulate organic carbon) ratio describes the relative amount of inorganic carbon in the algae and is a critical parameter in the ocean carbon cycle.
In this research we explore the use of microfluidic single-cell impedance spectroscopy in the field of calcifying algae. Microfluidic impedance spectroscopy enables us to characterize single-cell electrical properties in a noninvasive and label-free way. We use the ratio of the impedance at high frequency vs. low frequency, known as opacity, to discriminate between calcified coccolithophores and coccolithophores with a calcite exoskeleton dissolved by acidification (decalcified).
We have demonstrated that using opacity we can discriminate between calcified and decalcified coccolithophores with an accuracy of 94.1%. We have observed a correlation between the measured opacity and the cell height in the channel, which is supported by FEM simulations. The difference in cell density between calcified and decalcified cells can explain the difference in cell height and therefore the measured opacity.
Continue reading ‘Coccolithophore calcification studied by single-cell impedance cytometry: towards single-cell PIC:POC measurements’Autonomous in situ calibration of ion‐sensitive field effect transistor pH sensors
Published 14 January 2021 Science ClosedTags: chemistry, field, methods, South Pacific
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.
Continue reading ‘Autonomous in situ calibration of ion‐sensitive field effect transistor pH sensors’Use of a simple empirical model for the accurate conversion of the seawater pH value measured with NIST calibration into seawater pH scales
Published 5 January 2021 Science ClosedTags: chemistry, laboratory, methods
The seawater pH measurement is usually quite complicated because that matrix is characterized by a high ionic strength leading to calibration errors if NIST standards are used. For this matrix, different pH scales like the “total hydrogen ion concentration scale” (TOT) and the “seawater scale” (SWS), are defined, and suitable synthetic seawater solutions must be prepared according to standard procedures to calibrate the glass electrode. This work provides a new approach to make seawater pH measurements by using the glass electrode calibrated with the NIST standards (pHNIST) converting the pHNIST into the right TOT or SWS scales by using empirical equations derived from theoretical thermodynamic data:
pHTOT=pHNIST+0.10383+4.33⋅10−5TS+3.633⋅10−5T2−4.921⋅10−5S2, and pHSWS=pHNIST+0.097733+4.1059⋅10−5TS+3.5437⋅10−5T2−4.941⋅10−5S2,
for the TOT and SWS scales, respectively. These equations are functions of two simple experimental parameters, namely, T = temperature (°C) and S = salinity (PSU, (g/L), Practical Salinity Units). These equations were experimentally validated and the uncertainty of pHTOT and pHSWS was demonstrated to have no statistical difference with the corresponding values obtained following the standard operative procedure (SOP) using commercially unavailable seawater-like buffers. The proposed method has therefore the same performances and it is largely preferable as it avoids long and tedious procedures of the synthetic seawater preparations.
Continue reading ‘Use of a simple empirical model for the accurate conversion of the seawater pH value measured with NIST calibration into seawater pH scales’An updated version of the global interior ocean biogeochemical data product, GLODAPv2.2020
Published 4 January 2021 Science ClosedTags: biogeochemistry, chemistry, field, methods
The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface-to-bottom ocean biogeochemical data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of seawater samples. GLODAPv2.2020 is an update of the previous version, GLODAPv2.2019. The major changes are data from 106 new cruises added, extension of time coverage to 2019, and the inclusion of available (also for historical cruises) discrete fugacity of CO2 (fCO2) values in the merged product files. GLODAPv2.2020 now includes measurements from more than 1.2 million water samples from the global oceans collected on 946 cruises. The data for the 12 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, CFC-11, CFC-12, CFC-113, and CCl4) have undergone extensive quality control with a focus on systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but updated to WOCE exchange format and (ii) as a merged data product with adjustments applied to minimize bias. These adjustments were derived by comparing the data from the 106 new cruises with the data from the 840 quality-controlled cruises of the GLODAPv2.2019 data product using crossover analysis. Comparisons to empirical algorithm estimates provided additional context for adjustment decisions; this is new to this version. The adjustments are intended to remove potential biases from errors related to measurement, calibration, and data-handling practices without removing known or likely time trends or variations in the variables evaluated. The compiled and adjusted data product is believed to be consistent to better than 0.005 in salinity, 1 % in oxygen, 2 % in nitrate, 2 % in silicate, 2 % in phosphate, 4 µmol kg−1 in dissolved inorganic carbon, 4 µmol kg−1 in total alkalinity, 0.01–0.02 in pH (depending on region), and 5 % in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete fCO2, were not subjected to bias comparison or adjustments.
The original data and their documentation and DOI codes are available at the Ocean Carbon Data System of NOAA NCEI (https://www.nodc.noaa.gov/ocads/oceans/GLODAPv2_2020/, last access: 20 June 2020). This site also provides access to the merged data product, which is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/2c8h-sa89 (Olsen et al., 2020). These bias-adjusted product files also include significant ancillary and approximated data. These were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2020 methods and provides a broad overview of the secondary quality control procedures and results.
Continue reading ‘An updated version of the global interior ocean biogeochemical data product, GLODAPv2.2020’Chapter: Manipulation of seawater carbonate chemistry
Published 4 January 2021 Science ClosedTags: biological response, chemistry, methods, phytoplankton, review
Different culture methods to grow microalgae could lead to different physical (light) and chemical environments in culture vessels. Photosynthetic carbon sequestration by the algae in light and their respiratory CO2 release in darkness, can affect stability of carbonate systems (pH, various forms of inorganic carbon, total alkalinity) in culture systems. Usually, pH could increase during light period with active photosynthesis, and decrease during dark period. Such changes in pH and associated carbonate chemistry depend on culture methods and cell biomass or densities of microalgae in water body. The greater the amount of carbon fixation in the water, the greater the changes of the carbonate system. In experiments on the influence of other environmental factors on algae, controlling pH and other carbonate system parameters within known stable ranges is one of the keys to obtain reliable data. This section introduces the seawater carbonate system, compares the existing several kinds of carbonate system control methods, and provides basic suggestions for ocean acidification simulation experiments on marine organisms.
Continue reading ‘Chapter: Manipulation of seawater carbonate chemistry’Establishing ocean acidification monitoring system for tropical waters of Indonesia facing regional climate variability
Published 4 January 2021 Science ClosedTags: biogeochemistry, methods, policy, review
Emission of greenhouse gasses, including high CO2 and other materials, initiating global warming and climate change. Atmospheric CO2 that affect the carbonate system of seawater cause ocean acidification. Indonesian sea with a unique geolocation has important role in this emerging phenomenon. Ocean acidification (OA) not only affect marine organism as a direct effect but also economic and ecological for the human being. Considering the high impact of OA and following the global responsibility on Sustainable Development Goals, it is necessary to conduct systematic research and monitoring on OA in Indonesia. In this review, we are informing the urgency of the OA monitoring system and suggest the carbonate system monitoring as well as carbon biogeochemistry studies for OA. We also introduce an initiative of biogeochemical monitoring for OA at Lombok island with the established protocols. Improvement of many aspects including analysis instrumentations, analysis method, sample treatment, and sampling frequency will be a new insight in conducting further research and monitoring of OA.
Continue reading ‘Establishing ocean acidification monitoring system for tropical waters of Indonesia facing regional climate variability’Evaluation of the temperature dependence of dissociation constants for the marine carbon system using pH and certified reference materials
Published 31 December 2020 Science ClosedTags: chemistry, methods
Highlights
- CO2 system calculation recommendations are made for near-surface ocean-open seawater.
- Nearly all K1∗ and K2∗ evaluated were internally consistent within the accuracy of pH measurements.
- The [B]T-S relation of Lee et al. (2010) is recommended for most applications.
- Measurements of pH at lower temperatures (≤ 20 °C) are more internally consistent than higher temperatures.
Abstract
Due to the uptake of anthropogenic carbon dioxide (CO2) from the atmosphere, and the resulting ocean acidification, long term monitoring of the marine carbon cycle is of utmost importance and requires high precision and accuracy across many laboratories over several decades. Despite this, many uncertainties still remain in carbon system measurements and calculations. Calculations of the carbon system are facilitated by publicly available software, but the large number of options for various constants make data and study inter-comparability challenging. Here, the carbon system is evaluated using internal consistency calculations and spectrophotometric pH measurements on two batches of Certified Reference Material over the full oceanic range of temperatures (−1.7–40 °C). The choice of formulation for the bisulfate dissociation constant is insignificant over at least the salinity range of the CRM (S = 33.4–33.8). The choice of formulation of the hydrogen fluoride dissociation constant adds a small amount of uncertainty, but the best option is unclear. The total boron concentration significantly impacts the calculated pH, with the value of Lee et al. (2010) being more internally consistent and, thus, recommended. Of the 8 carbonic acid dissociation constant sets evaluated, nearly all remain internally consistent at near-surface open-ocean salinities (~31–36) within the accuracy of pH measurements. Nevertheless, the values of Mehrbach et al. (1973), as refit by Dickson and Millero (1987), and Lueker et al. (2000) were the most internally consistent and therefore are preferred for current surface ocean studies (S ≈ 31–36, T = −1.7–40 °C, fCO2 < 500 μatm). The pH was more internally consistent at lower temperatures than higher temperatures.
Continue reading ‘Evaluation of the temperature dependence of dissociation constants for the marine carbon system using pH and certified reference materials’Self-referencing optical fiber pH sensor for marine microenvironments
Published 14 December 2020 Science ClosedTags: chemistry, methods
Highlights
- Self-referencing pH sensor for real-time pH measurement in marine microenvironments.
- Entrapped meta-cresol purple in an optimized TEOS/DDS sol-gel matrix.
- Simple sensor fabrication and uncomplicated supporting instrumentation.
- Conforms to the GOA-ON “weather” measurement quality standard.
Abstract
This study presents the development of an optical fiber pH sensor based on evanescent wave absorbance for continuous pH measurements in marine microenvironments. The sensing layer consists of an optimized sol-gel matrix of tetraethoxysilane and dimethyldiethoxysilane, which substantially improves the entrapment efficiency of the pH indicator meta-cresol purple, leading to a long usable lifetime. The optical fiber pH sensor conforms to the Global Ocean Acidification Observing Network “weather” measurement quality guideline with precision of approximately 0.02 pH units, has a dynamic pHT range of 7.4 to 9.7 in seawater, a response time of 6 minutes and a usable lifetime of 7 days. The optical fiber pH sensor has additional advantages of being self-referencing, without the need of an external sensor reference, having a simple fabrication method and basic spectrometer instrumentation. The suitability of the optical fiber pH sensor was demonstrated in real-time measurements of the ecologically significant green seaweed Ulva sp. The optical fiber pH sensor monitored pH variations due to metabolic activity over 7 days within the seaweed canopy and 4 days within the diffusion boundary layer interface, demonstrating the suitability for measurements in marine microenvironments.
Continue reading ‘Self-referencing optical fiber pH sensor for marine microenvironments’Review of pH sensing materials from macro- to nano-scale: recent developments and examples of seawater applications
Published 7 December 2020 Science ClosedTags: chemistry, methods, review
Over the last few decades, a large number of pH sensitive materials with new compositions and structures have been proposed. Solid state sensors based on organic, inorganic and composite materials are actively investigated, with an increasing interest in the performance offered by nano-scale materials. Our review provides a thorough, up-to-date knowledge of a wide range of pH measurement methods and related sensing materials, firstly by introducing well established materials and methods for pH sensing and then, by covering recent developments in inorganic, organic and nano-engineered devices. The main sensor parameters, including sensitivity, stability, response time and testing conditions are reported. Given the importance of pH sensing in environmental applications, in particular seawater monitoring, sensors tested in seawater are highlighted and discussed.
Continue reading ‘Review of pH sensing materials from macro- to nano-scale: recent developments and examples of seawater applications’CO2 reduction for C2+ in seawater using a graphitic frustrated Lewis pair catalyst
Published 26 November 2020 Science ClosedTags: chemistry, methods, mitigation
Ocean acidification due to the absorption of 40% of the world’s anthropogenic CO2 emissions severely affects the faltering marine ecosystem and the economy. However, there are few reports on reducing CO2 dissolved in seawater. Herein, we introduce an electrochemical CO2 reduction battery system for use in seawater with a graphitic frustrated Lewis pair catalytic cathode doped with boron and nitrogen (BN-GFLP). BN-GFLP converts CO2 dissolved in seawater to multi-carbon (C2+) products during the discharge process, thus increasing the pH of intentionally acidified seawater from 6.4 to 8.0 with more than 87% Faradaic efficiency. In computational chemistry and spectroscopy, BN-GFLP binds CO2 in a unique manner that enables exothermic C–C coupling pathway to deliver 95% selectivity for valuable C2+ products. Based on our results, we suggest a molecular design strategy for next-generation CO2 reduction catalysts for both green oceans and the atmosphere.
Continue reading ‘CO2 reduction for C2+ in seawater using a graphitic frustrated Lewis pair catalyst’Evaluating the sensor-equipped autonomous surface vehicle C-Worker 4 as a tool for identifying coastal ocean acidification and changes in carbonate chemistry
Published 24 November 2020 Science ClosedTags: chemistry, field, methods, North Atlantic
The interface between land and sea is a key environment for biogeochemical carbon cycling, yet these dynamic environments are traditionally under sampled. Logistical limitations have historically precluded a comprehensive understanding of coastal zone processes, including ocean acidification. Using sensors on autonomous platforms is a promising approach to enhance data collection in these environments. Here, we evaluate the use of an autonomous surface vehicle (ASV), the C-Worker 4 (CW4), equipped with pH and pCO2 sensors and with the capacity to mount additional sensors for up to 10 other parameters, for the collection of high-resolution data in shallow coastal environments. We deployed the CW4 on two occasions in Belizean coastal waters for 2.5 and 4 days, demonstrating its capability for high-resolution spatial mapping of surface coastal biogeochemistry. This enabled the characterisation of small-scale variability and the identification of sources of low pH/high pCO2 waters as well as identifying potential controls on coastal pH. We demonstrated the capabilities of the CW4 in both pre-planned “autonomous” mission mode and remote “manually” operated mode. After documenting platform behaviour, we provide recommendations for further usage, such as the ideal mode of operation for better quality pH data, e.g., using constant speed. The CW4 has a high power supply capacity, which permits the deployment of multiple sensors sampling concurrently, a shallow draught, and is highly controllable and manoeuvrable. This makes it a highly suitable tool for observing and characterising the carbonate system alongside identifying potential drivers and controls in shallow coastal regions.
Continue reading ‘Evaluating the sensor-equipped autonomous surface vehicle C-Worker 4 as a tool for identifying coastal ocean acidification and changes in carbonate chemistry’Retrieving monthly and interannual total-scale pH (pHT) on theEast China Sea shelf using an artificial neural network:ANN-pHT-v1 (update)
Published 23 November 2020 Science ClosedTags: biogeochemistry, chemistry, field, methods, modeling, North Pacific, regionalmodeling
While our understanding of pH dynamics has strongly progressed for open-ocean regions, for marginal seas such as the East China Sea (ECS) shelf progress has been constrained by limited observations and complex interactions between biological, physical and chemical processes. Seawater pH is a very valuable oceanographic variable but not always measured using high-quality instrumentation and according to standard practices. In order to predict total-scale pH (pH(T)) and enhance our understanding of the seasonal variability of pHT on the ECS shelf, an artificial neural network (ANN) model was developed using 11 cruise datasets from 2013 to 2017 with coincident observations of pHT, temperature (T), salinity (S), dissolved oxygen (DO), nitrate (N), phosphate (P) and silicate (Si) together with sampling position and time. The reliability of the ANN model was evaluated using independent observations from three cruises in 2018, and it showed a root mean square error accuracy of 0.04. The ANN model responded to T and DO errors in a positive way and S errors in a negative way, and the ANN model was most sensitive to S errors, followed by DO and T errors. Monthly water column pHT for the period 2000-2016 was retrieved using T, S, DO, N, P and Si from the Changjiang biology Finite-Volume Coastal Ocean Model (FVCOM). The agreement is good here in winter, while the reduced performance in summer can be attributed in large part to limitations of the Changjiang biology FVCOM in simulating summertime input variables.
Continue reading ‘Retrieving monthly and interannual total-scale pH (pHT) on theEast China Sea shelf using an artificial neural network:ANN-pHT-v1 (update)’
