High-resolution record of surface water pH at Sentry Shoal in the Northern Strait of Georgia

The northern Strait of Georgia (nSoG) in British Columbia, Canada is part of the large inland Salish Sea and has sparse carbonate system data coverage relative to the inter-seasonal and regional variability. The Environment Canada weather buoy at Sentry Shoal in the nSoG provides a platform of opportunity for collection of high frequency carbonate system measurements. During summer and fall of 2016 and 2017, autonomous sensors were deployed at the surface to measure in situ temperature, salinity, and pH. The effort to collect these data is part of the Hakai Institute’s directive to advance the understanding of carbon cycling in northeast Pacific coastal settings with specific emphasis on sea-air CO2 exchange and ocean acidification. This data contribution was made in collaboration with the Pacific Salmon Foundation.

Cite as: Pocock, K., W. Evans, A. Hare, and C. Weekes (2018). High-resolution record of surface water pH at Sentry Shoal in the Northern Strait of Georgia, British Columbia, Canada during summer and fall of 2016 and 2017. Version 1.0. Hakai Institute. Dataset. [access date].

Type of Study: High-resolution mooring data

Temporal Coverage: July 19 – Aug 23 2016, Sept 2 – Oct 31 2016, Nov 9 – Dec 1 2016, Jul 25 - Aug 14 2017, Oct 2 – Oct 24 2017.

Spatial Coverage: Sentry Shoal; 49° 54.4′ N 124° 59.1′ W

Geographic Names: Sentry Shoal; northern Strait of Georgia; Salish Sea; British Columbia coast; North Pacific Ocean

Platforms: Environment Canada mooring #46131

Version: 1.0

Submission Date: July 6th 2018

Variables:

Internal electrode raw voltage

Abbreviation: Vint Unit: volts Observation type: raw measurements from autonomous sensor In-situ/Manipulation/Response variable: In situ observation Measured or calculated: measured Sampling instrument: Satlantic SeaFET internal electrode Detailed sampling and analyzing information: The SeaFET sensor has two potentiometric cells, the internal cell, and the external cell. The internal cell consists of an ion-sensitive field effect transistor (ISFET) that acts as the ‘working electrode’ and an Ag/AgCl electrode bathed in a saturated KCl solution contained within the instrument which acts as the ‘reference electrode’. The KCl solution is electrically connected to the sample water through an annular frit which encircles the post and maintains the measured potential, independent of the chloride ion concentration in the sample. The instrument has a measurement range of 6.5 to 9.0 pH, typical stability of 0.005 pH per month, and a resolution of 0.0001 pH. The sensor was deployed vertically in the water column at approximately 1m depth and configured to sample every 30 minutes. Copper tape and a copper guard around the electrodes was used to prevent sensor biofouling. The raw electrode voltage readings are provided in this data contribution, these readings were utilized along with in situ calibration coefficients, and temperature data from a co-located Sea-Bird 37 MicroCAT to calculate in situ pH (see variable description below for details). Replicate information: The sensor was configured to average every 10 measurements for a total of 30 readings for each sampling event. One exception for this is during July 2017 where the sensor was configured to take a total of 300 readings for each sampling event. Quality flag convention: no quality flag applied

External electrode raw voltage

Abbreviation: Vext Unit: volts Observation type: raw measurements from autonomous sensor In-situ/Manipulation/Response variable: In situ observation Measured or calculated: measured Sampling instrument: Satlantic SeaFET external solid-state chloride ion selective electrode (Cl-ISE) Detailed sampling and analyzing information: The SeaFET external electrode is similar to the internal electrode in that it consists of an ISFET ‘working electrode’. However, it does not include the liquid junction, therefore the potential of the external reference electrode is expected to vary with the chloride concentration of the sensed medium. As such, in situ temperature and salinity data are required to estimate the chloride ion portion of the signal to obtain an accurate pH reading from this electrode. The instrument has a measurement range of 6.5 to 9.0 pH, typical stability of 0.005 pH per month, and a resolution of 0.0001 pH. The sensor was deployed vertically in the water column at approximately 1m depth and configured to sample every 30 minutes. Copper tape and a copper guard around the electrodes was used to prevent sensor biofouling. The raw electrode voltage readings are provided in this data contribution, these readings were utilized along with in situ calibration coefficients, and temperature and salinity data from a co-located Sea-Bird 37 MicroCAT to calculate in situ pH (see variable description below for details). Replicate information: The sensor was configured to average every 10 measurements for a total of 30 readings for each sampling event. One exception for this is during July 2017 where the sensor was configured to take a total of 300 readings for each sampling event. Quality flag convention: no quality flag applied

Internal electrode in situ pH

Abbreviation: pHint Unit: pH (total scale) Observation type: measurements from autonomous sensor In-situ/Manipulation/Response variable: in-situ observation Measured or calculated: calculated using internal electrode voltage readings, CTD temperature, and in situ calibration coefficients Sampling instrument: Satlantic SeaFET internal Ag/AgCl reference electrode (ISFET) Detailed sampling and analyzing information: To properly calculate pH from SeaFET voltage readings, an appropriate calibration coefficient is required. The factory calibration coefficients are unreliable following deployment given that the electrodes need to become conditioned to the environment, therefore a post-deployment calibration is recommended. We performed a single-point in situ calibration using discrete measurements taken following a 10-14 day sensor conditioning period at the deployment location. Discrete samples were collected by deploying a Niskin bottle at 1m depth adjacent to the sensor on the half hour to coincide with a sensor sampling event. Triplicate discrete samples were drawn directly into 350 mL amber glass bottles using a section of silicone tubing attached to the nipple of the Niskin bottle. The sample bottles were rinsed three times with sample, and filled from the bottom with care not to introduce bubbles. The tubing was pinched off to allow ~3 mL of headspace, fixed with 200 µL of saturated mercuric chloride solution (HgCl2), and crip-sealed with polyurethane-lined crimp-sealed metal caps. Samples were then analyzed for total carbon dioxide (TCO2) and carbon dioxide partial pressure (pCO2) with a Dakunalytics, LLC Burke-o-Lator (BoL). Instrument calibration functions were developed prior to and following analysis using gas and liquid standards of known concentrations. Instrument accuracy was monitored at regular intervals using Certified Reference Materials (CRMs) provided by Dr. Andrew Dickson (Scripps Institute of Oceanography). In situ pH (total scale) of the samples was subsequently calculated based on measured levels of TCO2, pCO2, in situ temperature, and salinity using the program CO2SYS. Dissociation constants of Lueker et al. (2000), and Dickson (1990) were used for this computation. Calibration coefficients for each electrode were then re-calculated using the average in situ pH of the triplicate discrete samples, and corresponding electrode voltage reading (equations detailed in Sea-Bird Scientific SeaFET Product Manual 2.0.0.). The calibration coefficients were calculated following any major sensor maintenance such as battery change or annual service, this occurred four times within the two-year deployment period. Additional discrete samples were collected during service visits throughout the deployment period to validate the single-point calibration, this occurred approximately once every two months, and no drift was observed in either electrode. The in situ calibration coefficients, along with temperature data from a co-located SBE-37 sensor were used to convert SeaFET internal electrode voltage readings to the in situ pH measurements provided in this dataset. Temperature data from the SeaFET thermistor was not used as current CTD data was available for the entire sensor deployment period. Replicate information: The sensor was configured to collect a total of 30 readings for each sampling event. One exception for this is during July 2017 where the sensor was configured to take a total of 300 readings for each sampling event. Standardization description: Specific to the calibration and validation discrete sampling, xCO2 calibration functions developed during analysis of gas (nominally 150, 450, 750 and 1500 ppm; Scott-Marin, Inc.) and liquid (nominally 800, 1600, 2400 µmol/kg) standards of known concentration Standardization frequency: Specific to the calibration and validation discrete sampling, 1) gas and liquid standard sequences were run at the beginning and end of a sample batch (less than 30 samples on average), 2) CRMs were measured three times at the beginning and end of a batch of discrete samples, and 3) triplicate samples were typically run within a sample batch CRM manufacturer: Dr. Andrew Dickson (Scripps Institution of Oceanography) Poison name: Saturated mercuric chloride solution Poison volume: 200 µL Uncertainty: <0.0137 units Quality flag convention: no quality flag applied Method reference: Bresnahan, P. J., Martz, T. R., Takeshita, Y., Johnson, K. S. and LaShomb, M. (2014), Best practices for autonomous measurement of seawater pH with the Honeywell Durafet, Methods Oceanogr., 9, 44–60, doi:10.1016/j.mio.2014.08.003; Martz, T. R., Connery, J. G. and Johnson, K. S. (2010), Testing the Honeywell Durafet® for seawater pH applications, Limnol. Oceanogr. Methods, 8(5), 172–184, doi:10.4319/lom.2010.8.172.

External electrode in situ pH

Abbreviation: pHext Unit: pH (total scale) Observation type: measurements from autonomous sensor In-situ/Manipulation/Response variable: in situ variable Measured or calculated: calculated using electrode voltage readings, temperature, salinity and in situ calibration coefficients Sampling instrument: Satlantic SeaFET external solid-state chloride ion selective electrode (Cl-ISE) Detailed sampling and analyzing information: Similar to the internal electrode, an in situ single point calibration was performed to re-calculate sensor calibration coefficients (see internal electrode in situ pH description for detailed calibration method). The in situ calibration coefficients, along with temperature and salinity data from a co-located SBE-37 sensor were used to convert SeaFET external electrode voltage readings to the in situ pH measurements provided in this dataset. Temperature data from the SeaFET thermistor was not used as current CTD data was available for the entire sensor deployment period. Replicate information: The sensor was configured to collect a total of 30 readings for each sampling event. One exception for this is during July 2017 where the sensor was configured to take a total of 300 readings for each sampling event. Standardization description: Specific to the calibration and validation discrete sampling, xCO2 calibration functions developed during analysis of gas (nominally 150, 450, 750 and 1500 ppm; Scott-Marin, Inc.) and liquid (nominally 800, 1600, 2400 µmol/kg) standards of known concentration Standardization frequency: Specific to the calibration and validation discrete sampling, 1) gas and liquid standard sequences were run at the beginning and end of a sample batch (less than 30 samples on average), 2) CRMs were measured three times at the beginning and end of a batch of discrete samples, and 3) triplicate samples were typically run within a sample batch CRM manufacturer: Dr. Andrew Dickson (Scripps Institution of Oceanography) Poison name: Saturated mercuric chloride solution Poison volume: 200 µL Uncertainty: <0.0137 units Quality flag convention: no quality flag applied Method reference: Bresnahan, P. J., Martz, T. R., Takeshita, Y., Johnson, K. S. and LaShomb, M. (2014), Best practices for autonomous measurement of seawater pH with the Honeywell Durafet, Methods Oceanogr., 9, 44–60, doi:10.1016/j.mio.2014.08.003; Martz, T. R., Connery, J. G. and Johnson, K. S. (2010), Testing the Honeywell Durafet® for seawater pH applications, Limnol. Oceanogr. Methods, 8(5), 172–184, doi:10.4319/lom.2010.8.172.

SBE-37 temperature

Abbreviation: SBE_T Unit: °C, ITS-90 scale Observation type: measurements from autonomous sensor In-situ/Manipulation/Response variable: In situ observation Measured or calculated: measured Sampling instrument: SeaBird 37-SMP MicroCAT temperature sensor Detailed sampling and analyzing information: A co-deployed Sea-Bird SBE 37 collected temperature and salinity mirroring the SeaFET sampling interval of 30 minutes. The sensor was deployed vertically in the water column at approximately 1m depth and operated autonomously. For every reading the SBE-37’s integral pump runs for 1 second pushing seawater through the internal-field conductivity cell and past the thermistor. The data were linearly interpolated across the deployment period and merged with SeaFET measurements. On average, temperature measurements were collected within one minute of the corresponding SeaFET sampling event. Uncertainty: 0.002 °C Quality flag convention: no quality flag applied

SBE-37 salinity

Abbreviation: SBE_S Unit: 1978 Practical Salinity Scale Observation type: measurements from autonomous sensor In-situ/Manipulation/Response variable: In situ observation Measured or calculated: calculated from conductivity and temperature measurements Sampling instrument: SeaBird 37-SMP MicroCAT conductivity sensor Detailed sampling and analyzing information: The Sea-Bird 37 conductivity sensor consists of a cylindrical flow-through glass cell with internal platinum electrodes. During each sampling event the SBE-37’s integral pump runs for 1 second pushing seawater through the conductivity cell prior to collecting a measurement. Anti-foulant devices at the pump intake and outlet provide bio-fouling protection during deployment. The sensor has a measurement range of 0 to 7 S/m, typical stability of 0.0003 S/m per month, and a resolution of 0.00001 S/m. The sensor unit was contained in an aluminum cage and deployed vertically in the water column at approximately 1m depth. The sensor operated autonomously, and collected a reading once every 30 minutes. Discrete salinity values were derived from calibrated conductivity, and temperature measurements. The data were linearly interpolated across the deployment period and merged with SeaFET measurements. On average, temperature and conductivity measurements were collected within one minute of the corresponding SeaFET sampling event. Uncertainty: 0.0003 S/cm Quality flag convention: no quality flag applied

Filename: SeaFET_SentryShoal_submission.txt

Column headings: (1) Yearday (2) Year (3) Matlab_Time (4) Date_Time[UTC] (5) V_int (6) V_ext (7) pH_int (8) pH_ext (9) SBE_T [°C] (10) SBE_S

Researcher Contact: Please direct questions regarding these data or requests for processing code, or processing descriptions to Wiley Evans (wiley.evans@hakai.org).

Researcher institution: Hakai Institute

Acknowledgement: We thank the University of Alaska Ocean Acidification Research Center for long-term use of their SeaFET, and the Pacific Salmon Foundation for providing the SBE 37.

Access and Use

Licence: Appropriate credit must be given to Hakai Institute and the authors of the dataset.

Data and Resources

Dates

Metadata Created October 26, 2018, 22:48 (UTC)
Metadata Updated October 26, 2018, 22:48 (UTC)
Reference Date(s) 2018-06-08 (Creation)
2018-07-06 (Publication)
Frequency of Update asNeeded
Metadata Date October 17, 2018, 22:41 (UTC)

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Additional Info

Field Value
Contact Email data@hakai.org
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metadata-language eng
progress completed
resource-type dataset
Responsible Party Hakai Institute (Principal Investigator, Point of Contact)