Abstract. The commercially available Sea-Bird SeaFET™ provides an accessible way
for a broad community of researchers to study ocean acidification and obtain
robust measurements of seawater pH via the use of an in situ autonomous sensor.
There are pitfalls, however, that have been detailed in previous best
practices for sensor care, deployment, and data handling. Here, we took
advantage of two distinctly different coastal settings to evaluate the
Sea-Bird SeaFET™ and examine the multitude of scenarios in which
problems may arise confounding the accuracy of measured pH. High-resolution
temporal measurements of pH were obtained during 3- to 5-month field
deployments in three separate locations (two in south-central Alaska, USA,
and one in British Columbia, Canada) spanning a broad range of nearshore
temperature and salinity conditions. Both the internal and external
electrodes onboard the SeaFET™ were evaluated against robust benchtop
measurements for accuracy using the factory calibration, an in situ
single-point calibration, or an in situ multi-point calibration. In addition, two
sensors deployed in parallel in Kasitsna Bay, Alaska, USA, were compared for
inter-sensor variability in order to quantify other factors contributing to
the sensor's intrinsic inaccuracies. Based on our results, the multi-point
calibration method provided the highest accuracy (< 0.025 difference
in pH) of pH when compared against benchtop measurements. Spectral analysis
of time series data showed that during spring in Alaskan waters, a range of
tidal frequencies dominated pH variability, while seasonal oceanographic
conditions were the dominant driver in Canadian waters. Further, it is
suggested that spectral analysis performed on initial deployments may be
able to act as an a posteriori method to better identify appropriate calibration regimes.
Based on this evaluation, we provide a comprehensive assessment of the
potential sources of uncertainty associated with accuracy and precision of
the SeaFET™ electrodes.
Printed 2D Proton Sensor for In-Situ Measurement in Glue Lines