High Resolution pH Measurements Using a Lab-on-Chip Sensor in Surface Waters of Northwest European Shelf Seas

Abstract

Increasing atmospheric CO2 concentrations are resulting in a reduction in seawater pH, with potential detrimental consequences for marine organisms. Improved efforts are required to monitor the anthropogenically driven pH decrease in the context of natural pH variations. We present here a high resolution surface water pH data set obtained in summer 2011 in North West European Shelf Seas. The aim of our paper is to demonstrate the successful deployment of the pH sensor, and discuss the carbonate chemistry dynamics of surface waters of Northwest European Shelf Seas using pH and ancillary data. The pH measurements were undertaken using spectrophotometry with a Lab-on-Chip pH sensor connected to the underway seawater supply of the ship. The main processes controlling the pH distribution along the ship’s transect, and their relative importance, were determined using a statistical approach. The pH sensor allowed 10 measurements h−1 with a precision of 0.001 pH units and a good agreement with pH calculated from a pair of discretely sampled carbonate variables dissolved inorganic carbon (DIC), total alkalinity (TA) and partial pressure of CO2 (pCO2) (e.g., pHDICpCO2). For this summer cruise, the biological activity formed the main control on the pH distribution along the cruise transect. This study highlights the importance of high quality and high resolution pH measurements for the assessment of carbonate chemistry dynamics in marine waters.

Advancing Observation of Ocean Biogeochemistry, Biology, and Ecosystems With Cost-Effective in situ Sensing Technologies

“…Prototype in situ alkalinity sensors, such as spectrophotometric SAMI-Alk (Sunburst Sensors, LLC) (Spaulding et al, 2014) and ISFET-based solid state alkalinity sensors (Briggs et al, 2017), are also emerging, and have the potential to achieve low cost, similar to other pH, pCO 2 , and DIC sensors due to the similarity of detection principles (i.e., spectrophotometric and ISFET). These new TA and DIC sensors have all been developed with the goal of climate-quality While originally applied for nutrient sensing, Lab-on-a-chip (LOC) technology has also been applied to the in situ detection of pH (Rerolle et al, 2018), DIC, and TA. LOC sensors have been developed with a target of being cost-effective, yet high performance in situ sensors suitable for mass deployment on various ocean observing platforms.…”

“…Another route to cost-effective deployments is through the use of multiple miniature sensors on a single platform. As an example, nitrate, phosphate and pH (Rerolle et al, 2018) LOCs were deployed simultaneously on the NERC Autosub Long Range (ALR) and on a lander (Sonardyne, United Kingdom) to develop monitoring systems for offshore carbon capture and storage reservoir integrity verification systems. Herein the systems on the lander were able to detect the stoichiometric signature of a simulated (deliberate gas release) leak.…”

Constraining the Oceanic Uptake and Fluxes of Greenhouse Gases by Building an Ocean Network of Certified Stations: The Ocean Component of the Integrated Carbon Observation System, ICOS-Oceans

“…Currently, the instrumentation for pCO 2 measurements can be considered mature and readily available (Pierrot et al, 2009). For in situ pH determination, the technology is becoming more mature, with commercial sensors and systems becoming available (Martz et al, 2010;Bresnahan et al, 2014;Rérolle et al, 2018). It has yet to be proven that these sensors fulfill the tight criteria required for using pH data to constrain the marine inorganic carbon system over the long deployments that are typical at the ICOS-Oceans stations.…”

The analysis of dissolved inorganic carbon in liquid using a microfluidic conductivity sensor with membrane separation of CO2

“…At present, CO 2 measurements are typically carried out by coulometry using large-volume sensors on research ships, according to Standard Operating Protocols (Dickson et al 2007). Although both pCO 2 and pH are very sensitive to temperature and pressure, they can be measured away from sampling depths under carefully controlled conditions, and while microfluidic miniaturisation approaches for in situ surface measurements are currently being developed, complementary autonomous measurements of DIC or A T would be preferred (Rérolle et al 2018;Clarke et al 2017). Given the technical challenges, however, such approaches have yet to be realised (Byrne 2014).…”