Developing a profiling glider pH sensor for high resolution coastal ocean acidification monitoring

Coastal and ocean acidification can alter ocean biogeochemistry, with ecological consequences that may result in economic and cultural losses. Yet few time series and high-resolution measurements exist to track the existence and movement of water low in pH and/or carbonate saturation. Past acidification monitoring efforts have either low spatial resolution (mooring) or high cost and low temporal and spatial resolution (research cruises). Therefore, there is a critical need to deploy new, cost-effective technologies that can routinely provide high resolution water column data on regional scales in our coastal ocean. We developed the first integrated glider platform and sensor system for sampling pH in the water column of the coastal ocean. A Deep-Sea ISFET (Ion Sensitive Field Effect Transistor) pH sensor system was modified and integrated into a Slocum G2 glider and tested during a deployment in the Mid-Atlantic Bight. Measurements of pH exhibited a time lag that shifted during the deployment, but shifts were applied to correct pH. Glider pH and spectrophotometric pH measured in discrete water samples were in good agreement for some comparisons but not others, and those offsets were likely the result of delayed or incomplete conditioning (at deployment start) or mismatches due to water sampling techniques. Glider pH data along the cross-shelf transect revealed higher pH associated with the depth of chlorophyll and oxygen maximums and a warmer, saltier water mass. Lower pH occurred in bottom waters of the middle shelf and slope, and nearshore following a period of heavy precipitation. These results demonstrate the application of glider-based acidification monitoring in other coastal regions, providing the foundation of what could become a national acidification monitoring network.