Using Sensors on Biogeochemical APEX Profiling Floats: Pre-deployment Characterization and Calibration of MBARI Built Deep-Sea-Durafet pH and ISUS NO3 Sensors

Peter M Walz, Carole M Sakamoto, Luke Coletti, Yuichiro Takeshita and Kenneth S Johnson, Monterey Bay Aquarium Research Institute, Moss Landing, CA, United States
The MBARI Chemical Sensor Lab has been designing and deploying a variety of in-situ nitrate and pH sensors for many years. Recent sensor developments and engineering efforts have focused on profiling floats as the platform of choice to study and observe ocean biogeochemical processes. Through the ongoing SOCCOM (Southern Ocean Carbon and Climate, Observations and Modeling) program, we are now supporting 138 biogeochemical (BGC) profiling floats equipped with nitrate and pH, as well as oxygen and bio-optical sensors. Participation in the SOCCOM project, in addition to deployments on 70 other profiling floats throughout the world and sensor deployments on moorings and gliders, has fostered and refined our methods used during assembly, preparation, and calibration of pH and NO3 sensors. Here, we present the current process and “best practices” that MBARI has adopted for optimum sensor performance during multi-year deployments on BGC-ARGO floats. This includes lab procedures used to calibrate sensors for the high pressure and low temperature conditions typical of Argo profiling float deployments. As other autonomous platforms become available to include biogeochemical sensors (AUVs, Wave Glider, Sail Drone, etc...) we hope these sensors will become more widely available and used by the oceanographic community.