Implementation of novel sensors on underwater gliders

• Main Author: Hemming, Michael
• Format: Thesis
• Language: English
• Published: 2018
• Subjects: Ocean acidification
• Online Access: https://ueaeprints.uea.ac.uk/id/eprint/71161/; https://ueaeprints.uea.ac.uk/id/eprint/71161/1/Hemming_Implementation_Thesis_2019.pdf

Around a quarter of global anthropogenic carbon emissions have been absorbed by the ocean. Underwater gliders have been identified as important tools for gathering information related to climate change and ocean acidification processes. The REP14 -MED experiment involved the deployment of eleven gliders in the northwestern Mediterranean Sea; one of these had an experimental ion sensitive field effect transistor (ISFET) sensor attached. A comparison between pH observed by the glider and ship during the deployment indicated problems with the sensor accuracy and stability. Sunlight caused an apparent sensor pH decrease of up to 0.1 close to the surface around local noon. The pH corrected for drift, temperature, and pressure is presented with other ocean variables measured by the glider. The timing of the phytoplankton spring bloom in the northwestern Mediterranean Sea varies year-on-year. A glider with an ISFET pH sensor was deployed close to the BOUSSOLE mooring site. This deployment offered a second opportunity to test the ISFET sensor with improvements. Similarly to during the REP14 -MED experiment, ISFET pH measurements were corrected for drift, temperature and pressure effects. Measurements at the BOUSSOLE mooring indicated that the spring bloom started around March 19. Mean net community production (N) rates were estimated from the glider dissolved oxygen concentrations, as well as glider and buoy dissolved inorganic carbon concentrations derived using other parameters. N ranged between -82±317 mmol m-2 d-1 and 460±870 mmol m-2 d-1. Horizontal spatial scales of variability highlight physical and biogeochemical processes, and are useful for designing ocean observing systems. Spatial scales of variability were estimated from semivariograms using glider measurements. Spatial scales of variability were mostly small at depths affected by biology, and large at depths affected by largescale processes, such as weather, although this was not true in every case. Some direction-dependency was found, which may be related ...