Glider-based O₂ and CO₂ observations in the Labrador Sea

von Oppeln-Bronikowski, Nicolai (2019) Glider-based O₂ and CO₂ observations in the Labrador Sea. Masters thesis, Memorial University of Newfoundland.

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Abstract

Ocean gliders can provide high-resolution gas observations necessary to interpret the space and time scales of highly dynamic processes such as gas uptake or outgassing in the ocean surface layer. There is a critical need to make high-resolution in situ gas measurements in the ocean for the biogeochemical community (Johnson et al., 2009). Small optical sensor, called optodes, have been used on gliders to measure dissolved oxygen in the oceans and recently optodes were modified to measure pCO₂ (Atamanchuk et al., 2014). The CO₂ optode is in an early prototype stage and has not undergone rigorous testing on a glider. Here we describe our approach to reference glider based O₂ and pCO₂ measurements to data from a vertical profiler mooring – the SeaCycler to validate the glider data. The SeaCycler carried a Pro- Oceanus Ltd., CO₂-Pro CV as part of its instrument float, an extensively tested gas analyzer, based on non-dispersive infrared refraction (NDIR), which has shown stable performance during lengthy observations (Jiang et al., 2014). We compare the glider data against the SeaCycler’s O₂ and CO₂ measurements to compute an isopycnal-matched in-situ optode correction. We conducted further glider tests of the sensor on the Newfoundland Shelf in 2018 and further characterized the response time in profiling applications. In this thesis, we show data from both deployments to characterize the sensor performance. We discuss the spatial and temporal structure in the Labrador Sea glider data and use frequency and correlation length scale analysis to infer the presence of short internal wave energies near the buoyancy frequency range. From the results of the glider missions, we present ideas to improve future glider missions into the Labrador Sea and glider based CO₂ measurements.

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