Seaglider observations of biogeochemical variability in the Iberian upwelling system.

• Main Author: Brown, Christopher
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: North Atlantic; Orca
• Online Access: https://ueaeprints.uea.ac.uk/id/eprint/48788/; https://ueaeprints.uea.ac.uk/id/eprint/48788/1/ChrisWBrown_PhD_thesis_2013_ENV_Biogeochemistry_of_Iberian_Upwelling.pdf

Seasonal upwelling events along the Galician coastline of the North Atlantic furnish the upper watercolumn with nutrients, resulting in strong summer phytoplankton blooms and the sustenance of one of Europe’s largest fisheries. The episodic nature of these upwelling events result in considerable challenges studying the region using traditional shipboard observations. This thesis demonstrates an alternative sampling technique, providing high spatial and temporal resolution biogeochemical data through the use of an autonomous underwater gliderthe Seaglider. SG510 “Orca” was outfitted with sensors to measure dissolved oxygen, temperature, salinity, chlorophyll a (chl a), coloured dissolved organic material (CDOM) and optical backscatter. Deployed for 113 days over summer 2010, Orca completed 17 zonal transects across the shelf, continental slope and open ocean at 42.1° N. Data collected during the campaign was used to assess both the physics of the watercolumn, and the effect these physical processes have on the region’s biogeochemistry. As part of this biogeochemical study, a novel attempt at calculating net community production (NCP) was completed using an oxygen inventory technique. Two major phytoplankton bloom events occurred during the deployment period, with respective peak Chl a concentrations of 9.65 and 11.23 mg m3. During these bloom events, NCP varied between (net autotrophic) values of 25 and 123 (±17 ) mmol m2. d1. Negative values of NCP were only observed twice for 24 and 60 hours respectively, with a maximum heterotrophy of 44 (±17) mmol m2 d1. Overall, the summer season featured a net autotrophic metabolic balance of +27 mmol m2 d1 .thus highlighting the importance of the region for net carbon sequestration. Finally, this thesis also demonstrates the success of using autonomous glider platforms for sustained biogeochemical and physical observations within a highly dynamic and challenging operational environment with strong currents and considerable shipping traffic.