Dissolved oxygen-based annual biological production from glider observations at the Porcupine Abyssal Plain (North Atlantic)

• Main Author: Binetti, Umberto
• Format: Thesis
• Language: English
• Published: 2016
• Subjects: North Atlantic
• Online Access: https://ueaeprints.uea.ac.uk/id/eprint/62680/; https://ueaeprints.uea.ac.uk/id/eprint/62680/1/Umberto_Binetti_PhD_Thesis.pdf

The OSMOSIS project used a fleet of gliders to survey at the Porcupine Abyssal Plain (North Atlantic) from September 2012 to September 2013. Different physical and biogeochemical parameters (salinity, temperature, oxygen concentration, chlorophyll fluorescence) were measured in the top 1000 m of the water column. The present study focused on calibrating and analysing the oxygen concentration data. The mixing layer depth was defined as the depth where oxygen concentration varied by more than 0.5% from its value at 5 m. The mixing layer was shallower than the mixed layer, defined by density and temperature. In cases of low turbulence, the mixing layer described the vertical extent of the biologically productive layer (except deep chlorophyll maximums). Net community production was calculated over a year-cycle with an oxygen-budget approach. Net autotrophy was found at the site with a net production of (6.4 ± 1.9) mol m-2 in oxygen equivalents. The period exhibiting a deep chlorophyll maximum contributed (1.5 ± 0.5) mol m-2 to the total production. The results were higher than most of the previous estimates and the productive season longer than that considered in previous studies. Increased net community production was related to the decrease in water turbulence and mixing layer shoaling, confirming the validity of the mechanism proposed by the model of Enriquez and Taylor (2015). Gross primary production was calculated from the difference between rate of oxygen increase during the day and decrease during the night, diel cycle shown by in situ data in the top 20 m of the column. Physical processes often disrupted the biological diel cycle and restricted the analysis to four periods during the year. The gross primary production ranged between 6 mmol m-2 d-1 and 13 mmol m-2 d-1. Results suggest an enhancement of the gross primary production when the mixing layer shoals.