Preprints
https://doi.org/10.5194/os-2022-6
https://doi.org/10.5194/os-2022-6
 
17 Feb 2022
17 Feb 2022
Status: this preprint is currently under review for the journal OS.

Net community production in the northwestern Mediterranean Sea from glider and buoy measurements

Michael P. Hemming1, Jan Kaiser2, Jacqueline Boutin3, Liliane Merlivat3, Karen J. Heywood2, Dorothee C. E. Bakker2, Gareth A. Lee2, Marcos Cobas García2, David Antoine4,5, and Kiminori Shitashima6 Michael P. Hemming et al.
  • 1Coastal and Regional Oceanography Lab, Centre for Marine Science and Innovation, UNSW Sydney, Sydney, Australia
  • 2Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom
  • 3Laboratoire d’Océanographie et du Climat, Sorbonne Université, Paris, France
  • 4Remote Sensing and Satellite Research Group, School of Earth and Planetary Sciences, Curtin University, Perth, Australia
  • 5Laboratoire d’Océanographie de Villefranche, Villefranche-sur-Mer, France
  • 6Tokyo University of Marine Science and Technology, Tokyo, Japan

Abstract. The Mediterranean Sea comprises just 0.8 % of the global oceanic surface, yet considering its size, it is regarded as a disproportionately large sink for anthropogenic carbon due to its physical and biogeochemical characteristics. An underwater glider mission was carried out in March–April 2016 close to the BOUSSOLE and DyFAMed time series moorings in the northwestern Mediterranean Sea. The glider deployment served as a test of a prototype ion-sensitive field-effect transistor pH sensor. Dissolved oxygen (O2) concentrations and optical backscatter were also observed by the glider and increased between 19 March and 1 April, along with pH. These changes indicated the start of a phytoplankton spring bloom, following a period of intense mixing. Concurrent measurements of CO2 fugacity and O2 concentrations at the BOUSSOLE mooring buoy showed fluctuations, in qualitative agreement with the pattern of glider measurements. Mean net community production rates (N) were estimated from glider and buoy measurements of dissolved O2 and inorganic carbon (DIC) concentrations. Glider and buoy DIC concentrations were derived from a salinity-based total alkalinity parameterisation, glider pH, and buoy CO2 fugacity. The spatial coverage of glider data allowed calculating advective O2 and DIC fluxes. Mean N estimates for the euphotic zone between 10 March and 3 April were (−17 ± 35) for glider O2, (44 ± 94) for glider DIC, (17 ± 35) for buoy O2 and (49 ± 86) mmol m–2 d–1 for buoy DIC, all indicating net metabolic balance over these 25 days. However, these 25 days were actually split into a period of net DIC increase and O2 decrease between 10 and 19 March and a period of net DIC decrease and O2 increase between 19 March and 3 April. The latter period is interpreted as the onset of the spring bloom. The regression coefficients between O2 and DIC-based N estimates were 0.25 ± 0.08 for the glider data and 0.54 ± 0.06 for the buoy, significantly lower than the canonical metabolic quotient of 1.45 ± 0.15. This study shows the added value of co-locating a profiling glider with moored time series buoys, but also demonstrates limitations in achievable precision.

Michael P. Hemming et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2022-6', Anonymous Referee #1, 18 Feb 2022
  • RC2: 'Comment on os-2022-6', Anonymous Referee #2, 07 Apr 2022

Michael P. Hemming et al.

Michael P. Hemming et al.

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Short summary
An underwater glider mission was carried out in spring 2016 near a mooring in the northwestern Mediterranean Sea. The glider deployment served as a test of a prototype ion-sensitive field-effect transistor pH sensor. Mean net community production rates were estimated from glider and buoy measurements of dissolved oxygen and inorganic carbon concentrations before and during the spring bloom. Incorporating advection is important for accurate mass budgets. Unexpected metabolic quotients were found.