Preprints
https://doi.org/10.5194/bg-2021-123
https://doi.org/10.5194/bg-2021-123

  18 May 2021

18 May 2021

Review status: this preprint is currently under review for the journal BG.

Biological production in two contrasted regions of the Mediterranean Sea during the oligotrophic period: An estimate based on the diel cycle of optical properties measured by BGC-Argo profiling floats

Marie Barbieux1, Julia Uitz1, Alexandre Mignot2, Collin Roesler3, Hervé Claustre1, Bernard Gentili1, Vincent Taillandier1, Fabrizio D'Ortenzio1, Hubert Loisel4, Antoine Poteau1, Edouard Leymarie1, Christophe Penkerc'h1, Catherine Schmechtig5, and Annick Bricaud1 Marie Barbieux et al.
  • 1CNRS and Sorbonne Université, Laboratoire d’Océanographie de Villefranche, LOV, 06230 Villefranche-sur-Mer, France
  • 2Mercator Océan, 31520 Ramonville-Saint-Agne, France
  • 3Bowdoin College, Earth and Oceanographic Science, Brunswick, Maine 04011, USA
  • 4Université Littoral Côte d’Opale, Université Lille, CNRS, Laboratoire d’Océanologie et de Géosciences, 59000 Lille, France
  • 5OSU Ecce Terra, UMS 3455, CNRS and Sorbonne Université, Paris 6, 4 place Jussieu, 75252 Paris CEDEX 05, France

Abstract. This study assesses marine biological production of organic carbon based on the diel variability of bio-optical properties monitored by two BioGeoChemical-Argo (BGC-Argo) floats. Experiments were conducted in two distinct Mediterranean systems, the Northwestern Ligurian Sea and the Central Ionian Sea during summer months. We derived particulate organic carbon (POC) stock and gross community production integrated within the surface, euphotic and subsurface chlorophyll maximum (SCM) layers, using an existing approach applied to diel cycle measurements of the particulate beam attenuation (cp) and backscattering (bbp) coefficients. The diel cycle of cp provided a robust proxy for quantifying biological production in both systems; that of bbp was comparatively less robust. Derived primary production estimates vary by a factor of 2 depending upon the choice of the bio-optical relationship that converts the measured optical coefficient to POC, which is thus a critical step to constrain. Our results indicate a substantial, yet variable, contribution to the water column production of the SCM layer (16–42%). In the Ligurian Sea, the SCM is a seasonal feature that behaves as a subsurface biomass maximum (SBM) with the ability to respond to episodic abiotic forcing by increasing production. In contrast, in the Ionian Sea, the SCM is permanent, induced by phytoplankton photoacclimation and contributes moderately to water column production. These results emphasize the strong potential for transmissometers deployed on BGC-Argo profiling floats to quantify non-intrusively in situ biological production of organic carbon in the water column of stratified oligotrophic systems with recurring or permanent SCMs, which are widespread features in the global ocean.

Marie Barbieux 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 bg-2021-123', Anonymous Referee #1, 10 Jun 2021
  • RC2: 'Comment on bg-2021-123', Anonymous Referee #2, 16 Jun 2021

Marie Barbieux et al.

Marie Barbieux et al.

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Short summary
This study assesses marine biological production in two Mediterranean systems representative of the vast desert-like (oligotrophic) areas encountered in the global ocean. In this aim, we use a novel approach based on non-intrusive high-frequency in-situ measurements by two profiling robots, the BGC-Argo floats. Our results indicate substantial, yet variable, production rates and contribution to the whole water column of the subsurface layer that is typically considered steady and non-productive.
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