08 Apr 2022
08 Apr 2022
Status: a revised version of this preprint is currently under review for the journal BG.

Subsurface oxygen maximum in oligotrophic marine ecosystems: mapping the interaction between physical and biogeochemical processes

Valeria Di Biagio, Stefano Salon, Laura Feudale, and Gianpiero Cossarini Valeria Di Biagio et al.
  • National Institute of Oceanography and Applied Geophysics - OGS

Abstract. The subsurface oxygen maximum (SOM) is observed in oligotrophic oceans and is associated with different physical and biological processes. This study characterises the SOM in the Mediterranean Sea at the basin scale and investigates its driving mechanisms by analysing the output of the 1/24° resolution biogeochemical reanalysis provided by the Copernicus Marine Service for the 1999–2019 time period.

We validated the model-derived oxygen concentration in the epipelagic layer at different spatial and temporal scales, including a novel process validation associated with community production and respiration. Moreover, using Biogeochemical-Argo (BGC-Argo) float observations, we estimated the model uncertainty in reproducing the SOM concentration and depth in summer (13 mmol m-3 and 13 m, respectively).

The western and eastern Mediterranean Sea depict different SOM signatures in summer, with higher oxygen values and shallower depths in the western Mediterranean. The concentrations and depths (in the ranges of 230–250 mmol m-3 and 30–100 m, respectively) are in agreement with the estimations from the literature and show mesoscale variability patterns. The western Mediterranean also shows a stronger biological activity, specifically oxygen production and consumption, along the whole epipelagic layer and higher oxygen concentrations at the surface throughout the year, but heavy undersaturated waters are associated with winter deep convection in the northwestern Mediterranean Sea. A one-year analysis conducted on selected areas that are representative of the heterogeneity of summer SOM highlighted that the SOM can actually be sustained by biological production (as in northwestern Mediterranean areas), or it can be a residual of the confinement of spring production (as in the central Ionian area), and vertical motions influence its depth (as in the Levantine subduction area).

Valeria Di Biagio 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-2022-70', Anonymous Referee #1, 13 Jun 2022
    • AC1: 'Reply on RC1', Valeria Di Biagio, 01 Aug 2022
  • RC2: 'Comment on bg-2022-70', Anonymous Referee #2, 20 Jun 2022
    • AC2: 'Reply on RC2', Valeria Di Biagio, 01 Aug 2022

Valeria Di Biagio et al.

Valeria Di Biagio et al.


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Short summary
The amount of dissolved oxygen in the ocean is the result of interacting physical and biological processes. Oxygen vertical profiles show a subsurface maximum in a large part of the ocean. We used a numerical model to map this subsurface maximum in the Mediterranean Sea and to link local differences in its properties to the driving processes. This emerging feature can help to better understand the marine ecosystem functioning, also under the impacts of climate change.