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

[摘要] The subsurface oxygen maximum (SOM) is observed inoligotrophic oceans and is associated with different physical and biologicalprocesses. This study characterizes the SOM in the Mediterranean Sea at thebasin scale and investigates its driving mechanisms by analysing the outputof the 1 / 24 ∘ resolution biogeochemical reanalysis provided by theCopernicus Marine Service for the 1999–2019 time period. We validated themodel-derived oxygen concentration in the epipelagic layer at differentspatial and temporal scales, including novel process comparisons withestimates from in situ observations. Moreover, using Biogeochemical Argo(BGC-Argo) float observations, we estimated the model uncertainty inreproducing the SOM concentration and depth in summer (13 mmol O 2  m −3 and 13 m, respectively). The western and eastern Mediterranean Seadepicts different SOM signatures in summer, with higher oxygen values andshallower depths in the western Mediterranean. The concentrations and depths(in the ranges of 230–250 mmol O 2  m −3 and 30–100 m, respectively)are in agreement with the estimations from the literature and show mesoscalevariability patterns. The western Mediterranean also shows a strongerbiological activity, specifically oxygen production and consumption, alongthe whole epipelagic layer and higher oxygen concentrations at the surfacethroughout the year, but heavy undersaturated waters are associated withwinter deep convection in the northwestern Mediterranean Sea. A 1-yearanalysis conducted on selected areas that are representative of theheterogeneity of summer SOM highlighted that the SOM can actually besustained by biological production (as in northwestern Mediterranean areas),or it can be a residual of the confinement of spring production (as in thecentral Ionian area) and vertical motions influence its depth (as in theLevantine subduction area).

[学科分类] 大气科学