Dissolved oxygen budget in the eastern Mediterranean over the period of 2012 - 2020 using a 3D physical-biogeochemical model

The Levantine basin is the area of formation of the Levantine Intermediate Water. In this study, a 3D hydrodynamic-biogeochemical model (Symphonie/Eco3MS) was used to gain understanding in the dynamics of dissolved oxygen in the Levantine basin and estimate its annual budget and its interannual variability over the period of 2012-2020. Comparisons of model results with compiled in situ data from cruises and Argo floats showed that the model was able to reproduce well the seasonal variability of the dissolved oxygen. They also show that during winter, surface temperature decreased, generating  oxygen  undersaturation in the Levantine basin that absorbed atmospheric oxygen. From March to September, due to the increase of surface temperature the basin became oversaturated and released oxygen into the atmosphere. The estimate of the annual oxygen budget revealed that the Levantine basin acted as a sink of atmospheric oxygen. Gain of oxygen in the upper layer through air-sea exchanges and biogeochemical processes were counterbalanced by the loss of oxygen through physical processes via downward export into  intermediate depths and lateral transport towards the western regions. At the annual scale, the air-sea oxygen exchange term dominated the biogeochemical process term in the budget. Regarding the spatial distribution, maximum annual atmospheric oxygen uptake and biogeochemical fluxes were found in the Levantine Intermediate Water formation area of the Rhodes gyre where oxygen-poor and nutrient-rich waters were supplied in the upper layer and surface temperature was minimum. The current study revealed high interannual variability with large oxygen uptakes and physical exports during winters marked by intense heat losses.