EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

Basin scale dissolved oxygen interannual variability of the Mediterranean Sea: Analysis of long-term observations

Apostolia-Maria Mavropoulou, Vassilios Vervatis, and Sarantis Sofianos
Apostolia-Maria Mavropoulou et al.
  • National and Kapodistrian University of Athens, School of Science, Department of Physics, Athens, Greece (

The Mediterranean Sea is characterized by a combination of long-term trends and climatic shifts known in the literature as “transients”, that impact the biogeochemical processes.  We focus on the dissolved oxygen (DO) concentration, as it is an essential oceanic parameter for the marine ecosystem functioning. Dissolved oxygen distribution in the ocean interior is controlled by air-sea interaction processes, ocean circulation patterns, and biological effects. Understanding the related mechanisms and the variability of the above processes requires systematic oceanographic measurements over long periods and at high spatial resolution. Taking advantage of the Mediterranean monitoring systems, we can examine the sensitive physical and biogeochemical processes in the Mediterranean ecosystem. In this study, we investigate and combine all available data of temperature, salinity and dissolved oxygen over the period 1960-2011 (taking into consideration the scarcity of the available DO observations during the last years). In order to receive a direct and accurate evaluation of the interannual changes in the Mediterranean Sea, we constructed a gridded dataset interpolated into 1/8ο x 1/8ο grid using Data-Interpolating Variational Analysis (DIVA). At the surface layer, the solubility-driven changes determine the dissolved oxygen concentration. In deeper layers, the interannual variability is more related to dynamical processes that may involve dense-water convection, biological consumption or mixing, rather than temperature trends. The observed changes in minimum/maximum oxygen zones are mostly related to abrupt shifts. The attribution of the observed variability involves complex physical and biogeochemical processes as well as anthropogenic activities and requires further analysis using modeling techniques and available operational tools.

How to cite: Mavropoulou, A.-M., Vervatis, V., and Sofianos, S.: Basin scale dissolved oxygen interannual variability of the Mediterranean Sea: Analysis of long-term observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15189,, 2020


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  • CC1: Comment on EGU2020-15189, Katrin Schroeder, 04 May 2020

     Is the increasing occurrence of Oxygen Minimum Zones an issue also for the Mediterranean Sea, as it is for the global ocean? or will it become an issue in the future?

    • CC2: Reply to CC1, Laurent Coppola, 04 May 2020

      Few observations have be able to observe a trend of oxygen minimum layer near the LIW. But the results (in the NW MedSea) show that with the slowdown of convection intensity and its occurrence (extent and frequency) the minO2 will be an issue in the MedSea in the next 30 years if the temperature warming increase as we expect. Then the OML (becoming thicker) and decrease of O2 inside this layer could have an impact on marine ecosystem. 

      Of course more we will have high quality O2 data, more our understanding and prediction will be robust and reliable.

    • AC1: Reply to CC1, Apostolia-Maria Mavropoulou, 04 May 2020

      Hi Laurent and Katrin,

      Your comments are very interesting. If we look at the period that is analyzed in the poster (1960-2011), we find that the interannual variability presents shifts between decades. However, if we examine for both sub-basins the OML for the period after 1990, it will be extended and the variability of DO seems to be under long-term trends.

  • CC3: Comment on EGU2020-15189, Laurent Coppola, 04 May 2020

    Any comparaison with salinity - oxygen in addition to temperature - oxygen as we mentioned in your paper ? What is the result from this relationshion O2-S ?

    • AC2: Reply to CC3, Apostolia-Maria Mavropoulou, 05 May 2020

      We did not calculate exactly the correlation coefficient map between salinity and oxygen (as for temperature), but its variability is involved in O2sat for the calculation of AOU index. Also, supporting evidence for the dynamical processes, which could explain the dissolved oxygen is obtained from the thermohaline properties (both salinity and temperature). The interannual variability of the dissolved oxygen is linked to the salinity changes. In the Eastern Mediterranean, for example, from the early 1990s increased salinity along with an increase of dissolved oxygen concentration was observed in the entire water column.