Earth Observation satellites and environmental models are able to monitor changes of ecological parameters in the marine environment. Radionuclides cannot be directly measured using satellite remote sensing, because they are not currently detectable by the satellite instruments. Nevertheless, the levels of radionuclides, in the marine environment are known to be associated with physical and biogeochemical parameters of the natural environment. Considering this attribute, we investigate the potential relation between ¹³⁷Cs activity concentration and sea surface salinity. We select the parameter of salinity, as the element of Cesium in the seawater is conservative and contributes to it. Cs-137 activity concentration measurements are issued from the database of the Environmental Radioactivity Laboratory (ERL) of NCSR “D” for the period 1993 to 2006. Salinity corresponds to sea surface salinity (SSS) data issued from Copernicus Marine Environment Monitoring Service (CMEMS) database spanning also the period 1993 to 2006. A total of 15 measurements are used for the establishment of a linear regression model for the marine environment of the Island of Lemnos (Greece). The Island of Lemnos is located in the Aegean, southwest of the Dardanelles Strait and its waters are constantly enriched with ¹³⁷Cs of Black Sea origin. The resulting linear model (R²=0.82) is then validated using recent ¹³⁷Cs measurements spanning November 2018 and July 2019. During two sampling cruises that took place, on 12-15 November 2018 and on 24-28 July 2019, a total of 11 samples were collected and analyzed. The measured concentrations obtained by gamma spectrometry, in terms of activity concentrations (Bq/m³), are then compared with the estimated ¹³⁷Cs concentrations obtained by the model. The estimations present a relative error of less than 25%. Finally, in order to conduct the risk assessment in the studied area, the dose rate thematic maps in the marine area of Lemnos are calculated with the ERICA Assessment Tool and QGIS for pelagic fish, as one of the most representative organism of the studied environment and the most important, in terms of commercial value. The doses in pelagic fish are calculated for each pixel within the estimated ¹³⁷Cs activity concentrations thematic maps for November 2018 and July 2019. The results show the corresponding dose rate maps for the pelagic fish during November 2018 and July 2019 for the Lemnos Island. The dose rates in the thematic maps vary from 0.7 to 1.1 μGy/year, which are far lower than the intervention levels, indicating low impact due to the ¹³⁷Cs exposure.

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