The anthropogenic radionuclide 137Cs is used as a valuable oceanographic tracer for the study of sea water masses identification and water movement. In the present work, 137Cs activity concentrations have been investigated in deep basins of Aegean Sea. Seawater samples were collected from five different sampling stations, during scientific oceanic campaigns from the period March to April 2008. The applied methodology was based on the adsorption of radiocaesium from dissolved AMP (Ammonium Phosphomolybdate Hydrate) in 20 L water samples. Moreover, during the pre- concentration procedure, the 134Cs was used as reference tracer for determining the chemical efficiency and consequently to measure the activity concentration in a High Purity Ge detector. In terms of vertical records, the activity concentration in the selected basins ranged between 3-8.5 Bq/m3, depending on the region and the depth of the basins. The higher concentration (8.5 Bq/m3) was found in the region between Lemnos Island and the narrows of Dardanelles. The maximum concentrations were observed at the North Aegean Sea basins, between 20 and 40 m of depth, caused by the water masses coming from the Black Sea. At the Cretan Sea the vertical activity concentration of 137Cs was homogeneous down to 2000 m depth, with an exception at the 800 m where it was decreasing significantly due to the transient deep-water masses from Adriatic Sea.
137Cs activity concentration in seawater is an efficient radio-tracing technique to separate and identify the origin of different water masses along with depth. This technique has been applied for the study of deep basins at the North Aegean Sea [1], a marine region which is continuously enriched with 137Cs originated from the Black Sea, through the Dardanelles Straits. In this work, a second sampling campaign (from 2008 to 2013) was carried out in Lemnos’s deep basin and water quantities were collected from different depths. These quantities were chemically treated at HCMR to pre-concentrate 137Cs by using the AMP precipitation method [2]. The produced samples were measured by means of γ- ray spectroscopy. The 137Cs data profile in combination with other oceanographic data (salinity and temperature), provides significant information for the water masses origin with respect to depth. More specifically, at the surface layer, Black Sea water masses (characterized by enriched concentrations of 137Cs) are observed, with 137Cs concentrations about 4 Bq/m3. At the intermediate layers, Levantine water masses (characterized by low concentrations of 137Cs) appear with 137Cs activity reduced to 2 Bq/m3, while the deep layer dense water masses exhibit intermediate 137Cs concentrations of 3 Bq/m3. The 137Cs concentration results are compared with previous measurements performed in the same basin from 1999 to 2013, where the decline of 137Cs concentrations in the surface layer is observed and similar concentrations about 3 Bq/m3(within uncertainties) in the deep layer are obtained.
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