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Local spatial heterogeneity, both horizontal and vertical, is accompanied by daily temporal variations which we detected at sampling point 5. Between 28.08.86 and 03.09.86, the 137Cs concentration of the surface waters, under the permanent influence of Rhone deposits, fluctuated between 4 and 24 mBq/1 (Figure 4). This spread of values reflects both the variations in deposits over the period of time in question and the variable rates at which freshwater and seawater mix. The Golfe du Lion In September 1986, levels of 137Cs in the surface waters of the continental shelf of the Golfe du Lion varied from 1.5 to 6.5 mBq/1 with an average of 3.0 mBq/1 and a 137Cs/ 134Cs between 2.5 to 5.0. These figures were much lower than those obtained at sampling points at the eastern boundary of the gulf, on average 12 mBq/1 (4.5 mBq/1 of 134Cs), but slightly higher than those at the southern boundary which were equal to 2.5 mBq/1 (1.0 mBq/1 of 134Cs) on average (Figure 5A). The decreasing spatial gradient from east to west seems to correspond to a stock of cesium carried by waters in the Ligurian-Provenal geostrophic current coming from the north-west Mediterranean basin. The absence of major rainfall prior to the dates of the sampling definitely restricted the amount of soil washed away into the Rhone and thus the quantity of 137 Cs the latter was carrying. The levels recorded in the Gulf must therefore have been chiefly due to direct atmospheric fallout onto the surface waters in the eastern part of the north-west basin. At the time of the sampling operation in December 1986 (Figure 5B), the mean 137Cs and 134Cs activities of the surface waters of the continental shelf were higher: 7.0 mBq/1, for activity levels between 6.0 and 8.0 mBq/1 of 137Cs and 1.0 to 2.5 mBq/1 for 134Cs. A central strip running from north east to south west, joining the Rhone delta to the Cote Vermeil, had the highest 137 Cs readings which were constantly in the region of 8.0 mBq/1 (Figure 5B). These findings are to be compared with those of ALAIN (6), MINAS (7) and TOURNIER (8). The higher volume of deposits in the waters of the Rhone after the autumn rains and the increase of low level industrial releases made it possible to track the Rh6ne water across the gulf. Sampling points at the east and south boundaries of the continental layer of surface water characterised by high 137Cs levels and appearance of 134 Cs reflects the gradual spread of these elements towards the sea bed.
DOI link for Local spatial heterogeneity, both horizontal and vertical, is accompanied by daily temporal variations which we detected at sampling point 5. Between 28.08.86 and 03.09.86, the 137Cs concentration of the surface waters, under the permanent influence of Rhone deposits, fluctuated between 4 and 24 mBq/1 (Figure 4). This spread of values reflects both the variations in deposits over the period of time in question and the variable rates at which freshwater and seawater mix. The Golfe du Lion In September 1986, levels of 137Cs in the surface waters of the continental shelf of the Golfe du Lion varied from 1.5 to 6.5 mBq/1 with an average of 3.0 mBq/1 and a 137Cs/ 134Cs between 2.5 to 5.0. These figures were much lower than those obtained at sampling points at the eastern boundary of the gulf, on average 12 mBq/1 (4.5 mBq/1 of 134Cs), but slightly higher than those at the southern boundary which were equal to 2.5 mBq/1 (1.0 mBq/1 of 134Cs) on average (Figure 5A). The decreasing spatial gradient from east to west seems to correspond to a stock of cesium carried by waters in the Ligurian-Provenal geostrophic current coming from the north-west Mediterranean basin. The absence of major rainfall prior to the dates of the sampling definitely restricted the amount of soil washed away into the Rhone and thus the quantity of 137 Cs the latter was carrying. The levels recorded in the Gulf must therefore have been chiefly due to direct atmospheric fallout onto the surface waters in the eastern part of the north-west basin. At the time of the sampling operation in December 1986 (Figure 5B), the mean 137Cs and 134Cs activities of the surface waters of the continental shelf were higher: 7.0 mBq/1, for activity levels between 6.0 and 8.0 mBq/1 of 137Cs and 1.0 to 2.5 mBq/1 for 134Cs. A central strip running from north east to south west, joining the Rhone delta to the Cote Vermeil, had the highest 137 Cs readings which were constantly in the region of 8.0 mBq/1 (Figure 5B). These findings are to be compared with those of ALAIN (6), MINAS (7) and TOURNIER (8). The higher volume of deposits in the waters of the Rhone after the autumn rains and the increase of low level industrial releases made it possible to track the Rh6ne water across the gulf. Sampling points at the east and south boundaries of the continental layer of surface water characterised by high 137Cs levels and appearance of 134 Cs reflects the gradual spread of these elements towards the sea bed.
Local spatial heterogeneity, both horizontal and vertical, is accompanied by daily temporal variations which we detected at sampling point 5. Between 28.08.86 and 03.09.86, the 137Cs concentration of the surface waters, under the permanent influence of Rhone deposits, fluctuated between 4 and 24 mBq/1 (Figure 4). This spread of values reflects both the variations in deposits over the period of time in question and the variable rates at which freshwater and seawater mix. The Golfe du Lion In September 1986, levels of 137Cs in the surface waters of the continental shelf of the Golfe du Lion varied from 1.5 to 6.5 mBq/1 with an average of 3.0 mBq/1 and a 137Cs/ 134Cs between 2.5 to 5.0. These figures were much lower than those obtained at sampling points at the eastern boundary of the gulf, on average 12 mBq/1 (4.5 mBq/1 of 134Cs), but slightly higher than those at the southern boundary which were equal to 2.5 mBq/1 (1.0 mBq/1 of 134Cs) on average (Figure 5A). The decreasing spatial gradient from east to west seems to correspond to a stock of cesium carried by waters in the Ligurian-Provenal geostrophic current coming from the north-west Mediterranean basin. The absence of major rainfall prior to the dates of the sampling definitely restricted the amount of soil washed away into the Rhone and thus the quantity of 137 Cs the latter was carrying. The levels recorded in the Gulf must therefore have been chiefly due to direct atmospheric fallout onto the surface waters in the eastern part of the north-west basin. At the time of the sampling operation in December 1986 (Figure 5B), the mean 137Cs and 134Cs activities of the surface waters of the continental shelf were higher: 7.0 mBq/1, for activity levels between 6.0 and 8.0 mBq/1 of 137Cs and 1.0 to 2.5 mBq/1 for 134Cs. A central strip running from north east to south west, joining the Rhone delta to the Cote Vermeil, had the highest 137 Cs readings which were constantly in the region of 8.0 mBq/1 (Figure 5B). These findings are to be compared with those of ALAIN (6), MINAS (7) and TOURNIER (8). The higher volume of deposits in the waters of the Rhone after the autumn rains and the increase of low level industrial releases made it possible to track the Rh6ne water across the gulf. Sampling points at the east and south boundaries of the continental layer of surface water characterised by high 137Cs levels and appearance of 134 Cs reflects the gradual spread of these elements towards the sea bed.
ABSTRACT
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