All of the seawater samples were filtered (0.45 gm) in order to remove radioelements associated with the particles, the quantity of which varied according to the area studied, especially in the Rh6ne estuary area where cesium isotopes are mainly linked to suspended matter. Gamma-emitting radioelements were measured by radiochemical methods described elsewhere (3,4). RESULTS AND DISCUSSION The results of our research are presented according to two areas: the coastal fringe subjected to river pollution, and the area defined by the continental shelf of the Golfe du Lion, where the river deposits are diluted. The coastal fringe The results of seawater sampling conducted between February and April 1986 (LITTORAL86A), at less than 2 nautical miles from the coast, reveal the presence of a single artificial radioelement: 137 Cs. 134 Cs was not detected. Levels in the region of 1 mBq/1 are typical of the eastern part of the coast whereas the west has slightly higher readings in the region of 4 mBq/1 emphasing the action of the waters of the Rh6ne in this part of the coast (Figure 1A) where 134Cs could also be detected ( 137Cs/134 Cs between 4 to 9). In November 1986 (LITTORAL86B), 137 Cs activity levels were higher all along the coast, varying from 3 to 9 mBq/1 with a 13/Cs/ 134 Cs from 2.3 to 4.0 , eliminating the differences between east and west as found in previous surveys (Figure 1B). Thus the Chernobyl fallout is clearly discernible, especially in the eastern part of the French Mediterranean coast. These observations are in line with those results obtained from atmospheric and land sampling (2). During these two cruises, the coastal area directly under the influence of water from the Rhone appears to have a higher 137 Cs content. A detailed study of the area in August, September and November 1986 during the DYPOL 01 and 02 cruises confirmed the presence of a decreasing spatial gradient of 137 Cs levels from the estuary towards the open sea (Figure 2). The Rhone water area of dilution corresponds to a situation classically described as a fundamental current flow, under the influence of the Ligurian-Provenal current (5). The vertical distribution of 137 Cs at 3 levels defined as a function of turbidity contours, at 3 sampling points distributed along a radial perpendicular to the coast, reveals the predominance of 137 Cs in the surface waters (Figure 3). The 3 sampling points display a marked discontinuity between the surface level of activity and the intermediate and deep levels. The discontinuity corresponds to the surface dispersal of the waters of the Rhone, which are less dense than the receiving seawater.

DOI link for All of the seawater samples were filtered (0.45 gm) in order to remove radioelements associated with the particles, the quantity of which varied according to the area studied, especially in the Rh6ne estuary area where cesium isotopes are mainly linked to suspended matter. Gamma-emitting radioelements were measured by radiochemical methods described elsewhere (3,4). RESULTS AND DISCUSSION The results of our research are presented according to two areas: the coastal fringe subjected to river pollution, and the area defined by the continental shelf of the Golfe du Lion, where the river deposits are diluted. The coastal fringe The results of seawater sampling conducted between February and April 1986 (LITTORAL86A), at less than 2 nautical miles from the coast, reveal the presence of a single artificial radioelement: 137 Cs. 134 Cs was not detected. Levels in the region of 1 mBq/1 are typical of the eastern part of the coast whereas the west has slightly higher readings in the region of 4 mBq/1 emphasing the action of the waters of the Rh6ne in this part of the coast (Figure 1A) where 134Cs could also be detected ( 137Cs/134 Cs between 4 to 9). In November 1986 (LITTORAL86B), 137 Cs activity levels were higher all along the coast, varying from 3 to 9 mBq/1 with a 13/Cs/ 134 Cs from 2.3 to 4.0 , eliminating the differences between east and west as found in previous surveys (Figure 1B). Thus the Chernobyl fallout is clearly discernible, especially in the eastern part of the French Mediterranean coast. These observations are in line with those results obtained from atmospheric and land sampling (2). During these two cruises, the coastal area directly under the influence of water from the Rhone appears to have a higher 137 Cs content. A detailed study of the area in August, September and November 1986 during the DYPOL 01 and 02 cruises confirmed the presence of a decreasing spatial gradient of 137 Cs levels from the estuary towards the open sea (Figure 2). The Rhone water area of dilution corresponds to a situation classically described as a fundamental current flow, under the influence of the Ligurian-Provenal current (5). The vertical distribution of 137 Cs at 3 levels defined as a function of turbidity contours, at 3 sampling points distributed along a radial perpendicular to the coast, reveals the predominance of 137 Cs in the surface waters (Figure 3). The 3 sampling points display a marked discontinuity between the surface level of activity and the intermediate and deep levels. The discontinuity corresponds to the surface dispersal of the waters of the Rhone, which are less dense than the receiving seawater.

All of the seawater samples were filtered (0.45 gm) in order to remove radioelements associated with the particles, the quantity of which varied according to the area studied, especially in the Rh6ne estuary area where cesium isotopes are mainly linked to suspended matter. Gamma-emitting radioelements were measured by radiochemical methods described elsewhere (3,4). RESULTS AND DISCUSSION The results of our research are presented according to two areas: the coastal fringe subjected to river pollution, and the area defined by the continental shelf of the Golfe du Lion, where the river deposits are diluted. The coastal fringe The results of seawater sampling conducted between February and April 1986 (LITTORAL86A), at less than 2 nautical miles from the coast, reveal the presence of a single artificial radioelement: 137 Cs. 134 Cs was not detected. Levels in the region of 1 mBq/1 are typical of the eastern part of the coast whereas the west has slightly higher readings in the region of 4 mBq/1 emphasing the action of the waters of the Rh6ne in this part of the coast (Figure 1A) where 134Cs could also be detected ( 137Cs/134 Cs between 4 to 9). In November 1986 (LITTORAL86B), 137 Cs activity levels were higher all along the coast, varying from 3 to 9 mBq/1 with a 13/Cs/ 134 Cs from 2.3 to 4.0 , eliminating the differences between east and west as found in previous surveys (Figure 1B). Thus the Chernobyl fallout is clearly discernible, especially in the eastern part of the French Mediterranean coast. These observations are in line with those results obtained from atmospheric and land sampling (2). During these two cruises, the coastal area directly under the influence of water from the Rhone appears to have a higher 137 Cs content. A detailed study of the area in August, September and November 1986 during the DYPOL 01 and 02 cruises confirmed the presence of a decreasing spatial gradient of 137 Cs levels from the estuary towards the open sea (Figure 2). The Rhone water area of dilution corresponds to a situation classically described as a fundamental current flow, under the influence of the Ligurian-Provenal current (5). The vertical distribution of 137 Cs at 3 levels defined as a function of turbidity contours, at 3 sampling points distributed along a radial perpendicular to the coast, reveals the predominance of 137 Cs in the surface waters (Figure 3). The 3 sampling points display a marked discontinuity between the surface level of activity and the intermediate and deep levels. The discontinuity corresponds to the surface dispersal of the waters of the Rhone, which are less dense than the receiving seawater.