Radionuclide tracing of water masses and processes in the water column and sediment in the Algerian Basin

• Published in: Journal of environmental radioactivity Vol. 99; no. 8; pp. 1224 - 1232
• Main Authors: Noureddine, A., Benkrid, M., Maoui, R., Menacer, M., Boudjenoun, R., Kadi-hanifi, M., Lee, S.-H., Povinec, P.P.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-08-2008; Elsevier
• Subjects: 137Cs, Pu isotopes; 210Pb sediment geochronology; Algeria; Algerian Basin; Applied sciences; Dynamics of the ocean (upper and deep oceans); Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; External geophysics; Geologic Sediments - chemistry; Marine; Marine and continental quaternary; Mediterranean; Natural water pollution; Physics of the oceans; Pollution; Pollution, environment geology; Radionuclides; Seawater; Seawaters, estuaries; Surficial geology; Water Pollutants, Radioactive - analysis; Water treatment and pollution; North Africa; Algeria; Mediterranean Sea; West Mediterranean; Africa; Ukraine, Chernobyl; MED, Western Mediterranean, Algerian Basin; A, Atlantic; MED, Eastern Mediterranean, Levantine Intermediate Water; MED, Algeria; 137Cs, Pu isotopes; Mediterranean; Radionuclides; 210Pb sediment geochronology; Algerian Basin; Seawater; Natural origin pollution; Cesium 137; geochronology; Radionuclides;137Cs; Water mass; Radioactive pollution; Atmospheric fallout; Lead 210; Ocean dynamics; Isotope dating; plutonium; Pu isotopes;Seawater;210pb sediment geochronology;Algerian Basin;Mediterranean; Exchange flow; Sedimentation rate; Fission reactor accidents; oceanography; radioactive isotopes; marine sedimentation; ocean circulation; radioactive tracers; Anthropogenic factor
• ISSN: 0265-931X; 1879-1700
• DOI: 10.1016/j.jenvrad.2008.02.007

Caesium-137 and
239,240PU were analysed in the water column along the Algerian coast. The
137Cs activity concentration in surface water increased from the west to the east from 1.6 to 3.3
mBq
L
−1, documenting a presence of Modified Atlantic Water (MAW) in the region. Higher concentrations observed in deep waters may be due to an intrusion of Levantine Intermediate Water (LIW), which has been carrying higher levels of
137Cs from Chernobyl accident. The
239,240Pu sub-surface concentration peaked at about 250
m water depth as a result of biogeochemical processes in the water column. The observed
239,240Pu/
137Cs activity ratio at the surface (0.003) was significantly lower than that in global fallout (0.04). This decrease exceeds that expected from radioactive decay of
137Cs, and confirms that Pu due to its adsorption on sinking particles is more effectively removed from surface layers than is
137Cs. An increase of the
239,240Pu/
137Cs activity ratio with depth suggests that
239,240Pu, similarly as
137Cs, should be also transported by advection to maintain the observed ratios in deep waters. An intrusion of LIW may enhance therefore both the
137Cs and
239,240Pu concentrations in deep waters. The average
238Pu/
239+240Pu activity ratio in seawater was 0.03
±
0.02, confirming a global fallout origin of Pu in the Algerian Basin. Caesium-137 and
239,240Pu inventories in the water column were estimated to be from 2.7
±
0.5
kBq
m
−2 to 3.8
±
0.7
kBq
m
−2, and from 13.8
±
2.6
Bq
m
−2 to 41
±
7
Bq
m
−2, respectively. The
137Cs massic activities in surface sediment were almost constant, the average activity was 9.0
±
0.8
Bq
kg
−1. Sedimentation rates obtained using the
210Pb method were from 0.1 to 0.7
cm
y
−1, and resulting penetration depths of
137Cs in the sediment cores were from 15 to over 40
cm. The
137Cs peaks found in the sediment cores were associated with the Chernobyl accident (1986) and global fallout (1964). The
137Cs inventories in the sediment were increasing from the west (180
Bq
m
−2) to the east (350
Bq
m
−2).