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RADINUCLIDES IN THE OCEANS: a tool for understanding the ecosystems functioning Roberta Delfanti ENEA – Marine Environment Research Centre, La Spezia IAEA.

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Presentation on theme: "RADINUCLIDES IN THE OCEANS: a tool for understanding the ecosystems functioning Roberta Delfanti ENEA – Marine Environment Research Centre, La Spezia IAEA."— Presentation transcript:

1 RADINUCLIDES IN THE OCEANS: a tool for understanding the ecosystems functioning Roberta Delfanti ENEA – Marine Environment Research Centre, La Spezia IAEA Regional Training Course on Sediment Core Dating Techniques. RAF7/008 Project CNESTEN, Rabat, 5 – 9 July

2 1.Sources of anthropogenic and natural radionuclides to the oceans. 2.Radionudlides behaviour in the marine environment. 3.The “tracer” concept. RADIONUCLIDES IN THE OCEANS OUTLINE 2

3 3 Sources of radionuclides to the marine environment Cosmic radiation. In environmental studies: 3 H, 7 Be, 14 C 3 H, 7 Be, 14 C formed by neutron capture in the atmosphere.

4 4 Sources of radionuclides to the marine environment Primordial radionuclides Series 238 U t 1/2 = 4.5 x 10 9 a 232 Tht 1/2 = 1.4 x a 232 Tht 1/2 = 1.4 x a 235 Ut 1/2 = 7.1 x 10 8 a They decay, through a long series of radionuclides, to stable isotopes of Pb. 40 Kt 1/2 = 1.3 x 10 9 a

5 5 Anthropogenic radionuclides: Fallout from atmospheric weapons testing Fallout from atmospheric weapons testing Chernobyl accident Chernobyl accident Nuclear Industry Nuclear Industry Nuclear accidents Nuclear accidents Sources of radionuclides to the marine environment

6 Global fallout Trinity test, Alamogordo July 16, 1945 Nuclear tests ban treaty

7 Fission yield curves for 235 U and 239 Pu 8

8 Fallout radionuclides still present in the environment: 137 Csfission t 1/ years 90 Srfission t 1/ years 14 C (n,p) + cosm t 1/ years 3 Hfuel residue + cosm.t 1/ years 3 Hfuel residue + cosm.t 1/ years 238 Pufuel residue/prod t 1/ years 239 Pufuel residue/prod t 1/ years 240 Pufuel residue/prod t 1/ years To the oceans: 380 PBq of 90 Sr and 660 PBq of 137 Cs 9

9 Hamilton, 2004 Atmospheric nuclear detonations 9

10 Globalfalloutlatitudinaldeposition Modified from Hamilton,

11 The Chernobyl accident April 26,

12 The Chernobyl Accident Simulation of the dispersion of the Chernobyl plume 12

13 137 Cs input to the oceans: 16 PBq Chernobyl 137 Cs deposition in Europe (kBqm -2 ) 13

14 Atmospheric Flux of 137 Cs La Spezia (NW Italy), 1957 –

15 Nuclear Industry: Reprocessingplants Sellafield La Hague 137 Cs input to the ocean: 40 PBq 15

16 Waste disposal (sea dumping) Linsley et al.,

17 Nuclear Accidents Linsley et al.,

18 Summary sources anthropogenic radionuclides NUCLEAR WEAPON TESTING NUCLEAR REPROCESSING NUCLEAR REPROCESSING CHERNOBYL CHERNOBYL ALL OTHER SOURCES CONTRIBUTE ORDERS OF MAGNITUDE LESS TO THE CONTAMINATION OF THE WORLD OCEAN 18

19 Conservative, like Cs (in open sea), H, Sr: soluble, pathway related to water movements. Non conservative, like Pu, Th, Pb, high affinity for particles, settle with them. Radionuclide behaviour in the marine environment 19

20 Transported by the oceanic currents…. 20

21 Adsorbed onto particles in costal areas…….. 21

22 Scavenged by particles in the open sea…….. 22

23 Stocker et al., 2010 Taken up by organisms…….. 23

24 Bathimetry of the Mediterranean Sea Continental shelves only 10% of its surface 24

25 Spring climatological map of SeaWiFS derived chlorophyll concentration (D’Ortenzio, 2003) 25

26 The Med Sea is oligothrophic, characterised by low particle population. Saharan dust, although sporadically important, does not transfer to the sea bottom significant quantities of radionuclides. 26

27 Inventory of 137 Cs and 239,240 Pu in the Mediterranean Sea (2010) 27

28 Radionuclidesconcentration in surface water of the world seas (IAEA, 2005) 28

29 Natural radionuclides and their behaviour 29

30 i) t 1/2 of progenitor >> t 1/2 daughters ii) time from beginning of progenitor’s decay >> t ½ daughters ii) time from beginning of progenitor’s decay >> t ½ daughters all radionuclides in the series have the same activity Secular equilibrium 30

31 IsotopeDaughterHalf-life(yr) Surface Water Conc. (Bq/m 3 ) 238 U parent Th U Th 75,2 2 x Ra Rn Pb Po Approximate activities of 238 U series isotopes in surface seawater Broecker and Peng, 1982, modified 31

32 Atmospheric particles Riverine Particles Marine biogenic Particles Degradation of organic matter Sediment accumulation In the water column: deficiency of particle-associated radionuclides with respect to their parents In sediments: excess of particle-associated radionuclides with respect to their parents Radionuclides interaction with particles 32

33 The tracer concept Particle reactive nuclides produced in situ by decay of their parents. Production rate determined by measuring parent’s conc. Comparing concentrations of parent and daughter we can show whether the daughter is being removed onto particles, but also the rate at which this occurs. 33

34 Knowing: ◊ input function (time and space) ◊ chemical/biological behaviour ◊ evolution of their distributions within the sea The tracer concept Information on oceanographic processes. Patterns and rates of ◊ circulation ◊ ventilation ◊ sediment transport ◊ particle (carbon) fluxes….. } Soluble radionuclides Particle-reactiveRadionuclides { 34

35 The tracer concept Radionuclides as tracers of marine processes Swimming radionuclides Ra-226, Ra-228, H-3 (C-14) Running radionuclides U-Th series Diving radionuclides Th-234, Th-228, Th-230, Pb-210 Sediments: C-14, Pb-210, Th-234 Ra-226, Ra-228, Ra-222 Flying radionuclides (Radon Rn-222) 35

36 Pb as tracer of sedimentation processes Rn-222 Pb-210 Pb-210 exU-238Pb-210 matrix +

37 Pb as sedimentation tracer The fraction of 210 Pb reaching the sediment in association with settling particles, the so-called excess 210 Pb, IS NOT in secular equilibrium with its parent 226 Ra and decays with its own half-life (22 yr). Its vertical profile in the sediment depends on physical decay and sediment accumulation rate.

38 38 Vertical profile of 210 Pb and 226 Ra in a sediment core

39 The levels of anthropogenic radionuclides in the marine envirnment are presently low and will decrease in the future (except in a few hot spots) due to the decrease in the input. In conclusion: 39

40 In conclusion.. Doses to man from anthropogenic radionuclides are generally lower than those deriving from natural radionuclides (in the marine environment mainly 210 Po). 40

41 Dose rates to the world population from marine radi from marine radioactivity Linsley et al.,

42 Dose rates to the crtical groups from marine radi from marine radioactivity Linsley et al.,

43 Radionuclides are powerful tools to define the rates of oceanographic process, that often can not be derived in any other way. RADINUCLIDES IN THE OCEANS: a tool for understanding the ecosystems functioning They have produced essential information on water circulation, particle dynamics and pollution studies and are a foundamental tool to validate models. 43


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