IAEA Regional Training Course on Sediment Core Dating Techniques.  RAF7/008 Project
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IAEA Regional Training Course on Sediment Core Dating Techniques. RAF7/008 Project CNESTEN, Rabat, 5 – 9 July 2010. RADINUCLIDES IN THE OCEANS: a tool for understanding the ecosystems functioning Roberta Delfanti ENEA – Marine Environment Research Centre , La Spezia.

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IAEA Regional Training Course on Sediment Core Dating Techniques. RAF7/008 Project

CNESTEN, Rabat, 5 – 9 July 2010

RADINUCLIDES IN THE OCEANS:

a toolforunderstanding

the ecosystemsfunctioning

Roberta Delfanti

ENEA – Marine EnvironmentResearchCentre, La Spezia


RADIONUCLIDES IN THE OCEANS Techniques. RAF7/008 Project

OUTLINE

Sourcesofanthropogenic and naturalradionuclidesto the oceans.

Radionudlidesbehaviour in the marine environment.

The “tracer” concept.


Sources of radionuclides to the marine environment
Sources Techniques. RAF7/008 Projectofradionuclidesto the marine environment

  • Cosmicradiation.

  • In environmentalstudies:

  • 3H, 7Be, 14C

  • formedbyneutroncapture in the atmosphere.


Sources of radionuclides to the marine environment1
Sources Techniques. RAF7/008 Projectof radionuclidesto the marine environment

  • Primordial radionuclides

  • Series238U t1/2 = 4.5 x 109 a

  • 232Th t1/2 = 1.4 x 1010 a

  • 235U t1/2 = 7.1 x 108 a

  • Theydecay, through a long seriesofradionuclides,

  • tostableisotopesofPb.

  • 40K t1/2 = 1.3 x 109 a


Sources of radionuclides to the marine environment2
Sources Techniques. RAF7/008 Projectof radionuclidesto the marine environment

  • Anthropogenicradionuclides:

    • Fallout fromatmosphericweaponstesting

    • Chernobyl accident

    • NuclearIndustry

    • Nuclearaccidents


Global fallout Techniques. RAF7/008 Project

Trinity test, Alamogordo

July 16, 1945

Nucleartestsbantreaty

1963


Fission Techniques. RAF7/008 Projectyieldcurvesfor235U and 239Pu

8


Fallout radionuclides Techniques. RAF7/008 Project

stillpresent in the environment:

137Cs fission t1/2 30.2 years

90Sr fission t1/2 28.6 years

14C (n,p) + cosm t1/2 5730 years

3H fuel residue + cosm. t1/2 12.3 years

238Pu fuel residue/prod t1/2 87.7 years

239Pu fuel residue/prod t1/2 24119 years

240Pu fuel residue/prod t1/2 6570 years

To the oceans: 380 PBqof90Sr and 660 PBqof137Cs

9


Atmospheric Techniques. RAF7/008 Projectnucleardetonations

Hamilton, 2004


Global Techniques. RAF7/008 Project

fallout

latitudinal

deposition

10

Modified from Hamilton, 2004


The Chernobyl Techniques. RAF7/008 Project

accident

April 26,

1986

11


The Chernobyl Techniques. RAF7/008 Project

Accident

Simulationof the

dispersion

of the

Chernobyl plume

12


Chernobyl Techniques. RAF7/008 Project137Cs deposition in Europe (kBqm-2)

137Cs input to the oceans: 16 PBq


Atmospheric Techniques. RAF7/008 ProjectFluxof137Cs

La Spezia (NW Italy), 1957 – 2009


Nuclear Techniques. RAF7/008 ProjectIndustry:

Reprocessing

plants

137Cs input to the ocean: 40 PBq

Sellafield

La Hague


Waste Techniques. RAF7/008 Projectdisposal (sea dumping)

Linsley et al., 2004


Nuclear Accidents Techniques. RAF7/008 Project

Linsley et al., 2004


Summary Techniques. RAF7/008 Project

sourcesanthropogenicradionuclides

  • NUCLEAR WEAPON TESTING

  • NUCLEAR REPROCESSING

  • CHERNOBYL

ALL OTHER SOURCES

CONTRIBUTE ORDERS OF MAGNITUDE LESS TO

THE CONTAMINATION OF THE WORLD OCEAN


Radionuclide Techniques. RAF7/008 Projectbehaviour

in the marine environment

Conservative, like Cs (in open sea), H, Sr:

soluble, pathwayrelatedto water movements.

Non conservative, like Pu, Th, Pb,

high affinityforparticles, settlewiththem.


Transported by the oceanic currents…. Techniques. RAF7/008 Project




Taken up by organisms…….. Techniques. RAF7/008 Project

Stocker et al., 2010


Bathimetry Techniques. RAF7/008 Projectof the MediterraneanSea

Continental shelvesonly 10% ofitssurface


Spring climatological map Techniques. RAF7/008 Project

of SeaWiFS derived chlorophyll concentration

(D’Ortenzio, 2003)


The Techniques. RAF7/008 ProjectMedSeaisoligothrophic, characterisedby

low particlepopulation.

Saharandust, althoughsporadicallyimportant,

doesnot transfer to the seabottom

significantquantitiesof radionuclides.


Inventory of Techniques. RAF7/008 Project137Cs and 239,240Pu

in the Mediterranean Sea (2010)


Radionuclides Techniques. RAF7/008 Project

concentration

in surface water

of the

world seas

(IAEA, 2005)


Natural Techniques. RAF7/008 Projectradionuclides and theirbehaviour


Secular Techniques. RAF7/008 Projectequilibrium

i) t1/2 ofprogenitor >> t1/2daughters

ii) timefrombeginningofprogenitor’s decay >> t ½ daughters

allradionuclides in the serieshave the sameactivity


Approximate Techniques. RAF7/008 Projectactivitiesof238U seriesisotopes

in surfaceseawater

Broecker and Peng, 1982, modified


Radionuclides Techniques. RAF7/008 Projectinteractionwithparticles

Atmospheric

particles

Riverine

Particles

In the water column:

deficiencyof

particle-associated

radionuclideswithrespecttotheirparents

Marine

biogenic

Particles

In sediments: excessofparticle-associatedradionuclideswithrespecttotheirparents

Sediment

accumulation

Degradation of organic matter


The Techniques. RAF7/008 Projecttracerconcept

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.


The tracer concept Techniques. RAF7/008 Project

Knowing:

◊ input function (time and space)

◊ chemical/biological behaviour

◊ evolution of their distributions within the sea

  • Information on oceanographic processes.

  • Patterns and rates of

    • ◊ circulation

    • ◊ ventilation

    • ◊ sediment transport

    • ◊ particle (carbon) fluxes…..

}Solubleradionuclides

{

Particle-reactive

Radionuclides


Flying radionuclides Techniques. RAF7/008 Project

(Radon Rn-222)

Running radionuclides

U-Th series

Diving radionuclides

Th-234, Th-228, Th-230,

Pb-210

Swimming

radionuclides

Ra-226, Ra-228, Ra-222

Ra-226, Ra-228,

H-3 (C-14)

Sediments: C-14, Pb-210, Th-234

The tracer concept

Radionuclides as tracers of marine processes


210 pb as tracer of sedimentation processes

Rn-222 Techniques. RAF7/008 Project

Pb-210

210Pb astracerofsedimentationprocesses

Pb-210

U-238

Pb-210 matrix +

Pb-210 ex


210 pb as sedimentation tracer
210 Techniques. RAF7/008 ProjectPb assedimentationtracer

The fraction of 210Pb reaching the sediment in association

with settling particles, the so-called excess 210Pb,

IS NOT

in secular equilibrium with its parent 226Ra and decays with its

own half-life (22 yr).

  • Its vertical profile in the sediment depends on

    • physical decay and

    • sediment accumulation rate.


Vertical profile of 210 pb and 226 ra in a sediment core

Ra-226 Techniques. RAF7/008 Project

Pb-210 (Bq/kg)

0

50

100

150

200

0

10

20

Prof. (cm)

30

40

Vertical profile of 210Pb and 226Rain a sediment core


In Techniques. RAF7/008 Projectconclusion:

The levelsofanthropogenicradionuclides

in the marine envirnment are presently low

and willdecrease in the future

(except in a few hot spots)

due to the decrease in the input.


In conclusion.. Techniques. RAF7/008 Project

Dosesto man fromanthropogenic radionuclides

are generallylowerthanthosederivingfromnatural radionuclides

(in the marine environmentmainly210Po).


Dose Techniques. RAF7/008 Projectratesto the world population

from marine radioactivity

Linsley et al., 2004


Dose Techniques. RAF7/008 Projectratesto the crticalgroups

from marine radioactivity

Linsley et al., 2004


RADINUCLIDES IN THE OCEANS: Techniques. RAF7/008 Project

a toolforunderstanding

the ecosystemsfunctioning

Radionuclides are powerfultoolstodefine the ratesofoceanographicprocess, thatoften can notbederived in anyother way.

Theyhaveproducedessential information on water circulation, particledynamics and

pollutionstudies and are a foundamentaltoolto validate models.


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