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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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slide1

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

slide2

RADIONUCLIDES IN THE OCEANS

OUTLINE

Sourcesofanthropogenic and naturalradionuclidesto the oceans.

Radionudlidesbehaviour in the marine environment.

The “tracer” concept.

sources of radionuclides to the marine environment
Sourcesofradionuclidesto the marine environment
  • Cosmicradiation.
  • In environmentalstudies:
  • 3H, 7Be, 14C
  • formedbyneutroncapture in the atmosphere.
sources of radionuclides to the marine environment1
Sourcesof 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
Sourcesof radionuclidesto the marine environment
  • Anthropogenicradionuclides:
    • Fallout fromatmosphericweaponstesting
    • Chernobyl accident
    • NuclearIndustry
    • Nuclearaccidents
slide6

Global fallout

Trinity test, Alamogordo

July 16, 1945

Nucleartestsbantreaty

1963

slide8

Fallout radionuclides

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

slide10

Global

fallout

latitudinal

deposition

10

Modified from Hamilton, 2004

slide11

The Chernobyl

accident

April 26,

1986

11

slide12

The Chernobyl

Accident

Simulationof the

dispersion

of the

Chernobyl plume

12

slide13

Chernobyl 137Cs deposition in Europe (kBqm-2)

137Cs input to the oceans: 16 PBq

slide14

AtmosphericFluxof137Cs

La Spezia (NW Italy), 1957 – 2009

slide15

NuclearIndustry:

Reprocessing

plants

137Cs input to the ocean: 40 PBq

Sellafield

La Hague

slide16

Wastedisposal (sea dumping)

Linsley et al., 2004

slide17

Nuclear Accidents

Linsley et al., 2004

slide18

Summary

sourcesanthropogenicradionuclides

  • NUCLEAR WEAPON TESTING
  • NUCLEAR REPROCESSING
  • CHERNOBYL

ALL OTHER SOURCES

CONTRIBUTE ORDERS OF MAGNITUDE LESS TO

THE CONTAMINATION OF THE WORLD OCEAN

slide19

Radionuclide behaviour

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.

slide23

Taken up by organisms……..

Stocker et al., 2010

slide24

Bathimetryof the MediterraneanSea

Continental shelvesonly 10% ofitssurface

slide25

Spring climatological map

of SeaWiFS derived chlorophyll concentration

(D’Ortenzio, 2003)

slide26

The MedSeaisoligothrophic, characterisedby

low particlepopulation.

Saharandust, althoughsporadicallyimportant,

doesnot transfer to the seabottom

significantquantitiesof radionuclides.

slide27

Inventory of 137Cs and 239,240Pu

in the Mediterranean Sea (2010)

slide28

Radionuclides

concentration

in surface water

of the

world seas

(IAEA, 2005)

slide30

Secularequilibrium

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

ii) timefrombeginningofprogenitor’s decay >> t ½ daughters

allradionuclides in the serieshave the sameactivity

slide31

Approximateactivitiesof238U seriesisotopes

in surfaceseawater

Broecker and Peng, 1982, modified

slide32

Radionuclidesinteractionwithparticles

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

slide33

The tracerconcept

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.

slide34

The tracer concept

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

slide35

Flying radionuclides

(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

Pb-210

210Pb astracerofsedimentationprocesses

Pb-210

U-238

Pb-210 matrix +

Pb-210 ex

210 pb as sedimentation tracer
210Pb 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

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
slide39

In conclusion:

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.

slide40

In conclusion..

Dosesto man fromanthropogenic radionuclides

are generallylowerthanthosederivingfromnatural radionuclides

(in the marine environmentmainly210Po).

slide41

Dose ratesto the world population

from marine radioactivity

Linsley et al., 2004

slide42

Dose ratesto the crticalgroups

from marine radioactivity

Linsley et al., 2004

slide43

RADINUCLIDES IN THE OCEANS:

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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