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Transient tracers studies of the ocean circulation

Transient tracers studies of the ocean circulation. Roberta Delfanti ENEA, Marine Environment Research Centre. “ Transient tracers' studies of the ocean circulation ”. The transient tracer concept The input functions Tracer selection Examples. The tracer concept. Knowing:

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Transient tracers studies of the ocean circulation

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  1. Transient tracers studies of the ocean circulation Roberta Delfanti ENEA, Marine Environment Research Centre

  2. “Transient tracers' studies of the ocean circulation” • The transient tracer concept • The input functions • Tracer selection • Examples

  3. 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…..

  4. The most important tracers ◊ Anthropogenic substances CFC’s 3H – 3He, 14C 137Cs, 90Sr, 99Tc, 129I, 125Sb ◊ Primordial radionuclides (mainly: U-Th series)

  5. 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-224 The tracer concept Radionuclides as tracers of marine processes.

  6. The tracer concept Ex. Th-234 as tracer of particle dynamics in the upper ocean Café Thorium web page: http://www.whoi.edu/science/MCG/cafethorium/website

  7. The tracer concept 14C as tracer of sediment accumulation rates in deep-sea environments Bq g-1 C Vertical profile of 14C in a sediment core of the deep N Atlantic. Const rate of supply and costant concentration at sed-water interface. Decrease of concentration along core due to physical decay, clock of the process.

  8. The tracer concept In physical oceanography: Use of conservative tracers: - “soluble” in seawater - known input function for radioactive tracers, select: t1/2 compatible with time scale of the process studied. Most used: CFC’s, SF6 3H – 3He 14C 137Cs, 90Sr, 125Sb, 99Tc, 129I

  9. Input functions Time series of atmospheric concentrations of CFC-11, CFC-12, CFC-113 and SF6. Time series of tritium in North Atlantic Ocean surface waters. http://www.jhu.edu/~dwaugh1/ttd_tracerages.html

  10. Atmosphere Gas exchange with atmosphere at surface Ocean The tracers of ventilation - CFCs • CFCs enter the ocean at the sea surface through gas exchange • Each year the imprinted concentrations in the mixed layer increase with the atmospheric concentrations • CFCs are anthropogenic substances • Their atmospheric concentrations have increased with time

  11. Tritium input function Time history of Tritium input fuction at 50°N and 50°S (Roether and Rhein, 1989)

  12. The tracer concept Information from tracer distribution: Water mass spreading and pathways Deep ventilation and water mass transformation processes “Ages” Rates of movements and amount of dilution Model validation.

  13. Selected features of transient tracers Roether, 1994

  14. THE OCEAN CONVEYOR Carries warm surface waters from the tropics northward. At high latitudes, the waters cool, releasing heat to the atmosphere and moderating wintertime climate in the North Atlantic region. The colder (and denser) waters sink and flow southward in the deep ocean to keep the conveyor moving. (Illustration by Jack Cook, WHOI)

  15. Information from tracer distributions CFC-11 invasion in N-Atlantic along a section at 19.5°W, 1955-83 http://puddle.mit.edu/~mick/cfcall.html

  16. Information from tracer distributions CFC-11 invading deep N-Atlantic at 1975 m depth, 1955-83 http://puddle.mit.edu/~mick/cfcall.html

  17. Information from tracer distributions GEOSECS - Geochemical Ocean Sections 1972-78

  18. Information from tracer distributions TRANSIENT TRACERS IN THE OCEANS TTO 1980-83

  19. Information from tracer distributions WOCE – World Ocean Circulation Experiment 1990-98 Cruise tracks in the Atlantic Ocean

  20. Information from tracer distributions FUTURE: GEOTRACES is an international study of the global marine biogeochemical cycles of trace elements and their isotopes. Promoted by SCOR

  21. Information from tracer distributions – spreading and pathways GEOSECS ATLAS – Salinity, 1972 EQ 40°N

  22. Information from tracer distributions – spreading and pathways GEOSECS ATLAS – Tritium (TU), 1972 EQ 30° N

  23. Information from tracer distributions – spreading and pathways 80°N 10°S 30° N Western North Atlantic GEOSECS, 1972 TTO, 1981 Östlund and Rooth, 1990

  24. Information from tracer distributions – spreading and pathways BERMUDA TIME SERIES STATION 32°N – Tritium Jenkins and Smethie, 1996

  25. The “age” concept Elapsed time since a water mass was last at the ocean surface in direct contact with the atmosphere. The age information can be derived from radioactive decay as for tritium, or from the temporally changing atmospheric concentrations, as for the CFCs.

  26. T= 1 3He ( ) loge 1 + λ 3H The tritium/helium age 3H 3He + β t1/2= 12.5 y λ= 0.055 y-1 The time elapsed since the water left the surface, τ, can then be calculated from the concentrations of 3H and excess 3He. In the mixed layer 3He is in equilibrium with atmospheric He, while in the ocean interior tritium decay leads to ingrowth of an excess 3He.

  27. The tracer age Tritium and tritium-helim age in the core of the Deep Water Boundary Current vs. distance downstream from its origin. Jenkins and Smethie, 1996

  28. The CFC age Ages can also be computed from CFC concentrations and can be defined as 1. elapsed time since the surface concentration was equal to the one we measure at time t. c(t) = C0 (t – τconc) 2. elapsed time since the ratio of two tracers concentrations at the surface was equal to the interior ratio. R(t) = R0 (t – τconc)

  29. CFC age distribution along the isopycnal sigth=27.8, characterising the Labrador Sea Water, LSW (depth 2000m). (Rhein et al., 2001).

  30. CFC age distribution along the patway of DSOW. (Rhein et al., 2001).

  31. The CFC age The calculated ages are correct if: ◊the water mass was in equilibrium with the atmosphere at the time of formation; ◊mixing occurs only with tracer-free water.

  32. The tracer ages Differences in ages calculated using different tracers. Ages reflect the character of the tracers as well as chronometric time. Differences can be quantified and used to infer mixing rates. See. Waugh et al., JGR 2003 Doney et al., DSR 1997. Doney et al., 1997, North-Central Atlantic

  33. The CaribbeanSea

  34. Coralrecordsof water characteristics in the CaribbeanSea Massive coral Montastrraea faviolata

  35. Source water variations in the Caribbean Sea Radiocarbon of seawater DIC 1981 - 1983 (Nydal and Løvseth 1996; Ostlund and Grall 1987) and coral radiocarbon values at Bermuda, Puerto Rico and Cabo for 1983 outlined in black. Kilbourne et al. 2007

  36. Florida Current water Red: Puerto Rico Grey: South Atlantic Black: SubtropicalGyre 1963-70: Subtropical origin 1977-83: Equatorial origin Kilbourne et al. 2007

  37. Anthropogenic radionuclides 137Cs, 99Tc, 125Sb and 129I have mainly been used in specific areas, where point sources are present. Nuclear fuel reprocessing plants Sellafield La Hague

  38. Example: transit time of water mass in N-Atlantic - Arctic Sellafield Point source: Sellafield reprocessing plant

  39. Example: transit time of water mass in N-Atlantic - Arctic Circulation of surface waters of the North,Norwegian, Greenland and Barents Seas.

  40. Example: transport time of radionuclides in N-Atlantic and Arctic AMAP, 1997

  41. 4-6y 6-8y 3-4y 3y 1y Example: transit time of water mass and transfer factors in N-Atlantic - Arctic 6-8y Transport time of 137Cs in surface water Dahlgaard et al.,1995

  42. Example: transit time of water mass and transfer factors in N-Atlantic - Arctic Consequence of dumping of nuclear wastes in the Arctic Ocean: transport and dispersion of 137Cs in the Arctic. Nies et al., 1998

  43. Example: transit time of water mass and transfer factors in N-Atlantic - Arctic Consequence of dumping of nuclear wastes in the Arctic Ocean: transport and dispersion of 137Cs in the Arctic. Sellafield hindcast scenario 1965-1995 Nies et al., 1998

  44. Example: transit time of water mass and transfer factors in N-Atlantic - Arctic Discharges of 99Tc from Sellafield and La Hague (Kershaw et al., 2004)

  45. Example: transit time of water mass and transfer factors in N-Atlantic - Arctic More rapid transport to North Sea (6-9 months) Slow northward transport with NwCC and WSC. Correspondence with variations in NAO winter index. Kershaw et al., 2004

  46. Vertical section of 129I in the Arctic Ocean Smith et al., 1998

  47. Transient tracers help to constrain circulation and mixing in the ocean and give information that cannot be obtained by hydrographic data alone. • estimate deep water formation/renewal rates  • detect and follow the paths of water masses  • estimate time scales of spreading • validate models

  48. Thanks for your attention !!

  49. Alfimov et al., 2004

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