1. Abigail Spieler Oral Examination Presentation March 28, 2005
Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations
Abigail Spieler
Oral Examination Presentation
March 28, 2005

2. Outline Introduction Box model design Input functions
Box model simulations
Scenarios
Conclusions

3. Canadian Basin Kara Sea Eurasian Basin Barents Sea Greenland Sea
Amundsen Basin
Lomonosov Ridge (1800m)
Nansen Basin
Kara Sea
Eurasian Basin
Fram Strait
(2600m)
Barents Sea
Greenland
Sea
Mid-Atlantic Ridge
Norwegian Sea

4. Arctic Ocean-Nordic Seas Thermohaline circulation

5. Vertical structure of the Greenland Sea gyre

6. Outline Introduction Box model design Input functions
Box model simulations
Scenarios
Conclusions

7. Model Design

8. Model design, ctd. Water masses are represented by homogeneous boxes
ci = concentration in box i
Jji= volumetric flux from box j to box i
q = source/sink in box, e.g. radioactive decay
Water masses are represented by homogeneous boxes
Tracers conserved in deep water boxes
Surface water boxes represent boundary conditions of model
: assume steady state (Bönisch and Schlosser, 1995) and volume conservation
Integrate using forward differences in time

9. Outline Introduction Box model design Input functions
Box model simulations
Scenarios
Conclusions

10. Tritium input
Natural 3H concentration in surface ocean ≈ 0.2 TU. Bomb peak in mid-1960s; half life = years.
Precipitation is the main source of 3H in Atlantic-derived waters
For Norwegian and Greenland Sea surface waters, scale D-R curve to observations; exponential decay after 1974
North Atlantic surface water (Dreisigacker and Roether, 1978)
Norwegian Sea Surface water

11. Tritium input, ctd.
The two components of GSUW are Greenland Sea Surface Water (GSSW) and Upper Arctic Intermediate Water
GSUW = 0.82*GSSW *NSSW (lagged by 5 years)
Greenland Sea Upper Water

12. Tritium input, ctd.
Barents Sea surface water consists of Atlantic-derived water with 3H/3He age ≈ 3 years, and river runoff.
BS = 0.004*river runoff (2 year lag) *NSSW (3 year lag)
15% reduction of 3H in Atlantic-derived component due to radioactive decay.
Barents Sea surface water

13. CFC-11 and CFC-12 input functions
100% of solubility in NSSW; 85% of solubility in GSUW and BS.
Assume linear decline of CFC-11 and CFC-12 after 2005.
Northern hemisphere atmospheric CFC-11 and CFC-12
CFC-12
CFC-11
CFC-11 in surface boxes

14. 3He inputs Atmosphere (δ3Heatm ≡ 0) Radioactive decay of 3H  3He
Produced in deep waters
Supplied to deep waters by BS and GSUW
Mantle source at spreading ridges
GSDW = 1.6 atoms cm-2
NSDW = 1.0 atoms cm-2
EBBW = 0.9 atoms cm-2

15. Outline Introduction Box model design Input functions
Box model simulations
Scenarios
Conclusions

16. Model simulation requirements
Salinity and potential temperature increasing in GSDW

17. Model simulation requirements
Concentrations of CFC-11, CFC-12 and 3H in GSDW remain low

18. Model simulation requirements
δ3He of GSDW rapidly increasing in 1990s
Volume reduction in GSDW as upper boundary of GSDW moves downward.

19. Model simulation, continued
Steady state, with 0.47 flux from GSUW to GSDW, before 1979 (steady-state fluxes derived by Bönisch and Schlosser, 1995).
Flux from GSUW to GSDW reduced to 0.1 Sv, ; volume reduced by 30%; upper boundary of GSDW descends to 2000m
: flux from GSUW to GSDW reduced to 0.03 Sv, while flux from EBDW to GSDW increases
Average GSUW flux to GSDW, ≈ 0.07
Fluxes,
Fluxes,
Fluxes,

20. Model simulation, ctd. Salinity Potential temperature EBDW EBBW EBBW
NSDW
EBDW
NSDW
GSDW
GSDW
1994: GSUW flux reduced,
EBDW flux increased (to GSDW)
1979: GSUW flux reduced

21. Model simulation, ctd.
Tritium
GSDW
EBDW
NSDW
EBBW

22. Model simulation, 3He GSDW NSDW EBDW EBBW δ3He δ3He 3Hetritiogenic

23. Model simulation, ctd. CFC-11 CFC-12 GSDW GSDW NSDW NSDW EBDW EBDW
EBBW
EBBW

24. Outline Introduction Box model design Input functions
Box model simulations
Scenarios
Conclusions

25. Scenario: no flux reduction after 1979
Much higher CFC-11 and tritium than observed
Warming and salinification trends not explained 3H
CFC-11

26. Scenario: fluxes constant after 1979
After 1979, flux from GSUW to GSDW reduced to 0.1 Sv
GSDW volume remains constant
Increased flux from EBDW to GSDW
Export to Atlantic from EBDW and NSDW reduced

27. Scenario: fluxes constant after 1979, ctd.
δ3He
salinity
3He/3H
age
Potential
temp.

28. Scenario: fluxes constant after 1979, ctd.3H
Predicted CFC-11 concentration is too high
Good match with helium, tritium and age data
Salinity and temperature increase in GSDW underestimated
CFC-11

29. Scenario: three years of rapid ventilation in late 1980’s
From , flux from GSUW to GSDW = 0.1 Sv, GSDW volume decreases
From , flux from GSUW to GSDW restored to 0.47 Sv.
After 1990, zero flux from GSUW to GSDW while flux from EBDW to GSDW increases.
Average ventilation of GSDW is ≈0.85 Sv between
volume reduced by 18%
Fluxes,
Fluxes,
Fluxes,

30. Scenario: high GSUW flux, 1987-1990, ctd.
δ3He
salinity
3He/3H
age
Potential
temp.

31. Scenario: high GSUW flux, 1987-1990, ctd.
Good fit for helium and tritium data
Predicted CFC-11 too high
Rates of increase for GSDW salinity and temperature match observations
Deep water formation rate in GS varies from year to year
CFC-11

32. Scenario: pre-1979 fluxes restored in 20053H
δ3He
salinity
CFC-11
3He/3H
age
potential
temp.
CFC and δ3He will remain sensitive to the renewal rate in the
Greenland Sea for the near future.

33. Outline Introduction Box model design Input functions
Box model simulations
Scenarios
Conclusions

34. Conclusions
CFC concentrations in GSDW remained constant or declined in the late 1990’s, while GSDW temperature and salinity evolved towards EBDW
Model reproduces the warming and salinification trends and low transient tracer concentrations in GSDW between 1980 and 2005
Average GSUW flux to GSDW between ≈ Sv
The rate of GSDW formation is variable from year to year during the period
Most uncertainty with respect to modeled tracer concentrations in Eurasian Basin Deep water and Eurasian Basin Bottom Water

35. Projected changes in freshwater fluxes: +0.05 Sv;
Loss of freshwater
(sea ice)
Increased glacial melting
Increased freshwater
inventory in GIN seas
Increased P – E
Increased river runoff
Decrease in salinity
in overflows
Freshening
Subpolar Gyre
Freshening in LS