Presentation on theme: "Abigail Spieler Oral Examination Presentation March 28, 2005"— Presentation transcript:
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 calculationsAbigail SpielerOral Examination PresentationMarch 28, 2005
2 Outline Introduction Box model design Input functions Box model simulationsScenariosConclusions
8 Model design, ctd. Water masses are represented by homogeneous boxes ci = concentration in box iJji= volumetric flux from box j to box iq = source/sink in box, e.g. radioactive decayWater masses are represented by homogeneous boxesTracers conserved in deep water boxesSurface water boxes represent boundary conditions of model: assume steady state (Bönisch and Schlosser, 1995) and volume conservationIntegrate using forward differences in time
9 Outline Introduction Box model design Input functions Box model simulationsScenariosConclusions
10 Tritium inputNatural 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 watersFor Norwegian and Greenland Sea surface waters, scale D-R curve to observations; exponential decay after 1974North 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 WaterGSUW = 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-12CFC-12CFC-11CFC-11 in surface boxes
14 3He inputs Atmosphere (δ3Heatm ≡ 0) Radioactive decay of 3H 3He Produced in deep watersSupplied to deep waters by BS and GSUWMantle source at spreading ridgesGSDW = 1.6 atoms cm-2NSDW = 1.0 atoms cm-2EBBW = 0.9 atoms cm-2
15 Outline Introduction Box model design Input functions Box model simulationsScenariosConclusions
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 1990sVolume 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 increasesAverage GSUW flux to GSDW, ≈ 0.07Fluxes,Fluxes,Fluxes,
24 Outline Introduction Box model design Input functions Box model simulationsScenariosConclusions
25 Scenario: no flux reduction after 1979 Much higher CFC-11 and tritium than observedWarming and salinification trends not explained3HCFC-11
26 Scenario: fluxes constant after 1979 After 1979, flux from GSUW to GSDW reduced to 0.1 SvGSDW volume remains constantIncreased flux from EBDW to GSDWExport to Atlantic from EBDW and NSDW reduced
27 Scenario: fluxes constant after 1979, ctd. δ3Hesalinity3He/3HagePotentialtemp.
28 Scenario: fluxes constant after 1979, ctd. 3HPredicted CFC-11 concentration is too highGood match with helium, tritium and age dataSalinity and temperature increase in GSDW underestimatedCFC-11
29 Scenario: three years of rapid ventilation in late 1980’s From , flux from GSUW to GSDW = 0.1 Sv, GSDW volume decreasesFrom , 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 betweenvolume reduced by 18%Fluxes,Fluxes,Fluxes,
30 Scenario: high GSUW flux, 1987-1990, ctd. δ3Hesalinity3He/3HagePotentialtemp.
31 Scenario: high GSUW flux, 1987-1990, ctd. Good fit for helium and tritium dataPredicted CFC-11 too highRates of increase for GSDW salinity and temperature match observationsDeep water formation rate in GS varies from year to yearCFC-11
32 Scenario: pre-1979 fluxes restored in 2005 3Hδ3HesalinityCFC-113He/3Hagepotentialtemp.CFC and δ3He will remain sensitive to the renewal rate in theGreenland Sea for the near future.
33 Outline Introduction Box model design Input functions Box model simulationsScenariosConclusions
34 ConclusionsCFC concentrations in GSDW remained constant or declined in the late 1990’s, while GSDW temperature and salinity evolved towards EBDWModel reproduces the warming and salinification trends and low transient tracer concentrations in GSDW between 1980 and 2005Average GSUW flux to GSDW between ≈ SvThe rate of GSDW formation is variable from year to year during the periodMost 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 meltingIncreased freshwaterinventory in GIN seasIncreased P – EIncreased river runoffDecrease in salinityin overflowsFresheningSubpolar GyreFreshening in LS