Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences...
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![Page 1: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/1.jpg)
Deep water formation and exchange rates
in the Greenland and Norwegian Seas in the 1990s:
inferences from box model calculations
Abigail SpielerOral Examination Presentation
March 28, 2005
![Page 2: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/2.jpg)
Outline
• Introduction• Box model design• Input functions• Box model
simulations• Scenarios• Conclusions
![Page 3: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/3.jpg)
Norwegian S
ea
Greenland Sea
Eurasian Basin
Mid-Atlantic Ridge
Barents Sea
Kara Sea
Canadian Basin
Nan
sen
Bas
in
Amun
dsen
Bas
in
Fram Strait
(2600m)
Lom
onos
ov R
idge
(180
0m)
![Page 4: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/4.jpg)
Arctic Ocean-Nordic Seas Thermohaline
circulation
![Page 5: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/5.jpg)
Vertical structure of the Greenland Sea gyre
![Page 6: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/6.jpg)
Outline
• Introduction• Box model design• Input functions• Box model simulations• Scenarios• Conclusions
![Page 7: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/7.jpg)
Model Design
![Page 8: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/8.jpg)
Model design, ctd.
qvolume
Jc
dt
dc
i
jij
j
i
• Water masses are represented by homogeneous boxes
• Tracers conserved in deep water boxes• Surface water boxes represent boundary conditions of
model• 1940-1980: assume steady state (Bönisch and
Schlosser, 1995) and volume conservation• Integrate using forward differences in time
ci = concentration in box i
Jji= volumetric flux from box j to box i
q = source/sink in box, e.g. radioactive decay
![Page 9: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/9.jpg)
Outline
• Introduction• Box model design• Input functions• Box model simulations• Scenarios• Conclusions
![Page 10: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/10.jpg)
Tritium input• Natural 3H concentration in surface ocean ≈ 0.2 TU. Bomb
peak in mid-1960s; half life = 12.43 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
![Page 11: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/11.jpg)
Tritium input, ctd.
• The two components of GSUW are Greenland Sea Surface Water (GSSW) and Upper Arctic Intermediate Water
• GSUW = 0.82*GSSW + 0.12*NSSW (lagged by 5 years)
Greenland Sea Upper Water
![Page 12: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/12.jpg)
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) +0.996*NSSW (3 year lag)
• 15% reduction of 3H in Atlantic-derived component due to radioactive decay.
Barents Sea surface water
![Page 13: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/13.jpg)
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.
CFC-12
CFC-11
Northern hemisphere atmospheric CFC-11 and CFC-12
CFC-11 in surface boxes
![Page 14: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/14.jpg)
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
![Page 15: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/15.jpg)
Outline
• Introduction• Box model design• Input functions• Box model simulations• Scenarios• Conclusions
![Page 16: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/16.jpg)
Model simulation requirements
• Salinity and potential temperature increasing in GSDW
Salinity of Greenland Sea Deep Water (below 2000m)
34.895
34.9
34.905
34.91
34.915
1990 1992 1994 1996 1998 2000 2002 2004
year
salinity
Potential temperature of Greenland Sea Deep Water (below 2000m)
-1.2
-1.1
-1
-0.9
-0.8
1990 1992 1994 1996 1998 2000 2002 2004
year
Cel
sius
![Page 17: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/17.jpg)
Model simulation requirements• Concentrations of CFC-11, CFC-12 and 3H
in GSDW remain low
![Page 18: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/18.jpg)
Model simulation requirements• δ3He of GSDW rapidly increasing in 1990s• Volume reduction in GSDW as upper
boundary of GSDW moves downward.
![Page 19: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/19.jpg)
Fluxes, 1994-2005
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, 1979-1994; volume reduced by 30%; upper boundary of GSDW descends to 2000m
• 1994-2005: flux from GSUW to GSDW reduced to 0.03 Sv, while flux from EBDW to GSDW increases
• Average GSUW flux to GSDW, 1979-2005 ≈ 0.07Fluxes, 1979-1994Fluxes, 1940-1979
![Page 20: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/20.jpg)
1979: GSUW flux reduced
1994: GSUW flux reduced,EBDW flux increased (to GSDW)
Salinity Potential temperature
EBBW EBBW
EBDW
EBDW
NSDW
NSDW
GSDWGSDW
Model simulation, ctd.
![Page 21: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/21.jpg)
Model simulation, ctd.
GSDW
NSDW
EBDW
EBBW
Tritium
![Page 22: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/22.jpg)
Model simulation, 3He
GSDW NSDW
EBDW EBBW
δ3He
3Hetritiogenic
δ3He
3Hetritiogenic
δ3He
3Hetritiogenic
δ3He
3Hetritiogenic
![Page 23: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/23.jpg)
Model simulation, ctd.
CFC-11
CFC-12
GSDW
GSDW
NSDW NSDW
EBDWEBDW
EBBW EBBW
![Page 24: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/24.jpg)
Outline
• Introduction• Box model design• Input functions• Box model simulations• Scenarios• Conclusions
![Page 25: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/25.jpg)
Scenario: no flux reduction after 1979
• Much higher CFC-11 and tritium than observed
• Warming and salinification trends not explained
3H
CFC-11
![Page 26: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/26.jpg)
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
![Page 27: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/27.jpg)
Scenario: fluxes constant after 1979, ctd.
δ3He
3He/3Hage
Potentialtemp.
salinity
![Page 28: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/28.jpg)
Scenario: fluxes constant after 1979, ctd.
• Predicted CFC-11 concentration is too high
• Good match with helium, tritium and age data
• Salinity and temperature increase in GSDW underestimated
3H
CFC-11
![Page 29: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/29.jpg)
Scenario: three years of rapid ventilation in late 1980’s
• From 1980-1987, flux from GSUW to GSDW = 0.1 Sv, GSDW volume decreases
• From 1987-1990, 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 1979-2005– volume reduced by 18%Fluxes, 1990-2020Fluxes, 1987-1990Fluxes, 1979-1987
![Page 30: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/30.jpg)
Scenario: high GSUW flux, 1987-1990, ctd.
δ3He
3He/3Hage
Potentialtemp.
salinity
![Page 31: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/31.jpg)
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
3H
CFC-11
![Page 32: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/32.jpg)
Scenario: pre-1979 fluxes restored in 2005
CFC and δ3He will remain sensitive to the renewal rate in the Greenland Sea for the near future.
δ3He3H salinity
potential
temp.
3He/3Hage
CFC-11
![Page 33: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/33.jpg)
Outline
• Introduction• Box model design• Input functions• Box model simulations• Scenarios• Conclusions
![Page 34: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/34.jpg)
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 1979-2005 ≈ 0.07-0.08 Sv
• The rate of GSDW formation is variable from year to year during the period 1980-2002
• Most uncertainty with respect to modeled tracer concentrations in Eurasian Basin Deep water and Eurasian Basin Bottom Water
![Page 35: Deep water formation and exchange rates in the Greenland and Norwegian Seas in the 1990s: inferences from box model calculations Abigail Spieler Oral Examination.](https://reader036.fdocuments.net/reader036/viewer/2022062517/56649e755503460f94b77240/html5/thumbnails/35.jpg)
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
FresheningSubpolar Gyre
Freshening in LS