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ICES/NAFO Symposium Santander May 11 2011

Seasonal to interannual variability of temperature and salinityin the Nordic Seas:heat and freshwater budgets

Katrin LatariusDetlef QuadfaselZMAWInstitut für Meereskunde Hamburg

Funding:Deutsche Forschungsgemeinschaft (SFB512)EU-MERSEA, EuroArgo, THOR

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Background/Motivation

Transformation on the way through the Arctic Mediterenean

Nordic Seas: 1.5 x 1012m2, -50 W/m2

Nordic Seas contribute ~25%

Atlantic inflow8 Sv, 12°C, 35.25, 26.8 kg/m3

Overflow6 Sv, 0.2°C34.92, 28 kg/m3

+near the surface2 Sv polar water

total transformation:∆T: 12°C∆S: 0.37

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Argo float data - circulation

Quasi-Eulerian mean circulation of the Nordic Seas (1000-1500 dbar)

Voet et al. ( 2010)

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Argo float data - circulation

Quasi-Eulerian mean circulation of the Nordic Seas (1000-1500 dbar)

Voet et al. ( 2010)

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Argo float data – Profiles

Greenland Sea

Lofoten Basin

Norwegian Basin

Iceland Plateau

total: 3000 profiles of T, S, and σ, 0-2000m

Argo-DK, Argo-Germany, Argo-Norway, MERSEA, SFB-512

2001 2005 2011

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0

-2

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ptemp

Hydrography – Temperature time series

Norwegian Basin

Lofoten Basin

Iceland Plateau

Greenland Sea

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35.0

34.9

34.8

34.7

sal

Hydrography – Salinity time series

Greenland Sea

Iceland Plateau Norwegian Basin

Lofoten Basin

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Heat and freshwater budget

 

Concept

surrounding gyre

max. conv depth

The development of the heat and freshwater content in the ocean is derived from ARGO-float profile data

Lateral exchange and vertical convective mixing is estimated as the residuumsummer: only lateral exchangewinter: lateral + vertical exchange

Seasonal cycle of heat and freshwaterfluxes,from 7 meteorological models

annual mean:-53 ± 10 W/m2 22 ± 15 mm/mon

Latarius & Quadfasel, 2010

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Greenland Sea Gyre: heat is imported laterally (50-1500m) and exported to the atmosphere and in the upper 50m freshwater is imported from the atmosphere and

exported laterally

The surrounding of the gyre between 50 – 1500m looses heat and salt by exchange with the Greenland Sea Gyre

Heat and freshwater budget – Greenland Sea

 

Mean annual budgets

heat (W/m2) freshwater (mm/month)

22.4± 14.6

53.4± 10.2

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Heat and freshwater budget – all basins

Greenland Seawinter-MLD: max. 1400mlateral exchange 50-600m: heat: + 70 W/m2

freshwater: - 35 mm/monthArea: 1.0 x 1011 m3

Iceland Plateauwinter-MLD: max. 250mlateral exchange 50-600m: heat: + 22 W/m2

freshwater: - 8 mm/monthArea: 0.4 x 1011 m3

Norwegian Basinwinter-MLD: max. 350mlateral exchange 50-600m: heat: + 76 W/m2

freshwater: - 31 mm/monthArea: 1.7 x 1011 m3

Lofoten Basinwinter-MLD: max. 500mlateral exchange 50-600m: heat: + 101 W/m2

freshwater: - 18 mm/monthArea: 0.9 x 1011 m3

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Heat and freshwater budget – all basins

Greenland SeaT: -0.33°C 2.6%S: -0.0084 2.3%

Iceland PlateauT: -0.04°C 0.3%S: -0.0007 0.2%

Norwegian BasinT: -0.53°C 4%S: -0.0125 3.4%

Lofoten BasinT: -0.35°C 2.8%S: -0.0037 1%

Contribution to the water mass transformation in direction to the overflow (50-600m)

In: 12°C Out: 0°C ∆T=12°CIn: 35.25 Out: 34.89 ∆S=0.37

~ 10%

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Heat and freshwater budget – all basins

Greenland SeaT: -0.33°C 10%S: -0.0084 17%

Iceland PlateauT: -0.04°C 1%S: -0.0007 1%

Norwegian BasinT: -0.53°C 18%S: -0.0125 25%

Lofoten BasinT: -0.35°C 12%S: -0.0037 7%

Contribution to the water mass transformation in direction to the overflow (50-600m)

In: 12°C Out: 0°C ∆T=12°CIn: 35.25 Out: 34.89 ∆S=0.37

Nordic Seas:~ 25/14% of total heat/freshwatertransformation∆T=3°C∆S=0.05

~ 50%west ~ 15% east ~ 35%

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Conclusion

 

Greenland Sea, Norwegian Basin, Lofoten Basin (and the Iceland Plateau) of the Nordic Seas transform and redistribute the water masses at least down to 600m

residence time within the basins is long winter cooling forces deep vertical mixing

~ 50% of the water mass transformation of the Nordic Seas takes please in the basins (they account for only 25% of the total area)

contribution of the Nordic Seas to the total water mass transformation from Atlantic inflow to the overflow is only approx. 25%transformation in the eastern part is dominant

climate induced increase of freshwater in the surface layer of the western part will at most influence 15% of the total tranformation!

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Thank you for your attention!

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Dataset

Dataprocessing:

Receiving data from Argos, converting from hex to decimal and real-time quality check at Coriolis Data Centre(within 1 day after profile is measured)

Quality check by eye

Delayed mode quality control for S at ARGO standard: Objective mapping procedure to compare with recent and historical CTD data (Böhme, Send, 2005), correction if difference is larger than 0.01 psu.(every ½ to 1 year)

Using only profiles within f/h contour of GS gyre

Computing monthly mean values of all floats in the gyre

Deleting extreme values

2 from 8 floats have been corrected because of distinct offset/trend in S

Reduction from 915 to 546 profiles