1 ICES/NAFO Symposium Santander May Seasonal to interannual variability of temperature and salinity in the Nordic Seas: heat and freshwater budgets Katrin Latarius Detlef Quadfasel ZMAW Institut für Meereskunde Hamburg Funding: Deutsche Forschungsgemeinschaft (SFB512) EU-MERSEA, EuroArgo, THOR

2 Background/Motivation Transformation on the way through the Arctic Mediterenean Nordic Seas: 1.5 x m 2, -50 W/m 2  Nordic Seas contribute ~25% Atlantic inflow 8 Sv, 12°C, 35.25, 26.8 kg/m 3 Overflow 6 Sv, 0.2°C 34.92, 28 kg/m 3 + near the surface 2 Sv polar water total transformation: ∆T: 12°C ∆S: 0.37

3 Argo float data - circulation Quasi-Eulerian mean circulation of the Nordic Seas ( dbar) Voet et al. ( 2010)

4 Argo float data - circulation Quasi-Eulerian mean circulation of the Nordic Seas ( dbar) Voet et al. ( 2010)

5 Argo float data – Profiles Greenland Sea Lofoten Basin Norwegian Basin Iceland Plateau total: 3000 profiles of T, S, and σ, m Argo-DK, Argo-Germany, Argo-Norway, MERSEA, SFB

ptemp Hydrography – Temperature time series Norwegian Basin Lofoten Basin Iceland Plateau Greenland Sea

sal Hydrography – Salinity time series Greenland Sea Iceland PlateauNorwegian Basin Lofoten Basin

8 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 residuum summer: only lateral exchange winter: lateral + vertical exchange Seasonal cycle of heat and freshwater fluxes, from 7 meteorological models annual mean: -53 ± 10 W/m2 22 ± 15 mm/mon Latarius & Quadfasel, 2010

9 Greenland Sea Gyre: heat is imported laterally ( m) 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 ± ± 10.2

10 Heat and freshwater budget – all basins Greenland Sea winter-MLD: max. 1400m lateral exchange m: heat: + 70 W/m 2 freshwater: - 35 mm/month Area: 1.0 x m 3 Iceland Plateau winter-MLD: max. 250m lateral exchange m: heat: + 22 W/m 2 freshwater: - 8 mm/month Area: 0.4 x m 3 Norwegian Basin winter-MLD: max. 350m lateral exchange m: heat: + 76 W/m 2 freshwater: - 31 mm/month Area: 1.7 x m 3 Lofoten Basin winter-MLD: max. 500m lateral exchange m: heat: W/m 2 freshwater: - 18 mm/month Area: 0.9 x m 3

11 Heat and freshwater budget – all basins Greenland Sea T: -0.33°C  2.6% S:  2.3% Iceland Plateau T: -0.04°C  0.3% S:  0.2% Norwegian Basin T: -0.53°C  4% S:  3.4% Lofoten Basin T: -0.35°C  2.8% S:  1% Contribution to the water mass transformation in direction to the overflow (50-600m) In: 12°C Out: 0°C  ∆T=12°C In: Out:  ∆S=0.37 ~ 10%

12 Heat and freshwater budget – all basins Greenland Sea T: -0.33°C  10% S:  17% Iceland Plateau T: -0.04°C  1% S:  1% Norwegian Basin T: -0.53°C  18% S:  25% Lofoten Basin T: -0.35°C  12% S:  7% Contribution to the water mass transformation in direction to the overflow (50-600m) In: 12°C Out: 0°C  ∆T=12°C In: Out:  ∆S=0.37 Nordic Seas: ~ 25/14% of total heat/freshwater transformation  ∆T=3°C ∆S=0.05 ~ 50% west ~ 15% east ~ 35%

13 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!

14 Thank you for your attention!

15 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