Indirect estimate of fluxes between boundary current and deep basins in the Nordic Seas:

1. Ocean Science meeting February 2014 Honolulu Indirect estimate of fluxes between boundary current and deep basins in the Nordic Seas: heat and freshwater budgets Katrin Latarius1and Detlef Quadfasel2 1Alfred-Wegener-Institut Bremerhaven, Germany 2Institut für Meereskunde, University Hamburg, Germany Contributions from: Jan Backhaus, Bert Rudels, Johannes Karstensen, Bogi Hansen, Manuela Köllner, Antje Müller-Michaelis, Kerstin Jochumsen, Gereon Budéus This work is financed by national funding from the DFG (SFB 512 E2) and BMBF (NA) and European funding (MERSEA, THOR, NACLIM).

2. Circulation and ice coverage Sea Ice coverage in the Arctic Mediterranean blue-max, red-min Rudels et al., 2012 McCartney et al., 1997 2

3. Focus on the Nordic Seas 3

4. Interplay of boundary currents and gyres in the interior GS LB IP NB 4

5. Interplay of boundary currents and gyres in the interior Extrem heat loss during winter 4

6. Interplay of boundary currents and gyres in the interior Induces vertical mixing 4

7. Interplay of boundary currents and gyres in the interior Eddy exchange between boundary current and interior basins HowimportantarethebasinsforthetransformationfrominflowingAtlanticWaterto Overflow Water? i.e. how large istheheat/frehswaterexchangebetweenboundarycurrentandinteriorbasins? Whatkindofobservations do wehavetoanswerthisquestion? 4

8. What kind of measurements are available to observe the transformation? Inflow of Atlantic Water ~ 9 °C, 35.33, 8 Sv Hansen et al., 2010, Berx et al., 2012 Overflow ~ 0.2°C, 34.9, 6 Sv Hansen & Østerhus, 2007; Jochumsen et al., 2012 5

9. What kind of measurements are available to observe the transformation? CTD measurements NISE data set Summer bias 5

10. What kind of measurements are available to observe the transformation? Underway-CTD survey summer 2012 Polarfront 5

11. What kind of measurements are available to observe the transformation? Since 2001 Argo float measurements in the Nordic Seas 5

12. The dataset Argo-Float-Profiles 2001-2012 total: 6000 (4000) mean: 3-4 floats per basin and month Greenland Sea Lofoten Basin Icelandic Plateau Norwegian Basin Measurements are concentrated on the deep basins of the Nordic Seas 2001 2003 2005 2007 2009 2011 6

13. Large-scale hydrography - temperature LB GS Θ Θ Arctic domain Atlantic domain IP NB °C temperature time series 7

14. Heat and freshwater budgets - concept the seasonal cycle of heat and freshwater fluxes is given by NCEP with corrections according to Renfrew et al. (2002) the development of the heat and freshwater content in the basins is determined from the float data (mean annual cycle) residuum: lateral exchange and vertical mixing lateral exchange – contribution to the water mass transformation with a number of assumptions lateral exchange and vertical mixing are separeted from each other 8

15. Heat and freshwater budgets 100:1 1:2 annual heat budget [W/m²] annual freshwater budget [mm/month] GS Heat loss to the atmosphere introduces the destabilization of the water column and thus vertical mixing and redistribution of properties in the water column. Lateral exchange 50-800m: contribution of the basins to the water mass transformation from Atlantic water into overflow water. This contribution is understimated when taken only fluxes between ocean and atmosphere into account. 9

16. Contribution of the deep basins to the total water mass transformation from Atlantic water inflow (9°C, 35.33) to overflow (0.2°C, 34.9) ∆T=8.8 K ∆S=0.43 deepbasinsofthe Nordic Seas ∆T=1.4 K 17% ∆S=0.03 7% althoughonly 4% of total area 10

17. Importance of the individual basins Greenland Sea ∆ T:-0.45°C -> 31% ∆ S: -0.015 -> 49% Lofoten Basin ∆ T: - 0.42°C -> 29% ∆ S: -0.004 -> 12% Icelandic-Plateau ∆ T: -0.07°C -> 5% ∆ S: +0.002 -> 1% Norwegian Basin ∆ T: -0.5°C -> 35% ∆ S: -0.012 -> 39% ∆ T: 36% ∆ S: 49% ∆ T: 64% ∆ S: 51% west: important for salinity characteristic east: for densification 11

18. Conclusions From heat and freshwater budgets for the deep basins of the Nordic Seas the lateral exchange between basins and boundary current is estimated, i.e. the contribution of the basins to the water mass transformation The basins contribute 17% (temperature) and 7% (salinity) to the total transformation in the Arctic Mediterranean although they account for only 4% of the total area More than 50% of the transformation takes place in the eastern Nordic Seas Additional input of freshwater at first reaches the western Nordic Seas and thus influences less than half of the transformation Transformation is underestimated when taking only atmospheric fluxes into account Heat loss to the atmosphere introduces the destabilization of the water column in the basins 12

19. Thank you for your attention!

20. The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 NACLIM www.naclim.eu