Indirect estimate of fluxes between boundary current and deep basins in the Nordic Seas: heat and freshwater budgets Katrin Latarius 1 and Detlef Quadfasel 2 1 Alfred-Wegener-Institut Bremerhaven, Germany 2 Institut 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). Ocean Science meeting February 2014 Honolulu

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

Focus on the Nordic Seas 3

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

4 Extrem heat loss during winter

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

Interplay of boundary currents and gyres in the interior 4 Eddy exchange between boundary current and interior basins How important are the basins for the transformation from inflowing Atlantic Water to Overflow Water? i.e. how large is the heat/frehswater exchange between boundary current and interior basins? What kind of observations do we have to answer this question?

What kind of measurements are available to observe the transformation? 5 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

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

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

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

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

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

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

Heat and freshwater budgets 9 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 m: 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. 1:2 100:1

deep basins of the Nordic Seas ∆T=1.4K17% ∆S=0.03 7% although only 4% of total area from Atlantic water inflow (9°C, 35.33) to overflow (0.2°C, 34.9) ∆T=8.8 K ∆S=0.43 Contribution of the deep basins to the total water mass transformation 10

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

Conclusions 12 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

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The research leading to these results has received funding from the European Union 7th Framework Programme (FP ), under grant agreement n NACLIM