1. EGU meeting 8 April 2013 Vienna FBC Overflow Bogi Hansen HAV

2. AGU, 2003 image:AGU 2003 The densest overflow from the Nordic Seas has become warmer and more saline since 1995 Bogi Hansen, Karin M. H. Larsen, Hjálmar Hátún, Regin Kristiansen, Ebba Mortensen, Svein Østerhus, Detlef Quadfasel Greenland Iceland Shet- land Faroes FBC-overflow: 2 Sv entrained water: 2 Sv + Faroe Bank Channel Sill depth: 840 m With entrainment, the FBC-overflow feeds ~ 25% of NADW

3. FBC - overflow ADCP in flotation Monitored since November 1995 Dinner

4. Volume transport (monthly averaged “kinematic” overflow) Average: 2.15 Sv Change: 0.18 ± 0.15 Sv = 8% ± 7%

5. Potential temperature at OWSM OWSM Warming FBC sill: 840 m

6. Bottom temperature at sill 199619982000200220042006200820102012 -0.6 -0.5 -0.4 -0.3 0 0.5 1.0 1.5 2.0 2.5 Bottom temperature (°C) Volume transport (Sv) Bottom temperature Volume transport

7. Bottom temperature decreases with increasing volume transport Correlation coefficient: -0.49 Bernoulli aspiration Weak flow Strong flow

8. OWSM 800 m 1000 m Section N 800 m 900 m Bottom temperature 199619982000200220042006200820102012 -0.6 -0.5 -0.4 -0.3 FBC sill 840 m OWSM Section N FBC bottom temperature adjusted for transport variations

9. FBC bottom temperature has increased since ~ 2000 199619982000200220042006200820102012 -0.6 -0.5 -0.4 -0.3 0 0.5 1.0 1.5 2.0 2.5 Bottom temperature (°C) Volume transport (Sv) Uncertainty ~ 0.1ºC Δσ θ ≈ -0.004 kg/m 3

10. Salinity at fixed temperature at section S Salinity at -0.45ºC Salinity at 1ºC ΔS ≈ 0.005 Δσ θ ≈ +0.004 kg/m 3 Section S Δσ θ ≈ +0.025 kg/m 3

11. Faroe Bank Channel overflow Volume transport has not decreased probably, it has increased The overflow has become warmer, but also more saline The density has not decreased probably, it has increased

12. The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreements n.308299 NACLIM www.naclim.euwww.naclim.eu and n.212643 THOR www.eu-thor.euwww.eu-thor.eu