EGU meeting 8 April 2013 Vienna FBC Overflow Bogi Hansen HAV

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

FBC - overflow ADCP in flotation Monitored since November 1995 Dinner

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

Potential temperature at OWSM OWSM Warming FBC sill: 840 m

Bottom temperature at sill Bottom temperature (°C) Volume transport (Sv) Bottom temperature Volume transport

Bottom temperature decreases with increasing volume transport Correlation coefficient: Bernoulli aspiration Weak flow Strong flow

OWSM 800 m 1000 m Section N 800 m 900 m Bottom temperature FBC sill 840 m OWSM Section N FBC bottom temperature adjusted for transport variations

FBC bottom temperature has increased since ~ Bottom temperature (°C) Volume transport (Sv) Uncertainty ~ 0.1ºC Δσ θ ≈ kg/m 3

Salinity at fixed temperature at section S Salinity at -0.45ºC Salinity at 1ºC ΔS ≈ Δσ θ ≈ kg/m 3 Section S Δσ θ ≈ kg/m 3

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

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