Bogi Hansen, Hjálmar Hátún, Regin Kristiansen, Steffen M. Olsen and Svein Østerhus Iceland Scot- land Nordic Seas Faroes 0.8 Sv 3.8 Sv Greenland Østerhus.

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Presentation transcript:

Bogi Hansen, Hjálmar Hátún, Regin Kristiansen, Steffen M. Olsen and Svein Østerhus Iceland Scot- land Nordic Seas Faroes 0.8 Sv 3.8 Sv Greenland Østerhus et al., GRL 2005 Thermohaline forcing maintains the Iceland-Faroe inflow of heat and salt to the Arctic IF-inflow %

Didn’t we know that already ?

The Feedback Mechanism Greenland Scotland Ridge World Ocean Nordic Seas + Arctic Ocean Cooling Salt Overflow Entrainment NADW

The Feedback Mechanism implies: Greenland Scotland Ridge World Ocean Nordic Seas + Arctic Ocean Atlantic inflow Removal of water from the Nordic Seas maintains the Atlantic inflow through sea-level forcing Estuarine Thermoh. But !!

Maybe Sea-level forcing maintains the average Atlantic inflow Wind stress dominates the variations ?

The IF-inflow 4 CTD cruises a year since 1988 ADCPs since 1997

The Standard section through the IF-inflow Salinity Velocity (cm/s) ADCPs

Monthly and annually averaged Atlantic water transport of the IF-inflow Average: 3.5 Sv No trend

The flow changes character across the Ridge It is accelerated and becomes focused This requires a local (and very stable) force Not local wind stress PVDs at 225 m depth

Iceland Scot- land Faroes Transport Sea-level drop: SLHW - SLHE Monthly correlation: R = 0.63 Annual correlation: R = 0.87 Atlantic inflow and sea-level drop across the Ridge SLHW SLHE Bernoulli Geostrophy implies: ~ 0.2 Sv per cm +

Iceland-Faroe Atlantic inflow Atlantic Ocean Nordic Seas Atlantic inflow Iceland Faroe Ridge IFR-overflow FBC-overflow To Arctic Ocean To Denmark Str. Remote wind forcing could raise sea-level west of the Ridge R > 0 R < 0 West East Outflow from Nordic Seas tends to reduce sea-level east of the Ridge 8.5 Sv out implies lowering of Nordic Seas SLH by 30 cm/day

Correlation coefficient between monthly sea-level height and IF-inflow

Conclusions Sea-level forcing drives the flow across the Iceland-Faroe Ridge Processes west (upstream) of the Ridge do not dominate the forcing Water removal east (downstream) of the Ridge generates the average IF-inflow –and its variations

Thermohaline forcing dominates the outflow 70 %

IF-inflow and FBC-overflow FBC-overflow (Sv) IF-flow (Sv) Negative correlation

Coupling between IF-inflow and FBC-overflow U D R<0 R>0

Correlation coefficient between monthly sea-level height and IF-inflow -0.4

The equation of motion Sea-level forcing External forcing (wind)

T and S in the core of the IF-inflow