The Faroe Current: T-S properties and volume, heat and salt transports

Karin Margretha H. LarsenBogi Hansen, Hjálmar Hátún,

Svein ØsterhusExtended Ellett Line Workshop, 27-28. Apr 2015

North Atlantic Gyres

SPG

STG

EEL

Faroes

Faroese Standard Sections

N

V E

S

The Faroe Current

Atlantic Water properties

Rockall Trough- From ICES IROC

Warming due to Subpolar Gyre changes(Hátún et al, 2005)

Modulation by air-sea heatflux variability (Larsen et al, 2012)

Atlantic Water properties

Increasing salinity due to Subpolar Gyre changes

Salinity variability due to changes in source water properties

Modifications in the Faroe area

TW, SW

TN, SN

Cooling/freshening

The salinity difference and Faroe Current volume transports

Low volume transports increase the residence time:- Increased amospheric influence- Increased admixture

S

Vol . tr

Atlantic water on monitoring section

ADCPs: 1997-2015

AtlanticArctic

Sea level difference across the flow

Satellite altimetry

Weekly averaged volume transport 1997-2013 based on in-situ observations

Hansen et al, 2010. Ocean Science

Combining altimetry and in-situ obs.

1. Velocity fieldusing long-term ADCP and CTD records to calibrate altimetry, we can generate daily estimates of the velocity field every day since 1st January 1993

2. Temperature and salinity field altimetry + seasonal variation + long-term Atlantic water temperature and salinityto generate daily estimates of the property fields

Monthly averaged volume transport of Atlantic water 1993 - 2013

Average volume transport of Atlantic water: 3.8 ± 0.5 Sv

Hansen et al, 2015. Submitted to OS

AW transport 1993 - 2013

Weak seasonal variationAmplitude < 10% of avg transport

± standard error

20 year trend: 9±8%

(95% confidence)

Annual mean

3-yearmean

Heat transport relative to 0°C

20 year trend: 18±8%

20 year trend: 130±30%

Salt transport relative to 34.93(≈ FBC-overflow salinity)

Conclusions• Variation of AW (T,S) is dominated the Subpolar Gyre

and modulated by source water variability and atmospheric heat loss variability

• Faroe Current volume, heat and salt transports towards the Arctic have increased in the last 20 years

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