http://www.smi.ac.uk/images/north-atlantic-surface-currents-sams/view

Bee Berx1, Bogi Hansen2, Svein Østerhus3, Karin Margaretha Larsen2, Toby Sherwin4 and Kerstin Jochumsen5

 1 Marine Scotland Science (b.berx@marlab.ac.uk); 2 Faroe Marine Research Institute; 3 University of Bergen; 4 Scottish Association for Marine Science; 5 Universität Hamburg

Is the Transport of Atlantic Water in the Faroe Shetland Channel changing? – A summary of 20 years of observations

Ocean Sci., 9, 639-654, 2013

Why are we interested in the Faroe Shetland Channel (FSC)?

NAW

MNAW

Atlantic Water

MEIW

NSAIW

Intermediate Water

NSDW

DeepWater

Circulation in the Faroe Shetland Channel

NAW

MNAW

Atlantic Water

Circulation in the Faroe Shetland Channel

Atlantic Water is defined as warmer than 5°C.

Observing Circulation in the FSC

Temperature and Salinity in the FSCon the FIM section

How to estimate Atlantic Water transport in the Faroe Shetland Channel?

The assumption of geostrophy [where large ocean currents are an equilibrium of the pressure gradient and Coriolis] allows us to convert sea level height measurements into

current speeds.

http://www.seos-project.eu/modules/oceancurrents/oceancurrents-

c06-s02-p01.html

SEOS Project

Regression of Atlantic Water velocities from the current meter against sea surface height allows estimation of altimetry-based AW velocity.

Average volume, relative heat and salt transports in the FSC

NE SW Net (Atl. Inflow)

Surface-to-bottom 3.5 Sv -3.1 Sv 0.4 Sv

Warmer than 5°C 3.5 Sv -0.8 Sv 2.7 Sv

Colder than 5°C 0.0 Sv -2.3 Sv -2.3 Sv

Relative Heat Transport 131 TW -24 TW 107 TW

Salt Transport 125x106 kg s-1 -27x106 kg s-1 98x106 kg s-11 Sv = 106 m3 s-1

Average volume, relative heat and salt transports in the FSC

NE SW Net (Atl. Inflow)

Surface-to-bottom 3.5 Sv -3.1 Sv 0.4 Sv

Warmer than 5°C 3.5 Sv -0.8 Sv 2.7 Sv

Colder than 5°C 0.0 Sv -2.3 Sv -2.3 Sv

Relative Heat Transport 131 TW -24 TW 107 TW

Salt Transport 125x106 kg s-1 -27x106 kg s-1 98x106 kg s-1

Net (Atl. Inflow)

Surface-to-bottom (OSSP) ~160

Warmer than 5°C (OSSP) ~1,100

Colder than 5°C (OSSP) ~940

Relative Energy Transport (Mars) ~100 million

Salt Transport (Gritter) ~9700

© All rights reserved by Thomas_Ashley (via Flickr)

1 OSSP = 1 Olympic Size Swimming Pool

1 standard Mars bar (58g)

DAF Gritter (CPD Engineering)

1 Sv = 106 m3 s-1

Transport of Atlantic water in the FSC

Jan-98 Jan-00 Jan-02 Jan-04 Jan-06 Jan-08 Jan-100

1

2

3

4

5

6

Vol

ume

Tra

nspo

rt (

Sv)

Altimetry

ADCP

Seasonal cycle in volume transport

Jan Mar May Jul Sep Nov0

1

2

3

4

5

6

Vol

ume

Tra

nspo

rt (

Sv)

Monthly Avg. ADCP-Tr.

Seas. Fit ADCPAvg. Alt.-Tr Std. Alt.TrSeas. Fit Alt.

Seasonal amplitude of Atlantic water transport in FSC ~ 0.7-0.9 Sv

This is ~ 25% of the average transport

Maximum transport in winter-time, lowest transport in summer.

Different amplitude based on calculation method

Transport of Atlantic Water in the FSC 1992-2012

Jan-92 Jan-94 Jan-96 Jan-98 Jan-00 Jan-02 Jan-04 Jan-06 Jan-08 Jan-100.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

Vol

ume

Tra

nspo

rt (

Sv)

No

long

term

tren

d !

Conclusions

• Combined temperature and salinity measurements with current meter and sea elevation observations to estimate transport of Atlantic water through the FSC.

• On average 2.7±0.5 Sv is transported into the Nordic Seas.• Although variable, the net volume transport shows consistent

seasonality with maximum Dec-Jan, and an amplitude of 0.7 Sv. • No significant long-term trend in volume transport between 1992

and 2011.• We have observed increases in temperature and salinity, and

may therefore expect trends in relative heat and salt transports (but difficult to verify statistically based on this time series).

• Currently studying whether less variable observations can be made in an area to the south-west of the FIM section

Ocean Sci., 9, 639-654, 2013

Thank you! For questions/collaborations, please email b.berx@marlab.ac.uk

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

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