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Ocean circulation in the Nordic Seas PowerPoint Presentation

Ocean circulation in the Nordic Seas

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Contents

- Results from Argo floats
- Combining hydrography and altimetry
- Variability in the western branch of the NwAC in the Svinøy secion

The bottom/deep circulation in the Nordic Seas

- Models of the deep circulation:
- The time-mean circulation is along f/H contours (Nøst and Isachsen, 2003; Eldevik et al., 2005)
- Wind forced fluctuations in circulation along f/H contours (e.g. Legutke, 1991; Isachsen et al., 2003; Eldevik et al., 2005)

Red vectors are observations

- However, few observations of the deep ocean circulation in the Nordic Seas, until some years ago when Argo floats were deployed

From Nøst and Isachsen (2003)

Argo floats locations (2002-2006)

- Drift at 1000-2000 m depths.
- Total: 35 floats
- IMR: 9 floats
- Univ. Hamburg: 26 floats
- About 2000 observations (June 2006)
- IMR: +2 floats (2006)

10 days

Deployment

June 2002 – April 2005

: first pass

: second pass

Topographic steering

3000

2000

3000

Bottom depth: contour interval is 500 m

Mork and Søiland (2006)

Deep currents from Argo floats

- The floats drift at: 1000, 1500 or 2000 m depth.
- Red vectors: speed larger than 10 cm/s
- Quadfasel et al. (2006)

Monthly means of speed from velocity along and across the isobaths

- Quadfasel et al. (2006)

”Mean” velocity

”Residual(eddy)” velocity

Monthly means of speed (bottom depth<3000 m) isobaths

- ”Mean” velocity

”Residual(eddy)” velocity

Quadfasel et al. (2006)

Spring isobaths

Winter

Seasonal anomalous bottom currents

(relative to annual mean)

Summer

Autumn

Calculated by

combining

altimetry and

hydrography

Mork and Skagseth (2005)

Spring isobaths

Comparing the changes in the circulation with the integrated wind stress curl over the area (within a closed H-contour)

Autumn

wind

change in speed

Jan

Mar

May

Sep

Nov

Mork and Skagseth (2005)

Mean velocity, April 2003-May/June 2005 isobaths

Measurement depth:

Red vector : 500 m

Blue vector: 1000 m

Black vector: 2000 m

The numbers indicate stability (in %) of the current, from 0 to 100.

Stability=average velocity/average speed

Volume transport through the Svinøy section isobaths

Combine altimetry and hydrography reference velocity (Challenor et al., 1996)

Western branch

Eastern branch

?

Vref

Sigma-theta in the Svinøy section

Atlantic water

Coastal water

Arctic water

Mork and Skagseth (in prep.)

Interannual volume transport of Atlantic water in the Svinøy section

Seasonal variation removed. One year moving averages.

Time series of the branches Svinøy section

Western branch coupled to wind forcing? Svinøy section

- Compare the transport with the averaged wind stress curl over the Norwegian Basin

Western branch coupled to wind forcing? Svinøy section

- Compare the transport with the averaged wind stress curl over the Norwegian Basin

Wind stress curl moved forward four months

Mork and Skagseth (in prep.)

Western branch coupled to wind forcing? Svinøy section

Wind stress curl moved forward four months

Black line is 5 years moving averages

Conclusion Svinøy section

- Deep currents are cyclonic and show strong topographic steering
- Annual speed of current along the isobaths: 1.5-4 cm/s with seasonal variation: 0-2 cm/s.
- Highest residual(eddy) current in the Lofoten Basin
- Transport estimates coupled to the wind stress curl over the Norwegian Basin.

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