Ocean circulation in the nordic seas
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Ocean circulation in the Nordic Seas. Kjell Arne Mork IMR/BCCR. NOClim, Geilo 4/9-06. 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.

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Ocean circulation in the Nordic Seas

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Ocean circulation in the nordic seas

Ocean circulation in the Nordic Seas

Kjell Arne Mork

IMR/BCCR

NOClim, Geilo 4/9-06


Contents

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

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

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

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

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

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

Monthly means of speed (bottom depth<3000 m)

  • ”Mean” velocity

”Residual(eddy)” velocity

Quadfasel et al. (2006)


Ocean circulation in the nordic seas

Spring

Winter

Seasonal anomalous bottom currents

(relative to annual mean)

Summer

Autumn

Calculated by

combining

altimetry and

hydrography

Mork and Skagseth (2005)


Ocean circulation in the nordic seas

Spring

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

Mean velocity, April 2003-May/June 2005

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 svin y section

Volume transport through the Svinøy section

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.)


Method

Method

?

Altimeter data (SSH) in the section

Mork and Skagseth (in prep.)


Interannual volume transport of atlantic water in the svin y section

Interannual volume transport of Atlantic water in the Svinøy section

Seasonal variation removed. One year moving averages.


Time series of the branches

Time series of the branches


Western branch coupled to wind forcing

Western branch coupled to wind forcing?

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


Western branch coupled to wind forcing1

Western branch coupled to wind forcing?

  • 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 forcing2

Western branch coupled to wind forcing?

Wind stress curl moved forward four months

Black line is 5 years moving averages


Conclusion

Conclusion

  • 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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