On the modifications of the Denmark Strait overflow plume during its descent into the North Atlantic
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Kerstin Jochumsen 1 , Detlef Quadfasel 1 , Manuela Köllner 1,2 , and Stephen Dye 3 PowerPoint PPT Presentation


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On the modifications of the Denmark Strait overflow plume during its descent into the North Atlantic. Kerstin Jochumsen 1 , Detlef Quadfasel 1 , Manuela Köllner 1,2 , and Stephen Dye 3 1 University of Hamburg, ZMAW, Germany 2 now at GEOMAR, Kiel, Germany 3 CEFAS, Lowestoft, UK.

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Kerstin Jochumsen 1 , Detlef Quadfasel 1 , Manuela Köllner 1,2 , and Stephen Dye 3

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Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

On the modifications of the Denmark Strait overflow plume during its descent into the North Atlantic

Kerstin Jochumsen1, Detlef Quadfasel1, Manuela Köllner1,2, and Stephen Dye3

1 University of Hamburg, ZMAW, Germany

2 now at GEOMAR, Kiel, Germany

3 CEFAS, Lowestoft, UK


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Motivation

Denmark Strait Overflow Water (DSOW) forms the densest part of North Atlantic Deep Water (~6 Sv after entrainment)

Dickson et al., 2002

Fischer et al., 2010

van Akenand de Jong, 2012


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Open questions

Will Arctic temperature/salinity variability be seen in downstream DSOW measurements?

Which water masses are responsible for the variability observed in the Deep Western Boundary Current?

EG Spill Jet

  • Is the influence of the East Greenland Spill Jet detectable in the downstream mooring time series?

from Vage et al. (2011), modified


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Observations

Mooring arrays

DenmarkStraitsill (NORTH) – DSOW entrainmentregion (CENTRAL) – DSOW atAmmassalik (SOUTH)


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Mooring designs

Denmark Strait sill array (NORTH)NORTH

σθ=27.8

σθ=27.85

σθ=27.8

Ammassalik array (SOUTH)


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Array coherence

Pot. temperature fluctuations are similar within the mooring arrays

NORTH

mean: -0.08°C ± 0.13°C

r=0.8

CENTRAL

pot. temperature [°C]

r>0.9

mean: 1.10°C ± 0.21°C

r>0.7

mean: 1.45°C ± 0.16°C

SOUTH


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Array coherence

Salinity fluctuations are small at DS sill and increase downstream

NORTH

mean: 34.900 ± 0.004

r=0.6

CENTRAL

r>0.8

salinity

mean: 34.897 ± 0.008

mean: 34.895 ± 0.010

r>0.9

SOUTH


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Array coherence

Velocity fluctuations are dependent on the plume position

NORTH

r=0.4

r=-0.4

SOUTH


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Signal propagation

pot. temperature

salinity

velocity

NORTH

NORTH

NORTH

r=0.8, 2d lag

r<0.3

CENTRAL

CENTRAL

r<0.4

16d lag

r<0.3

16d lag

r>0.7

10-14d lag

r>0.6

8-12 d lag

r>0.5

13-16d lag

SOUTH

SOUTH

SOUTH

Pot. temperature signals are advected (mean speed: 45 cm/s), salinity and velocity signals are strongly modified by entrainment


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Mixing of Water Masses

DeepAmmassalik (SOUTH) measurementscloseto DS 5-7(CENTRAL)

→ entrainmentoccursmainlybetweenDS silland DS 5-7 (180 km downstream)


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Mixing of Water Masses

Modified Atlantic Water

(from CTD sections)

East Greenland

CurrentWater

(e.g. Rudels et al., 2002)

DSOW at

Ammassalik

DSOW atthesill


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Conclusions

  • good correlation of temperature time series→ temp. signals are advected from the sill

  • low/no significant correlation in salinity and velocity

  • → entrainment processes strongly modify salinity/velocity

  • East Greenland current water is needed to obtain low salinities

  • entrainment is dominant between DS sill and DS 5-7 EGC spill jet plays a minor role for DSOW south of 64°Nintermittent spill events likely combine to long term effects

  • downstream DSOW properties do not necessarily reflect NordicSeas conditions (especially in salinity)


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Conclusions

Will Arctic temperature/salinity variability be seen in downstream DSOW measurements?

Probably not, only if the signals are very pronounced.

Which water masses are responsible for the variability observed in the Deep Western Boundary Current?

The original overflow crossing the GSR, but also the Atlantic Water in the Irminger Sea, as well as the EGC spill jet waters.

  • Is the influence of the East Greenland Spill Jet detectable in the downstream mooring time series?

Yes, in low salinity signals.


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

Longtermperspective

DSOW transports, updated from Jochumsen et al. (2012) and Dickson et al. (2007)

no trends in transports, warming from 1998 - 2006, since then t is rather stable


Kerstin jochumsen 1 detlef quadfasel 1 manuela k llner 1 2 and stephen dye 3

  • This work was supported by the Co-Operative Project ‘‘RACE - Regional Atlantic Circulation and Global Change’’ funded by the German Federal Ministry for Education and Research (BMBF), 03f0651a RACE

  • http://race.zmaw.de

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

NACLIM http://www.naclim.eu


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