Kerstin Jochumsen 1 , Detlef Quadfasel 1 , Manuela Köllner 1,2 , and Stephen Dye 3
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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
description
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. - PowerPoint PPT Presentation
Transcript of Kerstin Jochumsen 1 , Detlef Quadfasel 1 , Manuela Köllner 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, Germany2 now at GEOMAR, Kiel, Germany
3 CEFAS, Lowestoft, UK
Motivation
Fischer et al., 2010
Denmark Strait Overflow Water (DSOW) forms the densest part of North Atlantic Deep Water (~6 Sv after entrainment)
Dickson et al., 2002
van Aken and de Jong, 2012
Open questions
from Vage et al. (2011), modified
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?
Is the influence of the East Greenland Spill Jet detectable in the downstream mooring
time series?
EG Spill Jet
Observations
Denmark Strait sill (NORTH) – DSOW entrainment region (CENTRAL) – DSOW at Ammassalik (SOUTH)
Mooring arrays
Mooring designs
Denmark Strait sill array (NORTH)
NORTH
Ammassalik array (SOUTH)
σθ=27.8
σθ=27.8
σθ=27.85
Array coherencePot. temperature fluctuations are similar within the mooring arrays
r>0.7
r>0.9
r=0.8
mean: 1.45°C ± 0.16°C
mean: 1.10°C ± 0.21°C
mean: -0.08°C ± 0.13°C
pot.
tem
pera
ture
[°C
]
NORTH
CENTRAL
SOUTH
Salinity fluctuations are small at DS sill and increase downstream
r>0.8
r=0.6
r>0.9
Array coherencesa
linity
mean: 34.895 ± 0.010
mean: 34.897 ± 0.008
mean: 34.900 ± 0.004 NORTH
CENTRAL
SOUTH
Velocity fluctuations are dependent on the plume position
r=0.4
r=-0.4
Array coherence
NORTH
SOUTH
Signal propagation
Pot. temperature signals are advected (mean speed: 45 cm/s), salinity and velocity signals are strongly modified by entrainment
r=0.8, 2d lag
r>0.710-14d lag
CENTRAL
NORTH
SOUTH
r>0.513-16d lag
r<0.3
r>0.68-12 d lag
r<0.416d lag
pot. temperature salinity
r<0.316d lag
velocity
CENTRAL
NORTH
SOUTH
NORTH
SOUTH
Deep Ammassalik (SOUTH)
measurements close to DS 5-7
(CENTRAL)
→ entrainment occurs mainly between DS sill and DS 5-7
(180 km downstream)
Mixing of Water Masses
Modified Atlantic Water(from CTD sections)
East Greenland Current Water(e.g. Rudels et
al., 2002)
DSOW at the sill
DSOW atAmmassalik
Mixing of Water Masses
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)
ConclusionsWill 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?
Is the influence of the East Greenland Spill Jet detectable in the downstream mooring time series?
Probably not, only if the signals are very pronounced.
The original overflow crossing the GSR, but also the Atlantic Water in the Irminger Sea,
as well as the EGC spill jet waters.
Yes, in low salinity signals.
Longterm perspectiveDSOW 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
The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299NACLIM http://www.naclim.eu
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
