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BUOYANT EDDIES ENTERING THE LABRADOR SEA OBSERVED WITH
GLIDERS, FLOATS AND ALTIMETRY*
By Hjálmar Hátún (1,2), Charles C. Eriksen (1), and Peter B. Rhines (1)
1) University of Washington, 2) Faroese Fisheries Laboratory
*JPO,vol. 37
Thanks to Jonathan Lilly
See also Williams, et al., 2008
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The spring (March-June) bloom in the NE Lab. Sea
April (2nd half)
Wu, Y. et al., 2008: Marine Ecology Progress Series, Vol. 355.
SeaWifsSix-year composite
(1998–2003)
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...Caused by a shallow mixed layerMLD
(m)(Wu, Y. et al., 2008)
Six-year composite (1998–2003)
SSS
...associated with low-salinity surface water
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Origin of the low-salinity water?
West Greenland Current
2. Off-shelf advection of low-salinity WGC water
Hypothesis in Wu et al., 2008:
1.Regional high precipitation rate
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Salinity (50m)
Synoptic hydrography (March-April, 1966)
Salinity (500m)
Temp. (500m)
Temp. (50m)
But It’s a deep hydrographic anomaly...
West Greenland Current Water
Irminger Current Water
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Origin of the low-salinity water?
1.Regional high precipitation rate
2. Off-shelf advection of low-salinity WGC water
2a. Due to a mean flow?2b. Due to eddies?
And what about interannual variability?
Unlikely
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Eddy activity
Eddy-kinetic energy (EKE)based on satellite altimetry(Lilly et al. 2003)
Seaglider 015 Seaglider 014
Seaglider
(Hatun, Rhines and Eriksen, 2008, JPO, Vol. 37)
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Sea surface temperature signature of eddies
19 March, 2005
Courtesy:Physical Oceanography Distributed
Active Archive Center (PO.DAAC)
Position of Seagliders
Eddies
(Hatun, Rhines and Eriksen, 2008)
sg014
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Salinity
Hydrographic cross-sectionsof an Irminger Ring
IW
WGCW
(Hatun, Rhines and Eriksen, 2008)
Temperature
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Velocity
Density and velocity cross-sections of an Irminger Ring
(Hatun, Rhines and Eriksen, 2008)
Density
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Strongest influence on the NE Lab. Sea
(Chanut et al., 2007 in JPO)
Simulated eddy tracks
The eddies advect much low-salinity water (and buoyancy) into the NE Labrador Sea!
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0
1
2
3
4
5
6
0 2 4 6 8 10 12 14
1998
1999
2000
2001
2002
2003
2004
(Courtesy: E. Head)
Month
Chl
orop
hyll
(mg/
m
)3
Next challenge: Interannual Variability- BiologyChlorophyll
5.64.71.83.83.84.83.2
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-60 -58 -56 -54 -52 -50 -48 -46
59
60
61
62
63
64
-0.05
-0.048
-0.046
-0.044
-0.042
-0.04
-0.038
-0.036
-0.034
-0.032
First SST EOF
AMSREdata
-62 -60 -58 -56 -54 -52 -50 -48 -46 -44
55
56
57
58
59
60
61
62
63
64
First SSH EOF
CLS (gridded)data
Note: All valuesare negative!
Larger variability
Less variability
Challenge: Interannual Variability- physics
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1992 1995 1997 2000 2002 2005 2007
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
Summer 2000
SSH time series
SS
H in
crea
sin
g
SST time series(AMSRE)
SS
T in
cre
asi
ng
Increasingchlorophyll
Challenge: Interannual Variability- Physics and Biology
Covariation between the bloom intensity and the physics (SSH and SST) the following summer
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Two messages
Persistent background stratification due to Irminger Rings
Similar inter-annual variability in biology and in physics