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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
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)
...Caused by a shallow mixed layerMLD
(m)(Wu, Y. et al., 2008)
Six-year composite (1998–2003)
SSS
...associated with low-salinity surface water
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
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
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
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)
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
Salinity
Hydrographic cross-sectionsof an Irminger Ring
IW
WGCW
(Hatun, Rhines and Eriksen, 2008)
Temperature
Velocity
Density and velocity cross-sections of an Irminger Ring
(Hatun, Rhines and Eriksen, 2008)
Density
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!
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
-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
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
Two messages
Persistent background stratification due to Irminger Rings
Similar inter-annual variability in biology and in physics