1. 1) University of Washington, 2) Faroese Fisheries Laboratory
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
Thanks to Jonathan Lilly 
See also Williams, et al., 2008
*JPO,vol. 37

2. The spring (March-June) bloom in the NE Lab. Sea
April
(2nd half)
SeaWifs
Six-year composite
(1998–2003)
Wu, Y. et al., 2008:
Marine Ecology Progress Series, Vol. 355.

3. ...Caused by a shallow mixed layer
MLD
(m)
(Wu, Y. et al., 2008)
Six-year composite
(1998–2003)
SSS
...associated with low-salinity surface water

4. Origin of the low-salinity water?
Hypothesis in Wu et al., 2008:
Regional high
precipitation rate
West Greenland Current
2. Off-shelf advection of
low-salinity WGC water

5. But It’s a deep hydrographic anomaly...
Synoptic hydrography (March-April, 1966)
Salinity
(50m)
Temp.
(50m)
West Greenland Current Water
Salinity
(500m)
Temp.
(500m)
Irminger Current Water

6. Origin of the low-salinity water?
Regional high precipitation rate
Unlikely
2. Off-shelf advection of low-salinity WGC water
2a. Due to a mean flow?
2b. Due to eddies?
And what about interannual variability?

7. Eddy activity Eddy-kinetic energy (EKE) based on satellite altimetry
Seaglider 014
Eddy-kinetic energy (EKE)
based on satellite altimetry
(Lilly et al. 2003)
Seaglider 015
Seaglider
The eddy kinetic energy was mapped from altimetry sea surface height data by Lilly et al It shows as spreading of EKE from the generation region, but mainly confined to the northern recirculation gyre.
(Hatun, Rhines and Eriksen, 2008, JPO, Vol. 37)

8. Sea surface height signature of eddies
(courtesy:
SSALTO/DUACS)
16 February, 2005
Back to the LS. The gridded SSH maps from many satellites are useful for qualitatively illustrate individual eddies. The anticyclonic eddies are associated with a bump in the sea surface topography on the order of 20 cm, here shown with reddish colors. Individual eddies are numbered and the trajectory of eddies is shown with the black dashed arrow and Seaglider dives are shown with white dots. I will now show a sequence of the maps from 16. feb 2005 to late March. This in order to illustrate the encounters between Seagliders and eddies. Extracting ssh data from the path shown with the white arrow and plotting as a (space-time) howmoller diagram
(Hatun, Rhines and Eriksen, 2008)

9. Sea surface temperature signature of eddies
19 March, 2005
Eddies
Position of
Seagliders
sg014
During March 19, SG015 was within eddy 2 and SG014 was within eddy 3. A SST image from satellite radiometry clearly reveals the cold (and fresh) blobs of water above the eddies, and it shows that this water originates from the Greenland shelf. I will now look at eddy 3 in detail…
Courtesy:
Physical Oceanography Distributed
Active Archive Center (PO.DAAC)
(Hatun, Rhines and Eriksen, 2008)

10. Hydrographic cross-sections of an Irminger Ring
Temperature
Salinity IW
WGCW
…maps of the eddy properties. This shows one radial cross-section of potential temperature, (depth and radius) and the vertical lines show Glider dives (peika a core). The presence of a warm IW core and a cold WGCW top is clear. The salinity section show a saline deep core and a fresh hat. This is the first in situ proof that these eddies have a cold and fresh top.
(Hatun, Rhines and Eriksen, 2008)

11. Density and velocity cross-sections of an Irminger Ring
From temperature and salinity, we can calculate the potential density, which reveals the bowl shape of the eddy, with lighter water on top. And from the direct current velocity observations we find the total velocity field in the eddy. Very large current velocities are found at about 25 km from the center, especially on the surface.
(Hatun, Rhines and Eriksen, 2008)

12. Strongest influence on the NE Lab. Sea
Simulated
eddy tracks
(Chanut et al., 2007 in JPO)
The eddies advect much low-salinity water
(and buoyancy) into the NE Labrador Sea!

13. Interannual Variability
Next challenge:
Interannual Variability
- Biology
Chlorophyll
(Courtesy: E. Head)
Month
Chlorophyll (mg/m ) 3
5.6
4.7
1.8
3.8
4.8
3.2

14. Interannual Variability
Challenge:
Interannual Variability
- physics
Note: All values
are negative!
First SST EOF
First SSH EOF
CLS (gridded)
data
AMSRE
data
Less variability
Larger variability

15. Interannual Variability
- Physics and Biology
Challenge:
Covariation between the bloom intensity and
the physics (SSH and SST) the following summer
SST time series
(AMSRE)
SST increasing
SSH time series
SSH increasing
Increasing
chlorophyll
Summer 2000

16. Two messages Persistent background stratification
due to Irminger Rings
Similar inter-annual variability
in biology and in physics