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