NIOZ is part of the Netherlands Organisation for Scientific Research (NWO)

Koninklijk Nederlands Instituut voor ZeeonderzoekRoyal Netherlands Institute for Sea Research

Variability of Denmark Strait Overflow Water

Hendrik M. van Aken & M. Femke de Jong

THOR meeting, November 2009, Paris

45 43 41 39 37 35 33 3154

55

56

57

58

59

60

61

62

Irminger Sea

LOCO2 LOCO3

34.95

34.975

42 40 38 36 34 32 30

Longitude (W)

3000

2500

2000

1500

1000

500

02 3

3.542 40 38 36 34 32 30

Longitude (W)

3000

2500

2000

1500

1000

500

0

Pre

ssur

e (d

bar)

Q S

NEADW

2009 survey AR7E

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010Year

0.7

0.8

0.9

1.0

1.1

1.2

1.3

Pot

entia

l Tem

pera

ture

(o C

)

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010Year

34.9

34.9

34.9

34.9

34.9

34.9

34.9

Sal

inity

(P

SS

-78)

D SO W ( m inim um )

Time series from repeat surveys AR7E

34.82 34.84 34.86 34.88 34.90 34.92 34.94 34.96Salin ity (PSS-78)

0.5

1.0

1.5

2.0

2.5

3.0

Pot

entia

l Tem

pera

ture

(oC

)

AR 7E surveys

LO C O -2

LO C O -3

M in im umtem peratures

L inear fitm in. tem p.

41.40

41.45

41.50

41.55

41.60

41.65

41.7041.75

D SO W S

D SO W F

The DSOW in different years lies near isopycnal,

41.67 (±0.02) kg/m3, but with varying -S

combinations. Different DSOW sources?? Two main contrasts!!

minima since 1991

34.82 34.84 34.86 34.88 34.90 34.92 34.94 34.96Salin ity (PSS-78)

0.5

1.0

1.5

2.0

2.5

3.0

Pot

entia

l Tem

pera

ture

(o C

)

AR 7E surveys

LO C O -2

LO C O -3

M in im umtem peratures

L inear fitm in. tem p.

41.40

41.45

41.50

41.55

41.60

41.65

41.7041.75

D SO W S

D SO W F

N EAD W

All near-bottom observations since 1991, between the ~2500 m isobaths. Transition from

DSOW to NEADW.

1/1 /04 1/1 /05 1/1 /06 1/1 /07 1/1 /08 1/1 /09D ate

34.84

34.86

34.88

34.90

Sal

inity

(P

SS

-78)

41.58

41.60

41.62

41.64

41.66

41.68

41.70

3 (kg/m

3)

LOCO-2

The LOCO-2 mooring

Temporal variation in DSOWs-DSOWf contrast

1/1 /04 1/1 /05 1/1 /06 1/1 /07 1/1 /08 1/1 /09D ate

34.84

34.86

34.88

34.90

Sal

inity

(P

SS

-78)

41.58

41.60

41.62

41.64

41.66

41.68

41.70

3 (kg/m

3)

LOCO-2

The LOCO-2 mooring

Temporal variation in DSOW density

The LOCO-2 mooring

Temporal variation in DSOW density

1/1 /04 1/1 /05 1/1 /06 1/1 /07 1/1 /08 1/1 /09D ate

34.84

34.86

34.88

34.90

Sal

inity

(P

SS

-78)

41.58

41.60

41.62

41.64

41.66

41.68

41.70

3 (kg/m

3)

LOCO-2

Annual cycle as the dominant periodicity in density??

34.82 34.84 34.86 34.88 34.90 34.92 34.94 34.96Salin ity (PSS-78)

0.5

1.0

1.5

2.0

2.5

3.0

Pot

entia

l Tem

pera

ture

(o C

)

AR 7E surveys

LO C O -2

LO C O -3

M in im umtem peratures

L inear fitm in. tem p.

41.40

41.45

41.50

41.55

41.60

41.65

41.7041.75

D SO W S

D SO W F

N EAD W

5 years of high-frequency LOCO-2 observations

also show the DSOWs-DSOWf contrast.

34.82 34.84 34.86 34.88 34.90 34.92 34.94 34.96Salin ity (PSS-78)

0.5

1.0

1.5

2.0

2.5

3.0

Pot

entia

l Tem

pera

ture

(o C

)

AR 7E surveys

LO C O -2

LO C O -3

M in im umtem peratures

L inear fitm in. tem p.

41.40

41.45

41.50

41.55

41.60

41.65

41.7041.75

D SO W S

D SO W F

N EAD W

LOCO-3 shows the connecting water mass

between DSOWs/f and the NEADW, with salinity

bimodality.

1/1 /04 1/1 /05 1/1 /06 1/1 /07 1/1 /08 1/1 /09D ate

34.84

34.86

34.88

34.90

Sal

inity

(P

SS

-78)

LOC

O-3

DS

OW

Mode

D SO W S

D SO W F

N o LO C O -3data

LOCO-3 follows the DSOWs/f signal of LOCO-2 with a delay of

~1.5 month

1/1 /04 1/1 /05 1/1 /06 1/1/07 1/1/08 1/1/09D ate

41.45

41.50

41.55

41.60

41.65

41.70

3 (

kg/m

3 )

N o LO C O -3data

LO CO -3

LO CO -2

But no apparent relation between the density variability at LOCO-2 and LOCO-3

LOCO-2: annual cycle

LOCO-3: higher-frequency sloshing in canyon in Reykjanes Ridge?

1/1 /04 1/1 /05 1/1 /06 1/1/07 1/1/08 1/1/09D ate

41.45

41.50

41.55

41.60

41.65

41.70

3 (

kg/m

3 )

N o LO C O -3data

LO CO -3

LO CO -2 R = 0.79

R = 0.29

Near parallel 5-year trends in density are found at both moorings

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010Year

41.64

41.66

41.68

41.70

3 (

kg/m

3) R = 0.45

The 5 year trend at LOCO-2 contrasts the long-term (19 year) trend of DSOW from the AR7E

repeat surveys.

Concluding Questions:

What is the cause of the observed DSOWs-DSOWf

contrast? Something happening in Denmark Strait?

Why is there an annual signal in the density at LOCO-2; Plume dynamics or meteorology in Denmark Strait?

What causes the long-term trends in density, and do they tell us something about changes in the THC?

Are these signals also found further downstream?