pathways of atlantic water

Norwegian Meteorological InstituteM/S Nordkapp Fall 2003

Pathways of Atlantic Water

Cecilie Mauritzen – Norwegian Meteorological Institute

NOClim 2 Workshop, M/S Nordkapp, October 1 2003


Meridional overturning circulation

EQ 60N

Water sinks.But this is not

where it get dense


Greenland-Scotland Ridge

60N

700m

3000 m

Sin

kin

g

En

trai

nm

ent

Nordic Seas

Dense, but still shallow

6Sv

6Sv


Erika Dan 1962, o

Northward boundwarm water

Southward bound cold water

Velocity cores (”branches”)≠ distribution of warm water

Schematic


8-9 degrees in core

Faroe-Shetland Channel:Dense water fills 600m;

AIW, NSDWWarm water on slope


7-8 degrees in

core

Summer Winter

Svinøy (example from 1988)


Gimsøy (winter 1988)

6-7 degrees in core


Grand Banks

Rockall

Lofoten basin

Fram Strait

Eurasian Basin

Overflows (wide range)

In a budget: account for transports

and air sea fluxes

Cooling and significant freshening

Magical boundary

Enough water (7 Sv) istransformed to the right

density range


• Transformation in the warm Atlantic Current does not involve deep mixed layers. So whats up with the deep mixed layer sites, the Greenland and Iceland Seas?

• Attempts to quantify export of dense water from open-ocean deep convection sites result in small numbers (< 1 Sv). The tracer release experiment in the Greenland Sea (TRACTOR) showed qualitatively the same thing; it took for example two years before any dense water reached the overflows. I.e. not a BIG player.

• BUT: is it possible that there has been times when significant amounts of the Atlantic Water did take a shortcut through the Iceland or Greenland Seas?

Schematic


Air-Sea Heat Exchange

Air-sea heat fluxes not any larger in the Iceland and Greenland Seas than

in the rest of the Nordic Seas


Hydrographic Conditions in the Iceland Sea


Irminger Current

1992?


Conclusions

• Establishment of pathways requires quantification

• Get the most important players (say, 4 out of 5 Sverdrup)

• There has been very significant hydrographic changes in the Nordic Seas in the 20th century – need to establish whether the pathways may have changed, just as we need to establish whether the strength has changed.

• Stay tuned……slow detective work (and, getting access to the most useful data isn’t always so easy)


Moving into the Nordic Seas…

• Roughly 7 Sv warm water in• Roughly 1 Sv cold water in

• Roughly 3 Sv cold, light water out

• Roughly 5 Sv cold, dense water out


Typiske snitt – hvordan komme fram til sirkulasjonsbilde


Evolution of warm Atlantic Water:Cooling AND freshening!

Temperature Salinity

Grand Banks 12 35.5

Rockall 8 35.3

Norskehavsbassenget 7.5 35.2

Lofoten/Barents Sea 6.5 35.1

Arctic Ocean Entrance 3 35

Arctic Ocean 0.5 34.9


Svinøy section

Orvik and Skagseth 2002

Time series is short, but suggest time variability in volume flux of warm inflow water


Gimsøy

900 800 700 600 500 400 300 200 100 0

500

1000

1500

2000

2500

3000

3500

Distance [km]

Dep

th [

m]

34.91

34.905

35.1

33.2

34.7

34.8

34.85

34.88

34.9

34.905

34.91

34.912

34.913

34.92

34.95

35

35.1

35.2

35.25 552 541540 538 533 528 526 524 522 519 513

Salinity Gimsøy - North West

900 800 700 600 500 400 300 200 100 0

500

1000

1500

2000

2500

3000

3500

Distance [km]

Dep

th [

m]

-0.9

-0.8

0

-1.1

-1.05

-1

-0.9

-0.8

-0.5

0

0.5

1

2

3

4

5

6

7

8

9

10 552 541540 538 533 528 526 524 522 519 513

Potential temperature [oC]Gimsøy - North West


Schematic of the MOCHow do we determine the

pathways of water masses?

pathways of atlantic water

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