NOClim/ProClim 4-6/9/2006

Tor EldevikNansen Center/Bjerknes Centre, Bergen, Norway

The Greenland Sea and me

NOClim/ProClim 4-6/9/2006

ProClim papers:• Eldevik, T., F. Straneo, A.B. Sandø, and T. Furevik, 2005: Pathways and export of Greenland

Sea Water. The Nordic Seas: An integrated perspective, H. Drange, T.M. Dokken, T. Furevik, R. Gerdes, and W. Berger, Eds., Geophysical Monograph Series, AGU, 89-103.

• Eldevik, T., J.E.Ø. Nilsen, K.A. Olsson, A.B. Sandø, and D. Iovino, 2006: Little trace of the Greenland Sea in the Atlantic Conveyor. In preparation.

• Johannessen, O.M., K. Lygre, and T. Eldevik, 2005: Convective chimneys and plumes in the northern Greenland Sea. The Nordic Seas: An integrated perspective, H. Drange, T.M. Dokken, T. Furevik, R. Gerdes, and W. Berger, Eds., Geophysical Monograph Series, AGU, 251-272.

• Nilsen, J.E.Ø., T. Eldevik, Ø. Skagseth, I. Fer, K.A. Mork et al., 2006: Ventilation, pathways and overflows of the Nordic Seas. In preparation.

• Oliver, K.I.C., T. Eldevik, D.P. Stevens and A. Watson, 2006: Simulating the life of post-convective eddies in the Greenland Sea. In revision.

• Olsson, K.A., E. Jeansson, L.G. Anderson, B. Hansen, T. Eldevik, R. Kristiansen, M.-J. Messias, T. Johannessen, and A.J. Watson, 2005: Intermediate water from the Greenland Sea in the Faroe Bank Channel: spreading of released sulphur hexafluoride. Deep Sea Res. I, 52, 279-294.

• ESOP-2 group (1999). The Thermohaline Circulation in the Greenland Sea, ESOP-2 Final Scientific Report, Bergen, Norway.

• TRACTOR group (2004). TRACTOR, Tracer and circulation in the Nordic Seas Region, Final science report. Report Series for the Bjerknes Centre for Climate Research 1503-8734, Bjerknes Centre for Climate Research, Bergen, Norway.

NOClim/ProClim 4-6/9/2006

From the folklore“Until recently we would find giant ‘chimneys’ in the sea where columns of cold, dense water were sinking from the surface to the seabed 3,000 metres below, but now they have almost disappeared,” Wadhams said. “As the water sank it was replaced by warm water flowing in from the south, which kept the circulation going. If that mechanism is slowing, it will mean less heat reaching Europe.” Sunday Times 8/5/05

Tor Sponga, BT

NOClim/ProClim 4-6/9/2006

Is the Greenland Sea a major part of the Atlantic Conveyor?

Hansen and Østerhus 2000

The rate of water mass transformation must match the strength of the circulation

From Nansen (1906)to Hansen et al (2001)

Mauritzen (1996)

NOClim/ProClim 4-6/9/2006

The capacity of the Greenland Sea

uE~0.3×Ugeo=2×10-3m/s

F~0.5Sv (FGSDW~0.2SV)

Q~2TW (QNwAC~200TW), q=50W/m2

0.5Sv ↔ sinking ~100m/yr ←?→ NWAC

r~100km, L~50km, H~500m, ΔT=1ºC

Q

NOClim/ProClim 4-6/9/2006

The recent GSW contribution to the Atlantic Conveyor

Hansen and Østerhus 2000

DS: ~0.1 SvGSW × 0.6Sv (Girton et al 2001)

FBC: ~0.3 SvGSW × 1.7Sv (Hansen and Østerhus 2000)

0.4/6 = 7%

SF6: 10% + 45%Consistent with OGCM

Eldevik et al. (2005)Olsson et al. (2005)

NOClim/ProClim 4-6/9/2006

So what? There’s been no real convection in the Greenland Sea

since the 70s…

Let’s look at the available data back to 1950

NOClim/ProClim 4-6/9/2006

Content

The GSW contribution to AMOC from hydrographic data (NISE)

DS

FSC

NOClim/ProClim 4-6/9/2006

Fluxes

FSC

The GSW contribution to AMOC from hydrographic data (NISE)

DS

NOClim/ProClim 4-6/9/2006

The GSW contribution to AMOC from model data (NERSC)

DS

FSC

GSea

1Sv

1Sv

No correlation

NOClim/ProClim 4-6/9/2006

The GSW contribution to AMOC from model data (NERSC)

DS

FSC

GSea

1Sv

1Sv

No correlation (Bentsen et al., 2004)

NOClim/ProClim 4-6/9/2006

1. The GSTRE traces out the pathways of the Nordic Seas, and the exchanges with the Atlantic and Arctic oceans.

2. It is a real and suitable benchmark for ocean models.

3. The variability in tracer pathways and export reflects changes in the patterns and strength of the internal circulation of the Nordic Seas, and not in the fluxes of the overflows.

4. There is no clear link between the ventilation of the Greenland Sea and the "Atlantic Conveyor".

The GSTRE and what I have learned from it

NOClim/ProClim 4-6/9/2006

Simulating the life of post-convective vortices in the Greenland Sea

(in revision, 2006)

Kevin OliverSchool of Environmental

SciencesUniversity of East Anglia

Norwich, U.K.

Andrew WatsonSchool of Environmental Sciences

University of East Anglia

David StevensSchool of Mathematics

University of East Anglia

Tor EldevikG. C. Rieber Climate InstituteNansen Environmental and

Remote Sensing CentreBergen, Norway

NOClim/ProClim 4-6/9/2006

SCVs in the Greenland SeaAn SCV at 75N 0E, near the Greenland

Fracture Zone (GFZ)

Gascard et al, 2002. See also Wadhams et al, 2002, 2004, Budeus et al, 2004, Kasajima et al, 2006

NOClim/ProClim 4-6/9/2006

Boreas Basin

GFZGreenland Basin

Boundary between two sub-gyres

No EGC but gyre around both basins

Mean anticyclone in centre of Greenland Basin

Mean density and circulation in the model at 850m

400 km

NOClim/ProClim 4-6/9/2006

Tracer and velocity at 850m depth

Zoom in on green box

NOClim/ProClim 4-6/9/2006

Tracer and velocity at 850m depth

Zoom in on green box

NOClim/ProClim 4-6/9/2006

Tracer Temperature Velocity sectionFormation and migration of an

SCV

Ambient vertical shear

Quasi-dipole formation

Migration down the isopycnal slope

NOClim/ProClim 4-6/9/2006

Summary- Greenland Sea and AMOC

• The ”capacity” of the GSea/contribution to the conveyor is <10%• Pre- or post 1970s (deep convection) does not matter

• Nordic Seas: the rate of water mass transformation must match the strength of the circulation• What is the link between convection and circulation?