View
218
Download
2
Category
Preview:
Citation preview
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?
Recommended