1. Past, current and envisioned activities in the Labrador Sea
of IFM-GEOMAR (Kiel)
Torsten Kanzow
Input from Jürgen Fischer, Nuno Nunez, Rainer Zantopp

2. Outline History of boundary current measurements at 53°N
Goals of proposed experiment
envisioned implementation, logistics, etc
Future funding propects for 53°N
Central Labrador Sea Mooring continued?

3. DWBC measurements at the exit of Labrador Sea
Fischer et al. (2004)

4. DWBC measurements at the exit of Labrador Sea
Warming of LSW at K9
Fischer et al. (2004)
Fischer et al. (2010)
Annual mean
Velocity profiles

5. “The Impact of Ocean Margin Processes in the Labrador Sea on the Atlantic Meridional Overturning Circulation”
proposed to German Science Association (DFG) by T. Kanzow and C. Böning (IFM-GEOMAR, KIEL)
OSNAP Subpolar Observing System

6. Goals Observe seasonal changes of newly formed Labrador Sea Water in
the DWBC at 53°N continuously (transports in density classes).
Verify Pickart and Spall.
What mechanism sets downwelling: Eddies or surface buoyancy
fluxes? Are there strong seasonal changes in sinking?
Link DWBC measurements to other OSNAP elements to infer
Labrador Sea overturning continuously
Maintain 53°N measurements as MOC indicator
Role of boundary processes in Labrador Sea for the strength and
temporal variability of the basin-wide MOC

7. Background
A. Estimates for overturning in Labrador Sea are very uncertain
Pickart and Spall (2007): 1 Sv (depth space) or 2 Sv (density space)
 Based on spring /summer hydrographic data
Numerical Simulation at 53°N:
Same year ventilated / total transport
Numerical Simulation:
Ventilation tracer in May
Brandt et al. (2007)

8. Downwelling 2. Lateral heat flux
B. Downwelling in Labrador Sea takes place along boundaries
(e.g. Spall 2004)
Two main processes for downwelling: DWBC looses heat due to
2. Lateral heat flux
1. Heat loss to the atmosphere
Eddy
kinetic
energy
(Funk et al.,
2009)
Pickart et al.
(2008)

9. Downwelling Downwelling produces along-boundary pressure
change of opposite sign in upper and deep layer

10. Elements of proposed observing system
53°N array (red circles) to compute export
of LSW, in collaboration with DFO-BIO, UW.
Use of pressure sensor (blue triangle)at 3
isobaths (500m, 1000m, 1500m) both
upstream (60.5°N) an downstream (53°N) of
downwelling area at western boundary.
Miguel Maqueda (Liverpool) will deploy
additional pressure sensors at eastern end of
AR7W line.
Density mooring upstream of 53°N at the
continental slope at western end of AR7W
(green square) to observe mixed layer depths
(near-boundary water transformation) , in
collaboration with DFO-BIO.

11. The proposed modified 53°N array
Current meter + density (CTD) to compute transport in density classes.
Density (salinity) and oxygen to detect newly transformed waters near the boundary
Upslope pressure sensors to compute downwelling

12. Propects of Future Funding for 53°N
funded through BMBF (ministry of education and research)
Second 4-year phase 2008 – 2012
Unclear whether 3rd observational phase will be possible
(no call issued, yet; but positive signs received)
Submitted proposal to DFG (German Research Association)
to cover 2012 – 2014
Possibilities might also come up during
next phase of EU THOR
IFM-GEOMAR is progressing from
Leibniz Association (WGL)
to Helmholtz Association (HGF)
 Long-term monitoring in Labrador Sea has been identified as
activity to be covered through HGF basic funding (5 year funding;
has yet to be reviewed)

13. High resolution modelling (Böning / Biastoch)
Use of a high resolution (1/20°) nest in a global eddy-permitting (1/4°, ORCA025) model. Perform 50 year runs and sensitivity studies (e.g. isolation of buoyancy or wind forcing) to:
Infer role of boundary processes in Labrador Sea for the strength and temporal variability of the basin-wide MOC
Understand mechanisms for downwelling & locate areas of downwelling.

14. Logistics 2012 cruise Fischer & Quadfasel
service ADCP in Flemish Pass (U Ham)
service 53N array
recover CentraL Labrador Sea mooring
deploy BPRs at 60°N & 53°N
hydrography in Labrador Sea of 53°N
section to Cape Farewell
Service Central Irminger Sea mooring
(CIS; IFM-GEOMAR,KIEL)
service Angmagssalik array
Service Denmark Strait ADCPs (U Ham)
Mixing/entrainment in overflow plume
(U HAM: hydrography + moorings;
IFM-GEOMAR: Micrstructure on AUV)
2014 cruise proposal need to be submitted in November 2011

15. Central Labrador Sea mooring
Monitoring of mixed layer depths since 1995
Gaps party filled with Argo Float data
Currenly funded through EU THOR Programme (ends 2012)
Future is uncertain: Can Argo floats take over?
will be a topic during Canada-Germany workshop (Halifax; 06/2011)