Past, current and envisioned activities in the Labrador Sea

of IFM-GEOMAR (Kiel)Torsten Kanzow (tkanzow@ifm-geomar.de)

Input from Jürgen Fischer, Nuno Nunez, Rainer Zantopp

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?

DWBC measurements at the exit of Labrador Sea

Fischer et al. (2004)

DWBC measurements at the exit of Labrador Sea

Fischer et al. (2010)

Fischer et al. (2004)

Warming of LSW at K9

Annual mean Velocity profiles

OSNAP Subpolar Observing System

“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)

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

BackgroundA. Estimates for overturning in Labrador Sea are very uncertainPickart and Spall (2007): 1 Sv (depth space) or 2 Sv (density space) Based on spring /summer hydrographic data

Brandt et al. (2007)

Numerical Simulation: Ventilation tracer in May

Numerical Simulation at 53°N: Same year ventilated / total transport

Downwelling

B. Downwelling in Labrador Sea takes place along boundaries

Two main processes for downwelling: DWBC looses heat due to

(e.g. Spall 2004)

2. Lateral heat flux

Pickart et al. (2008)

1. Heat loss to the atmosphere

Eddy kinetic energy(Funk et al.,2009)

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

Downwelling

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.

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

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)

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:

i.Infer role of boundary processes in Labrador Sea for the strength and temporal variability of the basin-wide MOCii.Understand mechanisms for downwelling & locate areas of downwelling.

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

2016 ...

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)