THOR CT3 Meeting – Torshavn 2009 – Fischer/Visbeck/Zantopp/Nunes In the Labrador Sea, overflow water from the Denmark Strait and from the Iceland-Scotland region, which has been modified and augmented by entrainment, joins with newly formed deep water masses, produced by deep convection in the Labrador and Irminger Seas. This water is exported from the Labrador Sea mainly by the boundary current and subsequently out of the subpolar region. As all deep water mass components are included, the total deep water export and variability is one possible indicator of THC-strength and variability. This will be monitored by a moored array across the boundary current. In combination with the current measurements at key depths, both the salinity and temperature field will be measured to derive a transport index for all water masses in the Deep Water range. In THOR, the results will be combined with high resolution modeling and assimilation efforts to both interpret the observations and for adjusting the observational design if necessary. Moored records will be supplemented by repeat hydrography and velocity sections along the former WOCE lines: AR7W and AR7E. Task aims at interpreting decadal time series of currents and water mass variability to: Determine inter-annual to decadal boundary current variability Develop and continue an index of Deep Water Export (THC-Index) in combination with other available data for validation of model and assimilation products (Core Theme 2). Evaluate the penetration of newly formed water masses into the boundary current in combination with other observations (e.g., those derived from the ARGO program) and THOR model results. Task Monitoring the export of deep waters at the exit of the Labrador Sea

THOR CT3 Meeting – Torshavn 2009 – Fischer/Visbeck/Zantopp/Nunes Task Monitoring the export of deep waters at the exit of the Labrador Sea Herein the focus is on the interpretation of the data and the generation of products for the THOR modelling and assimilation community -- Plans for the first 18 months: Moored Array is designed for next deployment period: May 2009 to Summer moorings recovered and deployed Update of existing hydrographic (including Argo) and mooring data for estimating interannual to decadal variability of DWBC export from Labrador Sea (underway) index of deep water export in the DWBC (THC-index) will be developed and continued make data and products available to other WP‘s (Modeling and observational groups) Fieldprogram: 1)Joint (Quadfasel/Fischer) cruise with RV Merian in May/June 2009 finished 2)Proposed (Quadfasel/Fischer) cruise with RV Meteor in summer approved

D06: Reference data set for pre-existing data on properties and fluxes through key sections: Greenland-Scotland Ridge, Deep Western Boundary Current and across 26.5° N. (Month 12) LS Boundary Current Data 1.Two years with full array 2.10 years reduced coverage Full Array Reduced Array Structure by EOF‘s Expl. Variances Det. of uncertainties regress to EOF‘s Integrate 12 y BC Transport + Error time series ScienceTHOR

Current meter array at 53°N in and actual array Complete array from June July 1997 only : 2 moorings : 3 moorings : 1 mooring : 1 mooring : 3 moorings : 5 moorings planned (funded elsewhere) 53°N Present -- DSOW part will be strengthened THOR CT3 Meeting – Torshavn 2009 – Fischer/Visbeck/Zantopp/Nunes

Task Monitoring the export of deep waters at the exit of the Labrador Sea temperature at 1500m increases by about 0.05° per year between 1997 and 2007 Are there any trends for the other water masses? Igor Y. works on DSOW variability --- collaboration envisioned 53°N Average K2: 0.14m/s 0.17m/s k9: 0.12m/s 0.15m/s THOR CT3 Meeting – Torshavn 2009 – Fischer/Visbeck/Zantopp/Nunes

Task Monitoring the export of deep waters at the exit of the Labrador Sea THOR CT3 Meeting – Torshavn 2009 – Fischer/Visbeck/Nunes Overview of available current data at single station K9; rotated to 310° for mean outflow direction annual mean profiles and decadal mean Variations O 20% of decadal mean K7 K8 K9 K10 K16

Task Monitoring the export of deep waters at the exit of the Labrador Sea THOR CT3 Meeting – Torshavn 2009 – Fischer/Visbeck/Nunes Short term variability Intraseasonal Variability: Max near surface Peak day periods Min at DSOW Level, but mean is highest No sytematic variations of energy level

Task Monitoring the export of deep waters at the exit of the Labrador Sea THOR CT3 Meeting – Torshavn 2009 – Fischer/Visbeck/Nunes EOF‘s Mode 0 – mean flow field Mode 1 – LC-mode with annual cycle Mode 2 – meander mode Mode 3 – BC pulsation Modes for annual subsets very similar! Modes 1-3 explain 80% of the variance

Task Monitoring the export of deep waters at the exit of the Labrador Sea Spectra of EOF time series (above) – max high frequency energy in meander mode (2) at 10 to 30d periods Explained variance plot (rhs) – K10 and K9 are most important for variance Mean

Task Monitoring the export of deep waters at the exit of the Labrador Sea THOR CT3 Meeting – Torshavn 2009 – Fischer/Visbeck/Zantopp/Nunes Reference-Dataset (40 hlp data) southward Transports only time period 1997 – 1999 from 500m to the bottom 12h resolution Low-passed at 10d includes meanders Low-passed at 60d no meanders Green line is for two year mean transport (32.4Sv) below sth=27.68

Task Monitoring the export of deep waters at the exit of the Labrador Sea Special Focus on DSOW core --- LADCP and Moorings

Task Monitoring the export of deep waters at the exit of the Labrador Sea Time series of DSOW at various places in the SPNA (I. Yashayaev, pers. com.) CTD measurements aided by moored instruments (microcats)