THOR meeting Paris November 25-26, 2009 North Atlantic Subpolar Gyre forcing on the fresh water exchange with the Arctic Ocean Christophe HERBAUT and Marie-Noëlle HOUSSAIS LOCEAN, UPMC, PARIS Contribution to WP 2.3

THOR meeting Paris November 25-26, 2009  hindcasts simulation with ORCA05 (regional configuration) forced by the ERA40 reanalysis  sensitivity experiments to NAO-like atmospheric forcing (10 years Link to the MOC LOCEAN regional Arctic North Atlantic model (ORCA05) Analysis the fresh water content variability of the Arctic-North Atlantic Ocean based upon :

THOR meeting Paris November 25-26, 2009 Hindcast experiment : salinity (200 – 500 m) EOF analysis GSA

THOR meeting Paris November 25-26, 2009 WOCE A01E 1992 OVIDE 2004 Thierry et al., 2008 Johnson et Gruber, Subpolar gyre salinity : link to NAO Salinity at 20°W

THOR meeting Paris November 25-26, 2009 NAO + and NAO neutral composite years NAO+ : 1973, 1976, 1983,1989, 1990, 1992, 1993, 1995, 2000 NAO neutral : 1959, 1968, 1972, 1981, 1982, 1984, 1986, 1988, 1998 NAO index : ERA40 reanalysis

THOR meeting Paris November 25-26, 2009 Composite patterns (NAO + - NAO neutral ) Heat flux Winter (NDJFM) Wind stress Winter (NDJFM)

THOR meeting Paris November 25-26, 2009 Western gyre Eastern gyre Salinity anomalies (NAO + - NAO neutral ) m All fluxes Wind-only All fluxes m EOF 1 Wind-only All fluxes Herbaut and Houssais, 2009

THOR meeting Paris November 25-26, 2009 Regional versus global wind stress forcing Wind-onlyArctic wind-only m salinity anomalies

THOR meeting Paris November 25-26, 2009 Intergyre gyre (Marshall et al., 2001)

THOR meeting Paris November 25-26, 2009 Gyre index Hakkinen and Rhines, 2004 All fluxesWind-only Sea Surface Height anomalies – Gyre Index Wind-only All fluxes

THOR meeting Paris November 25-26, 2009 Progression of salinity anomalies around the SPG Western European Basin Iceland basin --- Advection by velocity anomalies -.-. Advection of salinity anomalies Year 4 Year 8 Year 6

THOR meeting Paris November 25-26, 2009 Arctic fresh water content EOF analysis :

THOR meeting Paris November 25-26, 2009 Fresh water content and NAO PC2 PC1 PC3 NAO leads NAO lags

THOR meeting Paris November 25-26, 2009 Fresh water export through the CAA Annual mean Volume (Sv) Fresh water (mSv) Liquid Smith1.370 Liquid Lancaster Liquid total CAA Ice (liquid equ.) 5

THOR meeting Paris November 25-26, 2009 Fresh water export through the CAA Relative contributions of velocity and salinity anomalies Volume transport CAA FW transport Davis Strait (S<34.6) Normalized transports

THOR meeting Paris November 25-26, 2009 Lancaster McClure Byam Martin Penny Amundsen Outflow to Lancaster Sound

THOR meeting Paris November 25-26, 2009 Correlation Lancaster outflow with:. SSH McClure. SSH Lancaster Upstream and downstream forcing on Lancaster outflow

THOR meeting Paris November 25-26, 2009 SSH Nares-SSH Smith SSH Nares SSH Smith Correlation Nares outflow with SSH Downstream forcing on Nares Srait outflow

THOR meeting Paris November 25-26, 2009 SSH forcing on Lancaster outflow SSH climatology SSH on SSH in McClure

THOR meeting Paris November 25-26, 2009 Regression FWC on Lancaster outflow Correlation FWC PC3-Lancaster FW content - EOF3 Link to arctic fresh water content (FWC)

THOR meeting Paris November 25-26, 2009 SSH regressed on transport in Nares Strait Subpolar SSH forcing on Nares Strait transport SSH regressed on SSH in Smith Sound  Only weak SSH forcing in central Arctic

THOR meeting Paris November 25-26, 2009 Air-sea heat flux on SSH in Smith Sound  Lagged response of Baffin Bay to buoyancy driven SSH changes in the Labrador Sea Mechanisms of SSH variability in Baffin Bay

THOR meeting Paris November 25-26, 2009 SLP on Lancaster outflow Atmospheric modes driving CAA variability SLP on SSH in Smith Sound  NAO-like SLP patterns

THOR meeting Paris November 25-26, 2009 Idealized NAO experiments 3 sensitivity experiments : Wind stress-only Buoyancy forcing (SAT and SHU)-only Buoyancy forcing restricted to south of Davis and GISR  Arctic/subpolar influence on CAA outflow  Wind stress/buoyancy forcing on CAA outflow

THOR meeting Paris November 25-26, 2009 Idealized NAO experiments Wind-only Buoyancy Atlantic  Wind driven Arctic SSH anomalies  SSH pattern impacting on McClure  Buoyancy driven subpolar anomalies  SSH pattern impacting on Nares

THOR meeting Paris November 25-26, 2009 Time evolution of the response WIND BUOYANCY BUOYANCY_ATL Total CAA outflow Distribution between passages --- Nares Strait __ Lancaster Sound

THOR meeting Paris November 25-26, 2009 Year 4-6 Year 1-3 Meridional overturning anomalies Wind-only All forcings

THOR meeting Paris November 25-26, 2009 Wind driven variability of SPG is able to drive east-west redistribution of the upper fresh water content within the gyre wich are linked to shifts in the NAC rather than gyre intensification Transport of upper salinity anomalies by the mean gyre circulation may impact on the subsurface fresh water content in the Labrador Sea and on the salinity of the inflow of Atlantic water to the Arctic  potential control of the strength of the THC Buoyancy driven SSH changes in the Labrador Sea may propagate to Baffin Bay, therefore exerting a remote control on the FW export through the Canadian Archipelago. This effect adds to that of the wind-driven changes linked to the upstream variability of the Arctic fresh water content. All these processes have strong link to the NAO, although with different timing. Conclusions