Marie-Noëlle HOUSSAIS Mechanisms driving the interannual variability of the Canadian Arctic Archipelago outflow Christophe HERBAUT Marie-Noëlle HOUSSAIS LOCEAN/IPSL, PARIS

Variability of the CAA outflow (observations) Lancaster Sound Correlation to NAO Melling et al., 2008

Arctic fresh water content (annual mean, S<34.8) Simulated (1959-2001) PHC 3

Arctic fresh water content (ctd.) EOF analysis : leading modes 1959-2001

AOMIP Workshop WHOI 21-23 October 2009 Fresh water content and NAO NAO leads NAO lags PC1 PC2 PC3 AOMIP Workshop WHOI 21-23 October 2009

What controls the variability of the FW export through the CAA ? Link to the atmospheric forcing Link to the Arctic FW reservoir

Arctic – North Atlantic model (NEMO/ORCA05) Regional Configuration ORCA05: Arctic+ Atlantic ( 30°S): résolution : ~20-25 km in the Arctic 46 vertical levels, partial steps Sea ice model LIM2 (Hibler 1979 two-level sea ice model) Viscous plastic rheology 3 layers thermodynamics Forcings Atmospheric forcing :ERA40 reanalysis (1958-2001) Relaxation on climatological SSS (trelax= 30 days) Open boundaries at 30°S (Atlantic) and 50°N (Pacific) :monthly climatological T, S, u from global simulation

Canadian Arctic Archipelago outflow Closed straits : - Cardigan Strait + Hell Gate - Fury and Hecla Strait Arctic Ocean outflow Inflow to Baffin Bay Nares Strait Smith Sound McClure Strait Amundsen Gulf Byam Martin Channel + Penny Strait Lancaster Sound

Fresh water export through the CAA Annual mean Volume (Sv) Fresh water (mSv) Liquid Smith 1.3 70 Liquid Lancaster 1.1 90 Liquid total CAA 2.4 160 Ice (liquid equ.) 5

Fresh water export through the CAA Relative contributions of velocity and salinity anomalies Normalized transports Volume transport CAA FW transport Davis Strait (S<34.6)

Outflow to Lancaster Sound McClure Byam Martin Penny Amundsen

AOMIP Workshop WHOI 21-23 October 2009 Subsurface velocity anomalies in McClure Strait Cross-strait velocity regressed on Lancaster outflow AOMIP Workshop WHOI 21-23 October 2009

Regression on Lancaster outflow Bifurcation of the boundary current in Mc Clure Strait Current velocity at 110 m Climatology Regression on Lancaster outflow McClure

Upstream and downstream forcing on Lancaster outflow Correlation Lancaster outflow with: . SSH McClure-SSH Lancaster . SSH McClure . SSH Lancaster

SSH forcing on Lancaster outflow SSH climatology SSH on SSH in McClure

Downstream forcing on Nares Srait outflow Correlation Nares outflow with SSH SSH Nares-SSH Smith SSH Nares SSH Smith

Subpolar SSH forcing on Nares Strait transport SSH regressed on transport in Nares Strait SSH regressed on SSH in Smith Sound Unsignificant SSH forcing in central Arctic

Wind driven SSH variability in the Arctic Ekman drift regressed on Lancaster outflow Accumulation of the Ekman flow against the CAA coast

Mechanisms of SSH variability in Baffin Bay Air-sea heat flux on SSH in Smith Sound  Lagged response of Baffin Bay to buoyancy driven SSH changes in the Labrador Sea

Atmospheric modes driving CAA variability SLP on SSH in Smith Sound SLP on Lancaster outflow  NAO-like SLP patterns

Response to NAO-like atmospheric forcing  Arctic/subpolar influence on CAA outflow  Wind stress/buoyancy forcing on CAA outflow SLP Idealized experiments : Construct NAO+ composites of NDJFM forcing fields 10-year experiments with repeated annual cycle of composite forcing

Idealized experiments 3 sensitivity experiments : Wind stress Buoyancy forcing (SAT and SHU) Buoyancy forcing restricted to south of Davis and GISR NAO wind stress NAO heat flux

SSH anomalies in idealized experiments Buoyancy Atlantic Wind Buoyancy Wind driven Arctic SSH anomalies : same pattern as SSH pattern impacting on McClure Strait Buoyancy driven subpolar anomalies : same pattern as SSH pattern impacting on Nares Strait

Time evolution of the response Distribution between passages Total CAA outflow WIND BUOYANCY BUOYANCY_ATL --- Nares Strait __ Lancaster Sound

Link to arctic fresh water content (FWC) Correlation PC3-Lancaster Regression FWC on Lancaster outflow FW content - EOF3

Summary The fresh water outflow through the CAA is mainly controlled by volume transports, in agreement with observations. Both ouflows to Lancaster and Smith sounds correlate high (~0.8) with the along channel SSH difference (Jahn et al., 2009). However distinct mechanisms : Lancaster Sound : largely controlled by the SSH variability at the periphery of the Beaufort Gyre  slowing-down of the boundary current north of the CAA  more water to McClure Smith Sound : primarily controlled by the downstream SSH variability in Baffin Bay Both channels respond to the dominant mode of the winter atmosphere variability (Condron et al., 2009): SSH in the Arctic : local convergence of the Ekman drift against the CAA SSH in Baffin Bay : lagged response to buoyancy forcing in the Labrador Sea. SSH forcing in McClure not directly linked to the leading modes of variability of the Arctic FW content (variations of thickness and extent of the Beaufort Gyre FW reservoir) but rather to a regional redistribution of the FW north of the Archipelago