1. Variability of the Fresh water content in the Beaufort Gyre
C. Herbaut, M.-N. Houssais, D. Iovino
LOCEAN, Paris

2. Beaufort Gyre fresh water content :
Seasonal and interannual variability
Seasonal variability :
Maximum in winter, minimum in summer
 due to Ekman Pumping
Yang and Comiso, 2007; Proshutinsky et al., 2009
Proshutinsky et al., 2009
Interannual Variability
driven by Ekman pumping
no link to Arctic Oscillation (Yang, 2009)
Proshutinsky et al., 2009

3. Annual cycle of Beaufort Gyre FWC
ORCA05 model
PHC
0-50 m
0-50 m
Observations m m
Proshutinsky et al. 2009

4. Fresh water content Surface forcing Cumulative sea ice melt
FWC 0-50 m
Cumulative sea ice melt
FWC m
Wind stress curl
1/10
 sea ice melt dominates over wind stress curl effect

5. Interannual variability
FW water storage (103km3)
Validation:
Arctic: some similar tendencies but with different amplitudes
BG: the high FWC in 90s is not reproduced in the model BG AO
BG small contribution to the variability of the total Arctic
Whole Arctic Ocean
Very different variability, but similar averaged shape of variability.
Liquid FW storage amount varies between 55,000 km3 and 88,000 km3
ORCA and LOCEAN have very different variability
Polyakov et al. 2008

6. Monthly rate of salinity change
Mean monthly rate
of FWC change
Monthly rate of salinity change
NDJFM AM
JJA SO
No correlation between seasons
No correlation between upper and lower layers except in SO
Seasonal contribution to the annual mean rate of FWC change :
NDJFM: 36% , JJA: 16% SO:25%
Small contribution of the top layer

7.  Wind stress curl is the main driver of interannual variability
Normalized wind stress curl versus normalized rate of FW change
NDJFM AM
JJA SO
 Wind stress curl is the main driver of interannual variability

8. Regression of SLP on the wind stress curl over BG
NDJFM AM SO
2nd EOF winter SLP ~winter PNA
Quadrelli and Wallace, 2004
Variability in NDJFM, AM, SO associated with a Pacific Mode

9. Regression of SLP on the wind stress curl over BG
JJA
Different SLP mode in JJA : Arctic intensified

10. Correlation Sea ice melt and dFWdt 0-50 m
NDJFM AM
JJA SO

11. Regression on sea ice melt (winter)
SAT
SLP
Ice thickness
Winter : AO-like pattern

12. Regression on sea ice melt (summer)
SST
SAT
SIC
Summer : Ocean influence

13. Conclusions
1/ Seasonal and interannual variability of the fresh water content in the BG linked to different driving mechanisms :
Seasonal linked to sea ice melt/growth
Interannual linked to wind stress curl
2/ The seasonal contribution to interannual changes implies different atmospheric modes :
Winter : Pacific Mode
Summer : Beaufort-Gyre intensified mode
3/ There is a contrasted, vertical distribution of interannual FWC anomalies
0-50 m linked to sea ice melt-growth , not dominant, AO-driven in winter, ocean-controlled in summer
m linked to wind stress curl, dominant
No vertical correlation except in fall