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

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

Annual cycle of Beaufort Gyre FWC ORCA05 model PHC 0-50 m 0-50 m Observations 2003-07 50-250 m 120-500 m Proshutinsky et al. 2009

Fresh water content Surface forcing Cumulative sea ice melt FWC 0-50 m Cumulative sea ice melt FWC 50-250 m Wind stress curl 1/10  sea ice melt dominates over wind stress curl effect

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

Monthly rate of salinity change Mean monthly rate of FWC change Monthly rate of salinity change 1958-2001 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

 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

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

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

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

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

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

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 50- 250 m linked to wind stress curl, dominant No vertical correlation except in fall