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Arctic sea ice, both extent and thickness,has undergone accelerated decline in recent years1-4.Especially in boreal summer, Arctic sea ice extent (SIE) reaches its minimum-the recorded lowest in 2012.Model simulations show that summer ice-free Arctic ocean will appear in 20-40 years in the future5-7.However, most evaluations focused on summer sea ice fast melting rate and seldom pay attention to sea ice seasonality.Here we find that the Arctic SIE does not decline in the past 6-7 years from 2007.Monthly mean SIE anomaly time series from 1979 to 2012 appears a significant regime shift at 2007, with accelerated decline dominant before 2007 turning to amplified seasonal oscillation dominated without significant trend after 2007.