Abstract: This work investigates the spatial and temporal features of boreal autumn (August—October) East Siberian—Beaufort (EsCB) sea ice on decadal timescales during the period of 1950—2020 based on monthly Sea Surface Temperature (SST), Sea Ice Concentration (SIC) from the Hadley Center and atmospheric reanalysis dataset provided by the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). The possible modulation effects of Atlantic Multidecadal Oscillation (AMO) on the EsCB sea ice are further elaborated. The EsCB sea displays the strongest decadal component of sea ice in the Arctic, accounting for more than 40% of the local total variance of SIC anomalies. Our further analyses show that the AMO exerts a prominent modulation on the EsCB sea ice. In the positive AMO phase, warm North Atlantic SST anomalies trigger poleward propagating atmospheric Rossby waves, favoring the establishment of an anomalous high over the central Arctic region. The corresponding adiabatic descending motion warms the lower troposphere and causes the EsCB sea ice to melt. The surface warming and EsCB sea ice melting can simultaneously give rise to an increase in local cloud amount and downward longwave radiation, which in turn increases the surface air temperature. This surface air temperature-cloud-longwave positive feedback is beneficial for the long-term maintenance of the decadal sea ice signal. The North Atlantic pacemaker experiments can realistically reproduce the observed physical process as shown above, which further supports our main conclusions.