Climate data operator (CDO) code for the analyses: #subset set ice variable from base file cdo selname,ICEFRAC,time decadal_mean_annual_seaice.nc ice.nc cdo seltimestep #calculate annual mean values cdo timmean -seltimestep,496/506 ice.nc 17kamean.nc cdo timmean -seltimestep,596/606 ice.nc 16kamean.nc cdo timmean -seltimestep,646/656 ice.nc 15.5kamean.nc cdo timmean -seltimestep,696/706 ice.nc 15kamean.nc cdo timmean -seltimestep,746/756 ice.nc 14.5kamean.nc #Autumn Cdo selname,ICEFRAC,time trace.01-36.22000BP.cam2.ICEFRAC.22000BP_decavgSON_400BCE.nc Autumn.nc cdo timmean -seltimestep,496/506 Autumn.nc 17kaAutumn.nc cdo timmean -seltimestep,596/606 Autumn.nc 16kaAutumn.nc cdo timmean -seltimestep,646/656 Autumn.nc 15.5kaAutumn.nc cdo timmean -seltimestep,696/706 Autumn.nc 15kaAutumn.nc cdo timmean -seltimestep,746/756 Autumn.nc 14.5kaAutumn.nc #Spring Cdo selname,ICEFRAC,time trace.01-36.22000BP.cam2.ICEFRAC.22000BP_decavgMAM_400BCE.nc Spring.nc cdo timmean -seltimestep,496/506 Spring.nc 17kaSpring.nc cdo timmean -seltimestep,596/606 Spring.nc 16kaSpring.nc cdo timmean -seltimestep,646/656 Spring.nc 15.5kaSpring.nc cdo timmean -seltimestep,696/706 Spring.nc 15kaSpring.nc cdo timmean -seltimestep,746/756 Spring.nc 14.5kaSpring.nc #Summer Cdo selname,ICEFRAC,time trace.01-36.22000BP.cam2.ICEFRAC.22000BP_decavgJJA_400BCE.nc Summer.nc cdo timmean -seltimestep,496/506 Summer.nc 17kaSummer.nc cdo timmean -seltimestep,596/606 Summer.nc 16kaSummer.nc cdo timmean -seltimestep,646/656 Summer.nc 15.5kaSummer.nc cdo timmean -seltimestep,696/706 Summer.nc 15kaSummer.nc cdo timmean -seltimestep,746/756 Summer.nc 14.5kaSummer.nc #Winter Cdo selname,ICEFRAC,time trace.01-36.22000BP.cam2.ICEFRAC.22000BP_decavgDJF_400BCE.nc Winter.nc cdo timmean -seltimestep,496/506 Winter.nc 17kaWinter.nc cdo timmean -seltimestep,596/606 Winter.nc 16kaWinter.nc cdo timmean -seltimestep,646/656 Winter.nc 15.5kaWinter.nc cdo timmean -seltimestep,696/706 Winter.nc 15kaWinter.nc cdo timmean -seltimestep,746/756 Winter.nc 14.5kaWinter.nc