Interannual changes of springtime ozone over the Arctic follow from anomalous transport and chemical depletion, two mechanisms that control the wintertime increase of ozone. Attempts to disentangle these contributions to anomalous ozone rest upon the isolation of air over the Arctic. To elucidate changes of Arctic ozone between warm and cold winters, their latitude-height structure is investigated in the solar backscatterd ultraviolet record and then related to contemporaneous changes of dynamical structure in the National Centers for Environmental Prediction record. Structural differences between warm and cold winters imply a major contribution to anomalous Arctic ozone from horizontal transport. Anomalous isentropic mixing by planetary waves appears conspicuously in the structure of March ozone, which has been driven into coincidence with θ surfaces following warm winters but remains deflected across them following cold winters. In concert with anomalous downwelling of ozone-rich air, this mechanism accounts for at least two thirds of the observed deficit of springtime ozone over the Arctic following cold winters. About half of the observed deficit during March is erased during April, when weakening of the vortex following cold winters eventually opens the Arctic to isentropic mixing by planetary waves. Delayed relative to warm winters, isentropic mixing during cold winters ultimately leads to much the same ozone structure. This significantly reduces the anomaly between warm and cold winters from that found a month earlier. The observed reduction is consistent with the estimated contribution to anomalous Arctic ozone from isentropic mixing.