Vertical turbulent fluxes of O3 were measured by eddy correlation from a 12-m high tower erected over mixed tundra terrain (dry upland tundra, wet meadow tundra, and small lakes) in western Alaska during the Arctic Boundary Layer expedition (ABLE 3A). The measurements were made continuously for 30 days in July--August 1988. The mean O3 deposition flux was 1.3¿1011 molecules cm-2 s-1. The mean O3 deposition velocity was 0.24 cm s-1 in the daytime and 0.12 cm s-1 at night. The day-to-night difference in deposition velocity was driven by both atmospheric stability and surface reactivity. The mean surface resistance to O3 deposition was 2.6 s cm-1 in the daytime and 3.4 s cm-1 at night. The relatively low surface resistance at night is attributed to light-insensitive uptake of O3 at dry upland tundra surfaces (mosses, lichens). The small day-to-night difference in surface resistance is attributed to additional stomatal uptake by wet meadow tundra plants in the daytime. Flux measurements from the ABLE 3A aircraft flying over the tower are in agreement with the tower data. The mean O3 deposition flux to the world north of 60¿N in July--August is estimated at 8.2¿1010 molecules cm-2 s-1, comparable in magnitude to the O3 photochemical loss rate in the region derived from the ABLE 3A aircraft data. Suppression of photochemical loss by small anthropogenic inputs of nitrogen oxides could have a major effect on O3 concentrations in the summertime Arctic troposphere.