Surface mixing ratios of ozone, C2-C6 hydrocarbons, and selected organohalogens were measured at a camp on the Arctic Ocean ice northwest of Ellesmere Island during an 18-day period in April 1992. Ozone was strongly depleted (at or below instrument detection limits of 0.4 parts per billion by volume (ppbv)) more than 40% of the time and exceeded 20 ppbv only during two brief events, in marked contrast to free tropospheric mixing ratios of about 45 ppbv observed at Alert. Alkanes, bromoform, and trichloroethylene, which have been reported to be correlated with O3 at Alert, were found to have mixing ratios at the sea ice surface similar to the levels observed during O3 depletion events at Alert. Meteorological and back-trajectory analyses did not reveal significant correlations with any source region or prevailing local meteorological condition. Elevated mixing ratios of O3 and alkanes over the sea ice were associated with periods of increased dynamic mixing or transport of air from higher altitudes. Prolonged periods of undetectable ozone were correlated with air parcels whose trajectories showed they had been in close proximity to the surface sometime in the previous five days. ¿ American Geophysical Union 1994