ABSTRACT: The effect of hurricanes on the thermal and physical structure of the upper ocean has been described but their influence on the ocean carbon cycle and the exchange of carbon between ocean and atmosphere is not well understood. Here we present observations from the Sargasso Sea, before and after hurricane Felix in summer 1995, that show a short-lived (2-3 weeks) surface seawater cooling of about 4 degree C, and a decrease in seawater partial pressure of CO ₂ by about 60 mu atm. Despite the localized decrease in seawater partial pressure of CO ₂, strong winds during the passage of hurricane Felix increased the efflux of CO ₂ from ocean to atmosphere. We estimate that hurricane Felix and two other hurricanes increased the summertime efflux of CO ₂ into the atmosphere over this part of the Sargasso Sea by nearly 55%. We estimate that hurricanes contribute to the global ocean-to-atmosphere flux of CO ₂ by between +0.04 to +0.51 Pg C (10 ¹⁵ g C) per year. Such hurricane-forced effluxes are quantitatively significant compared to regional (14 degree to 50 degree N zone) and global effluxes. Hurricanes therefore exert an important influence on ocean-atmosphere CO ₂ exchange and the inferred year-to-year variability of CO ₂ fluxes over the subtropical oceans.