We examined the biogeochemical impact of pairs of mesoscale cyclones and anticyclones in spatial proximity (<200 km apart) in the North Pacific Subtropical Gyre. While previous studies have demonstrated that upwelling associated with the intensification of cyclonic eddies supplies nutrients to the euphotic zone, we find that cyclonic eddies in their mature stage sustain plankton growth by increasing the diapycnal flux of nutrients to the lower portion of the euphotic zone. This increased supply results from enhanced vertical gradients in inorganic nutrients due to erosion of the nutricline that accompanied plankton growth during eddy intensification. From a biological standpoint, increased nutrient flux was linked with expansion of eukaryotic phytoplankton biomass and intensification of the deep chlorophyll maximum layer. This perturbation in the plankton community was associated with increased fluxes of biominerals (opal and calcium carbonate) and isotopically enriched nitrogen in particles exported in the cyclone. The time-integrated effects of thermocline uplifts and depressions were predictable deficits and surpluses of inorganic nutrients and dissolved oxygen in the lower euphotic zone. However, the stoichiometry of changes in oxygen and inorganic nutrients differed from that predicted for production and consumption of phytoplankton biomass, consistent with additional biological processes that decouple changes in oxygen and nutrient concentrations. The dynamics revealed by this study may be a common feature of oligotrophic ecosystems, where mesoscale biogeochemical perturbations are buffered by the deep chlorophyll maximum layer, which limits the ecological impact of eddies in the well-lit, near-surface ocean.