Mesoscale eddies are increasingly viewed as enhancing primary production and carbon export in otherwise nutrient-deficient systems.This paper reports how a cold-core cyclonic eddy,Cyclone Opal,affects water column biogeochemistry,in particular,air-sea CO2 exchange and surface water dissolved inorganic carbon (DIC) cycling in the lee of the main of Hawaiian Islands in the subtropical North Pacific Gyre.Within Cyclone Opal,we identified three unique relationships between pCO2 and sea surface temperature (SST).A positive correlation between pCO2 and SST was observed in the waters surrounding the eddy suggesting surface CO2 is controlled primarily by thermodynamics.In contrast,a negative relationship was observed in the eddy core as a result of the upwelling of CO2-enriched subsurface waters.A third relationship existed within the eddy with reduced pCO2 suggesting a combination of biological uptake,physical upwelling and thermodynamic controls.Sea surface pCO2 and its relationship to other environmental parameters were further explored by using multivariate analysis and time-series analysis.The regional air-sea CO2 exchange and factors affecting CO2 exchange rate were discussed.In the absence of an eddy,this region is a CO2 sink,with the passage of the mesoscale eddy decreasing the magnitude of the sink by ~17%.However,if the general temperature correlation is used to predict pCO2 inside the cold eddy,it would overestimate the CO2 sink by 100%.