Ocean acidification from anthropogenic CO 2 has focused our attention on the importance of understanding the rates and mechanisms of CaCO 3 formation so that changes can be monitored and feedbacks predicted. We present a method for determining the rate of CaCO 3 production using in situ measureme nts of fCO 2 and pH in surface waters of the eastern subarctic Pacific Ocean. These quantities were determined on a surface mooring every 3 h for a period of about 9 months in 2007 at Ocean Station Papa (50N, 145W). We use the data in a simple surface ocean, mass balance model of dissolved inorganic carbon (DIC) and alkalinity (Alk) to constrain the CaCO 3: organic carbon (OC) production ratio to be approximately 0.5. A CaCO 3 production rate of 8 mmol CaCO 3 m -2 d -1 in the summer of 2007 (1.2 mol m -2 yr -1) is derived by combining the CaCO 3: OC ratio with the a net organic carbon production rate (2.5 mol C m -2 yr -1) determined from in situ measurements of oxygen and nitrogen gas concentrations measured on the same mooring (Emerson and Stump, 2010). Carbonate chemistry data from a meridional hydrographic section in this area in 2008 indicate that isopycnal surfaces that outcrop in the winter in the subarctic Pacific and deepen southward into the subtropics are a much stronger source for alkalinity than vertical mixing. This pathway has a high enough Alk:DIC ratio to support the CaCO 3:OC production rate implied by the fCO 2 and pH data.