PMEL Publications Abstract

FY 2011

Quantifying the flux of CaCO₃ and organic carbon from the surface ocean using in situ measurements of O₂, N₂, pCO₂ and pH

Emerson, S., C. Sabine, M.F. Cronin, R. Feely, S. Cullison, and M. DeGrandpre

Global Biogeochem. Cycles, 25, GB3008, doi: 10.1029/2010GB003924, 12 pp (2011)

Ocean acidification from anthropogenic CO₂ has focused our attention on the importance of understanding the rates and mechanisms of CaCO₃ formation so that changes can be monitored and feedbacks predicted. We present a method for determining the rate of CaCO₃ production using in situ measureme nts of fCO₂ 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 (50°N, 145°W). We use the data in a simple surface ocean, mass balance model of dissolved inorganic carbon (DIC) and alkalinity (Alk) to constrain the CaCO₃: organic carbon (OC) production ratio to be approximately 0.5. A CaCO₃ production rate of 8 mmol CaCO₃ m⁻² d⁻¹ in the summer of 2007 (1.2 mol m⁻² yr⁻¹) is derived by combining the CaCO₃: 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 CaCO₃:OC production rate implied by the fCO₂ and pH data.

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