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

• Published in: Global biogeochemical cycles Vol. 25; no. 3
• Main Authors: Emerson, Steven, Sabine, Christopher, Cronin, Meghan F., Feely, Richard, Cullison Gray, Sarah E., DeGrandpre, Mike
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01.09.2011
• Subjects: Acidification; Alkalinity; Anthropogenic factors; Biological oceanography; CaCO3; Carbon; Carbon dioxide; carbonate chemistry; Chemical oceanography; Dissolved inorganic carbon; Geobiology; Geochemistry; In situ measurement; Marine; Ocean acidification; Organic carbon; pCO2; Surface water; Upper ocean; INE, Subarctic Pacific; IN, North Pacific
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1029/2010GB003924

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. Key Points The effect of ocean acidification can be monitored remotely In situ measurements of net biological organic carbon and CaCO3 production CaCO3 fluxes from the upper ocean in the North Pacific are high