Comparison of two methods for measuring dissolved organic carbon in sea water

Abstract

RECENT measurements¹ of the amount of dissolved organic carbon (DOC) in sea water using a high-temperature catalytic oxidation (HTCO) method have generated intense interest because they indicated concentrations several times greater than those obtained from conventional wet chemical oxidation (WCO) methods^2–4. As dissolved organic matter in the oceans represents one of the major pools of organic matter in the biosphere^5,6, these findings of 'new' DOC have prompted important revisions to models of the oceanic carbon cycle^7–9. A satisfactory explanation for the origin of the 'new' DOC, however, which seems to be chemically refractory¹, biologically labile¹⁰ and of high molecular mass¹, has not been forthcoming. Here we present a comparison of measurements of seawater DOC using the HTCO and WCO methods. We obtain fairly good agreement between the two methods, with the HTCO results being considerably lower than those reported previously¹. Our data suggest that the WCO technique may not fail to detect so much DOC as had been previously supposed, and that any carbon that is missed by this method may be in the low- rather than the high-molecular-mass fraction.