Rate and extent of decomposition of dissolved organic matter in surface seawater

Abstract

An experiment on the decomposition of the dissolved organic matter (DOM) in surface seawater was carried out under controlled laboratory conditions during a cruise of the R.V. “Hakuho-Maru” in the North-Equatorial Pacific (August/November, 1969). Surface seawater was placed in 300 ml oxygen bottles and incubated in the dark at 25°C. After selected time intervals, the dissolved organic-carbon (DOC) and the dissolved oxygen (DO) were determined for each bottle. The DOM in the surface seawater was described in terms of two labile fractions and a refractory one. The DOC decreased from 0.96 to 0.74 mgC/l during the first 50 days of incubation. Approximately 20% of the initial DOC (Fraction FI) was oxidized. The other labile fraction, FII was assumed to be 30 to 40% of the total DOM. The remaining half of the total DOM (Fraction FIII) is probably refractory and resistant to biochemical oxidation. The rate constant for decomposition was 0.0052 day−1 for the total DOM and 0.033 day−1 for FI.