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.

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