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Project group „Dynamics of the oxygen depletion“,

Subproject: Investigations of the organic matter mineralization kinetics



Bernd Schneider, Hildegard Kubsch

The investigations of the kinetics of organic matter mineralization are based on measurements of the CO2 accumulation in the Gotland Sea deep water. The vertical profiles of total CO2 (CT) are determined at time intervals of about two to three months. The CT fraction generated by mineralization (minCT) is estimated by subtracting the CT background which is defined by the CT of the water during its last contact with the atmosphere and which may be obtained from estimates of the corresponding alkalinity and CO2 partial pressure. Taking into account vertical mixing, the temporal increase of the minCT is used to calculate mineralization rates for different depth levels. Relating the mineralization rates to the availability of organic matter and to the O2 (SO42-) concentrations will give rate constants for the decomposition of organic matter at different redox conditions.

Fig. 1: Increase of the total CO2 in the bottom water of the Gotland Sea during a long-lasting stagnation period. The longterm trend is superimposed by a periodicity that is caused by increased organic matter sedimentation during the productive period