On the production of particulate organic carbon by heterotrophic processes in sea water

It is suggested that the amount of heterotrophic carbon assimilation by micro-organisms in the sea may be a significant fraction of the photosynthetic production, when considering the whole water column in a deep ocean.

A method is described, allied to the carbon-14 method for measuring photosynthesis, whereby the heterotrophic uptake of any chosen substrate in sea water can be measured using the substrate labelled by carbon-14. The method is rapid and convenient and can give values of ‘relative-heterotrophic potential’. As with the radiochemical method for measuring marine photosynthesis, the exact interpretation of results presents many problems but the technique should prove a useful exploratory tool. Tests have been made using fully labelled acetate and glucose.

By a method of progressive radio-isotopic dilution it is possible to measure either the concentration or organic substrate in sea water or obtain information of the enzyme kinetics of the microorganisms assimilating a given substrate. A description is given of this method. A few preliminary trials to test its applicability have been encouraging.