A SIMPLE AND RAPID DEVICE FOR MEASURING PLANKTONIC PRIMARY PRODUCTION BY INSITU SAMPLING, AND C-14 INJECTION AND INCUBATION

A system (LET GO) is described that enables measurements of primary production at sea after in situ incubations, with C-14 being injected at depth immediately after enclosure of the sample. Each incubation cell, about 200 ml, is made of two transparent plexiglass cups facing each other. Mechanical energy to operate the system is provided by the tension of the nylon line between the drifting buoy, which holds the experimental equipment, and a weight at the bottom: when the line is strained. the two cups enclose the water sample, and the C-14 is delivered by a syringe. Absence of metallic or rubber parts ensures that toxicity effects are minimized and that reliable results can be expected. Furthermore, in situ incubations can start 1 or 2 min after arrival on station, leaving the research vessel and winches available for other tasks. These points make it possible to make in situ C-14 incubations during most oceanographic cruises and to increase greatly the acquisition rate of primary production data. The LET GO device has been tested in parallel with the conventional technique. Both techniques showed similar vertical patterns. Carbon fixation measured with the LET GO. however, was greater by a factor 1.3.