Methodological aspects of time-course measurements of ¹⁴C fixation in marine phytoplankton

A series of time-course studies were made in conjunction with productivity measurements to determine: (1) the time required for purging sorbed H¹⁴CO₃^- from glass fiber filters, (2) the duration of linearity in H¹⁴CO₃^- uptake in several oceanic environments, and (3) the time required for an "equilibrium" to be established among solvent-extractable and particulate fractions of natural phytoplankton populations. Acidification of sorbed H¹⁴CO₃^- on Whatman GF F filters requires a 60-min period before the sorbed label is reduced to background levels. Time course measurements of H¹⁴CO₃^- fixation in three regions of the northwestern Atlantic (two warm-core rings and the Sargasso Sea) indicated that carbon uptake was linear for at least 4-6 h. The distribution of ¹⁴C among various soluble and particulate fractions of labelled natural phytoplankton populations showed that an "equilibrium" was achieved among the various fractions after 1 to 2 h of incubation.