Current 14C methods for measuring primary production: Gross underestimates in oceanic waters

Abstract

The amount of organic matter produced through autotrophic processes in the euphotic zone of the tropical open ocean and available for respiration of autotrophs and heterotrophs was at least 5 to 15 times higher than values derived from the common 14C method suggested. The new estimates are based on measurements of 14C incorporation in organic matter of ocean samples incubated in bottles of up to 4 litres. Oceanic phytoplankton appeared to have a high growth rate, with generation times of hours, not days. High heterotrophic activity, finding its expression in high dark fixation rates of 14C, took place in conjunction with this high primary production of organic matter. Incubation in smaller bottles was the cause of abnormally high rates of photochemical pigment destruction in the enclosed samples, presumably as a consequence of enhanced algal mortality. This detrimental enclosure effect was most serious in samples contained in 30 ml bottles for 12 hours; it was not alarming in samples larger than 4 litres. Mortality in bottles may have been caused directly by contact with the glass wall, or, indirectly, because the delicate balance between production and consumption of organic matter in oligotrophic waters is easily upset due to enclusure of a small sample. In the uppermost part of the euphotic zone primary production was further underestimated because chlorophyll in algal cells incubated at a fixed depth was bleached more rapidly than chlorophyll in cell freely circulating in the vertically mixed surface layer. Existing concepts of carbon cycling in the open ocean must be reconsidered because estimates of fluxes have always been based on far too low figures of primary production. Calculations of the efficiency of conversion of solar energy into organic matter should also be reconsidered. An important observation in this respect is that the measurement of “functional” chlorophyll a with methods other than those incorporating chromatography is probably unreliable: high concentrations of “changed” chlorophylls with spectrophotometric and fluorometric characteristics different from but close to those of “real” chlorophyll a were found in the euphotic zone.