Faults in the Radiocarbon Method and Problems in its Calibration
65
may be used successfully for primary production estimations. After incubation
they only need to be shaken with 1O-20ml of 5% Na2C03 solution, rinsed once
with distilled water, and dried by being turned upside down. So, my advice is
to check the validity of recommended operations personally to be sure that
they suit yours conditions of work.
Concermng the bottle effect, it also vanes in different kinds of water
bodies and under different incubation conditions. The confinement of samples
most rapidly and drastically influences the natural assemblages of microplankton in samples of oceanic waters, and especially of oligotrophic tropical waters.
Most alarms about the validity of the 14C-method and the bottle effect began
just here (Venrick et al. 1977; Gieskes et al.1979; Shushkina et al.1984; Sorokin
1987; Krupatkina 1990). In bottles of -300-ml capacity, which are normally in
use under such circumstances, obvious changes in microplankton composition
become detectable after some 6-8h of incubation under in situ temperature
and light conditions. Under full sunlight it can happen even earlier, after 45 h (Harris and Picchinin 1977; Harris 1986). The first reaction of microplankton on confinement is the appearance of large bacterioplankton cells and the
shrinkage or even death of the phytoflagellates. The best indicator of this
impact could in any case be the linearity of CO2 uptake, which continues
usually for 4 to 6h in warm surface waters (Rodhe 1958; Eppley et al. 1973;
Sorokin 1987). It lasts during the first 4 h of incubation even in tropical waters
in bottles of 350-600ml capacity. So the regime recommended here of shortterm incubation (2-3 h) actually avoids the problem of the bottle effect when
using the 14C-method. Another point is the use of the oxygen method either
as basic for primary production measurements, or as reference for calibration
of the 14C-method (see below). The oxygen method needs long-term incubations - at least half of the light day - which can lead to the bottle effect. In
any case, when using the oxygen method, incubations of 24 h should be avoided
by any means.
The discussion on the faults of the radiocarbon method itself revolved
mostly around the following problems:
1. The quality of the working solution of 14C-carbonate (Williams et al.
1972; Sharp 1977; Harris 1980; Brest et al. 1987). The grade of working solutions ready for use which are supplied by corresponding agencies was usually
recognized as very low. They can contain heavy metals, radiolabeled particulated, and dissolved organic matter, which might variously influence the results
of primary production measurements. Especially this concerns the estimation
of losses of 14C-assimilates as a consequence of filtration (Thomas 1971). In
fact, for such experiments it is necessary to clean the working solution personally by passing the stock of the batch through the CO2 gas phase (see Sect.
2.3.2.1). Standard working solutions of 14C-bicarbonate supplied commercially
can be used only for work in produtive waters. In this case also, however, the
batch must first be tested for zero time or Lugol fixed background, which
should be less than 10cpm. For work in oligotrophic water, as for experiments
65
may be used successfully for primary production estimations. After incubation
they only need to be shaken with 1O-20ml of 5% Na2C03 solution, rinsed once
with distilled water, and dried by being turned upside down. So, my advice is
to check the validity of recommended operations personally to be sure that
they suit yours conditions of work.
Concermng the bottle effect, it also vanes in different kinds of water
bodies and under different incubation conditions. The confinement of samples
most rapidly and drastically influences the natural assemblages of microplankton in samples of oceanic waters, and especially of oligotrophic tropical waters.
Most alarms about the validity of the 14C-method and the bottle effect began
just here (Venrick et al. 1977; Gieskes et al.1979; Shushkina et al.1984; Sorokin
1987; Krupatkina 1990). In bottles of -300-ml capacity, which are normally in
use under such circumstances, obvious changes in microplankton composition
become detectable after some 6-8h of incubation under in situ temperature
and light conditions. Under full sunlight it can happen even earlier, after 45 h (Harris and Picchinin 1977; Harris 1986). The first reaction of microplankton on confinement is the appearance of large bacterioplankton cells and the
shrinkage or even death of the phytoflagellates. The best indicator of this
impact could in any case be the linearity of CO2 uptake, which continues
usually for 4 to 6h in warm surface waters (Rodhe 1958; Eppley et al. 1973;
Sorokin 1987). It lasts during the first 4 h of incubation even in tropical waters
in bottles of 350-600ml capacity. So the regime recommended here of shortterm incubation (2-3 h) actually avoids the problem of the bottle effect when
using the 14C-method. Another point is the use of the oxygen method either
as basic for primary production measurements, or as reference for calibration
of the 14C-method (see below). The oxygen method needs long-term incubations - at least half of the light day - which can lead to the bottle effect. In
any case, when using the oxygen method, incubations of 24 h should be avoided
by any means.
The discussion on the faults of the radiocarbon method itself revolved
mostly around the following problems:
1. The quality of the working solution of 14C-carbonate (Williams et al.
1972; Sharp 1977; Harris 1980; Brest et al. 1987). The grade of working solutions ready for use which are supplied by corresponding agencies was usually
recognized as very low. They can contain heavy metals, radiolabeled particulated, and dissolved organic matter, which might variously influence the results
of primary production measurements. Especially this concerns the estimation
of losses of 14C-assimilates as a consequence of filtration (Thomas 1971). In
fact, for such experiments it is necessary to clean the working solution personally by passing the stock of the batch through the CO2 gas phase (see Sect.
2.3.2.1). Standard working solutions of 14C-bicarbonate supplied commercially
can be used only for work in produtive waters. In this case also, however, the
batch must first be tested for zero time or Lugol fixed background, which
should be less than 10cpm. For work in oligotrophic water, as for experiments