Life in the shelf seas - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 138

Figure 5.4 Biochemists exercising their plumbing skills, setting up the apparatus for a
simulated in situ incubation experiment on the aft deck of the RRS Discovery, June 2010.
The boxes will contain the bottles of incubating samples, with surface seawater continuously
pumped through them to keep the samples cool. Different light filters are fitted over the
boxes to reduce the light received by the samples, mimicking the light variation with depth
below the sea surface. (Photo by J. Sharples.)
incubated are spiked with 14 C and are then placed in large containers on a clear area
of the ship's deck, exposed to daylight between dawn and dusk. Seawater from the
sea surface is continuously pumped around the sample bottles to prevent them from
over-heating. The light received by the samples is controlled using neutral-density
and blue filters over the containers, attempting to simulate both the reduction of light
and the change in the spectrum with depth. Each light 'treatment' will have several
replicates to provide some statistical reliability to the production estimates. At dusk,
some of the replicates at each light level are removed and analysed, yielding the net
uptake of carbon during daylight hours. The others are left in the incubators
overnight, subsequently analysed to yield net carbon uptake over 24 hours and, by
comparing with the daylight uptake values, provide a measure of carbon loss during
the night. An example of such an experimental set-up is shown in Fig. 5.4 .
Short-term incubations and the photosynthesis-PAR curve
Understanding how photosynthesis of an autotroph population varies in response to
light can be achieved using short-term (1-2 hour) incubations with 14 C. A large
number of samples are collected from one depth, either set by the light level or
perhaps targeting a particular layer of phytoplankton. The water samples are placed
in small bottles along with the isotope spike. The bottles are then placed in a
laboratory incubator called a 'photosynthetron' where they are incubated, each at