adopted until it had been described in English (Gaarder and Gran, 1927). Although it was possible at that time to estimate carbon dioxide uptake in similar bottles, essentially through the use of pH-sensitive indicator dyes, the measurement of photosynthetic rate through changes in oxygen concentration in light and dark bottles was soon adopted as a standard method in biological limnology and oceanography.
In this section, the focus moves towards the physiology of photosynthetic behaviour of phy-toplankton in natural lakes and seas, especially its relationship with underwater light availability. According to a recently compiled history of phytoplankton productivity (Barber and Hilting, 2002), quantification of pelagic photosynthesis developed through a series of sharp conceptual and (especially) methodological jumps. After a rapid series of discoveries in the late eighteenth century, establishing that plants need light and carbon dioxide to produce oxygen and organic matter from carbon dioxide, there was much slower progress in estimating the rates and magnitude of the exchanges. This is especially true for aquatic primary production, until the idea that it could have much bearing on the tropho-dynamics of the sea became a matter of serious debate (see Section 1.2). It was not until the beginning of the twentieth century, as concerns came to focus increasingly on the rates of reproduction and consumption of planktic food plants, that the pressing need for quantitative measures of plankton production was identified (Gran, 1912). Building on the techniques and observations of Whipple (1899), who had shown a light dependence of the growth of phytoplankton in closed bottles suspended at various depths of water, and using the Winkler (1888) back-titration method for estimating dissolved oxygen concentration, Gran and colleagues devised a method of measuring the photosynthetic evolution of oxygen in sealed bottles of natural phytoplankton, within measured time periods. Darkened bottles were set up to provide controls for respirational consumption. They published (in 1918) the results of a study of photosynthesis carried out in the Christiania Fjord (now Oslofjord). According to Barber and Hilting (2002), the method was not widely
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