John Francis Talling. 23 March 1929—20 June 2017

John (Jack) Francis Talling was a master limnologist who pioneered much of our understanding of the River Nile, the great lakes of the African Rift Valley and those of the English Lake District. He was one of the world's leading authorities on the ecophysiology of freshwater phytoplankton and specialized in the control of their productivity by light and carbon dioxide. His perspectives were formed by interaction with leading scientists of the day, mainly at the Freshwater Biological Association, Cumbria, but also at laboratories in Africa and at the Scripps Institution of Oceanography, California. Jack's work on the effects of light on phytoplankton productivity was based on detailed measurements of the underwater light climate in lakes and oceans as well as laboratory and field measurements of the response of phytoplankton photosynthesis to light, involving the development of new or improved measurement methods. Calculation procedures were developed to estimate how light controls primary productivity. He devised the widely used characteristic ‘ I k ’ to quantify the onset of light saturation in the curve that defines the response of photosynthesis to light quantity. Experiences in extremely productive African soda lakes stimulated an interest in the possibility of CO 2 being a limiting factor controlling phytoplankton productivity and, more generally, Jack had the ecological insight to recognize that ecological dynamics resulted from interactions among factors rather than a response to a single variable.