Diurnal behavior of the flux and partial pressure of carbon dioxide in the surface water in solar time coordinates (the period of open water in the South Baikal littoral in 2004–2015)

A long-term series of regular measurements of the carbon dioxide concentration in the surface water and СО2 fluxes in the Baikal littoral zone demonstrated a diurnal rhythm related to processes of photosynthesis activity of plankton during the entire period of open water (from May to December). To isolate the role of only the photoperiodicity process on the background of many various factors having an effect on the change in the concentration of carbon dioxide in the surface water and СО2 fluxes in the atmosphere–water system, the scheme of the diurnal behavior of СО2 during the open water period in 2007–2015 in the littoral zone of South Baikal is considered in coordinates of sunshine duration which was calculated proceeding from the theoretically possible sunshine duration (from sunrise to sunset in the case of clear sky and open horizon). The proposed scheme of parameterization and reconstruction of these characteristics for any time instant can find application in estimating calculations in carbon cycle models and be useful in planning the optimum regime for studying biological and chemical processes in Lake Baikal.