Roughly half of all primary production on Earth occurs in the ocean. The so-called light reactions of photosynthesis are understood in the context of the Z-Scheme of photosynthesis. Based on that understanding, a minimum of 8 photons of light are required to generate the reducing power required to fix one carbon atom. Additional reducing power is required for other purposes, such as the reduction of nitrate if nitrate is the source of nitrogen. Remarkably, quantum requirements derived from analysis of field data have sometimes indicated that fewer than 8 photons are associated with the fixation of one carbon atom. The explanation for this discrepancy may reflect an imperfect understanding of the fate of photons absorbed by so-called antenna pigments and/or difficulties associated with estimating the amount of light absorbed by phytoplankton cells and used to fix carbon. Models of the relationship between irradiance and photosynthetic rates in the euphotic zone of the ocean typically ignore the fact that the spectral characteristics of submarine light change dramatically with depth, the result being that there is a much better match between the spectral characteristics of submarine light in the lower half of the euphotic zone and the absorption bands of the major light-absorbing pigments. Expressing photosynthetic rates as a function of absorbed light rather than incident light leads to functional relationships between light and photosynthesis that are different from results obtained in laboratory experiments in which the spectral characteristics of light are constant and only the intensity varies.
Dr. Edward Laws received his Ph.D in Chemical Physics from Harvard University in 1972. He was an instructor in the oceanography department at Florida State University from 1971 to 1974. He joined the faculty of the oceanography department at the University of Hawaii in 1974, where he became a professor of oceanography in 1984. He moved to Louisiana State University (LSU) in 2005 and served as the dean of the School of the Coast & Environment until 2008. He is currently a professor in the Department of Environmental Sciences at LSU. Dr. Laws has published more than 170 refereed papers in scientific journals and is the author of two books, Mathematical Methods for Oceanographers and Aquatic Pollution. Aquatic Pollution is now in its 4th edition and has been translated into both Japanese and Chinese. Dr. Laws served on the editorial board of Limnology & Oceanography from 1981 to 1984. He received the Best Paper Award from the Organic Geochemistry Division of the Geochemical Society in 1995 and the Tyge Christensen Prize for best algal paper in Phycologia in 2007. He received the Qingdao Award from the Qingdao Municipal Government in 2012 and 2015 and delivered the Nanqiang Lecture “The Earth’s Changing Climate: Natural Cycles and Human Effects” atXiamen University on July 23, 2013.