The Physical Chemistry of Predicting the Biogeochemical Consequences of Ocean Warming: Old Rules Still Apply in a New Game

Global warming, dominantly ocean warming since over 90% of the greenhouse gas generated heat is absorbed by the ocean, is having a profound effect on marine biogeochemical systems and driving the poleward migration of fisheries. Our ability to describe the trajectory of this is poor. While the physics of circulation of a warming ocean are well described by the equations of motion, the biological and geochemical aspects of the problem have not received equal treatment. The tradition has been to adopt ad hoc statistical fits to data, often as a function of depth or as a linear function of ΔT Celsius, rather than make use of the formal rules governing the thermal behavior of chemical and biogeochemical systems. Here we show that the basic van `t Hoff and Arrhenius laws of physical chemistry have been largely ignored or overlooked in the ocean sciences. We have carried out a quantitative literature search for such citations in all publications from 1960 to the present as covered by the Scopus abstract and citation database. We have compared these to IPCC reports and to all AGU journals over the same period. Our search shows that, while there are over 20,000 citations to these equations in the chemical sciences, articles using these laws to discuss how temperature affects chemical and biological process in the ocean are only in the double digits in AGU journals and applications are scant in the IPCC reports. There are no simple answers to complex problems, but we could use a better signpost. We posit that the long term trends will be better represented as a log function of 1/T Kelvin than by any other formulation. Such a rule well describes ocean oxygen consumption rates, and the physical structure of water itself. And we note that a small tendency to polar magnification of impacts is built in here as a constant ΔT offset has a greater impact at colder temperatures than warmer ones. In brief and as always we have a better chance of seeing farther ahead if we stand on the shoulders of giants.