The Molecular Basis for Understanding the Impacts of Ocean Warming

A grand challenge for ocean chemists in the years ahead lies in the need to tackle the chemical consequences of ocean warming with the same rigor and intensity that has been brought to bear on the physical chemistry of ocean acidification. For over 50 years ocean chemistry has been dominated by the study of pH‐dependent processes, but to address the biogeochemical impacts of ocean warming, we will need to rapidly advance the discipline of ocean chemical physics where temperature is the master variable and the basic unit is the Joule. Just as it would be impossible to understand the ocean CO2 system without awareness of the essential pH‐dependent CO2‐HCO3‐CO3 equilibria, so too is it impossible to describe ocean chemical physics without knowledge of the bimolecular structure of water. Water, and water in sea water, is composed of a complex of dominant hydrogen bonded forms, and the singlet molecular H2O species, in temperature‐controlled equilibrium and the ratio of these forms, can now be precisely determined. The physical properties of sea water are traditionally described by fitting an ad hoc collection of coefficients to experimental data. They are more accurately described as temperature and pressure perturbations of the underlying molecular equilibrium state. Ocean oxygen consumption rates are accurately described as an Arrhenius function, and not as an exponential function of depth as has been the tradition for over 50 years. We do not now have good correlation between ocean models and observed warming and oxygen declines, and full anoxia with the emergence of hydrogen sulfide over large regions of the ocean is possible. The parallel ocean invasions of heat and fossil fuel CO2 must be combined to estimate their full impact. Plain Language Summary The ocean absorbs some 93% of all greenhouse gas‐generated heat, and ocean warming is already creating observable impacts on marine life. To make reliable projections for the future, we cannot rely on Ptolemy‐like rules, built as something to match field observations, to apply in the years to come. Instead, we will need to apply the laws of chemical physics to calculate and predict the changes that ocean warming will have on the physical properties of sea water and the associated impacts on marine life. This includes treating water as a fluid with defined temperature‐ and pressure‐dependent chemical structures. Sea water is 96.5% water, and some 78–85% of water in the oceans has a form with a much higher mol