||The complexities of the marine carbon cycle continue to be uncovered. In this issue, Fassbender et al. (2018, ) combined measured surface ocean partial pressure of carbon dioxide (pCO(2)) with model predictions of increases in dissolved inorganic carbon to explore seasonal pCO(2) changes. They find that when seasonal cycles of other variables (temperature, salinity, total alkalinity, and dissolved inorganic carbon) are maintained to climatological means, seasonal amplitudes of pCO(2) are affected asymmetrically. Thus, even ignoring other natural or climate change factors, the assumption that the seasonal cycle of pCO(2) will be preserved may not be valid. Fassbender et al. (2018) intentionally ignore the influence of other variables such as a global warming signal in order to hone in explicitly on carbon system dynamics. The results show that when studying CO2 fluxes, especially into the future, the full seasonal cycle must be investigated, as what happens at one time of year may not translate to the rest of the year. Practically, this means that in order to fully understand the marine carbon cycle and its control over atmospheric CO2 levels, there is an urgent need for more surface pCO(2) data covering more months of the year particularly in the polar oceans that are highly seasonally biased.