Torres, O., Kwiatkowski, L., Sutton, A. J., Dorey, N., Orr, J. C. (2021) Characterising mean and extreme diurnal variability of ocean CO2 system variables across marine environments, Geophys. Res. Lett., e2020GL090228, accepted, https://doi.org/10.1029/2020GL090228
Our understanding of how ocean pH and related chemical variables vary during the day (known as diurnal variability) is not well established. In this study, a recent data set was used of such observations collected every 3 h during 8–140 months from 37 buoys located across the oceans to assess these diurnal variations and what drives them. In extreme cases, observed changes over 24 h were found to be greater than those observed between seasons. Diurnal variations in these chemical variables are particularly large in coastal waters and near coral reefs and are not negligible further offshore. Along with the more gradual, long‐term acidification of the ocean from atmospheric CO2 increases year after year, diurnal and seasonal variability of ocean chemistry is also expected to change dramatically. Understanding how this diurnal variability will change in the future is important because it modulates the levels of acidification experienced by marine organisms from long‐term yearly changes.