Diurnal variability of ocean CO2 system variables is poorly constrained. Here this variability and its drivers are assessed using 3‐hourly observations collected over 8‐140 months at 37 stations located in diverse marine environments. Extreme diurnal variability, i.e. when the daily amplitude exceeds the 99th percentile of diurnal variability, is comparable in magnitude to the seasonal amplitude and can surpass projected changes in mean states of pCO2 and [H+] over the twenty‐first century. At coastal sites and near coral reefs, extremes in diurnal amplitudes reach 187±85 and 149±106 μatm for pCO2, 0.21±0.08 and 0.11±0.07 for pH, and 1.2±0.5 and 0.8±0.4 for Ωarag, respectively. Extreme diurnal variability is weaker in the open ocean, but still reaches 47±18 μatm for pCO2, 0.04±0.01 for pH, and 0.25±0.11 for Ωarag. Diurnal variability of the ocean CO2 system is considerable and likely to respond to increasing CO2. Therefore, it should be represented in Earth system models.
Torres O., Kwiatkowski L., Sutton A. J., Dorey N., & Orr J. C., in press. Characterising mean and extreme diurnal variability of ocean CO2 system variables across marine environments. Geophysical Research Letters. Article (subscription required).