Characterizing Mean and Extreme Diurnal Variability of Ocean CO2 System Variables Across Marine Environments

Diurnal variability of ocean CO2 system variables is poorly constrained. Here, this variability and its drivers are assessed using 3-h observations collected over 8-140 months at 37 stations located in diverse marine environments. Extreme diurnal variability, that is, when the daily amplitude exceeds the 99(th) percentile of diurnal variability, is comparable in magnitude to the seasonal amplitude and can surpass projected changes in mean states of pCO(2) and [H+] over the twenty-first century. At coastal sites and near coral reefs, extremes in diurnal amplitudes reach 187 +/- 85 and 149 +/- 106 mu atm for pCO(2), 0.21 +/- 0.08 and 0.11 +/- 0.07 for pH, and 1.2 +/- 0.5 and 0.8 +/- 0.4 for omega(arag), respectively. Extreme diurnal variability is weaker in the open ocean, but still reaches 47 +/- 18 mu atm for pCO(2), 0.04 +/- 0.01 for pH, and 0.25 +/- 0.11 for omega(arag). 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.

Automated summary

The diurnal variability of ocean CO2 system variables is considerable and can exceed the seasonal amplitude, especially at coastal sites and near coral reefs. Extreme diurnal variability may surpass the projected changes in mean states of pCO(2) and [H+], highlighting its importance in Earth system models.