Impact of ecosystem metabolism on CO2 emissions: Insights from high-resolution time series of pH measured in situ

•In-situ pH measurements provide continuous DIC and CO2 concentrations over months.•Time-series of metabolic rates of carbon were assessesd with a diel pH technique.•CO2 emission does not depend on current but on the preceding sequence of production.•Numerical experiments illustrate why DIC and CO2 are not well correlated to NEP.•Average CO2 emissions derived from sporadic CO2 data or productivity is unreliable.