Geochemical Evidence of Hourly Ecosystem Photosynthetic Plasticity within a Pristine Coral Atoll - Supplementary Material

Data is organized with explanatory column headers. Total alkalinity (µmol*kg-1) was determined through open-cell automated titration (876 Dosimat plus, Metrohm AG) with a solution of 0.1M hydrochloric acid (HCl) + 0.6M sodium chloride (NaCl). Total dissolved inorganic carbon (µmol*kg-1) was obtained through coulometric determination (VINDTA 3D, Marianda with UIC coulometer).

Remaining carbonate system parameters were calculated via CO2SYS v2.1 for Microsoft Excel using the total pH scale with carbonate equilibrium constants refit from Mehrbach et al. (1973) by Dickson and Millero (1987); borate alkalinity was calculated using the boron/chlorinity (salinity) relationship provided by Uppström (1974) and equilibrium constants from Dickson (1990). Long-term precision on DIC and TA based on repeated measurements of CRM materials was ± 3.7 µmol*kg-1 (n = 46; 2σ std. dev.) and ± 4.3 µmol*kg-1 (n = 41; 2σ std. dev.), respectively. δ13C of DIC (in the form of CO2) extracted from the seawater was measured at the University of Washington School of Oceanography via mass spectrometry according to the procedure described in Quay et al. (Quay et al., 1992).

The reproducibility of all δ13CDIC values based on replicate internal seawater standard measurements is ±0.1‰ (1σ std. dev.). Temperature (± 0.005ºC) and salinity (± 0.005) at the sampling site were obtained using an SBE 16plus V2 SeaCAT CTD Recorder.