Temperature and glucose effects on dunite weathering, dissolved inorganic carbon, and CO₂ fluxes in soil incubations (5–50 °C)

This dataset reports measurements from soil incubations examining the effects of temperature (5–50 °C, 18 increments) and labile organic carbon (glucose) on dunite weathering, dissolved inorganic carbon (DIC) production, and CO₂ fluxes. Treatments included soil alone, soil + dunite, soil + glucose, and soil + dunite + glucose, which were incubated for three days. Raw data include dissolved inorganic and organic carbon (DIC and DOC) concentrations, headspace CO₂, pH, total alkalinity, and dissolved cations (Ca²⁺, Mg²⁺, Na⁺ and K⁺). Calculated weathering rates and the 'seacarb' calculated bicarbonate and carbonate sum (DIC species minus dissolved CO₂) are also reported (Gattuso et al., 2024). The incubations were performed on a heat block with 18 wells, one end was cooled and the other heated providing a temperature gradient. Temperature loggers (DS1921G Thermochron iButton, Analog Devices, Inc., USA) were placed in wells 1, 4, 7, 9, 11, 13, 15, and 18, and the temperatures of the remaining wells were calculated via linear regression. Each treatment was run separately on the temperature block. The treatment vessels were sealed periodically (time = 0–6 h, 24–30 h and 48–54 h) and samples were collected for analysis (described below). The water from all the vials for each treatment was collected then centrifuged at 3300 rpm for 10 minutes (Kubota 8420, Japan). Subsamples were taken for alkalinity (via titration to pH 4.2 with 0.01 mol/l HCl) and pH measurements (10 ml) (SI Analytics Titroline 7000); and dissolved inorganic (DIC) and organic carbon (DOC) measurements (10 ml) (OI Analytical Aurora 1030 TOC analyser, Xylem, USA). A 5–10 mL subsample was also taken, filtered to 0.45 µm and acidified to 2 % v/v with HNO₃, for Mg, Ca, K, and Na analysis via ICP-MS (Agilent 8900 ICP−MS, Agilent Technologies, California, USA). Alkalinity titrations provided the moles of H⁺ for the samples (gravimetrically determined volume) to reach pH 4.2. The moles of H⁺ were converted to meq and divided by the sample volume. DIC and DOC analyses were performed alongside a gravimetrically produced calibration set of Potassium Hydrogen Phthalate, via wet oxidation which provided CO₂ peak area. Peak area was plotted against the known molar concentrations of the calibration set, and a linear regression was used to solve for the unknown sample molar concentrations. Dissolved cations (Ca²⁺, Mg²⁺, Na⁺ and K⁺) measured via ICP−MS were converted from µg/l to mmol using the atomic mass and solution volume of the treatment, for weathering rate calculations. Headspace CO₂ samples were measured alongside known volumes of high purity (>99%) CO₂, which were used for calibration standards, as peak area in mV. The moles of CO₂ in the standards were calculated using the known volume, pressure and the ideal gas law, the peak area of the samples used to solve for moles against the linear calibration. The measured sample (moles) were converted to mmol/l by dividing by the volume injected into the analyser, which was subsequently multiplied by the headspace volume of the treatment vessels to get the moles of CO₂ reported here. Seacarb (flag 8, salinity = 0) was used to calculate the total alkalinity based bicarbonate and carbonate for soil + dunite and soil + dunite + glucose, after subtracting the total alkalinity of soil and soil + glucose respectively. Seacarb (flag 9, salinity = 0) was also used to calculate the DIC based bicarbonate and carbonate for soil + dunite and soil + dunite + glucose, after subtracting the DIC of soil and soil + glucose respectively. Weathering rates were calculated using the net total cation sums (i.e. ∑[Mg²⁺], [Ca²⁺], [K⁺], [Na⁺]). The total cation sums for soil alone and soil + glucose were subtracted from the total cation sums of soil + dunite and soil + dunite + glucose respectively, to provide net total cation sum. The net cation molar sum was divided by the specific surface area (m² g⁻¹), dunite mass (g) and t = time (s), to provide weathering rates which were subsequently log transformed.