| Summary: | Organic carbon decomposition was measured in rhodolith beds using the Teabag Index (TBI; Keuskamp et al., (2013; https://doi.org/10.1016/j.ecolind.2022.109077). The data includes measurements relating to carbon decomposition including mass loss, organic carbon loss, decomposition rate (k) and stability factor (S). Oxygen (O2), dissolved inorganic carbon (DIC) and calcium carbonate (CaCO3) flux measurements were also obtained to measure sediment respiration and photosynthesis rates (using O2 and DIC fluxes) and calcification and dissolution rates (using CaCO3 fluxes). Measurements were obtained from in vitro incubations of rhodolith bed community samples (contained in Perspex cores). Samples were collected by hand using scuba from Loch Sween (Scotland; 56.031837, -5.601581; Water depth = 7m) and contained sediment (~8cm), macroalgae and calcifying fauna on the top of the sediment. Experiments were run in the summer and winter. Samples were collected on 2021/04/28 for the summer experiments and 2021/01/01 for the winter experiments. Separate mesocosms (referred to as cores) collected for each sampling campaign. There were 4 treatments for this experiment: T CO2: Ambient pCO2 (Bubbled gas composition = 400ppm) and temperature; T+ CO2: Ambient pCO2 (400ppm) and elevated temperature (3°C); T CO2: Elevated pCO2 (750ppm) and ambient temperature; T+ CO2+: Elevated pCO2 (750ppm) and elevated temperature (+3°C). For each core, light and dark incubations were run for 2 hours to calculate light and dark flux measurements. Net (daily) flux was calculated by multiplying light and dark incubations by the respective amount of hours spent in the light or dark. O2 fluxes were calculated by using optic spots, with O2 concentrations taken at the start and end of the incubation. DIC fluxes were determined by measuring the DIC concentration of water samples at the start and end of the incubation. DIC was determined using an Automated Infra-Red Inorganic Carbon Analyser (AIRICA). CaCO3 fluxes were calculated using the alkalinity ...
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