Total mass of carbon respired as CO₂ (bars) and mass-weighted average (A) δ¹³C and (B) ∆¹⁴C during monoculture (measured by Mahmoudi et al. [29]) and coculture incubations of Vibrio splendidus 1A01 and Pseudoalteromonas sp. 3D05 with hydrothermal and unimpacted Guaymas Basin sediment; total respired CO₂ was determined by manometric quantification of microbially respired CO₂ collected during mono- and coculture incubation experiments; in order to obtain a mass-weighted average δ¹³C and ∆¹⁴C value, the isotopic value for each CO₂ fraction was multiplied by the relative mass of that fraction; these values were then summed over all the fractions within a single incubation.