Alternatively, volatile OSCs could potentially form with an
equilibrium isotope effect if they derive from a Sx
2 pool that has
a different isotopic composition from porewater HS. Such an isolated
pool would need to be substantially more 34S-depleted than
porewater HS and might be present within cells or in microenvironments
in the sediment. Without corroborating evidence for the
existence of such an isolated reservoir, this explanation remains
speculative. Still, if their existence is supported by future work,
non-porewater Sx
2 reactants could explain OSCs with d34S values
that differ from porewater S2 d34S without invoking a large kinetic
isotope effect during OSC formation.