Sunk biomass will likely decompose, and the resulting dissolved products will mix in the water reservoir. When the mixing dynamics of the reservoir bring decomposition products back to the surface, they will equilibrate with the atmosphere, which could result in the outgassing of CO₂ or other greenhouse gases. The estimated timescale of this outgassing is dependent on the location of sinking, the storage depth achieved, and local stratification and circulation dynamics. Any claim about the volume of total carbon removal from biomass sinking should therefore be accompanied by a clear claim about the portion of biomass that is assumed to remain in solid-phase storage and a clear disclosure of the time horizon over which outgassing dynamics are considered. In the absence of clear evidence that the sunk biomass resists decomposition, it is conservative to assume that all sunk biomass is remineralized at the bottom of the reservoir in which it is sunk. The outgassing of such non-CO₂ gasses such as methane, nitrous oxide, and sulfide should be quantified, and any GWP assumptions used to incorporate non-CO₂ outgassing into the calculation of net carbon removal should be transparently disclosed. Our evaluation reflects the uncertainties associated with estimating carbon stored for 1000+ years, and those interested in longer storage timescales may find it appropriate to adjust these uncertainties.