Incommensurate Global Cold-Seep Area Constructions and Their Consequences for an Iron-Bound Organic-Carbon Stock

Luigi Caputi

Global biogeochemical inventories require a spatial domain that is commensurate with the
measured concentration, sediment mass, and ecosystem state. We re-evaluate the area term
used by Ye et al. (2026) to estimate 142–218 Tg C of iron-bound organic carbon (Fe-OC)
in the upper 30 cm of mature cold-seep sediment. Two primary results emerge. First,
Ye et al. state that cold seeps occupy less than 0.05% of continental-slope area, citing a
source that gives approximately 41 million km2 of slope. That statement implies less than
2.05 × 104 km2, yet the same article later applies 2.05–3.15 × 105 km2 without a domain
conversion. Second, the two values in that reported span are not shown to be bounds from
a common estimator. The identifiable lower-source premises form a top-down slope-area–
occupation calculation; the upper numerical fingerprint is a bottom-up extrapolation of
an approximately 350-km2 Haima field descriptor across a discovery-limited count of more
than 900 seeps. The methods, spatial objects, sampling frames, and error structures are
incommensurate, and “more than 900” cannot generate an upper bound at a nominal count
of 900. Independent fluid-expulsion compilations and regional acoustic surveys document
substantial inventory incompleteness and heterogeneity but do not supply a global activesediment
area. The absolute stock also contains an undisclosed sediment-mass coefficient:
reproducing both endpoints with the reported depth and Fe-OC content requires an effective
value near 1.65 g cm−3. Interpreted as dry bulk density, this value is high relative
to available regional and near-surface seep analogs, although not physically impossible.
Replacing only 205,000 by the printed-premise product of 20,500 km2 still changes the
corresponding endpoint from about 142 to 14.2 Tg C, but this is a controlled sensitivity,
not a new lower bound. The disclosed record therefore does not support interpreting the
published area pair or derived stock span as empirical global intervals.