Supplementary tables for 'Black carbon formation at cold seeps and its potential contribution to the marine black carbon budget'

The long-term carbon sequestration capacity of black carbon (BC) is among the factors controlling climate change dynamics. Culture experiments have revealed that anaerobic methanotrophic archaea possess the ability to produce BC, but the impact of microbially-derived BC on the marine BC cycle has not been thoroughly investigated. This study examined the geochemical properties of BC preserved in seep carbonates from the South China Sea and Gulf of Mexico. δ¹³C_BC values as low as −45.2‰ in seep carbonates were observed, representing the first documented case of microbially-produced BC in natural settings — may account for 1-26% of total BC content. Examination of the radiocarbon (Δ¹⁴C) compositions suggests that BC is usually of greater age than the associated organic carbon. Given that the organic carbon found in seeps typically exhibits an ancient age, BC originating from seeps could serve as a plausible origin of aged dissolved BC in the deep sea.