In studies to determine and quantify the natural carbon storage capacity of marine sediments, a large number of different approaches, measurement methods and reference values have been used to date, making it difficult to reliably assess their suitability as a long-term carbon sink and, above all, making it largely impossible to compare different habitats in terms of their carbon storage capacity. In addition, the possible release of methane from carbon-rich sediment accumulation areas, which is antagonistic in terms of climate impact, is generally not included. In particular, data on carbon flux, the size of the sedimentary carbon reservoir or carbon inventory and biomass are often used synonymously, which has led to controversial discussions and assessments in the past. One example of this are classic “blue carbon” approaches, which in our view have so far only partially and in some cases insufficiently included or taken into account the role of natural sediments as a long-term carbon sink.