A large part of the shallow subsurface in the Netherlands consists of Holocene fluvial and coastal deposits, which are rich in organic matter. On longer time scales, such as the Holocene, these deposits form a more or less permanent carbon sink. It is however so-far not well known what the magnitude of this terrestrial carbon sink is, due to the high variability of the amount of carbon in sediments and soils. Quantification of this sink is important to better understand the magnitude of the lateral and vertical fluxes within the terrestrial part of the global carbon cycle, and to determine the storage capacity of fluvial and coastal deposits. Within the Dutch Holocene subsurface, three forms of organic carbon storage are distinguished: (i) peat deposits, (ii) particulate organic matter intercalated in fluvial deposits, and (iii) organic carbon absorbed to clay minerals.