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<p>Continental margins play a central role in the global carbon cycle, but the heterogenous OC origin, sediment transport processes, and depositional environments lead to complex patterns of distribution and accumulation of OC that render it challenging to quantitatively assess their role in global biogeochemical cycles. While previous studies have focused on predicting the distribution of sedimentary OC, comprehensive spatial constraints that link the provenance and composition of OC with the processes affecting its storage on continental margins are lacking. For example, radiocarbon is a powerful tool for understanding the origin and depositional fate of OC but it is not extensively used due to its cost and measurement accessibility, leading to sparse data coverage on continental margins.</p><p>The Modern Ocean Sediment Archive and Inventory of Carbon (MOSAIC) database (Van der Voort et al., 2021) was recently established to compile and curate data on the OC content and its composition in continental margin sediments worldwide together with relevant sedimentological and environmental variables. This database is continuously being revised and presently includes > 60 % more published and unpublished data, > 100 % more variables, and executes harmonization techniques designed to increase its richness and utility. Using this new database in combination with geostatistical and geospatial techniques, we aim to explore relationships between depositional settings and the content and composition of organic carbon, with the goal of ultimately predicting sedimentary organic carbon properties over a range of spatial scales.</p><p>Here, we use the East Asian marginal seas as a case study. This expansive marginal sea (~4 million km<sup>2</sup>) is characterized by highly heterogenous OC inputs, dynamic sediment transport processes, and diverse depositional environments, while presenting a wealth of sedimentological and geochemical data, which makes this area the perfect natural laboratory to assess the influence of these environmental factors on the spatial distribution of sedimentary OC content, composition, and age. A spatial model predictor was developed with over 2000 data points of organic carbon and its isotopic composition (δ<sup>13</sup>C, <sup>14</sup>C) as well as sedimentological properties extracted from the updated version of MOSAIC, coupled with relevant spatial environmental explanatory variables. Results indicate that the distribution of sedimentary organic carbon throughout this margin is non-stationary due to the regional influences of different depositional environments. Observing this on a regional scale emphasizes the need to incorporate the local effect of depositional environments to accurately predict the fate of organic carbon in marine sediments worldwide.</p><p>Van der Voort, T. S., Blattmann, T., Usman, M., Montluçon, D., Loeffler, T., Tavagna, M. L., et al. (2021). MOSAIC (Modern Ocean Sediment Archive and Inventory of Carbon): a (radio)carbon-centric database for seafloor surficial sediments.<em> Earth Syst. Sci. Data</em> 13, 2135–2146. doi:10.5194/essd-13-2135-2021</p>

Abstract. Marine sediments play a crucial role in the global carbon cycle by acting as the ultimate sink of both terrestrial and marine organic carbon. To understand the spatiotemporal variability in the content, sources and dynamics of organic carbon in marine sediments, a curated and harmonized database of organic carbon and associated parameters is needed, which has prompted the development of the Modern Ocean Sediment Archive and Inventory of Carbon (MOSAIC) database. We present here MOSAIC version 2.0, which has expanded the spatiotemporal coverage of the original database by ~400 %, and now holds data from more than 17000 individual sediment cores from different continental margins on a global scale. Additional variables have also been incorporated into MOSAIC v.2.0 that are crucial to interpret the distribution of the quantity, origin and age of organic carbon in marine sediments globally. Sedimentological parameters (e.g., grain size fractions, mineral surface area) help understand the effect of hydrodynamic sorting and mineral protection in the distribution of organic carbon, while molecular biomarker signatures (e.g., lignins phenols, fatty acids, alkanes) can constrain the origin of organic matter with a greater level of specificity. MOSAIC v.2.0 also stores data from analyses performed on specific sediment and molecular fractions, which provide further insight of the processes that affect the degradation and ageing of organic carbon in marine sediments. While data included within MOSAIC is not exhaustive, it is continuously expanding and version control will allow users to benefit from updated versions while ensuring reproducibility of their findings.