Predicting spatial variability in sedimentary organic carbon content and composition on continental margins – the East Asian marginal seas as a case study

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.

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 60 % more published and unpublished data, 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.

Here, we use the East Asian marginal seas as a case study. This expansive marginal sea (~4 million km²) 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 (δ¹³C, ¹⁴C) 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.

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. Earth Syst. Sci. Data 13, 2135–2146. doi:10.5194/essd-13-2135-2021