CASCADE – The Circum-Arctic Sediment CArbon DatabasE
Authors: Martens Jannik , Romankevich Evgeny , Semiletov Igor , Wild Birgit , van Dongen Bart , Vonk Jorien , Tesi Tommaso , Shakhova Natalia , Dudarev Oleg V. , Kosmach Denis , Vetrov Alexander , Lobkovsky Leopold , Belyaev Nikolay , Macdonald Robie , Pieńkowski Anna J. , Eglinton Timothy I. , Haghipour Negar , Dahle Salve , Carroll Michael L. , Åström Emmelie K. L. , Grebmeier Jacqueline M. , Cooper Lee W. , Possnert Göran , Gustafsson Örjan 
Published: December 2020

Abstract. Biogeochemical cycling in the extensive shelf seas and in the interior basins of the semi-enclosed Arctic Ocean are strongly influenced by land-ocean transport of carbon and other elements. The Arctic carbon cycle system is also inherently connected with the climate, and thus vulnerable to environmental and climate changes. Sediments of the Arctic Ocean are an active and integral part in Arctic biogeochemical cycling, and provide the opportunity to study present and historical input and fate of organic matter (e.g., through permafrost thawing). To compare differences between the Arctic regions and to study Arctic biogeochemical budgets, comprehensive sedimentary records are required. To this end, the Circum-Arctic Sediment CArbon DatabasE (CASCADE) was established to curate data primarily on concentrations of organic carbon (OC) and OC isotopes (δ13C, Δ14C), yet also on total N (TN) as well as of terrigenous biomarkers and other sediment geochemical and physical properties drawn both from the published literature and from earlier unpublished records through an extensive international community collaboration. This paper describes the establishment, structure and current status of CASCADE. This first public version includes OC concentrations in surface sediments at 4244 oceanographic stations including 2317 with TN concentrations, 1555 with δ13C-OC values, 268 with Δ14C-OC values and 653 records with quantified terrigenous biomarkers (high molecular weight n-alkanes, n-alkanoic acids and lignin phenols) distributed over the shelves and the central basins of the Arctic Ocean. CASCADE also includes data from 326 sediment cores, retrieved by shallow box- or multi-coring and deep gravity/piston coring, as well as sea-bottom drilling. The comprehensive dataset reveals several large-scale features, including clear differences in both OC content and isotope-based diagnostics of OC sources between the shelf sea recipients. This indicates, for instance, the release of strongly pre-aged terrigenous OC to the East Siberian Arctic shelf and younger terrigenous OC to the Kara Sea and thus provides clues about land-ocean transport of material released by thawing permafrost. CASCADE enables synoptic analysis of OC in Arctic Ocean sediments and facilitates a wide array of future empirical and modelling studies of the Arctic carbon cycle. CASCADE is openly and freely available online (https://doi.org/10.17043/cascade; Martens et al., 2020b), is provided in various machine-readable data formats (data tables, GIS shapefile, GIS raster), and also provides ways for contributing data for future CASCADE versions. CASCADE will be continuously updated with newly published and contributed data over the foreseeable future as part of the database management of the Bolin Centre for Climate Research at Stockholm University.