CASCADE – The Circum-Arctic Sediment CArbon DatabasE

Biogeochemical cycling in the semi-enclosed Arctic Ocean is strongly influenced by land–ocean transport of carbon and other elements and is vulnerable to environmental and climate changes. Sediments of the Arctic Ocean are an important part of biogeochemical cycling in the Arctic and provide the opportunity to study present and historical input and the fate of organic matter (e.g., through permafrost thawing). Comprehensive sedimentary records are required to compare differences between the Arctic regions and to study Arctic biogeochemical budgets. 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 terrigenous biomarkers and other sediment geochemical and physical properties. This new database builds on the published literature and earlier unpublished records through an extensive international community collaboration. This paper describes the establishment, structure and current status of CASCADE. The first public version includes OC concentrations in surface sediments at 4244 oceanographic stations including 2317 with TN concentrations, 1555 with δ13C-OC values and 268 with Δ14C-OC values and 653 records with quantified terrigenous biomarkers (high-molecular-weight n-alkanes, n-alkanoic acids and lignin phenols). CASCADE also includes data from 326 sediment cores, retrieved by shallow box or multi-coring, deep gravity/piston coring, or sea-bottom drilling. The comprehensive dataset reveals large-scale features of both OC content and OC sources between the shelf sea recipients. This offers insight into release of pre-aged terrigenous OC to the East Siberian Arctic shelf and younger terrigenous OC to the Kara Sea. Circum-Arctic sediments thereby reveal patterns of terrestrial OC remobilization and provide clues about thawing of permafrost. CASCADE enables synoptic analysis of OC in Arctic Ocean sediments and facilitates a wide array of future empirical and modeling studies of the Arctic carbon cycle. The database is openly and freely available online (https://doi.org/10.17043/cascade; Martens et al., 2021), 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. We will continuously update CASCADE 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.

Patterns of terrestrial carbon distribution in the Arctic Ocean deduced from the Circum-Arctic Sediment CArbon DatabasE (CASCADE)

<p>Climate change is expected to affect the release of organic carbon (OC) from Arctic permafrost systems and other terrestrial deposits. In addition to greenhouse gas emissions on land, a fraction of the organic matter is liberated to the aquatic cycle and migrates to the Arctic Ocean where it is either degraded or buried in sediments, foremost on the vast continental shelves.</p><p>The Arctic Ocean basin represents a large footprint for contemporary and past land-ocean transport of terrestrial OC. To this end, the Circum-Arctic Sediment CArbon DatabasE (CASCADE; https://doi.org/10.5194/essd-2020-401) was established to curate and harmonize data on OC and total nitrogen concentrations, carbon isotopes (δ<sup>13</sup>C, Δ<sup>14</sup>C) and terrestrial biomarkers (long-chain n-alkanes, n-alkanoic acids and lignin phenols) in an openly accessible data collection. CASCADE was populated using carbon data from both published records and unpublished data from a large community collaboration. The first release of CASCADE includes observations at thousands of oceanographic stations distributed over the shelves and the central basins of the Arctic Ocean, and also includes hundreds of sediment cores, representing a range of time scales (decadal to orbital).</p><p>Mapping CASCADE data provides an overview to start deducing sources, pathways and deposition of carbon in different regions of the Arctic Ocean. Dual-isotope (δ<sup>13</sup>C, Δ<sup>14</sup>C) source apportionment of OC and <sup>210</sup>Pb dating of centennial-scale sediment cores permit quantitative analysis of sequestration of carbon transported from permafrost systems and other deposits to the Arctic Ocean. Preliminary results suggest that surface soils (incl. permafrost active layer) are the dominating terrestrial carbon source to Circum-Arctic shelf sediments. The second largest terrestrial source are Pleistocene ice-rich permafrost compartments (Ice Complex Deposits), which stretch along coastlines of the Laptev, East Siberian, Chukchi and Beaufort Seas and are highly vulnerable to coastal erosion and thermal collapse in a warming climate.</p><p>Climate change is likely to cause permafrost thawing by further deepening of the seasonal active layer and accelerated coastal erosion of permafrost, as well as disturbance of the vast boreal peatlands. CASCADE provides an integrated perspective and benchmark for lateral carbon remobilization and will fuel further empirical and modelling studies of Arctic biogeochemical cycles.</p>

CASCADE – The Circum-Arctic Sediment CArbon DatabasE

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.