Adult kelp blade carbon and nitrogen content along the depth gradient monitored at Hansneset, Kongsfjorden, Spitsbergen in 2021

Surveys of C:N ratios, carbon and nitrogen content in the blades of adult kelps at Hansneset, Blomstrand in Kongsfjorden, Svalbard, were performed along a depth transect down to 10m in June - August 2021. As major coastal foundation species, kelps contribute substantially to the coastal carbon cycle. The kelp forest at the sampling site changed substantially over the last 25 years and serves as a case study to document changes in Arctic kelp forest dynamics in an Arctic fjord system influenced by Arctic warming and glacial melt. The study showed that carbon and nitrogen allocation strategies significantly vary between the three prevailing kelps: A. esculenta, S. latissima, and 'Digitate Kelps' (i.e. the visually similar Laminaria digitata and Hedophyllum nigripes). Species dominance relationships in the kelp forest changed over time, which implies consequences for the coastal carbon budget and biological carbon sequestration in the fjord system. The data contains the percent of Nitrogen (N [%]), Carbon ([%]), and the ratio between the two (C:N [ratio]) found within the blades of kelps by depth, quadrat (replicate), and species. Up to five individuals were taken from each quadrat when possible. Within the species column there is a 'Digitate kelps' value. This is due to the complication of the visual similarity of Laminaria digitata and Hedophyllum nigripes. Because these are field data, and the distinction between these species requires genetic lab work, the exact species identification is not possible here. Historically these kelps were considered Laminaria digitata.