Mapping vulnerable organic carbon in Norway’s continental margin sediments

Continental margin sediments are a major hotspot for organic carbon burial and play a vital role in the carbon cycle. Disturbance of sedimentary organic carbon by human activities such as mobile bottom fishing might lead to (i) reductions of the organic carbon stocks, (ii) impacts on carbon cycling, primary productivity and biodiversity and (iii) ocean acidification and atmospheric CO₂ emissions. Spatially explicit studies that have been conducted to inform marine management have so far looked at organic carbon stocks that have already been affected by mobile bottom fishing. Here, we focus instead on areas on the Norwegian continental margin that have not been fished previously, based on fishing data covering the years 2009 – 2020. We estimate that the surface sediment layer (0 – 2 cm) in unfished areas covering 765,600 km² contains 139.2 Tg of organic carbon. Based on data from a meta-analysis of demersal fishing impacts on organic carbon density, we estimate that 16.4 Tg (1.8 – 29.6 Tg) of organic carbon might be vulnerable to mobile bottom fishing. Of this, approximately one third is currently located in existing area-based protection measures. Additional protection could be guided by hotspots of vulnerable organic carbon, which are found in the Barents Sea. We argue that the protection of vulnerable organic carbon that is at high risk of being lost in areas becoming accessible to fishing due to sea ice retreat in the northern Barents Sea should be prioritised over easing pressure on already impacted organic carbon stocks.