Natural controls and anthropogenic impacts on organic carbon burial and remineralisation in fine-grained shelf sediments of the Helgoland Mud Area, North Sea

Since the industrial revolution, the global carbon cycle has significantly changed due to rising anthropogenic CO2 emissions from burning fossil fuels. Continental shelf sediments play a crucial role in the global carbon cycling. However, due to the dynamic nature of organic carbon-rich deposits, the mechanisms and quantities are yet not fully constrained. The North Sea is an ideal area to study the interplay between natural variability and anthropogenic impacts on organic carbon storage in shelf sediments, particularly in the Helgoland Mud Area (HMA), as the most important depot centre for fine-grained sediments in the German Bight of the North Sea. This thesis investigates the key factors influencing organic carbon burial and remineralisation in the HMA over space and time.
Key findings show organic carbon burial efficiency varied between 30 % and 78 %, primarily driven by high sedimentation rates and terrestrial organic carbon accumulation. Whereas high bottom-trawling activity seems to decrease organic carbon burial by approximately 30%.
In the HMA aerobic respiration is the most important pathway for organic carbon remineralisation, followed by sulphate reduction. Unexpectedly, the results show that various depositional parameters do not significantly influence the relative contributions of the different remineralisation pathways. Intensive bottom trawling was found to lower aerobic respiration contributions while enhancing sulphate reduction and total remineralisation.
Over the last millennium, major reductions in sedimentation and organic carbon accumulation rates of up to 93 % and 95 %, respectively, were found. The organic carbon storage capacity is estimated to have been reduced by 67 % in the HMA, due to changes in natural conditions and strong anthropogenic interventions in the shelf and coastal area, as well as in the catchment area of the rivers and waterway management.