Bottom Trawling Effects on Air–Sea CO₂ Exchange: A Modeling Study of the North Sea

Understanding the dynamic drivers of the marine carbon cycle is essential for predicting how human activities shape ocean-atmosphere CO2 fluxes in a changing climate. Bottom trawling disturbs natural carbon flows through sediment resuspension. However, the impacts of bottom trawling-induced resuspension on air-sea CO2-exchange remain uncertain due to the complexity of the underlying processes involved. To address this, we used a 3D coupled physical-biogeochemical model SCHISM-ECOSMO-CO2, including a carbonate chemistry module, to investigate the impacts of bottom trawling-induced resuspension on the North Sea's carbon cycle. We estimate the impacts for the period 2000-2005 using two model simulations: one accounting only for natural resuspension and another incorporating a parameterization for bottom trawling-induced resuspension. For the latter, we integrate detailed fishing activity data, including vessel position, size, fishing gear type, and engine power to generate daily forcings for trawling-induced resuspension. The results show that bottom trawling causes small, spatio-temporally varying changes in particulate organic carbon (POC), dissolved inorganic carbon (DIC), and air–sea CO2 fluxes, driven by the interplay of remineralization, productivity, and material transport. In the North Sea, CO2 outgassing increases in shallow, mixed regions, while deeper, stratified areas experience enhanced CO2 uptake. At the basin scale, these opposing effects balance through carbon fixation and respiration, resulting in a small net increase (~0.0013 molCm-2yr-1) in oceanic CO2 uptake. These results indicate that shifts in biological carbon pathways, rather than physical disturbance alone, dominate the ecosystem response to bottom trawling.Keywords: Carbonate, Air-sea flux, North Sea, bottom trawling, remineralization.