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.