Marine carbonate system responses to storms in the Dutch North Sea

Storms can disrupt the marine carbon cycle through processes including enhanced air-sea CO₂ exchange, vertical mixing and, in shallow continental shelf seas like the North Sea, sediment resuspension. Storms can therefore have an influence on seawater chemistry that is disproportionately large relative to their duration. However, their consequences for the marine carbonate system and net air-sea CO₂ fluxes remain poorly understood due to a history of sparse observations during and around such events. During a research expedition in the Dutch North Sea in October-November 2023, we collected discrete water samples of the marine carbonate system parameters pH, total alkalinity (TA), and dissolved inorganic carbon (DIC) before and after a storm. The results revealed a decrease in seawater pH, along with increases in TA, DIC and seawater fugacity of CO₂ (fCO₂), suggesting the influence of the storm. These observed changes can be attributed to storm-induced mixing of the water column, transporting DIC and TA from bottom waters and sediments into the overlaying water column. This upward transport of DIC in particular explains the observed increase in fCO₂ and the corresponding decrease in pH. As a result, this could enhance the air-sea CO₂ exchange leading to more outgassing of CO₂ from the seawater towards the atmosphere. To determine whether these observations represented the marine carbonate system response to storms in general, we extended our analysis to a larger dataset from the ocean acidification monitoring programme of the Dutch Ministry of Infrastructure and Water Management (Rijkswaterstaat). As the frequency and intensity of stormy weather are  projected to increase in the future due to climate change, this could alter the North Sea’s role as a CO₂ sink, potentially leading to a shift towards increased CO₂ outgassing into the atmosphere.