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This special issue brings together a selection of papers resulting from the STEMM-CCS (Strategies for Environmental Monitoring of Marine Carbon Capture and Storage) project. STEMM-CCS was an ambitious, four-year, project on offshore geologic carbon dioxide storage funded under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 654,462). The aim was to deliver new insights, guidelines, and tools for the monitoring of CO2 storage at putative offshore Carbon dioxide Capture and Storage (CCS) sites. CCS is an important potential mitigation strategy to reduce anthropogenic CO2 emissions.

Phytoplankton phenology and the length of the growing season have implications that cascade through trophic levels and ultimately impact the global carbon flux to the seafloor. Coupled hydrodynamic‐ecosystem models must accurately predict timing and duration of phytoplankton blooms in order to predict the impact of environmental change on ecosystem dynamics. Meteorological conditions, such as solar irradiance, air temperature and wind‐speed are known to strongly impact the timing of phytoplankton blooms. Here, we investigate the impact of degrading the temporal resolution of meteorological forcing (wind, surface pressure, air and dew point temperatures) from 1‐24 hours using a 1D coupled hydrodynamic‐ecosystem model at two contrasting shelf‐sea sites: one coastal intermediately stratified site (L4) and one offshore site with constant summer stratification (CCS). Higher temporal resolutions of meteorological forcing resulted in greater wind stress acting on the sea surface increasing water column turbulent kinetic energy. Consequently, the water column was stratified for a smaller proportion of the year producing a delayed onset of the spring phytoplankton bloom by up to 6 days, often earlier cessation of the autumn bloom, and shortened growing season of up to 23 days. Despite opposing trends in gross primary production between sites, a weakened microbial loop occurred with higher meteorological resolution due to reduced dissolved organic carbon production by phytoplankton caused by differences in resource limitation: light at CCS and nitrate at L4. Caution should be taken when comparing model runs with differing meteorological forcing resolutions. Recalibration of hydrodynamic‐ecosystem models may be required if meteorological resolution is upgraded. Plain Language Summary Computer models are used to predict the impact of changes in environmental pressures such as climate change on marine ecosystems. To predict these changes models need to accurately simulate the pe

We demonstrate for the first time a direct oceanic link between climate‐driven change in the North Atlantic and Arctic oceans and the circulation of the northwest European shelf‐seas. Downscaled scenarios show a shutdown of the exchange between the Atlantic and the North Sea, and a substantial decrease in the circulation of the North Sea in the second half of the 21st Century. The northern North Sea inflow decreases from 1.2‐1.3Sv (1Sv=106 m3s‐1) to 0.0‐0.6Sv with Atlantic water largely bypassing the North Sea. This is traced to changes in oceanic haline stratification and gyre structure, and to a newly identified circulation‐salinity feedback. The scenario presented here is of a novel potential future state for the North Sea, with wide‐ranging environmental management and societal impacts. Specifically, the sea would become more estuarine and susceptible to anthropogenic influence with an enhanced risk of coastal eutrophication. Plain Language Summary Little is known about how climate change might impact the long‐term circulation of shelf‐seas. In this paper, we use a high‐resolution shelf‐sea model to demonstrate how end‐of‐century changes in the wider ocean can lead to a substantial reduction in the flow of water from the North Atlantic into the North Sea. This, in turn, reduces the circulation of this sea, which becomes more influenced by rivers and less by oceanic waters. River water generally contains higher levels of nutrients and our simulations show that this future scenario leads to enhanced levels of phytoplankton growth in local regions of the North Sea. This may lead to undesirable disturbances to the marine ecosystems, such as depletion of oxygen near the seabed. The reduced circulation would also disrupt the transport of larvae around the sea and lead to increased retention of pollutants. The reduction in circulation arises from several causes relating to increased density layering at the continental shelf‐edge; changes in the large‐scale ocean circul