Processes driving trace metal, nutrient, and dissolved inorganic carbon distributions in the Norwegian Trench

Shelf seas filter terrestrial inputs of important macronutrients and bio-essential trace metals such as iron (Fe) and manganese (Mn), which support primary productivity and long-term carbon dioxide (CO₂) storage in the sediments and the deep ocean. The North Sea is a biologically productive shelf sea and a net sink of atmospheric CO₂, yet the exchange of essential (trace) nutrients between the North Sea and the North Atlantic Ocean as well as the role of trace elements in the carbon cycle are poorly constrained. This limits our ability to accurately model biogeochemical interactions and calculate CO₂ fluxes in this region. Within the NoSE (North Sea-Atlantic Exchange) project, we investigate the North Sea's role in the Atlantic Ocean's biogeochemical system, focussing on the Norwegian trench for its pivotal role in the nutrient and inorganic carbon outflow to the Atlantic and sediment accumulation. Here, we present an observational dataset of trace metals, nutrients, and marine carbonate system parameters from the first NoSE expedition in May-June 2023. We analyse the spatial distributions, sources and sinks of (trace) nutrients in the water column and discuss their relationships with carbonate system and other hydrographic parameters. We found clear latitudinal differences as well as differences between shallower (< 200 m) waters above the shelf proper and the deeper waters of the trench. Linear correlations between salinity and certain trace nutrients in the surface waters indicated a fresh water source either from the Baltic Sea or the Norwegian rivers and fjords while correlations between turbidity and Fe and Mn concentrations close to the seafloor suggested sedimentary inputs.