Biogeochemical time-series and surveys in the North Sea, Skagerrak and Kattegat, 1990 – 2024

This dataset contains biogeochemical samples analyzed by the Plankton Chemistry Laboratory at the Institute of Marine Research (IMR), from the North Sea, Skagerrak and Kattegat. The number of surveys and stations have varied greatly over the last 3.5 decades. IMR is conducting one annual Ecosystem Survey in April-May each year, with trawl surveys and multiple net tows at selected stations, but only CTD water collections are reported here. Three transects constitute the core of the time-series and are visited multiple times each year (Torungen-Hirtshals, Utsira-West, Hanstholm-Aberdeen). On each station, the CTD cast is sampled for dissolved inorganic nutrients (nitrate, nitrite, phosphate, silicate) and phytoplankton chlorophyll-a and phaeopigments (ChlA, Phaeo) at predetermined depths. At the open ocean part of Torungen-Hirtshals and a number of adjacent transects in the Skagerrak-Kattegat region, a smaller number of additional environmental samples are also collected for dissolved ammonia (AMON) analysis and Winkler determinations of dissolved oxygen (DOW). This unique data set has seen limited use over the years but is a great contribution towards global ocean research and climate change investigations.