Porewater chemistry from sediment core CDISK4-5 from the North Pacific CDisK-IV expedition

Samples were collected at six oceanographic stations during cruise CDisK-IV on board RV Kilo Moana from Hawaii to Alaska in August 2017 using an 8-barrel multi-corer. Sediment porewaters were extracted in a cold room, using Rhizon samplers inserted into pre-drilled holes in the core liner, from two cores with undisturbed sediment-water interfaces, from each multi-corer cast. Pre-treatment of the Rhizon samplers and the sampling protocol was different for each of the two cores. Rhizons inserted to core number 1 from each cast were new from the box, and the samples were used for nutrient and major element analyses. A 20 ml syringe was filled from each Rhizon, inserted dry, and the extracted water was filtered again via a 0.45 µm filter. Rhizons inserted to core number 2 were acid-cleaned with 0.001 N HNO3 for at least 24 hours, rinsed with de-ionised water (Milli-Q, Millipore) and kept in de-ionised water until use. The first 1 mL extracted was discarded, and the next 2 mL were stored in acid cleaned polypropylene (PP) vials. These samples, destined for analyses of trace and major elements, were acidified with HNO3 to final acid concentration of 0.035 M.