Pore water dissolved organic carbon (DOC) and inorganic nutrients were collected by Rhizon samplers from the water 2 cm above the sediment and the top 10 cm of the sediment cores with a 2 cm interval. The sediment cores were recovered using a GeMax sampler. These samples were collected between 2020 and 2021 during cruises onboard RV Oceania (Institute of Oceanology of the Polish Academy of Sciences), which took place in spring, autumn, and winter, to the Central and Southern Baltic Sea, i.e., Eastern Gotland Basin, Bornholm Basin, and Gdansk Basin. The pore-water DOC (µmol/L) - dissolved organic carbon concentrations in µmol per Liter
DOC samples were analyzed by high-temperature catalytic oxidation (Pt) (680 °C) oxidation using a total organic carbon analyzer (TOC-L, Shimadzu) equipped with a nondispersive infrared detector. The quality of the results was confirmed by daily analyses of certified reference material (CRM) (North Atlantic water) obtained from the Hansell Laboratory, University of Miami (recovery: 98.9%, RSD: 0.9%).; \nAmmonium (NH^(+)4 (µmol/L)), nitrate and nitrite mixture (NO^(-)x (µmol/L)), and phosphate (PO^(3-)4 (µmol/L)) concentrations analyses were performed after Hansen and Koroleff (2007) using the SEAL AA500 AutoAnalyzer (Seal Analytical). The quality of the measurements was controlled by repeated measurements of two different CRMs, QC3179, Sigma Aldrich, and HAMIL-20.2, Environment Canada. Therefore, the detection limits of 0.33 µmol L-1 for NO^(-)x, 0.27 µmol L-1 for NH^(+)4 and 0.1 µmol L-1 for PO^(3-)4 were determined with an accuracy of 98.8%, 98.6%, 98.8% and 99.0% and a precision of 0.7%, 1.1%, and 0.5% for NO^(-)x, NH^(+)4 and PO^(3-)4, respectively. b.d.- below detection.
