The goal of the 363th cruise of R/V Poseidon in March 2008 was to study the state of the pelagic and benthic ecosystems on the western Black Sea shelf in late winter/early spring. This data set contains data on nutrients in the water (dissolved inorganic and organic forms) and particle-bound nutrient forms on the western Black Sea shelf during March 2008. Further details can be found in the cruise report of POS363 cruise (see "Related to:").Water samples were taken on transects across the shelf at selected stations using 5L Niskin bottles attached to a rosette + CTD system. For analysis of dissolved nutrients, the water was filtered through 0.45µM polycarbonate filters. Immediately after sampling and filtration, soluble reactive phosphate (HPO42-) was analysed using the ammonium-molybdate method (Murphy and Riley, 1962, doi:10.1016/S0003-2670(00)88444-5), and reactive silicate (Si(OH)4 with the molybdenum blue method (Strickland and Parsons, 1972, hdl:10013/epic.46454.d001), both measured on a Spectroquant Nova 60 spectrophotometer (MERCK). Ammonia (NH4+) was measured by flow-injection analysis (Hall and Aller, 1992, doi:10.4319/lo.1992.37.5.1113). For NOx, NO2 and dissolved organic nutrient analysis, sample aliquots were poisoned with HgCl2 and stored until analysis at the home laboratory. There, NOx and NO2 analysed by standard colorimetric methods (Deutsche Einheitsverfahren, 1998) on a continuous flow analyser (Alliance Evolution III); for NOx using the 2,6-dimethylphenole method, and for nitrite (N-NO2-) using the diazo method. Nitrate was calculate as the difference between NOx and NO2.Total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) were determined as nitrate and phosphate on a continuous flow analyser (Alliance Evolution III) after potassium peroxodisulphate digestion in an autoclave (Valderrama, 1981, doi:10.1016/0304-4203(81)90027-X). Filter blanks and blanks of the chemicals were subtracted from the measured values. Dissolved organic phosphorus (DOP) and dissolved organic nitrogen (DON) were calculated as the difference between TDP and HPO42- and TDN and the sum of inorganic nitrogen compounds NH4+, NO3- and NO2-, respectively.Water samples for nutrients in suspended particulates (POC, PN, PP) were filtered through precombusted GFF filters (nµm) and the filters were stored frozen until analysis. For particulate organic carbon (POC) and particulate nitrogen (PN) analysis, the filters were exposed to HCl steam to remove inorganic carbon, dried and analysed with a Carlo-Erba CNS analyser. For analysis of particulate phosphorus, the filters were digested in a mixture of HCl and potassium peroxodisulphate in an autoclave (Valderrama, 1981, doi:10.1016/0304-4203(81)90027-X), and measured with a continuous flow analyser (Alliance Evolution III). Filter blanks and blanks of the chemicals were subtracted from the measured values.DOC samples were collected from Niskin bottles and filtered through precombusted GFF filters immediately after sampling. Samples were stored in precombusted sealed glass ampoules at -20°C until analysis at the home laboratory. DOC was measured using the high-temperature combustion method in a Shimadzu TOC 5000 analyzer (Benner and Strom, 1993, doi:10.1016/0304-4203(93)90113-3). The deep-sea standard used for quality control (50.5 µM DOC) averaged 45.0 ± 2.9 µM C (n = 21) for the Shimadzu TOC 5000.