摘要 : Stable isotope values are useful for elucidating C and N cycling and pathways in marine and aquatic ecosystems. Variations in the base-line isotope values, the delta ¹³C and delta ¹⁵N values of phytoplankton,... 展开 Stable isotope values are useful for elucidating C and N cycling and pathways in marine and aquatic ecosystems. Variations in the base-line isotope values, the delta ¹³C and delta ¹⁵N values of phytoplankton, put constraints on their usefulness as tracers for trophic interactions and sources of organic matter in food web studies, however. We investigated the C and N stable isotope values of suspended particulate organic matter in relation to uptake of total dissolved inorganic carbon and nitrate, chlorophyll <i>a</i> concentration and the isotope composition of dissolved inorganic carbon in an Arctic marine environment (northern Barents Sea) in order to improve the understanding of factors regulating the variation in stable isotope values at the base of the marine food web. The stable isotope values of water-column suspended particulate organic carbon ( delta ¹³C_org) and nitrogen ( delta ¹⁵N_org) varied from -28.3 per mil to -20.2 per mil and 2.9 per mil to 8.3 per mil, respectively, among stations sampled during spring and summer. delta ¹³C_org was not linearly related to carbon uptake, but the values were on average 3 per mil higher at stations in a late-bloom stage, characterised by higher carbon uptake compared to early-bloom stations. Accumulation of phytoplankton biomass had a strong impact on delta ¹³C_org values, reflected in a positive relationship between delta ¹³C_org and chlorophyll <i>a</i> concentration. delta ¹⁵N_org was positively related to the percentage of nitrate taken up from initial (winter) concentrations. These results indicate a strong relationship between bloom progression and isotope composition of particulate organic C and N pools. Synoptic data on stable isotope compositions, nutrient concentrations and phytoplankton biomass therefore improve the interpretation of isotope values when these are compared across pools with different turnover times, such as phytoplankton and consumers or suspended and sedimentary organic matter. 收起