The estimated D 13 C ant and DC ant and their relationship to each other and to water mass distribution suggest that the Polar Water entering the Nordic seas from the north is undersaturated with respect to the present atmospheric anthropogenic CO 2 levels and promotes a local uptake of C ant within the Nordic seas. In contrast, the Atlantic Water entering from the south appears equilibrated. It carries with it anthropogenic carbon which will be sequestered at depth as the water overturns. This preequilibration leaves no room for further uptake of C ant in the parts of the Nordic seas dominated by Atlantic Water. The upper ocean pCO 2 in these regions appears to have increased at a greater rate than the atmospheric pCO 2 over the last 2 decades; this is reconcilable with a large lateral advective supply of C ant .Citation: Olsen, A., et al. (2006), Magnitude and origin of the anthropogenic CO 2 increase and 13 C Suess effect in the Nordic seas since 1981, Global Biogeochem. Cycles, 20, GB3027,

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 d 13 C and d 15 N 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 a 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 (d 13 C org ) and nitrogen (d 15 N org ) varied from -28.3% to -20.2% and 2.9% to 8.3%, respectively, among stations sampled during spring and summer. d 13 C org was not linearly related to carbon uptake, but the values were on average 3% 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 d 13 C org values, reflected in a positive relationship between d 13 C org and chlorophyll a concentration. d 15 N 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.

No abstract

Shelf seas play an important role in the global carbon cycle, absorbing atmospheric carbon dioxide (CO2) and exporting carbon (C) to the open ocean and sediments. The magnitude of these processes is poorly constrained, because observations are typically interpolated over multiple years. Here, we used 298500 observations of CO2 fugacity (fCO2) from a single year (2015), to estimate the net influx of atmospheric CO2 as 26.2 ± 4.7 Tg C yr−1 over the open NW European shelf. CO2 influx from the atmosphere was dominated by influx during winter as a consequence of high winds, despite a smaller, thermally-driven, air-sea fCO2 gradient compared to the larger, biologically-driven summer gradient. In order to understand this climate regulation service, we constructed a carbon-budget supplemented by data from the literature, where the NW European shelf is treated as a box with carbon entering and leaving the box. This budget showed that net C-burial was a small sink of 1.3 ± 3.1 Tg C yr−1, while CO2 efflux from estuaries to the atmosphere, removed the majority of river C-inputs. In contrast, the input from the Baltic Sea likely contributes to net export via the continental shelf pump and advection (34.4 ± 6.0 Tg C yr−1).