Seasonal field observations show that the North Sea, a Northern European shelf sea, is highly efficient in pumping carbon dioxide from the atmosphere to the North Atlantic Ocean. The bottom topography-controlled stratification separates production and respiration processes in the North Sea, causing a carbon dioxide increase in the subsurface layer that is ultimately exported to the North Atlantic Ocean. Globally extrapolated, the net uptake of carbon dioxide by coastal and marginal seas is about 20% of the world ocean's uptake of anthropogenic carbon dioxide, thus enhancing substantially the open ocean carbon dioxide storage.

Abstract.A carbon budget has been established for the North Sea, a shelf sea on the NW European continental shelf.

No abstract

Abstract. The seasonal variability of the partial pressure of CO 2 (pCO 2 ) has been investigated in the North Sea, a northwest European shelf sea. Based on a seasonal and high spatial resolution data set the main controlling factors -biological processes and temperature -have been identified and quantified. In the central and northern parts being a CO 2 -sink all year round, the biological control dominates the temperature control. In the southern part, the temperature control dominates the biological control at an annual scale, since the shallow water column prevents stronger net-CO 2 removal from the surface layer due to the absence of seasonal stratification. The consequence is a reversal of the CO 2 seato-air flux during the spring bloom period, the only time, when CO 2 is taken up from the atmosphere in the southern region. Net community production in the mixed layer has been estimated to 4 mol C m −2 yr −1 with higher values (4.3 mol C m −2 yr −1 ) in the northern part and lower values in the southern part (2.6 mol C m −2 yr −1 ).

We used a seasonal North Sea data set comprising dissolved inorganic carbon (DIC), partial pressure of CO 2 (pCO 2 ), and inorganic nutrients to assess the abiotic and biological processes governing the monthly variations of DIC. During winter, advection and air-sea exchange of CO 2 control and increase the DIC content in the surface and deeper layers of the northern and central North Sea, with the atmosphere supplying CO 2 on the order of 0.2 mol C m 22 month 21 to these areas. From February to July, net community production (NCP) controls the seasonal variations of DIC in the surface waters of the entire North Sea, with a net uptake ranging from 0.5 to 1.4 mol C m 22 month 21 . During the August-December period, NCP controls the seasonal variations of DIC in the southern North Sea, with a net release ranging from 0.5 to 0.8 mol C m 22 month 21 . Similarly, during the April-August period in the deeper layer of the northern North Sea, the NCP was the main factor controlling DIC concentrations, with a net release ranging from 0.5 to 5.5 mol C m 22 month 21 . In the surface layer of the North Sea, NCP on the basis of DIC was 4.3 6 0.4 mol C m 22 yr 21 , whereas, NCP on the basis of nitrate was 1.6 6 0.2 mol C m 22 yr 21 . Under nutrient-depleted conditions, preferential recycling (extracellular) of nutrients and intracellular mechanisms occurred and were responsible for the non-Redfield uptake of DIC versus nitrate and phosphate.Coastal and marginal seas play a key role in the global carbon cycle by linking terrestrial, oceanic, and atmospheric reservoirs (Walsh 1991;Mackenzie et al. 2004). They occupy only 7% of the global ocean surface area but house 10-30% of the global marine primary production (Gattuso et al. 1998). Recent investigations have underlined the importance of coastal seas in the global carbon cycle and the necessity of introducing them into realistic models, notably to quantify the air-sea exchange of CO 2 (Chen 2004; Thomas et al. 2004;Muller-Karger et al. 2005). However, even the latest global estimates of the oceanic uptake of anthropogenic CO 2 (Sabine et al. 2004) do not include coastal seas in the calculations because of the smallscale variability observed within each marginal sea and between all marginal seas worldwide and because of the difficulty in increasing the spatial resolution of global numerical models.Despite growing interest and debate on the role of all coastal seas in the global carbon cycle, robust estimates of the CO 2 air-sea fluxes are only available for a few individual coastal ecosystems. The air-sea exchange of CO 2 has been more intensively investigated in temperate marginal seas. Marginal seas account for a relatively large portion of the CO 2 uptake of the entire coastal ocean because they cover 55.6% of the total surface area of the coastal ocean (see for overview Borges 2005;Borges et al. 2005;Bozec et al. 2005). The links between air-sea exchange of CO 2 , biological processes, and physical forcing have also been investigated to determine the net community ...

a b s t r a c t Downward flux of zooplankton faecal pellets and carcasses was studied during and after the spring bloom in an oligotrophic coastal area of the Western Mediterranean using a 'swimmer-excluding' sediment trap. Zooplankton detritus retrieved in the trap were comprised of cylindrical faecal pellets (from meso-and macrozooplankton) and copepod carcasses with a respective carbon flux of 0.05. Carbon and nitrogen flux of carcasses always exceeded that of faecal pellets, except at the beginning of the bloom due to a higher contribution of macrozooplankton faecal material. During the peak of phytoplankton biomass, total faecal flux essentially comprised of copepod faecal pellets (68e86% of the total faecal carbon), whereas before and after this period, macrozooplankton faecal material dominated (88e91% of total faecal carbon flux). Copepod faecal flux was positively correlated with phytoplankton biomass. Estimates of non-predatory biomass mortality rates (from <0.01 to 0.05 d À1) were negatively correlated with chl a with a time lag of 12 days and were lower than predatory mortality values reported in the same area. The paper discusses the relative importance of carcasses versus faecal pellet flux and of non-predatory versus predatory mortality, as well as the potential role of these zooplankton detritus in supporting the production of benthos in oligotrophic areas.

Modelling of seagrasses can be an effective tool to assess factors regulating their growth. Growth and production model of Posidonia oceanica, the dominant submerged aquatic macrophyte occurring in the Bay of Calvi (Corsica, Ligurian Sea, Northwestern (NW) Mediterranean) was developed. The state variables are the above-and below-ground biomass of P. oceanica, the epiphyte biomass, and the internal nitrogen concentration of the whole plant. Light intensity and water temperature are the forcing variables. The model reproduces successfully seasonal growth and production for each variable at various depths (10, 20 and 30 m). The model can simulate also a number of consecutive years. Sensitivity analysis of model's parameters showed that the maximum nitrogen quota n max rate is the most sensitive parameter in this model. The results simulations imply that light intensity is one of the most important abiotic factors, the diminution of which can cause an important reduction in seagrass density.

No abstract