Description: The benthic diagenetic model OMEXDIA has been used to reproduce observed benthic pore water and solid phase profiles obtained during the OMEX study in the Goban Spur Area (N.E. Atlantic), and to dynamically model benthic profiles at site OMEX III (3660-m depth), with the sediment trap organic flux as external forcing. The results of the dynamic modelling show that the organic flux as determined from the lowermost sediment trap (400 metres above the bottom) at OMEX III is insufficient to explain the organic carbon and pore water profiles. The best fitting was obtained by maintaining the seasonal pattern as observed in the traps, while multiplying the absolute values of the flux by a factor of 1.85. The “inverse modelling” of diagenetic processes resulted in estimates of total mineralisation rate and of degradability of the organic matter at the different stations. These diagenetic model-based estimates are used to constrain the patterns of lateral and vertical transports of organic matter. Using the observed degradability as a function of depth, we show that the observed organic matter fluxes at the different depths are consistent with a model where at all stations along the gradient the same vertical export flux occurs at 200 m, and where organic matter sinks with a constant sinking rate of around 130 m d−1. If sinking rates were higher, in the order of 200 m d−1, the observations could be consistent with an off-slope gradient in export production of approximately a factor of 1.5 between the shallowest and deepest sites. The derived high degradability of the arriving organic matter and the consistency of the mass fluxes at the different stations exclude the possibility of a massive deposition, on the margin, of organic matter produced on the shelf or shelf break. However, other hypotheses to explain the patterns found in the sediment trap data of both OMEX and other continental margin study sites also suffer from different inconsistencies. Further, close examination of the flow patterns at the margin will be needed to examine the question.

Description: Sinking particles, once caught in sediment trap jars, release dissolved elements into the surrounding medium through leaching from their pore fluids, chemical dissolution and the activity of free exoenzymes. This results in an increase in dissolved elements in the trap jar supernatant. Elemental fluxes as traditionally measured by sediment traps underestimate total export when this particle-associated dissolved flux is not considered. The errors introduced are variable and alter both the absolute levels of flux as well as the stoichiometry of export. These errors have been quantified and corrections applied for samples from sediment traps in the North Atlantic based on measurements of excess dissolved carbon, nitrogen, phosphorus, silica and calcium in the supernatant of the collection cups. At the base of the winter mixed layer, on average 90±6% of phosphorus fluxes are found as excess phosphate whereas for carbon and nitrogen dissolved concentrations account for 30 (±8)% and 47(±11)% of total fluxes respectively. Excess dissolved silica is on average 61 (±17)% of total biogenic silica flux. Little (〈10%) of calcium is solubilized. The proportion of dissolved to total flux decreases with trap deployment depth. Calculations of the C:N:P ratios for particles only are well above the Redfield ratios of 106:16:1 (Redfield et al., 1963), although the mid-water dissolved N:P and N:Si values as well as the C:N:P ratios of remineralisation along isopycnals conform to the Redfield ratios at this site. Accounting for dissolved fluxes of all these elements brings the stoichiometry of export in agreement with the Redfield Ratio and with other geochemical estimates of winter mixed layer export. A factor of 3 to 4 higher ratios of organic: inorganic carbon export also implies that the net atmospheric CO2 sequestration by the biological pump is about 50% higher at this site when the dissolved elemental fluxes are considered. Solubilization is thus a process that should be accounted for in protocols used to measure vertical fluxes with sediment traps.

Description: Taxon-specific microzooplankton dynamics were studied along a transect through the North Atlantic Drift from 70°N 04°E to 40°N 20°W during July 1997 using serial dilution and nutrient-enrichment experiments. Nutrient concentrations and microzooplankton composition indicated postbloom conditions at 40°N, 47°N, and 50°N, a transitional system at 54°N, and bloom conditions at 62°N and 70°N. The ratio of microzooplankton to phytoplankton biomass was inversely related to nitrate and phosphate concentrations. Potential grazing thresholds were observed in four of nine experiments at 40–66% of the initial phytoplankton concentration. Grazing losses were determined for six pigment-specific classes of phytoplankton. Selective grazing losses of phytoplankton taxa ranged from 73% to 248% of the nonselective grazing losses predicted according to their biomass contributions. The grazing selectivity varied considerably between communities, with the microherbivores showing positive selection for cyanobacteria and dinoflagellates and predominantly avoidance of chlorophyta and bacillariophyceae. Microzooplankton did not show a preference for the dominant phytoplankton taxa, but grazed preferentially on fast-growing phytoplankton with minor contributions (〈15%) to the phytoplankton biomass. However, bacillariophyceae were the major contributors to phytoplankton biomass and accounted for major fractions of the total losses through microzooplankton grazing. Microzooplankton consumed the equivalent of 0.12–5.5 times their own biomass daily on a carbon basis, amounting to 65–197% of gross phytoplankton production. With the conservative assumption that 20% of the consumed phytoplankton was converted to microzooplankton biomass, the latter was estimated to contribute 27–381% to the net production of the entire microzooplankton community. We therefore conclude that the taxonomic structure and the net production of the microzooplankton communities were significantly affected by the intensity and selectivity of herbivorous microzooplankton grazing.

Description: Pelagic processes and their relation to vertical flux have been studied in the Norwegian and Greenland Seas since 1986. Results of long-term sediment trap deployments and adjoining process studies are presented, and the underlying methodological and conceptional background is discussed. Recent extension of these investigations at the Barents Sea continental slope are also presented. With similar conditions of input irradiation and nutrient conditions, the Norwegian and Greenland Seas exhibit comparable mean annual rates of new and total production. Major differences can be found between these regions, however, in the hydrographic conditions constraining primary production and in the composition and seasonal development of the plankton. This is reflected in differences in the temporal patterns of vertical particle flux in relation to new production in the euphotic zone, the composition of particles exported and in different processes leading to their modification in the mid-water layers. In the Norwegian Sea heavy grazing pressure during early spring retards the accumulation of phytoplankton stocks and thus a mass sedimentation of diatoms that is often associated with spring blooms. This, in conjunction with the further seasonal development of zooplankton populations, serves to delay the annual peak in sedimentation to summer or autumn. Carbonate sedimentation in the Norwegian Sea, however, is significantly higher than in the Greenland Sea, where physical factors exert a greater control on phytoplankton development and the sedimentation of opal is of greater importance. In addition to these comparative long-term studies a case study has been carried out at the continental slope of the Barents Sea, where an emphasis was laid on the influence of resuspension and across-slope lateral transport with an analysis of suspended and sedimented material.

Description: A decade of particle flux measurements providse the basis for a comparison of the eastem and westem provinces ofthe Nordic Seas. Ice-related physical and biological seasonality as well as pelagic settings jointly control fluxes in the westem Polar Province which receives southward flowing water of Polar origin. Sediment trap data from this realm highlight a predominantly physical flux control which leads to exports of siliceous particles within the biological marginal ice zone as a prominent contributor. In the northward flowing waters of the eastem Atlantic Province, feeding Strategie . life histories and the succession of dominant mesozooplankters (copepods and pteropods) are central in controlling fluxes. Furthermore, more calcareous matter is exported here with a shift in flux seasonality towards surnrner/autumn. Dominant pelagic processes modeled numerically as to their impact on annual organic carbon exports for both provinces confirrn that interannual flux variability is related to changes in the respective control mechanisms. Annual organic carbon exports are strikingly similar in the Polar and Atlantic Provinces (2.4 and 2.9 g m-2 y-1 at 500 m depth). despite major differences in flux control. The Polar and Atlantic Provinces. however, can be distinguished according to annual fluxes of opal ( l.4 and 0.6 g m-2 y-1) and carbonate (6.8 and 10.4 g m-2 y-1). lnterannual variability may blur this in single years. Thus. it is vital to use multi-annual data sets when including particle exports in general biogeochemical province descriptions. Vertical flux profiles (collections from 500 m, l000 min both provinces and 300-600 m above the seafloor deviate from the general vertical decline of fluxes due to particle degradation during sinking. At depths 〉 1000 m secondary fluxes (laterally advected/re uspended particles) are often juxtaposed to primary (pelagic) fluxes, a pattem which is most prominent in the Atlantic Province. Spatial variability within theAtlantic Province remains poorly understood. and the same holds true for interannual variability. No proxies are at hand for this province to quantitatively relate fluxes to physical or biological pelagic properties. For the easonally ice-covered Polar Province a robust relationship exists between particle export and ambient ice-regime (Ramseier et al. this volume; Ramseier et al. 1999). Spatial flux pattems may be differentiated and interannual variability can be analyzed in this manner to improve our ability to couple pelagic export pattems with benthic and geochemical sedimentary processes in seasonally ice-covered seas.

Description: The changing climate of the planet is closely linked to biogeochemical processes in the oceans with important feedbacks between oceanic, atmospheric and terrestrial components of the earth system. This chapter identifies key processes that mediate the response of marine ecosystems to a changing environment and recommends implementation strategies for future studies. Technological and methodological advances such as the use of new biochemical and molecular techniques have led to the discovery of unknown metabolic pathways and identification of genetic diversity in marine systems. Ecosystem changes, reflected in shifts in dominant plankton groups are likely to have a !arge global but also regional impact in the European context. In terms of marine biogeochemical cycling, key processes that respond to a changing climate include photosynthesis (and its modulation by trace meta! availability and nitrogen fixation), calcification and the production and release of a suite of volatile, climate-reactive gasses. Implementation of future research strategies should focus on the ability to monitor key variables from stationary platforms and ships of opportunity with sufficient stability and accuracy to resolve natural and anthropogenic signals. Large-scale in situ manipulation experiments and mesocosm studies are also recommended as well as the application of molecular and genetic techniques that are a powerful means to investigate physiological and biogeochemical transformations that drive the oceans's response to climate change.