Patterns of production and sedimentation in the boreal and polar Northeast Atlantic

Abstract

Pelagic systems are potentially capable of retaining and recycling all autochthonous organic material, although some losses due to sinking particles inevitably occur. Relating processes in the surface layers quantitatively to vertical particle flux is difficult because only a small percentage of the total production is lost annually via sinking in the open ocean. Further, only a few types of particles contribute to this flux and only a smalt proportion of these may actually reach greater depths. Measurements of vertical flux with sediment traps revealed seasonal and regional patterns also within the northwestern Atlantic and indicate imbalances between particle formation and degradation. The classical pattern of spring bloom sedimentation followed by reduced loss rates has been found in shelf and shallow water regions such as the Norwegian Coastal Current and fjords and is also encountered in the Barents Sea. In the Norwegian Sea. however, the seasonal pattern appears different as the seasonal maximum has been observed during late summer/autumn. The physical environment determines nutrient availability and hence the particles potentially available for sedimentation. The relationship between phyto- and zooplankton governs vertical flux seasonality, and zooplankters with different life cycles and feeding strategies further modify the principle patterns. Herbivores with life-cycle strategies involving overwintering of large biomass and predictable seasonal appearance (copepods, cuphausiids) will have a different impact than opportunistic organisms with very low overwintering biomass, for example salps and ptcropods. The latter exhibit much greater interannual biomass variation and may thus contribute to interannual variability of the vertical flux. Shelf systems of similar latitude arc generally comparable with respect to their flux patterns and also share similarities with marginal ice zones. Open ocean systems as the Norwegian Sea, however, exhibit different patterns which are similar to the subarctic Pacific.