Particulate organic carbon flux of moored sediment traps

We report primary production of organic matter and organic carbon removal from three subtropical open ocean time-series stations, two located in the Atlantic and one in the Pacific, to quantify the biological components of the oceanic carbon pump. We find that within subtropical gyres, export production varies considerably despite similar phytoplankton biomass and productivity. We provide evidence that the removal of organic carbon is linked to differences in nutrient input into the mixed layer, both from eddy induced mixing and dinitrogen fixation. These findings contribute to our knowledge of the spatial heterogeneity of the subtropical oceans, which make up more than 50% of all ocean area and are thought to spread in the course of CO2- induced global warming.

Particle flux determined from traps in the Canary Island region

We present a 3 year record of deep water particle flux at the recently initiated ESTOC (European Station for Time-series in the Ocean, Canary Islands) located in the eastern subtropical North Atlantic gyre. Particle flux was highly seasonal, with flux maxima occurring in late winter-early spring. A comparison with historic CZCS (Coastal Zone Colour Scanner) data shows that these flux maxima occurred about 1 month after maximum chlorophyll was observed in surface waters in a presumed primary source region 100 km * 100 km northeast of the trap location. The main components of the particles collected with the traps were mineral particles and carbonate, both correlating strongly with organic matter sedimentation. Mineral particles in the sinking matter are indicative of the high aeolian input from the African desert regions. Comparing particle fluxes at 1 km and 3 km depth, we find that particle sedimentation increased substantially with depth. Yearly organic carbon sedimentation was 0.6 g m**-2 at 1 km depth compared with 0.8 g m**-2 at 3 km. We hypothesize that higher phytoplankton biomass observed further north could be a source of laterally advecting particles that interact with fast sinking particles originating from the primary source region. This hypothesis is also supported by the differences in size distribution of lithogenic matter found at the two trap depths.