The role of off-shore advection for open ocean export in the Mauritanian upwelling region

Steffen Swoboda1, Arjun Chennu2, Hannah Marchant2, Soeren Ahmerkamp2, Kai Schwalfenberg3, Jan-Hendrik Hehemann4, Hagen Buck-Wiese5 and Morten H. Iversen6, (1)MARUM Center for Marine Environmental Sciences, Bremen, Germany, (2)Max Planck Institute for Marine Microbiology, Bremen, Germany, (3)University of Oldenburg, Marine Sensor Systems Group, Institute for Chemistry and Biology of the Marine Environment, Oldenburg, Germany, (4)Max Planck Institute for Marine Microbiology and MARUM Center for Marine Environmental Sciences, Bremen, Germany, (5)Max Planck Insitute for Extraterrestrial Physics, Garching, Germany, (6)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Polar Biological Oceanography, Bremerhaven, Germany
Abstract:
The biological pump drives organic matter export and CO2 sequestration in the ocean. Export of organic matter from the surface to the deep ocean is generally considered as unidimensional where horizontal movement is ignored. To study the lateral transport of vertical export, we followed fluxes and aggregate dynamics from the shallow shelf to the open ocean off Cape Blanc, NW Africa. Sampling included particle export, vertical profiles of in situ particle size-distributions and abundances as well as determination of size-specific sinking velocities, respiration and composition of in situ sampled aggregates. Aggregates formed on or near the shelf were more ballasted and had faster size-specific sinking velocities than those formed off-shore. First results suggest that non-aggregated phytoplankton are advected off-shore in surface filaments while aggregates formed on the shelf are ballasted by re-suspended sediment and form a deep cloud along the slope during off-shore advection. The phytoplankton in the filaments aggregate off-shore and contribute to the open ocean export, which may be enhanced when ballasted by Saharan dust. We will estimate the contribution from shelf primary production to open ocean organic carbon export and determine the role of fecal pellets versus marine snow for the different regions.
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