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We present inorganic carbon data from the coastal upwelling region west of Vancouver Island, Canada (∼48.5°N, 126°W) directly after an upwelling event and during summer downwelling in July 1998. The inner-shelf buoyancy current, the outer-shelf and the slope regions are contrasted for both wind regimes (up- and downwelling). Results show strong biological drawdown of the partial pressure of carbon dioxide (pCO2) in response to upwelling over the outer-shelf. In contrast, measured pCO2 is exceptionally high (pCO2>1000 ppm) in the inner-shelf current, where biological uptake of carbon is consistently large. The biological C:N uptake ratio appears to increase when nitrogen becomes limiting (during downwelling), while the POC:PON ratio is relatively constant (slightly lower than the Redfield ratio) suggesting that excess carbon uptake does not go into the POC pool. As expected, large cells dominate where measured primary productivity is greatest. Sub-surface inorganic carbon (and pCO2) is high over the shelf. We suggest that carbon concentrations may be higher in coastal waters because of remineralization associated with high productivity that is confined to a smaller volume of water by bathymetry. At the coast these sub-surface concentrations are more efficiently mixed into the surface (especially during winter) relative to deeper offshore regions. Thus, despite high primary production, coastal waters may not aid in sequestration of atmospheric carbon. [Copyright &y& Elsevier]

The downward transport of surface particle production constitutes an important mechanism for carbon sequestration by the ocean. Only a small fraction (≃10%) of the flux that leaves the euphotic zone reaches 1000 m depth because the particulate organic matter is consumed and transformed in the oceanic midwater column. The depth at which this transformation occurs is crucial to estimate carbon sequestration. Description of the particle flux and remineralization with depth below the euphotic zone has previously been limited to empirical relationships that neglect physical and biological mechanisms. Because several particle properties and functions (settling speed, rates of coagulation and consumption) are related to particle size, measurements of particle size spectra provide an important tool to understand particle dynamics. Most of the mechanisms affecting particle dynamics known for the surface layer should continue in the mesopelagic region. We review the different mechanisms and formulate equations describing changes in particle size distributions throughout the water column as a result of particle sinking, coagulation, disaggregation, and bacterial and zooplankton consumption. The resulting model describes the midwater particle population by its mass distribution for the size range 1 μm to 1 cm. Most of the particle data sets have a narrower size range but we suggest that model results are not greatly affected by the lack of data on particles smaller than 200 μm because most of the particle mass is in particles larger than 100 μm, as seen in a full size-range particle spectrum. The combination of this model with a unique particle size spectra data set, obtained during an inter-annual survey at the French JGOFS site in the NW Mediterranean Sea, give an insight into the key processes for particle dynamics in the unknown midwater layers. [Copyright &y& Elsevier]