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It has been suggested that TEP (transparent exopolymer particles) may provide a vehicle for non-Redfield excess carbon export into the deep sea. Here, the hypothesis that organic carbon produced in excess of the Redfield C:N ratio is sequestered in the deep ocean is tested by a model-based mass balance approach. The model looks for a value of the C:N ratio of export production which is consistent with current knowledge of the rapid change of organic matter fluxes over depth, the remineralisation C:N ratio in the interior of the ocean, and the observed C:N ratios of sinking particles in the deep sea and at the sea floor. It is estimated that the contribution of excess carbon export into the deep ocean is equivalent to 3 to 5.6% (medians, depending on model assumptions; overall range: –16 to 21%) of the conventional Redfield biological pump (C:N = 6.6). Elevated C:N ratios of sinking particles in the deep ocean of 9 to 23, and their increase with depth, can be explained by C:N ratios of export production being only slightly larger than the vertically integrated C:N ratio of remineralisation in the interior of the ocean. The basin scale effect of this preferential nitrogen remineralisation, within the seasonal thermocline, on carbon sequestration is 1 order of magnitude lower compared with Redfield equivalent remineralisation or CaCO3 sequestration. The often observed increase in the C:N ratio of sinking particles with depth does not require that the remineralisation C:N ratio increases with depth, but can also arise under conditions of constant C:N remineralisation ratios. It is concluded that only a small fraction of carbon overconsumption in the surface ocean is sequestered into the deep ocean. The majority appears to be remineralised in the upper twilight zone

Magnitude of excess carbon sequestration into the deep ocean and the possible role of TEP