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Summary of literature concerning primary production in subtropycal gyre in observations and modelsΒΆ

The facts are:

  1. observed input of inorganic nitrate (N) into the euphotic zone is smaller than observed export production (EP)
  2. modelled PP is smaller than observed (PP)

Concerning the first fact, either the observed input is too low (hypothesis A), the observed EP is too high (B), some other process bring nitrogen in the euphotic zone (C) or there is a combination of all these hypothesis. An argument supporting hypothesis A is that the observations of input of inorganic N have a too small coverage in time and space missing especially the transient submesoscale features believed to contribute for a large portion to the input. An evidence supporting hypothesis B is that all numerical models succeed to reproduce the correct amount of N input despites the models differing largely in resolution and atmospheric forcing (Oschlies 2002; McGillicuddy et al. 2003). Note, however, that the relative contribution of the various mechanisms responsible fro bringing inorganic N to the euphotic layer varies between model, with higher-resolution models favorizing vertical advection as the dominant mechanism (McGillicuddy et al. 2003). Other processes (hypothesis C) that could balance the nitrogen budget are: nitrogen fixation, horizontal advection of particulate and dissolved organic matter within the surface layer, subduction and oxidation of dissolved organic matter (see Kremeur et al. 2009 for a confirmation of this hypothesis). In the model of Oschlies (2002), horizontal advection of particulare organic matter was positive but too small to account for the imbalance in the observations of the central North Pacific subtropical gyre.

Here is a diagram that summarizes the processes concerning the first fact:


Concerning the second fact, either the input of organic N from below is underestimated (hypothesis A above), other process not included in the model, such as nitrogen fixation, might contribute to the new PP and/or the regenerated PP is underestimated in the model.