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Notes on “An eddy-permitting coupled physical-biological model of the North Atlantic. 2. Ecosystem dynamics and comparison with satellite and JGOFS local studies data” by Oschlies et al. (2000)

Analysis of a model run with the same biological component as in OFES. The run is forced with a climatological forcing. What are studied: 1) the seasonal cycle of the surface chlorophyll, 2) basin-wide primary production, 3) detailed analysis for the ecosystem at three locations in the North Atlantic (BATS, NABE and EUMELI).

  • The model is more oligotropic than in the observations for the North Atlantic subtropical gyre.

  • The model annual primary production is too low in the oligotrophic ocean and too large in the subpolar gyre.

  • Their table 2 gives estimate of horizontal and vertical advection as well as vertical mixing for the three regions that have an observed time series. At BATS, transport of nutrients is dominated by vertical mixing with downwelling nearly ancelling input from horizontal advection. Phytoplankton is also dominated by vertical mixing with negligible amount of horizontal and vertical transport.

  • They compare the annual cycle of the upper 200-m temperature, nitrate and chlorophyll.

    “However, the large contribution due to convective mixing in winter is in contrast to recent compilations of McGillicuddy et al. [1998] and Siegel et al. [1999], who suggest that eddy-induced nitrate fluxes are the dominant term in the annual mean. To clarify this issue, a more detailed analysis of mesoscale transport processes in the present high-resolution model is under way.”

    “To significantly improve the model results in oligotrophic regions, it is suggested to introduce a more efficient recycling loop that enhances regenerated production. Possible solutions include the introduction of the ammonium and microbial loops.”

Questions

  • How do they compute chlorophyll from the NPZD model?
  • How do they compute primary production rate?