P : -O2 in MARBL

[MalinOdalen]

Hello,
In MARBL, what are the ratios of nutrient remineralization to oxygen consumption (most importantly P : -O2)? First of all, are they fixed or flexible, as nutrient to carbon stoichiometries in are flexible? I cannot seem to work this out from the publications Danabasoglu et al. (2020), or Moore et al. (2013, 2004, 2002), but I might be missing something.

 

[mlevy]

I don't know if these ratios are documented anywhere, but I'll make an issue ticket to update the MARBL documentation and remedy that. In the mean time, I can show you bits of the Fortran code to help answer your question... these are fixed ratios that are set as parameters in marbl_settings_mod.F90:

  real(r8), parameter :: &
       Q_10      =   1.7_r8,                                 & ! factor for temperature dependence (non-dim)
       xkw_coeff =   6.97e-9_r8,                             & ! in s/cm, from a = 0.251 cm/hr s^2/m^2 in Wannikhof 2014
       parm_Red_D_C_P  = 117.0_r8,                           & ! carbon:phosphorus
       parm_Red_D_N_P  =  16.0_r8,                           & ! nitrogen:phosphorus
       parm_Red_D_O2_P = 170.0_r8,                           & ! oxygen:phosphorus
       parm_Remin_D_O2_P = 138.0_r8,                         & ! oxygen:phosphorus
       parm_Red_P_C_P  = parm_Red_D_C_P,                     & ! carbon:phosphorus
       parm_Red_D_C_N  = parm_Red_D_C_P/parm_Red_D_N_P,      & ! carbon:nitrogen
       parm_Red_P_C_N  = parm_Red_D_C_N,                     & ! carbon:nitrogen
       parm_Red_D_C_O2 = parm_Red_D_C_P/parm_Red_D_O2_P,     & ! carbon:oxygen
       parm_Remin_D_C_O2 = parm_Red_D_C_P/parm_Remin_D_O2_P, & ! carbon:oxygen
       parm_Red_P_C_O2 = parm_Red_D_C_O2,                    & ! carbon:oxygen
       parm_Red_Fe_C   = 3.0e-6_r8,                          & ! iron:carbon
       parm_Red_D_C_O2_diaz = parm_Red_D_C_P/150.0_r8          ! carbon:oxygen
                                                               ! for diazotrophs

Specifically, you are asking about parm_Remin_D_O2_P = 138.0_r8; all the computation in the model is done in carbon units, so the variable parm_Remin_D_C_O2 = parm_Red_D_C_P/parm_Remin_D_O2_P (where parm_Red_D_C_P = 117.0_r8 so the ratio is 117/138, or approximately 0.8478) is what is used to compute the oxygen tendency in the code; it appears when computing o2_production and o2_consumption.