Problems about output vertical pCO2 into dia.nc from Fennel

[kent]

Recently, I am trying to output a new diagnostics_bio variable, which is the pCO2 in the vertical of seawater using Bio_Fennel Model. And the output routine in bio_Fennel.h was added as follow:
#ifdef CARBON
!----------------------------------------------------------------------
! CALCULATING
! pCO2 at all depth
!----------------------------------------------------------------------
Do k=1,N(ng)
CALL pCO2_water_vertical (Istr, Iend, LBi, UBi, LBj, UBj, &
& IminS, ImaxS, j, DoNewton, &
# ifdef MASKING
& rmask, &
# endif
& Bio(IminS:,k,itemp), Bio(IminS:,k,isalt), &
& Bio(IminS:,k,iTIC_), Bio(IminS:,k,iTAlk), &
& Bio(IminS:,k,iPO4_), Bio(IminS:,k,iSiOH), &
& pH, pHv, pCO2v)
Do i=Istr,Iend
# ifdef DIAGNOSTICS_BIO
DiaBio3d(i,j,k,ipHsea)=DiaBio3d(i,j,k,ipHsea)+ &
# ifdef WET_DRY
& rmask_io(i,j)* &
# endif
& pHv(i)*dtdays
!
DiaBio3d(i,j,k,ipCO2ver)=pCO2v(i)
# ifdef WET_DRY
DiaBio3d(i,j,k,ipCO2ver)=pCO2v(i)*rmask_io(i,j)
# endif
# endif
END DO
#endif

I also add the dia_output variable for ipCO2ver in other Fennel_mod.h, Fennel_var.h, and so on.
After running for a month, I found the data of vertical pCO2 is very small value, about 11-30, while pH has a normal value, as shown in the uploaded file.
When I use the same subrountine to calculate the vertical pCO2 using Matlab, it shows a normal value.
What results in the wrong pCO2 value in the seawater? Was it a wrong rountine?

[kfennel]

Hi Kent,

There is no problem. The behavior you are describing is to be expected since pCO2 is only calculated in the surface layer.

During ROMS time-stepping, knowledge of pCO2 is only required at the surface for the calculation of the air-sea CO2 flux. Since the calculation of pCO2 from DIC and alkalinity is computationally expensive, there is no point calculating it for the whole 3D field.

I would suggest you remove the code you have added. If you want to know 3D pCO2, you can easily calculate it offline from DIC and alkalinity.

Best, Katja