CESM2 ocean POP iron forcing files

[ccyao]

I am using CESM2.1.3 to run a G-case to test ocean iron fertilization simulation. Firstly I want to improve the Fe concentration in the forcing files. I find that there are three Fe-related forcing files in the 'pop/gx1v6/forcing' folder, they are, 'fesedfluxTot_gx1v6_cesm2_2018_c180618.nc', 'feventflux_gx1v6_5gmol_cesm1_97_2017.nc' and 'solFe_scenario4_current_gx1v6_8gmol_cesm1_93_20161114.nc'. The first .nc file represents for the iron flux from sediment and the second represents for the vent source, just as the description in the paper "Simulations With the Marine Biogeochemistry Library (MARBL)". Here are my questions:
1. As said in the paper, there is also iron source from river. However, I don't find any file related to iron river source in the folder 'pop/gx1v6/forcing'. Is it in other folder or somewhere?
2. What does the third file ''solFe_scenario4_current_gx1v6_8gmol_cesm1_93_20161114.nc' represent for? Is it the sum of solFe from sediment, vent, river and dust？
3. If I want to improve Fe input in a G-case, shall I make changes in which one of these three files? For example, if I have doubled Fe input flux in the first file, does it mean the iron source from sediment also double in my simulations? What if I have changed the third file?
Greatly appreciate any help!

 

[mlevy]

POP was designed as a flexible model, with features added over a pretty long period of time... which means it can be pretty tough to track down what the code is doing for particular processes. To answer your questions, though:

1. The river fluxes are read in from riv_flux_shr_stream_file; the default input file is in the inputdata repository: ocn/pop/gx1v7/forcing/riv_nut.gnews_gnm.rx1_to_gx1v7_nn_open_ocean_nnsm_e1000r300_marginal_sea_170413.20190602.nc, and one of the fields it contains is dfe_riv_flux
2. solFe_scenario4_current_gx1v6_8gmol_cesm1_93_20161114.nc is the atmospheric iron flux, but in CESM 2.1 it is not used by default. Previous versions of CESM and its predecessor CCSM read dust flux and iron flux from a file, but now the ocean component receives dust flux and a black carbon flux from the atmosphere and sea ice. Dust flux is passed on to MARBL, while iron flux is computed from the dust and black carbon fluxes
3. If you want to improve iron input from sediments or rivers, you should modify the input files. If you want to modify the iron flux from the atmosphere in a G compset, look at CaseDocs/CaseDocs/datm.streams.txt.presaero.clim_1850. Atmospheric black carbon is the sum of the bcphiwet, bcphodry, and bcphidry fields, atmospheric fine dust is dstwet1 plus dstdry1, and atmospheric coarse dust is the sum of the other dstwet? and dstdry? terms (the atmosphere passes 4 size classes of wet and dry dust). To answer your specific questions: yes, doubling the Fe input flux in fesedfluxTot_gx1v6_cesm2_2018_c180618.nc will double the iron sediment flux but changing solFe_scenario4_current_gx1v6_8gmol_cesm1_93_20161114.nc should not have any impact on your simulation since that file is no longer used by the model

 

[ccyao]

Thank you very much for clearing up my confusion!

POP was designed as a flexible model, with features added over a pretty long period of time... which means it can be pretty tough to track down what the code is doing for particular processes. To answer your questions, though:

1. The river fluxes are read in from riv_flux_shr_stream_file; the default input file is in the inputdata repository: ocn/pop/gx1v7/forcing/riv_nut.gnews_gnm.rx1_to_gx1v7_nn_open_ocean_nnsm_e1000r300_marginal_sea_170413.20190602.nc, and one of the fields it contains is dfe_riv_flux
2. solFe_scenario4_current_gx1v6_8gmol_cesm1_93_20161114.nc is the atmospheric iron flux, but in CESM 2.1 it is not used by default. Previous versions of CESM and its predecessor CCSM read dust flux and iron flux from a file, but now the ocean component receives dust flux and a black carbon flux from the atmosphere and sea ice. Dust flux is passed on to MARBL, while iron flux is computed from the dust and black carbon fluxes
3. If you want to improve iron input from sediments or rivers, you should modify the input files. If you want to modify the iron flux from the atmosphere in a G compset, look at CaseDocs/CaseDocs/datm.streams.txt.presaero.clim_1850. Atmospheric black carbon is the sum of the bcphiwet, bcphodry, and bcphidry fields, atmospheric fine dust is dstwet1 plus dstdry1, and atmospheric coarse dust is the sum of the other dstwet? and dstdry? terms (the atmosphere passes 4 size classes of wet and dry dust). To answer your specific questions: yes, doubling the Fe input flux in fesedfluxTot_gx1v6_cesm2_2018_c180618.nc will double the iron sediment flux but changing solFe_scenario4_current_gx1v6_8gmol_cesm1_93_20161114.nc should not have any impact on your simulation since that file is no longer used by the model