Biogeochemistry

Biogeochemistry#

Biogeochemistry in CESM#

Caveat: Support for coupled biogeochemistry in CESM3 is still under development. So this content describes biogeochemical features in the context of CESM2. For example, resolutions that are referenced are resolutions used in CESM2.#

Biogeochemistry features have been available since CESM1.0 and are on by default in CESM2.0.

Three components of CESM have biogeochemistry features:

CAM

  • CO\(_{2}\) constituents in CAM that use the land and ocean fluxes of CO\(_{2}\) as surface boundary conditions.

  • CAM passes CO\(_{2}\) to the coupler for land and ocean flux computations.

  • The CO\(_{2}\) consitutients are coupled with radiation computations.

POP

  • Includes the MARBL ecosystem library in CESM2.0

CLM

  • Features covered elsewhere [LINK]

Coupled BGC Compsets#

Terminology

  • BGC CO\(_{2}\): what is used by surface components

  • RAD CO\(_{2}\): what is used by the atmospheric radiative code

  • Diagnostic CO\(_{2}\): prescribed atmospheric CO\(_{2}\) concentrations. (E.g. constant, read from file, 1% ramp, etc.)

  • Prognostic CO\(_{2}\): predicted atmospheric CO\(_{2}\) concentrations. Atmospheric consitutent is computed from surface CO\(_{2}\) fluxes.

B1850, BHIST

  • Compset long name has BCG%BDRD

  • Coupled model, BGC & RAD CO\(_{2}\) are diagnostic

B1850_BPRP, BHIST_BPRP

  • Shortnames introduced in CESM2.1.1

  • Compset long name has BGC%BPRP

  • Coupled model, BGC & RAD CO\(_{2}\) are prognostic

Ocean Specific BGC Compsets#

C1850ECO

  • Ocean alone, 1850 aerosols, normal year forcing

G1850ECO

  • Ocean and sea ice, 1850 aerosols, normal year forcing

G1850ECOIAF

  • Ocean and sea ice, 1850 aerosols, interannually varying forcing

These can be found by using the following command in the same directory as create_newcase

./query_config --compsets pop

BGC Initial Conditions#

Coupled BDRD compsets

  • BDRD is default RUN_REFCASE set for f09_g17 or f19_g17 resolution experiments

  • Provided initial conditions were spun-up with f09_g17 resolution model. Note that the carbon cycle is not as well balanced in f19_g17 resolution experiments as it is with f09_g17 resolution.

Coupled BPRP compsets

  • PBRP is the default RUN_REFCASE set for f09_g17

Ocean alone or Ocean-ice compsets

  • Initial conditions are provided but are not spun up.

BGC env*xml variables#

CCSM_BGC

  • Controls which CO\(_{2}\) fields are exchanged between CESM components.

bgc_settings

Figure: CCSM_BGC settings.

  • CO2A: land only or ocean only runs.

  • CO2B: atmosphere-land runs. Ocean and fossil fuel CO\(_{2}\) fluxes are read for m a file.

  • CO2C: fully coupled runs.

CCSM_CO2_PPMV

  • Constant CO\(_{2}\) reference value used in some configurations.

OCN_CO2_TYPE or LND_CO2_TYPE

  • Controls CO\(_{2}\) used by ocean and land components.

  • Constant, prognistic, diagnostic.

OCN_TRACER_MODULES

  • Controls which ocean tracers are used.

  • Ocean ecosystem model is called ecosys.

BGC units and sign conventions#

bgc_units

Figure: BGC units and sign conventions.

  • CAM variables CO2, CO2_LND, CO2_OCN, CO2_FF all have units of (kg CO2)/(kg dry air). Note that these are not typical units for carbon cycle modelers. To convert to ppmv multipy by 1.0e6*28.966/44.0 . 28.966 is the molecular weight of dry air and 44.0 is the molecular weight of CO\(_{2}\).

  • Same quantity in different CESM component output has: different names, different units, different sign conventions (for fluxes).

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