Vision for WOMBAT ocean BGC

Copying the google doc here so we can continue the discussion started at the COSIMA2022 workshop.


  1. Who is using ocean-BGC? What for? What scale/resolution?
  • As the boundary conditions for regional models (GBR)
  • A lot of Southern Ocean and Antarctic productivity/elemental cycling/C cycling, using high-resolution model in current climate conditions.
  • Strong interest in validation
  • Some interest in using it to feed into higher trophic levels
  1. WOMBAT vs Bling vs COBALT in MOM6? What level of complexity is required?
  • A previous discussion ‘eliminated’ BLING
  • COBALT has some advantages but they could be implemented in WOMBAT if we wanted to
  1. Ocean CFCs - stand alone tracer package available is standard MOM#
  • Not really a BGC question but it’s helpful for diagnostics. It’s a feature that can be turned on in MOM5 and MOM6 and should be ‘encouraged’

Capability Development

  1. More nutrients? (nitrogen, phosphorus, silicon, iron)
  • Moderate-to-strong demand for iron in runoff or Antarctic meltwater
  1. More phytoplankton/zooplankton classes? (e.g. size, diatoms, diazotrophs)
  • Moderate-to-strong demand for at least 2 phytoplankton classes
  1. Nutrients and iron in runoff?.. see above
  2. …other coastal processes (sediments)
  3. Sea ice BGC - working in ACCESS-OM2, any next steps?
  4. Non-CO2 greenhouse gases?
  5. Isotopes: Some interest but maybe mainly on paleo time scales?
  6. Extra diagnostics?
  7. Biophysical coupling?


  1. RYF equilibrium at 0.25°?
  2. How to improve calibration and equilibration?
  3. Is there scope for data assimilation? If so, how can IMOS can help to make this happen?

Ocean BGC model schematics - for reference

From Kearney et al 2021 review of CMIP6 OBGC, doi: 10.3389/fmars.2021.622206

Boxes indicate state variables, and solid arrows represent fluxes between state variables; dashed lines indicate that the rate of change of one state variable is calculated proportionately to another. Colors indicate the base element for each state variable, with blue, green, pink, orange, and gray representing nitrogen, phosphorous, silicon, iron, and carbon, respectively. State variable boxes are positioned vertically based on functional role, indicating whether the functional group includes producers (and within that, subcategories of nitrogen fixers, Si-users, and CaCO3-users), consumers, or detritus. Horizontal position indicates the approximate mean size of the cells/bodies/particles represented by each state variable.




CSIRO Environmental Modelling Suite (EMS)

From Baird et al. 2020 CSIRO Environmental Modelling Suite, doi: 10.5194/gmd-13-4503-2020.

Figure 3: Schematic of the CSIRO Environmental Modelling Suite illustrating the biogeochemical processes in the water column, epipelagic and sediment zones, as well as the carbon chemistry and gas exchange used in vB3p0 for the Great Barrier Reef application. Orange labels represent components that scatter or absorb light.

had these comments in the google doc:

Laurie M:

it is my understanding that Bling is simpler than WOMBAT or at least would not be an improvement on WOMBAT. COBALT is much more complex and could be a next step forward if computational resources allow


Yes, Bling is simple and parameterises productivity and export, it doesn’t even carry phyto-/zoo- plankton tracers (see schematic above).
COBALT or TOPAZ have interesting new capabilities. While GFDL versions of MOM6 are being tested, it should be straight forward to turn these tracer packages on; there are test cases with prepared boundary conditions(?) (It will be more complicated once MOM6 is coupled to CICE#.)

had these comments on the google doc:

Laurie M:

iron is already included, no? It would be nice add silicon

Matt C:

Yes, there is iron in WOMBAT already.
Silicon is included in TOPAZ and COBALT.

Hi all,

Just catching up on this topic.

Personally, I think there is value in developing WOMBAT “in-house”, rather than using COBALT or others as our national BGC model. The reason for this is three-fold:

  1. It ensures we know the model we are using. There are no unexplainable results.
  2. It ensures we develop BGC capability that caters to the Australian scientific community.
  3. It ensures that Australia has BGC capability for naval operations that doesn’t rely on the tools of other countries.

This of course doesn’t mean that we can’t use COBALT when we want to.

I’m going to write out some key developments I want to make as the new BGC modeller at CSIRO, and I will add collaborators names here who have expressed interest in being closely involved in the developments steps.

Wish-list for WOMBAT (open to discussion!)


  • 3 phytoplankton - 2 Zooplankton (Tyler Rohr)
  • 2 classes of Detritus (fast and slow sinking)
  • DOM
  • Explicit Si cycle
  • Explicit N cycle
  • Major renovations to the Fe cycle (Alessandro Tagliabue)


  • Explicit N2O dynamics
  • Quota approach for N and P (non-Redfieldian ratios)
  • Pico-phytoplankton class
  • Macro-zooplankton class
  • Two DOM classes (semi-labile and semi-relcalcitrant)
  • N, O and C isotopes
  • Explicit bacterial types (copiotrophs and oligotrophs)


  • Particle microenvironment


If you wish to follow the developments as I make them, please follow this Github repository. I plan to do the initial development steps in a 1D water column set-up I just wrote in python. I plan to upload jupyter notebooks detailing the developments as I go, so you should be able to see changes caused by adding new phytoplankton classes and by considering different grazing parameterisations, for example.

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