evansmn
commented
6 months ago We are making carbonate this morning. The problem seemed to be my fundamental misunderstanding :| of the experimental setup that Andy described in Chs 12 and 22.9. Sorry!
As Andy writes in Ch 12:
"To properly (quantitatively) appreciate the role of ocean-sediment interaction (and weathering) and controlling atmospheric pCO2 , you need to contrast these experiments with as similar a model configuration as possible – for instance, one that is identical excepting having no sediments (or weathering). You can achieve this quite simply:
edit the lines :
"# set an ’OPEN’ system"
bg_ctrl_force_sed_closedsystem=.false.
changing it to:
"# set a ’CLOSED’ system" bg_ctrl_force_sed_closedsystem=.true.
What this does is to force the model to always maintain an exact balance between the preservation and burial in marine sediments of CaCO3, with the supply of solutes derived from the weathering of CaCO3 on land. Because no excess or deficit of weathering vs. sedimentation is allowed to occur, no changes in ocean chemistry (other than by air-sea gas exchange) occur. This configuration hence acts (geochemically and dynamically) exactly the same way as a configuration without any sediments or weathering being present (and as used previously)."
And then in Ch. 22.9:
"... a non-zero [carbonate] weathering flux must be prescribed. This could be derived from ... a previous closed system model experiment with no weathering flux specified (diagnosing weathering from total global CaCO3 burial as described earlier)... or from the literature.... you are looking for convergence in the mean wt% CaCO3 value (averaged sediment composition), which is recorded in the BIOGEM time-series file: biogem_series_sed_CaCO3.res."
In my experiment I had the same configuration as in Andy's EXAMPLE._rwlma.PO4.S18s18.SPIN1, only I forced it to 560ppm pCO2 and not 278ppm pCO2. Maybe that was enough to keep the ocean from precipitating carbonate, even with the closed system and at the prescribed rate of CaCO3 weathering of 0.10E+14 mol Ca+2/yr? (I can check.) In which case, I might need to first run a spinup to climate conditions (no sediments or weathering) at 560ppm, then the first SRG spinup, then the second SRG spinup. As I believe Andy also suggested in Ch 22.9.
Mike
derpycode
After reading muffin.pdf (Jan 11, 2024 version) Ch 12, and Ch 22.9...
I created an experiment with a paleogeography different from the idealized one in this example user-config, different solar constant for that paleogeography (obtained using muffingen); but otherwise patterned on base-config: cgenie.eb_go_gs_ac_bg_sg_rg_gl._rwlma.BASES.config and user-config: EXAMPLE._rwlma.PO4_S18x18.SPIN1. I also set the pCO2 forcing to 560ppm for the .SPIN1 experiment (vs 278ppm for the EXAMPLE).
The idea was to get a ROKGEM configuration for a .SPIN2 experiment with an open weathering system, similar to EXAMPLE._rwlma.PO4_S18x18.SPIN2 using the same base-config.
However, after spinning up to steady state (100ky run), for which the SLT is 10.6C, I get no nonzero % carbonate (biogem_series_sed_CaCO3.res).
I don't have the EXAMPLE._rwlma.PO4_S18x18.SPIN1 outputs, but the differences between my output and EXAMPLE._rwlma.PO4_S18x18.SPIN2 output are that:
I have 196 deep sea grid points and 0.31e15 m^2 area (vs 216 and 0.34e15 m^2 in the EXAMPLE). Mean ocean depth is 3551m vs 3643 in _rwlma_depth_18x18x18.rnd.
I have zero POC rain, dissolution and total POC (vs 0.3059e14 mol/yr in the EXAMPLE)
I have zero CaCO3 rain, dissolution and mean weight % CaCO3 (vs (0.3575e+14 mol/yr in the EXAMPLE)
I can also get zero carbonate produced, with 278 ppm CO2.
Why might my experiment be producing no CaCO3 (or POC)? Am I missing something very fundamental? I am not sure how the paleogeography alone could have caused this. But if that is the case: how can I get the system to reasonable produce carbonate?
Thank you very much for any suggestions. - Mike