[MITgcm-support] Sediments in BLING

[Dave Munday - BAS]

Dear MITgcm-ers,

I’m using BLING in an idealised two basin sector model to look at Weddell Sea carbon budgets. I’m anticipating doing a carbon pump decomposition and to do that I need to know that my carbon & nutrient inventories are fixed. For my carbon inventory I’ve been adding up

DIC + 6.75*DON + Atmospheric_molar_mass*pCO2

(I’ve hacked the code to have an atmospheric pCO2 that responds to the air-sea flux with a fixed total molar mass). This gives a total inventory of about 1E18 with a small year-to-year drift of about 1E9-1E10. There are also drifts in the nitrate and phosphate, which, relative to their inventories, are much bigger. I’m now trying to convince myself that I haven’t introduced a horrible leak with my horrible hack and after poking around in the code I think the drift might be due to the flux from the sediments.

I want to test my sediment idea by turning this aspect of BLING off, although not understanding how the model works too well yet I’m also concerned this might not be as simple as I think. I’ve been looking at bling_bio_nitrogen.F and it looks like if I set NO3_btmflx and PO4_btmflx to zero, I’ll get the desired result. This would leave O2_btmflx alone and not touch the iron flux, which appears more complex. I don’t understand the iron cycle at all and decided that not messing with what I don’t understand was more sensible than going in all gung ho.

Is this a sensible approach? Will I actually disable the sediment fluxes, or just do something weird to the nutrients, like leave them building up in the bottom model level? And is there even a carbon sediment flux to worry about?

Many thanks,

Dave


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