Questions about the atmospheric deposition of soluble iron in MARBL

[zhangheng]

It was illustrated that "Atmospheric deposition of soluble iron is computed prognostically as a function of dust and black carbon deposition provided by the atmospheric model." in the "Simulations With the Marine Biogeochemistry Library (MARBL)".
But I haven't found the explicit algorithm about it. What's the role of the black carbon? Can you give me some clew information?

 

[klindsay]

Dust is assumed to have a fixed iron to carbon ratio. However, the fraction of the iron in the dust that is bioavailable varies. Loosely speaking, the model computes the ratio of coarse dust deposition to fine dust deposition as a proxy for how long the dust has been in the atmosphere. Coarse dust drops out the atmosphere more readily than fine dust, so small coarse/fine ratios indicate that the dust has been in the atmosphere longer. Longer residence time by the dust in the atmosphere increases bioavailability of iron in the dust.

Black carbon is assumed to have a fixed iron to carbon ratio and fixed bioavailability.

The Fortran that implements this in POP is available on github.