Nick, I read here on Habitable Zone that you had some theories about Martian climate. I hope you will find some ideas in this hypothesis that you might find useful. Please feel free to develop any of them further. Perhaps you could answer some of the questions explicit and implicit therein. It is more than a little disorganized and certainly faulty, but I think you may find the main idea interesting.

From Mars, a Redplanet Roundtable Discussion:
by Phil Simon
Deliquescent mineral equilibria fluxes and dust storms
Fri Mar 12, 2004 09:10
12.45.169.2

I am starting to develop a theory, still much in its infancy, that phase changes of deliquescent minerals at and near the surface of Mars could provide a mechanism for cyclic global dust storm outbreaks.

As the dust storm abates, fine dark dust (iron?) slowly settles from the air, and the skies clear. The upper layers of the air cool down, but greater amounts of radiation reach the ground, and are absorbed there by the fine dark dust. The ground gradually heats up underneath this insulating dust layer until a deliquescent mineral layer concentrated just underneath begins to dissolve, liberating brine. The surface layers then become moist, wetting and resorbing the dust. The dust may also contain a different type of salt, which could dissolve. The fluidity allows surfaces to flatten out on the larger scales. Now, the surface is rougher on the small scale, even wet in parts, which makes it much more reflective, so it begins to cool. Crystalization then slowly begins, with the most deliquescent minerals crystalizing last closer to or at the surface, and some regions of the surface wet with late stage brines of minerals (or chemicals) that are too deliquescent to dry out. The crystalization releases heat, which slows down the cooling. Gradually more and more deliquescent minerals form, drawing more water vapor from the atmosphere. This gradually allows more radiation to reach the ever drier surface. The dryness, radiation, heating and cooling cycles, and chemical erosion cause more dust to gradually form across most of the Martian surface. This flattens the surface, and the dust particles are better able to absorb radiation. The ground warms up. This sets up very strong atmospheric temperature gradients near the surface. Then all that is needed is a few dust devils to kick up a bunch of dust and fill the lower air column with the fine dust particles. This causes rapid heating of the air, and more instability (latitudinal), so a flurry of dust devils is kicked off, and a global dust storm ensues. This causes the upper air layers to heat up, and less radiation reaches the ground. The ground cools down. This reduces the atmospheric temperature gradients, so the wind dies down and the dust settles. The cycle can then repeat itself, each time Mars becoming a little drier as water vapor is lost to space from the upper atmosphere.

Well, sorry for such a convoluted tale (first draft), it is not well worked out yet. The principal cause for this theory was the observation of the apparently dust free flat zones in the Lagunas where the surface seems to be crystalized (as recent experimentation suggests!) Some of the main points are:

1) The sulfate content at Mars may be quite high. That, coupled with Chloride and Bromide could allow for great amounts of deliquescent salts near the surface. Brines may also exist that would be liquid under all conditions of this cycle, especially if sulfuric acid was present.

2) There could be large amounts of deliquescent minerals near equilibrium and close enough to the surface to interact with the atmosphere.

3) The dust could have a salt component that redistributes deliquescent minerals around the planet.

4) Water could cylce in and out of the ground and atmosphere as deliquescent minerals crystalized, or changed hydration states, or mineral phases.

5) There could be a cyclic flux between different hydrated minerals, generally driven by seasonal and orbital factors.

6) The deliquescent minerals would be great moderators, stalling the loss of water from the planet by harboring it in the ground. This would be similar to the role of water on Earth, creating a balancing effect. You could call this the "salt cycle".

Earth, the water planet. Mars, the soggy salt planet.

PS: One of the holes in the above theory is that the surface crust seems to be much lighter in color than the very dark material underneath. This suggests that the dust is light in color compared with the mineral zones underneath. A bit more work might "iron out" some of these problems with the dust - salt - water equilibria theory.

Another problem is that I am uncertain if a rougher surface is more reflective. Thought that was true, now uncertain, its getting late!