The primary problem I have with the White Mars model is that I haven't seen it explain, to my satisfaction, how the northern plains were formed (with splash craters and all). I can imagine Co2 being the active agent in short and chaotic outflow chanels, but it it's hard for me to imagine it leveling out such a large part of the planet. So, I'm still clinging to the ocean hypothesis. If this theory is correct, then the nothern plains should be full of carbonates, somewhere under the dust where TES can't see them.

Christensen & company say that, if there are significant carbonates on Mars, they should at least poke out from under the dust *somewhere*, cliffs of Dover style. But such formations, on Earth, are the product of plate tectonics lifting up the seabed. No such processes would have ever occured on Mars.

So, it's still possible for me to imagine carbonates forming in the low spots of the planet, and staying there ever after.