The problem of the 'missing carbonates' on Mars

The message we receive from Mars about the presence of carbonates on its surface and in its atmosphere is quite contradictory. On one hand, many images of the Martian surface show clearly the signature of past bodies of standing water, where the precipitation of sedimentary deposits should have occurred. On the other hand, the apparent absence of carbonates in the strikingly homogeneous fines covering the Martian surface raises the question: where carbonates could hide now, if they ever had formed on Mars?
The subject will be addressed in some detail, showing that a proposed destruction mechanism of carbonates, the photodecomposition due to solar radiation, cannot account alone for the absence of such compounds.
Preliminary numerical simulations of the infrared emission/transmission of the surface and the aerosol suggest that the difficult detection of carbonates can be ascribed to the low temperature of the emitting zones, observed up to now.