system
Given the following post, respond as if you're commenting on Reddit:
human
Why aren't polar deserts sandy?

I realise there's no requirement for a desert to be sandy, but I'm wondering if there's a particular reason that the polar deserts on Earth are nearly all rock or gravel rather than having sand. Is there a reason for it, or is it just one of those things? Is a sandy polar desert on an earthlike planet possible? What conditions would need to be met for a polar desert to become sandy?
gpt
Eolian sand systems commonly associated to deserts (think of the golden dune fields of the Sahara), require a source of sediment. In the case of the Sahara for instance, there was a pre-existing layer of sediment emplaced during the Holocene Wet Phase. When aridification went hog-wild and the rains failed, this sediment layer was remobilised by eolian processes. These processes essentially did three things:

* They picked up fines as suspension load, such as clay minerals, and lifted them into the upper atmosphere;

* They moved sand-sized particules as traction/saltation load along the desert floor;

* They isolated areas of coarser material through deflation  (lag).

Of these fractions, the sand is interesting as it provides an erosive force susceptible to abrade coarser fragments and *in-situ* bedrock to generate additionnal particulate material. In other words, "Sand blasting" is a powerfull motive force to producing more sand.

Back to the poles now, or Antarctica really as the North pole is an ocean. Antarctica's dry valleys at the small end of the scale for deserts, And there has'nt really been a prolonged period of rainfall to get sedimentation and erosion going for a long long time. So there is very little sediment to work with from the start and get things going, on one hand. And when what little sediment is present gets remobilised, it gets relatively limited opportunity to interact with the substratum and generate additionnal sediment before getting carried away over the icecap.