[dan-robertson]

Well for the actual trading they will be operating out of the same datacentres as the exchanges which are not particularly massive and will have relatively small limits on the heat (and therefore power). There will be other computers in other bigger cheaper datacentres for analysis and suchlike. And office buildings of course. But not really comparable to e.g. the energy usage of Argentina. I would guess the total is less than one of the massive internet companies like Google or fb but that might be a bit low.