whence

Lake’s sub-expedition into the unknown, as everyone will recall, sent out its own reports from the shortwave transmitters on the planes; these being simultaneously picked up by our apparatus at the southern base and by the Arkham at McMurdo Sound, whence they were relayed to the outside world on wave lengths up to fifty meters.

Context: Arkham is a ship anchored at McMurdo Sound.

Earlier in the novel, there was mentioned that "the ship's outfit, communicating with the outside world, was to convey press reports to the Arkham Advertiser's powerful wireless station on Kingsport Head, Massachusetts," so I'm inclined to think only the apparatus at the Arkham can relay the reports. But the placement of the word "whence" kinda make me doubt it.

So does "whence" here refer specifically to the Arkham at McMurdo Sound, or both the Arkham and the southern base?

Source: At the Mountains of Madness

I think both.