Wonderful find!
With these new pieces of informtation, I think we now have a very fine understanding of the mechanics of Venalem:
The age is a hollow iceberg floating in an arctic ocean. There are pockets of water inside this iceberg, whereupon grow some giant vegetable pods which contain a substance used to make Ink (the chemical process which generates this substance must require some pretty low temperatures, otherwise I'm sure the D'ni would have written a more mild harvest age. I wonder, though, didn't Gehn mention that Ink was made from beetles? Oh, I digress...).
Scuba divers cut the pods from the plants; then, the pods probably floated to the surface and were snatched by this "Hourglass Harvester" (beautiful name, by the way). It appears that, once a pod has been ensared, the "hourglass" rotates so that a second pod can be caught. The harvester floats on the water thanks to two balloons attached at the sides, which also could provide light at night (hinting that this Age might have a day/night cycle).
It is unclear whether the ink extraction process happened on the pod itself or on some "land" facility (there are structures built into the ice); but the empty pods weren't discarded, but rather reutilized to make living quarters and such for the harvesting crew (it appears that the workers lived in the Age, at least for some periods of time).
The Age probably also involved some sort of gameplay with the "sea cows", animals depicted in previously seen concept art and which are said to have a nest in the iceberg (perhaps in the underwater cave seen in the side view of the Age?)