There aren't many truly seasonal events, but a few stand out. There are regular summer voyages from Scotland to Hudson's Bay, and from Holland up to

There aren't many truly seasonal events, but a few stand out. There are regular summer voyages from Scotland to Hudson's Bay, and from Holland up towards Spitsbergen, for example: both these appear as huge convoys moving in sync. (What were those about?) The yearly trips from the Netherlands up to the North are most likely whalers going out to hunt and coming back with their catch.