Ocean sourced Trade goods in a Renaissance era Earth
I am in the process of writing a fantasy book that is set in a post-apocalyptic late medieval/renaissance era society.
This is on Earth, about 1300-1500 years in the future following a complete societal collapse of decades.
A group of aquatic humanoids (I call them Delphians,) need to trade for metalwork goods, and I'm having difficulty finding trade goods that would be valuable to the land-dwellers that would be found in the ocean, other than seafood.
I've come across a few of them in my research that are available in today's society (regardless of legality or morality), such as:
- whale ivory
- mineral or metal nodules
- pearls (rarely, very druidic/harmonistic society underwater)
- sea snails for the old fashioned purple dye
Thus far in the build, the aquatic humans are the only unusual biological presence other than a semi-intelligent parasite.
My question is, What sort of resources valuable to a Renaissance era society would come from the Continental shelf of the ocean?
Especially if it would be different from what is available or valuable in our modern era.