screws, bolts or nails for ground level deck framing
Traditionally I would have just used 20d galvanized box nails, 4 per joist end.. Since you're nailing into end grain you need a substantial fastener. Hot-dipped galvanized nails have a rougher texture that grabs fairly well.

However, since your deck is floating I'd maybe want to use screws. This will keep any motion that occurs from working things loose. 3-1/2" Torx drive  screws that are coated for exterior use would be good.