Is there any obligation to turn over treasure you find yourself? And why?

There is when you take $12 million from investors:

> A total of 161 investors had given Thompson $12.7m (£9.4m) to find the ship on the understanding that they would see returns on their investment.

Both the criminal and civil contempt arose from his refusal to abide court orders from the civil suit.[1]

[1] https://www.justice.gov/usao-sdoh/pr/treasure-hunter-sentenc...

If investors gave you $12.7 million to fund your expedition, you have an obligation to split the treasure as you promised.

    > "Is there any obligation to turn over treasure you find yourself?"

For example, the UK Treasure Act:

    "Under the Act, treasure is owned by the Crown"
    "The act requires finders of treasure—specifically, gold/silver objects >300 years old, coin hoards, or significant metallic items >200 years old—to report them to a local coroner within 14 days"

    "all wreck material recovered in UK territorial waters or brought into the UK must be reported to the Receiver of Wreck within 28 days."

There's also the United Nations Convention on the Law of the Sea (UNCLOS) which applies to international waters.

     "All objects of archaeological and historical nature in [international waters] must be preserved or disposed of for the benefit of mankind, with particular regard to the country of origin, cultural origin, or historical/archaeological origin."

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