Mryntu

The year was 2019, somewhere in the middle of North Atlantic Ocean (between Bermuda & Ponta Delgada) a new volcano errupted violently for a year. The volcano created a tiny island around 100 km squares.

A fishing ship discovered a new kind of fish coming out of underwater caves beneath the island. The fish have semi-translucent body, it glows faintly in the dark and in its stomach a random jewelry is visible. The jewelry is ranging from simple ruby ring to diamond ring, gemstone rings, pearl necklace.. all kinds of normal accessory that you could buy with money nowaday. The only special thing about them is that the ring/band/chain is made of low enriched uranium.

At first, people didn't know what it was. Later, every country want to help the island, or give the island some freedom. It got heated very quickly and nukes are ready to be launched.

Which country is likely to have the biggest claim on the island? Providing nobody successfully claimed the island, what policy could be used to share the resources so that the world's powers are satisfied enough to not go to wars?

Which country is likely to have the biggest claim on the island?

Whichever has the interest. For a historical reference, look at what happened with Ferdinandea/Graham Island, a volcanic island appeared in the Mediterranean sea:

When it last rose above sea level after erupting in 1831, a four-way dispute over its sovereignty began, which was still unresolved when it disappeared beneath the waves again in early 1832.

It was subject to a four-way dispute over its sovereignty, originally claimed for the United Kingdom and given the name Graham Island. The King of the Two Sicilies, Ferdinand II, after whom Sicilians named the island Ferdinandea, sent ships to the nascent island to claim it for the Bourbon crown. The French Navy also made a landing, and called the island Julia. Spain also declared its territorial ambitions. Each wanted the island for its useful position in the Mediterranean trade route (to England and France) and its close position to Spain and Italy.

Therefore any interested country can place a claim on the island.

Then the usual options are either an armed confrontation or a diplomatic approach to solve the dispute.

No nation has any claim to that location. However it's on the opposite side of the World from China, Russia has no sphere of influence in the region. Closest powers are Britain (Bermuda, nuclear) and Portugal (Ponta Delgada, not nuclear [research only]).

Which means the power in ultimate control of this apparent source of manufactured uranium products would be some sort of US special investigation team. There's no point having any pretensions about who is in charge when it comes to matters significant to NATO and nuclear materials.

The island would become a NATO protectorate, administered under the Antarctic Treaty System.

An island full of riches will turn into a free-for-all, with a great risk of damaging the resource. Access must be controlled to limit the possibility of damage, make sure benefit from resources is equitable, and especially to allow cool-blooded scientific study of the phenomenon without risk of looting or harm to the scientists by loot-seekers. Being as this island is in the Atlantic, it falls under the aegis of NATO and NATO ships would keep order.

Operation Ocean Shield is something like this - here a cooperative (including non-Nato members) to suppress pirates and allow desired activities (mostly mercantile shipping).

https://en.wikipedia.org/wiki/Operation_Ocean_Shield

NATO's contribution to Operation Enduring Freedom – Horn of Africa
(OEF-HOA), an anti-piracy initiative in the Indian Ocean, Guardafui
Channel, Gulf of Aden and Arabian Sea. It follows the earlier
Operation Allied Protector. Naval operations began on 17 August 2009
after being approved by the North Atlantic Council, the program was
terminated on 15 December 2016 by NATO. Operation Ocean Shield
focused on protecting the ships of Operation Allied Provider, which
transported relief supplies as part of the World Food Programme's
mission in the region. The initiative also helped strengthen the
navies and coast guards of regional states to assist in countering
pirate attacks. Additionally, China and South Korea sent warships to
participate in these activities.

In the interest of science and fairness, the island can be administered like Antarctica, through an extension of the Antarctic Treaty System. There is a clear analogy - like Antarctica this is a land without a native population but with natural resources at risk of being exploited for the benefit of one party or another.

In addition to administration this administrative arm would distribute fish to zoos and jewelry to museums. Select pieces of jewelry would be sold, proceeds going to fund the administrative arm and standing NATO protection operation.

This article sums up who gets an island quite well.
https://www.google.com/amp/s/www.vice.com/amp/en_au/article/exmjvz/how-to-claim-and-name-a-new-island-192
Basically if it is in a nations 12 mile zone it's theirs automatically and if it's within 200 miles they have a strong claim on it. As shown in the article some naval muscle flexing can extend the zone if noone pushes back. If the island truely is in international waters, whoever plants his flag there and can back up the claim with force gets it. There are no rules as far as I found out, just realpolitics.

Now mind you that these kind of islands are a common occurrence, yet only one in ten survives for a significant time. So governments and even courious explorers aren't fast to claim these lands.

I might even have a good location for your islands. I checked out Google Maps in the satellite mode and along the line you described there seems to be a group of underwater volcanos south of Newfoundland. (I could be wrong, wasn't able to find much else about those) But having one of those rise above the surface seems plausable.

Thus considering the islands position I'm 90% certain that the island would be claimed by the USA. It is the worlds strongest naval power. Portugal, France, Britain, Canada and possibly Denmark and Iceland might claim it, but I only see that happening if 'murica isn' t interested for some reason.

No matter who gets it I dont see how the issue is settled in a non civil way. All these nations are NATO and important trade partners. In fact Denmark and Canada had contested territory in the Arktic until quite recently, yet the "conflict" was based arround flag stealing and leaving whisky and a note claiming the island. No matter the resources, how are they worth a trade war or war with important partners?

Now to the fishes and the jewelery. I don't intend to bash your idea, these are just some points you might wanna consider. Uranium is a quite poisonous heavy metal. In fact, if you where to consume a dose of Uranium salts, whose radiation would kill you, you wouldn't die by radiation. The hevy metal poisoning gets you first. Look up lead poisoning for details. How do the fishes survive the contact with the metal? And how do dead fishes don't poison the entire Atlantic?

Concerning the valuables the quantity of these fishes is important. If they are rare, the resources would not be economically extractable and noone would fight for the island. If they are common they can ruin the market. You see, the high sale value of precious stones comes from their scarcity. (and market speculation and artificial scarcity induced by the traders, but that's a different story) If you now have this island where you can fish up metric tons of these scarce resources they are no longer scarce, so no longer as valuable. The current yearly gem production ranges from 30 kg (diamonds) to ca. 8000 t (amethysts). So if there are lots of your fishes they might upset the markets strongly.

If the island truely is contested viciously a UN mandate or a joint US EU research initiative backed by those countries is consivable. This could be modeld after the Antarctica treaty, as the situation seems similar. A uninhabited island with ample resources. So you might get numerous sientific stations (joined or not) but no resource exploitation.

United States would have the strongest claim on it, but United Nations can suspend all claims and declare it a natural preserve, similar to Antarctica.

This land, undoubtedly, would attract a great interest. But unless it lies close to any nation's shore, any territorial claim would be weak. United States has the strongest navy, and is located reasonably close, but other nations, particularly Russia and China, should object to it, even if they don't have enough firepower to push US away from it.

If it was before the mid-XX century, the strongest and closest navy would be the one and only deciding factor. But this is modern world, and politicians usually think twice and trice before starting a war, or even doing something that may lead to a war. If Russia and China's stance would be very combative, US may decide that the island does not worth the risk of going to war, and the matter should be settled diplomatically. Then the issue would be discussed at United Nations to fashion an agreement what the nations can, and can't do with this land. Likely such an agreement would prevent any nation from claiming this land as their own or introduce any military presence on or around the island. But the use of resources may be permitted, and some nations may have a bigger share of those resources.