What would a giant corpse island actually be like?

Question

Context

There is an inland sea called the Poisoned sea (name subject to change), which is around the size of the Mediterranean sea. A vast majority of the land masses in the Poisoned sea are the corpses of utterly ginormous chimeric kaiju called God-eaters.
Relevant information on the God-Eaters

• The God-Eaters' anatomy varies for each individual God-Eater, with each individual having a different the body parts of earthly animals, think something like the Tarraque or the Manticore.
• All of the God-Eaters are warm blooded.
• Relevant terrestrial creature: Spinosaurus
• The God-Eaters' sizes range from 150 feet to 10 miles.
• The only magic the God-eaters have is the magic that allows them to exist at such a large size.
• The the age of the corpses range from to 1 year to 60 million years.
• Most of the corpses rest on the seafloor, and on average 50% of the corpse is above the water.
• The 2 most common ways a God-Eater would die is ether being partially eaten by another God-Eater or being killed from the inside by god stabbing its heart.

The Question

What environment would these giant corpse islands actually be like?

Answer 1

You will get an island rich in fossil fuel

At first, the surface of the God Eater will be decomposed by scavengers, fungi, and bacteria, etc. Larger scavengers like vultures will do the most damage at first assuming they can get past however thick the skin is of this thing... however, when everything within a few miles is just more meat, this means that the scavengers will be forced to poop where they eat, eventually covering the outer lay of the creature in excrement. This will prevent other large animals from wanting to keep eating away at it. Below the surface, maggots and worms will be busily turning the outer few feet of flesh and excrement into soil; however, the deeper you get, the less air there will be. This will prevent the worms and maggots from getting too deep. Beyond this outer layer, decomposition will be very slow and limited. Studies of landfills show that buried organic matter can decompose hundreds or even thousands of times slower than on the surface, and those studies are not for nearly as deeply burred organics as the insides of a God-Eater. As the surface of this creature becomes soil, plants will begin to take root which will help prevent the new soil from eroding enough to expose more flesh.

Slowly, the outer layer of this creature will begin to sink as water is pressed out of it by its own weight and forced up to the surface. About 50% of the creatures mass thought will never be pressed out or decomposed. It will become a fossil fuel like petroleum or coal. Assuming the creature started off sticking out of the water by enough to not sink under the surface, the bulk of the creature will become a solid mass of fossil fuel with its skeleton mostly in tact to maintain some of its shape, and only a thin outer layer of soil (relatively speaking) will form any time soon.

Answer 2

First, an inhospitable nightmare landscape

The island, if it can be called that, is mired in black fog. If you were closer, you would be able to see that the fog is an impossibly dense swarm of blowflies, flesh flies, and carrion beetles.

Of course, getting closer is impossible. Even a mile out, the stench of death is overpowering. Scavenging birds, awaiting their turn, have settled to perch on every rail, mast, and inch of rigging on your ship.

Your hear a distant, fleshy thump, and through a spyglass witness a horrific geyser of rotting flesh spewing from somewhere near the edge of the gargantuan corpse. The bloated form is rupturing in a dozen places, gaseous columns of air fountaining fluids and half-rotted solids, to land wetly on the landscape.

With a shudder, you turn your ship around. The bulk of the terrestrial frenzy will last another three months. You don't want to be around when the bigger gaseous ruptures start.

Then, an underwater reef

When you next return, most of what remains above the waves is yellowed bone and scraps of tattered and desiccated flesh, even now being picked at by the scavenger birds, but the stench still lingers, an impenetrable wall of putrid fetor. There's a temptation to sail in and take souvenirs of the body, but you know that this scent will cling to anything it touches in a thin, greasy layer for years.

The water still teems with life, as the bulk of the creature that lies in the sea is consumed by worms, clouds of ampiphods, hagfish, and sleeper sharks. If eating fish that had fed on kaiju flesh were not the quickest way to a miserable death, you could make yourself rich with a harvest of prawns.

There is little of interest for you here, but the bones have not begun to crumble yet, so your ship cannot sail past. With a sigh, you turn your ship and return to land.

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A year later, the waves, the scavengers, and the marine life have sundered and cracked the skeleton into pieces, letting it settle beneath the water entirely. An ignorant captain might sail through here with great confidence, only to founder his craft upon a rare jutting bone spur.

You navigate carefully, gazing into the blue depths. Your son, who is only a baby now, will be older than you by the time the last of the skeleton below is fullly consumed, leaving behind only colorful colonies of coral that have formed along some of its calcified ribs, mimicking for grim centuries to come the vanished shapes of the menacing kaiju.