When the BP oil well blew out earlier this year, the 4 million barrels that flowed into the sea didn’t simply vanish. There’s growing evidence that a good portion of it sunk to the bottom of the Gulf of Mexico, where some of it remains.

To get to the sea floor a few miles from the blown-out Macondo well, we clamber into a titanium-hulled submarine named Alvin and are gently hoisted off the deck of its mother ship, the Atlantis, into a surprisingly blue and inviting Gulf of Mexico. Mike Skowronski is our pilot.

As we descend, the water turns from bright blue to cobalt, twilight to black. Samantha Joye, a researcher from the University of Georgia, and I press our faces to our tiny windows and watch as glowing animal life streams by.

It’s very peaceful.

“That’s why I like diving in the submarine,” Joye says. “It takes you to another place. It’s calm and quiet, and then you hit the bottom and you’re like, wow!”

Joye is trying to see what happened to all the oil that spewed from the BP well. As we reach the bottom, my first impression is, well, it’s not here. Everything looks pretty normal.

There are tons of fish on the bottom. “I don’t see any invertebrates in the sediments,” Joye says. “But it’s hard to say — sometimes they hide. But there’s definitely shrimp and critter crawling around on the sediments.”

Some of the clams look happy as clams. But when the Alvin scrapes the bottom, we discover we’re not actually sitting on the usual dark gray mud that forms the seafloor.

“There’s oil on the bottom,” Joye says. “If you look at the camera, you can see the brown coloration.”

We see this brown stuff on coral fans, hit like pine trees along a dusty dirt road. More slimy brown stuff hangs over some of the odd formations of frozen natural gas here half a mile below the surface. Crabs here normally pick at worms that actually live in this methane ice.

“The crabs don’t look healthy. See all the dark spots and lesion looking things? That’s not normal,” she says.

It’s impossible to say from this single dive how much this ecosystem is hurting. After all, many of these animals have evolved to live in or near natural seeps of oil and gas. And clearly some of the routine commerce of undersea life is still taking place. Joye and other scientists will keep diving until they can flesh out this story.

But as our questions mount, Alvin’s batteries run down. It’s time to drop our weights and leave this eerie world behind.

Twenty five contemplative minutes later, we are back on the surface. Copyright 2010 National Public Radio.