In the late 1960s, a submersible named Alvin suffered a mishap off the coast of Martha’s Vineyard. The bulbous white vessel, holding a crew of three, was being lowered for a dive when a cable snapped. Suddenly, Alvin was sinking. The scientists clambered out, shocked and a little bruised, as the vessel plunged, hatch ajar, eventually settling in the seabed some 4,500 feet below. Alvin was in a slightly embarrassing situation. Though the sub was only a few years old, it had an eclectic résumé that included, in 1966, helping to recover a 70-kiloton hydrogen bomb that was dropped when two military planes collided over the Spanish coast. Now it was the one that needed saving.
Ten months later, Alvin was pulled from the depths—a blip in the life of a vessel that makes dives to this day (though a steady replacement of parts means none of the original sub remains). But the accident left behind its own legacy in the form of a mysteriously preserved lunch. In their frantic escape, the crew had left behind six sandwiches, two thermoses filled with bouillon, and a handful of apples. After retrieving Alvin, researchers from the Woods Hole Oceanographic Institution marveled at the state of this waterlogged feast. The apples looked slightly pickled by the briny water, but otherwise intact. The sandwiches smelled fresh, and the bologna (this being 1968) was still pink. They even still tasted good, the researchers confirmed upon taking a few bites. Similarly, although the thermoses had been crushed by the water pressure, the soup, once warmed up, was deemed “perfectly palatable.”
Those observations were published in the journal Science in 1971, after the surprised scientists raced to study the meal before it spoiled—which it did, within a few weeks under refrigeration. In addition to nibbling the bologna, the researchers measured the chemical properties of the food and the activity of the microbes gathered on it. Eventually, they concluded that the spoilage had been happening at 1 percent of the rate it would have at the surface, controlling for temperature. The question—one that has vexed researchers for decades—was why. In the 1960s, researchers had little experience in the cold, highly pressurized deep ocean, but they expected it to be filled with microbes ready to break down organic matter, even in extreme conditions. Perhaps there were fewer of those microbes than they thought, or not the right kinds. Or maybe not enough oxygen. Or it was just too cold or too pressurized. The answer was difficult to pin down.
Over time, the question at the heart of the preserved-lunch mystery has become more urgent as scientists have come to understand the role that the oceans play in sequestering carbon. Around a third of the carbon people have put into the air has been sucked back out of it by the oceans—and much of it is thought to be stored in the deepest pools of water. So an accurate picture of how much carbon goes in and how much escapes back into the air is important. It’s especially important if you want to manipulate that process, as some do, by doing things like growing seaweed—which removes carbon from the air through photosynthesis to build its tendrils—and then sinking it into deep ocean trenches to store that carbon away.
In large part, the difficulty for researchers studying deep water carbon is that conditions at the seafloor are hard to replicate at sea level. Typically, researchers pull water up to the deck of a research vessel where they have equipment that can measure microbial activity. But this has resulted in a mismatch, says Gerhard Herndl, a bio-oceanographer at the University of Vienna. Aboard a ship, microbes are generally happy to chomp down on the nutrients available to them. Their appetite is so great, in fact, that it doesn’t make much sense, because it is far greater than the nutrients found in the deep ocean can provide. “When you do these measurements at the surface, there is always a gap,” he says.
So instead, following the long legacy of the Alvin sandwiches, Herndl’s team tried a new experiment. By sending autonomous instruments to incubate microbes where they actually live, they quickly found that microbes in the depths were far less happy and hungry. The differentiating factor, they wrote in a study recently published in Nature Geoscience, was pressure. Some organisms like being under extreme pressure—they’re what’s known as piezophilic—and happily metabolize material in the deep. But they represent a small slice of the microbial communities Herndl studied—about 10 percent. The rest were ill-adapted; chances are they were suited to some other, shallower environment and had floated their way down.