At the end of 1960s, a submersible named Alvin suffered an accident off Martha’s Vineyard. The bulbous white vessel, carrying a crew of three, was being lowered for a dive when a cable snapped. Suddenly, Alvin flowed. The scientists came out, shocked and a little bruised, as the ship dived, listened ajar, eventually settling on the seabed some 4,500ft below. Alvin was in a slightly awkward situation. Even though the submarine was only a few years old, it had an eclectic CV this included, in 1966, helping to recover a 70 kiloton hydrogen bomb that was dropped when two military planes collided over the Spanish coast. Now he was the one to save.
Ten months later, Alvin was pulled from the depths – a jolt in the life of a ship that done dives to date (although regular parts replacement means none of the original subs remain). But the accident left its own legacy in the form of a mysteriously preserved lunch. In their frantic flight, the crew had left behind six sandwiches, two thermoses filled with broth and a handful of apples. After recovering Alvin, researchers from the Woods Hole Oceanographic Institution marveled at the state of this waterlogged feast. The apples seemed slightly marinated by the salt water, but otherwise undamaged. The sandwiches smelled fresh and the bologna (it was 1968) was still pink. They even still tasted good, the researchers confirmed by taking a few bites. Likewise, although the thermoses were crushed by the pressure of the water, the soup, when reheated, was deemed “perfectly tasty”.
These observations were published in the journal Science in 1971, after startled scientists rushed to study the meal before it spoiled, which it did, within weeks under refrigeration. In addition to munching bologna, the researchers measured the chemical properties of the food and the activity of microbes collected on it. Eventually, they concluded that the deterioration had occurred at 1% of the rate it would have on the surface, controlling for temperature. The question, which 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 under extreme conditions. Maybe there were fewer of these microbes than they thought, or the wrong kinds. Or maybe not enough oxygen. Or it was too cold or too pressurized. The answer was hard to pin down.
Over time, the question at the heart of the canned lunch mystery has become more urgent as scientists have come to understand the role that the oceans play by sequestering carbon. About a third of the carbon people put into the air was sucked up by the oceans – and much of it is believed to be stored in the deepest pools of water. It is therefore important to have an accurate picture of how much carbon is going in and how much is escaping into the air. This is especially important if you want to manipulate this process, as some do, by doing things like grow algae– which removes carbon from the air through photosynthesis to build its tendrils – then sinks it into the deep ocean trenches to store that carbon.
Much of the difficulty for researchers studying deep-sea carbon is that conditions on the sea floor are difficult to replicate at sea level. Typically, researchers pull water up to the deck a research vessel where they have equipment capable of measuring microbial activity. But that caused a lag, says Gerhard Herndl, a bio-oceanographer at the University of Vienna. On board a ship, microbes are usually happy to nibble on whatever nutrients they have. Their appetites are so great, in fact, that it doesn’t make a whole lot of sense, since it’s far beyond what the nutrients found in the deep ocean can provide. “When you do these measurements on the surface, there’s 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 the microbes where they actually live, they quickly found that the deep-sea microbes were much less happy and hungry. The differentiating factor, they wrote in a study recently published in nature geoscience, was the pressure. Some organisms like to be under extreme pressure – they are called piezophiles – and happily metabolize matter in the depths. But they represent a small slice of the microbial communities studied by Herndl – about 10%. The others were unsuitable; chances are they were adapted to another shallower environment and floated down.