How a sandwich unlocked the secrets of the deep

Mapping the Deep: The extraordinary story of ocean science by Robert Kunzig (Sort Of Books, £8.99)

Mapping the Deep: The extraordinary story of ocean science by Robert Kunzig (Sort Of Books, £8.99)

In the history of the ocean, there can be few yarns more fantastical than the one about the bologna sandwich. In 1968, a submersible called Alvin was being lowered into the sea when its cable snapped. As water poured in through the open hatch, the three men inside struggled to escape. They managed to swim to safety, but left their lunchboxes behind - three apples and three bologna sandwiches. The submersible sank 5,000 feet.

Ten months later, Alvin was recovered from the ocean floor. When the sandwiches were pulled out, they looked so fresh that a couple of scientists took a bite. They tasted a bit salty, but were otherwise fine. A significant scientific experiment had taken place. It was concluded that life processes, reflected in the rate at which bacteria rot a bologna sandwich, are much slower in the deep sea than in an ordinary refrigerator. Robert Kunzig doesn't mention the condition of the apples, but we can guess.

A guess is as good as any method to predict what might happen in the depths of the ocean. As Mapping the Deep demonstrates, theories about the ocean are just that - theories. From continental drift to the melting of the icecap, all have had their supporters and detractors. In such a hostile environment, nothing is provable beyond reasonable doubt.

Mapping the Deep starts at the very bottom of this uncharted territory and drifts up to sea level. We begin with detailed descriptions of the seabed, float to the top of the underwater sea-mounts, and, by the last chapters, are swimming with cod and testing the circulation of currents.

These waters are home to creatures that could have been invented by a pubescent schoolboy: the xenophyophore, made of just one cell but as big as a human fist; the echiuran worm, only a few inches long but with a tongue that extends for 18 inches; and the holothurian, or sea cucumber, which breathes through its anus.

Their discovery is often presented as the lone work of individual scientists. Major scientific research usually relies on teamwork, but, by introducing us to just a few men and women who made breakthroughs, Kunzig creates a cast of loveable eccentrics. There's Graf von Rumford, the 18th-century British spy who, before conducting experiments that laid the foundations for theories of warm-water currents, invented the soup crouton. Two centuries later, the ornithologist Bill Hammer developed an allergy to feathers; he turned to the water and the jellyfish that live in it, theorising that their transparency was to protect them from predators.

The machines these men design and drive are no less heroic - or ridiculous. It was in the bathyscape, designed by Auguste Piccard (who held the record for the highest ascent in a balloon), that, in 1960, Jacques Piccard and Don Walsh descended into the deepest chasm on earth - the Challenger Deep of the Mariana Trench. Soon afterward, it was the Monster Camera - a camera with fresh mackerel attached as bait - that proved that in the abyss there were fast, smart animals that could chase their food.

Kunzig dwells upon the destruction being visited upon this wondrous ocean. Not only may there soon be less to discover; there are now far fewer people discovering it. The height of ocean science was the 1960s and 1970s, largely thanks to support from the US and Soviet navies. Since the Cold War, that funding has shrunk. Today, the mid-water range is regularly investigated only from the Monterey Bay Aquarium Research Institute in California, financed by the computer millionaire David Packard. Below 3,000 feet is hardly visited at all.

"We live at a time when the outside chance of finding a fossil bacterium on Mars is enough to generate tremendous enthusiasm for billion-dollar missions of exploration to that planet. And yet we are content to pass over in complacency and almost total ignorance the largest and strangest habitat on Earth," says Kunzig. This book, at least, alleviates our ignorance. But it is, by necessity, partial. Mapping the Deep whets our appetite. We simply have so much more to learn.