Marvels of our unknown planet

An alien observer would see this planet as a water world. The oceans cover two-thirds of the earth's surface to an average depth of more than two miles. For most of earth's history life was confined to the oceans. They still provide a mobile, three-dimensional tapestry of habitats with a total volume of 320 million cubic miles that house the majority of the earth's inhabitants. In this extraordinary book Robert Kunzig provides a lucid and compelling description of our evolving understanding of these vast and sparsely studied areas of our planet.

His account is based upon interviews with leading ocean scientists in the United States. As a result Kunzig has produced a predominantly American perspective, with relatively little coverage being given to the contributions of scientists based elsewhere. Nonetheless, he has succeeded in identifying and illuminating most of the key developments in our understanding of the oceans. Through his fresh style and his obvious enthusiasm he projects the frisson felt by the ocean scientists as they have explored new environments and discovered unexpected phenomena.

Despite its title, this book is not primarily about cartography. Only four of the 15 chapters are concerned with mapping the seafloor. Kunzig shows how the first truly global picture of the seabed (where only items larger than two miles or so across could be discerned) was provided in the late 1990s by satellites measuring undulations of 100 feet or so in the surface of the sea, arising from the differential gravitational pull felt above mountains and trenches on the seabed. The state of our ignorance of the oceans is starkly illustrated here. Only 10 per cent of the ocean floor has been mapped with a resolution of 1,000 feet. In contrast more than 90 per cent of the surface of Venus has been mapped to this resolution. Sea-floor maps in the open ocean are consequently more like conceptual portraits with much of the detail filled in by intelligent guesswork. Yet the ocean bed contains features that are of great significance on a global scale. The mid-oceanic ridges, for example, are the largest mountain ranges on earth. They mark the lines along which continental plates are pulling apart and new sea floor is being formed at about the same rate as our fingernails grow.

The bulk of the book deals with life in the oceans. Kunzig romps through the extraordinary habitats, enthusiastically pointing out wonders at every turn. Most are not the habitats replete with sharks, whales and coral reef fish normally explored by the likes of Jacques Cousteau or David Attenborough. They are nonetheless the key habitats for understanding how life in the ocean works and how the various ecosystems interlace and produce a coherent whole.

Kunzig opens up these habitats in a creative way by presenting personal accounts of their discovery. A geologist and a geochemist chanced upon one of the most astonishing biological discoveries of the 20th century. Cramped in a tiny submersible nearly a mile down they edged nervously along the barren slopes of an active submarine volcano sampling hot-water vents. They turned a corner and found "... an oasis. Reefs of mussels and fields of giant clams were bathed in the shimmering water, along with crabs, anemones and large pink jellyfish."

At these deep-sea volcanic vents, there are worms six feet long and as thick as your wrist with no mouth and no gut that grow at the rate of four inches a month - powered by bacteria packed within their body walls. These surreal congregations of worms form the densest concentrations of biomass on the planet. On the adjacent abyssal plains, vast areas under crushing pressures, with temperatures close to freezing and in permanent darkness, life is sparse and clams grow at the rate of only one-third of an inch per century.

On the flanks of seamounts there are single-celled animals eight inches across that are so convoluted in outer form that they provide habitats for hundreds of smaller but more complex organisms. In the sunlit zone near the ocean surface in the world of the drifting organisms (the plankton), the whole food web is based on single-celled photosynthesisers so small that five or ten of them could be encompassed by the full stop at the end of this sentence. Nonetheless, they form blooms that are visible from space, that help regulate the carbon dioxide level of the atmosphere (and hence the climate) and that are responsible for generating most of the clouds above the open ocean. These surface ocean communities are sensitive to disturbance and the scientists who carried out the first experiments to fertilise the ocean with iron were shocked by their achievements. "It was almost biblical. In a week the ocean went from desert to jungle, from clear blue to dark green. There were some of us who were quite pleased and others of us who would walk out onto the fantail and burst into tears." This mixed reaction is understandable since one of the originators of the experiment told the Washington Post : "You give me half a tanker of iron and I'll give you another ice age."

Climate change is dealt with in a single chapter, which focuses on the rapid shifts in temperature that accompanied the emergence of the northern hemisphere from the last ice age. Here there are some salutary warnings about the instability of the earth's climate and its propensity to spring surprises. This instability is not taken into account in the chapter dealing with the demise of major world fisheries, which does however provide a lucid summary of the impact of market forces on our predation of the oceans' resources.

This fascinating book captures the pioneering spirit of ocean exploration and provides a dramatic and accessible picture of the world beneath the sea.

Michael Whitfield is visiting professor in marine science, University of Plymouth.