This book keeps returning to the theme of how little we know about the oceans. Moreover, we have already altered their nature in ways we are unable to judge; modern ocean scientists can never know the ecosystem as it was before human activity altered it irrevocably.
Until about thirty years ago little was known about the ocean floor; all that was available was the result of soundings, difficult to carry out and inevitably sampling only a tiny fraction of the floor. Sonograhic maps made by Bruce Heezen and Marie Tharp began to appear in 1967, the year that plate tectonics transformed geologists' thinking about the continents. They were dramatic but were misleading in various ways; large parts of them were filled in by guesswork. Kunzig makes the important point that the scale of the slopes in all the maps we generally see is exaggerated by a factor of about four. Later advances in sonography allowed more accurate maps to be made, although the funds made available for this vital work are pathetically small in comparison with those supplied for outer space exploration. There are still large areas of the oceans that are unmapped in any detail, although our knowledge is much greater now than it was before the 1960s. The picture that has emerged from this research is described in some detail, but the verbal descriptions are not always easy to take in and some line drawings would have helped.
Early explorers of the depths thought the deep sea floor would be largely unpopulated by animals, but this turned out to be far from the case. A surprising variety of organisms is to be found, the principal kind being species of holothurians (sea cucumbers), varying in length from an inch to six feet. But the most astonishing discovery was the finding of life in the vicinity of the hot springs, laden with metal sulphides, known as black smokers. Mussels, giant clams, and tube worms exist in this hostile environment, using symbiotic chemosynthetic bacteria to produce energy. Some speculate that life may have orginated in an environment of this kind rather than in the 'warm soup' generally favoured by biologists as a likely scenario.
Different kinds of organism live at various levels in the ocean. Most are transparent and jelly-like: not just jellyfish, but also 'winged snails' (pteropods) and salps, all with strange methods of catching their prey. Kunzig provides a fascinating account of their peculiar ways of life. There are undoubtedly many other species still undiscovered, and, given the lack of research resources, likely to remain so for the foreseeable future.
Not all the organisms floating and swimming in the oceans are animals; there are also single-celled plants (phytoplankton). These play a large, important, but unquantified part in recycling carbon dioxide, and hence are relevant to the man-made problem of global warming. Experiments have shown that the number of these plants depends on the amount of iron-containg dust that falls on the water, and it is possible to increase the population artificially by seeding the ocean with iron, but whether this would be safe to do on a large scale is questionable. As Kunzig remarks, we are already disturbing the balance drastically by burning fossil fuels and it may therefore not be unreasonable to think of counteracting the damage by a further intervention. As with most other issues concerning the ocean, however, there are vast uncertainties about almost everything, including how big a difference such seeding would really make.
Pollution by nutrients is thought to be the cause of spectacular growths of red algal blooms, especially a type of dinoflagellate that produces a highly potent toxin capable of killing all fish. Even worse, the toxin can become airborne and cause asthma, nausea, and memory loss, so that researchers who study it have to treat it as if it were a lethal virus.
The story of overfishing resulting in the virtual extinction of the once-abundant cod is told in some detail; the analogy with the disappearance of the bison herds of North America seems particularly appropriate. Other kinds of fish seem destined to go the same way as the cod; a case of sawing off the branch on which you are sitting if ever there was one.
The final threat to our wellbeing or even survival that Kunzig contemplates emerges from work on ocean currents. These extraordinarly complex phenomena have in the past been closely bound up with periodic glaciations and with the numerous sudden and extreme fluctuations in temperature that occurred within the glaciations as well as in the interglacials. There is plenty of evidence based on core samples and on computer modelling to suggest that alterations in climate can trigger abrupt slowing or even cessation of flow in currents like the Gulf Stream; such an event would plunge much of Europe into deep freeze. How likely this is to happen is impossible to know; as Kunzig remarks, there are many maybes. The models may all be wrong; even if they are right, the assumptions on which they are based may be wrong. A mild degree of cooling in the Northern Hemisphere might even be a welcome antidote to global warming. But it could also be a catastrophe.
This book is somewhat alarming in what it implies but is generally well balanced. It is also readable, but unless you have a good mental picture of the world map in your memory banks you really need an atlas handy to follow the explanations. It surely would not have increased the cost too much if the publishers had included a few outline maps to supplement the text.