Marine life

In his satirical Devil’s Dictionary, Ambrose Bierce defined the ocean as ‘a body of water occupying about two thirds of a world made for man – who has no gills’. Bierce may have been right to poke fun at human arrogance, but he underestimated the importance of the seas. Averaging almost 3,700 metres (12,000ft) deep, the ocean constitutes around nine tenths of the habitable space on our planet. It plays a commensurate role in the Earth system, not least as an engine – a ‘blue machine’ in the phrase that also titles an excellent book by the physicist and science presenter Helen Czerski – that moves heat around the planet.

I recently learned to dive in the bay of Dakar. It was exciting. I’d started learning in a Leeds swimming pool and though I knew the ocean would feel different, I didn’t expect it to feel comfortable. It shouldn’t. It is not my element, and humans have long since left it to the rest of the ocean’s creatures. I also didn’t think the ocean would sound like my neck when I roll it during yoga: that same crackle. With their remarkable sonar, dolphins can even tell when a human is pregnant That the ocean is not quiet is one of the most pleasing revelations of the past century (I mean

Streamlined, musclebound, warm-blooded and with fins that retract into body slots like a switchblade so it can attain swimming speeds of more than 40 mph, the Atlantic Bluefin Tuna is a wonder of the marine world – the Clan Chief of the Scombridae, that can weigh up to 1,500 lb. It has long been prized by sport fishermen, from Charlie Chaplin to the dentist-turned-bestseller Zane Grey, and there is nothing tentative about a tunny strike. In 1927, after a four-hour battle with one eight-foot giant, Grey wrote: ‘If it were possible for a man to fall in love with a fish, that was what happened to me. I hung over

When we observe the ocean we rarely peek beneath its surface. As Helen Czerski shows in her lively and engrossing account of the physics of ocean spaces, we would not see much anyway. Sounds travel well in water, and blue whales talk to one another across thousands of miles; but light soon disappears, apart from the glow emitted by luminous fish. Historians of the oceans (myself included) have looked at how, when and why people have crossed the surface of these spaces, uninhabitable except in the security of a boat or on islands, such as those in Polynesia with which Czerski begins her book. But we need to dive deeper.