Out of the blue: New exhibition Aquatopia explores our relationship with the sea

In a remarkable new exhibition, Aquatopia – the Imaginary of the Ocean Deep, acclaimed curator Alex Farquharson has assembled art on the theme of what the sea means to us. Five years in the making, with works from JMW Turner to the Otolith Project, from Barbara Hepworth to Wolfgang Tillmans, Lucian Freud to Spartacus Chetwynd, Aquatopia aspires to be an allusive and cutting-edge tribute to the element.

Yet we have to admit that, for all its ingenuity, art often fails in its task. Artists, like writers, soon realise that the sea is ultimately unknowable. That is its abiding mystery and power; its promise of life and sensuality, but of death and destruction, too.

Summer brings us close to the water. We marvel at it, swim or surf or sail in it as an expression of our devotion. Who isn't fascinated by the sea and what it contains? Seventy per cent of the Earth's surface is covered by ocean; little wonder that Arthur C Clarke said our planet was ill-named; it ought to be called the Ocean. We know more about the moon than we do about the profound depths; only one-quarter of its species have been identified. The sea provides the air we breathe, the food we eat. It is our last wilderness, yet we mistreat it through our ignorance, pumping it with chemical and aural pollution – all because of our inability to peer through the "ocean's skin", as Herman Melville called it.

According to Elaine Morgan's theory, however, we may have been more recently connected to the sea. In the 1980s, Morgan posited that we were once "aquatic apes", descending from the trees to the sea in search of shellfish whose fatty acids sustained our growing brains. She reasoned that we owe our long legs to forebears who foraged in the shallows. Our ratio of body fat to muscle is found in no other primate, but is more akin to that of a whale's blubber. Our kidneys evolved to deal with excess salt to which our ancestors were subject, while our every cell is held taut by water. We all contain the sea inside us.

Such ideas speak to science-fiction notions of "Homo aquaticus" and submarine aliens. As a boy, one of my fantasies was to grow gills and be able to breathe underwater. I was inspired by a 1960s, Japanese-animated cartoon in which Marine Boy chewed oxy-gum and rode a dolphin; while in Gerry Anderson's Stingray, the mermaid-like Marina swam unaided in the depths. But there was an even earlier model for my amphibious ambitions: Charles Kingsley's novel of 1863, The Water Babies.

In one of the most memorable yet oddly disturbing of all Victorian transformation scenes, the chimney-sweep boy, Tom, takes off his clothes to get clean and falls asleep in the water. He wakes to find himself swimming, "having round the parotid region of his fauces a set of external gills" ("I hope you understand all the big words," says Kingsley, "just like those of a sucking eft, which he mistook for a lace frill, till he pulled at them, found he hurt himself, and made up his mind that they were part of himself, and best left alone". Tom's "black shell" is later found, evidence to the rest of the world that he has drowned.

Kingsley, a Darwinian as well as a clergyman, used his moral fable to reinforce new ideas of evolution, reprimanding his sceptical readers, "till you know a great deal more about nature than Professor [Richard] Owen and Professor [Thomas] Huxley, put together, don't tell me about what cannot be…" But Kingsley's book was also a characteristically mid-19th- century mix of innocence and knowingness (Lewis Carroll wrote Alice's Adventures in Wonderland in the same year that The Water Babies appeared), with a subtle sexual undertone.

Other Victorians made the same association. Algernon Swinburne, the poet obsessed with swimming off his native Isle of Wight, boasted of yielding to the waves "like a young sea-beast… pressed up against their soft fierce bosoms… as lover with lover". Baudelaire said swimming was like being kissed a thousand times.

From Byron and Hardy to Conrad and Woolf, authors joined artists such as Turner, Odilon Redon and Edward Wadsworth in their attempts to quantify, if not qualify, the unsettling call of the sea; a fugitive element caught between land and sky, neither one nor the other. Even its colour is chameleonic, merely reflecting the light from above or absorbing the darkness below. In Turner's paintings, for instance, the sea becomes a sort of nothingness, an abstraction of itself. Little wonder that the artist, obsessed by the element, was rumoured to have had himself tied to the mast of a ship during a storm so as to truly experience the power of the ocean.

Culturally, the sea is a route of escape and transformation. Sailors, for instance, are loosely-dressed, liberated figures – just as the proximity of the sea is liberating for the landlubber. Where else but on the beach (tellingly, a resort) would near-nakedness be allowed? The sea offers sensual and illicit pleasures, from saucy Regency sea-bathers to Quentin Crisp sashaying along a Portsmouth promenade surrounded by admiring jack-tars. Melville's writing in particular celebrates that sensuality. In his watery world, the ocean is freighted with allusion and metaphor, avowedly homoerotic in its exclusively male society. From Moby-Dick to Billy Budd, the sea is a sounding of the deeper, unaddressable themes of a pre-homosexual age, what Melville calls "the half-known life".

That same sense of suspension and threat flows through the work of his later interpreter Benjamin Britten, who grew up in sight and sound of the North Sea (perhaps it is no coincidence that one of the earliest photographs of Britten as a child shows him dressed up as Tom the Water Baby). For Britten, the sea itself became a character in operas such as Peter Grimes and Billy Budd, heady with the threat of the other.

Later 20th-century authors would also read psychological menace into the same medium. In 1978, Iris Murdoch published her strange novel, The Sea, The Sea – itself a replaying of Shakespeare's The Tempest. In it, the celebrated but self-deluded actor Charles Arrowby retreats to a ramshackle house on an unidentified English coast, lured to the sea by the prospect of "monastic mysticism".

As Arrowby relishes his solitude, swimming naked off the rocky shore, his coastal idyll is broken one morning by what he imagines or perhaps actually sees: "I saw a monster rising from the waves", twenty or thirty feet high, coiled and spiny, its head crested and with sharp teeth and a pink mouth, "I could see the sky through the coils." Although he puts this terrifying sight down to an acid flashback, an augury of the emotional cataclysm he is about to experience, the serpentine horror of Arrowby's vision has its feminine counterpoint in the 19th-century Japanese artist Hokusai's psychosexual woodcut of an octopus engulfing and penetrating a courtesan's pudenda.

Murdoch was writing in a new, post-Freudian, scientific era. The underwater camera and the aqualung had realised Jules Vernian dreams; Jacques Cousteau had begun to demystify the deep. Its monsters were catalogued and given their Latin names. Now, in the 21st century, we no longer need to lash ourselves to a mast like Turner to experience the sea; we can watch it on our screens. (And how apt that it was a film director, James Cameron, who became only the third-ever human to reach the bottom of the Mariana Trench). Yet for all that, the primal lure of the sea abides.

Aquatopia, Nottingham Contemporary (0115 948 9750) to 22 September; Tate St Ives (01736 796 226) 12 October to 26 January

Philip Hoare's 'The Sea Inside' is published by Fourth Estate (£18.99)