And then something happened. The sea shrank. Quite abruptly, it stopped being epic or terrible, and became something else; a paddling pool or a childish plaything. Art stopped lashing itself to masts and, like William Dyce at Pegwell Bay, took to dabbling around on beaches instead. Marine painting became the feeble old relative of landscape, a place where painters could eke out a second-rate dotage by the seaside. For most of the 20th century - with a few honourable exceptions - marine art was what you did when you’d failed at the other stuff. So what happened? How did the sea get so small?

Maritime art has a long and distinguished history in Britain. When Willem van der Velde arrived in England from Holland 1672 with his son, he established a school of marine painting in London which in time developed a distinctive British style. Though many artists were themselves sailors or shipwrights, sketching their subjects with an expert’s attention to accuracy, their preoccupations were often as much political as elemental. Painting the sea became a form of patriotic duty - commemorating great battles, recording the conquering voyages, reminding all those snug back home of the terrors of the deep. In the time of Elizabeth I and, later, of Nelson, maritime painting was a gorgeous form of propaganda. You couldn’t get much more reassuring than a painting of England’s defeat of the Spanish Armada, or of the victory at Trafalgar. Wars on land tended to be complicated smoky affairs full of blood and machinery, but wars at sea came free with a handy backdrop of sunsets, storms and picturesque vessels.
By the 18th Century, marine painting also had other forms of philosophical justification. ‘The ocean itself is an object of no small terror,’ wrote Edmund Burke in 1757. ‘Terror is in all cases whatsoever, either more openly or latently, the ruling principle of the sublime.’ All art was commanded to lift its gaze away from the mundane to more transcendental matters and to use natural subjects as a way of accessing the nobler aspects of human endeavour. The artists responded in their droves. Among the writers, Shelley drowned in it (a fittingly Romantic death, though that had more to do with his uselessness as a sailor than anything else) and Coleridge wrote the Rime of the Ancient Mariner, probably the greatest single piece of literature ever written about the sea by someone who had never actually sailed on it.

Part of that Romantic fascination with the ocean was its ability to overwhelm every standard landbound code. On water, time is different, geography is different, history is different. Time is guided by the flow of tides and the movement of stars rather than the rotations of a clock. What lies underfoot is as mysterious as what lies ahead, and even familiar landmarks have a habit of creeping around in the night. Even once sailors had mastered the tricky business of wind, tide and weather, there were other horrors; freak waves, whirlpools, monstrous fish. Plus, of course, the more prosaic business of conditions on board. Two centuries ago, approximately a third of all seamen died pursuing their trade, sacrificed either to storms and drownings or to the brutalities of maritime existence. No wonder the sea made men superstitious, that there were rumours of sea-serpents, mermaids and leviathans.

When Turner began painting, the sea had reached its greatest moment. Sailing had been refined down to a point of perfect precision, trade was booming, the empire was tinting the whole world pink, and the Napoleonic wars required so much manpower that the authorities were forced to resort to impressment of prisoners and vagabonds. By the time Snowstorm was first exhibited in 1842, all that had changed. In his 1839 painting, The Fighting Temeraire, Turner managed to capture not just what had changed, but why.

The Temeraire was the 98-gun warship used alongside HMS Victory by Nelson during the Battle of Trafalgar. Provided they were not shot to splinters or destroyed by storms, the great warships’ life expectancies were probably double those of the men who served in her, and their deaths attended with the same passionate sense of loss as the death of Nelson himself. Turner used the Temeraire, towed to her end in the shipbreaking yard by a seedy little steamboat, to illustrate another kind of death; the grave of sail. The early steamships which replaced the old frigates might have provided less picturesque subjects for artists, but they were solid and reliable, and they allowed their skippers to sail to places which would previously have been unthinkable.

The end of Napoleon also marked the final decline of Britain’s sea power. By the time of the First and Second World Wars, aggression had taken other forms; through the air, over the trenches, in tanks and mortar bombs and gas. By the 20th century, the St Ives group were snug into pictures of dabbling bathers, more absorbed with the depiction of light than of water and more interested in catching the no-man’s-land of the shoreline than in trying to deal with the foreignness of the ocean itself. At the other end of the scale, LS Lowry saw the sea as something which could provide some relief from the clutter and scramble of ordinary life, but which was no longer the natural holy of holies that it had appeared to Turner or the Romantics. Its interest lay in its size and emptiness, rather than its capacity to inspire terror. To him, the sea was a prosaic element taken up with fuggy steam-boats and bedraggled passengers, no more sublime than the average bus stop. It was still fascinating, but it wasn’t necessary.

Lowry’s vision also provided the best expression of something else; the sea as a piece of pure Britain. His seascapes, with their creamy grey waves and their overcast light, look as grimly English as any northern cotton mill. For artists, it wasn’t just landscape which could say something about our island identity, it was water as well. If the Romantic artists had used it for propaganda purposes, then Lowry and the St Ives group could also use it to sum up a little of our distinctiveness, our insularity and our wariness about what might lie beyond the thin white horizon.

When it was not providing a commentary on national identity, however, the sea disappeared. It was not that it no longer had things to say, but that there were other, more pressing artistic considerations. And besides, there was another, more subtle problem; that of access. Until comparatively recently, it has been almost impossible to paint the sea itself; all that can be painted is the surface of the sea. And, if you’re being really pedantic about this, you don’t even paint the surface of the sea, you paint the light reflected off the surface. Admittedly, the sea makes it difficult to do otherwise; the first ten metres of water filter out 90% of all light. And art has great difficulty clambering down into a place of utter darkness with pressures so great that, if you lower a full beerbottle down a few thousand feet, it returns to you perfect, unopened and replaced with prime-quality seawater. If all you can deal with is storms and ships and surfaces, at some point making art out of an endless series of airy horizons gets pretty frustrating.

Which also poses problems for scientific researchers; as several oceanographers have pointed out, we know more about the Rings of Saturn than we do about the Mid-Atlantic Ridge. The image of the sea as a black and limitless abyss persisted well into the 20th century. Since it was considered that it was biologically impossible for anything to survive beyond a certain depth, objects dropped into the sea were thought to reach a place where the water’s salinity was so great that they could fall no further. When the Titanic sank in 1912 the White Star Line was contacted by hundreds of relatives terrified that the victims of the disaster would remain floating in perpetual mid-ocean purgatory. Even now, oceanographers complain that researching underwater much akin to someone hauling a bucket through a forest from a plane and deducing their results from the three mangled leaves, two earthworms and a startled parakeet which return. The only way to research the sea - apart from using submersibles - is to remove its contents from their native element. Which, cunningly, instantly renders any results from that research redundant.

The first serious attempt to examine underwater life was undertaken in 1872 by a group of British scientists on board the research ship HMS Challenger. They dredged sections of the ocean floor which had never been investigated before, taking samples from three or four miles down. What they found caused, in its time, a sensation. Far from finding a lifeless abyss, as the expedition leader Wyville Thompson announced, the water was teeming. ‘The most ... remarkable biological result of the recent investigations is the final establishment of the fact that the distribution of living beings has no depth-limit,’ he wrote. ‘Animals ... exist over the whole floor of the ocean.’

Thompson’s samples were, in their turn, enthusiastically taken up by Ernest Haeckel, a naturalist and keen advocate of Darwinist theory, who used the Challenger’s findings not only to corroborate his own evolutionary findings, but as the source material for other forms of endeavour. Haeckel had been struck by the symmetries he saw in deep-sea organisms, and in 1913, having studied and redrawn the Challenger specimens, he published a book called Art Forms in Nature. The illustrations he made of jellyfish, coral and radiolarians were a stylised form of science; biologically accurate, but pleasingly decorative as well. He encouraged the use of his drawings by architects, sculptors and ceramicists; Louis Comfort Tiffany was one of many to use the Art Forms in his glasswork, and the architect Rene Binet confessed that he had taken much of his design of the Paris World Exposition in 1900 from Haeckel’s drawings. “Everything about it,’ he wrote later, ‘from the general composition to the smallest details, has been inspired by your studies.’

It was only a short step from there to Richard Deacon’s exploration of patterning and repetition in natural forms, and to the work of Richard Long. In many cases, it is the artists most closely associated with land who have made most of the sea. Perhaps it is just that art isn’t really the creative form best suited to fifty fathoms of lightless water; perhaps only writing can cope with the bivalve style of life. Jules Verne, a keen sailor, wrote the best-known account of underwater life, Twenty Thousand Leagues Under the Sea, using the researches provided by contemporary science. He himself never went down in a submarine. During his training as an engineer, Robert Louis Stevenson wrote an account of going down in a diving bell and James Hamilton-Paterson recently took a journey three miles down in a Russian MIR submersible. But what returns from all their accounts is, above all, confirmation that the sea is above all an element which is both utterly necessary to our survival and utterly impossible for us to survive in.

There have been other responses as well Hiroshi Sugimoto’s series of photographic seascapes, begun in 1980 and still continuing, hark back to the old notions of the sea as the first and the last of the great unchanged facts of nature. Mariele Neudecker takes another approach, and miniaturises the sea into something the size of a fishtank. She condenses the vast dreaming imagery of Caspar David Friedrich’s paintings down into tiny replicas, putting a shipwreck or a whole polar winter into a space no greater than a sea-trunk. Tacita Dean has a film of a wave in a box, part of an abandoned project to measure the impact of liquid motion on solid land. There’s something beautiful in the swaying unbroken motion of the wave, but mournful as well, as if the sea shouldn’t rightly be trapped behind bars and bits of glass.

What is striking about all these artists is that they have reverted straight back to the old image of the ocean once exemplified by Turner and Coleridge. All three draw directly off the old Kantian idea of the sublime; in their work, the sea is big again, unquantifiable; damaged perhaps but still gloomily heroic. It doesn’t take too much knowledge of Romantic history to figure out the resonance in Dean’s images of solitary lighthouse beams sweeping over an empty shore. In her vision, the sea has gone full-circle from everything to nothing and back again. Even so, given the richness of the potential material and the opportunities provided by new technology, it is surprising that so few contemporary artists have looked out to sea.

Perhaps the best analogy is a biological one; marine art is to landscape what neurology is to surgery. The study of the human brain is approximately 300 years behind the study of the human body. It too is hampered by inaccessibility and mystique, and it too has progressed hugely in recent years through the development of more sophisticated technology. But the workings of the human mind, like the workings of the sea, are still the most beguiling mystery of all, beset as they are with beauty, fear and superstition. Art can choose to take the well-travelled path through landscape and anatomy, or it can look deeper inside and down into the untravelled depths. It no longer has to find itself a ship and a gale and a mast to discover what Turner always knew; the sea is the biggest subject of all.