I stood once at the centre of Asia, the furthest point from the sea on this planet. The great Yenisei River, sludgy with tumbled ice floes, had more than 2,000 miles to run to the Arctic Ocean, and south were the vast steppes trampled back and forth by nomadic people for hundreds of generations. The city itself, Kyzyl, was dropped on to the plains a century ago, a grid of roads at the end of which concrete abruptly gives way to flowing green. The central point is marked by a globe and pillar, prayer flags snapping in the wind, a place of Siberian mystery many days of conventional travel from the rest of the modern world.

In my hotel room with wooden balcony, and a mix of otherwise Buddhist and Soviet icons, was a single large painting. It depicted a tropical beach, a line of coconut palms leaning over the sandy shore, a cobalt sky and crumpled waves on the reef. Yet no one there had seen such a salty sea. The sea, in this way, has ended up in all our imaginations, regardless it seems of location.

At the seaside, things of mystery happen. Whales beach. Seals smile. Birds congeal with oil. People sit in deckchairs and consent to do nothing, and watch other people doing nothing. Our relationship with the sea – we of an island nation – is always changing. In North Norfolk, the cottages of former seamen have no windows facing the sea. Why look, they would have said, at waters that with great force we spend all our days and nights seeking to outwit? They will take us anyway. Meanwhile, the waters rise, the CO₂ in the atmosphere passes 400 parts per million, and the waters rise further still. It could be that we are lost already.

In The Sea Inside, Philip Hoare’s compelling journeys are in and over white, inland, azure, southern, wandering and silent seas. Inside the sea, Hoare reckons “the fixity of the sea and sky is a supreme deception”. His elegant essays weave alongside authors, scientists, monks: he travels with Darwin, five years in the HMS Beagle, a ship so unseaworthy as to be dubbed a coffin brig; with Thomas Merton and other hermits; with J. A. Baker of The Peregrine and Essex marshes fame; with T. H. White and the obscure island life that seemed to accentuate his peculiarities; with Tennyson, too; and Melville, of course. Whales feature prominently. Hoare stitches oyster-catchers into England’s shores, birds once prized in dishes such as sea pies, then seen as oyster-stealing pests and shot in great numbers until the 1960s. These longest living of waders (individuals can live 40 years or more) now describe the edge-seas of mud and lapping wavelets with piping echoes. The sea wanders under London, too, the Thames’ many tributaries bound and strangled and paved, but still flowing underground and salty with the tides. The Strand commemorates what was once a beach, and on old maps the names Temple Stairs, Surrey Stairs and Whitehall Stairs appear, all of them descents to the water.

From space, our planet is clearly more blue than green. Arthur C. Clarke thought a better name for it would be Ocean

Hoare swims with blue whales off Sri Lanka and watches humpbacks off Cape Cod. So little is known of cetaceans and their societies that any engagement is a mystery part revealed. “He is seldom seen,” observed Ishmael of the blue. Not surprising, given our remorseless harvesting: 40,000 blues were caught in the Southern Ocean in 1939 alone; so many hundreds of thousands killed that blue whale populations can never recover – they just do not meet enough. David Collins, the governor of Tasmania at the time, complained that the estuary at Hobart was so full of southern rights that it was almost too dangerous to navigate. They kept him awake at night with their huffing and blowing, he grumbled.

In water, noise travels faster and further than in air, and whales chatter. Sperm whales click, toothed whales beep sonar. If a sperm whale shouted as loud as it could, at more than 200 decibels, it would cause life-threatening harm to any whales nearby. They presumably know when to behave properly. Both whales and dolphins have enlarged amygdalae, the processing centre of brains that controls emotions and social connections. Hoare also swims with sperm whales in the Azores, in their blue world where beneath is utter darkness. Their sweet high-pitched song rises around him, he only 5ft 8ins and they 50 tonnes of flukes and fins and baleful eyes. The post-hunting population of sperm whales is estimated to be 360,000: there are 316 million sq km of ocean, nearly a thousand for each individual. He describes how two whales come head to head, touching brows and lolling in the water. In a cetacean crèche, adults deliberately caress and touch the youngsters, reassuring as we do with our children, too.

Yet the question of why whales beach remains deeply troubling. What do they know, that we do not? Hundreds, sometimes thousands beach themselves on the shores of New Zealand each year and are regarded as tapu, sacred signs. On one occasion, 59 stranded sperm whales were declared human and buried in a communal 500ft grave. People rush to the shores when they hear of such mass actions by the world’s largest animals, but do not know what to do. Recently, a Māori elder carried his sleeping bag to the shore to spend the night with a pod of pilot whales so that they would not die alone. Perhaps this is all we can do.

Hoare writes with passion too of birds. There are clever cliff corvids, able to call foxes or wolves to a dead animal to let them do the hard work; able in modern cities to put nuts on pedestrian crossings for cars to crack, and then wait for the red light to retrieve them. There is also the long-extinct moa, and the albatrosses that may spend a decade topside never touching land, becoming whiter as they age, tending towards Coleridge’s ghostly soul-bird. “God save thee, ancient Mariner!…with my cross-bow, I shot the albatross.” There are shearwaters wing-locked over oceans, nesting in burrows, diving to pick sand eels from the mouths of whales. Our language, though, remains rooted in land. We speak of whales and dolphins off Cape Cod, off Charlotte Sound. We are always on islands, not in them, just as if they were ships, ready to return to port one day.

I have walked far along a coast, let the water and light in, and salt encrust, let blisters invade, let the ebb and flow and the Moon and wind change every place. This seaside is a liminal zone, a place of uncertainty and of innovation, too. It’s the one place in the world that responds minute by minute to the pull of Earth’s satellite. Ecosystems mostly change by the day or week or month; the tidal coastline moves at a different pace. From space, our planet is clearly more blue than green. Arthur C. Clarke thought a better name for it would be Ocean.

At home, I have a crooked walking stick hewed from hedgerow ash by John Masefield. To me, Sea Fever captures simply the sea inside us all. Masefield wrote: “I must go down to the seas again, to the lonely sea and the sky/…To the gull’s way and the whale’s way, where the wind’s like a whetted knife./And all I ask…and all I ask, is a/…Quiet sleep and a sweet dream when the long trick’s over.”