“Being British comes with a catalogue of sea-themed cliches,” Charlotte Runcie muses early in her first book, “fish and chips on the beach, or in the car while the rain pelts down, ‘Rule, Britannia!’ at the BBC Proms, the shipping forecast playing out over and over every night, a warning for sailors, a lullaby for those of us safe in our beds and never at sea.” She doubts she would feel “this saline connection” if she had grown up in a landlocked country. Salt on Your Tongue is the story of her deepening love and longing for the ocean while pregnant, aged 28, with her first child. By the end of the book, her generic, gently nationalist appreciation of the sea has transformed into a specific, strongly feminist position: “The call of the sea is the call to the absolute strength of women, telling their stories and making music of beauty and imagination, and eternal mothers and grandmothers making eternal daughters and rocking them in the night as they sing while the tide comes and goes.”

Runcie is not suggesting that the sea is unimportant to men. She recalls her love of John Masefield’s poem “Sea Fever”: “I must go down to the seas again, for the call of the running tide / Is a wild call and a clear call that may not be denied”. But the experience of pregnancy draws her focus away from sailors and those who have mastered the waves, toward the women who traditionally waited on the shore: “The voices of people whose lives are shaped by the sea without them ever walking across it. The people who are only ever interested in the possibility, the taste of maybe on their tongues, the scent of freedom and the beginnings of things.”

Each of the book’s seven sections is fronted by a female figurehead and named after one of the stars of the Pleiades: Alkyone who drowns and becomes a kingfisher; Kelaino, loved by Poseidon and tied to the sea; Elektre who marries the sea god Thaumas and gives birth to the rainbow goddess, Iris. Following the progress of her pregnancy, Runcie ranges freely over references to the sea in folklore, painting and song. A wide, eclectic cast of characters wash in and out on the tide of her poetic prose.

Runcie now lives in Edinburgh. Of the artist Joan Eardley, she writes: “Eardley painted Scotland the way it feels to me.” She quotes Eardley writing to her mother in 1954 having just moved to a new cottage: “I’m sitting looking out at the darkness and the sea. I think I shall paint here.” Runcie’s favourite of Eardley’s paintings is The Wave from 1961. “The waves aren’t gentle, playful, eddying things: they are one solid mass of destructive power.” Eardley died of breast cancer aged 41; her ashes are scattered on the beach at Catterline and her paintings are in the National Galleries of Scotland. She is one among the crowd of strong creative women that Runcie communes with while pregnant.

Alongside visual and literary representations of the sea, Runcie is attracted to its presence in song. She joins a choir and is “drawn to sea shanties, working songs of hardship and struggle and longing for women left behind on shore”. Enjoying the irony that her mostly female choir chooses to rehearse “old masculine sea songs about seagoing terms we have never known before”, she begins to research Stan Hugill’s book, Shanties from the Seven Seas, published in 1961. Hugill described himself as “the last known shantyman”, he was shipwrecked many times and his life, Runcie remarks, was “a swashbuckling boy’s own story”. She imagines Hugill nursing a pint at the back of the pub where her choir is performing, listening to women sing songs that were not written for them. “It’s our version of a sea shanty, a shorebound telling of the hardships of sea, the only version we are capable of making.”

Pregnancy can be a morbid, anxious time. Runcie writes compellingly about the way her body’s new role as “a mobile aquarium” causes her mind to dwell on death. At an antenatal class she mentions her stretchmarks, “thinking of the torn purple lines spreading across my abdomen and thighs, deeper and angrier every time I look at them”, but everyone else in the room denies having such marks. Runcie wonders if she is a different species, “a mermaid covered in scales”, until her mother reassures her that everyone else is lying and a friend tells her the marks will fade over time. The convener of the antenatal class announces: “We won’t go into anything that can go wrong or anything dangerous that might happen. That’s all covered in week four.” Runcie decides to miss week four. Her dread needs no encouragement. Passing a “wellington boot garden”, where children have planted old outgrown boots with cheerful flowers, all she can think of is dead or lost children. She is torn between disbelief that a real baby will emerge from her body, and terror of losing or damaging it. Pregnancy brings women closer to other women, especially mothers and grandmothers. Runcie inherited her love of music and the sea from one of her grandmothers, who, though dead, is more present in her story than the living characters.

Occasionally, Runcie’s beautiful, fanciful prose falters. When discussing her habit of collecting sea glass, for example, she worries that all the plastic we use instead of glass and cast into the sea will mean “that future generations might not have as much luck hunting for sea glass as we do”. This will be the least of the problems her child and our own children must face if we continue to despoil our majestic ancient habitat.

• Salt on Your Tongue is published by Canongate. To order a copy for £14.99 (RRP £10.99) go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99.