Zachariah is sailing for glory, his brother Erasmus to make his name as a naturalist. The others have joined because it's a job. The story slowly twists away from the reader's expectations. Psychological vistas open like cracks in the polar ice. What seemed heroic one day appears futile another.
Modest characters turn out to be heroes, and arrogant characters turn out to be cowards.
The Narwhal expedition had departed like troops to glorious battle. The survivors return to find themselves in disgrace and treated like abject failures. They have no provable artifacts of Franklin, although they saw the Esquimaux cooking in copper pots. If this reminds readers of the disillusionment that follows major wars the effect certainly is not accidental. After all, the Narwhal voyage finishes just a few years before the outbreak of the Civil War.