Most of the images at the beginning of "The Seafarer" refer to what?
The Anglo-Saxon poem "The Seafarer" is one hundred and twenty-four lines long; the first twenty five of them are thematically linked and can therefore be considered "the beginning," as you mention in your question. In those first twenty-five lines, most of the imagery centers around the cold conditions which cause the seaman such misery.
The deep coldness of the sea is seen over and over in the sensory imagery of this section of the poem. The sailor is "sweating in the cold" during his time at watch, his feet are "cast in icy bands" and tied down with "icy chains." The sea itself is "ice-cold," "hung with icicles" and fraught with "freezing waves."
This tale is true, and mine. It tells
How the sea took me, swept me back
And forth in sorrow and fear and pain,
Showed me suffering in a hundred ships,
5 In a thousand ports, and in me. It tells
Of smashing surf when I sweated in the cold
Of an anxious watch, perched in the bow
As it dashed under cliffs. My feet were cast
In icy bands, bound with frost,
10 With frozen chains, and hardship groaned
Around my heart. Hunger tore
At my sea-weary soul. No man sheltered
On the quiet fairness of earth can feel
How wretched I was, drifting through winter
15 On an ice-cold sea, whirled in sorrow,
Alone in a world blown clear of love,
Hung with icicles. The hailstorms flew.
The only sound was the roaring sea,
The freezing waves.
As bad as the physical cold is for him, the figurative coldness he finds from being at sea makes him feel just as wretched. This emotional freezing is shown through much pain and suffering, and the icy conditions on the outside matches the emotional numbness inside of him. He is "[a]lone in a world blown clear of love" and instead of laughter and love (friendship and camaraderie) he only hears the screams of terns and eagles.
...The song of the swan
20 Might serve for pleasure, the cry of the sea-fowl,
The death-noise of birds instead of laughter,
The mewing of gulls instead of mead.
Storms beat on the rocky cliffs and were echoed
By icy-feathered terns and the eagle’s screams;
25 No kinsman could offer comfort there,
To a soul left drowning in desolation.
The speaker of this poem leaves little doubt about the miseries of living life on the seas, as his opening lines are replete with images of physical and emotional cold and misery; however, he will soon make it clear that this life, despite its miseries, is one he loves.