What are some literary devices used in "The Seafarer" by Ezra Pound?

There are two main poems entitled "The Seafarer." The first was written in Anglo-Saxon and published in the tenth century. The second was a re-imagining of the poem by Ezra Pound in the first part of the twentieth century. Other poets have also undertaken to write poetry based on the original poem, but Pound's poem is probably the most prominent. 
Ezra Pound was remarkably aware of the history of literature, including Medieval literature. His poetry often reflected his knowledge, and his version of the Seafarer is no exception. In order to understand how he used the techniques of poetry (literary devices), let's look at the Medieval Seafarer. 
Referenced below is a webpage that has both the original Anglo-Saxon and a modern English translation. You can get the meaning of the poem from the modern translation, but to understand the construction of the poem, it is important to look at the Anglo-Saxon version. The poet uses short lines which are grouped in pairs, but one technique used is that of alliteration. Here are some examples:
"siþas secgan" (line 2a)
"bitre breostceare" (line 4a)
Poets use the sound of words as a way of uniting a poem. Sometimes they use rhyme, sometimes meter, and sometimes the vowel and consonant sounds of the words themselves. This attention to sound differentiates poetry from prose. The Medieval writer uses alliteration quite often; that is, the first letter of each word in some lines is the same. 
Pound's version does the same:

May I for my own self song's truth reckon, 
Journey's jargon, how I in harsh days 
Hardship endured oft. 
Bitter breast-cares have I abided (lines 1-4)

A second device Pound uses is imagery. Pound was part of a movement called Imagism, which encouraged poets to use just the words they needed to flesh out an image and not all the flowery filler words Victorian poets used to fill a metrical pattern. Imagist poetry records experiences in vivid ways. 
 
Pound likely chose the original poem to work with because the Medieval writer wrote in a vivid style without filler.

Storms there beat the stony cliffs,where the tern spoke,icy-feathered;always the eagle cried at it,dewy-feathered (Modern translation of Seafarer, lines 24a-25a)

It's easy to imagine these images. Pound does a similar thing with his version:


Did for my games the gannet's clamour, 
Sea-fowls, loudness was for me laughter, 
The mews' singing all my mead-drink. 
Storms, on the stone-cliffs beaten, fell on the stern 
In icy feathers; full oft the eagle screamed 
With spray on his pinion (lines 21-25).

Literary devices are part of the craft of poetry. Poets allow them to surface in their poems and then polish their poems to bring out these relationships between words. They do so to enhance meaning and unity in their work.
http://www.anglo-saxons.net/hwaet/?do=get&type=text&id=Sfr

https://en.wikipedia.org/wiki/The_Seafarer_(poem)

https://www.poetryfoundation.org/poems/44917/the-seafarer