The Anglo-Saxon or Old English poem "The Seafarer," from the Exeter Book, was most likely written in the early 10thC. sometime between 925CE and 950CE. It's most important distinction is that it is the first Old English poem we have that deals solely with the hardships of a sea-faring life.
Imagery of weather and suffering from the cold at sea abound but not in the first stanza (as we usually divide the poem into stanzas). Several translations into Modern English divide the poem differently from the original in order to make the poem read more smoothly and coherently in Modern English, but I will discuss the weather imagery as it appears in the poem's original configuration.
In the second stanza, for example, the seafarer, in his "true song" about the hardships he has suffered, refers to
many worries [cearselda fela]/the terrible tossing of the waves [atol ytha gewealc]
Fettered by cold were my feet/bound by frost in cold clasps
As he does throughout the poem, the seafarer describes the essentially hostile environment of life at sea. In this case, he uses metaphorical language to compare the cold and frost to (probably) iron clasps that bind his feet.
The seafarer continues the harsh imagery of life at sea in the third stanza when he tells us that
how I, wretched and sorrowful, on the ice-cold sea/. . .hung about with icicles; hail flew in showers. . . [and he heard nothing but] the roaring sea, the ice-cold wave.
In this stanza, he also describes himself as "in the paths of exile, bereft of friendly kinsman," an important statement because it tells us that he is not on a voyage of discovery with other men familiar to him but that he has, for whatever reason, left his homeland and embarked on a lonely voyage.
The importance of the seafarer's description of the harshness of the weather is to remind the reader that life itself can be harsh and lonely and that, ultimately, peace can be found in the "eternal blessedness" in the afterlife.