Sentence:  Nearly twenty-five years before , Captain John Davis had noted , as he sailed near the <WSD>Arctic</WSD> Circle , `` a very great gulf , the water whirling and roaring , as it were the meeting of tides '' . 
Meaning of the word marked with <WSD> tags:  a line of latitude near but to the south of the north pole; it marks the northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice