The reckless men froze to death during the Antarctic expedition.
Literal
Reckless men [topic-は] South-Pole expedition [mid-中] [at-に] froze-to-death.
無謀 ('reckless, rash') is a formal Sino-Japanese adjective. 凍死 ('freezing death') is a compound noun that verbs as 凍死する. 南極 is 'Antarctica' (literally 'south pole'). A dramatic, documentary-style sentence.