Complex sentence: All three men, barely alive, returned from Cape Crozier with their egg specimens, which were stored as the expedition swung into preparations for a march from Cape Evans to the as-yet-unreached South Pole.
Split into simpler sentences: All three men, barely alive, returned from Cape Crozier with their egg specimens, which were stored. The expedition then swung into preparations for a march from Cape Evans to the as-yet-unreached South Pole.