Complex sentence: In 1978, immediately upon her return from Turkey, Luna got a message from Keith, who was working at the Institute of Nautical Archaeology in Texas, who alerted her that sports divers had located some guns in the Gulf of Mexico.
Split into simpler sentences: In 1978, immediately upon her return from Turkey, Luna got a message from Keith, who was working at the Institute of Nautical Archaeology in Texas. He alerted her that sports divers had located some guns in the Gulf of Mexico.