THE NAVY OCEAN SCIENCE PROGRAM 



35 



Magnetic measurements have been made at sea for many 

 years, but for over two decades excellent measurements of 

 the magnitude of the total field have been possible. Magnetom- 

 eters towed by aircraft and located in a fish towed behind a 

 ship provided the earlier means of measurement. Magnetom- 

 eters are now being towed near the sea floor as well to detect 

 small variations in the magnetic field associated with crustal 

 rocks, and to locate man-made objects such as submarines or 

 sunken ships. Such a deep-towed magnetometer helped investi- 

 gate the THRESHER disaster. 



The magnetic data are being used primarily for interpreting 

 crustal structures. Recent measurements have provided the 

 main evidence for sea-floor spreading, the current concept of 

 great interest that the sea floors are spreading laterally away 

 from ocean ridges. Surprisingly, it has been found that the 

 magnetic-field variations over ridges in diffierent oceans are 

 quite alike, even in detail. Another recent finding is that oceanic 

 ridges have been displaced laterally by a series of faults. 



Profiles of magnetic anomalies measured on the sea surface (upper graph) 

 and measured near the ocean floor (lower graph) 



