presently active on the ocean floor. To interpret quantitatively the 

 reflection arrivals from the sedimentary column, another program 

 has developed an in situ velocimeter attached to the head of a 

 sediment corer. The in situ velocity data are now in the process of 

 being analyzed and compared with sediment velocities obtained 

 with remote-sensing techniques. Navy scientists are attempting to 

 establish a correlation between the mineralogical and physical 

 properties of marine sediments through in situ as well as laboratory 

 measurements of their acoustic properties. Important results of this 

 study include the finding that sound-wave attenuation is a function 

 of grain size, porosity, and the frequency of the propagating sound 

 wave. 



Only recently, with the development of deeply towed instrument 

 packages and deep-diving submersibles, have scientists been able to 

 view the processes of sediment transport and erosion on the deep-sea 

 floor. The most extensive transport occurs in areas characterized by 

 vigorous, thermohaline-driven, bottom water circulation. 



An NSF-sponsored program on the Blake-Bahamas Outer Ridge 

 has recently returned startling evidence of sediment in that part of 

 the Atlantic. The ridge itself is a thick sequence of sediments 

 deposited from a deep current that flows southward off the 

 continental margin of the eastern United States. For many years 

 scientists had observed strange bottom echo patterns from this 

 ridge. It was believed that these patterns were produced by 

 sediment-dune formations. Examination by a deeply-towed instru- 

 ment package, however, has shown that the strange echo patterns 

 are produced by steep-sided, flat-floored furrows ranging from 1 to 

 100 meters wide and from 1/2 to 20 meters deep. The spacing of these 

 furrows is typically on the order of hundreds of meters, and 

 individual furrows are commonly traceable over several kilometers. 

 The origin of these erosional features has not been definitely 

 established, but they may be related to a secondary component of 

 water flow, which acts in a direction perpendicular to the direction 

 of the main flow. Under NSF and ONR support, similar features have 

 been found near Samoa in the western Pacific. Programs are 

 presently underway in the Atlantic to examine other sediment 

 accumulations like the Blake-Bahamas Outer Ridge for similar 

 evidence of sediment erosion and transport. 



A completely different type of evidence has been found for deep- 

 sea sediment transports at a 2,500-meter depth on the Carnegie River 

 in the eastern equatorial Pacific. Using a deeply towed instrument 

 package, scientists were able to observe a field of crescentic 

 (barchan) sand dunes composed of foraminifera on the north flank of 

 the ridge. The dunes are apparently propelled by fast currents of 

 dense bottom water that spill northward across the ridge. A 



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