Abstract 



This report describes the investigation of the sea floor in the vicinity, 

 of Wilmington submarine canyon (38°00'N to 38°35'N Lat. ; 72°35'W to 

 73°40'W Long.) by means of underwater photography. The techniques 

 of both equipment operation and of interpretation are detailed. More 

 than 1200 photographs were obtained from a net of 54 stations on 

 the continental shelf, slope and upper continental rise in the region 

 encompassing the Wilmington submarine canyon. These photographs, 

 linked to precise navigation, enable assessment of the areal distribution of 

 several sedimentary attributes, notably the texture of bottom sediments, 

 the patterns of recent current activity (neocurrents) and movement of 

 materials, and the role of benthic organisms in modifying bottom sediments. 



Studies of bottom texture indicate that the head of this canyon is 

 presently acting as a sediment trap. Admixtures of sand, silt and evten 

 coarse gravel are characteristic of the headward part of the canyon, 

 whereas silt (near the canyon) and silty clay are dominant on the lower 

 slope and upper rise. However, patches of gravel, sand and silt are 

 associated with rock-ledges on the lower part of the Nyckel Ridge, a 

 topographic elevation forming the southern margin of Wilmington Canyon. 



The inferred patterns of recent bottom current movement suggest 

 westward supply of course shelf sediment to the canyon head, some 

 southerly, down-axis transport in the shallower portions of the canyon, and 

 weaker southwesterly moving contour currents on the outer part of the 

 upper rise. Significant transport of coarse sediment in a general northerly 

 direction has also been observed in the vicinity of the Nyckel Ridge, near 

 the base of the continental slope. 



Organisms living on or near the sea floor profoundly affect bottom 

 sediment, thus the distribution of the more important groups of such 

 animals has been plotted. 



Although underwater photography has proved valuable in elucidating 

 the nature of the bottom in this canyon, some caution must be exercised 

 in extending these conclusions to the geologically recent past. Cores 

 indicate that the thin, fine-grained sediment veneer presently being 

 reworked by benthic organisms actually masks the effects of recently active 

 sedimentation in the canyon area. The combined pattern of current activity 

 and sediment distribution as observed in the bottom photographs suggests 

 that the Wilmington submarine canyon has played an important role in 

 funnelling sediments from the shelf area to the deep-sea in the recent past. 



