■ Although trace-metal levels are low in the surface sediments along the 

 Outer Continental Shelf and slope, the concentrations of cadmium, 

 chromium, copper, and lead--normal ized for differences in grain size-- 

 are higher in the canyon axis than in adjacent areas. 



SEDIMENT RESUSPENSION 



It is commonly reported in the literature that fine-grained sediments 

 provide active surfaces which can adsorb many dissolved inorganic and organic 

 contaminants in sea water. Resuspension of bottom sediments is one important 

 mechanism through which the opportunity for such adsorption reactions by 

 particulates can take place. 



On each of the five current-meter deployments in and around Lydonia 

 Canyon, discussed in a previous talk by Butman, we fixed sediment traps at 

 various heights above the bottom in order to determine the RELATIVE intensity 

 of sediment resuspension in different areas and heights above bottom. 



We claim only to measure the relative intensity of resuspension, because 

 the absolute efficiency of these sediment traps is unknown in a current flow 

 that is both strong and highly variable. However, all the results have been 

 normalized to a trap of standard dimensions and so a comparison of the 

 collection rates for different areas is possible (Bothner and others 1985). 



Figure 10 summarizes the differences in the flux of trapped sediment 

 collected in Lydonia Canyon during the first experiment (12/1/80 to 4/29/81) 

 when areal coverage was the most extensive. 



The rate of sediment collection (g/mVday) increases greatly (almost 

 logarithmically) as the distance above the bottom decreases. This indicates 

 that resuspended bottom sediment is the source of the material collected. 



The highest collection rates are observed near the bottom in the canyon 

 axis at locations in 300- and 600-m water depth. There, the rates are as much 



37 



