difficult to explain the region of very high sus- 

 pended sediment concentration along the shelf 

 break reported by Naidu and Sharma. In studying 

 particulate concentration at depth, they note a 

 lack of systematic vertical differences. A com- 

 parison of these data with individual transmis- 

 someter records and the stations where the data 

 were gathered shows no correlation. 



As a result of this differing distribution. Naidu 

 and Sharma's conclusions regarding the move- 

 ment of particulate matter are unique. They call 

 for an eastward transport of sediment-laden 

 coastal ice or river effluent from the Colville and 

 Kuparuk Rivers to explain the region of high 

 values (Naidu and Sharma, 1972, p. 6). This is 

 inconsistent with the fact that: l)most, if not all of 

 the coastal ice would have melted by the time of 

 their study (August) and thus would be an insig- 

 nificant contributor of sediments, 2) the ice pres- 

 ent in the spring off rivers contains negligible 

 amounts of sediments (Reimnitz and Bruder, 

 1972; Barnes and Reimnitz, 1972), and 3) the 

 bulk of river sediment is discharged during 

 breakup in June (Amborge and others, 1967), 2 

 months earlier than Naidu and Sharma's study. In 

 any event, considering their data and the data of 

 this report, a complete definition of the fine- 

 grained transport regime is lacking. 



Values of surface particulate concentration 

 and turbidity for the Beaufort Sea (figs. 2-5 and 

 Appendix A) are similar to values from lower 

 latitude shelves (Drake and others, 1972; and 

 Manheim and others, 1970). Surface values of 

 particulate matter decreased rapidly away from 

 the coast to concentrations less than 1 mg/1 for 

 the outer shelf and open sea. Two points regard- 

 ing the comparison of lower latitude studies with 

 those of this report remain uncertain: 1) whether 

 or not the 9-month ice cover, or its development 

 and attrition, seriously influences the distribu- 

 tion; and 2) whether the concentration of organic 

 versus inorganic constituents is similar to that at 

 lower latitudes. 



Bottom Sediments 



The surface deposits of the arctic shelf of 

 Alaska are a heterogeneous mixture of sediments 

 which exhibit a strong influence of ice. The pres- 

 ence of a thick ice cover during more than half the 



year makes sampling difficult, and interpretatiori| 

 of conditions during the period of ice cover is no 

 doubt important, but, at present somewhat 

 speculative. Field observations have been limited 

 from the end of July into early September, when 

 icebreaker operation is feasible. We are aided in 

 our interpretation of year-round conditions by the 

 "memory" of past events recorded in sediment 

 cores. 



The statistical grain-size parameters of surface 

 sediments presented in Appendix A attest to the 

 heterogenous nature of the sediments. The varia- 

 bility is greater along the nearshore zone and at 

 the shelf break, as seen in the contorted contours 

 of mean grain size and sediment sorting (figs. 7, 

 8, 9). At the shelf break, bimodal gravel-muds 

 are present which are characterized by poor sort- 

 ing (4-6 phi) and unrealistic sand size mean 

 daimeters (50-300 fi). Modal analysis of these 

 samples shows primary modes in the coarse sand 

 and fine silt size materials, while the means fall in 

 between. The wide variety of sediments present in 

 this shelf is illustrated in the span of points shown 

 in the scatter plot of mean diameter vs. sorting 

 (fig. 10). However, it is possible to recognize 

 three groupings. Using these divisions, three en- 

 vironments or sediment types can be distin- 

 guished (figs. 10 & 11): a) a poorly sorted, gener- 

 ally coarser sediment found along the shelf break 

 and on the central shelf off Prudhoe Bay, b) a 

 fairly well sorted, sand-and silt-size sediment 

 characteristic of the inshore areas, and c) moder- 

 ate to well-sorted fine-grained sediment of the 

 central shelf and continental slope. One end 

 member designated by the solid triangles on fig- 

 ure 9 is a fairly well sorted (possible aeolian) 

 silt-clay that was collected from ice flows (fig. 

 10). 



In the densly sampled nearshore area between 

 Oliktok Point and the Sagavanirktok River, the 

 sediment pattern is very complex. This suggests 

 that the distribution of sediment types in this area 

 may be patchy. Here many sand samples are 

 found with excellent sorting (less than 1 phi unit 

 standard deviation), although some poorly sorted 

 gravelly muds have been found north of Cross and 

 Reindeer Islands, and a gravel and boulder 

 "patch" is present on the lagoon floor northeast of 

 the Sagavanirktok River (fig. 7 & 8). Areas of 



188 



