then measured before pressure and vacuum filtra- 

 tion. The fihers were then carefully rinsed with 

 filtered distilled water to remove all traces of salt. 

 All filter weighings were done using a five-place 

 analytical balance. 



RESULTS 



Suspended Particulate Matter 



In 1971 inshore surface waters of the Beaufort 

 Sea had concentrations of suspended matter 

 which averaged 1.0 mg/1 and ranged from 0.1 

 mg/1 to 4.2 mg/1, while in 1972, values averaged 

 2.8 mg/1 and ranged from 0.5 mg/1 to 31.0 mg/1. 

 (See figs. 2 & 3, Appendix A.) The most obvious 

 difference between 1971 and 1972 concentration 

 of particulate matter is the two-fold increase from 

 one year to the next. Offshore, in water depths 

 greater than 20 meters, suspended sediment con- 

 centrations for 1971 averaged .5 mg/1, but in 

 1972 the concentrations averaged 1.2 mg/1. 



The distributional patterns of suspended par- 

 ticulate matter (figs. 2 & 3) show that the higher, 

 1972 values were not localized in any one area. 

 As a result the distribution pattern is similar, but 

 the absolute values are higher in 1972. For exam- 

 ple, central and outer shelf waters northwest of 

 the Canning River generally have higher sus- 

 pended particulate values in both years. The data 

 off of Barter Island indicated an offshore dis- 

 placement of contours in both 1971 and 1972 

 data, perhaps due to the influence of MacKenzie 

 River water. 



However, in 1972 the gradients around river 

 mouths are much more pronounced than in the 

 previous year. Concentrations in the surface wa- 

 ters of Harrison Bay off the Colville River were 

 greater than 30 mg/1 at one.station in the western 

 part of tile bay. 



Turbidity 



The average turbidity of surficial Beaufort Sea 

 waters as measured by Secchi disc shows very 

 clear water (20 m) in the seaward parts of the 

 study area beyond the shelf (figs. 4 & 5 and 

 Appendix A). Secchi readings also confirm that 

 shelf waters were more turbid in 1972 than in 

 1971. For example, the 10 m Secchi visibility 



186 



contour was displaced 30-40 km farther seaward 

 in August 1972 than in August 1971 (figs. 4 & 5). 

 The 15-m contour shows much less displacement. 

 This suggests that most of the turbid water is 

 confined to the continental shelf. M 



Turbidity, measured as transmissivity or at- 

 tenuation of light over a .1- or 1-m path, presents 

 a more complex picture, partly because light at- 

 tenuation is measured by the transmissometer at 

 many points in the water column. The Secchi disc 

 is different in that it integrates attenuation factors 

 over the path from the observer's eye to the disc. 



In 1971, a four-part attenuation profile was 

 recognized that peristed more or less throughout 

 the summer. A surface layer of moderately clear 

 water up to 5 meters thick (layer A, fig. 6) was 

 underlain by a turbid layer 5-10 m thick (layer B, 

 fig. 6). These two layers are believed to represent 

 ice melt and river runoff, respectively. In areas 

 where ice was rarely found, the surface layer was 

 absent or poorly developed. Layer B was most 

 pronounced and turbid inshore, often appearing 

 as the surface layer in absence of layer A. The 

 entire four-part profile was best developed on the 

 inner shelf in areas where the ice front was not too 

 distant from shore. 



Below these two layers was generally clear 

 water that extended to within about 15 m of the 

 bottom on the shelf and to at least 65 m (the 

 maximum depth of measurement) in deeper water 

 (layer C, fig. 6). This water is believed to repre- 

 sent Arctic Surface Water (Hufford, this volume). 



The bottom 10 to 15 m of the transmissity 

 profile usually showed an increase in turbidity 

 toward the sea floor (layer D, fig. 6). A bottom 

 turbid layer of this type is a common feature on 

 other continental shelves (Rodolfo and others, 

 1971; Swift and others, 1973). Wave activity is 

 often thought to be the agent responsible for re- 

 suspension of bottom sediments into the near 

 bottom turbid layer. This is not a likely 

 mechanism in this environment due to the ice 

 cover which severely curtails the wave activity on 

 the shelf. Important exceptions may be the occa- 

 sional open season storm such as those observed 

 in 1970 (Sept. 13-16, MacKenzie delta region) 

 and 1972 (Hufford, this volume). Thus a large 

 part of this bottom layer could be due to biological 

 activity and to bottom gouging by moving ice 

 (Reimnitz and others, 1972a). 



