Summary of Particulate Transport 



Values of turbidity and suspended matter are a 

 result of both organic and inorganic detritus in the 

 water. Unfortunately this study lacks a determi- 

 nation of the ratio between organic matter and 

 inorganic mineral detritus. 



Observations during the summer of 1971 and 

 1972 indicate a remarkable difference in particu- 

 late matter and turbidity from one year to the next. 

 Concentrations of particulate matter in 1972 were 

 about double those of the previous year. In addi- 

 tion, turbidity values show clearer surface water 

 in 1971, compared to 1972 values, especially 

 over the shelf. The lower concentrations of ice 

 found during 1972 and the resultant increase in 

 wave activity (Hufford, this volume) would sug- 

 gest that much of the increase in particulate sus- 

 pension and transport results from increased 

 wave activity on the inner shelf. Indeed, it was 

 observed that coastal and lagoonal waters were 

 much more turbid than shelf waters during late 

 July when the ice cover was still quite extensive; 

 however, by the latter part of August, aerial ob- 

 servations showed turbid waters (often the most 

 turbid) occurring on the shelf outside the lagoons. 

 This suggests wave resuspension of nearshore 

 sediments seaward of the lagoons was an impor- 

 tant mechanism during 1972. 



The lower ice concentrations found over the 

 shelf in 1972 also influenced turbidity by de- 

 creasing the contribution of relatively clean ice 

 melt water. Yet to be evaluated is the variance in 

 river runoff, which might result in a change in 

 sediment contribution as this is known to vary 

 considerably from year to year (U.S. Geological 

 Survey, unpub. data). 



Meager current and oceanographic data for this 

 sea suggest a weak westward drift (Coachman, 

 1968; Naval Hydrographic Office, 1958). How- 

 ever, studies along the Alaskan Coast show the 

 currents to be more complex; 'local currents are 

 closely related to wind stresses and are locally 

 strong in both east and west directions (Kinney 

 and others, 1972; Shore, 1973). A further com- 

 plication is the intrusion of relatively warm Ber- 

 ing Sea water along the shelf break. This is dis- 

 cussed more fully by Hufford in this volume. 



Short-term observations of bottom currents in 

 1971 (table 1), show considerable variance in 



speed and direction. Thus at present it is prob- 

 lematical to determine the dominant transport 

 direction for su.spended and resuspended particu- 

 late matter. It is nonetheless intriguing to specu- 

 late on the cross shelf region of increased particu- 

 late matter and turbidity (figs. 2, 3, 4 & 5) as an 

 area of convergence and seaward transport of 

 suspended matter. It is in this region that the 

 bottom currents show a net northward transport of 

 water (Sta. 23, table 1). This is also the area 

 where Hufford (this volume) reports that the 

 "westward"-moving Beaufort Gyre generally 

 meets the "eastward"-moving Bering Sea water. 

 Hufford also reports consistently higher concen- 

 trations of sea ice in this same general region 

 (ibid.). If this area is a zone of suspensate con- 

 centration it is not reflected in the underlying 

 sediments, which will be shown to be gravel muds 

 coarser than elsewhere on the shelf (see discus- 

 sion of bottom sediments). 



Table 7. -Net current (including tidal components) deter- 

 mined from progressive vector summation. (See fig. 1 for 

 location) 



Note; As the period of record is nearly 1 or 2 full tidal cycles, 

 the influence of tidal currents is minimal. 



Naidu and Sharma (1972) also studied sus- 

 pended particulate matter during the same 1971 

 cruise on which our data were gathered, and they 

 used similar techniques. Their data indicate a 

 markedly different distribution of particulate mat- 

 ter. Thev are generally higher and do not show the 

 seaward decrease in concentration of suspended 

 matter that we report here but do indicate a region 

 of extremely high values (up to 1 1 mg/1 ) along the 

 shelf break north of Prudhoe Bay. Elsewhere their 

 values of surface suspensates are only slightly 

 liigher than ours. In view of the high water clarity 

 found along the shelf break (see figs. 2 & 4), it is 



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