The physical properties of sediments presented in this report include their resistance to deformation (shear strength) and penetration (penetration rate), and values of salinity within their pore water. This data, covering large areas of the Beaufort Sea shelf off Alaska, has been gathered over the years, but especially during the 1976 field season. Shear strength and penetration rate, occasionally determined at the same station, are of value to the designer of offshore structures, in

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... feasibility of dredging operations, the potential for slumping of sediments, and in studies of ice forces involved in producing the gouges found on the high latitude shelf areas. Shear strengths of surficial sedinents were measured with a simple, hand-held shear vane, either on board ship from samples that appeared to be relatively undisturbed, or directly on the bottom by divers. The penetration rates were obtained during sediment sampling operations using a vibratory coring device with 2-ra long core barrels. The resistance of sediments to shearing and penetration are not interpreted in this report, except by noting that icecemented sediments may occur at two shallow water stations. Since the average annual water temperatures in the study area are below the freezing point of fresh water, the absence of ice-cemented surficial sediments may be explained by the presence of antifreeze in the form of sea salts within the sediments. Our study of the salinity of pore waters within the sediments was done to learn at what temperatures the sediments should freeze,and to evaluate in what environments and at what 1 times of the year this may occur. This problem is of utmost importance to many aspects of offshore developments, and to the study of related environmental problems. Using the relation between the salinity of sea water and its freezing point, most of the localities sampled should freeze during the winter. An equation from the Russian literature, using the salinity of pore water and moisture content, appears to give reasonable results on the temperature at which bottom sediments become ice cemented. So far almost no data on mass physical properties of shelf sediments in the Alaskan Beaufort Sea has been published. This type of data is important for several reasons. For example, Kovacs and Mellor (1974) attempted to calculate the driving forces on grounded ice producing gouges on the sea floor. Such calculations require knowledge of the mechanical properties of surface sediments encountered by the ice. An understanding of the mechanical properties is also valuable in dredging and offshore construction projects. For these reasons we have compiled pertinent information obtained in previous operations, and made additional measurements on the physical properties of sediments during the 1976 field season. The data is reported herein without attempts to interpret the results. For a general description of sediment types found on the shelf within the study area the reader is referred to Bames and Reirnnitz (1974). A compilation of mean diameter particle size of the surJicial sediments is shown in Figure 1 , Shear Strength Values from Bottorn Samples During bottom sampling operation in the p?st, undrained shear strength values (S ) of relatively undisturbed samples have been measured aboard ship with a simple hand held vane shear device (Dill and Moore, 1965). These results, along with on-site location, water depth, sampler type, and sediment type have been compiled in Table 1, The station locations are shown in Figure 2. In Situ Shear Strength Values Obtained by Divers A few in situ vane shear measurements, using the same hand held instrument, were obtained during diving operations in 1972. A number of additional measurements were made in the same way during summer 1976 diving operations. 1 On a number of dives more than one reading was taken. This was done particularly in ice gouged areas, where differences are to be expected between flat, undisturbed bottom, gouge flanks, and gouge floors. At each site the maximum reading (peak) and the. reading obtained during the shearing event (residual) were recorded by the diver. See Table II . . All these values along vjith information on station location, water depth, depth below sea floor, bottom type, sediment type, etc, are presented in Table II . Station locations are shown in Figure 2 . Although care was taken by the divers to increase torque slowly and evenly to obtain reliable readings ( Fig. 3), currents and other factors did not allow them to do so in all cases. These in situ shear strength values still are considered to be more accurate than those obtained from partly drained and possibly disturbed bottom samples aboard ship. It should be noted that vane shear readings obtained in sandy and gravelly sediments with little or no plasticity are not considered to be good tests due to particle interlocking and other factors. Penetration Rates of Vibrocore Barrels Twentyfour vibrocore samples were obtained during the summer of 1976 (Fig. 4), with core length of up to 1.80 m. The rates of oenetration were recorded for most stations. These rates provide a qualitative measure of the soil properties in different environments of the inner shelf. In several instances divers using a vane shear measured in situ shear strength of surface sediments near vibrocore stations (Fig. 2). The vibrocorer is driven by two electric motors producing a combined driving force of 700 kg at a rate of 2,840 impulses/min. Square steel barrels and tubular fiberglass barrels were used in all instances. The steel barrels propagated the vibratory impulse more efficiently to the core nose than the fiberglass barrels, because of the greater damping characteristics associated 2 with the fiberglass barrels. Along with the penetration rates, the barrel type used at each station is shown in Figure 5 . Station locations and water depths are listed in Table 3 . Only preliminary core studies have been performed so far and we therefore did not'include sediment descriptions with the penetration rates. However, by comparing sediment characteristics in the penetrated section with penetration rates, we feel fairly certain that cores 19 and 20 from the Colville Delta were stopped at the top of the underlying ice bonded sediments. Salinity of Insterstitial Water, Sea Floor Temperatures, and Sediment Freezing Points A variety of data pertinent to offshore permafrost problems has been gathered by our Beaufort Sea project over the years. During the 1976 summer field season on the R/V KARLUK. we made a special effort to obtain reliable data on the salinity of interstitial waters in surficial sediments on the inner shelf. Our main objectives in this study are to gain an understanding of the sedimentary environment on the arctic shelf. The shelf surface is affected and modified by waves, currents, strudel scour, ice gouging, small critters, and many other factors. Our thinking about bottom processes has been based on the assumption that the sediment surface is unfrozen (Reimnitz and Barnes, 1974). There is some justification for this assumption, at least for summer conditions. In our sampling, driving of thermoprobes, diving, boat anchoring, etc., we apparently have never encountered ice bonded sediments, (except possibly at several vibrocoring stations in very shallow water near the Colville River, as stated earlier in this report. Even during the driving of a thermoprobe in bottom-fast ice off the Kuparuk Rixrer, when some of the data reported herein was obtained, penetration was not prevented 'or retarded by ice bonding within the sediment, as far as we can determine. 3 If the surficial sediments did become ice bonded in certain environments during the peak of the winter" this would be very important for studies of bottom processes, for biological studies of bottom dwelling organisms, and for offshore construction projects. For example, high flow velocities recorded by current, meters could indicate that sediment transport is taking place, while in fact the seabed may actually be frozen. An example of potential environmental impact may be envisioned by considering the influence of a cold pipe line carrying natural gas buried on the shelf. If the shelf sediments are close to the freezing point, the cooling effect of such a pipe line may result in the freezing of overburden. Bedload transport of sediment might be affected such that individual grains in transit, temporarily contacting the bottom, may become adfrozen. This in turn could result in the formation of a sediment dike along the pipeline corridor. Sediment Salinity Interstitial salinities were determined from sediment samples collected in 1972 and 1976. In 1972, deep water samples were obtained by gravity corers on the outer shelf (Table IV, stations 1-5). From these cores 10 cm sub-samples were taken, squeezed, and processed on board by diluting 40 ml of interstitial water to 200 ml, on which the conductivity was measured. The 1976 values (Table IV , stations 6-21) were obtained from samples collected in plastic tubes by divers, and stored at 0 C until processing. Since these inner shelf samples were quite variable in composition, different methods had to be used for water extraction and salinity determination. Some of the samples were centrifuged for 15 minutes at 15,000 rpm. 20 yl of interstitial water were titrated against a Copenhagen Standard seawater of known chlorinity, using a London Co. Automatic Chloride Titrator. Values obtained by this method are given in Table IV . The remainder of the samples required a dilution method to obtain an adequate o volume for titration. A portion of the subsample was oven-dried at 110 C to determine moisture content. The remainder was diluted with 2 ml of distilled water, shaken on a wrist action shaker for 20 minutes, and centrifuged for 15 minutes at 2,000 rpm. Again, 20 yJ were titrated using the automatic titrator. The values obtained by this technique are identified in Table IV by asterisks (*). Chlonnities were converted to salinities using the relation Salinity (°/oo) -0.03 + 1.805 x Chlorinity (°/oo). Using the salinity values of interstitial water, we calculated the hypothetical freezing temperatures of the sediment from two different relationships: 1) Molochushkin and Gavuliev (1970) show that: T f = 28.4 x (a 0 ' 22 X S/W -1) -Be' 35 * (W ~ 0 ' 035 >, where T is the freezing temperature in degrees Centigrade, S is the salinity of pore water in parts per hundred, and W is the moisture content in "relative -units" (from our translation), and e = 2.7. For the simple-minded geologist this relation has only one minor problem: it gives positive freezing temperatures. Changing the term 0.022 x S/W -0.022 x S/W e to e we obtain what appear to be reasonable values for freezing temperatures, and therefore assume a printing error was made. The equation now reads: T f = 28.4 x (e-°-°22 * S/W-1, -So' 35 X (W ' 0 '°35) . Only for the samples processed by the dilution method did we obtain values for moisture content (Table IV ). In our calculations of freezing temperature we assumed a moisture content of 50% for the remaining samples. This assumed value was slightly greater than the measured, which averaged between 35 and 40% in moisture content. Possible deviation of +_ 20% in moisture content from the assumed 50% value would result in freezing point errors of +_ 1. 5 C for the most saline samples to +_ 1.0 C for the least saline samples. 2) Osterkamp and Harrison (1976) , working on offshore permafrost problems in the Prudhoe Bay area, calculated the freezing temperature of sediments using an equation that applies to seawater alone (Doherty and Kester, 1974) , and disregards the fact that the deposit is a mixture of water and sediment: -5.199 x 10~2 S -7.225 x 10~5 S 2 * Where S is salinity in parts per thousand. For the soil samples they obtained, the error in this procedure was estimated to be less than 20%. A two-meter long thermoprobe, with thermistors, coupled to a Wheatstone Bridge, was used in two different field operations to measure sea floor temperatures. Nine measuring stations occupied by the R/V LOON during the middle of September in 1976 are shown in Figure 6 (inset, black dots). The values obtained at these stations, shown in Figure 7, represent sea floor conditions close to the end of the open water period, probably slightly past the time when the sea floor is the warmest. The measurements around the mouth of the Kuparuk River were made in late May, 1972, using the sea ice as a base of operations. These values represent temperature conditions just prior to river flooding of the sea ice, shortly after the temperature-low of the winter. Thus, the temperature data shown in Figure 7 does not represent the extremes encountered from winter's low to summer's peak. The sediment surface temperatures were extrapolated and the results are shown in Table V. These extrapolated sea floor temperatures are plotted with the respective station locations in Figure 6. Sea floor temperatures extrapolated by Lachenbrach and Marshall (1977) from May, 1976, data are in general agreement with these values. Speculating on the implications of the presented data, we sketched in Figure 8 . This is based on the assumption that the average annual temperature and environmental conditins fro the thermoprobe stations off the Kuparuk River are rather similar to those in the Prudhoe Bay vicinity, occupied at a different time of the year. From this assumption, we sketched a hypothetica cross-section through a shallow lagoon or bay across a sill with a depth less than the maxi-6 mum fast ice thickness (approx. 2 m), and into the open ocean (Fig. 8) . Winter and summer bottom temperatures (Fig. 8 ) measured in the very shallow lagoon, in the deepest part of the lagoon, at the shallow sill, and at several water depths offshore are shown. Note that no values are available for the shallow sill during winter conditions. In the deepest part of Prudhoe Bay and near the sill, the summer temperatures show a considerable range of values. These are shown as vertical bars in Figure 8 . Also shown in Figure 8 are the freezing temperatures for the seabed calculated from our data on salinity of interstitial waters and moisture content, using the two different equations. Freezing temperatures calculated from the equation applying to pure sea water suggest that the seabed from shore to a water depth of about 7 m would become ice-bonded during the winter. This equation therefore probably should not be used. The equation from Molochushkin and Gavuliev (1970) shows that only those areas shallower than 2 m of water depth are close to the freezing point during the winter, and this seems reasonable. Plans are being made to obtain more of this type of data during the coming field season. ACKNOWLEDGMENT