Paul V. Sellmann

Mummified pleistocene ostracods in alaska.

Preserved soft parts of ostracod specimens were recovered from beach and lagoon sediments from the Gubik Formation, of Quaternary age, at Barrow, Alaska.

Determining subsea permafrost characteristics with a cone penetrometer — Prudhoe Bay, Alaska

Abstract Sediments beneath the Beaufort Sea near Prudhoe Bay, Alaska, were probed at 27 sites using a static cone penetrometer to determine engineering properties and distribution of material types, including ice-bonded sediments. The probe, designed and constructed at the Cold Regions Research and Engineering Laboratory, provided both point and casing resistance data and thermal profiles. At five sites these data were correlated with information from adjacent drilled and sampled holes. These control data and the quality of the probe information permitted profiles of sediment type and occurrence of ice-bonded material to be developed along three lines that included various geological features and depositional environments. Material properties were quite variable in the upper 14 m of sediments probed. In general, softer, finer-grained sediments occurred in the upper layers, while penetration refusal was met in stiff gravels 10 to 12 m below the seabed. Seabed temperatures during the study were all below 0°C. However, because of uncertainties in freezing point values caused by brines, evaluation of the penetration resistance data was required to identify the occurrence of ice-bonded sediments. The coupling of thermal and penetration resistance data revealed that seasonally ice-bonded sediments occurred where the sea ice froze back to or near the seabed. Deeper, perennially frozen sediments also appeared to be present at several probe sites.

Radiocarbon Dating of Coastal Peat, Barrow, Alaska

A buried, frozen section of peat from sea level yielded radiocarbon dates between 700 and 2600 B.C.; it suggests burial by a transgressing sea.

Seafloor temperature and conductivity data from Stefansson Sound, Alaska

Abstract Overconsolidated sediments, seasonal seafloor freezing, and ice-bonded permafrost are unique features in shallow arctic coastal waters. They are related to low seawater temperatures and varying salinities. Seabed temperatures can be less than −1.0°C for much of the year, with noticeable warming occurring only during the summer months. Observations from recent deployment of three instruments in Stefansson Sound and data from an earlier deployment, which included sites in Harrison Bay, showed decreasing mean annual seafloor temperatures with increasing water depth, ranging from −0.9°C in 4.4 m of water to −1.6°C in 14 m of water. Salinities also varied seasonally, with noticeable freshening developing during the summer and highly uniform values occurring during the winter. Periodic temperature and salinity measurements at sites in Stefansson Sound, made during August 1987 and August 1989, also helped verify the data obtained with the seabottom instruments. Seasonal freezing of the seabed can begin in late September and may noticeably change its engineering properties. In areas of coarse-grained sediments, ice bonding and strengthening of the seabed can result. In areas of fine-grained sediments it appears that seasonal freezing of the seafloor can cause overconsolidation of the seabed sediments. This densification process can result in a significant permanent increase in strength.

Radon measurements as indicators of permafrost distribution

Abstract Observations in central Alaska indicate that radon concentrations in surface soils over discontinuous permafrost seem to correspond with frozen-ground distribution. These observations were made to determine if radon measurements might provide a method for obtaining information on permafrost distribution. Radon levels from an area of silty soils varied from 14 to 348 pCi 1 −1 and averaged 51 pCi 1 −1 where the top of permafrost was within a meter of the ground surface, compared to an average of 190 pCi 1 −1 where permafrost was absent.