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P. W. Barnes

Publications and source records attributed to P. W. Barnes.

At least 37 records · Page 2Linked to original sources
USGS1988

Icebergs rework shelf sediments to 500 m off Antarctica

Icebergs and sea ice rework the sediments of high-latitude shelves, producing modern diamicts (ice-keel turbates) unrelated to glacial proximity. Off Antarctica, sidescan sonar data indicate the presence of ice-gouge features formed by the physical interaction between ice keels and the sea bed. These are recognized as incisions a few metres deep and tens of metres wide, in water depths up to 500 m. On the submarine bank tops and slopes off Wilkes Land and in the Weddell Sea, subcircular depressions 30 to 150 m in diameter, a washboard pattern, and hummocky bed features also represent iceberg-resting sites. The freshness of sea-bed morphology, nearby Holocene sediment ponding, and active hydraulic sedimentary processes indicate that the sea floor is being reworked by iceberg keels. Tabular iceberg drafts in excess of 330 m have been measured, and modeling studies suggest that nontabular iceberg drafts of 500 m are possible. We conclude that a modern ice-keel turbate deposit in the form of a poorly stratified diamicton is probably widespread on that part (54%) of the Antarctic shelf less than 500 m deep.

Geology↗
USGS1987

Ice erosion of a sea-floor knickpoint at the inner edge of the stamukhi zone, Beaufort Sea, Alaska

In 1981 and 1982, detailed bathymetric and side-scan sonar surveys were made of an area of the sea floor north of Prudhoe Bay, Alaska, to study the changing characteristics of the seabed at the inner boundary of the stamukhi zone, the coast-parallel zone of grounded ice ridges that occurs in water depths between 15 and 50 m in the arctic. The fathograms and sonographs resolved 10-cm features and electronic navigation gave relocations accurate to about 10 m. Year after year an ice boundary develops at the inner edge of the stamukhi zone where major shear and pressure deformation occur in about the same location. Associated with this ice boundary, the bathymetry shows a pronounced break in slope — the knickpoint — on the shelf profile at about 20 m depth. The 2–3 m-high knickpoint is cut in a consolidated gravelly mud of pre-Holocene age. A well-defined gravel and cobble shoal a few meters high usually occurs at the inshore edge of the knickpoint. The sonograph mosaic shows that seaward of the knickpoint, ice gouges saturate the sea floor and are well defined; inshore the gouges are fewer in number and are poorly defined on the records. Few gouges can be traced from the seaward side of the knickpoint across the shoals to the inshore side of the knickpoint. Studies of ice gouging rates in two seabed corridors that cross the stamukhi zone reveal the highest rates of gouging seaward of the knickpoint. We believe that the knickpoint results from ice erosion at the inner boundary of the stamukhi zone. Intensified currents associated with this boundary winnow away fine sediments. Ice bulldozing and currents shape the shoals, which perch atop the knickpoint. The knickpoint helps to limit ice forces on the seabed inshore of the stamukhi zone.

Marine Geology↗
USGS1987

SEA-ICE INFLUENCE ON ARCTIC COASTAL RETREAT.

Recent studies document the effectiveness of sea ice in reshaping the seafloor of the inner shelf into sharp-relief features, including ice gouges with jagged flanking ridges, ice-wallow relief, and 2- to 6-m-deep strudel-scour craters. These ice-related relief forms are in disequilibrium with classic open-water hydraulic processes and thus are smoothed over by waves and currents in one to two years. Such alternate reworking of the shelf by ice and currents - two diverse types of processes, which in the case of ice wallow act in unison-contributes to sediment mobility and, thus, to sediment loss from the coast and inner shelf. The bulldozing action by ice results in coast-parallel sediment displacement. Additionally, suspension of sediment by frazil and anchor ice, followed by ice rafting, can move large amounts of bottom-derived materials. Our understanding of all these processes is insufficient to model Arctic coastal processes.

Conference Paper↗
USGS1982

Ice rafting of fine-grained sediment, a sorting and transport mechanism, Beaufort Sea, Alaska

The presence of turbid, sediment-rich fast ice in the Arctic is a major factor affecting transport of fine-grained sediment. Turbid ice was found to be present in a zone 10 to 20 km wide along the coast of the Beaufort Sea. Sediment concentrations observed in cores taken in seasonal fast ice ranged from 3 to more than 1,600 g/m 3 . Finely disseminated silt and clay-sized particles dominated, discoloring the upper segments of the cores in a layer up to 1 m thick. In almost all of the cores the upper-most 10 cm of ice was relatively less turbid, and the relief at the base of the turbid layer was 10 to 20 cm over distances of 1 to 2 m. Observers have documented the widespread, sporadic occurrence of sediment-rich fast ice in both the Beaufort and Bering Seas. The known sources and transport relations of suspended sediment did not explain this distribution of turbid ice. The occurrence of sediment in only the upper part of the seasonal fast ice indicates that sediment-rich ice forms early during ice growth. The most likely mechanism for the formation of sediment-laden ice and preferential sorting of fine sediments requires resuspension of nearshore bottom sediment during storms, accompanied by formation of frazil ice and subsequent lateral advection before the fast ice is stabilized. We estimate that the sediment incorporated in the Beaufort ice canopy formed a significant proportion of the seasonal influx of terrigenous fine-grained sediment. The dominance of fine-grained sediment suggests that in the Arctic and sub-Arctic these size fractions may be ice rafted in greater volumes than the coarse fraction of traditionally recognized ice-rafted sediment. The incorporation and transport mechanism may be a significant factor in the transport of fine-grained sediments in the Arctic basin.

Journal of Sedimentary Petrology↗