Stamukhi Zone Processes: Implications for Developing the Arctic Offshore Area

Abstract

Offshore islands and shoals in the Beaufort Sea interact with the westward pack-ice drift, causing the formation of major grounded-ridge systems of pack-ice drift, causing the formation of major grounded-ridge systems of the Stamukhi zone. These systems resist the forces of pack ice and protect the inner shelf. Fully exposed islands and shoals show little modification for the past 25 years, suggesting that similar artificial structures, properly placed, should also survive and might modify sea-ice zonation. properly placed, should also survive and might modify sea-ice zonation. Introduction Landsat-1 and National Oceanographic and Atmospheric Admin. satellite imagery for the winter of 1972-73 and a variety of ice and sea-bed data, including side-scan sonar, high-resolution (Uniboom) seismic reflection, and precisely controlled bathymetric surveys, were used to precisely controlled bathymetric surveys, were used to study sea-ice zonation and dynamics and their relation to bottom morphology and geologic processes on the Beaufort Sea continental shelf of the Alaskan arctic. During early winter, the location of the boundary between undeformed fast ice and the westward-drifting polar-pack ice is controlled by major coastal polar-pack ice is controlled by major coastal promontories. Pronounced linear pressure and shear ridges, and promontories. Pronounced linear pressure and shear ridges, and hummock fields form along the boundary and are stabilized by grounding, generally between the 10- to 20-m isobaths. Slippage along this boundary occurs intermittently at, or seaward of, the grounded ridges, forming new grounded-ridge systems in a widening zone (the Stamukhi zone) that by late winter may extend out to the 40-m isobath. The Stamukhi zone protects the inner shelf and coast from pack-ice forces. There is a causal relationship between the spatial distribution of major ice-ridge systems and offshore shoals, downdrift of major coastal promontories. Ice has forced the shoals to migrate shoreward for distances of up to 400 m in the last 25 years. The sea floor seaward of such shoals (within the Stamukhi zone) shows a high density of ice gouging and depth of incision, and a high degree of disruption of internal sedimentary structures. The concentration of large-scale ice deformation and intense sea-floor disruption in the Stamukhi zone indicate that much of the available marine energy is expended here during winter. The inner shelf and coast (where the relatively undeformed fast ice grows) is sheltered. Certain aspects of the results reported here are directly applicable to planned offshore development in the Beaufort Sea. Artificial structures similar to offshore shoals, properly placed, should be able to withstand the forces of the ice, should serve to modify the observed ice zonation, and might be used to make the inner shelf environment less hostile to man's endeavors. Stamukhi Zone Processes Studies by the USGS of the Beaufort Sea shelf region of northern Alaska, using remote-sensing techniques and sea-floor data, have found a correlation between shelf morphology and the yearly development of sea-ice zonation. This relationship may have critical implications for the economic development of the continental shelf in arctic Alaska. Offshore development within the seasonal fast-ice zone on the inner shelf, extending to the 10- to 20-m isobath, generally is considered economically and technically feasible. However, development of expected high oil and gas potential beyond the relatively protected fast-ice zone will involve untried technology and high risks. Here, where the polar pack of the Pacific Gyre rubs against the continental margin, ice dynamics and deformational processes have the highest intensities of anywhere in the Arctic Basin.