Arctic Continental Shelf Research Articles

Coupled circulation and ice floe movement model for partially ice‐covered continental shelves

A coupled ice‐ocean model has been developed for use in the short‐term (order of days) prediction of the ice and water movement on the shallow Arctic continental shelf. Our interest in partially ice‐covered conditions allows the neglect of ice‐ice interactions. Thermodynamic effects are also assumed negligible over the short time scale of interest. The intended application to shallow‐water regions permits the use of the vertically integrated water momentum equations but necessitates the inclusion of finite depth effects. Model comparison with actual measurements of ice floe movement in the Beaufort Sea are extremely encouraging, especially when compared with predictions afforded by uncoupled or ice‐only formulations. The use of the depth‐averaged circulation model has been found to weaken the algorithm's ability to simulate ice floe movement in a wind field rapidly varying in time. Recommendations for future improvements include refinement of wind forecasting methods for inclusion in a coupled air‐ice‐ocean model.

Angular distribution of ice cracking events in the Arctic

The measured vertical directionality of ice events in the polar ice pack is presented. Concurrent 345‐s samples of ambient noise measured with four vertically spaced hydrophones suspended over the Arctic continental shelf were searched for corresponding peaks in the envelope of the acoustic pressure. In a previous analysis [P. Zakarauskas, J. Acoust. Soc. Am. Suppl. 1 82, S30 (1987)], the ice events were shown to be of thermal origin. The resulting angular distribution of the 765 ice events observed during the sample has its maximum at 15 deg below the horizontal, with most of the events arriving between 0 and 25 deg below the horizontal. An explanation for this observation is given in terms of a simple ray‐based model of the propagation of ice cracking noise. The model includes the seafloor and under‐ice angular reflection coefficients measured at a neighboring location.

Eastern Cordilleran Foldbelt of Northern Canada: Its Structural Geometry and Hydrocarbon Potential

The eastern Cordilleran foldbelt of northern Canada embraces that part of the foreland thrust and foldbelt north of lat. 60°N, including the continental shelf of southern Beaufort Sea. The sedimentary succession there lies with pronounced unconformity on continental crust, presumably crystalline rocks of the Hudsonian (1,750 Ma) basement, and ranges in thickness from an estimated 4 mi (7 km) along the eastern margin of the foldbelt to more than 12 mi (20 km) in the interior. Regional and interregional unconformities divide the succession into five discrete tectono-stratigraphic sequences, ranging in age from Proterozoic (Helikian) to Holocene. These sequences are termed, from oldest to youngest, Inuvikian, Rapitanian, Franklinian, Ellesmerian, and Brookian. The region is characterized by bundles of en echelon folds cut by two major fault systems, the Richardson fault array bordering the foreland and the Kaltag fault zone transecting the foldbelt. Late Cretaceous and Tertiary horizontal contraction with concomitant vertical thickening of the supracrustal wedge is roughly one-fourth that of the eastern Cordillera of southern Canada. Potential hydrocarbon traps in Paleozoic and Mesozoic rocks of the northern Cordillera commonly occur within these en echelon fold bundles. Thus, their locations are predictable because they are arranged systematically right- and left-hand en echelon. In the Cenozoic succession of the Arctic coastal plain and continental shelf, however, closures are arranged only crudely en echelon. Current estimates of the combined oil and gas resources of the eastern Cordilleran foldbelt of northern Canada and the adjacent interior platform are about 10 billion bbl of oil and 123 tcf of natural gas, with the preponderance of resources being confined to the Upper Cretaceous and Tertiary (Brookian) sequence.

Late Weichselian ice sheet of Northern Eurasia

A considerable portion of Northern Eurasia, and particularly its continental shelf, was glaciated by inland ice during late Weichsel time. This was first inferred from such evidence as glacial striae, submarine troughs, sea-bed diamictons, boulder trains on adjacent land, and patterns of glacioisostatic crustal movements. Subsequently, the inference was confirmed by data on the occurrence and geographic position of late Weichselian end moraines and proglacial lacustrine deposits. The south-facing outer moraines in the northeastern Russian Plain, northern West Siberia, and on Taimyr Peninsula are underlain by sediments containing wood and peat, the radiocarbon dating of which yielded ages of 22,000 to 45,000 yr B.P. The youngest late-glacial moraines are of Holocene age: the double Markhida moraine in the lower Pechora River basin, presumably associated with “degradational” surges of the Barents Ice Dome, is underlain by sediments with wood and peat dated at 9000 to 9900 yr B.P.: this suggests that deglaciation of the Arctic continental shelf of Eurasia was not completed until after 9000 yr B.P. The reconstructed ice-front lines lead to the conclusion that the late Weichselian ice sheet of Northern Eurasia (proposed name: the Eurasian Ice Sheet) extended without interruptions from southwestern Ireland to the northeastern end of Taimyr Peninsula, a distance of 6000 km: it covered an area of 8,370,000 km 2, half of which lay on the present-day continental shelves and a quarter on lowlands that were depressed isostatically below sea level. Hence, the ice sheet was predominantly marine-based. A contour map of the ice sheet based both on the dependence of the heights of ice domes upon their radii and on factual data concerning the impact of bedrock topography upon ice relief has been constructed. The major features of the ice sheet were the British, Scandinavian, Barents, and Kara Ice Domes that had altitudes of 1.9 to 3.3 km and were separated from one another by ice saddles about 1.5 km high. At the late Weichselian glacial maximum, all the main ice-dispersion centers were on continental shelves and coastal lowlands, whereas mountain centers, such as the Polar Urals and Byrranga Range, played only a local role. The portions of the ice sheet that were grounded on continental shelves some 700 to 900 m below sea level were inherently unstable and could exist only in conjunction with confined and pinned floating ice shelves that covered the Arctic Ocean and the Greenland and Norwegian Seas. The Eurasian Ice Sheet impounded the Severnaya Dvina, Mezen, Pechora, Ob, Irtysh, and Yneisei Rivers, and caused the formation of ice-dammed lakes on the northern Russian Plain and in West Siberia. Until about 13,500 yr B.P. the proglacial system of lakes and spillways had a radial pattern; it included large West Siberian lakes, the Caspian and Black Seas, and ended in the Mediterranian Sea. Later, the system became marginal and discharged proglacial water mainly into the Norwegian Sea.

The last Eurasian ice sheet

Abstract A considerable portion of northern Eurasia, especially the Arctic continental shelves, was glaciated during the Late Wurm. This conclusion was first reached on the basis of glacial striae, submarine troughs, seabed diamictons, boulder trains and the patterns of glacio‐isostatic crustal movements. It was subsequently conclusively confirmed by data on the occurrence and positions of Late Wurm terminal moraines and proglacial lacustrine deposits. Reconstruction of ice‐front positions revealed that the last ice sheet in northern Eurasia (to be called the Eurasian Ice Sheet) extended without interruption from southwestern Ireland to the northeastern tip of the Taymyr Peninsula, a distance of 6,000 km, and covered an area of 8,370,000 km2. One half of this area was located on present‐day continental shelves. The Eurasian Ice Sheet impounded the waters of the Northern Dvina, Mezen’, Pechora, Ob’ and Yenisey rivers, resulting in the formation of vast ice‐dammed lakes in the northeast of the Russian plain and in the West Siberian Plain. These lakes drained southward successively into the Aral, Caspian, Black and Mediterranean seas.

Oil in the Arctic 2. The Outer Continental Shelf Environmental Assessment Program

AbstractPetroleum exploration and development is proceeding rapidly in the ice-covered waters of the arctic continental shelves. A a consequence of this development, environmental catastrophes on an unprecedented scale are possible in this harsh yet sensitive environment, where the cleanup of spilled oil is extremely difficult, if not virtually impossible. What are the likely damages to the arctic marine ecosystem which will result from petroleum-related impacts? What kinds of studies should be conducted in order to assess these impact to mitigate or remove them entirely? And how do we judge the success of these studies? The oiled state Outer Continental Shelf Environmental Assessment Program (OCSEAP) a large, multidisciplinary research project, which attempts to address such question, is described; more than 150 individual projects costing this year $21 million, are in progress around the coast of Alaska. Those conducted in the Arctic – north of Bering trail – are here reviewed. Their chances for success...

The Construction of Artificial Islands in the Beaufort Sea

Arctic petroleum exploration has moved offshore into the ice-covered waters of the Beaufort Sea. Artificial earth-fill islands have been used successfully as temporary shallow-water drilling platforms. Introduction Petroleum exploration activities in the offshore Arctic Petroleum exploration activities in the offshore Arctic were initiated in the mid-1960's, when permits covering acreage on the Arctic continental shelf were issued to several petroleum exploration companies (Fig. 1). At that time, Imperial Oil Ltd. obtained permits in the shallow waters of the Beaufort Sea adjacent to the Mackenzie River delta. Preliminary studies of offshore drilling feasibility that were undertaken during the late 1960's soon brought to light the tremendous dearth of knowledge concerning the offshore Arctic environment. It was apparent that the major problems to be solved while developing the technology required to support offshore Arctic drilling were (1) the definition of forces exerted on stationary structures by the mobile annual and multiyear ice; (2) the influence of violent, shortduration summer storms; (3) an apparent scarcity of easily accessible construction materials; and (4) the mobilization of suitable construction equipment that would be effective during the short open-water operating season. In 1969 Imperial initiated data-gathering and ice-testing programs; these were followed in succeeding yens by many additional studies sponsored by Imperial and other interested Arctic operators. Numerous concepts, both conventional and unique, were considered for Arctic offshore drilling. These concepts included artificial islands, bottom-founded mobile structures, monopods, cones, and ice-breaking floating vessels. These are all viable concepts and may have application for a specific set of conditions. However, Imperial determined that the dredged artificial island was the safest and most economically attractive type of structure for use in support of its exploration drilling program. In 1971 a permit was received from the Canadian ept. of Indian Affairs and Northern Development authorizing construction of an experimental island at what was later to become Imperial Immerk B-44 wellsite. Construction began early in Aug. 1972 but, under the terms of the permit, drilling operations were not to take place until the stability of the structure under winter ice conditions had been assessed adequately. This initial island proved to be a stable and competent platform. To date, Imperial has drilled eight exploratory platform. To date, Imperial has drilled eight exploratory wells from islands constructed in water depths ranging from 5 to 25 ft (Fig. 2). Environment Very few regions of the world experience greater extremes of weather conditions than those encountered in the Arctic. During the summer months of July through September, temperatures may reach a high of 80 degrees F, dropping to −60 degrees F for much of the winter period. Strong winds and shifting ice during both summer and winter add to the difficulties of working in this harsh and inhospitable climate. The environment of the shallow shelf north of the Mackenzie River delta is influenced by two dominant factors: the polar ice cap, and outflow from the Mackenzie River system. JPT P. 365

The Law of the Sea of the Arctic: With Special Reference to Canada

Abstract : Seven major questions are studied: The applicability of the right of innocent passage to the Northwest and Northeast Passages; the status of the waters of the Canadian Arctic Archipelago; the possibility of claiming a historic title to some of the Arctic waters; the applicability of the principle of 'the freedom of the seas' to the Arctic Ocean; the status of ice shelves and ice islands; the international validity of the Canadian Arctic pollution prevention legislation and the state boundaries of the Arctic continental shelf and sea-bed.

Shallow-Water Propagation in the Arctic Ocean

Dispersion characteristics of underwater sound on the Arctic continental shelf north of Alaska were investigated at ranges between 2 and 250 km and for frequencies between 3 and 250 cps. Explosive charges were used as sources, and geophones were used as detectors. Observations were interpreted in terms of normal-mode theory, and good agreement between theory and experiment was found for both phase and group velocity. Portions of the first and second modes were recognized at all ranges, and, at short ranges, “leaking modes,” associated with the ice layer, were also noted. For long ranges, the water wave amplitude varied as the −1.85 power of range.

Shallow Water Sound Propagation in the Arctic Ocean

Experiments on underwater sound propagation in the shallow water of the Arctic continental shelf were conducted at Fletcher's Ice Island (T-3) during April and May 1960. Shots were made along two profiles, 6.8 and 8.2 km long in water depths of 62 and 50 km, respectively. The records show a characteristic sequence of arrivals in all cases. These wave groups, in order of arrival, are identified as (1) a “leaking mode,” associated with the ice layer, which travels with a velocity of about 3 km/sec, (2) a “second mode” with a velocity about 2.2 km/sec and associated with the bottom sediments, (3) a “first mode” of large amplitude and low frequency, (4) a high-frequency water wave which is superimposed on the “first mode.” The identification of these wave groups is made on the basis of comparison between observed phase and group velocity dispersion with calculated dispersion curves. The agreement between theory and experiment, using phase and group velocity and the first and second mode, is good.