Multiyear Pack Ice Research Articles

Iñupiaq Knowledge of Polar Bears (<i>Ursus maritimus</i>) in the Southern Beaufort Sea, Alaska

Successful wildlife management depends upon coordination and consultation with local communities. However, much of the research used to inform management is often derived solely from data collected directly from wildlife. Indigenous people living in the Arctic have a close connection to their environment, which provides unique opportunities to observe their environment and the ecology of Arctic species. Further, most northern Arctic communities occur within the range of polar bears (nanuq, Ursus maritimus) and have experienced significant climatic changes. Here, we used semi-structured interviews from 2017 to 2019 to document Iñupiaq knowledge of polar bears observed over four decades in four Alaskan communities in the range of the Southern Beaufort Sea polar bear subpopulation: Wainwright, Utqiaġvik, Nuiqsut, and Kaktovik. All but one of 47 participants described directional and notable changes in sea ice, including earlier ice breakup, later ice return, thinner ice, and less multiyear pack ice. These changes corresponded with observations of bears spending more time on land during the late summer and early fall in recent decades—observations consistent with scientific and Indigenous knowledge studies in Alaska, Canada, and Greenland. Participants noted that polar bear and seal body condition and local abundance either varied geographically or exhibited no patterns. However, participants described a recent phenomenon of bears being exhausted and lethargic when arriving on shore in the summer and fall after extensive swims from the pack ice. Further, several participants suggested that maternal denning is occurring more often on land than sea ice. Participants indicated that village and regional governments are increasingly challenged to obtain resources needed to keep their communities safe as polar bears spend more time on land, an issue that is likely to be exacerbated both in this region and elsewhere as sea ice loss continues.

Natural variability of the Arctic Ocean sea ice during the present interglacial

The impact of the ongoing anthropogenic warming on the Arctic Ocean sea ice is ascertained and closely monitored. However, its long-term fate remains an open question as its natural variability on centennial to millennial timescales is not well documented. Here, we use marine sedimentary records to reconstruct Arctic sea-ice fluctuations. Cores collected along the Lomonosov Ridge that extends across the Arctic Ocean from northern Greenland to the Laptev Sea were radiocarbon dated and analyzed for their micropaleontological and palynological contents, both bearing information on the past sea-ice cover. Results demonstrate that multiyear pack ice remained a robust feature of the western and central Lomonosov Ridge and that perennial sea ice remained present throughout the present interglacial, even during the climate optimum of the middle Holocene that globally peaked ∼6,500 y ago. In contradistinction, the southeastern Lomonosov Ridge area experienced seasonally sea-ice-free conditions, at least, sporadically, until about 4,000 y ago. They were marked by relatively high phytoplanktonic productivity and organic carbon fluxes at the seafloor resulting in low biogenic carbonate preservation. These results point to contrasted west-east surface ocean conditions in the Arctic Ocean, not unlike those of the Arctic dipole linked to the recent loss of Arctic sea ice. Hence, our data suggest that seasonally ice-free conditions in the southeastern Arctic Ocean with a dominant Arctic dipolar pattern, may be a recurrent feature under "warm world" climate.

Regional characteristics of sea ice thickness in Canadian shelf and Arctic Archipelago measured by Ground Penetrating Radar

Ground Penetrating Radar (GPR) measurements of sea ice thickness including undeformed ice and ridged ice were carried out in the central north Canadian Archipelago in spring 2010. Results have shown a significant spatial heterogeneity of sea ice thickness across the shelf. The undeformed multi-year fast ice of (2.05±0.09) m thick was investigated southern inshore zone of Borden island located at middle of the observational section, which was the observed maximum thickness in the field work. The less thick sea ice was sampled across a flaw lead with the thicknesses of (1.05±0.11) m for the pack ice and (1.24±0.13) m for the fast ice. At the northernmost spot of the section, the undeformed multi-year pack ice was (1.54±0.22) m thick with a ridged ice of 2.5 to 3 m, comparing to the multi-year fast ice with the thickness of (1.67±0.16) m at the southernmost station in the Prince Gustaf Adolf Sea.

What Risks Remain: Maritime Activity and the New Calculus of Risk in the North American Arctic

Conditions in the Arctic are changing rapidly and maritime activity has risen sharply in recent years. Although ice-free periods within the Northwest Passage could eventually hold great promise for shortening shipping routes between the Pacific and Atlantic Oceans, the area remains hazardous for the time being. Weather remains challenging; ice dynamics remain poorly understood; dense, multi-year pack ice drifts into potential sea-lanes; first-responder capacity is low; and information useful to mariners is comparatively scarce. The uptick in maritime activity has been met with calls for a policy response to mitigate risk to human life, livelihoods, and the environment. This paper uses the literature of systems-risk assessment to consider the best course of action under uncertainty. With different elements of risk reduction falling to different policy agents, this paper explores the roles that different entities can play. Ultimately this paper concludes that characterizing the area as experiencing an “Arctic Gold Rush” is inappropriate, at least in the short term. Extractive resource companies have all but abandoned hopes for drilling anytime soon, and shipping companies rely more on reliability than the shortest distance between two points when route planning. With development interest faltering for the time being, this paper ultimately concludes that the best policy is one of investment in information. Rather than aggressive new regulatory interventions and expensive enhancements of physical infrastructure, for now at least the focus should be on research and communications. Better maritime communications technology, remote sensing, and physical science hold great promise and respond to an immediate need.

Fracture of summer perennial sea ice by ocean swell as a result of Arctic storms

The Arctic summer minimum sea ice extent has experienced a decreasing trend since 1979, with an extreme minimum extent of 4.27 × 106 km2 in September 2007, and a similar minimum in 2011. Large expanses of open water in the Siberian, Laptev, Chukchi, and Beaufort Seas result from declining summer sea ice cover, and consequently introduce long fetch within the Arctic Basin. Strong winds from migratory cyclones coupled with increasing fetch generate large waves which can propagate into the pack ice and break it up. On 06 September 2009, we observed the intrusion of large swells into the multiyear pack ice approximately 250 km from the ice edge. These large swells induced nearly instantaneous widespread fracturing of the multiyear pack ice, reducing the large, (>1 km diameter) parent ice floes to small (100–150 m diameter) floes. This process increased the total ice floe perimeter exposed to the open ocean, allowing for more efficient distribution of energy from ocean heat fluxes, and incoming radiation into the floes, thereby enhancing lateral melting. This process of sea ice decay is therefore presented as a potential positive feedback process that will accelerate the loss of Arctic sea ice.

On the effective aerodynamic and scalar roughness length of Weddell Sea ice

We study the effective aerodynamic roughness length z0_eff and scalar roughness length for temperature zT_eff over different compact sea ice types in the Antarctic Weddell Sea by aircraft measurements during two austral summer seasons. z0_eff and zT_eff are highly variable in the Weddell Sea ice area. The averaged value of in all main sea ice areas was smaller than the averaged value of . The ratio between the two roughness lengths was relatively small for new/young sea ice with / ≈ 2, but the ratio became significantly large for the multiyear pack ice with / ≈ 227. For the pack ice area, with sea ice concentration ranging between 95% to 100%, we determined a median = 4.1 × 10−03 m and a median = 1.8 × 10−05 m. In the new, young sea ice area, with sea ice concentration ranging between 98% and 100%, we observed a median = × 10−04 m and a median = 2.2 × 10−04 m. These values of and differ from published observations conducted in a pack ice and new, young sea ice area in the northern hemisphere, such as the Arctic. Most model parameterizations require the roughness lengths as constant values as boundary input parameters. Our study shows that by using the $\overline{z_{0}\_ {\rm eff}}$ and values of this study, instead of commonly used sea ice roughness length values, the accuracy of parameterized heat and momentum fluxes in the Weddell Sea ice area can significantly be improved.

Physical and biological characteristics of the pelagic system across Fram Strait to Kongsfjorden

The Fram Strait is very important with regard to heat and mass exchange in the Arctic Ocean, and the large quantities of heat carried north by the West Spitsbergen Current (WSC) influence the climate in the Arctic region as a whole. A large volume of water and ice is transported through Fram Strait, with net water transport of 1.7–3.2 Sv southward in the East Greenland Current and a volume ice flux in the range of 0.06–0.11 Sv. The mean annual ice flux is about 866,000 km 2 yr −1. The Kongsfjorden–Krossfjorden fjord system on the coast of Spitsbergen, or at the eastern extreme of Fram Strait, is mainly affected by the northbound transport of water in the WSC. Mixing processes on the shelf result in Transformed Atlantic Water in the fjords, and the advection of Atlantic water also carries boreal fauna into the fjords. The phytoplankton production is about 80 g C m −2 yr −1 in Fram Strait, and has been estimated both below and above this for Kongsfjorden. The zooplankton fauna is diverse, but dominated in terms of biomass by calanoid copepods, particularly Calanus glacialis and C. finmarchicus. Other important copepods include C. hyperboreus, Metridia longa and the smaller, more numerous Pseudocalanus ( P. minutus and P. acuspes), Microcalanus ( M. pusillus and M. pygmaeus) and Oithona similis. The most important species of other taxa appear to be the amphipods Themisto libellula and T. abyssorum, the euphausiids Thysanoessa inermis and T. longicaudata and the chaetognaths Sagitta elegans and Eukrohnia hamata. A comparison between the open ocean of Fram Strait and the restricted fjord system of Kongsfjorden–Krossfjorden can be made within limitations. The same species tend to dominate, but the Fram Strait zooplankton fauna differs by the presence of meso- and bathypelagic copepods. The seasonal and inter-annual variation in zooplankton is described for Kongsfjorden based on the record during July 1996–2002. The ice macrofauna is much less diverse, consisting of a handful of amphipod species and the polar cod. The ice-associated biomass transport of ice-amphipods was calculated, based on the ice area transport, at about 3.55 × 10 6 ton wet weight per year or about 4.2 × 10 5 t C yr −1. This represents a large energy input to the Greenland Sea, but also a drain on the core population residing in the multi-year pack ice (MYI) in the Arctic Ocean. A continuous habitat loss of MYI due to climate warming will likely reduce dramatically the sympagic food source. The pelagic and sympagic food web structures were revealed by stable isotopes. The carbon sources of particulate organic matter (POM), being Ice-POM and Pelagic-POM, revealed different isotopic signals in the organisms of the food web, and also provided information about the sympagic–pelagic and pelagic–benthic couplings. The marine food web and energy pathways were further determined by fatty acid trophic markers, which to a large extent supported the stable isotope picture of the marine food web, although some discrepancies were noted, particularly with regard to predator–prey relationships of ctenophores and pteropods.

Sea ice algae in the White and Barents seas: composition and origin

To examine algae populations, three expeditions (in March 2001, April 2002 and February 2003) were conducted in the Guba Chupa (Chupa Estuary; north-western White Sea), and one cruise was carried out in the open part of the White Sea in April 2003 and in the northern part of the Barents Sea in July 2001. Sea ice algae and phytoplankton composition and abundance and the content of sediment traps under the land-fast ice in the White Sea and annual and multi-year pack ice in the Barents Sea were investigated. The community in land-fast sea ice was dominated by pennate diatoms and its composition was more closely related to that of the underlying sediments than was the community of the pack ice, which was dominated by flagellates, dinoflagellates and centric diatoms. Algae were far more abundant in land-fast ice: motile benthic and ice-benthic species found favourable conditions in the ice. The pack ice community was more closely related to that of the surrounding water. It originated from plankton incorporation during sea ice formation and during seawater flood events. An additional source for ice colonization may be multi-year ice. Algae may be released from the ice during brine drainage or sea ice melting. Many sea ice algae developed spores before the ice melt. These algae were observed in the above-bottom sediment traps all year around. Three possible fates of ice algae can be distinguished: 1) suspension in the water column, 2) sinking to the bottom and 3) ingestion by herbivores in the ice, at the ice-water interface or in the water column.

Sea ice algae in the White and Barents seas: composition and origin

To examine algae populations, three expeditions (in March 2001, April 2002 and February 2003) were conducted in the Guba Chupa (Chupa Estuary; north-western White Sea), and one cruise was carried out in the open part of the White Sea in April 2003 and in the northern part of the Barents Sea in July 2001. Sea ice algae and phytoplankton composition and abundance and the content of sediment traps under the land-fast ice in the White Sea and annual and multi-year pack ice in the Barents Sea were investigated. The community in land-fast sea ice was dominated by pennate diatoms and its composition was more closely related to that of the underlying sediments than was the community of the pack ice, which was dominated by flagellates, dinoflagellates and centric diatoms. Algae were far more abundant in land-fast ice: motile benthic and ice-benthic species found favourable conditions in the ice. The pack ice community was more closely related to that of the surrounding water. It originated from plankton incorporation during sea ice formation and during seawater flood events. An additional source for ice colonization may be multi-year ice. Algae may be released from the ice during brine drainage or sea ice melting. Many sea ice algae developed spores before the ice melt. These algae were observed in the above-bottom sediment traps all year around. Three possible fates of ice algae can be distinguished: 1) suspension in the water column, 2) sinking to the bottom and 3) ingestion by herbivores in the ice, at the ice-water interface or in the water column.

Comparison between in situ and MODIS-derived spectral reflectances of snow and sea ice in the Amundsen Sea, Antarctica

The spectral albedo and directional reflectance of snow and sea ice were measured on sea ice of various types, including nilas, grey ice, pancake ice, multi-year pack ice, and land-fast ice in the Ross, Amundsen and Bellingshausen seas during a summer cruise in February through March 2000. Measurements were made using a spectroradiometer that has 512 channels in the visible and near-infrared (VNIR) region in which 16 of the 36 bands of the Moderate Resolution Imaging Spectroradiometer (MODIS) are covered. Directional reflectance is also retrieved from the MODIS radiometrically calibrated data (Level 1B) concurrently acquired from the first National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) satellite, Terra. The locations of the ground ice stations are identified accurately on the MODIS images, and the spectral albedo and directional reflectance values at the 16 VNIR MODIS bands are extracted for those pixel locations. MODIS-derived reflectance is then corrected for the intervening atmosphere whose parameters are retrieved from the MODIS atmospheric profiles product (MOD07_L2) for the same granule. The corresponding spectral albedo and directional reflectance with the same viewing geometry as MODIS are derived from our ground-based spectroradiometer measurements. Because the footprint of the ground spectroradiometer is much smaller than the pixel sizes of MODIS images, the averaged spectral reflectance and albedo in the vicinity of each ice station are simulated for the corresponding MODIS pixel from the ground spectral measurements by weighting over different surface types (various ice types and open water). An accurate determination of ice concentration is important in deriving ground reflectance of a simulated pixel from in situ measurements. The best agreement between the in situ and MODIS measurements was found when the ground had 10/10 ice concentration (discrepancy range 0.2–11.69%, average 4.8%) or was oneice-type dominant (discrepancy range 0.8–16.9%, average 6.2%). The more homogeneous the ground surface and the less variable the ground topography, the more comparable between the in situ and satellite-derived reflectance is expected.

Sea Ice-Albedo Climate Feedback Mechanism

Abstract The sea ice-albedo feedback mechanism over the Arctic Ocean multiyear sea ice is investigated by conducting a series of experiments using several one-dimensional models of the coupled sea ice-atmosphere system. In its simplest form, ice-albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature, further decreasing the areal cover of snow and ice. It is shown that the sea ice-albedo feedback can operate even in multiyear pack ice, without the disappearance of this ice, associated with internal processes occurring within the multiyear ice pack (e.g., duration of the snow cover, ice thickness, ice distribution, lead fraction, and melt pond characteristics). The strength of the ice-albedo feedback mechanism is compared for several different thermodynamic sea ice models: a new model that includes ice thickness distribution, the Ebert and Curry model, the Maykut and Untersteiner model, and the Semtner level-3 an...

Low‐frequency vibrational motion of Arctic pack ice

The mechanisms responsible for vibrational motions of Arctic ice at frequencies below about 100 Hz are know to be a combination of wave types, namely, gravity waves, flexural waves, and a variety of acoustic and/or elastic waves. Surface motion measurements using geophones and accelerometers on multiyear pack ice are used to establish the energy level of these motions and to differentiate between the different modes of propagation. Gravity waves are dominant below about 0.05 Hz, with their direction and dispersion relation being confirmed with vector measurements of acceleration from two stations. Motions driven by surface pressure fluctuations in the local wind appear at somewhat higher frequencies up to about 0.3 Hz and are particularly evident on thinner first‐year ice during periods of high wind. The band from 0.1 to 10 Hz comprises mainly flexural waves, as determined by their dispersion relation, and these are prominent during local ridge building events. At frequencies above 10 Hz, there is a combination of acoustic and flexural modes of propagation, with one or the other being dominant during specific environmental events. The probability density function of power in octave wide bands is approximately lognormal as a result of the high level of intermittence of local events. The variance in power level is significantly smaller for waterborne noise from more distant sources. Specific examples are used to illustrate the nature of the events.

Behavioral and Physiological Characteristics of the Antarctic Krill,Euphausia superba

The antarctic krill, Euphausia superba , is considered a success in the intensely seasonal environment of the Southern Ocean because of its abundance and central role as an important food item for many of the larger carnivores in the ecosystem. The behavioral and physiological characteristics that foster this success are: (1) the ability to find concentrations of food in several types of habitat and efficiently exploit whatever food is available; (2) the close correspondence of the life cycle with seasonal cycles of food availability; and (3) a combination of physiological mechanisms that enable krill to survive the long winter period of low food availability. We evaluated the relative importance of the following four major winter-over mechanisms that have been proposed for adult krill west of the Antarctic Peninsula. The three-fold reduction in metabolic rate is the most important winter-over mechanism for these adults, although lipid utilization and shrinkage also help satisfy energy requirements in the winter. Alternate food sources did not appear to contribute significantly as a winter energy source. However, the extent, predictability and complexity of the ice cover in a region during winter may have a great influence on the relative importance of these winter-over mechanisms for different populations. Ice cover in the waters west of the Antarctic Peninsula is unpredictable and smooth surfaced when it occurs, providing the krill with little refuge from predation. In multi-year pack ice of the Weddell Sea, however, ice cover is predictable and extensive, and there is a complex undersurface that provides hiding places. In this multi-year ice, adult krill have been observed under the ice feeding, whereas west of the Antarctic Peninsula most adult krill are in the water column in the winter and are not feeding. The balance between acquiring energy and avoiding predation may be different in these two regions in the winter because of differences in predictability and complexity of the ice cover.

High‐frequency under‐ice reflection losses and spatial coherence

Propagation of high‐frequency acoustic signals under a multiyear pack ice results in a scattered acoustic field of fluctuating amplitude and coherence. High‐frequency scattering from under‐ice surfaces is complicated by out‐of‐plane and multiple scattering because acoustic wavelengths may be many orders of magnitude smaller than ice relief. In addition, the transition layer between water and ice, ice inhomogeneities, and ice anisotropy become important scattering sources. Measurements are presented of horizontal spatial coherence at 24 and 42 kHz from linear FM slide pulses of 800‐Hz bandwidth and 100‐ms duration. Measurements were made with a linear array of 16 hydrophones distributed over a 16‐m aperture and deployed 61 m below the ice surface. The data presented here were taken at a nominal range of 1000 m and results from array bearings at endfire, broadside, and 45° are compared. Results are presented for a fixed source at depths of 30, 61, and 91 m. Deconvolution of the source waveform is used to separate direct and reflected arrivals. Relative amplitudes of these arrivals are compared with what would be expected for a perfect reflector. The amplitude differences may be as high as 30 dB and the ice reflected coherence may increase slightly with range. In addition to hydrophone spacing, frequency, and source depth, the reflected arrival coherence is found to be sensitive to the physical location of the hydrophone in the aperture. This sensitivity is due to multipath interference from the scattering region. [Work supported by the Office of Naval Technology.]

Ice island detection and characterization with airborne synthetic aperture radar

A 1∶300,000 scale airborne synthetic aperture radar (SAR) image of an area of the Arctic Ocean adjacent to the Queen Elizabeth Islands, Canadian High Arctic, is examined to determine the number and characteristics of ice islands in the image and to assess the capability of airborne and satellite SAR to detect ice islands. Twelve ice islands have been identified, and their dimensions range from as large as 5.7 km by 8.7 km to as small as 0.15 km by 0.25 km. A significant SAR characteristic of the shelf ice portions of ice islands is a return with a ribbed texture of alternating lighter and darker grey tones resulting from the undulating shelf ice surfaces of the ice islands. The appearance of the ribbed texture varies according to the ice islands' orientation relative to the illumination direction and consequently the incidence angle. Some ice islands also include extensive areas of textureless dark tone attached to the shelf ice. The weak returns correspond to (1) multiyear landfast sea ice that was attached to the front of the Ward Hunt Ice Shelf at the time of calving and which has remained attached since then and (2) multiyear pack ice that has become attached and consolidated since the calving, indicating that ice islands can increase their area and mass significantly as they drift. Other SAR characteristics include straight, bright returns along the edges arising from sea ice pressure ridges or shelf ice cliffs. Other physical characteristics of ice islands that make them identifiable in SAR images include their greater size and shapes longer, thinner, and more angular than those of surrounding pack ice floes. It is evident that ice islands are easily discernible in SAR images and for the future SAR represents a promising technique to obtain a census of ice islands in the Arctic Ocean. However, any SAR‐based census probably will be conservative because ice islands smaller than 300–400 m across are likely to remain undetected, particularly in areas of heavy ice ridging which produces strong SAR clutter.

An early Holocene narwhal tusk from the Canadian high Arctic

A narwhal (Monodon monoceros) tusk from 34 m above sea level and located at 82°N on the northwest coast of Ellesmere Island has been radiocarbon dated at 6,830 ± 50 B.P. It was collected from a narrow coastal strip which is isolated from the adjacent Arctic Ocean by glacier ice, ice shelf and multiyear pack ice. The specimen represents an early Holocene range extension of 400–700 km over the present. Because the narwhal requires abundant open water to survive, the Holocene tusk is an important independent item of proxy data on palaeoclimatic change. Contemporary migration routes are directly related to seasonal sea ice in the inter‐island channels of the central Canadian Arctic archipelago. The presence of a narwhal on the northwest Ellesmere Island coast at 6,830 ± 50 B. P. suggests that sea ice and ice‐shelf conditions were more favourable at that time. A comprehensive chronological framework for late Quaternary and Holocene geomorphic/climatic events from northern Ellesmere Island records a warm early Holocene characterized by abundant driftwood entry into the high Arctic. This was followed by a mid‐Holocene climatic deterioration during which the ice shelves of the Ellesmere coast formed. Therefore, the narwhal tusk is further evidence that a period of maximum postglacial warmth occurred during the early Holocene in the Canadian high Arctic.

Satellite observations of sea ice

An overview is presented of Antarctic and Arctic sea ice studies using data from the Nimbus-5 ESMR and the Nimbus-7 SMMR passive microwave radiometers. Four years (1973–1976) of ESMR data for the Antarctic Ocean define the characteristics of the seasonal cycle including regional contrasts and interannual variations. Major advances include the discovery of the Weddell polynya and the presence of substantial areas of open water in the Antarctic winter pack ice. Regional differences in sea ice extent on time-scales of about a month are shown to be associated with variations in surface-wind fields. In the Arctic, the computation of sea ice concentration is complicated by the presence of multiyear ice, but the amount of multiyear ice becomes an important measurable quantity with dual-polarized, multifrequency passive microwave sensors. Analysis of SMMR data demonstrates its advantage for studying the spatial and temporal variability of the Arctic ice cover. Large observed interannual variations in the distribution of the multiyear pack ice and the presence of significant divergent areas in the central Arctic during winter contrast markedly with the classical view of the Arctic pack ice.

Construction Of Artificial Islands As Beaufort Sea Drilling Platforms

Abstract The Beaufort Sea environment imposes unique constraints for drilling operations. Activity in the area must overcome wave attacks, multi-year pack ice invasion in the summer and moving ice sheets in the winter. As well, drilling systems must contend with a very short marine season (July to October). For its Beaufort Sea acreage, Imperial Oil Limited decided to use artificial sand islands as drilling platforms. The islands have been designed to withstand waves in the area plus loading of ice sheets up to 7 feet thick. Imperial has constructed 14 islands in' water depths ranging from 5 to 42 feet employing three different construction techniques. Three of the islands were winter-constructed islands. Ice blocks were removed at the site and the island till was placed with material hauled by trucks from onshore gravel deposits. Eight islands were summer-constructed "conventional" islands. An Imperial conventional island consists of sand fill and uses large sandbags to retain a portion of the fill and protect the slopes. Three islands were summer-constructed "sacrificial beach" islands, where the island is protected from wave attack by gradually sloping beaches that force the waves to break, so that their energy is dissipated before they reach the island's working surface. Introduction Potential oil and gas reserves have provided incentive for exploration drilling in the Mackenzie Delta region since the mid 1960's. After several years of onshore activity, the first offshore location was drilled by Imperial Oil Limited in 1,973, from an artificial island.(1,2) In the five years since starting the offshore drilling program, Imperial has constructed fourteen islands in water depths from 5 feet (1.5 m) to 42 feet (12.8 m). Drilling has occurred from thirteen of these islands and has been able to proceed uninterrupted through all seasons. The Arctic offshore environment to which the islands are exposed is harsh and its features have dictated the applicability of islands and influenced their design. Environment of the Southern Beaufort Figure 1 is a map of the area of interest to Imperial. The permit acreage is limited to the shallow waters of the Beaufort Sea, roughly extending from Shingle Point on the Yukon Coast east to the northern tip of the Tuktoyaktuk Peninsula. The northern boundary approximately follows, the 60-foot (18-m) water depth contour, Island construction to date has been concentrated in the Mackenzie Bay and Kugmallit Bay areas. Sea Conditions The open water period usually extends from mid July to early October. About 1 year in 5, the open water season is half the average, with break-up two to three weeks late and freeze-up two to three weeks early.(3) Wave conditions in the Beaufort Sea are quite mild when compared with other ocean areas, because ‘both’ the fetch and the water depth are limited. The available fetch is restricted by the closeness of the Polar ice pack in the summer (usually within 200 miles). In the shallow water regions, the significant wave height is limited to 40% (±5%) of the water depth. Higher waves break and dissipate their energy.