Northern Chukchi Sea Research Articles

Uptake of atmospheric carbon dioxide in Arctic shelf seas: evaluation of the relative importance of processes that influence pCO 2 in water transported over the Bering–Chukchi Sea shelf

The uptake of atmospheric carbon dioxide in the water transported over the Bering–Chukchi shelves has been assessed from the change in carbon-related chemical constituents. The calculated uptake of atmospheric CO 2 from the time that the water enters the Bering Sea shelf until it reaches the northern Chukchi Sea shelf slope (∼1 year) was estimated to be 86±22 g C m −2 in the upper 100 m. Combining the average uptake per m 3 with a volume flow of 0.83×10 6 m 3 s −1 through the Bering Strait yields a flux of 22×10 12 g C year −1. We have also estimated the relative contribution from cooling, biology, freshening, CaCO 3 dissolution, and denitrification for the modification of the seawater pCO 2 over the shelf. The latter three had negligible impact on pCO 2 compared to biology and cooling. Biology was found to be almost twice as important as cooling for lowering the pCO 2 in the water on the Bering–Chukchi shelves. Those results were compared with earlier surveys made in the Barents Sea, where the uptake of atmospheric CO 2 was about half that estimated in the Bering–Chukchi Seas. Cooling and biology were of nearly equal significance in the Barents Sea in driving the flux of CO 2 into the ocean. The differences between the two regions are discussed. The loss of inorganic carbon due to primary production was estimated from the change in phosphate concentration in the water column. A larger loss of nitrate relative to phosphate compared to the classical ΔN/ΔP ratio of 16 was found. This excess loss was about 30% of the initial nitrate concentration and could possibly be explained by denitrification in the sediment of the Bering and Chukchi Seas.

Drift Velocities of Ice Floes in Alaska's Northern Chukchi Sea Flaw Zone : Determinants of Success by Spring Subsistence Whalers in 2000 and 2001

By March each year, coast-influenced sea ice in Alaska's northern Chukchi Sea consists of the shorefast ice itself plus ice floes moving in a zone that extends from immediately beyond the shorefast ice to coherent pack ice, some 100 km farther offshore. Because westward-drifting polar pack ice encounters fewer landmasses (and less resistance from them) once it passes Point Barrow, a semipermanent polynya or flaw zone dominates coastal ice in this region. Inupiat residents use open water in flaw leads to hunt migrating bowhead whales from mid-April to early June. Although Inupiat hunters grasp the nature and importance of ice in motion beyond their horizon, the flaw zone has received less scientific attention than either shorefast ice or polar pack ice farther offshore. Synthetic aperture radar (SAR) satellite imagery is a form of remote sensing recently made available that allows us to address ice movement at a spatial scale familiar to traditional hunters. SAR-tracked ice movements differed between 2000 and 2001, illustrating contrasts between adverse and optimal conditions for spring whaling at Barrow. Case studies of ice-floe accelerations in the two contrasting seasons suggest that many variables influence ice motion. These include weather, seafloor topography, currents, sea-level changes, and events that occurred earlier during an annual accretion of ice. Adequate prediction of threats to ice integrity in the northern Chukchi Sea will require adjustments of our current concepts, including 1) recognizing the pervasive influence of the flaw zone; 2) replacing a focus on vessel safety in ice-dominated waters with an emphasis on ice integrity in high-energy environments; and 3) chronicling ice motions through coordinated ground observation and remote sensing of March-June events in future field studies.

Sources of sediment found in sea ice from the western Arctic Ocean, new insights into processes of entrainment and drift patterns

The geochemical fingerprint of entrained Fe oxide mineral grains in Arctic Ocean sea ice is used to determine precise sources of this sediment. This approach substantiates the importance of the Laptev Sea as a source of sea ice and even the presence of Russian ice in the Beaufort Sea off Alaska. Fe oxide grains from the Laptev Sea were found in floes in the Beaufort Sea, Chukchi Borderland, and central Arctic Ocean, demonstrating the importance of sea ice in distributing itself throughout the Arctic Ocean and the potential of transporting sediment from Russian rivers to North American shelves. Banks Island shelf is the most important source of sediment sampled from ice floes in the Beaufort Sea, northern Chukchi Sea, and Chukchi Borderland area. Although most of the entrained sediment fits the criteria for suspension freezing in shallow water, the presence of winter polynyas with offshore winds and not the size of shallow areas appears to be the critical factor for sea ice entrainment. Seven of the 18 ice floes sampled contained Fe oxide grains from more than one source area. The two most common sources that are found in the same ice floes are Banks Island and the Laptev Sea. Multiple sources in ice floes suggest that either mingling of fragmented ice floes occurs or that a source area containing grains from both these sources has yet to be located. The addition of fine, sand‐sized, windblown sediment is not thought to be significant.

Tracer studies of pathways and rates of meltwater transport through Arctic summer sea ice

At the Surface Heat Budget of the Arctic Ocean (SHEBA) program's field site in the northern Chukchi Sea, snow and ice meltwater flow was found to have a strong impact on the heat and mass balance of sea ice during the summer of 1998. Pathways and rates of meltwater transport were derived from tracer studies (H218O, 7Be, and release of fluorescent dyes), complemented by in situ sea‐ice permeability measurements. It was shown that the balance between meltwater supply at the surface (averaging between 3.5 and 10.5 mm d−1) and ice permeability (between <10−11 and >10−9 m2) determines the retention and pooling of meltwater, which in turn controls ice albedo. We found that the seasonal evolution of first‐year and multiyear ice permeability and surface morphology determine four distinct stages of melt. At the start of the ablation season (stage 1), ponding is widespread and lateral melt flow dominates. Several tens of cubic meters of meltwater per day were found to drain hundreds to thousands of square meters of ice through flaws and permeable zones. Significant formation of underwater ice, composed between <30 and >50% of meteoric water, formed at these drainage sites. Complete removal of snow cover, increase in ice permeability, and reductions in hydraulic gradients driving fluid flow mark stage 2, concurrent with a reduction in pond coverage and albedo. During stage 3, maximum permeabilities were measured, with surface meltwater penetrating to 1 m depth in the ice and convective overturning and desalination found to dominate the lower layers of first‐year and thin multiyear ice. Enhanced fluid flow into flaws and permeable zones was observed to promote ice floe breakup and disintegration, concurrent with increases in pond salinities and 7Be. Advective heat flows of several tens of watts per square meter were derived, promoting widening of ponds and increases in pond coverage. Stage 4 corresponds to freeze‐up. Roughly 40% of the total surface melt was retained by the ice cover within the ice matrix as well as in surface and under‐ice ponds (with a total net retention of 15%). Based on this work, areas of improvement for fully prognostic simulations of ice albedo are identified, calling for parameterizations of sea‐ice permeability and the integration of ice topography and refined ablation schemes into atmosphere‐ice‐ocean models.

Indirect measurements of the mass balance of summer Arctic sea ice with an electromagnetic induction technique

AbstractIn the framework of the Surface Heat Budget of the Arctic (SHEBA) study, indirect, non-invasive ice mass-balance measurements were carried out at a drifting station in the northern Chukchi Sea between May and August 1998. Ice thickness was derived from electromagnetic induction (EM) measurements of apparent conductivity along 13 profiles (60−900 m long). As shown through sensitivity studies with a one-dimensional model, the apparent conductivity data from individual points can be inverted to yield estimates of ice thickness and ablation with an accuracy of approximately 0.05 m (for 2 m thick level ice). Ablation rates were 8−18 mm d−1, with total ablation amounting to roughly 0.9−1.2 m. Measurements of thickness and melt rates along different profiles in undeformed multi-year ice corresponded closely, indicating that the sampling statistics are adequate. The roughness of undeformed ice has been found to increase during the summer due to deepening of melt ponds and enhanced bottom melt. Ice under melt ponds was disproportionately thinner, most likely a result of thicker snow cover reducing winter accretion.

Variability of Cetacean Distribution and Habitat Selection in the Alaskan Arctic, Autumn 1982-91

Ten years (1982-91) of autumn sighting data from aerial surveys offshore northern Alaska were analyzed to investigate variability in cetacean distribution and habitat selection. Habitat selection indices were calculated for bowhead, white, and gray whales in heavy, moderate, and light ice conditions; and for high, moderate, and low transport (inflow) conditions at Bering Strait. Bowhead whales selected shallow inner-shelf waters during moderate and light ice, and deeper slope habitat in heavy ice conditions (chi², p < 0.05-0.001). White whales selected slope habitat (chi², p < 0.001), and gray whales selected coastal/shoal and shelf/trough habitat (chi², p < 0.025-0.001), in all ice conditions. In the Alaskan Beaufort Sea, bowheads selected shelf waters and white whales chose slope waters, without regard to transport conditions (chi², p < 0.01-0.001). In the northern Chukchi Sea, gray whales selected coastal/shoal habitat in high transport conditions (chi², p < 0.005), and shelf/trough habitat (chi², p < 0.001) during moderate and low transport conditions. Variability in distribution and habitat selection among these species is likely linked to prey availability at dissimilar trophic levels, although this hypothesis has yet to be rigorously tested.

Multiple-Stage Deformation along the Southern Flank of the North Chukchi High, Chukchi Sea, Alaska: ABSTRACT

Structural and stratigraphic relations along the southern edge of the North Chukchi high provide insights into the timing and mechanics of Late Cretaceous and Cenozoic tectonic events in the northern Chukchi Sea. In this area, the easternmost strand of the north-trending Hanna wrench fault zone is deflected to the northeast and terminates in a series of reverse faults along the southern edge of the high. Areas east of the Hanna fault zone were characterized by tectonic stability during this period of time. Within the fault zone, east-west-trending box folds and reverse faults accompanied uplift of the North Chukchi high and erosion of the entire Ellesmerian sequence along its southern margin. Stratigraphic and structural relations indicate that this compressional deformation began during the Early Cretaceous (Albian ) but ceased prior to the Late( ) Cretaceous. During the early Cenozoic( ), the northern part of the Hanna fault zone was reactivated as an extensional systems which controlled the development of a local basin. Some faults which showed an early history of reverse displacement were reactivated as normal faults during this late-stage tectonic event. This data is consistent with a model for Early Cretaceous impingement of adjacent blocks at a constrained corner nearmore » the North Chukchi high during the rift opening of the North Chukchi basin. The compressional deformation ceased prior to the Cenozoic when the opposing blocks in the constrained corner finally escaped past each other. Continued rifting and subsidence of the North Chukchi basin resulted in late-stage extensional overprinting of earlier compressional structures.« less

Quaternary Stratigraphy of Northern Chukchi Sea, Alaska: ABSTRACT

Quaternary Stratigraphy of Northern Chukchi Sea, Alaska: ABSTRACT

Incidental Sighting of a Ribbon Seal (<i>Phoca fasciata</i>) in the Western Beaufort Sea

On 29 August 1983, an adult ribbon seal (Phoca fasciata) was seen by one of us (EIB) resting on ice in the western Beaufort Sea (71 41 N, 152 41 W), during the course of an aerial survey. The seal did not move from the ice when over-flown at 200 m, and was positively identified by its distinctive pelage. Ribbon seals are commonly found along the ice front in the Bering Sea in winter and early spring, then disperse in late spring as the sea ice breaks up and presumably become solitary and pelagic with poorly known distribution in the summer (Wilke, 1954; Naito and Konno, 1979; Burns, 1970, 1981; Stewart and Everett, 1983). Ribbon seals are rarely seen or taken by Eskimo hunters from coastal villages north of the Bering Strait, and sightings at Wainwright and Point Barrow in the northern Chukchi Sea have been described as "most unusual" (Burns, 1981). ... The observed ribbon seal may have drifted north and east with the ice from the Chukchi Sea during the summer. To our knowledge, this report constitutes the northeasternmost record of a ribbon seal.

Fatty acid composition of Pacific walrus skin and blubber fats

The fatty acid composition of skin and blubber lipids was analyzed from four apparently healthy adult Pacific walrus (Odobenus rosmarus divergens) taken in the Bering Sea and one moribund walrus from the vicinity of Barrow in the northern Chukchi Sea. All specimens had similar fatty acid complements; 13 fatty acids predominated ranging from chain lengths of 14 to 22 carbons with zero to six double bonds. There were no major differences between males and females nor between the one lactating and the nonlactating female. There were specific differences from inner blubber to outer blubber and skin and between the four healthy and one moribund animal. Double-bond indices (indicating degree of unsaturation) were relatively high in all samples, which reflects the large amount of long-chain polyunsaturated acids in the skin and blubber lipids. Inner blubber lipids were more highly unsaturated than outer blubber or skin lipids similar to the patterns observed in baleen whales. Melting points of blubber lipid ranged from 2.2 to −6.8 °C for some components; all components melted below 21.5 °C. Fatty acid composition of hind flipper tissues did not differ significantly from those in the trunk skin and blubber.

Geologic Framework and Related Hydrocarbon Potential of Beaufort and Northern Chukchi Seas: ABSTRACT

Geologic Framework and Related Hydrocarbon Potential of Beaufort and Northern Chukchi Seas: ABSTRACT

Holocene Oceanography of Chukchi Sea: ABSTRACT

Piston cores from the southeastern Chukchi Sea have permitted differentiation of modern from Holocene sediments deposited when sea level stood about 20 m lower. Because microfossil distributions in modern sediments are associated closely with ice-free oceanographic conditions, the following trends appear to be related to Holocene oceanographic conditions. Eggerella advena, indicative of warm, dilute Alaskan coastal water, is as abundant in Holocene as in modern sediments, but Reophax arctica, indicative of central shelf water, and Spiroplectammina biformis, indicative of cold bottom water in the northern Chukchi Sea, are much less abundant in Holocene sediments. Frustules of the planktonic diatom Coscinodiscus, presently displaced northward by the Bering Strait current fr m regions of maximum phytoplankton concentrations in the overlying water, are more abundant in Holocene than in modern sediments in cores directly north of Bering Strait. The northward-flowing Bering Strait current controls conditions in the southeastern Chukchi Sea. This flow was reduced during the Holocene because the cross-section area of the strait was smaller; apparently, however, the flow was reduced at the expense of central shelf water as Alaskan coastal water filled the southeastern Chukchi Sea. Although currents were slight in the central part of the southeastern Chukchi Sea, waters still piled up against the coast near the present settlement of Kivalina and produced a high-velocity northwest current. As evidence of this, Holocene sediments northwest of Point Hope contain more plant fragments and sand than nearby areas, and these presumably were deposited from the current. End_of_Article - Last_Page 716------------

Studies of the Mass Budget of Arctic Pack-Ice Floes

Abstract The processes of melting, freezing, precipitation, evaporation and condensation were considered in the computation of the mass budget of an ice floe in the northern Chukchi Sea. It was bound that condensation and evaporation contribute negligible amounts, and that melting accounted for the largest loss from the upper surface of the floe. From an original mass of 270 g. cm.−2 a unit ice column lost 9.2 g. cm.−2 by melting of snow and 35.2 g. cm.−2 by melting of ice during the melt season. During the freezing period 5.8 g. cm.−2 were regained by the accumulation of snow and frost. Measurements at the bottom of the ice indicate an estimated net loss of 5 g. cm.−2 over a seven-month study. A comparison of six summers at three stations shows no obvious correlation of ablation and latitude, and an average loss of ice at the surface of 40 g. cm.−2.

Studies of the Mass Budget of Arctic Pack-Ice Floes

AbstractThe processes of melting, freezing, precipitation, evaporation and condensation were considered in the computation of the mass budget of an ice floe in the northern Chukchi Sea. It was bound that condensation and evaporation contribute negligible amounts, and that melting accounted for the largest loss from the upper surface of the floe. From an original mass of 270 g. cm.−2 a unit ice column lost 9.2 g. cm.−2 by melting of snow and 35.2 g. cm.−2 by melting of ice during the melt season. During the freezing period 5.8 g. cm.−2 were regained by the accumulation of snow and frost. Measurements at the bottom of the ice indicate an estimated net loss of 5 g. cm.−2 over a seven-month study. A comparison of six summers at three stations shows no obvious correlation of ablation and latitude, and an average loss of ice at the surface of 40 g. cm.−2.

A long range seismic-recording buoy

The transport of Pacific-origin water across the eastern Chukchi Sea during summer is studied using shipboard hydrographic and Acoustic Doppler Current Profiler data from multiple surveys. The study identifies two major transport pathways in this region. The well-known Alaskan Coastal Current (ACC) flows poleward along the Alaska coast, while a more recently discovered and slower current flows northward through the Central Channel between Herald and Hanna Shoals. The two currents separate past Point Hope and appear to merge again in Barrow Canyon via previously unresolved pathways flowing west to east across the Chukchi Sea. The collective flow that transports Pacific water from Bering Strait to Barrow Canyon is termed the Bering to Barrow Current System (BBCS). The coastal branch of the BBCS, which encompasses the ACC, is a weakly baroclinic flow with a maximum speed in excess of 80 cm/s inside Barrow Canyon. The Central Channel branch of the BBCS is considerably weaker, with a maximum flow speed under 20 cm/s. A portion of the Pacific water that flows towards Herald Canyon to the west may also contribute to the BBCS, the amount, but the amount is within the margin of error of our data. The difference in the advective time scales of the various branches allows water masses of different seasonal characteristics to be transported simultaneously by the BBCS. Summer water masses occupy most of the southern and central Chukchi Sea while winter water masses occupy Hanna Shoal and shelfbreak regions in the northern Chukchi Sea during summer. The total BBCS volume transport in summer is measured at four different locations in the eastern Chukchi Sea and found to be generally consistent. The overall mean transport is 0.86 Sv, compared to the summer Bering Strait transport of 1.08 Sv. This study suggests that the BBCS is the main transport pathway delivering Pacific water masses into the western Arctic Basin.