Search

The Bruun/Dean relation between water depth and distance from the shore with a constant profile shape factor is widely used to describe shoreface profiles in temperate environments. However, it has been shown that the sediment scale parameter (A) and the profile shape factor (m) are interrelated variables. An analysis of 63 Arctic erosional shoreface profiles shows that both coefficients are highly variable. Relative frequency of the average m value is only 16% by the class width 0.1. No other m value frequency exceeds 21%. Therefore, there is insufficient reason to use average m to characterize Arctic shoreface profile shape. The shape of each profile has a definite combination of A and m values. Coefficients A and m show a distinct inverse relationship, as in temperate climate. A dependence of m values on coastal sediment grain size is seen, and m decreases with increasing grain size. With constant m = 0.67, parameter A obtains a dimension unit m1/3. But A equals the water depth in meters 1 m f...

Coastal dynamics and shoreface relief in ice-free seas are a function of hydrodynamic interactions between the sea and bottom sediments. In the Arctic, additional, cryogenic factors such as permafrost and the action of sea ice influence coastal processes. The goal of our paper is to assess this influence, mainly on the profile shape. Mathematical analyses of the shape of 63 shoreface profiles from the Laptev, Beaufort, and Chukchi Seas were carried out. The shapes of Arctic shoreface profiles and those of ice-free seas are compared. We found that large ice and silt content in perennially frozen sediments composing Arctic coasts favor their erosion. Sea ice plays an important role in sediment transport on the shoreface and correspondingly changes shoreface relief significantly. Some effects of ice intensify coastal erosion considerably, but others play a protective role. The overall influence of cryogenic processes on Arctic coasts composed of loose sediments is seen in that the average rate of co...

Dinkum Sands was mapped in 1949 as a small island, one link in a 95-km-long chain of barrier islands near Prudhoe Bay, Alaska. Questions about its status as an Arctic island and the submerged land ownership led to a Federal/State joint monitoring program using topographic surveys, tide gauges, and other approaches. On the basis of the results the Supreme Court concluded that Dinkum Sands is a shoal rather than an island. The shoal attracts the yearly formation of pressure ridges at least as high as 15 m and undergoes drastic changes in location, shape, and elevation. Pressure ridges form from 10-cm-thick new ice when shifting and compression result in crumbling and the introduction of ice slabs into the sandy gravel shoal. This leads to a seasonal increase in shoal volume and height. With summer warming and sea-ice melting, part of the ice in the crest of the shoal (∼50%) melts and its height accordingly drops to below sea level. This lowering requires neither wave action nor lateral sediment transport. The original disappearance of the island in the 1950s, however, probably was not caused by diminished sediment supply from rivers or from coastal erosion, but by diminished local sediment supply through ice pile-ups or by increased erosion from wave attack. Similar changes in sediment volume as those observed in Dinkum Sands probably also occur on fully submerged shoals ranging to water depths of 20 or more meters, which are also marked by seasonal pressure ridge formation.

Anchor ice, i.e., ice attached to the bed in a lake, stream, or ocean, is common in the nearshore zone of southwestern Lake Michigan during winter. Lacustrine anchor ice has at least four distinct morphologies and was observed on sand, pebble, and boulder substrates in water depths to 4 m, the limit of diving traverses. The maximum depth of anchor ice formation may be much greater. Anchor ice is released from the lake bed on mornings following formation events. Released, floating anchor ice carries sediment to the water surface. This sediment is ice-rafted along shore and offshore under the influence of prevailing winds. We estimate that 0.85 m3 of sand per meter of beach is being removed from the nearshore zone of southwestern Lake Michigan by anchor ice annually. Melting ice drops this sand in deep water far from shore. This is a significant loss of sand from the sediment-starved nearshore zone of southwestern Lake Michigan.

This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45x10(6) t a(-1)) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10x10(6) t a(-1), more than 70% of which an related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. Ln the Laptev Sea sediment input by coastal erosion (58.4x10(6) t a(-1)) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6x10(6) t a(-1) is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.

Sea ice characteristics were investigated during July and August on the 1994 transect across the Arctic Ocean. Properties examined from ice cores included salinity, temperature, and ice structure. Salinities measured near zero at the surface, increasing to 3–4‰ at the ice-water interface. Ice crystal texture was dominated by columnar ice, comprising 90% of the ice sampled. Surface albedos of various ice types, measured with radiometers, showed integrated shortwave albedos of 0.1 to 0.3 for melt ponds, 0.5 for bare, discolored ice, and 0.6 to 0.8 for a deteriorated surface or snow-covered ice. Aerial photography was utilized to document the distribution of open melt ponds, which decreased from 12% coverage of the ice surface in late July at 76°N to almost none in mid-August at 88°N. Most melt ponds were shallow, and depth bore no relationship to size. Sediment was pervasive from the southern Chukchi Sea to the north pole, occurring in bands or patches. It was absent in the Eurasian Arctic, where it had been observed on earlier expeditions. Calculations of reverse trajectories of the sediment-bearing floes suggest that the southernmost sediment was entrained during ice formation in the Beaufort Sea while more northerly samples probably originated in the East Siberian Sea, some as far west as the New Siberian Islands.

Modern dispersal of sea-ice-rafted debris (IRD) is important for the Arctic Ocean sediment budget from sources to sinks. Sediment entrainment occurs mainly through the action of small ice crystals (frazil) attaching to sedimentary particles in shallow water, a mechanism that could be selective. The principal source for entrainment of IRD by suspension freezing into the Beaufort Gyre, western Arctic Ocean, is the adjacent shallow ( 250 m) lithology, and carbon and carbonate content of IRD in the Beaufort Gyre were compared to sediments from the probable source surface, in order to determine whether preferential entrainment occurs with any of these sediment parameters. IRD is generally much finer grained than the source surface, showing that silt- and clay-size particles are preferentially entrained by frazil ice, although anchor ice can locally incorporate very high percentages of sand and coarser clasts. The coarsest IRD is also the most poorly sorted. The clay mineralogy of the < 2 m IRD fraction is very similar to that of the source surface, indicating no selective entrainment within the clay fraction. The lithology of sand in IRD also matches that of the source surface, although the number of coarse grains is too small (< 100) in most samples for a statistically meaningful count. The average organic-carbon content of IRD is three times higher than that of the source surface, but we attribute this to summer algal growth on ice floes rather than to selective entrainment. A relatively low carbonate content in IRD may be because much of the carbonate in the source is of silt size while about 50% of the IRD measured is clay size. The low carbonate content may also reflect solution under acidic summer conditions on sea ice. Selective export of silt- and clay-size particles by ice rafting from the shallow shelf with time should lead to the formation of a slightly coarser lag, even though some of the dirty ice drops its sediment load in the entrainment area. Further mineralogical and lithological analysis on IRD promises to become a useful tool for the study of sediment dispersal paths by drift ice in the Arctic today and in the past, and also for the study of sources of anthropogenic pollutants found in sea ice.

Ice and ice-borne sediments were collected across the Arctic Basin during the Arctic Ocean Section, 1994 (AOS-94), a recent US/Canada trans-Arctic expedition. Sediments were analysed for 137Cs, clay mineralogy and carbon. Concentrations of 137Cs ranged from 5 to 73 Bq kg−1 in the ice-borne sediments. Concentrations of ice samples without sediment were all less than 1 Bq m−3. The sediment sample with the highest 137Cs concentration (73 Bq kg−1) was collected in the Beaufort Sea. This concentration was significantly higher than in bottom sediments collected in the same area, indicating an ice transport mechanism from an area with correspondingly higher concentrations. Recent results from the application of ice transport models and sediment analyses indicate that it is very likely that sediments are transported by ice, from the Siberian shelf areas to the Beaufort Sea.

Based on remote-sensing data and an expedition during August-September 1993, the importance of the Laptev Sea as a source area for sediment-laden sea ice was studied. Ice-core analysis demonstrated the importance of dynamic ice-growth mechanisms as compared to the multi-year cover of the Arctic Basin. Ice-rafted sediment (IRS) was mostly associated with congealed frazil ice, although evidence for other entrainment mechanisms (anchor ice, entrainment into freshwater ice) was also found. Concentrations of suspended particulate matter (SPM) in patches of dirty ice averaged at 156 g m(-3) (standard deviation sigma = 140 g m(-3)), with a background concentration of 5 g m(-3). The potential for sediment entrainment over the broad, shallow Laptev Sea shelf during fall freeze-up was studied through analysis of remote-sensing data and weather-station records for the period 1979-1994. Freeze-up commences on 26 September (sigma = 7 d) and is completed after 19 days (sigma = 6 d). Meteorological conditions as well as ice extent prior to and during freeze-up vary considerably, the open-water area ranging between 107 x 10(3) and 447 x 10(3) km(2). Ice motion and transport of IRS were derived from satellite imagery and drifting buoys for the period during and after the expedition (mean ice velocities of 0.04 and 0.05 m s(-1), respectively). With a best-estimate sediment load of 16 t km(-2) (ranging between 9 and 46 t km(-2)), sediment export from the eastern Laptev Sea amounts to 4 x 10(6) t yr(-1), with extremes of 2 x 10(6) and 11 x 10(6) t yr(-1). Implications for the sediment budget of the Laptev shelf, in particular with respect to riverine input of SPM, which may be of the same order of magnitude, are discussed.

The winter ice-regime of the 500 km) from the mainland than in the Beaufort Sea. As a result, the annual freeze-up does not incorporate old, deep-draft ice, and with a lack of compression, such deep-draft ice is not generated in situ, as on the Beaufort Sea shelf. The Laptev Sea has as much as 1000 km of fetch at the end of summer, when freezing storms move in and large (6 m) waves can form. Also, for the first three winter months, the polynya lies inshore at a water depth of only 10 m. Turbulence and freezing are excellent conditions for sediment entrainment by frazil and anchor ice, when compared to conditions in the short-fetched Beaufort Sea. We expect entrainment to occur yearly. Different from the intensely ice-gouged Beaufort Sea shelf, hydraulic bedforms probably dominate in the Laptev Sea. Corresponding with the large volume of ice produced, more dense water is generated in the Laptev Sea, possibly accompanied by downslope sediment transport. Thermohaline convection at the midshelf polynya, together with the reduced rate of bottom disruption by ice keels, may enhance benthic productivity and permit establishment of open-shelf benthic communities which in the Beaufort Sea can thrive only in the protection of barrier islands. Indirect evidence for high benthic productivity is found in the presence of walrus, who also require year-round open water. By contrast, lack of a suitable environment restricts walrus from the Beaufort Sea, although over 700 km farther to the south. We could speculate on other consequences of the different ice regimes in the Beaufort and Laptev Seas, but these few examples serve to point out the dangers of exptrapolating from knowledge gained in the North American Arctic to other shallow Arctic shelf settings.

Coastal ice does not protect the coast but enhances erosion by displacing severe winter wave energy from the beach to the shoreface and by entraining and transporting sediment alongshore and offshore. Three aspects of winter ice in Lake Michigan were studied over a 3-year period and found to have an important influence on coastal sediment dynamics and the coastal sediment budget: (1) the influence of coastal ice on shoreface morphology, (2) the transport of littoral sediments by ice, and (3) the formation of anchor and underwater ice as a frequent and important event entraining and transporting sediment. Coastal lake ice includes a belt of mobile brash (ice blocks) and slush and a dynamic nearshore ice complex consisting of an icefoot, a lakeward sequence of wave-generated ice ridges, and intervening ice lagoons. Our studies indicate that the nearshore ice complex contains a sediment load (0.2 - 1.2 t/m of coast) that is roughly equivalent to the average amount of sand eroded from the coastal bluffs and to the amount sand ice-rafted offshore to the deep lake basin each year. Up to 0.28 t/m of coast can be entrained by ice in a single anchor-ice event, and separate events occurred on 15 days in January 1991. The brash/slush belt is the most important system component responsible for ice-induced sediment transport. Estimates of longshore ice drift, ice volume, and ice-borne sediment load suggest that 0.36 to 4.14 × 103 t/d are transported alongshore.

Widespread occurrence of sediment-laden (turbid) sea ice and high concentrations of diatoms and foraminifers in ice have recently been reported from both polar regions. Many possible mechanisms of particle entrainment into ice have been postulated, among which scavenging by rising frazil ice and nucleation or adhesion of ice onto suspended particles appear to be the most likely ones. No reliable experimental data on the mechanisms, however, are available. Because of the importance of turbid ice for sediment transport, tanks for laboratory-scale experiments were constructed, in which frazil crystals produced at the base were monitored rising through water column laden with various types of particulate matter, including plankton. Observations made in salt water are reported here. Over a distance of 1.5 m, frazil

Frazil and anchor ice forming in turbulent, supercooled water have been studied extensively because of problems posed to man-made hydraulic structures. In spite of many incidental observations of interactions of these ice forms with sediment, their geologic effects remain unknown. The present flume study was designed to learn about the effects of salinity, current speed, and sediment type on sediment dynamics in supercooled water. In fresh-water, frazil ice formed flocs as large as 8 cm in diameter that tended to roll along a sandy bottom and collect material from the bed. The heavy flocs often came to rest in the shelter of ripples, forming anchor ice that subsequently was buried by migrating ripples. Burial compressed porous anchor ice into ice-bonded, sediment-rich masses. This process disrupts normal ripple cross-bedding and may produce unique sedimentary structures. Salt-water flocs were smaller, incorporated less bed load, and formed less anchor ice than their fresh-water counterparts. In four experiments, frazil carried a high sediment load only for a short period in supercooled salt water, but released it with slight warming. This suggests that salt-water frazil is either sticky or traps particles only while surrounded by supercooled water (0.05 to 0.1 °C supercooling), a short-lived phase in simple, small tanks. Salt water anchor ice formed readily on blocks of ice-bonded sediment, which may be common in nature. The theoretical maximum sediment load in neutrally-buoyant ice/sediment mixture is 122 g/l, never reported in nature so far. The maximum sediment load measured in this laboratory study was 88 g/l. Such high theoretical and measured sediment concentrations suggest that frazil and anchor ice are important sediment transport agents in rivers and oceans.

Ice observations and sediment samples were collected in the Beaufort Gyre in 1988. Fine sediment occurred in very small patches of turbid ice, as thin spotty surface layers, in mud pellets or in old snowdrifts. The latter were widespread south of 74°N, containing an estimated 22 tonnes of silt and clay km−2. Average particle concentration in sea ice (40mg l−1) was much higher than in sea water (0.8 mg l−1) or in new snow, but the sediment load was significantly smaller and of finer texture compared to that observed in a shelfal source area after a major entrainment event. About 30% of the sediment consisted of small pellets. Mud in pellets has similar texture, clay minerals and organic/inorganic carbon content as dispersed mud. Particle sizes −1). Therefore, modern sea-ice rafting represents a substantial fraction of the total Arctic Ocean sediment budget.

Ice observations and sediment collected in a summer transit through the Northwest Passage provide insights on suspension freezing, the most important sediment entrainment mechanism for the Arctic Ocean. No evidence was seen for entrainment by bottom adfreezing, bluff slumping, river flooding, dragging ice keels, or significant eolian transport from land to sea. Lack of eolian sediment loading in the Northwest Passage, together with that already reported for northern Alaska, eliminates wind as an important source for fine sediment in the pack of the Beaufort Gyre and related parts of the Transpolar Drift. Muddy sediment with pebbles and cobbles, algae with holdfasts, ostracodes with appendages, and well-preserved mollusks and sea urchins were collected from two sites in a 50 km long stretch of turbid ice. These materials indicate that suspension freezing reaching to a water depth of 25–30 m during the previous fall was responsible for entrainment. This mechanism requires rapid ice formation in open, shallow water during a freezing storm, when the ocean becomes supercooled, and frazil and anchor ice attach to and ultimately lift sediment and living organisms to the sea surface. The mechanism, already known to be important in the Beaufort Sea, probably also affects wide, shallow Siberian shelves and leads to cross-shelf transport of shallow-water organisms and dropstones with "glacial striations" toward deep basins. This makes distinguishing glacial–interglacial cycles more difficult.

The orientations and termination directions of newly formed ice gouges, identified in a 5-year study of two offshore corridors in eastern Harrison Bay, Alasaka, indicate a bimodal distribution of sediment transport directions: west-southwest and southeast, due to ice-keel bulldozing. The westerly sediment transport results from the dominant westward drift of sea ice and ocean currents, whereas the southeasterly transport results from episodic fall storms with winds from the northwest. Transport associated with ice gouging occurs by bulldozing and by resuspension during the bulldozing processes. Fine-grained ( μ m) sediment transport may also involve transport of resuspended sediment by intensified currents found near the grounded floes, leaving behind a lag of coarser sediments. In Harrison Bay, about 6000 m 3 of sediment is reworked each year by ice gouging for every square kilometer of the seafloor between water depths of 5 and 18 m. Over 50% of this sediment is moved onshore to the southeast, whereas 35% is moved alongshore to the west. The actual distance of sediment transport is dependent upon the grain size of the seafloor sediment. Coarse-grained material (> 63 μ m) is bulldozed as far as 7 m in the direction of ice movement, whereas sediment finer than 63 μm may be transported by intensified bottom currents up to 80 times this distance.

The surface morphology of the northern slope of the Brooks Range (North Slope) from the Canning River, Alaska, eastward is dominated by a series of large alluvial fans and braided streams floored by coarse alluvium. On the basis of the absence of sediment on the seasonal sea ice after spring flooding, the measured stability of fan fronts during a 30year period, and the sparsity or absence of Holocene marine sedimentary deposits seaward of the fans, we conclude that the fans are not prograding now nor have they been prograding at any time during the Holocene. In numerous areas, surficial fan alluvium terminates on land at or below 2-m-thick glaciomarine deposits. These deposits, the Flaxman Member of the Gubik Formation, formed during the latest major interglacial transgression (oxygen-isotope stage 5a), about 85-80 ka. We therefore believe that the fans are still older. Our observations suggest that during the latest transgression and the following sea-level highstand, the North Slope depositional environment and climate differed greatly from the present ones.

Ice rafting is the dominant mechanism responsible for the transport of fine-grained sediments from coastal zones to the deep Arctic Basin. Therefore, the drift of ice-rafted debris (IRD) could be a significant transport mechanism from the shelf to the deep basin for radionuclides originating from nuclear fuel cycle activities and released to coastal Arctic regions of the former Soviet Union. In this study, 28 samples of IRD collected from the Arctic ice pack during expeditions in 1989-95 were analyzed for 137Cs by gamma spectrometry and for 239Pu and 240Pu by thermal ionization mass spectrometry. 137Cs concentrations in the IRD ranged from less than 0.2 to 78 Bq/kg (dry weight basis). The two samples with the highest 137Cs concentrations were collected in the vicinity of Franz Josef Land, and their backward trajectories suggest origins in the Kara Sea. Among the lowest 137Cs values are seven measured on sediments entrained on the North American shelf in 1989 and 1995, and sampled on the shelf less than six months later. Concentrations of 239Pu + 240Pu ranged from about 0.02 to 1.8 Bq/kg. The two highest values came from samples collected in the central Canada Basin and near Spitsbergen; calculated backward trajectories suggest at least 14 years of circulation in the Canada Basin in the former case, and an origin near Severnaya Zemlya (at the Kara Sea/Laptev Sea boundary) in the latter case. While most of the IRD samples showed 240Pu/239Pu ratios near the mean global fallout value of 0.185, five of the samples had lower ratios, in the 0.119 to 0.166 range, indicative of mixtures of Pu from fallout and from the reprocessing of weapons-grade Pu. The backward trajectories of these five samples suggest origins in the Kara Sea or near Severnaya Zemlya. Normal.dotm 0 0 1 11 63 University of Calgary 1 1 77 12.0 0 false 18 pt 18 pt 0 0 false false false Key words: sea ice, ice-rafted debris, radionuclides, cesium-137, plutonium

Detailed studies of the Alaskan Beaufort Sea shelf using fathograms, bottom samples, sono-graphs, photographs and diving observations indicate widespread occurrence of outcrops of overconsolidated mud [Reimnitz et al., 1973; Reimnitz and Barnes, 1974]. The locations at which such outcrops had been recorded were later summarized by Reimnitz et al. [1980], and shown to extend from the shoreface to the outer shelf. Chamberlain [1978] and Chamberlain et al. [1978] thought that overconsolidation was the result of de-watering by a seasonal cycle of freeze/thaw, and divers subsequently confirmed surficially ice-bonded sediments at the onset of winter [Reimnitz et al., 1987]. Based on interpretation of borehole data, Lee and Winters [1985] speculate that overconsolidation most likely was inherited from times of shelf-surface exposure to the cold atmosphere during the last glaciation.

Distinctive surficial morphology (Fig. 1) and stratification are generated when sea-ice keels are driven along the seabed in the Beaufort Sea (Fig. 2). The morphology consists of linear ice-gouge furrows that criss-cross extensive shallow shelves in overlapping patterns (Fig. 3). Intense ice gouging in the Arctic is associated with the stamukhi zone [Reimnitz and Barnes, 1974], where sea-ice ridges form and are grounded on the shelf between 15–50 m water depth. Ice gouges in the Beaufort Sea typically are incised 1 m into the sea floor with maximum incisions over 4 m deep, relief of over 7 m and densities greater than 200 km-2 [Barnes et al., 1984]. The orientations and terminations of ice gouges indicate oblique uphill scouring as well as strong shore-parallel movement. Sea-floor morphology linked to studies of ice motion at Barrow, Alaska (Fig. 4) support the idea that gouging occurred during ice break-up [Shapiro and Barnes, 1991]. In contrast, investigations of ice-gouge terminations off Canada indicate ice-push events resulted from ice motion in response to storms during freeze-up [Hequette et al.,1995].

Sea-bed morphology and stratigraphy changes can be linked to sea-ice zonation on Arctic shelves. The stamukhi zone [Reimnitiz et al., 1978] marks the boundary between the moving arctic pack ice and more stable coastal ice, and it is composed of abundant coast-parallel, shear and pressure ridges of sea ice in water depths of 15–50 m (Fig. 1). Many of the stamukhi zone ice ridges form in the same location year after year. Most of the larger ice ridges of the stamukhi zone are grounded. This is a zone where a large amount of energy is expended building ice ridges and gouging the sea floor [Barnes et al., 1984].Inshore of this zone, smoother and less deformed fast ice extends to the coast. The sea-floor features associated with this boundary include an extensive series of shoals [Reimnitz et al., 1984] and a pronounced break in slope or knickpoint at about 20 m depth [Barnes et al., 1987].

The irregular morphology of the Beaufort Sea shoreface consists of broad, gentle depressions and rounded knolls, as revealed in contour charts prepared from U.S. Coast and Geodetic Survey data (Fig. 1), and a detailed diving-observations diagram (Fig. 2) [Reimnitz et al., 1972; Reimnitz and Barnes, 1974]. In most summers, this shoreface is marked by grounded ice floes, a relationship that has been noted in our earliest investigations of the area [Reimnitz et al., 1972]. Closely spaced, tightly navigated, and repeated bathymetric surveys were used to explain the morphology as dynamic ice-wallow relief [Reimnitz and Kempema, 1982]. The action of grounded ice wobbling on the bottom in a seaway, and of intensified currents scouring around grounded ice keels that present obstacles to flow, produces the characteristic relief (Figs. 3 and 4). Relief formation combines erosion and deposition, which result in complex ripple patterns and internal sedimentary structures, as shown in Figs. 3 and 4.

Driftwood appears to be absent in the Beaufort Gyre but abundant in parts of the Transpolar Drift (TPD), which crosses the Arctic Ocean from the Chukchi Sea to the vicinity of northeastern Greenland. Nearly 300 radiocarbon dates on Holocene driftwood from the Canadian Arctic Archipelago reveal two regions with contrasting histories of driftwood incursion: the region accessible to wood brought into Baffin Bay by the West Greenland Current and the rest of the archipelago, which receives wood from the Arctic Ocean. We hypothesize that when the TPD was deflected westward along northern Greenland, wood was delivered widely to the Canadian Arctic Archipelago; when the TPD exited entirely through Fram Strait via the East Greenland Current, little or no wood was delivered to most of the archipelago, but some continued into Baffin Bay via the West Greenland Current. A split TPD delivered wood to both regions. The regional driftwood incursion histories exhibit multiple maxima and minima that can be explained through this hypothesis. The Larix t o Picea ratio of wood arriving in the Canadian Arctic Archipelago has also changed through time. This may indicate varying contributions from Russian versus North American sources, which in turn may indicate variable mixing of wood en route. The inferred discharge paths of the TPD were apparently stable for intervals ranging from several millennia to centuries or perhaps only decades. The last major switch broadly correlates with the onset of Neoglaciation. Variations in the path and strength of the TPD may have important oceanographic and climatic consequences downstream in the North Atlantic Ocean. Key words: driftwood, Transpolar Drift, Beaufort Gyre, sea ice, ocean currents

Strudel scours are craters in the sea floor, typically 3 m deep and 15 m wide, but ranging to as much as 7.5 m deep and greater than 30 m wide (Figs. 1 and 2). They are excavated by vertical drainage spouts of fresh water during the yearly spring flooding of vast reaches of shore-fast ice surrounding arctic deltas (Fig.3)[Reimnitz and Bruder, 1972; Reimnitz et al., 1974]. Off northern Alaska, the craters form as far as 15 km from river mouths, to water depths of 5 to 8 m. In one particular year, an average of 2–3 craters was estimated to have actually formed every km2 across a shallow prodelta, and filled with sandy, organic-rich sediments within a period of 2 to 3 years [Reimnitz and Kempema, 1983; Alpha and Reimnitz, 1995]. Internal sedimentary structures in vibra-cores from Alaskan Arctic deltas record this history of repeated strudel-scour excavation and filling (cut-and-fill), and show that this filling occurs by bedload transport from the east (Fig. 4). Cut-and-fill is also recorded in high-resol-ution seismic profiles of Arctic prodeltas that cross the outer boundary of a flooded area (Fig. 5).

A 20 km wide zone of fast ice, reaching offshore to the 20 m isobath and sealing off coastal embayments along the Taymyr Peninsula, survived until at least 23 November 1993, becoming multiyear land-fast sea ice (MLSI). Barrier islands show characteristic recurved spits indicating dominant southeastward direction of longshore transport in intermittent years. At the time of observation, the fast ice was undisturbed, only heaving vertically with tides, protecting the coastal zone from wave reworking. The 1 to 2 m thick ice cover affects light and oxygen, creating profound effects on marine life in the zone. A herd of walrus, in other summers reported to haul out on local beaches, was displaced by the fast ice. We saw no evidence for sediment loading of the ice by rivers or eolian deposition on ice. MLSI is considered an incipient ice shelf, which could grow in thickness and strength in successive winters. Salinity and delta 18O profiles in ice cores from some smaller areas of MLSI provide a record of environmental conditions during the first year of ice growth, such as local hydrography and contribution of congealed snow to the solid fast ice. On ice charts we found no record of waxing and waning MLSI in the area, and do not know whether the observed ice survived the next summer. Since arctic ice shelves have developed from MLSI in the past, the observed phenomenon permits a view of how transitions from interglacial to full glacial conditions can begin. Key words: multiyear land-fast sea ice, incipient ice shelves, sediment entrainment, interglacial/glacial transition, Siberia, Laptev Sea

Despite the Arctic sea ice cover's recognized sensitivity to environmental change, the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood. Sea ice sediment inclusions were studied in the central Arctic Ocean during the Arctic 91 expedition and in the Laptev Sea (East Siberian Arctic Region Expedition 1992). Results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central Arctic Ocean. This study documents the regional distribution and composition of particle-laden ice, investigates and evaluates processes by which sediment is incorporated into the ice cover, and identifies transport paths and probable depositional centers for the released sediment. In April 1992, sea ice in the Laptev Sea was relatively clean. The sediment occasionally observed was distributed diffusely over the entire ice column, forming turbid ice. Observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment. In the central Arctic Ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes. The surface sediment accumulation in central Arctic multi-year sea ice exceeds by far the amounts observed in first-year ice from the Laptev Sea in April 1992. Sea ice sediments are generally fine grained, although coarse sediments and stones up to 5 cm in diameter are observed. Component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles. The biogenous components, namely shells of pelecypods and benthic foraminiferal tests, point to a shallow, benthic, marine source area. Apparently, sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing. Clay mineralogy of ice-rafted sediments provides information on potential source areas. A smectite maximum in sea ice sediment samples repeatedly occurred between 81°N and 83°N along the Arctic 91 transect, indicating a rather stable and narrow smectite rich ice drift stream of the Transpolar Drift. The smectite concentrations are comparable to those found in both Laptev Sea shelf sediments and anchor ice sediments, pointing to this sea as a potential source area for sea ice sediments. In the central Arctic Ocean sea ice clay mineralogy is significantly different from deep-sea clay mineral distribution patterns. The contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms.

Experiments were performed to evaluate the effects of advancing freeze fronts on movements of fine-grained sediment particles in seawater- and freshwater-slush ice slurries. In the freshwater experiment, the horizontal migrations of clay-sized particles in response to a laterally advancing freeze front were documented photographically. Differential migration of particles as a function of their size was also noted. In the seawater-slush ice experiment involving downward movement of a freeze front through a sediment-laden slush ice layer, time-series measurements were taken for 1) accumulations of sediment released from the ice into the underlying water column, 2) decreases in temperature in the ice matrix, and 3) increases in salinity in the water beneath the ice. Results of the latter experiment support the contention that a downward congealing slush ice matrix can purge itself of at least a portion of an entrained sediment load during an evolving freezing process. However, most of the sediment load initially carried by the slush ice remained at the conclusion of the experiment. This observation has implications for the importance of spatial transport and deposition of ice-rafted sediments to overall sediment budgets in regions affected by sea ice. In summary, migration of sediment particles in congealing slush ice matrices due to freeze front advances can be important to geological, physical and biological processes as well as commercial activities in arctic marine and nearshore regions.

Living with the Coast of Alaska is one of 20 books in the “Living with the Shore” series. It covers a wide range of Alaskan coastal settings, including the ice-stressed shores of the low-relief, desert-like, high Arcticsemi; the coasts of the vast Bering Seasemi; the barren volcanic islands of the Aleutian chainsemi; and south central and southeastern Alaska with their high mountains, large glaciers, steep-sided fjords, heavy precipitation, and active tectonism. Even for the well-seasoned Alaskan, this book offers an education in the incredible diversity of this state's coastal zone. Treating such a broad topic with its multitude of coastal hazards must have been difficult in comparison with other areas covered in the series. But it wasaccomplished quite well through the assistance of experts on coastal hazards and hazard mitigation in construction.

Strong offshore winds in early 1989 produced a shore polynya that reached along the entire north coast of Alaska and eastward beyond the mouth of the Mackenzie River in Canada. From January through...

Landsat-1 and NOAA satellite imagery for the winter 1972–1973, and a variety of ice and sea-floor data were used to study sea-ice zonation and dynamics and their relation to bottom morphology and geology on the Beaufort Sea continental shelf of arctic Alaska. In early winter the location of the boundary between undeformed fast ice and westward-drifting pack ice of the Pacific Gyre is controlled by major coastal promontories. Pronounced linear pressure- and shear-ridges, as well as hummock fields, form along this boundary and are stabilized by grounding, generally between the 10- and 20-m isobaths. Slippage along this boundary occurs intermittently at or seaward of the grounded ridges, forming new grounded ridges in a widening zone, the stamukhi zone, which by late winter extends out to the 40-m isobath. Between intermittent events along the stamukhi zone, pack-ice drift and slippage is continuous along the shelf edge, at average rates of 3–10 km/day. Whether slippage occurs along the stamukhi zone or along the shelf edge, it is restricted to a zone several hundred meters wide, and ice seaward of the slip face moves at uniform rates without discernible drag effects. A causal relationship is seen between the spatial distribution of major ice-ridge systems and offshore shoals downdrift of major coastal promontories. The shoals appear to have migrated shoreward under the influence of ice up to 400 m in the last 25 years. The sea floor seaward of these shoals within the stamukhi zone shows high ice-gouge density, large incision depths, and a high degree of disruption of internal sedimentary structures. The concentration of large ice ridges and our sea floor data in the stamukhi zone indicate that much of the available marine energy is expended here, while the inner shelf and coast, where the relatively undeformed fast ice grows, are sheltered. There is evidence that anomalies in the overall arctic shelf profile are related to sea-ice zonation, ice dynamics, and bottom processes. A proposed ice zonation, including zones of (1) bottom-fast ice, (2) floating fast ice, (3) stamukhi, and (4) seasonal pack ice, emphasizes ice interaction with the shelf surface and differs from previous zonation. Certain aspects of the results reported here are directly applicable to planned offshore developments in the Prudhoe Bay oil field. Properly placed artificial structures similar to offshore shoals should be able to withstand the forces of the ice, serve to modify the observed ice zonation, and might be used to make the environment less hostile to human activities.

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.

High-resolution seismic reflection data, recorded offshore from Prudhoe Bay, Alaska, were processed digitally to determine the reflectivity structure of the uppermost layers of the seafloor. A prominent reflector, found at 27 m below the mud line (water depths 7–9 m), has a negative reflection coefficient greater than 0.5. The large acoustic impedance contrast, coupled with a report of gas encountered at a corresponding depth in a nearby drillhole, shows that the reflector is the upper boundary of a zone containing gas. The gas exists in sandy gravel capped by stiff, silty clay. Analysis of unprocessed conventional high-resolution records from the region indicates that the gas-bearing layer may extend over an area of at least 50 km2 at a depth of 20–35 m below the mud line. Similar-appearing reflectors (Reimnitz, 1972), previously unexplained, occur in patches over wide regions of the shelf where offshore oil development is beginning at a rapid pace. This suggests the exercise of caution with respect to possible hazards from shallow gas pockets.

Strudel scours are craters in the sea floor as much as 25 m wide and 6 m deep, that are excavated by vertical drainage flow during the yearly spring flooding of vast reaches of shorefast ice surrounding arctic deltas; they form at a rate of about 2.5 km−2 y−1. We monitored two such craters in the Beaufort Sea and found that in relatively unprotected sites they fill in by deposition from bedload in 2 to 3 years. Net westward sediment transport results in sand layers dipping at the angle of repose westward into the strudel-scour crater, whereas the west wall of the crater remains steep to vertical. At the bottom the crater traps almost all bedload: sand, pebbles, and organic detritus. As infilling progresses, the materials are increasingly winnowed, and bypassing must occur. Over a 20m wide sector, an exposed strudel scour trapped 360 m3 of bedload during two seasons; this infilling represents a bedload transport rate of 9 m3 y−1 m−1. This rate should be applicable to a 4.5-km wide zone with equal exposure and similar or shallower depth. Within this zone, the transport rate is 40,500 m3 y−1, similar to estimated longshore transport rates on local barrier beaches. Based on the established rate of cut and fill, all the delta-front deposits should consist of strudel-scour fill. Vibracores typically show dipping interbedded sand and lenses of organic material draped over steep erosional contacts, and an absence of horizontal continuity of strata—criteria that should uniquely identify high-latitude deltaic deposits. Given a short 2- to 3-year lifespan, most strudel scours seen in surveys must be old and partially filled. The same holds true for ice gouges and other depressions not adjusted to summer waves and currents, and therefore such features record events of only the past few years. In view of such high rates of bottom reworking of the shallow shelf, any human activities causing turbidity, such as dredging, would have little effect on the environment. However, huge amounts of transitory material trapped by long causeways planned for offshore development would result in major changes in the environment.

Side-scan sonar records collected in a shallow arctic lagoon (2–2.5 m depth) reveal a herringbone pattern of current-aligned linear reflectors with branching diagonals. The major longitudinal reflectors have no detectable relief (

In some years, large volumes of slush ice charged with sediment are generated from frazil crystals in the shallow Beaufort Sea during strong storms at the time of freeze-up. Such events terminate the navigation season, and because of accompanying hostile conditions, little is known about the processes acting. The water-saturated slush ice, which may reach a thickness of 4 m, exists for only a few days before freezing from the surface downward arrests further wave motion or pancake ice forms. Movements of small vessels and divers in the slush ice occurs only in phase with passing waves, producing compression and rarefaction, and internal pressure pulses. Where in contact with the seafloor, the agitated slush ice moves cobble-size material, generates large sediment ripples, and may possibly produce a flat rampart observed on the arctic shoreface in some years. Processes charging the slush ice with as much as 1000 m 3 km −2 of sediment remain uncertain, but our field observations rule out previously proposed filtration from turbid waters as a likely mechanism. Sedimentary particles apparently are only trapped in the interstices of the slush ice rather than being held by adhesion, since wave-related internal pressure oscillations result in downward particle movement and cleansing of the slush ice. This loss of sediment explains the typical downward increase in sediment concentration in that part of the fast-ice canopy composed largely of frazil ice. The congealing slush ice in coastal water does not become fast ice until grounded ridges are formed in the stamukhi zone, one to two months after freeze-up begins. During this period of new-ice mobility, long-range sediment transport occurs. The sediment load held by the fast-ice canopy in the area between the Colville and Sagavanirktok River deltas in the winter of 1978–1979 was 16 times larger than the yearly river input to the same area. This sediment most likely was rafted from Canada, more than 400 km to the east, during a brief time period in the previous fall. Ocean turbulence is greatly reduced while the congealing slush ice drifts about. Therefore, new ice then forming in intervening open-water areas is clean. These events explain the patchy appearance of the fast ice after the summer snowmelt. More work on the important phenomena reported here is needed to close a major gap in the knowledge of the arctic marine environment.

The Sea Sled is a simple, easily constructed device for obtaining relatively accurate and quick bottom profiles in the surf zone. The onshore — offshore motion associated with the passage of waves propels the sled on both its seaward traverse and the shoreward return. The device has been successfully used along the California coast.

The Alaska Good Friday earthquake (its epicenter about 80 mi from the Copper River delta) and the events associated with the quake left indelible marks on the recent sediments of the delta. A relatively dense pattern of earthquake shock structures is found in the upper part of the section. These include sand dikes, sand pipes, slumps, faults, and joints. The structures increase in abundance toward the central part of the delta, where sediments are thickest, and become rare along its fringes, where sediments are thinnest. The 6-ft uplift of the region was responsible for some erosion and other immediate changes. But the establishment of a new equilibrium, biologically as well as geologically, for barrier islands, tidal flats, and marshes, will advance only gradually over the next few years. Seiches, brought about by the earthquake, with current velocities of up to 20 or 30 knots, regionally planed off the upper 2 or 3 ft of the tidal flats. These areas often are marked by accumulations of clam shells. The eroded materials were dumped into deep channels and troughs.

Alaska's Beaufort Sea shelf is characterized by small-scale relief with an average amplitude of 1–2 m and wavelength of 50–100 m. Diving observations confirm that much of the bottom roughness reflects the action of grounded ice. Except for areas in the shadow of islands, bars, and offshore bathymetric highs, the entire shelf surface from the beach to at least the 75-m contour is now or has been modified by ice gouging. Ice contact with the bottom is more common, and rates of sedimentation higher on the inner shelf than on the outer shelf; the density of gouge features is about equal in both areas. Therefore, the chances are that an area of gouging on the inner shelf contains younger gouges than a similar area on the outer shelf. When ice grounds, it becomes an important agent in the sedimentary and morphologic environment of the Arctic shelf, directly by deforming bottom deposits and secondarily by affecting the current regime near the sediment/ice contact. While bulldozing action and rafting do not seem to contribute significantly to the direct transport of sediment, re-suspension of bottom material during bulldozing, which makes sediment available for transport, may be significant.