Ice Scour Research Articles

Competition, mortality and diversity in South Atlantic coastal boulder communities

Boulder shores are common at all latitudes and dominate the intertidal and subtidal zones of sub-Antarctic coastlines. The encrusting benthos of boulders was examined on similar shore types at four locations: Tierra del Fuego, East Falkland, West Falkland and Bird Island (off South Georgia). Bird Island is unusual in experiencing high trampling and organic enrichment from fur seals. The results were compared to a Patagonian site and a non-trampled South Georgia site (Husvik) and other sites taken from the literature. Principal Component Analysis revealed South Atlantic/Southern Ocean encrusting faunas formed a distinct cluster when compared to assemblages from elsewhere at similar latitudes. Bray Curtis cluster analysis of the South Atlantic-Southern Ocean sites showed the major division was between Southern Ocean and South Atlantic Ocean sites, beyond which there were three distinct clusters centred around Patagonia (Magellanic), the Falklands and Southern Ocean sites. The organisation of competitive interactions between species was mostly determinate and transitive (essentially hierarchical). The transitivity index scores were higher than most similar assemblages studied to date. The diversity of encrusting assemblages ranged from Shannon Weaver H values of 2.38–0.77 (East Falkland and Bird Island, respectively) in the intertidal to 1.27–0.73 (Patagonia and South Georgia, respectively) in the subtidal zone. Annual mortality (of bryozoan colonies) varied from 85–97% in the intertidal to 65–92% in the subtidal, being higher in the Southern Ocean than South Atlantic sites, largely due to ice scour and wave action. The Bird Island mortality values may be high even for a Southern Ocean site.

Model Tests On Ice Scour Events Under Various Conditions

Ice Scour (Ice Gouge) is a phenomenon that occurs when ice comes into contact withseabed. Ice gouge has been reported to have caused damage to communication cables and water intake pipelines. Since oil and natural gas exploration projects in offshore areas of arctic seas are becoming popular, more care must be taken over the design and installation of oil pipelines in such areas in order to avoid accidents due to ice scour. It will be very important to acknowledge mechanisms (ice motions, sub-seabed conditions on gouge events). In addition to our previous tests (Kioka and Saeki, 2000), we have performed many series of model tests under various conditions. We revealed relationships between pore water pressure in the sand and bulldozing force due to velocity of the model keel, and we also prospected depression of model keel during scour events.

MEDIUM-SCALE MODEL TESTS ON ICE SCOUR EVENT

Ice Scour is a phenomenon that occurs when ice comes into contact with seabed. Ice Scour has been reported to have caused damage to communication cables and water intake pipelines. It will be very important to acknowledge the mechanisms. We have performed a series of small-scale (1-g) model experiments. Furthermore, we performed a series of medium-scale model experiments on ice scour events at a sandy beach in order to try to determine the effect of scale. The model ridge-keel was placed in the sea and pulled at a constant velocity toward the shore by a crane, and the bulldozing force and the motion of the model keel were measured, Furthermore, a model pipeline to which a strain gauge had been attached was buried at a depth of 15-20 cm from the predicted scour surface, and stress and strain acting on the model pipeline during a gouging event were measured. We showed our mechanical model could be applied to scour events not only on a small scale but also on a medium scale. We also discuss similarity law between medium-scale test results and small-scale test results, stress and deformation acting on the model pipeline.

A growth cline in encrusting benthos along a latitudinal gradient within Antarctic waters

Growth and mortality of 3 species (Inversiula nutrix, Celleporella bougainvillei, Fenestrulina rugula) of encrusting bryozoans were examined from 5 Antarctic localities, along a latitudinal gradient. Typically, growth in marine invertebrates is, for ecological equivalents, slower or much slower in cold seas than warm waters. Contrary to the general trend, growth rates of 3 bryozoans were found to accelerate with increasing latitude in Antarctic waters. Population age structure also showed a dramatic change across the 5 study sites (from 54 to 68 degrees S) through hugely increased mortality with increasing latitude. Reduction in inter-specific competition is theorised as explaining higher growth rates. Increased levels of ice scour are probably responsible for the differential mortality.

STUDY ON THE BEHAVIOR OF ICE, MECHNISMS AND ICE FORCES DUE TO ICE SCOURING

Ice scouring is a phenomenon which occurs when moves in contact with seabed. It has been reported tohave caused damage to communication cables and water intake pipelines. Therefore, it will be veryi mportant to estimate rational maximum scour depth due to complicate behavior of ice, and will also bevery important to evaluate forces acting on sea bed and stress that is transmitted via the seabed andd eformation of soil.We have developed the rational experimental device system as compared to previous device system. Under the renewal conditions, we conducted a lot of test series, and werevealed relationships between iceforces and beha vior of ice, variations of its behavior due to varies condition (attack angle, travellingvelocity). And we also revealed the probability distribution of some random variable under the same experimental condition.

FIRST RECORD OF NOTOBALANUS FLOSCULUS (DARWIN, 1854) (CIRRIPEDIA, ARCHAEOBALANIDAE) FROM THE SOUTH ATLANTIC COAST OF SOUTH AMERICA

Fil: Calcagno, Javier Angel. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Geochemistry of Surficial and Ice-rafted Sediments from the Laptev Sea (Siberia)

The Laptev Sea, as a part of the world’s widest continental shelves surrounding the Arctic Ocean, is a key area for understanding the land–ocean interaction in high latitude regions. With a yearly freshwater input of 511km3, the Lena River—one of the eight major world rivers—has an influencing control over the environment of this Arctic marginal sea, which is ice-covered during most of the year.In this paper, the first measurements are presented of the major and trace element distribution within the <20μm grain size fraction of surficial sediments and of particulate matter in new and young ice from the Laptev Sea (Siberian Arctic). The concentration and distribution of major and trace elements have been determined in 51 surficial sediment samples covering the whole Laptev Sea shelf south of the 50m isobath. Thirty-one samples of particulate matter in newly formed ice were taken during the freeze-up period in 1995.Median concentration levels of heavy metals in surficial sediments (Ni (46μg g−1), Cu (26μg g−1), Zn (111μg g−1) and Pb (21μg g−1) are within the concentration range of marine unpolluted sediments. Also the sediment-laden ice showed no indication of anthropogenic perturbation of the trace metal inventory. Spatial distribution patterns of heavy metals are mainly determined by variation of mineral composition and different fluvial sediment sources in the eastern and western Laptev Sea.The Laptev Sea shelf is cut by five north–south trending submarine valleys. Enrichment of manganese in the oxic surficial sediment layer within these valleys and the occurrence of small ferromanganese nodules are caused by a high input of dissolved and particulate Mn from the Lena River and a strong diagenetic cycling of Mn on the Laptev Sea shelf. Evidence is given that the content of As in surficial sediments is also strongly affected by diagenetic cycling. This causes surficial sediment As concentrations of more than 100μg g−1. Enrichment of Mn and As was mainly observed in the submarine valleys distant from the major river mouth. The sediment dilution due to higher sedimentation rates near the river outlets and a strong sediment re-working by ice gouging in the shallow areas are the principle causes for the absence of diagenetic accumulation in this region.During the formation of new ice scavenging of riverine suspended matter and resuspension of sediments followed by an incorporation of particles into the ice are important processes for the river–shelf–ocean transport of particulate trace elements. It could be shown that particle-loaded ice posseses the same geochemical signatures as the suspended matter and surficial seafloor sediments in the area of ice origin. This has also strong implications for the contaminant transport on the Arctic shelves and allows to use the geochemical signature of sea ice for the reconstruction of ice drift pattern within the Arctic Ocean.

The influence of ice on polar nearshore benthos

Polar benthic communities are subject to a range of disturbance levels from a variety of sources, principal amongst which is ice. This occurs in four main forms: the ice-foot, ice scour, anchor ice and fast ice, each of which influences benthos in a very different temporal and spatial manner. The four described forms of ice disturbance are all seasonal, but combined, influence communities throughout the year. The magnitude of ice mediated disturbance is often catastrophic and as a result both dominates benthic community structure and makes recolonization and development rates critical. This disturbance extremity results in high temporal and spatial heterogeneity, very low intertidal zone diversity and in places low mid–sublittoral diversity. It may also, however, be important in generating and maintaining the typically high sublittoral zone diversity observed at many polar localities. Intermediate frequencies or magnitudes of disturbance have been controversially discussed as important in maintaining diversity by prevention of space monopolization by overgrowth dominants in such environments as the deep sea. The shelf areas examined to date certainly suggest intermediate disturbance is important in maintaining polar sublittoral zone diversity. The combination of slow colonization and development with high frequencies of disturbance means most polar nearshore environments that have been described are permanently in a state of change or recovery.

Nearshore erosion by combined ice scouring and near-bottom currents in eastern Hudson Bay, Canada

A study of nearshore sedimentary processes was carried out in Manitounuk Sound, a sheltered environment protected by rocky islands along eastern Hudson Bay. High-resolution seismic profiles suggest that up to 10 m of Holocene sediments were eroded in less than 15 m water depth although these shallow depths are affected by low-energy waves and currents. According to our measurements of near-bottom currents at 3.7 and 5.6 m water depths, the threshold velocity for sediment motion (20 cm s −1) is only seldom exceeded, and consequently the significant erosion of the nearshore deposits can hardly be explained by hydraulic processes alone. Geophysical data (seismic and echosounding profiles) suggest that the observed erosion is mainly due to bottom scouring by dragging ice keels. These data show that the zone of maximum ice scouring, between 8 and 12 m water depths, corresponds to the zone of maximum erosion of Holocene sediments. Because ice scouring in this area occurs when the sea is largely ice-free, wind-induced near-bottom currents probably contribute to the dispersal of the sediments resuspended by ice.

Experimental Evidence for the Origin of Alternative Communities on Rocky Intertidal Shores

Ecological theory of alternative stable communities suggests the switch between different species assemblages occurs when environmental conditions alter species composition so that it crosses a critical threshold and enters a different basin of attraction. The theory implies that once the threshold is crossed, rates of key ecological processes, such as predation and competition, will change. This conjecture was tested on sheltered intertidal shores of New England that are dominated by either mussel (Mytilus edulis) beds or algal (Ascophyllum nodosum) stands. Twelve sets of clearings of different sizes, which mimicked effects of ice scour, were created in algal stands, and mortality of transplanted mussels was monitored. Clearings were 1, 2, 4 and 8 m in diameter. Mussel mortality due to the predatory snail Nucella lapillus declined in a step-like manner in clearings > 4 m in diameter. Initial densities of the predator did not vary among experimental clearings or sites and were not correlated with mussel mortality. Mussel mortality was correlated with predatory snail densities during and at the end of the experiment. These results provide experimental evidence supporting conjectures about the switch between alternative states in ecological communities.

BASIC STUDY ON INTERACTION BEWEEN SEA ICE AND SEA BED

Ice Scour (Ice Gouging) is a phenomenon in which sea ice (pressure ridge, ice keel) attached to the sea bottom in a shallow sea area scrapes the sea bottom while it is pushed by wind and water current from offshore ice field to shallow sea area. There have been reported instances of damage to transatlantic submarine telecommunication, water intake pipeline at Great Slave Lake etc. So, the problem of Ice Scour by sea ice and ridge keels is of concern in the planning and design ofseabed installation.In this study we describe the mechanism of Ice Scour andobtain basic knowledge necessary to take preventive measures in future against damage by sea ice.

Riparian ecosytems of semi-arid North America: Diversity and human impacts

Riparian ecosystems in the semi-arid West of North America are diverse but have many similarities. The mountainous landscape with wide range of latitude, longitude, and elevation offers diverse opportunities for streamside vegetation. All riparian ecosystems in the region are dependent on supplemental water, usually from the shallow, valley alluvial aquifer. Western riparian ecosystems provide several ecological services. They stabilize streambanks, trap sediment, improve water quality, and help control or modulate hydrologic processes. They function as habitat for many western animal species, serving as a small mesic island or strip within an arid landscape. They also serve as recreational sites for humans. Riparian systems are controlled by interacting hydrologic and geomorphic processes. Floods may alter river channel characteristics and the extent of riparian vegetation while enhancing recruitment of riparian species and recharging the alluvial water table. Geomorphic features, such as canyons and valleys, control the size of the riparian zone, as well as depth of the water table. Driving variables may differ from north to south, especially hydrology. For example, northern riparian zones are influenced by ice scour, while southern zones often have flash floods. Riparian systems occur along spatial and temporal gradients. Along elevational gradients, riparian vegetation may change from simple deciduous forests to mixed deciduous to coniferous and possibly alpine wetlands. Differences among channel, terrace, and upland plant communities decrease with increasing clevation as moisture stress decreases. Temporal gradients occur within a location in the riparian zone as early pioneer communities such as cottonwood/willow give way to late successional communities such as mesquite or sagebrush, often a consequence of sediment accumulation. Many similarities among western riparian ecosystems exist because several dominant genera (e.g.,Populus) are common throughout the West, and many geomorphic and hydrologic processes that influence riparian establishment are similar. Western riparian ecosystems have been greatly altered by human activity. Major factors include natural resource use, urbanization, alteration of stream flows through dam construction and ground-water withdrawal, modification of biotic conditions through grazing, agriculture, and introduction of non-native species, and alteration within watersheds. Better understanding of the ecology of western riparian ecosystems will increase potential for restoration and protection of remaining areas.

Field and Laboratory Studies of Zebra Mussel (Dreissena polymorpha) Infection by the CiliateConchophthirus acuminatusin the Republic of Belarus

This study quantifies the infection prevalence and intensity of the European, commensal, host-specific ciliateConchophthirus acuminatus(Scuticociliatida: Conchophthiridae) in five zebra mussel populations within the Republic of Belarus. Laboratory and field experiments were also conducted to assess variables affecting infection.C. acuminatuswas found in zebra mussels in all five waterbodies sampled: Naroch, Myastro, and Lukomskoe Lakes, Skema Stream, and in the Svisloch River. Prevalence was always 100%, with the exception of shallow areas (≤0.5 m depth) in the Svisloch River. This was possibly the result of the elimination of the majority of infected zebra mussels each winter by a combination of factors, including ice scour, mallard duck predation, and fluctuating water levels. As a result, zebra mussels are not permanently present at shallow depths, and the mussels that we randomly sampled there during the summer were thus smaller (i.e., younger) and less infected than those present in deeper sections of the river. This is the first study to quantify the intensity ofConchophthirusinfection in zebra mussels. When infection prevalence was 100%, it was not uncommon for zebra mussels to have 500–2,000C. acuminatusin their mantle cavities, particularly those mussels ca. 15–30 mm in length. Zebra mussels, while relatively small bivalves, have one of the highest intensities ever reported for ciliates in the order Scuticociliatida. Infection intensity correlated directly with mussel length (range inr2=0.83–0.92). Transinfection of zebra mussels withC. acuminatuswas achieved both in the laboratory and field, and represented the first successful trials to initiate protozoan infection inDreissena.Laboratory experiments demonstrated thatC. acuminatusrapidly leave their dying zebra mussel hosts, and this suggested that these mussels are likely a major source for the spread ofC. acuminatusinfection. Field trials indicated that the presence of mussels with high intensity infections can cause an increase in the levels of infection (both prevalence and intensity) in other zebra mussels in their microhabitat.

Creation and maintenance of habitat downstream from a weir for the greenside darter, Etheostoma blennioides – a rare fish in Canada

The biology, microhabitat use and migratory behaviour of the greenside darter, Etheostoma blennioides, was studied at the Mannheim Weir on the Grand River, Ontario during the summer of 1995 and 1996. Officially listed as vulnerable in Canada, greenside darters reached maturity at age 1 and lived up to 4 years. They were found in riffle habitats that consisted of cobble and loose boulders, with large mats of Cladophora. This type of unembedded substrate is uncommon in the Grand River watershed. However, local abundance of greenside darters immediately downstream from the Mannheim Weir was likely due to high water velocities from weir discharge, freshets and ice scour which help maintain unembedded riffle areas. Trap data indicated that greenside darters temporally partition this habitat with the stonecat, Noturus flavus. Other darter species were not commonly found in areas with greenside darters, whose depth selection and habitat choices were influenced by predators and morphology. Denil fishways at the Mannheim Weir rarely passed greenside darters due to prohibitively high water velocities and exclusion by larger fish.

Fluvial disturbance patches and cottonwood recruitment along the upper Missouri River, Montana

The disturbance patches most suitable for seedling establishment of pioneer riparian trees are also subject to future disturbances that produce high seedling mortality. We are monitoring plains cottonwood seedling establishment and mortality along the Wild and Scenic reach of the Missouri River upstream of Fort Peck Reservoir, Montana at four sites subject to livestock grazing and four paired, ungrazed exclosures. New seedlings at these sites were largely restricted to surfaces inundated by spring and summer flows. Winter ice drives and livestock grazing are important mortality factors along the study reach. Livestock grazing reduced seedling densities, although the position of these seeclings in normal flow years means it is unlikely that they will survive future disturbance. Average values of the maximum density parameter of a Gaussian curve of seedling distribution along a hydraulic gradient of inundating discharge were 30 and 114 seedlings/m2 on ungrazed sites in 1996 and 1997, compared to 19 and 18 seedlings/m2 for grazed sites. Water-surface elevations produced, by ice drives and damming in the severe winter of 1995–1996 corresponded to inundating discharges of 1,670 to 4,580 m3/s. No existing trees at the study sites occurred at inundating discharges below 1,625 m3/s. Seedlings established as a result of maximum summer flows of 827 and 1,201 m3/s in 1996 and 1997 were all below the elevation of the 10-year return flow of 1,495 m3/s. Recruitment of plains cottonwood trees along this reach of the Missouri River is strongly dependent on infrequent high flows that position moist, bare disturbed patches high enough for seedlings to establish and survive subsequent flooding and ice scour, in contrast to other reaches and streams where hydrogeomophic processes of channel meandering and narrowing produce different patterns of disturbance patches.

Black pools of death:hypoxic, brine-filled ice gouge depressions become lethal traps for benthic organisms in a shallow Arctic embayment

Black pools of death:hypoxic, brine-filled ice gouge depressions become lethal traps for benthic organisms in a shallow Arctic embayment

Ice scour disturbance to benthic communities in the Canadian High Arctic

Ice scour disturbance to benthic communities in the Canadian High Arctic

Iceberg rafting and scouring in the Early Permian Shoalhaven Group of New South Wales, Australia: Evidence of Heinrich-like events?

Abstract This paper describes multiple layers of ice-rafted debris and an ice-scour structure in Early Permian marine strata within the Shoalhaven Group of the Sydney Basin, New South Wales, Australia. Strata were deposited on a high-latitude, glacially influenced continental margin during the final stages of Late Palaeozoic glaciation between 277 and 260 Ma. Poorly sorted ice-rafted debris, forming layers up to 1.25 m thick, is common within inner to outer shelf and continental slope facies of the Shoalhaven Group. More than 120 layers can be identified. These are argued to record the enhanced delivery of debris by icebergs drifting north from marine-based Antarctic ice margins. Deformation structures in associated sediments are interpreted as iceberg scours and ice keel turbates. Associated glendonites record early diagenesis of organic-rich sediment and bottom water temperatures close to freezing. A speculative hypothesis relates layers of ice-rafted debris within the Shoalhaven Group to multiple episodes of accelerated calving at the margins of a marine-based Early Permian ice sheet in East Antarctica. These events may be analogous to late Pleistocene Heinrich events, when huge armadas of icebergs were released from the marine-based Laurentide Ice Sheet and triggered abrupt changes in ocean circulation and climate. Similar forcing may have characterized the Early Permian ice-ocean system. Regardless of the climatic significance of ice-rafted layers, this is the first time such facies have been documented in the pre-Pleistocene literature; to date, few ice scour structures, and no ice keel turbates, have been reported.

Geotechnical evidence of ice scour as a guide to pipeline burial depth

Cette note suggere que la profondeur maximale de l'affouillement de la glace dans les fonds marins arctiques est indiquee par un bris dans les proprietes geotechniques. Ceci nous donne un moyen alternatif economique de trouver la profondeur d'enfouissement requise pour proteger un pipeline en utilisant des donnees qui sont de toute facon requises pour d'autres fins.

Periglacial trimlines, former nunataks and the altitude of the last ice sheet in Wester Ross, northwest Scotland

High-level weathering limits separating ice-scoured topography from frost-weathered detritus were identified on 28 mountains in Wester Ross at altitudes of 700–960 m, and a further 22 peaks support evidence of ice scouring to summit level. Weathering limits are defined most clearly on sandstone and gneiss, which have resisted frost shattering during the Late Devensian Lateglacial, but can also be distinguished on schists and quartzite. Schmidt hammer measurements and analyses of clay mineral assemblages indicate significantly more advanced rock and soil weathering above the weathering limits. The persistence of gibbsite above weathering limits indicates that they represent the upper limit of Late Devensian glacial erosion. The regular decline of weathering-limit altitudes along former flowlines eliminates the possibility that the weathering limits represent former thermal boundaries between protective cold-based and erosive warm-based ice. The weathering limits are therefore interpreted as periglacial trimlines that define the maximum surface altitude of the last ice sheet. Calculated basal shear stresses of 50–95 kPa are consistent with this interpretation. Reconstruction of ice-sheet configuration indicates that the former ice-shed lay above 900 m along the present watershed, and that the ice surface descended northwestwards, with broad depressions along major troughs and localised domes around independent centres of ice dispersal. Extrapolation of the ice surface gradient and altitude suggests that the ice sheet did not overrun the Outer Hebrides, but was confluent with the independent Outer Hebrides ice-cap in the North Minch basin. Erratics located up to 140 m above the reconstructed ice surface are inferred to have been emplaced by a pre-Late Devensian ice sheet (or ice sheets) of unknown age. © 1997 John Wiley & Sons, Ltd.