Ninth International Conference on Permafrost ... - IARC Research

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The Role of Sea Ice in Coastal and Bottom Dynamics in the Baidaratskaya BayS.A. OgorodovLomonosov Moscow State University, Faculty of Geography, Moscow, RussiaSea ice, as a zonal factor associated with the highlatitudeposition of arctic seas, plays an important role in theevolution of their coastal zone. The ongoing development ofoil and gas fields and the construction of relevant engineeringfacilities in the coastal and shelf areas (navigation channels,water scoop, terminals, drilling platforms, submarinepipelines) require new information on the effect of sea iceon the dynamics of coasts and sea floor. The effect of sea iceon coastal and bottom dynamics is one of the most importantfactors that determines the selection of a site for pipelinescrossing from an offshore slope to land, method and a valueof pipeline deepening. In Russia, special studies of sea iceimpacts (first of all, the effect of ice gouging) were carriedout in the areas of construction of submarine pipelines: theBaidaratskaya Bay of the Kara Sea (Fig. 1), the Pechora Sea,and the Sakhalin Island shelf.The so-called “Nothern-Europe Gas Pipeline” mustdirectly connect Russia and Germany through the bottom ofthe Baltic Sea to 2011. To provide gas for this pipeline, theproject “Yamal-Europe” pipeline design, which lines wouldcross the Baidaratskaya Bay of Kara Sea, was renewed.Since 2005 and in connection with renewing of the project,investigations on coastal zone dynamics and sea ice effectswas continued after a 10-year break.Ice gouging is a destructive mechanical impact of iceonto the underlying surface. This impact onto the shore andbottom of the arctic seas is due to ice dynamics and mobility,hummocking, and formation of grounded hummocks, andit is controlled by hydrometeorological factors and coastaltopography. In the Baidaratskaya Bay, the sea ice impact isobserved in the coastal zone within the altitudes from firstmeters above the sea level down to 26 m depths.Sea coasts are subjected to ice impact during the periodsof both ice formation in autumn and fast-ice destruction andseas clearing of ice in spring. The relief of coasts composedof coarse debris material features a wide occurrence ofridges formed under the ice-push effect (Fig. 2). In autumnand in early winter, young sea ice (20–40 cm thick) can bepushed onto land during periods of surge. While moving, thissolid ice cover cuts off beach sediments and forms ridges ofunsorted material from it.On maritime lowlands that can be flooded during highstorm surges, sea ice can be brought inland as far as tensand even hundreds of meters, causing surface and buildingdestruction.The mechanical action of ice on the sea bottom lasts fromthe onset of ice formation until the sea is completely freeof ice. After young ice freezes to the sea floor in the wateredge zone, this new strip of ice serves as a protective buffer.The ridges of hummocks closest to the coast develop abovesubmarine bars. Because of decreased sea depth over thesebars, they become the centers of hummocking; hence, thenumber of hummock ridges commonly corresponds to thenumber of submarine bars. Due to the onshore pushingimpact of sea ice, ice gouges in this zone are mostly orientednormally to the coastline (Fig. 3).Further in the sea, the pattern of hummock ridges andbarriers is irregular and controlled by hydrodynamic factors,particularly by the location of the fast ice edge duringperiods when storm wind is blowing. Storm winds destroythe fast ice edge and form a new ridge of hummocks orsingle-grounded hummocks. The ice gouges plowed in thiscase are either chaotic or parallel to the coastline. This is dueto the prevailing along-shore drift of hummock formations.The fast ice edge (within Baidaratskaya Bay, at about 10–15Figure 2. Ural Coast of Baidaratskaya Bay; ice-pushed ridge.Figure 1. Location of research areaFigure 3. Sonar record at 12 m depth: Parallel and normally orientedto the shore ice gouges formed by multi-keels ice dam.231
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tm depth) is the zone where ice impact on the sea floor is thestrongest. Here, hummock ridges and barriers reaching thefloor develop during the whole winter.Within a beyond-fast-ice polynia up to 19–20 m depthssea ice influence on the bottom is also high, since hummocksfrozen into the ice fields drift here during the winter as singlelarge bergs which have high kinetic energy due to their mass.As a result, the largest ice gouges can reach 1.8 m deep, 10–40 m wide, and several km long (Fig. 4). They are orientedconformably with the direction of tidal currents—lengthwisethe Baidaratskaya Bay.The main method of indirect estimation of ice gougingintensity is the estimation of density and deepness (Fig. 5) ofice gouges. Meanwhile, the lifetime of such forms essentiallycan vary according to sea depth, types of sediment, andduration of the dynamically-active period; so the questionabout sea ice gouging intensity of the coasts and bottom isdirectly connected with the problem of safety of ice gougingforms.Investigations on the Baidaratskaya Bay, Kara Sea,show that the frequency of occurrence and the density ofice-gouging forms is the largest at 17–19 m depth; but thatdoes not mean that the intensity of ice gouging is lower inshallow depths with rarer occurrence and smaller depths ofice gouges.The effect of coastal hummock ridges and barriers onbeaches and in shallow areas (down to a depth of 7–10 m)can be traced only immediately after fast ice is destroyed. Thelife period of ice-gouged forms developed on sand beachesand shallow areas is very short—until the first summerstorm. These forms, whose depth is mainly < 0.5 m here,commonly disappear with first strong waves in summer andautumn. Therefore, as a rule, the age of ice gouges in shallowareas does not exceed one year. Due to high hydrodynamicactivity here, the gouges quickly smooth over, and the gougedensity in shallow areas is lower than in the zone of the fastice edge.At depths of 14–16 m, the occurrence and density ofgouges turn out to be lower than at higher depths, thoughice gouging is the most intense (most of the mobile systemsof hummocks and grounded hummocks are formed here).The above situation is due to more active hydrodynamicsat smaller depths, where the effect of waves still manifestsitself and the velocities of tidal currents are higher. Due tothis, the gouges can exist over several years here (as distinctfrom their short existence in shallow areas), graduallysmoothing over and vanishing. The lifetime of ice gouges issubstantially determined by proportion between the freezingperiod and the dynamically-active period, and hence differsin diverse seas. For example, in the Pechora Sea, with adynamically-active period two times longer in comparisonwith the Kara Sea, it is quite difficult to find ice gouges atthe same depth. Another significant factor for the lifetimeof a gouge is wave action. While comparing ice gouges atBaidaratskaya Bay at 12–14 m depth, the fewer number ofgouges in the western part as compared with the eastern oneis obvious. Indeed, the frequency of strong waves higherFigure 4. Sonar record, 19 m depth: Largest and deepest icegouges.Figure 5. Winter underwater photo at a depth of 7 m: ice gougedeepness measurement. Stamukhi generated holes and gouges willbecome level by the first strong summer storm.than 3 m, which can transfer sediments at stated depths, is afew times higher on the western coast as compared with theeastern one.Deeper than 19 m, the ice gouges occur rather frequently.However, ice formations, particularly grounded hummocks,rarely occur at these depths. This situation is caused by lowhydrodynamic activity and low sedimentation rates. Undersuch conditions, the gouges, especially large ones, can existon the floor surface over decades. Thus, low intensity of icegouging is compensated by a long life of gouge forms. This“accumulation” effect gives a wrong idea of high intensityice gouging here.The depth of ice-gouging forms depends not only on seadepth, ice thickness, and intensity of sheer stress, but also oncomposition and the state of bottom deposits. The safety of icegouging forms probably depends also on plasticity, mobility,and granulometric composition of sediments. Attemptsto find regularity between field data about occurrence anddensity of gouges on the one hand and the type of sedimentson the other hand were not successful, except single examplesof correspondence. Observations show that ice gouges,especially large ones, have considerable lengths, sometimesup to several kilometers; that is, hummocks can constantlygouge the bottom for a long time due to their large kineticenergy. Therefore hummocks can gouge bottom sectionswith rather different characteristics of the sediments.232
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NICOP 2008 Ninth <
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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xvi
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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370Huang, B. 339Hugelius, G. 105, 1
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