Shorefast Sea Ice Research Articles

Real-time acoustic observations in the Canadian Arctic Archipelago.

The main sources of noise in the Arctic Ocean are naturally occurring, rather than related to human activities. Sustained acoustic monitoring at high latitudes provides quantitative measures of changes in the sound field attributable to evolving human activity or shifting environmental conditions. A 12-month ambient sound time series (September 2018 to August 2019) recorded and transmitted from a real-time monitoring station near Gascoyne Inlet, Nunavut is presented. During this time, sound levels in the band 16-6400 Hz ranged between 10 and 135 dB re 1 μPa2/Hz. The average monthly sound levels follow seasonal ice variations with a dependence on the timing of ice melt and freeze-up and with higher frequencies varying more strongly than the lower frequencies. Ambient sound levels are higher in the summer during open water and quietest in the winter during periods of pack ice and shore fast ice. An autocorrelation of monthly noise levels over the ice freeze-up and complete cover periods reveal a ∼24 h periodic trend in noise power at high frequencies (>1000 Hz) caused by tidally driven surface currents in combination with increased ice block collisions or increased stress in the shore fast sea ice.

Changes in sea ice travel conditions in Uummannaq Fjord, Greenland (1985–2019) assessed through remote sensing and transportation accessibility modeling

ABSTRACT Shorefast sea ice provides an important platform for winter and spring travel between coastal Arctic communities unconnected by road networks. In the past two decades, local Arctic residents have reported thinning and earlier breakup of shorefast ice. Despite these assertions, however, there are few quantitative assessments of how these changes have impacted travel on sea ice. In this study, we use high-resolution satellite remote sensing and transportation modeling to assess snow mobile travel in Uummannaq Fjord, Greenland. Following classification of satellite imagery, we generate optimal least-cost travel routes according to surface types present in the fjord. We then estimate distance and duration of snowmobile travel potential between communities from 1985 through 2019. We find that snowmobile travel in Uummannaq Fjord has potentially become slower and more unpredictable in recent years (2014–2019) relative to thirty years prior (1985–2000), with greater changes for communities located more proximal to the shorefast ice edge. Our results also suggest that reductions in on-ice snow cover impede snowmobile travel more than fractures do. Overall, our analysis demonstrates how remote sensing and transportation modeling may be used to quantify the community-scale impacts of changing shorefast ice conditions and has potential to help manage localized climate-related risk.

How sea ice can affect coastal swells, infragravity waves and leaky wave modes: Spectral adaptation from modulation

Several months of seafloor-mounted, pressure-transducer data collected in Mordvinova Bay off the south-east coast of Sakhalin Island in the Sea of Okhotsk are used to interpret surface-gravity waves across a wide range of periods, during intervals when the sea surface was free of sea ice, covered by drift ice of 0.5–1 m thickness, and when both drift ice and consolidated shore fast sea ice was present. A substantial fraction of the data set is shown to be frequency modulated by the diurnal tide and, to a lesser extent, by the semidiurnal tide. Whereas amplitude modulation by the tide has been found in the past in the open ocean, frequency modulation is less common and neither tidal amplitude modulation nor angle modulation have been observed and recorded under sea ice to the authors’ knowledge. Three theoretical oceanographic modalities that could excite the modulation are discussed. Although the sea ice affected the wind-generated waves and swells in the measured energy spectra as predicted, namely by preferential attenuation that causes spectra to become narrower by progressively reducing shorter periods with distance travelled, its effect on waves of longer periods, i.e. 1–10 min, was unanticipated. Oscillations in this band, present as infragravity (IG) waves, leaky waves and an edge wave mode are shown to be affected as well; especially spectral peaks corresponding to IG/leaky waves, which respond to the sea ice by shifting to a slightly longer mean period and becoming broader. The period shift is explained by the spectral sharpening previously mentioned, whilst the broadening is conjectured to be associated with changes to the frequency modulation.

Aspects of surface wave propagation with and without sea ice on the south-eastern shelf of Sakhalin Island

A long data set of wave measurements is discussed, collected by means of bottom-mounted pressure recorders located on the shelf off the coast of south-east Sakhalin Island when the Sea of Okhotsk in the vicinity was free of ice, covered by drift ice composed of loose ice floes and ice cakes that had migrated south, or blanketed by a sheet of shore fast sea ice and drift ice. Coastally trapped, barotropic edge waves, leaky wave modes and infragravity waves detected in the data are analyzed using spectral methods—including gain and phase comparisons between the sites where devices were deployed, supported by coherence plots. As well as preferentially eliminating noise and systematically low pass filtering waves to deliver a stabilizing influence, spectrograms suggest that the presence of sea ice also affects the attributes of longer oscillations, e.g. infragravity waves and consequently those arising from the passage of leaky modes offshore and trapped edge waves. The gain and an apparent monotonically increasing phase difference between two nearshore sites are respectively investigated using a well-established solution for how the standing leaky wave envelope decays with distance from the shore and a conceptual model of synchronization.

Attenuation of Ocean Surface Waves in Pancake and Frazil Sea Ice Along the Coast of the Chukchi Sea

AbstractAlaskan Arctic coastlines are protected seasonally from ocean waves by the presence of coastal and shorefast sea ice. This study presents field observations collected during the autumn 2019 freeze up near Icy Cape, a coastal headland in the Chukchi Sea of the Western Arctic. The evolution of the coupled air‐ice‐ocean‐wave system during a 4‐day wave event was monitored using drifting wave buoys, a cross‐shore mooring array, and ship‐based measurements. The incident wavefield with peak period of 2.5 s was attenuated by coastal pancake and frazil sea ice, reducing significant wave height by 40% over less than 5 km of cross‐shelf distance spanning water depths from 13 to 30 m. Spectral attenuation coefficients are evaluated with respect to wave and ice conditions and the proximity to the ice edge. Attenuation rates are found to be three times higher within 500 m of the ice edge, relative to values farther in the ice cover. Attenuation coefficients are in the range of 〈2.3, 2.7〉x10‐3 m−1, and follow a power‐law dependence on frequency.

Coldest Canadian Arctic communities face greatest reductions in shorefast sea ice

Shorefast sea ice comprises only about 12% of global sea-ice cover, yet it has outsized importance for Arctic societies and ecosystems. Relatively little is known, however, about the dominant drivers of its breakup or how it will respond to climate warming. Here, we use 19 years of near-daily satellite imagery to document the timing of shorefast ice breakup in 28 communities in northern Canada and western Greenland that rely on shorefast ice for transportation and traditional subsistence activities. Breakup timing is strongly correlated with springtime air temperature, but the sensitivity of the relationship varies substantially among communities. We combine these observations with future warming scenarios to estimate an annual reduction of 5–44 days in the length of the springtime shorefast ice season by 2100. Paradoxically, the coldest communities are projected to experience the largest reductions in springtime ice season duration. Our results emphasize the local nature of climate change and its varied impacts on Arctic communities. Shorefast sea ice, which forms along the Arctic shore in winter and spring, is important for local communities and ecosystems. Satellite and climate model data are used to estimate a decrease in shorefast ice season length of 5–44 days by 2100, with the coldest areas experiencing the largest reductions.

Crack formation and breakout of shore fast sea ice in Mordvinova Bay, south-east Sakhalin Island

Recognizing that cyclical flexural fluctuations in sea ice sheets stimulated by waves can potentially initiate and perpetuate cracks that may ultimately lead to the destruction of an ice cover, we discuss some winter observations collected beneath the fast ice cover of Mordvinova Bay in the south-east of Sakhalin Island during 2018–2019 when a large crack formed that subsequently detached the offshore sea ice from the inshore ice plate by a wide lead. Energy density spectra show the ramifications of surface-gravity waves from the open ocean—primarily at swell frequencies—penetrating far into the ice from offshore, together with comparatively long, resonant leaky wave modes that gradually dissipate as they propagate alongshore but present a diminishing standing wave envelope of antinodes perpendicular to the coast. By evaluating amplitudes over different ranges of period, three swell wave events are assessed to determine whether they alone could have induced enough bending in the sea ice plate to cause breakage, acknowledging that this would normally occur much closer to the peripheral ice edge where the stresses are largest or as the swells run ashore. The foreshortened seaward standing curvature profile of leaky wave antinodes is also considered as a prospective source of cracking. Whilst neither pathway is found conclusively to be independently responsible for breaking the ice in this case, it is conjectured that the combined influence of swell and leaky waves acting together could cause the observed crack to form. In this case, fracture would occur at a distance of less than about four or so kilometres from the shore, where the antinodal curvatures induced by the standing leaky modes are sufficient. Conceding that the unrelenting flexing of the ice plate by waves and swell could affect the longevity of the sea ice as well, fatigue-precipitated weakening is explored. By determining the value of the mechanical stress at which an ensuing rupture of the fast ice could happen, it is shown that ice destruction can eventuate approximately 17 h after the swell first arrives at the ice edge from the Sea of Okhotsk, appreciating that breakup will depend on prevailing and prior meteorological conditions, the form and state of the sea ice including any preexisting defects, and the specific periods of swell waves that infiltrate the Mordvinova Bay ice sheet.

Synoptic forcing of wave states in the southeast Chukchi Sea, Alaska, at nearshore locations

Two bottom-mounted recording Doppler current profilers (RDCP) were deployed at nearshore locations (approximately 3 and 8 km offshore, in about 18 m water depth) in the southeast Chukchi Sea, Alaska, from October 2009 to September 2010 (UTC) with the goal of linking observed wave activity—wind-sea and swells—to their synoptic drivers. The northerly RDCP recorded a total of 16 events of elevated wave states: 15 exceeding 1 m significant wave height (SWH), and 1 exceeding 2 m SWH. The southerly RDCP recorded a total of 25 events of elevated wave states: 23 exceeding 1 m SWH, 2 m exceeded on two occasions and a SWH of 3 m was observed. Detailed analysis of the three large events (i.e., SWH events ≥2 m), including comparison with high-resolution reanalysis wind data (North America regional reanalysis), strongly suggested the wave energy evolved from a distant storm and would be defined as swell. Due to the close proximity of the shoreline to the east of the instruments, wind speeds based on reanalysis were constrained so fetch was westerly. Wave direction was also westerly, varying about 25° to the north (clockwise) or the south (counterclockwise) from the wind direction which is believed to be influenced by fetch and the strong current flow located where the nearshore RDCPs were deployed. Shore-fast sea ice is also believed to play a role but shown to only dampen wave activity for 3 months (January–April 2010), thus implying early ice breakup in this nearshore region. Two events appeared to be driven by southwesterly winds associated with cyclonic systems that moved into the eastern Chukchi Sea and then stalled. However, the second storm event appeared to be driven by northwesterly winds associated with a cyclonic system over the Brooks Range, a less common occurrence. Given that the typical storm activity in the region occurs as storms move into the Bering Sea in fall, this represents another potential source for wave conditions posing danger to people on the water or to coastal infrastructure.

Late Holocene cyclic glaciomarine sedimentation in a subpolar fjord of the South Shetland Islands, Antarctica, and its paleoceanographic significance: Sedimentological, geochemical, and paleontological evidence

The glaciomarine sedimentary record of the fjord head (Collins Harbor) in Maxwell Bay, South Shetland Islands (West Antarctica), a large marine calving embayment, contains repeating couplets of organic-rich massive diamicton and organic-poor stratified diamicton. The massive diamicton is characterized by high total organic carbon (TOC) content and carbon to nitrogen (C/N) ratios and was deposited in a cold climate regime by iceberg-rafted sedimentation from coastal fast ice in which algal plants, as well as gravels, were entrained. The stratified diamicton is characterized by low TOC content and C/N ratios and was formed in a warmer climate regime when the flux of icebergs was suppressed, but turbid meltwater discharge continued to produce lamination. When the meltwater discharge decreased in cold climatic conditions, and resultant phytoplankton productivity was reduced due to the increased sea-ice coverage, ice rafting from shorefast sea ice might have played a major role in entraining benthic algae, as well as loads of sand and gravel, along the coastal area, resulting in an increased C/N ratio and gravel content in the massive diamicton. Accelerator mass spectrometry (AMS) radiocarbon analyses conducted on well-preserved calcite shells were used to construct a chronology for the past 3000 years. Fluctuations in TOC are recorded (approximately four cycles over this time period), with the average duration of a cooling cycle being ∼500 years. These cycles may be correlative with the high-frequency (550 yr) variability in reduced Circumpolar Deep Water (CDW) on the West Antarctic Peninsula shelf, because a decrease in CDW may be related to reduced deep water production in the North Atlantic during colder periods, as demonstrated for glacial intervals throughout the Pleistocene.

The effect of submergence on wave scattering across a transition between two floating flexible plates

The reflection and transmission of flexural-gravity waves at a sudden change of properties of finite extent, e.g., an irregularity such as an entrapped iceberg, in an otherwise uniform sea-ice sheet is considered theoretically. Although similar in purpose to Squire and Dixon [V.A. Squire, T.W. Dixon, On modelling an iceberg embedded in shore fast sea ice, J. Eng. Math. 40 (3) (2001) 211–236], the current paper correctly incorporates changes of Archimedean draft, i.e., submergence, between the three adjoining plates and thereby allows the approximations in that work to be examined and quantified. This is unusual, as the bulk of the published work concerned with wave propagation beneath floating ice sheets ignores the effects of submergence on the basis that the wavelengths involved significantly exceed the ice thickness and hence the draft of the sheet. After validation, results are presented showing how the reflection coefficient depends on the geometry of the arrangement being modelled, including both isolated floes in the open sea, which may surge, and ice floes and bergs surrounded by a contiguous uninterrupted ice sheet. The effect of draft is investigated and a wide spacing approximation is also developed that allows the scattering coefficients for the boundary between two floating semi-infinite sheets to be deduced when submergence is included. This also enables us to approximate the scattering by a lead.

Spatial Variability of Barrow-Area Shore-Fast Sea Ice and Its Relationships to Passive Microwave Emissivity

Aircraft-acquired passive microwave data, laser radar height observations, RADARSAT synthetic aperture radar imagery, and in situ measurements obtained during the AMSR-Ice03 experiment are used to investigate relationships between microwave emission and ice characteristics over several space scales. The data fusion allows delineation of the shore-fast ice and pack ice in the Barrow area, AK, into several ice classes. Results show good agreement between observed and Polarimetric Scanning Radiometer (PSR)-derived snow depths over relatively smooth ice, with larger differences over ridged and rubbled ice. The PSR results are consistent with the effects on snow depth of the spatial distribution and nature of ice roughness, ridging, and other factors such as ice age. Apparent relationships exist between ice roughness and the degree of depolarization of emission at 10, 19, and 37 GHz. This depolarization would yield overestimates of total ice concentration using polarization-based algorithms, with indications of this seen when the NT-2 algorithm is applied to the PSR data. Other characteristics of the microwave data, such as effects of grounding of sea ice and large contrast between sea ice and adjacent land, are also apparent in the PSR data. Overall, the results further demonstrate the importance of macroscale ice roughness conditions such as ridging and rubbling on snow depth and microwave emissivity

Observations on Shorefast Ice Dynamics in Arctic Alaska and the Responses of the Iñupiat Hunting Community

Although shorefast sea ice forms a platform that facilitates travel, camping, and hunting by Inupiat subsistence hunters and fishers in the western Arctic, the nearshore sea-ice zone remains an unforgiving and dynamic environment. Traditional hunters constantly hone site-specific experiences and skills with which to optimize the reward-to-risk ratio inherent in operating from this coastal ice. Nearshore ice conditions nevertheless can change suddenly, endangering even the most experienced subsistence hunters. This study examines two (of several) 20th-century events, 40 years apart, in which shorefast ice failed, threatening Inupiat whale hunters with loss of confidence, livelihood, and life. These events differed in character. In one event, the shorefast ice was crushed by moving ice floes. In the other, the shorefast ice broke free of land. Our examination focuses on the relationship of subsistence hunters to the ice, the environmental causes of ice failures, the evolving technology for predicting ice behavior, and the longer-term implications of global change for this system. The complexity of geophysical processes underlying coastal ice behavior makes ice failures unpredictable. Thus, hunters must assume and manage risk. The variable and uncertain environment to which whale hunters are accustomed has produced an inherent flexibility that has helped them adapt to new conditions and will continue to do so in the future.

Historical Fluctuations of the Matusevich Ice Shelf, Severnaya Zemlya, Russian High Arctic

Dramatic retreat of ice shelves in Antarctica in recent years, linked to climatic warming, is well documented. In contrast, the ice shelves of the Russian Arctic remain largely unstudied. A time-series analysis of the largest ice shelf in the Russian High Arctic, the Matusevich Ice Shelf, Severnaya Zemlya, was undertaken for the period 1931 to 1994 using georeferenced Landsat satellite imagery and published maps. The positions of three major ice margins in 1931, 1955, 1962, 1973, 1985, 1988, and 1994 are compared. The floating margin of the ice shelf underwent at least two cycles of retreat followed by periods of advance between 1931 and 1994. These periodic calving events produce tabular icebergs up to several kilometers in length. This process is typical of floating ice shelves in Antarctica and Greenland, whereas grounded ice margins in, for example, Svalbard, produce smaller icebergs much more frequently. There is little evidence that these calving events are related to climate change.Landsat imagery is also used to track the movement of 50 icebergs identified in 1985 imagery of Matusevich Fjord. Iceberg release from the fjord between 1985 and 1994 was extremely slow, with 48 of the icebergs observed in 1985 still trapped in the fjord in 1994. The icebergs from Matusevich Ice Shelf remain in the fjord for many years, probably due to either grounding on submarine moraines or trapping by shore-fast sea ice. Much of the sediment load of the trapped icebergs may be melted out and deposited beneath the sea-ice cover of Matusevich Fjord, and little iceberg-rafted debris of heterogeneous grain size will be transported to the Laptev Sea.

Historical Fluctuations of the Matusevich Ice Shelf, Severnaya Zemlya, Russian High Arctic

Dramatic retreat of ice shelves in Antarctica in recent years, linked to climatic warming, is well documented. In contrast, the ice shelves of the Russian Arctic remain largely unstudied. A time-series analysis of the largest ice shelf in the Russian High Arctic, the Matusevich Ice Shelf, Severnaya Zemlya, was undertaken for the period 1931 to 1994 using georeferenced Landsat satellite imagery and published maps. The positions of three major ice margins in 1931, 1955, 1962, 1973, 1985, 1988, and 1994 are compared. The floating margin of the ice shelf underwent at least two cycles of retreat followed by periods of advance between 1931 and 1994. These periodic calving events produce tabular icebergs up to several kilometers in length. This process is typical of floating ice shelves in Antarctica and Greenland, whereas grounded ice margins in, for example, Svalbard, produce smaller icebergs much more frequently. There is little evidence that these calving events are related to climate change. Landsat imagery is also used to track the movement of 50 icebergs identified in 1985 imagery of Matusevich Fjord. Iceberg release from the fjord between 1985 and 1994 was extremely slow, with 48 of the icebergs observed in 1985 still trapped in the fjord in 1994. The icebergs from Matusevich Ice Shelf remain in the fjord for many years, probably due to either grounding on submarine moraines or trapping by shore-fast sea ice. Much of the sediment load of the trapped icebergs may be melted out and deposited beneath the sea-ice cover of Matusevich Fjord, and little iceberg-rafted debris of heterogeneous grain size will be transported to the Laptev Sea.

On modelling an iceberg embedded in shore-fast sea ice

The effect of long ice-coupled waves impinging on a tabular iceberg, an ice island or a thick sea ice floe trapped within a thin veneer of shore fast sea ice of substantial extent is considered. The waves most likely originate as ocean waves in the open sea beyond the fast ice boundary, from where they propagate into the sea ice. There their character is altered because of the flexural properties of the ice. The geophysical / engineering problem posed is solved by a Green's function method that redevelops, for a different surface boundary condition, an earlier study concerned with a freely floating ice floe. Reflection and transmission coefficients for the berg are found to depend strongly on its thickness and length. Amongst other things, the work relates to the operational safety of natural and artificially thickened Arctic ice platforms located in a contiguous ice sheet.

An origin for laminated glacimarine sediments through sea‐ice build‐up and suppressed iceberg rafting

Laminated glacimarine sediments are observed in visual core logs and x‐radiographs from Scoresby Sund and Nansen Fjord, east Greenland. They are mostly underlain and overlain by massive or stratified glacimarine diamicton (Dmm or Dms), which is a product of iceberg delivery of heterogeneous debris and, in Scoresby Sund, reworking by deep‐drafted iceberg keels. The laminated sediments are AMS radiocarbon dated to two cold periods since the last, Late Weichselian deglaciation: the Younger Dryas stadial (Milne Land Stadial in east Greenland) and the Little Ice Age. During cold climatic events, multiyear shorefast sea ice (‘sikussak’) formed in these fjords and trapped the icebergs. Fine‐grained, laminated muds (Fl) were deposited in Scoresby Sund when the flux of icebergs was suppressed, but turbid meltwater continued to provide some sediment flux to the fjord systems, varying through time to produce laminations. In Nansen Fjord, thinner and often massive mud layers (Fm) resulted from shorter intervals of sea‐ice cover with no ice rafting. Stratified diamicton layers (Dms), which alternate with mud deposition to produce a laminated unit, probably represent intervening times of more open conditions with iceberg rafting. In Scoresby Sund, foraminifera are either absent from the laminated unit or begin to appear towards the end of its deposition. The absence of both benthic and planktonic foraminifera also suggests that multiyear sea ice was covering the core sites. There is no evidence of macrofaunal activity, and bioturbation is absent from the laminated sediments. Satellite data show that multiyear shorefast sea ice is present in several areas of the high Arctic today, and this traps icebergs calved from interior ice‐cap drainage basins. Thus, the process of laminated glacimarine sediment formation is likely to be applicable to a number of areas of the modern and Quaternary Arctic.

Ringed seal diving behavior in the breeding season

The behavior of 14 ringed seals (Phoca hispida) diving under shore-fast sea ice was monitored acoustically during the spring breeding season. Frequent dives with extended periods at depth by subadult and adult seals, including lactating females, were interpreted to be foraging dives. Median dive durations were less than 10.0 min for all seals, and the maximal observed duration was 26.4 min. The maximal observed dive depth, 222 m, was limited by water depth in the study area. Modal dive depths were between 10 and 45 m for breeding-age males and between 100 and 145 m for subadult males and postparturient females. Median dive durations were 4.0 min for adult males and 7.5 min for adult females. Body mass was a better predictor of maximal dive duration (r2 = 0.94) than was age, but maximal durations were shorter than were predicted using measures of oxygen stores and presumed metabolic rates. There was no consistent relationship between light level and the frequency or depth of dives.

On the oblique reflexion and transmission of ocean waves at shore fast sea ice

A mathematical model is reported describing the oblique reflexion and penetration of ocean waves into shore fast sea ice. The arbitrary depth model allows all velocity potentials occurring in the open water region to be matched precisely to their counterparts in the ice-covered region. Matching is done using a preconditioned conjugate gradient technique which allows the complete solution to be found to a predefined precision. The model enables the reflexion and transmission coefficients at the ice edge to be found, and examples are reported for ice plates of different thicknesses. A critical angle is predicted beyond which no travelling wave penetrates the ice sheet; in this case the deflexion of the ice is due only to evanescent modes. Critical angle curves are provided for various ice thicknesses on deep, intermediate and shallow water. The strain field which is set up within the ice sheet due to the incoming waves is also discussed; principal strains are provided as are the strains normal to the ice edge. Finally the spreading function within the ice cover, and some consequences of this function to unimodal seas with realistic open water spreading functions, are reported with the aim of generalizing the work to model the effect of shore fast ice on an incoming directional wave spectrum of specified structure.

The breakup of shore fast sea ice

Recent theoretical studies of the reflection and transmission of ocean waves at a shore fast ice boundary (Fox and Squire, 1990, 1991a) have demonstrated conclusively that it is necessary to include the complete set of wave modes in the open water region and beneath the sea ice. In this paper these studies are extended by including viscosity in the model, so that the theory conforms to the few data which are available (Squire, 1984a; Squire and Fox, 1992). Consequential changes to the properties of the ice-coupled waves are then reported, and in particular a mechanism for the breakup of sea ice plates is proposed which is in accord with observations.

Reflection and transmission characteristics at the edge of shore fast sea ice

The reflection and transmission of ocean waves at a sea ice boundary is reconsidered. The sea ice is modelled as a continuous, thin elastic plate of uniform thickness, floating on water of arbitrary constant depth. Unlike earlier solutions, matching of potentials between the free surface domain and the ice‐covered domain is done at all depths; previous solutions were incompletely matched, as the potentials in each domain were deficient. In the present solution a number of the infinity of evanescent modes, which were hitherto ignored, are included in the solution and allow matching to be carried out by minimization of an integrated error term from surface to seafloor. Reflection and transmission are found to be markedly influenced by the inclusion of these modes, suggesting that conclusions based on the incomplete potentials may be substantially in error.