Sea Ice Floes Research Articles

Experimental and theoretical models of wave-induced flexure of a sea ice floe

An experimental model is used to validate a theoretical model of a sea ice floe’s flexural motion, induced by ocean waves. A thin plastic plate models the ice floe in the experiments. Rigid and compliant plastics and two different thicknesses are tested. Regular incident waves are used, with wavelengths less than, equal to, and greater than the floe length, and steepnesses ranging from gently sloping to storm-like. Results show the models agree well, despite the overwash phenomenon occurring in the experiments, which the theoretical model neglects.

Small-scale deformation of an Arctic sea ice floe detected by GPS and satellite imagery

Small-scale (~100–200m) deformations of an Arctic sea ice floe were detected from multiple GPS-equipped buoys that were deployed on the same ice floe. Over a nine-month period three deformation events were recorded. At each case the event was of limited duration, each lasting less than a day. The events were highly compressive in nature with the area occupied by the buoy array decreasing by over half of the original area. The strain rate during the deformation, of the order of 10−5s−1, is about three orders of magnitude larger than previous estimates for brittle fracturing for cracks of about 100m in length. On the 2 day time scale, the strain rate became too small and none of the deformation events could be detected. This suggests that satellite data with longer time scales may significantly underestimate the amount of intermittent, small-scale brittle failure of total deformation. Taken as a whole, our results show the influence that large-scale wind stress can have on small-scale deformation. However, it is important to note that the impact of large-scale wind stress is also dependent on the properties of sea ice as well as on the spatial and temporal evolution of the underlying forces that influence the fracturing process.

Sea-ice freeboard retrieval using digital photon-counting laser altimetry

AbstractAirborne and spaceborne altimeters provide measurements of sea-ice elevation, from which sea-ice freeboard and thickness may be derived. Observations of the Arctic ice pack by satellite altimeters indicate a significant decline in ice thickness, and volume, over the last decade. NASA’s Ice, Cloud and land Elevation Satellite-2 (ICESat-2) is a next-generation laser altimeter designed to continue key sea-ice observations through the end of this decade. An airborne simulator for ICESat-2, the Multiple Altimeter Beam Experimental Lidar (MABEL), has been deployed to gather pre-launch data for mission development. We present an analysis of MABEL data gathered over sea ice in the Greenland Sea and assess the capabilities of photon-counting techniques for sea-ice freeboard retrieval. We compare freeboard estimates in the marginal ice zone derived from MABEL photon-counting data with coincident data collected by a conventional airborne laser altimeter. We find that freeboard estimates agree to within 0.03 m in the areas where sea-ice floes were interspersed with wide leads, and to within 0.07 m elsewhere. MABEL data may also be used to infer sea-ice thickness, and when compared with coincident but independent ice thickness estimates, MABEL ice thicknesses agreed to within 0.65 m or better.

海氷群を伴った遡上津波のピロティ形式の建築物への作用に関する研究

海氷群を伴った遡上津波のピロティ形式の建築物への作用に関する研究

Influence of synoptic atmospheric conditions on movement of individual sea-ice floes in Fram Strait, late summer 2010

AbstractIn this paper we investigate the effect on sea-ice movement of changes in the synoptic atmospheric conditions in late boreal summer 2010. Our study area is the western Fram Strait, a crucial passage for the transport of ice out of the Arctic basin. Ice dynamics here affect the movement of ice in the East Greenland Current, the transpolar drift and ice extent in the Arctic Ocean. In contrast to other times of the year, when the Fram Strait wind field is characterized by strong, persistent northerlies, we show that the weaker, more variable winds typical during late summer for the Fram Strait can slow movement of ice floes out of the area, thus slowing the export of ice from the Arctic Ocean at the end of summer, a time crucial for ice export. The Arctic Ocean could lose even more of the ice that survives the summer if this was not the case. This would leave the Arctic Ocean in an even more vulnerable position with regard to the amount of multi-year ice remaining the following summer.

The seasonal evolution of sea ice floe size distribution

AbstractThe Arctic sea ice cover undergoes large changes over an annual cycle. In winter and spring, the ice cover consists of large, snow‐covered plate‐like ice floes, with very little open water. By the end of summer, the snow cover is gone and the large floes have broken into a complex mosaic of smaller, rounded floes surrounded by a lace of open water. This evolution strongly affects the distribution and fate of the solar radiation deposited in the ice‐ocean system and consequently the heat budget of the ice cover. In particular, increased floe perimeter can result in enhanced lateral melting. We attempt to quantify the floe evolution process through the concept of a floe size distribution that is modified by lateral melting and floe breaking. A time series of aerial photographic surveys made during the SHEBA field experiment is analyzed to determine evolution of the floe size distribution from spring through summer. Based on earlier studies, we assume the floe size cumulative distribution could be represented by a power law D−α, where D is the floe diameter. The exponent α as well as the number density of floes Ntot are estimated from measurements of total ice area and perimeter. As summer progressed, there was an increase in α as the size distribution shifted toward smaller floes and the number of floes increased. Lateral melting causes the distribution to deviate from a power law for small floe sizes.

Arctic melt ponds and bifurcations in the climate system

Understanding how sea ice melts is critical to climate projections. In the Arctic, melt ponds that develop on the surface of sea ice floes during the late spring and summer largely determine their albedo – a key parameter in climate modeling. Here we explore the possibility of a conceptual sea ice climate model passing through a bifurcation point – an irreversible critical threshold as the system warms, by incorporating geometric information about melt pond evolution. This study is based on a bifurcation analysis of the energy balance climate model with ice-albedo feedback as the key mechanism driving the system to bifurcation points.

Experimental study of wave-driven impact of sea ice floes on a circular cylinder

The impact of isolated sea ice floes with offshore structures is a significant environmental hazard for Arctic offshore operations. Most attention to date has focused on the impact of glacial icebergs, and very large drifting ice floes with offshore structures. There appears to be a lack of data in the case of isolated, wave-forced floe–structure interactions. To address this an experimental investigation was conducted to identify impact characteristics of floes of various shapes and sizes with a single circular cylinder. A wide selection of regular and irregular wave conditions were examined and the floe kinematics and impact characteristics determined. In regular waves, the results showed floe kinematic heave and surge responses was unaffected by the presence of the structure at distances of x/D~≥10. At x/D≤10 a slight increase in heave response was observed. In the same region, surge was markedly reduced regardless of whether there was an eventual impact. Drift velocity appeared to be the main control on whether the floe would impact (if drift velocity was high enough) or become trapped in the lee of the cylinder and be deflected to one side before impact. 3D analysis of impacts showed that two broad types of impact occurred; a relatively head-on impact and a more side-on impact. Head-on impacts were dominated by linear kinetic energy, while side on and secondary impacts exhibited increased rotational kinetic energy. In irregular waves, the impacts were found to occur at any point in the wave cycle, whereas the impacts in regular waves tended to occur at the point of maximum surge near the crest of the wave. The influence of λ/Lc and H/λ on impact occurrence and characteristics was investigated. While H/λ did not have a significant effect on impact occurrence, it appeared that the lower the λ the greater the chance of impact. The influence of Lc and shape in irregular waves indicated larger Lc and cross-sectional area of the floe relative to the cylinder increased impact occurrence.

Spatio-temporal video segmentation with shape growth or shrinkage constraint.

We propose a new method for joint segmentation of monotonously growing or shrinking shapes in a time sequence of noisy images. The task of segmenting the image time series is expressed as an optimization problem using the spatio-temporal graph of pixels, in which we are able to impose the constraint of shape growth or of shrinkage by introducing monodirectional infinite links connecting pixels at the same spatial locations in successive image frames. The globally optimal solution is computed with a graph cut. The performance of the proposed method is validated on three applications: segmentation of melting sea ice floes and of growing burned areas from time series of 2D satellite images, and segmentation of a growing brain tumor from sequences of 3D medical scans. In the latter application, we impose an additional intersequences inclusion constraint by adding directed infinite links between pixels of dependent image structures.

An improved CryoSat-2 sea ice freeboard retrieval algorithm through the use of waveform fitting

Abstract. We develop a physical model capable of simulating the mean echo power of CryoSat-2 SAR- and SARIn-mode waveforms over sea-ice-covered regions. The model simulations are used to show the importance of variations in the radar backscatter coefficient with incidence angle and surface roughness for the retrieval of surface elevation of both sea ice floes and leads. The physical model is used to fit CryoSat-2 waveforms to enable retrieval of surface elevation through the use of lookup tables and a bounded trust region Newton least-squares fitting approach. The use of a model to fit returns from sea ice regions offers advantages over currently used threshold retracking methods, which are here shown to be sensitive to the combined effect of bandwidth-limited range resolution and surface roughness variations. Laxon et al. (2013) have compared ice thickness results from CryoSat-2 and IceBridge, and found good agreement; however consistent assumptions about the snow depth and density of sea ice were not used in the comparisons. To address this issue, we directly compare ice freeboard and thickness retrievals from the waveform-fitting and threshold tracker methods of CryoSat-2 to Operation IceBridge data using a consistent set of parameterizations. The purpose of the comparison is to highlight the physical basis between differences in the retracking methods. For three IceBridge campaign periods from March 2011 to March 2013, mean differences (CryoSat-2 – IceBridge) of 0.144 and 1.351 m are found between the freeboard and thickness retrievals, respectively, using a 50% sea ice floe threshold retracker, while mean differences of 0.019 and 0.182 m are found when using the waveform-fitting method. This suggests the waveform-fitting technique is capable of better reconciling the sea ice thickness data record from laser and radar altimetry data sets through the usage of consistent physical assumptions.

Experimental study on kinematics of sea ice floes in regular waves

Ice floes in severe Arctic seas can gain significant kinetic energy. Such a fast moving floe presents a significant impact threat to offshore structures. Most attention to date has focused on glacial icebergs, which are now reasonably well understood; there appears a lack of knowledge in the case of isolated sea ice floes. To address this an experimental investigation of the relationships of the motion response of floes to the floe and wave characteristics was conducted. Of greatest importance to impact force calculations are the heave and surge motions, as well as the velocity and acceleration of a floe in waves. The tested variables included a wide range of regular waves with a variety of floe model shapes and sizes. The results showed that scale effect, floe size, floe orientation and surface roughness did not affect the heave and surge motion, and the motion observed was notably different to glacial icebergs. Wavelength affected motion the most; all models displayed fluid particle-like motion paths at λ between 3.3 and 5 times their characteristic lengths and the majority of scatter between different floe geometries in motion response was confined λ/Lc<8. Floe thickness also had a dramatic effect on heave and surge, with thicker models experiencing significant resonances. Drift velocity matched Stokes drift quite well, though the larger models appeared to show greater than predicted drift velocities. Maximum velocities did not generally exceed particle velocity, but remained >0.7 VP for surge and >0.8 VP for heave at λ/Lc≥5. Such high velocities at shorter λ suggest that a more conservative design approach may be necessary. An extrapolation of these velocities leads to a conclusion that prototype ice floes can obtain kinetic energies of 106J in certain conditions.

The anomalous low and high temperatures of 2012 over Greece – an explanation from a meteorological and climatological perspective

Abstract. 2012 was the hottest year in Greece on the basis of the available record dating back to 1958, displaying at the same time the widest annual temperature range. During the summer and autumn months, numerous regions in the domain of study experienced record-breaking maximum and minimum temperatures. Conversely, the winter period was particularly cold and January one of the coldest months over the last 55 yr. The analysis of the cold period indicates that the synoptic conditions resemble the positive phase of the Eastern Mediterranean Pattern (EMP). The predominance of these cool conditions seems to be related primarily to an intense NNW or NNE atmospheric circulation, as a consequence of the positive EMP phase. Moreover, the reduction in the floating sea ice emerges as a key driver of the formation of a low-pressure pattern and the reinforcement of the trough south of Scandinavia, which in turn strengthened the Siberia High east of the trough. This reinforcement resulted in a blocking pattern and in favorable conditions for the EMP formation. The atmospheric circulation during the prolonged high-temperature period resembles, respectively, the negative phase of North Sea–Caspian Pattern teleconnection. The observed positive pole, in conjunction with the strong southwestern circulation, results in temperature increases and in the development of a smooth pressure field that contributes to the weakening of the Etesian winds and therefore to calm conditions over the continental areas.

Carbon contribution of sea ice floes in the Arctic Ocean

To estimate detailed contributions of particulate organic carbon (POC) as a potential food source in various environments of the Arctic sea ice floes, intensive investigations were executed at two different types of sea ice stations (ST 1 and ST 2) in the northern Chukchi Sea during the summer period in 2011. The average uptake rates of carbon and nitrogen in melt ponds from this study were within the range measured previously. The surface ice of melt ponds at ST 1 had the highest POC concentration with a mean of 148.0mgCm−3 (S.D.=±86.0mgCm−3), followed by sea ice cores at ST 2 (mean±S.D.=125.7±128.2mgCm−3). The POC concentrations in melt ponds ranged between 90.0mgCm−3 (S.D.=±12.7mgCm−3) and 103.9mgCm−3 (S.D.=±47.7mgCm−3) at ST 1 and ST 2, respectively. Major POC contributors to melt ponds were diatoms with a mean biovolume contribution of 48.7% (S.D.=±39.1%) which was strongly related to in situ salinity. Although the total POC concentration of entire sea ice floes ranged from 2.8% to 5.3% of the POC concentration within the euphotic water column at the study locations, the carbon contribution of sea ice floes could be important to higher trophic levels because of the concentrated POC within sea ice floes.

海氷群を伴った市街地への津波遡上特性に関する検討

海氷群を伴った市街地への津波遡上特性に関する検討

Wave–ice interactions in the marginal ice zone. Part 2: Numerical implementation and sensitivity studies along 1D transects of the ocean surface

The theoretical foundation of a wave–ice interaction model is reported in Part 1 of this study. The model incorporates attenuation of ocean surface waves by sea ice floes and the concomitant breaking of the floes by waves that determines the structure of the marginal ice zone (MIZ). A numerical implementation of the method is presented here. Convergence of the numerical method is demonstrated, as temporal and spatial grids are refined. A semi-analytical method, which does not require time-stepping, is also developed to validate the numerical results, when dispersion is neglected. The wave energy lost during ice breakage is parameterized, as part of the numerical method. Sensitivity studies are conducted in relation to the energy loss and also dispersive effects, the choice of the attenuation model, the properties of the wave field, and sea ice properties such as concentration, thickness and breaking strain. Example simulations intended to represent conditions in the Fram Strait in 2007, which exploit reanalyzed wave and ice model data, are shown to conclude the results section. These are compared to estimates of MIZ widths based on a concentration criteria, and obtained from remotely-sensed passive microwave images.

Sea Ice Identification and Derivation of Its Velocity Field by X-Band Doppler Radar

Abstract In this study a 3D scanning X-band Doppler radar (XDR) was deployed near the coast of the Sea of Okhotsk, Hokkaido, Japan, in November 2005 to simultaneously observe sea ice and snow clouds. Doppler radars are commonly used to detect wind fields within precipitating clouds. However, thus far, there have been no reports of observing sea ice with Doppler radar. Making use of the radar reflectivity, Doppler velocity, and spectrum width, sea ice floes were identified under various weather conditions. Also presented is a new method that combines Doppler radar data and sea ice velocity—extracted using the cross-correlation method—to derive a high-spatial-resolution horizontal distribution of the velocity of sea ice floes. These methods will contribute to short-term forecasting of sea ice conditions and navigation through ice-covered seas and the development and verification of high-resolution dynamic sea ice models.

Brinicles as a Case of Inverse Chemical Gardens

Brinicles are hollow tubes of ice from centimeters to meters in length that form under floating sea ice in the polar oceans when dense, cold brine drains downward from sea ice to seawater close to its freezing point. When this extremely cold brine leaves the ice, it freezes the water it comes into contact with: a hollow tube of ice-a brinicle-growing downward around the plume of descending brine. We show that brinicles can be understood as a form of the self-assembled tubular precipitation structures termed chemical gardens, which are plantlike structures formed on placing together a soluble metal salt, often in the form of a seed crystal, and an aqueous solution of one of many anions, often silicate. On one hand, in the case of classical chemical gardens, an osmotic pressure difference across a semipermeable precipitation membrane that filters solutions by rejecting the solute leads to an inflow of water and to its rupture. The internal solution, generally being lighter than the external solution, flows up through the break, and as it does so, a tube grows upward by precipitation around the jet of internal solution. Such chemical-garden tubes can grow to many centimeters in length. In the case of brinicles, on the other hand, in floating sea ice we have porous ice in a mushy layer that filters out water, by freezing it, and allows concentrated brine through. Again there is an osmotic pressure difference leading to a continuing ingress of seawater in a siphon pump mechanism that is sustained as long as the ice continues to freeze. Because the brine that is pumped out is denser than the seawater and descends rather than rises, a brinicle is a downward-growing tube of ice, an inverse chemical garden.

Random Sample

An autonomous underwater vehicle has produced the first 3D map of the underside of an East Antarctic sea ice floe, revealing an upside-down landscape reminiscent of mountains, lakes, and valleys. In other news, Peter Liddicoat, a materials scientist at the University of Sydney in Australia, has won this year's "Dance Your Ph.D." contest for his burlesque interpretation of his thesis titled "Evolution of nanostructural architecture in 7000 series aluminium alloys during strengthening by age-hardening and severe plastic deformation."

Identification and tracking of individual sea ice floes from ENVISAT wide swath SAR images: a case study from Fram Strait

Observations from satellites play an important role in tracking sea ice movement. Synthetic aperture radar (SAR) images are preferred because they are neither weather nor daylight dependent. Tracking the movement of individual objects (icebergs or sea ice floes) that may threaten ships or installations is of particular interest. The Ice Tracking from SAR Images (ITSARI) algorithm was originally developed to track large icebergs in the Antarctic. An adaptation of this algorithm to identify and track the movement of sea ice floes in Arctic conditions is presented, using ENVISAT wide swath SAR images of the Fram Strait acquired at 1–3-day intervals during the month of February 2008. It is shown that the algorithm can be successfully adapted to gain a general sense of the direction of movement of the ice due to both winds and ocean currents and, significantly, to identify and track specific objects of interest over a series of images.

Influence of ice concentration and floe-size distribution on cluster formation in sea-ice floes

AbstractAt medium ice concentrations, sea ice consists of separate floes of different sizes interacting with each other through inelastic collisions, in a way similar to two-dimensional polydisperse granular gases. The dynamics of this type of ice cover is poorly understood. In this paper, a molecular-dynamics sea-ice model based on simplified momentum equations and a hard-disk collision model is used to analyze processes of cluster formation in sea-ice floes. The clusters, formed due to size-dependent equilibrium velocities of floes under a given forcing, have statistical properties dependent on the average ice concentration and on the parameters of the floe-size distribution. In particular, in terms of the size of the largest cluster in the system, two regimes are observed: one at low and one at high ice concentration. At high ice concentration, the dominating cluster spans the entire model domain and contains the majority of floes. The exponent of the cluster-size distribution increases with increasing exponent of the floe-size distribution. The results are discussed from the point of view of the collisional contribution to the internal stress in the ice, as well as from the role of clustering in the floe-formation processes. Thus, they may contribute to the formulation of more reliable sea-ice rheology models valid at medium ice concentrations.