Breakup Of Floes Research Articles

Revisiting Winter Arctic Ice Mass Balance Observations With a 1‐D Model: Sensitivity Studies, Snow Density Estimation, Flooding, and Snow Ice Formation

AbstractWe used a state‐of‐the art one‐dimensional snow and ice model (the LIM1D model), to simulate data collected in winter 2015 north of Svalbard with ice mass balance instruments. The quality of the simulations was assessed by comparing simulated temperature profiles and sea ice thicknesses with the data: The root‐mean‐square difference between observed and modeled temperature was 1.06 °C in snow and 0.19 °C in ice, and the root‐mean‐square difference between simulated and observed ice thickness was 2.0 cm (snow depth was prescribed). The long‐wave heat flux from the ERA‐I reanalysis was adequate to perform winter numerical simulations; in contrast, the ERA‐I air temperature induced large errors in the snow and ice temperature. Snow density had a direct impact on heat transfers and, thus, on the simulation. The joint use of the data and the simulations permitted the adjustment of the snow density profiles with a light (240 kg/m3) snow deposited on top of a denser (370 kg/m3) snow. The ice flooding, which occurred after a storm‐induced breakup of floes loaded with snow, was simulated by prescribing the observed lower limit of the snow. The simulations provided insights on the evolution of sea ice bulk salinity, brine fraction, and the amount of snow ice formed during the flooding event.

Seasonal evolution of the sea-ice floe size distribution in the Beaufort and Chukchi seas

The size distribution of ice floes in the polar seas affects the dynamics and thermodynamics of the ice cover, and ice-ocean models are beginning to include the floe size distribution (FSD) in their simulations. The FSD has previously been reported to follow a power law of the form x–α, where x is the floe size and –α characterizes how steeply the number of floes decreases as x increases. Different studies have found different values of α and different ranges of x over which the power law applies. We found that a power law describes the FSD in the Beaufort and Chukchi seas reasonably well over floe sizes from 2 to 30 km, based on 187 visible-band satellite images (resolution 250 m) acquired during spring through fall of 2013 and 2014. The mean power-law exponent goes through a seasonal cycle in which α increases in spring, peaks in July or August, and decreases in fall. June is the transition month from spring FSD to summer FSD. This cycle is consistent with the processes of floe break-up in spring followed by preferential melting of smaller floes in summer and the return of larger floes after fall freeze-up. We also analyzed 12 high-resolution satellite images acquired near the low-resolution images in space and time. We found that the FSDs from the high-resolution images follow power laws over floe sizes from 10 m to 3 km. While the power-law exponents of the corresponding high- and low-resolution images do not always match in a strict statistical sense, they suggest the plausibility that the FSD follows a single power law over a wide range of floe sizes. This study covers a larger spatial and temporal sampling space and is based on more satellite images than previous studies. Results have been used for model calibration and validation.

Modelling wave-induced sea ice break-up in the marginal ice zone.

A model of ice floe break-up under ocean wave forcing in the marginal ice zone (MIZ) is proposed to investigate how floe size distribution (FSD) evolves under repeated wave break-up events. A three-dimensional linear model of ocean wave scattering by a finite array of compliant circular ice floes is coupled to a flexural failure model, which breaks a floe into two floes provided the two-dimensional stress field satisfies a break-up criterion. A closed-feedback loop algorithm is devised, which (i) solves the wave-scattering problem for a given FSD under time-harmonic plane wave forcing, (ii) computes the stress field in all the floes, (iii) fractures the floes satisfying the break-up criterion, and (iv) generates an updated FSD, initializing the geometry for the next iteration of the loop. The FSD after 50 break-up events is unimodal and near normal, or bimodal, suggesting waves alone do not govern the power law observed in some field studies. Multiple scattering is found to enhance break-up for long waves and thin ice, but to reduce break-up for short waves and thick ice. A break-up front marches forward in the latter regime, as wave-induced fracture weakens the ice cover, allowing waves to travel deeper into the MIZ.

In situ observations of wave-induced sea ice breakup

Ocean waves can propagate hundreds of kilometers into sea ice, leaving behind a wake of broken ice floes. Three floe breakup events were observed during the second Sea Ice Physics and Ecosystem Experiment (SIPEX-2). We show that the three breakup events were likely influenced by ocean waves. We compare the observations to a wave induced floe breakup model which includes an empirical wave attenuation model, and show that the model underestimates the extent of floe breaking for long period waves.

Effects of sediment-induced stratification on floe breakup in an idealized tidal estuary: A numerical modelling study

Floe breakup dynamics are studied by a sediment transport numerical model in an idealized tidal estuary that has a constant water depth and rapid flocculation of cohesive sediments. The focus is placed on the effects of boundary layer stratification induced by a bottom nepheloid layer on floe breakup and size distribution in the water column. In a neutrally stratified estuary, the floe size distribution follows a parabolic function with maximum values at the surface and bottom. The sediment-induced stratification in the bottom boundary layer increases the median floe sizes. Furthermore, sediment-voided convection caused by the settling lutocline generates significant turbulent kinetic energy dissipation and reduces floe size at the depth where the convective mixing happens. Below that depth, a weak local maxima in the floe size is predicted due to presence of the lutocline. The effect of sediment-stratified bottom boundary layer on the floe breakup can be consistently approximated by a linear regression between the maximal floe size and flux Richardson number.

Forces on Spherical Particles in Terms of Upstream Flow Characteristics

The paper is devoted to the estimation of hydrodynamic forces induced by different flows around an isolated solid sphere. The goal of the study is to relate the stresses exerted by the flow around the particle to the upstream flow characteristics, in particular in terms of velocity gradient in the case of pure shear flow. Three-dimensional numerical simulations have been performed. Fluent® code has been used. The computational flow dynamics (CFD) code has been first validated in classical cases of (i) uniform flow around a fixed spherical particle at low and finite Reynolds numbers (1 to 300) and (ii) linear shear superimposed to a uniform flow past a fixed spherical particle at finite Reynolds numbers (10 to 100). After the validation step of the study, the CFD code has been applied to pure linear shear flow around a fixed spherical particle. The effect of free rotation of the sphere has been analysed. The magnitude of the forces exerted on each hemisphere of a spherical particle is derived in this paper compared to forces inducing floe breakup.

Tracer studies of pathways and rates of meltwater transport through Arctic summer sea ice

At the Surface Heat Budget of the Arctic Ocean (SHEBA) program's field site in the northern Chukchi Sea, snow and ice meltwater flow was found to have a strong impact on the heat and mass balance of sea ice during the summer of 1998. Pathways and rates of meltwater transport were derived from tracer studies (H218O, 7Be, and release of fluorescent dyes), complemented by in situ sea‐ice permeability measurements. It was shown that the balance between meltwater supply at the surface (averaging between 3.5 and 10.5 mm d−1) and ice permeability (between <10−11 and >10−9 m2) determines the retention and pooling of meltwater, which in turn controls ice albedo. We found that the seasonal evolution of first‐year and multiyear ice permeability and surface morphology determine four distinct stages of melt. At the start of the ablation season (stage 1), ponding is widespread and lateral melt flow dominates. Several tens of cubic meters of meltwater per day were found to drain hundreds to thousands of square meters of ice through flaws and permeable zones. Significant formation of underwater ice, composed between <30 and >50% of meteoric water, formed at these drainage sites. Complete removal of snow cover, increase in ice permeability, and reductions in hydraulic gradients driving fluid flow mark stage 2, concurrent with a reduction in pond coverage and albedo. During stage 3, maximum permeabilities were measured, with surface meltwater penetrating to 1 m depth in the ice and convective overturning and desalination found to dominate the lower layers of first‐year and thin multiyear ice. Enhanced fluid flow into flaws and permeable zones was observed to promote ice floe breakup and disintegration, concurrent with increases in pond salinities and 7Be. Advective heat flows of several tens of watts per square meter were derived, promoting widening of ponds and increases in pond coverage. Stage 4 corresponds to freeze‐up. Roughly 40% of the total surface melt was retained by the ice cover within the ice matrix as well as in surface and under‐ice ponds (with a total net retention of 15%). Based on this work, areas of improvement for fully prognostic simulations of ice albedo are identified, calling for parameterizations of sea‐ice permeability and the integration of ice topography and refined ablation schemes into atmosphere‐ice‐ocean models.

Seasonal changes in Arctic sea-ice morphology

AbstractThe morphology of the Arctic sea-ice cover undergoes large changes over an annual cycle. These changes have a significant impact on the heat budget of the ice cover, primarily by affecting the distribution of the solar radiation absorbed in the ice-ocean system. In spring, the ice is snow-covered and ridges are the prominent features. The pack consists of large angular floes, with a small amount of open water contained primarily in linear leads. By the end of summer the ice cover has undergone a major transformation. The snow cover is gone, many of the ridges have been reduced to hummocks and the ice surface is mottled with melt ponds. One surface characteristic that changes little during the summer is the appearance of the bare ice, which remains white despite significant melting. The large floes have broken into a mosaic of smaller, rounded floes surrounded by a lace of open water. Interestingly, this break-up occurs during summer when the dynamic forcing and the internal ice stress are small During the Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment we had an opportunity to observe the break-up process both on a small scale from the ice surface, and on a larger scale via aerial photographs. Floe break-up resulted in large part from thermal deterioration of the ice. The large floes of spring are riddled with cracks and leads that formed and froze during fall, winter and spring. These features melt open during summer, weakening the ice so that modest dynamic forcing can break apart the large floes into many fragments. Associated with this break-up is an increase in the number of floes, a decrease in the size of floes, an increase in floe perimeter and an increase in the area of open water.

A simple model for turbulence induced flocculation of cohesive sediment

The transport and fate of fine grained cohesive sediments in estuarine and coastal waters is influenced by the settling velocity of the sediment, which in turn is affected by flocculation effects. The flocculation processes depend on the physico-chemical properties of the sediment and the water, and on several physical mechanisms, of which turbulence is a major one. In the present paper the effects of turbulence are further analyzed. The floes are treated as self-similar fractal entities. As a result, the settling velocity is shown not to scale with the diameter D squared, as predicted by Stokes' law, but with Dnf-1 , where nf is the fractal dimension. Based on a collision frequency function and a floe breakup formulation, a simple flocculation model is proposed that can be solved analytically for uniform conditions. The flocculation and floe breakup coefficients were obtained from experiments described in literature. It is shown that the maximal attainable floe size and settling velocity are determined to a large extent, especially at low turbulence levels, by the available residence time, i.e. water depth.

Quantitative analysis of sea ice remote sensing imagery

Abstract Abstract. Mathematical morphology seems to provide a consistent framework for an automatic analysis and description of sea ice geometry that is accessible from remote sensing imagery. This paper reviews basic concepts of the actual theory used and illustrates it by several examples based on a digitized video image, a digitized aerial photograph and a SPOT image. By means of morphological operations, floe size distributions are estimated automatically and related to fractal dimensions. The paper outlines a fast algorithm to trace single ice floes surviving in an image time sequence. The technique can be extended to monitor ice floe breakup. The analysis is performed exclusively on the basis of information about the relative order of pixel values. Physical considerations are kept to a minimum.

Dispersion of coagulated particles by contractile flow to orifice.

The breakup of floes composed of a small number of constituent particles by orifice contractile flow is investigated extensively by measuring the size of broken floes of PSL particles on a Coulter counter. It is found that (1) floes of maximum strength are obtained when they are formed in an electrolyte concentration greater than the critical coagulation concentration, and the strength is independent of the valency of electrolyte; (2) the average size of broken floes and the maximum number of constituent particles in a broken floe are successfully expressed as a function of the energy dissipation at the orifice; and (3) the mechanism of floe breakup in the contractile flow is different from that by ultrasonication (flocs are split into smaller agglomerates in the former case, but particles are ripped off one by one from the surface of flocs in the latter case).

EFFECTS OF DOSING AND MIXING CONDITIONS ON POLYMER FLOCCULATION OF CONCENTRATED SUSPENSIONS

A simple monitoring technique has been used to derive information on Hoc growth and break-up in agitated clay suspensions of quite high solids content (1 and 3% w/v), under the influence of a high molecular weight cationic polymer. For fairly low polymer dosages and high mixing speeds floe growth in the 3% suspensions can be very fast initially, but the floes rapidly break up and do not re-form, even when the stirring speed is subsequently reduced. By reducing the mixing speed very soon after polymer dosing (typically after a few seconds), the break-up can be prevented and floes maintained at larger sizes. This effect is much less apparent for 1% solids suspensions, where longer periods of rapid mixing can be tolerated without significant floe break-up. For the higher solids case, great improvements in flocculation can be achieved by modifying the polymer dosing procedure—either by adding the solution over an extended period or by dosing a more dilute solution. These changes have much less effect at the l...

The Effects of Temperature on Turbulent Flocculation: Fluid Dynamics and Chemistry

One of the primary objectives of the research described here was to identify the best available measure of the intensity of turbulence with a view to correcting the mixing intensity of the flocculation process to compensate for temperature effects. It was concluded, however, that no one measure of turbulence intensity is better than another. The authors observed that flocculation efficiency at 20°C is not sensitive to impeller geometry, but at 5°C impeller geometry is much more important. A turbine impeller caused much more floe breakup than a stake and stator impeller. With metal coagulants, the use of constant pOH is appropriate for correcting system chemistry for temperature effects. Alum floc was significantly weaker than iron floc under all conditions tested.

Field experiments on wave-ice interaction in the Labrador and east Greenland currents, 1978

Two field experiments took place in 1978 as part of a project to study ocean wave attenuation in the marginal pack ice zone and the effect of ocean waves on floe break-up and ice dynamics. The main partners in the project are the Scott Polar Research Institute and the Electromagnetics Institute, Technical University of Denmark (TUD), Lyngby, with funding from the Office of Naval Research (ONR), Washington DC, and the Danish government. The first experiment was a pilot study carried out in co-operation with C-CORE (Centre for Cold Oceans Resources Engineering) at Memorial University of Newfoundland, St John's, and took place in the Labrador Sea. The second experiment was a major field study carried out in September 1978 from Mesters Vig, east Greenland. The project will be completed by a second main experiment at Mesters Vig in summer 1979, with supporting experiments in the Bering Sea and west Greenland in spring 1979.