Total Ice Mass Research Articles

What drove the dramatic retreat of arctic sea ice during summer 2007?

A model study has been conducted of the unprecedented retreat of arctic sea ice in the summer of 2007. It is found that preconditioning, anomalous winds, and ice‐albedo feedback are mainly responsible for the retreat. Arctic sea ice in 2007 was preconditioned to radical changes after years of shrinking and thinning in a warm climate. During summer 2007 atmospheric changes strengthened the transpolar drift of sea ice, causing more ice to move out of the Pacific sector and the central Arctic Ocean where the reduction in ice thickness due to ice advection is up to 1.5 m more than usual. Some of the ice exited Fram Strait and some piled up in part of the Canada Basin and along the coast of northern Greenland, leaving behind an unusually large area of thin ice and open water. Thin ice and open water allow more surface solar heating because of a much reduced surface albedo, leading to amplified ice melting. The Arctic Ocean lost additional 10% of its total ice mass in which 70% is due directly to the amplified melting and 30% to the unusual ice advection, causing the unprecedented ice retreat. Arctic sea ice has entered a state of being particularly vulnerable to anomalous atmospheric forcing.

Thickness distribution of Antarctic sea ice

Ship‐based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around Antarctica. The data set comprises 23,373 observations collected over more than 2 decades of activity and has been compiled as part of the Scientific Committee on Antarctic Research (SCAR) Antarctic Sea Ice Processes and Climate (ASPeCt) program. The results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness, surface ridging, snow cover, and local variability for each region and season. A simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography, to provide a best estimate of the total ice mass, including the ridged component. The long‐term mean and standard deviation of total sea ice thickness (including ridges) is reported as 0.87 ± 0.91 m, which is 40% greater than the mean level ice thickness of 0.62 m. Analysis of the structure function along north/south and east/west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100–300 km, which we use as a basis for presenting near‐continuous maps of sea ice and snow cover thickness plotted on a 2.5° × 5.0° grid.

The effect of aerosol composition and concentration on the development and anvil properties of a continental deep convective cloud

AbstractA 3‐D cloud‐resolving model including an explicit aerosol module is used to examine the influence of a range of hygroscopic (CCN) and hydrophobic (IN) aerosol concentrations on the development of a mid‐latitude, continental deep convective cloud. The model reproduces a response to changes in CCN which is in agreement with previous studies of continental convection, i.e. lower precipitation rates and a later onset of deep convection for high CCN concentrations. However, the response is non‐linear and for low increments of CCN, coalescence and graupel formation becomes more efficient, which increases the total precipitation, i.e. a response similar to what has been obtained for oceanic deep convection. This result indicates the importance of using a range of CCN concentrations when examining aerosol influence on deep convection. The simulations show that an increased IN concentration has a substantial influence on the convective cloud development. Higher IN concentrations generally result in higher updraught velocities, a prolonged precipitation event and larger total precipitation amounts. The radiative forcing exerted by the cloud is determined by the anvil extent and ice crystal size. The anvil area is linked to the average updraught velocity which in turn is found to be correlated with the IN concentration. Homogeneously nucleated ice crystals dominate the total anvil ice mass formed, but heterogeneously formed ice crystals may significantly alter the homogeneous freezing process. For the simulated case, a key parameter for determining whether the number of homogeneously nucleated ice crystals will decrease or increase with increasing IN concentration is the initial updraught velocity. This dependence makes the results sensitive to the amount of heterogeneously formed ice crystals. Copyright © 2007 Royal Meteorological Society

In fluence parameters for a polar mesocyclone development

Polar mesocyclones are small-scale, short-living phenomena in the Arctic and Antarctic. Their forecast is difficult due to a lack of knowledge of initial and boundary conditions. Idealised sensitivity studies are performed with the mesoscale atmosphere - sea ice model METRAS-MESIM to evaluate the relevance of the large-scale meteorological situation and sea ice cover for surface heat fluxes and a mesocyclone development. The evaluation area is 340 km x 340 km, and a sea ice distribution typical for the Fram Strait is used. The area averaged surface heat flux strongly depends on the ice distribution. The surface heat flux is about 95 W m -2 for a mesocyclone moving close to the ice edge and a high sea ice concentration of 97 % in the ice covered region. Ice thickness and ocean currents do not significantly influence the average surface heat fluxes. A large-scale situation that alters the cyclone track and forces the cyclone to mostly move over ice (cover 97 %) reduces the average surface heat flux by 30 %. An increase of the heat flux by 81 % is found for a homogeneous ice distribution with the same total sea ice mass. A decrease of sea ice concentration from 97 % to 75 % increases the average surface heat flux by 44 %. Thus, for the forecast of average surface heat fluxes during a cyclone passage the knowledge of the sea ice distribution is more relevant than the knowledge of the cyclone track. The break up of sea ice distant from the ice edge might trigger the development of enhanced baroclinicity over ice covered regions and, thus, favour conditions for a mesocyclone intensification. The mesocyclone development is mainly determined by intensification at the ice edge resulting from enhanced surface heat fluxes and horizontal temperature gradients in that region. If the cyclone moves over densely ice covered regions the central pressure is up to 6 hPa higher than when it passes close to the ice edge. A homogeneous sea ice cover leads to a maximum pressure difference of 4 hPa. A 22 % reduction of sea ice concentration in the ice covered regions results in maximum pressure deviations of 2 hPa and an increase of the area averaged wind speed by 2 m s -1 . Thus, for the forecast of minimum central pressure and wind speed of a polar mesocyclone the cyclone track with respect to the ice distribution needs to be known. The actual pressure may be influenced by the cyclone passage itself by changing the sea ice distribution.

Greenland mass balance from GRACE

We use 22 monthly GRACE (Gravity Recovery and Climate Experiment) gravity fields to estimate the linear trend in Greenland ice mass during 2002–2004. We recover a decrease in total ice mass of 82 ± 28 km3 of ice per year, consistent with estimates from other techniques. Our uncertainty estimate is dominated by the effects of GRACE measurement errors and errors in our post glacial rebound (PG) correction. The main advantages of GRACE are that it is sensitive to the entire ice sheet, and that it provides mass estimates with only minimal use of supporting physical assumptions or ancillary data.

Morphology of deformed first-year sea ice features in the Southern Ocean

A total of 42 deformed sea-ice features were identified in almost 19 km of drill profile data from the Ross, Amundsen, Bellingshausen and Weddell Seas. The features were classified according to the shapes of their keels underwater and the presence of a sail on the surface. Coupled ridges have triangular keels and sails and, with mean maximum keel depth of 3.61 m, they are the most massive of the deformed ice features. Widowed ridges have a triangular keel similar to those of coupled ridges but do not have a prominent ice sail. With a mean ridge width of 15 m, they are the narrowest of the deformed ice features. Rubble piles are the widest, but they contribute least to the total ice mass. Ignoring the ice mass of deformed ice features and approximating their thickness by surrounding level ice underestimates the total ice mass by 44–55%. First-year ridges in the Antarctic are flatter and less massive than those in the Arctic. We propose that the differences in morphology are due to differences in sampling strategies, parent-ice characteristics and the magnitude and duration of driving forces. For the purpose of estimating ice thickness from surface observations, we believe hydrostatic equilibrium is a fair assumption on large scales, but statistical relationships between variables that can be observed from the surface and variables that are hidden from the surface are not sufficiently strong and consistent for the estimation of ice thickness. In all cases, the fact that not all keels are associated with a sail and not all sails are associated with a keel should be addressed when estimating ice thickness from surface observations.

Estimating the thickness of ridged sea ice from ship observations in the Ross Sea

Ship-based observations of sea ice thickness using the Antarctic Sea Ice Processes and Climate (ASPeCt) protocol provide information on ice thickness distribution at relatively low cost. This protocol uses a simple formula to calculate the mass of ice in ridges based on surface observations. We present two new formulae and compare these with results from the “Original” formula using data obtained in the Ross Sea in autumn and winter. The new “r-star” formula uses a more realistic ratio of sail and keel areas to transform dimensions of sails to estimates of mean keel areas. As a result, estimates of “equivalent thickness” (i.e. mean thickness of ice in ridged areas) increased by over 200%. The new “Probability” formula goes one step further, by incorporating the probability that a sail is associated with a keel underwater, and the probability that keels may be found under level surfaces. This resulted in estimates of equivalent thickness comparable with the Original formula. Estimates of equivalent thickness at one or two degree latitude resolution are sufficiently accurate for validating sea ice models. Although ridges are small features in the Ross Sea, we have shown that they constitute a significant fraction of the total ice mass.

Submillimeter‐Wave Cloud Ice Radiometer: Simulations of retrieval algorithm performance

The Submillimeter‐Wave Cloud Ice Radiometer (SWCIR), developed by the Jet Propulsion Laboratory to fly on the NASA DC‐8, has ten channels from four receivers at 183, 325, 448, and 643 GHz. The SWCIR is designed to retrieve upper tropospheric cloud ice water path (IWP) and median mass equivalent sphere diameter (Dme). This paper describes the retrieval algorithm developed for the SWCIR, results from retrieval simulations, and the rationale for choosing the SWCIR frequencies. The retrieval algorithm uses Bayes theorem to combine prior information about atmospheric properties with radiative transfer simulations. The algorithm uses a precalculated database of stochastic cirrus/atmospheric profiles and corresponding simulated SWCIR brightness temperatures. Statistics of cirrus microphysics are derived from in situ cloud probe data obtained during midlatitude winter and tropical field experiments, and include correlations between temperature, particle size, and ice water content. The Bayesian algorithm effectively interpolates between database cases that approximately match the observed SWCIR brightness temperatures. Retrieval experiments are performed for midlatitude winter ice clouds with the SWCIR viewing downward from 12 km and for tropical anvil cirrus with the SWCIR viewing upward from 10 km. Each experiment simulates SWCIR brightness temperatures (with 1 K added noise) from 10000 random cloud/atmosphere profiles. For clouds with IWP greater than 5 g/m2 (which contain 97% of the simulated total ice mass) the overall median retrieval error is about 30% for IWP and 15% for Dme. The effects of liquid clouds just below ice clouds and of nonspherical ice particle shapes are small.

Autumn sea ice thickness, ridging and heat flux variability in and adjacent to Terra Nova Bay, Ross Sea, Antarctica

The variability of sea ice thickness and snow depth observed from the R/V Nathaniel B. Palmer in late May 1998 in and adjacent to Terra Nova Bay (TNB), Ross Sea, Antarctica, is described. Conductive heat fluxes are estimated on the basis of the observed snow and ice thicknesses. There was only 6% areal coverage of open water in TNB and 87% of the areal coverage of unridged ice was ≤0.3 m thick. Between the western and eastern margins of TNB there were increases in the area‐weighted unridged ice thickness (0.05–0.25 m) and the areal extent of ridging (2.5–18.5%). Ridged ice accounted for 44–66% of the total ice mass in TNB and was as vital to thickening the ice cover as it was outside the bay, where 30–60% of the total ice mass was contained within the 5–35% of ice that was ridged. Satellite passive microwave (Special Sensor Microwave Imager SSM/I) data show that the extensive ice cover in TNB was normal for this time of year probably because of the blocking effect of thick, ridged, 100% concentration pack ice outside the bay. Despite the extensive ice cover in TNB, there was an order of magnitude difference in area‐weighted mean heat flux between the bay and the pack ice. For example, depending on the choice of bulk snow thermal conductivity value ks (0.14 or 0.31 W m−1 K−1), the heat flux values for unridged ice were 199 or 216 W m−2 in TNB versus 35 or 49 W m−2 on the inbound pack ice leg and 20 or 39 W m−2 on the outbound pack ice leg. Factoring in the contribution of ridges to the ice thickness distribution decreased the heat flux in the bay and the pack ice by 25 or 36%, depending on ks. The greatest proportion of the heat flux in TNB occurred through the ice; no more than 30% of the heat loss was from open water. Since the ice conditions observed in TNB were apparently normal for the time of year, the heat fluxes also must have been quite normal.

Snow-ice accretion and snow-cover depletion on Antarctic first-year sea-ice floes

AbstractBetween austral late winter 1993 and austral autumn 1998, during five cruises aboard the research vessel Nathaniel B. Palmer, almost 300 m of core was obtained from first-year ice floes in the Ross, Amundsen and Bellingshausen Seas. Analysis of the texture, stratigraphy and stable-isotopic composition of the ice was used to assess the magnitude of the role of flooding and snow-ice formation at the base of the snowpack in the thickening of the ice cover and the thinning of the snow cover. Snow ice occurred in all ice-thickness categories and made a significant contribution to the total ice mass (12−36%) in both autumn and winter. Although the amount of snow ice was often exceeded by the amount of frazil ice and congelation ice, the thickness of individual layers of each ice type indicated that snow ice often made a greater contribution to the thermodynamic thickening of the ice cover than the other ice types. The larger quantities of frazil ice and congelation ice were primarily the result of dynamic thickening. Flooding and snow-ice formation reduced the snow cover to 42−70% of the total snow accumulation depending on time and location. On the basis of this information, ship-based snow-depth estimates were adjusted to estimate the total snow accumulation on different ice-thickness categories.

Physical and stable isotopic properties and growth processes of sea ice collected in the southern Sea of Okhotsk

This study presents physical and stable isotopic properties of sea ice in the southernmost section of the Sea of Okhotsk on the basis of observations and measurements made in 1995 and 1996 midwinter cruises. Structural analysis revealed that ice was predominantly of the granular type. Saucer‐shaped cores and wedges were seen in the cross sections of the pancakes, which indicate a rafting event in the early stage of the pancake formation. The fraction of snow with respect to the total ice mass was estimated at ∼8% from independent δ18O and density measurements. From these findings we conclude that the initial growth mechanisms of the sea ice over this region are by the frazil pancake cycle with rafting and by the snow ice formation. Analysis also shows that the formation of the snow ice induces ∼10% more salt flux through the additional freezing of the seawater. In a short (synoptic) timescale this implies that snow becomes a negative (salting) rather than a positive (freshening) source for the buoyancy flux. These results suggest critical influence of the rapid formation of the frazil pancakes and snow ice under stormy conditions on the salt and buoyancy fluxes over the region.

Recent changes in Arctic Ocean sea ice motion associated with the North Atlantic Oscillation

Examination of a new ice motion dataset of the Arctic Ocean over a recent eighteen year period (1978–1996) reveals patterns of variability that can be linked directly to the North Atlantic Oscillation. The intensity of the Icelandic Low, one of its centers of action, modulates the sea level pressure distribution over a broad region of the Arctic Ocean and the Greenland‐Iceland‐Norwegian and Barents Seas. Over the winters of 1988 through 1995, the Oscillation has remained in its positive phase contributing to coherent large‐scale changes in the intensity and character of ice transport in the Arctic Ocean. The significant changes include: the weakening of the Beaufort Gyre; the increase in ice export through the Fram Strait; the increase in ice import from the Barents/Kara Seas; the enhanced eastward transport of sea ice from the Laptev Sea; the weakening of the Transpolar Drift Stream; and, the reduction in ice extent in the Nordic Seas. All of these changes affect the regional and total sea ice mass balance of the Arctic Ocean.

Surface elevation, ice thickness, and subglacial-bedrock topography of Ekström Ice Shelf (Antarctica) and its catchment area

AbstractEkström Ice Shelf and its catchment area form a comparatively small (∼29 000 km2) drainage system in northern Dronning Maud Land, Antarctica. Aerial-altimetry and radio-echo-sounding data of this region have been used to derive detailed maps of ice-surface and bedrock topographies and ice thickness. With the new database the volumes of the floating and grounded ice in the drainage system are calculated to be ∼3200 km3 and ∼16 000 km3, respectively. This corresponds to a total ice mass of ∼17 000 Gt. Four significant graben-like depressions in the bedrock topography have been identified, which incline from inland towards the grounding line and are up to ∼16 km wide there. These structures coincide with the particular zones of concentrated ice flux into the ice shelf. The total mean annual mass discharge over the grounding line of the larger western part and the smaller eastern part of Ekström Ice Shelf is estimated to be about 3.7 Gt and 0.4 Gt, respectively. Both parts represent individual ice-shelf systems with different catchment areas, geometric characteristics and flow regimes.

Brine infiltration in the snow cover of sea ice in the eastern Weddell Sea, Antarctica

The snow cover on Antarctic sea iee often depresses the ice below sea level, allowing brine or seawaier to infíltrale, or flood the snowpack. This significantly reduces the thermal insulation properties of the snow cover, and increases the ocean/ atmosphere heat flux. The subsequent refreezing of this saturated snow or slush layer, to form snow-ice, can account for a significant percentage of the total ice mass in some regions. The extent of saturated snow cannot presently be estimated from satellite remote-sensing data and, because it is often hidden by a layer of dry snow, cannot be estimated from visual observations. Here, we use non-parametric statistics to combine sea-ice and snow thickness data from drillhole measurements with routine visual observations of snow and ice characteristics to estimate the extent of brine-infiltrated snow. The data were collected duringjuly-August 1994 from the R/V Nathaniel B. Palmer in the eastern Weddell Sea from 60° to 68° S latitude and from 20° wto 5° E longitude.

Seasonal variations in the properties and structural composition of sea ice and snow cover in the Bellingshausen and Amundsen Seas, Antarctica

AbstractSixty-three ice cores were collected in the Bellingshausen and Amundsen Seas in August and September 1993 during a cruise of the R.V.Nathaniel B. Palmer. The structure and stable-isotopic composition (18O/16O) of the cores were investigated in order to understand the growth conditions and to identify the key growth processes, particularly the contribution of snow to sea-ice formation. The structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the Bellingshausen Sea in March 1992 are reassessed. Frazil ice and congelation ice contribute 44% and 26%, respectively, to the composition of both the winter and summer ice-core sets, evidence that the relatively calm conditions that favour congelation-ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil-ice growth and pancake-ice formation. Both frazil- and congelation-ice layers have an av erage thickness of 0.12 m in winter, evidence that congelation ice and pancake ice thicken primarily by dynamic processes. The thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover. Snow-ice layers have a mean thickness of 0.20 and 0.28 m in the winter and summer cores, respectively, and the contribution of snow ice to the winter (24%) and summer (16%) core sets exceeds most quantities that have been reported previously in other Antarctic pack-ice zones. The thickness and quantity of snow ice may be due to a combination of high snow-accumulation rates and snow loads, environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow/ice interface, and bottom melting losses being compensated by snow-ice formation. Layers of superimposed ice at the top of each of the summer cores make up 4.6% of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice. The accumulation of superimposed ice is evidence that melting in the snow cover on Antarctic sea-ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass.

Seasonal variations in the properties and structural composition of sea ice and snow cover in the Bellingshausen and Amundsen Seas, Antarctica

AbstractSixty-three ice cores were collected in the Bellingshausen and Amundsen Seas in August and September 1993 during a cruise of the R.V. Nathaniel B. Palmer. The structure and stable-isotopic composition (18O/16O) of the cores were investigated in order to understand the growth conditions and to identify the key growth processes, particularly the contribution of snow to sea-ice formation. The structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the Bellingshausen Sea in March 1992 are reassessed. Frazil ice and congelation ice contribute 44% and 26%, respectively, to the composition of both the winter and summer ice-core sets, evidence that the relatively calm conditions that favour congelation-ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil-ice growth and pancake-ice formation. Both frazil- and congelation-ice layers have an av erage thickness of 0.12 m in winter, evidence that congelation ice and pancake ice thicken primarily by dynamic processes. The thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover. Snow-ice layers have a mean thickness of 0.20 and 0.28 m in the winter and summer cores, respectively, and the contribution of snow ice to the winter (24%) and summer (16%) core sets exceeds most quantities that have been reported previously in other Antarctic pack-ice zones. The thickness and quantity of snow ice may be due to a combination of high snow-accumulation rates and snow loads, environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow/ice interface, and bottom melting losses being compensated by snow-ice formation. Layers of superimposed ice at the top of each of the summer cores make up 4.6% of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice. The accumulation of superimposed ice is evidence that melting in the snow cover on Antarctic sea-ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass.

Physical Processes determining the Antarctic Sea Ice Environment

The Antarctic sea ice zone undergoes one of the greatest seasonal surface changes on Earth, with an annual change in extent of around 15 × 10 6 km 2 . This ice, and its associated snow cover, plays a number of important roles in the ocean-atmosphere climate system: the high albedo ice cover restricts surface absorption of solar radiation and acts as a barrier to the exchange of mass and energy between the ocean and atmosphere, and salt rejected by the growing ice cover affects the ocean structure and circulation. Additionally, a number of sea ice feedback processes have the potential to play an important role in climate change. The extent to which a sea ice cover modifies ocean-atmosphere interaction is primarily determined by the thickness and concentration of the ice, but these themselves are determined by ocean and atmospheric interaction. The thickness distribution of the pack is determined by both thermodynamic and dynamic processes: most important at the geophysical scale are the dynamic processes of ice drift and deformation, and of lead formation. Compared to the ice cover in the central Arctic Basin, the Antarctic sea ice is highly mobile. Drifting buoy studies show that the Antarctic pack can move at speeds of up to 60 km per day or greater, and that around most of the Antarctic coast, the drift of the pack ice is generally divergent, with divergence rates of 10% or more per day being observed under some circumstances. Consequently there is generally some open water within the Antarctic pack and much of the total ice mass forms by rapid growth within these areas. This influences the crystal structure of the ice and results in a considerable portion of the Antarctic pack (up to 25% in spring-time) having a thickness of less than 0 · 3 m. In general much of the Antarctic sea ice only grows thermodynamically to about 0·5 m thick, with thickness increases beyond that resulting from the deformational processes of rafting and ridge-building.

Effects of the snow cover on Antarctic sea ice and potential modulation of its response to climate change

Based on presented field data, it is shown that snow contributes roughly 8% to the total mass of ice in the Weddell Sea. Snow depth averages 0.16 m on first-year ice (average thickness 0.75 m) and 0.53 m on second-year ice (average thickness 1.70 m). Due to snow loading, sea ice is depressed below water level and flooded by sea water. As a result of flooding, snow ice forms through congelation of sea water and brine in a matrix of meteoric ice (i.e. snow). Sea-ice growth has been simulated with a one-dimensional model, treating the evolution of salinity, porosity and thermal properties of the ice. Simulations demonstrate that in the presence of a snow cover, ice growth is significantly reduced. Brine volumes increase by a factor of 1.5–2, affecting properties such as ice strength. Snow-ice formation depends on the evolution of freeboard and ice permeability. Effects of accumulation-rate changes have been assessed, for the Weddell Sea with a large-scale sea-ice model accounting for snow-ice formation. Results for different scenarios are presented and compared with field data and one-dimensional simulations. The role of snow in modulating the response of Antarctic sea ice to climate change is discussed.

Effects of the snow cover on Antarctic sea ice and potential modulation of its response to climate change

Based on presented field data, it is shown that snow contributes roughly 8% to the total mass of ice in the Weddell Sea. Snow depth averages 0.16 m on first-year ice (average thickness 0.75 m) and 0.53 m on second-year ice (average thickness 1.70 m). Due to snow loading, sea ice is depressed below water level and flooded by sea water. As a result of flooding, snow ice forms through congelation of sea water and brine in a matrix of meteoric ice (i.e. snow). Sea-ice growth has been simulated with a one-dimensional model, treating the evolution of salinity, porosity and thermal properties of the ice. Simulations demonstrate that in the presence of a snow cover, ice growth is significantly reduced. Brine volumes increase by a factor of 1.5–2, affecting properties such as ice strength. Snow-ice formation depends on the evolution of freeboard and ice permeability. Effects of accumulation-rate changes have been assessed, for the Weddell Sea with a large-scale sea-ice model accounting for snow-ice formation. Results for different scenarios are presented and compared with field data and one-dimensional simulations. The role of snow in modulating the response of Antarctic sea ice to climate change is discussed.

Estimation of Arctic ice thickness from ambient noise

An estimate of total ice mass in the Arctic is an important parameter for global climate studies, but there are no direct means for providing this information. A surrogate measurement, spatial integration of ice thickness, is being pursued by several groups using active acoustic and electromagnetic methods. As a complement to these efforts, the passive estimation of ice thickness using ambient noise caused by thermal and mechanical stress cracks in the ice sheet is focused on. The acoustic signal received from propagating stress cracks is the convolution of an elemental fracture source function and the spatial distribution function (array) of the propagating crack. This analytic result predicts a tonal spectral component of O(1 kHz) that relates directly to ice thickness. Experimental data collected in the Beaufort Sea during the spring of 1994 demonstrates the presence of this spectral peak, which correlates well with the measured ice thickness at the site.