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Platelet ice is a unique type of sea ice; its occurrence has numerous implications for physical and ecological systems. Mostly, platelet ice has been reported from the Antarctic where ice crystals grow in supercooled ice shelf water and accumulate below sea ice to form sub-ice platelet layers. In the Arctic however, platelet ice formation has only been sparsely documented so far. The associated formation processes and morphology differ significantly from the Antarctic, but currently remain poorly understood. Here, we present the first comprehensive, repeat in-situ observations of a decimeter thick sub-ice platelet layer under drifting pack ice of the Central Arctic in winter. Observations carried out with a remotely operated underwater vehicle (ROV) during the midwinter leg of the MOSAiC drift expedition provided clear evidence of the growth of platelet layers from supercooled water present in the ocean mixed layer. This process was observed under all ice types present during the surveys. Oceanographic data from autonomous observing platforms leads us to the conclusion that platelet ice formation is a widespread yet overlooked feature of Arctic winter sea ice growth.

Landfast sea ice is an important seasonal feature along most Arctic coastlines, such as that of the Chukchi Sea near Barrow, Alaska. Its stability throughout the ice season is determined by many factors but grounded pressure ridges are the primary stabilizing component. Landfast ice breakouts occur when these grounded ridges fail or unground, and previously stationary ice detaches from the coast and drifts away. Using ground-based radar imagery from a coastal ice and ocean observatory at Barrow, we have developed a method to estimate the extent of grounded ridges by tracking ice motion and deformation over the course of winter and have derived ice keel depth and potential for grounding from cumulative convergent ice motion. Estimates of landfast ice grounding strength have been compared to the atmospheric and oceanic stresses acting on the landfast ice before and during breakout events to determine prevailing causes for the failure of stabilizing features. Applying this approach to two case studies in 2008 and 2010, we conclude that a combination of atmospheric and oceanic stresses may have caused the breakouts analyzed in this study, with the latter as the dominant force. Preconditioning (as weakening) of grounded ridges by sea level variations may facilitate failure of the ice sheet leading to breakout events.

In the Arctic, land-fast sea ice growth can be influenced by fresher water from rivers and residual summer melt. This paper examines a method to reconstruct changes in water masses using oxygen isotope measurements of sea ice cores. To determine changes in sea water isotope composition over the course of the ice growth period, the output of a sea ice thermodynamic model (driven with reanalysis data, observations of snow depth, and freeze-up dates) is used along with sea ice oxygen isotope measurements and an isotopic fractionation model. Direct measurements of sea ice growth rates are used to validate the output of the sea ice growth model. It is shown that for sea ice formed during the 2011/2012 ice growth season at Barrow, Alaska, large changes in isotopic composition of the ocean waters were captured by the sea ice isotopic composition. Salinity anomalies in the ocean were also tracked by moored instruments. These data indicate episodic advection of meteoric water, having both lower salinity and lower oxygen isotopic composition, during the winter sea ice growth season. Such advection of meteoric water during winter is surprising, as no surface meltwater and no local river discharge should be occurring at this time of year in that area. How accurately changes in water masses as indicated by oxygen isotope composition can be reconstructed using oxygen isotope analysis of sea ice cores is addressed, along with methods/strategies that could be used to further optimize the results. The method described will be useful for winter detection of meteoric water presence in Arctic fast ice regions, which is important for climate studies in a rapidly changing Arctic. Land-fast sea ice effective fractionation coefficients were derived, with a range of +1.82‰ to +2.52‰. Those derived effective fractionation coefficients will be useful for future water mass component proportion calculations. In particular, the equations given can be used to inform choices made when engaging in end member determination for working out the component proportions of water masses.

Arctic sea ice has undergone rapid changes during the last few decades, with negative implications for over-ice travel and on-ice operations, which benefit from services provided by the sea ice. A Parameter-based Trafficability Hierarchy (PATH) is presented here as a framework for developing quantitative assessment strategies that can guide planning and execution of operations on or near sea ice and quantify the impacts of recent changes on ice use. A PATH assessment has been completed for three case studies in Arctic Alaska. These cases, which correspond to a range of different icescapes and ice uses, identify and quantify different parameters linked to trafficability and safe operations. For ice road applications, PATH was used to determine an ice thickness compensation factor, a factor increasing the minimal thickness threshold for operations, to help translate sporadic auger ice thickness measurements along the Kotzebue–Kiana community ice road into an envelope for safe operations. A compensation factor as high as 1.5 was found to be necessary to ensure safety because of the high local thickness variability that is currently a concern for ice road operators. A PATH assessment of ice roughness for ice trail routing at Utqiaġvik draws on satellite remote sensing and is relevant for over-ice travel in general, including escape, evacuation, and rescue. We compared the routing of local snowmobile trails with Synthetic Aperture Radar (SAR) data products to identify specific ranges of ice conditions, roughness, and topography favored for ice trail construction. The same combination of data sources was used to identify potentially beneficial trail routes. Finally, an ice stability and safety assessment was completed for ice road construction and maintenance by industry near the Northstar Island oil production facility. We evaluated small-scale ice displacement data obtained from SAR interferometry to infer internal ice strain and stress and used these data in assessing the potential for fractures to reduce load-bearing capacity.

Through analysis of over 2500 synthetic aperture radar (SAR) scenes spanning the period 1996–2008, we have compiled the most comprehensive dataset to date on landfast sea ice extent and its annual cycle in the Chukchi and Beaufort Seas. Our results show that landfast ice in the central and western Beaufort Sea forms earlier, breaks up later, occupies deeper water and extends further from shore than that in the Chukchi Sea. The differences in the timing of the annual landfast ice cycle are largely due to regional contrasts in the southward advance of pack ice in early winter and the onset of spring thaw. On the other hand, we suggest that the differences in landfast ice extent between the two seas are related to the number and distribution of recurring grounded ice features. These grounded features appear as “nodes” where the seaward landfast ice edge (SLIE) persistently recurs in multiple years. In the Beaufort Sea there are several such nodes that occur in water depths around 20 m, giving rise to the similarity between the average SLIE location and the 20 m isobath. We attribute the narrower landfast ice in the Chukchi Sea and lack of a consistent relationship with bathymetry to the sparsity of nodes in the Chukchi Sea. In comparing our results with data from the period 1973–76, we find that landfast ice extent in the Beaufort Sea has not changed significantly in the last four decades. However, in the Chukchi Sea our results show the landfast ice width has decreased by a coast-wide average of 13 km over this period. We again attribute this difference between the two seas to the distribution of recurring grounded ice features. Over the 12 annual cycles in the study period, we identify trends indicating that landfast ice is forming later and disappearing earlier by approximately one week per decade. Although these trends are not statistically significant, they are in agreement with an overall shortening of the landfast ice season by as much as two months over the past three decades, revealed by a comparison with earlier findings for the period 1973–77.

The pore space in the bottom-most layers of growing sea ice is directly connected to the ocean beneath, allowing for fluid exchange while providing a sheltered environment for sea-ice microbial communities. Because of its role as a habitat and its high porosity and permeability, potential entrainment of oil into this pore space is of broader concern. We estimate the ice volume that can potentially be infiltrated by oil and other buoyant pollutants in surface ocean water evaluating several years of sea ice measurements on undeformed landfast first-year sea ice at Barrow, Alaska. This ice is representative of undeformed sea ice in areas targeted for offshore oil development. The calculated ice volume is related to crude oil entrainment volumes with empirical relationships derived from field and laboratory measurements. We synthesize 12 years of sea-ice core salinity data and 6 years of quasi-continuous sea ice temperature profile measurements to derive the seasonal evolution of ice thickness and temperature gradients in sea ice. Porosity profiles are calculated from temperature and salinity profiles. Based on previous observations, an oil penetration depth is defined by a porosity threshold of 0.1 to 0.15. Ice thickness is found to increase from 0.6 m in January to its maximum of 1.5 m in May, and average temperature gradients at the ice–water interface range from − 15 °C/m in January to − 2 °C/m in May. Depending on ice temperature conditions, derived depths of fluid penetration range from 0.02 to 0.10 m in January to 0.12 to 0.25 m in May for a porosity threshold of 0.10. These penetration depths are approximately halved for a porosity threshold of 0.15. For average temperature conditions, expected entrainment of crude oil is less than 2 L/m2 in January and may be as high as 5 to 10 L/m2 in May. Accessible ice volume and entrainment potential are expected to increase during warm spells and with the opening of brine channel networks in late spring. Considering inhomogeneous spread and pooling of oil under ice, entrainment in warm sea ice is expected to add approximately 20% to previous estimates of the under-ice pooling capacity.

1. Abstract The recognized importance of the annual cycle of sea ice in the Arctic to heat budgets, human behavior, and ecosystem functions, requires consistent definitions of such key events in the ice cycle as break-up and freeze-up. An internally consistent and reproducible approach to characterize the timing of these events in the annual sea-ice cycle is described. An algorithm was developed to calculate the start and end dates of freeze-up and break-up and applied to time series of satellite-derived sea-ice concentration from 1979 to 2013. Our approach builds from discussions with sea-ice experts having experience observing and working on the sea ice in the Bering, Chukchi and Beaufort Seas. Applying the algorithm to the 1979–2013 satellite data reveals that freeze-up is delayed by two weeks per decade for the Chukchi coast and one week per decade for the Beaufort coast. For both regions, break-up start is arriving earlier by 5–7 days per decade and break-up end is arriving earlier by 10–12 days per decade. In the Chukchi Sea, “early” break-up is arriving earlier by one month over the 34-year period and alternates with a “late” break-up. The calculated freeze-up and break-up dates provide information helpful to understanding the dynamics of the annual sea-ice cycle and identifying the drivers that modify this cycle. The algorithm presented here, and potential refinements, can help guide future work on changes in the seasonal cycle of sea ice. The sea-ice phenology of freeze-up and break-up that results from our approach is consistent with observations of sea-ice use. It may be applied to advancing our understanding and prediction of the timing of seasonal navigation, availability of ice as a biological habitat, and assessment of numerical models.

Environmental change and increasing industrial activity in the maritime Arctic require strategies to adapt to change and ensure safe operations. This problem has been defined at the broader strategic level. We evaluate key aspects of environmental security in ice-covered waters, focusing on tactical and operational information needs, which have received less attention. Monitoring of environmental hazards and effective emergency response in sea ice environments require high-resolution data of ice hazard distributions (e.g., multiyear ice, landfast ice breakout, and ice push events), ice movement and deformation, as well as ice characteristics and dynamics relevant to emergency response. We have developed a prototype coastal observing system at Barrow, Alaska, that addresses such information needs. Imagery obtained from a marine X-band radar with a digital controller is combined with data from on-ice sensors (ice thickness, ice and water temperature, sea level) and assessments of potentially hazardous ice conditions by local experts. Digital imagery and data are processed and disseminated in near-real time. Using a combination of image processing approaches (optical flow, Lucas-Kanade tracker), ice velocity fields, floe trajectories, and boundaries of stationary ice are derived automatically. Early onset of hazardous events is detected through Hidden Markov Modeling, providing potential decision support in operational settings. We evaluate the utility of the system and strategies towards integration with broader emergency response efforts.

As an inhomogeneous mixture of pure ice, brine, air and solid salts the physical properties of sea ice depend on its highly temperature-dependent microstructure. Understanding the microstructure and the way it responds to variations in temperature and salinity is crucial in developing an improved understanding of the interaction between sea ice and the environment. However, measurements monitoring the internal structure of sea ice are difficult to obtain without disturbing its natural state. We have recently developed an application of cross-borehole d.c. resistivity tomography to make in situ measurements that resolve the anisotropic resistivity structure of first-year sea ice. We present results from measurements made in 2008 off Barrow, Alaska, and in 2009 off Ross Island, Antarctica. the sea ice in these two regions forms in different environments: at Barrow, relatively quiescent conditions typically lead to a predominance of columnar ice, while more turbulent conditions and underwater ice formation in McMurdo Sound tend to produce a larger component of frazil or platelet ice. Interpretation of the resistivity measurements carried out in association with temperature and salinity data collected simultaneously allows both observation of the temporal evolution of the ice structure and, in the case of the Antarctic measurements, the identification of different ice types.

The summer extent of the Arctic sea-ice cover has decreased in recent decades and there have been alterations in the timing and duration of the summer melt season. These changes in ice conditions have affected the partitioning of solar radiation in the Arctic atmosphere–ice–ocean system. the impact of sea-ice changes on solar partitioning is examined on a pan-Arctic scale using a 25 km × 25 km Equal-Area Scalable Earth Grid for the years 1979–2007. Daily values of incident solar irradiance are obtained from NCEP reanalysis products adjusted by ERA-40, and ice concentrations are determined from passive microwave satellite data. the albedo of the ice is parameterized by a five-stage process that includes dry snow, melting snow, melt pond formation, melt pond evolution, and freeze-up. the timing of these stages is governed by the onset dates of summer melt and fall freeze-up, which are determined from satellite observations. Trends of solar heat input to the ice were mixed, with increases due to longer melt seasons and decreases due to reduced ice concentration. Results indicate a general trend of increasing solar heat input to the Arctic ice–ocean system due to declines in albedo induced by decreases in ice concentration and longer melt seasons. the evolution of sea-ice albedo, and hence the total solar heating of the ice–ocean system, is more sensitive to the date of melt onset than the date of fall freeze-up. the largest increases in total annual solar heat input from 1979 to 2007, averaging as much as 4%a–1, occurred in the Chukchi Sea region. the contribution of solar heat to the ocean is increasing faster than the contribution to the ice due to the loss of sea ice.

The air–sea ice CO 2 flux was measured over landfast sea ice in the Chukchi Sea, off Barrow, Alaska in late May 2008 with a chamber technique. The ice cover transitioned from a cold early spring to a warm late spring state, with an increase in air temperature and incipient surface melt. During melt, brine salinity and brine dissolved inorganic carbon concentration (DIC) decreased from 67.3 to 18.7 and 3977.6 to 1163.5 μmol kg −1 , respectively. In contrast, the salinity and DIC of under-ice water at depths of 3 and 5 m below the ice surface remained almost constant with average values of 32.4±0.3 (standard deviation) and 2163.1±16.8 μmol kg −1 , respectively. The air–sea ice CO 2 flux decreased from +0.7 to −1.0 mmol m −2 day −1 (where a positive value indicates CO 2 being released to the atmosphere from the ice surface). During this early to late spring transition, brought on by surface melt, sea ice shifted from a source to a sink for atmospheric CO 2 , with a rapid decrease of brine DIC likely associated with a decrease in the partial pressure of CO 2 of brine from a supersaturated to an undersaturated state compared to the atmosphere. Formation of superimposed ice coincident with melt was not sufficient to shut down ice–air gas exchange.

Measurements of sea-ice thickness were obtained from drill holes, an ice-based electromagnetic induction instrument (IEM), and a ship-borne electromagnetic induction instrument (SEM) during the early-melt season in the southern Chukchi Sea in 2002 and 2004, and in late summer 2003 at the time of minimum ice extent in the northern Chukchi Sea. An ice roughness criterion was applied to distinguish between level and rough or ridged ice. Ice-thickness modes in the probability density functions (PDFs) derived from drill-hole and IEM measurements agreed well, with modes at 1.5–1.6 and 1.8–1.9 m for all data from level ice. The PDFs derived from SEM measurements show that the primary modes are at 0.1 and 1.1 m in 2003 and 0.7 m in 2004. In 2002 and 2004, significant fractions (between one-third and one-half) of level ice were found to consist of rafted ice segments. Snow depth varied significantly between years, with 2004 data showing more than half the snow cover on level ice to be at or below 0.05 m depth in late spring. Ice growth simulations and examination of ice drift and deformation history indicate that impacts of atmospheric and oceanic warming on level-ice thickness in the region over the past few decades are masked to a large extent by variability in snow depth and the contribution of deformation processes. In comparison with submarine sonar ice-thickness data from previous decades, a reduction in ice thickness by about 0.5–1 m is in part explained by the replacement of multi-year with first-year ice over the Chukchi and Beaufort shelves.

The presence of brine inclusions with an alignment that is preferentially vertical means that the bulk resistivity structure of sea ice is anisotropic. This complicates the interpretation of surface resistivity soundings of sea ice. We show that consideration of the theory of resistivity measurements in an anisotropic medium suggests that cross-borehole measurements using one current and one potential electrode in each borehole should allow the determination of the horizontal component of the anisotropic bulk resistivity. A series of cross-borehole measurements made in first-year sea ice near Barrow, Alaska, as the ice warmed through the spring, yields 3D models of the resistivity structure which support this prediction. The derived models show an evolution of the resistivity structure which (1) at temperatures less than − 5 °C is broadly consistent with the expected variation with brine volume fraction predicted by Archie's Law and (2) shows evidence of a percolation transition in the horizontal component of the resistivity when brine volume fractions exceed 8–10%.

During the two winters between 2003 and 2005, a land-based marine radar observed the nearshore ice motion during the development and decay of landfast ice near Barrow, Alaska. The radar imagery captured individual events at high temporal resolution, revealing deformation processes and allowing calculation of ice velocity and acceleration. Atmospheric forcing during these events appeared to be irrelevant since no corollary was found in local meteorological observations. Detailed examination of the radar imagery showed that backscatter from sea ice targets oscillated in signal strength (flickered) prior to detachment, as previously observed by (Shapiro, L.H. (1987), Mechanical Properties of Sea Ice Deformation in the near Shore Zone, in OCSEAP Final Reports, V.72, pp. 357–584, U.S. Dept. of Commerce, NOAA). Determination of ice acceleration after detachment allowed estimation of water drag beneath the ice. The distribution of grounded ridges at the end of each annual cycle was determined from field measurements of ice elevation, ice thickness and water depth. Applying a simple theoretical treatment of coupling between a first-year ridge keel and the seabed, we calculate that the anchoring strength provided by ridges was 2–3 orders of magnitude greater than typical wind or water stresses. Therefore, we conclude that additional decoupling processes, such as sea level surges or thermal erosion of keels, must occur in addition to offshore current stress in order to cause the landfast ice to detach. Although the nature of these processes is not clear, they are likely to be the cause of the flickering observed in radar imagery, which could therefore be useful in short-term prediction of detachment events.

We present results from a comprehensive field study carried out near Barrow, Alaska, USA, designed to characterize local- to intermediate-scale sea-ice processes in the Arctic coastal zone of central importance to the annual cycle and evolution of the coastal sea ice. Included in this are the behavior of the snow cover of the ice and adjacent tundra and lake system; concurrent studies of mass balance of the sea ice and lake ice; interaction of shortwave radiation with the shore-fast ice and the adjacent land surfaces; evolution of the area coverage and distribution of the various surface types; and the resulting regional albedo values. Maximum snow depths decreased during 2000–02 from 0.38 m to 0.26 m. Ice-melt rates in 2001 were 0.05 and 0.028md–1at the top and bottom of the sea ice respectively, two to three times larger than observations from the central Arctic. Detailed surface results combined with aircraft photography were used to calculate regional albedos for the late spring and early summer of 2001. Values ranged from 0.8 for all cold snow-covered surfaces to approximately 0.4 for melting sea ice and lake ice vs 0.18 for bare tundra. Regional and surface-based values of cumulative shortwave radiation entering the ice were consistent, indicating that albedo sampling on a scale of 200m can provide a useful representation for regional sea-ice albedo.

Sediment-laden sea ice is widespread over the shallow, wide Siberian Arctic shelves, with off-shelf export from the Laptev and East Siberian Seas contributing substantially to the Arctic Ocean's sediment budget. By contrast, the North American shelves, owing to their narrow width and greater water depths, have not been deemed as important for basin-wide sediment transport by sea ice. Observations over the Chukchi and Beaufort shelves in 2001/02 revealed the widespread occurrence of sediment-laden ice over an area of more than 100,000 km2 between 68 and 74°N and 155 and 170°W. Ice stratigraphic studies indicate that sediment inclusions were associated with entrainment of frazil ice into deformed, multiple layers of rafted nilas, indicative of a flaw-lead environment adjacent to the landfast ice of the Chukchi and Beaufort Seas. This is corroborated by buoy trajectories and satellite imagery indicating entrainment in a coastal polynya in the eastern Chukchi Sea in February of 2002 as well as formation of sediment-laden ice along the Beaufort Sea coast as far eastward as the Mackenzie shelf. Moored upward-looking sonar on the Mackenzie shelf provides further insight into the ice growth and deformation regime governing sediment entrainment. Analysis of Radarsat Synthetic Aperture (SAR) imagery in conjunction with bathymetric data help constrain the water depth of sediment resuspension and subsequent ice entrainment (>20 m for the Chukchi Sea). Sediment loads averaged at 128 t km–2, with sediment occurring in layers of roughly 0.5 m thickness, mostly in the lower ice layers. The total amount of sediment transported by sea ice (mostly out of the narrow zone between the landfast ice edge and waters too deep for resuspension and entrainment) is at minimum 4×106 t in the sampling area and is estimated at 5–8×106 t over the entire Chukchi and Beaufort shelves in 2001/02, representing a significant term in the sediment budget of the western Arctic Ocean. Recent changes in the Chukchi and Beaufort Sea ice regimes (reduced summer minimum ice extent, ice thinning, reduction in multi-year ice extent, altered drift paths and mid-winter landfast ice break-out events) have likely resulted in an increase of sediment-laden ice in the area. Apart from contributing substantially to along- and across-shelf particulate flow, an increase in the amount of dirty ice significantly impacts (sub-)ice algal production and may enhance the dispersal of pollutants.

The interaction between river water and landfast sea ice was investigated through synthetic aperture radar (SAR) remote sensing, ice-growth modeling, and ground-based ice-core and hydrographic studies in the Laptev Sea, Siberian Arctic, in 1996/1997 and 1998/1999. Ice-core data in conjunction with ice-growth and SAR backscatter modeling demonstrated that the contrasts in dielectric and microstructural properties between freshwater/brackish (salinity < 1 parts per thousand) and sea ice allow a mapping of the distribution of freshwater and brackish ice as influenced by Lena River discharge. This brackish zone (surface water salinities < 5) extended over 2000-3000 km(2) inshore of the 10-m isobath and exhibited distinct SAR backscatter coefficients and image texture. In the nearshore zone, bottomfast ice growth could be identified and tracked over the growth season. Occupying up to 250 km(2) along the Lena Delta, bottomfast ice was not as widespread as previously hypothesized, possibly due to ice being thinner by 10-20% relative to the signatures of any ice long-term mean. In SAR and ERS-2 scatterometer data, Laptev Sea landfast ice exhibits the lowest backscatter si a type in the Arctic Ocean, due to the lack of major deformation features. Stable-isotope data show that the landfast ice is composed of about 62% of river water, locking up 24% of the total annual Lena and Yana discharge. From ice-growth/isotopic-fractionation modeling and ice-core analysis, time series of surface water salinity have been derived, indicating freshening of under-ice waters during winter and north-/northeastward spreading of the river plume with under-ice spreading rates of 1.0-2.7 cm s(-1). A river freshwater budget for the inner Laptev shelf indicates flushing times of a year or more with cross-shelf export of 627 km(3) during the winter of 1998/1999. Based on these findings, the southeastern Laptev Sea can be considered an open, seasonally frozen estuary. This system contrasts with North American shelf environments, which show a different response to climate variability and change.

Based on hydrological data from 1979 to 1999 the average long-term salinity of the flaw polynya in the Eastern Laptev Sea is estimated. A new method to evaluate ice production based on hydrological rather than sea-ice observations is proposed. Average annual ice production in the polynya ranges between 3 and 4 m. The probability of convective mixing penetrating down to the seafloor is highest in the regions of the flaw polynya, but does not exceed 20% in the Eastern and 70% in the Western Laptev Sea. Conductivity-temperature-depth (CTD) measurements and observations of currents carried out in April-May 1999 allowed us to investigate the surface circulation along the margins of the Laptev Sea flaw polynya. The convective nature of the surface currents, with velocities measured as high as 62 cm/s, is discussed. Currents are most likely part of circulation cells, which arise as a result of brine rejection due to intensive ice formation in the polynya. It is shown that the spatial alignment of sea ice crystals in the marginal part of the polynya is most likely a consequence of the quasi-stationary cellular circulation

To better understand constraints on bacteria at extremely low temperatures in ice, we describe here the adaptation of methods previously developed for sea ice to high magnification imaging of bacteria within fluid inclusions of Arctic lake ice under insitu conditions. Bacterial staining procedures, using the DNA-specific fluorescent stain DAPI, epifluorescence microscopy and image analysis were applied to lake-ice sections at in situ temperature (-5°C). Abundances of total, attached, free-living and metabolically active lake-ice bacteria were also determined from samples melted at 0°C using the fluorescent stains DAPI and CTC. Initial results indicate that, compared to sea ice at the same in situ temperature, lake ice contains fewer and more isolated liquid inclusions, limiting transport of fluids and motion of bacteria. Metabolically active cells were found in all ice samples (0.1 to 2.0% of the total counts), but on average less than in sea ice. Up to 50% of the total bacterial community were found to be associated with particles > 3 μm in size; of the metabolically active cells, a smaller fraction may be attached than in sea ice. Our results expand the spectrum of information available on bacteria in ice on a scale relevant to the organism and provide insight into characteristics of frozen microbial habitats on Earth and perhaps elsewhere in the Universe.

An ice shove along the Alaskan Chukchi Sea coast occurred in June 2001, affecting the communities of Barrow and Wainwright, some 150 km apart. Aerial photography before and after the event allowed measurement of ice displacement vectors near Barrow where up to 395 m of ice motion was accommodated almost entirely in discrete ridges up to 5 m high. The forces required to build these ridges are estimated at 35−62 kN m-1, and driving forces of the whole event are investigated. Most ice deformation at or near the beach coincided with local onshore winds, but the event was preceded by the compaction of pack ice in the central Chukchi Sea and the closure of the coastal flaw lead, driven by the larger-scale wind field acting over several days beforehand. Whether this acted to impart pack-ice stress to the coast or simply to create a critical fetch of consolidated ice is uncertain. The near-melting near-isothermal state of the ice may have been a complicit factor and affected the behavior of the land-fast ice. Coastal morphology and bathymetry affected the location of deformation. This study highlights the range of scales at which processes act and culminate to have implications for Arctic communities.

Snow on Antarctic sea ice plays a complex and highly variable role in air-sea-ice interaction processes and the global climate system. This paper presents snow data collected during the past ten years, and reviews major findings. These include: differences in regional and seasonal snow properties and thicknesses; the unique consequences of snow on Antarctic pack ice relative to the Arctic (e.g. the importance of flooding and snow-ice formation); the potential impact if global change increases snowfall; lower observed values of snow thermal conductivity than those used in models; periodic large-scale melt in winter; and the contrast in summer melt in the Antarctic and Arctic. The new findings have significant implications for modelling and remote-sensing studies. Different snow properties from Arctic conditions are recommended for use in Antarctic models; similar differences could affect the interpretation of remote-sensing data over sea ice.

Extensive drill hole and electromagnetic induction measurements of sea ice thickness in the Siberian and central Arctic Seas in the summers of 1993, 1995, and 1996 reveal significant interannual variability. In the Laptev Sea, minimum and maximum modal first-year ice thicknesses amounted to 1.25 and 1.85 m in 1995 and 1996, respectively. Ice thickness correlates with ice extent, which reached a record minimum in August 1995 and was well above average in 1996. These differences are explained by the strength and location of a summer cyclonic atmospheric circulation pattern affecting both ice advection and surface melt. From drifting buoys deployed in 1995 and satellite radar backscatter data, first- and second-year ice regimes are delineated. Differences in first-year ice backscatter coefficients between 1993, 1995, and 1996 are explained by differences in level ice surface roughness. The Lagrangian evolution of ice thickness between 1995 and 1996 is studied. While the shape of the thickness distribution does not change significantly, the mean (modal) ice thickness of the ice field increases from 1.80 m (1.25 m) in 1995 to 2.86 m (2.25 m) in 1996. The thickness distribution of second-year ice in 1996 closely agrees with that of level multiyear ice downstream in the Transpolar Drift obtained in 1991. In 1996, mean level ice thickness increases at 0.23 and 0.16 m deg−1 with latitude in the Kara and Laptev Sea sectors of the Arctic Ocean, respectively.

In the framework of the Surface Heat Budget of the Arctic (SHEBA) study, indirect, non-invasive ice mass-balance measurements were carried out at a drifting station in the northern Chukchi Sea between May and August 1998. Ice thickness was derived from electromagnetic induction (EM) measurements of apparent conductivity along 13 profiles (60−900 m long). As shown through sensitivity studies with a one-dimensional model, the apparent conductivity data from individual points can be inverted to yield estimates of ice thickness and ablation with an accuracy of approximately 0.05 m (for 2 m thick level ice). Ablation rates were 8−18 mm d−1, with total ablation amounting to roughly 0.9−1.2 m. Measurements of thickness and melt rates along different profiles in undeformed multi-year ice corresponded closely, indicating that the sampling statistics are adequate. The roughness of undeformed ice has been found to increase during the summer due to deepening of melt ponds and enhanced bottom melt. Ice under melt ponds was disproportionately thinner, most likely a result of thicker snow cover reducing winter accretion.

Sea ice circulation in the Laptev Sea and ice exchange with the Arctic Ocean have been studied based on remote sensing data and numerical modeling. Ice drift patterns for short- and long-term periods were retrieved from successive Okean radar images and Special Sensor Microwave/Imager data for the winters 1987/1988 and 1994/1995. Seasonal and interannual variabilities of ice drift in the Laptev Sea and ice exchange with the Arctic Ocean during the period from 1979 to 1995 were studied with a large-scale dynamic-thermodynamic sea ice model. During an “average year,” sea ice was exported from the Laptev Sea through its northern and eastern boundaries, with maximum and minimum export occurring in February and August, respectively. The winter ice outflow from the Laptev Sea varied between 251,000 km2 (1984/1985) and 732,000 km2 (1988/1989) with the mean value of 483,000 km2. Sea ice was exported into the East Siberian Sea mostly in summers with the mean value of 69,000 km2. Out of the 17 investigated summers, 12 were characterized by sea ice import from the Arctic Ocean into the Laptev Sea through its northern boundary. Magnitude and direction of ice export from the Laptev Sea corresponded with the large-scale Arctic Ocean drift patterns during periods of prevailing cyclonic or anticyclonic circulation. Based on a semiempirical method that has been validated with the large-scale model and satellite data, ice exchange between the Laptev Sea and the Arctic Ocean during the period from 1936 to 1995 has been estimated as 309,000km2 with strong interannual variability and no significant trend apparent.

Summer sea-ice conditions in the Laptev Sea are characterized by high interannual variability. The impact of Lena River discharge, one of the Arctic's major rivers discharging roughly 525 km3 annually onto the Laptev shelf, and the regional meteorological regime affect the spring and summer ice regime of the Laptev Sea. Using ground and remote-sensing data and statistical analyses, it is shown that river discharge plays an insignificant role in the large-scale decay of the Laptev Sea ice cover. Hydrological and remote sensing data for the period 1979-1990 show that discharge/sea-ice interactions are confined to the coastal regions, with Lena River water flooding a fast-ice belt, roughly 25 km wide, in early to mid-June. Sea-ice decay and summer ice extent are shown to be affected most strongly by dynamic atmospheric forcing and by opening and enlargement of coastal polynyas in early spring.

A high-resolution study of bulk salinity was undertaken on laboratory-grown sea ice to determine the extent of spatial variability of salinity and whether this was associated with brine channel structures. Ice samples at two different stages of development were compared with respect to physical state, brine distribution, and brine channel structures. Cold, growing sea ice is shown to have steep bulk salinity gradients and a highly variable brine distribution that is closely linked to the location and morphology of brine channels. Areas of high bulk salinity are found to correspond directly to the positions of the brine channels, and these areas are surrounded by ice that shows significant brine depletion. It is observed that redistribution of the brine occurs as the ice cover goes through warming and melting phases. The redistribution is attributed to an increase in porosity and pore connectivity permitting migration of brine through the ice. The distribution of brine in “warm” ice is shown to be more homogeneous and independent of brine channel structures. A number of mechanisms exploiting the enhanced mobility of brine in warm sea ice are used to explain the changes in the salinity profiles and brine distribution.

Based on remote-sensing data and an expedition during August-September 1993, the importance of the Laptev Sea as a source area for sediment-laden sea ice was studied. Ice-core analysis demonstrated the importance of dynamic ice-growth mechanisms as compared to the multi-year cover of the Arctic Basin. Ice-rafted sediment (IRS) was mostly associated with congealed frazil ice, although evidence for other entrainment mechanisms (anchor ice, entrainment into freshwater ice) was also found. Concentrations of suspended particulate matter (SPM) in patches of dirty ice averaged at 156 g m(-3) (standard deviation sigma = 140 g m(-3)), with a background concentration of 5 g m(-3). The potential for sediment entrainment over the broad, shallow Laptev Sea shelf during fall freeze-up was studied through analysis of remote-sensing data and weather-station records for the period 1979-1994. Freeze-up commences on 26 September (sigma = 7 d) and is completed after 19 days (sigma = 6 d). Meteorological conditions as well as ice extent prior to and during freeze-up vary considerably, the open-water area ranging between 107 x 10(3) and 447 x 10(3) km(2). Ice motion and transport of IRS were derived from satellite imagery and drifting buoys for the period during and after the expedition (mean ice velocities of 0.04 and 0.05 m s(-1), respectively). With a best-estimate sediment load of 16 t km(-2) (ranging between 9 and 46 t km(-2)), sediment export from the eastern Laptev Sea amounts to 4 x 10(6) t yr(-1), with extremes of 2 x 10(6) and 11 x 10(6) t yr(-1). Implications for the sediment budget of the Laptev shelf, in particular with respect to riverine input of SPM, which may be of the same order of magnitude, are discussed.

Foster partnerships and share data to reduce hazards in fast-changing northern waters, says Hajo Eicken.

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.

Drifting sea ice in the Arctic may transport contaminants from coastal areas across the pole and release them during melting far from the source areas. Arctic sea ice often contains sediments entrained on the Siberian shelves and receives atmospheric deposition from Arctic haze. Elevated levels of some heavy metals (e.g. lead, iron, copper and cadmium) and organochlorines (e.g. PCBs and DDTs) have been observed in ice sampled in the Siberian seas, north of Svalbard, and in Baffin Bay. In order to determine the relative importance of sea ice transport in comparison with air/sea and oceanic processes, more data is required on pollutant entrainment and distribution in the Arctic ice pack.

Studies on the life strategy of the small calanoid copepod Stephos longipes were carried out in the eastern Weddell Sea during four expeditions (January/February 1985, August 1986, October/December 1986 and April/May 1992). Samples were taken from the water column, the ice/water interface and the sea ice. In winter (August 1986) S. longipes copepodite stage CIV occurred mainly in the upper water layers of the ice covered eastern Weddell Sea, while only nauplii were found in the sea ice. In late winter/early spring (October-December 1986) very low numbers of S. longipes were found in the water column, mainly in the upper 50m, but high numbers occurred immediately below and within the sea ice. Adults dominated in the water column and in the under ice water layer while the sea ice contained nauplii and copepodite stage CI. During summer (January/February 1985) the eastern Weddell Sea was almost entirely free of ice with the exception of fast ice fields atthe ice shelf. During this time S. longipes was concentrated in the upper 50m of the water column and in the ice/water interface where an ice cover was present. Young copepodite stages (CI-CIII) comprised the largest fraction of the population. In autumn (April/May 1992) as new ice began to develop, S. longipes , dominated by copepodite stage CIV, occurred in greatest number within mid-water layers. The abundance of S. longipes in autumn was similar to late winter/early spring highest in the sea ice and lowest in the water column. During all periods of investigation the population structure differed between the various habitats with the youngest population occurring in the sea ice and the oldest in the water column. A younger generation of the S. longipes population appears to overwinter in the sea ice and ice/water interface and an older one in deeper water layers or near the bottom.

The location of snow dunes over the course of the ice-growth season 2007/08 was mapped on level landfast first-year sea ice near Barrow, Alaska. Landfast ice formed in mid-December and exhibited essentially homogeneous snow depths of 4-6 cm in mid-January; by early February distinct snow dunes were observed. Despite additional snowfall and wind redistribution throughout the season, the location of the dunes was fixed by March, and these locations were highly correlated with the distribution of meltwater ponds at the beginning of June. Our observations, including ground-based light detection and ranging system (lidar) measurements, show that melt ponds initially form in the interstices between snow dunes, and that the outline of the melt ponds is controlled by snow depth contours. The resulting preferential surface ablation of ponded ice creates the surface topography that later determines the melt pond evolution.

[1] Seasonal breakup of landfast sea ice consists of movement and irreversible ice detachment in response to winds or oceanic forces in the late stages of ice decay. The breakup process of landfast sea ice in the Chukchi Sea at Barrow, Alaska, was analyzed for the years 2000 through 2010 on the basis of local observations of snow and ice conditions, weather records, image sequences obtained from cameras, coastal X band marine radar, and satellite imagery. We investigated the relation of breakup to winds, tides, and nearshore current measurements from a moored acoustic Doppler current profiler. Two breakup modes are distinguished at Barrow on the basis of the degree of ice decay. Mechanical breakup due to wind and oceanic forces follows ablation and weakening of the ice. Thermal breakup is the result of ice disintegration under melt ponds, requiring little force to induce dispersion. Grounded pressure ridges are pivotal in determining the breakup mode. The timing of thermal breakup of the nearshore ice cover was found to correlate with the measured downwelling solar radiation in June and July. This linkage allows for the development of an operational forecast of landfast ice breakup. Results from forecasts during 2 years demonstrate that thermal breakup can be predicted to within a couple of days 2 weeks in advance. The cumulative shortwave energy absorbed by the ice cover provides for a measure of the state of ice decay and potential for disintegration. Discriminating between the two modes of breakup bears the potential to greatly increase forecasting skill.

[1] Cross-borehole DC resistivity tomography has recently been used to monitor the temporal variation of the anisotropic bulk electrical resistivity of first-year Arctic sea ice during the period of spring warming. These measurements cannot be explained by standard models of sea ice microstructure which treat the brine phase as isolated ellipsoidal pores. A simple structural model which does satisfy the observed electrical data shows that the brine phase must be connected both vertically and horizontally. Calculation of the temporal and thermal evolution of the microstructure suggests that although vertical connectivity is through pore tubes and sheets with widths of ∼100 μm, horizontal connectivity is through much thinner connections which are interpreted as inter- and intragranular brine layers. As the temperature increases the width of vertical channels increases smoothly. In contrast, at temperatures above about −2°C there is a rapid increase in the thickness of horizontal connections which we interpret as a change from conduction through intergranular brine layers to the development of horizontal pores. The electrical data also broadly exhibit a percolation transition predicted by mathematical models. However, the critical brine volume fraction for vertical electrical connection is very small, while that for horizontal electrical connection is derived to be about 0.5%. The difference between these and the critical threshold of 5% for fluid permeability is presumed to arise because of the strong dependence of the latter on brine channel width.

Satellite data have revealed dramatic losses of Northern Hemisphere sea ice since the end of the 1970s. To place these changes in a longer-term context, we draw on daily observations taken from logbooks and journals of whaling vessels cruising in the Bering and Chukchi seas to investigate sea-ice conditions in this region of the Arctic between 1850 and 1910. We compare these observations to sea-ice data from 1972 to 1982, which predate the majority of the recent changes and cover a period recognized as a relative maximum in recent Bering Sea ice extent. Records from May indicate that end-of-winter sea-ice extent in the Bering Sea during the mid 19th century closely resembled that in the 1972 – 82 data. However, the historical data reveal that sea ice was more extensive during summer, with the greatest difference occurring in July. This pattern indicates a later and more rapid seasonal retreat. These conclusions highlight the value of historical data, which we have far from exhausted in this study.

The physical properties of Arctic sea ice determine its habitability. Whether ice-dwelling organisms can change those properties has rarely been addressed. Following discovery that sea ice contains an abundance of gelatinous extracellular polymeric substances (EPS), we examined the effects of algal EPS on the microstructure and salt retention of ice grown from saline solutions containing EPS from a culture of the sea-ice diatom, Melosira arctica . We also experimented with xanthan gum and with EPS from a culture of the cold-adapted bacterium Colwellia psychrerythraea strain 34H. Quantitative microscopic analyses of the artificial ice containing Melosira EPS revealed convoluted ice-pore morphologies of high fractal dimension, mimicking features found in EPS-rich coastal sea ice, whereas EPS-free (control) ice featured much simpler pore geometries. A heat-sensitive glycoprotein fraction of Melosira EPS accounted for complex pore morphologies. Although all tested forms of EPS increased bulk ice salinity (by 11–59%) above the controls, ice containing native Melosira EPS retained the most salt. EPS effects on ice and pore microstructure improve sea ice habitability, survivability, and potential for increased primary productivity, even as they may alter the persistence and biogeochemical imprint of sea ice on the surface ocean in a warming climate.

[1] While summer Arctic sea-ice extent has decreased over the past three decades, it is subject to large interannual and regional variations. Methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice-thickness distribution to recent change, limiting the ability to forecast sea-ice change over the next decade. We present results from a 2400 km long pan-Arctic airborne electromagnetic (EM) ice thickness survey in April 2009, the first-ever large-scale EM thickness dataset obtained by fixed-wing aircraft over key regions of old ice in the Arctic Ocean between Svalbard and Alaska. The data provide detailed insight into ice thickness distributions characteristic for the different regions. Comparison with previous EM surveys shows that modal thicknesses of old ice had changed little since 2007, and remained within the expected range of natural variability.

A dense diatom bloom growing in a shallow stratified layer maintained in position by loose ice platelets was found underlying pack-ice bordering the coastal polynyas of the Weddell Sea ice shelf south of 74°S in early spring well before the onset of seasonal melt. This rich bloom, which covered ca 20,000 km 2 , contrasted with the barrenness of the entire area between 74°S and the northern edge of the pack-ice at 58°S; its presence is explained by favourable conditions for accumulation of several decimetre-thick ice platelet layers under pack-ice of the southern shelf. Nutrient exhaustion and mass sinking of diatom chains were observed in this layer. Centric diatoms suspended in interstitial water dominated this bloom, which contrasted strongly with the flora of attached pennates typical of ice platelet layers underlying fast ice. Superblooms have been described previously from the southern Weddell Sea, although their developmental dynamics were not known at the time. We provide explanations for several perplexing features of this superbloom and show that they are significant in enhancing productivity of the Weddell Sea.

The pelagic foraminifer Neogloboquadrina pachyderma (Ehrenberg, 1861) occurs in new ice, congelation ice, and the underlying water column of the Weddell Sea. Neogloboquadrina pachyderma is incorporated into the ice in large numbers at the time of its formation. The average number of foraminifers per liter of ice was 87 and numbers ranged between 0 and 1,075. Sea ice contained 70 times more foraminifers per unit volume than the underlying water column and on an areal basis the sea ice cover has approximately the same number of specimens as 60 m of underlying water column. The foraminifera are usually incorporated into the ice when it is being formed dynamically and are thus subsequently associated mainly with granular ice. Many foraminifers are able to survive and grow in the ice where algal biomass in winter is high compared to the water column, perhaps indicating an overwintering strategy. Arctic sea ice, on the other hand, is practically devoid of foraminifers. These observations may have implications for paleoceanographers who use N. pachyderma as a tool to reconstruct past surface water conditions.

We report on studies of sea-ice texture conducted during a number of expeditions into the Weddell Sea. Sea ice in the Antarctic is dominated by granular ice of frazil origin in floes of all ages, in contrast to ice in the Arctic, which consists predominantly of columnar ice of congelation origin. The large fraction of granular ice in first-year sea ice is a result of the dominant ice-formation process in the advancing ice edge, the pancake cycle. The dominance of granular over columnar ice in second- and/or multi-year ice is a result of the large degree of deformational activity in the Southern Ocean.

Motivation and context The scope and individual chapters of this book provide an indication of the importance of sea ice over a wide range of scales in time and space. Considering the degree to which the ice cover is intertwined with other phenomena and processes, this brief introduction and overview can only skim the surface and cover selected aspects but not do justice to the subject matter as a whole. For more complete and rigorous treatises of the growth, structure and properties of sea ice, readers are referred in particular to the overview articles by Weeks and Ackley [1986], Weeks [1998] and Wettlaufer [1999] in the comprehensive monograph by Lepparanta [1998]. The same monograph also includes a highly relevant chapter on the optical properties of sea ice by Perovich [1998]. Aspects of sea-ice characteristics relevant for microwave remote sensing are covered by Tucker et al. [1992] and Hallikainen and Winebrenner [1992] as well as the paper by Golden et al. [1998b] introducing a series of studies of sea-ice electromagnetic properties. While Maykut [1986] provides a thorough treatment of ice growth and properties in the context of the sea-ice energy and mass balance, Steele and Flato [2000] extend this to include a detailed discussion of ice growth models. A useful summary and review of sea-ice physical property data sets and measurements has been provided by Yen et al.[1991]. Articles by Reimnitz et al. [1992] and Pfirman et al. [1990] provide further insight into the importance of sea ice as a geologic agent. The topic of sea-ice ecology is well covered in several chapters in this book.

[1] Over the past few decades the Arctic sea ice cover has decreased in areal extent. This has altered the solar radiation forcing on the Arctic atmosphere-ice-ocean system by decreasing the surface albedo and allowing more solar heating of the upper ocean. This study addresses how the amount of solar energy absorbed in areas of open water in the Arctic Basin has varied spatially and temporally over the past few decades. A synthetic approach was taken, combining satellite-derived ice concentrations, incident irradiances determined from reanalysis products, and field observations of ocean albedo over the Arctic Ocean and the adjacent seas. Results indicate an increase in the solar energy deposited in the upper ocean over the past few decades in 89% of the region studied. The largest increases in total yearly solar heat input, as much as 4% per year, occurred in the Chukchi Sea and adjacent areas.

[1] We present final results from a program to measure the thermal conductivity of sea ice with in situ thermistor arrays using an amended analysis of new and previously reported ice temperatures. Results from landfast first-year (FY) ice near Barrow, Alaska, and McMurdo Sound, Antarctica, are consistent with predictions from effective-medium models but 10–15% higher than values from the parameterization currently used in most sea ice models. We observe no previously reported anomalous near-surface reduction, which is now understood to have been an artifact, nor a convective enhancement to the heat flow, although our analysis is limited to temperatures below � 5C at which brine percolation is restricted. Results for landfast multiyear (MY) ice in McMurdo Sound are also consistent with effective-medium predictions, and emphasize the density dependence. We compare these and historical measurements with effective-medium predictions and the representation commonly used in sea ice models, developed originally for MY Arctic ice. We propose an alternative expression derived from effective-medium models, appropriate for both MY and FY ice that is consistent with ��

[1] Using Radarsat Synthetic Aperture Radar (SAR) imagery of northern Alaska and northwestern Canada, we calculated a mean climatology of the annual landfast ice cycle for the period 1996–2004. We also present the monthly minimum, mean, and maximum landfast ice extents throughout the study area. These data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events. Stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge (SLIE) into waters around 18 m deep. Isobaths near this depth are a good approximation for midseason landfast ice extent. Comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the Arctic, due to later formation and earlier breakup. This will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities, which are intimately linked to the timing of marine mammal migration patterns. Interannually, landfast ice formation correlates with the incursion of pack ice into coastal waters, suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge. The timing of breakup correlates well with onset of thawing air temperatures. Analysis of regional data shows a multidecadal trend toward earlier thaw onset, which suggests that the observed change in breakup dates may be part of a longer-term trend.

Landfast sea ice is a seasonal phenomena in the Alaskan Arctic and throughout its annual existence, between formation in late fall and break-up in late spring, it is shaped by a range of thermodynamic and dynamic forces. The results of a manual and an automated technique to derive positions of the seaward landfast ice edge (SLIE) as it changes over time from synthetic aperture radar (SAR) data covering the Alaskan Arctic coast and nearshore waters from east of Point Lay, Alaska to the Mackenzie delta. Observing the variability in the position of the SLIE for a large study area over the course of the year identifies the occurrences of significant change including the timing of freeze-up and break-up and episodic events in between. It is also possible to identify the maximum stable extent of the landfast ice for a given period, which should prove valuable for all nearshore activity in the Arctic. We can give a greater understanding of the factors controlling the SLIE position by calculating the standard deviation in landfast ice width along the coast. This analysis identifies stable nodes along the SLIE where variability is small and processes, as of yet unidentified, helps to stabilize the landfast ice edge

[1] Linkages between albedo, surface morphology, melt pond distribution, and properties of first-year and multiyear sea ice have been studied at two field sites in the North American Arctic between 1998 and 2001. It is shown that summer sea-ice albedo depends critically on surface melt-pond hydrology, controlled by melt rate, ice permeability, and topography. Remarkable short-term and interannual variability in pond fraction varying by more than a factor of 2 and hence area-averaged albedo (varying between 0.28 and 0.49 over the period of a few days) were observed to be forced by millimeter to centimeter changes in pond water level. Tracer studies show that the depth of the snow cover, by controlling the amount of superimposed ice formation in early summer, critically affects the retention of meltwater at the ice surface and hence affects pond coverage. Ice roughness as determined by deformation and aging processes explains a significant portion of the contrasts in pond coverage and albedo between ice of different ages, suggesting that a reduction in multiyear ice area and sea-ice residence time in the Arctic Ocean is accompanied by large-scale ice albedo decreases. Our work indicates that ice-albedo prediction in large-scale models with conventional methods is inherently difficult, if not impossible. However, a hydrological model, incorporating measured statistics of ice topography, reproduces observed pond features and variability, pointing toward an alternative approach in predicting ice albedo in numerical simulations.

[1] Horizontal banding features, alternating dark and bright horizontal bands apparent in ice cores and stratigraphic cross sections have long been observed in first-year sea ice and are frequently associated with bands of high and low brine or gas porosity. Observations on the land-fast ice near Barrow, Alaska, in recent years have revealed particularly striking banding patterns and prompted a study of their macroscopic and microscopic characteristics. The banding patterns are quantified from photographs of full-depth sections of the ice, and examples are presented from the Chukchi Sea and Elson Lagoon. Statistics on band spacing are presented, and the growth records for three seasons are employed to estimate their time of formation. These data provide insight into the periodicity of the underlying phenomena. Micrographs are used to examine the microstructural variations associated with various banding features and to quantify the geometry of the constituent brine inclusions associated with high- and low-porosity bands. The micrography revealed that the area fraction of brine inclusions varied by a factor of nearly 3 through the more pronounced high- and low-porosity bands. Vertical micrographs obtained shortly after the materials' removal from the ice sheet showed that significantly larger inclusions form abruptly at the start of the high-porosity bands and frequently terminate abruptly at the end of the band. Crystallographic observations indicated that the high-porosity bands supported the nucleation and growth of crystals having substantially different orientations from the very well aligned columnar structure that characterized the bulk of the sheet.

δ18O profiles in drifting Arctic sea ice are coupled with back trajectories of ice drift and an ice growth model to reconstruct the surface hydrography of the Arctic Ocean interior. The results compare well with δ18O values obtained by traditional oceanographic methods and known water mass distributions. Analysis of the stable isotopic composition of sea ice floes sampled at strategic and relatively accessible locations, e.g., Fram Strait, could aid in mapping spatial and temporal variations in Arctic Ocean surface waters.