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The need for data from an Arctic observing network to help stakeholders with planning and action is generally recognized. Two key research concerns arise: (1) potential contrasts between fundamental and applied science in the design of an observing system, and (2) development of best practices to ensure that stakeholder needs both inform and can be met from such an observing system. We propose a framework based on the concept of sea-ice system services (SISS) to meet these challenges and categorize the ways in which stakeholders perceive, measure, and use sea ice. Principal service categories are (1) climate regulator, marine hazard, and coastal buffer; (2) transportation and use as a platform; (3) cultural services obtained from the “icescape”; and (4) support of food webs and biological diversity. Our research focuses on cases of ice as platform and marine hazard in Arctic Alaska. We identify the information for each SISS category that users need to track, forecast, and adapt to changes. The resulting framework can address multiple information needs and priorities, integrate information over the relevant spatio-temporal scales, and provide an interface with local knowledge. To plan for an integrated Arctic Observing Network, we recommend a consortium-based approach with the academic community as an impartial intermediary that uses the SISS concept to identify common priorities across the range of sea-ice users.

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.

The texture of a material is closely connected to both its development and its properties. Aided by fully automated image-processing techniques developed for a simple PC-based system, we extract textural information from sea-ice thin sections. As a quantifier of mean size and orientation of grains, the “contrast gradient” has been defined. The skewness of the chord-size distribution aptly describes the grain-size distribution. Through a combination of these two parameters, granular and columnar textures can be distinguished. Samples of mixed columnar/granular texture may be further specified through their fractal properties. Fully automated techniques may be of use due to their objective scrutiny and their ability to draw information from large databases. In addition, they allow for highly specific descriptions of texture and may further the understanding of its development.

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.

The Arctic is presently undergoing rapid changes that cross the physical, biogeochemical and human domains. Understanding the causes of these changes and designing response strategies from the local to the hemispheric scale requires the implementation of an integrated, cross-disciplinary pan-Arctic observing system that is capable of capturing the evolution of the ongoing changes in near real-time. Due to the large spatial extent and the many variables that have to be covered by such an observing system it requires an international effort. This paper presents the status of the U.S. interagency effort to implement a component of the emerging Arctic Observing System that has been established during the past few years, in large part during the International Polar Year, in support of the Study of Environmental Arctic Change (SEARCH).

[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] The fluid permeability k of sea ice constrains a broad range of processes, such as the growth and decay of seasonal ice, the evolution of summer ice albedo, and biomass build-up. Such processes are critical to how sea ice and associated ecosystems respond to climate change. However, studies of k and its dependence on brine porosity ϕ and microstructure are sparse. Here we present a multifaceted theory for k(ϕ) which closely captures laboratory and field data. X-ray computed tomography provides an unprecedented look at the brine phase and its connectivity. We find that sea ice displays universal transport properties remarkably similar to crustal rocks, yet over a much narrower temperature range. Our results yield simple parameterizations for fluid transport in terms of temperature and salinity, and permit more realistic representations of sea ice in global climate and biological models.

[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.

Arctic observing networks exist in many countries and often cross international boundaries. We review their status and the development of networked long-term observations as part of a U.S. Arctic Observing System, highlighting major challenges and opportunities for prioritizing observations, designing a network, and increasing coordination. Most Arctic observing activities focus on specific themes and ecosystem services, resulting in a relatively narrow scope of observations for each network. Across all networks there is a need to improve national and international coordination to (1) reduce potential mismatch between identified science needs and outcomes desired by society, (2) link current observing networks to emerging agency and private-sector observing programs across disciplines, and (3) present a stable set of goals and priorities to increase network utility in view of the limited funding resources. We survey the landscape of observing activities and efforts to coordinate them internationally and present a framework for prioritization and coordination based on the activities of the U.S. Study of Environmental Arctic Change (SEARCH). This framework includes a hierarchy of interconnected activities involved in the design and implementation of observing networks. Across the hierarchy, definition of “actionable” science questions helps drive network design, with priorities set by the breadth and depth of the societal applications or policy requirements that these questions can inform. We present an example of applying this design hierarchy to observations that support policy and management decisions about offshore resource development in the Chukchi Sea.

[1] High interannual variability of summer surface salinity over the Laptev and East Siberian Sea shelves derived from historical records of the 1950s–2000s is attributed to atmospheric vorticity variations. In the cyclonic regime (positive vorticity) the eastward diversion of the Laptev Sea riverine water results in a negative salinity anomaly to the east of the Lena Delta and farther to the East Siberian Sea, and a positive anomaly to the north of the Lena Delta. Anticyclonic (negative) vorticity results in negative salinity anomalies northward from the Lena Delta due to freshwater advection toward the north, and a corresponding salinity increase eastward.

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.

The putative ocean of Europa has focused considerable attention on the potential habitats for life on Europa. By generally clement Earth standards, these Europan habitats are likely to be extreme environments. The objectives of this paper were to examine: (1) the limits for biological activity on Earth with respect to temperature, salinity, acidity, desiccation, radiation, pressure, and time; (2) potential habitats for life on Europa; and (3) Earth analogues and their limitations for Europa. Based on empirical evidence, the limits for biological activity on Earth are: (1) the temperature range is from 253 to 394 K; (2) the salinity range is a(H2O) = 0.6-1.0; (3) the desiccation range is from 60% to 100% relative humidity; (4) the acidity range is from pH 0 to 13; (5) microbes such as Deinococcus are roughly 4,000 times more resistant to ionizing radiation than humans; (6) the range for hydrostatic pressure is from 0 to 1,100 bars; and (7) the maximum time for organisms to survive in the dormant state may be as long as 250 million years. The potential habitats for life on Europa are the ice layer, the brine ocean, and the seafloor environment. The dual stresses of lethal radiation and low temperatures on or near the icy surface of Europa preclude the possibility of biological activity anywhere near the surface. Only at the base of the ice layer could one expect to find the suitable temperatures and liquid water that are necessary for life. An ice layer turnover time of 10 million years is probably rapid enough for preserving in the surface ice layers dormant life forms originating from the ocean. Model simulations demonstrate that hypothetical oceans could exist on Europa that are too cold for biological activity (T253 K). These simulations also demonstrate that salinities are high, which would restrict life to extreme halophiles. An acidic ocean (if present) could also potentially limit life. Pressure, per se, is unlikely to directly limit life on Europa. But indirectly, pressure plays an important role in controlling the chemical environments for life. Deep ocean basins such as the Mariana Trench are good analogues for the cold, high-pressure ocean of Europa. Many of the best terrestrial analogues for potential Europan habitats are in the Arctic and Antarctica. The six factors likely to be most important in defining the environments for life on Europa and the focus for future work are liquid water, energy, nutrients, low temperatures, salinity, and high pressures.

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.

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

The main objective of this chapter is to assess recent fluxes of terrigenous dissolved and particulate organic carbon into the Arctic Ocean. The most important terrigenous sources of organic matter (OM) in the ocean are (1) river and groundwater discharge, (2) coastal erosion, (3) sea-ice input and (4) aeolian material fluxes. The organic carbon fluxes of each of these pathways will be considered separately and a evaluation will be made of their roles in the total balance of OM input to the ocean.

We examined the Arctic bacterium Colwellia psychrerythraea strain 34H for motility at temperatures from −1 to −15°C by using transmitted-light microscopy in a temperature-controlled laboratory. The results, showing motility to −10°C, indicate much lower temperatures to be permissive of motility than previously reported (5°C), with implications for microbial activity in frozen environments.

Field observations and SAR imagery of coastal ice off the Lena Delta (Laptev Sea) in 1996/97 show a strong zonation of ice types associated with gradients in ice dielectric properties and microstructure. Ice-growth and radar-backscatter modelling indicate that the distinct transition between ice of high mean, low variance and low mean, high variance backscatter corresponds to an increase in parent water-mass salinity above 2 to 5/sup 0///sub 00/. High radar penetration depths allow for detection and mapping of bottomfast ice.

Permeability and meltwater flow have been studied in sea ice in the Siberian and central Arctic during the summers of 1995 and 1996. A bail-test technique has been adapted to allow for measurements of in situ permeability, found to range between 10−11 and 10−8 m2. Permeability varied by about a factor of 2 between 1995 (above-normal melt rates) and 1996 (below-normal melt rates). Release of fluorescent tracers (fluorescein, rhodamine) furthermore allowed the derivation of flow velocities and assessment of the relevant driving forces. Hydraulic gradients in rough ice and wind stress in ponded ice were found to be particularly important, driving meltwater over distances of several meters per day. The mid- to late-summer ice was found to be permeable enough to completely divert meltwater from the surface into the ice interior. It is shown, however, that lower permeabilities of the upper ice layers as well as refreezing of meltwater, particularly during the early melt season, foster the development of surface melt ponds.

[1] As part of a large interdisciplinary study of the Surface Heat Budget of the Arctic Ocean (SHEBA), we installed more than 135 ice thickness gauges to determine the sea ice mass balance. While installing these gauges during the fall of 1997, we found that much of the multiyear ice cover was only 1 m thick, considerably thinner than expected. Over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types, including first-year ice, ponded ice, unponded ice, multiyear ice, hummocks, new ridges, and old ridges. Initial ice thicknesses for these sites ranged from 0.3 to 8 m, and snow depths varied from a few centimeters to more than a meter. However, for all of their differences and variety, these thickness gauges sites shared a common trait: at every site, there was a net thinning of the ice during the SHEBA year. The thin ice found in October 1997 was even thinner in October 1998. The annual cycle of ice thickness was also similar at all sites. There was a steady increase in thickness through the winter that gradually tapered off in the spring. This was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze-up began. Maximum surface melting was in July, while bottom ablation peaked in August. Combining results from the sites, we found an average winter growth of 0.51 m and a summer melt of 1.26 m, which consisted of 0.64 m of surface melt and 0.62 m of bottom melt. There was a weak trend for thicker ice to have less winter growth and greater net loss for the year; however, ice growth was also impacted by the snow depth. Considerable variability was observed between sites in both accretion and ablation. The total accretion during the 9-month growth season ranged from zero for thick ridged ice to more than a meter for young ice. Ponds tended to have a large amount of surface melting, while ridges had considerable bottom ablation.

[1] A model is presented that describes the simultaneous growth and ablation of a layer of ice between an under-ice melt pond and the underlying ocean. Such “false bottoms” are the only significant source of ice formation in the Arctic during summer. Analytical solutions for diffusional transport of heat and salt are calculated that illustrate the importance of salt transport in effecting phase change. The model is extended to account for turbulent transports and applied to make predictions of bottom ablation rates of sea ice given the far-field properties of the ocean from the AIDJEX and SHEBA field experiments. The model predictions show that false bottoms may play a significant role in the summer heat budget of the ice-ocean system, causing localized heat fluxes of more than 10 W m−2 into the mixed layer. The thickening of thin ice by false-bottom formation leads to longer-lasting sea ice and thus smaller ice-free areas, which might be an important mechanism affecting the surface albedo.

The ultimate goal of the proposed research is to understand the creation of the preserved stratigraphic record, seabed formation and modification over the Russian Arctic continental shelves as the product of geologic, biologic, cryologic and oceanographic processes. The emphasis is on the upper 100 m of sections and the last 100,000 years of Earth's history.

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

Combining field measurements, remote sensing data and numerical modelling, a key sitefor entrainment and dispersal of sediments throughout the Arctic has been identified near the NewSiberian Islands. At this location, the relevant boundary conditions are shown to be highlyconducive to sediment entrainment and export. The total ice-bound sediment export of 18.5 x 10 6t for an entrainment event documented in 1994/95 is of the same order of magnitude as annualsediment supply to the deep sea sector of the Eurasian Arctic and the Greenland Sea. Satelliteimagery from different years and ancillary data indicate that ice advection from this source mayplay an important role in sedimentation downstream in the Transpolar Drift.

Russian and German scientists have investigated the extreme environmental system in and around the Laptev Sea in the Siberian Arctic. For the first time a major comprehensive research program combining the efforts of several projects addressed both oceanic and terrestrial processes, and their consequences for marine and terrestrial biota, landscape evolution as well as land-ocean interactions. The primary scientific goal of the multidisciplinary program was to decipher past climate variations and their impact on contemporary environmental changes. Extensive studies of the atmosphere, sea ice, water column, and sea-floor on the Laptev Sea Shelf, as well as of the vegetation, soil development, carbon cycle, permafrost behaviour and lake hydrology, and sedimentation on Taymyr Peninsula and Severnaya Zemlya Archipelago were performed during the past years under a framework of joint research activities. They included land and marine expeditions during spring (melting), summer (ice free), and autumn (freezing) seasons. The close bilateral cooperation between many institutions in Russia and Germany succeeded in drawing a picture of important processes shaping the marine and terrestrial environment in northern Central Siberia in Late Quaternary time. The success of the projects, which ended in late 1997, resulted in the definition and establishment of a new major research effort which will concentrate on establishing a better understanding of the paleoclimatic and paleoenvironmental record of the area. This is important because it allows to be able to judge rates and extremes of potential future environmental changes.

Seasonal and interannual variability of ice drift in the Laptev Sea and ice exchange with the Arctic Ocean have been investigated using remote sensing data, a large-scale dynamic-thermodynamic numerical sea ice model and semi-empirical method. During the period 1979-1995 sea ice was exported from the Laptev Sea with maximum export occuring in February and minimum in August. The average winter ice outflow during this period was equal to 482700 km/sup 2/. Estimates of ice exchange between the northern and southern parts of the Laptev Sea during the period 1936 to 1996 exhibited a strong interannual variability, but did not reveal significant trends.

Recent studies have indicated that drifting Arctic sea ice plays an important role in the redistribution of sediments and contaminants. Here we present a method to reconstruct the back- ward trajectory of sea ice from its sampling location in the Eurasian Arctic to its possible site of ori- gin on the shelf, based on historical drift data from the International Arctic Buoy Program. This method is verified by showing that origins derived from the backward trajectories are generally con- sistent with other indicators, such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions. The trajectories are then used to identify regions where sediment-laden ice is exported to the Transpolar Drift Stream: from the New Siberian Islands and the Central Kara Plateau. Calculation of forward trajectories shows that the Kara Sea is a major contributor of ice to the Barents Sea and the southern limb of the Transpolar Drift Stream.

Ice cores were collected between 10.03.93 and 15.03.93 along a 200 m profile on a large ice floe in Fram Strait. The ice was typical of Arctic multi-year ice, having a mean thickness along the profile of 2.56 ±0.53 m. It consisted mostly of columnar ice (83%) grown through congelation of seawater at the ice bottom, and the salinity profiles were characterized by a linear increase from 0 psu at the top to values ranging between 3 and 5 psu at depth. Distributions of dissolved organic carbon (DOC) and nitrogen (DON) and major nutrients were compared with ice texture, salinity and chlorophyll a. DOC, DON, dissolved inorganic nitrogen (DIN), NH4 + and NO2 − were present in concentrations in excess of that predicted by dilution curves derived from Arctic surface water values. Only NO3 − was depleted, although not exhausted. High DOC and DON values in conjunction with high NH4 + levels indicated that a significant proportion of the dissolved organic matter (DOM) was a result of decomposition/grazing of ice algae and/or detritus. The combination of high NH4 + and NO2 − points to regeneration of nitrogen compounds. There was no significant correlation between DOC and Chl a in contrast to DON, which had a positively significant correlation with both salinity and Chl a, and the distribution of DOM in the cores might best be described as a combination of both physical and biological processes. There was no correlation between DOC and DON suggesting an uncoupling of DOC and DON dynamics in multi year ice.

A 20 km wide zone of fast ice, reaching offshore to the 20 m isobath and sealing off coastal embayments along the Taymyr Peninsula, survived until at least 23 November 1993, becoming multiyear land-fast sea ice (MLSI). Barrier islands show characteristic recurved spits indicating dominant southeastward direction of longshore transport in intermittent years. At the time of observation, the fast ice was undisturbed, only heaving vertically with tides, protecting the coastal zone from wave reworking. The 1 to 2 m thick ice cover affects light and oxygen, creating profound effects on marine life in the zone. A herd of walrus, in other summers reported to haul out on local beaches, was displaced by the fast ice. We saw no evidence for sediment loading of the ice by rivers or eolian deposition on ice. MLSI is considered an incipient ice shelf, which could grow in thickness and strength in successive winters. Salinity and delta 18O profiles in ice cores from some smaller areas of MLSI provide a record of environmental conditions during the first year of ice growth, such as local hydrography and contribution of congealed snow to the solid fast ice. On ice charts we found no record of waxing and waning MLSI in the area, and do not know whether the observed ice survived the next summer. Since arctic ice shelves have developed from MLSI in the past, the observed phenomenon permits a view of how transitions from interglacial to full glacial conditions can begin. Key words: multiyear land-fast sea ice, incipient ice shelves, sediment entrainment, interglacial/glacial transition, Siberia, Laptev Sea

U.S. Arctic Observing Coordination Workshop;Anchorage, Alaska, 20–22 March 2012 The Arctic is undergoing tremendous changes. Permafrost is thawing, ice sheets are melting, and sea ice is thinning and retreating. These changes are impacting ecosystems and human activities. Observing, understanding, and responding to these changes are the central themes of the U.S. Interagency Study of Environmental Arctic Change (SEARCH, http://www.arcus.org/search/index.php). SEARCH brings together academic and government agency scientists and stakeholders to prioritize, plan, conduct, and synthesize research focused on Arctic environmental change. The U.S. Arctic Observing Coordination Workshop (http://www.arcus.org/search/meetings/2012/coordination-workshop/) focused on two key themes for cross-disciplinary and cross-agency collaboration: (1) understanding and predicting sea ice changes and their consequences for ecosystems, human activities, and climate and (2) determining consequences of loss and warming of shallow permafrost on Arctic and global systems.

Climate and Cryosphere Arctic Sea Ice Workshop; Boulder, Colorado, 31 October to 2 November 2011 The Arctic sea ice cover is undergoing tremendous changes. The end-of-summer ice extent is decreasing, the ice is thinning, and there is a fundamental shift from perennial to seasonal ice. These changes have important implications for both the Arctic and the global climate system. This importance creates a need to observe and understand the ongoing changes and to predict future changes in the Arctic sea ice cover

Despite the Arctic sea ice cover's recognized sensitivity to environmental change, the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood. Sea ice sediment inclusions were studied in the central Arctic Ocean during the Arctic 91 expedition and in the Laptev Sea (East Siberian Arctic Region Expedition 1992). Results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central Arctic Ocean. This study documents the regional distribution and composition of particle-laden ice, investigates and evaluates processes by which sediment is incorporated into the ice cover, and identifies transport paths and probable depositional centers for the released sediment. In April 1992, sea ice in the Laptev Sea was relatively clean. The sediment occasionally observed was distributed diffusely over the entire ice column, forming turbid ice. Observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment. In the central Arctic Ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes. The surface sediment accumulation in central Arctic multi-year sea ice exceeds by far the amounts observed in first-year ice from the Laptev Sea in April 1992. Sea ice sediments are generally fine grained, although coarse sediments and stones up to 5 cm in diameter are observed. Component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles. The biogenous components, namely shells of pelecypods and benthic foraminiferal tests, point to a shallow, benthic, marine source area. Apparently, sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing. Clay mineralogy of ice-rafted sediments provides information on potential source areas. A smectite maximum in sea ice sediment samples repeatedly occurred between 81°N and 83°N along the Arctic 91 transect, indicating a rather stable and narrow smectite rich ice drift stream of the Transpolar Drift. The smectite concentrations are comparable to those found in both Laptev Sea shelf sediments and anchor ice sediments, pointing to this sea as a potential source area for sea ice sediments. In the central Arctic Ocean sea ice clay mineralogy is significantly different from deep-sea clay mineral distribution patterns. The contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms.

Results of uniaxial compression test are compared to porosity and chlorophyll content of granular seaice samples, collected in the Weddell Sea from June to November of 1986. Compressive failure stresses are significantly correlated with the total porosity of the ice, but exhibit no correlation with chlorophyll concentration. We suggest that high chlorophyll concentrations may accompany low ice strengths only because high porosities, which are responsible for low mechanical strength, can be linked to sea-ice biology. High concentrations of ice algae may be either cause or effect of high porosities (through absorption of solar radiation in the first case or due to enhanced nutrient supply and environmental space in the second case). As a cause of high porosities, ice organisms could therefore indirectly influence the spring breakup of floes and thus the course of the ablation season.

Until recently the main motivation in sea ice modeling has been toward the development of large-scale models for climate studies. These models describe sea ice as a plastic material, with a smooth yield surface and ice strength dependent on a thickness distribution that is based on statistical representations of sea ice deformation through ridging. With tuning, they are found to reproduce ice extent and concentration in the Arctic and Antarctic, though velocity fields are overly smooth and many details, such as polynyas and leads, are not captured. There is increasing interest in regional ice modeling. In the near-shore Beaufort and Chukchi seas, there is considerable interest from the oil industry in the formation and breakup of landfast ice, the propagation of oil spills, and prediction of sea ice conditions. The importance of resolving eddies in the ocean and modeling small-scale (sub-10-km) sea ice processes is becoming apparent, as we begin to understand the non-linear effect of small-scale processes on the large-scale motion. Recently, there have been advances in the direction of small-scale process research and regional ice-ocean model development. The most pertinent of these are outlined in this article.

The results of multispectral passive microwave observations (6.7 to 90-GHz) are presented from the cruises of the FS Polarstern in the Weddell Sea from July to December 1986. This paper includes primarily the analysis of radiometric observations taken at ice station sites. Averaged emissivity spectra for first-year (FY) ice were relatively constant throughout the experiment and were not statistically different from FY ice signatures in the Arctic. Detailed ice characterization was carried out at each site to compare the microwave signatures of the ice with the physical properties. Absorption optical depths of FY ice were found to be sufficiently high that only the structure in the upper portions of the ice contributed significantly to interstation emissivity variations. The emissivities at 90-GHz, e(90), had the greatest variance. Both e(90) at vertical polarization and GR(sub e)(90, 18.7)(defined as (e(sub V)(90)-e(sub V)(18.7))/e(sub V)(90 + e(sub V)(18.7)) depended on the scattering optical depth which is a function of the snow grain diameter and layer thickness. The variance showed a latitude dependence and is probably due to an increase in the strength of snow metamorphism nearer the northern edge of the ice pack. The contribution of variations of near-surface brine volume to the emissivity was not significant over the range of values encountered at the station sites. Emissivity spectra are presented for a range of thin ice types. Unsupervised principal component analysis produced three significant eigenvectors and showed a separation among four different surface types: open water, thin ice, FY ice, and FY ice with a thick snow cover. A comparison with SMMR satellite data showed that average ice concentrations derived from the ship's ice watch log were consistent with the satellite concentrations. The surface based emissivities for FY ice were also compared with emissivities calculated from scanning multichannel microwave radiometer (SMMR) satellite radiances. Best agreement was found at 6.7 and 10-GHz, while at 18 and 37-GHz, SMMR emissivities were slightly lower than surface based results. For the three lower frequencies agreement was found within a confidence limit of 95% and for 37-GHz within about 90%.

In order to describe and compare sea ice salinity distributions, which are of interest in the study of physical and biological ice characteristics as well as ice-ocean interaction, we have computed composite profiles and fitted third-degree polynomials to salinity data of 129 cores from the Weddell Sea. Four characteristic profile shapes have been recognized and described through the polynomial coefficients (C-, S-, I- and ?-type profiles). The field data have been compared with “ideal” salinity profiles generated by a simulation scheme based on thermodynamic growth under climatological conditions representative of the Weddell Sea. Composite salinity profiles agree well with simulations, irrespective of the growth mechanism (i.e., frazil or congelation), suggesting that ice properties which depend on salinity or porosity may evolve independent of ice growth conditions. Analysis of salinity and 18O data in conjunction with the simulations demonstrates that apart from meteorological conditions controlling growth velocity and temperature distribution within the ice, flooding and upward brine expulsion are important in raising top salinities as frequently observed. Low top salinities are typical of ice that has undergone retexturing and differential desalination. Salinity decreases towards the bottom of a floe are a result of high oceanic heat fluxes and snow-cover effects. As a consequence of these processes the bulk salinity of Weddell Sea ice cannot be described by a simple linear age-thickness relationship as characteristic of Arctic first-year ice.