Elson Lagoon Research Articles

Microwave Signatures of Snow on Sea Ice: Modeling

Accurate knowledge of snow-depth distribution over sea ice is critical for polar climate studies. Current snow-depth-over-sea-ice retrieval algorithms do not sufficiently account for variations in snow and ice physical properties that can affect the accuracy of retrievals. For this reason, airborne microwave observations were coordinated with ground-based measurements of snow depth and snow properties in the vicinity of Barrow, AK, in March 2003. In this paper, the effects of snowpack properties and ice conditions on microwave signatures are examined using detailed surface-based measurements and airborne observations in conjunction with a thermal microwave-emission model. A comparison of the Microwave Emission Model of Layered Snowpacks (MEMLS) simulations with detailed snowpack and ice data from stakes along the Elson Lagoon and the Beaufort Sea and radiometer data taken from low-level flights using a Polarimetric Scanning Radiometer (PSR-A) shows that MEMLS can be used to simulate snow on sea ice and is a useful tool for understanding the limitations of the snow-depth algorithm. Analysis of radiance data taken over the Elson Lagoon and the Beaufort Sea using MEMLS suggests that the radiometric differences between the two locations are due to the differences in sea-ice emissivity. Furthermore, measured brightness temperatures suggest that the current snow-depth retrieval algorithm is sufficient for areas of smooth first-year sea ice, whereas new algorithm coefficients are needed for rough first-year sea ice. Snowpack grain size and density remain an unresolved issue for snow-depth retrievals using passive-microwave radiances

Geostatistical Characterization of Snow-Depth Structures on Sea Ice Near Point Barrow, Alaska—A Contribution to the AMSR-Ice03 Field Validation Campaign

The objective of this paper is to characterize spatial properties of snow-depth structures and their role as indicators of sea-ice properties and sea-ice-morphogenetic processes, and to provide quantitative measures of sea-ice properties that may be utilized in analyses of passive-microwave data. Snow-depth data collected near Point Barrow, Alaska, as part of the AMSRIce03 Field Validation Campaign for Advanced Microwave Scanning Radiometer (AMSR)-E-Sea-Ice Products from NASA earth-observing-systems satellite AQUA, are analyzed and compared to P-3 polarimetric scanning radiometer (PSR) data, a proxy for AMSR-E brightness temperatures. The approach taken in the analysis is geostatistical characterization. Various functions of first and second order are calculated for the snow-depth profiles, then geostatistical classification parameters are extracted and combined into feature vectors, on which the characterization is based. The complexity of sea ice requires a generalization of the method by introduction of the hyperparameter concept. Results include a quantitative characterization of sea-ice provinces from field transects in the Beaufort Sea, Chukchi Sea, and Elson Lagoon, which represent a good subset of Arctic sea-ice types, an internal segmentation of the longer profiles, and a derivation of surface-roughness length and of sea-ice-type complexity. PSR data reflect complexity of spatial snow-depth structures as captured in multidimensional feature vectors and, less directly, snow-depth and surface-roughness length. These results indicate that passive-microwave data in general may be affected by spatial snow depth and surface roughness, with a dependence on scale and quantified by geostatistical classification

Microwave Signatures of Snow on Sea Ice: Observations

Part of the Earth Observing System Aqua Advanced Microwave Scanning Radiometer (AMSR-E) Arctic sea ice validation campaign in March 2003 was dedicated to the validation of snow depth on sea ice and ice temperature products. The difficulty with validating these two variables is that neither can currently be measured other than in situ. For this reason, two aircraft flights on March 13 and 19, 2003, were dedicated to these products, and flight lines were coordinated with in situ measurements of snow and sea ice physical properties. One flight was in the vicinity of Barrow, AK, covering Elson Lagoon and the adjacent Chukchi and Beaufort Seas. The other flight was farther north in the Beaufort Sea (about 73degN, 147.5degW) and was coordinated with a Navy ice camp. The results confirm the AMSR-E snow depth algorithm and its coefficients for first-year ice when it is relatively smooth. For rough first-year ice and for multiyear ice, there is still a relationship between the spectral gradient ratio of 19 and 37 GHz, but a different set of algorithm coefficients is necessary. Comparisons using other AMSR-E channels did not provide a clear signature of sea ice characteristics and, hence, could not provide guidance for the choice of algorithm coefficients. The limited comparison of in situ snow-ice interface and surface temperatures with 6-GHz brightness temperatures, which are used for the retrieval of ice temperature, shows that the 6-GHz temperature is correlated with the snow-ice interface temperature to only a limited extent. For strong temperature gradients within the snow layer, it is clear that the 6-GHz temperature is a weighted average of the entire snow layer

Observations of banding in first‐year Arctic sea ice

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.

Three decades of investigations on heavy metals in coastal sediments, North Arctic Alaska: A synthesis

Concentrations of V, Cr, Cu, Ni, Zn, As, Cd, Pb, Ba, Fe, Mn, total and methyl Hg were measured in muddy sediments from urbanized Elson Lagoon adjacent to Barrow Village, industrialized Colville Delta-Prudhoe Bay, and relatively pristine Beaufort Lagoon adjacent to the Arctic National Wildlife Refuge, Beaufort Sea, north Arctic Alaska. Comparison of the mean concentrations of the metals at approximately 10-year intervals (1977, 1986, 1997), within the Colville Delta-Prudhoe Bay shows significantly increased concentrations of V in 1986 and 1997 from 1977 and an increase in Ba from 1986 to 1997. No significant changes were noted in the concentrations of other elements. The sources of V and Ba contaminants are unknown. The levels of all metals are below or similar to those in unpolluted marine sediments. The geochemical partitioning of selected metals was deduced from metal analyses in the lithogenous and non-lithogenous sediment fractions. Of the total contents -50% of Mn, 25-35% Co, 15-20% Zn, Cu and Ni, 10% of V and Fe and <3% of Cr are bound in the non-lithogenous phase, presumably in organic matter, clays and Fe-Mn oxide/hydroxides. In contrast, almost all of Cr, Cd and Ba are lattice-held, and <1% of Hg is methylated.

Sediment Inclusions in Alaskan Coastal Sea Ice: Spatial Distribution, Interannual Variability, and Entrainment Requirements

We investigated the spatial characteristics of sedimentary inclusions and elucidated processes controlling their spatial and temporal variability in the fast ice cover of the shallow-marine environment of Elson Lagoon near Barrow, Alaska. This was accomplished by examining the frazil ice layer of sea-ice cores representing the 1998, 1999, and 2000 fall freeze-up periods and comparing the results with a sediment resuspension model. Sediments occur exclusively as aggregates of clay to fine-silt sized particles that were confined to brine inclusions in the frazil ice. The average cross-sectional area of these aggregates is positively correlated with sediment concentration of the frazil ice (R2 = 0.82, P < 0.01). The minimum distance between neighboring aggregates (nearest-neighbor distance) is negatively correlated with sediment concentration (R2 = 0.78, P < 0.01). However, little correlation exists between the number of aggregates and sediment concentration. Sediment concentrations ranged from 24 to 1470 mg L–1 and sediment loads ranged from 2 g m–2 to 384 g m–2, with 1998 and 2000 sediment loads being one to two orders of magnitude smaller than 1999 sediment loads. Similarly, the potential for bottom-sediment resuspension was greater in 1999 than in 1998 and 2000 by more than a factor of two. Resuspension potential is controlled spatially by the local bathymetry and interannually by wind velocity and fetch. At submeter scales, increases in bottom sediment resuspension result in greater sea-ice sediment concentrations, larger aggregates, and smaller nearest-neighbor distances.

Sediment Inclusions in Alaskan Coastal Sea Ice: Spatial Distribution, Interannual Variability, and Entrainment Requirements

We investigated the spatial characteristics of sedimentary inclusions and elucidated processes controlling their spatial and temporal variability in the fast ice cover of the shallow-marine environment of Elson Lagoon near Barrow, Alaska. This was accomplished by examining the frazil ice layer of sea-ice cores representing the 1998, 1999, and 2000 fall freeze-up periods and comparing the results with a sediment resuspension model. Sediments occur exclusively as aggregates of clay to fine-silt sized particles that were confined to brine inclusions in the frazil ice. The average cross-sectional area of these aggregates is positively correlated with sediment concentration of the frazil ice (R2 = 0.82, P < 0.01). The minimum distance between neighboring aggregates (nearest-neighbor distance) is negatively correlated with sediment concentration (R2 = 0.78, P < 0.01). However, little correlation exists between the number of aggregates and sediment concentration. Sediment concentrations ranged from 24 to 1470 mg L–1 and sediment loads ranged from 2 g m–2 to 384 g m–2, with 1998 and 2000 sediment loads being one to two orders of magnitude smaller than 1999 sediment loads. Similarly, the potential for bottom-sediment resuspension was greater in 1999 than in 1998 and 2000 by more than a factor of two. Resuspension potential is controlled spatially by the local bathymetry and interannually by wind velocity and fetch. At submeter scales, increases in bottom sediment resuspension result in greater sea-ice sediment concentrations, larger aggregates, and smaller nearest-neighbor distances.

Observations of brine drainage networks and microstructure of first‐year sea ice

Brine drainage networks and the microstructure of first‐year sea ice have been examined at two locations near Barrow, northern Alaska. A method for obtaining full‐depth sections of ice sheets up to 1.8 m thick is presented and shown to provide information on the spatial distribution and geometry of brine drainage networks on a scale of meters. A number of such sections from the two test sites are presented which reveal a greater variety of main channel and side branch configurations than is typically observed in ice grown in the laboratory. Vertical and horizontal micrographs and thin section photographs were obtained in November 1993, and March and May 1994 at a test site in the relatively protected Elson Lagoon. The resulting time series of photographic records provide detailed information on the size, shape, and spatial distribution of the brine‐ and gas‐filled inclusions and a means to quantify their size and shape changes with time. An example of the changes with time in inclusion sizes and aspect ratios in the vertical and horizontal directions for a depth of 0.2 m, with a given thermal history is also presented.

Core-Based SCB Fracture of Aligned First-Year Sea Ice (Phases III and IV)

This paper provides the results of two small-scale testing programs linked to large-scale field programs carried out by the writers and others. The large-scale in-situ sea ice testing program was part of the Office of Naval Research's (ONR's) Sea Ice Mechanics Initiative (SIMI). Three field trips to Barrow, Alaska, were completed to examine the seasonal evolution of the first-year sea ice growing on Elson Lagoon. Trips were made in November, March, and May, when significant changes in thickness and temperature profile were evident. The experiments were designed to determine the fracture behavior of sea ice in situ and make comparisons with small-scale lab tests. Due to the unique microstructure of the sea ice tested, it was necessary to complete small-scale (0.1 m) tests for comparative purposes. A detailed study of the ice fabric at the site revealed a very strong alignment of the c-axis. This prompted a study of the fracture properties parallel (hard-fail) and perpendicular (easy-fail) to the preferred c-axes orientation plane in both the largeand small-scale tests. The effects of c-axis alignment, temperature and microstructure on the fracture toughness and tensile strength are investigated.

Overview of Recent Program on Mechanical Properties of Sea Ice

This paper describes field and laboratory measurements of the evolving physical and mechanical properties of first-year sea ice through a growth season. The primary objectives were to (1) examine sample size effects on the in situ strength and constitutive behavior; (2) improve understanding of the interrelations between physical and mechanical properties; and (3) verify models based on small-scale isothermal behavior. Replicate sets of observations were made at a site in Elson Lagoon, near Barrow, Alaska, covering fall, midwinter and spring conditions. Each set consisted of in situ fracture, creep, creep recovery, and cyclic loading experiments and laboratory measurements of flexural strength along with a complete description of the physical properties. In situ experiments employed square double cantilever beam specimens ranging in size from 0.25 m to 30 m. Electromagnetic and acoustic emissions generated by fracturing were monitored. Small-scale isothermal laboratory experiments were performed to profil...

Vertical distribution of bacteria in arctic sea ice

Heterotrophic bacteria were enumerated in north polar sea ice cores obtained near Point Barrow, Alaska. Highest concentrations of total and viable bacteria were found in the layer containing the sea ice microbial community identified by the maximum chlorophyll a content. Gas vacuolate bacteria were also found in the sea ice, a discovery which is consistent with their recent report from antarctic sea ice microbial communities. The gas vacuolate bacteria comprised 0.2% or less of the viable bacteria isolated from sea ice cores, lower than concentrations reported for most antarctic samples. Most gas vacuolate isolates from the sea ice cores were pigmented pink, orange, or yellow. An ice core from nearby saline Elson Lagoon contained an inverted sea ice microbial community with highest chlorophyll a concentrations and bacterial counts found in the top 0–20 cm of the ice. This surface layer also contained high numbers (up to 186 bacteria/ml) of a nonpigmented, gas vacuolate, elongated rod-shaped bacterium.

Heat and mass transport processes in subsea permafrost 1. An analysis of molecular diffusion and its consequences

Some heat and mass transport processes in subsea permafrost are discussed. An exact solution is given for a coupled model in which both heat and salt are transported solely by diffusion. The model describes the development of a thawed layer beneath the seabed after an ocean transgression over deeply frozen ground and is a generalization of the well‐known Stefan problem. A stability calculation indicates that such a diffusive regime should be unstable to convection of the interstitial water in the thawed layer after a critical thickness has been reached. The theory is compared with observations from two sites in the Beaufort Sea, Alaska. In western Elson Lagoon, near Barrow, the diffusive regime may be stable, but at Prudhoe Bay it is not, and interstitial water motion is important. At Prudhoe Bay the salt and heat transport regimes are convective and diffusive, respectively.

THE PRESENCE OF BACTERIA IN PERMAFROST OF THE ALASKAN ARCTIC.

Abstract : The possible occurrence of viable microbes and other forms of life in permanently frozen material has intrigued microbioligists for many years. If present, these may well be the oldest living things on this planet, having survived over a long period of time under frozen conditions. Because of the difficulties of sampling through permanently frozen ground and due to logistics and other problems of methodology, only few studies on the mocrobial flora of permafrost have been made. To extend these studies and to include quantitative studies of the Alaskan Arctic, a series of holes 32 in. in diameter were drilled to depths of 8-15 ft. in permafrost along a traverse between Elson Lagoon and the village of Barrow. Samples were collected from the wall of the hole for analysis. Throughout the depth of the soil section the number of thermophilic bacteria was more or less constant; markedly fewer mesophilic forms were observed in the permafrost than in the active layer. In general, molds were restricted to the upper 6 in. of the soil and psychrophilic bacteria to the upper 12 in. During this work, many colonies of the thermophilic bacteria were isolated and examined, and almost all were able to produce spores. The question of age of these soil bacteria could only be answered by radiocarbon dating. (Author)

Recent Changes in the Shoreline near Point Barrow, Alaska

Contains a study of the shoreline, its erosion and factors causing it along a stretch of some 30 miles southwest and southeast of Point Barrow. The rapid changes in shoreline configuration, especially at Nuwuk the triangulation station at the tip of Point Barrow, and along the south shore of Elson Lagoon were found to be not the result of vigorous action of waves or currents, but due to the presence of ground ice along the shores, which when thawing during the brief summer is easily removed even by feeble sea action. Author's observations were made while at Arctic Research Laboratory at Barrow, engaged in a geothermal project. Bibliographical footnotes.