Brian J. Moorman

Preservation of viral genomes in 700-y-old caribou feces from a subarctic ice patch

Significance Knowledge of ancient viruses is limited due to their low concentration and poor preservation in ancient specimens. Using a viral particle-associated nucleic acid enrichment approach, we genetically characterized one complete DNA and one partial RNA viral genome from a 700-y-old fecal sample preserved in ice. Using reverse genetics, we reconstituted the DNA virus, which replicated and systemically spread in a model plant species. Under constant freezing conditions, encapsidated viral nucleic acids may therefore be preserved for centuries. Our finding indicates that cryogenically preserved materials can be repositories of ancient viral nucleic acids, which in turn allow molecular genetics to regenerate viruses to study their biology. Viruses preserved in ancient materials provide snapshots of past viral diversity and a means to trace viral evolution through time. Here, we use a metagenomics approach to identify filterable and nuclease-resistant nucleic acids preserved in 700-y-old caribou feces frozen in a permanent ice patch. We were able to recover and characterize two viruses in replicated experiments performed in two different laboratories: a small circular DNA viral genome (ancient caribou feces associated virus, or aCFV) and a partial RNA viral genome (Ancient Northwest Territories cripavirus, or aNCV). Phylogenetic analysis identifies aCFV as distantly related to the plant-infecting geminiviruses and the fungi-infecting Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1 and aNCV as within the insect-infecting Cripavirus genus. We hypothesize that these viruses originate from plant material ingested by caribou or from flying insects and that their preservation can be attributed to protection within viral capsids maintained at cold temperatures. To investigate the tropism of aCFV, we used the geminiviral reverse genetic system and introduced a multimeric clone into the laboratory model plant Nicotiana benthamiana. Evidence for infectivity came from the detection of viral DNA in newly emerged leaves and the precise excision of the viral genome from the multimeric clones in inoculated leaves. Our findings indicate that viral genomes may in some circumstances be protected from degradation for centuries.

Bathymetric mapping and sub-bottom profiling through lake ice with ground-penetrating radar

Bathymetric mapping of lakes with sonar is essentially limited to the ice-free summer months. Recent developments in ground-penetrating radar technology have greatly increased its portability and capabilities for imaging through fresh water. The suitability of a backpack portable ground-penetrating radar (GPR) system for bathymetric mapping of ice-covered Arctic lakes was investigated by performing grid surveys on three lakes with water depths up to 19 m. It was demonstrated that GPR can now be used to quickly produce high quality bathymetric maps and sub-bottom profiles showing sediment type and lacustrine sediment thickness. While water depths were measured with a precision of ±3%, lacustrine sediment thickness measurements (up to 5 m) had an estimated precision of ±15%.

Small unmanned aircraft systems for remote sensing and Earth science research

To understand and predict Earth-surface dynamics, scientists often rely on access to the latest remote sensing data. Over the past several decades, considerable progress has been made in the development of specialized Earth observation sensors for measuring a wide range of processes and features. Comparatively little progress has been made, however, in the development of new platforms upon which these sensors can be deployed. Conventional platforms are still almost exclusively restricted to piloted aircraft and satellites. For many Earth science research questions and applications these platforms do not yet have the resolution or operational flexibility to provide answers affordably. The most effective remote sensing data match the spatiotemporal scale of the process or feature of interest. An emerging technology comprising unmanned aircraft systems (UAS), also known as unmanned aerial vehicles (UAV), is poised to offer a viable alternative to conventional platforms for acquiring high-resolution remote sensing data with increased operational flexibility, lower cost, and greater versatility (Figure 1).

Glacial hydrological system characterization using ground‐penetrating radar

Hydrological systems near the terminus of a high Arctic glacier and a proglacial icing on Bylot Island, Canada, were investigated using ground-penetrating radar (GPR). The ice thickness and the location and depth of tunnels within the glacier and icing were imaged. Modelling of the GPR response was utilized to predict the data quality and to assist in its interpretation. The unique properties of the ice enabled velocity determinations from the diffraction patterns generated by point-source reflectors as well as traditional velocity surveys. The propagation velocity of the radar pulses through the ice depended on the air and water content in the ice. The identification of drainage tunnels was attained through pulse polarity analysis and interpolation between the profiles in gridded surveys. It was found that reflectivity analysis may enable GPR to be used for acquiring three-dimensional information on the thermal structure of glaciers. The much more complicated structure of the icing was imaged with higher frequency antennae and it was found that general ice types could be mapped using radar stratigraphical analysis. Both buried slush mounds and subsurface channel fills were identified within the icing. A portion of the icing near the centre of the valley floor, that has persisted perennially for over 50 years, was found to be sitting on a slightly higher area of the valley bottom and thus was not subjected to the same hydrothermal erosional forces as the edges of the icing, setting up a feed-back loop encouraging the preservation of the central core of ice and promoting the destruction and rebuilding of the edges every year.

Glacier-permafrost hydrological interconnectivity: Stagnation Glacier, Bylot Island, Canada

Abstract The complex thermal structure in areas where polythermal glaciers and continuous permafrost are present increases the potential for direct linkages between subsurface water conduits within glaciers and permafrost. In this study, hydrologic features of a glacier and the surrounding ice-cored moraines were examined and the potential for englacial water to flow out of the glacier and into the moraine was investigated. Ground-penetrating radar investigations, dye trace tests and direct observations of hydrological features (e.g., moulins, springs and caves) on and around Stagnation Glacier on Bylot Island, Arctic Canada, were undertaken. Data reveal that englacial conduits extend from the glacier into the adjacent ice-cored moraine. Glacial meltwater may have experienced variable flow conditions over the last 10 years and the conduit closures have occurred over a much longer time period. The study illustrates the interconnectivity of the glacial and permafrost hydrological systems.

An Interacting Multiple-Model-Based Abrupt Change Detector for Ground-Penetrating Radar

In this letter, we propose an interacting multiple-model (IMM)-based abrupt change detector for ground-penetrating radar (GPR) applications. Ground clutter varies with surface roughness, soil nature, as well as depth of the soil layer, necessitating a multiple-model approach. The IMM is first trained for a chosen number of models and then used to characterize the GPR data. The IMM predictor segments the entire GPR data into regions of identical models and then identifies targets by detecting abrupt changes in model parameters. The number of models is determined using the minimum prediction error criterion. The prediction performance of the IMM predictor is theoretically analyzed, and its detection performance is also evaluated through an receiver operating characteristics analysis to illustrate the improved performance of the proposed detector.

Cryological processes implied in Arctic proglacial stream sediment dynamics using principal components analysis and regression

Abstract In high latitudes, recent research has demonstrated that both thermo-erosion and temperature dependence influence sediment release into fluvial systems. An analysis of proglacial suspended sediment concentration (SSC) dynamics is presented for three glacierized basins: cold-based Austre Brøggerbreen (Svalbard), polythermal Midre Lovénbreen (Svalbard) and polythermal Glacier B28 (Bylot Island). The temporal variation in processes dominating SSC patterns is assessed using stepwise multivariate regression following the subdivision of the time series. Partitioning of the time series is achieved through principal components and change point analyses. The regression models use discharge and surrogate predictor variables to model SSC, while improvements are made by using air temperature and radiation terms as independent variables. Comparisons are drawn between two sets of models with contrasting subseasonal division. By interpretation of the regression model characteristics, temporal changes in physical processes are implied over the course of the time periods. Numerical analyses suggest there is a trend for changes between fluvial, glacial and periglacial factors forcing responses in SSC. Therefore, it is conjectured that glaciofluvial sediment transfer at high latitudes is influenced by periglacial processes and conditions. This has implications for the predictions of fluvial sediment loads in a changing environment, and the use of sedimentary records for environmental reconstruction.

Near-surface hydraulic conductivity of northern hemisphere glaciers

The hydrology of near‐surface glacier ice remains a neglected aspect of glacier hydrology despite its role in modulating meltwater delivery to downstream environments. To elucidate the hydrological characteristics of this near‐surface glacial weathering crust, we describe the design and operation of a capacitance‐based piezometer that enables rapid, economical deployment across multiple sites and provides an accurate, high‐resolution record of near‐surface water‐level fluctuations. Piezometers were employed at 10 northern hemisphere glaciers, and through the application of standard bail–recharge techniques, we derive hydraulic conductivity (K) values from 0.003 to 3.519 m day−1, with a mean of 0.185 ± 0.019 m day−1. These results are comparable to those obtained in other discrete studies of glacier near‐surface ice, and for firn, and indicate that the weathering crust represents a hydrologically inefficient aquifer. Hydraulic conductivity correlated positively with water table height but negatively with altitude and cumulative short‐wave radiation since the last synoptic period of either negative air temperatures or turbulent energy flux dominance. The large range of K observed suggests complex interactions between meteorological influences and differences arising from variability in ice structure and crystallography. Our data demonstrate a greater complexity of near‐surface ice hydrology than hitherto appreciated and support the notion that the weathering crust can regulate the supraglacial discharge response to melt production. The conductivities reported here, coupled with typical supraglacial channel spacing, suggest that meltwater can be retained within the weathering crust for at least several days. Not only does this have implications for the accuracy of predictive meltwater run‐off models, but we also argue for biogeochemical processes and transfers that are strongly conditioned by water residence time and the efficacy of the cascade of sediments, impurities, microbes, and nutrients to downstream ecosystems. Because continued atmospheric warming will incur rising snowline elevations and glacier thinning, the supraglacial hydrological system may assume greater importance in many mountainous regions, and consequently, detailing weathering crust hydraulics represents a research priority because the flow path it represents remains poorly constrained.

Imaging the past: Archaeological radar stratigraphic analysis at Mahram Bilqis

A detailed GPR survey at the Mahram Bilqis was undertaken to investigate the architectural features buried beneath the desert sands. GPR used in combination with trenching and hand augering for depth verification and material identification, was found to be very effective at mapping the three dimensional location of buried buildings and other subsurface architectural and sedimentary structures. The unique characteristics of the sediment covering the site and the scale of the architectural elements (above and below the surface) presented a number of issues in designing the survey and interpreting the data. The GPR profiles revealed a variety of different structures to a depth of 8 m. The extensive survey and multitude of subsurface features enabled a radar stratigraphic analysis at the site. This was undertaken to classify features according to their geophysical character.

Determination of variations in glacier surface movements through high resolution interferometry; Bylot Island, Canada

Interferograms were generated from 10 TerraSAR-X image pairs, with the objective of obtaining estimates of winter surface motion for a slow-moving polythermal arctic glacier. Flow directions were computed using both ascending and descending-pass interferograms for each period, with the median value being adopted as the final direction. The weighted average flow was computed, with weighting based on the inverse of the difference between the ascending and descending-pass displacement estimates for each date. This study uses multiple interferograms with different imaging geometries to provide estimates of down-glacier flow. The methodology adopted minimizes the effects of glacier / satellite track alignment and those resulting from vertical motion of the glacier surface. Current velocities were compared with flow estimates derived from a 1992 ERS-1 image pair. The velocities were similar over most of the glacier, but current velocities were found to be 30% to 50% lower on the lower glacier.