Lake Ice Thickness Research Articles

Northwest Territories and Nunavut Snow Characteristics from a Subarctic Traverse: Implications for Passive Microwave Remote Sensing

Abstract During April 2007, a coordinated series of snow measurements was made across the Northwest Territories and Nunavut, Canada, during a snowmobile traverse from Fairbanks, Alaska, to Baker Lake, Nunavut. The purpose of the measurements was to document the general nature of the snowpack across this region for the evaluation of satellite- and model-derived estimates of snow water equivalent (SWE). Although detailed, local snow measurements have been made as part of ongoing studies at tundra field sites (e.g., Daring Lake and Trail Valley Creek in the Northwest Territories; Toolik Lake and the Kuparak River basin in Alaska), systematic measurements at the regional scale have not been previously collected across this region of northern Canada. The snow cover consisted of depth hoar and wind slab with small and ephemeral fractions of new, recent, and icy snow. The snow was shallow (<40 cm deep), usually with fewer than six layers. Where snow was deposited on lake and river ice, it was shallower, denser, and more metamorphosed than where it was deposited on tundra. Although highly variable locally, no longitudinal gradients in snow distribution, magnitude, or structure were detected. This regional homogeneity allowed us to identify that the observed spatial variability in passive microwave brightness temperatures was related to subgrid fractional lake cover. Correlation analysis between lake fraction and Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) brightness temperature showed frequency dependent, seasonally evolving relationships consistent with lake ice drivers. Simulations of lake ice thickness and snow depth on lake ice produced from the Canadian Lake Ice Model (CLIMo) indicated that at low frequencies (6.9, 10.7 GHz), correlations with lake fraction were consistent through the winter season, whereas at higher frequencies (18.7, 36.5 GHz), the strength and direction of the correlations evolved consistently with the penetration depth as the influence of the subice water was replaced by emissions from the ice and snowpack. A regional rain-on-snow event created a surface ice lens that was detectable using the AMSR-E 36.5-GHz polarization gradient due to a strong response at the horizontal polarization. The appropriate polarization for remote sensing of the tundra snowpack depends on the application: horizontal measurements are suitable for ice lens detection; vertically polarized measurements are appropriate for deriving SWE estimates.

Arctic Lake Physical Processes and Regimes with Implications for Winter Water Availability and Management in the National Petroleum Reserve Alaska

Lakes are dominant landforms in the National Petroleum Reserve Alaska (NPRA) as well as important social and ecological resources. Of recent importance is the management of these freshwater ecosystems because lakes deeper than maximum ice thickness provide an important and often sole source of liquid water for aquatic biota, villages, and industry during winter. To better understand seasonal and annual hydrodynamics in the context of lake morphometry, we analyzed lakes in two adjacent areas where winter water use is expected to increase in the near future because of industrial expansion. Landsat Thematic Mapper and Enhanced Thematic Mapper Plus imagery acquired between 1985 and 2007 were analyzed and compared with climate data to understand interannual variability. Measured changes in lake area extent varied by 0.6% and were significantly correlated to total precipitation in the preceding 12 months (p < 0.05). Using this relation, the modeled lake area extent from 1985 to 2007 showed no long-term trends. In addition, high-resolution aerial photography, bathymetric surveys, water-level monitoring, and lake-ice thickness measurements and growth models were used to better understand seasonal hydrodynamics, surface area-to-volume relations, winter water availability, and more permanent changes related to geomorphic change. Together, these results describe how lakes vary seasonally and annually in two critical areas of the NPRA and provide simple models to help better predict variation in lake-water supply. Our findings suggest that both overestimation and underestimation of actual available winter water volume may occur regularly, and this understanding may help better inform management strategies as future resource use expands in the NPRA.

A controlled experiment to retrieve freshwater ice characteristics from an FM-CW radar system

Abstract A controlled experiment was conducted at the Cold Region Research and Engineering Laboratory (CRREL) facilities for retrieving freshwater ice characteristics using a Frequency Modulated Continuous Wave (FM-CW) radar system. The purpose of this study is to quantify the interactions between a backscattered radar signal and ice cover characteristics such as thickness and air bubble content; and to provide a comprehensive data set for testing a theoretical radar backscattering model currently under development. The experiment was held in an indoor test basin (36.5 m × 9.4 m × 2.5 m), where an ice sheet was grown from 0 to 24 cm thickness and monitored with a series of radar and geophysical measurements. Backscattering of the ice cover using an in-house FM-CW C-band radar was repeatedly measured at incidence angles varying from 0 to 50° for four polarisation combinations, HH, VV, HV, and VH. Ancillary data, such as ice thickness, crystalline structure and air bubble content, air temperature and hoarfrost water equivalent were collected to support the analysis and interpretation of the radar data. Analysis of the radar backscattered signal indicates that the received power is notably affected by ice thickness. For example, the HH/HV ratio of power signals correlated with ice thickness between 8 and 24 cm with R 2 value ranging from 0.75 to 0.90. It was shown through modeling of the radar reflectivity that the lack of correlation at less than 8 cm was caused by the coherent addition of the multiple reflections at the air/ice and the ice/water boundaries. These results are encouraging as for the potential of retrieving lake and river ice thickness from satellite SAR sensors operating at C-band frequencies and at 20 to 50° incidence angles, such as Radarsat 1 and 2 and Envisat, although their current radiometric resolution may limit ice thickness retrieval to thicker ice covers. Also, a number of unresolved issues must be addressed before taking full advantage of these sensors for operational retrieving of freshwater ice thickness. For one, additional controlled experiments must be carried out with ice covers embracing a range of surface roughness values. Ice covers with more diversified air inclusions and snow cover characteristics also need to be investigated, which probably can be best done by deploying radar systems next to natural ice covers.

Bottomfast Ice Mapping and the Measurement of Ice Thickness on Tundra Lakes Using C‐Band Synthetic Aperture Radar Remote Sensing1

Abstract: Industrial activity in Canada’s north is increasing, placing demands on the use of water from lakes to build ice roads. Winter water withdrawal from these lakes has the potential to impact overwintering fish. Removal of water from small lakes can decrease oxygen and habitat available to fish. To address this issue, a protocol has been developed by the Department of Fisheries and Oceans outlining water withdrawal thresholds. Bathymetric surveys are the traditional method to determine lake depth, but are costly given the remoteness of northern lakes. This paper investigates the use of satellite C‐band synthetic aperture radar (SAR) remote sensing technology as a potential alternative or complement to traditional survey methods. Previous research has shown that a SAR can detect the transition from grounded to floating ice on lakes, or if a lake is completely frozen. Grounded ice has a dark signature while floating ice appears very bright in contrast. Similar results were observed for the datasets acquired in the study area. This suggests that lakes that freeze completely to the bottom can be identified using SAR. Such water bodies would not be viable fish overwintering habitat and can therefore be used as water sources without thresholds necessary. However, attempts to accurately calculate the depth of the ice at the grounded‐floating ice boundary using bathymetric profiles acquired in the summer and lake ice thickness measurements from a reference lake near Inuvik proved to be unreliable.

Late Holocene changes in ultraviolet radiation penetration recorded in an East Antarctic lake

Late Holocene changes in the ultraviolet radiation (UVR) penetration in a lake in the Larsemann Hills (East Antarctica) were reconstructed using sediment core proxies based on fossil pigments (scytonemins and its derivatives) and siliceous microfossils. The influence of changes in lake depth on the UVR proxy was excluded by applying a correction, based on the non-linear relation between modern scytonemin concentrations and lake depth in a regional reference data set, and the record of past lake depths inferred using a diatom based transfer function in the sediment core. Results showed four well-defined maxima in the UVR proxy during the last 1600–1800 years, centred around 1820–1780, 1580–1490, 790–580 and 680–440 AD. Several mechanisms may account for these observed changes in UVR penetration, including past variability in cloud cover, atmospheric turbidity, ozone column depth, snow cover on the lake ice, DOM concentrations and lake-ice thickness and transparency resulting from temperature fluctuations. Although some gaps remain in our knowledge of scytonemin production in relation to the limnology of Antarctic lakes, the results highlight the importance and potential of the sediments in these highly transparent water bodies as archives of changes in past UVR receipt at the Earth’s surface.

Modeling interdecadal variations of lake-ice thickness and sensitivity to climatic change in northernmost Alaska

AbstractA physically based finite-element heat-transfer model with phase change is used to simulate ice growth and thickness variability on shallow, thaw lakes on the North Slope of Alaska during the period 1947–97. The basic inputs to the model are air temperature and snow depth as recorded at the U.S. National Weather Service station, Barrow, Alaska. The simulated long-term mean maximum ice thickness was 1.91 ±0.21 m with a range from 1.33 m (1962) to 2.47 m (1976). Variations in the seasonal snow cover played a much greater role than air temperatures in controlling ice-thickness variability during the 50 year simulation period. The sensitivity of lake-ice growth to extremes of snow depth, air temperature and snow bulk thermal conductivity is investigated. This study shows that lake-ice thickness has varied significantly from year to year in northern Alaska. Continued variability combined with potential climate change could affect the area of ice that freezes completely to the bottom of lakes each winter, resulting in changes in water storage and availability, permafrost thermal regime and talik dynamics beneath lakes, and methane efflux and energy fluxes to the atmosphere. It is concluded that quantification and a full understanding of these potential effects will require systematic and continuous field measurements that will provide better forcing and validation fields for improved models.

Global patterns of lake ice phenology and climate: Model simulations and observations

Lake ice phenology parameters (dates of ice onset and thaw) provide an integrative climatic description of autumn to springtime conditions. Interannual variations in lake ice duration and thickness allow estimates of local climatic variability. In addition, long‐term changes in lake ice phenology may provide a robust indication of climatic change. The relationship between lake ice and climate enables the use of process‐based models for predicting the dates of freeze‐up and thaw. LIMNOS (Lake Ice Model Numerical Operational Simulator) is one such model, which was originally designed to simulate the ice phenology of several lakes in southern Wisconsin. In this study, LIMNOS is modified to run globally on a 0.5° by 0.5° latitude‐longitude grid using average monthly climate data. We initially simulate the ice phenology for lakes of 5‐ and 20‐m mean depths across the northern hemisphere to demonstrate the effects of lake depth, latitude, and elevation on ice phenology. To evaluate the results of LIMNOS we also simulate the ice phenology of 30 lakes across the northern hemisphere which have long‐term ice records. LIMNOS reproduces the general geographic patterns of ice‐on and ice‐off dates, although ice‐off dates tend to occur later in the model. Lakes with extreme depths, surface areas, or precipitation are simulated less accurately than small, shallow lakes. This study reveals strengths and weaknesses of LIMNOS and suggests aspects which need improving. Future investigations should focus on the use of geographically extensive lake ice observations and modeling to elucidate patterns of climatic variability and/or climate change.

The hydrologic regime of Mackenzie River and connection of "no-closure" lakes to distributary channels in the Mackenzie Delta, Northwest Territories

Mackenzie Delta lakes have been classified by the seasonal duration of their connection to Mackenzie River. "No-closure" lakes are determined on the basis of minimum summer water level. Such lakes may become disconnected from the Mackenzie in autumn or winter, as water level falls or if the sills between lakes and distributary channels are frozen through and so sealed. Water level in the central delta rises continuously after late November–early December, at first because discharge into the delta increases once the Mackenzie drainage basin has frozen over, and then as sea and channel ice thickens in the outer delta, impounding discharge. Since 1973 this seasonal increase in stage from its minimum in early December to the level on 1 April has been between 29 and 95 cm. Between 1987 and 1994, the rise in stage near Inuvik has been slightly greater than increases in lake-ice thickness (30–68 cm). Channels and lakes that are connected to the Mackenzie discharge system in December may remain connected throughout winter. A critical sill elevation for connection of such lakes to the river system is the minimum stage minus mid-December ice thickness. Recently, these elevations have been from 1.0 to 1.6 m lower than late summer water levels. Lakes with sill elevations still lower may remain connected to the Mackenzie throughout the year. In 1993-1994, only 3 of 16 "no-closure" lakes surveyed near Inuvik remained open to the Mackenzie discharge throughout winter, representing 2% of the lakes in this portion of the delta.

Spring Meltwater Mixing in Small Arctic Lakes

Meltwater mixing in small arctic lakes at Saqvaqjuac (63°68′N, 90°40′W) was studied in 1980 and 1981 to evaluate the applicability of theoretical lake water renewal times to the modeling of ice-covered lakes. Two 370-GBq tritium additions were made to 7.09-ha P&amp;N Lake. One was mixed with the unfrozen water at the time of maximum lake-ice thickness (May 1980) and the other was mixed with the lake immediately after freezing (October 1980). Dye experiments were also performed at four lakes to define the spatial and temporal distribution of the inflow and icemelt layers. Results from the tritiated water and dye addition experiments, as well as conductance and temperature profiles, showed that during ice-on, the cold low-density meltwater floated in a thin layer 0–100 cm beneath the ice, extended over the entire subice-surface area, and left the lake without mixing with the heavier subice water. These results imply that (1) lake models incorporating a lake flushing rate term need to be reevaluated to accommodate the lack of meltwater mixing beneath spring ice and (2) more attention should be given to the early spring meltwater chemistry and its distribution within the upper lake strata.

Remote Detection of Water Under Ice-covered Lakes on the North Slope of Alaska

Results from using an impulse radar sounding system on the North Slope of Alaska to detect the existence of water under lake ice are presented. It was found that both lake ice thickness and depth of water under the ice could be determined when the radar antenna was either on the ice surface or airborne in a helicopter. The findings also revealed that the impulse radar sounding system could detect where lake ice was bottom-fast and where water existed under the ice cover.

A spherical harmonic analysis of the Earth's topography

In 1964–1965 estimates were made of the percentage of land, average land elevation, and average ocean depth in each 1° × 1° square and of percentages of lake and ice and average lake depth and ice thickness in each 5° × 5° square. These estimates were made visually, and the following maps were used:

Research on the thickness of river and lake ice in North America

Research on the thickness of river and lake ice in North America