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Snow plays a vital role in near-shore landfast sea ice physical and biological processes. It needs to be monitored to understand sea ice processes and also to estimate sea ice thickness. However, snow depth remains difficult to estimate directly from space which forces the sea ice thickness products to use snow depth from model outputs or out-of-date climatology. Satellite altimetry based dual-radar and coincident laser/radar have been considered for providing regular estimates of snow depth on sea ice. In addition to the limitations associated with the functioning of individual altimeters, snow on landfast sea ice presents its challenges especially due to the lack of leads. While past studies have mostly focused on approaches suited to pack ice in the Central Arctic, this study aims to provide critical observations from landfast first-year sea ice in the Canadian Arctic. Surface-base altimeter retrievals from snow on sea ice at Churchill, Manitoba are compared to snow on lake ice demonstrating that the position of the Ku-band main scattering horizon is impacted by the presence of brine in the snowpack. The satellite-level study conducted at Dease Strait near Cambridge Bay is the first to assess the possibility of using coincident laser/radar altimeters (Cryo2Ice) for estimating snow depth on land-fast and lead-less sea ice at the Canadian Arctic Archipelago. The retrieved Cryo2Ice snow depths were underestimated by an average of 20.7 % which is slightly higher than the tidal adjustment applied. However, snow geophysical properties and surface roughness are seen to significantly bias Cryo2Ice retrievals. Both surface and satellite-based studies point towards the position of the Ku-band main scattering horizon being closer to the air-snow interface as opposed to the generally assumed snow-ice interface. Therefore, findings from this study may be useful for monitoring snow depth on land-fast sea ice using currently available and future satellite altimeters whereby sno

Climate change is causing seasonally ice‐covered lakes of the boreal region to undergo changes in their winter regime by altering patterns of precipitation and temperature, often reflected as reduced snow and ice cover duration. The duration, extent and quality of ice, and snow cover have a pivotal role for production and carbon cycling in lakes in winter, with potentially cascading effects for the following open water period. We investigated under‐ice carbon cycling by assessing bacterial growth (including bacterial production, bacterial respiration, and bacterial growth efficiency) and primary production at five water depths during early winter, midwinter, late winter and melting season in a boreal lake, and report significantly different temporal patterns. Bacterial respiration was dominant in early and midwinter, whereas the late winter and melting season were dominated by bacterial production. Multiple linear regression models indicated that high early winter bacterial respiration was associated with senescing phytoplankton, whereas bacterial production was promoted by the onset of spring processes. Collectively, bacterial growth indices were inherently linked with bacterioplankton community composition and specific biomarker taxa. Primary production under ice increased in late winter when light‐blocking snow cover melted, and primary production measured from the lake ice exceeded that of the water column at the melting season. Ice samples hosted diverse eukaryotic communities including photoautotrophs, suggesting that the habitat potential of the understudied lake ice and the role of ice for ecological processes at ice melt should be further explored.

Snow plays a vital role in near-shore landfast sea ice physical and biological processes. It needs to be monitored to understand sea ice processes and also to estimate sea ice thickness. However, snow depth remains difficult to estimate directly from space which forces the sea ice thickness products to use snow depth from model outputs or out-of-date climatology. Satellite altimetry based dual-radar and coincident laser/radar have been considered for providing regular estimates of snow depth on sea ice. In addition to the limitations associated with the functioning of individual altimeters, snow on landfast sea ice presents its challenges especially due to the lack of leads. While past studies have mostly focused on approaches suited to pack ice in the Central Arctic, this study aims to provide critical observations from landfast first-year sea ice in the Canadian Arctic. Surface-base altimeter retrievals from snow on sea ice at Churchill, Manitoba are compared to snow on lake ice demonstrating that the position of the Ku-band main scattering horizon is impacted by the presence of brine in the snowpack. The satellite-level study conducted at Dease Strait near Cambridge Bay is the first to assess the possibility of using coincident laser/radar altimeters (Cryo2Ice) for estimating snow depth on land-fast and lead-less sea ice at the Canadian Arctic Archipelago. The retrieved Cryo2Ice snow depths were underestimated by an average of 20.7 % which is slightly higher than the tidal adjustment applied. However, snow geophysical properties and surface roughness are seen to significantly bias Cryo2Ice retrievals. Both surface and satellite-based studies point towards the position of the Ku-band main scattering horizon being closer to the air-snow interface as opposed to the generally assumed snow-ice interface. Therefore, findings from this study may be useful for monitoring snow depth on land-fast sea ice using currently available and future satellite altimeters whereby sno

Snow plays a vital role in near-shore landfast sea ice physical and biological processes. It needs to be monitored to understand sea ice processes and also to estimate sea ice thickness. However, snow depth remains difficult to estimate directly from space which forces the sea ice thickness products to use snow depth from model outputs or out-of-date climatology. Satellite altimetry based dual-radar and coincident laser/radar have been considered for providing regular estimates of snow depth on sea ice. In addition to the limitations associated with the functioning of individual altimeters, snow on landfast sea ice presents its challenges especially due to the lack of leads. While past studies have mostly focused on approaches suited to pack ice in the Central Arctic, this study aims to provide critical observations from landfast first-year sea ice in the Canadian Arctic. Surface-base altimeter retrievals from snow on sea ice at Churchill, Manitoba are compared to snow on lake ice demonstrating that the position of the Ku-band main scattering horizon is impacted by the presence of brine in the snowpack. The satellite-level study conducted at Dease Strait near Cambridge Bay is the first to assess the possibility of using coincident laser/radar altimeters (Cryo2Ice) for estimating snow depth on land-fast and lead-less sea ice at the Canadian Arctic Archipelago. The retrieved Cryo2Ice snow depths were underestimated by an average of 20.7 % which is slightly higher than the tidal adjustment applied. However, snow geophysical properties and surface roughness are seen to significantly bias Cryo2Ice retrievals. Both surface and satellite-based studies point towards the position of the Ku-band main scattering horizon being closer to the air-snow interface as opposed to the generally assumed snow-ice interface. Therefore, findings from this study may be useful for monitoring snow depth on land-fast sea ice using currently available and future satellite altimeters whereby sno

Ice cover persists throughout summer over many lakes at extreme polar latitudes but is likely to become increasingly rare with ongoing climate change. Here we addressed the question of how summer ice-cover affects the underlying water column of Ward Hunt Lake, a freshwater lake in the Canadian High Arctic, with attention to its vertical gradients in limnological properties that would be disrupted by ice loss. Profiling in the deepest part of the lake under thick mid-summer ice revealed a high degree of vertical structure, with gradients in temperature, conductivity and dissolved gases. Dissolved oxygen, nitrous oxide, carbon dioxide and methane rose with depth to concentrations well above air-equilibrium, with oxygen values at >150% saturation in a mid water column layer of potential convective mixing. Fatty acid signatures of the seston also varied with depth. Benthic microbial mats were the dominant phototrophs, growing under a dim green light regime controlled by the ice cover, water itself and weakly colored dissolved organic matter that was mostly autochthonous in origin. In this and other polar lakes, future loss of mid-summer ice will completely change many water column properties and benthic light conditions, resulting in a markedly different ecosystem regime.

La fenologia del gel dels llacs pirinencs està poc estudiada tot i ser un bon indicador que milloraria la comprensió que tenim del canvi climàtic i dels seus impactes en aquests ecosistemes tan sensibles. Així doncs, en aquest treball, s'exploren les possibilitats de la teledetecció per a estanys d'alta muntanya de mida petita, entre les 5 i les 25ha en l'àmbit del Parc Nacional d'Aigüestortes i Estany de Sant Maurici, i al llarg de 22 temporades d'hivern, des de l'any 2000 fins al 2022, a la recerca de les dates de congelació completa. Al mateix temps, s'analitzen les problemàtiques dels píxels mixtes, noves tècniques de recollida de dades in situ, i un algorisme de detecció automàtica, La fenología del hielo de los lagos pirenaicos está poco estudiada a pesar de ser un buen indicador que mejoraría la comprensión del cambio climático y sus impactos en estos ecosistemas tan sensibles. Así pues, en este trabajo, se exploran las posibilidades de la teledetección para lagos de alta montaña de pequeño tamaño, entre las 5 y las 25 ha en el ámbito del Parque Nacional de Aigüestortes i Estany de Sant Maurici, y durante 22 temporadas de invierno, desde el año 2000 hasta el 2022, en busca de las fechas de congelación completa. Al mismo tiempo, se analizan las problemáticas de los píxeles mixtos, nuevas técnicas de recogida de datos in situ y un algoritmo de detección automática., The ice phenology of the Pyrenean lakes has been little studied despite being a good indicator that would improve the understanding of climate change and its impacts on these highly sensitive ecosystems. Thus, in this work, the possibilities of remote sensing for small high mountain lakes are explored, between 5 and 25ha around the Aigüestortes i Estany de Sant Maurici National Park, and for 22 winter seasons, from the year 2000 to 2022, looking for the freeze up ending dates. At the same time, the problems of mixed pixels, new data collection techniques in situ and an automatic detection algorithm are analyzed.

Long-term lake ice phenological records from around the Northern Hemisphere provide unique sensitive indicators of climatic variations, even prior to the existence of physical meteorological measurement stations. Here, we updated ice phenology records for 60 lakes with time-series ranging from 107-204 years to provide the first re-assessment of Northern Hemispheric ice trends since 2004 by adding 15 additional years of ice phenology records and 40 lakes to our study. We found that, on average, ice-on was 11.0 days later, ice-off was 6.8 days earlier, and ice duration was 17.0 days shorter per century over the entire record for each lake. Trends in ice-on and ice duration were six times faster in the last 25-year period (1992-2016) than previous quarter centuries. More extreme events in recent decades, including late ice-on, early ice-off, shorter periods of ice cover, or no ice cover at all, contribute to the increasing rate of lake ice loss. Reductions in greenhouse gas emissions could limit increases in air temperature and abate losses in lake ice cover that would subsequently limit ecological, cultural, and socioeconomic consequences, such as increased evaporation rates, warmer water temperatures, degraded water quality, and the formation of toxic algal blooms.

Long-term lake ice phenological records from around the Northern Hemisphere provide unique sensitive indicators of climatic variations, even prior to the existence of physical meteorological measurement stations. Here, we updated ice phenology records for 60 lakes with time-series ranging from 107-204 years to provide the first re-assessment of Northern Hemispheric ice trends since 2004 by adding 15 additional years of ice phenology records and 40 lakes to our study. We found that, on average, ice-on was 11.0 days later, ice-off was 6.8 days earlier, and ice duration was 17.0 days shorter per century over the entire record for each lake. Trends in ice-on and ice duration were six times faster in the last 25-year period (1992-2016) than previous quarter centuries. More extreme events in recent decades, including late ice-on, early ice-off, shorter periods of ice cover, or no ice cover at all, contribute to the increasing rate of lake ice loss. Reductions in greenhouse gas emissions could limit increases in air temperature and abate losses in lake ice cover that would subsequently limit ecological, cultural, and socioeconomic consequences, such as increased evaporation rates, warmer water temperatures, degraded water quality, and the formation of toxic algal blooms.

Long-term lake ice phenological records from around the Northern Hemisphere provide unique sensitive indicators of climatic variations, even prior to the existence of physical meteorological measurement stations. Here, we updated ice phenology records for 60 lakes with time-series ranging from 107-204 years to provide the first re-assessment of Northern Hemispheric ice trends since 2004 by adding 15 additional years of ice phenology records and 40 lakes to our study. We found that, on average, ice-on was 11.0 days later, ice-off was 6.8 days earlier, and ice duration was 17.0 days shorter per century over the entire record for each lake. Trends in ice-on and ice duration were six times faster in the last 25-year period (1992-2016) than previous quarter centuries. More extreme events in recent decades, including late ice-on, early ice-off, shorter periods of ice cover, or no ice cover at all, contribute to the increasing rate of lake ice loss. Reductions in greenhouse gas emissions could limit increases in air temperature and abate losses in lake ice cover that would subsequently limit ecological, cultural, and socioeconomic consequences, such as increased evaporation rates, warmer water temperatures, degraded water quality, and the formation of toxic algal blooms.

Ice cover persists throughout summer over many lakes at extreme polar latitudes but is likely to become increasingly rare with ongoing climate change. Here we addressed the question of how summer ice-cover affects the underlying water column of Ward Hunt Lake, a freshwater lake in the Canadian High Arctic, with attention to its vertical gradients in limnological properties that would be disrupted by ice loss. Profiling in the deepest part of the lake under thick mid-summer ice revealed a high degree of vertical structure, with gradients in temperature, conductivity and dissolved gases. Dissolved oxygen, nitrous oxide, carbon dioxide and methane rose with depth to concentrations well above air-equilibrium, with oxygen values at >150% saturation in a mid water column layer of potential convective mixing. Fatty acid signatures of the seston also varied with depth. Benthic microbial mats were the dominant phototrophs, growing under a dim green light regime controlled by the ice cover, water itself and weakly colored dissolved organic matter that was mostly autochthonous in origin. In this and other polar lakes, future loss of mid-summer ice will completely change many water column properties and benthic light conditions, resulting in a markedly different ecosystem regime.

Long-term lake ice phenological records from around the Northern Hemisphere provide unique sensitive indicators of climatic variations, even prior to the existence of physical meteorological measurement stations. Here, we updated ice phenology records for 60 lakes with time-series ranging from 107-204 years to provide the first re-assessment of Northern Hemispheric ice trends since 2004 by adding 15 additional years of ice phenology records and 40 lakes to our study. We found that, on average, ice-on was 11.0 days later, ice-off was 6.8 days earlier, and ice duration was 17.0 days shorter per century over the entire record for each lake. Trends in ice-on and ice duration were six times faster in the last 25-year period (1992-2016) than previous quarter centuries. More extreme events in recent decades, including late ice-on, early ice-off, shorter periods of ice cover, or no ice cover at all, contribute to the increasing rate of lake ice loss. Reductions in greenhouse gas emissions could limit increases in air temperature and abate losses in lake ice cover that would subsequently limit ecological, cultural, and socioeconomic consequences, such as increased evaporation rates, warmer water temperatures, degraded water quality, and the formation of toxic algal blooms.

Long-term lake ice phenological records from around the Northern Hemisphere provide unique sensitive indicators of climatic variations, even prior to the existence of physical meteorological measurement stations. Here, we updated ice phenology records for 60 lakes with time-series ranging from 107-204 years to provide the first re-assessment of Northern Hemispheric ice trends since 2004 by adding 15 additional years of ice phenology records and 40 lakes to our study. We found that, on average, ice-on was 11.0 days later, ice-off was 6.8 days earlier, and ice duration was 17.0 days shorter per century over the entire record for each lake. Trends in ice-on and ice duration were six times faster in the last 25-year period (1992-2016) than previous quarter centuries. More extreme events in recent decades, including late ice-on, early ice-off, shorter periods of ice cover, or no ice cover at all, contribute to the increasing rate of lake ice loss. Reductions in greenhouse gas emissions could limit increases in air temperature and abate losses in lake ice cover that would subsequently limit ecological, cultural, and socioeconomic consequences, such as increased evaporation rates, warmer water temperatures, degraded water quality, and the formation of toxic algal blooms.

In ice-covered polar lakes, a narrow ice-free moat opens up in spring or early summer, and then persists at the edge of the lake until complete ice loss or refreezing. In this study, we analyzed the horizontal gradients in Ward Hunt Lake, located in the High Arctic, and addressed the hypothesis that the transition from its nearshore open-water moat to offshore ice-covered waters is marked by discontinuous shifts in limnological properties. Consistent with this hypothesis, we observed an abrupt increase in below-ice concentrations of chlorophyll a beyond the ice margin, along with a sharp decrease in temperature and light availability and pronounced changes in benthic algal pigments and fatty acids. There were higher concentrations of rotifers and lower concentrations of viruses at the ice-free sampling sites, and contrasts in zooplankton fatty acid profiles that implied a greater importance of benthic phototrophs in their inshore diet. The observed patterns underscore the structuring role of ice cover in polar lakes. These ecosystems do not conform to the traditional definitions of littoral versus pelagic zones, but instead may have distinct moat, icemargin and ice-covered zones. This zonation is likely to weaken with ongoing climate change.

In ice-covered polar lakes, a narrow ice-free moat opens up in spring or early summer, and then persists at the edge of the lake until complete ice loss or refreezing. In this study, we analyzed the horizontal gradients in Ward Hunt Lake, located in the Canadian High Arctic, and addressed the hypothesis that the transition from its nearshore open-water moat to offshore ice-covered waters is marked by discontinuous shifts in limnological properties. Consistent with this hypothesis, we observed an abrupt increase in below-ice concentrations of chlorophyll a beyond the ice margin, along with a sharp decrease in temperature and light availability and pronounced changes in benthic algal pigments and fatty acids. There were higher concentrations of rotifers and lower concentrations of viruses at the ice-free sampling sites, and contrasts in zooplankton fatty acid profiles that implied a greater importance of benthic phototrophs in their inshore diet. The observed patterns underscore the structuring role of ice cover in polar lakes. These ecosystems do not conform to the traditional definitions of littoral versus pelagic zones but instead may have distinct moat, ice-margin, and ice-covered zones. This zonation is likely to weaken with ongoing climate change.

Field records, aerial photographs, and satellite imagery show that the perennial ice cover on Ward Hunt Lake at Canada's northern coast experienced rapid contraction and thinning after at least 50 years of relative stability. On all dates of sampling from 1953 to 2007, 3.5 to 4.3 m of perennial ice covered 65-85% of the lake surface in summer. The ice cover thinned from 2008 onward, and the lake became ice free in 2011, an event followed by 26 days of open water conditions in 2012. This rapid ice loss corresponded to a significant increase in melting degree days (MDD), from a mean (±SD) of 80.4 (±36.5) MDD (1996-2007) to 136.2 (±16.4) MDD (2008-2012). The shallow bathymetry combined with heat advection by warm inflows caused feedback effects that accelerated the ice decay. These observations show how changes across a critical threshold can result in the rapid disappearance of thick perennial ice.

Freshwater ice dominates the Arctic terrestrial environment and significantly impacts bio-physical and socio-economic systems. Unlike other major cryospheric components that either blanket large expanses (e.g., snow, permafrost, sea ice) or are concentrated in specific locations, lake and river ice are interwoven into the terrestrial landscape through major flow and storage networks. For instance, the headwaters of large ice-covered rivers extend well beyond the Arctic while many northern lakes owe their genesis to broader cryospheric changes. The effects of freshwater ice on climate mostly occur at the local/regional scale, with the degree of influence dependent on the magnitude, timing, location, and duration of ice cover, and the size of the water body. Freshwater-ice formation, growth, decay, and break-up are influenced by climatic variables that control surface heat fluxes, but these differ markedly between lakes and rivers. Despite the importance of freshwater ice, there has been a recent reduction in observational recordings.

Paleolimnological evidence from some Arctic lakes suggests that longer ice-free seasons have been experienced since the beginning of the nineteenth century. It has been inferred from some additional records that many Arctic lakes may have crossed an important ecological threshold as a result of recent warming. In the instrumental record, long-term trends exhibit increasingly later freeze-ups and earlier break-ups, closely corresponding to increasing air temperature trends, but with greater sensitivity at the more temperate latitudes. Broad spatial patterns in these trends are also related to major atmospheric circulation patterns. Future projections of lake ice indicate increasingly later freeze-ups and earlier break-ups, decreasing ice thickness, and changes in cover composition, particularly white-ice. For rivers, projected future decreases in south to north air-temperature gradients suggest that the severity of ice-jam flooding may be reduced but this could be mitigated by changes in the magnitude of spring snowmelt.

Climatic changes to freshwater ice in the Arctic are projected to produce a variety of effects on hydrologic, ecological, and socio-economic systems. Key hydrologic impacts include changes to low flows, lake evaporation regimes and water levels, and river-ice break-up severity and timing. The latter are of particular concern because of their effect on river geomorphology, vegetation, sediment and nutrient fluxes, and sustainment of riparian aquatic habitats. Changes in ice phenology will affect a wide range of related biological aspects of seasonality. Some changes are likely to be gradual, but others could be more abrupt as systems cross critical ecological thresholds. Transportation and hydroelectric production are two of the socio-economic sectors most vulnerable to change in freshwater-ice regimes. Ice roads will require expensive on-land replacements while hydroelectric operations will both benefit and be challenged. The ability to undertake some traditional harvesting methods will also be affected.

A field programme on light conditions in ice-covered lakes and optical properties of lake ice was performed in seven lakes of Finland and Estonia in February–April 2009. On the basis of irradiance measurements above and below ice, spectral reflectance and transmittance were determined for the ice sheet; time evolution of photosynthetically active radiation (PAR) transmittance was examined from irradiance recordings at several levels inside the ice sheet. Snow cover was the dominant factor for transmission of PAR into the lake water body. Reflectance was 0.74–0.92 in winter, going down to 0.18–0.22 in the melting season. The bulk attenuation coefficient of dry snow was 14–25 m–1; the level decreased as the spring was coming. The reflectance and bulk attenuation coefficient of snow-free ice were 0.1–0.4 and 1–5 m–1. Both were considerably smaller than those of snow cover. Seasonal evolution of light transmission was mainly due to snow melting. Snow and ice cover not only depress the PAR level in a lake but also influence the spectral and directional distribution of light.

A field programme on light conditions in ice-covered lakes and optical properties of lake ice was performed in seven lakes of Finland and Estonia in February–April 2009. On the basis of irradiance measurements above and below ice, spectral reflectance and transmittance were determined for the ice sheet; time evolution of photosynthetically active radiation (PAR) transmittance was examined from irradiance recordings at several levels inside the ice sheet. Snow cover was the dominant factor for transmission of PAR into the lake water body. Reflectance was 0.74–0.92 in winter, going down to 0.18–0.22 in the melting season. The bulk attenuation coefficient of dry snow was 14–25 m–1; the level decreased as the spring was coming. The reflectance and bulk attenuation coefficient of snow-free ice were 0.1–0.4 and 1–5 m–1. Both were considerably smaller than those of snow cover. Seasonal evolution of light transmission was mainly due to snow melting. Snow and ice cover not only depress the PAR level in a lake but also influence the spectral and directional distribution of light.

A field programme on light conditions in ice-covered lakes and optical properties of lake ice was performed in seven lakes of Finland and Estonia in February–April 2009. On the basis of irradiance measurements above and below ice, spectral reflectance and transmittance were determined for the ice sheet; time evolution of photosynthetically active radiation (PAR) transmittance was examined from irradiance recordings at several levels inside the ice sheet. Snow cover was the dominant factor for transmission of PAR into the lake water body. Reflectance was 0.74–0.92 in winter, going down to 0.18–0.22 in the melting season. The bulk attenuation coefficient of dry snow was 14–25 m–1; the level decreased as the spring was coming. The reflectance and bulk attenuation coefficient of snow-free ice were 0.1–0.4 and 1–5 m–1. Both were considerably smaller than those of snow cover. Seasonal evolution of light transmission was mainly due to snow melting. Snow and ice cover not only depress the PAR level in a lake but also influence the spectral and directional distribution of light.

A field programme on light conditions in ice-covered lakes and optical properties of lake ice was performed in seven lakes of Finland and Estonia in February–April 2009. On the basis of irradiance measurements above and below ice, spectral reflectance and transmittance were determined for the ice sheet; time evolution of photosynthetically active radiation (PAR) transmittance was examined from irradiance recordings at several levels inside the ice sheet. Snow cover was the dominant factor for transmission of PAR into the lake water body. Reflectance was 0.74–0.92 in winter, going down to 0.18–0.22 in the melting season. The bulk attenuation coefficient of dry snow was 14–25 m–1; the level decreased as the spring was coming. The reflectance and bulk attenuation coefficient of snow-free ice were 0.1–0.4 and 1–5 m–1. Both were considerably smaller than those of snow cover. Seasonal evolution of light transmission was mainly due to snow melting. Snow and ice cover not only depress the PAR level in a lake but also influence the spectral and directional distribution of light.

A field programme on light conditions in ice-covered lakes and optical properties of lake ice was performed in seven lakes of Finland and Estonia in February–April 2009. On the basis of irradiance measurements above and below ice, spectral reflectance and transmittance were determined for the ice sheet; time evolution of photosynthetically active radiation (PAR) transmittance was examined from irradiance recordings at several levels inside the ice sheet. Snow cover was the dominant factor for transmission of PAR into the lake water body. Reflectance was 0.74–0.92 in winter, going down to 0.18–0.22 in the melting season. The bulk attenuation coefficient of dry snow was 14–25 m–1; the level decreased as the spring was coming. The reflectance and bulk attenuation coefficient of snow-free ice were 0.1–0.4 and 1–5 m–1. Both were considerably smaller than those of snow cover. Seasonal evolution of light transmission was mainly due to snow melting. Snow and ice cover not only depress the PAR level in a lake but also influence the spectral and directional distribution of light.

A field programme on light conditions in ice-covered lakes and optical properties of lake ice was performed in seven lakes of Finland and Estonia in February–April 2009. On the basis of irradiance measurements above and below ice, spectral reflectance and transmittance were determined for the ice sheet; time evolution of photosynthetically active radiation (PAR) transmittance was examined from irradiance recordings at several levels inside the ice sheet. Snow cover was the dominant factor for transmission of PAR into the lake water body. Reflectance was 0.74–0.92 in winter, going down to 0.18–0.22 in the melting season. The bulk attenuation coefficient of dry snow was 14–25 m–1; the level decreased as the spring was coming. The reflectance and bulk attenuation coefficient of snow-free ice were 0.1–0.4 and 1–5 m–1. Both were considerably smaller than those of snow cover. Seasonal evolution of light transmission was mainly due to snow melting. Snow and ice cover not only depress the PAR level in a lake but also influence the spectral and directional distribution of light.

Among the perennially frozen lakes of the Dry Valleys of South Victoria Land (Antarctica), some are dry-based, i.e. frozen to the bottom. One of these is studied here by a multiparametric investigation (isotopic composition in δD and δ18O, ions, gas and ice texture analyses). A sediment layer about 10 cm thick appearing at a depth of 3.5 m is also studied by grain size, X-ray diffraction and scanning electron microscope analyses. The information retrieved indicates that this ice-block lake results from a build-up in two steps and explains how acolian sediments were included as a layer into the ice. Copyright © 2002 John Wiley and Sons, Ltd., SCOPUS: ar.j, FLWIN, info:eu-repo/semantics/published

Operating water intakes in lakes and rivers in northern regions is complicated by the presence of ice. One of the most difficult problems is the accumulation of frazil ice on the intake trash rack, which can completely block the trash rack and rapidly and unexpectedly shut down the intake facility. In extreme cases the blockage can cause the intake trash rack to collapse. Blockages of intake trash racks occur sporadically, most often at night, in cold weather and always underwater. As a result, opportunities for observation and measurement are limited. This report discusses the following topics: The blockage process in rivers and in lakes; Coping with frazil blockage; Suppressing frazil production by using heat; Mechanical removal; Back flushing, Vibration; Blasting; Removal of trash racks; and Operating under frazil conditions.

Measurements and analysis of seasonal ice growth and decay on Post Pond, New Hampshire, for the period 1973-1982 are presented. Observations included ice thickness measurements, examination of the various ice types contributing to the ice cover, and measurements of meteorological parameters for correlation with and modeling of the ice growth process. The overall nature of ice growth and decay (ice loss) on the Post Pond has been ascertained, the seasonal variability in the timing of freeze-up and ice-out and the duration of the ice cover have been determined, and the relationship of ice growth to freezing-degree-day (deg C) records evaluated on the basis of a Stefan conduction equation modified to deal with ice sheets covered with or free of snow. Ice growth occurs predominantly by the direct freezing of lake water, but snow ice may compose as much as 50% of the ice cover in winters with higher than average snowfall. Freeze-up leading to the establishment of a stable ice cover occurs during the 4-week period from the end of November to the end of December. Maximum seasonal ice thicknesses were from 45 to 67 cm and are generally attained during the first two weeks of March; ice-out, marking the final disappearance of ice from Post Pond, usually occurs by the third week of April. The overall rate of the ice loss is three to four times that of ice growth, and is dominated initially by melting from the top. As much as 50% of the ice may be lost in this way before the onset of any bottom melting. Final dissipation of the ice cover is usually expedited by candling resulting from preferential melting and disintegration of the ice at crystal boundaries.

The object of this study was to develop a method for forecasting the physical effects of the passage of commercial vessels through Great Lakes connecting waters during that period of time when traffic is normally at a minimum due to a more or less continuous ice cover. The physical impacts examined were sediment translocation, water quality effects, direct damage to existing structures, and changes in the gross hydraulic regime. Also associated with the report but bound separately are; the User's Manual for Prediction of Vessel Impacts in a Confined Waterway; Appendix A, Site and Soil Conditions; Appendix B, Observed Vessel Induced Water Level Drawdowns; and Appendix C, Observed Ice Thicknesses and Water Turbidities. Contents: St. Mary's River Hydraulics; Area Geology and Soil Conditions; Observation Sites--Selection and Characteristics; Analytical Prediction of Vessel-Induced Drawdown; A Comparison of Predicted and Observed Water Level Changes; Sediment Disturbance; Model Prediction of Relative Damage; River Turbidity and Light Extinction Characteristics; Vessel-Induced Ice Forces on Structures; Hydraulic Effects of Ice in the St. Mary's River System; Damage Evaluation for Two Fleet Mixes., See also Appendix A dated 31 Oct 1985, ADA202197.

The object of this study was to develop a method for forecasting the physical effects of the passage of commercial vessels through Great Lakes connecting waters during that period of time when traffic is normally at a minimum due to a more or less continuous ice cover. The physical impacts examined were sediment translocation, water quality effects, direct damage to existing structures, and changes in the gross hydraulic regime. Also associated with Appendix B but bound separately are; Development of a Predictive Model to Assess the Effects of Extended Season Navigation on Great Lakes Connecting Waters, Final Report; the User's Manual for Prediction of Vessel Impacts in a Confined Waterway; Appendix A, Site and Soil Conditions; and Appendix C, Observed Ice Thicknesses and Water Turbidities. This appendix contains the field measurements of short-term water surface changes at several sites along the St. Mary's River caused by passage of commercial vessels. All monitored passages during this contract period (10/84 to 10/85) are included. Additional measurement from the authors' files and previous reports are also included. The appendix is organized by site name and by date of observation. The locations and characteristics of the various sites can be found in Appendix A, Site and Soil Conditions., See also User's Manual dated 17 Oct 86, AD-A202 199.

The object of this study was to develop a method for forecasting the physical effects of the passage of commercial vessels through Great Lakes connecting waters during that period of time when traffic is normally at a minimum due to a more or less continuous ice cover. The physical impacts examined were sediment translocation, water quality effects, direct damage to existing structures, and changes in the gross hydraulic regime. Also associated with Appendix A but bound separately are; Development of a Predictive Model to Assess the Effects of Extended Season Navigation on Great Lakes Connecting Waters, Final Report; the User's Manual for Prediction of Vessel Impacts in a Confined Waterway; Appendix B, Observed Vessel Induced Water Level Drawdowns; and Appendix C, Observed Ice Thicknesses and Water Turbidities. This appendix contains the general locations of all data gathering sites used along the St. Mary's River as shown on portions of NOAA Great Lakes chart 14883. The general site locations are followed by detailed data arranged by site. Individual site data includes all soil data collected, detailed cross-section information as appropriate, and the specific locations of light extinction and turbidity data acquisition for the Lake Nicolet and Lake Munuscong sites. The light extinction and turbidity data are located d in Appendix C., See also Appendix B, ADA202198.

The object of this study was to develop a method for forecasting the physical effects of the passage of commercial vessels through Great Lakes connecting waters during that period of time when traffic is normally at a minimum due to a more or less continuous ice cover. The physical impacts examined were sediment translocation, water quality effects, direct damage to existing structures, and changes in the gross hydraulic regime. Also associated with the User's Manual but bound separately are; Development of a Predictive Model to Assess the Effects of Extended Season Navigation on Great Lakes Connecting Waters, Final Report; Appendix A, Site and Soil Conditions; Appendix B, Observed Vessel Induced Water Level Drawdowns; and Appendix C, Observed Ice Thicknesses and Water Turbidities. Keywords: BASIC programming language, IBM PC computers, Computer program listings., See also final report dated 31 Oct 1986, ADA202200.

A historical review of research is presented to establish the state- of-the-art for analyzing the behavior of vehicles in shallow snow. From this review, the most comprehensive and promising model is put together to establish a first-cut performance prediction model for vehicles operating in shallow snow, slush, ice and thawing soils.

Field observations support the interpretation that differences in the strength of radar returns from the ice covers of lakes on the North Slope of Alaska can be used to determine where the lake is frozen completely to the bottom. An ice/frozen soil interface is indicated by a weak return and an ice/ water interface by a strong return. The immediate value of this result is that SLAR (side-looking airborne radar) imagery can now be used to prepare maps of large areas of the North Slope showing where the lakes are shallower or deeper than 1.7m (the approximate draft of the lake ice at the time of the SLAR flights). The bathymetry of these shallow lakes is largely unknown and is not obvious from their sizes or outlines. Such information could be very useful, for example in finding suitable year-round water supplies.

An intake may be restricted or clogged by active frazil, passive frazil, brash, or a combination of these ice forms. The exact nature of the interactions among the intake structure, the ice and the hydraulic and meterorologic conditions that lead to icing problems is extremely site-specific. The better these parameters are quantified, the more tailored and economical the solution. A defense against these ice forms may be formulated in four areas: the origin of the ice, the tranportaiton mechanics of the ice, the accumulation characteristics of the ice, and the form of the ice when it is in the area of influence of the intake. To produce a lake intake structure that minimizes or eliminates icing problems, one may devise an unconstrained or a constrained design. To evaluate solutions to icing problems and/or to supplement incomplete data, a scale-model investigation is recommended. A universal, unconstrained solution would be extremely extremely expensive. The more data available through site monitoring and model studies, the better the problem (and therefore the solution) can be bracketed. This paper provides guidance for developing a site-specific solution.

This report represents the first comprehensive evaluation and ranking of all the auxiliary icebreaking devices which have been proposed over the last fifty years. An extensive literature search and interviews with experienced Coast Guard personnel produced a list of 19 alternatives to evaluate. Decision Analysis was used to rank order the alternatives based on their utility in meeting the goals and objectives of the Coast Guard. One system was clearly superior than the others. This was the Pitching System in which a set of rotating weights are used to induced a pitching motion to the hull while icebreaking. (Author)

This report presents the results of tests conducted on the Great Lakes during the 1982 winter season. Three vehicles were evaluated as potential replacements for the traditional method of dragging a 14-foot ice skiff by hand across the ice. Two of the craft, the all terrain vehicle (ATV) and the airboat, were subjects of preliminary testing during 1981. Preliminary tests of the air cushion vehicle (ACV) were conducted in Detroit, Michigan in January of 1982. The ACV proved to be unsuitable as an ice rescue platform because of its low payload capability, restricted maneuverability, and susceptability to skirt system damage. Te ATV and airboat were tested together, in side-by-side trials, at Marblehead, Ohio, on Lake Erie, in January of 1982. Based on these trials, this report recommends that the airboat be selected for inclusion in the Coast Guard inventory as the surface ice rescue vehicle.

This report presents data on the full-scale trails of the U.S. Coast Guard Icebreaker Katmai Bay, which was tested in plate ice that varied in thickness from 10 to 33 in. (25.4 to 83.82 cm) and had a snow cover of 1 to 6 in. (2.54 to 15.24 cm). In January the average temperature was -5 C, and the ice flexural strength was 13,363 lb/sq ft (640 kPa). In March the average temperature was -2 C and the ice flexural strength was 11,643 lb/sq ft (560 kPa). The specific weight (density) of the ice was 0.894 g/cc. The specific weight of the snow was in the area of 0.32 g/cc. The coefficient of friction between the ice/snow and steel plate (coated and uncoated) varied from a low of 0.02 in the dynamic case of ice on the Inerta 160 coating to 0.47 for the static case of snow on a rusty steel plate.

The possible extension of the navigation season through the entire winter or a portion thereof has been under consideration for the Great Lakes and the St. Lawrence Seaway for a number of years. To balance the benefits and costs of such an extension it is necessary to determine the damage costs to shore structures that might result from ice loosened by ship passage. This paper is concerned with the interconnecting channels of the Lakes where there is estimated to be $18,000,000 (1976 dollars) worth of small, private, vulnerable shore structures. Based upon information from Corps of Engineers Permits, aerial photos and site visits, probability estimates are given for winter damage on identifiable river reaches for differing season lengths. These are related to replacement costs and tables are given showing estimated annual damage costs. Possible solutions are given which vary with ice damage susceptibility. (Author)

The ability to use radar to discriminate ice types has been investigated. Radar backscatter measurements were made of shorefast sea ice near Point Barrow, Alaska in May 1977 and April 1978, with a surface-based FM-CW scatterometer that swept from 1-2 GHz and from 8.5-17.5 GHz. The 1-2 GHz measurements showed that thick first-year and multiyear sea ice cannot be distinguished at 10 deg-70 deg incidence angles, but that undeformed sea ice can be discriminated from pressure-ridged thick first-year sea ice and lake ice. Results also indicate that frequencies between 8-18 GHz have the ability to discriminate between thick first-year sea ice, multiyear sea ice, and lake ice. The lowest frequency, 9 GHz, was found to provide the greatest separation between these ice categories with significant levels of separation existing between angles of incidence from 15 deg to 70 deg. The radar cross-sections for the like polarizations, VV and HH, were very similar in absolute level and angular response. The radar cross-sections for VV-polarization were usually the highest in absolute level. Cross-polarization provided a slightly greater separation between these categories of ice.

The lakes of the Arctic Coastal Plain of northern Alaska were classified, based on size, shape, orientation and distribution, into six lake units and three nonlake units. Regional slope and relief were demonstrated to control lake size, the largest lakes occurring on the flattest, northernmost segment of the Coastal Plain. Using ERTS-1 sequential imagery and existing photography and data, lakes were grouped according to three depth ranges, 1 m, 1-2 m and 2 m. Deepest lakes have the longest period of summer ice cover. Ice on shallow lakes melts the earliest. Maximum depths of lakes were computed based on ice volume content of the perennially frozen ground (permafrost) and these agreed with observed values and ranges. The lake classification and regional ERTS-1 coverage also appear to provide additional information on the limits of late-Pleistocene transgressions on the Coastal Plain.

Side-looking airborne radar (SLAR) imagery obtained in April-May 1974 from the North Slope of Alaska between Barrow and Harrison Bay indicates that tundra lakes can be separated into two classes based on the strength of the radar returns. Correlations between the areal patterns of the returns, limited ground observations on lake depths, and information obtained from ERTS imagery strongly suggest that freshwater lakes giving weak returns are frozen completely to the bottom while lakes giving strong returns are not. Brackish lakes also give weak returns even when they are not completely frozen. This is presumably the result of the brine present in the lower portion of the ice cover limiting the penetration of the X-band radiation into the ice. Although the physical cause of the differences in radar backscatter has not been identified, several possibilities are discussed. The ability to rapidly and easily separate the tundra lakes into these two classes via SLAR should be useful in a wide variety of different problems.

The seventh in a series of reports on lake and river ice and land-fast sea ice presents ice thickness measurements observed throughout the North American Arctic and subarctic during the 1970-71 and 1971-72 winter seasons. Information on surface ice conditions, dates of first ice, freeze-over and breakup, and detailed measurements of ice thickness across Alaskan rivers are also included. Some reports from the Alaska National Guard network on ice thickness measurements in remote areas of western Alaska are also presented. Analyses were made of maximum observed ice thicknesses reported during the two winters, and deviations from the mean ice thickness measured across rivers and creeks in southeast Alaska between 1965 and 1972., See also Part 6, AD-746 256.

This report presents results of small beam testing conducted in a test tank on ice corresponding in structure to the two major ice types, S1 and S2, encountered in lake ice sheets. Tests of 730 beams in the temperature range -1 to -19 C showed that macrocrystalline (S1) and columnar (S2) ice differ appreciably in their flexural characteristics, and that these differences are attributable to variations in the size and orientation of the crystals in the ice and the thermal condition of the beams. Parallel testing of cantilever and simply-supported beams indicated a virtual non-dependence of flexural strength on the temperature of the fiber in tension. It was also determined that the sharply terminated corners of conventional cantilever beams are a source of appreciable stress concentration that can reduce the intrinsic flexural strength by as much as one-half, but which, in most cases, can be substantially relieved by drilling holes at the beam roots. Overall, flexural strengths did not exceed 1200 kPa for cantilever beams or 1650 kPa for simply supported beams tested in parallel with cantilever beams. The highest flexural strengths were measured on isothermal simply supported beams of S2 ice tested with the top surface in tension, with average strengths for such ice increasing from 1650 kPa at -1 C to nearly 2600 kPa at -19 C. Beams made to fail with bottom in tension tested about 35% weaker because of the greatly increased size of crystals in the bottom of S2 ice sheets. Beams of S1 ice yielded flexural strengths midway between those measured on S2 ice.(EDC)

A nine-year record of the lake ice decay pattern of Post Pond in Lyme, New Hampshire, is analyzed using a simple algorithm. Quite good correlations between decay rates and thawing degree-days are obtained using heat transfer coefficients on the order of 15-20 W/sq. m./deg C. (Author)

Side-Looking Airborne Radar (SLAR) provides an all weather, all light level medium for imaging large areas of saline and fresh water ice. This report evaluates the use of SLAR imagery for determining winter sea and lake ice paremeters and compares winter sea ice pattern 'keys' with summer pattern 'keys'. The report also makes a preliminary evaluation of the effects of snow cover on the SLAR imagery and on the interpretation of ice conditions. In addition, an interpretation technique is developed which permits the interpreter to analyze ice environments to a greater degree than is possible through the use of image pattern keys. The study points out the requirement for additional research to correlate lake ice image patterns with age, thickness, condition, and snow cover parameters through a combined remote sensor and on-ice study.

The object of this study was to investigate the possibility of melting ice formed on the surfaces of rivers and lakes in the northern parts of the United States by applying a layer of a material that would absorb more of the available solar energy. Heat losses from water surfaces during the winter months were calculated based on a literature survey. Under the conditions existing in the northern United States the growth of an ice sheet and the effect of solar energy absorbed on the rate of the ice formation was analyzed. The effect of an absorbent layer applied to the ice surface on the growth of the ice sheet is studied. The extent to which the melting rate could be altered by such a layer is investigated. A discussion is made of the materials that can be used for this purpose and it is suggested that industrial waste materials be given first consideration. It is estimated that 105,000 lb of industrial slag of dark color (absorptivity ranging from 0.70 to 0.80) would give a layer 0.03 in. thick, 100 ft wide and 1 mile long. It is recommended that industrial waste materials as well as others be studied to determine their applicability as possible absorbers.

An impulse radar system was developed to perform shallow subsurface investigations. The technique is known as Electromagnetic Subsurface Profiling (ESP) and is the electrical analog of the seismic sub-bottom profiling method used in marine geology. The radar system operates by detecting the interface between two materials having different electrical properties. For sea ice and lake ice, an electromagnetic pulse is generated near the ice surface and the reflections from the surface and the ice/water interface are displayed on a continuous strip-chart recorder. Large masses of ground ice in perma-frost have been located with the system. Theoretical considerations indicate that the system also should be able to determine the approximate volume of interstitial ice in frozen soils. (Modified author abstract)

In order to clarify the interrelationships of basic drill rig parameters with the drilling regime, studies were made of torque, axial feed load, drilling speed, and a number of drill revolutions. In order to determine the qualitative and quantitative dependence of feed load and torque on the diameter of the working member and its feed per revolution, experiments were conducted with cyclic and continuous drilling and with two types of bits: with lobed tips and flat tips. The number of drill revolutions, penetration speed and feed per bit revolution were varied for each test, with two series of tests conducted for each form and type of bit. All tests were conducted on lake ice and Volga ice. (Author), Draft trans. of Rybnoe Khozyaistvo (USSR) n6 p52-53 Jun 69.

Beach ridges may be formed by ice pressure as the result of temperature variations and subsequent volume changes of the ice cover, or by ice thrusting due to wind action pushing the ice against the shore. The latter type predominates in Germany. A specific minimum basin area is a prerequisite for large-scale thrust action. Several cases of ice thrust on the Ploner Lake (Germany) are described. The ice blocks pile up parallel over each other along the shore and push inland. (Author), Trans. of Natur und Volk (West Germany) v71 p63-70 1941.