Science.gov

Sample records for lake fagnano ice

  1. Large residuals on geoidal heights determined on the Fagnano Lake, Tierra del Fuego-Argentina

    NASA Astrophysics Data System (ADS)

    Gomez, M. E.; Del Cogliano, D.; Perdomo, R.

    2013-05-01

    A new geoid model was developed in Tierra del Fuego and it was evaluated in the area of Fagnano Lake. The model was developed by means of the Equivalent Source Technique combining gravity data, levelling information measured on the province and observations of a GPS buoy on the Fagnano Lake. Those GPS buoy measurements provide information of the mean lake level surface (Del Cogliano et al., 2007). A cross validation process was realized in order to evaluate the model on the lake. What allowed determining a 6 cm geoid in the area of Fagnano Lake. Also, an evaluation of the EGM2008 (Pavlis et al., 2008) was made on the lake. Its behaviour was compared to that observed on the levelling lines. Differences of several decimetres were found when EGM2008 undulations were compared to observed geoid undulations in the lake area. In the regions where EGM2008 has included real gravimetric observations, differences between model and observations were only of a few centimetres. Such model has the particularity that includes fill-in gravity in that region. The above mentioned evaluation derived in an analysis of the effect that not representative gravity information could have on the estimation of geoid undulations in high mountainous regions. We found that this effect could be significant if there is no real information in the computing area (Gomez et al, 2012).

  2. Tracking tectonic activity and climate change in Southernmost Patagonia - The Lago Fagnano record

    NASA Astrophysics Data System (ADS)

    Waldmann, N.; Ariztegui, D.; Anselmetti, F. S.; Austin, J. A.; Moy, C.; Dunbar, R.

    2005-12-01

    The climate of southernmost Patagonia is influenced by the westerly winds, the Southern Ocean circumpolar flow, and the South Pacific gyre. Therefore, continental sediment records from this area are ideal to track high-latitude climate variability through time. Located at 55° S in Tierra del Fuego, Lago Fagnano occupies the deepest of a chain of tectonic depressions along the Fagnano-Magallanes fault system. Fagnano is the biggest (~110 km long), southernmost non-ice covered lake in the world. In March 2005, >800 km of geophysical data were acquired in the lake, combining simultaneously 3.5 kHz (pinger) single-channel with 1 in3 airgun multi-channel systems. These data provide a unique opportunity to look at the most recent lacustrine sediments with high-resolution, while imaging the oldest sediments at the same time. Preliminary interpretations show that the lake is divided into two sub-basins: a deep eastern sub-basin (~200 m water depth), and a shallower western sub-basin (~100 m). The seismic survey penetrated more than several tens of meters of sediments, exhibiting both lacustrine and glacial provenance, probably comprising the LGM and the Holocene. Seismic reflectors indicate the presence of neo-tectonic structures affecting even the most recent sedimentary package, including some mega-turbidites, suggesting continuing tectonic impact on sedimentation. Gravity cores from both sub-basins reveal a regular alternation of light and dark laminae with abundant diatom content. Ultra-high resolution X-ray fluorescence micro-profiles show fluctuations at mm scale in major and trace elements that may indicate seasonal influx changes into the basin. These core data will provide a unique record of decadal changes in regional climate that will be compared with other marine and continental archives to improve our understanding of the forcing mechanisms behind climate change that can be further used to validate the outcome of ocean and atmospheric climatic models for the

  3. Astrobiology of Antarctic ice Covered Lakes

    NASA Astrophysics Data System (ADS)

    Doran, P. T.; Fritsen, C. H.

    2005-12-01

    Antarctica contains a number of permanently ice-covered lakes which have often been used as analogs of purported lakes on Mars in the past. Antarctic subglacial lakes, such as Lake Vostok, have also been viewed as excellent analogs for an ice covered ocean on the Jovian moon Europa, and to a lesser extend on Mars. Lakes in the McMurdo Dry Valleys of East Antarctica have ice covers that range from 3 to 20 meters thick. Water salinities range from fresh to hypersaline. The thinner ice-covered lakes have a well-documented ecology that relies on the limited available nutrients and the small amount of light energy that penetrates the ice covers. The thickest ice-covered lake (Lake Vida in Victoria Valley) has a brine beneath 20 m of ice that is 7 times sea water and maintains a temperature below -10 degrees Celsius. This lake is vastly different from the thinner ice-covered lakes in that there is no communication with the atmosphere. The permanent ice cover is so thick, that summer melt waters can not access the sub-ice brine and so the ice grows from the top up, as well as from the bottom down. Brine trapped beneath the ice is believed to be ancient, stranded thousands of years ago when the ice grew thick enough to isolate it from the surface. We view Lake Vida as an excellent analog for the last aquatic ecosystem to have existed on Mars under a planetary cooling. If, as evidence is now increasingly supporting, standing bodies of water existed on Mars in the past, their fate under a cooling would be to go through a stage of permanent ice cover establishment, followed by a thickening of that ice cover until the final stage just prior to a cold extinction would be a Lake Vida-like lake. If dust storms or mass movements covered these ancient lakes, remnants may well be in existence in the subsurface today. A NASA Astrobiology Science and Technology for Exploring Planets (ASTEP) project will drill the Lake Vida ice cover and access the brine and sediments beneath in

  4. RADARSAT-2 Polarimetry for Lake Ice Mapping

    NASA Astrophysics Data System (ADS)

    Pan, Feng; Kang, Kyung-Kuk; Duguay, Claude

    2016-04-01

    Changes in the ice regime of lakes can be employed to assess long-term climate trends and variability in high latitude regions. Lake ice cover observations are not only useful for climate monitoring, but also for improving ice and weather forecasts using numerical prediction models. In recent years, satellite remote sensing has assumed a greater role in observing lake ice cover for both purposes. Radar remote sensing has become an essential tool for mapping lake ice at high latitudes where cloud cover and polar darkness severely limits ice observations from optical systems. In Canada, there is an emerging interest by government agencies to evaluate the potential of fully polarimetric synthetic aperture radar (SAR) data from RADARSAT-2 (C-band) for lake ice monitoring. In this study, we processed and analyzed the polarization states and scattering mechanisms of fully polarimetric RADARSAT-2 data obtained over Great Bear Lake, Canada, to identify open water and different ice types during the freeze-up and break-up periods. Polarimetric decompositions were employed to separate polarimetric measurements into basic scattering mechanisms. Entropy, anisotropy, and alpha angle were derived to characterize the scattering heterogeneity and mechanisms. Ice classes were then determined based on entropy and alpha angle using the unsupervised Wishart classifier and results evaluated against Landsat 8 imagery. Preliminary results suggest that the RADARSAT-2 polarimetric data offer a strong capability for identifying open water and different lake ice types.

  5. Thickness of ice on perennially frozen lakes

    USGS Publications Warehouse

    McKay, C.P.; Clow, G.D.; Wharton, R.A.; Squyres, S. W.

    1985-01-01

    The dry valleys of southern Victoria Land, constituting the largest ice-free expanse in the Antarctic, contain numerous lakes whose perennial ice cover is the cause of some unique physical and biological properties 1-3. Although the depth, temperature and salinity of the liquid water varies considerably from lake to lake, the thickness of the ice cover is remarkably consistent1, ranging from 3.5 to 6m, which is determined primarily by the balance between conduction of energy out of the ice and the release of latent heat at the ice-water interface and is also affected by the transmission and absorption of sunlight. In the steady state, the release of latent heat at the ice bottom is controlled by ablation from the ice surface. Here we present a simple energy-balance model, using the measured ablation rate of 30 cm yr-1, which can explain the observed ice thickness. ?? 1985 Nature Publishing Group.

  6. ROV dives under Great Lakes ice

    USGS Publications Warehouse

    Bolsenga, S.J.; Gannon, John E.; Kennedy, Gregory; Norton, D.C.; Herdendorf, Charles E.

    1989-01-01

    Observations of the underside of ice have a wide variety of applications. Severe under-ice roughness can affect ice movements, rough under-ice surfaces can scour the bottom disturbing biota and man-made structures such as pipelines, and the flow rate of rivers is often affected by under-ice roughness. A few reported observations of the underside of an ice cover have been made, usually by cutting a large block of ice and overturning it, by extensive boring, or by remote sensing. Such operations are extremely labor-intensive and, in some cases, prone to inaccuracies. Remotely operated vehicles (ROV) can partially solve these problems. In this note, we describe the use, performance in a hostile environment, and results of a study in which a ROV was deployed under the ice in Lake Erie (North American Great Lakes).

  7. Depth, ice thickness, and ice-out timing cause divergent hydrologic responses among Arctic lakes

    USGS Publications Warehouse

    Arp, Christopher D.; Jones, Benjamin M.; Liljedahl, Anna K.; Hinkel, Kenneth M.; Welker, Jeffery A.

    2015-01-01

    Lakes are prevalent in the Arctic and thus play a key role in regional hydrology. Since many Arctic lakes are shallow and ice grows thick (historically 2-m or greater), seasonal ice commonly freezes to the lake bed (bedfast ice) by winter's end. Bedfast ice fundamentally alters lake energy balance and melt-out processes compared to deeper lakes that exceed the maximum ice thickness (floating ice) and maintain perennial liquid water below floating ice. Our analysis of lakes in northern Alaska indicated that ice-out of bedfast ice lakes occurred on average 17 days earlier (22-June) than ice-out on adjacent floating ice lakes (9-July). Earlier ice-free conditions in bedfast ice lakes caused higher open-water evaporation, 28% on average, relative to floating ice lakes and this divergence increased in lakes closer to the coast and in cooler summers. Water isotopes (18O and 2H) indicated similar differences in evaporation between these lake types. Our analysis suggests that ice regimes created by the combination of lake depth relative to ice thickness and associated ice-out timing currently cause a strong hydrologic divergence among Arctic lakes. Thus understanding the distribution and dynamics of lakes by ice regime is essential for predicting regional hydrology. An observed regime shift in lakes to floating ice conditions due to thinner ice growth may initially offset lake drying because of lower evaporative loss from this lake type. This potential negative feedback caused by winter processes occurs in spite of an overall projected increase in evapotranspiration as the Arctic climate warms.

  8. Depth, ice thickness, and ice-out timing cause divergent hydrologic responses among Arctic lakes

    NASA Astrophysics Data System (ADS)

    Arp, Christopher D.; Jones, Benjamin M.; Liljedahl, Anna K.; Hinkel, Kenneth M.; Welker, Jeffery A.

    2015-12-01

    Lakes are prevalent in the Arctic and thus play a key role in regional hydrology. Since many Arctic lakes are shallow and ice grows thick (historically 2 m or greater), seasonal ice commonly freezes to the lake bed (bedfast ice) by winter's end. Bedfast ice fundamentally alters lake energy balance and melt-out processes compared to deeper lakes that exceed the maximum ice thickness (floating ice) and maintain perennial liquid water below floating ice. Our analysis of lakes in northern Alaska indicated that ice-out of bedfast ice lakes occurred on average 17 days earlier (22 June) than ice-out on adjacent floating ice lakes (9 July). Earlier ice-free conditions in bedfast ice lakes caused higher open-water evaporation, 28% on average, relative to floating ice lakes and this divergence increased in lakes closer to the coast and in cooler summers. Water isotopes (18O and 2H) indicated similar differences in evaporation between these lake types. Our analysis suggests that ice regimes created by the combination of lake depth relative to ice thickness and associated ice-out timing currently cause a strong hydrologic divergence among Arctic lakes. Thus, understanding the distribution and dynamics of lakes by ice regime is essential for predicting regional hydrology. An observed regime shift in lakes to floating ice conditions due to thinner ice growth may initially offset lake drying because of lower evaporative loss from this lake type. This potential negative feedback caused by winter processes occurs in spite of an overall projected increase in evapotranspiration as the Arctic climate warms.

  9. HOLOCENE MASS-WASTING EVENTS IN LAGO FAGNANO, TIERRA DEL FUEGO (54°S): IMPLICATIONS FOR PALEOSEISMICITY OF THE MAGALLANES-FAGNANO TRANSFORM FAULT

    NASA Astrophysics Data System (ADS)

    Ariztegui, D.; Waldmann, N.; Austin, J. A.; Anselmetti, F.; Moy, C.; Dunbar, R. B.

    2009-12-01

    High-resolution seismic imaging and sediment coring in Lago Fagnano, located along the Magallanes-Fagnano plate boundary in Tierra del Fuego, have revealed a chronologic catalog of Holocene mass-wasting events. These event layers are interpreted as resulting from slope instabilities that load the slope-adjacent lake floor during mass flow deposition thus mobilizing basin floor sediments through gravity spreading. A total of 22 mass flow deposits have been identified combining results from an 800 km-long dense grid of seismic profiles with a series of sediment cores. Successions of up to 6 m-thick mass-flow deposits pond the basin floor spreading eastward and westward following the main axis of the eastern sub-basin of Lago Fagnano. An age model on the basis of information from previous studies and from new radiocarbon dating allowed establishing a well-constrained chronologic mass-wasting event catalogue covering the last ~15000 years. Simultaneously-triggered basin-wide lateral slope failure and the formation of multiple debris flow and megaturbidite deposits are interpreted as the fingerprint of paleo-seismic activity along the Magallanes-Fagnano transform fault that runs along the entire lake basin. The slope failures and megaturbidites are interpreted as recording large earthquakes occurring along the transform fault since the early Holocene. The results from this study provide new data about the frequency and possible magnitude of Holocene earthquakes in Tierra del Fuego, which can be applied in the context of seismic hazard assessment in southernmost Patagonia.

  10. Arctic sea ice decline contributes to thinning lake ice trend in northern Alaska

    NASA Astrophysics Data System (ADS)

    Alexeev, Vladimir A.; Arp, Christopher D.; Jones, Benjamin M.; Cai, Lei

    2016-07-01

    Field measurements, satellite observations, and models document a thinning trend in seasonal Arctic lake ice growth, causing a shift from bedfast to floating ice conditions. September sea ice concentrations in the Arctic Ocean since 1991 correlate well (r = +0.69, p < 0.001) to this lake regime shift. To understand how and to what extent sea ice affects lakes, we conducted model experiments to simulate winters with years of high (1991/92) and low (2007/08) sea ice extent for which we also had field measurements and satellite imagery characterizing lake ice conditions. A lake ice growth model forced with Weather Research and Forecasting model output produced a 7% decrease in lake ice growth when 2007/08 sea ice was imposed on 1991/92 climatology and a 9% increase in lake ice growth for the opposing experiment. Here, we clearly link early winter ‘ocean-effect’ snowfall and warming to reduced lake ice growth. Future reductions in sea ice extent will alter hydrological, biogeochemical, and habitat functioning of Arctic lakes and cause sub-lake permafrost thaw.

  11. Arctic sea ice decline contributes to thinning lake ice trend in northern Alaska

    USGS Publications Warehouse

    Alexeev, Vladimir; Arp, Christopher D.; Jones, Benjamin M.; Cai, Lei

    2016-01-01

    Field measurements, satellite observations, and models document a thinning trend in seasonal Arctic lake ice growth, causing a shift from bedfast to floating ice conditions. September sea ice concentrations in the Arctic Ocean since 1991 correlate well (r = +0.69,p < 0.001) to this lake regime shift. To understand how and to what extent sea ice affects lakes, we conducted model experiments to simulate winters with years of high (1991/92) and low (2007/08) sea ice extent for which we also had field measurements and satellite imagery characterizing lake ice conditions. A lake ice growth model forced with Weather Research and Forecasting model output produced a 7% decrease in lake ice growth when 2007/08 sea ice was imposed on 1991/92 climatology and a 9% increase in lake ice growth for the opposing experiment. Here, we clearly link early winter 'ocean-effect' snowfall and warming to reduced lake ice growth. Future reductions in sea ice extent will alter hydrological, biogeochemical, and habitat functioning of Arctic lakes and cause sub-lake permafrost thaw.

  12. Lake ice cover and its influence on lake ecology in a Finnish lake district

    NASA Astrophysics Data System (ADS)

    Leppäranta, Matti; Arvola, Lauri

    2014-05-01

    A wintertime research program on the physics and biology of lakes in Häme lake district in Finland has been performed in the last five years. The set of study lakes contains a wide spectrum in size, depth and trophic status. In this region the lakes freeze over annually for 4-6 months and the mean ice thickness is around 0.5 m. The ice sheet consists of congelation ice and snow-ice. The snow-ice fraction ranges from 0 to 90 per cent depending on the snow fall history and its magnitude makes a major contribution to the ice properties and conditions in the water body beneath the ice, in particular the mechanical strength and optical thickness are much less than for congelation ice. The e-folding depth of light intensity was 50-100 cm for congelation ice and 5-10 cm for snow. A numerical model has been developed to simulate the annual cycle of ice stratigraphy, temperature and thickness. The water bodies had a 1-4 m thick upper mixed layer thick thermocline, and in deeper lakes a lower homogeneous layer. Fall cooling process was crucial to determine the temperature of the lower layer at freeze-up, anything within 0-4°C. Oxygen concentration decreased in winter, especially close to the bottom sediments, and carbon dioxide concentration increased due to respiration activity. Phytoplankton production and biomass level were low or very low and, therefore, heterotrophic and mixotrophic species were abundant. Oxygen depletion in the hypolimnium had several chemical and ecological consequences, such as release of phosphorus from the bottom sediments. In spring, just before the ice-out, photosynthesis was at a high level beneath the ice due to improved light conditions and started to elevate the oxygen concentration in the topmost water layer. Primary production under the ice is limited or prohibited by low level of available light.

  13. Climate vs. Tectonics at the end of the World: the Lago Fagnano Sedimentary Record, Tierra del Fuego, Southernmost South America.

    NASA Astrophysics Data System (ADS)

    Waldmann, N.; Ariztegui, D.; Anselmetti, F.; Austin, J.; Moy, C.; Dunbar, R.; Recasens, C.

    2006-12-01

    Lacustrine sediments provide one of the best continental archives to reconstruct climate change. Additionally, many lakes are located in tectonically active regions and, therefore, their sediments also store regional tectonic events. Located at 55°S on the island of Tierra del Fuego, Lago Fagnano is the largest (~110 km long), southernmost non-ice covered lake in the world. It occupies the deepest basin in a chain of tectonic depressions along the Magallanes-Fagnano transform system (MFT). Ca. 800 km of reflection seismic data, comprising simultaneously-acquired single-channel 3.5 kHz (pinger) lines and multi-channel 1 in3 airgun lines, revealed an over 100 m-thick sedimentary succession. A preliminary seismic stratigraphic analysis of the high- resolution 3.5 kHz pinger data identified three major seismostratigraphic units defined by different seismic facies. While the lowermost unit is interpreted as product of subglacial to proglacial sedimentation probably deposited at the end of the Late Glacial period, the middle and uppermost unit represent an upward gradual change from a proglacial environment into typical lacustrine facies. The seismic stratigraphic analysis further allows us to recognize several mass-flows and megaturbidite events suggesting a substantial tectonic impact on the most recent lake sedimentation. The mass-flow frequency increases upward probably documenting the onset of Holocene hemipelagic-type sedimentation, thus indicating slope-sediment mobilization in the observed lateral slides. In contrast, Late Glacial mass flows were not initiated on the lateral slopes but rather originated in proglacial settings as reflected by the basinwide distributions of associated redeposits. The internal seismic architecture of the uppermost seismic unit coincides well with the petrophysical properties measured in the cores, allowing a precise core-to-seismic correlation. Preliminary sedimentological analyses of the cores show a diatom-rich and perfectly

  14. A Geochemical and Sedimentary Record of High Southern Latitude Holocene Climate Evolution from Lago Fagnano, Tierra del Fuego

    SciTech Connect

    Moy, C M; Dunbar, R B; Guilderson, T P; Waldmann, N; Mucciarone, D A; Recasens, C; Austin, J A; Anselmetti, F S

    2010-11-19

    Situated at the southern margin of the hemispheric westerly wind belt and immediately north of the Antarctic Polar Frontal zone, Tierra del Fuego is well-positioned to monitor coupled changes in the ocean-atmosphere system of the high southern latitudes. Here we describe a Holocene paleoclimate record from sediment cores obtained from Lago Fagnano, a large lake in southern Tierra del Fuego at 55{sup o}S, to investigate past changes in climate related to these two important features of the global climate system. We use an AMS radiocarbon chronology for the last 8,000 years based on pollen concentrates, thereby avoiding contamination from bedrock-derived lignite. Our chronology is consistent with a tephrochronologic age date for deposits from the middle Holocene Volcan Hudson eruption. Combining bulk organic isotopic ({delta}{sup 13}C and {delta}{sup 15}N) and elemental (C and N) parameters with physical sediment properties allow us to better understand sediment provenance and transport mechanisms and to interpret Holocene climate and tectonic change during the last 8,000 years. Co-variability and long-term trends in C/N ratio, carbon accumulation rate, and magnetic susceptibility reflect an overall Holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin. We attribute this variability to westerly wind-derived precipitation. Increased wind strength and precipitation in the late Holocene drives the Nothofagus forest eastward and enhances run-off and terrigenous inputs to the lake. Superimposed on the long-term trend are a series of abrupt 9 negative departures in C/N ratio, which constrain the presence of seismically-driven mass flow events in the record. We identify an increase in bulk {delta}{sup 13}C between 7,000 and 5,000 cal yr BP that we attribute to enhanced aquatic productivity driven by warmer summer temperatures. The Lago Fagnano {delta}{sup 13}C record shows similarities with Holocene records of sea surface

  15. A geochemical and sedimentary record of high southern latitude Holocene climate evolution from Lago Fagnano, Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Moy, Christopher M.; Dunbar, Robert B.; Guilderson, Thomas P.; Waldmann, Nicolas; Mucciarone, David A.; Recasens, Cristina; Ariztegui, Daniel; Austin, James A.; Anselmetti, Flavio S.

    2011-02-01

    Situated at the southern margin of the hemispheric westerly wind belt and immediately north of the Antarctic Polar Frontal zone, Tierra del Fuego is well-positioned to monitor coupled changes in the ocean-atmosphere system of the high southern latitudes. Here we describe a Holocene paleoclimate record from sediment cores obtained from Lago Fagnano, a large lake in southern Tierra del Fuego at 55°S, to investigate past changes in climate related to these two important features of the global climate system. We use an AMS radiocarbon chronology for the last 8000 yr based on pollen concentrates, thereby avoiding contamination from bedrock-derived lignite. Our chronology is consistent with a tephrochronologic age date for deposits from the middle Holocene Volcán Hudson eruption. Combining bulk organic isotopic (δ13C and δ15N) and elemental (C and N) parameters with physical sediment properties allows us to better understand sediment provenance and transport mechanisms and to interpret Holocene climate and tectonic change during the last 8000 yr. Co-variability and long-term trends in C/N ratio, carbon accumulation rate, and magnetic susceptibility reflect an overall Holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin. We attribute this variability to westerly wind-derived precipitation. Increased wind strength and precipitation in the late Holocene drives the Nothofagus forest eastward and enhances run-off and terrigenous inputs to the lake. Superimposed on the long-term trend are a series of abrupt 9 negative departures in C/N ratio, which constrain the presence of seismically-driven mass flow events in the record. We identify an increase in bulk δ13C between 7000 and 5000 cal yr BP that we attribute to enhanced aquatic productivity driven by warmer summer temperatures. The Lago Fagnano δ13C record shows similarities with Holocene records of sea surface temperature from the mid-latitude Chilean continental

  16. Microbiota within the perennial ice cover of Lake Vida, Antarctica.

    PubMed

    Mosier, Annika C; Murray, Alison E; Fritsen, Christian H

    2007-02-01

    Lake Vida, located in the McMurdo Dry Valleys, Antarctica, is an 'ice-sealed' lake with approximately 19 m of ice covering a highly saline water column (approximately 245 ppt). The lower portions of the ice cover and the lake beneath have been isolated from the atmosphere and land for circa 2800 years. Analysis of microbial assemblages within the perennial ice cover of the lake revealed a diverse array of bacteria and eukarya. Bacterial and eukaryal denaturing gradient gel electrophoresis phylotype profile similarities were low (<59%) between all of the depths compared (five depths spanning 11 m of the ice cover), with the greatest differences occurring between surface and deep ice. The majority of bacterial 16S rRNA gene sequences in the surface ice were related to Actinobacteria (42%) while Gammaproteobacteria (52%) dominated the deep ice community. Comparisons of assemblage composition suggest differences in ice habitability and organismal origin in the upper and lower portions of ice cover. Specifically, the upper ice cover microbiota likely reflect the modern day transport and colonization of biota from the terrestrial landscape, whereas assemblages in the deeper ice are more likely to be persistent remnant biota that originated from the ancient liquid water column of the lake that froze.

  17. Does ice float in Titan’s lakes and seas?

    NASA Astrophysics Data System (ADS)

    Hofgartner, Jason D.; Lunine, Jonathan I.

    2013-03-01

    We model Titan’s lakes and seas as methane-ethane-nitrogen systems and model the buoyancy of solids in these systems assuming thermodynamic equilibrium. We find that ice will float in methane-rich lakes for all temperatures below the freezing point of pure methane and that ice will also float in ethane-rich seas provided the ice has an air porosity of greater than 5% by volume.

  18. Composition, Diversity, and Stability of Microbial Assemblages in Seasonal Lake Ice, Miquelon Lake, Central Alberta

    PubMed Central

    Bramucci, Anna; Han, Sukkyun; Beckers, Justin; Haas, Christian; Lanoil, Brian

    2013-01-01

    The most familiar icy environments, seasonal lake and stream ice, have received little microbiological study. Bacteria and Eukarya dominated the microbial assemblage within the seasonal ice of Miquelon Lake, a shallow saline lake in Alberta, Canada. The bacterial assemblages were moderately diverse and did not vary with either ice depth or time. The closest relatives of the bacterial sequences from the ice included Actinobacteria, Bacteroidetes, Proteobacteria, Verrucomicrobia, and Cyanobacteria. The eukaryotic assemblages were less conserved and had very low diversity. Green algae relatives dominated the eukaryotic gene sequences; however, a copepod and cercozoan were also identified, possibly indicating the presence of complete microbial loop. The persistence of a chlorophyll a peak at 25–30 cm below the ice surface, despite ice migration and brine flushing, indicated possible biological activity within the ice. This is the first study of the composition, diversity, and stability of seasonal lake ice. PMID:24832796

  19. Ancient ice islands in salt lakes of the Central Andes

    USGS Publications Warehouse

    Hurlbert, S.H.; Chang, Cecily C.Y.

    1984-01-01

    Massive blocks of freshwater ice and frozen sediments protrude from shallow, saline lakes in the Andes of southwestern Bolivia and northeastern Chile. These ice islands range up to 1.5 kilometers long, stand up to 7 meters above the water surface, and may extend out tens of meters and more beneath the unfrozen lake sediments. The upper surfaces of the islands are covered with dry white sediments, mostly aragonite or calcite. The ice blocks may have formed by freezing of the fresh pore water of lake sediments during the "little ice age." The largest blocks are melting rapidly because of possibly recent increases in geothermal heat flux through the lake bottom and undercutting by warm saline lake water during the summer.

  20. Ancient ice islands in salt lakes of the central andes.

    PubMed

    Hurlbert, S H; Chang, C C

    1984-04-20

    Massive blocks of freshwater ice and frozen sediments protrude from shallow, saline lakes in the Andes of southwestern Bolivia and northeastern Chile. These ice islands range up to 1.5 kilometers long, stand up to 7 meters above the water surface, and may extend out tens of meters and more beneath the unfrozen lake sediments. The upper surfaces of the islands are covered with dry white sediments, mostly aragonite or calcite. The ice blocks may have formed by freezing of the fresh pore water of lake sediments during the "little ice age." The largest blocks are melting rapidly because of possibly recent increases in geothermal heat flux through the lake bottom and undercutting by warm saline lake water during the summer.

  1. Subglacial lake drainage detected beneath the Greenland ice sheet

    PubMed Central

    Palmer, Steven; McMillan, Malcolm; Morlighem, Mathieu

    2015-01-01

    The contribution of the Greenland ice sheet to sea-level rise has accelerated in recent decades. Subglacial lake drainage events can induce an ice sheet dynamic response—a process that has been observed in Antarctica, but not yet in Greenland, where the presence of subglacial lakes has only recently been discovered. Here we investigate the water flow paths from a subglacial lake, which drained beneath the Greenland ice sheet in 2011. Our observations suggest that the lake was fed by surface meltwater flowing down a nearby moulin, and that the draining water reached the ice margin via a subglacial tunnel. Interferometric synthetic aperture radar-derived measurements of ice surface motion acquired in 1995 suggest that a similar event may have occurred 16 years earlier, and we propose that, as the climate warms, increasing volumes of surface meltwater routed to the bed will cause such events to become more common in the future. PMID:26450175

  2. Shrinking sea ice, increasing snowfall and thinning lake ice: a complex Arctic linkage explained

    NASA Astrophysics Data System (ADS)

    Brock, Ben W.

    2016-09-01

    The dramatic shrinkage of Arctic sea ice is one of the starkest symptoms of global warming, with potentially severe and far-reaching impacts on arctic marine and terrestrial ecology (Post et al 2013 Science 341 519-24) and northern hemisphere climate (Screen et al 2015 Environ. Res. Lett. 10 084006). In their recent article, Alexeev et al (2016 Environ. Res. Lett. 11 074022) highlight another, and unexpected, consequence of Arctic sea ice retreat: the thinning of lake ice in northern Alaska. This is attributed to early winter ‘ocean effect’ snowfall which insulates lake surfaces and inhibits the formation of deep lake ice. Lake ice thinning has important consequences for Arctic lake hydrology, biology and permafrost degradation.

  3. Geomicrobiology of subglacial ice above Lake Vostok, Antarctica

    USGS Publications Warehouse

    Priscu, J.C.; Adams, E.E.; Lyons, W.B.; Voytek, M.A.; Mogk, D.W.; Brown, R.L.; McKay, C.P.; Takacs, C.D.; Welch, K.A.; Wolf, C.F.; Kirshtein, J.D.; Avci, R.

    1999-01-01

    Data from ice 3590 meters below Vostok Station indicate that the ice was accredit from liquid water associated with Lake Vostok. Microbes were observed at concentrations ranging from 2.8 x 103 to 3.6 x 104 cells per milliliter; no biological incorporation of selected organic substrates or bicarbonate was detected. Bacterial 165 ribosomal DNA genes revealed low diversity in the gene population. The phylotypes were closely related to extant members of the alpha- and beta-Proteobacteria and the Actinomycetes. Extrapolation of the data from accretion ice to Lake Vostok implies that Lake Vostok may support a microbial population, despite more than 106 years of isolation from the atmosphere.

  4. Diatom assemblages promote ice formation in large lakes.

    PubMed

    D'souza, N A; Kawarasaki, Y; Gantz, J D; Lee, R E; Beall, B F N; Shtarkman, Y M; Koçer, Z A; Rogers, S O; Wildschutte, H; Bullerjahn, G S; McKay, R M L

    2013-08-01

    We present evidence for the directed formation of ice by planktonic communities dominated by filamentous diatoms sampled from the ice-covered Laurentian Great Lakes. We hypothesize that ice formation promotes attachment of these non-motile phytoplankton to overlying ice, thereby maintaining a favorable position for the diatoms in the photic zone. However, it is unclear whether the diatoms themselves are responsible for ice nucleation. Scanning electron microscopy revealed associations of bacterial epiphytes with the dominant diatoms of the phytoplankton assemblage, and bacteria isolated from the phytoplankton showed elevated temperatures of crystallization (T(c)) as high as -3 °C. Ice nucleation-active bacteria were identified as belonging to the genus Pseudomonas, but we could not demonstrate that they were sufficiently abundant to incite the observed freezing. Regardless of the source of ice nucleation activity, the resulting production of frazil ice may provide a means for the diatoms to be recruited to the overlying lake ice, thereby increasing their fitness. Bacterial epiphytes are likewise expected to benefit from their association with the diatoms as recipients of organic carbon excreted by their hosts. This novel mechanism illuminates a previously undescribed stage of the life cycle of the meroplanktonic diatoms that bloom in Lake Erie and other Great Lakes during winter and offers a model relevant to aquatic ecosystems having seasonal ice cover around the world.

  5. Diatom assemblages promote ice formation in large lakes

    PubMed Central

    D'souza, N A; Kawarasaki, Y; Gantz, J D; Lee, R E; Beall, B F N; Shtarkman, Y M; Koçer, Z A; Rogers, S O; Wildschutte, H; Bullerjahn, G S; McKay, R M L

    2013-01-01

    We present evidence for the directed formation of ice by planktonic communities dominated by filamentous diatoms sampled from the ice-covered Laurentian Great Lakes. We hypothesize that ice formation promotes attachment of these non-motile phytoplankton to overlying ice, thereby maintaining a favorable position for the diatoms in the photic zone. However, it is unclear whether the diatoms themselves are responsible for ice nucleation. Scanning electron microscopy revealed associations of bacterial epiphytes with the dominant diatoms of the phytoplankton assemblage, and bacteria isolated from the phytoplankton showed elevated temperatures of crystallization (Tc) as high as −3 °C. Ice nucleation-active bacteria were identified as belonging to the genus Pseudomonas, but we could not demonstrate that they were sufficiently abundant to incite the observed freezing. Regardless of the source of ice nucleation activity, the resulting production of frazil ice may provide a means for the diatoms to be recruited to the overlying lake ice, thereby increasing their fitness. Bacterial epiphytes are likewise expected to benefit from their association with the diatoms as recipients of organic carbon excreted by their hosts. This novel mechanism illuminates a previously undescribed stage of the life cycle of the meroplanktonic diatoms that bloom in Lake Erie and other Great Lakes during winter and offers a model relevant to aquatic ecosystems having seasonal ice cover around the world. PMID:23552624

  6. Diatom assemblages promote ice formation in large lakes.

    PubMed

    D'souza, N A; Kawarasaki, Y; Gantz, J D; Lee, R E; Beall, B F N; Shtarkman, Y M; Koçer, Z A; Rogers, S O; Wildschutte, H; Bullerjahn, G S; McKay, R M L

    2013-08-01

    We present evidence for the directed formation of ice by planktonic communities dominated by filamentous diatoms sampled from the ice-covered Laurentian Great Lakes. We hypothesize that ice formation promotes attachment of these non-motile phytoplankton to overlying ice, thereby maintaining a favorable position for the diatoms in the photic zone. However, it is unclear whether the diatoms themselves are responsible for ice nucleation. Scanning electron microscopy revealed associations of bacterial epiphytes with the dominant diatoms of the phytoplankton assemblage, and bacteria isolated from the phytoplankton showed elevated temperatures of crystallization (T(c)) as high as -3 °C. Ice nucleation-active bacteria were identified as belonging to the genus Pseudomonas, but we could not demonstrate that they were sufficiently abundant to incite the observed freezing. Regardless of the source of ice nucleation activity, the resulting production of frazil ice may provide a means for the diatoms to be recruited to the overlying lake ice, thereby increasing their fitness. Bacterial epiphytes are likewise expected to benefit from their association with the diatoms as recipients of organic carbon excreted by their hosts. This novel mechanism illuminates a previously undescribed stage of the life cycle of the meroplanktonic diatoms that bloom in Lake Erie and other Great Lakes during winter and offers a model relevant to aquatic ecosystems having seasonal ice cover around the world. PMID:23552624

  7. Mathematical Modelling of Melt Lake Formation On An Ice Shelf

    NASA Astrophysics Data System (ADS)

    Buzzard, Sammie; Feltham, Daniel; Flocco, Daniela

    2016-04-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. These structures have been implicated in crevasse propagation and ice-shelf collapse; the Larsen B ice shelf was observed to have a large amount of melt lakes present on its surface just before its collapse in 2002. Through modelling the transport of heat through the surface of the Larsen C ice shelf, where melt lakes have also been observed, this work aims to provide new insights into the ways in which melt lakes are forming and the effect that meltwater filling crevasses on the ice shelf will have. This will enable an assessment of the role of meltwater in triggering ice-shelf collapse. The Antarctic Peninsula, where Larsen C is situated, has warmed several times the global average over the last century and this ice shelf has been suggested as a candidate for becoming fully saturated with meltwater by the end of the current century. Here we present results of a 1-D mathematical model of heat transfer through an idealized ice shelf. When forced with automatic weather station data from Larsen C, surface melting and the subsequent meltwater accumulation, melt lake development and refreezing are demonstrated through the modelled results. Furthermore, the effect of lateral meltwater transport upon melt lakes and the effect of the lakes upon the surface energy balance are examined. Investigating the role of meltwater in ice-shelf stability is key as collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea-level rise.

  8. Mathematical Modelling of Melt Lake Formation On An Ice Shelf

    NASA Astrophysics Data System (ADS)

    Buzzard, S. C.; Feltham, D. L.; Flocco, D.; Sammonds, P. R.

    2015-12-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. These structures have been implicated in crevasse propagation and ice-shelf collapse; the Larsen B ice shelf was observed to have a large amount of melt lakes present on its surface just before its collapse in 2002. Through modelling the transport of heat through the surface of the Larsen C ice shelf, where melt lakes have also been observed, this work aims to provide new insights into the ways in which melt lakes are forming and the effect that meltwater filling crevasses on the ice shelf will have. This will enable an assessment of the role of meltwater in triggering ice-shelf collapse. The Antarctic Peninsula, where Larsen C is situated, has warmed several times the global average over the last century and this ice shelf has been suggested as a candidate for becoming fully saturated with meltwater by the end of the current century. Here we present results of a 1-D mathematical model of heat transfer through an idealized ice shelf. When forced with automatic weather station data from Larsen C, surface melting and the subsequent meltwater accumulation, melt lake development and refreezing are demonstrated through the modelled results. Furthermore, the effect of lateral meltwater transport upon melt lakes and the effect of the lakes upon the surface energy balance are examined. Investigating the role of meltwater in ice-shelf stability is key as collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea-level rise.

  9. The influence of ice on southern Lake Michigan coastal erosion

    USGS Publications Warehouse

    Barnes, P.W.; Kempema, E.W.; Reimnitz, E.; McCormick, M.

    1994-01-01

    Coastal ice does not protect the coast but enhances erosion by displacing severe winter wave energy from the beach to the shoreface and by entraining and transporting sediment alongshore and offshore. Three aspects of winter ice in Lake Michigan were studied over a 3-year period and found to have an important influence on coastal sediment dynamics and the coastal sediment budget: (1) the influence of coastal ice on shoreface morphology, (2) the transport of littoral sediments by ice, and (3) the formation of anchor and underwater ice as a frequent and important event entraining and transporting sediment. The nearshore ice complex contains a sediment load (0.2 - 1.2 t/m of coast) that is roughly equivalent to the average amount of sand eroded from the coastal bluffs and to the amount of sand ice- rafted offshore to the deep lake basin each year. -from Authors

  10. Constraints on methane oxidation in ice-covered boreal lakes

    NASA Astrophysics Data System (ADS)

    Denfeld, Blaize A.; Ricão Canelhas, Monica; Weyhenmeyer, Gesa A.; Bertilsson, Stefan; Eiler, Alexander; Bastviken, David

    2016-07-01

    Boreal lakes can be ice covered for a substantial portion of the year at which time methane (CH4) can accumulate below ice. The amount of CH4 emitted at ice melt is partially determined by the interplay between CH4 production and CH4 oxidation, performed by methane-oxidizing bacteria (MOB). Yet the balance between oxidation and emission and the potential for CH4 oxidation in various lakes during winter is largely unknown. To address this, we performed incubations at 2°C to screen for wintertime CH4 oxidation potential in seven lakes. Results showed that CH4 oxidation was restricted to three lakes, where the phosphate concentrations were highest. Molecular analyses revealed that MOB were initially detected in all lakes, although an increase in type I MOB only occurred in the three lake water incubations where oxidation could be observed. Accordingly, the increase in CO2 was on average 5 times higher in these three lake water incubations. For one lake where no oxidation was measured, we tested if temperature and CH4 availability could trigger CH4 oxidation. However, regardless of incubation temperatures and CH4 concentrations, ranging from 2 to 20°C and 1-500 μM, respectively, no oxidation was observed. Our study indicates that some lakes with active wintertime CH4 oxidation may have low emissions during ice melt, while other and particularly nutrient poor lakes may accumulate large amounts of CH4 below ice that, in the absence of CH4 oxidation, will be emitted following ice melt. This variability in CH4 oxidation rates between lakes needs to be accounted for in large-scale CH4 emission estimates.

  11. Holocene paleoclimate characterization in Lago Fagnano (Tierra del Fuego) using sedimentary, physical and geochemical proxies

    NASA Astrophysics Data System (ADS)

    Vizcaino Marti, A.; Dunbar, R. B.; Wahl, D.; Moy, C. M.; Mucciarone, D. A.; Anderson, L.; Guilderson, T. P.

    2010-12-01

    Tierra del Fuego is the world's southernmost landmass outside of Antarctica. Two features of ocean circulation control the climate of Tierra del Fuego: the Southern Ocean circumpolar flow and the South Pacific Gyre. Together with Patagonia, Tierra del Fuego is the only terrestrial region directly influenced by the southern hemisphere westerly winds. This region is also a tectonically active area affected by volcanic and seismic activity related to South American and Scotia-Antarctic plate boundaries. Accommodated along the Magallanes-Fagnano fault system, as part of the plate boundary, the Lago Fagnano is the largest lake in Tierra del Fuego. This E-W trending lake is 100 km long and 5-15 km wide. Our investigations were carried out on the upper 4 meters of an 8.4 m long piston core obtained at 69 m water depth in Bahía Grande (LF06-PC8); a southwestern lake sub-basin separated from the main lake by a shallow sill. Our studies are based on the integration of sediment description, physical properties, pollen, and geochemical analyses including C and N isotopes (1cm interval) and XRF scan (1mm interval). The age model for the core is based on radiocarbon ages and tephrochronology. Additionally, a 800 km long grid of high resolution seismic profiles support the sedimentary analyses and allow the correlation with other cores from within the lake basin. LF06-PC8 yields continuous and high accumulation-rate sedimentary sections for Lago Fagnano. The presented sediment record corresponds to a laminated hemipelagite with presence of a single but complex mass transport deposit interval. An accurate sedimentological interpretation of the core together with the radiocarbon ages and tephra dates allow to identify and characterize the main sedimentary processes occurring in the lake over the last 8 kyr. In addition, proxy data (C and N isotopes and XRF scan data) from the laminated hemipelagic interval provide a reliable record of past variability in the westerly wind field as

  12. An operational all-weather Great Lakes ice information system

    NASA Technical Reports Server (NTRS)

    Gedney, R. T.

    1975-01-01

    A description is given of the NASA developed all-weather ice information system for the Great Lakes winter navigation program. The system utilizes an X-band side looking airborne radar (SLAR) for determining type, location, and areal distribution of the ice cover in the Great Lakes and an airborne, S band, down looking short pulse radar for obtaining ice thickness. Digitized SLAR data are relayed in real time via the NOAA-GOES satellite in geosynchronous orbit. The SLAR images along with hand drawn interpretative ice charts for various Great Lakes winter shipping areas are broadcast to facsimile recorders aboard vessles is the area via the MARAD marine VHF-FM radio network. These data assist such vessels in navigating both through and around the ice.

  13. Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover

    NASA Technical Reports Server (NTRS)

    Squyres, S. W.; Andersen, D. W.; Nedell, S. S.; Wharton, R. A. Jr; Wharton RA, J. r. (Principal Investigator)

    1991-01-01

    Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites.

  14. Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover.

    PubMed

    Squyres, S W; Andersen, D W; Nedell, S S; Wharton, R A

    1991-01-01

    Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites. PMID:11538650

  15. 27 m of lake ice on an Antarctic lake reveals past hydrologic variability

    NASA Astrophysics Data System (ADS)

    Dugan, H. A.; Doran, P. T.; Wagner, B.; Kenig, F.; Fritsen, C. H.; Arcone, S.; Kuhn, E.; Ostrom, N. E.; Warnock, J.; Murray, A. E.

    2014-07-01

    Lake Vida, located in Victoria Valley, is one of the largest lakes in the McMurdo Dry Valleys. Unlike other lakes in the region, the surface ice extends at least 27 m, which has created an extreme and unique habitat by isolating a liquid-brine with salinity of 195 g L-1. Below 21 m, the ice is marked by well-sorted sand layers up to 20 cm thick, within a matrix of salty ice. From ice chemistry, isotopic abundances of 18O and 2H, ground penetrating radar profiles, and mineralogy, we conclude that the entire 27 m of ice formed from surface runoff, and the sediment layers represent the accumulation of fluvial and aeolian deposits. Radiocarbon and optically stimulated luminescence dating limit the maximum age of the lower ice to 6300 14C yr BP. As the ice cover ablated downwards during periods of low surface inflow, progressive accumulation of sediment layers insulated and preserved the ice and brine beneath; analogous to the processes that preserve shallow ground ice. The repetition of these sediment layers reveals climatic variability in Victoria Valley during the mid- to late Holocene. Lake Vida is an excellent Mars analog for understanding the preservation of subsurface brine, ice and sediment in a cold desert environment.

  16. Patterns and trends in Southern Ontario lake ice phenology.

    PubMed

    Futter, Martyn N

    2003-01-01

    An analysis is presented of 46 ice break up and 15 ice free season phenology data series obtained largely through volunteer monitoring efforts in Southern Ontario. Observations spanned the years 1853-2001. Available data included dates of ice formation and ice break up as well as the number of ice free days in a year. A high degree of temporal coherence in ice phenology between lakes was observed (137/365 pairwise correlations significant at P < 0.05). Significant monotonic trends towards earlier break up dates and longer ice free seasons were observed across the region both in the entire series and in the last thirty years of data. Trends in longer series may be associated with the end of the Little Ice Age. The significantly longer ice free seasons and earlier ice break up dates observed in the study area have important implications for lakes in other parts of Canada where climate change effects are predicted to be more extreme than in South-Central Ontario.

  17. Microwave properties of ice from The Great Lakes

    NASA Technical Reports Server (NTRS)

    Vickers, R. S.

    1975-01-01

    The increasing use of radar systems as remote sensors of ice thickness has revealed a lack of basic data on the microwave properties of fresh-water ice. A program, in which the complex dielectric constant was measured for a series of ice samples taken from the Great Lakes, is described. The measurements were taken at temperatures of -5, -10, and -15 C. It is noted that the ice has considerable internal layered structure, and the effects of the layering are examined. Values of 3.0 to 3.2 are reported for the real part of the dielectric constant, with an error bar of + or - 0.01.

  18. Recent lake ice-out phenology within and among lake districts of Alaska, U.S.A.

    USGS Publications Warehouse

    Arp, Christopher D.; Jones, Benjamin M.; Grosse, Guido

    2013-01-01

    The timing of ice-out in high latitudes is a fundamental threshold for lake ecosystems and an indicator of climate change. In lake-rich regions, the loss of ice cover also plays a key role in landscape and climatic processes. Thus, there is a need to understand lake ice phenology at multiple scales. In this study, we observed ice-out timing on 55 large lakes in 11 lake districts across Alaska from 2007 to 2012 using satellite imagery. Sensor networks in two lake districts validated satellite observations and provided comparison with smaller lakes. Over this 6 yr period, the mean lake ice-out for all lakes was 27 May and ranged from 07 May in Kenai to 06 July in Arctic Coastal Plain lake districts with relatively low inter-annual variability. Approximately 80% of the variation in ice-out timing was explained by the date of 0°C air temperature isotherm and lake area. Shoreline irregularity, watershed area, and river connectivity explained additional variation in some districts. Coherence in ice-out timing within the lakes of each district was consistently strong over this 6 yr period, ranging from r-values of 0.5 to 0.9. Inter-district analysis of coherence also showed synchronous ice-out patterns with the exception of the two arctic coastal districts where ice-out occurs later (June–July) and climatology is sea-ice influenced. These patterns of lake ice phenology provide a spatially extensive baseline describing short-term temporal variability, which will help decipher longer term trends in ice phenology and aid in representing the role of lake ice in land and climate models in northern landscapes.

  19. Large subglacial lakes in East Antarctica at the onset of fast-flowing ice streams.

    PubMed

    Bell, Robin E; Studinger, Michael; Shuman, Christopher A; Fahnestock, Mark A; Joughin, Ian

    2007-02-22

    Water plays a crucial role in ice-sheet stability and the onset of ice streams. Subglacial lake water moves between lakes and rapidly drains, causing catastrophic floods. The exact mechanisms by which subglacial lakes influence ice-sheet dynamics are unknown, however, and large subglacial lakes have not been closely associated with rapidly flowing ice streams. Here we use satellite imagery and ice-surface elevations to identify a region of subglacial lakes, similar in total area to Lake Vostok, at the onset region of the Recovery Glacier ice stream in East Antarctica and predicted by ice-sheet models. We define four lakes through extensive, flat, featureless regions of ice surface bounded by upstream troughs and downstream ridges. Using ice velocities determined using interferometric synthetic aperture radar (InSAR), we find the onset of rapid flow (moving at 20 to 30 m yr(-1)) of the tributaries to the Recovery Glacier ice stream in a 280-km-wide segment at the downslope margins of these four subglacial lakes. We conclude that the subglacial lakes initiate and maintain rapid ice flow through either active modification of the basal thermal regime of the ice sheet by lake accretion or through scouring bedrock channels in periodic drainage events. We suggest that the role of subglacial lakes needs to be considered in ice-sheet mass balance assessments. PMID:17314977

  20. Great Lakes all-weather ice information system

    NASA Technical Reports Server (NTRS)

    Schertler, R. J.; Mueller, R. A.; Jirberg, R. J.; Cooper, D. W.; Heighway, J. E.; Holmes, A. D.; Gedney, R. T.; Mark, H.

    1975-01-01

    A system is described which utilizes an X-band Side-Looking-Airborne-Radar (SLAR) for determining type, location, and aerial distribution of the ice cover in the Great Lakes and an airborne, S-band, short pulse radar for obtaining ice thickness. The SLAR system is currently mounted aboard a U.S. Coast Guard C-130B aircraft. Digitized SLAR data are relayed in real-time via the NOAA-GOES-1 satellite in geosynchronous orbit to the U.S. Coast Guard Ice Center in Cleveland, Ohio. SLAR images along with hand-drawn interpretative ice charts for various winter shipping areas in the Great Lakes are broadcast to facsimile recorders aboard Great Lakes vessels. The operational aspects of this ice information system are being demonstrated by NASA, U.S. Coast Guard, and NOAA/National Weather Service. Results from the 1974-75 winter season demonstrated the ability of this system to provide all-weather ice information to shippers in a timely manner.

  1. Oxygen budget of a perennially ice-covered Antarctic lake

    NASA Technical Reports Server (NTRS)

    Wharton, R. A., Jr.; Mckay, C. P.; Simmons, G. M., Jr.; Parker, B. C.

    1986-01-01

    A bulk O2 budget for Lake Hoare, Antarctica, is presented. Five years of seasonal data show the lake to be persistently supersaturated with O2. Oxygen is carried into the lake in glacial meltstreams and is left behind when this water is removed as ice by ablation and sublimation. A diffusive loss of O2 from the lake through the summer moat is suggested. Measured values of the total O2 in the water column indicate that the time scale of O2 turnover is much longer than a year. Based on these results, it is suggested that the amount of O2 in the water does not change significantly throughout the year and that the lake is also supersaturated with N2.

  2. Pathways of Snowmelt Water into an Ice-Covered Lake

    NASA Astrophysics Data System (ADS)

    Cortes, A.; MacIntyre, S.; Sadro, S.

    2015-12-01

    Discharge of water into ice-covered arctic lakes during snowmelt can be high, but no general framework exists to quantify the pathway of the flow into the lakes and the associated distribution of incoming resources including dissolved organic carbon (DOC) or greenhouse gases. In this study, we characterize the fate of the snowmelt water flowing into 1.5 km2 Toolik Lake, Alaska, in 2014 and 2015. We deployed arrays with temperature, conductivity, and oxygen sensors in the water column over the winter, performed high temporal and spatial resolution CTD surveys on four 500 m to 1 km long transect lines during spring, and obtained correlative meteorological and discharge data. During both study spring periods, we observed different snowmelt inflow regimes based on the discharge rate (low and high) which led to differences in the extent of vertical and horizontal dilution of the lake water. Our first estimates of horizontal dispersion of snowmelt water in Toolik Lake under a high discharge regime are in the upper range of values found for ice-covered lakes (O ~ (102) cm2 s-1). In both years, the incoming water spread over ~75% of the basin near the surface with associated loading of DOC and methane. Spring 2014 was typical of other years with a gradual snowmelt and restricted depth of penetration of the incoming water. In fact, the increased density gradient in the upper few meters created conditions which retarded subsequent mixing at ice off. In contrast, persistent high pressures over the Alaskan region caused an exceptionally warm spring and rapid snowmelt in 2015. The subsequent warming of stream waters meant that the within lake vertical density gradient was weakened and facilitated later mixing. The differences in magnitude of discharge and temperature of incoming water during the more average and the warm springs enable interpretations and predictions of the fate of solutes flowing into lakes during snowmelt under variable weather regimes.

  3. Hydrogeomorphic processes of thermokarst lakes with grounded-ice and floating-ice regimes on the Arctic coastal plain, Alaska

    USGS Publications Warehouse

    Arp, C.D.; Jones, Benjamin M.; Urban, F.E.; Grosse, G.

    2011-01-01

    Thermokarst lakes cover > 20% of the landscape throughout much of the Alaskan Arctic Coastal Plain (ACP) with shallow lakes freezing solid (grounded ice) and deeper lakes maintaining perennial liquid water (floating ice). Thus, lake depth relative to maximum ice thickness (1·5–2·0 m) represents an important threshold that impacts permafrost, aquatic habitat, and potentially geomorphic and hydrologic behaviour. We studied coupled hydrogeomorphic processes of 13 lakes representing a depth gradient across this threshold of maximum ice thickness by analysing remotely sensed, water quality, and climatic data over a 35-year period. Shoreline erosion rates due to permafrost degradation ranged from L) with periods of full and nearly dry basins. Shorter-term (2004–2008) specific conductance data indicated a drying pattern across lakes of all depths consistent with the long-term record for only shallow lakes. Our analysis suggests that grounded-ice lakes are ice-free on average 37 days longer than floating-ice lakes resulting in a longer period of evaporative loss and more frequent negative P − EL. These results suggest divergent hydrogeomorphic responses to a changing Arctic climate depending on the threshold created by water depth relative to maximum ice thickness in ACP lakes.

  4. Heat flux at the base of lake ice cover estimated from fine structure of the ice-water boundary layer

    NASA Astrophysics Data System (ADS)

    Kirillin, Georgiy; Aslamov, Ilya; Kozlov, Vladimir; Granin, Nikolay; Engelhardt, Christof; Förster, Josephine

    2016-04-01

    Seasonal lake ice is a highly changeable part of the cryosphere undergoing remarkable impact by global warming. Vertical heat transport across the boundary layer under ice affects strongly the growth and melting of lake ice cover. The existing models of ice cover dynamics focus basically on the dependence of the ice thickness on the air temperature with implicit account of the snow cover effects. The heat flux at the water-ice boundary, in turn, is usually neglected or parameterized in a very simplistic form. However, neglecting of the basal ice melting due to heat flux at the ice-water interface produces appreciable errors in the modeled ice cover duration. We utilize fine-structure observations taken during 2009-2015 in ice-water boundary layers of Lake Baikal and arctic Lake Kilpisjärvi to reveal the major physical drivers of the heat exchange at the ice bottom and to explain the high geographical, spatial, and temporal variability in the heat flux magnitudes. The methods provide first detailed estimations of the heat exchange beneath the ice cover, available previously only from bulk estimations. The fluxes in Lake Baikal have magnitudes of 101 W m-2 and vary strongly between different parts of the lake being influenced by large-scale horizontal circulation with current velocities amounting at up to 7 cm s-1. The shallow lake fluxes, while an order of magnitude weaker, are highly non-stationary, being affected by the turbulence due to oscillating currents under ice. Our results demonstrate the role played by the boundary layer mixing in the ice growth and melting, as well as characterize the physical processes responsible for the vertical heat exchange and provide a basis for an improved parameterization of ice cover in coupled lake-atmosphere models.

  5. GIS-modeling of an ice-dammed lake in the Lake Onega depression ca 14500-12500 Yrs BP

    NASA Astrophysics Data System (ADS)

    Subetto, Dmitry; Zobkov, Mikhail; Potakhin, Maksim; Tarasov, Aleksey

    2016-04-01

    Palaeogeographical reconstructions of the Onego ice-dammed lake development ca 14500-125000 yrs BP were based on the GIS approach. The palaeo-water-level surfaces were interpolated using a point-kriging approach. 14500-14000 Yrs BP: An ice-dammed lake occupied the southern part of the Lake Onega depression. The level of this lake was at 130-120 m a.s.l. and was controlled by a threshold of the water divide between the River Oshta and River Oyat', with discharge southwestward into the Oyat' basin. The surface area of the ice-dammed lake was 3500 sq.km. 14000-13300 Yrs BP: When the ice melted away from the mouth of the River Svir, the lake level dropped to 85-80 m a.s.l. and runoff was directed into the Lake Ladoga - easternmost part of The Baltic Ice Lake at that time. 13300-12500 Yrs BP: As the glacier retreated from the Lake Onega depression, the ice-dammed lake was occupied it and reached the maximum sizes (the surface area was 33000 sq.km). The new threshold in the northern part was opened and runoff was directed into the White Sea basin. During the conference new digital paleogeographical maps of the Onego ice-dammed lake will be presented. The study has been financially supported by the Russian Science Foundation (#14-17-00766).

  6. Antarctic lakes (above and beneath the ice sheet): Analogues for Mars

    NASA Technical Reports Server (NTRS)

    Rice, J. W., Jr.

    1992-01-01

    The perennial ice covered lakes of the Antarctic are considered to be excellent analogues to lakes that once existed on Mars. Field studies of ice covered lakes, paleolakes, and polar beaches were conducted in the Bunger Hills Oasis, Eastern Antarctica. These studies are extended to the Dry Valleys, Western Antarctica, and the Arctic. Important distinctions were made between ice covered and non-ice covered bodies of water in terms of the geomorphic signatures produced. The most notable landforms produced by ice covered lakes are ice shoved ridges. These features form discrete segmented ramparts of boulders and sediments pushed up along the shores of lakes and/or seas. Sub-ice lakes have been discovered under the Antarctic ice sheet using radio echo sounding. These lakes occur in regions of low surface slope, low surface accumulations, and low ice velocity, and occupy bedrock hollows. The presence of sub-ice lakes below the Martian polar caps is possible. The discovery of the Antarctic sub-ice lakes raises possibilities concerning Martian lakes and exobiology.

  7. Declining Sea Ice Extent Links Early Winter Climate to Changing Arctic Lakes

    NASA Astrophysics Data System (ADS)

    Alexeev, V. A.; Arp, C. D.; Jones, B. M.; Cai, L.

    2015-12-01

    Lakes on the Alaskan North Slope regulate surface energy balance and interactions with permafrost as well as providing important habitat. Winter lake ice regimes (floating-ice or bedfast-ice conditions) determine whether lakes develop and maintain taliks and can support overwintering fish habitat. Lake ice thickness is a key variable determining whether a lake has a bedfast or floating-ice regime. Recent observations suggest a trend towards more lakes with floating-ice conditions due to thinner ice growth, but the broader scale associated climate conditions driving these regime shift are less certain. This study finds that the changing arctic summer/fall sea ice conditions might be affecting lake ice thickness on the North Slope. Late ocean freeze-up near the Alaskan coast leads to warmer weather and more snowfall in the early winter. Warmer early winters and thicker snowpack result in thinner lake ice the following winter thus potentially developing more ice-floating lakes before the start of the summer. Experiments with a regional atmospheric model WRF for two years with very different sea ice conditions indicate that the extent of open water next to the North Slope is a crucial factor for developing thicker snowpack, also warmer air temperature in early winter.

  8. Ice on rivers and lakes : a bibliographic essay

    USGS Publications Warehouse

    Ficke, Eleanore R.; Ficke, John F.

    1977-01-01

    Ice on rivers and lakes influences design and construction of structures, operation of shipping, flow and circulation, water quality, and other factors related to the use of water. Interest in understanding these influences has led to many programs of data collection, research, and investigations for a century or more. The body of literature reporting on these studies includes several thousand items in textbooks, proceedings, journals, and technical reports. By far, the largest portion of the studies were in the United States, Canada, or the Soviet Union. The literature can be classified as dealing with basic characteristics of ice; freezing and melting processes and their prediction and control on rivers, and on lakes; effects of river and lake ice on navigation, flow, and structures; and influences of ice on chemical, biological, and thermal aspects of water quality. This bibliography cites 750 publications, but the body of literature is large and this bibliography is not exhaustive. It does provide, however, a cross section of the scope of work in the field. (Woodard-USGS)

  9. CARBON TRACE GASES IN LAKE AND BEAVER POND ICE NEAR THOMPSON, MANITOBA, CANADA

    EPA Science Inventory

    Concentrations of CO2, CO, and CH4 were measured in beaver pond and lake ice in April 1996 near Thompson, Manitoba to derive information on possible impacts of ice melting on corresponding atmospheric trace gas concentrations. CH4 concentrations in beaver pond and lake ice ranged...

  10. Mining cosmic dust from the blue ice lakes of Greenland

    NASA Technical Reports Server (NTRS)

    Maurette, M.; Brownlee, D. E.; Fehrenback, L.; Hammer, C.; Jehano, C.; Thomsen, H. H.

    1985-01-01

    Extraterrestrial material, most of which invisible settles to Earth's surface as dust particles smaller than a millimeter in size were investigated. Particles of 1/10 millimeter size fall at a rate of one/sq m/yr collection of extraterrestrial dust is important because the recovered cosmic dust particles can provide important information about comets. Comets are the most important source of dust in the solar system and they are probably the major source of extraterrestrial dust that is collectable at the Earth's surface. A new collection site for cosmic dust, in an environment where degradation by weathering is minimal is reported. It is found that the blue ice lakes on the Greenland ice cap provide an ideal location for collection of extraterrestrial dust particles larger than 0.1 mm in size. It is found that the lakes contain large amounts of cosmic dust which is much better preserved than similar particles recovered from the ocean floor.

  11. Backscatter from ice growing on shallow tundra lakes near Barrow, Alaska, winter 1991-1992

    NASA Technical Reports Server (NTRS)

    Jeffries, M. O.; Wakabayashi, H.; Weeks, W. F.; Morris, K.

    1993-01-01

    The timing of freeze-up and break-up of Arctic lake ice is a potentially useful environmental indicator that could be monitored using SAR. In order to do this, it is important to understand how the properties and structure of the ice during its growth and decay affect radar backscatter and thus lake ice SAR signatures. The availability of radiometrically and geometrically calibrated digital SAR data time series from the Alaska SAR Facility has made it possible for the first time to quantify lake ice backscatter intensity (sigma(sup o)) variations. This has been done for ice growing on shallow tundra lakes near Barrow, NW Alaska, from initial growth in September 1991 until thawing and decay in June 1992. Field and laboratory observations and measurements of the lake ice were made in late April 1992. The field investigations of the coastal lakes near Barrow confirmed previous findings that, (1) ice frozen to the lake bottom had a dark signature in SAR images, indicating weak backscatter, while, (2) ice that was floating had a bright signature, indicating strong backscatter. At all sites, regardless of whether the ice was grounded or floating, there was a layer of clear, inclusion-free ice overlaying a layer of ice with dense concentrations of vertically oriented tubular bubbles. At some sites, there was a third layer of porous, snow-ice overlaying the clear ice.

  12. Ice cover, landscape setting, and geological framework of Lake Vostok, East Antarctica

    USGS Publications Warehouse

    Studinger, M.; Bell, R.E.; Karner, G.D.; Tikku, A.A.; Holt, J.W.; Morse, D.L.; David, L.; Richter, T.G.; Kempf, S.D.; Peters, M.E.; Blankenship, D.D.; Sweeney, R.E.; Rystrom, V.L.

    2003-01-01

    Lake Vostok, located beneath more than 4 km of ice in the middle of East Antarctica, is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment. Melting and freezing at the base of the ice sheet, which slowly flows across the lake, controls the flux of water, biota and sediment particles through the lake. The influx of thermal energy, however, is limited to contributions from below. Thus the geological origin of Lake Vostok is a critical boundary condition for the subglacial ecosystem. We present the first comprehensive maps of ice surface, ice thickness and subglacial topography around Lake Vostok. The ice flow across the lake and the landscape setting are closely linked to the geological origin of Lake Vostok. Our data show that Lake Vostok is located along a major geological boundary. Magnetic and gravity data are distinct east and west of the lake, as is the roughness of the subglacial topography. The physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake's circulation. Lake Vostok is a tectonically controlled subglacial lake. The tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small, but significant amounts of thermal energy into the lake. ?? 2002 Elsevier Science B.V. All rights reserved.

  13. Local response of a glacier to annual filling and drainage of an ice-marginal lake

    USGS Publications Warehouse

    Walder, J.S.; Trabant, D.C.; Cunico, M.; Fountain, A.G.; Anderson, S.P.; Anderson, R. Scott; Malm, A.

    2006-01-01

    Ice-marginal Hidden Creek Lake, Alaska, USA, outbursts annually over the course of 2-3 days. As the lake fills, survey targets on the surface of the 'ice dam' (the glacier adjacent to the lake) move obliquely to the ice margin and rise substantially. As the lake drains, ice motion speeds up, becomes nearly perpendicular to the face of the ice dam, and the ice surface drops. Vertical movement of the ice dam probably reflects growth and decay of a wedge of water beneath the ice dam, in line with established ideas about jo??kulhlaup mechanics. However, the distribution of vertical ice movement, with a narrow (50-100 m wide) zone where the uplift rate decreases by 90%, cannot be explained by invoking flexure of the ice dam in a fashion analogous to tidal flexure of a floating glacier tongue or ice shelf. Rather, the zone of large uplift-rate gradient is a fault zone: ice-dam deformation is dominated by movement along high-angle faults that cut the ice dam through its entire thickness, with the sense of fault slip reversing as the lake drains. Survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. The horizontal strain rate also undergoes a reversal across this zone, being compressional as the lake fills, but extensional as the lake drains. Frictional resistance to fault-block motion probably accounts for the fact that lake level falls measurably before the onset of accelerated horizontal motion and vertical downdrop. As the overall fault pattern is the same from year to year, even though ice is lost by calving, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as ice is advected toward the lake basin.

  14. Ice-cover variability on shallow lakes at high latitudes: model simulations and observations

    NASA Astrophysics Data System (ADS)

    Duguay, Claude R.; Flato, Greg M.; Jeffries, Martin O.; Ménard, Patrick; Morris, Kim; Rouse, Wayne R.

    2003-12-01

    A one-dimensional thermodynamic model for simulating lake-ice phenology is presented and evaluated. The model can be driven with observed daily or hourly atmospheric forcing of air temperature, relative humidity, wind speed, cloud amount and snowfall. In addition to computing the energy balance components, key model output includes the temperature profile at an arbitrary number of levels within the ice/snow (or the water temperature if there is no ice) and ice thickness (clear ice and snow-ice) on a daily basis, as well as freeze-up and break-up dates. The lake-ice model is used to simulate ice-growth processes on shallow lakes in arctic, sub-arctic, and high-boreal forest environments. Model output is compared with field and remote sensing observations gathered over several ice seasons. Simulated ice thickness, including snow-ice formation, compares favourably with field measurements. Ice-on and ice-off dates are also well simulated when compared with field and satellite observations, with a mean absolute difference of 2 days. Model simulations and observations illustrate the key role that snow cover plays on the seasonal evolution of ice thickness and the timing of spring break-up. It is also shown that lake morphometry, depth in particular, is a determinant of ice-off dates for shallow lakes at high latitudes. Copyright

  15. Ice patterns and hydrothermal plumes, Lake Baikal, Russia - Insights from Space Shuttle hand-held photography

    NASA Technical Reports Server (NTRS)

    Evans, Cynthia A.; Helfert, Michael R.; Helms, David R.

    1992-01-01

    Earth photography from the Space Shuttle is used to examine the ice cover on Lake Baikal and correlate the patterns of weakened and melting ice with known hydrothermal areas in the Siberian lake. Particular zones of melted and broken ice may be surface expressions of elevated heat flow in Lake Baikal. The possibility is explored that hydrothermal vents can introduce local convective upwelling and disrupt a stable water column to the extent that the melt zones which are observed in the lake's ice cover are produced. A heat flow map and photographs of the lake are overlaid to compare specific areas of thinned or broken ice with the hot spots. The regions of known hydrothermal activity and high heat flow correlate extremely well with circular regions of thinned ice, and zones of broken and recrystallized ice. Local and regional climate data and other sources of warm water, such as river inlets, are considered.

  16. Shifting ice regimes of Arctic thermokarst lakes and implications for permafrost and surface-water dynamics

    NASA Astrophysics Data System (ADS)

    Arp, C. D.; Jones, B.; Urban, F. E.; Grosse, G.; Whitman, M.

    2011-12-01

    Thermokarst lakes cover >20% of the landscape throughout much of the Arctic Coastal Plain (ACP) of northern Alaska with shallow lakes freezing solid (grounded ice) and deeper lakes maintaining perennial liquid water (floating ice). Thus, lake depth relative to maximum ice thickness represents an important threshold that impacts permafrost, aquatic habitat, and potentially geomorphic and hydrologic behavior. We studied coupled hydrogeomorphic processes of 13 lakes in the Teshekpuk Lake Special Area (TLSA) representing a depth gradient across this threshold of maximum ice thickness by analyzing remotely sensed imagery, water quality surveys, and climatic data over a 35-year period. Shoreline erosion rates due to permafrost degradation ranged from <0.2 m/yr in very shallow lakes (0.4 m) up to 1.8 m/yr in the deepest lakes (2.6 m) and appear to be partly linked to variation in mean annual lake temperature (MALT). This pattern of thermokarst expansion masked detection of lake hydrologic change using remotely sensed imagery except for the shallowest lakes with stable shorelines. Changes in the surface area of these shallow lakes tracked interannual variation in precipitation minus evaporation (P-E) with periods of full and nearly dry basins. Our analysis suggests that grounded-ice lakes are ice-free on average 37 days longer than floating-ice lakes resulting in a longer period of evaporative loss and more frequent negative P-E. These results suggest divergent hydrogeomorphic responses to a changing Arctic climate depending on the threshold created by water depth relative to maximum ice thickness in ACP lakes. With respect to these findings there is particular interest in ACP lakes of depths encompassing the range of interannual variation in maximum ice thickness because these lakes will most readily show a shift of ice regimes with either a change in water balance or ice growth. For instance, a positive summer P-E and slow winter ice growth can result in a higher

  17. Perennially ice-covered Lake Hoare, Antarctica: physical environment, biology and sedimentation

    NASA Technical Reports Server (NTRS)

    Wharton, R. A. Jr; Simmons, G. M. Jr; McKay, C. P.; Wharton RA, J. r. (Principal Investigator)

    1989-01-01

    Lake Hoare (77 degrees 38' S, 162 degrees 53' E) is a perennially ice-covered lake at the eastern end of Taylor Valley in southern Victoria Land, Antarctica. The environment of this lake is controlled by the relatively thick ice cover (3-5 m) which eliminates wind generated currents, restricts gas exchange and sediment deposition, and reduces light penetration. The ice cover is in turn largely controlled by the extreme seasonality of Antarctica and local climate. Lake Hoare and other dry valley lakes may be sensitive indicators of short term (< 100 yr) climatic and/or anthropogenic changes in the dry valleys since the onset of intensive exploration over 30 years ago. The time constants for turnover of the water column and lake ice are 50 and 10 years, respectively. The turnover time for atmospheric gases in the lake is 30-60 years. Therefore, the lake environment responds to changes on a 10-100 year timescale. Because the ice cover has a controlling influence on the lake (e.g. light penetration, gas content of water, and sediment deposition), it is probable that small changes in ice ablation, sediment loading on the ice cover, or glacial meltwater (or groundwater) inflow will affect ice cover dynamics and will have a major impact on the lake environment and biota.

  18. First evidence of testate amoebae in Lago Fagnano (54° S), Tierra del Fuego (Argentina): Proxies to reconstruct environmental changes

    NASA Astrophysics Data System (ADS)

    Caffau, Mauro; Lenaz, Davide; Lodolo, Emanuele; Zecchin, Massimo; Comici, Cinzia; Tassone, Alejandro

    2015-12-01

    We report here the first findings of testate amoebae at high southern latitudes (54° S) from four gravity cores recovered in the Lago Fagnano (Tierra del Fuego, Argentina), where twelve taxa have been recognized. Among them, Centropyxis constricta "constricta", Centropyxis elongata, Difflugia globulus, Difflugia oblonga "oblonga", and Difflugia protaeiformis "amphoralis" are always present, while other taxa are randomly distributed. According to the sand/silt ratio in the different cores, the Total Organic Carbon content and the Carbon/Nitrogen ratio, as well as the presence/disappearance and abundance of testate amoebae from cluster analysis, we infer a correlation between major textural/granulometrical changes found in the cores and environmental changes. A seismic event occurred on 1949, which substantially modified the morphology of the eastern Lago Fagnano shoreline and the supply pattern from two main eastern tributaries of the lake, is recorded in the studied cores. This event has in part modified the distribution of testate amoebae taxa within the studied cores. Present results show that testate amoebae represent important indicators to detect changes occurring in the environment in which they live.

  19. A C-band backscatter model for lake ice in Alaska

    NASA Technical Reports Server (NTRS)

    Wakabayashi, H.; Weeks, W. F.; Jeffries, M. O.

    1993-01-01

    ERS-1 SAR imagery of lake ice growing on shallow tundra lakes in northern Alaska shows interesting radar backscatter variations. Based on the analysis of ice cores from these lakes, a multi-layer backscatter model comprised of the following elements has been developed: (1) specular air-ice; ice-water and ice-frozen soil boundaries; (2) an ice layer of variable thickness; (3) ice sub-layers with air inclusions of variable density, size and shape including spheres, prolate spheroids, and cylinders of finite length. Preliminary model results confirm that backscatter is a sensitive function of greater reflectivity than from an ice-frozen soil interface. The model has also been tested using bubble data derived from ice cores in April 1992. The modelled backscatter is compared with backscatter derived from ERS-1 SAR images obtained at the same time as the fieldwork.

  20. The influence of a model subglacial lake on ice dynamics and internal layering

    NASA Astrophysics Data System (ADS)

    Gudlaugsson, Eythor; Humbert, Angelika; Kleiner, Thomas; Kohler, Jack; Andreassen, Karin

    2016-04-01

    As ice flows over a subglacial lake, the drop in bed resistance leads to an increase in ice velocities and a draw down of isochrones and cold ice. The ice surface flattens as it adjusts to the lack of resisting forces at the base. The rapid transition in velocity induces changes in ice viscosity and releases deformation energy that can raise the temperature locally. Recent studies of Antarctic subglacial lakes indicate that many lakes experience very fast and possibly episodic drainage, during which the lake size is rapidly reduced as water flows out. Questions that arise are what effect this would have on internal layers within the ice and whether such past drainage events could be inferred from isochrone structures downstream. Here, we study the effect of a subglacial lake on ice dynamics as well as the influence that such short timescale drainage would have on the internal layers of the ice. To this end, we use a full Stokes, polythermal ice flow model. An enthalpy-gradient method is used to account for the evolution of temperature and water content within the ice. We find that a rapid transition between slow-moving ice outside the lake, and full sliding over the lake, can release considerable amounts of deformational energy, with the potential to form a temperate layer at depth in the transition zone. In addition, we provide an explanation for a characteristic surface feature commonly seen at the edges of subglacial lakes, a hummocky surface depression in the transition zone between little to full sliding. We also conclude that rapid changes in the horizontal extent of subglacial lakes and slippery patches, compared to the average ice column velocity, can create a traveling wave at depth within the isochrone structure that transfers downstream with the advection of ice, thus indicating the possibility of detecting past drainage events with ice penetrating radar.

  1. Climatic changes near the Great Lakes inferred from 141 year ice records

    USGS Publications Warehouse

    Assel, Raymond A.; Robertson, Dale M.

    1992-01-01

    Freeze-up and break-up dates and duration of ice cover for lakes and rivers represent an integration of weather conditions prior to the specified event(s). Changes in mean ice conditions may be used as quantitative indicators of climatic changes if long homogenous ice records are accompanied by sufficiently homogenous air temperature records to calibrate the changes in mean ice cover in terms of climatic variables. Historical ice records dating back to 1855 are available for Lake Mendota, WI (located on the southwestern side of Lake Michigan) and back to 1851 for Grand Traverse Bay, MI (located on the northeastern side of Lake Michigan). Changes in the mean ice cover of these two systems were used to describe changes in fall, winter, and spring air temperatures in the area near the Great Lakes during the past 141 years. 

  2. Shifting balance of thermokarst lake ice regimes across the Arctic Coastal Plain of northern Alaska

    USGS Publications Warehouse

    Arp, Christopher D.; Jones, Benjamin M.; Lu, Zong; Whitman, Matthew S.

    2012-01-01

    The balance of thermokarst lakes with bedfast- and floating-ice regimes across Arctic lowlands regulates heat storage, permafrost thaw, winter-water supply, and over-wintering aquatic habitat. Using a time-series of late-winter synthetic aperture radar (SAR) imagery to distinguish lake ice regimes in two regions of the Arctic Coastal Plain of northern Alaska from 2003–2011, we found that 18% of the lakes had intermittent ice regimes, varying between bedfast-ice and floating-ice conditions. Comparing this dataset with a radar-based lake classification from 1980 showed that 16% of the bedfast-ice lakes had shifted to floating-ice regimes. A simulated lake ice thinning trend of 1.5 cm/yr since 1978 is believed to be the primary factor driving this form of lake change. The most profound impacts of this regime shift in Arctic lakes may be an increase in the landscape-scale thermal offset created by additional lake heat storage and its role in talik development in otherwise continuous permafrost as well as increases in over-winter aquatic habitat and winter-water supply.

  3. Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

    NASA Astrophysics Data System (ADS)

    Livingstone, S. J.; Clark, C. D.; Woodward, J.; Kingslake, J.

    2013-11-01

    We use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of >60% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are observed. Hence we suggest that thousands of subglacial lakes remain to be found. Applying our technique to the Greenland Ice Sheet, where very few subglacial lakes have so far been observed, recalls 1607 potential lake locations, covering 1.2% of the bed. Our results will therefore provide suitable targets for geophysical surveys aimed at identifying lakes beneath Greenland. We also apply the technique to modelled past ice-sheet configurations and find that during deglaciation both ice sheets likely had more subglacial lakes at their beds. These lakes, inherited from past ice-sheet configurations, would not form under current surface conditions, but are able to persist, suggesting a retreating ice-sheet will have many more subglacial lakes than advancing ones. We also investigate subglacial drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are suggested to have been susceptible to subglacial drainage switching. We discuss how our results impact our understanding of meltwater drainage, basal lubrication and ice-stream formation.

  4. The influence of a model subglacial lake on ice dynamics and internal layering

    NASA Astrophysics Data System (ADS)

    Gudlaugsson, E.; Humbert, A.; Kleiner, T.; Kohler, J.; Andreassen, K.

    2015-07-01

    As ice flows over a subglacial lake, the drop in bed resistance leads to an increase in ice velocities and a subsequent draw-down of isochrones and cold ice from the surface. The ice surface flattens as it adjusts to the lack of resisting forces at the base. The rapid transition in velocity induces changes in temperature and ice viscosity, releasing deformation energy which raises the temperature locally. Recent studies of Antarctic subglacial lakes indicate that many lakes experience very fast and possibly episodic drainage, during which the lake size is rapidly reduced as water flows out. A question is what effect this would have on internal layers within the ice, and whether such past events could be inferred from isochrone structures downstream. Here, we study the effect of a subglacial lake on the dynamics of a model ice stream as well as the influence that such short timescale drainage would have on the internal layers of the ice. To this end, we use a Full-Stokes, polythermal ice flow model. An enthalpy gradient method is used to account for the evolution of temperature and water content within the ice. We find that the rapid transition between slow-moving ice outside the lake, and full sliding over the lake, releases large amounts of deformational energy, which has the potential to form a temperate layer at depth in the transition zone. In addition, we provide an explanation for a characteristic surface feature, commonly seen at the edges of subglacial lakes, a hummocky surface depression in the transition zone between little to full sliding. We also conclude that rapid changes in lake geometry or basal friction create a travelling wave at depth within the isochrone structure that transfers downstream with the advection of ice, thus indicating the possibility of detecting past events with ice penetrating radar.

  5. Triple Isotope Water Measurements of Lake Untersee Ice using Off-Axis ICOS

    NASA Astrophysics Data System (ADS)

    Berman, E. S.; Huang, Y. W.; Andersen, D. T.; Gupta, M.; McKay, C. P.

    2015-12-01

    Lake Untersee (71.348°S, 13.458°E) is the largest surface freshwater lake in the interior of the Gruber Mountains of central Queen Maud Land in East Antarctica. The lake is permanently covered with ice, is partly bounded by glacier ice and has a mean annual air temperature of -10°C. In contrast to other Antarctic lakes the dominating physical process controlling ice-cover dynamics is low summer temperatures and high wind speeds resulting in sublimation rather than melting as the main mass-loss process. The ice-cover of the lake is composed of lake-water ice formed during freeze-up and rafted glacial ice derived from the Anuchin Glacier. The mix of these two fractions impacts the energy balance of the lake, which directly affects ice-cover thickness. Ice-cover is important if one is to understand the physical, chemical, and biological linkages within these unique, physically driven ecosystems. We have analyzed δ2H, δ18O, and δ17O from samples of lake and glacier ice collected at Lake Untersee in Dec 2014. Using these data we seek to answer two specific questions: Are we able to determine the origin and history of the lake ice, discriminating between rafted glacial ice and lake water? Can isotopic gradients in the surface ice indicate the ablation (sublimation) rate of the surface ice? The triple isotope water analyzer developed by Los Gatos Research (LGR 912-0032) uses LGR's patented Off-Axis ICOS (Integrated Cavity Output Spectroscopy) technology and incorporates proprietary internal thermal control for high sensitivity and optimal instrument stability. This analyzer measures δ2H, δ18O, and δ17O from water, as well as the calculated d-excess and 17O-excess. The laboratory precision in high performance mode for both δ17O and δ18O is 0.03 ‰, and for δ2H is 0.2 ‰. Methodology and isotope data from Lake Untersee samples are presented. Figure: Ice samples were collected across Lake Untersee from both glacial and lake ice regions for this study.

  6. Index for hazard of Glacier Lake Outburst flood of Lake Merzbacher by satellite-based monitoring of lake area and ice cover

    NASA Astrophysics Data System (ADS)

    Xie, Zunyi; ShangGuan, Donghui; Zhang, Shiqiang; Ding, Yongjian; Liu, Shiyin

    2013-08-01

    Previous studies show that the area of a moraine-dammed lake can provide a good indicator of the significance of its outburst. For a glacier-dammed lake however, because its area and depth fluctuates with the melting of its ice dam, it is difficult to predict the outburst of the glacier-dammed lake by using its area alone.A characteristic of the surface of Lake Merzbacher is a large amount of floating ice therefore, a method is proposed in this article to extract the area of floating ice on the lake and the area of ice free water in the lake by using Environment and Disaster Monitoring Small Satellite images respectively. Furthermore, based on the area of floating ice extracted through the image information of Lake Merzbacher in 2009 and 2010, we determined the relationship between the ice area and the outburst of the lake, then formulated the Index for hazard of Glacier Lake Outburst Flood (IGLOF) of Lake Merzbacher, which cannot only predict the flood outburst, but also determine the specific outburst period after the lake drainage had occurred. This can be shown in a recalculation of the lake drainages in the years 2009 and 2010. Research results indicate that when IGLOF is less than 0.5 and the lake area is larger than 3 km2, the outburst process is in early-warning period and GLOF will occur in the next 5-8 days. Also, the successful outburst prediction of Lake Merzbacher in 2011 showed that the index described in this paper provides a quick methodology for forecasting and warning against Lake Merzbacher outburst floods. However,as our research was based on a short observation period (2009-2011) and also cannot be supplemented by other images, it will still be needed to be checked and validated by continuous observation and improvement in future.

  7. Changes in ice cover thickness and lake level of Lake Hoare, Antarctica - Implications for local climatic change

    NASA Technical Reports Server (NTRS)

    Wharton, Robert A., Jr.; Mckay, Christopher P.; Clow, Gary D.; Andersen, Dale T.; Simmons, George M., Jr.; Love, F. G.

    1992-01-01

    Results are reported from 10 years of ice-thickness measurements at perennially ice-covered Lake Hoare in southern Victoria Land, Antarctica. The ice cover of this lake had been thinning steadily at a rate exceeding 20 cm/yr during the last decade but seems to have recently stabilized at a thickness of 3.3 m. Data concerning lake level and degree-days above freezing are presented to show the relationship between peak summer temperatures and the volume of glacier-derived meltwater entering Lake Hoare each summer. From these latter data it is inferred that peak summer temperatures have been above 0 C for a progressively longer period of time each year since 1972. Possible explanations for the thinning of the lake ice are considered. The thickness of the ice cover is determined by the balance between freezing during the winter and ablation that occurs all year but maximizes in summer. It is suggested that the term most likely responsible for the change in the ice cover thickness at Lake Hoare is the extent of summer melting, consistent with the rising lake levels.

  8. Winter 1994 Weather and Ice Conditions for the Laurentian Great Lakes.

    NASA Astrophysics Data System (ADS)

    Assel, Raymond A.; Janowiak, John E.; Young, Sharolyn; Boyce, Daron

    1996-01-01

    The Laurentian Great Lakes developed their most extensive ice cover in over a decade during winter 1994 [December-February 1993/94 (DJF 94)]. Extensive midlake ice formation started the second half of January, about 2 weeks earlier than normal. Seasonal maximal ice extent occurred in early February, again about 2 weeks earlier than normal. Winter 1994 maximum (normal) ice coverages on the Great Lakes are Lake Superior 96% (75%), Lake Michigan 78% (45%), Lake Huron 95% (68%), Lake Erie 97% (90%), and Lake Ontario 67% (24%). Relative to the prior 31 winters (1963-93), the extent of seasonal maximal ice cover for winter 1994 for the Great Lakes taken as a unit is exceeded by only one other winter (1979); however, other winters for individual Great Lakes had similar maximal ice covers.Anomalously strong anticyclonic circulation over the central North Pacific (extending to the North Pole) and an abnormally strong polar vortex centered over northern Hudson Bay combined to produce a circulation pattern that brought frequent air masses of Arctic and polar origin to the eastern third of North America. New records were set for minimum temperatures on 19 January 1994 at many locations in the Great Lakes region. A winter severity index consisting of the average November-February air temperatures averaged over four sites on the perimeter of the Great Lakes (Duluth, Minnesota; Sault Ste. Marie, Michigan; Detroit, Michigan; and Buffalo, New York) indicates that winter 1994 was the 21st coldest since 1779. The unseasonably cold air temperatures produced much-above-normal ice cover over the Great Lakes and created problems for lake shipping. Numerous fatalities and injuries were attributed to the winter weather, which included several ice and snow storms. The much-below-normal air temperatures resulted in enhanced lake-effect snowfall along downwind lake shores, particularly during early to midwinter, prior to extensive ice formation in deeper lake areas. The low air temperatures

  9. Oxygen supersaturation in ice-covered Antarctic lakes - Biological versus physical contributions

    NASA Technical Reports Server (NTRS)

    Craig, H.; Wharton, R. A., Jr.; Mckay, C. P.

    1992-01-01

    Lake Hoare is one of a number of ice-covered polar lakes in the Dry Valley Region of southern Victoria Land, Antarctica. Analysis of N2, O2, and Ar in bubbles from this lake's ice indicates that while O2 is about 2.4 times supersaturated in the water below the ice, only 11 percent of the O2 input to this lake is due to biological activity and the balance is derived from meltwater inflow. In Lake Hoare, as much as 70 percent of total gas loss may occur by advection through the ice cover; the remaining gas fractions are removed by respiration at the lower boundary in the case of O2, and by molecular exchange with the atmosphere in the peripheral summer moat around the ice.

  10. Characterizing C-band backscattering from thermokarst lake ice on the Qinghai-Tibet Plateau

    NASA Astrophysics Data System (ADS)

    Tian, Bangsen; Li, Zhen; Engram, Melanie J.; Niu, Fujun; Tang, Panpan; Zou, Pengfei; Xu, Juan

    2015-06-01

    On the basis of weather observations and field measurements of lake ice, this study investigates multi-temporal C-band VV-polarized radar backscattering values from the thermokarst lakes and alpine meadow on the QTP during the period 2003-2010. In order to understand the scattering mechanism of lake ice, a scattering model is developed for lake ice that updates some assumptions adopted in previously developed models, including the roughness of the ice-water interface and the shape of vertically stacked centimeter-sized bubbles in the lake ice. We conclude the following: First, with a incidence angle range near 24°, the backscattering intensities of C-band VV-polarized ENVISAT-ASAR data exhibit a strong dependence on time, which is related to the processes of ice growth and decay on the QTP. Some unique backscattering characteristics of lake ice in this high-altitude region, as compared to those for high-latitude regions, are also discussed and documented in the paper. Secondly, the timing of lake ice-on in fall and ice-off in spring for this region can be identified in radar images by using a threshold of -12 dB for the backscatter intensity of the surrounding alpine meadow. Finally, the results of applying the scattering model indicate that surface scattering from the ice-water interface and volume scattering from gas bubbles embedded in the lake ice are the dominant scattering mechanisms for C-band VV polarized SAR and that the roughness of the ice-water interface and also bubble size are the most sensitive factors.

  11. Lake ice records used to detect historical and future climatic changes

    USGS Publications Warehouse

    Robertson, Dale M.; Ragotzkie, R.A.; Magnuson, John J.

    1992-01-01

    With the relationships between air temperature and freeze and break up dates, we can project how the ice cover of Lake Mendota should respond to future climatic changes. If warming occurs, the ice cover for Lake Mendota should decrease approximately 11 days per 1 °C increase. With a warming of 4 to 5 °C, years with no ice cover should occur in approximately 1 out of 15 to 30 years.

  12. Biological Diversity Comprising Microbial Structures of Antarctic Ice Covered Lakes

    NASA Astrophysics Data System (ADS)

    Matys, E. D.

    2015-12-01

    Analysis of microbial membrane lipids is a rapid and non-selective method for evaluating the composition of microbial communities. To fully realise the diagnostic potential of these lipids, we must first understand their structural diversity, biological sources, physiological functions, and pathways of preservation. Particular environmental conditions likely prompt the production of different membrane lipid structures. Antarctica's McMurdo Dry Valleys host numerous ice-covered lakes with sharp chemical gradients that vary in illumination, geochemical structure, and benthic mat morphologies that are structured by nutrient availability and water chemistry. The lipid contents of these benthic mats have not received extensive study nor have the communities yet been thoroughly characterized. Accordingly, a combination of lipid biomarker and nucleic acid sequence data provides the means of assessing species diversity and environmental controls on the composition and diversity of membrane lipid assemblages. We investigated the richness and diversity of benthic microbial communities and accumulated organic matter in Lake Vanda of the McMurdo Dry Valleys. We have identified diverse glycolipids, aminolipids, and phospholipids in addition to many unknown compounds that may be specific to these particular environments. Light levels fluctuate seasonally, favoring low-light-tolerant cyanobacteria and specific lipid assemblages. Adaptations to nutrient limitations are reflected in contrasting intact polar lipid assemblages. For example, under P-limiting conditions, phospholipids are subsidiary to membrane-forming lipids that do not contain P (i.e. ornithine, betaine, and sulfolipids). The bacteriohopanepolyol (BHP) composition is dominated by bacteriohopanetetrol (BHT), a ubiquitous BHP, and 2-methylhopanoids. The relative abundance of 2-methylhopanoids is unprecedented and may reflect the unusual seasonal light regime of this polar environment. By establishing correlations

  13. Coast Guard/NOAA/NASA Great Lakes Project Icewarn. [ice mapping for winter navigation

    NASA Technical Reports Server (NTRS)

    Brennan, T. D.; Gedney, R. T.

    1975-01-01

    The operational feasibility of using remote sensing to provide all weather ice formation for Great Lakes winter navigation is explored. A combination airborne pulsed radar system to measure actual ice thickness, a satellite data link system, and a hand drawn interpretive ice chart proved valuable for extending winter navigation through the icepack.

  14. Microbiological and Biogeochemical Investigations of the Accreted Ice Above Subglacial Lake Vostok, Antarctica

    NASA Astrophysics Data System (ADS)

    Christner, B. C.; Foreman, C. F.; Arnold, B. R.; Welch, K. A.; Lyons, W. B.; Priscu, J. C.

    2004-12-01

    Subglacial Lake Vostok is located ~4 km beneath the surface of the East Antarctic ice sheet and has been isolated from the atmosphere for at least 15 million years. The lake has a surface area near 14,000 km2 and a depth exceeding 1000 m. While the nature of the environment within Subglacial Lake Vostok remains uncertain, if a sustained microbial ecosystem is present, life in this subsurface environment operates under arguably the most extreme conditions in the biosphere (i.e., high pressure, constant cold, high oxygen concentrations, and no light). The lake represents an analogue for ecosystems that may exist in Europa's ice-covered ocean and also provides an Earthly-based model for the evaluation of technology to search for life in icy extraterrestrial subsurface environments. Concerns for environmental protection have prevented direct sampling of the lake water thus far, as a prudent sampling plan that will not contaminate this pristine environment has yet to be developed and tested. However, an ice core has been retrieved at Vostok Station in which the bottom ~85 meters consists of lake water that has accreted to the bottom of the ice sheet, providing frozen samples of water from the lakes' surface. The ice from 3539 to 3609 mbs (accretion ice I) contains visible inclusions due to accretion in the shallow embayment or western grounding line, whereas ice from 3610-3623 mbs (accretion ice II) is very clean, forming above the deep eastern basin of the main lake. Using a multifaceted protocol to monitor cellular and molecular decontamination of ice cores, we show that the microbiology and geochemistry (i.e., dissolve organic carbon, nutrients, and ions) of accretion ice is very different from the overlying glacial ice. The numbers of cells are 2- to 7-fold higher in accretion ice I than in the overlying glacial ice, and decrease with increasing depth in accretion ice II. Cell viability in accretion ice samples has been confirmed by the measurable respiration of 14C

  15. ERS-1 SAR backscatter changes associated with ice growing on shallow lakes in Arctic Alaska

    NASA Technical Reports Server (NTRS)

    Jeffries, M. O.; Wakabayashi, H.; Weeks, W. F.

    1993-01-01

    Spatial and temporal backscatter intensity (sigma(sup o)) variations from ice growing on shallow lakes during winter 1991-92 near Barrow, NW Alaska, have been quantified for the first time using ERS-I C-band SAR data acquired at the Alaska SAR Facility. A field and laboratory validation program, including measurements of the thickness and structure-stratigraphy of the ice, indicates that sigma(sup o) values are strongly dependent on whether the ice freezes to the lake bottom, or remains afloat. Backscatter intensity decreases significantly when the ice grounds on the bottom. Strong backscatter from floating ice is attributed to a specular ice-water interface and vertically oriented tubular bubbles. During the spring thaw, backscatter undergoes a reversal; sigma(sup o) values from ice that was grounded increase, while sigma(sup o) values from ice that was afloat decrease. This phenomenon has not previously been reported.

  16. Modeling the impediment of methane ebullition bubbles by seasonal lake ice

    DOE PAGES

    Greene, S.; Walter Anthony, K. M.; Archer, D.; Sepulveda-Jauregui, A.; Martinez-Cruz, K.

    2014-07-15

    Microbial methane (CH4) ebullition (bubbling) from anoxic lake sediments comprises a globally significant flux to the atmosphere, but ebullition bubbles in temperate and polar lakes can be trapped by winter ice cover and later released during spring thaw. This "ice-bubble storage" (IBS) constitutes a novel mode of CH4 emission. Before bubbles are encapsulated by downward-growing ice, some of their CH4 dissolves into the lake water, where it may be subject to oxidation. We present field characterization and a model of the annual CH4 cycle in Goldstream Lake, a thermokarst (thaw) lake in interior Alaska. We find that summertime ebullition dominatesmore » annual CH4 emissions to the atmosphere. Eighty percent of CH4 in bubbles trapped by ice dissolves into the lake water column in winter, and about half of that is oxidized. The ice growth rate and the magnitude of the CH4 ebullition flux are important controlling factors of bubble dissolution. Seven percent of annual ebullition CH4 is trapped as IBS and later emitted as ice melts. In a future warmer climate, there will likely be less seasonal ice cover, less IBS, less CH4 dissolution from trapped bubbles, and greater CH4 emissions from northern lakes.« less

  17. Modeling the impediment of methane ebullition bubbles by seasonal lake ice

    DOE PAGES

    Greene, S.; Walter Anthony, K. M.; Archer, D.; Sepulveda-Jauregui, A.; Martinez-Cruz, K.

    2014-12-08

    Microbial methane (CH4) ebullition (bubbling) from anoxic lake sediments comprises a globally significant flux to the atmosphere, but ebullition bubbles in temperate and polar lakes can be trapped by winter ice cover and later released during spring thaw. This "ice-bubble storage" (IBS) constitutes a novel mode of CH4 emission. Before bubbles are encapsulated by downward-growing ice, some of their CH4 dissolves into the lake water, where it may be subject to oxidation. We present field characterization and a model of the annual CH4 cycle in Goldstream Lake, a thermokarst (thaw) lake in interior Alaska. We find that summertime ebullition dominatesmore » annual CH4 emissions to the atmosphere. Eighty percent of CH4 in bubbles trapped by ice dissolves into the lake water column in winter, and about half of that is oxidized. The ice growth rate and the magnitude of the CH4 ebullition flux are important controlling factors of bubble dissolution. Seven percent of annual ebullition CH4 is trapped as IBS and later emitted as ice melts. In a future warmer climate, there will likely be less seasonal ice cover, less IBS, less CH4 dissolution from trapped bubbles, and greater CH4 emissions from northern lakes.« less

  18. Chronological framework for the deglaciation of the Lake Michigan lobe of the Laurentide ice sheet from ice-walled lake deposits

    USGS Publications Warehouse

    Curry, B.; Petras, J.

    2011-01-01

    A revised chronological framework for the deglaciation of the Lake Michigan lobe of the south-central Laurentide Ice Sheet is presented based on radiocarbon ages of plant macrofossils archived in the sediments of low-relief ice-walled lakes. We analyze the precision and accuracy of 15 AMS 14C ages of plant macrofossils obtained from a single ice-walled lake deposit. The semi-circular basin is about 0.72km wide and formed of a 4- to 16-m-thick succession of loess and lacustrine sediment inset into till. The assayed material was leaves, buds and stems of Salix herbacea (snowbed willow). The pooled mean of three ages from the basal lag facies was 18 270??50 14C a BP (21 810cal. a BP), an age that approximates the switch from active ice to stagnating conditions. The pooled mean of four ages for the youngest fossil-bearing horizon was 17 770??40 14C a BP (21 180cal. a BP). Material yielding the oldest and youngest ages may be obtained from sediment cores located at any place within the landform. Based on the estimated settling times of overlying barren, rhythmically bedded sand and silt, the lacustrine environment persisted for about 50 more years. At a 67% confidence level, the dated part of the ice-walled lake succession persisted for between 210 and 860cal. a (modal value: 610cal. a). The deglacial age of five moraines or morainal complexes formed by the fluctuating margin of the Lake Michigan lobe have been assessed using this method. There is no overlap of time intervals documenting when ice-walled lakes persisted on these landforms. The rapid readvances of the lobe during deglaciation after the last glacial maximum probably occurred at some point between the periods of ice-walled lake sedimentation. ?? 2011 John Wiley & Sons, Ltd.

  19. Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica

    NASA Technical Reports Server (NTRS)

    Obryk, M. K.; Doran, P. T.; Hicks, J. A.; McKay, C. P.; Priscu, J. C.

    2016-01-01

    A one-dimensional ice cover model was developed to predict and constrain drivers of long term ice thickness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface radiative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 years (between 1996 and 2012) of ice thickness changes for west lobe of Lake Bonney (average ice thickness = 3.53 m; RMSE = 0.09 m, n = 118) and Lake Fryxell (average ice thickness = 4.22 m; RMSE = 0.21 m, n = 128). Long-term ice thickness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or facilitate ice thickness change depending on the predominant climatic trend (temperature cooling or warming). As such, shallow (< 20 m deep water columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation.

  20. Measurements of supraglacial lake drainage and surface streams over West Greenland and effects on ice dynamics

    NASA Astrophysics Data System (ADS)

    Tedesco, M.; Willis, I. C.; Alexander, P. M.; Banwell, A. F.

    2011-12-01

    During the summer of 2011 we measured the filling and draining of two surface lakes in the Paakitsoq region of the West Greenland Ice Sheet (49.79 W, 69.57 N), together with the level of streams flowing into the basins feeding the lakes. We also used GPS to record the horizontal and vertical movement of the ice sheet surface at five locations surrounding the lakes for a two week period (overlapping the draining of the two lakes). In this talk we report results concerning the processes of lake filling and draining between the two lakes. 'Lake Half Moon', with a smaller catchment area, filled slowly at a steady rate over several days, then drained gradually over a 24 hour period as an existing moulin located outside the bottom of the lake became active; the lake level continued to drop very slowly over the remaining week as the surface stream leading from the lake to the moulin incised. 'Lake Ponting', with the larger catchment area, filled more rapidly and at an accelerating rate as depressions upstream of the lake filled with water, overflowed and delivered increasing volumes of water to the lake. Lake Ponting drained by hydrofracture following a particularly rapid rise in water level, generating a new ~ 800m long extensional crevasse on the ice sheet surface. The entire ~ 3 x 106 m3 lake drained within a few hours. For the Lake Pointing, we show, for the first time, a movie of the lake draining, showing many features that we observed right after its drainage. The rate of lake level lowering during the drainage varied; initially moderately rapid while the fractures formed and accommodated the water, then exceptionally rapid as the fractures reached the bed allowing the lake to drain completely. The analysis of the GPS data suggest that the different styles of lake draining affect the vertical and horizontal movement of the ice sheet in different ways. We also anticipate that the effect of the draining of Lake Ponting was affecting the GPS sensors in a different

  1. An interesting natural phenomenon - giant rings on Lake Baikal ice

    NASA Astrophysics Data System (ADS)

    Kouraev, Alexei; Shimaraev, Michail; Remy, Frederique; Ivanov, Andrei; Golubov, Boris

    2010-05-01

    Starting from May 2009 scientific community and large public have been puzzled by the formation of giant rings on Baikal ice. These rings (diameter 5-7 km, thickness of dark layer - 1 - 1.8 km) have almost perfect circular shape what makes them so interesting and attractive not only to scientists, but also for large public. . The rings have been observed since 1999 by various satellites and sensors (AVHRR, MODIS, Landsat, SPOT) as early as 1999 but probably also in 1984 and 1994 (Shuttle missions). These rings are usually well observed in April, when snow cover is thin or absent. Rings have been observed in the southern tip of the lake (2009), and in three places in the central part: near Krestovskiy cape (1999, 2003, 2005 and 2008), near Turka (2008), and near Cape Nizhnee Izgolovye (2009). All these places are located in the region of steep bottom topography, over depths of more than 500 m. According to in situ measurements done by the Limnological Institute in Irkutsk in 2009, ice thickness is about 70 cm in the center and on the outside of the ring, and 40 cm in the ring itself. It is known that the Baikal lake has important hydrothermal activity, and there are numerous observations of gas (methane etc) seepage from its 7 km-thick layer of bottom sediments. Local-scale absence of ice cover (steamthroughs or "propariny") is typical for some places in Lake Baikal. They result from gas emissions (associated with rise of warm water), near capes and straits (due to better vertical mixing), thermal sources, outlets of large rivers. Often they are observed near Capes Big and Small Kadil'niy, and in the Olkhonskiye vorota strait. However they size ranges from just a half a meter to several hundreds of meters (but not several kilometers) and this could not be an explanation for the formation of giant rings. We present several existing hypotheses of the origin of these rings including gas emission, heat flux, cyclonic subsurface currents and mega-bubble formation due to

  2. Stratigraphy of Lake Vida, Antarctica: hydrologic implications of 27 m of ice

    NASA Astrophysics Data System (ADS)

    Dugan, H. A.; Doran, P. T.; Wagner, B.; Kenig, F.; Fritsen, C. H.; Arcone, S. A.; Kuhn, E.; Ostrom, N. E.; Warnock, J. P.; Murray, A. E.

    2015-03-01

    Lake Vida, located in Victoria Valley, is one of the largest lakes in the McMurdo dry valleys and is known to contain hypersaline liquid brine sealed below 16 m of freshwater ice. For the first time, Lake Vida was drilled to a depth of 27 m. Below 21 m the ice is marked by well-sorted sand layers up to 20 cm thick within a matrix of salty ice. From ice chemistry, isotopic composition of δ18O and δ2H, and ground penetrating radar profiles, we conclude that the entire 27 m of ice formed from surface runoff and the sediment layers represent the accumulation of surface deposits. Radiocarbon and optically stimulated luminescence dating limit the maximum age of the lower ice to 6300 14C yr BP. As the ice cover ablated downwards during periods of low surface inflow, progressive accumulation of sediment layers insulated and preserved the ice and brine beneath, analogous to the processes that preserve shallow ground ice. The repetition of these sediment layers reveals hydrologic variability in Victoria Valley during the mid- to late Holocene. Lake Vida is an exemplar site for understanding the preservation of subsurface brine, ice, and sediment in a cold desert environment.

  3. Semi-automated Digital Imaging and Processing System for Measuring Lake Ice Thickness

    NASA Astrophysics Data System (ADS)

    Singh, Preetpal

    Canada is home to thousands of freshwater lakes and rivers. Apart from being sources of infinite natural beauty, rivers and lakes are an important source of water, food and transportation. The northern hemisphere of Canada experiences extreme cold temperatures in the winter resulting in a freeze up of regional lakes and rivers. Frozen lakes and rivers tend to offer unique opportunities in terms of wildlife harvesting and winter transportation. Ice roads built on frozen rivers and lakes are vital supply lines for industrial operations in the remote north. Monitoring the ice freeze-up and break-up dates annually can help predict regional climatic changes. Lake ice impacts a variety of physical, ecological and economic processes. The construction and maintenance of a winter road can cost millions of dollars annually. A good understanding of ice mechanics is required to build and deem an ice road safe. A crucial factor in calculating load bearing capacity of ice sheets is the thickness of ice. Construction costs are mainly attributed to producing and maintaining a specific thickness and density of ice that can support different loads. Climate change is leading to warmer temperatures causing the ice to thin faster. At a certain point, a winter road may not be thick enough to support travel and transportation. There is considerable interest in monitoring winter road conditions given the high construction and maintenance costs involved. Remote sensing technologies such as Synthetic Aperture Radar have been successfully utilized to study the extent of ice covers and record freeze-up and break-up dates of ice on lakes and rivers across the north. Ice road builders often used Ultrasound equipment to measure ice thickness. However, an automated monitoring system, based on machine vision and image processing technology, which can measure ice thickness on lakes has not been thought of. Machine vision and image processing techniques have successfully been used in manufacturing

  4. Mapping Of Lake Ice In Northern Europe Using Dual-Polarization RadarSAT-2 Data

    NASA Astrophysics Data System (ADS)

    Hindberg, Heidi; Malnes, Erik

    2013-12-01

    In this paper, we investigate the potential of including cross-polarization data in an unsupervised classification method based on SAR data to determine ice extent over lakes in Northern Europe. By introducing cross-pol data we can increase the separability between open water and ice, and we can decrease misclassifications where open water with waves is classified as ice. Cross-pol data also helps with labelling of the classes. However, cross-pol data can decrease the separability between the classes if the ice on the lake is very thin.

  5. Measurement of lake ice thickness with a short-pulse radar system

    NASA Technical Reports Server (NTRS)

    Cooper, D. W.; Mueller, R. A.; Schertler, R. J.

    1976-01-01

    Measurements of lake ice thickness were made during March 1975 at the Straits of Mackinac by using a short-pulse radar system aboard an all-terrain vehicle. These measurements were compared with ice thicknesses determined with an auger. Over 25 sites were explored which had ice thicknesses in the range 29 to 60 cm. The maximum difference between radar and auger measurements was less than 9.8 percent. The magnitude of the error was less than + or - 3.5 cm. The NASA operating short-pulse radar system used in monitoring lake ice thickness from an aircraft is also described.

  6. The study of fresh-water lake ice using multiplexed imaging radar

    USGS Publications Warehouse

    Leonard, Bryan M.; Larson, R.W.

    1975-01-01

    The study of ice in the upper Great Lakes, both from the operational and the scientific points of view, is receiving continued attention. Quantitative and qualitative field work is being conducted to provide the needed background for accurate interpretation of remotely sensed data. The data under discussion in this paper were obtained by a side-looking multiplexed airborne radar (SLAR) supplemented with ground-truth data.Because of its ability to penetrate adverse weather, radar is an especially important instrument for monitoring ice in the upper Great Lakes. It has previously been shown that imaging radars can provide maps of ice cover in these areas. However, questions concerning both the nature of the surfaces reflecting radar energy and the interpretation of the radar imagery continually arise.Our analysis of ice in Whitefish Bay (Lake Superior) indicates that the combination of the ice/water interlace and the ice/air interface is the major contributor to the radar backscatter as seen on the imagery At these frequencies the ice has a very low relative dielectric permittivity (< 3.0) and a low loss tangent Thus, this ice is somewhat transparent to the energy used by the imaging SLAR system. The ice types studied include newly formed black ice, pancake ice, and frozen and consolidated pack and brash ice.Although ice thickness cannot be measured directly from the received signals, it is suspected that by combining the information pertaining to radar backscatter with data on the meteorological and sea-state history of the area, together with some basic ground truth, better estimates of the ice thickness may be provided. In addition, certain ice features (e.g. ridges, ice-foot formation, areas of brash ice) may be identified with reasonable confidence. There is a continued need for additional ground work to verify the validity of imaging radars for these types of interpretations.

  7. Lake

    ERIC Educational Resources Information Center

    Wien, Carol Anne

    2008-01-01

    The lake is blue black and deep. It is a glaciated finger lake, clawed out of rock when ice retracted across Nova Scotia in a northerly direction during the last ice age. The lake is narrow, a little over a mile long, and deep, 90 to 190 feet in places according to local lore, off the charts in others. The author loves to swim there, with a sense…

  8. Ground penetrating radar detection of subsnow slush on ice-covered lakes in interior Alaska

    NASA Astrophysics Data System (ADS)

    Gusmeroli, A.; Grosse, G.

    2012-12-01

    Lakes are abundant throughout the pan-Arctic region. For many of these lakes ice cover lasts for up to two thirds of the year. The frozen cover allows human access to these lakes, which are therefore used for many subsistence and recreational activities, including water harvesting, fishing, and skiing. Safe traveling condition onto lakes may be compromised, however, when, after significant snowfall, the weight of the snow acts on the ice and causes liquid water to spill through weak spots and overflow at the snow-ice interface. Since visual detection of subsnow slush is almost impossible our understanding on overflow processes is still very limited and geophysical methods that allow water and slush detection are desirable. In this study we demonstrate that a commercially available, lightweight 1 GHz, ground penetrating radar system can detect and map extent and intensity of overflow. The strength of radar reflections from wet snow-ice interfaces are at least twice as much in strength than returns from dry snow-ice interface. The presence of overflow also affects the quality of radar returns from the base of the lake ice. During dry conditions we were able to profile ice thickness of up to 1 m, conversely, we did not retrieve any ice-water returns in areas affected by overflow.

  9. Ice Cover as a Factor Driving Microbial Community Structure in the Laurentian Great Lakes

    NASA Astrophysics Data System (ADS)

    McKay, R. M.; Beall, B.; Oyserman, B.; Smith, D.; Bullerjahn, G.; Morris, P.; Twiss, M. R.

    2013-12-01

    Lakes serve as rapid responding sentinels of human influence on the natural environment rendering them powerful tools to advance our understanding of a changing climate on microbial community structure and function. Whereas we possess a baseline knowledge of microbial diversity in the Great Lakes, we know little about how these communities respond to the manifestations of climate change. Through collaboration with U.S.- and Canadian Coast Guards, winter surveys have been conducted on Lake Erie since 2007. The surveys have captured extremes in ice extent ranging from expansive ice cover through 2011 to nearly ice-free waters in winter 2012, a condition driven by a warm positive Arctic Oscillation. We showed that dramatic changes in annual ice cover were accompanied by equally dramatic shifts in phytoplankton community structure. Expansive ice cover documented for Lake Erie in winters 2010 and 2011 supported ice-associated phytoplankton blooms dominated by physiologically robust, filamentous centric diatoms. Transcriptomic analysis of the winter bloom offers insights into the success of this psychrophilic community. By comparison, ice free conditions promoted the growth of small-sized cells supported by analysis of size-fractionated chlorophyll a and flow cytometry. The phytoplankton community in winter 2013 was dominated by microplankton-sized filamentous diatoms, coincident with expansive ice cover and thus returning to the size structure of the 2010 and 2011 communities. Reduced size is recognized as a universal ecological response to global warming in aquatic systems although it usually marks a response to climate warming over multiple years, not a single season as reported here. Fig. 1. Winter surveys conducted on Lake Erie over two years demonstrated tight coupling between microplankton Chl a biomass and total Chl a during winter 2010-11 (purple, green), a year of expansive ice cover. A warm positive Arctic Oscillation resulted in negligible ice cover on Lake

  10. Potential methane emission from north-temperate lakes following ice melt

    USGS Publications Warehouse

    Michmerhuizen, C.M.; Striegl, R.G.; McDonald, M.E.

    1996-01-01

    Methane, a radiatively active 'greenhouse' gas, is emitted from lakes to the atmosphere throughout the open-water season. However, annual lake CH4 emissions calculated solely from open-water measurements that exclude the time of spring ice melt may substantially underestimate the lake CH4 source strength. We estimated potential spring CH4 emission at the time of ice melt for 19 lakes in northern Minnesota and Wisconsin. Lakes ranged in area from 2.7 to 57,300 ha and varied in littoral zone sediment type. Regression analyses indicated that lake area explained 38% of the variance in potential CH4 emission for relatively undisturbed lakes; as lake area increases potential CH4 emission per unit area decreases. Inclusion of a second term accounting for the presence or absence of soft organic-rich littoral-zone sediments explained 83% of the variance in potential spring CH4 emission. Total estimated spring CH4 emission for 1993 for all Minnesota lakes north of 45?? with areas ???4 ha was 1.5 x 108 mol CH4 assuming a 1 : 1 ratio of soft littoral sediment to hard littoral sediment lakes. Emission estimates ranged from 5.3 x 107 tool assuming no lakes have soft organic-rich littoral sediments to 4.5 x 108 mol assuming all lakes have soft organic-rich littoral sediments. This spring CH4 pulse may make up as much as 40% of the CH4 annually emitted to the atmosphere by small lakes.

  11. Evidence of deep circulation in two perennially ice-covered Antarctic lakes

    USGS Publications Warehouse

    Tyler, S.W.; Cook, P.G.; Butt, A.Z.; Thomas, J.M.; Doran, P.T.; Lyons, W.B.

    1998-01-01

    The perennial ice covers found on many of the lakes in the McMurdo Dry Valley region of the Antarctic have been postulated to severely limit mixing and convective turnover of these unique lakes. In this work, we utilize chlorofluorocarbon (CFC) concentration profiles from Lakes Hoare and Fryxell in the McMurdo Dry Valley to determine the extent of deep vertical mixing occurring over the last 50 years. Near the ice-water interface, CFC concentrations in both lakes were well above saturation, in accordance with atmospheric gas supersaturations resulting from freezing under the perennial ice covers. Evidence of mixing throughout the water column at Lake Hoare was confirmed by the presence of CFCs throughout the water column and suggests vertical mixing times of 20-30 years. In Lake Fryxell, CFC-11, CFC-12, and CFC-113 were found in the upper water column; however, degradation of CFC-11 and CFC-12 in the anoxic bottom waters appears to be occurring with CFC-113 only present in these bottom waters. The presence of CFC-113 in the bottom waters, in conjunction with previous work detecting tritium in these waters, strongly argues for the presence of convective mixing in Lake Fryxell. The evidence for deep mixing in these lakes may be an important, yet overlooked, phenomenon in the limnology of perennially ice-covered lakes.

  12. Glacial Lake Musselshell: Late Wisconsin slackwater on the Laurentide ice margin in central Montana, USA

    USGS Publications Warehouse

    Davis, N.K.; Locke, W. W.; Pierce, K.L.; Finkel, R.C.

    2006-01-01

    Cosmogenic surface exposure ages of glacial boulders deposited in ice-marginal Lake Musselshell suggest that the lake existed between 20 and 11.5 ka during the Late Wisconsin glacial stage (MIS 2), rather than during the Late Illinoian stage (MIS 6) as traditionally thought. The altitude of the highest ice-rafted boulders and the lowest passes on the modern divide indicate that glacial lake water in the Musselshell River basin reached at least 920-930 m above sea level and generally remained below 940 m. Exposures of rhythmically bedded silt and fine sand indicate that Lake Musselshell is best described as a slackwater system, in which the ice-dammed Missouri and Musselshell Rivers rose and fell progressively throughout the existence of the lake rather than establishing a lake surface with a stable elevation. The absence of varves, deltas and shorelines also implies an unstable lake. The changing volume of the lake implies that the Laurentide ice sheet was not stable at its southernmost position in central Montana. A continuous sequence of alternating slackwater lake sediment and lacustrine sheetflood deposits indicates that at least three advances of the Laurentide ice sheet occurred in central Montana between 20 and 11.5 ka. Between each advance, it appears that Lake Musselshell drained to the north and formed two outlet channels that are now occupied by extremely underfit streams. A third outlet formed when the water in Lake Musselshell fully breached the Larb Hills, resulting in the final drainage of the lake. The channel through the Larb Hills is now occupied by the Missouri River, implying that the present Missouri River channel east of the Musselshell River confluence was not created until the Late Wisconsin, possibly as late as 11.5 ka. ?? 2005 Elsevier B.V. All rights reserved.

  13. Tracing the Complex Ice Cover Evolution of Lake Vida, Antarctica Through Noble Gases

    NASA Astrophysics Data System (ADS)

    Malone, J. L.; Castro, M. C.; Hall, C. M.; Doran, P. T.; Kenig, F.; McKay, C. P.

    2008-12-01

    Unlike other lakes in the McMurdo Dry Valleys in Antarctica, Lake Vida has a very thick (~19 m) ice cover and a liquid brine body of unusually high salinity (~245 g/L). Because noble gases (He, Ne, Ar, Kr and Xe) are conservative in nature, they can be used to understand physical processes taking place during ice formation (e.g., partitioning of noble gases between the ice and residual liquid, bubble formation at the ice-liquid interface) thus, providing information with respect to the temporal evolution of the dry valley lakes. In an attempt to constrain the conditions under which the atypical Lake Vida ice cover formed and evolved, we collected 19 ice samples along a vertical profile from the surface down to a depth of ~14 m as well as three liquid brine samples from briny ice at a depth of ~16 m for analysis of all noble gases. Our results show that the broad pattern of noble gas concentrations for the Lake Vida ice cover and associated brines is fundamentally different from that expected for air saturated water (ASW). Overall, ice samples are relatively enriched in He, slightly depleted in Ne, and strongly depleted in the heavier noble gases (Ar, Kr, Xe) with respect to ASW. By contrast, brine samples are very enriched in heavy noble gases. To understand the mechanisms responsible for the observed noble gas distribution and fractionation in the Lake Vida cover, a conceptual three-phase (ice, brine, bubbles) partition model was tested. The model allows the lighter noble gases (He and Ne) to reside interstitially in ice while Ar, Kr, and Xe are totally excluded, causing supersaturation in the residual liquid as freezing progresses and formation of gas bubbles occurs at the ice-liquid interface. These bubbles are subsequently incorporated into the ice. While the general noble gas enrichment and depletion patterns of the model are consistent with our brine and ice data, quantitative agreement with output values is not as good under similar model conditions (e

  14. Evidence of recent changes in the ice regime of lakes in the Canadian High Arctic from spaceborne satellite observations

    NASA Astrophysics Data System (ADS)

    Surdu, Cristina M.; Duguay, Claude R.; Fernández Prieto, Diego

    2016-05-01

    Arctic lakes, through their ice cover phenology, are a key indicator of climatic changes that the high-latitude environment is experiencing. In the case of lakes in the Canadian Arctic Archipelago (CAA), many of which are ice covered more than 10 months per year, warmer temperatures could result in ice regime shifts. Within the dominant polar-desert environment, small local warmer areas have been identified. These relatively small regions - polar oases - with longer growing seasons and greater biological productivity and diversity are secluded from the surrounding barren polar desert. The ice regimes of 11 lakes located in both polar-desert and polar-oasis environments, with surface areas between 4 and 542 km2, many of unknown bathymetry, were documented. In order to investigate the response of ice cover of lakes in the CAA to climate conditions during recent years, a 15-year time series (1997-2011) of RADARSAT-1/2 ScanSAR Wide Swath, ASAR Wide Swath, and Landsat acquisitions were analyzed. Results show that melt onset occurred earlier for all observed lakes. With the exception of Lower Murray Lake, all lakes experienced earlier summer ice minimum and water-clear-of-ice (WCI) dates, with greater changes being observed for polar-oasis lakes (9-24 days earlier WCI dates for lakes located in polar oases and 2-20 days earlier WCI dates for polar-desert lakes). Additionally, results suggest that some lakes may be transitioning from a perennial/multiyear to a seasonal ice regime, with only a few lakes maintaining a multiyear ice cover on occasional years. Aside Lake Hazen and Murray Lakes, which preserved their ice cover during the summer of 2009, no residual ice was observed on any of the other lakes from 2007 to 2011.

  15. Trends in ice formation at Lake Neusiedl since 1931 and large-scale oscillation patterns

    NASA Astrophysics Data System (ADS)

    Soja, Anna-Maria; Maracek, Karl; Soja, Gerhard

    2013-04-01

    Ice formation at Lake Neusiedl (Neusiedler See, Fertitó), a shallow steppe lake (area 320 km2, mean depth 1.2 m) at the border of Austria/Hungary, is of ecological and economic importance. Ice sailing and skating help to keep a touristic off-season alive. Reed harvest to maintain the ecological function of the reed belt (178 km2) is facilitated when lake surface is frozen. Changes in ice formation were analysed in the frame of the EULAKES-project (European Lakes under Environmental Stressors, www.eulakes.eu), financed by the Central Europe Programme of the EU. Data records of ice-on, ice duration and ice-off at Lake Neusiedl starting with the year 1931, and air temperature (nearby monitoring station Eisenstadt - Sopron (HISTALP database and ZAMG)) were used to investigate nearly 80 winters. Additionally, influences of 8 teleconnection patterns, i.e. the Atlantic Multidecadal Oscillation (AMO), the East Atlantic pattern (EAP), the East Atlantic/West Russia pattern (EA/WR), the Eastern Mediterranean Pattern (EMP), the Mediterranean Oscillation (MO) for Algiers and Cairo, and for Israel and Gibraltar, resp., the North Atlantic Oscillation (NAO) and the Scandinavia pattern (SCA) were assessed. Ice cover of Lake Neusiedl showed a high variability between the years (mean duration 71±27 days). Significant trends for later ice-on (p=0.02), shorter ice duration (p=0.07) and earlier ice-off (p=0.02) for the period 1931-2011 were found by regression analysis and trend analysis tests. On an average, freezing of Lake Neusiedl started 2 days later per decade and ice melting began 2 days earlier per decade. Close relationships between mean air temperature and ice formation could be found: ice-on showed a dependency on summer (R=+0.28) and autumn air temperatures (R=+0.51), ice duration and ice off was related to autumn (R=-0.36 and -0.24), winter (R=-0.73 and -0.61) and concurrent spring air temperatures (R=-0.44). Increases of air temperature by 1° C caused an 8.4 days later

  16. Analysis of the variability of ice phenology on Great Bear Lake and Great Slave Lake, 2002-2009, from AMSR-E measurements

    NASA Astrophysics Data System (ADS)

    Kang, K.; Duguay, C. R.; Howell, S.

    2009-12-01

    Lake ice cover is a significant component of the Canadian terrestrial cryosphere. It is both a sensitive indicator of climate conditions and it plays a significant role in the energy and water balance of northern regions. Knowledge about the temporal and spatial variability of ice phenology (ice-on/ice-off dates and ice duration) is critical for improving our understanding of surface-atmosphere interactions at high latitudes within the context of a changing climate. Remote sensing in the most viable tool for obtaining frequent observations of ice cover conditions over large lakes and across large areas of the North. Obtaining ice phenological parameters with optical satellite sensors such as MODIS and AVHRR is difficult, especially during the freeze-up period due to polar darkness and extensive cloud cover. However, passive microwave satellite remote sensing can provide regular and weather-independent information on ice phenology over large northern lakes such Great Bear Lake (GBL) and Great Slave Lake (GSL), Northwest Territories, Canada. In this paper, the temporal evolution of brightness temperature at 18.7, 23.5, and 36.5 GHz from AMSR-E passive microwave measurements is analyzed to determine freeze-onset/melt-onset, ice-on/ice-off, and ice cover duration on GBL and GSL. In order to examine the interannual variability in ice cover on the two lakes, the polarization difference and horizontal polarized brightness temperature at various frequencies are explored to derive ice phenological parameters for ice seasons 2002-2003 to 2008-2009. Preliminary results show a difference of approximately two to four weeks in ice-on/ice-off dates between cold and warm winters. Passive microwave is shown to be an effective means for monitoring lake ice phenology and could, in part, replace the lost ground-based observational ice network for GBL and GSL.

  17. Insights into supraglacial lake evolution on the Larsen-B ice shelf

    NASA Astrophysics Data System (ADS)

    Leeson, A.; Shepherd, A.; Gilbert, L.; Ligtenberg, S.; van den Broeke, M.

    2015-12-01

    The Larsen-B ice shelf was the second largest component of the Larsen ice shelf system in the Antarctic Peninsula. It collapsed in 2002, losing an area more than double the size of London (~3200 km2) to the sea. The collapse of Larsen-B has been attributed to a range of factors, although the dominant control over the fidelity of the ice shelf is thought to be climatological (melting on the ice shelf was three times higher in 2002 than the 1998-2001 average). Supraglacial lakes in particular have been implicated in the collapse; by repeatedly filling and draining, they likely weaken an ice shelf and precondition it for disintegration. However, abundant supraglacial lake coverage has been observed on Larsen-B for many years prior to its break-up and, in fact, surface conditions have been conducive to lake formation for several decades. Here, we use satellite observations and a hydrological model forced with estimates of melting and runoff from a regional climate model in order to investigate the response of supraglacial lakes to extreme melting in 2002 specifically, in contrast with typical supraglacial lake evolution in previous years. We also use state-of-the-art observations of ice shelf topography acquired by CryoSat-2 to examine the potential role of supraglacial lakes on the fate of the Larsen remnant, currently thought to be at risk of collapse by 2020.

  18. Characteristics and indications of hydrogen and oxygen isotopes distribution in lake ice body.

    PubMed

    Zhen, Zhi-Lei; Li, Chang-You; Zhang, Sheng; Li, Wen-Bao; Shi, Xiao-Hong; Sun, Biao

    2015-01-01

    Stable isotopes have been used to identify the characteristics of precipitation, evaporation, basin hydrology, and residence times. However, lakes in the cold regions are usually covered by ice for 5-6 months. To get a better understanding of stable isotopes characteristics and indications in lake ice bodies, ice and water were sampled during the icebound season in both the ice and water bodies in Dali Lake, and deuterium, oxygen-18 total nitrogen (TN), and the major ions were analyzed. The results showed that deuterium and oxygen-18 compositions (δD-δ¹⁸O) compositions in the ice body were greater than in the water body beneath, scattered on a straight line, and deviating downward from the global meteoric water line in the top right. The ice profile showed that the δD-δ¹⁸O compositions increased from the ice surface downward and decreased near to the bottom. In contrast, the TN and the major ions in the ice decreased from the ice surface downward and increased near to the bottom, meaning that the concentrations of δ¹⁸O had a negative correlation with the concentrations of TN and major ions. These indicated that stable isotopes can be used for tracing the nutriment and ion transport processes in the ice body.

  19. ALBEDO MODELS FOR SNOW AND ICE ON A FRESHWATER LAKE. (R824801)

    EPA Science Inventory

    Abstract

    Snow and ice albedo measurements were taken over a freshwater lake in Minnesota for three months during the winter of 1996¯1997 for use in a winter lake water quality model. The mean albedo of new snow was measured as 0.83±0.028, while the...

  20. SIMULATED CLIMATE CHANGE EFFECTS ON DISSOLVED OXYGEN CHARACTERISTICS IN ICE-COVERED LAKES. (R824801)

    EPA Science Inventory

    A deterministic, one-dimensional model is presented which simulates daily dissolved oxygen (DO) profiles and associated water temperatures, ice covers and snow covers for dimictic and polymictic lakes of the temperate zone. The lake parameters required as model input are surface ...

  1. Great Lakes Ice Cover Classification and Mapping Using Satellite Synthetic Aperture Radar (SAR) Data

    NASA Technical Reports Server (NTRS)

    Nghiem, S.; Leshkevich, G.; Kwok, R.

    1998-01-01

    Owing to the size and extent of the Great Lakes and the variety of ice types features found there, the timely and objective qualities inherent in computer processing of satellite data make it well suited for monitoring and mapping ice cover.

  2. The geomorphology of Patagonian ice dammed lake basins: Insights from remote sensing of a modern lake and reconstruction of a Late Quaternary lake drainage event

    NASA Astrophysics Data System (ADS)

    Thorndycraft, Varyl

    2016-04-01

    The geomorphology of ice dammed lake basins can be complex due to geomorphic responses to multiple base level changes from repeated filling and emptying, as well as the potential for catastrophic drainage events. Refining landscape models of Quaternary ice dammed palaeolake systems has the potential to improve our understanding of glacier and meltwater dynamics during deglaciation phases. In this poster two case studies are presented to shed light on the range of geomorphic processes exhibited within ice dammed lake basins. Using Google Earth Pro and repeat LANDSAT imagery the geomorphology resulting from multiple base level changes of an ice dammed lake of the Viedma Glacier (Southern Patagonia Icefield) is presented. The LANDSAT imagery shows transgressive lake phases inundating already formed delta and terrace surfaces, whilst the high resolution Google Earth Pro images reveal a complex suite of incised terrace levels developed on the valley floor following lake drainage events. Secondly, the impact of catastrophic drainage of the Late Pleistocene Palaeolake Cochrane (Northern Patagonia Icefield) is investigated through geomorphological mapping. Here an outburst flood and rapid lowering of the lake has led to large scale eddy scouring of glacio-lacustrine sediments, with scarp slopes of ca. 30-40 m in height, and the formation of boulder bars during the final stages of lake fall. The implications of the mapping for interpretations of Late Quaternary palaeolake sediment-landform assemblages and rates of landscape change are discussed.

  3. Basal ice flow regime influenced by glacial lake formation in Rhonegletscher, Switzerland

    NASA Astrophysics Data System (ADS)

    Nishimura, D.; Tsutaki, S.; Sugiyama, S.

    2010-12-01

    After the retreat of glacier terminus over a bedrock bump, a glacial lake has formed in front of Rhonegletscher, Switzerland. It is suspected that ice flow regime is now significantly influenced by the lake water. To investigate the impact of lake formation on glacier dynamics, we carried out surface and borehole observations in the terminus region of Rhonegletscher. In 2008 and 2009 summer seasons, we drilled more than 20 boreholes to measure borehole deformation by repeated inclinometry. Ice surface speed was measured by surveying stakes installed nearby the boreholes. We used a borehole televiewer to measure basal sliding speed by tracking stones and markers at the bottom of the boreholes. We also measured basal sediment layer thickness by hammering a penetrometer at the bottom of the boreholes. Our measurements showed clear decrease in the ice deformation rate near the lake (Fig. 1). Ice deformation accounted for 60-80% in the upper part of our study site (e.g. boreholes 1 and 5), whereas it is less than 10% near the lake (e.g. boreholes 7, 10 and 11). This result suggests that the basal ice flow near the lake is enhanced by the lake water. According to the basal sliding speed measurement in borehole 2, sliding accounted for less than 10% of basal flow speed from 2 to 31 August 2009. Deformation of a subglacial sediment layer is thus important in this region. The penetrometer measurement confirmed that the study site is underlain by a subglacial sediment layer whose thickness was in a range of 0-70 m. Fig.1 Terminus of Rhonegletscher and proglacial lakes indicated by the shaded areas. The columns show ice surface and deformation speeds measured at each borehole site from 9 July to 5 September in 2009. Ice deformation speed was negligibly small at boreholes 7, 10, and 11. Surface contour spacing is 20 m.

  4. Towards automated mapping of lake ice using RADARSAT-2 and simulated RCM compact polarimetric data

    NASA Astrophysics Data System (ADS)

    Duguay, Claude

    2016-04-01

    The Canadian Ice Service (CIS) produces a weekly ice fraction product (a text file with a single lake-wide ice fraction value, in tenth, estimated for about 140 large lakes across Canada and northern United States) created from the visual interpretation of RADARSAT-2 ScanSAR dual-polarization (HH and HV) imagery, complemented by optical satellite imagery (AVHRR, MODIS and VIIRS). The weekly ice product is generated in support of the Canadian Meteorological Centre (CMC) needs for lake ice coverage in their operational numerical weather prediction model. CIS is interested in moving from its current (manual) way of generating the ice fraction product to a largely automated process. With support from the Canadian Space Agency, a project was recently initiated to assess the potential of polarimetric SAR data for lake ice cover mapping in light of the upcoming RADARSAT Constellation Mission (to be launched in 2018). The main objectives of the project are to evaluate: 1) state-of-the-art image segmentation algorithms and 2) RADARSAT-2 polarimetric and simulated RADARSAT Constellation Mission (RCM) compact polarimetric SAR data for ice/open water discrimination. The goal is to identify the best segmentation algorithm and non-polarimetric/polarimetric parameters for automated lake ice monitoring at CIS. In this talk, we will present the background and context of the study as well as initial results from the analysis of RADARSAT-2 Standard Quad-Pol data acquired during the break-up and freeze-up periods of 2015 on Great Bear Lake, Northwest Territories.

  5. Light transmission and reflection in perennially ice-covered Lake Hoare, Antarctica

    NASA Technical Reports Server (NTRS)

    Mckay, C. P.; Clow, G. D.; Andersen, D. T.; Wharton, R. A., Jr.

    1994-01-01

    We have investigated the transmission and albedo of the perennial ice cover on Lake Hoare, Antarctica. Our database consists of year-round measurements of the photosynthetically active radiation (400-700 nm) under the ice, measurements of the spatial variation of the under-ice light in midsummer, and spectrally resolved measurements from 400 to 700 nm of the albedo and transmission of the ice cover in early (November) and in midsummer (January). Our results show that the transmission decreases in the first part of summer, dropping by a factor of approximately 4 from November to January. We suggest that this is due to heating in the upper layers of the ice cover and the formation of Tyndall figures. Later in the summer when a significant liquid water fraction occurs within the ice cover, the transmission increases. In the fall when the ice cover freezes solid the transmission drops markedly. The spectrally resolved measurements from 400 to 700 nm show that approximately 2-5% of the incident light in this spectral region penetrates the 3.5-m thick ice cover. We have analyzed the spectral data using a two-stream scattering solution to the radiative transfer equation with three vertical layers in the ice cover. A surficial glaze of scattering ice 1 cm thick overlies a layer of sandy, bubbly ice about a meter thick, and below this is a thick layer of sand-free ice with bubbles. We find that the ice cover is virtually opaque at wavelengths longer than 800 nm. The net transmission of solar energy is approximately 2%. Significant changes in the thickness of the ice cover have been reported at Lake Hoare. These are due primarily to changes in the thickness of the bottom layer only. Because this layer is relatively clear, the effect on the transmission through the ice cover from these changes is less than would be predicted assuming a homogeneous ice cover.

  6. Beach profile modification and sediment transport by ice: an overlooked process on Lake Michigan

    USGS Publications Warehouse

    Barnes, P.W.; Kempema, E.W.; Reimnitz, E.; McCormick, M.; Weber, W.S.; Hayden, E.C.

    1993-01-01

    Coastal lake ice includes a belt of mobile crash and slush ice and a stable nearshore-ice complex (NIC). Sediment concentrations indicate that the NIC and the belt of brash and slush contains 180 to 280 t (113 to 175m3) of sand per kilometer of coast. This static sediment load is roughly equivalent to the average amount of sand eroded from the bluffs and to the amount accumulating in the deep lake basin each year. Sediment is being rafted alongshore in the mobile brash and slush at rates of 10 to 30 cm/sec. -from Authors

  7. Perennial Antarctic lake ice: an oasis for life in a polar desert

    NASA Technical Reports Server (NTRS)

    Priscu, J. C.; Fritsen, C. H.; Adams, E. E.; Giovannoni, S. J.; Paerl, H. W.; McKay, C. P.; Doran, P. T.; Gordon, D. A.; Lanoil, B. D.; Pinckney, J. L.

    1998-01-01

    The permanent ice covers of Antarctic lakes in the McMurdo Dry Valleys develop liquid water inclusions in response to solar heating of internal aeolian-derived sediments. The ice sediment particles serve as nutrient (inorganic and organic)-enriched microzones for the establishment of a physiologically and ecologically complex microbial consortium capable of contemporaneous photosynthesis, nitrogen fixation, and decomposition. The consortium is capable of physically and chemically establishing and modifying a relatively nutrient- and organic matter-enriched microbial "oasis" embedded in the lake ice cover.

  8. The drainage and freezing behaviour of lakes from all parts of the Greenland Ice Sheet (Invited)

    NASA Astrophysics Data System (ADS)

    Selmes, N.; Murray, T.; James, T.

    2013-12-01

    The rapid drainage of supraglacial lakes is capable of causing accelerations in ice-sheet flow even when efficient subglacial drainage prevents slower meltwater inputs from affecting ice velocity. In addition, the fractures generated during drainage are a major source of connections between the supraglacial and subglacial hydrological systems. However, a previous study has shown that only 13 % of lakes drain in this manner. It has been suggested that lakes can have one of three fates: sudden drainage to the ice bed, slower supraglacial drainage through incision of a drainage channel, or freezing at the end of the melt season. These processes have never been quantified at the ice-sheet scale, and little is known about their distribution. We took a combination of MODIS visible imagery, MODIS land surface temperature data, and a pre-existing database of lake-area time-series, and used these data to classify 2600 lakes from all parts of the ice sheet over the period 2005-2009 into the three proposed lake-types: fast-draining, slow-draining, and freezing. Of the lakes studied, 34 % slow-drained, presumably supraglacially, and 47 % froze over at the end of the melt season. Previous studies have found a lack of moulins and reduced melt/velocity feedback in the higher part of the lake-forming zone. We find that lakes in this area are very unlikely to drain to the bed of the ice sheet, and instead lakes are far more likely to freeze, despite apparently having sufficient size and lifespan to drain. We suggest that this is evidence that lake drainage may be inhibited at higher elevations. At lower elevations fast and slow-draining lakes dominate, and frequently switch drainage-types interannually. Fast-draining, slow-draining, and freezing lakes are easily confused if infrequent observations are used, a fact worth considering for future remote-sensing studies to avoid overestimating the amount and rate of meltwater delivery to the ice-bed.

  9. Characterization of subglacial Lake Vostok as seen from physical and isotope properties of accreted ice.

    PubMed

    Lipenkov, Vladimir Ya; Ekaykin, Alexey A; Polyakova, Ekaterina V; Raynaud, Dominique

    2016-01-28

    Deep drilling at the Vostok Station has reached the surface of subglacial Lake Vostok (LV) twice-in February 2012 and January 2015. As a result, three replicate cores from boreholes 5G-1, 5G-2 and 5G-3 became available for detailed and revalidation analyses of the 230 m thickness of the accreted ice, down to its contact with water at 3769 m below the surface. The study reveals that the concentration of gases in the lake water beneath Vostok is unexpectedly low. A clear signature of the melt water in the surface layer of the lake, which is subject to refreezing on the icy ceiling of LV, has been discerned in the three different properties of the accreted ice: the ice texture, the isotopic and the gas content of the ice. These sets of data indicate in concert that poor mixing of the melt (and hydrothermal) water with the resident lake water and pronounced spatial and/or temporal variability of local hydrological conditions are likely to be the characteristics of the southern end of the lake. The latter implies that the surface water may be not representative enough to study LV's behaviour, and that direct sampling of the lake at different depths is needed in order to move ahead with our understanding of the lake's hydrological regime. PMID:26667912

  10. Characterization of subglacial Lake Vostok as seen from physical and isotope properties of accreted ice.

    PubMed

    Lipenkov, Vladimir Ya; Ekaykin, Alexey A; Polyakova, Ekaterina V; Raynaud, Dominique

    2016-01-28

    Deep drilling at the Vostok Station has reached the surface of subglacial Lake Vostok (LV) twice-in February 2012 and January 2015. As a result, three replicate cores from boreholes 5G-1, 5G-2 and 5G-3 became available for detailed and revalidation analyses of the 230 m thickness of the accreted ice, down to its contact with water at 3769 m below the surface. The study reveals that the concentration of gases in the lake water beneath Vostok is unexpectedly low. A clear signature of the melt water in the surface layer of the lake, which is subject to refreezing on the icy ceiling of LV, has been discerned in the three different properties of the accreted ice: the ice texture, the isotopic and the gas content of the ice. These sets of data indicate in concert that poor mixing of the melt (and hydrothermal) water with the resident lake water and pronounced spatial and/or temporal variability of local hydrological conditions are likely to be the characteristics of the southern end of the lake. The latter implies that the surface water may be not representative enough to study LV's behaviour, and that direct sampling of the lake at different depths is needed in order to move ahead with our understanding of the lake's hydrological regime.

  11. Ice-Covered Lakes in Gale Crater Mars: The Cold and Wet Hypothesis

    NASA Astrophysics Data System (ADS)

    Kling, Alexandre; Haberle, Robert; McKay, Christopher P.; Bristow, Thomas

    2016-10-01

    Recent geological discoveries from the Mars Science Laboratory provide evidence that Gale crater may have intermittently hosted a fluvio-lacustine environment during the Hesperian, with individual lakes lasting for a period of tens to hundreds of thousands of years. (Grotzinger et al., Science, 350 (6257), 2015). Estimates of the CO2 content of the atmosphere at the time the Gale sediments formed are far less than needed by any climate model to warm early Mars (Bristow et al., Geology, submitted), given the low solar energy input available at Mars 3.5 Gya. We have therefore explored the possibility that the lakes in Gale during the Hesperian were perennially covered with ice using the Antarctic Lakes as an analog. Using our best estimate for the annual mean surface temperature at Gale at this time (~230K) we computed the thickness of an ice-covered lake. These thickness range from 10-30 meters depending on the ablation rate and ice transparency and would likely inhibit sediments from entering the lake. Thus, a first conclusion is that the ice must not be too cold. Raising the mean temperature to 245K is challenging, but not quite as hard as reaching 273K. We found that a mean annual temperature of 245K ice thicknesses range from 3-10 meters. These values are comparable to the range of those for the Antarctic lakes (3-6 m), and are not implausible. And they are not so thick that sediments cannot penetrate the ice. For the ice-covered lake hypothesis to work, however, a melt water source is needed. This could come from subaqueous melting of a glacial dam in contact with the lakes (as is the case for Lake Untersee) or from seasonal melt water from nearby glaciers (as is the case for the Dry Valley lakes). More work is needed to better assess these possibilities. However, the main advantage of the ice-covered lake model (and the main reason we pursued it) is that it relaxes the requirement for a long-lived active hydrological cycle involving rainfall and runoff, which

  12. Stable isotopic biogeochemistry of carbon and nitrogen in a perennially ice-covered Antarctic lake

    NASA Technical Reports Server (NTRS)

    Wharton, R. A. Jr; Lyons, W. B.; Des Marais, D. J.; Wharton RA, J. r. (Principal Investigator)

    1993-01-01

    Lake Hoare (77 degrees 38' S, 162 degrees 53' E) is an amictic, oligotrophic, 34-m-deep, closed-basin lake in Taylor Valley, Antarctica. Its perennial ice cover minimizes wind-generated currents and reduces light penetration, as well as restricts sediment deposition into the lake and the exchange of atmospheric gases between the water column and the atmosphere. The biological community of Lake Hoare consists solely of microorganisms -- both planktonic populations and benthic microbial mats. Lake Hoare is one of several perennially ice-covered lakes in the McMurdo Dry Valleys that represent the end-member conditions of cold desert and saline lakes. The dry valley lakes provide a unique opportunity to examine lacustrine processes that operate at all latitudes, but under an extreme set of environmental conditions. The dry valley lakes may also offer a valuable record of catchment and global changes in the past and present. Furthermore, these lakes are modern-day equivalents of periglacial lakes that are likely to have been common during periods of glacial maxima at temperate latitudes. We have analyzed the dissolved inorganic carbon (DIC) of Lake Hoare for delta 13C and the organic matter of the sediments and sediment-trap material for delta 13C and delta 15N. The delta 13C of the DIC indicates that 12C is differentially removed in the shallow, oxic portions of the lake via photosynthesis. In the anoxic portions of the lake (27-34 m) a net addition of 12C to the DIC pool occurs via organic matter decomposition. The dissolution of CaCO3 at depth also contributes to the DIC pool. Except near the Canada Glacier where a substantial amount of allochthonous organic matter enters the lake, the organic carbon being deposited on the lake bottom at different sites is isotopically similar, suggesting an autochthonous source for the organic carbon. Preliminary inorganic carbon flux calculations suggest that a high percentage of the organic carbon fixed in the water column is

  13. The geochemistry of methane in Lake Fryxell, an amictic, permanently ice-covered, antarctic lake

    USGS Publications Warehouse

    Smith, R.L.; Miller, L.G.; Howes, B.L.

    1993-01-01

    The abundance and distribution of dissolved CH4 were determined from 1987-1990 in Lake Fryxell, Antarctica, an amictic, permanently ice-covered lake in which solute movement is controlled by diffusion. CH4 concentrations were < 1 ??M in the upper oxic waters, but increased below the oxycline to 936 ??M at 18 m. Sediment CH4 was 1100 ??mol (1 sed)-1 in the 0-5 cm zone. Upward flux from the sediment was the source of the CH4, NH4 +, and DOC in the water column; CH4 was 27% of the DOC+CH4 carbon at 18 m. Incubations with surficial sediments indicated that H14CO3 - reduction was 0.4 ??mol (1 sed)-1 day-1 or 4?? the rate of acetate fermentation to CH4. There was no measurable CH4 production in the water column. However, depth profiles of CH4, NH4, and DIC normalized to bottom water concentrations demonstrated that a significant CH4 sink was evident in the anoxic, sulfate-containing zone of the water column (10-18 m). The ??13CH4 in this zone decreased from -72 % at 18 m to -76% at 12 m, indicating that the consumption mechanism did not result in an isotopic enrichment of 13CH4. In contrast, ??13CH4 increased to -55 % at 9 m due to aerobic oxidation, though this was a minor aspect of the CH4 cycle. The water column CH4 profile was modeled by coupling diffusive flux with a first order consumption term; the best-fit rate constant for anaerobic CH4 consumption was 0.012 yr-1. On a total carbon basis, CH4 consumption in the anoxic water column exerted a major effect on the flux of carbonaceous material from the underlying sediments and serves to exemplify the importance of CH4 to carbon cycling in Lake Fryxell. ?? 1993 Kluwer Academic Publishers.

  14. Examining Dual Frequency X- and Ku-band Backscatter of Snow on Lake Ice and First-Year Sea Ice in the Sub-Arctic Hudson Bay Lowlands

    NASA Astrophysics Data System (ADS)

    Gunn, G. E.; Duguay, C. R.; Howell, S.; Kelly, R. E.; Silis, A.

    2011-12-01

    Fully polarimetric dual frequency ground-based scatterometer observations were collected at X- and Ku-band (9.6 and 17.2 GHz, respectively) near Churchill, Manitoba, Canada in the winter of 2010-11 as part of the Canadian Snow and Ice Experiment (CASIX). Backscatter measurements were collected for five landcover types: lake ice, sea ice, dry tundra, open forest and wetland tundra (sedge fen); the combination of which comprises a unique dataset of dual-frequency backscatter signatures. Correlative data collected, including snow and ice properties, are utilized to characterize active microwave interactions and contribute to the development of snow/ice retrieval algorithms. This study presents backscatter signatures for lake and sea ice obtained during winter 2010-11. The seasonal backscatter evolution is compared to changes in snow and ice properties, including depth, density, snow water equivalent (SWE), ice thickness, ice type, and bubble concentration within the ice. Results over lake ice suggest that increases in backscatter at both X- and Ku-band frequencies correspond to increases in SWE, but are confounded by changes in the sub-nivian ice composition. Surface ice types (snow ice, rafted ice), high bubble concentrations at the ice/water interface and pressure/deformation cracks in the ice serve to confound backscatter at several monitoring sites. Over sea ice, preliminary results indicate that increased salinity levels near the ice/snow interface is the predominate factor influencing backscatter signatures. Physical phenomena encountered at sea ice sites are further explored to assess potential influences on scattering signatures. Preliminary findings presented here document the first ground-based dual frequency X- and Ku-band backscatter signatures collected over first year sea ice, and contribute to the scientific objectives of the proposed Cold Regions Hydrology High-resolution Observatory (CoReH2O), a candidate Earth Explorer mission of the European Space

  15. Diffusion model validation and interpretation of stable isotopes in river and lake ice

    USGS Publications Warehouse

    Ferrick, M.G.; Calkins, D.J.; Perron, N.M.; Cragin, J.H.; Kendall, C.

    2002-01-01

    The stable isotope stratigraphy of river- and lake-ice archives winter hydroclimatic conditions, and can potentially be used to identify changing water sources or to provide important insights into ice formation processes and growth rates. However, accurate interpretations rely on known isotopic fractionation during ice growth. A one-dimensional diffusion model of the liquid boundary layer adjacent to an advancing solid interface, originally developed to simulate solute rejection by growing crystals, has been used without verification to describe non-equilibrium fractionation during congelation ice growth. Results are not in agreement, suggesting the presence of important uncertainties. In this paper we seek validation of the diffusion model for this application using large-scale laboratory experiments with controlled freezing rates and frequent sampling. We obtained consistent, almost constant, isotopic boundary layer thicknesses over a representative range of ice growth rates on both quiescent and well-mixed water. With the 18O boundary layer thickness from the laboratory, the model successfully quantified reduced river-ice growth rates relative to those of a nearby lake. These results were more representative and easier to obtain than those of a conventional thermal ice-growth model. This diffusion model validation and boundary layer thickness determination provide a powerful tool for interpreting the stable isotope stratigraphy of floating ice. The laboratory experiment also replicated successive fractionation events in response to a freeze-thaw-refreeze cycle, providing a mechanism for apparent ice fractionation that exceeds equilibrium. Analysis of the composition of snow ice and frazil ice in river and lake cores indicated surprising similarities between these ice forms. Published in 2002 by John Wiley & Sons, Ltd.

  16. Simulation of lake ice and its effect on the late-Pleistocene evaporation rate of Lake Lahontan

    USGS Publications Warehouse

    Hostetler, S.W.

    1991-01-01

    A model of lake ice was coupled with a model of lake temperature and evaporation to assess the possible effect of ice cover on the late-Pleistocene evaporation rate of Lake Lahontan. The simulations were done using a data set based on proxy temperature indicators and features of the simulated late-Pleistocene atmospheric circulation over western North America. When a data set based on a mean-annual air temperature of 3?? C (7?? C colder than present) and reduced solar radiation from jet-stream induced cloud cover was used as input to the model, ice cover lasting ??? 4 months was simulated. Simulated evaporation rates (490-527 mm a-1) were ??? 60% lower than the present-day evaporation rate (1300 mm a-1) of Pyramid Lake. With this reduced rate of evaporation, water inputs similar to the 1983 historical maxima that occurred in the Lahontan basin would have been sufficient to maintain the 13.5 ka BP high stand of Lake Lahontan. ?? 1991 Springer-Verlag.

  17. Fault-dominated deformation in an ice dam during annual filling and drainage of a marginal lake

    USGS Publications Warehouse

    Walder, J.S.; Trabant, D.C.; Cunico, M.; Anderson, S.P.; Anderson, R. Scott; Fountain, A.G.; Malm, A.

    2005-01-01

    Ice-dammed Hidden Creek Lake, Alaska, USA, outbursts annually in about 2-3 days. As the lake fills, a wedge of water penetrates beneath the glacier, and the surface of this 'ice dam' rises; the surface then falls as the lake drains. Detailed optical surveying of the glacier near the lake allows characterization of ice-dam deformation. Surface uplift rate is close to the rate of lake-level rise within about 400 m of the lake, then decreases by 90% over about 100 m. Such a steep gradient in uplift rate cannot be explained in terms of ice-dam flexure. Moreover, survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. Evidently, the zone of steep uplift gradient is a fault zone, with the faults penetrating the entire thickness of the ice dam. Fault motion is in a reverse sense as the lake fills, but in a normal sense as the lake drains. As the overall fault pattern is the same from year to year, even though ice is lost by calving, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as ice is advected toward the lake basin.

  18. Hydrography and circulation of ice-marginal lakes at Bering Glacier, Alaska, U.S.A.

    USGS Publications Warehouse

    Josberger, E.G.; Shuchman, R.A.; Meadows, G.A.; Savage, S.; Payne, J.

    2006-01-01

    An extensive suite of physical oceanographic, remotely sensed, and water quality measurements, collected from 2001 through 2004 in two ice-marginal lakes at Bering Glacier, Alaska-Berg Lake and Vitus Lake-show that each has a unique circulation controlled by their specific physical forcing within the glacial system. Conductivity profiles from Berg Lake, perched 135 m a.s.l., show no salt in the lake, but the temperature profiles indicate an apparently unstable situation, the 4??C density maximum is located at 10 m depth, not at the bottom of the lake (90 m depth). Subglacial discharge from the Steller Glacier into the bottom of the lake must inject a suspended sediment load sufficient to marginally stabilize the water column throughout the lake. In Vitus Lake, terminus positions derived from satellite imagery show that the glacier terminus rapidly retreated from 1995 to the present resulting in a substantial expansion of the volume of Vitus Lake. Conductivity and temperature profiles from the tidally influenced Vitus Lake show a complex four-layer system with diluted (???50%) seawater in the bottom of the lake. This lake has a complex vertical structure that is the result of convection generated by ice melting in salt water, stratification within the lake, and freshwater entering the lake from beneath the glacier and surface runoff. Four consecutive years, from 2001 to 2004, of these observations in Vitus Lake show little change in the deep temperature and salinity conditions, indicating limited deep water renewal. The combination of the lake level measurements with discharge measurements, through a tidal cycle, by an acoustic Doppler Current Profiler (ADCP) deployed in the Seal River, which drains the entire Bering system, showed a strong tidal influence but no seawater entry into Vitus Lake. The ADCP measurements combined with lake level measurements established a relationship between lake level and discharge, which when integrated over a tidal cycle, gives a

  19. Bedfast and floating ice lake talik properties measured using surface nuclear magnetic resonance on the North Slope, Alaska

    NASA Astrophysics Data System (ADS)

    Parsekian, A.; Jones, B. M.; Arp, C. D.; Creighton, A.; Daanen, R. P.; Gaedeke, A.; Bondurant, A.

    2015-12-01

    Lakes within permafrost regions have been identified as a source of carbon gas emissions, however the geometry of the thawed sediments and water content below these lakes that hold the carbon-rich source sediment remains difficult to measure. Surface nuclear magnetic resonance (NMR) is a geophysical measurement that is unambiguously sensitive to liquid water and therefore is well suited to discriminating between the sub-lake talik (thaw bulb) and surrounding permafrost. Here we report on talik thickness, water content, and pore scale properties observed using surface NMR in lakes located on the Arctic Coastal Plain of northern Alaska. The study lakes range in size from 0.5 km - 2 km in diameter. They have formed within a Pleistocene sand sheet deposit where permafrost extends 200 to 300 m below the surface. Lake depth ranges from less than 1 m (bedfast ice) to 5 m (floating ice); drained lake basins with no water or water ice were also measured for comparison. Floating ice lakes are interpreted to have a talik between 20 - 25 m below the surface. Bedfast ice lakes had either no measureable talik, a talik to < 20 m, or an isolated talik. Drained lake basins had either no measureable talik or an isolated talik. The presence of isolated taliks below some bedfast ice lakes and drained lake basins was a surprising result, suggesting that zones of unfrozen sediment may be present in the region even when the surface conditions suggest otherwise. These results of talik presence/absence and geometry bring new insight into permafrost-influenced lake subsurface hydrology and provide value data for validating hydrological modeling outputs. Our application of using surface NMR on Arctic Lakes will be extended to the region with numerous thermokarst lakes and drained lake basins north of Teshekpuk Lake next April.

  20. Heating the Ice-Covered Lakes of the McMurdo Dry Valleys, Antarctica - Decadal Trends in Heat Content, Ice Thickness, and Heat Exchange

    NASA Astrophysics Data System (ADS)

    Gooseff, M. N.; Priscu, J. C.; Doran, P. T.; Chiuchiolo, A.; Obryk, M.

    2014-12-01

    Lakes integrate landscape processes and climate conditions. Most of the permanently ice-covered lakes in the McMurdo Dry Valleys, Antarctica are closed basin, receiving glacial melt water from streams for 10-12 weeks per year. Lake levels rise during the austral summer are balanced by sublimation of ice covers (year-round) and evaporation of open water moats (summer only). Vertical profiles of water temperature have been measured in three lakes in Taylor Valley since 1988. Up to 2002, lake levels were dropping, ice covers were thickening, and total heat contents were decreasing. These lakes have been gaining heat since the mid-2000s, at rates as high as 19.5x1014 cal/decade). Since 2002, lake levels have risen substantially (as much as 2.5 m), and ice covers have thinned (1.5 m on average). Analyses of lake ice thickness, meteorological conditions, and stream water heat loads indicate that the main source of heat to these lakes is from latent heat released when ice-covers form during the winter. An aditional source of heat to the lakes is water inflows from streams and direct glacieal melt. Mean lake temperatures in the past few years have stabilized or cooled, despite increases in lake level and total heat content, suggesting increased direct inflow of meltwater from glaciers. These results indicate that McMurdo Dry Valley lakes are sensitive indicators of climate processes in this polar desert landscape and demonstrate the importance of long-term data sets when addressing the effects of climate on ecosystem processes.

  1. Estimating Trapped Gas Concentrations as Bubbles Within Lake Ice Using Ground Penetrating Radar

    NASA Astrophysics Data System (ADS)

    Fantello, N.; Parsekian, A.; Walter Anthony, K. M.

    2015-12-01

    Climate warming is currently one of the most important issues that we are facing. The degradation of permafrost beneath thermokarst lakes has been associated with enhanced methane emissions and it presents a positive feedback to climate warming. Thermokarst lakes release methane to the atmosphere mainly by ebullition (bubbling) but there are a large number of uncertainties regarding the magnitude and variability of these emissions. Here we present a methodology to estimate the amount of gas released from thermokarst lakes through ebullition using ground-penetrating radar (GPR). This geophysical technique is well suited for this type of problem because it is non-invasive, continuous, and requires less effort and time than the direct visual inspection. We are studying GPR data collected using 1.2 GHz frequency antennas in Brooklyn Lake, Laramie, WY, in order to quantify the uncertainties in the method. Although this is not a thermokarst lake, gas bubbles are trapped in the ice and spatial variability in bubble concentration within the ice is evident. To assess the variability in bulk physical properties of the ice due to bubbles, we gathered GPR data from different types of ice. We compared the velocity of the groundwave and reflection obtained from radargrams, and found on each case a larger value for the groundwave velocity suggesting a non-homogeneous medium and that the concentration of bubbles is prone to be near the surface instead of at greater depths. We use a multi-phase dielectric-mixing model to estimate the amount of gas present in a sample of volume of ice and found an uncertainty in relative permittivity (estimated using reflection velocity) of 0.0294, which translates to an uncertainty of 1.1% in gas content; and employing groundwave velocity we found 0.0712 and 2.9%, respectively. If locations of gas seeps in lakes could be detected and quantified using GPR along with field measurements, this could help to constrain future lake-source carbon gas

  2. Lipophilic pigments from the benthos of a perennially ice-covered Antarctic lake

    NASA Technical Reports Server (NTRS)

    Palmisano, A. C.; Wharton, R. A. Jr; Cronin, S. E.; Des Marais, D. J.; Wharton RA, J. r. (Principal Investigator)

    1989-01-01

    The benthos of a perennially ice-covered Antarctic lake, Lake Hoare, contained three distinct 'signatures' of lipophilic pigments. Cyanobacterial mats found in the moat at the periphery of the lake were dominated by the carotenoid myxoxanthophyll; carotenoids: chlorophyll a ratios in this high light environment ranged from 3 to 6.8. Chlorophyll c and fucoxanthin, pigments typical of golden-brown algae, were found at 10 to 20 m depths where the benthos is aerobic. Anaerobic benthic sediments at 20 to 30 m depths were characterized by a third pigment signature dominated by a carotenoid, tentatively identified as alloxanthin from planktonic cryptomonads, and by phaeophytin b from senescent green algae. Pigments were not found associated with alternating organic and sediment layers. As microzooplankton grazers are absent from this closed system and transformation rates are reduced at low temperatures, the benthos beneath the lake ice appears to contain a record of past phytoplankton blooms undergoing decay.

  3. Evidence of recent warming and El Nino-related variations in ice breakup of Wisconsin lakes

    USGS Publications Warehouse

    Anderson, W.L.; Robertson, D.M.; Magnuson, J.J.

    1996-01-01

    Ice breakup dates from 1968 to 1988 were examined for 20 Wisconsin lakes to determine whether consistent interannual and long-term changes exist. Each ice record had a trend toward earlier breakup dates, as demonstrated by a negative slope with time, indicating a recent warming trend. The average change in breakup dates was 0.82 d earlier per year for the lakes in southern Wisconsin, which was more extreme than that for the northern Wisconsin lakes (0.45 d yr-1). Interannual variation in breakup dates was related to the warm phase of El Nino/Southern Oscillation (ENSO) episodes. El Nino events occurred five times during this period (1965, 1972, 1976, 1982, and 1986). Average breakup dates were significantly earlier than average (5-14 d) during the mature phase of El Nino. This variability was affected by the location of the lake: El Nino-related variation was more evident for the southern lakes than the northern lakes. This difference was caused by the average date of breakup for the southern lakes being in late March directly following the period when air temperatures were strongly related to El Nino events, whereas the average dates of breakup of the northern lakes was in mid- to late April following a period when air temperatures were not significantly related to El Nino events. Overall, the interannual and long-term patterns across Wisconsin were relatively consistent, indicating that recent warming and El Nino- related variation are regional climatic responses.

  4. Climate regulates alpine lake ice cover phenology and aquatic ecosystem structure

    NASA Astrophysics Data System (ADS)

    Preston, Daniel L.; Caine, Nel; McKnight, Diane M.; Williams, Mark W.; Hell, Katherina; Miller, Matthew P.; Hart, Sarah J.; Johnson, Pieter T. J.

    2016-05-01

    High-elevation aquatic ecosystems are highly vulnerable to climate change, yet relatively few records are available to characterize shifts in ecosystem structure or their underlying mechanisms. Using a long-term data set on seven alpine lakes (3126 to 3620 m) in Colorado, USA, we show that ice-off dates have shifted 7 days earlier over the past 33 years and that spring weather conditions—especially snowfall—drive yearly variation in ice-off timing. In the most well studied lake, earlier ice-off associated with increases in water residence times, thermal stratification, ion concentrations, dissolved nitrogen, pH, and chlorophyll a. Mechanistically, low spring snowfall and warm temperatures reduce summer stream flow (increasing lake residence times) but enhance melting of glacial and permafrost ice (increasing lake solute inputs). The observed links among hydrological, chemical, and biological responses to climate factors highlight the potential for major shifts in the functioning of alpine lakes due to forecasted climate change.

  5. Climate regulates alpine lake ice cover phenology and aquatic ecosystem structure

    USGS Publications Warehouse

    Preston, Daniel L.; Caine, Nel; McKnight, Diane M.; Williams, Mark W.; Hell, Katherina; Miller, Matthew P.; Hart, Sarah J.; Johnson, Pieter T.J.

    2016-01-01

    High-elevation aquatic ecosystems are highly vulnerable to climate change, yet relatively few records are available to characterize shifts in ecosystem structure or their underlying mechanisms. Using a long-term dataset on seven alpine lakes (3126 to 3620 m) in Colorado, USA, we show that ice-off dates have shifted seven days earlier over the past 33 years and that spring weather conditions – especially snowfall – drive yearly variation in ice-off timing. In the most well-studied lake, earlier ice-off associated with increases in water residence times, thermal stratification, ion concentrations, dissolved nitrogen, pH, and chlorophyll-a. Mechanistically, low spring snowfall and warm temperatures reduce summer stream flow (increasing lake residence times) but enhance melting of glacial and permafrost ice (increasing lake solute inputs). The observed links among hydrological, chemical, and biological responses to climate factors highlight the potential for major shifts in the functioning of alpine lakes due to forecasted climate change.

  6. Implications of optical properties of ocean, lake, and ice for ultrahigh-energy neutrino detection

    SciTech Connect

    Price, P.B.

    1997-03-01

    The collecting power and imaging ability of planned ultrahigh-energy neutrino observatories depend on wavelength-dependent absorption and scattering coefficients for the detector medium. Published data are compiled for deep ice at the South Pole, for deep fresh water at Lake Baikal, and for deep seawater. The effective scattering coefficient is smallest for the clearest deep ocean sites, whereas the absorption coefficient is an order of magnitude smaller for deep ice than for the ocean and lake sites. The effective volume per detector element as a function of energy is calculated for electromagnetic cascades produced by electron neutrinos interacting at the various sites. It is largest for deep bubble-free ice, smallest for shallow bubbly ice, and intermediate for lake and seawater. The effective volume per element is calculated for detection of positrons resulting from the capture of a few megaelectron volt supernova neutrinos by protons in the medium. This volume is proportional to the absorption length and independent of the scattering length; it is larger for ice than for seawater or lake water. {copyright} 1997 Optical Society of America

  7. Temperature fluctuations underneath the ice in Diamond Lake, Hennepin County, Minnesota

    NASA Astrophysics Data System (ADS)

    Kletetschka, Gunther; Fischer, Tomas; Mls, Jiří; DěDeček, Petr

    2013-06-01

    Diamond Lake in Minnesota is covered every winter with ice and snow providing a modified thermal insulation between water and air. Autonomous temperature sensors, data loggers, were placed in this lake so that hourly measurements could be obtained from the snow-covered ice and water. The sensors that became frozen measured damped and delayed thermal response from the air-temperature fluctuation. Those sensors that were deeper within the snow-covered ice measured continuous, almost constant, temperature values near freezing. Several of them were within the liquid water and responded with a fluctuation of 24 h periods of amplitudes up to 0.2°C. Our analysis of the vertical temperature profiles suggested that the source of periodic water heating comes from the lake bottom. Because of the absence of daily temperature variations of the snow-covered ice, the influence of the air-temperature fluctuation can be ruled out. We attribute the heating process to the periodic inflow of groundwater to the lake and the cooling to the heat diffusion to the overlying ice cover. The periodic groundwater inflow is interpreted due to solid Earth tides, which cause periodic fluctuations of the groundwater pressure head.

  8. Asynchronous ice lobe retreat and glacial Lake Bascom: Deglaciation of the Hoosic and Vermont valleys, southwestern Vermont

    SciTech Connect

    Small, E.; Desimone, D. . Dept. of Geology)

    1993-03-01

    Deglaciation of the Hoosic River drainage basin in southwestern Vermont was more complex than previously described. Detailed surficial mapping, stratigraphic relationships, and terrace levels/delta elevations reveal new details in the chronology of glacial Lake Bascom: (1) a pre-Wisconsinan proglacial lake was present in a similar position to Lake Bascom as ice advanced: (2) the northern margin of 275m (900 ft) glacial Lake Bascom extended 10 km up the Vermont Valley; (3) the 215m (705 ft) Bascom level was stable and long lived; (4) intermediate water planes existed between 215m and 190m (625 ft) levels; and (5) a separate ice tongue existed in Shaftsbury Hollow damming a small glacial lake, here named glacial Lake Emmons. This information is used to correlate ice margins to different lake levels. Distance of ice margin retreat during a lake level can be measured. Lake levels are then used as control points on a Lake Bascom relative time line to compare rate of retreat of different ice tongues. Correlation of ice margins to Bascom levels indicates ice retreat was asynchronous between nearby tongues in southwestern Vermont. The Vermont Valley ice tongue retreated between two and four times faster than the Hoosic Valley tongue during the Bascom 275m level. Rate of retreat of the Vermont Valley tongue slowed to one-half of the Hoosic tongue during the 215m--190m lake levels. Factors responsible for varying rates of retreat are subglacial bedrock gradient, proximity to the Hudson-Champlain lobe, and the presence of absence of a calving margins. Asynchronous retreat produced splayed ice margins in southwestern Vermont. Findings from this study do not support the model of parallel, synchronous retreat proposed by many workers for this region.

  9. Temporal coherence in water temperature and chemistry under the ice of boreal lakes (Finland).

    PubMed

    Järvinen, M; Rask, M; Ruuhijärvi, J; Arvola, L

    2002-09-01

    Temporal coherence was assessed for 11 limnological variables--water temperature, oxygen, conductivity, alkalinity, pH, colour, calcium (Ca), iron, aluminium, total phosphorus and total nitrogen--between 28 boreal lakes in southern Finland for the winter ice-covered period. The lakes were mainly small (<0.2 km2) and brown-coloured, and located within a circle of 10-km radius. A mean Pearson correlation coefficient for all lake pairs and variables averaged 0.37. Temporal coherence of variables across lake pairs was highest for conductivity, Ca, water temperature and alkalinity. The lake pairs with a direct surface water channel connection had a higher coherence than the lake pairs not connected by a stream. The size of the lake or catchment area had little effect on the coherence between the lakes. Temporal coherence was not strongly related to the difference in water colour (dystrophy) between the lakes. However, between polyhumic lakes (colour > 100 g Pt m(-3)) the coherence was generally higher than between less coloured lakes. Year-to-year variation in limnological characteristics could be partly explained by the variation in local weather. In March, water temperature and chemistry were infrequently related to winter weather, rather they correlated with the weather conditions of the previous autumn, while the ambient late winter weather seemed to have a stronger influence on lake conditions in April. Temporal variation in some variables was related to the atmospheric pressure changes over the North Atlantic (the North Atlantic Oscillation, NAO). Our results suggest that the potential effects of climatic change on lakes can be generalised regionally for brown-coloured dystrophic lakes. PMID:12405403

  10. Bubbles trapped in arctic lake ice: Potential implications for methane emissions

    NASA Astrophysics Data System (ADS)

    Wik, Martin; Crill, Patrick M.; Bastviken, David; Danielsson, Åsa; NorbäCk, Elin

    2011-09-01

    The amount of methane (CH4) emitted from northern lakes to the atmosphere is uncertain but is expected to increase as a result of arctic warming. A majority of CH4 is thought to be released through ebullition (bubbling), a pathway with extreme spatial variability that limits the accuracy of measurements. We assessed ebullition during early and late winter by quantifying bubbles trapped in the ice cover of two lakes in a landscape with degrading permafrost in arctic Sweden using random transect sampling and a digital image processing technique. Bubbles covered up to ˜8% of the lake area and were largely dominated by point source emissions with spatial variabilities of up to 1056%. Bubble occurrence differed significantly between early and late season ice, between the two lakes and among different zones within each lake (p < 0.001). Using a common method, we calculated winter fluxes of up to 129 ± 486 mg CH4 m-2 d-1. These calculations are, on average, two times higher than estimates from North Siberian and Alaskan lakes and four times higher than emissions measured from the same lakes during summer. Therefore, the calculations are likely overestimates and point to the likelihood that estimating CH4 fluxes from ice bubble distributions may be more difficult than believed. This study also shows that bubbles quantified using few transects will most likely be unsuitable in making large-scale flux estimates. At least 19 transects covering ˜1% of the lake area were required to examine ebullition with high precision in our studied lakes.

  11. Trends of ice cover duration in Finnish lakes in 1963-2015

    NASA Astrophysics Data System (ADS)

    Kuusisto, Esko

    2016-04-01

    Long data series of freezing and breakup observations are available from the lakes in Finland. Some of these series were started already in the former half of the 19th century. In this study, the duration of ice cover, together with the freezing and breakup dates in 1963-2015 have been analyzed for 50 lakes covering the whole country. A statistically significant linear trend (99.9%) towards a shorter duration was detected in 30 lakes. Fifteen lakes had a shortening trend with a significance of 99 per cent and the rest, three lakes with a significance of 95 per cent. For freezing, the corresponding numbers for a delaying date were seven, 14 and 20, for an earlier breakup they were 39, eight and three. None of the stations had opposite trends. In about half of the lakes, the shortening of the ice duration was 26-34 days. The shortening was almost twice as long in Southern Finland than in Northern Finland. For freezing date, half of the shifts were between 17-24 days, for breakup date between 11-14 days. Many lakes in Southern and Central Finland had their record early breakup in spring 2014. Most of the longest series had the previous record from the spring of 1921. By far the latest breakup during the observation history had occurred in 1867. In Southern and Central Finland, the difference from that breakup date to the second latest is typically 2-3 weeks.

  12. The distribution, structure, and composition of freshwater ice deposits in Bolivian salt lakes

    USGS Publications Warehouse

    Hurlbert, S.H.; Chang, Cecily C.Y.

    1988-01-01

    Freshwater ice deposits are described from seven, high elevation (4117-4730 m), shallow (mean depth <30 cm), saline (10-103 g l-1) lakes in the southwestern corner of Bolivia. The ice deposits range to several hundred meters in length and to 7 m in height above the lake or playa surface. They are located near the lake or salar margins; some are completely surrounded by water, others by playa deposits or salt crusts. Upper surfaces and sides of the ice deposits usually are covered by 20-40 cm of white to light brown, dry sedimentary materials. Calcite is the dominant crystalline mineral in these, and amorphous materials such as diatom frustules and volcanic glass are also often abundant. Beneath the dry overburden the ice occurs primarily as horizontal lenses 1-1000 mm thick, irregularly alternating with strata of frozen sedimentary materials. Ice represents from 10 to 87% of the volume of the deposits and yields freshwater (TFR <3 g l-1) when melted. Oxygen isotope ratios for ice are similar to those for regional precipitation and shoreline seeps but much lower than those for the lakewaters. Geothermal flux is high in the region as evidenced by numerous hot springs and deep (3.0-3.5 m) sediment temperatures of 5-10??C. This flux is one cause of the present gradual wasting away of these deposits. Mean annual air temperatures for the different lakes probably are all in the range of -2 to 4??C, and mean midwinter temperatures about 5??C lower. These deposits apparently formed during colder climatic conditions by the freezing of low salinity porewaters and the building up of segregation ice lenses. ?? 1988 Dr W. Junk Publishers.

  13. Stratified distribution of nutrients and extremophile biota within freshwater ice covering the surface of Lake Baikal.

    PubMed

    Bondarenko, Nina A; Belykh, Olga I; Golobokova, Ludmila P; Artemyeva, Olga V; Logacheva, Natalia F; Tikhonova, Irina V; Lipko, Irina A; Kostornova, Tatyana Ya; Parfenova, Valentina V; Khodzher, Tamara V; Ahn, Tae-Seok; Zo, Young-Gun

    2012-02-01

    Biological entities and gradients of selected chemicals within the seemingly barren ice layers covering Lake Baikal were investigated. Ice cores 40-68 cm long were obtained from in shore and offshore sites of Southern Lake Baikal during the cold period of a year (March-April) in 2007 and 2008. In microscopic observations of the melted ice, both algae and bacteria were found in considerable numbers (>10(3) cells/L and >10(4) cells/ml, respectively). Among all organisms found, diatom was generally the most predominant taxon in the ice. Interestingly, both planktonic and benthic algae were present in considerable numbers (2-4×10(4) cells/L). Dominant phototrophic picoplankton were comprised of small green algae of various taxa and cyanobacteria of Synechococcus and Cyanobium. The bacterial community consisted mostly of short rod and cocci cells, either free-living or aggregated. Large numbers of yeast-like cells and actinomycete mycelium were also observed. Concentrations of silica, phosphorus, and nitrate were low by an order of magnitude where biota was abundant. The profile of the ice could be interpreted as vertical stratification of nutrients and biomass due to biological activities. Therefore, the organisms in the ice were regarded to maintain high activity while thriving under freezing conditions. Based on the results, it was concluded that the freshwater ice covering the surface of Lake Baikal is considerably populated by extremophilic microorganisms that actively metabolize and form a detritus food chain in the unique large freshwater ecosystem of Lake Baikal. PMID:22367932

  14. Changes in winter air temperatures near Lake Michigan, 1851-1993, as determined from regional lake-ice records

    USGS Publications Warehouse

    Assel, R.A.; Robertson, Dale M.

    1995-01-01

    Records of freezeup and breakup dates for Grand Traverse Bay, Michigan, and Lake Mendota, Wisconsin, are among the longest ice records available near the Great Lakes, beginning in 185 1 and 1855, respectively. The timing of freezeup and breakup results from an integration of meteorological conditions (primarily air temperature) that occur before these events. Changes in the average timing of these ice-events are translated into changes in air temperature by the use of empirical and process-driven models. The timing of freezeup and breakup at the two locations represents an integration of air temperatures over slightly different seasons (months). Records from both locations indicate that the early winter period before about 1890 was - 15°C cooler than the early winter period after that time; the mean temperature has, however, remained relatively constant since about 1890. Changes in breakup dates demonstrate a similar 1.0-1 .5”C increase in late winter and early spring air temperatures about 1890. More recent average breakup dates at both locations have been earlier than during 1890-1940, indicating an additional warming of 1.2”C in March since about 1940 and a warming of 1 . 1°C in January-March since about 1980. Ice records at these sites will continue to provide an early indication of the anticipated climatic warming, not only because of the large response of ice cover to small changes in air temperature but also because these records integrate climatic conditions during the seasons (winter-spring) when most warming is forecast to occur. Future reductions in ice cover may strongly affect the winter ecology of the Great Lakes by reducing the stable environment required by various levels of the food chain. 

  15. EO-based lake-ice cover and surface temperature products: Advancing process understanding and modeling capabilities of lake-atmosphere interactions in cold regions

    NASA Astrophysics Data System (ADS)

    Duguay, C. R.; Kheyrollah Pour, H.; Ochilov, S.

    2011-12-01

    Our ability to determine the energy and water budgets of lakes is critical to modeling high latitude weather and climate. In recent years, the proper representation of lake processes in numerical weather prediction (NWP) and regional climate (RCM) models has become a topic of much interest by the scientific community. With the increased resolution of the NWP models and RCMs, it has now become possible and necessary to improve the representation of lake-atmosphere interactions to better describe the energy exchange between the atmosphere and the lake surface. Among other lake properties, knowledge about lake surface temperature and ice-coverage is critical. These two parameters can either be obtained from observations or through simulations. Although much progress is being made with lake models, as implemented in NWP/RCM models, the assimilation of data on lake temperature and fractional ice coverage has been identified as highly desirable. Spatially and temporally consistent lake ice and lake surface temperature (LST) products are invaluable in this respect. These can be derived from Earth Observation (EO) systems. However, satellite-based products must be compared with existing lake models, as well as validated and further improved as needed, to generate lake ice and LST products for operational use by the modeling community. The European Space Agency (ESA) is supporting the international efforts coordinated by the Climate and Cryosphere (CliC) project of the World Climate Research Programme (WCRP) to exploit the use of EO technology, models and in situ data to improve the characterization of river and lake ice processes and their contribution to the Northern Hydrology system. The ESA-sponsored North Hydrology project aims to develop a portfolio of novel multi-mission geo-information products, maximizing the use of ESA satellite data, to respond to the scientific requirements of the CliC community and the operational requirements of the weather and climate

  16. A decade of sedimentation in ice-contact, proglacial lakes, Bering Glacier, AK

    NASA Astrophysics Data System (ADS)

    Fleisher, P. Jay; Bailey, Palmer K.; Cadwell, Donald H.

    2003-08-01

    Bathymetric surveys during the 1991-2000 decade in two ice-contact, proglacial lakes on the eastern sector of Bering piedmont lobe captured the buildup effects of the 1993-1995 surge. Following ice-front advance of 1.0-1.5 km into Tsivat and Tsiu Lakes, the basins were significantly altered by surge-related sedimentation including the impact of a subglacial outburst into Tsivat Lake. The subsequent changes in basin shape, size, and morphology were monitored by six bathymetric surveys. Measured changes in water depth serve as a proxy for determining increments of sediment accumulation. Upwelling, ice-front vents fed by subglacial tunnels transported suspended fine sediment directly into the lake system. The rate of suspension settling within both lakes varied from 0.6 to 1.2 m year -1 prior to the surge. Suspended load during surge years increased sixfold from 1.7 to 13.9 g l -1, accompanied by increased sediment accumulation of 2.2-3.1 m year -1. Vent-related aggradation and subsequent filling of Tsivat Lake caused sediment bypassing to Tsiu Lake, where encroachment by delta growth contributed to a postsurge rate of bottomset accumulation of 3.0 m year -1. The total sediment influx from subglacial sources is represented by the sum of bathymetrically determined accumulation, plus an estimated volume of sediment that remained suspended, thus passing through the lake system. Total sediment flux along the eastern Bering piedmont lobe from 1991 to 2000 is approximately 227 million cubic meters.

  17. Statistical characterization of trapped bubbles in subarctic lake ice: Potential implications for methane emissions

    NASA Astrophysics Data System (ADS)

    Wik, M.; Crill, P. M.; Bastviken, D.; Danielsson; Norbäck, E.

    2010-12-01

    Methane (CH4) emissions from northern lakes to the atmosphere are highly uncertain but estimated to increase due to arctic climate change and subsequent permafrost thaw and sediment warming. A large amount of CH4, if not the most, is thought to be released through ebullition (bubbling), a pathway with extreme spatial patchiness that challenges the accuracy of measurements and budget extrapolations. The spatial variability of ebullition can be assessed on northern lakes because bubbles are trapped in the ice during winter. This study statistically characterized trapped bubbles over various depths across two ice covered subarctic lakes in a changing discontinuous permafrost landscape in northern Sweden. Observations were made through a 0.64 m2 quadrat that was placed every third meter along a large number of randomly distributed transects. This stratified random sampling design combined with a digital image processing technique determined that bubble patterns on average covered up to 7.7% of the lake area and were dominated by ebullition from frequently occurring but highly spatially dispersed point sources with variabilities of up to 1056%. Bubble frequency differed significantly between early and late season lake ice, between the two lakes and among different zones within each lake (p<0.001). Based on the high spatial variability it was calculated that almost 1% of a lake area was required to be measured along 15 randomly distributed transects to examine the patchiness of bubbles with high precision. Thus, the number and variability of bubbles observed along a small number of transects will most likely be unsuitable variables in large scale estimates and extrapolations aiming to reduce uncertainties in the budget of atmospheric CH4.

  18. Ultra-low rare earth element content in accreted ice from sub-glacial Lake Vostok, Antarctica

    NASA Astrophysics Data System (ADS)

    Barbante, C.; Gabrielli, P.; Turetta, C.; Planchon, F.; Boutron, C.; Petit, J. R.; Bulat, S.; Hong, S.; Cozzi, G.; Cescon, P.

    2009-12-01

    We report the first rare earth element (REE) concentrations in accreted ice refrozen from sub-glacial Lake Vostok (East Antarctica). REE were determined in various sections of the Vostok ice core in order to geochemically characterize its impurities. Samples were obtained from accreted ice and, for comparison, from the upper glacier ice of atmospheric origin (undisturbed, disturbed and glacial flour ice). REE concentrations ranged between 0.8-56 pg g-1 for Ce and 0.0035- 0.24 pg g-1 for Lu in glacier ice, and between <0.1-24 pg g-1 for Ce and <0.0004-0.02 pg g-1 for Lu in accreted ice. Interestingly, the REE concentrations in the upper accreted ice (AC1;characterized by visible aggregates containing a mixture of very fine terrigenous particles) and in the deeper accreted ice (AC2; characterized by transparent ice) are lower than those in fresh water and seawater, respectively. We suggest that such ultra-low concentrations are unlikely to be representative of the real REE content in Lake Vostok, but instead may reflect phase exclusion processes occurring at the ice/water interface during refreezing. In particular, the uneven spatial distribution (on the order of a few cm) and the large range of REE concentrations observed in AC1 are consistent with the occurrence/absence of the aggregates in adjacent ice, and point to the presence of solid-phase concentration/exclusion processes occurring within separate pockets of frazil ice during AC1 formation. Interestingly, if the LREE enrichment found in AC1 was not produced by chemical fractionation occurring in Lake Vostok water, this may reflect a contribution of bedrock material, possibly in combination with aeolian dust released into the lake by melting of the glacier ice. Collectively, this valuable information provides new insight into the accreted ice formation processes, the bedrock geology of East Antarctica as well as the water chemistry and circulation of Lake Vostok.

  19. Ultra-low rare earth element content in accreted ice from sub-glacial Lake Vostok, Antarctica

    NASA Astrophysics Data System (ADS)

    Gabrielli, Paolo; Planchon, Frederic; Barbante, Carlo; Boutron, Claude F.; Petit, Jean Robert; Bulat, Sergey; Hong, Sungmin; Cozzi, Giulio; Cescon, Paolo

    2009-10-01

    This paper reports the first rare earth element (REE) concentrations in accreted ice refrozen from sub-glacial Lake Vostok (East Antarctica). REE were determined in various sections of the Vostok ice core in order to geochemically characterize its impurities. Samples were obtained from accreted ice and, for comparison, from the upper glacier ice of atmospheric origin (undisturbed, disturbed and glacial flour ice). REE concentrations ranged between 0.8-56 pg g -1 for Ce and 0.0035-0.24 pg g -1 for Lu in glacier ice, and between <0.1-24 pg g -1 for Ce and <0.0004-0.02 pg g -1 for Lu in accreted ice. Interestingly, the REE concentrations in the upper accreted ice (AC 1; characterized by visible aggregates containing a mixture of very fine terrigenous particles) and in the deeper accreted ice (AC 2; characterized by transparent ice) are lower than those in fresh water and seawater, respectively. We suggest that such ultra-low concentrations are unlikely to be representative of the real REE content in Lake Vostok, but instead may reflect phase exclusion processes occurring at the ice/water interface during refreezing. In particular, the uneven spatial distribution (on the order of a few cm) and the large range of REE concentrations observed in AC 1 are consistent with the occurrence/absence of the aggregates in adjacent ice, and point to the presence of solid-phase concentration/exclusion processes occurring within separate pockets of frazil ice during AC 1 formation. Interestingly, if the LREE enrichment found in AC 1 was not produced by chemical fractionation occurring in Lake Vostok water, this may reflect a contribution of bedrock material, possibly in combination with aeolian dust released into the lake by melting of the glacier ice. Collectively, this valuable information provides new insight into the accreted ice formation processes, the bedrock geology of East Antarctica as well as the water chemistry and circulation of Lake Vostok.

  20. Ecology of Subglacial Lake Vostok (Antarctica), Based on Metagenomic/Metatranscriptomic Analyses of Accretion Ice

    PubMed Central

    Rogers, Scott O.; Shtarkman, Yury M.; Koçer, Zeynep A.; Edgar, Robyn; Veerapaneni, Ram; D’Elia, Tom

    2013-01-01

    Lake Vostok is the largest of the nearly 400 subglacial Antarctic lakes and has been continuously buried by glacial ice for 15 million years. Extreme cold, heat (from possible hydrothermal activity), pressure (from the overriding glacier) and dissolved oxygen (delivered by melting meteoric ice), in addition to limited nutrients and complete darkness, combine to produce one of the most extreme environments on Earth. Metagenomic/metatranscriptomic analyses of ice that accreted over a shallow embayment and over the southern main lake basin indicate the presence of thousands of species of organisms (94% Bacteria, 6% Eukarya, and two Archaea). The predominant bacterial sequences were closest to those from species of Firmicutes, Proteobacteria and Actinobacteria, while the predominant eukaryotic sequences were most similar to those from species of ascomycetous and basidiomycetous Fungi. Based on the sequence data, the lake appears to contain a mixture of autotrophs and heterotrophs capable of performing nitrogen fixation, nitrogen cycling, carbon fixation and nutrient recycling. Sequences closest to those of psychrophiles and thermophiles indicate a cold lake with possible hydrothermal activity. Sequences most similar to those from marine and aquatic species suggest the presence of marine and freshwater regions. PMID:24832801

  1. Physical background of the development of oxygen depletion in ice-covered lakes.

    PubMed

    Golosov, S; Maher, O A; Schipunova, E; Terzhevik, A; Zdorovennova, G; Kirillin, G

    2007-03-01

    The effect of the heat interaction between a water column and sediments on the formation, development, and duration of existence of anaerobic zones in ice-covered lakes is estimated based on observational data from five frozen lakes located in northwestern Russia and North America. A simple one-dimensional model that describes the formation and development of the dissolved oxygen deficit in shallow ice-covered lakes is suggested. The model reproduces the main features of dissolved oxygen dynamics during the ice-covered period; that is, the vertical structure, the thickness, and the rate of increase of the anaerobic zone in bottom layers. The model was verified against observational data. The results from the verification show that the model adequately describes the dissolved oxygen dynamics in winter. The consumption rates of DO by bacterial plankton and by bottom sediments, which depend on the heat transfer through the water-sediment interface, are calculated. The results obtained allow the appearance of potentially dangerous anaerobic zones in shallow lakes and in separate lake areas, which result from thermal regime changes, to be predicted.

  2. Ice Flow Dynamics and Outlet Zone Morphology of Subglacial Lake Ellsworth

    NASA Astrophysics Data System (ADS)

    Ross, N.; Smith, A.; Woodward, J.; Siegert, M. J.; Hindmarsh, R. C.; Corr, H.; King, E. C.; Vaughan, D.; Gillet-Chaulet, F.; Jay-Allemand, M.

    2009-12-01

    Subglacial Lake Ellsworth (SLE) is located beneath 2.95-3.28 km of ice at the base of a deep subglacial trench ~30 km from the central ice divide of the West Antarctic Ice Sheet. Seismic reflection surveys indicate a maximum water column thickness of 155 m. Radio-echo sounding (RES) data have been used to map the lake, the morphology of the subglacial catchment and the structure and thickness of the overlying ice sheet. Direct access, measurement and sampling of the lake waters and underlying sediments will be undertaken during the 2012-13 Antarctic field season by the Lake Ellsworth Consortium. Internal ice sheet layers throughout the SLE catchment have been picked and transformed into 3D surfaces as input for radar layer modelling. SLE is bounded on either side by steep, ~2 km high, mountainous subglacial topography. Over the lake, anomalies between modelled and observed internal layers are recognised near the steeper bedrock wall. We have sought to understand these in terms of perturbations to the velocity field from higher order mechanical effects as well as being caused by melt anomalies. A closely-spaced grid of RES lines (area coverage 7.5 x 7.5 km, line spacing ~500 m or less) has been used to map the outlet area of the lake in detail, with the aim of identifying possible drainage routes. The downstream margin of the lake is characterised by a pronounced topographic ridge, trending obliquely to ice flow, which rises ~200 m above the elevation of the water surface. Beyond the ridge a 5 km by 0.75 km linear depression has been mapped. A narrow, low-lying breach in the ridge that connects to this depression may provide a subglacial hydrological outlet from SLE. Potential mechanisms for the formation of these features include: i) subaerial or subglacial processes pre-dating ice sheet development; ii) water discharge from SLE. Such models are not necessarily mutually exclusive. The origins of the subglacial geomorphology and its possible influence on the routing

  3. Ice Processes and Growth History on Arctic and Sub-Arctic Lakes Using ERS-1 SAR Data

    NASA Technical Reports Server (NTRS)

    Morris, K.; Jeffries, M. O.; Weeks, W. F.

    1995-01-01

    A survey of ice growth and decay processes on a selection of shallow and deep sub-Arctic and Arctic lakes was conducted using radiometrically calibrated ERS-1 SAR images. Time series of radar backscatter data were compiled for selected sites on the lakes during the period ot ice cover (September to June) for the years 1991-1992 and 1992-1993. A variety of lake-ice processes could be observed, and significant changes in backscatter occurred from the time of initial ice formation in autumn until the onset of the spring thaw. Backscatter also varied according to the location and depth of the lakes. The spatial and temporal changes in backscatter were most constant and predictable at the shallow lakes on the North Slope of Alaska. As a consequence, they represent the most promising sites for long-term monitoring and the detection of changes related to global warming and its effects on the polar regions.

  4. Microbial processes in the ice cover of a newly detected subglacial lake in Antarctica

    NASA Astrophysics Data System (ADS)

    Sattler, B.; Dieser, M.; Wille, A.; Sipiera, P.; Psenner, R.

    2003-04-01

    A subglacial water body, called Lake Paula, was detected in Patriot Hills in the West Antarctic in 2002 and sampled for the first time ever for microbial life within the ice cover and the pelagic zone. It is permanently covered with an ice sheet of approximately 2,5 m thickness and the water body has a depth of about 10 m. The lake is situated near a moraine which partly ablates from snow and provides meltwater from the slopes to the lake during austral summer. These running waters which are kept liquid by the heating up of the dark soil are penetrating the lower ice cover and inoculating it with nutrients, microbes and diatoms of terrestrial origin, thus dividing the ice cover laterally in two different sections. The upper part which is exposed to the atmosphere and never in contact with meltwater is harboring an extremely low abundance of bacteria (811 ml-1), whereas bacterial numbers increase in the lower meter up to 1,14*105 ml-1. A similar pattern can be observed concerning bacterial production: The upside part shows carbon production of 0,2ng l-1h-1, the lakeside end of the ice core which is softened up by the intrusion had a nearly 10fold increase with 2,8 ng carbon l-1 h-1. Temperature sensitivity of the embedded microbes reveal completely diverse pictures as well: Bacteria isolated from the upper part showed growth optima at 10^oC, the lower part at 25^oC, phylogenetic affiliations done by 16s rDNA still have to be done. These results proof once more as already known from the unique Dry Valley Lakes that even in this harsh environment like the Antarctic continent microbial ice aggregates can be sustained and kept in a dynamic system as long as the supply of liquid water which is essential for an active bacterial metabolism is provided at least for a small time frame.

  5. Links Between Acceleration, Melting, and Supraglacial Lake Drainage of the Western Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Hoffman, M. J.; Catania, G. A.; Newmann, T. A.; Andrews, L. C.; Rumrill, J. A.

    2012-01-01

    The impact of increasing summer melt on the dynamics and stability of the Greenland Ice Sheet is not fully understood. Mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding. Here, we compare subdaily ice velocity and uplift derived from nine Global Positioning System stations in the upper ablation zone in west Greenland to surface melt and supraglacial lake drainage during summer 2007. Starting around day 173, we observe speedups of 6-41% above spring velocity lasting approximately 40 days accompanied by sustained surface uplift at most stations, followed by a late summer slowdown. After initial speedup, we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting. Most lake drainages were undetectable in the velocity record, and those that were detected only perturbed velocities for approximately 1 day, suggesting preexisting drainage systems could efficiently drain large volumes of water. The dynamic response to melt forcing appears to 1) be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses, and 2) decrease over the course of the summer, presumably as the subglacial drainage system evolves to greater efficiency. The relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers, suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here. Thus, increases in summer melting may not guarantee faster seasonal ice flow.

  6. Links Between Acceleration, Melting, and Supraglacial Lake Drainage of the Western Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Hoffman, M. J.; Catania, G. A.; Neumann, T. A.; Andrews, L. C.; Rumrill, J. A.

    2011-01-01

    The impact of increasing summer melt on the dynamics and stability of the Greenland Ice Sheet is not fully understood. Mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding. Here, we compare subdaily ice velocity and uplift derived from nine Global Positioning System stations in the upper ablation zone in west Greenland to surface melt and supraglacial lake drainage during summer 2007. Starting around day 173, we observe speedups of 6-41% above spring velocity lasting 40 days accompanied by sustained surface uplift at most stations, followed by a late summer slowdown. After initial speedup, we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting. Most lake drainages were undetectable in the velocity record, and those that were detected only perturbed velocities for approx 1 day, suggesting preexisting drainage systems could efficiently drain large volumes of water. The dynamic response to melt forcing appears to (1) be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses, and (2) decrease over the course of the summer, presumably as the subglacial drainage system evolves to greater efficiency. The relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers, suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here. Thus, increases in summer melting may not guarantee faster seasonal ice flow.

  7. Detection and spatiotemporal analysis of methane ebullition on thermokarst lake ice using high-resolution optical aerial imagery

    NASA Astrophysics Data System (ADS)

    Lindgren, P. R.; Grosse, G.; Anthony, K. M. Walter; Meyer, F. J.

    2016-01-01

    Thermokarst lakes are important emitters of methane, a potent greenhouse gas. However, accurate estimation of methane flux from thermokarst lakes is difficult due to their remoteness and observational challenges associated with the heterogeneous nature of ebullition. We used high-resolution (9-11 cm) snow-free aerial images of an interior Alaskan thermokarst lake acquired 2 and 4 days following freeze-up in 2011 and 2012, respectively, to detect and characterize methane ebullition seeps and to estimate whole-lake ebullition. Bubbles impeded by the lake ice sheet form distinct white patches as a function of bubbling when lake ice grows downward and around them, trapping the gas in the ice. Our aerial imagery thus captured a snapshot of bubbles trapped in lake ice during the ebullition events that occurred before the image acquisition. Image analysis showed that low-flux A- and B-type seeps are associated with low brightness patches and are statistically distinct from high-flux C-type and hotspot seeps associated with high brightness patches. Mean whole-lake ebullition based on optical image analysis in combination with bubble-trap flux measurements was estimated to be 174 ± 28 and 216 ± 33 mL gas m-2 d-1 for the years 2011 and 2012, respectively. A large number of seeps demonstrated spatiotemporal stability over our 2-year study period. A strong inverse exponential relationship (R2 > = 0.79) was found between the percent of the surface area of lake ice covered with bubble patches and distance from the active thermokarst lake margin. Even though the narrow timing of optical image acquisition is a critical factor, with respect to both atmospheric pressure changes and snow/no-snow conditions during early lake freeze-up, our study shows that optical remote sensing is a powerful tool to map ebullition seeps on lake ice, to identify their relative strength of ebullition, and to assess their spatiotemporal variability.

  8. Detection of Supra-Glacial Lakes on the Greenland Ice Sheet Using MODIS Images

    NASA Astrophysics Data System (ADS)

    Verin, Gauthier; Picard, Ghislain; Libois, Quentin; Gillet-Chaulet, Fabien; Roux, Antoine

    2015-04-01

    During melt season, supra-glacial lakes form on the margins of the Greenland ice sheet. Because of their size exceeding several kilometers, and their concentration, they affect surface albedo leading to an amplification of the regional melt. Furthermore, they foster hydro-fracturing that propagate liquid water to the bedrock and therefore enhance the basal lubrication which may affect the ice motion. It is known that Greenland ice sheet has strongly responded to recent global warming. As air temperature increases, melt duration and melt intensity increase and surface melt area extends further inland. These recent changes may play an important role in the mass balance of the Greenland ice sheet. In this context, it is essential to better monitor and understand supra-glacial spatio-temporal dynamics in order to better assess future sea level rise. In this study MODIS (Moderate Resolution Imaging Spectroradiometer) images have been used to detect supra-glacial lakes. The observation site is located on the West margin of the ice sheet, between 65°N and 70°N where the concentration of lake is maximum. The detection is performed by a fully automatic algorithm using images processing techniques introduced by Liang et al. (2012) which can be summarized in three steps: the selection of usable MODIS images, mainly we exclude images with too many clouds. The detection of lake and the automatic correction of false detections. This algorithm is capable to tag each individual lake allowing a survey of all lake geometrical properties over the entire melt season. We observed a large population of supra-glacial lakes over 14 melt seasons, from 2000 to 2013 on an extended area of 70.000 km2. In average, lakes are observed from June 9 ± 8.7 days to September 13 ± 13.9 days, and reach a maximum total area of 699 km2 ± 146 km2. As the melt season progresses, lakes form higher in altitude up to 1800 m above sea level. Results show a very strong inter-annual variability in term of

  9. ERS-1 SAR monitoring of ice growth on shallow lakes to determine water depth and availability in north west Alaska

    NASA Technical Reports Server (NTRS)

    Jeffries, Martin; Morris, Kim; Liston, Glen

    1996-01-01

    Images taken by the ERS-1 synthetic aperture radar (SAR) were used to identify and to differentiate between the lakes that freeze completely to the bottom and those that do not, on the North Slope, in northwestern Alaska. The ice thickness at the time each lake froze completely is determined with numerical ice growth model that gives a maximum simulated thickness of 2.2 m. A method combining the ERS-1 SAR images and numerical ice growth model was used to determine the ice growth and the water availability in these regions.

  10. The interdependence of lake ice and climate in central North America

    NASA Technical Reports Server (NTRS)

    Jelacic, A. J. (Principal Investigator)

    1972-01-01

    There are no author-identified significant results in this report. This investigation is to identify any correlations between the freeze/ thaw cycles of lakes and regional weather variations. ERTS-1 imagery of central Canada and north central United States is examined on a seasonal basis. The ice conditions of certain major study lakes are noted and recorded on magnetic tape, from which the movement of a freeze/thaw transition zone may be deduced. Weather maps and tables are used to establish any obvious correlations. The process of selecting major study lakes is discussed, and a complete lake directory is presented. Various routines of the software support library are described, accompanied by output samples. Procedures used for ERTS imagery processing are presented along with the data analysis plan. Application of these procedures to selected ERTS imagery has demonstrated their utility. Preliminary results show that the freeze/thaw transition zone can be monitored from ERTS.

  11. Ice-walled-lake plains: Implications for the origin of hummocky glacial topography in middle North America

    USGS Publications Warehouse

    Clayton, L.; Attig, J.W.; Ham, N.R.; Johnson, M.D.; Jennings, C.E.; Syverson, K.M.

    2008-01-01

    Ice-walled-lake plains are prominent in many areas of hummocky-till topography left behind as the Laurentide Ice Sheet melted from middle North America. The formation of the hummocky-till topography has been explained by: (1) erosion by subglacial floods; (2) squeezing of subglacial till up into holes in stagnant glacial ice; or (3) slumping of supraglacial till. The geomorphology and stratigraphy of ice-walled-lake plains provide evidence that neither the lake plains nor the adjacent hummocks are of subglacial origin. These flat lake plains, up to a few kilometers in diameter, are perched as much as a few tens of meters above surrounding depressions. They typically are underlain by laminated, fine-grained suspended-load lake sediment. Many ice-walled-lake plains are surrounded by a low rim ridge of coarser-grained shore sediment or by a steeper rim ridge of debris that slumped off the surrounding ice slopes. The ice-walled lakes persisted for hundreds to thousands of years following glacial stagnation. Shells of aquatic molluscs from several deposits of ice-walled-lake sediment in south-central North Dakota have been dated from about 13 500 to 10 500??B.P. (calibrated radiocarbon ages), indicating a climate only slightly cooler than present. This is confirmed by recent palaeoecological studies in nearby non-glacial sites. To survive so long, the stagnant glacial ice had to be well-insulated by a thick cover of supraglacial sediment, and the associated till hummocks must be composed primarily of collapsed supraglacial till. ?? 2007 Elsevier B.V. All rights reserved.

  12. Snow Pack and Lake Ice Pack Remote Sensing using Wideband Autocorrelation Radiometry

    NASA Astrophysics Data System (ADS)

    Mousavi, S.; De Roo, R. D.; Sarabandi, K.; England, A. W.

    2015-12-01

    A novel microwave radiometric technique, wideband autocorrelation radiometry (WiBAR), offers a deterministic method of remotely sensing the propagation time τdelay of microwaves through low loss layers at the bottom of the atmosphere. Terrestrial examples are the snow and lake ice packs. This technique is based on the Planck radiation from the surface beneath the pack which travels upwards through the pack towards the radiometer; such a signal we call a direct signal. On the other hand, part of this radiation reflects back from the pack's upper interface then from its lower interface, before traveling towards the radiometer's antenna. Thus, there are two signals received by the radiometer, the direct signal and a delayed copy of it. The microwave propagation time τdelay through the pack yields a measure of its vertical extent. We report a time series of measurements of the ice pack on Lake Superior from February to April 2014 to demonstrate this technique. The observations are done at frequencies from 7 to 10 GHz. At these frequencies, the volume and surface scattering are small in the ice pack. This technique is inherently low-power since there is no transmitter as opposed to active remote sensing techniques. The results of this paper is to present the WiBAR technique and show that the microwave travel time within a dry snow pack and lake ice pack can be deterministically measured for different thicknesses using this technique.

  13. Dissolved gases in perennially ice-covered lakes of the McMurdo Dry Valleys, Antarctica

    NASA Technical Reports Server (NTRS)

    Andersen, D. T.; McKay, C. P.; Wharton, R. A. Jr; Wharton RA, J. r. (Principal Investigator)

    1998-01-01

    Measurements of dissolved N2, O2, Ar, CO2, and CH4 were made in perennially ice-covered Lake Hoare. Results confirm previous reports that O2 concentrations in the upper water column exceed atmospheric equilibrium and that N2 and Ar are supersaturated throughout the water column. The mean supersaturation of N2 was found to be 2.0 (+/- 0.37) and Ar was 3.8 (+/- 1.1). The ratios of N2/Ar (20.3 +/- 13.8), and O2/Ar (22.5 +/- 4.0) at the ice-water interface are consistent with those previously measured, suggesting that bubble formation is the main process for removing gas from the lake. However, the saturations of N2 and Ar greatly exceed those previously predicted for degassing by bubble formation only at the ice-water interface. The data support the hypothesis that removal of gas by bubbles occurs in the water column to a depth of 11 m in Lake Hoare. CO2 concentration increases from near zero at the ice-water interface to 80-100 times saturation at and below the chemocline at c. 28 m. There is considerable variability in the gas concentrations throughout the water column; samples separated in depth by one metre may vary by more than 50% in gas content. It is likely that this phenomenon results from the lack of turbulent mixing in the water column. Methane (c. 2 micrograms l-1) was detected below the chemocline and immediately above the sediment/water interface at a depth of 30 m. Samples from lakes Vanda, Joyce, and Miers, also show supersaturations of O2, N2, and Ar at levels similar to levels found in Lake Hoare.

  14. Dissolved gases in perennially ice-covered lakes of the McMurdo Dry Valleys, Antarctica.

    PubMed

    Andersen, D T; McKay, C P; Wharton, R A

    1998-06-01

    Measurements of dissolved N2, O2, Ar, CO2, and CH4 were made in perennially ice-covered Lake Hoare. Results confirm previous reports that O2 concentrations in the upper water column exceed atmospheric equilibrium and that N2 and Ar are supersaturated throughout the water column. The mean supersaturation of N2 was found to be 2.0 (+/- 0.37) and Ar was 3.8 (+/- 1.1). The ratios of N2/Ar (20.3 +/- 13.8), and O2/Ar (22.5 +/- 4.0) at the ice-water interface are consistent with those previously measured, suggesting that bubble formation is the main process for removing gas from the lake. However, the saturations of N2 and Ar greatly exceed those previously predicted for degassing by bubble formation only at the ice-water interface. The data support the hypothesis that removal of gas by bubbles occurs in the water column to a depth of 11 m in Lake Hoare. CO2 concentration increases from near zero at the ice-water interface to 80-100 times saturation at and below the chemocline at c. 28 m. There is considerable variability in the gas concentrations throughout the water column; samples separated in depth by one metre may vary by more than 50% in gas content. It is likely that this phenomenon results from the lack of turbulent mixing in the water column. Methane (c. 2 micrograms l-1) was detected below the chemocline and immediately above the sediment/water interface at a depth of 30 m. Samples from lakes Vanda, Joyce, and Miers, also show supersaturations of O2, N2, and Ar at levels similar to levels found in Lake Hoare. PMID:11541288

  15. Paleoseismic observations of an onshore transform boundary: The Magallanes-Fagnano fault, Tierra del Fuego, Argentina

    USGS Publications Warehouse

    Costa, C.H.; Smalley, R.; Schwartz, D.P.; Stenner, H.D.; Ellis, M.; Ahumada, E.A.; Velasco, M.S.

    2006-01-01

    We present preliminary information on the geomorphologic features and paleoseismic record associated with the ruptures of two Ms 7.8 earthquakes that struck Tierra del Fuego and the southernmost continental margin of South America on December 17, 1949. The fault scarp was surveyed in several places cast of Lago Fagnano and a trench across a secondary fault trace of the Magallanes-Fagnano fault was excavated at the Ri??o San Pablo. The observed deformation in a 9 kyr-old peat bog sequence suggests evidence for two, and possibly three pre-1949 paleoearthquakes is preserved in the stratigraphy. The scarp reaches heights up to 11 m in late Pleistocene-Holocence(?) deposits, but the vertical component of the 1949 events was always less than ???1 m. This observation also argues for the occurrence of previous events during the Quaternary. Along die part of the fault we investigated east of Lago Fagnano, the horizontal component of the 1949 rupture does not exceed 4 m and is likely lower than 0.4 m, which is consistent with the kinematics of a local releasing bend, or at the end of a strike-slip rupture zone. ?? 2006 Revista de la Asociacio??n Geolo??gica Argentina.

  16. Formation and character of an ancient 19-m ice cover and underlying trapped brine in an “ice-sealed” east Antarctic lake

    PubMed Central

    Doran, Peter T.; Fritsen, Christian H.; McKay, Christopher P.; Priscu, John C.; Adams, Edward E.

    2003-01-01

    Lake Vida, one of the largest lakes in the McMurdo Dry Valleys of Antarctica, was previously believed to be shallow (<10 m) and frozen to its bed year-round. New ice-core analysis and temperature data show that beneath 19 m of ice is a water column composed of a NaCl brine with a salinity seven times that of seawater that remains liquid below −10°C. The ice cover thickens at both its base and surface, sealing concentrated brine beneath. The ice cover is stabilized by a negative feedback between ice growth and the freezing-point depression of the brine. The ice cover contains frozen microbial mats throughout that are viable after thawing and has a history that extends to at least 2,800 14C years B.P., suggesting that the brine has been isolated from the atmosphere for as long. To our knowledge, Lake Vida has the thickest subaerial lake ice cover recorded and may represent a previously undiscovered end-member lacustrine ecosystem on Earth. PMID:12518052

  17. Formation and character of an ancient 19-m ice cover and underlying trapped brine in an "ice-sealed" east Antarctic lake.

    PubMed

    Doran, Peter T; Fritsen, Christian H; McKay, Christopher P; Priscu, John C; Adams, Edward E

    2003-01-01

    Lake Vida, one of the largest lakes in the McMurdo Dry Valleys of Antarctica, was previously believed to be shallow (<10 m) and frozen to its bed year-round. New ice-core analysis and temperature data show that beneath 19 m of ice is a water column composed of a NaCl brine with a salinity seven times that of seawater that remains liquid below -10 degrees C. The ice cover thickens at both its base and surface, sealing concentrated brine beneath. The ice cover is stabilized by a negative feedback between ice growth and the freezing-point depression of the brine. The ice cover contains frozen microbial mats throughout that are viable after thawing and has a history that extends to at least 2,800 (14)C years B.P., suggesting that the brine has been isolated from the atmosphere for as long. To our knowledge, Lake Vida has the thickest subaerial lake ice cover recorded and may represent a previously undiscovered end-member lacustrine ecosystem on Earth.

  18. Dating the Little Ice Age Advance of Jakobshavn Isbrae, Greenland, Using Pro-glacial Lake Sediments.

    NASA Astrophysics Data System (ADS)

    Stewart, H. A.; Briner, J. P.; Csatho, B. M.

    2009-05-01

    The Greenland Ice Sheet's (GIS) largest and fastest outlet glacier, Jakobshavn Isbrae, is one of the most significant contributors to GIS mass loss, draining an estimated 6.5% of the GIS area (Rignot and Kanagaratnam, 2006). Jakobshavn Isbrae has retreated significantly since the Little Ice Age (LIA, ca. 1250- 1900; Csatho et al., 2008), and continues to exhibit rapid changes in velocity and ice calving front position (Joughin et al., 2004). However, it is unknown for how long Jakobshavn Isbrae was at or near its extensive LIA position because there is a lack of chronological control on the LIA advance phase. We collected sediment cores from lakes just beyond the LIA margin to constrain the time when the advancing glacier's silt-laden meltwater entered the lake basins. Sediment cores from South Oval and Ice Boom lakes (informal names), which no longer receive glacial meltwater from Jakobshavn Isbrae because it has retreated out of their catchments, contain gyttja/glacial-silt/gyttja sequences that represent their non-glacial/pro-glacial/non-glacial histories. One additional site, ice-dammed Lake Morten (informal name), completely drained sometime between 1985 and 2001 AD. Outcrops of laminated sediments in the lake basin overly an intact tundra landscape. Four AMS radiocarbon dates from macrofossils immediately below the LIA sediments from the three lake basins reveal that Jakobshavn Isbrae reached its LIA maximum extent between 530±10 and 370±60 cal yr BP (1400-1640 AD). Furthermore, the continuous nature of the LIA-sediment units in all sites indicates that Jakobshavn Isbrae remained at or near its LIA maximum position between 1400-1640 AD and into the 20th century. Finally, pre-LIA organic-rich sediments at all sites continue uninterrupted down to basal sediments deposited during regional deglaciation in the Early Holocene. AMS radiocarbon ages on macrofossils from basal sediments at all sites range from 7220±40 to 8130±60 cal yr BP. We therefore interpret

  19. Extreme events, trends, and variability in Northern Hemisphere lake-ice phenology (1855-2005)

    USGS Publications Warehouse

    Benson, Barbara J.; Magnuson, John J.; Jensen, Olaf P.; Card, Virginia M.; Hodgkins, Glenn; Korhonen, Johanna; Livingstone, David M.; Stewart, Kenton M.; Weyhenmeyer, Gesa A.; Granin, Nick G.

    2012-01-01

    Often extreme events, more than changes in mean conditions, have the greatest impact on the environment and human well-being. Here we examine changes in the occurrence of extremes in the timing of the annual formation and disappearance of lake ice in the Northern Hemisphere. Both changes in the mean condition and in variability around the mean condition can alter the probability of extreme events. Using long-term ice phenology data covering two periods 1855–6 to 2004–5 and 1905–6 to 2004–5 for a total of 75 lakes, we examined patterns in long-term trends and variability in the context of understanding the occurrence of extreme events. We also examined patterns in trends for a 30-year subset (1975–6 to 2004–5) of the 100-year data set. Trends for ice variables in the recent 30-year period were steeper than those in the 100- and 150-year periods, and trends in the 150-year period were steeper than in the 100-year period. Ranges of rates of change (days per decade) among time periods based on linear regression were 0.3−1.6 later for freeze, 0.5−1.9 earlier for breakup, and 0.7−4.3 shorter for duration. Mostly, standard deviation did not change, or it decreased in the 150-year and 100-year periods. During the recent 50-year period, standard deviation calculated in 10-year windows increased for all ice measures. For the 150-year and 100-year periods changes in the mean ice dates rather than changes in variability most strongly influenced the significant increases in the frequency of extreme lake ice events associated with warmer conditions and decreases in the frequency of extreme events associated with cooler conditions.

  20. Winter severity determines functional trait composition of phytoplankton in seasonally ice-covered lakes.

    PubMed

    Özkundakci, Deniz; Gsell, Alena S; Hintze, Thomas; Täuscher, Helgard; Adrian, Rita

    2016-01-01

    How climate change will affect the community dynamics and functionality of lake ecosystems during winter is still little understood. This is also true for phytoplankton in seasonally ice-covered temperate lakes which are particularly vulnerable to the presence or absence of ice. We examined changes in pelagic phytoplankton winter community structure in a north temperate lake (Müggelsee, Germany), covering 18 winters between 1995 and 2013. We tested how phytoplankton taxa composition varied along a winter-severity gradient and to what extent winter severity shaped the functional trait composition of overwintering phytoplankton communities using multivariate statistical analyses and a functional trait-based approach. We hypothesized that overwintering phytoplankton communities are dominated by taxa with trait combinations corresponding to the prevailing winter water column conditions, using ice thickness measurements as a winter-severity indicator. Winter severity had little effect on univariate diversity indicators (taxon richness and evenness), but a strong relationship was found between the phytoplankton community structure and winter severity when taxon trait identity was taken into account. Species responses to winter severity were mediated by the key functional traits: motility, nutritional mode, and the ability to form resting stages. Accordingly, one or the other of two functional groups dominated the phytoplankton biomass during mild winters (i.e., thin or no ice cover; phototrophic taxa) or severe winters (i.e., thick ice cover; exclusively motile taxa). Based on predicted milder winters for temperate regions and a reduction in ice-cover durations, phytoplankton communities during winter can be expected to comprise taxa that have a relative advantage when the water column is well mixed (i.e., need not be motile) and light is less limiting (i.e., need not be mixotrophic). A potential implication of this result is that winter severity promotes different

  1. Winter severity determines functional trait composition of phytoplankton in seasonally ice-covered lakes.

    PubMed

    Özkundakci, Deniz; Gsell, Alena S; Hintze, Thomas; Täuscher, Helgard; Adrian, Rita

    2016-01-01

    How climate change will affect the community dynamics and functionality of lake ecosystems during winter is still little understood. This is also true for phytoplankton in seasonally ice-covered temperate lakes which are particularly vulnerable to the presence or absence of ice. We examined changes in pelagic phytoplankton winter community structure in a north temperate lake (Müggelsee, Germany), covering 18 winters between 1995 and 2013. We tested how phytoplankton taxa composition varied along a winter-severity gradient and to what extent winter severity shaped the functional trait composition of overwintering phytoplankton communities using multivariate statistical analyses and a functional trait-based approach. We hypothesized that overwintering phytoplankton communities are dominated by taxa with trait combinations corresponding to the prevailing winter water column conditions, using ice thickness measurements as a winter-severity indicator. Winter severity had little effect on univariate diversity indicators (taxon richness and evenness), but a strong relationship was found between the phytoplankton community structure and winter severity when taxon trait identity was taken into account. Species responses to winter severity were mediated by the key functional traits: motility, nutritional mode, and the ability to form resting stages. Accordingly, one or the other of two functional groups dominated the phytoplankton biomass during mild winters (i.e., thin or no ice cover; phototrophic taxa) or severe winters (i.e., thick ice cover; exclusively motile taxa). Based on predicted milder winters for temperate regions and a reduction in ice-cover durations, phytoplankton communities during winter can be expected to comprise taxa that have a relative advantage when the water column is well mixed (i.e., need not be motile) and light is less limiting (i.e., need not be mixotrophic). A potential implication of this result is that winter severity promotes different

  2. Measurements of Mass, Momentum and Energy fluxes over an ice/snow covered lake

    NASA Astrophysics Data System (ADS)

    Salgado, Rui; Potes, Miguel; Mammarella, Ivan; Provenzale, Maria

    2016-04-01

    A better understanding of the interactions between ice and snow and the atmosphere requires improved measurements of energy, mass and momentum fluxes, which continue to have a high degree of uncertainty. In this communication, observed near surface fluxes of momentum, heat and mass (H2O and CO2) over a boreal lake during a freezing period (winter 2015/2016) will be analysed and compared with observations over ice free lakes. Continuously measurements of near surface fluxes of momentum, heat and mass (H2O and CO2) are obtained with a new eddy covariance (EC) system, the Campbell Scientific's IRGASON Integrated Open-Path CO2/H2O Gas Analyzer and 3D Sonic Anemometer, over lake Vanajavesi in Finland. The measurement site is located in a tip of narrow peninsula on the lake (61.133935° N ; 24.259119° E), offering very good conditions for eddy covariance flux measurements. The EC system was installed at 2.5m height above the lake surface and was oriented against the prevailing wind direction in the site.

  3. Sources of Sulfate Found in Mounds and Lakes at the Lewis Cliffs Ice Tongue, Transantarctic

    NASA Technical Reports Server (NTRS)

    Socki, Richard; Sun, Tao; Harvey, Ralph P.; Bish, David L.; Tonui, Eric; Bao, Huiming; Niles, Paul B.

    2012-01-01

    Massive but highly localized Na-sulfate mounds (mirabilite, Na2SO4.10H2O) have been found at the terminal moraine of the Lewis Cliffs Ice Tongue (LCIT), Antarctica. (Sigma)34S and (Sigma)18O values of LCIT mirabilite range from +48.8 to +49.3% (CDT), and -16.6 to -17.1% (V-SMOW), respectively, while (Delta)17O average -0.37% (V-SMOW). LCIT mirabilite mounds are isotopically different from other mirabilite mounds found in coastal regions of Antarctica, which have isotope values close to seawater compositions. (Sigma)18O and (Delta)17O values suggest the incorporation of isotopically light glacial water. Data point to initial sulfate formation in an anoxic water body, either as a stratified anoxic deep lake on the surface, a sub-glacial water reservoir, or a sub-glacial lake. Several surface lakes of varying size are also present within this region of the LCIT, and in some cases are adjacent to the mirabilite mounds. O and D isotope compositions of surface lakes confirm they are derived from a mixture of glacial ice and snow that underwent moderate evaporation. (Sigma)18O and (Sigma)D (V-SMOW) values of snow, ice, and lake water range from -64.2 to -29.7%, and -456.0 to -231.7%, respectively. However, the isotope chemistry of these surface lakes is extremely different from the mounds. Dissolved SO4-2 (Sigma)34S and (Sigma)18O values range from +12.0 to +20.0% and -12.8 to -22.2% (the most negative (Sigma)18O of terrestrial sulfate ever reported), respectively, with sulfate (Delta)17O ranging from +0.93 to 2.24%. Ion chromatography data show that lake water is fresh to brackish in origin, with TDS less than 1500 ppm, and sulfate concentration less than 431 ppm. Isotope and chemical data suggest that these lakes are unlikely the source of the mirabilite mounds. We suggest that lake water sulfate is potentially composed of a mixture of atmospheric sulfate and minor components of sulfate of weathering origin, much like the sulfate in the polar plateau soils of the Mc

  4. Quantifying supraglacial lake volumes on the Greenland ice sheet from spaceborne optical sensors

    NASA Astrophysics Data System (ADS)

    Moussavi, Mahsa S.

    The acceleration of mass loss from the Greenland ice sheet (GrIS) over the last two decades is of great significance when considering the associated increasing rates of its contribution to sea level rise. With meltwater runoff accounting for more than half of Greenland's contribution to sea level, it is imperative to improve our understanding of the ice sheet hydrologic processes. This dissertation describes research to quantify surface meltwater volumes, specifically stored in supraglacial lakes, over large areas of the ablation region from spaceborne observations made by current and future optical sensors. Methods for remote-derivation and validation of supraglacial water depths from WorldView-2, Landsat 7's Enhanced Thematic Mapper (ETM+), and Landsat 8's Operational Land Imager (OLI) are discussed. While enabling large-scale assessments of lake volumes with unprecedented levels of accuracy and precision, these methods address the major limitation of spaceborne bathymetry, which is its dependence on the availability of costly in-situ measurements. This dissertation also investigates the potential capability of the future ICESat-2 laser altimetry mission in providing depth information over supraglacial lakes, which could be used in conjunction with passive optical data to assess lake volumes. A nominal (first-order) prediction of ICESat-2's performance suggests that it might be able to retrieve lake depths down to 6 m. Given such a premise, this dissertation takes one step further to develop an automatic depth-retrieval algorithm from simulated ICESat-2 datasets, provided by the mission's Project team at Goddard Space Flight Center (GSFC). By developing a surface detection algorithm for the most complex surfaces that ICESat-2 will be looking at, namely forested ecosystems, this dissertation provides a method applicable to land ice, sea ice, and water surfaces. Furthermore, as part of ICESat-2's science definition team efforts and in direct support of the mission

  5. Carbon dioxide partial pressure and 13C content of north temperate and boreal lakes at spring ice melt

    USGS Publications Warehouse

    Striegl, R.G.; Kortelainen, Pirkko; Chanton, J.P.; Wickland, K.P.; Bugna, G.C.; Rantakari, M.

    2001-01-01

    Carbon dioxide (CO2) accumulates under lake ice in winter and degasses to the atmosphere after ice melt. This large springtime CO2 pulse is not typically considered in surface-atmosphere flux estimates, because most field studies have not sampled through ice during late winter. Measured CO2 partial pressure (pCO2) of lake surface water ranged from 8.6 to 4,290 Pa (85-4,230 ??atm) in 234 north temperate and boreal lakes prior to ice melt during 1998 and 1999. Only four lakes had surface pCO2 less than or equal to atmospheric pCO2, whereas 75% had pCO2 >5 times atmospheric. The ??13CDIC (DIC = ??CO2) of 142 of the lakes ranged from -26.28??? to +0.95.???. Lakes with the greatest pCO2 also had the lightest ??13CDIC, which indicates respiration as their primary CO2 source. Finnish lakes that received large amounts of dissolved organic carbon from surrounding peatlands had the greatest pCO2. Lakes set in noncarbonate till and bedrock in Minnesota and Wisconsin had the smallest pCO2 and the heaviest ??13CDIC, which indicates atmospheric and/or mineral sources of C for those lakes. Potential emissions for the period after ice melt were 2.36 ?? 1.44 mol CO2 m-2 for lakes with average pCO2 values and were as large as 13.7 ?? 8.4 mol CO2 m-2 for lakes with high pCO2 values.

  6. Airborne Polarimetric, Two-Color Laser Altimeter Measurements of Lake Ice Cover: A Pathfinder for NASA's ICESat-2 Spaceflight Mission

    NASA Technical Reports Server (NTRS)

    Harding, David; Dabney, Philip; Valett, Susan; Yu, Anthony; Vasilyev, Aleksey; Kelly, April

    2011-01-01

    The ICESat-2 mission will continue NASA's spaceflight laser altimeter measurements of ice sheets, sea ice and vegetation using a new measurement approach: micropulse, single photon ranging at 532 nm. Differential penetration of green laser energy into snow, ice and water could introduce errors in sea ice freeboard determination used for estimation of ice thickness. Laser pulse scattering from these surface types, and resulting range biasing due to pulse broadening, is assessed using SIMPL airborne data acquired over icecovered Lake Erie. SIMPL acquires polarimetric lidar measurements at 1064 and 532 nm using the micropulse, single photon ranging measurement approach.

  7. Bottom Fixed Platform Dynamics Models Assessing Surface Ice Interactions for Transitional Depth Structures in the Great Lakes: FAST8 – IceDyn

    SciTech Connect

    Karr, Dale G.; Yu, Bingbin; Sirnivas, Senu

    2015-04-01

    To create long-term solutions for offshore wind turbines in a variety of environmental conditions, CAE tools are needed to model the design-driving loads that interact with an offshore wind turbine system during operation. This report describes our efforts in augmenting existing CAE tools used for offshore wind turbine analysis with a new module that can provide simulation capabilities for ice loading on the system. This augmentation was accomplished by creating an ice-loading module coupled to FAST8, the CAE tool maintained by the NREL for simulating land-based and offshore wind turbine dynamics. The new module includes both static and dynamic ice loading that can be applied during a dynamic simulation of the response of an offshore wind turbine. The ice forces can be prescribed, or influenced by the structure’s compliant response, or by the dynamics of both the structure and the ice floe. The new module covers ice failure modes of spalling, buckling, crushing, splitting, and bending. The supporting structure of wind turbines can be modeled as a vertical or sloping form at the waterline. The Inward Battered Guide Structure (IBGS) foundation designed by Keystone Engineering for the Great Lakes was used to study the ice models coupled to FAST8. The IBGS foundation ice loading simulations in FAST8 were compared to the baseline simulation case without ice loading. The ice conditions reflecting those from Lake Huron at Port Huron and Lake Michigan at North Manitou were studied under near rated wind speed of 12 m/s for the NREL 5-MW reference turbine. Simulations were performed on ice loading models 1 through 4 and ice model 6 with their respective sub-models. The purpose of ice model 5 is to investigate ice loading on sloping structures such as ice-cones on a monopile and is not suitable for multi-membered jacketed structures like the IBGS foundation. The key response parameters from the simulations, shear forces and moments from the tower base and IBGS foundation

  8. POTENTIAL CLIMATE WARMING EFFECTS ON ICE COVERS OF SMALL LAKES IN THE CONTIGUOUS U.S. (R824801)

    EPA Science Inventory

    Abstract

    To simulate effects of projected climate change on ice covers of small lakes in the northern contiguous U.S., a process-based simulation model is applied. This winter ice/snow cover model is associated with a deterministic, one-dimensional year-round water tem...

  9. Unanticipated Geochemical and Microbial Community Structure under Seasonal Ice Cover in a Dilute, Dimictic Arctic Lake.

    PubMed

    Schütte, Ursel M E; Cadieux, Sarah B; Hemmerich, Chris; Pratt, Lisa M; White, Jeffrey R

    2016-01-01

    Despite most lakes in the Arctic being perennially or seasonally frozen for at least 40% of the year, little is known about microbial communities and nutrient cycling under ice cover. We assessed the vertical microbial community distribution and geochemical composition in early spring under ice in a seasonally ice-covered lake in southwest Greenland using amplicon-based sequencing that targeted 16S rRNA genes and using a combination of field and laboratory aqueous geochemical methods. Microbial communities changed consistently with changes in geochemistry. Composition of the abundant members responded strongly to redox conditions, shifting downward from a predominantly heterotrophic aerobic community in the suboxic waters to a heterotrophic anaerobic community in the anoxic waters. Operational taxonomic units (OTUs) of Sporichthyaceae, Comamonadaceae, and the SAR11 Clade had higher relative abundances above the oxycline and OTUs within the genus Methylobacter, the phylum Lentisphaerae, and purple sulfur bacteria (PSB) below the oxycline. Notably, a 13-fold increase in sulfide at the oxycline was reflected in an increase and change in community composition of potential sulfur oxidizers. Purple non-sulfur bacteria were present above the oxycline and green sulfur bacteria and PSB coexisted below the oxycline, however, PSB were most abundant. For the first time we show the importance of PSB as potential sulfur oxidizers in an Arctic dimictic lake. PMID:27458438

  10. Unanticipated Geochemical and Microbial Community Structure under Seasonal Ice Cover in a Dilute, Dimictic Arctic Lake.

    PubMed

    Schütte, Ursel M E; Cadieux, Sarah B; Hemmerich, Chris; Pratt, Lisa M; White, Jeffrey R

    2016-01-01

    Despite most lakes in the Arctic being perennially or seasonally frozen for at least 40% of the year, little is known about microbial communities and nutrient cycling under ice cover. We assessed the vertical microbial community distribution and geochemical composition in early spring under ice in a seasonally ice-covered lake in southwest Greenland using amplicon-based sequencing that targeted 16S rRNA genes and using a combination of field and laboratory aqueous geochemical methods. Microbial communities changed consistently with changes in geochemistry. Composition of the abundant members responded strongly to redox conditions, shifting downward from a predominantly heterotrophic aerobic community in the suboxic waters to a heterotrophic anaerobic community in the anoxic waters. Operational taxonomic units (OTUs) of Sporichthyaceae, Comamonadaceae, and the SAR11 Clade had higher relative abundances above the oxycline and OTUs within the genus Methylobacter, the phylum Lentisphaerae, and purple sulfur bacteria (PSB) below the oxycline. Notably, a 13-fold increase in sulfide at the oxycline was reflected in an increase and change in community composition of potential sulfur oxidizers. Purple non-sulfur bacteria were present above the oxycline and green sulfur bacteria and PSB coexisted below the oxycline, however, PSB were most abundant. For the first time we show the importance of PSB as potential sulfur oxidizers in an Arctic dimictic lake.

  11. Unanticipated Geochemical and Microbial Community Structure under Seasonal Ice Cover in a Dilute, Dimictic Arctic Lake

    PubMed Central

    Schütte, Ursel M. E.; Cadieux, Sarah B.; Hemmerich, Chris; Pratt, Lisa M.; White, Jeffrey R.

    2016-01-01

    Despite most lakes in the Arctic being perennially or seasonally frozen for at least 40% of the year, little is known about microbial communities and nutrient cycling under ice cover. We assessed the vertical microbial community distribution and geochemical composition in early spring under ice in a seasonally ice-covered lake in southwest Greenland using amplicon-based sequencing that targeted 16S rRNA genes and using a combination of field and laboratory aqueous geochemical methods. Microbial communities changed consistently with changes in geochemistry. Composition of the abundant members responded strongly to redox conditions, shifting downward from a predominantly heterotrophic aerobic community in the suboxic waters to a heterotrophic anaerobic community in the anoxic waters. Operational taxonomic units (OTUs) of Sporichthyaceae, Comamonadaceae, and the SAR11 Clade had higher relative abundances above the oxycline and OTUs within the genus Methylobacter, the phylum Lentisphaerae, and purple sulfur bacteria (PSB) below the oxycline. Notably, a 13-fold increase in sulfide at the oxycline was reflected in an increase and change in community composition of potential sulfur oxidizers. Purple non-sulfur bacteria were present above the oxycline and green sulfur bacteria and PSB coexisted below the oxycline, however, PSB were most abundant. For the first time we show the importance of PSB as potential sulfur oxidizers in an Arctic dimictic lake. PMID:27458438

  12. Temperature profile for glacial ice at the South Pole: implications for life in a nearby subglacial lake.

    PubMed

    Price, P Buford; Nagornov, Oleg V; Bay, Ryan; Chirkin, Dmitry; He, Yudong; Miocinovic, Predrag; Richards, Austin; Woschnagg, Kurt; Koci, Bruce; Zagorodnov, Victor

    2002-06-11

    Airborne radar has detected approximately 100 lakes under the Antarctic ice cap, the largest of which is Lake Vostok. International planning is underway to search in Lake Vostok for microbial life that may have evolved in isolation from surface life for millions of years. It is thought, however, that the lakes may be hydraulically interconnected. If so, unsterile drilling would contaminate not just one but many of them. Here we report measurements of temperature vs. depth down to 2,345 m in ice at the South Pole, within 10 km from a subglacial lake seen by airborne radar profiling. We infer a temperature at the 2,810-m deep base of the South Pole ice and at the lake of -9 degrees C, which is 7 degrees C below the pressure-induced melting temperature of freshwater ice. To produce the strong radar signal, the frozen lake must consist of a mix of sediment and ice in a flat bed, formed before permanent Antarctic glaciation. It may, like Siberian and Antarctic permafrost, be rich in microbial life. Because of its hydraulic isolation, proximity to South Pole Station infrastructure, and analog to a Martian polar cap, it is an ideal place to test a sterile drill before risking contamination of Lake Vostok. From the semiempirical expression for strain rate vs. shear stress, we estimate shear vs. depth and show that the IceCube neutrino observatory will be able to map the three-dimensional ice-flow field within a larger volume (0.5 km(3)) and at lower temperatures (-20 degrees C to -35 degrees C) than has heretofore been possible. PMID:12060731

  13. Islands in the ice stream: were spawning habitats for native salmonids in the Great Lakes created by paleo-ice streams?

    USGS Publications Warehouse

    Riley, Stephen; Binder, Thomas R.; Tucker, Taaja R.; Menzies, John; Eyles, Nick; Janssen, John; Muir, Andrew M.; Esselman, Peter C.; Wattrus, Nigel J.; Krueger, Charles C.

    2016-01-01

    Lake trout Salvelinus namaycush, lake whitefish Coregonus clupeaformis and cisco Coregonus artedi are salmonid fishes native to the Laurentian Great Lakes that spawn on rocky substrates in the fall and early winter. After comparing the locations of spawning habitat for these species in the main basin of Lake Huron with surficial substrates and the hypothesized locations of fast-flowing Late Wisconsinan paleo-ice streams, we hypothesize that much of the spawning habitat for these species in Lake Huron is the result of deposition and erosion by paleo-ice streams. This hypothesis may represent a new framework for the identification and protection of spawning habitat for these native species, some of which are currently rare or extirpated in some of the Great Lakes. We further suggest that paleo-ice streams may have been responsible for the creation of native salmonid spawning habitat elsewhere in the Great Lakes and in other glaciated landscapes.

  14. SARAL/AltiKa observations for the studies of ice cover on lakes and oceans

    NASA Astrophysics Data System (ADS)

    Kouraev, Alexei; Zakharova, Elena; Remy, Frederique; Fleury, Sara; Guerreiro, Kevin; Willmes, Sascha; Suknev, Andrei

    2015-04-01

    With the launch of SARAL/AltiKa satellite mission scientific community has now a new source of information to study ice cover on water bodies and oceans. AltiKa observations provide a continuity with the previous satellite radar altimetry observations from ERS-1, -2 and ENVISAT mission that have the same orbit. Moreover, with the new Ka-band altimeter it gives new insights into the ice cover structure and properties. We present studies of ice cover on lakes (Lake Baikal) and Arctic ocean (for leads and polynyas detection). For Lake Baikal we use the synergy of simultaneous active (radar altimeter) and passive (radiometer) observations from radar altimetric satellites - SARAL/Altika and also TOPEX/Poseidon, Jason-1, ENVISAT and Geosat Follow-On. We present ice discrimination methodology from different satellite missions and discuss specificity of AltiKa observations. We analyse temporal variability of altimetric waveform parameters over ice-covered and ice-free surface for AltiKa and complement this analysis by satellite imagery (MODIS, Landsat), as well as our dedicated field observations of ice cover properties along the AltiKa tracks in spring 2013 and 2014. For the Arctic ocean we investigate the performance of SARAL/AltiKa to detect the leads and the coastal polynyas as well as its ability to represent spatial and temporal dynamic of water openings. The method consists first in analysis of along-track radar waveforms with collocated high-resolution Landsat images in order to localise ice/water transitions. We discuss the potential of several techniques that could be used for leads and polynya studies and for freeboard estimation. This research has been done in the framework of the Russian-French cooperation GDRI "CAR-WET-SIB", CNES TOSCA AO, ANR "CLASSIQUE", IDEX Transversalité InHERA, CNRS-Russia "Franco-Siberian Center for Research and Education" and PICS BaLaLaICA, ESA Proposal C1P.13132, Russian FZP 1.5 and EU FP7 "MONARCH-A" projects.

  15. Field Investigation of Surface-Lake Processes on Ice Shelves: Results of the 2015/16 Field Campaign on McMurdo Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    MacAyeal, Doug; Banwell, Alison; Willis, Ian; Macdonald, Grant

    2016-04-01

    Ice-shelf instability and breakup of the style exhibited by Larsen B Ice Shelf in 2002 remains the most difficult glaciological process of consequence to observe in detail. It is, however, vital to do so because ice-shelf breakup has the potential to influence the buttressing controls on inland ice discharge, and thus to affect sea level. Several mechanisms enabling Larsen B style breakup have been proposed, including the ability of surface lakes to introduce ice-shelf fractures when they fill and drain, thereby changing the surface loads the ice-shelf must adjust to. Our model suggest that these fractures resulted in a chain-reaction style drainage of >2750 surface lakes on the Larsen B in the days prior to its demise. To validate this and other models, we began a field project on the McMurdo Ice Shelf (MIS) during the 2015/16 austral summer. Advantages of the MIS study site are: there is considerable surface melting during 3-6 weeks of the summer season, the ice is sufficiently thin (< 30 m in places) to allow observable viscoelastic responses to relatively small loads, and it is close to a center of logistical support (McMurdo Station). Here we show initial results from the field campaign, including GPS and water-depth observations of a lake that has filled and drained over multiple week timescales in previous austral summers. We also report on the analysis of high-resolution WorldView satellite imagery from several summers that reveals the complexity of surface meltwater movement in channels and subsurface void spaces. Initial reconnaissance of the largest surface-lake features reveal that they have a central circular depression surrounded by an uplifted ring, which supports one of the central tenets of our ice-shelf flexure theory. A second field season is anticipated for the 2016/17 austral summer.

  16. Response of ice cover on shallow Arctic lakes to contemporary climate conditions: Numerical modeling and remote sensing data analysis

    NASA Astrophysics Data System (ADS)

    Duguay, C.; Surdu, C.; Brown, L.; Samuelsson, P.

    2012-04-01

    Lake ice cover has been shown to be a robust indicator of climate variability and change. Recent studies have demonstrated that break-up dates, in particular, have been occurring earlier in many parts of the Northern Hemisphere over the last 50 years in response to warmer climatic conditions in the winter and spring seasons. The impacts of trends in air temperature and winter precipitation over the last five decades and those projected by global climate models will affect the timing and duration of ice cover (and ice thickness) on Arctic lakes. This will likely, in turn, have an important feedback effect on energy, water, and biogeochemical cycling in various regions of the Arctic. In the case of shallow tundra lakes, many of which are less than 3-m deep, warmer climate conditions could result in a smaller fraction of lakes that freeze to their bed in winter since thinner ice covers are expected to develop. Shallow lakes of the coastal plain of northern Alaska, and other similar regions of the Arctic, have likely been experiencing changes in seasonal ice thickness (and phenology) over the last few decades but these have not yet been documented. This paper presents results from a numerical lake ice modeling experiment and the analysis of ERS-1/2 synthetic aperture radar (SAR) data to elucidate the response of ice cover (thickness, freezing to bed, and phenology) on shallow lakes of the North Slope of Alaska (NSA)to climate conditions over the last three decades. New downscaled data specific for the Arctic domain (at a resolution of 0.44 degrees using ERA Interim Reanalysis as boundary condition) produced by the Rossby Centre regional atmospheric model (RCA4) was used to force the Canadian Lake Ice Model (CLIMo) for the period 1979-2010. Output from CLIMo included freeze-up and break-up dates as well as ice thickness on a daily basis. ERS-1/2 data was used to map areas of shallow lakes that freeze to bed and when this happens (timing) in winter for the period 1991

  17. Morphometric analysis of ice-walled lake plains in Northern Illinois: Implications of lake elongation by wind-induced dual-cycle currents

    NASA Astrophysics Data System (ADS)

    Allred, Kory; Luo, Wei; Konen, Mike; Curry, B. Brandon

    2014-09-01

    Ice-walled lake plains (IWLPs) are rounded, flat-topped mounds that formed in stagnant ice environments along the margins of the Laurentide Ice Sheet. We conducted detailed morphometric and statistical analyses of the shape, size, and orientation of more than 400 IWLPs identified from aerial photos aided with LiDAR data in DeKalb County, Illinois, USA. Lake elongation theories include extraterrestrial impact (e.g. the Carolina Bays), ice flow dynamics and crevasses, and wind induced currents that preferentially erode the shorelines perpendicular to the dominant wind direction. The results indicate that elliptical IWLPs with a perimeter greater than 3050 m have preferred orientations roughly normal to the paleo-wind direction as indicated by contemporaneous parabolic dunes located 50 km to the west. The orientations of the IWLPs with a perimeter less than 1220 m are scattered and show no apparent trend. The IWLP orientation is not related to ice flow dynamics or glacial crevasses because no statistically significant relationship exists with regard to the ice flow as proxied by the moraine direction. The orientation of large IWLPs in DeKalb County are consistent with wind-induced lake elongation observed in modern permafrost thaw lakes, suggesting that the prevailing wind also played an important role in controlling the orientation of IWLPs during the last glacial period and led to the preferred orientation we see today.

  18. Lake Ice Cover of Shallow Lakes and Climate Interactions in Arctic Regions (1950-2011): SAR Data Analysis and Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Surdu, C.; Duguay, C.; Brown, L.; Fernàndez-Prieto, D.; Samuelsson, P.

    2012-12-01

    Lake ice cover is highly correlated with climatic conditions and has, therefore, been demonstrated to be an essential indicator of climate variability and change. Recent studies have shown that the duration of the lake ice cover has decreased, mainly as a consequence of earlier thaw dates in many parts of the Northern Hemisphere over the last 50 years, mainly as a feedback to increased winter and spring air temperature. In response to projected air temperature and winter precipitation changes by climate models until the end of the 21st century, the timing, duration, and thickness of ice cover on Arctic lakes are expected to be impacted. This, in turn, will likely alter the energy, water, and bio-geochemical cycling in various regions of the Arctic. In the case of shallow tundra lakes, many of which are less than 3-m deep, warmer climate conditions could result in a smaller fraction of lakes that fully freeze to the bottom at the time of maximum winter ice thickness since thinner ice covers are predicted to develop. Shallow thermokarst lakes of the coastal plain of northern Alaska, and of other similar Arctic regions, have likely been experiencing changes in seasonal ice phenology and thickness over the last few decades but these have not yet been comprehensively documented. Analysis of a 20-year time series of ERS-1/2 synthetic aperture radar (SAR) data and numerical lake ice modeling were employed to determine the response of ice cover (thickness, freezing to bed, and phenology) on shallow lakes of the North Slope of Alaska (NSA) to climate conditions over the last three decades. New downscaled data specific to the Arctic domain (at a resolution of 0.44 degrees using ERA Interim Reanalysis as boundary condition) produced by the Rossby Centre Regional Atmospheric Climate Model (RCA4) was used to drive the Canadian Lake Ice Model (CLIMo) for the period 1950-2011. In order to assess and integrate the SAR-derived observed changes into a longer historical context, and

  19. Sedimentology and geochemistry of a perennially ice-covered epishelf lake in Bunger Hills Oasis, East Antarctica.

    PubMed

    Doran, P T; Wharton, R A; Lyons, W B; Des Marais, D J; Andersen, D T

    2000-01-01

    A process-oriented study was carried out in White Smoke lake, Bunger Hills, East Antarctica, a perennially ice-covered (1.8 to 2.8 m thick) epishelf (tidally-forced) lake. The lake water has a low conductivity and is relatively well mixed. Sediments are transferred from the adjacent glacier to the lake when glacier ice surrounding the sediment is sublimated at the surface and replaced by accumulating ice from below. The lake bottom at the west end of the lake is mostly rocky with a scant sediment cover. The east end contains a thick sediment profile. Grain size and delta 13C increase with sediment depth, indicating a more proximal glacier in the past. Sedimentary 210Pb and 137Cs signals are exceptionally strong, probably a result of the focusing effect of the large glacial catchment area. The post-bomb and pre-bomb radiocarbon reservoirs are c. 725 14C yr and c. 1950 14C yr, respectively. Radiocarbon dating indicates that the east end of the lake is >3 ka BP, while photographic evidence and the absence of sediment cover indicate that the west end has formed only over the last century. Our results indicate that the southern ice edge of Bunger Hills has been relatively stable with only minor fluctuations (on the scale of hundreds of metres) over the last 3000 years.

  20. Sedimentology and geochemistry of a perennially ice-covered epishelf lake in Bunger Hills Oasis, East Antarctica

    NASA Technical Reports Server (NTRS)

    Doran, P. T.; Wharton, R. A. Jr; Lyons, W. B.; Des Marais, D. J.; Andersen, D. T.; Wharton RA, J. r. (Principal Investigator)

    2000-01-01

    A process-oriented study was carried out in White Smoke lake, Bunger Hills, East Antarctica, a perennially ice-covered (1.8 to 2.8 m thick) epishelf (tidally-forced) lake. The lake water has a low conductivity and is relatively well mixed. Sediments are transferred from the adjacent glacier to the lake when glacier ice surrounding the sediment is sublimated at the surface and replaced by accumulating ice from below. The lake bottom at the west end of the lake is mostly rocky with a scant sediment cover. The east end contains a thick sediment profile. Grain size and delta 13C increase with sediment depth, indicating a more proximal glacier in the past. Sedimentary 210Pb and 137Cs signals are exceptionally strong, probably a result of the focusing effect of the large glacial catchment area. The post-bomb and pre-bomb radiocarbon reservoirs are c. 725 14C yr and c. 1950 14C yr, respectively. Radiocarbon dating indicates that the east end of the lake is >3 ka BP, while photographic evidence and the absence of sediment cover indicate that the west end has formed only over the last century. Our results indicate that the southern ice edge of Bunger Hills has been relatively stable with only minor fluctuations (on the scale of hundreds of metres) over the last 3000 years.

  1. Sedimentology and geochemistry of a perennially ice-covered epishelf lake in Bunger Hills Oasis, East Antarctica.

    PubMed

    Doran, P T; Wharton, R A; Lyons, W B; Des Marais, D J; Andersen, D T

    2000-01-01

    A process-oriented study was carried out in White Smoke lake, Bunger Hills, East Antarctica, a perennially ice-covered (1.8 to 2.8 m thick) epishelf (tidally-forced) lake. The lake water has a low conductivity and is relatively well mixed. Sediments are transferred from the adjacent glacier to the lake when glacier ice surrounding the sediment is sublimated at the surface and replaced by accumulating ice from below. The lake bottom at the west end of the lake is mostly rocky with a scant sediment cover. The east end contains a thick sediment profile. Grain size and delta 13C increase with sediment depth, indicating a more proximal glacier in the past. Sedimentary 210Pb and 137Cs signals are exceptionally strong, probably a result of the focusing effect of the large glacial catchment area. The post-bomb and pre-bomb radiocarbon reservoirs are c. 725 14C yr and c. 1950 14C yr, respectively. Radiocarbon dating indicates that the east end of the lake is >3 ka BP, while photographic evidence and the absence of sediment cover indicate that the west end has formed only over the last century. Our results indicate that the southern ice edge of Bunger Hills has been relatively stable with only minor fluctuations (on the scale of hundreds of metres) over the last 3000 years. PMID:11543521

  2. Measuring the Ice Floe Sizes of the Lake Akkeshi Broken by 2011 Tohoku Pacific-Coast Earthquake

    NASA Astrophysics Data System (ADS)

    Abe, T.; Yoshikawa, Y.

    2012-12-01

    Water level fluctuations in an open sea can sometimes cause large oscillations of water level in partially enclosed bodies of water such as lakes and bays. In cold and snowy regions, flooding caused by water level fluctuation and scattering of ice floes can occur due to these secondary undulation of tide, which little studies have assessed. The tsunami caused by 2011 Tohoku Pacific-Coast Earthquake reached the coast of Hokkaido, Japan. This tsunami broke up the ice on an unprecedented scale in the Lake Akkeshi, which is connected with Akkeshi Bay. Also, the intermittent tsunami intrusion caused a serious damage to local oyster fishery. On the other hand, lake ice was not broken in other lakes near the coast lines unconnected to the open sea. Therefore, in the Lake Akkeshi, the main cause of the ice breakup is thought to have been the tsunami intrusion. In this study, the sizes of floating lake ice were measured to clarify the effect of the tsunami and the water level fluctuation on lake ice. We used satellite images by WorldView-2 sensor obtained on March 9 and March 12, 2011. We measured the sizes and areas of lake ice by GIS analysis to compare these with the results from other sea ice size measurement and then attempted to clarify the difference in sizes from ice formed in sea ice zones. Firstly, we measured the area of lake ice formed before the tsunami intrusions. From the photograph obtained on March 12, we extracted the contours of ice floes formed by the tsunami. Based on the contours, we measured the areas and diameter d of floes. In the photograph obtained on March 9, the area of lake ice was estimated as about 15 km2. The figure shows a cumulative number distribution of floe diameter d on March 12. It is noticed from the figure that the graph is almost linear for the d between 8m and 20m. In other words, this means for this range N(d) behaves like d-α; that is, the floe size distribution is basically self-similar. Note that the value α=3.0 is

  3. Polarimetric analysis of snow-covered and bare lake ice from Ku and X-band scatterometer data

    NASA Astrophysics Data System (ADS)

    Ben Khadhra, K.; Gunn, G. E.; Duguay, C. R.; Kelly, R. E.

    2011-12-01

    Lake ice plays a key role in regional climate, and has significant physical, biological and socio-economic impacts (e.g. fish overwintering habitat, winter-road transportation, public safety). In the last two decades, there has been growing interest by the international remote sensing community to explore radar polarimetry for glaciological investigations, mainly for glaciers and ice sheet. Polarimetric synthetic aperture radar (SAR) could be a potential tool for lake ice cover mapping and ice thickness estimation. In this paper, we represent results from the first investigation of fully polarimetric Ku and X-band (9.6 and 17.2 GHz, respectively) scatterometer data collected over lake near Churchill, Manitoba. Several controlled and calibrated experimental measurements were carried out during winter 2010-2011, as a contribution to the Cold Regions Hydrology High-resolution Observatory (CoReH2O) candidate mission of the European Space Agency (ESA). Scatterometer scans were made on several occasions at five undisturbed static sites on Ramsey Lake. Measurements characterizing snow and ice properties were also gathered immediately after scatterometer scans. Snow depth and density, snow water equivalent, gain size, ice thickness, ice composition and air inclusion in ice volume were determined at each site. This field data set was very important for the interpretation of the polarimetric parameters, e.g. the copolarization ratio, the copolarization phase and the depolarization ratio. First, the polarimetric parameters have been analysed for the two layers (snow and ice) covariance matrix and where snow subsequently removed. Thus, the influence of the snow layer on the polarimetric data could be quantified. Also, the Pauli and Cloude/Pottier polarimetric decompositions were applied for the two-layer and one-layer scattering mechanisms (removed snow) to quantify the effectiveness of these decompositions. Results show that the polarimetric SAR could explain the different

  4. Structural and stratigraphic features and ERS 1 synthetic aperture radar backscatter characteristics of ice growing on shallow lakes in NW Alaska, winter 1991-1992

    NASA Astrophysics Data System (ADS)

    Jeffries, M. O.; Morris, K.; Weeks, W. F.; Wakabayashi, H.

    1994-11-01

    Changes in ERS 1 C band synthetic aperture radar (SAR) backscatter intensity (σ°) from ice growing on shallow tundra lakes at three locations in NW Alaska are described. Ice core analysis shows that at all lakes on the coast at Barrow the ice, whether floating or frozen to the bottom, includes an inclusion-free layer overlying a layer of ice with tubular bubbles oriented parallel to the direction of growth. The clear ice may also be overlain by a discontinuous layer of bubbly snow ice. Backscatter is low (-16 to -22 dB) at the time of initial ice formation, probably due to the specular nature of the upper and lower ice surfaces causing the radar pulse to be reflected away from the radar. As the ice thickens during the autumn, backscatter rises steadily. Once the ice freezes to the lake bottom, regardless of the presence of forward scattering tubular bubbles, low backscatter values of-17 to -18 dB are caused by absorption of the radar signal in the lake bed. For ice that remains afloat all winter the ice-water interface and the tubular bubbles combine, presumably via an incoherent double-bounce mechanism, to cause maximum backscatter values of the order of -6 to -7 dB. The σ° saturates at -6 to -7 dB before maximum ice thickness and tubular bubble content are attained. A simple ice growth model suggests that the layer of ice with tubular bubbles need be only a few centimeters thick midway through the growth season to cause maximum backscatter from floating ice. During the spring thaw a previously unreported backscatter reversal is observed on the floating and grounded portions of the coastal lakes but not on the lakes farther inland. This reversal may be related to the ice surface topography and wetness plus the effects of a longer, cooler melt period by the coast. Time series of backscatter variations from shallow tundra lakes are a record of (1) the development of tubular bubbles in the ice and, by association, changes in the gas content of the underlying

  5. Structural and stratigraphic features and ERS 1 synthetic aperture radar backscatter characteristics of ice growing on shallow lakes in NW Alaska, winter 1991-1992

    NASA Technical Reports Server (NTRS)

    Jeffries, M. O.; Morris, K.; Weeks, W. F.; Wakabayashi, H.

    1994-01-01

    Changes in Earth Remote-Sensing Satellite (ERS) 1 C band synthetic aperture radar (SAR) backscatter intensity (sigma(exp 0)) from ice growing on shallow tundra lakes at three locations in NW Alaska are described. Ice core analysis shows that all lakes on the coast at Barrow the ice, whether floating or frozen to the bottom, includes an inclusion-free layer overlying a layer of ice with tubular bubbles oriented parallel to the direction of growth. The clear ice may also be overlain by a discontinuous layer of bubbly snow ice. Backscatter is low (-16 to -22 dB) at the time of initial ice formation, probably due to the specular nature of the upper and lower ice surfaces causing the radar pulse to be reflected away from the radar. As the ice thickens during the autumn, backscatter rises steadily. Once the ice freezes to the lake bottom, regardless of the presence of foward scattering tubular bubbles, low backscatter values of -17 to -18 dB are caused by absorption of the radar signal in the lake bed. For ice that remains afloat all winter the ice-water interface and the tubular bubbles combine, presumably via an incoherent double-bounce mechanism, to cause maximum backscatter values of the order of -6 to -7 dB. The sigma(exp 0) saturates at -6 to -7 dB before maximum ice thickness and tubular bubble content are attained. A simple ice growth model suggests that the layer of ice with tubular bubbles need be only a few centimeters thick midway through the growth season to cause maximum backscatter from floating ice. During the spring thaw a previously unreported backscatter reversal is observed on the floating and grounded portions of the coastal lakes but not on the lakes farther inland. This reversal may be related to the ice surface topography and wetness plus the effects of a longer, cooler melt period by the coast. Time series of backscatter variations from shallow tundra lakes are a record of (1) the development of tubular bubbles in the ice and, by association

  6. Hellas as a possible site of ancient ice-covered lakes on Mars

    USGS Publications Warehouse

    Moore, Johnnie N.; Wilhelms, D.E.

    2001-01-01

    Based on topographic, morphologic, and stratigraphic evidence, we propose that ancient water-laid sediment is the dominant component of deposits within Hellas Planitia, Mars. Multiple-layered sediment is manifested by alternating benches and scarps visible in Mars orbiting camera narrow-angle (MOC NA) images. Viking Orbiter camera and MOC NA images were used to map contacts and stratigraphically order the different materials units within Hellas. Mars orbiting laser altimeter (MOLA) data reveal that the contacts of these sedimentary units, as well as a number of scarps or other abrupt changes in landscape texture, trace contours of constant elevation for thousands of km, and in one case all around the basin. Channels, consensually interpreted to be cut by water, lead into the basin. MOLA results indicate that the area encompassed by greater Hellas' highest closed contour is nearly one-fifth that of the entire northern plains, making the Hellas "drainage" area much larger than previously reported. If lakes formed under climatic conditions similar to the modern Martian climate, they would develop thick ice carapaces, then the lakes would eventually sublimate away. Two units within Hellas exhibit a reticulate or honeycomb pattern, which we speculate are impressions made by lake-lowered ice blocks grounding into initially soft mud.

  7. Hellas as a Possible Site of Ancient Ice-Covered Lakes on Mars

    NASA Technical Reports Server (NTRS)

    Moore, Jeffrey M.; Wilhelms, Don E.; DeVincenzi, Donald (Technical Monitor)

    2002-01-01

    Based on topographic, morphologic, and stratigraphic evidence, we propose that ancient water-laid sediment is the dominant component of deposits within Hellas Planitia, Mars. Multiply layered sediment is manifested by alternating benches and scarps visible in Mars Orbiting Camera narrow-angle (MOC NA) images. Viking Orbiter camera and MOC NA images were used to map contacts and stratigraphically order the different materials units within Hellas. Mar's Orbiting Laser Altimeter (MOLA) data reveal that the contacts of these sedimentary units, as well as a number of scarps or other abrupt changes in landscape texture, trace contours of constant elevation for thousands of km, and in one case all around the basin. Channels, consensually interpreted to be cut by water, lead into the basin. MOLA results indicate that the area encompassed by greater Hellas' highest closed contour is nearly one-fifth that of the entire northern plains, making the Hellas 'drainage' area much larger than previously reported. If lakes formed under climatic conditions similar to the modern Martian climate, they would develop thick ice carapaces, then the lakes would eventually sublimate away. Two units within Hellas exhibit a reticulate or honeycomb pattern we speculate are impressions made by lake-lowered ice blocks grounding into initially soft mud.

  8. Sub-Ice Microalgal and Bacterial Communities in Freshwater Lake Baikal, Russia.

    PubMed

    Bashenkhaeva, Maria V; Zakharova, Yulia R; Petrova, Darya P; Khanaev, Igor V; Galachyants, Yuri P; Likhoshway, Yelena V

    2015-10-01

    The sub-ice environment of Lake Baikal represents a special ecotope where strongly increasing microbial biomass causes an "ice-bloom" contributing therefore to the ecosystem functioning and global element turnover under low temperature in the world's largest freshwater lake. In this work, we analyzed bacterial and microalgal communities and their succession in the sub-ice environment in March-April 2010-2012. It was found out that two dinoflagellate species (Gymnodinium baicalense var. minor and Peridinium baicalense Kisselew et Zwetkow) and four diatom species (Aulacoseira islandica, A. baicalensis, Synedra acus subsp. radians, and Synedra ulna) predominated in the microalgal communities. Interestingly, among all microalgae, the diatom A. islandica showed the highest number of physically attached bacterial cells (up to 67 ± 16 bacteria per alga). Bacterial communities analyzed with pyrosequencing of 16S rRNA gene fragments were diverse and represented by 161 genera. Phyla Proteobacteria, Verrucomicrobia, Actinobacteria, Acidobacteria, Bacteroidetes, and Cyanobacteria represented a core community independently on microalgal composition, although the relative abundance of these bacterial phyla strongly varied across sampling sites and time points; unique OTUs from other groups were rare.

  9. The deglacial history of the Lake Michigan lobe in Illinois, USA, fleshed out by chronologies associated with ice-walled lakes

    NASA Astrophysics Data System (ADS)

    Curry, B.

    2009-12-01

    The onset of deglaciation of the Lake Michigan lobe (LML) in the western Great Lakes region of North America is well-defined by radiocarbon ages from terrestrial plant material that was buried by proglacial lake sediment and till. A small portion of the lobe began its final retreat during the Marengo Phase at about 24,780 C-14 yr BP (29,630 cal yr BP) [CalPal]; most of the lobe began its final retreat during the Shelby Phase starting at about 19,350 C-14 yr BP (23,010 cal yr BP)[Calib 5.02]. New radiocarbon ages from tundra plant fossils encased in the deposits of ice-walled lakes allow estimation periods of ice stagnation vs. margin advance as well as constraining the age of important events during the late Wisconsin Episode. For example, radiocarbon ages from fossils in ice-walled deposits indicate the LML margin began its final retreat from Illinois at the onset of the Mackinaw lake phase by about 13,650 C-14 yr BP (16,250 cal yr BP). Located on the Marseilles Morainic System, the oldest dated ice-walled lake deposit known in Illinois began to form at 18,210 C-14 yr BP (21,680 cal yr BP). From its end moraine located near Peoria to Chicago on the shores of southern Lake Michigan, the LML extended about 230 km. Collectively, the ages indicate that the outer 100 km of the LML margin retreated about three times faster than the inner 130 km (7.5 x 10-2 km/yr vs. 2.4 x 10-2 km/yr). Changes in ice thickness and dynamics, debris concentration, climate, and regional drainage are some of the likely factors that affected the difference in rate. The existing data provide conservative estimates for the formation of two moraines, the lake-border Deerfield Moraine (720 cal yrs) and the Tinley Moraine (850 cal yrs). Periods of stagnations, marked by radiocarbon ages from fossils in the ice-walled lake sediments, include about 320 years (Deerfield Moraine), 520 cal yrs (Tinley Moraine), 500 cal yrs (Woodstock Moraine), and 710 years (Ransom Moraine). These and other ages

  10. Preliminary Cosmogenic Surface Exposure Ages on Laurentide Ice-sheet Retreat and Opening of the Eastern Lake Agassiz Outlets

    NASA Astrophysics Data System (ADS)

    Leydet, D.; Carlson, A. E.; Sinclair, G.; Teller, J. T.; Breckenridge, A. J.; Caffee, M. W.; Barth, A. M.

    2015-12-01

    The chronology for the eastern outlets of glacial Lake Agassiz holds important consequences for the cause of Younger Dryas cold event during the last deglaciation. Eastward routing of Lake Agassiz runoff was originally hypothesized to have triggered the Younger Dryas. However, currently the chronology of the eastern outlets is only constrained by minimum-limiting radiocarbon ages that could suggest the eastern outlets were still ice covered at the start of the Younger Dryas at ~12.9 ka BP, requiring a different forcing of this abrupt climate event. Nevertheless, the oldest radiocarbon ages are still consistent with an ice-free eastern outlet at the start of the Younger Dryas. Here we will present preliminary 10-Be cosmogenic surface exposure ages from the North Lake, Flat Rock Lake, glacial Lake Kaministiquia, and Lake Nipigon outlets located near Thunder Bay, Ontario. These ages will date the timing of the deglaciation of the Laurentide ice sheet in the eastern outlet region of glacial Lake Agassiz. This will provide an important constraint for the hypothesized freshwater forcing of the cause of Younger Dryas cold event.

  11. Late-Holocene Fluctuations of the Greenland Ice Sheet: Insights from a south Greenland threshold lake

    NASA Astrophysics Data System (ADS)

    Sinclair, G.; Carlson, A. E.; Reilly, B.

    2015-12-01

    Several centennial-scale climate fluctuations during the late-Holocene make it an ideal test case for examining the effects of climate change on sea level at societally-relevant timescales. Across much of the Arctic, glaciers and ice sheets reached their maximum late-Holocene extent during the Little Ice Age (LIA, 1400-1900 C.E.), approximately coincident with the global temperature minima observed during this time. However, ongoing work suggests the south Greenland Ice Sheet (sGrIS) may have behaved differently during the late-Holocene, with several outlet glaciers retreating, rather than advancing, during the LIA, possibly due to regional warming in the region different from the Arctic trend. The Qassimiut lobe, a low-lying piedmont-like extension of the sGrIS, may be especially sensitive to late-Holocene climate changes. Geomorphic evidence outboard of Naujaat Sermia, an outlet glacier draining the Qassimiut lobe, suggests three distinct periods of land exposure. We hypothesize these occurred during the last deglacial period, after an advance from near or behind the present margin during the Neoglacial, and during warming following the Little Ice Age in the last 1-2 centuries. Here, we present data from threshold lake cores immediately outboard of the presumed Neoglacial moraine. A sharp contact divides glacial sands and silts from organic gyttja, indicating glacial retreat from the moraine and subsequent meltwater diversion. The contact is accompanied by several geochemical changes, including increased Fe/Ti ratios, increased Br, and decreased Si and K, indicating a switch from more clastic to organic sedimentation. Radiocarbon ages from eight macrofossils immediately above this contact are calibrated to 1350-1950 C.E., suggesting the ice sheet may have retreated from its late-Holocene maximum during the Little Ice Age, but the wide range in ages suggests reworking of organic material may be significant in this region.

  12. Modelling the influence of Lake Agassiz on Glacial Isostatic Adjustment and deglaciation of the Laurentide ice sheet

    NASA Astrophysics Data System (ADS)

    Berends, Tijn; van de Wal, Roderik; de Boer, Bas; Bradley, Sarah

    2016-04-01

    ANICE is a 3-D ice-sheet-shelf model, which simulates ice dynamics on the continental scale. It uses a combination of the SIA and SSA approximations and here it is forced with benthic δ18O records using an inverse routine. It is coupled to SELEN, a model, which solves the gravitationally self-consistent sea-level equation and the solid earth deformation of a spherically symmetrical rotating Maxwell visco-elastic earth, accounting for all major GIA effects. The coupled ANICE-SELEN model thus captures ice-sea-level feedbacks and can be used to accurately simulate variations in local relative sea-level over geological time scales. In this study it is used to investigate the mass loss of the Laurentide ice-sheet during the last deglaciation, accounting in particular for the presence of the proglacial Lake Agassiz by way of its GIA effects and its effect on the ice sheet itself. We show that the mass of the water can have a significant effect on local relative sea-level through the same mechanisms as the ice-sheet - by perturbing the geoid and by deforming the solid earth. In addition we show that calving of the ice-shelf onto the lake could have had a strong influence on the behaviour of the deglaciation. In particular, when allowing lake calving, the ice-sheet retreats rapidly over the deepening bed of Hudson Bay during the deglaciation, resulting in a narrow ice dam over Hudson Strait. This dam collapses around 8.2 Kyr causing a global sea level rise of approximately 1 meter - an observation that agrees well with field data (for example, LaJeunesse and St. Onge, 2008). Without lake calving the model predicts a drainage towards the Arctic ocean in the North.

  13. Protist diversity in a permanently ice-covered Antarctic lake during the polar night transition.

    PubMed

    Bielewicz, Scott; Bell, Elanor; Kong, Weidong; Friedberg, Iddo; Priscu, John C; Morgan-Kiss, Rachael M

    2011-09-01

    The McMurdo Dry Valleys of Antarctica harbor numerous permanently ice-covered lakes, which provide a year-round oasis for microbial life. Microbial eukaryotes in these lakes occupy a variety of trophic levels within the simple aquatic food web ranging from primary producers to tertiary predators. Here, we report the first molecular study to describe the vertical distribution of the eukaryotic community residing in the photic zone of the east lobe (ELB) and west lobe (WLB) of the chemically stratified Lake Bonney. The 18S ribosomal RNA (rRNA) libraries revealed vertically stratified populations dominated by photosynthetic protists, with a cryptophyte dominating shallow populations (ELB-6 m; WLB-10 m), a haptophyte occupying mid-depths (both lobes 13 m) and chlorophytes residing in the deepest layers (ELB-18 and 20 m; WLB-15 and 20 m) of the photic zone. A previously undetected stramenopile occurred throughout the water column of both lobes. Temporal variation in the eukaryotic populations was examined during the transition from Antarctic summer (24-h sunlight) to polar night (complete dark). Protist diversity was similar between the two lobes of Lake Bonney due to exchange between the photic zones of the two basins via a narrow bedrock sill. However, vertical and temporal variation in protist distribution occurred, indicating the influence of the unique water chemistry on the biology of the two dry valley watersheds.

  14. Protist diversity in a permanently ice-covered Antarctic lake during the polar night transition.

    PubMed

    Bielewicz, Scott; Bell, Elanor; Kong, Weidong; Friedberg, Iddo; Priscu, John C; Morgan-Kiss, Rachael M

    2011-09-01

    The McMurdo Dry Valleys of Antarctica harbor numerous permanently ice-covered lakes, which provide a year-round oasis for microbial life. Microbial eukaryotes in these lakes occupy a variety of trophic levels within the simple aquatic food web ranging from primary producers to tertiary predators. Here, we report the first molecular study to describe the vertical distribution of the eukaryotic community residing in the photic zone of the east lobe (ELB) and west lobe (WLB) of the chemically stratified Lake Bonney. The 18S ribosomal RNA (rRNA) libraries revealed vertically stratified populations dominated by photosynthetic protists, with a cryptophyte dominating shallow populations (ELB-6 m; WLB-10 m), a haptophyte occupying mid-depths (both lobes 13 m) and chlorophytes residing in the deepest layers (ELB-18 and 20 m; WLB-15 and 20 m) of the photic zone. A previously undetected stramenopile occurred throughout the water column of both lobes. Temporal variation in the eukaryotic populations was examined during the transition from Antarctic summer (24-h sunlight) to polar night (complete dark). Protist diversity was similar between the two lobes of Lake Bonney due to exchange between the photic zones of the two basins via a narrow bedrock sill. However, vertical and temporal variation in protist distribution occurred, indicating the influence of the unique water chemistry on the biology of the two dry valley watersheds. PMID:21390078

  15. Phytoplankton successions under ice cover in four lakes located in north-eastern Sweden: effects of liming.

    PubMed

    Wahlström, G; Danilov, R A

    2003-01-01

    Phytoplankton successions under ice cover (January-March) were determined in four oligotrophic lakes (Burtjärn, Aspen, Vialamptjärn and Storkorstjärn) located in North-Eastern Sweden. The total phosphorus concentration in the lakes was less than 10 micrograms/L. Lake Burtjärn (reference lake) had a similar hydrology as Lake Aspen. Storkorstjärn and Vialamptjärn were of similar hydrology and had heavily colored water (> 100 mgpt/L). Aspen as well as vialamptjärn became continuously limed with calcium carbonate annually during the last decades. Biodiversity was considerably higher in the limed lakes (Aspen and Vialamptjärn) than in the untreated lakes (Burtjärn and Storkorstjärn). In Lake Burtjärn the most frequent species were Rhodomonas lacustris, Tabellaria flocculosa and Botryococcus braunii. Cryptophyceae (R. lacustris and Cryptomonas marssonii) and Dinophyceae (especially Gymnodinium lantzschii) were common phytoplankton groups in Lake Aspen. Tabellaria flocculosa was also the most common organism in both humic lakes Storkorstjärn and Vialamptjärn, other phytoplankton groups were in the humic lakes scarce. Liming was found to have profound effects on phytoplankton communities studied.

  16. Monitoring phenological changes in lake ice as a robust indicator of regional climate change using the AVHRR

    SciTech Connect

    Wynne Randolph, H.; Lillesand, T.M. )

    1993-06-01

    The length of the growing season, effectively defined by the onset or breakup of ice, may be one of the more important ways in which climate change is likely to influence lake environments. In addition, interannual variation in the dates of lake ice formation and breakup has been shown to be an effective climate change indicator. We explored the use of data from the Advanced Very High Resolution Radiometer (AVHRR) to discriminate the presence of lake ice during the winter of 1990-1991 on the 45 lakes and reservoirs in Wisconsin with a surface area of greater than 1,000 hectares. Our results suggest both the feasibility of using the AVHRR to determine the date of lake ice breakup as well as the strong correlation (R=[minus]0.87) of the dates so derived with January-March mean local temperatures. These results indicate the inherent promise of utilizing archive satellite to detect the climate expected as a result of greenhouse warming.

  17. Integration of MODIS-derived metrics to assess interannual variability in snowpack, lake ice, and NDVI in southwest Alaska

    USGS Publications Warehouse

    Reed, B.; Budde, M.; Spencer, P.; Miller, A.E.

    2009-01-01

    Impacts of global climate change are expected to result in greater variation in the seasonality of snowpack, lake ice, and vegetation dynamics in southwest Alaska. All have wide-reaching physical and biological ecosystem effects in the region. We used Moderate Resolution Imaging Spectroradiometer (MODIS) calibrated radiance, snow cover extent, and vegetation index products for interpreting interannual variation in the duration and extent of snowpack, lake ice, and vegetation dynamics for southwest Alaska. The approach integrates multiple seasonal metrics across large ecological regions. Throughout the observation period (2001-2007), snow cover duration was stable within ecoregions, with variable start and end dates. The start of the lake ice season lagged the snow season by 2 to 3??months. Within a given lake, freeze-up dates varied in timing and duration, while break-up dates were more consistent. Vegetation phenology varied less than snow and ice metrics, with start-of-season dates comparatively consistent across years. The start of growing season and snow melt were related to one another as they are both temperature dependent. Higher than average temperatures during the El Ni??o winter of 2002-2003 were expressed in anomalous ice and snow season patterns. We are developing a consistent, MODIS-based dataset that will be used to monitor temporal trends of each of these seasonal metrics and to map areas of change for the study area.

  18. When a habitat freezes solid: Microorganisms over-winter within the ice column of a coastal Antarctic lake

    USGS Publications Warehouse

    Foreman, C.M.; Dieser, M.; Greenwood, M.; Cory, R.M.; Laybourn-Parry, J.; Lisle, J.T.; Jaros, C.; Miller, P.L.; Chin, Y.-P.; McKnight, Diane M.

    2011-01-01

    A major impediment to understanding the biology of microorganisms inhabiting Antarctic environments is the logistical constraint of conducting field work primarily during the summer season. However, organisms that persist throughout the year encounter severe environmental changes between seasons. In an attempt to bridge this gap, we collected ice core samples from Pony Lake in early November 2004 when the lake was frozen solid to its base, providing an archive for the biological and chemical processes that occurred during winter freezeup. The ice contained bacteria and virus-like particles, while flagellated algae and ciliates over-wintered in the form of inactive cysts and spores. Both bacteria and algae were metabolically active in the ice core melt water. Bacterial production ranged from 1.8 to 37.9??gCL-1day-1. Upon encountering favorable growth conditions in the melt water, primary production ranged from 51 to 931??gCL-1day-1. Because of the strong H2S odor and the presence of closely related anaerobic organisms assigned to Pony Lake bacterial 16S rRNA gene clones, we hypothesize that the microbial assemblage was strongly affected by oxygen gradients, which ultimately restricted the majority of phylotypes to distinct strata within the ice column. This study provides evidence that the microbial community over-winters in the ice column of Pony Lake and returns to a highly active metabolic state when spring melt is initiated. ?? 2011 Federation of European Microbiological Societies.

  19. Testing the sub-ice lake model for chaotic terrains on Mars: a numerical simulation

    NASA Astrophysics Data System (ADS)

    Roda, Manuel; Govers, Rob; Zegers, Tanja

    2013-04-01

    The identification of Hesperian chaotic terrains as the source of the outflow channels has led to a general scenario where water is rapidly discharged from the subsurface resulting in catastrophic outflows. However, the process leading to chaotic terrain formation and collection and discharge of catastrophic volumes of water has remained controversial. Geological and hydrological analysis of Aram Chaos suggests that a single, rapid and catastrophic event is sufficient to carve the outflow channel of Aram Chaos and the resulting Aram Chaos morphology imply large amount of subsidence (up to 1.5 km). These observations are in agreement with the sub-Ice lake hypothesis of catastrophic collapse of sediments induced as a consequence of melting of a buried ice sheet [1]. We use time-dependent numerical models to test different aspects of the hypothesis. The simulation starts from the complete freezing of an intra-crater lake. Subsequent ice melting and eventual destabilization is driven by planetary heat loss in combination with sediment blanketing and loading. The simulation ends when the complete sediments filling of the crater occurs. The results show that initial freezing occurs very rapidly, 360-1300 kyr, depending on the planetary heat flux (10-25 mW/m^2). Subsequent melting of the buried ice is slow and depends on the heat flux and sedimentation rate. For the lowest heat flux (10 mW/m^2) no melting occurs. The ice melting rate decreases linearly with increasing sedimentation rate, from 150 m/Myr for the fastest (0.1 mm/yr) sedimentation to 1.5 m/Myr for the slowest (0.001 mm/yr) The mechanical system remains stable until the complete filling of the crater, except in the case of slowest sedimentation (0.001 mm/yr) and 25 mW/m2 heat flow. Here, a complete top-bottom fracturing of the overburden starts at the transition between the wall and the floor of the crater, when the molten ice layer reaches a thickness of 1.5-1.6 km. The thickness of water generated beneath

  20. Gravity anomaly at a Pleistocene lake bed in NW Alaska interpreted by analogy with Greenland's Lake Taserssauq and its floating ice tongue

    USGS Publications Warehouse

    Barnes, D.F.

    1987-01-01

    A possible example of a very deep glacial excavation is provided by a distinctive gravity low located at the front of a valley glacier that once flowed into glacial Lake Aniuk (formerly Lake Noatak) in the western Brooks Range. Geologic and geophysical data suggest that sediments or ice filling a glacially excavated valley are the most probable cause of the 30-50 mGal anomaly. Reasonable choices of geometric models and density contrasts indicate that the former excavation is now filled with a buried-ice thickness of 700 m or sediment thicknesses greater than 1 km. No direct evidence of efficient excavation was observed in Greenland, but efficient glacial erosion behind a floating polar ice tongue could explain the excavation that caused the Alaskan gravity anomaly. -from Author

  1. Surface exposure dating of glacial lake shorelines: implications for constraining ice margin positions and meltwater outbursts during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Dube-Loubert, Hugo; Roy, Martin; Schaefer, Joerg

    2016-04-01

    The Laurentide ice sheet (LIS) played an important role in the climate variability of the last deglaciation, notably through large discharges of meltwater to the North Atlantic that disturbed the ocean's circulation and heat transport. Deglaciation of the northeastern sector of the LIS was complex and included the development of large ice-dammed lakes that were confined within the main river valleys draining northward into Ungava Bay. The history of these lakes is closely related to the temporal evolution of the Labrador ice dome, but large uncertainties regarding the position and dynamic of the ice margin through time currently limit our understanding of these glacial lakes. In the Ungava lowlands, glacial lake Naskaupi invaded the George River valley, leaving a series of well-developed shorelines and deltas. These spectacular raised shorelines are 10 to 20 meters wide and can be followed for several kilometers. Our field investigations and remote sensing analysis indicate that Lake Naskaupi experienced a complex history, as shown by the succession of shorelines that likely reflect the opening of new topographic outlets during ice retreat. Constraining the timing of the different phases of the lake and its drainage has traditionally been challenging, as organic material suitable for radiocarbon dating is scarce or lacking. Recent progress in Surface Exposure Dating (SED) by cosmogenic nuclides now inspires novel approaches to glacial and deglacial geomorphology. Here we apply 10Be SED to boulders that form part of these shorelines and mark the main (high-level) stage of Lake Naskaupi. We sampled 4-6 multi-meter size boulders at 4 different sites. Preliminary results show high internal consistency and, indicate that the main lake phase developed very late in the regional deglaciation, which extends from about 8500 to 6800 cal. yr BP (Dyke and Prest, 1987). We also present SED results from boulders deposited by a substantial outburst flood presumably associated with

  2. Time-varying imagery of ice features dynamic scattering in presence climate change: polytypical lakes Ladoga and Peipus as example

    NASA Astrophysics Data System (ADS)

    Melentyev, V.; Melentyev, K.; Pettersson, L.; Mushkudiany, M.

    2009-04-01

    The Problem of dynamical instability of ice conditions and modification of ice regime of polytypical lakes owing to global warming was investigated using time-varying satellite imagery. Deep-water Lake Ladoga and shallow-water Lake Peipus both situated at the north-western part of Russian Federation in moderate climatic zone but possessed different heat capacity were used for comparative studies. The comprehensive analysis of ERS/RADARSAT/Envisat SAR images was provided using the results of long-term studies of thermal structures of these inland water bodies and peculiarities of their variability during open water season as well calculations of heat supply in different weather conditions. 1993-2008 NERSC/NIERSC SAR archive as well materials sub-satellite experiments on board research vessel and research aircraft since 1960-s is used. Shipborne observations were used for validation satellite information. Thematic interpretation of satellite data shows that SAR signature of ice could be applied as tracer of various natural processes and phenomena, including climatically and ecologically important ones. As result dependence of hydrological features and the time of freeze-up and ice destruction in both selected lakes in consequence of climate change and softening of winter severity in nowadays was assessed. Wind regime patterns (speed and direction) were analyzed using algorithm CMOD 4 and in the upshot the increase of seasonal and regional variability of windy weather in studied regions was fixed. In frame of these studies wind cadastre appurtenant to the NW part of RF was composed on the basis of satellite SAR survey. In particular the modification of "wind climate" was disclosed. And what is more: it was revealed that intensification of windy weather resulted in intensification of dynamic range of water and ice exchange between the central part of both studied polytypical lakes and their gulfs. These natural processes took place due to widening duration of the open

  3. Time-varying imagery of ice features dynamic scattering in presence climate change: polytypical lakes Ladoga and Peipus as example

    NASA Astrophysics Data System (ADS)

    Melentyev, V. V.; Melentyev, K. V.; Pettersson, L. H.; Mushkudany, M. I.

    2009-04-01

    Problem of dynamical instability of ice conditions and modification of ice regime of polytypical lakes owing to global warming were investigated using time-varying satellite imagery. Deep-water Lake Ladoga and shallow-water Lake Peipus both situated at the north-western part of Russian Federation in moderate climatic zone but possessed different heat capacity were used for comparative studies. The comprehensive analysis of ERS/RADARSAT/Envisat SAR images was provided using the results of long-term studies of thermal structures of these inland waterbodies and peculiarities of their variability during open water season as well calculations of heat supply in different weather conditions. 1993-2008 NERSC/NIERSC SAR archive as well materials sub-satellite experiments onboard research vessel and research aircraft since 1960-s is used. Shipborne observations were used for validation satellite information. Thematic interpretation of satellite data shows that SAR signature of ice could be applied as tracer of various natural processes and phenomena, including climatically and ecologically important ones. As result dependence of hydrological features and the time of freeze-up and ice destruction in both selected lakes in consequence of climate change and softening of winter severity in nowadays was assessed. Wind regime patterns (speed and direction) were analyzed using algorithm CMOD 4 and in the upshot the increase of seasonal and regional variability of windy weather in studied regions was fixed. In frame of these studies wind cadastre appurtenant to the NW part of RF was composed on the basis of satellite SAR survey. In particular the modification of "wind climate" was disclosed. And what is more: it was revealed that intensification of windy weather resulted in intensification of dynamic range of water and ice exchange between the central part of both studied polytypical lakes and their gulfs. These natural processes took place due to widening duration of the open water

  4. A hydrothermal contribution to the Vostok subglacial lake (Antarctica) suggested from bacterial gene analysis and the stable isotope composition of deep ice core samples

    NASA Astrophysics Data System (ADS)

    Petit, J. R.; Alekhina, I. A.; Bulat, S. A.

    The largest subglacial lake (14,000 km2) underlies the Russian station of Vostok in Antarctica by 3.750 m of ice. Due to a particular setting of the glacier flow and the subglacial relief, the glacier-lake interface is inclined making a slope of 600 m over the 250 km of the lake length. This leads the deep glacier ice to melt and the high level of lake water (under Vostok area) to freeze. A 3623 m deep ice coring was performed at Vostok station for paleoclimate study, and was stopped 130 m above the lake interface. The last 85 m of the ice core was formed by refreezing from the water, and the ice samples represent good template of the lake for biological and chemical content. We performed bacterial 16S ribosomal gene analysis on several lake ice samples. Only one phylotype from 16 initially detected, was kept with confident relevance to the lake environment. On the other hand, the 15 other were presumed to be contamination on the basis of indexing contaminant criteria developed for the thorough ice samples processing. The retained phylotype represents the extant thermophilic bacterium Hydrogenophilus thermoluteolus (beta-Proteobacteria) that is encountered until now in only hot springs, and is potentially capable to grow as a chemolithoautotroph. Hot springs in the subglacial bedrock around Vostok are counterintuitive. On the other hand, assuming the lake is in steady state, a hydrothermal contribution is suggested by the stable isotope composition of the lake ice. Using the Deuterium and 18O content, an 18O enrichment of the lake ice (output) is observed with respect to composition of the melting ice (input). This effect (so-called 18O shift) characterize geothermal areas and may result from the 18O exchanges at hot temperature between water and silicates. The Vostok subglacial lake is an extreme environment and appear mostly germ free. On the other hand, we suggest some niches inside some bedrock faults of a hydrothermal system. We invoke scarce flushing events

  5. Comparison of the Microbial Diversity and Abundance Between the Freshwater Land-Locked Lakes of Schirmacher Oasis and the Perennially Ice-Covered Lake Untersee in East Antarctica

    NASA Technical Reports Server (NTRS)

    Huang, Jonathan; Hoover, Richard B.; Swain, Ashit; Murdock, Chris; Bej, Asim K.

    2010-01-01

    Extreme conditions such as low temperature, dryness, and constant UV-radiation in terrestrial Antarctica are limiting factors of the survival of microbial populations. The objective of this study was to investigate the microbial diversity and enumeration between the open water lakes of Schirmacher Oasis and the permanently ice-covered Lake Untersee. The lakes in Schirmacher Oasis possessed abundant and diverse group of microorganisms compared to the Lake Untersee. Furthermore, the microbial diversity between two lakes in Schirmacher Oasis (Lake L27C and L47) was compared by culture-based molecular approach. It was determined that L27Chad a richer microbial diversity representing 5 different phyla and 7 different genera. In contrast L47 consisted of 4 different phyla and 6 different genera. The difference in microbial community could be due to the wide range of pH between L27C (pH 9.1) and L47 (pH 5.7). Most of the microbes isolated from these lakes consisted of adaptive biological pigmentation. Characterization of the microbial community found in the freshwater lakes of East Antarctica is important because it gives a further glimpse into the adaptation and survival strategies found in extreme conditions.

  6. Spatial Analysis of Great Lakes Regional Icing Cloud Liquid Water Content

    NASA Technical Reports Server (NTRS)

    Ryerson, Charles C.; Koenig, George G.; Melloh, Rae A.; Meese, Debra A.; Reehorst, Andrew L.; Miller, Dean R.

    2003-01-01

    Abstract Clustering of cloud microphysical conditions, such as liquid water content (LWC) and drop size, can affect the rate and shape of ice accretion and the airworthiness of aircraft. Clustering may also degrade the accuracy of cloud LWC measurements from radars and microwave radiometers being developed by the government for remotely mapping icing conditions ahead of aircraft in flight. This paper evaluates spatial clustering of LWC in icing clouds using measurements collected during NASA research flights in the Great Lakes region. We used graphical and analytical approaches to describe clustering. The analytical approach involves determining the average size of clusters and computing a clustering intensity parameter. We analyzed flight data composed of 1-s-frequency LWC measurements for 12 periods ranging from 17.4 minutes (73 km) to 45.3 minutes (190 km) in duration. Graphically some flight segments showed evidence of consistency with regard to clustering patterns. Cluster intensity varied from 0.06, indicating little clustering, to a high of 2.42. Cluster lengths ranged from 0.1 minutes (0.6 km) to 4.1 minutes (17.3 km). Additional analyses will allow us to determine if clustering climatologies can be developed to characterize cluster conditions by region, time period, or weather condition. Introduction

  7. Deformation of the Batestown till of the Lake Michigan lobe, Laurentide ice sheet

    USGS Publications Warehouse

    Thomason, J.F.; Iverson, N.R.

    2009-01-01

    Deep, pervasive shear deformation of the bed to high strains (>100) may have been primarily responsible for flow and sediment transport of the Lake Michigan lobe of the Laurentide ice sheet. To test this hypothesis, we sampled at 0.2 m increments a basal till from one advance of the lobe (Batestown till) along vertical profiles and measured fabrics due to both anisotropy of magnetic susceptibility and sand-grain preferred orientation. Unlike past fabric studies, interpretations were guided by results of laboratory experiments in which this till was deformed in simple shear to high strains. Fabric strengths indicate that more than half of the till sampled has a <5% probability of having been sheared to moderate strains (7-30). Secular changes in fabric azimuth over the thickness of the till, probably due to changing ice-flow direction as the lobe receded, indicate that the bed accreted with time and that the depth of deformation of the bed did not exceed a few decimeters. Orientations of principal magnetic susceptibilities show that the state of strain was commonly complex, deviating from bed-parallel simple shear. Deformation is inferred to have been focused in shallow, temporally variable patches during till deposition from ice.

  8. Remote profiling of lake ice using an S-band short pulse radar aboard an all-terrain vehicle

    NASA Technical Reports Server (NTRS)

    Cooper, D. W.; Mueller, R. A.; Schertler, R. J.

    1975-01-01

    An airborne short-pulse radar system to measure ice thickness was designed. The system supported an effort to develop an all-weather Great Lakes Ice Information System to aid in extending the winter navigation season. Experimental studies into the accuracy and limitations of the system are described. A low power version was operated from an all-terrain vehicle on the Straits of Mackinac during March 1975. The vehicle allowed rapid surveying of large areas and eliminated the ambiguity in location between the radar system and the ground truth ice auger team. It was also possible to the effects of snow cover, surface melt water, pressure ridging, and ice type upon the accuracy of the system. Over 25 sites were explored which had ice thicknesses from 29 to 60 cm. The maximum radar overestimate was 9.8 percent, while the maximum underestimate was 6.6 percent. The average error of the 25 measurements was 0.1 percent.

  9. Microbial Mat Communities along an Oxygen Gradient in a Perennially Ice-Covered Antarctic Lake.

    PubMed

    Jungblut, Anne D; Hawes, Ian; Mackey, Tyler J; Krusor, Megan; Doran, Peter T; Sumner, Dawn Y; Eisen, Jonathan A; Hillman, Colin; Goroncy, Alexander K

    2016-01-01

    Lake Fryxell is a perennially ice-covered lake in the McMurdo Dry Valleys, Antarctica, with a sharp oxycline in a water column that is density stabilized by a gradient in salt concentration. Dissolved oxygen falls from 20 mg liter(-1) to undetectable over one vertical meter from 8.9- to 9.9-m depth. We provide the first description of the benthic mat community that falls within this oxygen gradient on the sloping floor of the lake, using a combination of micro- and macroscopic morphological descriptions, pigment analysis, and 16S rRNA gene bacterial community analysis. Our work focused on three macroscopic mat morphologies that were associated with different parts of the oxygen gradient: (i) "cuspate pinnacles" in the upper hyperoxic zone, which displayed complex topography and were dominated by phycoerythrin-rich cyanobacteria attributable to the genus Leptolyngbya and a diverse but sparse assemblage of pennate diatoms; (ii) a less topographically complex "ridge-pit" mat located immediately above the oxic-anoxic transition containing Leptolyngbya and an increasing abundance of diatoms; and (iii) flat prostrate mats in the upper anoxic zone, dominated by a green cyanobacterium phylogenetically identified as Phormidium pseudopriestleyi and a single diatom, Diadesmis contenta. Zonation of bacteria was by lake depth and by depth into individual mats. Deeper mats had higher abundances of bacteriochlorophylls and anoxygenic phototrophs, including Chlorobi and Chloroflexi. This suggests that microbial communities form assemblages specific to niche-like locations. Mat morphologies, underpinned by cyanobacterial and diatom composition, are the result of local habitat conditions likely defined by irradiance and oxygen and sulfide concentrations. PMID:26567300

  10. Stratigraphic evidence for rate of sedimentation in an ice-contact, proglacial lake, Bering Glacier, Alaska

    SciTech Connect

    Fleisher, P.J. . Dept. of Earth Sciences); Bailey, P.K. )

    1993-03-01

    A semi-continuous aerial photo record documents retreat positions of the eastern Bering Glacier and the development of a shallow embayment of ice-contact Tsiu Lake during the summer of 1986. An observed break out in August, 1989, abruptly dropped lake level 17 m and exposed lake sediments containing three annual couplets 54 cm thick. This continuous record of accumulation during a documented 3-year period yields an average annual accumulation rate of 18 cm/year. The lower portion of each annual couplet averages 11.5 cm in thickness and consists of fine, gray silt laminae, each approximately 0.7 mm thick. These grade upward into interlaminated light and dark gray silt and tan, very fine sand beds, each about 0.5 cm thick, with an average cumulative thickness of 6.5 cm. The sand is commonly cross bedded and contains subtle graded bedding. Because the uppermost interlaminated unit was the last to be deposited prior to the break out, it must represent summer-season sediments. This interpretation is consistent with intermittent higher summer discharge and associated currents that periodically introduce sand and hold silt in suspension. Lower energy conditions beneath frozen lakes during winter months favor quieter water and yield a thicker accumulation of uniform silt. Measurements of contemporary summer accumulation were made using cylinder sediment traps. Resulting data indicate that rates of sediment accumulation are directly related to length of collection column, trap depth, duration of sample period and turbidity, and may be an order of magnitude greater than that represented by the measured stratigraphic record. These field studies shed light on specific conditions of deposition and the glaciolacustrine environment during Laurentide retreat from central New York State.

  11. Microbial Mat Communities along an Oxygen Gradient in a Perennially Ice-Covered Antarctic Lake.

    PubMed

    Jungblut, Anne D; Hawes, Ian; Mackey, Tyler J; Krusor, Megan; Doran, Peter T; Sumner, Dawn Y; Eisen, Jonathan A; Hillman, Colin; Goroncy, Alexander K

    2015-11-13

    Lake Fryxell is a perennially ice-covered lake in the McMurdo Dry Valleys, Antarctica, with a sharp oxycline in a water column that is density stabilized by a gradient in salt concentration. Dissolved oxygen falls from 20 mg liter(-1) to undetectable over one vertical meter from 8.9- to 9.9-m depth. We provide the first description of the benthic mat community that falls within this oxygen gradient on the sloping floor of the lake, using a combination of micro- and macroscopic morphological descriptions, pigment analysis, and 16S rRNA gene bacterial community analysis. Our work focused on three macroscopic mat morphologies that were associated with different parts of the oxygen gradient: (i) "cuspate pinnacles" in the upper hyperoxic zone, which displayed complex topography and were dominated by phycoerythrin-rich cyanobacteria attributable to the genus Leptolyngbya and a diverse but sparse assemblage of pennate diatoms; (ii) a less topographically complex "ridge-pit" mat located immediately above the oxic-anoxic transition containing Leptolyngbya and an increasing abundance of diatoms; and (iii) flat prostrate mats in the upper anoxic zone, dominated by a green cyanobacterium phylogenetically identified as Phormidium pseudopriestleyi and a single diatom, Diadesmis contenta. Zonation of bacteria was by lake depth and by depth into individual mats. Deeper mats had higher abundances of bacteriochlorophylls and anoxygenic phototrophs, including Chlorobi and Chloroflexi. This suggests that microbial communities form assemblages specific to niche-like locations. Mat morphologies, underpinned by cyanobacterial and diatom composition, are the result of local habitat conditions likely defined by irradiance and oxygen and sulfide concentrations.

  12. Microbial Mat Communities along an Oxygen Gradient in a Perennially Ice-Covered Antarctic Lake

    PubMed Central

    Hawes, Ian; Mackey, Tyler J.; Krusor, Megan; Doran, Peter T.; Sumner, Dawn Y.; Eisen, Jonathan A.; Hillman, Colin; Goroncy, Alexander K.

    2015-01-01

    Lake Fryxell is a perennially ice-covered lake in the McMurdo Dry Valleys, Antarctica, with a sharp oxycline in a water column that is density stabilized by a gradient in salt concentration. Dissolved oxygen falls from 20 mg liter−1 to undetectable over one vertical meter from 8.9- to 9.9-m depth. We provide the first description of the benthic mat community that falls within this oxygen gradient on the sloping floor of the lake, using a combination of micro- and macroscopic morphological descriptions, pigment analysis, and 16S rRNA gene bacterial community analysis. Our work focused on three macroscopic mat morphologies that were associated with different parts of the oxygen gradient: (i) “cuspate pinnacles” in the upper hyperoxic zone, which displayed complex topography and were dominated by phycoerythrin-rich cyanobacteria attributable to the genus Leptolyngbya and a diverse but sparse assemblage of pennate diatoms; (ii) a less topographically complex “ridge-pit” mat located immediately above the oxic-anoxic transition containing Leptolyngbya and an increasing abundance of diatoms; and (iii) flat prostrate mats in the upper anoxic zone, dominated by a green cyanobacterium phylogenetically identified as Phormidium pseudopriestleyi and a single diatom, Diadesmis contenta. Zonation of bacteria was by lake depth and by depth into individual mats. Deeper mats had higher abundances of bacteriochlorophylls and anoxygenic phototrophs, including Chlorobi and Chloroflexi. This suggests that microbial communities form assemblages specific to niche-like locations. Mat morphologies, underpinned by cyanobacterial and diatom composition, are the result of local habitat conditions likely defined by irradiance and oxygen and sulfide concentrations. PMID:26567300

  13. Massive regime shifts and high activity of heterotrophic bacteria in an ice-covered lake.

    PubMed

    Bižić-Ionescu, Mina; Amann, Rudolf; Grossart, Hans-Peter

    2014-01-01

    In winter 2009/10, a sudden under-ice bloom of heterotrophic bacteria occurred in the seasonally ice-covered, temperate, deep, oligotrophic Lake Stechlin (Germany). Extraordinarily high bacterial abundance and biomass were fueled by the breakdown of a massive bloom of Aphanizomenon flos-aquae after ice formation. A reduction in light resulting from snow coverage exerted a pronounced physiological stress on the cyanobacteria. Consequently, these were rapidly colonized, leading to a sudden proliferation of attached and subsequently of free-living heterotrophic bacteria. Total bacterial protein production reached 201 µg C L(-1) d(-1), ca. five times higher than spring-peak values that year. Fluorescence in situ hybridization and denaturing gradient gel electrophoresis at high temporal resolution showed pronounced changes in bacterial community structure coinciding with changes in the physiology of the cyanobacteria. Pyrosequencing of 16S rRNA genes revealed that during breakdown of the cyanobacterial population, the diversity of attached and free-living bacterial communities were reduced to a few dominant families. Some of these were not detectable during the early stages of the cyanobacterial bloom indicating that only specific, well adapted bacterial communities can colonize senescent cyanobacteria. Our study suggests that in winter, unlike commonly postulated, carbon rather than temperature is the limiting factor for bacterial growth. Frequent phytoplankton blooms in ice-covered systems highlight the need for year-round studies of aquatic ecosystems including the winter season to correctly understand element and energy cycling through aquatic food webs, particularly the microbial loop. On a global scale, such knowledge is required to determine climate change induced alterations in carbon budgets in polar and temperate aquatic systems.

  14. Effects of glacial meltwater inflows and moat freezing on mixing in an ice-covered antarctic lake as interpreted from stable isotope and tritium distributions

    USGS Publications Warehouse

    Miller, L.G.; Aiken, G.R.

    1996-01-01

    Perennially ice-covered lakes in the McMurdo Dry Valleys have risen several meters over the past two decades due to climatic warming and increased glacial meltwater inflow. To elucidate the hydrologic responses to changing climate and the effects on lake mixing processes we measured the stable isotope (??18O and ??D) and tritium concentrations of water and ice samples collected in the Lake Fryxell watershed from 1987 through 1990. Stable isotope enrichment resulted from evaporation in stream and moat samples and from sublimation in surface lake-ice samples. Tritium enrichment resulted from exchange with the postnuclear atmosphere in stream and moat samples. Rapid injection of tritiated water into the upper water column of the make and incorporation of this water into the ice cover resulted in uniformly elevated tritium contents (> 3.0 TU) in these reservoirs. Tritium was also present in deep water, suggesting that a component of bottom water was recently at the surface. During summer, melted lake ice and stream water forms the moat. Water excluded from ice formation during fall moat freezing (enriched in solutes and tritium, and depleted in 18O and 2H relative to water below 15-m depth) may sink as density currents to the bottom of the lake. Seasonal lake circulation, in response to climate-driven surface inflow, is therefore responsible for the distribution of both water isotopes and dissolved solutes in Lake Fryxell.

  15. Diatoms in sediments of perennially ice-covered Lake Hoare, and implications for interpreting lake history in the McMurdo Dry Valleys of Antarctica

    USGS Publications Warehouse

    Spaulding, S.A.; McKnight, Diane M.; Stoermer, E.F.; Doran, P.T.

    1997-01-01

    Diatom assemblages in surficial sediments, sediment cores, sediment traps, and inflowing streams of perennially ice-covered Lake Hore, South Victorialand, Antarctica were examined to determine the distribution of diatom taxa, and to ascertain if diatom species composition has changed over time. Lake Hoare is a closed-basin lake with an area of 1.8 km2, maximum depth of 34 m, and mean depth of 14 m, although lake level has been rising at a rate of 0.09 m yr-1 in recent decades. The lake has an unusual regime of sediment deposition: coarse grained sediments accumulate on the ice surface and are deposited episodically on the lake bottom. Benthic microbial mats are covered in situ by the coarse episodic deposits, and the new surfaces are recolonized. Ice cover prevents wind-induced mixing, creating the unique depositional environment in which sediment cores record the history of a particular site, rather than a lake=wide integration. Shallow-water (<1 m) diatom assemblages (Stauroneis anceps, Navicula molesta, Diadesmis contenta var. parallela, Navicula peraustralis) were distinct from mid-depth (4-16 m) assemblages (Diadesmis contenta, Luticola muticopsis fo. reducta, Stauroneis anceps, Diadesmis contenta var. parallela, Luticola murrayi) and deep-water (2-31 m) assemblages (Luticola murrayi, Luticola muticopsis fo. reducta, Navicula molesta. Analysis of a sediment core (30 cm long, from 11 m water depth) from Lake Hoare revealed two abrupt changes in diatom assemblages. The upper section of the sediment core contained the greatest biomass of benthic microbial mat, as well as the greatest total abundance and diversity of diatoms. Relative abundances of diatoms in this section are similar to the surficial samples from mid-depths. An intermediate zone contained less organic material and lower densities of diatoms. The bottom section of core contained the least amount of microbial mat and organic material, and the lowest density of diatoms. The dominant process

  16. Direct Observations of Melt-Water Lake Drainage and the Establishment of an Efficient Surface to Basal Water Connection on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Das, S. B.; Joughin, I.; Behn, M. D.; Howat, I.; King, M. A.; Lizarralde, D.; Bhatia, M. P.

    2007-12-01

    Melt water lakes are recurrent features on the surface of the Greenland Ice Sheet margin that collect a large fraction of the annual surface melt across the ablation region. Many of these lakes fill and drain seasonally and are hypothesized to be a significant source of surface melt water to the ice sheet bed. We present results from field campaigns during the summers of 2006 and 2007 to investigate the filling and draining of two lakes, and the dynamic response of the ice sheet to drainage events. Measurements include air temperature, lake-water level, seismicity and local ice motion. One of the instrumented lakes was observed to be actively discharging water through a meltwater-cut channel in the side of the lake basin, which followed a deeply incised (5-10 m) supraglacial stream for nearly a kilometer before cascading into a moulin. The second instrumented lake drained catastrophically through a series of fractures and moulins that opened beneath the lake and that were subsequently mapped in the field following drainage. At this site, the 2.7-km-diameter lake, holding on the order of 0.03 km3 of water, drained entirely through 1 km of ice thickness in less than 2 hours. The peak rate of water flow during this event exceeds the average flow over Niagara Falls. This drainage event coincided with increased seismicity as well as rapid glacier uplift (1.2 m) and horizontal acceleration to nearly 8 km/yr as measured on the ice surface near the lake shoreline. Subsequent subsidence and deceleration of the ice sheet occurred over the following 24 hours. These observations provide evidence for the injection of surface melt water directly to the ice sheet bed, and also indicate the presence of an efficient basal drainage system that can quickly disperse large inputs of surface melt water.

  17. Over-wintering of Supraglacial Lakes on the Greenland Ice Sheet from Sentinel-1 and Landsat-8 Data

    NASA Astrophysics Data System (ADS)

    Benedek, C. L.; Tedesco, M.

    2015-12-01

    Supra-glacial lakes on the GrIS have become a focus of research relating to the contribution of the GrIS to sea level rise. Lakes have been observed to appear during the summer melt season. Though it appears that the quantity of water collected on the surface is small, it is thought that the fracture and drainage of these lakes delivers significant pulses of water to the ice sheet bed, influencing the dynamic movement of glaciers towards the sea. The pattern of this transport mechanism may be a central driver of its influence over dynamic losses, as the flow of the viscoelastic ice sheet will differ if the water is delivered in a short pulse or a slower constant supply. A number of studies have catalogued the traits of lakes with an aim to quantify lake areas, depths, and timing of formation and cessation using visible and near infrared remote sensing instruments mostly focused on the summer melt season. Little is known about the behaviour of the surface lakes over the winter. A recent examination of the over-wintering of surface lakes has been conducted by Koenig et al. [2015] using airborne radar. While the study is extensive in area covered, it is limited in its temporal resolution by the availability of Operation IceBridge data, typically at one pass per year. This study seeks to observe the development of lakes over the winter period. Sentinel-1A radar images are used to track the presence of surface lakes and their variation in three study sites on the Greenland ice sheet. The sites are as follows: upstream of Ryder glacier, upstream of Petermann glacier, and upstream of Jakobshavn glacier. Water masks are created based on summer Landsat-8 images following NDWIice and then compared to Sentinel images at monthly temporal resolution through the winter of 2014-2015. These radar images show persistence of liquid water through the winter in agreement with previous research as well as variation in the buried lake area over the span of the year studied.

  18. Lake carbonate-δ18 records from the Yukon Territory, Canada: Little Ice Age moisture variability and patterns

    USGS Publications Warehouse

    Anderson, Lesleigh; Finney, Bruce P.; Shapley, Mark D.

    2011-01-01

    A 1000-yr history of climate change in the central Yukon Territory, Canada, is inferred from sediment composition and isotope geochemistry from small, groundwater fed, Seven Mile Lake. Recent observations of lake-water δ18O, lake level, river discharge, and climate variations, suggest that changes in regional effective moisture (precipitation minus evaporation) are reflected by the lake’s hydrologic balance. The observations indicate that the lake is currently 18O-enriched by summer evaporation and that during years of increased precipitation, when groundwater inflow rates to the lake increase, lake-water δ18O values decrease. Past lake-water δ18O values are inferred from oxygen isotope ratios of fine-grained sedimentary endogenic carbonate. Variations in carbonate δ18O, supplemented by those in carbonate and organic δ13C, C/N ratios, and organic carbon, carbonate and biogenic silica accumulation rates, document changes in effective moisture at decadal time scales during the early Little Ice Age period to present. Results indicate that between ∼AD 1000 and 1600, effective moisture was higher than today. A shift to more arid climate conditions occurred after ∼AD 1650. The 19th and 20th centuries have been the driest of the past millennium. Temporal variations correspond with inferred shifts in summer evaporation from Marcella Lake δ18O, a similarly small, stratified, alkaline lake located ∼250 km to the southwest, suggesting that the combined reconstructions accurately document the regional paleoclimate of the east-central interior. Comparison with regional glacial activity suggests differing regional moisture patterns during early and late Little Ice Age advances.

  19. Climatic-change implications from long-term (1823-1994) ice records for the Laurentian Great Lakes

    USGS Publications Warehouse

    Assel, R.A.; Robertson, D.M.; Hoff, M.H.; Selgeby, J.H.

    1995-01-01

    Long-term ice records (1823-1994) from six sites in different parts of the Laurentian Great Lakes region were used to show the type and general timing of climatic changes throughout the region. The general timing of both freeze-up and ice loss varies and is driven by local air temperatures, adjacent water bodies and mixing, and site morphometry. Grand Traverse Bay and Buffalo Harbor represent deeper-water environments affected by mixing of off-shore waters; Chequamegon Bay, Memnominee, Lake Mendota, and Toronto Harbor represent relatively shallow-water, protected environments. Freeze-up dates gradually become later and ice-loss dates gradually earlier from the start of records to the 1890s in both environments, marking the end of the 'Little Ice Age.' After this, freeze-up dates remained relatively constant suggesting little change in early-winter air temperatures during the 20th century. Ice-loss dates at Grand Traverse Bay and Buffalo Harbor (but not at the other sites) became earlier during the 1940s and 1970s and became later during the 1960s. The global warming of the 1980s was marked by a trend toward earlier ice-loss dates in both environments.

  20. Brine Assemblages of Ultrasmall Microbial Cells within the Ice Cover of Lake Vida, Antarctica

    PubMed Central

    Kuhn, Emanuele; Ichimura, Andrew S.; Peng, Vivian; Fritsen, Christian H.; Trubl, Gareth; Doran, Peter T.

    2014-01-01

    The anoxic and freezing brine that permeates Lake Vida's perennial ice below 16 m contains an abundance of very small (≤0.2-μm) particles mixed with a less abundant population of microbial cells ranging from >0.2 to 1.5 μm in length. Fluorescent DNA staining, electron microscopy (EM) observations, elemental analysis, and extraction of high-molecular-weight genomic DNA indicated that a significant portion of these ultrasmall particles are cells. A continuous electron-dense layer surrounding a less electron-dense region was observed by EM, indicating the presence of a biological membrane surrounding a cytoplasm. The ultrasmall cells are 0.192 ± 0.065 μm, with morphology characteristic of coccoid and diplococcic bacterial cells, often surrounded by iron-rich capsular structures. EM observations also detected the presence of smaller unidentified nanoparticles of 0.020 to 0.140 μm among the brine cells. A 16S rRNA gene clone library from the brine 0.1- to 0.2-μm-size fraction revealed a relatively low-diversity assemblage of Bacteria sequences distinct from the previously reported >0.2-μm-cell-size Lake Vida brine assemblage. The brine 0.1- to 0.2-μm-size fraction was dominated by the Proteobacteria-affiliated genera Herbaspirillum, Pseudoalteromonas, and Marinobacter. Cultivation efforts of the 0.1- to 0.2-μm-size fraction led to the isolation of Actinobacteria-affiliated genera Microbacterium and Kocuria. Based on phylogenetic relatedness and microscopic observations, we hypothesize that the ultrasmall cells in Lake Vida brine are ultramicrocells that are likely in a reduced size state as a result of environmental stress or life cycle-related conditions. PMID:24727273

  1. Brine assemblages of ultrasmall microbial cells within the ice cover of Lake Vida, Antarctica.

    PubMed

    Kuhn, Emanuele; Ichimura, Andrew S; Peng, Vivian; Fritsen, Christian H; Trubl, Gareth; Doran, Peter T; Murray, Alison E

    2014-06-01

    The anoxic and freezing brine that permeates Lake Vida's perennial ice below 16 m contains an abundance of very small (≤0.2-μm) particles mixed with a less abundant population of microbial cells ranging from >0.2 to 1.5 μm in length. Fluorescent DNA staining, electron microscopy (EM) observations, elemental analysis, and extraction of high-molecular-weight genomic DNA indicated that a significant portion of these ultrasmall particles are cells. A continuous electron-dense layer surrounding a less electron-dense region was observed by EM, indicating the presence of a biological membrane surrounding a cytoplasm. The ultrasmall cells are 0.192 ± 0.065 μm, with morphology characteristic of coccoid and diplococcic bacterial cells, often surrounded by iron-rich capsular structures. EM observations also detected the presence of smaller unidentified nanoparticles of 0.020 to 0.140 μm among the brine cells. A 16S rRNA gene clone library from the brine 0.1- to 0.2-μm-size fraction revealed a relatively low-diversity assemblage of Bacteria sequences distinct from the previously reported >0.2-μm-cell-size Lake Vida brine assemblage. The brine 0.1- to 0.2-μm-size fraction was dominated by the Proteobacteria-affiliated genera Herbaspirillum, Pseudoalteromonas, and Marinobacter. Cultivation efforts of the 0.1- to 0.2-μm-size fraction led to the isolation of Actinobacteria-affiliated genera Microbacterium and Kocuria. Based on phylogenetic relatedness and microscopic observations, we hypothesize that the ultrasmall cells in Lake Vida brine are ultramicrocells that are likely in a reduced size state as a result of environmental stress or life cycle-related conditions.

  2. Subglacial Lake Vostok (Antarctica) Accretion Ice Contains a Diverse Set of Sequences from Aquatic, Marine and Sediment-Inhabiting Bacteria and Eukarya

    PubMed Central

    Edgar, Robyn; Veerapaneni, Ram S.; D’Elia, Tom; Morris, Paul F.; Rogers, Scott O.

    2013-01-01

    Lake Vostok, the 7th largest (by volume) and 4th deepest lake on Earth, is covered by more than 3,700 m of ice, making it the largest subglacial lake known. The combination of cold, heat (from possible hydrothermal activity), pressure (from the overriding glacier), limited nutrients and complete darkness presents extreme challenges to life. Here, we report metagenomic/metatranscriptomic sequence analyses from four accretion ice sections from the Vostok 5G ice core. Two sections accreted in the vicinity of an embayment on the southwestern end of the lake, and the other two represented part of the southern main basin. We obtained 3,507 unique gene sequences from concentrates of 500 ml of 0.22 µm-filtered accretion ice meltwater. Taxonomic classifications (to genus and/or species) were possible for 1,623 of the sequences. Species determinations in combination with mRNA gene sequence results allowed deduction of the metabolic pathways represented in the accretion ice and, by extension, in the lake. Approximately 94% of the sequences were from Bacteria and 6% were from Eukarya. Only two sequences were from Archaea. In general, the taxa were similar to organisms previously described from lakes, brackish water, marine environments, soil, glaciers, ice, lake sediments, deep-sea sediments, deep-sea thermal vents, animals and plants. Sequences from aerobic, anaerobic, psychrophilic, thermophilic, halophilic, alkaliphilic, acidophilic, desiccation-resistant, autotrophic and heterotrophic organisms were present, including a number from multicellular eukaryotes. PMID:23843994

  3. Atmospheric Mercury Depositional Chronology Reconstructed from Lake Sediments and Ice Core in the Himalayas and Tibetan Plateau.

    PubMed

    Kang, Shichang; Huang, Jie; Wang, Feiyue; Zhang, Qianggong; Zhang, Yulan; Li, Chaoliu; Wang, Long; Chen, Pengfei; Sharma, Chhatra Mani; Li, Qing; Sillanpää, Mika; Hou, Juzhi; Xu, Baiqing; Guo, Junming

    2016-03-15

    Alpine lake sediments and glacier ice cores retrieved from high mountain regions can provide long-term records of atmospheric deposition of anthropogenic contaminants such as mercury (Hg). In this study, eight lake sediment cores and one glacier ice core were collected from high elevations across the Himalaya-Tibet region to investigate the chronology of atmospheric Hg deposition. Consistent with modeling results, the sediment core records showed higher Hg accumulation rates in the southern slopes of the Himalayas than those in the northern slopes in the recent decades (post-World War II). Despite much lower Hg accumulation rates obtained from the glacier ice core, the temporal trend in the Hg accumulation rates matched very well with that observed from the sediment cores. The combination of the lake sediments and glacier ice core allowed us to reconstruct the longest, high-resolution atmospheric Hg deposition chronology in High Asia. The chronology showed that the Hg deposition rate was low between the 1500s and early 1800, rising at the onset of the Industrial Revolution, followed by a dramatic increase after World War II. The increasing trend continues to the present-day in most of the records, reflecting the continuous increase in anthropogenic Hg emissions from South Asia. PMID:26878654

  4. Atmospheric Mercury Depositional Chronology Reconstructed from Lake Sediments and Ice Core in the Himalayas and Tibetan Plateau.

    PubMed

    Kang, Shichang; Huang, Jie; Wang, Feiyue; Zhang, Qianggong; Zhang, Yulan; Li, Chaoliu; Wang, Long; Chen, Pengfei; Sharma, Chhatra Mani; Li, Qing; Sillanpää, Mika; Hou, Juzhi; Xu, Baiqing; Guo, Junming

    2016-03-15

    Alpine lake sediments and glacier ice cores retrieved from high mountain regions can provide long-term records of atmospheric deposition of anthropogenic contaminants such as mercury (Hg). In this study, eight lake sediment cores and one glacier ice core were collected from high elevations across the Himalaya-Tibet region to investigate the chronology of atmospheric Hg deposition. Consistent with modeling results, the sediment core records showed higher Hg accumulation rates in the southern slopes of the Himalayas than those in the northern slopes in the recent decades (post-World War II). Despite much lower Hg accumulation rates obtained from the glacier ice core, the temporal trend in the Hg accumulation rates matched very well with that observed from the sediment cores. The combination of the lake sediments and glacier ice core allowed us to reconstruct the longest, high-resolution atmospheric Hg deposition chronology in High Asia. The chronology showed that the Hg deposition rate was low between the 1500s and early 1800, rising at the onset of the Industrial Revolution, followed by a dramatic increase after World War II. The increasing trend continues to the present-day in most of the records, reflecting the continuous increase in anthropogenic Hg emissions from South Asia.

  5. New insights into the origin and evolution of Lake Vida, McMurdo Dry Valleys, Antarctica — A noble gas study in ice and brines

    NASA Astrophysics Data System (ADS)

    Malone, Jessica L.; Castro, M. Clara; Hall, Chris M.; Doran, Peter T.; Kenig, Fabien; McKay, Chris P.

    2010-01-01

    Unlike other lakes in the McMurdo Dry Valleys, Antarctica, Lake Vida has a thick (~ 19 m) ice cover sealing a liquid brine body of unusually high salinity (~ 245 g/L) from the atmosphere. To constrain the conditions under which the atypical Lake Vida ice cover formed and evolved, 19 ice samples were collected down to a depth of ~ 14 m, together with three brine samples trapped in the ice at ~ 16 m for analysis of helium, neon, argon, krypton, and xenon concentrations. The broad pattern of noble gas concentrations for Lake Vida samples is fundamentally different from that of air saturated water (ASW) at 0 °C and an elevation of 340 m for salinities of 0 (ice) and 245 g/L (brine). Overall, ice samples are enriched in He and depleted in Ne with saturation relative to ASW averages of 1.38 and 0.82, respectively, and strongly depleted in Ar, Kr, and Xe with relative saturations of 0.10, 0.06, and 0.05, respectively. By contrast, brine samples are generally depleted in He and Ne (relative saturation averages of 0.33 and 0.27, respectively) but enriched in Ar, Kr, and Xe, with relative saturation averages of 1.45, 3.15, and 8.86, respectively. A three-phase freezing partitioning model generating brine, ice and bubble concentrations for all stable noble gases was tested and compared with our data. Measured brine values are best reproduced for a salinity value of 175 g/L, a pressure of 1.1 atm, and a bubble volume of 20 cm 3 kg -1. Sensitivity tests for ice + bubble samples show an ideal fit for bubble volumes of ~ 1-2 cm 3 kg -1. Our results show that the conditions under which ice and brine formed and evolved at Lake Vida are significantly different from other ice-covered lakes in the area. Our brine data suggest that Lake Vida may be transitioning from a wet to a dry-based lake, while the ice + bubble data suggest at least partial re-equilibration of residual liquid with the atmosphere as ice forms at the top of Lake Vida ice cover.

  6. Study of the Microbial Diversity of a Newly Discovered East Antarctic Freshwater Lake, L27C, and of a Perennially Ice-Covered Lake Untersee

    NASA Technical Reports Server (NTRS)

    Huang, Jonathan P.; Hoover, Richard B.; Andersen, Dale; Bej, Asim K.

    2010-01-01

    The microbial communities that reside within freshwater lakes of Schirmacher and Untersee Oases in East Antarctica must cope with extreme conditions that may include cold temperature, annual freeze-thaw cycles, exposure to UV radiation, especially during the austral summer months, low light beneath thick ice-cover, followed by seasonal darkness. The objective of this study was to assess the microbial biodiversity and distribution from samples taken from two freshwater lakes (L27C and Lake Untersee) that were collected during the Tawani 2008 International Antarctic Expedition that conducted research in this region of Antarctica. L27C is a small, previously unreported lake residing 2 km WNW of Maitri Station at Schirmacher Oasis. Biodiversity and distribution of microorganisms within the lake were studied using both culture-independent and culture-dependent methodologies based upon the analysis of eubacterial 16S rRNA gene sequences. Lake Untersee, a perennially ice-covered, ultra-oligotrophic, lake in the Otto-von-Gruber-Gebirge (Gruber Mountains) of central Dronning Maud Land was also sampled and the microbial diversity was analyzed by eubacterial 16S rRNA gene sequences derived from pure cultures. Direct culturing of water samples from each lake on separate R2A growth medium exhibited a variety of microorganisms including: Janthinobacterium, Hymenobacter, Sphingamonas, Subtercola, Deinococcus, Arthrobacter, Flavobacterium, Polaromonas, Rhodoferax and Duganella. The evaluation of samples from L27C through culture-independent methodology identified a rich microbial diversity consisting of six different phyla of bacteria. The culture-independent analysis also displayed the majority of bacteria (56%) belonged to the Class gamma-proteobacteria within the phylum Proteobacteria. Within the Class gamma-proteobacteria, Acinetobacter dominated (48%) the total microbial load. Overall, L27C exhibited 7 different phyla of bacteria and 20 different genera. Statistical analysis

  7. The importance of record length in estimating the magnitude of climatic changes: an example using 175 years of lake ice-out dates in New England

    USGS Publications Warehouse

    Hodgkins, Glenn A.

    2013-01-01

    Many studies have shown that lake ice-out (break-up) dates in the Northern Hemisphere are useful indicators of late winter/early spring climate change. Trends in lake ice-out dates in New England, USA, were analyzed for 25, 50, 75, 100, 125, 150, and 175 year periods ending in 2008. More than 100 years of ice-out data were available for 19 of the 28 lakes in this study. The magnitude of trends over time depends on the length of the period considered. For the recent 25-year period, there was a mix of earlier and later ice-out dates. Lake ice-outs during the last 50 years became earlier by 1.8 days/decade (median change for all lakes with adequate data). This is a much higher rate than for longer historical periods; ice-outs became earlier by 0.6 days/decade during the last 75 years, 0.4 days/ decade during the last 100 years, and 0.6 days/decade during the last 125 years. The significance of trends was assessed under the assumption of serial independence of historical ice-out dates and under the assumption of short and long term persistence. Hypolimnion dissolved oxygen (DO) levels are an important factor in lake eutrophication and coldwater fish survival. Based on historical data available at three lakes, 32 to 46 % of the interannual variability of late summer hypolimnion DO levels was related to ice-out dates; earlier ice-outs were associated with lower DO levels.

  8. Ice cover extent drives phytoplankton and bacterial community structure in a large north-temperate lake: implications for a warming climate.

    PubMed

    Beall, B F N; Twiss, M R; Smith, D E; Oyserman, B O; Rozmarynowycz, M J; Binding, C E; Bourbonniere, R A; Bullerjahn, G S; Palmer, M E; Reavie, E D; Waters, Lcdr M K; Woityra, Lcdr W C; McKay, R M L

    2016-06-01

    Mid-winter limnological surveys of Lake Erie captured extremes in ice extent ranging from expansive ice cover in 2010 and 2011 to nearly ice-free waters in 2012. Consistent with a warming climate, ice cover on the Great Lakes is in decline, thus the ice-free condition encountered may foreshadow the lakes future winter state. Here, we show that pronounced changes in annual ice cover are accompanied by equally important shifts in phytoplankton and bacterial community structure. Expansive ice cover supported phytoplankton blooms of filamentous diatoms. By comparison, ice free conditions promoted the growth of smaller sized cells that attained lower total biomass. We propose that isothermal mixing and elevated turbidity in the absence of ice cover resulted in light limitation of the phytoplankton during winter. Additional insights into microbial community dynamics were gleaned from short 16S rRNA tag (Itag) Illumina sequencing. UniFrac analysis of Itag sequences showed clear separation of microbial communities related to presence or absence of ice cover. Whereas the ecological implications of the changing bacterial community are unclear at this time, it is likely that the observed shift from a phytoplankton community dominated by filamentous diatoms to smaller cells will have far reaching ecosystem effects including food web disruptions.

  9. A late Holocene record of trace metal deposition in lake sediments near Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Beal, S. A.; Kelly, M. A.; Jackson, B. P.; Osterberg, E. C.; Stroup, J. S.; Baker, R. A.

    2010-12-01

    Records of atmospheric metal deposition have been used extensively in the Northern Hemisphere to examine historical events ranging from the evolution of ancient metallurgy to climatic change. Establishing such a record in tropical South America is pertinent due to ongoing questions about the metallurgical history of pre-colonial Andean civilizations, recent atmospheric pollution levels, and late Holocene climate variability. Here we present a late Holocene record of the Ag, As, Cd, Co, Cu, Hg, Ni, Pb, Sr, Zn, and Pb isotopic compositions of atmospheric deposition from three 1.5 m-long lake cores and one 5 m-long bog core recovered near Quelccaya Ice Cap (13.9 °S), in the southeastern Peruvian Andes. The bog core, representing deposition from the present to at least 2415 yr BP, records relatively stable concentrations of As, Co, Cu, Hg, Ni, Pb, Sr, and Zn between 2415 (±78) and 916 (±29) yr BP. However, Ag and Cd exhibit brief gradual enrichments over background levels by factors of 6 and 11, respectively, shortly after 2415 (±78) yr BP as a possible result of ancient metallurgy. Sometime following the 916 (±29) yr BP date, Ag, As, Cd, Cu, Hg, Ni, Pb, and Sr abruptly become enriched by factors of 10, 37, 11, 11, 47, 6, 16, and 24, respectively, possibly from anthropogenic sources and/or the 1600 AD eruption of Huaynaputina in southern Peru. These enrichments are concurrent with a shift in 206Pb/207Pb to 1.182 from background levels of 1.213 (±0.002, n=20). A subsequent quiescent period in metal concentrations is marked by a brief return to background 206Pb/207Pb values, followed by erratic 206Pb/207Pb values yet decreased metal concentrations in the most recent sediments. Only Hg is enriched over background levels, by a factor of 3, in the most recent sediment. Forthcoming higher-resolution data from the three lake cores will utilize pre-industrial lead isotope ratios and Ti, Zr, and REE fluxes to examine past variability of the El Niño-Southern Oscillation

  10. Historical changes in lake ice-out dates as indicators of climate change in New England, 1850-2000

    USGS Publications Warehouse

    Hodgkins, G.A.; James, Ivan; Huntington, T.G.

    2002-01-01

    Various studies have shown that changes over time in spring ice-out dates can be used as indicators of climate change. Ice-out dates from 29 lakes in New England (USA) with 64 to 163 years of record were assembled and analysed for this study. Ice-out dates have become significantly earlier in New England since the 1800s. Changes in ice-out dates between 1850 and 2000 were 9 days and 16 days in the northern/mountainous and southern regions of New England respectively. The changes in the ice-out data over time were very consistent within each of the two regions of New England, and more consistent than four air-temperature records in each region. The ice-out dates of the two regions had a different response to changes in air temperature. The inferred late winter-early spring air-temperature warming in both regions of New England since 1850, based on linear regression analysis, was about 1.5 ??C. Published in 2002 by John Wiley & Sons, Ltd.

  11. Timescales of growth response of microbial mats to environmental change in an ice-covered antarctic lake.

    PubMed

    Hawes, Ian; Sumner, Dawn Y; Andersen, Dale T; Jungblut, Anne D; Mackey, Tyler J

    2013-01-25

    Lake Vanda is a perennially ice-covered, closed-basin lake in the McMurdo Dry Valleys, Antarctica. Laminated photosynthetic microbial mats cover the floor of the lake from below the ice cover to >40 m depth. In recent decades, the water level of Lake Vanda has been rising, creating a "natural experiment" on development of mat communities on newly flooded substrates and the response of deeper mats to declining irradiance. Mats in recently flooded depths accumulate one lamina (~0.3 mm) per year and accrue ~0.18 µg chlorophyll-a cm-2 y-1. As they increase in thickness, vertical zonation becomes evident, with the upper 2-4 laminae forming an orange-brown zone, rich in myxoxanthophyll and dominated by intertwined Leptolyngbya trichomes. Below this, up to six phycobilin-rich green/pink-pigmented laminae form a subsurface zone, inhabited by Leptolyngbya, Oscillatoria and Phormidium morphotypes. Laminae continued to increase in thickness for several years after burial, and PAM fluorometry indicated photosynthetic potential in all pigmented laminae. At depths that have been submerged for >40 years, mats showed similar internal zonation and formed complex pinnacle structures that were only beginning to appear in shallower mats. Chlorophyll-a did not change over time and these mats appear to represent resource-limited "climax" communities. Acclimation of microbial mats to changing environmental conditions is a slow process, and our data show how legacy effects of past change persist into the modern community structure.

  12. Timescales of growth response of microbial mats to environmental change in an ice-covered antarctic lake.

    PubMed

    Hawes, Ian; Sumner, Dawn Y; Andersen, Dale T; Jungblut, Anne D; Mackey, Tyler J

    2013-01-01

    Lake Vanda is a perennially ice-covered, closed-basin lake in the McMurdo Dry Valleys, Antarctica. Laminated photosynthetic microbial mats cover the floor of the lake from below the ice cover to >40 m depth. In recent decades, the water level of Lake Vanda has been rising, creating a "natural experiment" on development of mat communities on newly flooded substrates and the response of deeper mats to declining irradiance. Mats in recently flooded depths accumulate one lamina (~0.3 mm) per year and accrue ~0.18 µg chlorophyll-a cm-2 y-1. As they increase in thickness, vertical zonation becomes evident, with the upper 2-4 laminae forming an orange-brown zone, rich in myxoxanthophyll and dominated by intertwined Leptolyngbya trichomes. Below this, up to six phycobilin-rich green/pink-pigmented laminae form a subsurface zone, inhabited by Leptolyngbya, Oscillatoria and Phormidium morphotypes. Laminae continued to increase in thickness for several years after burial, and PAM fluorometry indicated photosynthetic potential in all pigmented laminae. At depths that have been submerged for >40 years, mats showed similar internal zonation and formed complex pinnacle structures that were only beginning to appear in shallower mats. Chlorophyll-a did not change over time and these mats appear to represent resource-limited "climax" communities. Acclimation of microbial mats to changing environmental conditions is a slow process, and our data show how legacy effects of past change persist into the modern community structure. PMID:24832656

  13. Under-ice noise generated from diamond exploration in a Canadian sub-arctic lake and potential impacts on fishes.

    PubMed

    Mann, D; Cott, P; Horne, B

    2009-11-01

    Mineral exploration is increasing in Canada, particularly in the north where extensive diamond mining and exploration are occurring. This study measured the under-ice noise produced by a variety of anthropogenic sources (drilling rigs, helicopters, aircraft landing and takeoff, ice-road traffic, augers, snowmobiles, and chisels) at a winter-based diamond exploration project on Kennady Lake in the Northwest Territories, Canada to infer the potential impact of noise on fishes in the lake. The root-mean-square noise level measured 5 m from a small diameter drill was approximately 46 dB greater (22 kHz bandwidth) than ambient noise, while the acoustic particle velocity was approximately 40 dB higher than ambient levels. The loudest sounds at the exploration site were produced by ice cracking, both natural and during landing and takeoff of a C130 Hercules aircraft. However, even walking on the snow above the ice raised ambient sound levels by approximately 30 dB. Most of the anthropogenic sounds are likely detectable by fishes with hearing specializations, such as chubs and suckers. Other species without specialized hearing adaptations will detect these sounds only close to the source. The greatest potential impact of noise from diamond exploration is likely to be the masking of sounds for fishes with sensitive hearing.

  14. Composition and biodegradation of a synthetic oil spilled on the perennial ice cover of Lake Fryxell, Antarctica.

    PubMed

    Jaraula, Caroline M B; Kenig, Fabien; Doran, Peter T; Priscu, John C; Welch, Kathleen A

    2009-04-15

    A helicopter crashed in January 2003 on the 5 m-thick perennial ice cover of Lake Fryxell, spilling synthetic turbine oil Aeroshell 500. Molecular compositions of the oils were analyzed by gas chromatography-mass spectrometry and compared to the composition of contaminants in ice, meltwater, and sediments collected a year after the accident. Aeroshell 500 is based on C20-C33 Pentaerythritol triesters (PET) with C5-C10 fatty acids susbstituents and contain a number of antioxidant additives, such as tricresyl phosphates. Biodegradation of this oil in the ice cover occurs when sediments are present PETs with short fatty acids substituents are preferentially degraded, whereas long chain fatty acids seem to hinder esters from hydrolysis by esterase derived from the microbial assemblage. It remains to be seen if the microbial ecosystem can degrade tricresyl phosphates. These more recalcitrant PET species and tricresyl phosphates are likely to persist and comprise the contaminants that may eventually cross the ice cover to reach the pristine lake water.

  15. Chemoautotrophic Bacterial Production in the Redoxycline of an Ice-Covered Antarctic Lake (Invited)

    NASA Astrophysics Data System (ADS)

    Mikucki, J.; Kong, W.; Priscu, J. C.; Morgan-Kiss, R.

    2010-12-01

    Chemolithoautotrophic organisms obtain energy for growth from inorganic substrates and use simple inorganic carbon molecules to construct biomass. As such, chemosynthetic processes are tightly linked to biogeochemical cycles. In polar regions, winter darkness shuts down photosynthetic inputs and the contribution of chemosynthesis to total ecosystem energetics and carbon fixation may be significant. Few reports exist on chemosynthesis in polar environments and the rates of these processes remain largely unexplored. Here we present data on chemoautotrophic activity in the redoxycline (~15m depth) of the permanently ice-covered Lake Bonney in the McMurdo Dry Valleys, Antarctica (MCM). Rates of radio-labeled bicarbonate incorporation were measured under light and dark conditions using whole community and bacterial sized-fraction (< 3 μm) samples. Rates of uptake in the bacterial sized-fraction (0.18 μg C L-1 d-1) were comparable to that of heterotrophic bacterial activity (0.16 μg C L-1 d-1) as measured by radio-labeled thymidine incorporation. Molecular analyses of the (cbbM) Rubisco gene, a key enzyme in the Calvin cycle, revealed relatives to the Thiobacillus genera confirming the genomic potential for in situ bacterial carbon fixation. Further, quantification of cbbM gene copy number by real time PCR from samples collected throughout the trophogenic zones of the west and east lobes of Lake Bonney confirmed that chemotrophic bacteria harboring form II RubisCO are restricted to depths at or below the redoxycline of the west lobe. These data provide insight into the structure-function relationship between the microbial consortia and carbon budget and imply that chemoautotrophic production in the MCM may provide a significant source of previously un-quantified fixed carbon to the lake system. Studies on other icy systems, including dark, isolated subglacial environments report evidence for chemolithoautotrophy suggesting that chemoautotrophic production can sustain

  16. Temporal and spatial trends in the chemistry of acidified lakes under ice cover

    SciTech Connect

    Hendrey, G R; Galloway, J N; Schofield, C L

    1980-03-01

    When preparing materials budgets for watersheds containing lakes, the spatial and temporal interchange between large compartments within the whole system must be considered. This paper addresses the lakes of the Integrated Lake-Watershed Acidification Study (ILWAS) and their role in our mass balance calculations for the period of winter stratification of 1978-1979, and presents data on lake metabolism.

  17. The drainage of the Baltic Ice Lake and a new Scandinavian reference 10Be production rate

    NASA Astrophysics Data System (ADS)

    Stroeven, Arjen P.; Heyman, Jakob; Fabel, Derek; Björck, Svante; Caffee, Marc W.; Fredin, Ola; Harbor, Jonathan M.

    2015-04-01

    An important constraint on the reliability of cosmogenic nuclide exposure dating is the derivation of tightly controlled production rates. We present a new dataset for 10Be production rate calibration from Mount Billingen, southern Sweden, the site of the final drainage of the Baltic Ice Lake, an event dated to 11,620 ± 100 cal yr BP. Nine samples of flood-scoured bedrock surfaces and depositional boulders and cobbles unambiguously connected to the drainage event yield a reference 10Be production rate of 4.09 ± 0.22 atoms g-1 yr-1 for the CRONUS Lm scaling and 3.93 ± 0.21 atoms g-1 yr-1 for the LSD general spallation scaling. We also recalibrate the reference 10Be production rates for four sites in Norway and combine these with the Billingen results to derive a tightly clustered Scandinavian reference 10Be production rate of 4.12 ± 0.10 (4.12 ± 0.25 for altitude scaling) atoms g-1 yr-1 for the Lm scaling scheme and 3.96 ± 0.10 (3.96 ± 0.24 for altitude scaling) atoms g-1 yr-1 for the LSD scaling scheme.

  18. Response of ice cover on shallow lakes of the North Slope of Alaska to contemporary climate conditions (1950-2011): radar remote sensing and numerical modeling data analysis

    NASA Astrophysics Data System (ADS)

    Surdu, C. M.; Duguay, C. R.; Brown, L. C.; Fernández Prieto, D.

    2013-07-01

    Air temperature and winter precipitation changes over the last five decades have impacted the timing, duration, and thickness of the ice cover on Arctic lakes as shown by recent studies. In the case of shallow tundra lakes, many of which are less than 3 m deep, warmer climate conditions could result in thinner ice covers and consequently, to a smaller fraction of lakes freezing to their bed in winter. However, these changes have not yet been comprehensively documented. The analysis of a 20 yr time series of ERS-1/2 synthetic aperture radar (SAR) data and a numerical lake ice model were employed to determine the response of ice cover (thickness, freezing to the bed, and phenology) on shallow lakes of the North Slope of Alaska (NSA) to climate conditions over the last six decades. Analysis of available SAR data from 1991-2011, from a sub-region of the NSA near Barrow, shows a reduction in the fraction of lakes that freeze to the bed in late winter. This finding is in good agreement with the decrease in ice thickness simulated with the Canadian Lake Ice Model (CLIMo), a lower fraction of lakes frozen to the bed corresponding to a thinner ice cover. Observed changes of the ice cover show a trend toward increasing floating ice fractions from 1991 to 2011, with the greatest change occurring in April, when the grounded ice fraction declined by 22% (α = 0.01). Model results indicate a trend toward thinner ice covers by 18-22 cm (no-snow and 53% snow depth scenarios, α = 0.01) during the 1991-2011 period and by 21-38 cm (α = 0.001) from 1950-2011. The longer trend analysis (1950-2011) also shows a decrease in the ice cover duration by ∼24 days consequent to later freeze-up dates by 5.9 days (α = 0.1) and earlier break-up dates by 17.7-18.6 days (α = 0.001).

  19. The Alaska Lake Ice and Snow Observatory Network (ALISON): Hands-on Experiential K- 12 Learning in the North

    NASA Astrophysics Data System (ADS)

    Morris, K.; Jeffries, M.

    2008-12-01

    The Alaska Lake Ice and Snow Observatory Network (ALISON) was initiated by Martin Jeffries (UAF polar scientist), Delena Norris-Tull (UAF education professor) and Ron Reihl (middle school science teacher, Fairbanks North Star Borough School District). The snow and ice measurement protocols were developed in 1999-2000 at the Poker Flat Research Range (PFRR) by Geophysical Institute, University of Alaska scientists and tested by home school teacher/students in winter 2001-2002 in Fairbanks, AK. The project was launched in 2002 with seven sites around the state (PFRR, Fairbanks, Barrow, Mystic Lake, Nome, Shageluk and Wasilla). The project reached its broadest distribution in 2005-2006 with 22 sites. The schools range from urban (Wasilla) to primarily Alaska native villages (Shageluk). They include public schools, charter schools, home schooled students and parents, informal educators and citizen scientists. The grade levels range from upper elementary to high school. Well over a thousand students have participated in ALISON since its inception. Equipment is provided to the observers at each site. Measurements include ice thickness (with a hot wire ice thickness gauge), snow depth and snow temperature (surface and base). Snow samples are taken and snow density derived. Snow variables are used to calculate the conductive heat flux through the ice and snow cover to the atmosphere. All data are available on the Web site. The students and teachers are scientific partners in the study of lake ice processes, contributing to new scientific knowledge and understanding while also learning science by doing science with familiar and abundant materials. Each autumn, scientists visit each location to work with the teachers and students, helping them to set up the study site, showing them how to make the measurements and enter the data into the computer, and discussing snow, ice and polar environmental change. A number of 'veteran' teachers are now setting up the study sites on

  20. The effect of warm summer 2012 on seasonal and annual methane dynamics in adjacent small lakes on the ice-free margin of Greenland

    NASA Astrophysics Data System (ADS)

    White, J. R.; Cadieux, S. B.; Pratt, L. M.

    2015-12-01

    In thermally stratified lakes, the greatest annual CH4 emissions typically occur during thermal overturn events. In July of 2012, Greenland experienced significant warming that resulted in substantial melting of the Greenland Ice Sheet and enhanced runoff events. This unusual climate phenomenon provided an opportunity to examine the effects of short-term natural heating on lake thermal structure and CH4 dynamics and compare these observations with those from the following year when temperatures were within normal conditions. In this study, we present CH4 concentrations within the water column of 5 adjacent small lakes on the ice-free margin of Southwest Greenland under open-water and ice-covered conditions from 2012-2014. Enhanced warming of the epilimnion in 2012 lead to strong thermal stability and the development of an anoxic hypolimnia in each of the lakes. As a result, mean dissolved CH4 concentrations were significantly (p < 0.0001) greater under open water conditions in 2012 than in 2013. In all of the lakes, mean CH4 concentrations under ice-covered conditions were significantly (p < 0.0001) greater than under open-water conditions, suggesting spring overturn may be the period with the largest annual CH4 flux to the atmosphere. As the climate continues to warm, greater heat income and warming of lake surface waters will lead to increased thermal stratification and hypolimnetic anoxia, which will result in increased water column inventories of CH4. Additionally, continual warming will result in shorter ice cover durations, which may reduce the winter inventory of CH4 and lead to a decrease in total CH4 flux during ice-melt. Taken together, these results indicate that in Arctic lakes, a shortening of winter ice cover and increased thermal stratification during open-water conditions will lead to increased CH4 production, higher water column CH4 inventories and greater CH4 emissions at fall overturn.

  1. Relationships between climate and geophysical processes: What climate histories can be inferred from glaciers, lakes, and ice streams?

    NASA Astrophysics Data System (ADS)

    Huybers, Kathleen

    lake- level variations [Mason et al., 1994, Lall and Mann, 1995, Abarbanel and Lall, 1996, Mohammed and Tarboton, 2011], my research shows that this persistence not only reflects any autocorrelation in the climate, but is also intrinsic to the dynamics of the lake system. My work also shows how the geometry of the lake influences the magnitude and persistence of lake level fluctuations. These results develop a null hypothesis in expected lake-level variability which can be compared to the magnitude and frequency of paleo lake-level variations. 3. Ice streams: Previous studies have used flowline models to understand the behavior of ice streams on idealized bed geometries [Schoof, 2007, Docquier et al., 2011]. This work applies the flowline model approach to a realistic basal topography beneath the West Antarctic Ice Sheet (WAIS), and evaluates changes in grounding line positions and upstream ice profiles in response to changes in model physics and environmental factors. These sensitivity studies demonstrate that the present positions of many Weddell Sea-sector grounding lines lie within an asymmetric trench, implying a strong stability to retreat, but also creating the potential for significant advance due to either sea-level lowering on the order of tens of meters, or conceivably, from precipitation increases of less than 10%. My evaluation reaffirms that the greatest concerns for WAIS retreat or collapse are locations of reverse slopes, muted basal topography, and limited lateral support. This dissertation uses models of low complexity, allowing for a complete understanding of the system, and providing a deeper and richer understanding of the temporal and spatial patterns of Earth's limitless complexity.

  2. The reproductive success of lake herring in habitats near shipping channels and ice-breaking operations in the St. Marys River, Michigan, USA

    USGS Publications Warehouse

    Blouin, Marc A.; Kostich, M.M.; Todd, T.N.; Savino, J.F.

    1998-01-01

    A study of the reproductive success of lake herring (Coregonus artedi) in the St. Marys River was conducted in the winters and springs of 1994, 1995, and 1996. The St. Marys River connects Lake Superior to the lower Great Lakes making it an important route for ship traffic. Recent pressure by commercial carriers to extend the shipping season by breaking ice earlier in spring, has raised concerns over the possible adverse effects on lake herring reproduction in the river caused by increased turbidity associated with vessel passage. Lake herring spawn in fall and their eggs overwinter under ice cover on the bottom of the St. Marys River. Hatching occurs in the spring after ice-out when water temperatures rise. Specialized incubators were used to hold fertilized lake herring eggs at four experimental sites, chosen to represent the range of various bottom substrate types of the St. Marys River from boulder rock reefs to soft sediments. In winter, incubators were placed under the ice on the bottom of the river at three sites each year. After ice-out, sites were relocated, and the incubators were retrieved and opened to determine the number of live and dead lake herring eggs and larvae. Survival was consistent from year to year at each site with the lowest survival percentage found at the site with the softest sediments, directly adjacent to the St. Marys River channel and downstream of the mouth of the Charlotte River. River bottom type and geographic location were the most important factors in determining egg survival. Sampling for indigenous larval lake herring was done throughout the spring hatching season in the areas adjacent to the incubator sites using nets and a diver-operated suction sampler. Result indicate that a small population (3) of larval lake herring was present throughout the sampling areas during the springs of 1994, 1995, and 1996 in the St. Marys River.

  3. ERTS computer compatible tape data processing and analysis. Appendix 1: The utility of imaging radars for the study of lake ice

    NASA Technical Reports Server (NTRS)

    Polcyn, F. C.; Thomson, F. J.; Porcello, L. J.; Sattinger, I. J.; Malila, W. A.; Wezernak, C. T.; Horvath, R.; Vincent, R. K. (Principal Investigator); Bryan, M. L.

    1972-01-01

    There are no author-identified significant results in this report. Remotely sensed multispectral scanner and return beam vidicon imagery from ERTS-1 is being used for: (1) water depth measurements in the Virgin Islands and Upper Lake Michigan areas; (2) mapping of the Yellowstone National Park; (3) assessment of atmospheric effects in Colorado; (4) lake ice surveillance in Canada and Great Lakes areas; (5) recreational land use in Southeast Michigan; (6) International Field Year on the Great Lakes investigations of Lake Ontario; (7) image enhancement of multispectral scanner data using existing techniques; (8) water quality monitoring of the New York Bight, Tampa Bay, Lake Michigan, Santa Barbara Channel, and Lake Erie; (9) oil pollution detection in the Chesapeake Bay, Gulf of Mexico southwest of New Orleans, and Santa Barbara Channel; and (10) mapping iron compounds in the Wind River Mountains.

  4. Life under ice: Investigating microbial-related biogeochemical cycles in the seasonally-covered Great Lake Onego, Russia

    NASA Astrophysics Data System (ADS)

    Thomas, Camille; Ariztegui, Daniel; Victor, Frossard; Emilie, Lyautey; Marie-Elodie, Perga; Life Under Ice Scientific Team

    2016-04-01

    The Great European lakes Ladoga and Onego are important resources for Russia in terms of drinking water, energy, fishing and leisure. Because their northern location (North of Saint Petersburgh), these lakes are usually ice-covered during winter. Due to logistical reasons, their study has thus been limited to the ice-free periods, and very few data are available for the winter season. As a matter of fact, comprehension of large lakes behaviour in winter is very limited as compared to the knowledge available from small subpolar lakes or perennially ice-covered polar lakes. To tackle this issue, an international consortium of scientists has gathered around the « life under ice » project to investigate physical, chemical and biogeochemical changes during winter in Lake Onego. Our team has mainly focused on the characterization and quantification of biological processes, from the water column to the sediment, with a special focus on methane cycling and trophic interactions. A first « on-ice » campaign in March 2015 allowed the sampling of a 120 cm sedimentary core and the collection of water samples at multiple depths. The data resulting from this expedition will be correlated to physical and chemical parameters collected simultaneously. A rapid biological activity test was applied immediately after coring in order to test for microbial activity in the sediments. In situ adenosine-5'-triphosphate (ATP) measurements were carried out in the core and taken as an indication of living organisms within the sediments. The presence of ATP is a marker molecule for metabolically active cells, since it is not known to form abiotically. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) were extracted from these samples, and quantified. Quantitative polymerase chain reactions (PCR) were performed on archaeal and bacterial 16S rRNA genes used to reconstruct phylogenies, as well as on their transcripts. Moreover, functional genes involved in the methane and nitrogen cycles

  5. Analysis of local AWS and NCEP/NCAR reanalysis data at Lake El'gygtytgyn, and its implications for maintaining multi-year lake-ice covers

    NASA Astrophysics Data System (ADS)

    Nolan, M.

    2012-04-01

    We compared 7 years of local automated weather station (AWS) data to NCEP/NCAR reanalysis data to characterize the modern environment of Lake El'gygytgyn, in Chukotka Russia. We then used this comparison to estimate the air temperatures required to initiate and maintain multi-year lake-ice covers to aid in paleoclimate reconstructions of the 3.6 M years sediment record recovered from there. We present and describe data from our AWS from 2002-2008, which recorded air temperatures, relative humidity, precipitation, barometric pressure, and wind speed/direction, as well as subsurface soil moisture and temperature. Measured mean annual air temperature (MAAT) over this period was -10.4 °C with a slight warming trend during the measurement period. NCEP/NCAR reanalysis air temperatures compared well to this, with annual means within 0.1 to 2.0 °C of the AWS, with an overall mean 1.1 °C higher than the AWS, and daily temperature trends having a correlation of over 96% and capturing the full range of variation. After correcting for elevation differences, barometric pressure discrepancies occasionally reached as high as 20 mbar higher than the AWS particularly in winter, but the correlation in trends was high at 92%, indicating that synoptic-scale weather patterns driving local weather likely are being captured by the reanalysis data. AWS cumulative summer rainfall measurements ranged between 70-200 mm during the record. NCEP/NCAR reanalysis precipitation failed to predict daily events measured by the AWS, but largely captured the annual trends, though higher by a factor of 2-4. NCEP air temperatures showed a strong trend in MAAT over the 1961-2009 record, rising from a pre-1995 mean of -12.0 °C to a post-1994 mean of -9.8 °C. We found that nearly all of this change could be explained by changes in winter temperatures, with mean winter degree days (DD) rising from -5043 to -4340 after 1994 and a much smaller change in summer DD from +666 to +700. Thus, the NCEP record

  6. A New Hot Water Drill for Glaciological, Geochemical and Biological Studies of the Subglacial Lakes Beneath the Vatnajokull Ice Cap, Iceland

    NASA Astrophysics Data System (ADS)

    Thorsteinsson, T.; Elefsen, S.; Johannesson, T.; Thorsteinsson, T.

    2005-12-01

    The center of hot-spot volcanic activity in Iceland is located beneath the NW-part of Vatnajokull, giving rise to frequent and intense ice-volcano interactions. Five subglacial lakes are known to exist in regions of high geothermal and/or volcanic activity within this area [1], which is now attracting the interest of researchers studying the possible presence of microbial life in Lake Vostok and other subglacial lakes beneath the Antarctic ice sheet [2]. In addition, the lakes beneath Vatnajokull are increasingly being viewed as terrestrial analogs of water bodies beneath ice covers on planets and moons in the Solar System, e.g. Mars and Europa. The ice shelf covering the Grimsvotn subglacial lake was penetrated with a hot water drill in June 2002, a few months after a jokulhlaup that released most of the water from the lake. The ice thickness was 280 m and the water depth was 20 m at the drilling site. The lake water was found to be at the melting point, dominated by glacial melt and not mixed with hydrothermal fluids from the geothermal system. The microbial population found in samples from the lake water (2*10e4 cells/ml) and bottom sediment (4*10e7 cells/g) [3] may be derived from organisms transported with windborne dust particles from nearby deserts and deposited on the surface of the ice shelf. Studies of an ice core drilled to 115 m depth at the same site revealed an average dust concentration of 4 ppmv in the ice shelf, and the timescale for downward transport through the ice shelf is estimated to be 150-200 years. Basal melting of the ice shelf leads to dust deposition on the lake bottom at an estimated rate of 0.024 kg/m2/yr [4]. A new hot water drilling system capable of drilling through 600 m of ice has now been constructed for follow-up studies of the subglacial lakes in Iceland. In this system, glycol is heated in a combustion unit and then circulated in a closed loop system through a heat exchanger located within a 0.6 m3 snow melter. The meltwater

  7. Derivation and Validation of Supraglacial Lake Volumes on the Greenland Ice Sheet from High-Resolution Satellite Imagery

    NASA Technical Reports Server (NTRS)

    Moussavi, Mahsa S.; Abdalati, Waleed; Pope, Allen; Scambos, Ted; Tedesco, Marco; MacFerrin, Michael; Grigsby, Shane

    2016-01-01

    Supraglacial meltwater lakes on the western Greenland Ice Sheet (GrIS) are critical components of its surface hydrology and surface mass balance, and they also affect its ice dynamics. Estimates of lake volume, however, are limited by the availability of in situ measurements of water depth,which in turn also limits the assessment of remotely sensed lake depths. Given the logistical difficulty of collecting physical bathymetric measurements, methods relying upon in situ data are generally restricted to small areas and thus their application to largescale studies is difficult to validate. Here, we produce and validate spaceborne estimates of supraglacial lake volumes across a relatively large area (1250 km(exp 2) of west Greenland's ablation region using data acquired by the WorldView-2 (WV-2) sensor, making use of both its stereo-imaging capability and its meter-scale resolution. We employ spectrally-derived depth retrieval models, which are either based on absolute reflectance (single-channel model) or a ratio of spectral reflectances in two bands (dual-channel model). These models are calibrated by usingWV-2multispectral imagery acquired early in the melt season and depth measurements from a high resolutionWV-2 DEM over the same lake basins when devoid of water. The calibrated models are then validated with different lakes in the area, for which we determined depths. Lake depth estimates based on measurements recorded in WV-2's blue (450-510 nm), green (510-580 nm), and red (630-690 nm) bands and dual-channel modes (blue/green, blue/red, and green/red band combinations) had near-zero bias, an average root-mean-squared deviation of 0.4 m (relative to post-drainage DEMs), and an average volumetric error of b1%. The approach outlined in this study - image-based calibration of depth-retrieval models - significantly improves spaceborne supraglacial bathymetry retrievals, which are completely independent from in situ measurements.

  8. Fault kinematics of the Magallanes-Fagnano fault system, southern Chile; an example of diffuse strain and sinistral transtension along a continental transform margin

    NASA Astrophysics Data System (ADS)

    Betka, Paul; Klepeis, Keith; Mosher, Sharon

    2016-04-01

    A system of left-lateral faults that separates the South American and Scotia plates, known as the Magallanes-Fagnano fault system, defines the modern tectonic setting of the southernmost Andes and is superimposed on the Late Cretaceous - Paleogene Patagonian fold-thrust belt. Fault kinematic data and crosscutting relationships from populations of thrust, strike-slip and normal faults from Peninsula Brunswick adjacent to the Magallanes-Fagnano fault system, presented herein, show kinematic and temporal relationships between thrust faults and sets of younger strike-slip and normal faults. Thrust fault kinematics are homogeneous in the study area and record subhorizontal northeast-directed shortening. Strike-slip faults record east-northeast-directed horizontal shortening, west-northwest-directed horizontal extension and form Riedel and P-shear geometries compatible with left-lateral slip on the main splay of the Magallanes-Fagnano fault system. Normal faults record north-south trending extension that is compatible with the strike-slip faults. The study area occurs in a releasing step-over between overlapping segments of the Magallanes-Fagnano fault system, which localized on antecedent sutures between basement terranes with differing geological origin. Results are consistent with regional tectonic models that suggest sinistral shearing and transtension in the southernmost Andes was contemporaneous with the onset of seafloor spreading in the Western Scotia Sea during the Early Miocene.

  9. Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback

    NASA Astrophysics Data System (ADS)

    Austin, Jay A.; Colman, Steven M.

    2007-03-01

    Lake Superior summer (July-September) surface water temperatures have increased approximately 2.5°C over the interval 1979-2006, equivalent to a rate of (11 +/- 6) × 10-2°C yr-1, significantly in excess of regional atmospheric warming. This discrepancy is caused by declining winter ice cover, which is causing the onset of the positively stratified season to occur earlier at a rate of roughly a half day per year. An earlier start of the stratified season significantly increases the period over which the lake warms during the summer months, leading to a stronger trend in mean summer temperatures than would be expected from changes in summer air temperature alone.

  10. Technology of nondestructive light gas extraction from ice tested on samples from a bore hole above Vostok Lake

    NASA Astrophysics Data System (ADS)

    Chetverikov, Yu. O.; Aruev, N. N.; Bulat, S. A.; Ezhov, V. F.; Lipenkov, V. Ya.; Solovei, V. A.; Tyukal'tsev, R. V.; Fedichkin, I. L.

    2016-07-01

    Nondestructive technology has been developed for the extraction of light gases dissolved in ice. The technology has been tested on samples of atmospheric and congealed ice of the 5-G3 bore hole of the Vostok station (East Antarctica) extracted from depths of 3457-3698 m. Down to 3539 m, ice is of an atmospheric origin, while ice deposited deeper is formed by natural water of Vostok Lake frozen on the glacier. Light gases were extracted into samplers (glass flasks) in the course of the 3-day degassing of samples freshly elevated from a bore hole. The samples were analyzed on the FT-1 time-of-flight mass spectrometer 6 months after sampling. Measurements reveal the presence of amounts of helium as well as molecular hydrogen considerably exceeding the atmospheric values. Measured values of gas ratio H2/4He = 5.4 ± 1.9 in the samples from depths of 3596-3698 m exceed the atmospheric values by more than an order of magnitude.

  11. Timescales of Growth Response of Microbial Mats to Environmental Change in an Ice-Covered Antarctic Lake

    PubMed Central

    Hawes, Ian; Sumner, Dawn Y.; Andersen, Dale T.; Jungblut, Anne D.; Mackey, Tyler J.

    2013-01-01

    Lake Vanda is a perennially ice-covered, closed-basin lake in the McMurdo Dry Valleys, Antarctica. Laminated photosynthetic microbial mats cover the floor of the lake from below the ice cover to >40 m depth. In recent decades, the water level of Lake Vanda has been rising, creating a “natural experiment” on development of mat communities on newly flooded substrates and the response of deeper mats to declining irradiance. Mats in recently flooded depths accumulate one lamina (~0.3 mm) per year and accrue ~0.18 µg chlorophyll-a cm−2 y−1. As they increase in thickness, vertical zonation becomes evident, with the upper 2-4 laminae forming an orange-brown zone, rich in myxoxanthophyll and dominated by intertwined Leptolyngbya trichomes. Below this, up to six phycobilin-rich green/pink-pigmented laminae form a subsurface zone, inhabited by Leptolyngbya, Oscillatoria and Phormidium morphotypes. Laminae continued to increase in thickness for several years after burial, and PAM fluorometry indicated photosynthetic potential in all pigmented laminae. At depths that have been submerged for >40 years, mats showed similar internal zonation and formed complex pinnacle structures that were only beginning to appear in shallower mats. Chlorophyll-a did not change over time and these mats appear to represent resource-limited “climax” communities. Acclimation of microbial mats to changing environmental conditions is a slow process, and our data show how legacy effects of past change persist into the modern community structure. PMID:24832656

  12. Lake Sediment Records as an Indicator of Holocene Fluctuations of Quelccaya Ice Cap, Peru and Regional Climate

    NASA Astrophysics Data System (ADS)

    Stroup, J. S.; Kelly, M. A.; Lowell, T. V.; Beal, S. A.; Smith, C. A.; Baranes, H. E.

    2012-12-01

    The past fluctuations of Quelccaya Ice Cap, (QIC; 13°S, 70°W, 5200 m asl) located in the southeastern Peruvian Andes, provide a record of tropical climate since the last glacial-interglacial transition. A detailed surficial geomorphic record of past glacial extents developed over the last several decades (e.g. Mercer and Palacios 1977; Buffen et al. 2009; Kelly et al. 2012 accepted) demonstrates that QIC is a dynamic glacial system. These records show that the ice cap was larger than present and retreating by ~11,500 yr BP, and smaller than present between ~7,000 and ~4,600 yr BP. The most recent advance occurred during the late Holocene (Little Ice Age;LIA), dated with 10Be surface exposure ages (510±90 yrs (n = 8)) (Stroup et al. in prep.). This overrode earlier deposits obscuring a complete Holocene record; we aim to address the gaps in glacial chronology using the sedimentary record archived in lakes. We retrieved two sets cores (8 and 5 m-long) from Laguna Challpacocha (13.91°S, 70.86°W, 5040 m asl), a lake that currently receives meltwater from QIC. Four radiocarbon ages from the cores suggest a continuous record dating to at least ~10,500 cal. yr BP. Variations in magnetic susceptibility, percent organic and inorganic carbon, bulk density, grayscale and X-ray fluorescence chemistry indicate changes in the amount of clastic sediment deposition. We interpret clastic sediments to have been deposited from ice cap meltwater, thus indicating more extensive ice. Clastic sediments compose the top of the core from 4 to 30 cm depth, below there is a sharp transition to organic sediments radiocarbon dated to (500±30 and 550±20 cal. yr BP). The radiocarbon ages are similar to the 10Be dated (LIA) glacial position. At least three other clastic units exist in the core; dating to ~2600-4300, ~4800-7300 and older then ~10,500 cal. yr BP based on a linear age model with four radiocarbon dates. We obtained two, ~4 m long, cores from Laguna Yanacocha (13.95°S,70.87

  13. Ice age fish in a warming world: minimal variation in thermal acclimation capacity among lake trout (Salvelinus namaycush) populations.

    PubMed

    Kelly, Nicholas I; Burness, Gary; McDermid, Jenni L; Wilson, Chris C

    2014-01-01

    In the face of climate change, the persistence of cold-adapted species will depend on their adaptive capacity for physiological traits within and among populations. The lake trout (Salvelinus namaycush) is a cold-adapted salmonid and a relict from the last ice age that is well suited as a model species for studying the predicted effects of climate change on coldwater fishes. We investigated the thermal acclimation capacity of upper temperature resistance and metabolism of lake trout from four populations across four acclimation temperatures. Individuals were reared from egg fertilization onward in a common environment and, at 2 years of age, were acclimated to 8, 11, 15 or 19°C. Although one population had a slightly higher maximal metabolic rate (MMR), higher metabolic scope for activity and faster metabolic recovery across all temperatures, there was no interpopulation variation for critical thermal maximum (CTM) or routine metabolic rate (RMR) or for the thermal acclimation capacity of CTM, RMR, MMR or metabolic scope. Across the four acclimation temperatures, there was a 3°C maximal increase in CTM and 3-fold increase in RMR for all populations. Above 15°C, a decline in MMR and increase in RMR resulted in sharply reduced metabolic scope for all populations acclimated at 19°C. Together, these data suggest there is limited variation among lake trout populations in thermal physiology or capacity for thermal acclimatization, and that climate change may impact lake trout populations in a similar manner across a wide geographical range. Understanding the effect of elevated temperatures on the thermal physiology of this economically and ecologically important cold-adapted species will help inform management and conservation strategies for the long-term sustainability of lake trout populations.

  14. Ice age fish in a warming world: minimal variation in thermal acclimation capacity among lake trout (Salvelinus namaycush) populations

    PubMed Central

    Kelly, Nicholas I.; Burness, Gary; McDermid, Jenni L.; Wilson, Chris C.

    2014-01-01

    In the face of climate change, the persistence of cold-adapted species will depend on their adaptive capacity for physiological traits within and among populations. The lake trout (Salvelinus namaycush) is a cold-adapted salmonid and a relict from the last ice age that is well suited as a model species for studying the predicted effects of climate change on coldwater fishes. We investigated the thermal acclimation capacity of upper temperature resistance and metabolism of lake trout from four populations across four acclimation temperatures. Individuals were reared from egg fertilization onward in a common environment and, at 2 years of age, were acclimated to 8, 11, 15 or 19°C. Although one population had a slightly higher maximal metabolic rate (MMR), higher metabolic scope for activity and faster metabolic recovery across all temperatures, there was no interpopulation variation for critical thermal maximum (CTM) or routine metabolic rate (RMR) or for the thermal acclimation capacity of CTM, RMR, MMR or metabolic scope. Across the four acclimation temperatures, there was a 3°C maximal increase in CTM and 3-fold increase in RMR for all populations. Above 15°C, a decline in MMR and increase in RMR resulted in sharply reduced metabolic scope for all populations acclimated at 19°C. Together, these data suggest there is limited variation among lake trout populations in thermal physiology or capacity for thermal acclimatization, and that climate change may impact lake trout populations in a similar manner across a wide geographical range. Understanding the effect of elevated temperatures on the thermal physiology of this economically and ecologically important cold-adapted species will help inform management and conservation strategies for the long-term sustainability of lake trout populations. PMID:27293646

  15. Trends and abrupt changes in 104 years of ice cover and water temperature in a dimictic lake in response to air temperature, wind speed, and water clarity drivers

    NASA Astrophysics Data System (ADS)

    Magee, Madeline R.; Wu, Chin H.; Robertson, Dale M.; Lathrop, Richard C.; Hamilton, David P.

    2016-05-01

    The one-dimensional hydrodynamic ice model, DYRESM-WQ-I, was modified to simulate ice cover and thermal structure of dimictic Lake Mendota, Wisconsin, USA, over a continuous 104-year period (1911-2014). The model results were then used to examine the drivers of changes in ice cover and water temperature, focusing on the responses to shifts in air temperature, wind speed, and water clarity at multiyear timescales. Observations of the drivers include a change in the trend of warming air temperatures from 0.081 °C per decade before 1981 to 0.334 °C per decade thereafter, as well as a shift in mean wind speed from 4.44 m s-1 before 1994 to 3.74 m s-1 thereafter. Observations show that Lake Mendota has experienced significant changes in ice cover: later ice-on date(9.0 days later per century), earlier ice-off date (12.3 days per century), decreasing ice cover duration (21.3 days per century), while model simulations indicate a change in maximum ice thickness (12.7 cm decrease per century). Model simulations also show changes in the lake thermal regime of earlier stratification onset (12.3 days per century), later fall turnover (14.6 days per century), longer stratification duration (26.8 days per century), and decreasing summer hypolimnetic temperatures (-1.4 °C per century). Correlation analysis of lake variables and driving variables revealed ice cover variables, stratification onset, epilimnetic temperature, and hypolimnetic temperature were most closely correlated with air temperature, whereas freeze-over water temperature, hypolimnetic heating, and fall turnover date were more closely correlated with wind speed. Each lake variable (i.e., ice-on and ice-off dates, ice cover duration, maximum ice thickness, freeze-over water temperature, stratification onset, fall turnover date, stratification duration, epilimnion temperature, hypolimnion temperature, and hypolimnetic heating) was averaged for the three periods (1911-1980, 1981-1993, and 1994-2014) delineated by

  16. Spatial Heterogeneity of Ice Cover Sediment and Thickness and Its Effects on Photosynthetically Active Radiation and Chlorophyll-a Distribution: Lake Bonney, Antarctica

    NASA Astrophysics Data System (ADS)

    Obryk, M.; Doran, P. T.; Priscu, J. C.; Morgan-Kiss, R. M.; Siebenaler, A. G.

    2012-12-01

    The perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica have been extensively studied under the Long Term Ecological Research project. But sampling has been spatially restricted due to the logistical difficulty of penetrating the 3-6 m of ice cover. The ice covers restrict wind-driven turbulence and its associated mixing of water, resulting in a unique thermal stratification and a strong vertical gradient of salinity. The permanent ice covers also shade the underlying water column, which, in turn, controls photosynthesis. Here, we present results of a three-dimensional record of lake processes obtained with an autonomous underwater vehicle (AUV). The AUV was deployed at West Lake Bonney, located in Taylor Valley, Dry Valleys, to further understand biogeochemical and physical properties of the Dry Valley lakes. The AUV was equipped with depth, conductivity, temperature, under water photosynthetically active radiation (PAR), turbidity, chlorophyll-and-DOM fluorescence, pH, and REDOX sensors. Measurements were taken over the course of two years in a 100 x 100 meter spaced horizontal sampling grid (and 0.2 m vertical resolution). In addition, the AUV measured ice thickness and collected 200 images looking up through the ice, which were used to quantify sediment distribution. Comparison with high-resolution satellite QuickBird imagery demonstrates a strong correlation between aerial sediment distribution and ice cover thickness. Our results are the first to show the spatial heterogeneity of lacustrine ecosystems in the McMurdo Dry Valleys, significantly improving our understanding of lake processes. Surface sediment is responsible for localized thinning of ice cover due to absorption of solar radiation, which in turn increases total available PAR in the water column. Higher PAR values are negatively correlated with chlorophyll-a, presenting a paradox; historically, long-term studies of PAR and chlorophyll-a have shown positive trends. We hypothesized

  17. Modular community structure suggests metabolic plasticity during the transition to polar night in ice-covered Antarctic lakes.

    PubMed

    Vick-Majors, Trista J; Priscu, John C; Amaral-Zettler, Linda A

    2014-04-01

    High-latitude environments, such as the Antarctic McMurdo Dry Valley lakes, are subject to seasonally segregated light-dark cycles, which have important consequences for microbial diversity and function on an annual basis. Owing largely to the logistical difficulties of sampling polar environments during the darkness of winter, little is known about planktonic microbial community responses to the cessation of photosynthetic primary production during the austral sunset, which lingers from approximately February to April. Here, we hypothesized that changes in bacterial, archaeal and eukaryotic community structure, particularly shifts in favor of chemolithotrophs and mixotrophs, would manifest during the transition to polar night. Our work represents the first concurrent molecular characterization, using 454 pyrosequencing of hypervariable regions of the small-subunit ribosomal RNA gene, of bacterial, archaeal and eukaryotic communities in permanently ice-covered lakes Fryxell and Bonney, before and during the polar night transition. We found vertically stratified populations that varied at the community and/or operational taxonomic unit-level between lakes and seasons. Network analysis based on operational taxonomic unit level interactions revealed nonrandomly structured microbial communities organized into modules (groups of taxa) containing key metabolic potential capacities, including photoheterotrophy, mixotrophy and chemolithotrophy, which are likely to be differentially favored during the transition to polar night.

  18. Anomalous ocean load tide signal observed in lake-level variations in Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Richter, A.; Hormaechea, J. L.; Dietrich, R.; Perdomo, R.; Fritsche, M.; Del Cogliano, D.; Liebsch, G.; Mendoza, L.

    2009-03-01

    We demonstrate the application of a 100 km long lake as a sensor for studying the tidal effects on Tierra del Fuego main island. The lake-level variations observed in Lago Fagnano reflect both the direct response to the tidal potential and the indirect effect of the ocean tidal loading. Modeling both contributions explains the observed tidal signal in the lake to about 70%. Underestimated model load tide amplitudes are found to be probably responsible for the remaining difference. We interpret this discrepancy as a hint for regional elastic lithosphere properties differing substantially from those represented by currently available global models.

  19. The Mungo Mega-Lake Event, Semi-Arid Australia: Non-Linear Descent into the Last Ice Age, Implications for Human Behaviour.

    PubMed

    Fitzsimmons, Kathryn E; Stern, Nicola; Murray-Wallace, Colin V; Truscott, William; Pop, Cornel

    2015-01-01

    The Willandra Lakes complex is one of the few locations in semi-arid Australia to preserve both paleoenvironmental and Paleolithic archeological archives at high resolution. The stratigraphy of transverse lunette dunes on the lakes' downwind margins record a late Quaternary sequence of wetting and drying. Within the Willandra system, the Lake Mungo lunette is best known for its preservation of the world's oldest known ritual burials, and high densities of archeological traces documenting human adaptation to changing environmental conditions over the last 45 ka. Here we identify evidence at Lake Mungo for a previously unrecognised short-lived, very high lake filling phase at 24 ka, just prior to the Last Glacial Maximum. Mega-lake Mungo was up to 5 m deeper than preceding or subsequent lake full events and represented a lake volume increase of almost 250%. Lake Mungo was linked with neighboring Lake Leaghur at two overflow points, creating an island from the northern part of the Mungo lunette. This event was most likely caused by a pulse of high catchment rainfall and runoff, combined with neotectonic activity which may have warped the lake basin. It indicates a non-linear transition to more arid ice age conditions. The mega-lake restricted mobility for people living in the area, yet archeological traces indicate that humans rapidly adapted to the new conditions. People repeatedly visited the island, transporting stone tools across water and exploiting food resources stranded there. They either swam or used watercraft to facilitate access to the island and across the lake. Since there is no evidence for watercraft use in Australia between initial colonization of the continent prior to 45 ka and the mid-Holocene, repeated visits to the island may represent a resurrection of waterfaring technologies following a hiatus of at least 20 ky.

  20. "The Effect of Alternative Representations of Lake Temperatures and Ice on WRF Regional Climate Simulations"

    EPA Science Inventory

    Lakes can play a significant role in regional climate, modulating inland extremes in temperature and enhancing precipitation. Representing these effects becomes more important as regional climate modeling (RCM) efforts focus on simulating smaller scales. When using the Weathe...

  1. Laser-induced fluorescence emission (L.I.F.E.): in situ nondestructive detection of microbial life in the ice covers of Antarctic lakes.

    PubMed

    Storrie-Lombardi, Michael C; Sattler, Birgit

    2009-09-01

    Laser-induced fluorescence emission (L.I.F.E.) images were obtained in situ following 532 nm excitation of cryoconite assemblages in the ice covers of annual and perennially frozen Antarctic lakes during the 2008 Tawani International Expedition to Schirmacher Oasis and Lake Untersee in Dronning Maud Land, Antarctica. Laser targeting of a single millimeter-scale cryoconite results in multiple neighboring excitation events secondary to ice/air interface reflection and refraction in the bubbles surrounding the primary target. Laser excitation at 532 nm of cyanobacteria-dominated assemblages produced red and infrared autofluorescence activity attributed to the presence of phycoerythrin photosynthetic pigments. The method avoids destruction of individual target organisms and does not require the disruption of either the structure of the microbial community or the surrounding ice matrix. L.I.F.E. survey strategies described may be of interest for orbital monitoring of photosynthetic primary productivity in polar and alpine glaciers, ice sheets, snow, and lake ice of Earth's cryosphere. The findings open up the possibility of searching from either a rover or from orbit for signs of life in the polar regions of Mars and the frozen regions of exoplanets in neighboring star systems.

  2. Records of Local Glacier Variability in Western Greenland During the Holocene From Lake Sediments, Ice-cap-killed Vegetation, and 10Be Dating

    NASA Astrophysics Data System (ADS)

    Schweinsberg, A.; Briner, J. P.; Miller, G. H.; Bennike, O.

    2015-12-01

    Local mountain glaciers and ice caps are common and widespread along the periphery of Greenland and provide valuable paleoclimatic records because they respond sensitively to climate change. In contrast to extensive research on Greenland Ice Sheet (GIS) margin changes, the relative timing of mountain glaciation during the Holocene is poorly documented. Here, we use a multi-proxy approach to document the timing of local glacier advance and retreat throughout the past ~10 ka in western Greenland by combining: (1) proglacial lake sediment analysis, (2) 14C-dating of ice-cap-killed in situ plants, and (3) cosmogenic 10Be dating. Radiocarbon-dated sediment cores from Sikuiui and Pauiaivik lakes, eastern Nuussuaq, provide minimum-limiting ages for local deglaciation of 9.4 ± 0.06 and 8.8 ± 0.16 ka, respectively, and are in agreement with 10Be ages of regional deglaciation that average 10.9 ± 0.7 ka (n=8). Radiocarbon ages (n=54) of in situ plants along retreating cold-based ice cap margins reveal net snowline lowering beginning ~5 ka and are concurrent with the onset of Neoglaciation recorded in both lake systems. Modes of vegetation kill dates highlight distinct ice cap expansion phases at ~3.7, ~3.0, ~1.5 ka, and during the Little Ice Age. The most pronounced snowline lowering event ~4-3 ka is expressed in both lake records by deposition of mineral-rich sediments between ~4.5 and 2.5 ka. Ice cap expansion phases are broadly correlative with elevated minerogenic input in both lakes with some modes in the vegetation ages occurring just prior to increases in mineral-rich sediment input. Published studies of the western GIS margin suggest a major cooling event between ~4.3-3.2 ka, which overlaps with periods of enhanced local glacier activity and ice cap expansion in our dataset. Lastly, the dominant ice cap expansion episode ~3.7 ka in western Greenland is synchronous with a significant snowline lowering event on Baffin Island, suggesting a common climate forcing

  3. The Mungo Mega-Lake Event, Semi-Arid Australia: Non-Linear Descent into the Last Ice Age, Implications for Human Behaviour

    PubMed Central

    Fitzsimmons, Kathryn E.; Stern, Nicola; Murray-Wallace, Colin V.; Truscott, William; Pop, Cornel

    2015-01-01

    The Willandra Lakes complex is one of the few locations in semi-arid Australia to preserve both paleoenvironmental and Paleolithic archeological archives at high resolution. The stratigraphy of transverse lunette dunes on the lakes’ downwind margins record a late Quaternary sequence of wetting and drying. Within the Willandra system, the Lake Mungo lunette is best known for its preservation of the world’s oldest known ritual burials, and high densities of archeological traces documenting human adaptation to changing environmental conditions over the last 45 ka. Here we identify evidence at Lake Mungo for a previously unrecognised short-lived, very high lake filling phase at 24 ka, just prior to the Last Glacial Maximum. Mega-lake Mungo was up to 5 m deeper than preceding or subsequent lake full events and represented a lake volume increase of almost 250%. Lake Mungo was linked with neighboring Lake Leaghur at two overflow points, creating an island from the northern part of the Mungo lunette. This event was most likely caused by a pulse of high catchment rainfall and runoff, combined with neotectonic activity which may have warped the lake basin. It indicates a non-linear transition to more arid ice age conditions. The mega-lake restricted mobility for people living in the area, yet archeological traces indicate that humans rapidly adapted to the new conditions. People repeatedly visited the island, transporting stone tools across water and exploiting food resources stranded there. They either swam or used watercraft to facilitate access to the island and across the lake. Since there is no evidence for watercraft use in Australia between initial colonization of the continent prior to 45 ka and the mid-Holocene, repeated visits to the island may represent a resurrection of waterfaring technologies following a hiatus of at least 20 ky. PMID:26083665

  4. Photosynthate distribution by microplankton in permanently ice-covered Antarctic desert lakes

    SciTech Connect

    Priscu, J.C.; Priscu, L.R.; Vincent, W.F.; Howard-Williams, C.

    1987-01-01

    The distribution of /sup 14/C-labeled photosynthate by microplankton in Lakes Vanda and Fryxell, Antarctica, was measured during the 1984-1985 austral summer. Both lakes had conspicuous deep chlorophyll maxima near the bottom of the oxygenated zone. DCMU sensitivity experiments revealed that photosynthesis below the chlorophyll maximum in Lake Fryxell was partially due to photosynthetic bacteria. These bacteria had notably higher protein and lower lipid labeling than overlying oxic microalgae. Protein labeling in the oxic microalgae had lower I/sub k/ and higher ..cap alpha.. values than for other photosynthetic end products, indicating that protein is synthesized more efficiently at low photosynthetic photon flux density than the other metabolites. The I/sub k/ values for complete photosynthesis are among the lowest yet recorded for phytoplankton.

  5. Significant melting of ice-wedges and formation of thermocirques on hill-slopes of thermokarst lakes in Central Yakutia (Siberia)

    NASA Astrophysics Data System (ADS)

    Séjourné, Antoine; Costard, François; Gargani, Julien; Fedorov, Alexander; Skorve, Johnny

    2013-04-01

    On Earth, permafrost containing a high ice volume (referred as ice-rich) are sensible to climate change, they have been regionally degraded (thermokarst) during the early Holocene climatic optimum forming numerous thermokarst lakes in Central Yakutia (eastern Siberia). Recent temperature increases in the Arctic and Subarctic have been significantly greater than global averages. The frequency and magnitude of terrain disturbances associated with thawing permafrost are increasing in these regions and are thought to intensify in the future. Therefore, understand how is the current development of thermokarst is a critical question. Here, we describe the significant melting of ice-wedges on slopes of thermokarst lakes that leads to formation of amphitheatrical hollows referred as thermocirques. The evolution of thermocirques in Central Yakutia has been little studied and analyzing their formation could help to understand the recent thermokarst in relation to climate change in Central Yakutia. We studied the thermocirques at two scales: (i) field surveys of different thermocirques in July 2009-2010 and October 2012 to examine the processes and origin of melting of ice-wedges and; (ii) photo-interpretation of time series of satellite images (KH-9 Hexagon images of 6-9 m/pixel and GeoEye images of 50 cm/pixel) to study the temporal evolution of thermocirques. The melting of ground-ice on the scarp of thermocirque triggers falls and small mud-flows that induce the retreat of the scarp parallel to itself. Based on field studies and on GeoEye image comparison, we show that their rate of retrogressive growth is 1-2 m/year. On the hill-slopes of lakes, the thermokarst could be initiated by different processes that lead to the uncover and then melting of ice-wedges: thermal erosion by the waves of the ice-rich bluff; active-layer detachment (a form of slope failure linked to detachment of the seasonally thawed upper ground); flowing of water on the slope (precipitation) or

  6. Microbial life at -13 °C in the brine of an ice-sealed Antarctic lake

    NASA Astrophysics Data System (ADS)

    Murray, Alison E.; Kenig, Fabien; Fritsen, Christian H.; McKay, Christopher P.; Cawley, Kaelin M.; Edwards, Ross; Kuhn, Emanuele; McKnight, Diane M.; Ostrom, Nathaniel E.; Peng, Vivian; Ponce, Adrian; Priscu, John C.; Samarkin, Vladimir; Townsend, Ashley T.; Wagh, Protima; Young, Seth A.; Yung, Pung To; Doran, Peter T.

    2012-12-01

    The permanent ice cover of Lake Vida (Antarctica) encapsulates an extreme cryogenic brine ecosystem (-13 °C; salinity, 200). This aphotic ecosystem is anoxic and consists of a slightly acidic (pH 6.2) sodium chloride-dominated brine. Expeditions in 2005 and 2010 were conducted to investigate the biogeochemistry of Lake Vida's brine system. A phylogenetically diverse and metabolically active Bacteria dominated microbial assemblage was observed in the brine. These bacteria live under very high levels of reduced metals, ammonia, molecular hydrogen (H2), and dissolved organic carbon, as well as high concentrations of oxidized species of nitrogen (i.e., supersaturated nitrous oxide and ∼1 mmolṡL-1 nitrate) and sulfur (as sulfate). The existence of this system, with active biota, and a suite of reduced as well as oxidized compounds, is unusual given the millennial scale of its isolation from external sources of energy. The geochemistry of the brine suggests that abiotic brine-rock reactions may occur in this system and that the rich sources of dissolved electron acceptors prevent sulfate reduction and methanogenesis from being energetically favorable. The discovery of this ecosystem and the in situ biotic and abiotic processes occurring at low temperature provides a tractable system to study habitability of isolated terrestrial cryoenvironments (e.g., permafrost cryopegs and subglacial ecosystems), and is a potential analog for habitats on other icy worlds where water-rock reactions may cooccur with saline deposits and subsurface oceans.

  7. Microbial life at −13 °C in the brine of an ice-sealed Antarctic lake

    PubMed Central

    Murray, Alison E.; Kenig, Fabien; Fritsen, Christian H.; McKay, Christopher P.; Cawley, Kaelin M.; Edwards, Ross; Kuhn, Emanuele; McKnight, Diane M.; Ostrom, Nathaniel E.; Peng, Vivian; Ponce, Adrian; Priscu, John C.; Samarkin, Vladimir; Townsend, Ashley T.; Wagh, Protima; Young, Seth A.; Yung, Pung To; Doran, Peter T.

    2012-01-01

    The permanent ice cover of Lake Vida (Antarctica) encapsulates an extreme cryogenic brine ecosystem (−13 °C; salinity, 200). This aphotic ecosystem is anoxic and consists of a slightly acidic (pH 6.2) sodium chloride-dominated brine. Expeditions in 2005 and 2010 were conducted to investigate the biogeochemistry of Lake Vida’s brine system. A phylogenetically diverse and metabolically active Bacteria dominated microbial assemblage was observed in the brine. These bacteria live under very high levels of reduced metals, ammonia, molecular hydrogen (H2), and dissolved organic carbon, as well as high concentrations of oxidized species of nitrogen (i.e., supersaturated nitrous oxide and ∼1 mmol⋅L−1 nitrate) and sulfur (as sulfate). The existence of this system, with active biota, and a suite of reduced as well as oxidized compounds, is unusual given the millennial scale of its isolation from external sources of energy. The geochemistry of the brine suggests that abiotic brine-rock reactions may occur in this system and that the rich sources of dissolved electron acceptors prevent sulfate reduction and methanogenesis from being energetically favorable. The discovery of this ecosystem and the in situ biotic and abiotic processes occurring at low temperature provides a tractable system to study habitability of isolated terrestrial cryoenvironments (e.g., permafrost cryopegs and subglacial ecosystems), and is a potential analog for habitats on other icy worlds where water-rock reactions may cooccur with saline deposits and subsurface oceans. PMID:23185006

  8. Microbial life at -13 °C in the brine of an ice-sealed Antarctic lake.

    PubMed

    Murray, Alison E; Kenig, Fabien; Fritsen, Christian H; McKay, Christopher P; Cawley, Kaelin M; Edwards, Ross; Kuhn, Emanuele; McKnight, Diane M; Ostrom, Nathaniel E; Peng, Vivian; Ponce, Adrian; Priscu, John C; Samarkin, Vladimir; Townsend, Ashley T; Wagh, Protima; Young, Seth A; Yung, Pung To; Doran, Peter T

    2012-12-11

    The permanent ice cover of Lake Vida (Antarctica) encapsulates an extreme cryogenic brine ecosystem (-13 °C; salinity, 200). This aphotic ecosystem is anoxic and consists of a slightly acidic (pH 6.2) sodium chloride-dominated brine. Expeditions in 2005 and 2010 were conducted to investigate the biogeochemistry of Lake Vida's brine system. A phylogenetically diverse and metabolically active Bacteria dominated microbial assemblage was observed in the brine. These bacteria live under very high levels of reduced metals, ammonia, molecular hydrogen (H(2)), and dissolved organic carbon, as well as high concentrations of oxidized species of nitrogen (i.e., supersaturated nitrous oxide and ∼1 mmol⋅L(-1) nitrate) and sulfur (as sulfate). The existence of this system, with active biota, and a suite of reduced as well as oxidized compounds, is unusual given the millennial scale of its isolation from external sources of energy. The geochemistry of the brine suggests that abiotic brine-rock reactions may occur in this system and that the rich sources of dissolved electron acceptors prevent sulfate reduction and methanogenesis from being energetically favorable. The discovery of this ecosystem and the in situ biotic and abiotic processes occurring at low temperature provides a tractable system to study habitability of isolated terrestrial cryoenvironments (e.g., permafrost cryopegs and subglacial ecosystems), and is a potential analog for habitats on other icy worlds where water-rock reactions may cooccur with saline deposits and subsurface oceans. PMID:23185006

  9. SPME-GCMS study of the natural attenuation of aviation diesel spilled on the perennial ice cover of Lake Fryxell, Antarctica.

    PubMed

    Jaraula, Caroline M B; Kenig, Fabien; Doran, Peter T; Priscu, John C; Welch, Kathleen A

    2008-12-15

    In January 2003, a helicopter crashed on the 5 m thick perennial ice cover of Lake Fryxell (McMurdo Dry Valleys, East Antarctica), spilling approximately 730 l of aviation diesel fuel (JP5-AN8 mixture). The molecular composition of the initial fuel was analyzed by solid phase microextraction (SPME) gas chromatography-mass spectrometry (GC-MS), then compared to the composition of the contaminated ice, water, and sediments collected a year after the spill. Evaporation is the major agent of diesel weathering in meltpool waters and in the ice. This process is facilitated by the light non-aqueous phase liquid properties of the aviation diesel and by the net upward movement of the ice as a result of ablation. In contrast, in sediment-bearing ice, biodegradation by both alkane- and aromatic-degraders was the prominent attenuation mechanism. The composition of the diesel contaminant in the ice was also affected by the differential solubility of its constituents, some ice containing water-washed diesel and some ice containing exclusively relatively soluble low molecular weight aromatic hydrocarbons such as alkylbenzene and naphthalene homologues. The extent of evaporation, water washing and biodegradation between sites and at different depths in the ice are evaluated on the basis of molecular ratios and the results of JP5-AN8 diesel evaporation experiment at 4 degrees C. Immediate spread of the aviation diesel was enhanced where the presence of aeolian sediments induced formations of meltpools. However, in absence of melt pools, slow spreading of the diesel is possible through the porous ice and the ice cover aquifer.

  10. Evidence for an ice sheet/frozen lake in Utopia Planitia, Mars

    NASA Technical Reports Server (NTRS)

    Chapman, M. G.

    1993-01-01

    Previous workers noted evidence for a lacustrine basin in Utopia Planitia, Mars. Geomorphic features within the basin that collectively suggest that water or ice may once have been present include channels within the basin, channels peripheral to the basin, etched basin floor, 'thumbprint' terrain (whorled patterns), polygonal outlines, smooth floors (infilled), shoreline indicators (terraces, platforms, lineaments), and small cratered cones (pseudo craters or pingos). The authors interpret these data to suggest that the basin may have been the locus of a large paleolake in the northern lowlands of Mars. Alternatively, the area was proposed to be part of an ancient circumpolar ocean. The hypothetical paleolake was probably frozen to some depth. In fact, features now present at its boundaries suggest that the edges may have been frozen solid. Plains units at the southwestern boundary of Utopia Planitia show ridges that were compared with those that form at the mouths of Antarctic ice streams, thumbprint terrain, and young, high deposits having lobate margins that suggest mudflows. Thumbprint terrains were interpreted as recessional moraines, ice-pushed ridges, or subglacially eroded tunnel valleys with eroded eskers. At the east boundary of Utopia Planitia, geologic mapping at 1:500,000 scale of the Granicus Valles area (MTM quadrangles 30227, 30222, and 25227) indicates the presence of a basal scarp around the northwest flank of Elysium that formed the east boundary of an ancient ice sheet.

  11. Response of ice cover on shallow lakes of the North Slope of Alaska to contemporary climate conditions (1950-2011): radar remote-sensing and numerical modeling data analysis

    NASA Astrophysics Data System (ADS)

    Surdu, C. M.; Duguay, C. R.; Brown, L. C.; Fernández Prieto, D.

    2014-01-01

    Air temperature and winter precipitation changes over the last five decades have impacted the timing, duration, and thickness of the ice cover on Arctic lakes as shown by recent studies. In the case of shallow tundra lakes, many of which are less than 3 m deep, warmer climate conditions could result in thinner ice covers and consequently, in a smaller fraction of lakes freezing to their bed in winter. However, these changes have not yet been comprehensively documented. The analysis of a 20 yr time series of European remote sensing satellite ERS-1/2 synthetic aperture radar (SAR) data and a numerical lake ice model were employed to determine the response of ice cover (thickness, freezing to the bed, and phenology) on shallow lakes of the North Slope of Alaska (NSA) to climate conditions over the last six decades. Given the large area covered by these lakes, changes in the regional climate and weather are related to regime shifts in the ice cover of the lakes. Analysis of available SAR data from 1991 to 2011, from a sub-region of the NSA near Barrow, shows a reduction in the fraction of lakes that freeze to the bed in late winter. This finding is in good agreement with the decrease in ice thickness simulated with the Canadian Lake Ice Model (CLIMo), a lower fraction of lakes frozen to the bed corresponding to a thinner ice cover. Observed changes of the ice cover show a trend toward increasing floating ice fractions from 1991 to 2011, with the greatest change occurring in April, when the grounded ice fraction declined by 22% (α = 0.01). Model results indicate a trend toward thinner ice covers by 18-22 cm (no-snow and 53% snow depth scenarios, α = 0.01) during the 1991-2011 period and by 21-38 cm (α = 0.001) from 1950 to 2011. The longer trend analysis (1950-2011) also shows a decrease in the ice cover duration by ~24 days consequent to later freeze-up dates by 5.9 days (α = 0.1) and earlier break-up dates by 17.7-18.6 days (α = 0.001).

  12. Biogeochemistry and limnology in Antarctic subglacial weathering: molecular evidence of the linkage between subglacial silica input and primary producers in a perennially ice-covered lake

    NASA Astrophysics Data System (ADS)

    Takano, Yoshinori; Kojima, Hisaya; Takeda, Eriko; Yokoyama, Yusuke; Fukui, Manabu

    2015-12-01

    We report a 6,000 years record of subglacial weathering and biogeochemical processes in two perennially ice-covered glacial lakes at Rundvågshetta, on the Soya Coast of Lützow-Holm Bay, East Antarctica. The two lakes, Lake Maruwan Oike and Lake Maruwan-minami, are located in a channel that drains subglacial water from the base of the East Antarctic ice sheet. Greenish-grayish organic-rich laminations in sediment cores from the lakes indicate continuous primary production affected by the inflow of subglacial meltwater containing relict carbon, nitrogen, sulfur, and other essential nutrients. Biogenic silica, amorphous hydrated silica, and DNA-based molecular signatures of sedimentary facies indicate that diatom assemblages are the dominant primary producers, supported by the input of inorganic silicon (Si) from the subglacial inflow. This study highlights the significance of subglacial water-rock interactions during physical and chemical weathering processes and the importance of such interactions for the supply of bioavailable nutrients.

  13. Ultrastructural and Single-Cell-Level Characterization Reveals Metabolic Versatility in a Microbial Eukaryote Community from an Ice-Covered Antarctic Lake

    DOE PAGES

    Li, Wei; Podar, Mircea; Morgan-Kiss, Rachael M.

    2016-04-15

    The McMurdo Dry Valleys (MCM) of southern Victoria Land, Antarctica, harbor numerous ice-covered bodies of water that provide year-round liquid water oases for isolated food webs dominated by the microbial loop. Single-cell microbial eukaryotes (protists) occupy major trophic positions within this truncated food web, ranging from primary producers (e.g., chlorophytes, haptophytes, and cryptophytes) to tertiary predators (e.g., ciliates, dinoflagellates, and choanoflagellates). To advance the understanding of MCM protist ecology and the roles of MCM protists in nutrient and energy cycling, we investigated potential metabolic strategies and microbial interactions of key MCM protists isolated from a well-described lake (Lake Bonney). Fluorescence-activatedmore » cell sorting (FACS) of enrichment cultures, combined with single amplified genome/amplicon sequencing and fluorescence microscopy, revealed that MCM protists possess diverse potential metabolic capabilities and interactions. Two metabolically distinct bacterial clades (FlavobacteriaandMethylobacteriaceae) were independently associated with two key MCM lake microalgae (IsochrysisandChlamydomonas, respectively). We also report on the discovery of two heterotrophic nanoflagellates belonging to the Stramenopila supergroup, one of which lives as a parasite ofChlamydomonas, a dominate primary producer in the shallow, nutrient-poor layers of the lake. Single-cell eukaryotes called protists play critical roles in the cycling of organic matter in aquatic environments. In the ice-covered lakes of Antarctica, protists play key roles in the aquatic food web, providing the majority of organic carbon to the rest of the food web (photosynthetic protists) and acting as the major consumers at the top of the food web (predatory protists). In this study, we utilized a combination of techniques (microscopy, cell sorting, and genomic analysis) to describe the trophic abilities of Antarctic lake protists and their potential

  14. Characterizing Microbial Mat Morphology with Structure from Motion Techniques in Ice-Covered Lake Joyce, McMurdo Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Mackey, T. J.; Leidman, S. Z.; Allen, B.; Hawes, I.; Lawrence, J.; Jungblut, A. D.; Krusor, M.; Coleman, L.; Sumner, D. Y.

    2015-12-01

    Structure from Motion (SFM) techniques can provide quantitative morphological documentation of otherwise inaccessible benthic ecosystems such as microbial mats in Lake Joyce, a perennially ice-covered lake of the Antarctic McMurdo Dry Valleys (MDV). Microbial mats are a key ecosystem of MDV lakes, and diverse mat morphologies like pinnacles emerge from interactions among microbial behavior, mineralization, and environmental conditions. Environmental gradients can be isolated to test mat growth models, but assessment of mat morphology along these gradients is complicated by their inaccessibility: the Lake Joyce ice cover is 4-5 m thick, water depths containing diverse pinnacle morphologies are 9-14 m, and relevant mat features are cm-scale. In order to map mat pinnacle morphology in different sedimentary settings, we deployed drop cameras (SeaViewer and GoPro) through 29 GPS referenced drill holes clustered into six stations along a transect spanning 880 m. Once under the ice cover, a boom containing a second GoPro camera was unfurled and rotated to collect oblique images of the benthic mats within dm of the mat-water interface. This setup allowed imaging from all sides over a ~1.5 m diameter area of the lake bottom. Underwater lens parameters were determined for each camera in Agisoft Lens; images were reconstructed and oriented in space with the SFM software Agisoft Photoscan, using the drop camera axis of rotation as up. The reconstructions were compared to downward facing images to assess accuracy, and similar images of an object with known geometry provided a test for expected error in reconstructions. Downward facing images identify decreasing pinnacle abundance in higher sedimentation settings, and quantitative measurements of 3D reconstructions in KeckCAVES LidarViewer supplement these mat morphological facies with measurements of pinnacle height and orientation. Reconstructions also help isolate confounding variables for mat facies trends with measurements

  15. A halophilic bacterium inhabiting the warm, CaCl2-rich brine of the perennially ice-covered Lake Vanda, McMurdo Dry Valleys, Antarctica.

    PubMed

    Tregoning, George S; Kempher, Megan L; Jung, Deborah O; Samarkin, Vladimir A; Joye, Samantha B; Madigan, Michael T

    2015-03-01

    Lake Vanda is a perennially ice-covered and stratified lake in the McMurdo Dry Valleys, Antarctica. The lake develops a distinct chemocline at about a 50-m depth, where the waters transition from cool, oxic, and fresh to warm, sulfidic, and hypersaline. The bottom water brine is unique, as the highly chaotropic salts CaCl2 and MgCl2 predominate, and CaCl2 levels are the highest of those in any known microbial habitat. Enrichment techniques were used to isolate 15 strains of heterotrophic bacteria from the Lake Vanda brine. Despite direct supplementation of the brine samples with different organic substrates in primary enrichments, the same organism, a relative of the halophilic bacterium Halomonas (Gammaproteobacteria), was isolated from all depths sampled. The Lake Vanda (VAN) strains were obligate aerobes and showed broad pH, salinity, and temperature ranges for growth, consistent with the physicochemical properties of the brine. VAN strains were halophilic and quite CaCl2 tolerant but did not require CaCl2 for growth. The fact that only VAN strain-like organisms appeared in our enrichments hints that the highly chaotropic nature of the Lake Vanda brine may place unusual physiological constraints on the bacterial community that inhabits it. PMID:25576606

  16. A Halophilic Bacterium Inhabiting the Warm, CaCl2-Rich Brine of the Perennially Ice-Covered Lake Vanda, McMurdo Dry Valleys, Antarctica

    PubMed Central

    Tregoning, George S.; Kempher, Megan L.; Jung, Deborah O.; Samarkin, Vladimir A.; Joye, Samantha B.

    2015-01-01

    Lake Vanda is a perennially ice-covered and stratified lake in the McMurdo Dry Valleys, Antarctica. The lake develops a distinct chemocline at about a 50-m depth, where the waters transition from cool, oxic, and fresh to warm, sulfidic, and hypersaline. The bottom water brine is unique, as the highly chaotropic salts CaCl2 and MgCl2 predominate, and CaCl2 levels are the highest of those in any known microbial habitat. Enrichment techniques were used to isolate 15 strains of heterotrophic bacteria from the Lake Vanda brine. Despite direct supplementation of the brine samples with different organic substrates in primary enrichments, the same organism, a relative of the halophilic bacterium Halomonas (Gammaproteobacteria), was isolated from all depths sampled. The Lake Vanda (VAN) strains were obligate aerobes and showed broad pH, salinity, and temperature ranges for growth, consistent with the physicochemical properties of the brine. VAN strains were halophilic and quite CaCl2 tolerant but did not require CaCl2 for growth. The fact that only VAN strain-like organisms appeared in our enrichments hints that the highly chaotropic nature of the Lake Vanda brine may place unusual physiological constraints on the bacterial community that inhabits it. PMID:25576606

  17. Sub-ice volcanoes and ancient oceans/lakes: A Martian challenge

    USGS Publications Warehouse

    Chapman, M.G.

    2003-01-01

    New instruments on board the Mars Global Surveyor (MGS) spacecraft began providing accurate, high-resolution image and topography data from the planet in 1997. Though data from the Mars Orbiter Laser Altimeter (MOLA) are consistent with hypotheses that suggest large standing bodies of water/ice in the northern lowlands in the planet's past history, Mars Orbiter Camera (MOC) images acquired to test these hypotheses have provided negative or ambiguous results. In the absence of classic coastal features to test the paleo-ocean hypothesis, other indicators need to be examined. Tuyas and hyaloclastic ridges are subice volcanoes of unique appearance that form in ponded water conditions on Earth. Features with similar characteristics occur on Mars. MOLA analyses of these Martian features provide estimates of the height of putative ice/water columns at the edge of the Utopia Planitia basin and within Ophir Chasma of Valles Marineris, and support the hypotheses of a northern ocean on Mars. ?? 2003 Elsevier Science B.V. All rights reserved.

  18. From dwindling ice to headwater lakes: could dams replace glaciers in the European Alps?

    NASA Astrophysics Data System (ADS)

    Farinotti, Daniel; Pistocchi, Alberto; Huss, Matthias

    2016-05-01

    The potential exploitation of areas becoming ice-free in response to ongoing climate change has rarely been addressed, although it could be of interest from the water management perspective. Here we present an estimate for the potential of mitigating projected changes in seasonal water availability from melting glaciers by managing runoff through reservoirs. For the European Alps we estimate that by the end of the century, such a strategy could offset up to 65% of the expected summer-runoff changes from presently glacierized surfaces. A first-order approach suggests that the retention volume potentially available in the areas becoming deglacierized is in excess of the volume required for achieving the maximal possible mitigation by more than one order of magnitude. Obviously, however, such a strategy cannot compensate for the reduction in annual runoff caused by glacier ice depletion. Our estimates indicate that by 2070-2099, 0.73 ± 0.67 km3 a-1 of this non-renewable component of the water cycle could be missing in Alpine water supplies.

  19. Lake Store Finnsjøen - a key for understanding Lateglacial/early Holocene vegetation and ice sheet dynamics in the central Scandes Mountains

    NASA Astrophysics Data System (ADS)

    Paus, Aage; Boessenkool, Sanne; Brochmann, Christian; Epp, Laura Saskia; Fabel, Derek; Haflidason, Haflidi; Linge, Henriette

    2015-08-01

    The Lateglacial (LG) deglaciation and vegetation development in the Scandes Mountains has been debated for a century. Here we present new evidence from microfossils, radiocarbon dated plant macrofossils and sedimentary ancient DNA from laminated sediments in Lake Store Finnsjøen (1260 m a.s.l.) at Dovre, Central Norway. Combined with previous results from three other Dovre lakes, this allows for new interpretations of events during and immediately after the LG deglaciation. The Finnsjøen sediments present the first uninterrupted record of local vegetation development in the Scandes Mountains from the late Younger Dryas (YD), ca 12,000 cal years BP, to the early Holocene around 9700 cal years BP. The local vegetation in late YD/early Holocene was extremely sparse with pioneer herbs (e.g. Artemisia norvegica, Beckwithia, Campanula cf. uniflora, Koenigia, Oxyria, Papaver, Saxifraga spp.) and dwarf-shrubs (Betula nana, Salix including Salix polaris). From 11,300 cal years BP, local vegetation rapidly closed with dominant Dryas, Saxifraga spp., and Silene acaulis. From ca 10,700 cal years BP, open birch-forests with juniper, Empetrum nigrum and other dwarf-shrubs developed. Pine forests established within the area from 10,300 cal years BP. We identified the cold Preboreal Oscillation (PBO), not earlier described from pollen data in South Norway, around 11,400 cal years BP by a regional pollen signal. Distinct local vegetation changes were not detected until the post-PBO warming around 11,300 cal years BP. Apparently, the earlier warming at the YD/Holocene transition at 11,650 cal years BP was too weak and short-lived for vegetation closure at high altitudes at Dovre. For the first time, we demonstrate a regional glacier readvance and local ice cap formations during the YD in the Scandes Mountains. In two of the deep lakes with small catchments, YD glaciation blocked sedimentation without removing old sediments and caused a hiatus separating sediments of the ice

  20. Metal and Phosphorous behavior in the water and sediment underneath ice cover: a comparative study between hyper- and eutrophic lake systems

    NASA Astrophysics Data System (ADS)

    Joung, D.; Xu, Y.; Isles, P. D.; Gearhart, T.; Stockwell, J.; O'Malley, B.; Schroth, A. W.; Ramcharitar, B.; Leduc, M.

    2015-12-01

    The behavior of metals and associated nutrients in lakes under ice cover is poorly understood, although wintertime metal nutrient dynamics near the sediment water interface (SWI) could impact water quality and algal ecosystems. To examine the behavior of these biogeochemical constituents under ice, we collected water column and sediment time series biogeochemical data from hyper-eutrophic Shelburne Pond (SP) and eutrophic Missisquoi Bay (MB), Vermont USA, from January to April 2015. Based on temporal changes in the concentration of Al, Ca, Fe, Mn and P in sediment, coupled with density and oxygen gradients in water, we demonstrate that water column variability in metal and P concentration and spatial distribution is impacted by redox cycling near the SWI, as well as episodic input from each system's watershed. These processes are manifest differently in each system due to differences in lake-watershed configuration and sediment composition. Our data suggest that under ice nutrient and metal partitioning, flux and concentration distribution is highly dynamic in both time and space, and a complex interaction between SWI redox chemistry, hydrodynamics, and winter weather. These drivers control the biogeochemical evolution of the under ice system during the winter, with the potential to impact water quality and spring/summer ecosystem productivity.

  1. Determining D/L Ratios of Amino Acids Found in Ice Above Lake Vostok Using ESI/CIT Mass Spectroscopy

    NASA Technical Reports Server (NTRS)

    Tsapin, A.; Kanik, I.; Beegle, L. W.; Wu, L.; Cooks, R. G.

    2003-01-01

    Astrobiology is an area where longevity of (micro) organisms is of great interest. Cryospheres are common phenomena in the solar system, particularly on satellites, comets and asteroids, as well as at least some of the planets. Recent data from the Mars Global Surveyor mission suggest the possibility of permafrost or perhaps even liquid water under the Martian surface [2]. These environments may be the areas in which the probability of finding life is the highest. This issue is of concern due to the probable evolution of planetary environments such as that of Mars from more hospitable to less hospitable conditions over the history of the solar system. In addition, evaluation of the possible transfer of living organisms between planets via impact ejecta [3] is dependent on knowledge of the maximum time periods over which microorganisms can remain dormant and subsequently revive and reproduce.Amino acid racemization dating, or aminostratigraphy, has been used for many years to date biological systems, and has been examined as a possible biosignature detection technique for Mars. We have suggested using amino acid racemization as one of the most indicative biosignatures [4]. Only life systems produce preferential synthesis of L-amino acids versus D-amino acids. Almost all amino acids in terrestrial organisms can be found only in the L-enantiomeric form.We studied the level of amino acid racemization, specifically of aspartic acid, in permafrost samples from eastern Siberia. Also we analyzed samples of ice from borehole drilled to lake Vostok, Antarctica.

  2. Testing of SIR (a transformable robotic submarine) in Lake Tahoe for future deployment at West Antarctic Ice Sheet grounding lines of Siple Coast

    NASA Astrophysics Data System (ADS)

    Powell, R. D.; Scherer, R. P.; Griffiths, I.; Taylor, L.; Winans, J.; Mankoff, K. D.

    2011-12-01

    A remotely operated vehicle (ROV) has been custom-designed and built by DOER Marine to meet scientific requirements for exploring subglacial water cavities. This sub-ice rover (SIR) will explore and quantitatively document the grounding zone areas of the Ross Ice Shelf cavity using a 3km-long umbilical tether by deployment through an 800m-long ice borehole in a torpedo shape, which is also its default mode if operational failure occurs. Once in the ocean cavity it transforms via a diamond-shaped geometry into a rectangular form when all of its instruments come alive in its flight mode. Instrumentation includes 4 cameras (one forward-looking HD), a vertical scanning sonar (long-range imaging for spatial orientation and navigation), Doppler current meter (determine water current velocities), multi-beam sonar (image and swath map bottom topography), sub-bottom profiler (profile sub-sea-floor sediment for geological history), CTD (determine salinity, temperature and depth), DO meter (determine dissolved oxygen content in water), transmissometer (determine suspended particulate concentrations in water), laser particle-size analyzer (determine sizes of particles in water), triple laser-beams (determine size and volume of objects), thermistor probe (measure in situ temperatures of ice and sediment), shear vane probe (determine in situ strength of sediment), manipulator arm (deploy instrumentation packages, collect samples), shallow ice corer (collect ice samples and glacial debris), water sampler (determine sea water/freshwater composition, calibrate real-time sensors, sample microbes), shallow sediment corer (sample sea floor, in-ice and subglacial sediment for stratigraphy, facies, particle size, composition, structure, fabric, microbes). A sophisticated array of data handling, storing and displaying will allow real-time observations and environmental assessments to be made. This robotic submarine and other instruments will be tested in Lake Tahoe in September, 2011 and

  3. Millennial scale Record of Terrestrial Pliocene-Pleistocene warmth from Lake El'gygytgyn, NE Russia: What does it mean for Greenland's Ice Sheet history?

    NASA Astrophysics Data System (ADS)

    Brigham-Grette, J.; Melles, M.; Minyuk, P.; DeConto, R.; Koenig, S. J.; Andreev, A.; Tarasov, P.; Nowaczyk, N.; Wennrich, V.; Cook, T.; Snyder, J. A.; Gebhardt, C.; Coletti, A. J.

    2012-12-01

    The Pliocene-Pleistocene climate evolution of the Arctic must have modulated the glacial history of Greenland. Yet what is known from the terrestrial stratigraphy of Arctic climate change comes from sites that are spatially and temporally fragmented. In 2009, International Continental Deep drilling at Lake El'gygytgyn (67o30' N, 172 o 05' E) recovered lacustrine sediments dating back to 3.58 Ma that now provide the first time-continuous Pliocene-Pleistocene Arctic paleoclimate record of alternating glacial-interglacial change. The warmest and wettest Pliocene interval of the lake record occurs from ~3.58-3.34 Ma and is dominated by exceptional tree pollen implying July temperatures nearly 7-8o C warmer than today with nearly ~3 times the annual precipitation. Atmospheric CO2 levels are estimated to have been 360 to 400 ppm implying exceptionally high climate sensitivity and polar amplification. In fact, pollen spectra and modern analog analysis show an unbroken persistence of summers much warmer and wetter than the last interglacial, MIS 5e until nearly 2.2 Ma with abrupt changes in boreal forest composition at 2.715-2.695, 2.56 ad 2.53 Ma punctuated by an abrupt change in precipitation at 2.94-2.91 Ma. Modeling sensitivity experiments using 300 and 400 ppm CO2 are consistent with sustained forests at Lake El'gygytgyn during this interval and restricted glacial ice over Greenland in both cold and warm boreal summer orbits especially for the PRISM interval. Extreme warmth in the Mid Pliocene Arctic occurs at the same time ANDRILL results suggest the West Antarctic Ice Sheet was non-existent. The Lake El'gygytgyn record includes a strong M2 cooling event in a number of proxies at ~3.3 Ma, with conditions comparable to the early Holocene Thermal Maximum, but not glacial climates. Our reconstructions do not preclude the existence of a Greenland Ice sheet during M2 but are unfavorable for the initiation of ice over parts of North America until after 3.0 Ma. This has

  4. Glacial areas, lake areas, and snowlines from 1975 to 2012: status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    NASA Astrophysics Data System (ADS)

    Hanshaw, M. N.; Bookhagen, B.

    2013-02-01

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 144 multi-spectral satellite images spanning almost four decades, from 1975-2012, to obtain glacial and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. In a second step, we have estimated the snowline altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: first, since 1988 glacial areas throughout the Cordillera Vilcanota have been declining at a rate of 5.46 ± 1.70 km2 yr-1 (22-yr average, 1988-2010, with 95% confidence interval). The Quelccaya Ica Cap, specifically, has been declining at a rate of 0.67 ± 0.18 km2 yr-1 since 1980 (31-yr average, 1980-2011, also with 95% confidence interval); Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2011) as compared to the preceding decade (1990-2000); Third, the snowline of the Quelccaya Ice Cap is retreating to higher elevations as glacial areas decrease, by a total of almost 300 m between its lowest recorded elevation in 1989 and its highest in 1998; and fourth, as glacial regions have decreased, 61% of lakes connected to glacial watersheds have shown a roughly synchronous increase in lake area, while 84% of lakes not connected to glacial watersheds have remained stable or have declined in area. Our new and detailed data on glacial and lake areas over 37 yr provide an important spatiotemporal assessment of climate variability in this area. These data can be integrated into further studies

  5. Glacial areas, lake areas, and snow lines from 1975 to 2012: status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    NASA Astrophysics Data System (ADS)

    Hanshaw, M. N.; Bookhagen, B.

    2014-03-01

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 158 multi-spectral satellite images spanning almost 4 decades, from 1975 to 2012, to obtain glacial- and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. Additionally, we have estimated the snow-line altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: first, since 1988 glacial areas throughout the Cordillera Vilcanota (1988 glacial area: 361 km2) have been declining at a rate of 3.99 ± 1.15 km2 yr-1 (22 year average, 1988-2010, with 95% confidence interval (CI), n = 8 images). Since 1980, the Quelccaya Ice Cap (1980 glacial area: 63.1 km2) has been declining at a rate of 0.57 ± 0.10 km2 yr-1 (30 year average, 1980-2010, with 95% CI, n = 14). Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2010) as compared to the preceding decade (1988-1999) with an average increase from 37.5 to 42.3 × 10-3 km2 yr-1 km-2 (13%). Third, glaciers with lower median elevations are declining at higher rates than those with higher median elevations. Specifically, glaciers with median elevations around 5200 m a.s.l. are retreating to higher elevations at a rate of ~1 m yr-1 faster than glaciers with median elevations around 5400 m a.s.l. Fourth, as glacial regions have decreased, 77% of lakes connected to glacial watersheds have either remained stable or shown a roughly synchronous increase in lake area, while 42% of lakes not connected to glacial

  6. Glacial areas, lakes areas, and snowlines from 1975-2012: Status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    NASA Astrophysics Data System (ADS)

    Hanshaw, Maiana Natania

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 144 multi-spectral satellite images spanning almost four decades, from 1975-2012, to obtain glacial and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. In a second step, we have estimated the snowline altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: First, since 1988 glacial areas throughout the Cordillera Vilcanota have been declining at a rate of 5.46 +/- 1.70 km2/yr (22-year average, 1988-2010, with 95 % confidence interval). The Quelccaya Ica Cap, specifically, has been declining at a rate of 0.67 +/- 0.18 km2/yr since 1980 (31-year average, 1980-2011, also with 95 % confidence interval); Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2011) as compared to the preceding decade (1990-2000); Third, the snowline of the Quelccaya Ice Cap is retreating to higher elevations as glacial areas decrease, by a total of almost 300 m between its lowest recorded elevation in 1989 and its highest in 1998; and fourth, as glacial regions have decreased, 61 % of lakes connected to glacial watersheds have shown a roughly synchronous increase in lake area, while 84 % of lakes not connected to glacial watersheds have remained stable or have declined in area. Our new and detailed data on glacial and lake areas over 37 years provide an important spatiotemporal assessment of climate variability in this area. These data can be integrated into further

  7. David Morrison on Lake Vostok

    NASA Video Gallery

    Dr. David Morrison discusses the implications of research possibilities at Lake Vostok, one of the largest subglacial lakes located over two miles beneath the ice in Antarctica. The lake has been c...

  8. Two Decades of Variability in Nutrient Budgets for Ice-Covered, Closed Basin Lakes in the McMurdo Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Truhlar, A. M.; Gooseff, M. N.; McKnight, D. M.; Priscu, J. C.; Doran, P. T.

    2013-12-01

    The McMurdo Dry Valleys (MCM) of Antarctica represent one of the world's driest deserts. A collection of permanently ice-covered lakes in the MCM provide an important refuge for microorganisms. Thus, it is of interest to understand the nutrient dynamics of these lakes and how these dynamics have changed over time. One to two decade-long records of physical, chemical, and biological characteristics in the East Lobe of Lake Bonney (ELB), Lake Fryxell (FRX), and Lake Hoare (HOR) allowed for development of annual nutrient budgets and analysis of possible causes of variability. Annual nutrient budgets were built by accounting for total seasonal streamflow and average seasonal nutrient concentration in streamflow, as well as nutrient diffusion across the chemocline, which roughly coincides with the bottom of the photic zone. Unaccounted-for changes in nutrient content were assumed to be caused by processes internal to the lake. Changes to the proportion of lake volume in the photic zone, seasonal streamflow, and biological activity, represented by chlorophyll-a (CHL) concentration, were considered as potential explanations. For all three lakes, nutrient diffusion either into or out of the photic zone was minimal compared to nutrient inputs from streamflow. The sole exception to this was NH4 inputs to FRX; for eight of the nine years considered, diffusive inputs of NH4 to the photic zone were greater than streamflow inputs. In most cases, internal processes appeared to dominate over streamflow inputs; this is likely because seasonal streamflow represented less than 8% of the photic zone volume in all three lakes. Three exceptions to this trend were the phosphorus budget in ELB, and the NH4 and NO3 budgets in HOR; in these cases, streamflow inputs represented a notable portion of the annual nutrient budgets. The MCM lakes decreased in volume from the early 1990s to the early 2000s; they have since been increasing in volume. The volume of the photic zone was positively

  9. Effect of permafrost thaw on the dynamics of lakes recharged by ice-jam floods: case study in Yukon Flats, Alaska

    USGS Publications Warehouse

    Steve M. Jepsen,; Walvoord, Michelle Ann; Voss, Clifford I.; Rover, Jennifer R.

    2015-01-01

    Large river floods are a key water source for many lakes in fluvial periglacial settings. Where permeable sediments occur, the distribution of permafrost may play an important role in the routing of floodwaters across a floodplain. This relationship is explored for lakes in the discontinuous permafrost of Yukon Flats, interior Alaska, using an analysis that integrates satellite-derived gradients in water surface elevation, knowledge of hydrogeology, and hydrologic modeling. We observed gradients in water surface elevation between neighboring lakes ranging from 0.001 to 0.004. These high gradients, despite a ubiquitous layer of continuous shallow gravel across the flats, are consistent with limited groundwater flow across lake basins resulting from the presence of permafrost. Permafrost impedes the propagation of floodwaters in the shallow subsurface and constrains transmission to “fill-and-spill” over topographic depressions (surface sills), as we observed for the Twelvemile-Buddy Lake pair following a May 2013 ice-jam flood on the Yukon River. Model results indicate that permafrost table deepening of 1–11 m in gravel, depending on watershed geometry and subsurface properties, could shift important routing of floodwater to lakes from overland flow (fill-and-spill) to shallow groundwater flow (“fill-and-seep”). Such a shift is possible in the next several hundred years of ground surface warming, and may bring about more synchronous water level changes between neighboring lakes following large flood events. This relationship offers a potentially useful tool, well-suited to remote sensing, for identifying long-term changes in shallow groundwater flow resulting from thawing of permafrost.

  10. Formation of mega-scale glacial lineations on the Dubawnt Lake Ice Stream bed: 1. size, shape and spacing from a large remote sensing dataset

    NASA Astrophysics Data System (ADS)

    Stokes, C. R.; Spagnolo, M.; Clark, C. D.; Ó Cofaigh, C.; Lian, O. B.; Dunstone, R. B.

    2013-10-01

    Mega-scale glacial lineations (MSGLs) are the largest flow parallel bedforms produced by ice sheets and are formed beneath rapidly-flowing ice streams. Knowledge of their characteristics and genesis is likely to result in an improved understanding of the rate at which ice and sediment are discharged by ice sheets, but there is little consensus as to how they are formed and there are few quantitative datasets of their characteristics with which to formulate or test hypotheses. This paper presents the results of a remote sensing survey of ˜46,000 bedforms on the Dubawnt Lake palaeo-ice stream bed, focussing on a central transect of 17,038 that includes highly elongate bedforms previously described as MSGLs. Within this transect, lineations exceed 10 km in length (max. >20 km) and 23% have elongation ratios >10:1 (max. 149:1). Highly elongate features are interspersed with much shorter drumlin-like features, but longer bedforms are typically narrower, suggesting that their length develops more quickly than, or at the expense of, their width. Bedforms are broadly symmetrical in plan-form and have a preferred lateral spacing of 50-250 m, which implies a regular, rather than random, pattern of corrugations. Comparison with drumlins reveals that the more attenuated MSGLs simply extend the 'tail' of the distribution of data, rather than plotting as a separate population. Taken together, this supports the idea of a subglacial bedform continuum primarily controlled by ice velocity, but existing hypotheses of MSGL formation are either not supported, or are insufficiently developed to explain our observations. Rather, we conclude that, under conditions of rapid ice flow, MSGLs attain their great length relatively quickly (decades) through a probable combination of subglacial deformation, which attenuates ridges, and erosional processes that removes material from between them.

  11. A late Holocene metal record of Andean climate and anthropogenic activity in lake sediments near Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Beal, S. A.; Kelly, M. A.; Jackson, B. P.; Stroup, J. S.; Osterberg, E. C.

    2011-12-01

    The tropical hypothesis maintains that major changes in global climate are motivated by phenomena based at tropical latitudes. Evidence for this hypothesis lies in: modern-day observations of El Niño Southern Oscillation (ENSO); East African lake sediment records of Intertropical Convergence Zone (ITCZ) position that precede high-latitude changes; and the potential for ITCZ shifts to cause major CO2 degassing from the Southern Ocean. In order to improve the understanding of these phenomena we present an ~1800 year record of atmospheric metal deposition in a lake sediment core near Quelccaya Ice Cap, Peru (13.9 °S). In June, 2010 we collected a 1.45 meter-long core from Yanacocha - a small, closed-basin tarn that has been isolated from glacial input since ~11,200 BP. The chronology for the core is based on 4 of 6 AMS 14C dates on aquatic macrofossils and one sharp Zr/Ti anomaly at 36 cm, likely derived from the 350 BP eruption of Huaynaputina. We completely digested organic-rich core samples at 1 cm resolution using HNO3, HCl, and HF in a closed-vessel microwave system, and then analyzed the digestates for 67 metals by inductively coupled plasma mass spectrometry. Here we show fluxes of lithogenic metals (Fe, Nb, Ti, and Zr) that reflect changes in wind strength and aridity, fluxes of lithogenic metal isotopes (REEs and Pb) that reflect wind direction, and enrichment factors (EFs) of metals (Ag, As, Cd, Cu, Hg, and Pb) that reflect anthropogenic activity. Five episodic peaks in lithogenic metal fluxes, centered around 1800, 1300, 900, 600, and 100 yrs BP, are thought to result from either drier or windier conditions, potentially caused by a northern ITCZ position or a more persistent El Niño state. The provenance of atmospheric deposition, evidenced by REE ratios (light REEs / heavy REEs), suggest that high lithogenic fluxes are associated with a change in wind direction, possibly caused by a change in the ENSO state, which will be explored with forthcoming Pb

  12. From dwindling ice to headwater lakes: Could dams replace glaciers in the European Alps?

    NASA Astrophysics Data System (ADS)

    Farinotti, Daniel; Pistocchi, Alberto; Huss, Matthias

    2016-04-01

    Environments significantly influenced by the presence of seasonal snow or glaciers are hotspots regarding the impacts on water availability in response to expected climate change. With warmer temperatures, both the duration and the spatial extent of the seasonal snow cover are projected to decrease, and glaciers are expected to retreat substantially. This is anticipated to have important influences on water availability, including changes in the seasonality of runoff, as well as an overall reduction in water yields from high-mountain catchments. Here we present an estimate for the potential of mitigating projected changes in seasonal water availability from melting glaciers by managing runoff through reservoirs. We compute the water volume that, in future, is expected to be in excess during winter and spring time, and transfer it seasonally through temporary storage in order to mitigate the water deficits during summer. Projections for future runoff evolution are retrieved from the glacier evolution model GloGEM, forced with ensembles of temperature and precipitation time series derived within CIMIP5. For the European Alps we estimate that by the end of the century, about 1 km3 of water from presently glacierized surfaces could be seasonally reallocated in order to mitigate expected changes. On average, the strategy could offset up to 25 % of the changes in summer runoff from presently glacierized surfaces. A first order approach suggests, moreover, that the retention volume potentially available in the areas becoming deglacierized is in excess of the volume required for achieving the maximal possible mitigation by more than one order of magnitude. Obviously, the proposed strategy cannot compensate for the reduction in annual runoff caused by glacier ice depletion. Our estimates indicate that by 2070-2099, 0.73 ± 0.67 km3 a-1 of this non-renewable component of the water cycle could be missing in Alpine water supplies.

  13. Present-day crustal deformation along the Magallanes-Fagnano Fault System in Tierra del Fuego from repeated GPS observations

    NASA Astrophysics Data System (ADS)

    Mendoza, L.; Perdomo, R.; Hormaechea, J. L.; Del Cogliano, D.; Fritsche, M.; Richter, A.; Dietrich, R.

    2011-03-01

    The present-day deformation of the earth crust in the Argentine part of Tierra del Fuego main island (southernmost South America) is here investigated based on repeated geodetic GPS observations. The island is traversed by the active transform boundary between the South American and Scotia tectonic plates, represented by the Magallanes-Fagnano fault system. Since 1993 a regional network comprising to date 29 GPS sites has been observed almost every year. The complete set of accumulated observations was processed using the Bernese GPS software and state-of-the-art processing strategies and models. The utilization of homogeneous GPS products resulting from a reprocessing of the global IGS network warrants a stable realization of a global reference frame. For each GPS site 3-D positions and linear velocities with error estimates were obtained. A strain analysis of the horizontal velocity components revealed the zones of major deformation activity. A 30-km-wide deformation belt centred on the main trace of the fault system was identified. This belt is bordered to the north (South America) and south (Scotia) by geodynamically stable zones, which move horizontally with a relative average velocity of 4.4 ± 0.6 (east) and -0.3 ± 0.4 (north) mm a-1. Within the deformation belt a maximum strain rate in the order of 0.25 μstrain per year has been detected. A pronounced change in the deformation style from transtension (east) to transpression (west) is observed. The area of predominating shortening of the crust coincides with a local rotation minimum and relative uplift. Throughout the period covered by the GPS observations the displacements and deformations occurred to be linear with time.

  14. Diversity and Expression of RubisCO Genes in a Perennially Ice-Covered Antarctic Lake during the Polar Night Transition

    PubMed Central

    Kong, Weidong; Ream, David C.; Priscu, John C.

    2012-01-01

    The autotrophic communities in the lakes of the McMurdo Dry Valleys, Antarctica, have generated interest since the early 1960s owing to low light transmission through the permanent ice covers, a strongly bimodal seasonal light cycle, constant cold water temperatures, and geographical isolation. Previous work has shown that autotrophic carbon fixation in these lakes provides an important source of organic matter to this polar desert. Lake Bonney has two lobes separated by a shallow sill and is one of several chemically stratified lakes in the dry valleys that support year-round biological activity. As part of an International Polar Year initiative, we monitored the diversity and abundance of major isoforms of RubisCO in Lake Bonney by using a combined sequencing and quantitative PCR approach during the transition from summer to polar winter. Form ID RubisCO genes related to a stramenopile, a haptophyte, and a cryptophyte were identified, while primers specific for form IA/B RubisCO detected a diverse autotrophic community of chlorophytes, cyanobacteria, and chemoautotrophic proteobacteria. Form ID RubisCO dominated phytoplankton communities in both lobes of the lake and closely matched depth profiles for photosynthesis and chlorophyll. Our results indicate a coupling between light availability, photosynthesis, and rbcL mRNA levels in deep phytoplankton populations. Regulatory control of rbcL in phytoplankton living in nutrient-deprived shallow depths does not appear to be solely light dependent. The distinct water chemistries of the east and west lobes have resulted in depth- and lobe-dependent variability in RubisCO diversity, which plays a role in transcriptional activity of the key gene responsible for carbon fixation. PMID:22492447

  15. Vernal Crater, SW Arabia Terra: MSL Candidate with Extensively Layered Sediments, Possible Lake Deposits, and a Long History of Subsurface Ice

    NASA Technical Reports Server (NTRS)

    Oehler, Dorothy Z.; Allen, Carlton C.

    2007-01-01

    Vernal Crater is a Mars Science Laboratory (MSL) landing site candidate providing relatively easy access to extensively layered sediments as well as potential lake deposits. Sediments of Vernal Crater are 400-1200 m below those being investigated by Opportunity in Meridiani Planum, and as such would allow study of significantly older geologic units, if Vernal Crater were selected for MSL. The location of Vernal Crater in SW Arabia Terra provides exceptional scientific interest, as rampart craters and gamma-ray spectrometer (GRS) data from the region suggest a long history of ice/fluids in the subsurface. The potential value of this MSL candidate is further enhanced by reports of atmospheric methane over Arabia, as any insight into the source of that methane would significantly increase our understanding of Mars. Finally, should MSL survive beyond its prime mission, the gentle slope within Vernal Crater would provide a route out of the crater for study of the once ice/fluid-rich plains.

  16. New lakes in deglaciating high-mountain areas: Regional intercomparison of current and future risks from impact waves due to rock/ice avalanches in the Swiss Alps

    NASA Astrophysics Data System (ADS)

    Schaub, Y.; Huggel, C.; Serraino, M.; Haeberli, W.

    2012-04-01

    location of the largest damage potentials, driving forces of different spatial development scenarios for the Swiss Alps will be implemented in a land allocation model for the Swiss Alps. By bringing together hazard, exposure and vulnerability analyses, a risk assessment for the entire Swiss Alps regarding lake-outburst floods triggered by impacts of rock/ice avalanches can be conducted for today, the middle of the century and even beyond.

  17. Deglaciation of the James Bay Lowlands and Northern Abitibi: Insights on Late-Glacial Ice Readvances and Drainage of Glacial Lake Ojibway

    NASA Astrophysics Data System (ADS)

    Roy, M.; Veillette, J. J.; Dell'Oste, F.

    2008-12-01

    Deglaciation in the James Bay region was marked by the scission of the Laurentide ice sheet margin into the Hudson dome to the west and the New-Quebec dome to the east, which subsequently retreated northward, in contact with the waters of glacial Lake Ojibway. Previous work based on air photo-interpretation and field observations indicate that ice retreat in the region was highly dynamic, with the occurrence of at least three ice readvances into the basin of Lake Objiway prior to the final deglaciation, and the incursion of the post- glacial Tyrrell Sea at ~8 ka (Hardy, 1976). Our investigations of stratigraphic sections exposed along the Harricana, Nottaway, Broadback, and Rupert rivers in the lowlands of Quebec indicate that only part of these events are preserved in these sedimentary sequences. The base of the late-glacial sequence generally consists of a carbonate-bearing clayey readvance till that lies on older tills of the last glacial cycle, or truncate Lake Ojibway glaciolacustrine sediments. None of the sections showed more than one till of the three (Cochrane I, Rupert, Cochrane II) readvances documented in the region. Nonetheless, an extensive Ojibway sequence located just south from the lowlands shows three intervals with significant increases in detrital carbonate and coarsening of the varve sequence that can be linked with these late-glacial surges. In the lowlands, the readvance till is commonly capped by a thick sequence of Ojibway varves. The contact between the glaciolacustrine sediments and the overlying Tyrrell Sea marine deposits is marked by a ~50 cm-thick horizon composed at the bottom of thinly laminated reddish and grey silt beds containing abundant rounded clay balls, overlain by coarser silts and fine sands with disseminated clasts. This horizon is here interpreted to reflect the abrupt drainage of Lake Ojibway. Recent radiocarbon dating of mollusks and foraminifers from the uppermost part of this horizon yielded ages of ~7.7 ka and ~8

  18. Life and death of ice cliffs and lakes on debris covered glaciers - insights from a new dataset from the Nepalese Himalaya

    NASA Astrophysics Data System (ADS)

    Steiner, Jakob; Buri, Pascal; Miles, Evan; Ragettli, Silvan; Pellicciotti, Francesca

    2016-04-01

    Numerous studies suggest that supraglacial ice cliffs and lakes could be one contributing factor to relatively high overall ablation rates on debris covered glaciers. While some studies have quantified backwasting rates, developments over the larger scale have not yet been assessed. Field work and earlier studies during three seasons in the Langtang catchment in the Nepalese Himalaya has given some insights into how these landforms develop, from initial emergence to persistence and disappearance. From 6 sets of concurrent high-resolution satellite imagery and DEMs between 2006 and 2015 and an additional image from 1974, we assembled an extensive dataset of these landforms on all glaciers in the catchment, including nearly 4000 individual lakes and cliffs. We show that ice cliffs appear in combination with lakes or without and there are lakes that are not bordered by a cliff. Numbers vary strongly between seasons, especially as lakes show strong seasonal variability. There are furthermore different types of cliff forms - circular, lateral and longitudinal - that give an indication of their formation process. Circular cliffs form with either collapsing subglacial channels or overdeepenings caused by water accumulating on the surface, while lateral cliffs are likely associated with underlying crevasses. Some of the cliff and lake systems remain at the same location on-glacier over a number of years, while most move with the whole glacier body down valley. From the DEMs determine preferential slopes and expositions of the cliffs in the catchment which have been shown to be essential aspects in explaining the backwasting process. In combination with field observations from one glacier, where most of these types were present, we can infer development processes of a number of systems over the whole catchment. It is also apparent that densities of these landforms vary greatly over the glacier surface, which can be explained with velocities or underlying bed topography in

  19. Peat accumulation in drained thermokarst lake basins in continuous, ice-rich permafrost, northern Seward Peninsula, Alaska

    USGS Publications Warehouse

    Jones, Miriam C.; Grosse, Guido; Jones, Benjamin M.; Anthony, Katey Walter

    2012-01-01

    Thermokarst lakes and peat-accumulating drained lake basins cover a substantial portion of Arctic lowland landscapes, yet the role of thermokarst lake drainage and ensuing peat formation in landscape-scale carbon (C) budgets remains understudied. Here we use measurements of terrestrial peat thickness, bulk density, organic matter content, and basal radiocarbon age from permafrost cores, soil pits, and exposures in vegetated, drained lake basins to characterize regional lake drainage chronology, C accumulation rates, and the role of thermokarst-lake cycling in carbon dynamics throughout the Holocene on the northern Seward Peninsula, Alaska. Most detectable lake drainage events occurred within the last 4,000 years with the highest drainage frequency during the medieval climate anomaly. Peat accumulation rates were highest in young (50–500 years) drained lake basins (35.2 g C m−2 yr−1) and decreased exponentially with time since drainage to 9 g C m−2 yr−1 in the oldest basins. Spatial analyses of terrestrial peat depth, basal peat radiocarbon ages, basin geomorphology, and satellite-derived land surface properties (Normalized Difference Vegetation Index (NDVI); Minimum Noise Fraction (MNF)) from Landsat satellite data revealed significant relationships between peat thickness and mean basin NDVI or MNF. By upscaling observed relationships, we infer that drained thermokarst lake basins, covering 391 km2 (76%) of the 515 km2 study region, store 6.4–6.6 Tg organic C in drained lake basin terrestrial peat. Peat accumulation in drained lake basins likely serves to offset greenhouse gas release from thermokarst-impacted landscapes and should be incorporated in landscape-scale C budgets.

  20. Luminescence chronology of non-glacial sediments in Changeable Lake, Russian High Arctic, and implications for limited Eurasian ice-sheet extent during the LGM

    NASA Astrophysics Data System (ADS)

    Berger, Glenn W.; Melles, Martin; Banerjee, Debabrata; Murray, Andrew S.; Raab, Alexandra

    2004-07-01

    A 10.5 m core from Changeable Lake in the Severnaya Zemlya Archipelago just north of the Taymyr Peninsula intersects ca. 30 cm of diamicton at its base, interpreted as a basal till. Because the upper 10.13 m of this core consists of non-glacial sediments, a maximum numeric age for these non-glacial sediments would provide a clear lower limit to the timing of the last glaciation in the area of Changeable Lake. Radiocarbon (14C) dating of several materials from this core yielded widely scattered results. Consequently we applied photonic dating to sediments above the diamicton. The experimental single-aliquot-regenerative (SAR) dose fine-grain method was applied to two samples, using the double SAR approach. With one exception, these fine-grain SAR results and the results of application of the SAR method to sand-sized quartz grains from two samples, at ca. 9.95 m and ca. 10.05 m depth, are discrepant with age estimates from the multi-aliquot infrared-photon-stimulated luminescence (IR-PSL) method applied to fine grains. Multi-aliquot IR-PSL dating of 10 samples produces ages increasing monotonically from ca. 4 ka at 2 m to 53 +/- 4 ka at 9.97 m. These self-consistent multi-aliquot IR-PSL ages, along with limiting 14C ages of >47 ka at ca. 10 m, provide direct evidence that glacial ice did not advance over this lake basin during the Last Glacial Maximum, and thus delimit the northeastern margin of the Barents-Kara Sea ice-sheet to somewhere west of this archipelago. The last regional glaciation probably occurred during marine isotope stage (MIS) 4 or earlier. Copyright

  1. The Imprints of the Solar Activity during the Little Ice Age and the Medieval Climatic Anomaly in SW Anatolia from Lake Sediments

    NASA Astrophysics Data System (ADS)

    Bauchi Danladi, Iliya; Akçer-Ön, Sena

    2016-04-01

    Due to the variability of the Little Ice Age (LIA) and Medieval Climatic Anomaly (MCA), several climatic forcing mechanisms have been invoked to enlighten the issue. The focus of this study is on the influence of the solar activity proxy (Total Solar Irradiance) during the LIA and MCA in a high altitude Lake Salda in south-western Anatolia. In order to understand this, we recovered 5 gravity cores with various lengths and from various locations in the lake. We used high-resolution multi proxy approach which includes Itrax XRF scanner at a resolution of 2mm, Multi Sensor Core Logger (MSCL) at a resolution of 5 mm and TOC/TIC analysis at a resolution of 30 mm. 210Pb-137Cs methods were employed for dating and afterwards were tuned with solar activity proxy (Total Solar Irradiance) data for age improvement. As a result, the sediment records cover the last millennium. We have observed the effect of the solar activity throughout the LIA and MCA in Lake Salda, with wet and dry spells corresponding to high and low TSI respectively. In addition, the Dalton Minimum, Maunder Minimum, Spörer Minimum, Wolf Minimum, the Medieval Maximum and the Oort Minimum have been observed.

  2. Linking the10Be continental record of Lake Baikal to marine and ice archives of the last 50 ka: Implication for the global dust-aerosol input

    USGS Publications Warehouse

    Aldahan, A.; Possnert, G.; Peck, J.; King, J.; Colman, S.

    1999-01-01

    We present here a 10Be profile from the continental sediments of Lake Baikal (the world's largest fresh water lake), which, for the first time, shows the ??? 40 ka 10Be enhancement and a pattern that strongly matches those from the marine and ice records for the last 50 ka. This finding provides a new horizon for global and regional correlation of continental archives. Additionally, our VADM-predicted 10Be production confirms and further strengthens a common global cause (geomagnetic field intensity) for the change in atmospheric 10Be over the last 50 ka. We also show that most of the 10Be inventory to the lake has been provided by riverine input, but with a significant addition from direct precipitation and dust-aerosol fallout. We estimate a higher dust-aerosol contribution of 10Be during the Holocene and interstadial stage 3 (22-50 ka) as compared with the glacial period (12-22 ka). Copyright 1999 by the American Geophysical Union.

  3. Hydrogeophysical characterisation of ice-marginal moraines, with reference to moraine dam stability, Miage Glacial Lake, Italy

    NASA Astrophysics Data System (ADS)

    Thompson, S. S.; Kulessa, B.

    2010-12-01

    In mountain regions, potentially hazardous glacial lakes are becoming increasingly common as a consequence of climatically driven glacier recession. Lakes can expand rapidly in the space between downwasting or receding glacier fronts and terminal or lateral moraines, and are prone to catastrophic drainage if the moraine dam is breached. Lake drainage can have severe impacts on both fragile mountain ecosystems and local economies. In addition to the moraine-dammed lakes currently in existence, it is likely that many more will form in the coming decades as more glaciers cross the threshold required for rapid lake expansion. A key factor in assessing the stability and future evolution of such systems is a better understanding of the subsurface structure and hydrology of the moraine dams. Here results are presented from electrical geophysical work carried out across the breach moraine complex at the Miage Glacial Lake, Italy. A combination of induced polarisation, normalised induced polarisation and self potentials have been used to characterise the local water table and to identify the subsurface connections between two moraines dammed glacial lakes. The results not only show the depth and distribution of subsurface flow but also the preferential flow pathways, indicating areas of maximum discharge. The results highlight the areas of the moraines where hydrological processes are causing internal degradation and impacting upon the longer term stability of the system. This model therefore, can be employed on much larger systems where the risk of outburst has far greater consequences.

  4. Dynamic Coupling of Iron, Manganese, and Phosphorus Behavior in Water and Sediment of Shallow Ice-Covered Eutrophic Lakes.

    PubMed

    Schroth, Andrew W; Giles, Courtney D; Isles, Peter D F; Xu, Yaoyang; Perzan, Zachary; Druschel, Gregory K

    2015-08-18

    Decreasing duration and occurrence of northern hemisphere ice cover due to recent climate warming is well-documented; however, biogeochemical dynamics underneath the ice are poorly understood. We couple time-series analyses of water column and sediment water interface (SWI) geochemistry with hydrodynamic data to develop a holistic model of iron (Fe), manganese (Mn), and phosphorus (P) behavior underneath the ice of a shallow eutrophic freshwater bay. During periods of persistent subfreezing temperatures, a highly reactive pool of dissolved and colloidal Fe, Mn, and P develops over time in surface sediments and bottom waters due to reductive dissolution of Fe/Mn(oxy)hydroxides below the SWI. Redox dynamics are driven by benthic O2 consumption, limited air-water exchange of oxygen due to ice cover, and minimal circulation. During thaw events, the concentration, distribution and size partitioning of all species changes, with the highest concentrations of P and "truly dissolved" Fe near the water column surface, and a relatively well-mixed "truly dissolved" Mn and "colloidal" Fe profile due to the influx of geochemically distinct river water and increased circulation. The partitioning and flux of trace metals and phosphorus beneath the ice is dynamic, and heavily influenced by climate-dependent physical processes that vary in both time and space.

  5. Insight into the geology of the East Antarctic hinterland: a study of sediment inclusions from ice cores of the Lake Vostok borehole

    USGS Publications Warehouse

    Leitchenkov, G.L.; Belyatsky, B.V.; Rodionov, N.V.; Sergeev, S.A.

    2007-01-01

    refrozen from the lake water. This ice layer contains random sediment inclusions, eight of which have been studied using state-of the-art analytical techniques. Six inclusions comprise soft aggregates consisting mainly of clay-mica minerals and micron-sized quartz grains while two others are solid clasts of fine-grained cemented rocks. The largest rock clast consists of poorly-rounded quartz and minor amounts of accessory minerals and is classified as quartzose siltstone. More than twenty grains of zircon and monazite have been identified in this siltstone and dated by SIMS SHRIMP-II. Two age clusters have been recognized for these detrital grains, in the ranges 0.8−1.2 Ga and 1.6−1.8 Ga. The compositions of the rock clasts suggest that the bedrock situated to the west of Lake Vostok is sedimentary. The age data on the detrital accessory minerals suggest that the provenance of these sedimentary rocks − the Gamburtsev Mountains and Vostok Subglacial Highlands, is mainly represented by Paleoproterozoic and MesoproterozoicNeoproterozoic crustal provinces

  6. The Interdependence of Lake Ice and Climate in Central North America. [correlation between freeze/than cycles of lakes and regional weather variations

    NASA Technical Reports Server (NTRS)

    Jelacic, A. J. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. A comparison of lake freeze transition zone migration with the movement of large pressure centers reveals the following consistencies: (1) polar continental cyclones originate within and/or travel along the trend of the transition zone; (2) polar continental anticyclones fail to cross the transition zone; (3) polar outbreak anticyclones pass through the transition zone, apparently unaffected. In addition, storm centers associated with the transition zone undergo significant intensification manifest by a deepening of the pressure through and increased precipitation outside the zone.

  7. Methane Gradients Associated With a Small, Deep Lake on the Ice-Free Margin of Western Greenland

    NASA Astrophysics Data System (ADS)

    Webster, K. D.; White, J. R.; Young, S.; Pratt, L. M.

    2012-12-01

    Northern wetlands are thought to contribute from < 6 - 25 % of Earth's annual atmospheric methane inputs. However, despite extensive areal coverage, little is known about methane emissions from small lakes (< 540 ha) in the Arctic. We report initial results of methane concentrations in air, soil and water column associated with Potentilla Lake (informal name), near Kangerlussuaq, Greenland (N 67° 04.888', W 050° 21.084'). Potentilla Lake has a surface area of 1.8 ha and a maximum depth of 8 m. We measured methane concentrations in the hypolimnion, metalimnion, and epilimnion of Potentilla Lake as well as surrounding soils and atmosphere. The dissolved methane concentrations in the water column were collected using a gas stripping method. Methane concentrations in atmosphere, soils and water were analyzed on a Los Gatos Instruments MCIA employing cavity enhanced absorption spectroscopy with off-axis ICOS technology. Additionally, a Boreal open-path laser (OPL) for methane was used to measure the average atmospheric methane concentration across the long axis (283 m) of the lake for a period of 37 hrs from 12:00 pm on July 20, to 1:00 am on July 22, 2012. The laser was 0.8 m above the surface of the lake and micrometeorology was collected with a Davis Vantage Vue meteorological station. The OPL measured atmospheric methane concentrations once every minute and 13 seconds while the meteorological station recorded conditions every minute. A linear interpolation was used to pair the data for statistical analysis in order to correct for the differing data collection rates. Hypolimnetic methane concentration was 6000 ppm, metalimnetic concentration was 22 ppm, and the concentration of methane in the epilimnion was 62 ppm. Atmospheric methane concentrations from the OPL ranged from 1.56 to 1.85 ppmv over the duration of the measurement period and showed statistically significant relationships with wind speed (y = -0.0237x + 1.7241, P << 0.01, R2 = 0.19) and humidity (y = 0

  8. Subglacial sediment provenance and transport in West Antarctica from micropaleontologic analysis of Subglacial Lake Whillans and the upstream sectors of the Whillans and Kamb ice streams

    NASA Astrophysics Data System (ADS)

    Scherer, Reed; Coenen, Jason; Warny, Sophie

    2014-05-01

    The WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) project recovered sediment cores from Subglacial Lake Whillans (SLW) in West Antarctica. We report preliminary micropaleontological analyses of SLW sediments, augmented by analysis of sediments previously recovered from beneath the upstream camps of the Whillans Ice Stream (WIS) and Kamb Ice Stream (KIS). Microfossils in these sediments (notably diatoms, sponge spicules, and organic-walled palynomorphs), include information regarding sediment transport, subglacial physical processes and ice sheet history. Absolute abundance (particles per gram dry sediment) of identifiable diatoms and diatom fragments in different size classes were calculated to compare and contrast each environment. Sponge spicules are being analyzed for taphonomic effects from subglacial transport and shearing. Palynomorphs are analyzed for abundance, diversity, and source rock ages. In SLW the upper 30 cm is softer and more water-rich than the underlying sediments. However, no statistically significant variation in microfossil and fragment abundance or taphonomy is noted in these diamictons, which is in agreement with the stratigraphic homogeneity evident from geochemical and geological analyses performed to date. SLW contains 1.52x106 to 1.13x107 diatom fragments per gram, compared with 6.43x106 to 4.63x108 at upstream WIS and 6.13 107 to 1.58x108 at KIS. Whole diatoms are orders of magnitude lower in concentration. Low abundance and poor preservation of diatoms and spicules at SLW suggests relatively long distance transport from their marine sediment source, with evidence of high shear strain, following the subglacial shearing index of Scherer et al. (2004). Upper Miocene diatoms dominate all samples analyzed, though older and younger diatoms are noted as well. The WIS samples exhibit the highest diversity of diatoms, including Paleogene freshwater diatoms. KIS sediments have the highest abundance of whole diatoms, but they

  9. Aeolian sand preserved in Silver Lake: a new signal of Holocene high stands of Lake Michigan

    USGS Publications Warehouse

    Fisher, Timothy G.; Loope, Walter L.

    2005-01-01

    Aeolian sand within lake sediment from Silver Lake, Michigan can be used as a proxy for the timing of high lake levels of Lake Michigan.We demonstrate that the sand record from Silver Lake plotted as percent weight is in-phase with the elevation curve of Lake Michigan since the mid-Holocene Nipissing Phase. Because fluctuations in Lake Michigan's lake level are recorded in beach ridges, and are a response to climate change, the aeolian sand record within Silver Lake is also a proxy for climate change. It appears that increases in dune activity and lake sand are controlled by similar climatic shifts that drive fluctuations in lake level of Lake Michigan. High lake levels destabilize coastal bluffs that drive dune sand instability, and along with greater wintertime storminess, increase niveo-aeolian transport of sand across lake ice. The sand is introduced into the lake each spring as the ice cover melts.

  10. Evidence for stagnation of the Harvard sublobe (Lake Michigan lobe) in Northeastern Illinois, U.S.A., from 24 000 to 17 600 BP and subsequent tundra-like ice-marginal paleoenvironments from 17 600 to 15 700 BP

    USGS Publications Warehouse

    Curry, B. Brandon; Yansa, C.H.

    2004-01-01

    Glacial deposits of the last glaciation associated with the Harvard sublobe (Lake Michigan lobe) in northeastern Illinois, U.S.A., occur between sediment with dateable organics. The lower organics include fragments of Picea sp. as young as 24 000 ?? 270 BP. The supraglacial organics occur sparsely in laminated silt and fine sand in landforms that are positioned relatively high on the landscape, such as deposits from ice-walled lakes. These terrestrial organics yield ages that are 2500 to 1300 14C years older than organics at the base of sediment successions in nearby kettle basins. Basal 14C ages from four upland sites range from 17 610 ?? 270 to 16 120 ?? 80 BP. Our revised time-distance diagram of the Harvard sublobe now reflects a period of stagnation from 24 000 to about 17 600 BP. The supraglacial lacustrine silt yielded plant macrofossil assemblages of primarily tundra plants, including Salix herbacea and Dryas integrifolia. These plants likely grew in supraglacial and ice-marginal environments. The ostracode fauna include Cytherissa lacustris and Limnocythere friabilis. Geomorphic relations and ostracode ecology indicate that more than 17 m of ice buttressed some of the supraglacial lakes.

  11. Northeast sector of the Greenland Ice Sheet to undergo the greatest inland expansion of supraglacial lakes during the 21st century

    NASA Astrophysics Data System (ADS)

    Ignéczi, Ádám.; Sole, Andrew J.; Livingstone, Stephen J.; Leeson, Amber A.; Fettweis, Xavier; Selmes, Nick; Gourmelen, Noel; Briggs, Kate

    2016-09-01

    The formation and rapid drainage of supraglacial lakes (SGL) influences the mass balance and dynamics of the Greenland Ice Sheet (GrIS). Although SGLs are expected to spread inland during the 21st century due to atmospheric warming, less is known about their future spatial distribution and volume. We use GrIS surface elevation model and regional climate model outputs to show that at the end of the 21st century (2070-2099) approximately 9.8 ± 3.9 km3 (+113% compared to 1980-2009) and 12.6 ± 5 km3 (+174%) of meltwater could be stored in SGLs under moderate and high representative concentration pathways (RCP 4.5 and 8.5), respectively. The largest increase is expected in the northeastern sector of the GrIS (191% in RCP 4.5 and 320% in RCP 8.5), whereas in west Greenland, where the most SGLs are currently observed, the future increase will be relatively moderate (55% in RCP 4.5 and 68% in RCP 8.5).

  12. Luminescence Chronology for the Formation of Glacial Lake Calgary, Southern Alberta, Canada: Age Constraints for the Initiation of the Late Pleistocene Retreat of the Laurentide Ice Sheet from its Western Margin

    NASA Astrophysics Data System (ADS)

    Munyikwa, K.; Rittenour, T. M.

    2014-12-01

    Glacial Lake Calgary in southern Alberta, Canada, was a Late Pleistocene proglacial lake that formed along the southwest margin of the Laurentide Ice Sheet (LIS), dammed by the retreating ice sheet margin. Attempts to constrain the age of the lake using radiocarbon methods have been hampered by the lack of datable organic material. In an effort to apply an alternative chronometer, this study uses two optically stimulated luminescence (OSL) dating approaches to date fine grained sand and silt that were deposited in the lake during its existence. OSL dating determines the depositional ages of sediments by measuring the energy from ionizing radiation that is stored in mineral grains such as quartz and feldspar. Dividing the stored energy, also referred to as the paleodose, by the rate at which the dose accumulated, allows an age to be ascertained. In one method applied in this study, the paleodose stored in the feldspar component of the sediment is determined using normalized infrared stimulated luminescence signals acquired using a portable OSL reader. In the second method, blue optically stimulated luminescence signals obtained from quartz separates from the sediment by employing a regular OSL reader and standard protocols are used to determine the paleodose. After correcting the feldspar data for anomalous fading, the age results from the two dating approaches are compared. The ages signify a time period by which the LIS had retreated from the study area and, hence, serve as constraints for the initiation of the retreat of the ice sheet from its western limit. Advantages and limitations of the dating methods are briefly discussed. Constraining the chronology of the retreat of the LIS from western Canada allows for a better understanding of the driving forces behind ice sheet retreat. Secondly, assigning a temporal scale to the postglacial evolution of the environment of the region permits a better insight into the dynamics of the physical and biological

  13. Late Pleistocene ice margin fluctuations in the Nahanni National Park-UNESCO World Heritage Site and their impact on glacial lake formation and architecture of drainage systems across the Yukon-NWT continental divide

    NASA Astrophysics Data System (ADS)

    Duk-Rodkin, A.; Barendregt, R. W.

    2009-12-01

    In the late Pleistocene the southern Mackenzie region was glaciated by ice masses from a Cordilleran and continental source (Laurentide). Stratigraphic and geomorphologic evidence indicate that the two glaciers occupied this region at different times during the Late Pleistocene. The continental ice sheet advanced over the foothills and up major valleys reaching its maximum extent, ca. 30 ka. B. P. This took place when Cordilleran glaciers were in their initial stages of development. The Laurentide Ice Sheet blocked the drainage of the South Nahanni River near Virginia Falls, forming a glacial lake which inundated an area of approximately 900 km2 at its maximum stand, and had an outlet to the southwest, across the continental divide into the Yukon Territory and eventually into the Pacific Ocean. Lacustrine sediments at various sites reach thicknesses ranging from 110 to 120 metres, at an elevation of around 700 m. Cordilleran glaciers advanced eastward and approximately 5000 years later blocked this southwestward drainage, rerouting it to the east and north along the Mackenzie Mountain front. The drainage was confined between the mountains and continental ice margin where it incised major canyons into the limestone bedrock, and produced a spectacular karst landscape, which today forms part of the Nahanni National Park. During the retreat of the Laurentide and advance of Cordilleran glaciers, glacial Lake Nahanni cut an outlet to the east at First Canyon. This outlet drained into a continuous northbound network of marginal meltwater channels joining the north-flowing drainage that eventually reached the Arctic Ocean, and during further retreat of the ice sheet established the Mackenzie River in its modern location. The presence of Laurentide ice in this region is evidenced by large granite boulders carried from the Canadian Shield. Erratics are found up to 100 km west of the mountain front. Neotectonic activity in the area is interpreted from exposures such as those

  14. Proglacial lakes: character, behaviour and geological importance

    NASA Astrophysics Data System (ADS)

    Carrivick, Jonathan L.; Tweed, Fiona S.

    2013-10-01

    Proglacial lakes are ubiquitous within the Quaternary record and can provide exceptional breadth and depth of palaeoenvironmental information. Present deglaciation is increasing the number and size of proglacial lakes around the world. This study provides a synthesis of knowledge on proglacial lake character and behaviour and critically evaluates the importance of proglacial lakes from a geological perspective. We show how ‘ice-marginal' or ‘ice-contact' lakes and other distal proglacial lakes can be distinguished from each other by geomorphological, sedimentological, chemical and biological characteristics. The key controls on proglacial lake geomorphology and sedimentology are outlined and discussed. Proglacial lakes can exacerbate mountain glacier and ice sheet margin ablation via mechanical and thermal stresses, but very large lakes can moderate summer air temperatures and relatively retard summer ice ablation. Proglacial lakes interrupt meltwater flux and are very efficient sediment traps. Hydrological routing and consequent geomorphological activity can be radically modified by sudden drainage of proglacial lakes and resultant glacial lake outburst floods; exceptionally large proglacial lake drainages affected global ocean circulation and global climate during the Quaternary. Overall, analyses of proglacial lakes can provide a valuable insight into (i) patterns, character and behaviour of mountain glaciers, ice sheets and glaciations, and (ii) the impacts of past, present and future deglaciation.

  15. An integrated approach to the remote sensing of floating ice

    NASA Technical Reports Server (NTRS)

    Campbell, W. J.; Ramseier, R. O.; Weeks, W. F.; Gloersen, P.

    1976-01-01

    Review article on remote sensing applications to glaciology. Ice parameters sensed include: ice cover vs open water, ice thickness, distribution and morphology of ice formations, vertical resolution of ice thickness, ice salinity (percolation and drainage of brine; flushing of ice body with fresh water), first-year ice and multiyear ice, ice growth rate and surface heat flux, divergence of ice packs, snow cover masking ice, behavior of ice shelves, icebergs, lake ice and river ice; time changes. Sensing techniques discussed include: satellite photographic surveys, thermal IR, passive and active microwave studies, microwave radiometry, microwave scatterometry, side-looking radar, and synthetic aperture radar. Remote sensing of large aquatic mammals and operational ice forecasting are also discussed.

  16. THERMODYNAMICS OF PARTIALLY FROZEN COOLING LAKES

    SciTech Connect

    Garrett, A.; Casterline, M.; Salvaggio, C.

    2010-01-05

    The Rochester Institute of Technology (RIT) collected visible, SWIR, MWIR and LWIR imagery of the Midland (Michigan) Cogeneration Ventures Plant from aircraft during the winter of 2008-2009. RIT also made ground-based measurements of lake water and ice temperatures, ice thickness and atmospheric variables. The Savannah River National Laboratory (SRNL) used the data collected by RIT and a 3-D hydrodynamic code to simulate the Midland cooling lake. The hydrodynamic code was able to reproduce the time distribution of ice coverage on the lake during the entire winter. The simulations and data show that the amount of ice coverage is almost linearly proportional to the rate at which heat is injected into the lake (Q). Very rapid melting of ice occurs when strong winds accelerate the movement of warm water underneath the ice. A snow layer on top of the ice acts as an insulator and decreases the rate of heat loss from the water below the ice to the atmosphere above. The simulated ice cover on the lake was not highly sensitive to the thickness of the snow layer. The simplicity of the relationship between ice cover and Q and the weak responses of ice cover to snow depth over the ice are probably attributable to the negative feedback loop that exists between ice cover and heat loss to the atmosphere.

  17. Inter- and intra-annual chemical variability during the ice-free season in lakes with different flushing rates and acid deposition histories.

    PubMed

    Arnott, Shelley E; Dillon, Peter J; Somers, Keith; Keller, Bill

    2003-01-01

    Quantifying chemical variability in different lake types is important for the assessment of both chemical and biological responses to environmental change. For monitoring programs that emphasize a large number of lakes at the expense of frequent samples, high variability may influence how representative single samples are of the average conditions of individual lakes. Intensive temporal data from long-term research sites provide a unique opportunity to assess chemical variability in lakes with different characteristics. We compared the intra- and inter-annual variability of four acidification related variables (Gran alkalinity, pH, sulphate concentration, and total base cation concentration) in four lakes with different flushing rates and acid deposition histories. Variability was highest in lakes with high flushing rates and was not influenced by historic acid deposition in our study lakes. This has implications for the amount of effort required in monitoring programs. Lakes with high flushing rates will require more frequent sampling intervals than lakes with low flushing rates. Consideration of specific lake types should be included in the design of monitoring programs.

  18. The contribution of ice cover to sediment resuspension in a shallow temperate lake: possible effects of climate change on internal nutrient loading.

    PubMed

    Niemistö, Juha P; Horppila, Jukka

    2007-01-01

    The effect of ice cover on sediment resuspension and internal total P (Tot-P) loading was studied in the northern temperate Kirkkojärvi basin in Finland. The gross sedimentation and resuspension rates were estimated with sediment traps during ice-cover and ice-free periods. After ice break, the average gross sedimentation rate increased from 1.4 to 30.0 g dw m(-2) d(-1). Resuspension calculations showed clearly higher values after ice break as well. Under ice cover, resuspension ranged from 50 to 78% of the gross sedimentation while during the ice-free period it constituted from 87 to 97% of the gross sedimentation. Consequently, the average resuspension rate increased from 1.0 g dw m(-2) d(-1) under ice-cover to 27.0 g dw m(-2) d(-1) after thaw, indicating the strong effect of ice cover on sediment resuspension. To estimate the potential effect of climate change on internal P loading caused by resuspension we compared the Tot-P loading calculations between the present climate and the climate with doubled atmospheric CO2 concentration relative to the present day values (ice cover reduced from current 165 to 105 d). The annual load increased from 7.4 to 9.4 g m(-2). In conclusion, the annual internal Tot-P loading caused by resuspension will increase by 28% in the Kirkkojärvi basin if the 2xCO2 climate scenario comes true.

  19. Multiple Nonconformities in Ice-Walled Lake Successions Indicate Periods with Cold Summers (24.4 - 22.5 ka, 21.1 - 19.2 ka, 18.5 - 18.1 ka) during the Last Deglaciation in Northeastern Illinois, USA

    NASA Astrophysics Data System (ADS)

    Curry, B. B.

    2014-12-01

    Unprecedented age control on many last glacial stratigraphic units and morainal ice-margin positions are interpreted from AMS radiocarbon ages of tundra plant macrofossils archived in low-relief ice-walled lake plain (IWLP) deposits the Lake Michigan Lobe (south-central Laurentide Ice Sheet). IWLPs are periglacial features that formed on morainal dead-ice permafrost. Lacustrine sediment, and the fossils contained therein, had physical and temporal proximity to the glacier which formed the underlying moraine. In modern ice-walled lakes, as the lake's ice cover begins to melt, moats form which allows access of sloughing tundra-mantled active layer sediment (soil) into the lakes. Multiple AMS ages from two sites with proglacial sediment buried by glacial max LIS diamicton, and IWLPs reveal evidence of episodic plant growth and sedimentation including ca. 24.0 to 24.4 ka (post Shelby Phase), 22.5 to 21.1 ka (post Livingston Phase), 18.1 to 17.4 ka (post Woodstock Phase). Although presently based on negative evidence, the associated nonconformities (listed in title) indicate periods when cold conditions did not promote development of the estival moat. Although the evidence does not preclude tundra growth during the cold summers, there was little landscape modification due to limited thawing of the active layer. At approximately the onset of the 19.2-18.5 "warm" period, at least two large deglacial discharge events flooded the Fox and Kankakee tributary valleys of the Illinois River. The latter, known as the Kankakee Torrent, occurred at 19.05 - 18.85 ka (σ1 range) at the Oswego channel complex. The temporal coincidence of the torrents and sedimentation in ice-walled lakes suggests that the post-Livingston Phase nonconformity (21.1 - 19.2 ka) was a period of lessened meltwater discharge through subglacial conduits (tunnel valleys) as the frozen toe promoted formation of subglacial lakes, buildup of pore-water pressures, and the release of subglacial water as "torrents

  20. Lake trout in northern Lake Huron spawn on submerged drumlins

    USGS Publications Warehouse

    Riley, Stephen C.; Binder, Thomas; Wattrus, Nigel J.; Faust, Matthew D.; Janssen, John; Menzies, John; Marsden, J. Ellen; Ebener, Mark P.; Bronte, Charles R.; He, Ji X.; Tucker, Taaja R.; Hansen, Michael J.; Thompson, Henry T.; Muir, Andrew M.; Krueger, Charles C.

    2014-01-01

    Recent observations of spawning lake trout Salvelinus namaycush near Drummond Island in northern Lake Huron indicate that lake trout use drumlins, landforms created in subglacial environments by the action of ice sheets, as a primary spawning habitat. From these observations, we generated a hypothesis that may in part explain locations chosen by lake trout for spawning. Most salmonines spawn in streams where they rely on streamflows to sort and clean sediments to create good spawning habitat. Flows sufficient to sort larger sediment sizes are generally lacking in lakes, but some glacial bedforms contain large pockets of sorted sediments that can provide the interstitial spaces necessary for lake trout egg incubation, particularly if these bedforms are situated such that lake currents can penetrate these sediments. We hypothesize that sediment inclusions from glacial scavenging and sediment sorting that occurred during the creation of bedforms such as drumlins, end moraines, and eskers create suitable conditions for lake trout egg incubation, particularly where these bedforms interact with lake currents to remove fine sediments. Further, these bedforms may provide high-quality lake trout spawning habitat at many locations in the Great Lakes and may be especially important along the southern edge of the range of the species. A better understanding of the role of glacially-derived bedforms in the creation of lake trout spawning habitat may help develop powerful predictors of lake trout spawning locations, provide insight into the evolution of unique spawning behaviors by lake trout, and aid in lake trout restoration in the Great Lakes.

  1. Mars Express MARSIS Radar: A Prediction of the Effect of Overlying Ice on Detecting Polar Basal Lakes and Inter-Glacial Aquifers

    NASA Technical Reports Server (NTRS)

    Farrell, W. M.; Plaut, J. J.; Gurnett, D. A.; Picardi, G.

    2004-01-01

    The penetration of the MARSIS radar signal into the polar ice mass is modeled to determine the capability of the instrument to locate sub-glacial aquifers. As a ground penetrating radar, the orbiting MARSIS transmits a signal greater than 1 W between 1-5 MHz. In this work we will investigate the effect of ice conductive losses on the radar-detection of subsurface aquifers. Based on wave propagation analysis, it is found that for a bulk ice conductivity below 10-5 S/m, conductive losses in the medium are not significant. However, if the bulk ice conductivity is relatively large (greater than 10-5 S/m), the reflected signal from any deep aquifer will be absorbed as it propagates in the lossy ice medium limiting the probing depth.

  2. Waterway Ice Thickness Measurements

    NASA Technical Reports Server (NTRS)

    1978-01-01

    The ship on the opposite page is a U. S. Steel Corporation tanker cruising through the ice-covered waters of the Great Lakes in the dead of winter. The ship's crew is able to navigate safely by plotting courses through open water or thin ice, a technique made possible by a multi-agency technology demonstration program in which NASA is a leading participant. Traditionally, the Great Lakes-St. Lawrence Seaway System is closed to shipping for more than three months of winter season because of ice blockage, particularly fluctuations in the thickness and location of ice cover due to storms, wind, currents and variable temperatures. Shippers have long sought a system of navigation that would allow year-round operation on the Lakes and produce enormous economic and fuel conservation benefits. Interrupted operations require that industrial firms stockpile materials to carry them through the impassable months, which is costly. Alternatively, they must haul cargos by more expensive overland transportation. Studies estimate the economic benefits of year-round Great Lakes shipping in the hundreds of millions of dollars annually and fuel consumption savings in the tens of millions of gallons. Under Project Icewarn, NASA, the U.S. Coast Guard and the National Oceanic Atmospheric Administration collaborated in development and demonstration of a system that permits safe year-round operations. It employs airborne radars, satellite communications relay and facsimile transmission to provide shippers and ships' masters up-to-date ice charts. Lewis Research Center contributed an accurate methods of measuring ice thickness by means of a special "short-pulse" type of radar. In a three-year demonstration program, Coast Guard aircraft equipped with Side-Looking Airborne Radar (SLAR) flew over the Great Lakes three or four times a week. The SLAR, which can penetrate clouds, provided large area readings of the type and distribution of ice cover. The information was supplemented by short

  3. State of Michigan, Lake Michigan and Lake Huron, USA

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Almost the entire state of Michigan and most of lakes Michigan and Huron (45.5N, 83.5W) can be seen in this single midwinter view of the Great Lakes region. Even under midwinter snow and ice conditions, the distinctive silhouette of the state of Michigan is still easy to recognize as well as Lakes Michigan and Huron. The Canadian province of Ontario is at the top of the scene on the opposite shore from Michigan.

  4. Rapid discharge connects Antarctic subglacial lakes.

    PubMed

    Wingham, Duncan J; Siegert, Martin J; Shepherd, Andrew; Muir, Alan S

    2006-04-20

    The existence of many subglacial lakes provides clear evidence for the widespread presence of water beneath the East Antarctic ice sheet, but the hydrology beneath this ice mass is poorly understood. Such knowledge is critical to understanding ice flow, basal water transfer to the ice margin, glacial landform development and subglacial lake habitats. Here we present ice-sheet surface elevation changes in central East Antarctica that we interpret to represent rapid discharge from a subglacial lake. Our observations indicate that during a period of 16 months, 1.8 km3 of water was transferred over 290 km to at least two other subglacial lakes. While viscous deformation of the ice roof above may moderate discharge, the intrinsic instability of such a system suggests that discharge events are a common mode of basal drainage. If large lakes, such as Lake Vostok or Lake Concordia, are pressurizing, it is possible that substantial discharges could reach the coast. Our observations conflict with expectations that subglacial lakes have long residence times and slow circulations, and we suggest that entire subglacial drainage basins may be flushed periodically. The rapid transfer of water between lakes would result in large-scale solute and microbe relocation, and drainage system contamination from in situ exploration is, therefore, a distinct risk. PMID:16625193

  5. Determining lake surface water temperatures worldwide using a tuned one-dimensional lake model (FLake, v1)

    NASA Astrophysics Data System (ADS)

    Layden, Aisling; MacCallum, Stuart N.; Merchant, Christopher J.

    2016-06-01

    A tuning method for FLake, a one-dimensional (1-D) freshwater lake model, is applied for the individual tuning of 244 globally distributed large lakes using observed lake surface water temperatures (LSWTs) derived from along-track scanning radiometers (ATSRs). The model, which was tuned using only three lake properties (lake depth, snow and ice albedo and light extinction coefficient), substantially improves the measured mean differences in various features of the LSWT annual cycle, including the LSWTs of saline and high altitude lakes, when compared to the observed LSWTs. Lakes whose lake-mean LSWT persists below 1 °C for part of the annual cycle are considered to be seasonally ice-covered. For trial seasonally ice-covered lakes (21 lakes), the daily mean and standard deviation (2σ) of absolute differences between the modelled and observed LSWTs are reduced from 3.07 °C ± 2.25 °C to 0.84 °C ± 0.51 °C by tuning the model. For all other trial lakes (14 non-ice-covered lakes), the improvement is from 3.55 °C ± 3.20 °C to 0.96 °C ± 0.63 °C. The post tuning results for the 35 trial lakes (21 seasonally ice-covered lakes and 14 non-ice-covered lakes) are highly representative of the post-tuning results of the 244 lakes. For the 21 seasonally ice-covered lakes, the modelled response of the summer LSWTs to changes in snow and ice albedo is found to be statistically related to lake depth and latitude, which together explain 0.50 (R2adj, p = 0.001) of the inter-lake variance in summer LSWTs. Lake depth alone explains 0.35 (p = 0.003) of the variance. Lake characteristic information (snow and ice albedo and light extinction coefficient) is not available for many lakes. The approach taken to tune the model, bypasses the need to acquire detailed lake characteristic values. Furthermore, the tuned values for lake depth, snow and ice albedo and light extinction coefficient for the 244 lakes provide some guidance on improving FLake LSWT modelling.

  6. Great Lakes' regional climate regimes

    NASA Astrophysics Data System (ADS)

    Kravtsov, Sergey; Sugiyama, Noriyuki; Roebber, Paul

    2016-04-01

    We simulate the seasonal cycle of the Great Lakes' water temperature and lake ice using an idealized coupled lake-atmosphere-ice model. Under identical seasonally varying boundary conditions, this model exhibits more than one seasonally varying equilibrium solutions, which we associate with distinct regional climate regimes. Colder/warmer regimes are characterized by abundant/scarce amounts of wintertime ice and cooler/warmer summer temperatures, respectively. These regimes are also evident in the observations of the Great Lakes' climate variability over recent few decades, and are found to be most pronounced for Lake Superior, the deepest of the Great Lakes, consistent with model predictions. Multiple climate regimes of the Great Lakes also play a crucial role in the accelerated warming of the lakes relative to the surrounding land regions in response to larger-scale global warming. We discuss the physical origin and characteristics of multiple climate regimes over the lakes, as well as their implications for a longer-term regional climate variability.

  7. Skylab floating ice experiment

    NASA Technical Reports Server (NTRS)

    Campbell, W. J. (Principal Investigator); Ramseier, R. O.; Weaver, R. J.; Weeks, W. F.

    1975-01-01

    The author has identified the following significant results. Coupling of the aircraft data with the ground truth observations proved to be highly successful with interesting results being obtained with IR and SLAR passive microwave techniques, and standard photography. Of particular interest were the results of the PMIS system which operated at 10.69 GHz with both vertical and horizontal polarizations. This was the first time that dual polarized images were obtained from floating ice. In both sea and lake ice, it was possible to distinguish a wide variety of thin ice types because of their large differences in brightness temperatures. It was found that the higher brightness temperature was invariably obtained in the vertically polarized mode, and as the age of the ice increases the brightness temperature increases in both polarizations. Associated with this change in age, the difference in temperature was observed as the different polarizations decreased. It appears that the horizontally polarized data is the most sensitive to variations in ice type for both fresh water and sea ice. The study also showed the great amount of information on ice surface roughness and deformation patterns that can be obtained from X-band SLAR observations.

  8. Tipping temperatures within Subglacial Lake Ellsworth, West Antarctica

    NASA Astrophysics Data System (ADS)

    Thoma, Malte; Grosfeld, Klaus; Mayer, Christoph; Smith, Andrew; Woodward, John

    2010-05-01

    One of the most remote and undiscovered regions on Earth are subglacial lakes. More than 275 of these lakes have been identified so far. However, from most lakes little more is known but the location or the lateral extent. Their inaccessibility increases the importance of numerical models to investigate the physical conditions in these environments. During the Southern Summer 2008/09, the British Antarctic Survey (BAS) performed field measurements in the Ellsworth Mountains, West Antarctica to survey Subglacial Lake Ellsworth. We apply a three-dimensional fluid-dynamics lake model on the geometry of this lake. We present results, indicating that Subglacial Lake Ellsworth has a unique temperature profile, constituted by the pressure induced by the ice thickness above as well as the slope of the ice-lake interface and compare this with the previously modelled Subglacial Lakes Vostok and Concordia. While Lake Vostok and Lake Concordia show a clear convective regime, driven by geothermal heating from the lakes bottom for the overall lake, the ice load on Lake Concordia constitutes a regime where the line of maximum water density crosses through the lake. This divides the lake into branches with completely different convective regimes Sensitivity studies for glacial and probable future scenarios, where the ice coverage might thin, are discussed.

  9. Biogeochemistry: Microbes eat rock under ice

    NASA Astrophysics Data System (ADS)

    Tranter, Martyn

    2014-08-01

    The first description of the microorganisms inhabiting a subglacial lake deep below the Antarctic ice sheet reveals some of the complex interactive metabolic processes that sustain these microbial communities. See Letter p.310

  10. On the nature of the dirty ice at the bottom of the GISP2 ice core

    USGS Publications Warehouse

    Bender, Michael L.; Burgess, Edward; Alley, Richard B.; Barnett, Bruce; Clow, Gary D.

    2010-01-01

    We present data on the triple Ar isotope composition in trapped gas from clean, stratigraphically disturbed ice between 2800 and 3040m depth in the GISP2 ice core, and from basal dirty ice from 3040 to 3053m depth. We also present data for the abundance and isotopic composition of O2 and N2, and abundance of Ar, in the basal dirty ice. The Ar/N2 ratio of dirty basal ice, the heavy isotope enrichment (reflecting gravitational fractionation), and the total gas content all indicate that the gases in basal dirty ice originate from the assimilation of clean ice of the overlying glacier, which comprises most of the ice in the dirty bottom layer. O2 is partly to completely depleted in basal ice, reflecting active metabolism. The gravitationally corrected ratio of 40Ar/38Ar, which decreases with age in the global atmosphere, is compatible with an age of 100-250ka for clean disturbed ice. In basal ice, 40Ar is present in excess due to injection of radiogenic 40Ar produced in the underlying continental crust. The weak depth gradient of 40Ar in the dirty basal ice, and the distribution of dirt, indicate mixing within the basal ice, while various published lines of evidence indicate mixing within the overlying clean, disturbed ice. Excess CH4, which reaches thousands of ppm in basal dirty ice at GRIP, is virtually absent in overlying clean disturbed ice, demonstrating that mixing of dirty basal ice into the overlying clean ice, if it occurs at all, is very slow. Order-of-magnitude estimates indicate that the mixing rate of clean ice into dirty ice is sufficient to maintain a steady thickness of dirty ice against thinning from the mean ice flow. The dirty ice appears to consist of two or more basal components in addition to clean glacial ice. A small amount of soil or permafrost, plus preglacial snow, lake or ground ice could explain the observations.

  11. On the nature of the dirty ice at the bottom of the GISP2 ice core

    NASA Astrophysics Data System (ADS)

    Bender, Michael L.; Burgess, Edward; Alley, Richard B.; Barnett, Bruce; Clow, Gary D.

    2010-11-01

    We present data on the triple Ar isotope composition in trapped gas from clean, stratigraphically disturbed ice between 2800 and 3040 m depth in the GISP2 ice core, and from basal dirty ice from 3040 to 3053 m depth. We also present data for the abundance and isotopic composition of O 2 and N 2, and abundance of Ar, in the basal dirty ice. The Ar/N 2 ratio of dirty basal ice, the heavy isotope enrichment (reflecting gravitational fractionation), and the total gas content all indicate that the gases in basal dirty ice originate from the assimilation of clean ice of the overlying glacier, which comprises most of the ice in the dirty bottom layer. O 2 is partly to completely depleted in basal ice, reflecting active metabolism. The gravitationally corrected ratio of 40Ar/ 38Ar, which decreases with age in the global atmosphere, is compatible with an age of 100-250 ka for clean disturbed ice. In basal ice, 40Ar is present in excess due to injection of radiogenic 40Ar produced in the underlying continental crust. The weak depth gradient of 40Ar in the dirty basal ice, and the distribution of dirt, indicate mixing within the basal ice, while various published lines of evidence indicate mixing within the overlying clean, disturbed ice. Excess CH 4, which reaches thousands of ppm in basal dirty ice at GRIP, is virtually absent in overlying clean disturbed ice, demonstrating that mixing of dirty basal ice into the overlying clean ice, if it occurs at all, is very slow. Order-of-magnitude estimates indicate that the mixing rate of clean ice into dirty ice is sufficient to maintain a steady thickness of dirty ice against thinning from the mean ice flow. The dirty ice appears to consist of two or more basal components in addition to clean glacial ice. A small amount of soil or permafrost, plus preglacial snow, lake or ground ice could explain the observations.

  12. Thermokarst lakes, drainage, and drained basins

    USGS Publications Warehouse

    Grosse, G.; Jones, B.; Arp, C.; Shroder, John F.

    2013-01-01

    Thermokarst lakes and drained lake basins are widespread in Arctic and sub-Arctic permafrost lowlands with ice-rich sediments. Thermokarst lake formation is a dominant mode of permafrost degradation and is linked to surface disturbance, subsequent melting of ground ice, surface subsidence, water impoundment, and positive feedbacks between lake growth and permafrost thaw, whereas lake drainage generally results in local permafrost aggradation. Thermokarst lakes characteristically have unique limnological, morphological, and biogeochemical characteristics that are closely tied to cold-climate conditions and permafrost properties. Thermokarst lakes also have a tendency toward complete or partial drainage through permafrost degradation and erosion. Thermokarst lake dynamics strongly affect the development of landscape geomorphology, hydrology, and the habitat characteristic of permafrost lowlands.

  13. Multifrequency passive microwave observation of saline ice grown in a tank

    NASA Technical Reports Server (NTRS)

    Grenfell, T. C.; Bell, D. L.; Lohanick, A. W.; Swift, C. T.; St.germain, K.

    1988-01-01

    Microwave radiometers observed artificial sea ice formation. During initial ice growth, interference fringe effects can occur both from changing ice thickness and snow or frost which may prove useful in interpreting layer thicknesses. A simulation of multiyear ice was attempted by allowing the ice to desalinate, but the resulting emissivity spectrum was more characteristic of lake ice. A multiyearlike spectrum was obtained when rubble was deposited on the ice surface.

  14. Viruses in Antarctic lakes

    NASA Technical Reports Server (NTRS)

    Kepner, R. L. Jr; Wharton, R. A. Jr; Suttle, C. A.; Wharton RA, J. r. (Principal Investigator)

    1998-01-01

    Water samples collected from four perennially ice-covered Antarctic lakes during the austral summer of 1996-1997 contained high densities of extracellular viruses. Many of these viruses were found to be morphologically similar to double-stranded DNA viruses that are known to infect algae and protozoa. These constitute the first observations of viruses in perennially ice-covered polar lakes. The abundance of planktonic viruses and data suggesting substantial production potential (relative to bacteria] secondary and photosynthetic primary production) indicate that viral lysis may be a major factor in the regulation of microbial populations in these extreme environments. Furthermore, we suggest that Antarctic lakes may be a reservoir of previously undescribed viruses that possess novel biological and biochemical characteristics.

  15. Passive microwave studies of frozen lakes

    NASA Technical Reports Server (NTRS)

    Hall, D. K.; Foster, J. L.; Rango, A.; Chang, A. T. C.

    1978-01-01

    Lakes of various sizes, depths and ice thicknesses in Alaska, Utah and Colorado were overflown with passive microwave sensors providing observations at several wavelengths. A layer model is used to calculate the microwave brightness temperature, T sub B (a function of the emissivity and physical temperatures of the object), of snowcovered ice underlain with water. Calculated T sub B's are comparable to measured T sub B's. At short wavelengths, e.g., 0.8 cm, T sub B data provide information on the near surface properties of ice covered lakes where the long wavelength, 21.0 cm, observations sense the entire thickness of ice including underlying water. Additionally, T sub B is found to increase with ice thickness. 1.55 cm observations on Chandalar Lake in Alaska show a T sub B increase of 38 K with an approximate 124 cm increase in ice thickness.

  16. Temperature Trends in Montane Lakes

    NASA Astrophysics Data System (ADS)

    Melack, J. M.; Sadro, S.; Jellison, R.

    2014-12-01

    Long-term temperature trends in lakes integrate hydrological and meteorological factors. We examine temperature trends in a small montane lake with prolonged ice-cover and large seasonal snowfall and in a large saline lake. Emerald Lake, located in the Sierra Nevada (California), is representative of high-elevation lakes throughout the region. No significant trend in outflow temperature was apparent from 1991to 2012. Snowfall in the watershed accounted for 93% of the variability in average summer lake temperatures. Mono Lake (California) lies in a closed, montane basin and is hypersaline and monomictic or meromictic. Temperature profiles have been collected from 1982 to 2010. In the upper water column, the July-August-September water temperatures increased 0.8-1.0°C over the 29 years. This rate of warming is less than published estimates based on satellite-derived skin temperatures and will discussed in the context of general limnological interpretation of temperature trends.

  17. Microbial life in ice and subglacial environments

    NASA Astrophysics Data System (ADS)

    Price, P. B.; Bramall, N.; Tatebe, K.

    2003-04-01

    Conditions for microbial life to exist in solid ice require the presence of liquid water and sources of energy and bioelements. In ice in thermal equilibrium, liquid water will exist in a three-dimensional network of micron-sized veins and in nanometer-thick films on mineral grains in ice. Ionic impurities lower the freezing temperature in the veins to as low as -95^oC. Depending on mineral type, the film on a grain surface will remain liquid down to ˜ -40^oC. The impurities provide both energy (via microbially catalyzed redox reactions) and bioelements. The maximum sustainable microbial population depends on metabolic rate, which in turn depends on species, temperature, and type and concentration of impurities in veins and surfaces. Microbes have been imaged by epifluorescence in veins in sea and Arctic lake ice and on grains in Dry Valleys lake ice. Indirect evidence exists for metabolism of microbes in Vostok glacial ice, in Greenland basal ice, and in Sajama (Bolivia) glacial ice. We will discuss several approaches to detection of microbes: epifluorescence microscopy of glacial ice at low temperature; fluorescence spectra taken with BSL (a new borehole logging instrument); fluorescence of microbes on surfaces of silt and volcanic ash in glacial ice; and in-situ cultivation of bacterial colonies at intersections of mineral grains and liquid veins in ice held in contact with a nutrient medium at subfreezing temperature. Based on measurements in the oligotrophic Lake Tahoe, BSL is sensitive to a concentration of ˜10^3 microbes cm-3, which may be adequate to detect life in Greenland ice and in Lake Vostok. A miniaturized version could be used to search for life in Martian permafrost and in diapirs in Europan ice.

  18. Simulation of Heavy Lake-Effect Snowstorms across the Great Lakes Basin by RegCM4

    NASA Astrophysics Data System (ADS)

    Notaro, M.; Zarrin, A.; Vavrus, S. J.; Bennington, V.

    2013-12-01

    A historical simulation (1976-2002) of the Abdus Salam International Centre for Theoretical Physics Regional Climate Model Version 4 (ICTP RegCM4), coupled to a one-dimensional lake model, is validated against observed lake ice cover and snowfall across the Great Lakes Basin. The model reproduces the broad temporal and spatial features of both variables in terms of spatial distribution, seasonal cycle, and interannual variability, including climatological characteristics of lake-effect snowfall, although the simulated ice cover is overly extensive largely due to the absence of lake circulations. A definition is introduced for identifying heavy lake-effect snowstorms in regional climate model output for all grid cells in the Great Lakes Basin, using criteria based on location, wind direction, lake ice cover, and snowfall. Simulated heavy lake-effect snowstorms occur most frequently downwind of the Great Lakes, particularly to the east of Lake Ontario and to the east and south of Lake Superior, and are most frequent in December-January. The mechanism for these events is attributed to an anticyclone over the central United States and related cold air outbreak for areas downwind of Lakes Ontario and Erie, in contrast to a nearby cyclone over the Great Lakes Basin and associated cold front for areas downwind of Lakes Superior, Huron, and Michigan. Projections of mid- and late-21st century lake-effect snowstorms in the Great Lakes Basin will be summarized, based on dynamically downscaled CMIP5 (Coupled Model Intercomparison Project Phase Five) simulations.

  19. Shrinking ice caps in the spotlight.

    PubMed

    Gross, Michael

    2014-10-01

    From the disappearing sea ice of the Arctic to the thriving microbial communities in subglacial lakes of Antarctica, the Earth's ice caps have often made the news in recent months and years, and polar science has emerged as being crucial to our understanding of our planet's biology and climate. Michael Gross reports.

  20. Europa's Great Lakes

    NASA Astrophysics Data System (ADS)

    Schmidt, B. E.; Blankenship, D. D.; Patterson, G. W.; Schenk, P. M.

    2012-04-01

    Unique to the surface of Europa, chaos terrain is diagnostic of the properties and dynamics of its icy shell. While models have suggested that partial melt within a thick shell or melt-through of a thin shell may form chaos, neither model has been able to definitively explain all observations of chaos terrain. However, we present a new model that suggests large melt lenses form within the shell and that water-ice interactions above and within these lenses drive the production of chaos. Our analysis of the geomorphology of Conamara Chaos and Thera Macula, was used to infer and test a four-stage lens-collapse chaos formation model: 1) Thermal plumes of warm, pure ice ascend through the shell melting the impure brittle ice above, producing a lake of briny water and surface down draw due to volume reduction. 2) Surface deflection and driving force from the plume below hydraulically seals the water in place. 3) Extension of the brittle ice lid generates fractures from below, allowing brines to enter and fluidize the ice matrix. 4) As the lens and now brash matrix refreeze, thermal expansion creates domes and raises the chaos feature above the background terrain. This new "lense-collapse" model indicates that chaos features form in the presence of a great deal of liquid water, and that large liquid water bodies exist within 3km of Europa's surface comparable in volume to the North American Great Lakes. The detection of shallow subsurface "lakes" implies that the ice shell is recycling rapidly and that Europa may be currently active. In this presentation, we will explore environments on Europa and their analogs on Earth, from collapsing Antarctic ice shelves to to subglacial volcanos in Iceland. I will present these new analyses, and describe how this new perspective informs the debate about Europa's habitability and future exploration.

  1. Imaging radar observations of frozen Arctic lakes

    NASA Technical Reports Server (NTRS)

    Elachi, C.; Bryan, M. L.; Weeks, W. F.

    1976-01-01

    A synthetic aperture imaging L-band radar flown aboard the NASA CV-990 remotely sensed a number of ice-covered lakes about 48 km northwest of Bethel, Alaska. The image obtained is a high resolution, two-dimensional representation of the surface backscatter cross section, and large differences in backscatter returns are observed: homogeneous low returns, homogeneous high returns and/or low returns near lake borders, and high returns from central areas. It is suggested that a low return indicates that the lake is frozen completely to the bottom, while a high return indicates the presence of fresh water between the ice cover and the lake bed.

  2. Glacioisostasy and Lake-Level Change at Moosehead Lake, Maine

    USGS Publications Warehouse

    Balco, G.; Belknap, D.F.; Kelley, J.T.

    1998-01-01

    Reconstructions of glacioisostatic rebound based on relative sea level in Maine and adjacent Canada do not agree well with existing geophysical models. In order to understand these discrepancies better, we investigated the lake-level history of 40-km-long Moosehead Lake in northwestern Maine. Glacioisostasy has affected the level of Moosehead Lake since deglaciation ca. 12,500 14C yr B.P. Lowstand features at the southeastern end and an abandoned outlet at the northwestern end of the lake indicate that the lake basin was tilted down to the northwest, toward the retreating ice sheet, by 0.7 m/km at 10,000 14C yr B.P. Water level then rose rapidly in the southeastern end of the lake, and the northwestern outlet was abandoned, indicating rapid relaxation of landscape tilt. Lowstand features at the northwestern end of the lake suggest that the lake basin was tilted to the southeast at ca. 8750 14C yr B.P., possibly as the result of a migrating isostatic forebulge. After 8000 14C yr B.P., water level at the southeastern end was again below present lake level and rose gradually thereafter. We found no evidence suggesting that postglacial climate change significantly affected lake level. The rebound history inferred from lake-level data is consistent with previous interpretations of nearby relative sealevel data, which indicate a significantly steeper and faster-moving ice-proximal depression and ice-distal forebulge than geophysical models predict. ?? 1998 University of Washington.

  3. Lake Life.

    ERIC Educational Resources Information Center

    Ohrn, Deborah Gore, Ed.

    1993-01-01

    This quarterly publication of the State Historical Society of Iowa features articles and activities for elementary school students. This summer issue focuses on the topic of lake life. The issue includes the following features: (1) "Where the Lakes Are Map"; (2) "Letter from the Lake"; (3) "Lake People"; (4) "Spirit Lake"; (5) "Lake Manawa"; (6)…

  4. Thickness of tropical ice and photosynthesis on a snowball Earth

    NASA Technical Reports Server (NTRS)

    McKay, C. P.

    2000-01-01

    On a completely ice-covered "snowball" Earth the thickness of ice in the tropical regions would be limited by the sunlight penetrating into the ice cover and by the latent heat flux generated by freezing at the ice bottom--the freezing rate would balance the sublimation rate from the top of the ice cover. Heat transfer models of the perennially ice-covered Antarctic dry valley lakes applied to the snowball Earth indicate that the tropical ice cover would have a thickness of 10 m or less with a corresponding transmissivity of > 0.1%. This light level is adequate for photosynthesis and could explain the survival of the eukaryotic algae.

  5. Thickness of tropical ice and photosynthesis on a snowball Earth.

    PubMed

    McKay, C P

    2000-07-15

    On a completely ice-covered "snowball" Earth the thickness of ice in the tropical regions would be limited by the sunlight penetrating into the ice cover and by the latent heat flux generated by freezing at the ice bottom--the freezing rate would balance the sublimation rate from the top of the ice cover. Heat transfer models of the perennially ice-covered Antarctic dry valley lakes applied to the snowball Earth indicate that the tropical ice cover would have a thickness of 10 m or less with a corresponding transmissivity of > 0.1%. This light level is adequate for photosynthesis and could explain the survival of the eukaryotic algae.

  6. Ice911 Research: Preserving and Rebuilding Multi-Year Ice

    NASA Astrophysics Data System (ADS)

    Field, L. A.; Chetty, S.; Manzara, A.

    2013-12-01

    A localized surface albedo modification technique is being developed that shows promise as a method to increase multi-year ice using reflective floating materials, chosen so as to have low subsidiary environmental impact. Multi-year ice has diminished rapidly in the Arctic over the past 3 decades (Riihela et al, Nature Climate Change, August 4, 2013) and this plays a part in the continuing rapid decrease of summer-time ice. As summer-time ice disappears, the Arctic is losing its ability to act as the earth's refrigeration system, and this has widespread climatic effects, as well as a direct effect on sea level rise, as oceans heat, and once-land-based ice melts into the sea. We have tested the albedo modification technique on a small scale over five Winter/Spring seasons at sites including California's Sierra Nevada Mountains, a Canadian lake, and a small man-made lake in Minnesota, using various materials and an evolving array of instrumentation. The materials can float and can be made to minimize effects on marine habitat and species. The instrumentation is designed to be deployed in harsh and remote locations. Localized snow and ice preservation, and reductions in water heating, have been quantified in small-scale testing. Climate modeling is underway to analyze the effects of this method of surface albedo modification in key areas on the rate of oceanic and atmospheric temperature rise. We are also evaluating the effects of snow and ice preservation for protection of infrastructure and habitat stabilization. This paper will also discuss a possible reduction of sea level rise with an eye to quantification of cost/benefit. The most recent season's experimentation on a man-made private lake in Minnesota saw further evolution in the material and deployment approach. The materials were successfully deployed to shield underlying snow and ice from melting; applications of granular materials remained stable in the face of local wind and storms. Localized albedo

  7. Quantification of Dead-ice Melting in Ice-Cored Moraines at the High-Arctic Glacier Holmströmbreen, Svalbard

    NASA Astrophysics Data System (ADS)

    Schomacker, A.; Kjaer, K. H.

    2007-12-01

    An extensive dead-ice area has developed at the stagnant snout of the Holmströmbreen glacier on Svalbard following its Little Ice Age maximum. Dead-ice appears mainly as ice-cored moraines, ice-cored eskers and ice- cored kames. The most common dead-ice landform is sediment gravity flows on ice-cored slopes surrounding a large ice-walled, moraine-dammed lake. The lake finally receives the sediment from the resedimentation processes. Dead-ice melting is described and quantified through field studies and analyses of high-resolution, multi-temporal aerial photographs and satellite imagery. Field measurements of backwasting of ice-cored slopes indicate short-term melting rates of c. 9.2 cm/day. Long-term downwasting rates indicate a surface lowering of ice-cored moraines of c. 0.9 m/yr from 1984-2004. Different measures for dead-ice melting are assessed in relation to the temperature record from Svalbard since the termination of the Little Ice Age. The most prominent impact of dead-ice melting is the evolution of the ice-walled lake with an area increasing near-exponentially over the last 40 years. As long as backwasting and mass movement processes prevent build-up of an insulating debris-cover and expose ice-cores to melting, the de-icing continues even though the area is characterized by continuous permafrost.

  8. Case for periodic, colossal jokulhlaups from Pleistocene glacial Lake Missoula.

    USGS Publications Warehouse

    Waitt, R.B., Jr.

    1985-01-01

    Lake Missoula (2500 km3) remained sealed as long as any segment of the glacial dam remained grounded; when the lake rose to a critical level c.600 m in depth, the glacier bed at the seal became buoyant, initiating underflow from the lake. Subglacial tunnels then grew exponentially, leading to catastrophic discharge. Calculations of the water budget for the lake basin (including input from the Cordilleran ice sheet) suggest that the lake filled every three to seven decades. -from Author

  9. Subglacial Lake McGregor, south-central Alberta, Canada

    NASA Astrophysics Data System (ADS)

    Munro-Stasiuk, Mandy J.

    2003-08-01

    It is proposed that a lake, here named "Subglacial Lake McGregor", existed beneath the Laurentide Ice Sheet at, or near, the last glacial maximum. The lake resided in the ancient buried McGregor and Tee Pee preglacial valleys, which are now mostly filled with glacigenic deposits. The greatest thickness of sediment in the valleys is in the form of chaotically deposited lake beds that were laid down in a subaqueous environment by a number of process: gravity flow, water transport, and suspension settling. Topographic, sedimentary, and stratigraphic evidence point to a subglacial, not a proglacial, origin for the beds. During the early stages of lake existence, ice movement was significant as there are numerous sets of shear planes in the sedimentary beds. This indicates that the lake filled (lake sedimentation) and drained (shearing of the beds by overlying ice when ice contacted the bed) often. Thus, early in its history, the lake(s) was/were ephemeral. During the later stages of lake existence, the lake was relatively stable with no rapid draining or influx of sediment. Gradual drainage of the lake resulted in lowering of the ice onto the lake beds resulting in subglacial till deposition. Drainage was not a single continuous event. Rather it was characterized by multiple phases of near total drainage (till deposition), followed by water accumulation (lake sedimentation). Water accumulation events became successively less significant reflected by thinning of lake beds and thickening of till beds higher in the stratigraphic sequence. Since subglacial lake sedimentation appears to be restricted to the subglacial valleys, it is suggested that the valleys acted as a large-scale interconnected cavity system that both stored and transported water. It is also suggested that these acted as the main routes of water flow beneath the Laurentide Ice Sheet.

  10. Drilling reaches Antarctic subglacial Lake Whillans

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2013-02-01

    A decade-long planning effort to drill through 800 meters of ice to directly and cleanly sample the waters and sediments of subglacial Lake Whillans in West Antarctica succeeded at 5:00 A.M. local time on 28 January. The effort "marks the first successful retrieval of clean whole samples from an Antarctic subglacial lake," according to a 28 January statement from the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project team.

  11. Sea Ice

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.; Cavalieri, Donald J.

    2005-01-01

    Sea ice covers vast areas of the polar oceans, with ice extent in the Northern Hemisphere ranging from approximately 7 x 10(exp 6) sq km in September to approximately 15 x 10(exp 6) sq km in March and ice extent in the Southern Hemisphere ranging from approximately 3 x 10(exp 6) sq km in February to approximately 18 x 10(exp 6) sq km in September. These ice covers have major impacts on the atmosphere, oceans, and ecosystems of the polar regions, and so as changes occur in them there are potential widespread consequences. Satellite data reveal considerable interannual variability in both polar sea ice covers, and many studies suggest possible connections between the ice and various oscillations within the climate system, such as the Arctic Oscillation, North Atlantic Oscillation, and Antarctic Oscillation, or Southern Annular Mode. Nonetheless, statistically significant long-term trends are also apparent, including overall trends of decreased ice coverage in the Arctic and increased ice coverage in the Antarctic from late 1978 through the end of 2003, with the Antarctic ice increases following marked decreases in the Antarctic ice during the 1970s. For a detailed picture of the seasonally varying ice cover at the start of the 21st century, this chapter includes ice concentration maps for each month of 2001 for both the Arctic and the Antarctic, as well as an overview of what the satellite record has revealed about the two polar ice covers from the 1970s through 2003.

  12. Over Ice

    NASA Video Gallery

    All about NASA's IceBridge P-3B plane and its IceBridge retrofit. Upgraded with 21st century "special modifications", the aircraft is less a cold war relic and more like the Space Agency's Millenni...

  13. Determining lake surface water temperatures (LSWTs) worldwide using a tuned 1-dimensional lake model (FLake, v1)

    NASA Astrophysics Data System (ADS)

    Layden, A.; MacCallum, S.; Merchant, C.

    2015-10-01

    FLake, a 1-dimensional freshwater lake model, is tuned for 244 globally distributed large lakes using lake surface water temperatures (LSWTs) derived from Along-Track Scanning Radiometers (ATSRs). The model, tuned using only 3 lake properties; lake depth, albedo (snow and ice) and light extinction co-efficient, substantially improves the measured biases in various features of the LSWT annual cycle, including the LSWTs of saline and high altitude lakes. The daily mean absolute differences (MAD) and the spread of differences (±2 standard deviations) across the trial seasonally ice covered lakes (lakes with a lake-mean LSWT remaining below 1 °C for part of the annual cycle) is reduced from 3.01± 2.25 °C (pre-tuning) to 0.84 ± 0.51 °C (post-tuning). For non-seasonally ice-covered trial lakes (lakes with a lake-mean LSWT remaining above 1 °C throughout its annual cycle), the average daily mean absolute difference (MAD) is reduced from 3.55 ± 3.20 °C to 0.96 ± 0.63 °C. The post tuning results for the trial lakes (35 lakes) are highly representative of the post tuning results of the 244 lakes. The sensitivity of the summer LSWTs of deeper lakes to changes in the timing of ice-off is demonstrated. The modelled summer LSWT response to changes in ice-off timing is found to be strongly affected by lake depth and latitude, explaining 0.50 (R2adj, p = 0.001) of the inter-lake variance in summer LSWTs. Lake depth alone explains 0.35 (p =0.003) of the variance. The tuning approach undertaken in this study, overcomes the obstacle of the lack of available lake characteristic information (snow and ice albedo and light extinction co-efficient) for individual lakes. Furthermore, the tuned values for lake depth, snow and ice albedo and light extinction co-efficient for the 244 lakes provide guidance for improving LSWTs modelling in FLake.

  14. Patagonian Lakes, Argentina, South America

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The Patagonian Lakes of Argentinas Los Glacieres National Park (50.0S, 73.0W) occupying the foothills of the southern Andes Mountains along the border with Chile, are some of the most scenic in South America. The range is covered by a permanent ice cap and glaciers. Glacier activity frequently reaches into the lake region causing blockage and impounding of the waters until water pressure causes the glacier to crack with a roar that can be heard for miles.

  15. Life in Ice: Implications to Astrobiology

    NASA Technical Reports Server (NTRS)

    Hoover, Richard B.

    2009-01-01

    During the 2008 Tawani International Expedition Schirmacher Oasis/Lake Untersee Antarctica Expedition, living and instantly motile bacteria were found in freshly thawed meltwater from ice of the Schirmacher Oasis Lakes, the Anuchin Glacier ice and samples of the that perennial ice sheet above Lake Untersee. This phenomenon of living bacteria encased in ice had previously been observed in the 32,000 year old ice of the Fox Tunnel. The bacteria found in this ice included the strain FTR1T which was isolated and published as valid new species (Carnobacterium pleistocenium) the first validly published living Pleistocene organism still alive today. Living bacteria were also extracted from ancient ice cores from Vostok, Antarctica. The discovery that many strains of bacteria are able to survive and remain alive while frozen in ice sheets for long periods of time may have direct relevance to Astrobiology. The abundance of viable bacteria in the ice sheets of Antarctica suggests that the presence of live bacteria in ice is common, rather than an isolated phenomenon. This paper will discuss the results of recent studies at NSSTC of bacteria cryopreserved in ice. This paper advances the hypothesis that cryopreserved cells, and perhaps even viable bacterial cells, may exist today--frozen in the water-ice of lunar craters, the Polar Caps or craters of Mars; or in the permafrost of Mars; ice and rocks of comets or water bearing asteroids; or in the frozen crusts of the icy moons of Jupiter and Saturn. The existence of bacterial life in ice suggests that it may not be necessary to drill through a thick ice crust to reach liquid water seas deep beneath the icy crusts of Europa, Ganymede and Enceladus. The presence of viable bacteria in the ice of the Earth s Polar Caps suggests that the possibility that cryo-panspermia (i.e., the trans-planetary transfer of microbial life by impact ejection/spallation of bacteria-rich polar ice masses) deserves serious consideration and study as a

  16. HISTORICAL SNOW AMOUNTS IN THE LAKE EFFECT REGION OF LAKE SUPERIOR: EVIDENCE OF CLIMATE CHANGE IN THE GREAT LAKES

    EPA Science Inventory

    Recent studies (Levitus et al., .2000) suggest a warming of the world ocean over the past 50 years. This could be occurring in the Great Lakes also but thermal measurements are lacking. Historical trends in natural phenomena, such as the duration of ice cover on lakes, provide in...

  17. Dynamics of CFCs in northern temperate lakes and adjacent groundwater

    USGS Publications Warehouse

    Walker, J.F.; Saad, D.A.; Hunt, R.J.

    2007-01-01

    [1] Three dimictic lakes and one meromictic lake in and near the Trout Lake, Wisconsin, watershed were sampled to determine the variation of chlorofluorocarbon (CFC) concentrations within the lakes. The lakes were sampled during stratified conditions, during fall turnover, and during ice cover. The results demonstrate a considerable variation in CFC concentrations and corresponding atmospheric mixing ratios in the lakes sampled, both with depth and season within a given lake, and across different lakes. CFC profiles and observed degradation were not related to the groundwater inflow rate and hence are likely the result of in-lake processes influenced by CFC degradation in the (lake) water column, CFC degradation in the lake-bed sediments, and gas exchange rates and the duration of turnover (turnover efficiency).

  18. The Global Climatology of Large Lakes

    NASA Astrophysics Data System (ADS)

    Merchant, Christopher J.; MacCallum, Stuart N.

    2010-12-01

    There are ~250 large lakes in the world, large here meaning lakes with surface areas exceeding 500 km2 . Lakes are potentially sensitive indicators of regional climatic changes and large lakes also significantly modulate climate locally, via their effects on surface atmosphere fluxes and atmospheric stability. The interactions of lakes and atmosphere are therefore significant for climatology and weather forecasting. Relatively few lakes are permanently instrumented (mostly in N America and Europe), and in assimilation systems for numerical weather prediction, highly simplistic approximations for lake surface temperature are giving way to lake temperature models within the land-atmosphere exchange schemes. It is therefore important to exploit satellite observations to inform and constrain lake and weather models, and to provide observations of lake temperature changes for a wider range of lakes. Here we present results from the first phase of an ESA-funded project, ARCLake, to demonstrate accurate lake surface temperatures and detection of ice cover, using ATSR-2 and AATSR, for large lakes globally. It is sometimes assumed that sea surface temperature (SST) techniques are applicable, but in fact, lake-specific approaches are required for cloud detection and for temperature retrieval. In this paper, we present preliminary results from application of the techniques described in a companion paper [1].

  19. Discovery of relict subglacial lakes and their geometry and mechanism of drainage.

    PubMed

    Livingstone, Stephen J; Utting, Daniel J; Ruffell, Alastair; Clark, Chris D; Pawley, Steven; Atkinson, Nigel; Fowler, Andrew C

    2016-06-13

    Recent proxy measurements reveal that subglacial lakes beneath modern ice sheets periodically store and release large volumes of water, providing an important but poorly understood influence on contemporary ice dynamics and mass balance. This is because direct observations of how lake drainage initiates and proceeds are lacking. Here we present physical evidence of the mechanism and geometry of lake drainage from the discovery of relict subglacial lakes formed during the last glaciation in Canada. These palaeo-subglacial lakes comprised shallow (<10 m) lenses of water perched behind ridges orientated transverse to ice flow. We show that lakes periodically drained through channels incised into bed substrate (canals). Canals sometimes trend into eskers that represent the depositional imprint of the last high-magnitude lake outburst. The subglacial lakes and channels are preserved on top of glacial lineations, indicating long-term re-organization of the subglacial drainage system and coupling to ice flow.

  20. Discovery of relict subglacial lakes and their geometry and mechanism of drainage

    PubMed Central

    Livingstone, Stephen J.; Utting, Daniel J.; Ruffell, Alastair; Clark, Chris D.; Pawley, Steven; Atkinson, Nigel; Fowler, Andrew C.

    2016-01-01

    Recent proxy measurements reveal that subglacial lakes beneath modern ice sheets periodically store and release large volumes of water, providing an important but poorly understood influence on contemporary ice dynamics and mass balance. This is because direct observations of how lake drainage initiates and proceeds are lacking. Here we present physical evidence of the mechanism and geometry of lake drainage from the discovery of relict subglacial lakes formed during the last glaciation in Canada. These palaeo-subglacial lakes comprised shallow (<10 m) lenses of water perched behind ridges orientated transverse to ice flow. We show that lakes periodically drained through channels incised into bed substrate (canals). Canals sometimes trend into eskers that represent the depositional imprint of the last high-magnitude lake outburst. The subglacial lakes and channels are preserved on top of glacial lineations, indicating long-term re-organization of the subglacial drainage system and coupling to ice flow. PMID:27292049

  1. Discovery of relict subglacial lakes and their geometry and mechanism of drainage.

    PubMed

    Livingstone, Stephen J; Utting, Daniel J; Ruffell, Alastair; Clark, Chris D; Pawley, Steven; Atkinson, Nigel; Fowler, Andrew C

    2016-01-01

    Recent proxy measurements reveal that subglacial lakes beneath modern ice sheets periodically store and release large volumes of water, providing an important but poorly understood influence on contemporary ice dynamics and mass balance. This is because direct observations of how lake drainage initiates and proceeds are lacking. Here we present physical evidence of the mechanism and geometry of lake drainage from the discovery of relict subglacial lakes formed during the last glaciation in Canada. These palaeo-subglacial lakes comprised shallow (<10 m) lenses of water perched behind ridges orientated transverse to ice flow. We show that lakes periodically drained through channels incised into bed substrate (canals). Canals sometimes trend into eskers that represent the depositional imprint of the last high-magnitude lake outburst. The subglacial lakes and channels are preserved on top of glacial lineations, indicating long-term re-organization of the subglacial drainage system and coupling to ice flow. PMID:27292049

  2. Seasonal Greenland Ice Sheet ice flow variations in regions of differing bed and surface topography

    NASA Astrophysics Data System (ADS)

    Sole, A. J.; Livingstone, S. J.; Rippin, D. M.; Hill, J.; McMillan, M.; Quincey, D. J.

    2015-12-01

    The contribution of the Greenland Ice Sheet (GrIS) to future sea-level rise is uncertain. Observations reveal the important role of basal water in controlling ice-flow to the ice sheet margin. In Greenland, drainage of large volumes of surface meltwater to the ice sheet bed through moulins and hydrofracture beneath surface lakes dominates the subglacial hydrological system and provides an efficient means of moving mass and heat through the ice sheet. Ice surface and bed topography influence where meltwater can access the bed, and the nature of its subsequent flow beneath the ice. However, no systematic investigation into the influence of topographic variability on Greenland hydrology and dynamics exists. Thus, physical processes controlling storage and drainage of surface and basal meltwater, and the way these affect ice flow are not comprehensively understood. This presents a critical obstacle in efforts to predict the future evolution of the GrIS. Here we present high-resolution satellite mapping of the ice-surface drainage network (e.g. lakes, channels and moulins) and measurements of seasonal variations in ice flow in south west Greenland. The region is comprised of three distinct subglacial terrains which vary in terms of the amplitude and wavelength and thus the degree to which basal topography is reflected in the ice sheet surface. We find that the distribution of surface hydrological features is related to the transfer of bed topography to the ice sheet surface. For example, in areas of thinner ice and high bed relief, moulins occur more frequently and are more uniformly dispersed, indicating a more distributed influx of surface-derived meltwater to the ice sheet bed. We investigate the implications of such spatial variations in surface hydrology on seasonal ice flow rates.

  3. Sturgis and Tekonsha ice advances: Evidence for thin ice sheets in southern Michigan

    SciTech Connect

    Straw, W.T.; Kehew, A.E.; Passero, R.N. . Dept. of Geology)

    1993-03-01

    Advance of an ice sheet through the Saginaw Lowland to the position of Sturgis, in St. Joseph County, Michigan initially produced the Sturgis Moraine and adjacent outwash apron. As this ice sheet down wasted, meltwater impounded by it overtopped ice divides to form meltwater streams that cut canyons in the ice and underlying glacial sediments. Continued wasting was attended by formation of supraglacial streams that developed waterfalls as they eroded headward. Complete melting of the ice revealed a subglacial topography marked by drumlins, many of which are irregular, attesting to formation near the attenuated margin of the ice sheet. Prior to complete wasting of this stagnant ice mass, ice of the Lake Michigan Lobe advanced from the west-northwest to form the Tekonsha Moraine. Exposed only where this relatively thin ice sheet advanced onto a highland in east-central Kalamazoo County, the southwestern extension of this moraine was buried by outwash from ice that formed the very prominent Kalamazoo Moraine. That the Tekonsha ice sheet stagnated and wasted in place is revealed by two prominent elongate kames, several escarpments, lake and wetland basins produced by melting of ice masses buried by glacial outwash, and sequential filling of the lowland produced by melting of this ice sheet by a series of alluvial fans. The sequence of fan emplacement is indicated by marginal relationships of the fans and the number and size of depressions formed by melting of relic blocks of ice. The first-formed Dry Prairie fan is marked by numerous large depressions while the Prairie Ronde, the last formed fan exhibits only small widely spaced depressions formed by melting of the last vestiges of this ice sheet.

  4. Buoyant Rover for Under-Ice Exploration

    NASA Astrophysics Data System (ADS)

    Berisford, D. F.; Leichty, J. M.; Klesh, A. T.; Matthews, J. B.; Hand, K. P.

    2012-12-01

    We have designed, constructed and tested a prototype robotic mobility platform for exploring the underside of ice sheets in frozen lake or ocean environments. The ice-water interface often provides some of the most interesting and dynamic chemistry in partially frozen systems, as dissolved impurities are rejected from the advancing freezing front. Higher concentrations of microorganisms can be found in this region, and the topography of the ice underside can help reveal the history of its formation. Furthermore, in lake environments ice cover can serve to trap gases released from biological and geological processes in the subsurface. The rover uses a two-wheeled design with a flexible dragging tail, enabling it to fit into a 10-inch diameter ice borehole. The sealed air-filled cylindrical body, along with closed-cell foam inside of cone-shaped wheels, provides buoyancy force to enable roving along the underside of the ice. The prototype contains two cameras that stream live video via a tethered connection to a ground station and uses semi-autonomous control via a PC. Preliminary testing of the prototype in a cold lab and in northern Alaskan thermokarst lakes demonstrates the utility and simplicity of this type of robotic platform for exploring the ice-water interface. This technology has potential future use in landed missions to icy ocean worlds in the solar system.

  5. Ancient ice streams and their megalineated beds

    NASA Astrophysics Data System (ADS)

    Eyles, Nick; Ross, Martin

    2016-06-01

    Ice streams are corridors of fast-flowing (~ 800 m yr- 1) ice inset within otherwise sluggish-moving ice sheets. According to reported estimates, as much as 90% of the total discharge of the Antarctic Ice Sheet, for example, occurs through such corridors. Recognition of ice stream records in paleo-ice sheet research has profoundly changed the discipline of glacial geology. The key has been identification of the distinctive corrugated or 'megalineated' geomorphology of their beds, consisting of elongate ridges that are parallel to ice flow direction and often transitional to drumlins. Access to new satellite imagery has enabled mapping of megascale glacial lineations (MSGLs) over large swaths of terrain and the recognition of regional-scale ice stream flow paths and origins. At the peak of the last ice age, just after 20,000 years ago, there were more than 100 ice streams within the Laurentide Ice Sheet. Only now are we beginning to fully appreciate the fundamental role that such streams (which have been called the 'arteries' of ice sheets) have had on glaciated landscapes, by moving enormous volumes of sediment and releasing armadas of floating ice to the Arctic and Atlantic oceans. There is also a growing awareness of the erosional role of ice streams in overdeepening of lakes, fiords and other troughs along coastlines. Much remains to be learnt and new discoveries surely await. The picture of past ice sheets, like the Laurentide and Fennoscandian Ice Sheets, that is emerging today is very different from that of 20 years ago.

  6. Digital data base of lakes on the North Slope, Alaska

    USGS Publications Warehouse

    Walker, Kim-Marie; York, James; Murphy, Dennis; Sloan, C.E.

    1986-01-01

    The National Mapping Division and Water Resources Division of the U.S. Geological Survey have produced a digital data base of approximately 23,330 lakes on the North Slope of Alaska. The inventoried region consists of the area north of the 69th parallel and is composed of sixteen 1 degree by 3 degree quadrangles. The data base includes (1) locations of lake centers in latitude and longitude, (2) a unique number for each lake within a quadrangle, and (3) acreage for water classes (deep, shallow or turbid, and ice) within each lake and lake total. The digital data base is an easily accessible storage and retrieval system that will allow for rapid identification of a particular lake or region of lakes and its characteristics. The data base is designed to accommodate field study data such as lake depth, water quality, volume of water, ice thickness, and other pertinent information. (Author 's abstract)

  7. Supraglacial lakes on Himalayan debris-covered glacier (Invited)

    NASA Astrophysics Data System (ADS)

    Sakai, A.; Fujita, K.

    2013-12-01

    Debris-covered glaciers are common in many of the world's mountain ranges, including in the Himalayas. Himalayan debris-covered glacier also contain abundant glacial lakes, including both proglacial and supraglacial types. We have revealed that heat absorption through supraglacial lakes was about 7 times greater than that averaged over the whole debris-covered zone. The heat budget analysis elucidated that at least half of the heat absorbed through the water surface was released with water outflow from the lakes, indicating that the warm water enlarge englacial conduits and produce internal ablation. We observed some portions at debris-covered area has caved at the end of melting season, and ice cliff has exposed at the side of depression. Those depression has suggested that roof of expanded water channels has collapsed, leading to the formation of ice cliffs and new lakes, which would accelerate the ablation of debris-covered glaciers. Almost glacial lakes on the debris-covered glacier are partially surrounded by ice cliffs. We observed that relatively small lakes had non-calving, whereas, calving has occurred at supraglacial lakes with fetch larger than 80 m, and those lakes expand rapidly. In the Himalayas, thick sediments at the lake bottom insulates glacier ice and lake water, then the lake water tends to have higher temperature (2-4 degrees C). Therefore, thermal undercutting at ice cliff is important for calving processes in the glacial lake expansion. We estimated and subaqueous ice melt rates during the melt and freeze seasons under simple geomorphologic conditions. In particular, we focused on valley wind-driven water currents in various fetches during the melt season. Our results demonstrate that the subaqueous ice melt rate exceeds the ice-cliff melt rate above the water surface when the fetch is larger than 20 m with the water temperature of 2-4 degrees C. Calculations suggest that onset of calving due to thermal undercutting is controlled by water

  8. Sea Ice

    NASA Technical Reports Server (NTRS)

    Perovich, D.; Gerland, S.; Hendricks, S.; Meier, Walter N.; Nicolaus, M.; Richter-Menge, J.; Tschudi, M.

    2013-01-01

    During 2013, Arctic sea ice extent remained well below normal, but the September 2013 minimum extent was substantially higher than the record-breaking minimum in 2012. Nonetheless, the minimum was still much lower than normal and the long-term trend Arctic September extent is -13.7 per decade relative to the 1981-2010 average. The less extreme conditions this year compared to 2012 were due to cooler temperatures and wind patterns that favored retention of ice through the summer. Sea ice thickness and volume remained near record-low levels, though indications are of slightly thicker ice compared to the record low of 2012.

  9. Exploring Ice-Covered Waters with an Autonomous Underwater Vehicle

    NASA Astrophysics Data System (ADS)

    Hamilton, A.; Forrest, A.; Laval, B.

    2009-12-01

    Reductions in lake- and sea-ice extent and ice-shelf collapse in both the Arctic and Antarctic are exposing underlying waters to significant increases in light and heat penetration, altering water mass properties and current dynamics. These physical changes likely drive rapid biological evolution and succession in associated marine ecosystems, influencing the biogeochemical transformation of matter and energy in previously ice-covered waters. However the unaltered, or pristine state of waters covered by thick (>3m) or moving ice is poorly understood, as these environments are largely inaccessible to investigation from the surface. Advancement of autonomous underwater vehicle (AUV) technology now allows these vehicles to be utilized as platforms for polar oceanographic research, permitting exploration of previously uncharted ice-covered waters. UBC-Gavia, a 2.5 m long AUV operated out of the University of British Columbia, has been involved in several under-ice (both lake and sea) missions making it one of the few such vehicles to be successfully deployed under-ice. Results of three under-ice case studies are presented in this work: Pavilion Lake, Canada - an ice-covered temperate lake; Lake Thingvallavatn, Iceland - a subarctic lake experiencing spring ice break-up; and Joliffe Bay, Lincoln Sea, Canadian High Arctic - a near shore multi- and first-year sea ice environment. The focus of each of these case studies was to examine physical processes in the water column under ice (e.g. radiatively driven convection) using a Conductivity-Temperature-Depth (CTD) profiler mounted on the front of the vehicle. In addition, various engineering lessons were acquired in order to adapt the vehicle for deployment, operation and recovery in ice-covered waters. The next phase of research will also be presented; a planned deployment of UBC-Gavia near the McMurdo Ice Shelf in Antarctica, to map under ice structure, ice thickness and convective processes in the water column. These

  10. ICE911 Research: Preserving and Rebuilding Reflective Ice

    NASA Astrophysics Data System (ADS)

    Field, L. A.; Chetty, S.; Manzara, A.; Venkatesh, S.

    2014-12-01

    We have developed a localized surface albedo modification technique that shows promise as a method to increase reflective multi-year ice using floating materials, chosen so as to have low subsidiary environmental impact. It is now well-known that multi-year reflective ice has diminished rapidly in the Arctic over the past 3 decades and this plays a part in the continuing rapid decrease of summer-time ice. As summer-time bright ice disappears, the Arctic is losing its ability to reflect summer insolation, and this has widespread climatic effects, as well as a direct effect on sea level rise, as oceans heat and once-land-based ice melts into the sea. We have tested the albedo modification technique on a small scale over six Winter/Spring seasons at sites including California's Sierra Nevada Mountains, a Canadian lake, and a small man-made lake in Minnesota, using various materials and an evolving array of instrumentation. The materials can float and can be made to minimize effects on marine habitat and species. The instrumentation is designed to be deployed in harsh and remote locations. Localized snow and ice preservation, and reductions in water heating, have been quantified in small-scale testing. We have continued to refine our material and deployment approaches, and we have had laboratory confirmation by NASA. In the field, the materials were successfully deployed to shield underlying snow and ice from melting; applications of granular materials remained stable in the face of local wind and storms. We are evaluating the effects of snow and ice preservation for protection of infrastructure and habitat stabilization, and we are concurrently developing our techniques to aid in water conservation. Localized albedo modification options such as those being studied in this work may act to preserve ice, glaciers, permafrost and seasonal snow areas, and perhaps aid natural ice formation processes. If this method is deployed on a large enough scale, it could conceivably

  11. Deeply Frozen Lakes in a Terrestrial Peri-Glacial Environment

    NASA Astrophysics Data System (ADS)

    Doran, P. T.; Fritsen, C. H.

    1998-01-01

    Some of the largest lakes in the McMurdo Dry Valleys, Antarctica, have largely been ignored during past limnological studies because they were thought to be frozen solid. However, recent investigations have revealed the presence of saline water bodies beneath up to 19 m of permanent ice in two of these so-called "ice block" lakes (Lake Vida and Lake House). Lakes throughout the dry valleys that have been studied in detail more typically have ice covers ranging between 3 and 5 m. The existence of saline lakes with extremely thick ice covers is atypical, even among lakes in this region, which are themselves unique aquatic systems. These "deeply ice-covered" lakes are aquatic systems on the edge of cold-termination, and they warrant study as analogs of lakes purported to have existed on the surface of Mars in the past. Several lakes in the McMurdo Dry Valleys were presumed in the past to be frozen solid based largely on attempts at drilling the lake ice covers. Lake Vida has been the most intriguing because it is one of the two largest (in terms of surface area) lakes in the dry valleys, and yet it apparently contained no year-round liquid water at depth. Recently a ground-penetrating radar (GPR) survey was carried out on Lake Vida and another purported ice block lake, Lake House. In a large central portion of Lake Vida, the survey showed attenuation of the radar signal at approximately 19 m, suggesting saline water at this depth. Because GPR radar signals are absorbed by saline water, the depth of the water body (i.e., distance from the ice bottom to sediments) could not be determined. In Lake House, a similar water body was inferred at about 12 m depth. Ice Coring and Physical Properties: Ice cores (to 14 and 15.8 in depth) extracted in 1996 from Lake Vida contained ice bubbles with unique morphologies that were atypical when compared to other vapor inclusions in 3-5 in ice covers. Most of the vapor inclusions at depths greater than about 6 m contained hoar frost

  12. Investigation of SMOS Sea Ice Thickness Retrieval with respect to the Ice Temperature Gradient within an Ice Layer

    NASA Astrophysics Data System (ADS)

    Tulaczyk, S. M.; Schwartz, S. Y.; Fisher, A. T.; Powell, R. D.; Fricker, H. A.; Anandakrishnan, S.; Horgan, H. J.; Scherer, R. P.; Walter, J. I.; Siegfried, M. R.; Mikucki, J.; Christianson, K.; Beem, L.; Mankoff, K. D.; Carter, S. P.; Hodson, T. O.; Marsh, O.; Barcheck, C. G.; Branecky, C.; Neuhaus, S.; Jacobel, R. W.

    2014-12-01

    Interactions of West Antarctic ice streams with meltwater at their beds, and with seawater at their grounding lines, are widely considered to be the primary drivers of ice stream flow variability on different timescales. Understanding of processes controlling ice flow variability is needed to build quantitative models of the Antarctic Ice Sheet that can be used to help predict its future behavior and to reconstruct its past evolution. The ice plain of Whillans Ice Stream provides a natural glaciological laboratory for investigations of Antarctic ice flow dynamics because of its highly variable flow rate modulated by tidal processes and fill-drain cycles of subglacial lakes. Moreover, this part of Antarctica has one of the longest time series of glaciological observations, which can be used to put recently acquired datasets in a multi-decadal context. Since 2007 Whillans Ice Stream has been the focus of a regional glaciological experiment, which included surface GPS and passive-source seismic sensors, radar and seismic imaging of subglacial properties, as well as deep borehole geophysical sensors. This experiment was possible thanks to the NSF-funded multidisciplinary WISSARD project (Whillans Ice Stream Subglacial Access Research Drilling). Here we will review the datasets collected during the WISSARD glaciological experiment and report on selected results pertaining to interactions of this ice stream with water at its bed and its grounding line.

  13. Deglacial and lake level fluctuation history recorded in cores, Beaver Lake, Upper Peninsula, Michigan

    USGS Publications Warehouse

    Fisher, Timothy G.; Whitman, Richard L.

    1999-01-01

    Sediment cores collected from the littoral and pelagic zones of Beaver Lake, Michigan record fluctuations in the water level of Lake Superior. Beaver Lake is a small 300 ha lake in Pictured Rocks National Lakeshore (PRNL) now separated from Lake Superior by a dune-capped barrier bar. Cores were collected using a vibracorer from a lake-ice platform in February 1997. A 2.85 m long core in 10 m of water contains well-sorted sand, rhythmites, peat, interbedded sand and gyttja, and is capped with 1 m of massive gyttja. A 9480 BP AMS age from the basal sand provides a minimum deglacial date for the area. Further analysis indicates a sand-dominated depositional environment from a low lake stand at approximately 8500 BP to present. An approximate 8800 BP red to gray sediment color transition records either the cessation of meltwater input from Lake Agassiz or receding ice, while a younger similarly colored transition, 6600 BP in age, likely records sediment reworking in the coastal zone. Four AMS ages on peat range from 8520 to 7340 BP and are indicative of the Houghton low phase. Burial of the peat by stratified sand and gyttja after 7340 BP indicates a rising lake level. Peat at a higher level in the lake basin, encountered in shallow littoral cores, ranges in age from 6800 to 6420 BP, which estimates a 0.91 m rise/century in lake level to the Nipissing level by 5000 BP.

  14. Review of Mariana Gosnell's 'ICE: The Nature, the History, and the Uses of an Astonishing Substance'

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    2006-01-01

    ICE: The Nature, the History, and the Uses of an Astonishing Substance is a recently published book by Mariana Gosnell about ice. It covers not just the ice that is readily seen, such as sea ice, lake ice, icebergs, glaciers, ice sheets, and ice cubes, but also ice in the ground, in the atmosphere, inside plants and animals, and in outer space, plus new ice forms being created in scientific laboratories. Gosnell treats the reader to a well-written, easy-going mixture of science, adventure, history, applications, science methods and controversies, and philosophy, all centered in one way or another on ice. The book is 563 pages long and is filled with fascinating anecdotes and details, such as beetles in the Canadian Rockies that can supercool to 60 C below freezing and a lake in Minnesota where each winter typically 65,000 fishing shanties are set up on the lake's ice, many with couches, beds, television sets, and bathrooms. Gosnell also includes many practical suggestions. Among them: When driving on lake ice, keep your windows open, in case your vehicle breaks through the ice and you need to make a rapid exit.

  15. Sedimentary record of ice divide migration and ice streams in the Keewatin core region of the Laurentide Ice Sheet

    NASA Astrophysics Data System (ADS)

    Hodder, Tyler J.; Ross, Martin; Menzies, John

    2016-06-01

    The Aberdeen Lake region of central mainland Nunavut is a former core region of the Laurentide Ice Sheet that is characterized by streamlined glacial landforms classified into multiple crosscutting flow sets and near continuous till blanket. The presence of widespread till near the centre of the Keewatin Ice Dome raises questions about its origin. Detailed drillcore logging revealed a complex stratigraphy consisting of at least 6 till units, variably preserved across the study area. Till provenance analysis indicates deposition by near opposite-trending ice flow phases, interpreted as evidence of reconfiguration of the Keewatin Ice Divide. At the surface, large north-northwesterly aligned landforms are present across the study area. The till stratigraphy within these landforms indicates the same NNW ice flow phase is responsible for considerable till production. This ice flow phase is also correlated to a long regional dispersal train of erratics toward the Gulf of Boothia. The production of an extensive, thick (~ 12 m), till sheet during the NNW-trending ice flow phase occurred far from the ice margin at a time of extensive ice cover of mainland Nunavut, likely from an east-west oriented ice divide. A deglacial westerly trending ice flow phase formed small drumlins atop the larger NNW streamlined till ridges and deposited a surficial till unit that is too thin to mask the NNW flow set across the study area. It is proposed that the Boothia paleo-ice stream catchment area propagated deep into the Laurentide Ice Sheet and contributed to significant till production in this core region of the Keewatin Sector prior to the westerly ice flow shift. The apparent relationship between till thickness and the size of the associated or correlated drumlins, flow sets, and dispersal trains indicates complex erosion/deposition interplay is involved in the formation of streamlined subglacial landforms.

  16. Application of ERTS imagery to environmental studies of Lake Champlain

    NASA Technical Reports Server (NTRS)

    Lind, A. O.

    1974-01-01

    ERTS Imagery has provided data relating to a number of environmental and limnological concerns such as water quality, lake flooding and lake ice formation. Pollution plume data provided by ERTS was recently used in the Supreme Court case involving the States of Vermont and New York and a paper company. Flooding of lowland tracts has been a major concern due to a repetitive pattern of high lake levels over the past three years, and ERTS imagery is being used to construct the first series of flood maps of the affected areas. Lake ice development and turbidity patterns have also been studied from ERTS, since these have significance for shore erosion studies.

  17. Modeling Antarctic Subglacial Lake Filling and Drainage Cycles

    NASA Technical Reports Server (NTRS)

    Dow, Christine F.; Werder, Mauro A.; Nowicki, Sophie; Walker, Ryan T.

    2016-01-01

    The growth and drainage of active subglacial lakes in Antarctica has previously been inferred from analysis of ice surface altimetry data. We use a subglacial hydrology model applied to a synthetic Antarctic ice stream to examine internal controls on the filling and drainage of subglacial lakes. Our model outputs suggest that the highly constricted subglacial environment of our idealized ice stream, combined with relatively high rates of water flow funneled from a large catchment, can combine to create a system exhibiting slow-moving pressure waves. Over a period of years, the accumulation of water in the ice stream onset region results in a buildup of pressure creating temporary channels, which then evacuate the excess water. This increased flux of water beneath the ice stream drives lake growth. As the water body builds up, it steepens the hydraulic gradient out of the overdeepened lake basin and allows greater flux. Eventually this flux is large enough to melt channels that cause the lake to drain. Lake drainage also depends on the internal hydrological development in the wider system and therefore does not directly correspond to a particular water volume or depth. This creates a highly temporally and spatially variable system, which is of interest for assessing the importance of subglacial lakes in ice stream hydrology and dynamics.

  18. Modeling Antarctic subglacial lake filling and drainage cycles

    NASA Astrophysics Data System (ADS)

    Dow, Christine F.; Werder, Mauro A.; Nowicki, Sophie; Walker, Ryan T.

    2016-07-01

    The growth and drainage of active subglacial lakes in Antarctica has previously been inferred from analysis of ice surface altimetry data. We use a subglacial hydrology model applied to a synthetic Antarctic ice stream to examine internal controls on the filling and drainage of subglacial lakes. Our model outputs suggest that the highly constricted subglacial environment of our idealized ice stream, combined with relatively high rates of water flow funneled from a large catchment, can combine to create a system exhibiting slow-moving pressure waves. Over a period of years, the accumulation of water in the ice stream onset region results in a buildup of pressure creating temporary channels, which then evacuate the excess water. This increased flux of water beneath the ice stream drives lake growth. As the water body builds up, it steepens the hydraulic gradient out of the overdeepened lake basin and allows greater flux. Eventually this flux is large enough to melt channels that cause the lake to drain. Lake drainage also depends on the internal hydrological development in the wider system and therefore does not directly correspond to a particular water volume or depth. This creates a highly temporally and spatially variable system, which is of interest for assessing the importance of subglacial lakes in ice stream hydrology and dynamics.

  19. Method for measuring brash ice thickness with impulse radar

    NASA Astrophysics Data System (ADS)

    Martinson, C. R.; Dean, A. M., Jr.

    1981-06-01

    A subsurface impulse radar system on board a cutter was used to measure brash ice thickness in the Great Lakes. Manual ice thickness measurements were made in the test area to calibrate the radar data and to determine radar range settings. Radar collected data were recorded on magnetic tape and later played back to a graphic recorder for interpretation.

  20. Holocene fluctuations of Bregne ice cap, Scoresby Sund, eastern Greenland

    NASA Astrophysics Data System (ADS)

    Levy, L.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.

    2011-12-01

    The Arctic cryosphere is responding rapidly to modern global warming. Documenting past changes in the Arctic cryosphere, particularly during times of warmer than present conditions such as the Holocene Thermal Maximum (HTM; 9,000-5,000 yr BP) provides an important background against which the present response and potential for future changes can be compared. Small ice caps located adjacent to the Greenland Ice Sheet respond sensitively to climate change and their past extents provide a proxy for the climatic conditions that have influenced the ice sheet margin. In order to document cryosphere and climatic changes during warmer conditions, we are constructing records of Holocene fluctuations of small ice caps in the Scoresby Sund region of eastern Greenland (71° N, 25.6° W). We use geomorphic mapping, lake sediment records, radiocarbon, and surface exposure (10Be) dating to reconstruct past ice extents. Lake sediment records are from both glacially fed (i.e., threshold) lakes and lakes with no glacial input during the time of interest (i.e., control). Here we present a record of the Holocene extents of Bregne ice cap, Milne Land, western Scoresby Sund, ~50 km southeast of Renland ice cap. Sediments from Two Move Lake (TML), a threshold lake, register the entire Holocene in a thickness of ~70 cm. Radiocarbon dates of lake sediments indicate that the onset of organic accumulation in the lake following the Last Glacial Maximum occurred 8,890±120 cal yr BP. The mid-Holocene is characterized by organic rich mud that is finely laminated in some sections. The onset of Neoglaciation (cooling after HTM) occurs at 2,810±50 cal yr BP and finely laminated sediments during Neoglaciation may register annual deposition. The sediment record from Last Chance Lake, a control lake located 0.5 km from TML, indicates that there has been no glacial input since deglaciation from the Last Glacial Maximum. Unweathered moraines occur <0.5 km from the modern ice cap margin, inboard from

  1. Effect of ice cover on hydropower production

    SciTech Connect

    Yapa, P.D.; Shen H.T.

    1984-09-01

    For hydropower developments in northern regions, the annual occurrence of river ice cover presents various problems of operation and management. The existence of an ice cover can lead to a substantial loss in power production. This loss in power due to the presence of ice cover, however, can be minimized with appropriate ice control measures. In this technical note, a quantitative analysis of power loss is carried out for the St. Lawrence Power Project. Major factors that affect the magnitude of power loss are examined to provide some information for future ice-related hydropower operations. The St. Lawrence River, which conveys water from the Great Lakes Basin to the Atlantic Ocean, has been utilized for hydroelectric power production since the early 1900's. The St. Lawrence Seaway and Power Project, constructed in 1954-58, developed the hydropower potential of the upper St. Lawrence River. The Moses-Saunders Power Dam is located about 100 miles downstream of the outlet of Lake Ontario. Since the development of this power project, the regulation of flow through the dam in relation to the ice conditions has been an important element in its winter operation. The existence of an ice cover reduces the power production capability of the river significantly.

  2. Exploring former subglacial Hodgson Lake, Antarctica Paper I: site description, geomorphology and limnology

    NASA Astrophysics Data System (ADS)

    Hodgson, Dominic A.; Roberts, Stephen J.; Bentley, Michael J.; Smith, James A.; Johnson, Joanne S.; Verleyen, Elie; Vyverman, Wim; Hodson, Andy J.; Leng, Melanie J.; Cziferszky, Andreas; Fox, Adrian J.; Sanderson, David C. W.

    2009-11-01

    At retreating margins of the Antarctic Ice Sheet, there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice-covered. This paper presents a site description of one of these lakes, Hodgson Lake, situated on southern Alexander Island, west of the Antarctic Peninsula (72° 00.549‧ S, 68° 27.708‧ W). First, we describe the physical setting of the lake using topographic and geomorphological maps. Second, we determine local ice sheet deglaciation history and the emergence of the lake using cosmogenic isotope dating of glacial erratics cross-referenced to optically stimulated luminescence dating of raised lake shoreline deltas formed during ice recession. Third we describe the physical and chemical limnology including the biological and biogeochemical evidence for life. Results show that the ice mass over Hodgson Lake was at least 295 m thick at 13.5 ka and has progressively thinned through the Holocene with the lake ice cover reaching an altitude of c. 6.5 m above the present lake ice sometime after 4.6 ka. Thick perennial ice cover persists over the lake today and the waters have remained isolated from the atmosphere with a chemical composition consistent with subglacial melting of catchment ice. The lake is ultra-oligotrophic with nutrient concentrations within the ranges of those found in the accreted lake ice of subglacial Lake Vostok. Total organic carbon and dissolved organic carbon are present, but at lower concentrations than typically recorded in continental rain. No organisms and no pigments associated with photosynthetic or bacterial activity were detected in the water column using light microscopy and high performance liquid chromatography. Increases in SO4 and cation concentrations at depth and declines in O2 provide some evidence for sulphide oxidation and very minor bacterial demand upon O2 that result in small, perhaps undetectable changes in the carbon biogeochemistry. However, in general

  3. Lake Eyre

    Atmospheric Science Data Center

    2013-04-16

    ...   View Larger Image Lake Eyre is a large salt lake situated between two deserts in one of Australia's driest regions. ... the effect of sunglint at the nadir camera view angle. Dry, salt encrusted parts of the lake appear bright white or gray. Purple areas have ...

  4. A habitat for psychrophiles in deep Antarctic ice

    PubMed Central

    Price, P. Buford

    2000-01-01

    Microbes, some of which may be viable, have been found in ice cores drilled at Vostok Station at depths down to ≈3,600 m, close to the surface of the huge subglacial Lake Vostok. Two types of ice have been found. The upper 3,500 m comprises glacial ice containing traces of nutrients of aeolian origin including sulfuric acid, nitric acid, methanosulfonic acid (MSA), formic acid, sea salts, and mineral grains. Ice below ≈3,500 m comprises refrozen water from Lake Vostok, accreted to the bottom of the glacial ice. Nutrients in the accretion ice include salts and dissolved organic carbon. There is great interest in searching for living microbes and especially for new species in deepest Antarctic ice. I propose a habitat consisting of interconnected liquid veins along three-grain boundaries in ice in which psychrophilic bacteria can move and obtain energy and carbon from ions in solution. In the accretion ice, with an age of a few 104 years and a temperature a few degrees below freezing, the carbon and energy sources in the veins can maintain significant numbers of cells per cubic centimeter that are metabolizing but not multiplying. In the 4 × 105-year-old colder glacial ice, at least 1 cell per cm3 in acid veins can be maintained. With fluorescence microscopy tuned to detect NADH in live organisms, motile bacteria could be detected by direct scanning of the veins in ice samples. PMID:10655516

  5. Subglacial Lake Whillans, West Antarctica; Solute Dynamics and Fluxes to the Ross Sea

    NASA Astrophysics Data System (ADS)

    Skidmore, M. L.; Michaud, A. B.; Achberger, A.; Barbante, C.; Christner, B. C.; Mikucki, J.; Mitchell, A. C.; Priscu, J. C.; Purcell, A. M.; van Gelder, W.; Vick-Majors, T.

    2014-12-01

    Subglacial Lake Whillans is located beneath the Whillans Ice Stream in West Antarctica. The lake is situated beneath 800 m of ice and ~ 70 km upstream of the grounding line where Whillans Ice Stream terminates into the Ross Sea. Subglacial Lake Whillans is a shallow lake and a component of a complex subglacial hydrological system that may resemble a large wetland along the Siple Coast of West Antarctica. Subglacial Lake Whillans drains and refills on a sub-decadal time scale discharging water towards the Ross Sea. Water and sediment samples were recovered from the lake, using clean access drilling technologies, in January, 2013. Isotopic analysis of the lake waters indicates basal meltwater from the ice sheet as the dominant water source. Geochemical analysis of the lake water reveals it is freshwater with mineral weathering as a significant solute source, with a minor contribution from sea water likely from relict marine sediments. Subglacial hydrothermal activity upstream may also contribute solutes. Nutrients N and P are present at micromolar concentrations. Sediment porewaters from shallow cores (~ 40 cm depth) of the subglacial lake sediments indicate increasing solute concentration with depth, with up to ~ five times greater solute concentrations than in the lake water. The waters and sediment contain metabolically active organisms which are likely involved in elemental cycling within the lake system. Here we will discuss solute sources to the lake, solute dynamics within the lake waters and sediment, and the fluxes of solute and nutrients to the Ross Sea and their implications for these marine ecosystems.

  6. Physical processes in Subglacial Lake Whillans, West Antarctica: Inferences from sediment cores

    NASA Astrophysics Data System (ADS)

    Hodson, T. O.; Powell, R. D.; Brachfeld, S. A.; Tulaczyk, S.; Scherer, R. P.

    2016-06-01

    The hydrologic system beneath the Antarctic Ice Sheet is thought to influence both the dynamics and distribution of fast flowing ice streams, which discharge most of the ice lost by the ice sheet. Despite considerable interest in understanding this subglacial network and its affect on ice flow, in situ observations from the ice sheet bed are exceedingly rare. Here we describe the first sediment cores recovered from an active subglacial lake. The lake, known as Subglacial Lake Whillans, is part of a broader, dynamic hydrologic network beneath the Whillans Ice Stream in West Antarctica. Even though "floods" pass through the lake, the lake floor shows no evidence of erosion or deposition by flowing water. By inference, these floods must have insufficient energy to erode or transport significant volumes of sediment coarser than silt. Consequently, water flow beneath the region is probably incapable of incising continuous channels into the bed and instead follows preexisting subglacial topography and surface slope. Sediment on the lake floor consists of till deposited during intermittent grounding of the ice stream following flood events. The fabrics within the till are weaker than those thought to develop in thick deforming beds suggesting subglacial sediment fluxes across the ice plain are currently low and unlikely to have a large stabilizing effect on the ice stream's grounding zone.

  7. Arctic epishelf lakes as sentinel ecosystems: Past, present and future

    NASA Astrophysics Data System (ADS)

    Veillette, Julie; Mueller, Derek R.; Antoniades, Dermot; Vincent, Warwick F.

    2008-12-01

    Ice shelves are a prominent but diminishing feature of the northern coastline of Ellesmere Island in the Canadian High Arctic (latitude 82-83°N). By blocking embayments and fiords, this thick coastal ice can create epishelf lakes, which are characterized by a perennially ice-capped water column of freshwater overlying seawater. The goal of this study was to synthesize new, archived, and published data on Arctic epishelf lakes in the context of climate change. Long-term changes along this coastline were evaluated using historical reports, cartographic analysis, RADARSAT imagery, and field measurements. These data, including salinity-temperature profiling records from Disraeli Fiord spanning 54 years, show the rapid decline and near disappearance of this lake type in the Arctic. Salinity-temperature profiling of Milne Fiord, currently blocked by the Milne Ice Shelf, confirmed that it contained an epishelf lake composed of a 16-m thick freshwater layer overlying seawater. A profiling survey along the coast showed that there was a continuum of ice-dammed lakes from shallow systems dammed by multiyear landfast sea ice to deep epishelf lakes behind ice shelves. The climate warming recently observed in this region likely contributed to the decline of epishelf lakes over the last century, and the air temperature trend predicted for the Arctic over the next several decades implies the imminent loss of this ecosystem type. Our results underscore the distinctive properties of coastal ice-dammed lakes and their value as sentinel ecosystems for the monitoring of regional and global climate change.

  8. Bed conditions of Subglacial Lake Whillans, West Antarctica

    NASA Astrophysics Data System (ADS)

    Powell, Ross; Hodson, Timothy

    2014-05-01

    Subglacial Lake Whillans (SLW) sediment is a typical subglacial till; a homogenized, structureless diamicton. Debris from local basal ice is likely not contributed to the lake by rainout, because based on theoretical estimates, ice is below the pressure melting point. Therefore, the lake floor diamicton likely was transported to the lake by deformation while the ice stream was grounded at the drill site both prior to lake formation and during lake "lowstands". Satellite altimetry has been used to infer that SLW experiences short (~7 month) discharge events, lowering the ice surface and lake water level by between 1-4m. The lake lowstands are separated by longer periods of gradual recharge, but over the period of many lowstands the ice stream is suspected to touch down and couple with the lake floor, potentially shearing new till into the lake. Subglacial hydrological diversions also likely play a role in the history of the lake, and if water is captured by another drainage basin, then the bed at SLW will also act as a till. The lack of sorted sediment (apart from a lamina of mud at the sediment-water interface) and erosional lags indicate water flow during discharge/recharge events has had a low current velocity with quiescent conditions in the lake. Although important volumes of water are moved during such events, water velocities are not those of classic "floods" due to low hydropotential gradients on the ice plain. Del18O values of lake water indicate that it is from ice sheet melt (it must be from up-stream); however, Cl and Br ion concentrations indicate a seawater source likely recycled from deeper sediments deposited when WAIS grounding line was retreated back up-stream from this site, perhaps during past interglacials. Biologists show that chemolithoautotrophs dominate an active microbial community at SLW indicating they play a significant role in breakdown of subglacial particulates. The most notable variability in the cores is a uniformly weak, critical

  9. Subglacial Lake Ellsworth: A candidate for in situ exploration in West Antarctica

    NASA Astrophysics Data System (ADS)

    Siegert, Martin J.; Hindmarsh, Richard; Corr, Hugh; Smith, Andy; Woodward, John; King, Edward C.; Payne, Antony J.; Joughin, Ian

    2004-12-01

    Radio-echo sounding reveals a 10 km-long lake beneath ~3.4 km of ice near the Ellsworth Mountains in West Antarctica, 20 km from the ice divide. Subglacial Lake Ellsworth is located within a distinct topographic hollow, which is ~1.5 km deeper than the surrounding bed. Judging by bed slopes flanking the lake, the water depth is at least 10s of metres. Calculations of basal temperature reveal the ice base to be warm both now and during full glacial periods. As the environments of subglacial lakes are broadly similar, life may be expected in Lake Ellsworth as in any other. Given this, its physical characteristics, and the fact that the West Antarctic Ice Sheet has been accessed on several occasions, Lake Ellsworth is an excellent candidate for in situ examination.

  10. Changing Lake Bathymetry with Deglaciation: The Mendenhall Glacier System

    NASA Astrophysics Data System (ADS)

    Connor, C.; Korzen, N.; Knuth, E.; Sauer, D.; Heavner, M.

    2008-12-01

    Ongoing rapid ice ablation and glacier thinning has continued the buoyancy-driven, large-scale calving events and ice terminus collapse of the Mendenhall Glacier. New bathymetric data collected from Mendenhall Lake between 2004 and 2008 reveal lake shallowing adjacent to the 2008 glacier terminus. Since 2000, the lake has expanded beyond its former 3.4 km2 footprint to 4.02 km2 and enlarged its volume from 0.05 km3 to 0.23 km3 as it elongates to the north, following the receding lakefront terminus and filling its Pleistocene ice-scoured cirque basin. In 2004, the northeastern-most deep in the lake basin reached a maximum depth of ~97 meters below mean lake level. Since that time this deep has shallowed to the north decreasing along the 2008 glacier terminus to depths ranging from 79.85 to 0 m below mean lake level. This new bathymetric data will be used for ongoing mass balance studies as well as for determination of changes in lake sedimentation rates and lake basin morphology since the 1970s when original lake surveys were conducted by the Alaska Dept of Fish and Game personnel. Comparison of lake basin volume with river discharge data will help to better define the seasonal contribution of glacier melt water to Mendenhall River summer discharge, which reached 50 percent during the summer of 1998.

  11. Observing a catastrophic thermokarst lake drainage in northern Alaska

    USGS Publications Warehouse

    Jones, Benjamin M.; Arp, Christopher D.

    2015-01-01

    The formation and drainage of thermokarst lakes have reshaped ice-rich permafrost lowlands in the Arctic throughout the Holocene. North of Teshekpuk Lake, on the Arctic Coastal Plain of northern Alaska, thermokarst lakes presently occupy 22.5% of the landscape, and drained thermokarst lake basins occupy 61.8%. Analysis of remotely sensed imagery indicates that nine lakes (>10 ha) have drained in the 1,750 km2 study area between 1955 and 2014. The most recent lake drainage was observed using in situ data loggers providing information on the duration and magnitude of the event, and a nearby weather station provided information on the environmental conditions preceding the lake drainage. Lake 195 (L195), an 80 ha thermokarst lake with an estimated water volume of ~872,000 m3, catastrophically drained on 05 July 2014. Abundant winter snowfall and heavy early summer precipitation resulted in elevated lake water levels that likely promoted bank overtopping, thermo-erosion along an ice-wedge network, and formation of a 9 m wide, 2 m deep, and 70 m long drainage gully. The lake emptied in 36 hours, with 75% of the water volume loss occurring in the first ten hours. The observed peak discharge of the resultant flood was 25 m3/s, which is similar to that in northern Alaska river basins whose areas are more than two orders of magnitude larger. Our findings support the catastrophic nature of sudden lake drainage events and the mechanistic hypotheses developed by J. Ross Mackay.

  12. Antarctic subglacial lake exploration: first results and future plans.

    PubMed

    Siegert, Martin J; Priscu, John C; Alekhina, Irina A; Wadham, Jemma L; Lyons, W Berry

    2016-01-28

    After more than a decade of planning, three attempts were made in 2012-2013 to access, measure in situ properties and directly sample subglacial Antarctic lake environments. First, Russian scientists drilled into the top of Lake Vostok, allowing lake water to infiltrate, and freeze within, the lower part of the ice-core borehole, from which further coring would recover a frozen sample of surface lake water. Second, UK engineers tried unsuccessfully to deploy a clean-access hot-water drill, to sample the water column and sediments of subglacial Lake Ellsworth. Third, a US mission successfully drilled cleanly into subglacial Lake Whillans, a shallow hydraulically active lake at the coastal margin of West Antarctica, obtaining samples that would later be used to prove the existence of microbial life and active biogeochemical cycling beneath the ice sheet. This article summarizes the results of these programmes in terms of the scientific results obtained, the operational knowledge gained and the engineering challenges revealed, to collate what is known about Antarctic subglacial environments and how to explore them in future. While results from Lake Whillans testify to subglacial lakes as being viable biological habitats, the engineering challenges to explore deeper more isolated lakes where unique microorganisms and climate records may be found, as exemplified in the Lake Ellsworth and Vostok missions, are considerable. Through international cooperation, and by using equipment and knowledge of the existing subglacial lake exploration programmes, it is possible that such environments could be explored thoroughly, and at numerous sites, in the near future.

  13. Life in the Ice

    NASA Technical Reports Server (NTRS)

    Allen, C. C.; Wainwright, N. R.; Grasby, S. E.; Harvey, R. P.

    2003-01-01

    The current Martian surface environment is extremely hostile to any known form of life. The combination of subfreezing temperature, low atmospheric pressure and high ultraviolet flux, combined with desiccated and possibly oxidizing soil, could destroy even the hardiest microorganisms. The Viking biology experiments are generally interpreted to indicate that the surface of Mars is currently devoid of life and organic molecules at the part-per-billion level. Speculation on the possibility of extant or preserved microbial life on Mars thus centers on refuges in some manner protected from the current surface environment, either in space or time. Terrestrial analogs include hydrothermal systems, lakes, caves and subsurface aquifers as well as more clement conditions in the distant past. We are examining the evidence for microbiology in Earth's glaciated polar regions as analogs to the polar caps of Mars. This research concerns the detection of microorganisms or their preserved remains at the surface and within polar glacial ice.

  14. Operation IceBridge: Sea Ice Interlude

    NASA Video Gallery

    Sea ice comes in an array of shapes and sizes and has its own ephemeral beauty. Operation IceBridge studies sea ice at both poles, and also runs across interesting formations en route to other targ...

  15. Vostok Subglacial Lake: A Review of Geophysical Data Regarding Its Discovery and Topographic Setting

    NASA Technical Reports Server (NTRS)

    Siegert, Martin J.; Popov, Sergey; Studinger, Michael

    2011-01-01

    Vostok Subglacial Lake is the largest and best known sub-ice lake in Antarctica. The establishment of its water depth (>500 m) led to an appreciation that such environments may be habitats for life and could contain ancient records of ice sheet change, which catalyzed plans for exploration and research. Here we discuss geophysical data used to identify the lake and the likely physical, chemical, and biological processes that occur in it. The lake is more than 250 km long and around 80 km wide in one place. It lies beneath 4.2 to 3.7 km of ice and exists because background levels of geothermal heating are sufficient to warm the ice base to the pressure melting value. Seismic and gravity measurements show the lake has two distinct basins. The Vostok ice core extracted >200 m of ice accreted from the lake to the ice sheet base. Analysis of this ice has given valuable insights into the lake s biological and chemical setting. The inclination of the ice-water interface leads to differential basal melting in the north versus freezing in the south, which excites circulation and potential mixing of the water. The exact nature of circulation depends on hydrochemical properties, which are not known at this stage. The age of the subglacial lake is likely to be as old as the ice sheet (approx.14 Ma). The age of the water within the lake will be related to the age of the ice melting into it and the level of mixing. Rough estimates put that combined age as approx.1 Ma.

  16. Microbiology of the subglacial Lake Vostok: first results of borehole-frozen lake water analysis and prospects for searching for lake inhabitants.

    PubMed

    Bulat, Sergey A

    2016-01-28

    This article examines the question of the possible existence of microbial life inhabiting the subglacial Lake Vostok buried beneath a 4 km thick Antarctic ice sheet. It represents the results of analysis of the only available frozen lake water samples obtained upon the first lake entry and subsequent re-coring the water frozen within the borehole. For comparison, results obtained by earlier molecular microbiological studies of accretion ice are included in this study, with the focus on thermophiles and an unknown bacterial phylotype. A description of two Lake Vostok penetrations is presented for the first time from the point of view of possible clean water sampling. Finally, the results of current studies of Lake Vostok frozen water samples are presented, with the focus on the discovery of another unknown bacterial phylotype w123-10 distantly related to the above-mentioned unknown phylotype AF532061 detected in Vostok accretion ice, both successfully passing all possible controls for contamination. The use of clean-room facilities and the establishment of a contaminant library are considered to be prerequisites for research on microorganisms from Lake Vostok. It seems that not yet recorded microbial life could exist within the Lake Vostok water body. In conclusion, the prospects for searching for lake inhabitants are expressed with the intention to sample the lake water as cleanly as possible in order to make sure that further results will be robust. PMID:26667905

  17. Breakup of Pack Ice, Antarctic Ice Shelf

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Breakup of Pack Ice along the periphery of the Antarctic Ice Shelf (53.5S, 3.0E) produced this mosaic of ice floes off the Antarctic Ice Shelf. Strong offshore winds, probably associated with strong katabatic downdrafts from the interior of the continent, are seen peeling off the edges of the ice shelf into long filamets of sea ice, icebergs, bergy bits and growlers to flow northward into the South Atlantic Ocean. 53.5S, 3.0E

  18. Seismicity on the western Greenland Ice Sheet: Surface fracture in the vicinity of active moulins

    SciTech Connect

    Carmichael, Joshua D.; Joughin, Ian; Behn, Mark D.; Das, Sarah; King, Matt A.; Stevens, Laura; Lizarralde, Dan

    2015-06-25

    We analyzed geophone and GPS measurements collected within the ablation zone of the western Greenland Ice Sheet during a ~35 day period of the 2011 melt season to study changes in ice deformation before, during, and after a supraglacial lake drainage event. During rapid lake drainage, ice flow speeds increased to ~400% of winter values, and icequake activity peaked. At times >7 days after drainage, this seismicity developed variability over both diurnal and longer periods (~10 days), while coincident ice speeds fell to ~150% of winter values and showed nightly peaks in spatial variability. Approximately 95% of all detected seismicity in the lake basin and its immediate vicinity was triggered by fracture propagation within near-surface ice (<330 m deep) that generated Rayleigh waves. Icequakes occurring before and during drainage frequently were collocated with the down flow (west) end of the primary hydrofracture through which the lake drained but shifted farther west and outside the lake basin after the drainage. We interpret these results to reveal vertical hydrofracture opening and local uplift during the drainage, followed by enhanced seismicity and ice flow on the downstream side of the lake basin. This region collocates with interferometric synthetic aperture radar-measured speedup in previous years and could reflect the migration path of the meltwater supplied to the bed by the lake. The diurnal seismic signal can be associated with nightly reductions in surface melt input that increase effective basal pressure and traction, thereby promoting elevated strain in the surficial ice.

  19. Analysis of ERS 1 synthetic aperture radar data of frozen lakes in northern Montana and implications for climate studies

    USGS Publications Warehouse

    Hall, Dorothy K.; Fagre, Daniel B.; Klasner, Fritz; Linebaugh, Gregg; Liston, Glen E.

    1994-01-01

    Lakes that freeze each winter are good indicators of regional climate change if key parameters, such as freeze-up and breakup date and maximum ice thickness, are measured over a decade-scale time frame. Synthetic aperture radar (SAR) satellite data have proven to be especially useful for measurement of climatologically significant parameters characteristic of frozen lakes. In this paper, five lakes in Glacier National Park, Montana, have been studied both in the field and using Earth Remote-Sensing Satellite (ERS) 1 SAR data during the 1992-1993 winter. The lakes are characterized by clear ice, sometimes with tubular or rounded bubbles, and often with a layer of snow ice on top of the clear ice. They are also often snow covered. Freeze-up is detected quite easily using ERS 1 SAR data as soon as a thin layer of ice forms. The effect of snow ice on the backscatter is thought to be significant but is, as yet, undetermined. On the five lakes studied, relative backscatter was found to increase with ice thickness until a maximum was reached in February. Breakup, an often ill-defined occurrence, is difficult to detect because surface water causes the SAR signal to be absorbed, thus masking the ice below. Comparison of the bubble structure of thaw lakes in northern Alaska with lakes in northern Montana has shown that the ice structure is quite different, and this difference may contribute to differential SAR signature evolution in the lakes of the two areas.

  20. 22. Lake Whitney Dam, 1895 Photocopied from an original photograph, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    22. Lake Whitney Dam, 1895 Photocopied from an original photograph, NHCHSL. Shows the rear of the dam building, and on Lake Whitney, Day's Store and Boathouse, and an ice house and steam-powered elevators. - Eli Whitney Armory, West of Whitney Avenue, Armory Street Vicinity, Hamden, New Haven County, CT

  1. Geological nature of subglacial Lake Vostok

    NASA Astrophysics Data System (ADS)

    Leitchenkov, G. L.; Masolov, V. N.; Lukin, V. V.; Bulat, S. A.; Kurinin, R. G.; Lipenkov, V. Ya.

    2003-04-01

    Lake Vostok is located at the edge of vast upland of East Antarctic (Precambrian) Crystalline Shield and represents a typical extensionally-induced intracontinental rift zone. Type indicators of rift nature are: width (60-80 km) and length (about 300 km) of the lake depression; several (3-5) kilometers of sediments (modeled from gravity data) infilling the lake graben, considerable amplitudes of faults bounding the lake (up to 2 km in bedrock relief and in excess of 5 km in basement topography), half-graben-like structures (rotated crustal blocks) at flanks of the lake traceable to crustal extension; along-strike segmentation of the depression (the presence of two isolated basins, recognized from seismic and gravity data); knee-shaped spatial configuration of the lake and existence of diagonal fractures (displayed in bedrock topography) normally nascent in conditions of tensional stress. The rift graben of Lake Vostok is considered to be a part (branch) of more spacious rift system, main arm of which stretched from the Prydz Bay trough the Lambert Glacier and the eastern foot of Gamburtsev Mts. to, at least, 110E. This rift system is a result of large-scale extensional event, which occurred in East Antarctica in Late Jurassic - Early Cretaceous prior to East Gondwana break-up. Sedimentary infill of this age is proposed to dominate in Vostok Lake, although postrift, preglacial (Cretaceous - Paleogene) strata can also forms significant part of depositional section. Helium isotopes data give evidence that the Lake Vostok rift is not active. On the other hand, thermophilic bacteria found in accretion ice suggest the possibility of hydrothermal activity in lake bottom. The conduits for warm underwater can be provided by deep crustal faults bordering rift graben. Microseismicity recorded in the area of Lake Vostok suggests the possibility of crustal deformations (likely during more dramatic earthquakes) providing a necessary fault permeability for water seepage from

  2. Recent Changes in Arctic Glaciers, Ice Caps, and the Greenland Ice Sheet: Cold Facts About Warm Ice

    NASA Astrophysics Data System (ADS)

    Abdalati, W.

    2005-12-01

    One of the major manifestations of Arctic change can be observed in the state of balance of Arctic glaciers and ice caps and the Greenland ice sheet. These ice masses are estimated to contain nearly 3 million cubic kilometers of ice, which is more than six times greater than all the water stored in the Earth's lakes, rivers, and snow combined and is the equivalent of over 7 meters of sea level. Most of these ice masses have been shrinking in recent in years, but their mass balance is highly variable on a wide range of spatial and temporal scales. On the Greenland ice sheet most of the coastal regions have thinned substantially as melt has increased and some of its outlet glaciers have accelerated. Near the equilibrium line in West Greenland, we have seen evidence of summer acceleration that is linked to surface meltwater production, suggesting a relatively rapid response mechanism of the ice sheet change to a warming climate. At the same time, however, the vast interior regions of the Greenland ice sheet have shown little change or slight growth, as accumulation in these areas may have increased. Throughout much of the rest of the Arctic, many glaciers and ice caps have been shrinking in the past few decades, and in Canada and Alaska, the rate of ice loss seems to have accelerated during the late 1990s. These recent observations offer only a snapshot in time of the long-term behavior, but they are providing crucial information about the current state of ice mass balance and the mechanisms that control it in one of the most climatically sensitive regions on Earth. As we continue to learn more through a combination of remote sensing observations, in situ measurements and improved modeling capabilities, it is important that we coordinate and integrate these approaches effectively in order to predict future changes and their impact on sea level, freshwater discharge, and ocean circulation.

  3. Aerosolization of two strains (ice+ and ice-) of Pseudomonas syringae in a Collison nebulizer at different temperatures

    NASA Astrophysics Data System (ADS)

    Pietsch, Renee; David, Ray; Marr, Linsey; Vinatzer, Boris; Schmale, David

    2015-04-01

    The aerosolization of microorganisms from aquatic environments is understudied. In this study, an ice nucleation active (ice+) strain and a non-ice nucleation active (ice-) strain of the bacterium Pseudomonas syringae were aerosolized from aqueous suspensions under artificial laboratory conditions using a Collison nebulizer. The aerosolization of P. syringae was not influenced by water temperatures between 5° and 30°C. In general, the culturability (viability) of P. syringae in aerosols increased with temperature between 5 and 30°C. The ice+ strain was aerosolized in greater numbers than the ice- strain at all temperatures studied, suggesting a possible connection between the ice nucleation phenotype and aerosol production. Together, our results suggest that P. syringae has the potential to be aerosolized from natural aquatic environments, such as streams, rivers, ponds, and lakes; known reservoirs of P. syringae. Future work is needed to elucidate the mechanisms of aerosolization of P. syringae from natural aquatic systems.

  4. Current trends in seasonal ice storage. [Compilation of projects

    SciTech Connect

    Gorski, A.J.

    1986-05-01

    This document is a compilation of modern research projects focused upon the use of naturally grown winter ice for summer cooling applications. Unlike older methods of ice-based cooling, in which ice was cut from rivers and lakes and transported to insulated icehouses, modern techniques grow ice directly in storage containers - by means of heat pipes, snow machines, and water sprays - at the site of application. This modern adaptation of an old idea was reinvented independently at several laboratories in the United States and Canada. Applications range from air conditioning and food storage to desalinization.

  5. On siphons and sediments: A new model for draining active subglacial lakes in Antarctica informed with satellite radar and laser altimeter observations.

    NASA Astrophysics Data System (ADS)

    Carter, S. P.; Fricker, H. A.; Siegfried, M. R.

    2014-12-01

    With the advent of repeat-pass satellite-based surface altimetry over much of Antarctica, approximately 130 new subglacial lakes have been discovered entirely from observations of surface uplift and subsidence; these are commonly referred to as "active lakes". In contrast to the ~160 lakes detected by radar sounding ("RES" lakes), which are typically in mountains bedrock terrain near the ice divide and static with residence times spanning millenia, active lakes are typically located in fast flowing ice streams far from the divides, and have short residence times. To understand how water transfers through active lake systems we have developed a new model based on earlier theoretical work and informed by lake-volume estimates inferred from of ice surface displacements detected by satellite radar and laser altimetry. We find that although the overall pattern of filling and drainage is similar to that for ice dammed lakes in alpine regions via channels thermally eroded into the ice that then creeps shut as water pressure declines, Antarctic lake drainage is better simulated by invoking a channel mechanically eroded into the underlying sediment. The necessity of an erodable deformable substrate to explain lake drainage suggests that the distribution of active lakes is an indicator for the presence of sediment. Furthermore the process of lake drainage appears quite sensitive to the composion and strength of the underlying till. We explore these possibilities by testing the model on subglacial lakes in both East and West Antarctica, including Recovery Glacier and MacAyeal Ice stream.

  6. Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization

    USGS Publications Warehouse

    Mark Torre Jorgenson,; Mikhail Kanevskiy,; Yuri Shur,; Natalia Moskalenko,; Dana Brown,; Wickland, Kimberly P.; Striegl, Rob; Koch, Joshua C.

    2015-01-01

    Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3 m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water-filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9°C among degradation and stabilization stages and by 9.9°C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice-poor transient layer, ice-rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.

  7. Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization

    NASA Astrophysics Data System (ADS)

    Jorgenson, M. T.; Kanevskiy, M.; Shur, Y.; Moskalenko, N.; Brown, D. R. N.; Wickland, K.; Striegl, R.; Koch, J.

    2015-11-01

    Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3 m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water-filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9°C among degradation and stabilization stages and by 9.9°C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice-poor transient layer, ice-rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.

  8. Modeling the fracture of ice sheets on parallel computers.

    SciTech Connect

    Waisman, Haim; Bell, Robin; Keyes, David; Boman, Erik Gunnar; Tuminaro, Raymond Stephen

    2010-03-01

    The objective of this project is to investigate the complex fracture of ice and understand its role within larger ice sheet simulations and global climate change. At the present time, ice fracture is not explicitly considered within ice sheet models due in part to large computational costs associated with the accurate modeling of this complex phenomena. However, fracture not only plays an extremely important role in regional behavior but also influences ice dynamics over much larger zones in ways that are currently not well understood. Dramatic illustrations of fracture-induced phenomena most notably include the recent collapse of ice shelves in Antarctica (e.g. partial collapse of the Wilkins shelf in March of 2008 and the diminishing extent of the Larsen B shelf from 1998 to 2002). Other fracture examples include ice calving (fracture of icebergs) which is presently approximated in simplistic ways within ice sheet models, and the draining of supraglacial lakes through a complex network of cracks, a so called ice sheet plumbing system, that is believed to cause accelerated ice sheet flows due essentially to lubrication of the contact surface with the ground. These dramatic changes are emblematic of the ongoing change in the Earth's polar regions and highlight the important role of fracturing ice. To model ice fracture, a simulation capability will be designed centered around extended finite elements and solved by specialized multigrid methods on parallel computers. In addition, appropriate dynamic load balancing techniques will be employed to ensure an approximate equal amount of work for each processor.

  9. ERTS-1 views the Great Lakes

    NASA Technical Reports Server (NTRS)

    Lyons, W. A.; Pease, S. R.

    1973-01-01

    The meteorological content of ERTS images, particularly mesoscale effects of the Great Lakes and air pollution dispersion is summarized. Summertime lake breeze frontal clouds and various winter lake-effect convection patterns and snow squalls are revealed in great detail. A clear-cut spiral vortex over southern Lake Michigan is related to a record early snow storm in the Chicago area. Marked cloud changes induced by orographic and frictional effects on Lake Michigan's lee shore snow squalls are seen. The most important finding, however, is a clear-cut example of alterations in cumulus convection by anthropogenic condensation and/or ice nuclei from northern Indiana steel mills during a snow squall situation. Jet aircraft condensation trails are also found with surprising frequency.

  10. Recent climate extremes alter alpine lake ecosystems

    PubMed Central

    Parker, Brian R.; Vinebrooke, Rolf D.; Schindler, David W.

    2008-01-01

    Here, we show that alpine lake ecosystems are responsive to interannual variation in climate, based on long-term limnological and meteorological data from the Canadian Rockies. In the 2000s, in years with colder winter temperatures, higher winter snowfall, later snowmelt, shorter ice-free seasons, and dryer summers, relative to the 1990s, alpine lakes became clearer, warmer, and mixed to deeper depths. Further, lakes became more dilute and nutrient-poor, the latter leading to significant declines in total phytoplankton biomass. However, increased concentrations of dissolved organic carbon in lake water stimulated the appearance of small mixotrophic algal species, partially offsetting the decline in autotrophic phytoplankton biomass and increasing algal species richness. The climate regime in the 2000s altered the physical, chemical, and biological character and the function of high-elevation aquatic ecosystems. Forecasts of increased climatic variability in the future pose serious ramifications for both the biodiversity and ecosystem function of high-elevation lakes. PMID:18725641

  11. Effect of glacier ablation on the Snettisham Hydroelectric Project, Long Lake and Crater Lake Basins, Alaska

    USGS Publications Warehouse

    Sloan, C.E.; Emery, P.A.; Fair, Diana

    1986-01-01

    Long Lake Basin in the Snettisham Project Area southeast of Juneau, Alaska, yields water used for the production of hydroelectric power. Development of adjacent Crater Lake is planned to increase the Project 's generating capacity. Estimates of the hydroelectric potential of the lakes are based on streamflow records which are influenced by glaciers that cover 25% of the combined basins. Analysis of streamflow records shows that the quality and extent of records in the area are sufficient to predict flow from the Crater Creek basin with a fairly high degree of confidence. Comparison of aerial photographs indicates that glacier ablation and recession have been continuous since at least 1929. Estimates of ice-volume change from photogrammetric measurements indicate that less than 2.5% of the average runoff from the basins of Long and Crater Lakes has been from reduction in glacier-ice storage. (Author 's abstract)

  12. Exploration of Subglacial Lake Ellsworth

    NASA Astrophysics Data System (ADS)

    Ross, N.

    2012-12-01

    Antarctic subglacial lakes are thought to be extreme habitats for microbial life and may contain important records of ice sheet history within their lake-floor sediments. To find if this is true, and to answer the science questions that would follow, direct measurement and sampling of these environments is required. Ever since the water depth of Vostok Subglacial Lake in East Antarctica was shown to be >500 m, attention has been given to how these unique, ancient and pristine subglacial environments may be entered without contamination and adverse disturbance. Several organizations have offered guidelines on the desirable cleanliness and sterility requirements for direct sampling experiments, including the US National Academy of Sciences and the Scientific Committee on Antarctic Research. The aims, design and implementation of subglacial lake access experiments have direct relevance for the exploration of extra-terrestrial ice-covered bodies (e.g. Europa) and the search for microbial life elsewhere in the Solar System. This presentation summarizes the scientific protocols and methods being developed for the exploration of Ellsworth Subglacial Lake in West Antarctica, and provides an up-to-date summary of the status of the project. The proposed exploration, planned for December 2012, involves accessing the lake using a hot-water drill and deploying a sampling probe and sediment corer to allow in situ measurement and sample collection. Details are presented on how this can be undertaken with minimal environmental impact that maximizes scientific return without compromising the environment for future experiments. The implications of this experiment for the search for extra-terrestrial life will be discussed.

  13. Lake Constance

    Atmospheric Science Data Center

    2013-04-17

    article title:  Lake Constance, Europe     View ... This Multi-angle Imaging SpectroRadiometer (MISR) image of Lake Constance covers an area measuring 355 kilometers x 287 kilometers, and ... wastewater and fertilizers. This leads to overproduction of algae and aquatic plants, exhaustion of available oxygen, loss of some fish ...

  14. Source of Lake Vostok Cations Constrained with Strontium Isotopes

    NASA Astrophysics Data System (ADS)

    Lyons, William; Welch, Kathleen; Priscu, John; Tranter, Martyn; Royston-Bishop, George

    2016-08-01

    Lake Vostok is the largest sub-glacial lake in Antarctica. The primary source of our current knowledge regarding the geochemistry and biology of the lake comes from the analysis of refrozen lake water associated with ice core drilling. Several sources of dissolved ions and particulate matter to the lake have been proposed, including materials from the melted glacier ice, the weathering of underlying geological materials, hydrothermal activity and underlying, ancient evaporitic deposits. A sample of Lake Vostok Type 1 accretion ice has been analyzed for its 87Sr/86Sr signature as well as its major cation and anion and Sr concentrations. The strontium isotope ratio of 0.71655 and the Ca/Sr ratio in the sample strongly indicate that the major source of the Sr is from aluminosilicate minerals from the continental crust. These data imply that at least a portion of the other cations in the Type 1 ice also are derived from continental crustal materials and not hydrothermal activity, the melted glacier ice, or evaporitic sources.

  15. Contaminant Monitoring Strategy for Henrys Lake, Idaho

    SciTech Connect

    John S. Irving; R. P. Breckenridge

    1992-12-01

    result of severe cattle grazing along riparian areas and deltas. Groundwater and springs also feed the lake, and are likely critical for oxygen supply during winter stratification. During the winter of 1991, Henrys Lake experienced low dissolved oxygen levels resulting in large fish kills. It is thought that thick ice cover combined with an increase in nutrient loads created conditions resulting in poor water quality. The Idaho Department of Health and Welfare, DEQ is currently conducting a study to determine the water quality of Henrys Lake, the sources contributing to its deterioration, and potential remedial actions to correct problem areas.

  16. Contributions of an ancient evaporitic-type reservoir to subglacial Lake Vostok chemistry

    NASA Astrophysics Data System (ADS)

    De Angelis, M.; Petit, J.-R.; Savarino, J.; Souchez, R.; Thiemens, M. H.

    2004-06-01

    We present here the first comprehensive study of the chemical composition of accretion ice from Lake Vostok. Ion chromatographic analyses were performed on samples obtained along the deeper part of the Vostok ice core. Samples were taken from 3350 down to 3611 m depth, both in glacier ice and subglacial lake ice. The total ionic contents of two accretion ice layers—a few meters thick and centered around 3540 and 3590 m depth—are several times lower than those of glacier ice. Very low concentrations were also observed in the deeper part of accretion ice, below 3609 m depth. Elsewhere, the total ionic content is variable but remains 5 to 50 times higher than in glacier ice. Whatever its total ionic content, the ionic composition of accretion ice is significantly different from what is observed in glacier ice. It is dominated by sodium chloride, homogeneously distributed throughout the ice lattice, as well as calcium and magnesium sulfate, likely located in solid inclusions, or to a lesser extent at grain boundaries. Chemical considerations combined with additional studies of sulfur and oxygen isotopes in sulfate, and iron measurements strongly suggest that glacier water recycling and bedrock hydrolysis do not play a prominent role in providing impurities to accretion ice. It is more likely that NaCl rich water carrying fine sulfate salt particles is sporadically incorporated in the ice accreting in a shallow bay upstream from Vostok. The origin of such salty water, which should also contribute to Lake salinity, is discussed.

  17. Amino acids in the Tagish Lake Meteorite

    NASA Technical Reports Server (NTRS)

    Kminek, G.; Botta, O.; Glavin, D. P.; Bada, J. L.

    2002-01-01

    High-performance liquid chromatography (HPLC) based amino acid analysis of a Tagish Lake meteorite sample recovered 3 months after the meteorite fell to Earth have revealed that the amino acid composition of Tagish Lake is strikingly different from that of the CM and CI carbonaceous chondrites. We found that the Tagish Lake meteorite contains only trace levels of amino acids (total abundance = 880 ppb), which is much lower than the total abundance of amino acids in the CI Orgueil (4100 ppb) and the CM Murchison (16 900 ppb). Because most of the same amino acids found in the Tagish Lake meteorite are also present in the Tagish Lake ice melt water, we conclude that the amino acids detected in the meteorite are terrestrial contamination. We found that the exposure of a sample of Murchison to cold water lead to a substantial reduction over a period of several weeks in the amount of amino acids that are not strongly bound to the meteorite matrix. However, strongly bound amino acids that are extracted by direct HCl hydrolysis are not affected by the leaching process. Thus even if there had been leaching of amino acids from our Tagish Lake meteorite sample during its 3 month residence in Tagish Lake ice and melt water, a Murchison type abundance of endogenous amino acids in the meteorite would have still been readily detectable. The low amino acid content of Tagish Lake indicates that this meteorite originated fiom a different type of parent body than the CM and CI chondrites. The parent body was apparently devoid of the reagents such as aldehyldes/ketones, HCN and ammonia needed for the effective abiotic synthesis of amino acids. Based on reflectance spectral measurements, Tagish Lake has been associated with P- or D-type asteroids. If the Tagish Lake meteorite was indeed derived fiom these types of parent bodies, our understanding of these primitive asteroids needs to be reevaluated with respect to their potential inventory of biologically important organic compounds.

  18. Remote sensing of snow and ice: A review of the research in the United States 1975 - 1978

    NASA Technical Reports Server (NTRS)

    Rango, A.

    1979-01-01

    Research work in the United States from 1975-1978 in the field of remote sensing of snow and ice is reviewed. Topics covered include snowcover mapping, snowmelt runoff forecasting, demonstration projects, snow water equivalent and free water content determination, glaciers, river and lake ice, and sea ice. A bibliography of 200 references is included.

  19. Global patterns in lake surface temperature trends

    NASA Astrophysics Data System (ADS)

    O'Reilly, C.; Sharma, S.; Gray, D.; Hampton, S. E.; Read, J. S.; Rowley, R.; McIntyre, P. B.; Lenters, J. D.; Schneider, P.; Hook, S. J.

    2014-12-01

    Temperature profoundly affects dynamics in the water bodieson which human societies depend worldwide. Even relatively small water temperature changes can alter lake thermal structure with implications for water level, nutrient cycling, ecosystem productivity, and food web dynamics. As air temperature increases with climate change and human land use transforms watersheds, rising water temperatures have been reported for individual lakes or regions, but a global synthesis is lacking; such a synthesis is foundational for understanding the state of freshwater resources. We investigated global patterns in lake surface water temperatures between 1985 and 2009 using in-situ and satellite data from 236 lakes. We demonstrate that lakes are warming significantly around the globe, at an average rate of 0.34 °C per decade. The breadth of lakes in this study allowed examination of the diversity of drivers across global lakes, and highlighted the importance of ice cover in determining the suite of morphological and climate drivers for lake temperature dynamics. These empirical results are consistent with modeled predictions of climate change, taking into account the extent to which water warming can be modulated by local environmental conditions and thus defy simple correlations with air temperature. The water temperature changes we report have fundamental importance for thermal structure and ecosystem functioning in global water resources; recognition of the extent to which lakes are currently in transition should have broad implications for regional and global models as well as for management.

  20. Recent advances in understanding Antarctic subglacial lakes and hydrology.

    PubMed

    Siegert, Martin J; Ross, Neil; Le Brocq, Anne M

    2016-01-28

    It is now well documented that over 400 subglacial lakes exist across the bed of the Antarctic Ice Sheet. They comprise a variety of sizes and volumes (from the approx. 250 km long Lake Vostok to bodies of water less than 1 km in length), relate to a number of discrete topographic settings (from those contained within valleys to lakes that reside in broad flat terrain) and exhibit a range of dynamic behaviours (from 'active' lakes that periodically outburst some or all of their water to those isolated hydrologically for millions of years). Here we critique recent advances in our understanding of subglacial lakes, in particular since the last inventory in 2012. We show that within 3 years our knowledge of the hydrological processes at the ice-sheet base has advanced considerably. We describe evidence for further 'active' subglacial lakes, based on satellite observation of ice-surface changes, and discuss why detection of many 'active' lakes is not resolved in traditional radio-echo sounding methods. We go on to review evidence for large-scale subglacial water flow in Antarctica, including the discovery of ancient channels developed by former hydrological processes. We end by predicting areas where future discoveries may be possible, including the detection, measurement and significance of groundwater (i.e. water held beneath the ice-bed interface).

  1. Recent advances in understanding Antarctic subglacial lakes and hydrology.

    PubMed

    Siegert, Martin J; Ross, Neil; Le Brocq, Anne M

    2016-01-28

    It is now well documented that over 400 subglacial lakes exist across the bed of the Antarctic Ice Sheet. They comprise a variety of sizes and volumes (from the approx. 250 km long Lake Vostok to bodies of water less than 1 km in length), relate to a number of discrete topographic settings (from those contained within valleys to lakes that reside in broad flat terrain) and exhibit a range of dynamic behaviours (from 'active' lakes that periodically outburst some or all of their water to those isolated hydrologically for millions of years). Here we critique recent advances in our understanding of subglacial lakes, in particular since the last inventory in 2012. We show that within 3 years our knowledge of the hydrological processes at the ice-sheet base has advanced considerably. We describe evidence for further 'active' subglacial lakes, based on satellite observation of ice-surface changes, and discuss why detection of many 'active' lakes is not resolved in traditional radio-echo sounding methods. We go on to review evidence for large-scale subglacial water flow in Antarctica, including the discovery of ancient channels developed by former hydrological processes. We end by predicting areas where future discoveries may be possible, including the detection, measurement and significance of groundwater (i.e. water held beneath the ice-bed interface). PMID:26667914

  2. Recent advances in understanding Antarctic subglacial lakes and hydrology

    PubMed Central

    Siegert, Martin J.; Ross, Neil; Le Brocq, Anne M.

    2016-01-01

    It is now well documented that over 400 subglacial lakes exist across the bed of the Antarctic Ice Sheet. They comprise a variety of sizes and volumes (from the approx. 250 km long Lake Vostok to bodies of water less than 1 km in length), relate to a number of discrete topographic settings (from those contained within valleys to lakes that reside in broad flat terrain) and exhibit a range of dynamic behaviours (from ‘active’ lakes that periodically outburst some or all of their water to those isolated hydrologically for millions of years). Here we critique recent advances in our understanding of subglacial lakes, in particular since the last inventory in 2012. We show that within 3 years our knowledge of the hydrological processes at the ice-sheet base has advanced considerably. We describe evidence for further ‘active’ subglacial lakes, based on satellite observation of ice-surface changes, and discuss why detection of many ‘active’ lakes is not resolved in traditional radio-echo sounding methods. We go on to review evidence for large-scale subglacial water flow in Antarctica, including the discovery of ancient channels developed by former hydrological processes. We end by predicting areas where future discoveries may be possible, including the detection, measurement and significance of groundwater (i.e. water held beneath the ice-bed interface). PMID:26667914

  3. Hydrology of the lakes in Central Wohlthat Massif, East Antarctica: new results.

    PubMed

    Haendel, Dietmar; Hermichen, Wolf-Dieter; Höfling, Reiner; Kowski, Peter

    2011-12-01

    In 1983/1984, in the course of the 28th Soviet Antarctic Expedition, waterbody, ice cover, and surrounding glaciers of the lakes Untersee and Obersee were sampled along some depth profiles. The geochemical data of those samples, now available, show the homogeneity of both large lakes in vertical (down to the maximum depth) as well as in lateral directions. The comparison of isotope and chemical composition of lake water and adjoining glacier ice suggests strong differences in the long-term evolution between the lakes Untersee and Obersee. First data from a lakelet, embedded in the large morainic area to the west of Lake Untersee, are of special interest: the δ(2)H values of the lakelet water are lower than those of recent regional glacier ice by 50‰ SMOW. This fact indicates that the lakelet is fed episodically by Pleistocene dead ice, covered by the morainic material.

  4. Forecasting Lake-Effect Precipitation in the Great Lakes Region Using NASA Enhanced-Satellite Data

    NASA Technical Reports Server (NTRS)

    Cipullo, Michelle; Molthan, Andrew; Shafer, Jackie; Case, Jonathan; Jedlovec, Gary

    2011-01-01

    Lake-effect precipitation is common in the Great Lakes region, particularly during the late fall and winter. The synoptic processes of lake-effect precipitation are well understood by operational forecasters, but individual forecast events still present a challenge. Locally run, high resolution models can assist the forecaster in identifying the onset and duration of precipitation, but model results are sensitive to initial conditions, particularly the assumed surface temperature of the Great Lakes. The NASA Short-term Prediction Research and Transition (SPoRT) Center has created a Great Lakes Surface Temperature (GLST) composite, which uses infrared estimates of water temperatures obtained from the MODIS instrument aboard the Aqua and Terra satellites, other coarser resolution infrared data when MODIS is not available, and ice cover maps produced by the NOAA Great Lakes Environmental Research Lab (GLERL). This product has been implemented into the Weather Research and Forecast (WRF) model Environmental Modeling System (WRF-EMS), used within forecast offices to run local, high resolution forecasts. The sensitivity of the model forecast to the GLST product was analyzed with a case study of the Lake Effect Storm Echinacea, which produced 10 to 12 inches of snowfall downwind of Lake Erie, and 8 to 18 inches downwind of Lake Ontario from 27-29 January 2010. This research compares a forecast using the default Great Lakes surface temperatures from the Real Time Global sea surface temperature (RTG SST), in the WRF-EMS model to the enhanced NASA SPoRT GLST product to study forecast impacts. Results from this case study show that the SPoRT GLST contained less ice cover over Lake Erie and generally cooler water temperatures over Lakes Erie and Ontario. Latent and sensible heat fluxes over Lake Ontario were decreased in the GLST product. The GLST product decreased the quantitative precipitation forecast (QPF), which can be correlated to the decrease in temperatures and heat

  5. The distribution of basal water between Antarctic subglacial lakes from radar sounding.

    PubMed

    Young, D A; Schroeder, D M; Blankenship, D D; Kempf, Scott D; Quartini, E

    2016-01-28

    Antarctica's subglacial lakes have two end member geophysical expressions: as hydraulically flat, radar reflective regions highlighted in ice surface topography and radar sounding profiles ('definite lakes'), and as localized sites of elevation change identified from repeat elevation observations ('active lakes') that are often found in fast flowing ice streams or enhanced ice flow tributaries. While 'definite lakes' can be identified readily by high bed reflectivity in radar sounding, the identification and characterization of less distinct subglacial lakes and water systems with radar sounding are complicated by variable radio-wave attenuation in the overlying ice. When relying on repeat elevation observations, the relatively short times series and biased distribution of elevation observations, along with the episodic nature of 'active lake' outflow and replenishment, limit our understanding of how water flows under the ice sheet. Using recently developed methods for quantifying the radar scattering behaviour of the basal interface of the ice, we can avoid the