Up-going Red Water in the Ice at the Bottom of the World: Picture Taking Boxes and Listening Boxes Tell Us How and Why

NASA Astrophysics Data System (ADS)

Carr, C. G.; Pettit, E. C.

2017-12-01

Blood Falls is a place where red water comes out from under ice to the top of the ice and makes a strange red water fall. This ice is part of the big ice at the bottom of the world. The red water only comes out at some times and not every year, but it always comes out at the same place. The red water is important because it has tiny tiny not-animal life that tells us how life could be on other worlds. Knowing about the ice and red water is important because this ice is cold, colder than other ice in other places, and we want to know how water can get through. We didn't know why the red water comes up from under the ice when it does or how. We wanted to understand how the ice breaks and we watched the ice by taking pictures all year to see when the red water comes out. We found out that in the cold part of one year, the red water came out even though the air was not warm enough for water to be water! We think the red water comes out because the red water is blocked under the heavy ice and gets pushed tight. In the cold part of the year, cracks break down from the air into the ice and other cracks break up from under the ice because the red water is so pushed. The cracks from the top and bottom of the ice join, and the red water comes out. We used listening boxes that can feel how the ground moves to understand that the ice is breaking at the bottom and we can see that it breaks at the top of the ice. The red water can stay water and not ice inside the big ice because the red water has tiny pieces of the same stuff that can turn ice into water on the roads. If the ice breaks in the cold time, no water can get in from the top of the ice, so the red water under the ice stays clean from the air water. If the ice breaks in the warm time of year, water could get in from the top of the ice and make the red water under the ice not clean from the air. Since we saw in our pictures that the red water came out in the cold time of year, this means the red water could stay clean from the air. Maybe we can use this to tell us how life on other worlds could stay clean and safe under ice. It can also tell us how water can get through very cold ice.

Laboratory Studies of Sea-Ice-Wave Interactions

NASA Astrophysics Data System (ADS)

Monty, J.; Meylan, M. H.; Babanin, A. V.; Toffoli, A.; Bennetts, L.

2016-12-01

A world-first facility for studying the Marginal Ice Zone has been constructed in the Michell Hydrodynamics Laboratory at the University of Melbourne. A 14m long wave tank (0.75m wide, 0.6m deep) resides in a freezer, where air temperature can be controlled down to -15C. This permits the freezing of the water surface. Large stainless steel ice-making trays (up to 4 m long) are also available to create ice of desired thickness and microstructure, which can be lowered onto the water surface. A computer controlled wave generator is capable of creating waves of any desired form. The temperature of the water in the tank can also be controlled between 2 and 30C. The tank frame is constructed of marine-treated wood and the entire tank is glass and acrylic, permitting the use of corrosive fluids, such as salt water. Here we present the first laboratory experiments of break-up of a controlled thickness, fresh water ice sheet impacted by regular and JONSWAP spectrum surface waves. The geometry of the resultant ice-floes is measured with high-resolution, time-resolved imaging, providing the crucial data of floe size distribution. Initial observations show that, in the case of high steepness waves, the primary mechanisms of ice break-up at the ice edge are overwash and rafting, both of which put weight on the ice interior to the ice-water interface. This additional weight (and impact in the case of rafting) breaks more ice, which allows overwash and rafting deeper into the ice sheet, breaking more ice and so on. For lower steepness waves, overwash and rafting are still present but far less significant. Finally, results of vertical ice movement using laser height gauges will be presented showing the attenuation of waves into an ice sheet and through a pack of ice floes. These results are compared with field data and theory available (e.g. Squire & Moore, Nature, 1980 and Kohout et al., Nature, 2014).

Snowmelt Pattern and Lake Ice Phenology around Tibetan Plateau Estimated from Enhanced Resolution Passive Microwave Data

NASA Astrophysics Data System (ADS)

Xiong, C.; Shi, J.; Wang, T.

2017-12-01

Snow and ice is very sensitive to the climate change. Rising air temperature will cause the snowmelt time change. In contrast, the change in snow state will have feedback on climate through snow albedo. The snow melt timing is also correlated with the associated runoff. Ice phenology describes the seasonal cycle of lake ice cover and includes freeze-up and breakup periods and ice cover duration, which is an important weather and climate indicator. It is also important for lake-atmosphere interactions and hydrological and ecological processes. The enhanced resolution (up to 3.125 km) passive microwave data is used to estimate the snowmelt pattern and lake ice phenology on and around Tibetan Plateau. The enhanced resolution makes the estimation of snowmelt and lake ice phenology in more spatial detail compared to previous 25 km gridded passive microwave data. New algorithm based on smooth filters and change point detection was developed to estimate the snowmelt and lake ice freeze-up and break-up timing. Spatial and temporal pattern of snowmelt and lake ice phonology are estimated. This study provides an objective evidence of climate change impact on the cryospheric system on Tibetan Plateau. The results show significant earlier snowmelt and lake ice break-up in some regions.

Sea Ice and Oceanographic Conditions.

ERIC Educational Resources Information Center

Oceanus, 1986

1986-01-01

The coastal waters of the Beaufort Sea are covered with ice three-fourths of the year. These waters (during winter) are discussed by considering: consolidation of coastal ice; under-ice water; brine circulation; biological energy; life under the ice (including kelp and larger animals); food chains; and ice break-up. (JN)

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).

Late-Quaternary glaciation and postglacial emergence, southern Eureka Sound, high-Arctic Canada

NASA Astrophysics Data System (ADS)

O Cofaigh, Colm Seamus

Eureka Sound is the inter-island channel separating Ellesmere and Axel Heiberg islands, High Arctic Canada. This thesis reconstructs the glacial and sea level history of southern Eureka Sound through surficial geological mapping, studies of glacial sedimentology and geomorphology, surveying of raised marine shorelines, radiocarbon dating of marine shells and driftwood and surface exposure dating of erratics and bedrock. Granite dispersal trains, shelly till and ice-moulded bedrock record westerly-flow of warm-based, regional ice into Eureka Sound from a source on southeastern Ellesmere Island during the late Wisconsinan. Regional ice was coalescent with local ice domes over Raanes and northern Svendsen peninsulas. Marine limit (dating <=9.2 ka BP; <=9.9 ka cal BP) is inset into the dispersal trains and records early Holocene deglaciation of regional ice. Collectively these data indicate an extensive ice-cover in southern Eureka Sound during the Last Glacial Maximum. Ice-divides were located along the highlands of central Ellesmere and Axel Heiberg islands, from which ice converged on Eureka Sound, and subsequently flowed north and south along the channel. Deglaciation was characterised by a two-step retreat pattern, likely triggered by eustatic sea level rise and abrupt early Holocene warming. Initial break-up and radial retreat of ice in Eureka Sound and the larger fiords, preceded terrestrial stabilisation along coastlines and inner fiords. Location of deglacial depocentres was predominantly controlled by fiord bathymetry. Regionally, two-step deglaciation is reflected by prominent contrasts in glacial geomorphology between the inner and outer parts of many fiords. Glacial sedimentological and geomorphological evidence indicates spatial variation in basal thermal regime between retreating trunk glaciers. Holocene emergence of up to 150 m asl along southern Eureka Sound is recorded by raised marine deltas, beaches and washing limits. Emergence curves exhibit marked contrasts in the form and rate of initial unloading. Isobases drawn on the 8.5 ka shoreline for greater Eureka Sound demonstrate that a cell of highest emergence extends along the length of the channel, and closes in the vicinity of the entrance to Norwegian Bay. The isobase pattern indicates a distinct loading centre over the sound, and in conjunction with glacial geological evidence, suggests that the thickest late Wisconsinan ice lay over the channel.

Circulation and water properties in the landfast ice zone of the Alaskan Beaufort Sea

NASA Astrophysics Data System (ADS)

Weingartner, Thomas J.; Danielson, Seth L.; Potter, Rachel A.; Trefry, John H.; Mahoney, Andy; Savoie, Mark; Irvine, Cayman; Sousa, Leandra

2017-09-01

Moorings, hydrography, satellite-tracked drifters, and high-frequency radar data describe the annual cycle in circulation and water properties in the landfast ice zone (LIZ) of the Alaskan Beaufort Sea. Three seasons, whose duration and characteristics are controlled by landfast ice formation and ablation, define the LIZ: ;winter;, ;break-up;, and ;open-water;. Winter begins in October with ice formation and ends in June when rivers commence discharging. Winter LIZ ice velocities are zero, under-ice currents are weak ( 5 cm s-1), and poorly correlated with winds and local sea level. The along-shore momentum balance is between along-shore pressure gradients and bottom and ice-ocean friction. Currents at the landfast ice-edge are swift ( 35 cm s-1), wind-driven, with large horizontal shears, and potentially unstable. Weak cross-shore velocities ( 1 cm s-1) imply limited exchanges between the LIZ and the outer shelf in winter. The month-long break-up season (June) begins with the spring freshet and concludes when landfast ice detaches from the bottom. Cross-shore currents increase, and the LIZ hosts shallow ( 2 m), strongly-stratified, buoyant and sediment-laden, under-ice river plumes that overlie a sharp, 1 m thick, pycnocline across which salinity increases by 30. The plume salt balance is between entrainment and cross-shore advection. Break-up is followed by the 3-month long open-water season when currents are swift (≥20 cm s-1) and predominantly wind-driven. Winter water properties are initialized by fall advection and evolve slowly due to salt rejection from ice. Fall waters and ice within the LIZ derive from local rivers, the Mackenzie and/or Chukchi shelves, and the Arctic basin.

Baggie: A unique solution to an orbiter icing problem

NASA Technical Reports Server (NTRS)

Walkover, L. J.

1982-01-01

The orbiter icing problem, located in two lower surface mold line cavities, was solved. These two cavities are open during Shuttle ground operations and ascent, and are then closed after orbit insertion. If not protected, these cavities may be coated with ice, which may be detrimental to the adjacent thermal protection system (TPS) tiles if the ice breaks up during ascent, and may hinder the closing of the cavity doors if the ice does not break up. The problem of ice in these cavities was solved by the use of a passive mechanism called baggie, which is purge curtain used to enclose the cavity and is used in conjunction with gaseous nitrogen as the local purge gas. The baggie, the final solution, is unique in its simplicity, but its design and development were not. The final baggie design and its development testing are discussed. Also discussed are the baggie concepts and other solutions not used.

RADARSAT-2 Polarimetric Radar Imaging for Lake Ice Mapping

NASA Astrophysics Data System (ADS)

Pan, F.; Kang, K.; Duguay, C. R.

2016-12-01

Changes in lake ice dates and duration are useful indicators for assessing long-term climate trends and variability in northern countries. Lake ice cover observations are also a valuable data source for predictions with numerical ice and weather forecasting models. In recent years, satellite remote sensing has assumed a greater role in providing observations of lake ice cover extent for both modeling and climate monitoring purposes. Polarimetric radar imaging has become a promising tool for lake ice mapping at high latitudes where meteorological conditions and polar darkness severely limit observations from optical sensors. In this study, we assessed and characterized the physical scattering mechanisms of lake ice from fully polarimetric RADARSAT-2 datasets obtained over Great Bear Lake, Canada, with the intent of classifying open water and different ice types during the freeze-up and break-up periods. Model-based and eigen-based decompositions were employed to construct the coherency matrix into deterministic scattering mechanisms. These procedures as well as basic polarimetric parameters were integrated into modified convolutional neural networks (CNN). The CNN were modified via introduction of a Markov random field into the higher iterative layers of networks for acquiring updated priors and classifying ice and open water areas over the lake. We show that the selected polarimetric parameters can help with interpretation of radar-ice/water interactions and can be used successfully for water-ice segmentation, including different ice types. As more satellite SAR sensors are being launched or planned, such as the Sentinel-1a/b series and the upcoming RADARSAT Constellation Mission, the rapid volume growth of data and their analysis require the development of robust automated algorithms. The approach developed in this study was therefore designed with the intent of moving towards fully automated mapping of lake ice for consideration by ice services.

The Autumn of break-ups: When Jakobshavn Isbrae lost its floating tongue

NASA Astrophysics Data System (ADS)

Aschwanden, A.; Fahnestock, M. A.; Truffer, M.; Motyka, R. J.

2015-12-01

Capturing the temporal variability in outlet glacier flow remains one of the holy grails in ice sheet modeling. Here we demonstrate progress using the three-dimensional Parallel Ice Sheet Model. Using a first-order calving law and prescribed subshelf basal melt rates, we performed high-resolution (<1km) hindcasts of the Greenland Ice Sheet of the 1989-2012 period. These hindcasts allow us to study the processes governing ice-shelf thinning, break-up, and subsequent speed-ups and dynamic thinning. Focussing our analysis on the Jakobshavn basin we show that our simulations are able to capture the thinning of the floating tongue resulting from increased subshelf basal melt rates. Furthermore, our simulations capture both the magnitude and the timing of the dynamic thinning associated with the loss of the floating tongue, as well as the speed-up. We find little seasonal variations in surface speeds prior to 1995, and strong variations thereafter, in good agreement with observations of Echelmeyer and Harrison (1991) and Joughin et al (2012).

Long-term patterns of benthic irradiance and kelp production in the central Beaufort sea reveal implications of warming for Arctic inner shelves

NASA Astrophysics Data System (ADS)

Bonsell, Christina; Dunton, Kenneth H.

2018-03-01

This study synthesizes a multidecadal dataset of annual growth of the Arctic endemic kelp Laminaria solidungula and corresponding measurements of in situ benthic irradiance from Stefansson Sound in the central Beaufort Sea. We incorporate long-term data on sea ice concentration (National Sea Ice Data Center) and wind (National Weather Service) to assess how ice extent and summer wind dynamics affect the benthic light environment and annual kelp production. We find evidence of significant changes in sea ice extent in Stefansson Sound, with an extension of the ice-free season by approximately 17 days since 1979. Although kelp elongation at 5-7 m depths varies significantly among sites and years (3.8-49.8 cm yr-1), there is no evidence for increased production with either earlier ice break-up or a longer summer ice-free period. This is explained by very low light transmittance to the benthos during the summer season (mean daily percent surface irradiance ± SD: 1.7 ± 3.6 to 4.5 ± 6.6, depending on depth, with light attenuation values ranging from 0.5 to 0.8 m-1), resulting in minimal potential for kelp production on most days. Additionally, on month-long timescales (35 days) in the ice-free summer, benthic light levels are negatively related to wind speed. The frequent, wind-driven resuspension of sediments following ice break-up significantly reduce light to the seabed, effectively nullifying the benefits of an increased ice-free season on annual kelp growth. Instead, benthic light and primary production may depend substantially on the 1-3 week period surrounding ice break-up when intermediate sea ice concentrations reduce wind-driven sediment resuspension. These results suggest that both benthic and water column primary production along the inner shelf of Arctic marginal seas may decrease, not increase, with reductions in sea ice extent.

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).

Mechanical sea-ice strength parameterized as a function of ice temperature

NASA Astrophysics Data System (ADS)

Hata, Yukie; Tremblay, Bruno

2016-04-01

Mechanical sea-ice strength is key for a better simulation of the timing of landlock ice onset and break-up in the Canadian Arctic Archipelago (CAA). We estimate the mechanical strength of sea ice in the CAA by analyzing the position record measured by the several buoys deployed in the CAA between 2008 and 2013, and wind data from the Canadian Meteorological Centre's Global Deterministic Prediction System (CMC_GDPS) REforecasts (CGRF). First, we calculate the total force acting on the ice using the wind data. Next, we estimate upper (lower) bounds on the sea-ice strength by identifying cases when the sea ice deforms (does not deform) under the action of a given total force. Results from this analysis show that the ice strength of landlock sea ice in the CAA is approximately 40 kN/m on the landfast ice onset (in ice growth season). Additionally, it becomes approximately 10 kN/m on the landfast ice break-up (in melting season). The ice strength decreases with ice temperature increase, which is in accord with results from Johnston [2006]. We also include this new parametrization of sea-ice strength as a function of ice temperature in a coupled slab ocean sea ice model. The results from the model with and without the new parametrization are compared with the buoy data from the International Arctic Buoy Program (IABP).

Worldwide Emerging Environmental Issues Affecting the U.S. Military. March 2008 Report

DTIC Science & Technology

2008-03-01

Shelf of western Antarctica, a chunk of ice with an area of about 400 sq km broke up into icebergs . This might trigger the disintegration of a larger...allafrica.com/stories/200803041273.html Earth from Space: Further break-up of Antarctic ice shelf http://www.esa.int/esaEO/SEMMX4R03EF_index_0.html...200803041273.html Antarctic Ice Shelf Disintegration Underscores a Warming World http://nsidc.org/news/press/20080325_Wilkins.html Antarctic ice shelf

Strong and highly variable push of ocean waves on Southern Ocean sea ice.

PubMed

Stopa, Justin E; Sutherland, Peter; Ardhuin, Fabrice

2018-06-05

Sea ice in the Southern Ocean has expanded over most of the past 20 y, but the decline in sea ice since 2016 has taken experts by surprise. This recent evolution highlights the poor performance of numerical models for predicting extent and thickness, which is due to our poor understanding of ice dynamics. Ocean waves are known to play an important role in ice break-up and formation. In addition, as ocean waves decay, they cause a stress that pushes the ice in the direction of wave propagation. This wave stress could not previously be quantified due to insufficient observations at large scales. Sentinel-1 synthetic aperture radars (SARs) provide high-resolution imagery from which wave height is measured year round encompassing Antarctica since 2014. Our estimates give an average wave stress that is comparable to the average wind stress acting over 50 km of sea ice. We further reveal highly variable half-decay distances ranging from 400 m to 700 km, and wave stresses from 0.01 to 1 Pa. We expect that this variability is related to ice properties and possibly different floe sizes and ice thicknesses. A strong feedback of waves on sea ice, via break-up and rafting, may be the cause of highly variable sea-ice properties.

Meteorological conditions influencing the formation of level ice within the Baltic Sea

NASA Astrophysics Data System (ADS)

Mazur, A. K.; Krezel, A.

2012-12-01

The Baltic Sea is covered by ice every winter and on average, the ice-covered area is 45% of the total area of the Baltic Sea. The beginning of ice season usually starts in the end of November, ice extent is the largest between mid-February and mid-March and sea ice disappears completely in May. The ice covered areas during a typical winter are the Gulf of Bothnia, the Gulf of Finland and the Gulf of Riga. The studies of sea ice in the Baltic Sea are related to two aspects: climate and marine transport. Depending on the local weather conditions during the winter different types of sea ice can be formed. From the point of winter shipping it is important to locate level and deformed ice areas (rafted ice, ridged ice, and hummocked ice). Because of cloud and daylight independency as well as good spatial resolution, SAR data seems to be the most suitable source of data for sea ice observation in the comparatively small area of the Baltic Sea. We used ASAR Wide Swath Mode data with spatial resolution 150 m. We analyzed data from the three winter seasons which were examples of severe, typical and mild winters. To remove the speckle effect the data were resampled to 250 m pixel size and filtred using Frost filter 5x5. To detect edges we used Sobel filter. The data were also converted into grayscale. Sea ice classification was based on Object-Based Image Analysis (OBIA). Object-based methods are not a common tool in sea ice studies but they seem to accurately separate level ice within the ice pack. The data were segmented and classified using eCognition Developer software. Level ice were classified based on texture features defined by Haralick (Grey Level Co-Occurrence Matrix homogeneity, GLCM contrast, GLCM entropy and GLCM correlation). The long-term changes of the Baltic Sea ice conditions have been already studied. They include date of freezing, date of break-up, sea ice extent and some of work also ice thickness. There is a little knowledge about the relationship of short term changes in sea ice cover and meteorological conditions. In following studies we analyzed the formation of level sea ice depending on some weather conditions (temperature, humidity, pressure at sea level, 10 meter wind). It can be clearly seen that the most important factors influencing formation of level ice are the temperature and wind.

Deciphering the evolution of the last Eurasian ice sheets

NASA Astrophysics Data System (ADS)

Hughes, Anna; Gyllencreutz, Richard; Mangerud, Jan; Svendsen, John Inge

2016-04-01

Glacial geologists need ice sheet-scale chronological reconstructions of former ice extent to set individual records in a wider context and compare interpretations of ice sheet response to records of past environmental changes. Ice sheet modellers require empirical reconstructions on size and volume of past ice sheets that are fully documented, specified in time and include uncertainty estimates for model validation or constraints. Motivated by these demands, in 2005 we started a project (Database of the Eurasian Deglaciation, DATED) to compile and archive all published dates relevant to constraining the build-up and retreat of the last Eurasian ice sheets, including the British-Irish, Scandinavian and Svalbard-Barents-Kara Seas ice sheets (BIIS, SIS and SBKIS respectively). Over 5000 dates were assessed for reliability and used together with published ice-sheet margin positions to reconstruct time-slice maps of the ice sheets' extent, with uncertainty bounds, every 1000 years between 25-10 kyr ago and at four additional periods back to 40 kyr ago. Ten years after the idea for a database was conceived, the first version of results (DATED-1) has now been released (Hughes et al. 2016). We observe that: i) both the BIIS and SBKIS achieve maximum extent, and commence retreat earlier than the larger SIS; ii) the eastern terrestrial margin of the SIS reached its maximum extent up to 7000 years later than the westernmost marine margin; iii) the combined maximum ice volume (~24 m sea-level equivalent) was reached c. 21 ka; iv) large uncertainties exist; predominantly across marine sectors (e.g. the timing of coalescence and separation of the SIS and BKIS) but also in well-studied areas due to conflicting yet equally robust data. In just three years since the DATED-1 census (1 January 2013), the volume of new information (from both dates and mapped glacial geomorphology) has grown significantly (~1000 new dates). Here, we present the DATED-1 results in the context of the climatic changes of the last glacial, discuss the implications of emerging post-census data, and describe plans for the next version of the database, DATED-2. Hughes, A. L. C., Gyllencreutz, R., Lohne, Ø. S., Mangerud, J., Svendsen, J. I. 2016: The last Eurasian ice sheets - a chronological database and time-slice reconstruction, DATED-1. Boreas, 45, 1-45. 10.1111/bor.12142

Impacts of a lengthening open water season on Alaskan coastal communities: deriving locally relevant indices from large-scale datasets and community observations

NASA Astrophysics Data System (ADS)

Rolph, Rebecca J.; Mahoney, Andrew R.; Walsh, John; Loring, Philip A.

2018-05-01

Using thresholds of physical climate variables developed from community observations, together with two large-scale datasets, we have produced local indices directly relevant to the impacts of a reduced sea ice cover on Alaska coastal communities. The indices include the number of false freeze-ups defined by transient exceedances of ice concentration prior to a corresponding exceedance that persists, false break-ups, timing of freeze-up and break-up, length of the open water duration, number of days when the winds preclude hunting via boat (wind speed threshold exceedances), the number of wind events conducive to geomorphological work or damage to infrastructure from ocean waves, and the number of these wind events with on- and along-shore components promoting water setup along the coastline. We demonstrate how community observations can inform use of large-scale datasets to derive these locally relevant indices. The two primary large-scale datasets are the Historical Sea Ice Atlas for Alaska and the atmospheric output from a regional climate model used to downscale the ERA-Interim atmospheric reanalysis. We illustrate the variability and trends of these indices by application to the rural Alaska communities of Kotzebue, Shishmaref, and Utqiaġvik (previously Barrow), although the same procedure and metrics can be applied to other coastal communities. Over the 1979-2014 time period, there has been a marked increase in the number of combined false freeze-ups and false break-ups as well as the number of days too windy for hunting via boat for all three communities, especially Utqiaġvik. At Utqiaġvik, there has been an approximate tripling of the number of wind events conducive to coastline erosion from 1979 to 2014. We have also found a delay in freeze-up and earlier break-up, leading to a lengthened open water period for all of the communities examined.

Thermal processes of thermokarst lakes in the continuous permafrost zone of northern Siberia - observations and modeling (Lena River Delta, Siberia)

NASA Astrophysics Data System (ADS)

Boike, J.; Georgi, C.; Kirilin, G.; Muster, S.; Abramova, K.; Fedorova, I.; Chetverova, A.; Grigoriev, M.; Bornemann, N.; Langer, M.

2015-10-01

Thermokarst lakes are typical features of the northern permafrost ecosystems, and play an important role in the thermal exchange between atmosphere and subsurface. The objective of this study is to describe the main thermal processes of the lakes and to quantify the heat exchange with the underlying sediments. The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) were investigated using hourly water temperature and water level records covering a 3-year period (2009-2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. Lakes were covered by ice up to 2 m thick that persisted for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increased at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. Prior to ice break-up, solar radiation effectively warmed the water beneath the ice cover and induced convective mixing. Ice break-up started at the beginning of June and lasted until the middle or end of June. Mixing occurred within the entire water column from the start of ice break-up and continued during the ice-free periods, as confirmed by the Wedderburn numbers, a quantitative measure of the balance between wind mixing and stratification that is important for describing the biogeochemical cycles of lakes. The lake thermal regime was modeled numerically using the FLake model. The model demonstrated good agreement with observations with regard to the mean lake temperature, with a good reproduction of the summer stratification during the ice-free period, but poor agreement during the ice-covered period. Modeled sensitivity to lake depth demonstrated that lakes in this climatic zone with mean depths > 5 m develop continuous stratification in summer for at least 1 month. The modeled vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W m-2 in summer and with heat released back into the water column at a rate of less than 1 W m-2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C.

Insights into the effects of patchy ice layers on water balance heterogeneity in peatlands

NASA Astrophysics Data System (ADS)

Dixon, Simon; Kettridge, Nicholas; Devito, Kevin; Petrone, Rich; Mendoza, Carl; Waddington, Mike

2017-04-01

Peatlands in boreal and sub-arctic settings are characterised by a high degree of seasonality. During winter soils are frozen and snow covers the surface preventing peat moss growth. Conversely, in summer, soils unfreeze and rain and evapotranspiration drive moss productivity. Although advances have been made in understanding growing season water balance and moss dynamics in northern peatlands, there remains a gap in knowledge of inter-seasonal water balance as layers of ice break up during the spring thaw. Understanding the effects of ice layers on spring water balance is important as this coincides with periods of high wildfire risk, such as the devastating Fort McMurrary wildfire of May, 2016. We hypothesise that shallow layers of ice disconnect the growing surface of moss from a falling water table, and prevent water from being supplied from depth. A disconnect between the evaporating surface and deeper water storage will lead to the drying out of the surface layer of moss and a greater risk of severe spring wildfires. We utilise the unsaturated flow model Hydrus 2D to explore water balance in peat layers with an impermeable layer representing ice. Additionally we create models to represent the heterogeneous break up of ice layers observed in Canadian boreal peatlands; these models explore the ability of breaks in an ice layer to connect the evaporating surface to a deeper water table. Results show that peatlands with slower rates of moss growth respond to dry periods by limiting evapotranspiration and thus maintain moist conditions in the sub-surface and a water table above the ice layer. Peatlands which are more productive continue to grow moss and evaporate during dry periods; this results in the near surface mosses drying out and the water table dropping below the level of the ice. Where there are breaks in the ice layer the evaporating surface is able to maintain contact with a falling water table, but connectivity is limited to above the breaks, with limited lateral transfer of water above the ice. Conceptually this means that peatlands which tend to have lower rates of growth are largely unaffected by the presence of a shallow ice layer in the early growing season, and are able to maintain moist sub-surface conditions in the absence of precipitation. They will thus be more resistant to severe wildfire. Conversely, peatlands which tend towards higher levels of moss productivity are able to maintain moss growth during dry periods. In the presence of an ice layer this greater productivity leads to a disconnection from deep water sources, extensive drying out of moss above the ice, and a greater susceptibility to severe wildfires. Our study gives important insights into the mechanisms behind heterogeneity in burning and depth of burn in northern peatland wildfires, as well as into burn heterogeneity within peatland microtopography.

A prediction method of ice breaking resistance using a multiple regression analysis

NASA Astrophysics Data System (ADS)

Cho, Seong-Rak; Lee, Sungsu

2015-07-01

The two most important tasks of icebreakers are first to secure a sailing route by breaking the thick sea ice and second to sail efficiently herself for purposes of exploration and transportation in the polar seas. The resistance of icebreakers is a priority factor at the preliminary design stage; not only must their sailing efficiency be satisfied, but the design of the propulsion system will be directly affected. Therefore, the performance of icebreakers must be accurately calculated and evaluated through the use of model tests in an ice tank before construction starts. In this paper, a new procedure is developed, based on model tests, to estimate a ship's ice breaking resistance during continuous ice-breaking in ice. Some of the factors associated with crushing failures are systematically considered in order to correctly estimate her ice-breaking resistance. This study is intended to contribute to the improvement of the techniques for ice resistance prediction with ice breaking ships.

Eastern Hudson Bay, Canada

NASA Image and Video Library

2017-12-08

Each winter sea ice forms over the salty waters of frigid northeastern Canada's Hudson Bay. As sunlight lengthens and weather warms, ice begins to break up and melt, with retreat typically starting in May and melt-out completed sometime in July. Since the 1970s, the timing of sea ice breakup in Hudson Bay has changed, with melting beginning earlier in the spring. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite captured this a true-color image of Hudson Bay on March 26, 2013. Although snow still covers the surrounding land, ice has already begun to retreat from much of the eastern shore of the Bay visible in the image. A ring of bright white ice remains solidly frozen around the Belcher Islands in the southeast section of the Bay, but this ring is surrounded by blue waters and large chunks of ice. In the southwest, a similar situation is seen at Akimiski Island. The shelf of bright white ice gives way to open water in the south, as well as fractured, blue-tinted ice. The blue tint generally indicates water logging as ice begins to soften. The Aqua satellite captured a similar image of early ice melt on Hudson Bay on April 6, 2012. That image can be viewed at: modis.gsfc.nasa.gov/gallery/individual.php?db_date=2012-0... NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Fragmentation and melting of the seasonal sea ice cover

NASA Astrophysics Data System (ADS)

Feltham, D. L.; Bateson, A.; Schroeder, D.; Ridley, J. K.; Aksenov, Y.

2017-12-01

Recent years have seen a rapid reduction in the summer extent of Arctic sea ice. This trend has implications for navigation, oil exploration, wildlife, and local communities. Furthermore the Arctic sea ice cover impacts the exchange of heat and momentum between the ocean and atmosphere with significant teleconnections across the climate system, particularly mid to low latitudes in the Northern Hemisphere. The treatment of melting and break-up processes of the seasonal sea ice cover within climate models is currently limited. In particular floes are assumed to have a uniform size which does not evolve with time. Observations suggest however that floe sizes can be modelled as truncated power law distributions, with different exponents for smaller and larger floes. This study aims to examine factors controlling the floe size distribution in the seasonal and marginal ice zone. This includes lateral melting, wave induced break-up of floes, and the feedback between floe size and the mixed ocean layer. These results are then used to quantify the proximate mechanisms of seasonal sea ice reduction in a sea ice—ocean mixed layer model. Observations are used to assess and calibrate the model. The impacts of introducing these processes to the model will be discussed and the preliminary results of sensitivity and feedback studies will also be presented.

A technique for breaking ice in the path of a ship

NASA Technical Reports Server (NTRS)

Saunders, A. R.; Hess, R. V.; Lucht, R. A. (Inventor)

1972-01-01

A technique is described for breaking ice in the path of a ship. A laser is placed on the bow of the ship with apparatus to scan the ice in the path of the ship with the laser beam. The beam cuts or shatters the ice, enabling the ship to break the ice in its path.

Breaking Ice: Fracture Processes in Floating Ice on Earth and Elsewhere

NASA Astrophysics Data System (ADS)

Scambos, T. A.

2016-12-01

Rapid, intense fracturing events in the ice shelves of the Antarctic Peninsula reveal a set of processes that were not fully appreciated prior to the series of ice shelf break-ups observed in the late 1990s and early 2000s. A series of studies have uncovered a fascinating array of relationships between climate, ocean, and ice: intense widespread hydrofracture; repetitive hydrofracture induced by ice plate bending; the ability for sub-surface flooded firn to support hydrofracture; potential triggering by long-period wave action; accelerated fracturing by trapped tsunamic waves; iceberg disintegration, and a remarkable ice rebound process from lake drainage that resembles runaway nuclear fission. The events and subsequent studies have shown that rapid regional warming in ice shelf areas leads to catastrophic changes in a previously stable ice mass. More typical fracturing of thick ice plates is a natural consequence of ice flow in a complex geographic setting, i.e., it is induced by shear and divergence of spreading plate flow around obstacles. While these are not a result of climate or ocean change, weather and ocean processes may impact the exact timing of final separation of an iceberg from a shelf. Taking these terrestrial perspectives to other ice-covered ocean worlds, cautiously, provides an observational framework for interpreting features on Europa and Enceladus.

Glacier Surface Lowering and Stagnation in the Manaslu Region of Nepal

NASA Astrophysics Data System (ADS)

Robson, B. A.; Nuth, C.; Nielsen, P. R.; Hendrickx, M.; Dahl, S. O.

2015-12-01

Frequent and up-to-date glacier outlines are needed for many applications of glaciology, not only glacier area change analysis, but also for masks in volume or velocity analysis, for the estimation of water resources and as model input data. Remote sensing offers a good option for creating glacier outlines over large areas, but manual correction is frequently necessary, especially in areas containing supraglacial debris. We show three different workflows for mapping clean ice and debris-covered ice within Object Based Image Analysis (OBIA). By working at the object level as opposed to the pixel level, OBIA facilitates using contextual, spatial and hierarchical information when assigning classes, and additionally permits the handling of multiple data sources. Our first example shows mapping debris-covered ice in the Manaslu Himalaya, Nepal. SAR Coherence data is used in combination with optical and topographic data to classify debris-covered ice, obtaining an accuracy of 91%. Our second example shows using a high-resolution LiDAR derived DEM over the Hohe Tauern National Park in Austria. Breaks in surface morphology are used in creating image objects; debris-covered ice is then classified using a combination of spectral, thermal and topographic properties. Lastly, we show a completely automated workflow for mapping glacier ice in Norway. The NDSI and NIR/SWIR band ratio are used to map clean ice over the entire country but the thresholds are calculated automatically based on a histogram of each image subset. This means that in theory any Landsat scene can be inputted and the clean ice can be automatically extracted. Debris-covered ice can be included semi-automatically using contextual and morphological information.

Automated Glacier Mapping using Object Based Image Analysis. Case Studies from Nepal, the European Alps and Norway

NASA Astrophysics Data System (ADS)

Vatle, S. S.

2015-12-01

Frequent and up-to-date glacier outlines are needed for many applications of glaciology, not only glacier area change analysis, but also for masks in volume or velocity analysis, for the estimation of water resources and as model input data. Remote sensing offers a good option for creating glacier outlines over large areas, but manual correction is frequently necessary, especially in areas containing supraglacial debris. We show three different workflows for mapping clean ice and debris-covered ice within Object Based Image Analysis (OBIA). By working at the object level as opposed to the pixel level, OBIA facilitates using contextual, spatial and hierarchical information when assigning classes, and additionally permits the handling of multiple data sources. Our first example shows mapping debris-covered ice in the Manaslu Himalaya, Nepal. SAR Coherence data is used in combination with optical and topographic data to classify debris-covered ice, obtaining an accuracy of 91%. Our second example shows using a high-resolution LiDAR derived DEM over the Hohe Tauern National Park in Austria. Breaks in surface morphology are used in creating image objects; debris-covered ice is then classified using a combination of spectral, thermal and topographic properties. Lastly, we show a completely automated workflow for mapping glacier ice in Norway. The NDSI and NIR/SWIR band ratio are used to map clean ice over the entire country but the thresholds are calculated automatically based on a histogram of each image subset. This means that in theory any Landsat scene can be inputted and the clean ice can be automatically extracted. Debris-covered ice can be included semi-automatically using contextual and morphological information.

Seasonal and Interannual Fast-Ice Variability from MODIS Surface-Temperature Anomalies, and its Link to External Forcings in Atka Bay, Antarctica

NASA Astrophysics Data System (ADS)

Paul, S.; Hoppmann, M.; Willmes, S.; Heinemann, G.

2016-12-01

Around Antarctica, sea ice is regularly attached to coastal features. These regions of mostly seasonal fast ice interact with the atmosphere, ocean and coastal ecosystem in a variety of ways. The growth and breakup cycles may depend on different factors, such as water- and air temperatures, wind conditions, tides, ocean swell, the passage of icebergs and the presence of nearby polynyas. However, a detailed understanding about the interaction between these factors and the fast-ice cycle is missing. In order to better understand the linkages between general fast-ice evolution and external forcing factors, we present results from an observational case study performed on the seasonal fast-ice cover of Atka Bay, eastern Weddell Sea. The ice conditions in this region are critical for the supply of the German wintering station Neumayer III. Moreover, the fast ice at Atka Bay hosts a unique ecosystem based on the presence of a sub-ice platelet layer and a large emperor penguin colony. While some qualitative characterizations on the seasonal fast-ice cycle in this region exist, no proper quantification was carried out to date. The backbone of this work is a new algorithm, which yields the first continuous time series of open-water fractions from Moderate-Resolution Imaging Spectroradiometer (MODIS) surface temperatures. The open-water fractions are derived from a range of running multi-day median temperature composites, utilizing the thermal footprint of warm open water and thin ice in contrast to cold pack-ice/ice-shelf areas. This unique, and manually validated dataset allows us to monitor changes in fast-ice extent on a near daily basis, for a period of 14 years (2002-2015). In a second step, we combine these results with iceberg observations, data from the meteorological observatory, and auxiliary satellite data in order to identify the main factors governing fast-ice formation and break-up.

Spatial and temporal patterns of sea ice variations in Vilkitsky strait, Russian High Arctic

NASA Astrophysics Data System (ADS)

Ci, T.; Cheng, X.; Hui, F.

2013-12-01

The Arctic Ocean has been greatly affected by climate change. Future predications show an even more drastic reduction of the ice cap which will open new areas for the exploration of natural resources and maritime transportation.Shipping through the Arctic Ocean via the Northern Sea Route (NSR) could save about 40% of the sailing distance from Asia (Yokohama) to Europe (Rotterdam) compared to the traditional route via the Suez Canal. Vilkitsky strait is the narrowest and northest portion of the Northern Sea Route with heaviest traffic between the Taimyr Peninsular and the Severnaya Zemlya archipelago. The preliminary results of sea ice variations are presented by using moderate-resolution imaging spectro radiometer(MODIS) data with 250-m resolution in the Vilkitsky strait during 2009-2012. Temporally, the first rupture on sea ice in Vilkitsky strait usually comes up in April and sea ice completely break into pieces in early June. The strait would be ice-free between August and late September. The frequency of ice floes grows while temperature falls down in October. There are always one or two months suitable for transport. Spatially, Sea ice on Laptev sea side breaks earlier than that of Kara sea side while sea ice in central of strait breaks earlier than in shoreside. The phenomena are directly related with the direction of sea wind and ocean current. In summmary, study on Spatial and temporal patterns in this area is significant for the NSR. An additional research issue to be tackled is to seeking the trends of ice-free duration in the context of global warming. Envisat ASAR data will also be used in this study.

The Effects of Changing Sea Ice on Marine Mammals and Their Hunters in Northern Alaska

NASA Astrophysics Data System (ADS)

Huntington, H.; Quakenbush, L.; Nelson, M.

2015-12-01

Marine mammals are important sources of food for indigenous residents of northern Alaska. Changing sea ice patterns affect the animals themselves as well as access by hunters. Documenting the traditional knowledge of Iñupiaq and Yupik hunters concerning marine mammals and sea ice makes accessible a wide range of information and insight relevant to ecological understanding, conservation action, and the regulation of human activity. We interviewed hunters in villages from northern Bering Sea to the Beaufort Sea, focusing on bowhead whales, walrus, and ice seals. Hunters reported extensive changes in sea ice, with resulting effects on the timing of marine mammal migrations, the distribution and behavior of the animals, and the efficacy of certain hunting methods, for example the difficulty of finding ice thick enough to support a bowhead whale for butchering. At the same time, hunters acknowledged impacts and potential impacts from changing technology such as more powerful outboard engines and from industrial activity such as shipping and oil and gas development. Hunters have been able to adapt to some changes, for example by hunting bowhead whales in fall as well as spring on St. Lawrence Island, or by focusing their hunt in a shorter period in Nuiqsut to accommodate work schedules and worse weather. Other changes, such as reduced availability of ice seals due to rapid retreat of pack ice after spring break-up, continue to defy easy responses. Continued environmental changes, increased disturbance from human activity, and the introduction of new regulations for hunting may further challenge the ability of hunters to provide food as they have done to date, though innovation and flexibility may also provide new sources of adaptation.

Channelized bottom melting and stability of floating ice shelves

NASA Astrophysics Data System (ADS)

Rignot, E.; Steffen, K.

2008-01-01

The floating ice shelf in front of Petermann Glacier, in northwest Greenland, experiences massive bottom melting that removes 80% of its ice before calving into the Arctic Ocean. Detailed surveys of the ice shelf reveal the presence of 1-2 km wide, 200-400 m deep, sub-ice shelf channels, aligned with the flow direction and spaced by 5 km. We attribute their formation to the bottom melting of ice from warm ocean waters underneath. Drilling at the center of one of channel, only 8 m above sea level, confirms the presence of ice-shelf melt water in the channel. These deep incisions in ice-shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously.

Brief Communication: Mapping river ice using drones and structure from motion

NASA Astrophysics Data System (ADS)

Alfredsen, Knut; Haas, Christian; Tuhtan, Jeffrey A.; Zinke, Peggy

2018-02-01

In cold climate regions, the formation and break-up of river ice is important for river morphology, winter water supply, and riparian and instream ecology as well as for hydraulic engineering. Data on river ice is therefore significant, both to understand river ice processes directly and to assess ice effects on other systems. Ice measurement is complicated due to difficult site access, the inherent complexity of ice formations, and the potential danger involved in carrying out on-ice measurements. Remote sensing methods are therefore highly useful, and data from satellite-based sensors and, increasingly, aerial and terrestrial imagery are currently applied. Access to low cost drone systems with quality cameras and structure from motion software opens up a new possibility for mapping complex ice formations. Through this method, a georeferenced surface model can be built and data on ice thickness, spatial distribution, and volume can be extracted without accessing the ice, and with considerably fewer measurement efforts compared to traditional surveying methods. A methodology applied to ice mapping is outlined here, and examples are shown of how to successfully derive quantitative data on ice processes.

A coupled ice-ocean model of ice breakup and banding in the marginal ice zone

NASA Technical Reports Server (NTRS)

Smedstad, O. M.; Roed, L. P.

1985-01-01

A coupled ice-ocean numerical model for the marginal ice zone is considered. The model consists of a nonlinear sea ice model and a two-layer (reduced gravity) ocean model. The dependence of the upwelling response on wind stress direction is discussed. The results confirm earlier analytical work. It is shown that there exist directions for which there is no upwelling, while other directions give maximum upwelling in terms of the volume of uplifted water. The ice and ocean is coupled directly through the stress at the ice-ocean interface. An interesting consequence of the coupling is found in cases when the ice edge is almost stationary. In these cases the ice tends to break up a few tenths of kilometers inside of the ice edge.

Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics.

PubMed

Cherry, Seth G; Derocher, Andrew E; Thiemann, Gregory W; Lunn, Nicholas J

2013-07-01

Understanding how seasonal environmental conditions affect the timing and distribution of synchronized animal movement patterns is a central issue in animal ecology. Migration, a behavioural adaptation to seasonal environmental fluctuations, is a fundamental part of the life history of numerous species. However, global climate change can alter the spatiotemporal distribution of resources and thus affect the seasonal movement patterns of migratory animals. We examined sea ice dynamics relative to migration patterns and seasonal geographical fidelity of an Arctic marine predator, the polar bear (Ursus maritimus). Polar bear movement patterns were quantified using satellite-linked telemetry data collected from collars deployed between 1991-1997 and 2004-2009. We showed that specific sea ice characteristics can predict the timing of seasonal polar bear migration on and off terrestrial refugia. In addition, fidelity to specific onshore regions during the ice-free period was predicted by the spatial pattern of sea ice break-up but not by the timing of break-up. The timing of migration showed a trend towards earlier arrival of polar bears on shore and later departure from land, which has been driven by climate-induced declines in the availability of sea ice. Changes to the timing of migration have resulted in polar bears spending progressively longer periods of time on land without access to sea ice and their marine mammal prey. The links between increased atmospheric temperatures, sea ice dynamics, and the migratory behaviour of an ice-dependent species emphasizes the importance of quantifying and monitoring relationships between migratory wildlife and environmental cues that may be altered by climate change. © 2013 The Authors. Journal of Animal Ecology © 2013 British Ecological Society.

Capturing total chronological and spatial uncertainties in palaeo-ice sheet reconstructions: the DATED example

NASA Astrophysics Data System (ADS)

Hughes, Anna; Gyllencreutz, Richard; Mangerud, Jan; Svendsen, John Inge

2017-04-01

Glacial geologists generate empirical reconstructions of former ice-sheet dynamics by combining evidence from the preserved record of glacial landforms (e.g. end moraines, lineations) and sediments with chronological evidence (mainly numerical dates derived predominantly from radiocarbon, exposure and luminescence techniques). However the geomorphological and sedimentological footprints and chronological data are both incomplete records in both space and time, and all have multiple types of uncertainty associated with them. To understand ice sheets' response to climate we need numerical models of ice-sheet dynamics based on physical principles. To test and/or constrain such models, empirical reconstructions of past ice sheets that capture and acknowledge all uncertainties are required. In 2005 we started a project (Database of the Eurasian Deglaciation, DATED) to produce an empirical reconstruction of the evolution of the last Eurasian ice sheets, (including the British-Irish, Scandinavian and Svalbard-Barents-Kara Seas ice sheets) that is fully documented, specified in time, and includes uncertainty estimates. Over 5000 dates relevant to constraining ice build-up and retreat were assessed for reliability and used together with published ice-sheet margin positions based on glacial geomorphology to reconstruct time-slice maps of the ice sheets' extent. The DATED maps show synchronous ice margins with maximum-minimum uncertainty bounds for every 1000 years between 25-10 kyr ago. In the first version of results (DATED-1; Hughes et al. 2016) all uncertainties (both quantitative and qualitative, e.g. precision and accuracy of numerical dates, correlation of moraines, stratigraphic interpretations) were combined based on our best glaciological-geological assessment and expressed in terms of distance as a 'fuzzy' margin. Large uncertainties (>100 km) exist; predominantly across marine sectors and other locations where there are spatial gaps in the dating record (e.g. the timing of coalescence and separation of the Scandinavian and Svalbard-Barents-Kara ice sheets) but also in well-studied areas due to conflicting yet apparently equally robust data. In the four years since the DATED-1 census (1 January 2013), the volume of new information (from both dates and mapped glacial geomorphology) has grown significantly ( 1000 new dates). Here, we present work towards the updated version of results, DATED-2, that attempts to further reduce and explicitly report all uncertainties inherent in ice sheet reconstructions. Hughes, A. L. C., Gyllencreutz, R., Lohne, Ø. S., Mangerud, J., Svendsen, J. I. 2016: The last Eurasian ice sheets - a chronological database and time-slice reconstruction, DATED-1. Boreas, 45, 1-45. 10.1111/bor.12142

Breaking up is hard to do: how teens end violent dating relationships.

PubMed

Martsolf, Donna S; Draucker, Claire Burke; Brandau, Melvina

2013-01-01

Dating violence affects nearly 30% of teens and is associated with numerous negative health outcomes. Teens do not tend to use adult or peer assistance to end violent dating relationships, and little is known about how they manage to end them. The purpose of this study was to determine the common ways in which teens end violent dating relationships. Grounded theory methods were used to analyze transcribed interviews conducted with a community sample of 83 young adults who had experienced dating violence as teens. Participants described six ways of ending violent dating relationships: deciding enough is enough; becoming interested in someone else; being on again, off again; fading away; deciding it's best for us both; and moving away. Professionals working with teens can present the six ways of breaking up as a tool to initiate discussion about the issues involved in ending violent dating relationships.

Wave-induced stress and breaking of sea ice in a coupled hydrodynamic discrete-element wave-ice model

NASA Astrophysics Data System (ADS)

Herman, Agnieszka

2017-11-01

In this paper, a coupled sea ice-wave model is developed and used to analyze wave-induced stress and breaking in sea ice for a range of wave and ice conditions. The sea ice module is a discrete-element bonded-particle model, in which ice is represented as cuboid grains floating on the water surface that can be connected to their neighbors by elastic joints. The joints may break if instantaneous stresses acting on them exceed their strength. The wave module is based on an open-source version of the Non-Hydrostatic WAVE model (NHWAVE). The two modules are coupled with proper boundary conditions for pressure and velocity, exchanged at every wave model time step. In the present version, the model operates in two dimensions (one vertical and one horizontal) and is suitable for simulating compact ice in which heave and pitch motion dominates over surge. In a series of simulations with varying sea ice properties and incoming wavelength it is shown that wave-induced stress reaches maximum values at a certain distance from the ice edge. The value of maximum stress depends on both ice properties and characteristics of incoming waves, but, crucially for ice breaking, the location at which the maximum occurs does not change with the incoming wavelength. Consequently, both regular and random (Jonswap spectrum) waves break the ice into floes with almost identical sizes. The width of the zone of broken ice depends on ice strength and wave attenuation rates in the ice.

Sedimentology and chronology of the advance and retreat of the last British-Irish Ice Sheet on the continental shelf west of Ireland

NASA Astrophysics Data System (ADS)

Peters, Jared L.; Benetti, Sara; Dunlop, Paul; Ó Cofaigh, Colm; Moreton, Steven G.; Wheeler, Andrew J.; Clark, Christopher D.

2016-05-01

The last British-Irish Ice Sheet (BIIS) had extensive marine-terminating margins and was drained by multiple large ice streams and is thus a useful analogue for marine-based areas of modern ice sheets. However, despite recent advances from investigating the offshore record of the BIIS, the dynamic history of its marine margins, which would have been sensitive to external forcing(s), remain inadequately understood. This study is the first reconstruction of the retreat dynamics and chronology of the western, marine-terminating, margin of the last (Late Midlandian) BIIS. Analyses of shelf geomorphology and core sedimentology and chronology enable a reconstruction of the Late Midlandian history of the BIIS west of Ireland, from initial advance to final retreat onshore. Five AMS radiocarbon dates from marine cores constrain the timing of retreat and associated readvances during deglaciation. The BIIS advanced without streaming or surging, depositing a bed of highly consolidated subglacial traction till, and reached to within ∼20 km of the shelf break by ∼24,000 Cal BP. Ice margin retreat was likely preceded by thinning, grounding zone retreat and ice shelf formation on the outer shelf by ∼22,000 Cal BP. This ice shelf persisted for ≤2500 years, while retreating at a minimum rate of ∼24 m/yr and buttressing a >150-km long, 20-km wide, bathymetrically-controlled grounding zone. A large (∼150 km long), arcuate, flat-topped grounding-zone wedge, termed here the Galway Lobe Grounding-Zone Wedge (GLGZW), was deposited below this ice shelf and records a significant stillstand in BIIS retreat. Geomorphic relationships indicate that the BIIS experienced continued thinning during its retreat across the shelf, which led to increased topographic influence on its flow dynamics following ice shelf break up and grounding zone retreat past the GLGZW. At this stage of retreat the western BIIS was comprised of several discrete, asynchronous lobes that underwent several readvances. Sedimentary evidence of dilatant till deposition suggests that the readvances may have been rapid and possibly associated with ice streaming or surging. The largest lobe extended offshore from Galway Bay and deposited the Galway Lobe Readvance Moraine by <18,500 Cal BP. Further to the north, an ice lobe readvanced at least 50 km offshore from Killary Harbour, possibly by ≤15,100 Cal BP. The existing chronology currently does not allow us to determine conclusively whether these readvances were a glaciodynamic (internally-driven) response of the ice sheet during deglaciation or were climatically-driven. Following the <18,500 Cal BP readvance, the Galway Lobe experienced accelerated eastward retreat at an estimated rate of ∼113 m/yr.

Breaking Up is Hard to do: The Impact of Unmarried Relationship Dissolution on Mental Health and Life Satisfaction

PubMed Central

Rhoades, Galena K.; Kamp Dush, Claire M.; Atkins, David C.; Stanley, Scott M.; Markman, Howard J.

2011-01-01

This study was the first to examine the impact of unmarried relationship break-up on psychological distress and life satisfaction using a within-subjects design. Among unmarried 18 to 35-year olds (N = 1295), 36.5% had one or more break-ups over a 20-month period. Experiencing a break-up was associated with an increase in psychological distress and a decline in life satisfaction (from pre- to post-dissolution). In addition, several characteristics of the relationship or of the break-up were associated with the magnitude of the changes in life satisfaction following a break-up. Specifically, having been cohabiting and having had plans for marriage were associated with larger declines in life satisfaction while having begun to date someone new was associated with smaller declines. Interestingly, having higher relationship quality at the previous wave was associated with smaller declines in life satisfaction following a break-up. No relationship or break-up characteristics were significantly associated with the magnitude of changes in psychological distress after a break-up. Existing theories are used to explain the results. Implications for clinical work and future research on unmarried relationships are also discussed. PMID:21517174

Jurassic high heat production granites associated with the Weddell Sea rift system, Antarctica

NASA Astrophysics Data System (ADS)

Leat, Philip T.; Jordan, Tom A.; Flowerdew, Michael J.; Riley, Teal R.; Ferraccioli, Fausto; Whitehouse, Martin J.

2018-01-01

The distribution of heat flow in Antarctic continental crust is critical to understanding continental tectonics, ice sheet growth and subglacial hydrology. We identify a group of High Heat Production granites, intruded into upper crustal Palaeozoic metasedimentary sequences, which may contribute to locally high heat flow beneath the West Antarctic Ice Sheet. Four of the granite plutons are exposed above ice sheet level at Pagano Nunatak, Pirrit Hills, Nash Hills and Whitmore Mountains. A new Usbnd Pb zircon age from Pirrit Hills of 178.0 ± 3.5 Ma confirms earlier Rbsbnd Sr and Usbnd Pb dating and that the granites were emplaced approximately coincident with the first stage of Gondwana break-up and the developing Weddell rift, and 5 m.y. after eruption of the Karoo-Ferrar large igneous province. Aerogeophysical data indicate that the plutons are distributed unevenly over 40,000 km2 with one intruded into the transtensional Pagano Shear Zone, while the others were emplaced within the more stable Ellsworth-Whitmore mountains continental block. The granites are weakly peraluminous A-types and have Th and U abundances up to 60.7 and 28.6 ppm respectively. Measured heat production of the granite samples is 2.96-9.06 μW/m3 (mean 5.35 W/m3), significantly higher than average upper continental crust and contemporaneous silicic rocks in the Antarctic Peninsula. Heat flow associated with the granite intrusions is predicted to be in the range 70-95 mW/m2 depending on the thickness of the high heat production granite layer and the regional heat flow value. Analysis of detrital zircon compositions and ages indicates that the high Th and U abundances are related to enrichment of the lower-mid crust that dates back to 200-299 Ma at the time of the formation of the Gondwanide fold belt and its post-orogenic collapse and extension.

Modeling tabular icebergs submerged in the ocean

NASA Astrophysics Data System (ADS)

Stern, A. A.; Adcroft, A.; Sergienko, O.; Marques, G.

2017-08-01

Large tabular icebergs calved from Antarctic ice shelves have long lifetimes (due to their large size), during which they drift across large distances, altering ambient ocean circulation, bottom-water formation, sea-ice formation, and biological primary productivity in the icebergs' vicinity. However, despite their importance, the current generation of ocean circulation models usually do not represent large tabular icebergs. In this study, we develop a novel framework to model large tabular icebergs submerged in the ocean. In this framework, tabular icebergs are represented by pressure-exerting Lagrangian elements that drift in the ocean. The elements are held together and interact with each other via bonds. A breaking of these bonds allows the model to emulate calving events (i.e., detachment of a tabular iceberg from an ice shelf) and tabular icebergs breaking up into smaller pieces. Idealized simulations of a calving tabular iceberg, its drift, and its breakup demonstrate capabilities of the developed framework.

78 FR 52337 - Migratory Bird Hunting; Proposed Frameworks for Late-Season Migratory Bird Hunting Regulations

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-22

... conducted using fixed- wing aircraft, helicopters, and ground crews and encompass principal breeding areas... conditions in the north-country was Alaska's Yukon-Kuskokwim Delta (YKD), where ice break-up was the latest...

Methane emission from high-latitude (>50N) lakes: Annual cycle of climatological emissions using satellite-derived lake-ice phenology and freeze-thaw dynamics

NASA Astrophysics Data System (ADS)

Matthews, E.; Romanski, J.; Du, J.; Watts, J. D.

2017-12-01

Lakes are increasingly recognized as potentially important contributors to global methane emissions despite occupying only a few percent of Earth's ice-free land surface. More than 40% of the global lake area lies in regions of amplified warming north of 50˚N. As with wetlands, lake emissions are sensitive to interannual fluctuations in, e.g., temperature and duration of thaw season. Several estimates of CH4emission from high-latitude lakes have been published but none relies on geospatial lake distributions and satellite-based duration and timing of thaw seasons. We report on a climatology of weekly, spatially-explicit methane emissions from high-latitude lakes. Lake break-up and freeze-up dates for lakes >50km^2 were determined from a lake-ice phenology data set derived from brightness temperature (Tb) observations of space-borne Advanced Microwave Scanning Radiometer (AMSR-E/2) sensors. The lake-ice conditions for smaller lakes were estimated using an Earth System Data Record for Land Surface Freeze-Thaw State derived from Tb observations of Scanning Multichannel Microwave Radiometer (SMMR), Special Sensor Microwave Imager (SSM/I), and SSM/I Sounder (SSMIS). Climatologies encompass 2002-2015 for lake ice phenology and 1979 to 2010 for the land surface freeze-thaw state. Climatologies encompass 2003-2014 for ice phenology and 1979 to 2010 for freeze-thaw dynamics. Length and timing of typical methane-emission periods, derived from the satellite data, were integrated with daily diffusive and ebulliative methane fluxes for lake types following the work of Wik et al. (Nature, 2016) to estimate a full annual cycle of emissions from lakes >50˚N. We explored several approaches to estimate the large bursts of emissions observed over short periods during lake-ice breakup immediately prior to full lake thaw since several studies suggest that a substantial fraction of total annual emissions may occur at this time. While highly uncertain, we plan to investigate whether the modest, short-lived but annual uptick in atmospheric methane concentrations in late winter/early spring may be associated with these bursts of methane from lakes.

Changes in ice dynamics and mass balance of the Antarctic ice sheet.

PubMed

Rignot, Eric

2006-07-15

The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 degrees C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

Progress on wave-ice interactions: satellite observations and model parameterizations

NASA Astrophysics Data System (ADS)

Ardhuin, Fabrice; Boutin, Guillaume; Dumont, Dany; Stopa, Justin; Girard-Ardhuin, Fanny; Accensi, Mickael

2017-04-01

In the open ocean, numerical wave models have their largest errors near sea ice, and, until recently, virtually no wave data was available in the sea ice to. Further, wave-ice interaction processes may play an important role in the Earth system. In particular, waves may break up an ice layer into floes, with significant impact on air-sea fluxes. With thinner Arctic ice, this process may contribut to the growing similarity between Arctic and Antarctic sea ice. In return, the ice has a strong damping impact on the waves that is highly variable and not understood. Here we report progress on parameterizations of waves interacting with a single ice layer, as implemented in the WAVEWATCH III model (WW3 Development Group, 2016), and based on few in situ observations, but extensive data derived from Synthetic Aperture Radars (SARs). Our parameterizations combine three processes. First a parameterization for the energy-conserving scattering of waves by ice floes (assuming isotropic back-scatter), which has very little effect on dominant waves of periods larger than 7 s, consistent with the observed narrow directional spectra and short travel times. Second, we implemented a basal friction below the ice layer (Stopa et al. The Cryosphere, 2016). Third, we use a secondary creep associated with ice flexure (Cole et al. 1998) adapted to random waves. These three processes (scattering, friction and creep) are strongly dependent on the maximum floe size. We have thus included an estimation of the potential floe size based on an ice flexure failure estimation adapted from Williams et al. (2013). This combination of dissipation and scattering is tested against measured patterns of wave height and directional spreading, and evidence of ice break-up, all obtained from SAR imagery (Ardhuin et al. 2017), and some in situ data (Collins et al. 2015). The combination of creep and friction is required to reproduce a strong reduction in wave attenuation in broken ice as observed by Collins et al. (2015). Ongoing developments include the coupling of WAVEWATCH III to the NEMO-LIM3 and NEMO-CICE models using the OASIS3-MCT communicator. This coupled system will provide a meaningful memory of the ice floe sizes, as the ice is advected. It will also make possible the investigation of feedback processes on the ice.

On the Formation of Rifts in Ice Shelves

NASA Astrophysics Data System (ADS)

Sayag, R.; Worster, G.

2017-12-01

Ice calving accounts for significant part in the mass loss of present ice sheets. Several processes could lead to calving, among them is the formation of rifts near the fronts of ice shelves. Here we combine laboratory-scale experiments of ice sheets together with theoretical modeling to investigate the formation of rifts in ice shelves. We model the deformation of ice with a thin viscous film that is driven axisymmetrically by buoyancy. When the viscous fluid intrudes a bath of an inviscid fluid that represents the ocean, the circular symmetry of the front breaks up into a set of tongues with a characteristic wavelength that coarsens over time, a pattern that is reminiscent of ice rifts. Theoretically, we model the formation of rifts as a hydrodynamic instability of powerlaw fluid. Our model demonstrates the formation of rifts and the coarsening of the characteristic wavelength, and predicts coarsening transition times that are consistent with our experimental measurements.

Massive subsurface ice formed by refreezing of ice-shelf melt ponds

PubMed Central

Hubbard, Bryn; Luckman, Adrian; Ashmore, David W.; Bevan, Suzanne; Kulessa, Bernd; Kuipers Munneke, Peter; Philippe, Morgane; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Tison, Jean-Louis; O'Leary, Martin; Rutt, Ian

2016-01-01

Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km across, several kilometres long and tens of metres deep, located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and radar measurements with remote sensing and firn modelling to investigate the layer, found to be ∼10 °C warmer and ∼170 kg m−3 denser than anticipated in the absence of ponding and hitherto used in models of ice-shelf fracture and flow. Surface ponding and ice layers such as the one we report are likely to form on a wider range of Antarctic ice shelves in response to climatic warming in forthcoming decades. PMID:27283778

Calving and rifting on McMurdo Ice Shelf, Antarctica

NASA Astrophysics Data System (ADS)

Banwell, Alison; Willis, Ian; MacAyeal, Douglas; Goodsell, Becky; Macdonald, Grant; Mayer, David; Powell, Anthony

2017-04-01

On March 2, 2016, a series of small en échelon tabular icebergs calved from the seaward front of the McMurdo Ice Shelf, and a previously inactive ice-shelf rift suddenly widened and propagated by 3km, 25% of its previous length, setting the stage for future calving of an approximately 8 km2 segment of the ice shelf. Immediately prior to these events, perhaps within 24 hours, all remaining land-fast sea ice buttressing the ice shelf broke up and drifted away. The events were witnessed by time-lapse cameras at nearby Scott Base giving a unique opportunity to document the timing of the events and conditions leading up to them. In addition, the events can be put into context using nearby seismic and automatic weather station data, satellite imagery, and ground observation made 8 months later. Although the observations cannot be used definitively to identify the exact trigger of calving and rifting, the seismic records reveal superimposed sets of long-period (>10 s) sea swell, propagating into McMurdo Sound from distant storm sources in the Pacific Ocean, at the time of, and immediately prior to, the break-up of sea ice and associated ice shelf calving and rifting. This conspicuous presence suggests that sea swell should be studied further as a proximal cause of ice-shelf calving and rifting; if proven, it suggests that ice-shelf stability is tele-connected with far-field storm conditions at lower latitudes, adding a global dimension to the physics of potential ice-shelf breakup.

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.

Earth Observation taken by the Expedition 20 crew

NASA Image and Video Library

2009-09-06

ISS020-E-039083 (6 Sept. 2009) --- Glacier outlet in the Southern Patagonian Ice Field of Chile is featured in this image photographed by an Expedition 20 crew member on the International Space Station. The Southern Patagonian Ice Field of Chile and Argentina hosts a spectacular array of glaciers and associated glacial features within the southern Andes Mountains. Glaciers flowing downhill on the eastern side of the mountains have outlets into several large freshwater lakes. On the western side of the mountains, glaciers release ice into the Pacific Ocean via an intricate network of fjords. Fjords are steep valleys originally cut by glaciers during periods of lower sea level that are now inundated. As glaciers flow into the fjord, ice at the front of the glacier begins to break off and form icebergs that can float out to sea ? a process known as calving. This detailed photograph shows the merged outlet of Penguin Glacier and HPS 19 into a fjord carved into the snow-covered mountains of the southern Andes. The designation HPS stands for Hielo Patagonico Sur (e.g. Southern Patagonian Ice field) and is used to identify glaciers that have no other geographic name. Ice flowing into the fjord begins to break up at center, forming numerous icebergs ? the largest visible in this image is approximately 2 kilometers in width. The large ice masses visible at center have a coarse granular appearance due to variable snow cover, and mixing and refreezing of ice fragments prior to floating free.

Circumpolar Deep Water transport and current structure at the Amundsen Sea shelf break

NASA Astrophysics Data System (ADS)

Assmann, Karen M.; Wåhlin, Anna K.; Heywood, Karen J.; Jenkins, Adrian; Kim, Tae Wan; Lee, Sang Hoon

2017-04-01

The West Antarctic Ice Sheet has been losing mass at an increasing rate over the past decades. Ocean heat transport to the ice-ocean interface has been identified as an important contributor to this mass loss and the role it plays in ice sheet stability makes it crucial to understand its drivers in order to make accurate future projections of global sea level. While processes closer to the ice-ocean interface modulate this heat transport, its ultimate source is located in the deep basin off the continental shelf as a core of relatively warm, salty water underlying a colder, fresher shallow surface layer. To reach the marine terminating glaciers and the base of floating ice shelves, this warm, salty water mass must cross the bathymetric obstacle of the shelf break. Glacial troughs that intersect the Amundsen shelf break and deepen southwards towards the ice shelf fronts have been shown to play an important role in transporting warm, salty Circumpolar Deep Water (CDW) towards the ice shelves. North of the shelf break, circulation in the Amundsen Sea occupies an intermediate regime between the eastward Antarctic Circumpolar Current that impinges on the shelf break in the Bellingshausen Sea and the westward southern limb of the Ross Gyre that follows the shelf break in the Ross Sea. Hydrographic and mooring observations and numerical model results at the mouth of the central shelf break trough leading to Pine Island and Thwaites Glaciers show a westward wind-driven shelf break current overlying an eastward undercurrent that turns onto the shelf in the trough. It is thought that the existence of the latter feature facilitates the on-shelf transport of CDW. A less clearly defined shelf break depression further west acts as the main pathway for CDW to Dotson and eastern Getz Ice shelves. Model results indicate that a similar eastward undercurrent exists here driving the on-shelf transport of CDW. Two moorings on the upper slope east of the trough entrance show a persistent westward current in the CDW layer. We use hydrographic and ADCP sections to discuss the mechanisms that could be responsible for the formation of this feature and the implications for oceanic heat transport towards the western Amundsen ice shelves.

Predicting climate change impacts on polar bear litter size.

PubMed

Molnár, Péter K; Derocher, Andrew E; Klanjscek, Tin; Lewis, Mark A

2011-02-08

Predicting the ecological impacts of climate warming is critical for species conservation. Incorporating future warming into population models, however, is challenging because reproduction and survival cannot be measured for yet unobserved environmental conditions. In this study, we use mechanistic energy budget models and data obtainable under current conditions to predict polar bear litter size under future conditions. In western Hudson Bay, we predict climate warming-induced litter size declines that jeopardize population viability: ∼28% of pregnant females failed to reproduce for energetic reasons during the early 1990s, but 40-73% could fail if spring sea ice break-up occurs 1 month earlier than during the 1990s, and 55-100% if break-up occurs 2 months earlier. Simultaneously, mean litter size would decrease by 22-67% and 44-100%, respectively. The expected timeline for these declines varies with climate-model-specific sea ice predictions. Similar litter size declines may occur in over one-third of the global polar bear population.

Predicting climate change impacts on polar bear litter size

PubMed Central

Molnár, Péter K.; Derocher, Andrew E.; Klanjscek, Tin; Lewis, Mark A.

2011-01-01

Predicting the ecological impacts of climate warming is critical for species conservation. Incorporating future warming into population models, however, is challenging because reproduction and survival cannot be measured for yet unobserved environmental conditions. In this study, we use mechanistic energy budget models and data obtainable under current conditions to predict polar bear litter size under future conditions. In western Hudson Bay, we predict climate warming-induced litter size declines that jeopardize population viability: ∼28% of pregnant females failed to reproduce for energetic reasons during the early 1990s, but 40–73% could fail if spring sea ice break-up occurs 1 month earlier than during the 1990s, and 55–100% if break-up occurs 2 months earlier. Simultaneously, mean litter size would decrease by 22–67% and 44–100%, respectively. The expected timeline for these declines varies with climate-model-specific sea ice predictions. Similar litter size declines may occur in over one-third of the global polar bear population. PMID:21304515

Remote Sensing of Lake Ice Phenology in Alaska

NASA Astrophysics Data System (ADS)

Zhang, S.; Pavelsky, T.

2017-12-01

Lake ice phenology (e.g. ice break-up and freeze-up timing) in Alaska is potentially sensitive to climate change. However, there are few current lake ice records in this region, which hinders the comprehensive understanding of interactions between climate change and lake processes. To provide a lake ice database with over a comparatively long time period (2000 - 2017) and large spatial coverage (4000+ lakes) in Alaska, we have developed an algorithm to detect the timing of lake ice using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. This approach generally consists of three major steps. First, we use a cloud mask (MOD09GA) to filter out satellite images with heavy cloud contamination. Second, daily MODIS reflectance values (MOD09GQ) of lake surface are used to extract ice pixels from water pixels. The ice status of lakes can be further identified based on the fraction of ice pixels. Third, to improve the accuracy of ice phenology detection, we execute post-processing quality control to reduce false ice events caused by outliers. We validate the proposed algorithm over six lakes by comparing with Landsat-based reference data. Validation results indicate a high correlation between the MODIS results and reference data, with normalized root mean square error (NRMSE) ranging from 1.7% to 4.6%. The time series of this lake ice product is then examined to analyze the spatial and temporal patterns of lake ice phenology.

77 FR 37445 - Notice of Permit Modification Received Under the Antarctic Conservation Act of 1978 (Pub. L. 95-541)

Federal Register 2010, 2011, 2012, 2013, 2014

2012-06-21

... for various activities in Antarctica and designation of certain animals and certain geographic areas a... whales in the penguin's foraging area within the leads of the McMurdo Sound fast ice as it breaks up. The...

The Effect of Break Edge Configuration on the Aerodynamics of Anti-Ice Jet Flow

NASA Astrophysics Data System (ADS)

Tatar, V.; Yildizay, H.; Aras, H.

2015-05-01

One of the components of a turboprop gas turbine engine is the Front Bearing Structure (FBS) which leads air into the compressor. FBS directly encounters with ambient air, as a consequence ice accretion may occur on its static vanes. There are several aerodynamic parameters which should be considered in the design of anti-icing system of FBS, such as diameter, position, exit angle of discharge holes, etc. This research focuses on the effects of break edge configuration over anti-ice jet flow. Break edge operation is a process which is applied to the hole in order to avoid sharp edges which cause high stress concentration. Numerical analyses and flow visualization test have been conducted. Four different break edge configurations were used for this investigation; without break edge, 0.35xD, 74xD, 0.87xD. Three mainstream flow conditions at the inlet of the channel are defined; 10m/s, 20 m/s and 40 m/s. Shear stresses are extracted from numerical analyses near the trailing edge of pressure surface where ice may occur under icing conditions. A specific flow visualization method was used for the experimental study. Vane surface near the trailing edge was dyed and thinner was injected into anti-ice jet flow in order to remove dye from the vane surface. Hence, film effect on the surface could be computed for each testing condition. Thickness of the dye removal area of each case was examined. The results show noticeable effects of break edge operation on jet flow, and the air film effectiveness decreases when mainstream inlet velocity decreases.

Phase boundaries, nucleation rates and speed of crystal growth of the water-to-ice transition under an electric field: a simulation study

NASA Astrophysics Data System (ADS)

Zaragoza, Alberto; Espinosa, Jorge R.; Ramos, Regina; Cobos, José Antonio; Aragones, Juan Luis; Vega, Carlos; Sanz, Eduardo; Ramírez, Jorge; Valeriani, Chantal

2018-05-01

We investigate with computer simulations the effect of applying an electric field on the water-to-ice transition. We use a combination of state-of-the-art simulation techniques to obtain phase boundaries and crystal growth rates (direct coexistence), nucleation rates (seeding) and interfacial free energies (seeding and mold integration). First, we consider ice Ih, the most stable polymorph in the absence of a field. Its normal melting temperature, speed of crystal growth and nucleation rate (for a given supercooling) diminish as the intensity of the field goes up. Then, we study polarised cubic ice, or ice Icf, the most stable solid phase under a strong electric field. Its normal melting point goes up with the field and, for a given supercooling, under the studied field (0.3 V nm‑1) ice Icf nucleates and grows at a similar rate as Ih with no field. The net effect of the field would then be that ice nucleates at warmer temperatures, but in the form of ice Icf. The main conclusion of this work is that reasonable electric fields (not strong enough to break water molecules apart) are not relevant in the context of homogeneous ice nucleation at 1 bar.

Phase boundaries, nucleation rates and speed of crystal growth of the water-to-ice transition under an electric field: a simulation study.

PubMed

Zaragoza, Alberto; Espinosa, Jorge R; Ramos, Regina; Antonio Cobos, José; Luis Aragones, Juan; Vega, Carlos; Sanz, Eduardo; Ramírez, Jorge; Valeriani, Chantal

2018-05-02

We investigate with computer simulations the effect of applying an electric field on the water-to-ice transition. We use a combination of state-of-the-art simulation techniques to obtain phase boundaries and crystal growth rates (direct coexistence), nucleation rates (seeding) and interfacial free energies (seeding and mold integration). First, we consider ice Ih, the most stable polymorph in the absence of a field. Its normal melting temperature, speed of crystal growth and nucleation rate (for a given supercooling) diminish as the intensity of the field goes up. Then, we study polarised cubic ice, or ice Icf, the most stable solid phase under a strong electric field. Its normal melting point goes up with the field and, for a given supercooling, under the studied field (0.3 V nm -1 ) ice Icf nucleates and grows at a similar rate as Ih with no field. The net effect of the field would then be that ice nucleates at warmer temperatures, but in the form of ice Icf. The main conclusion of this work is that reasonable electric fields (not strong enough to break water molecules apart) are not relevant in the context of homogeneous ice nucleation at 1 bar.

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.

On the use of δ18Oatm for ice core dating

NASA Astrophysics Data System (ADS)

Extier, Thomas; Landais, Amaelle; Bréant, Camille; Prié, Frédéric; Bazin, Lucie; Dreyfus, Gabrielle; Roche, Didier M.; Leuenberger, Markus

2018-04-01

Deep ice core chronologies have been improved over the past years through the addition of new age constraints. However, dating methods are still associated with large uncertainties for ice cores from the East Antarctic plateau where layer counting is not possible. Indeed, an uncertainty up to 6 ka is associated with AICC2012 chronology of EPICA Dome C (EDC) ice core, which mostly arises from uncertainty on the delay between changes recorded in δ18Oatm and in June 21st insolation variations at 65°N used for ice core orbital dating. Consequently, we need to enhance the knowledge of this delay to improve ice core chronologies. We present new high-resolution EDC δ18Oatm record (153-374 ka) and δO2/N2 measurements (163-332 ka) performed on well-stored ice to provide continuous records of δ18Oatm and δO2/N2 between 100 and 800 ka. The comparison of δ18Oatm with the δ18Ocalcite from East Asian speleothems shows that both signals present similar orbital and millennial variabilities, which may represent shifts in the InterTropical Convergence Zone position, themselves associated with Heinrich events. We thus propose to use the δ18Ocalcite as target for δ18Oatm orbital dating. Such a tuning method improves the ice core chronology of the last glacial inception compared to AICC2012 by reconciling NGRIP and mid-latitude climatic records. It is especially marked during Dansgaard-Oeschger 25 where the proposed chronology is 2.2 ka older than AICC2012. This δ18Oatm - δ18Ocalcite alignment method applied between 100 and 640 ka improves the EDC ice core chronology, especially over MIS 11, and leads to lower ice age uncertainties compared to AICC2012.

A Southern Hemisphere origin for campanulid angiosperms, with traces of the break-up of Gondwana

PubMed Central

2013-01-01

Background New powerful biogeographic methods have focused attention on long-standing hypotheses regarding the influence of the break-up of Gondwana on the biogeography of Southern Hemisphere plant groups. Studies to date have often concluded that these groups are too young to have been influenced by these ancient continental movements. Here we examine a much larger and older angiosperm clade, the Campanulidae, and infer its biogeographic history by combining Bayesian divergence time information with a likelihood-based biogeographic model focused on the Gondwanan landmasses. Results Our analyses imply that campanulids likely originated in the middle Albian (~105 Ma), and that a substantial portion of the early evolutionary history of campanulids took place in the Southern Hemisphere, despite their greater species richness in the Northern Hemisphere today. We also discovered several disjunctions that show biogeographic and temporal correspondence with the break-up of Gondwana. Conclusions While it is possible to discern traces of the break-up of Gondwana in clades that are old enough, it will generally be difficult to be confident in continental movement as the prime cause of geographic disjunctions. This follows from the need for the geographic disjunction, the inferred biogeographic scenario, and the dating of the lineage splitting events to be consistent with the causal hypothesis. PMID:23565668

Coastal sea-ice processes in Alaska and their relevance for sediment dynamics and coastal retreat (Invited)

NASA Astrophysics Data System (ADS)

Eicken, H.; Kapsch, M.; Johnson, M. A.; Weyapuk, W. U., Jr.

2009-12-01

Sea ice plays an important, complicated role in Arctic coastal sediment dynamics. It helps protect the shoreline from wave action and constrains coastal permafrost thaw; at the same time, sea ice is a highly effective sediment erosion and transport agent. For the coastline of (sub-)Arctic Alaska we have examined key processes that govern the role of sea ice as a geologic agent. Based on passive microwave satellite data for the time period 1979 to 2008 and augmented by field measurements and observations conducted by local sea-ice experts in coastal communities from 2006 onwards, we determined the onset of coastal ice spring break-up and fall freeze-up. These two events define the start and end of the open-water season during which the coast is rendered most vulnerable to thermal and dynamic processes promoting erosion. Satellite data show significant trends toward later fall freeze-up in many locations and moreover provide a picture of the statistical significance and variability of such trends in great spatio-temporal detail. Coastal ice observations suggest that important sea-ice processes (such as formation of ice berms) that precede freeze-up as detected by passive microwave data need to be taken into consideration in evaluating the vulnerability of the coastline and the specific threat of individual storms. Field observations, satellite data and local knowledge also highlight the substantial change in winter sea-ice regimes over the past two decades, with a much more mobile ice cover enhancing winter sediment transport. Ultimately, the shorter sea-ice season and the greater mobility and the lack of stability of winter coastal sea ice work in concert to increase the vulnerability of the coastline to erosion and flooding. At the same time, these changes provide a mechanism for effective redistribution and cross-shelf transport of sediments that prepares the stage for further erosive action in subsequent seasons.

The safety band of Antarctic ice shelves

NASA Astrophysics Data System (ADS)

Fürst, Johannes Jakob; Durand, Gaël; Gillet-Chaulet, Fabien; Tavard, Laure; Rankl, Melanie; Braun, Matthias; Gagliardini, Olivier

2016-05-01

The floating ice shelves along the seaboard of the Antarctic ice sheet restrain the outflow of upstream grounded ice. Removal of these ice shelves, as shown by past ice-shelf recession and break-up, accelerates the outflow, which adds to sea-level rise. A key question in predicting future outflow is to quantify the extent of calving that might precondition other dynamic consequences and lead to loss of ice-shelf restraint. Here we delineate frontal areas that we label as `passive shelf ice’ and that can be removed without major dynamic implications, with contrasting results across the continent. The ice shelves in the Amundsen and Bellingshausen seas have limited or almost no `passive’ portion, which implies that further retreat of current ice-shelf fronts will yield important dynamic consequences. This region is particularly vulnerable as ice shelves have been thinning at high rates for two decades and as upstream grounded ice rests on a backward sloping bed, a precondition to marine ice-sheet instability. In contrast to these ice shelves, Larsen C Ice Shelf, in the Weddell Sea, exhibits a large `passive’ frontal area, suggesting that the imminent calving of a vast tabular iceberg will be unlikely to instantly produce much dynamic change.

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.

Luminescence dating of paleolake deltas and glacial deposits in Garwood Valley, Antarctica: Implications for climate, Ross ice sheet dynamics, and paleolake duration

USGS Publications Warehouse

Levy, Joseph S.; Rittenour, Tammy M.; Fountain, Andrew G.; O'Connor, Jim E.

2017-01-01

The formation of perched deltas and other lacustrine deposits in the McMurdo Dry Valleys of Antarctica is widely considered to be evidence of valley-filling lakes dammed by the grounded Ross Sea ice sheet during the local Last Glacial Maximum, with lake drainage interpreted as a record of grounding line retreat. We used luminescence dating to determine the age of paleolake deltas and glacial tills in Garwood Valley, a coastal dry valley that opens to the Ross Sea. Luminescence ages are stratigraphically consistent with radiocarbon results from algal mats within the same delta deposits but suggest radiocarbon dates from lacustrine carbonates may overestimate deposit ages by thousands of years. Results suggest that late Holocene delta deposition into paleolake Howard in Garwood Valley persisted until ca. 3.5 ka. This is significantly younger than the date when grounded ice is thought to have retreated from the Ross Sea. Our evidence suggests that the local, stranded ice-cored till topography in Garwood Valley, rather than regional ice-sheet dynamics, may have controlled lake levels for some McMurdo Dry Valleys paleolakes. Age control from the supraglacial Ross Sea drift suggests grounding and up-valley advance of the Ross Sea ice sheet into Garwood valley during marine oxygen isotope stage (MIS) 4 (71–78 ka) and the local Last Glacial Maximum (9–10 ka). This work demonstrates the power of combining luminescence dating with existing radiocarbon data sets to improve understanding of the relationships among paleolake formation, glacial position, and stream discharge in response to climate change.

Ice shelf breaking and increase velocity of glacier: the view from analogue experiment

NASA Astrophysics Data System (ADS)

Corti, Giacomo; Iandelli, Irene

2013-04-01

Collapse of the Larsen II platform during the late 90s has generated an increase in velocity if ice sheet discharge, highlighting that these processes may strongly destabilize large ice masses speeding up the plateau discharge toward the sea. Parameters such as ice thickness, valley width and slope, ice pack dimensions may contribute to modulate the effect of increase in ice flow velocity following the removal of ice. We analyze this process through scale analogue models, aimed at reproducing the flow of ice from a plateau into the sea through a narrow valley. The ice is reproduced with a transparent silicone (Polydimethisiloxane), flowing at velocities of a few centimeters per hour and simulating natural velocities in the range of a few meters per year. Having almost the same density of the ice, PDMS floats on water and simulate the ice-shelf formation. Results of preliminary experimental series support that this methodology is able to reasonably reproduce the process and support a significant increase in velocity discharge following the removal of ice pack. Additional tests are designed to verify the influence of the above-mentioned parameters on the increase in ice velocity.

Polarimetric C-/X-band Synthetic Aperture Radar Observations of Melting Sea Ice in the Canadian Arctic Archipelago

NASA Astrophysics Data System (ADS)

Casey, J. A.; Beckers, J. F.; Brossier, E.; Haas, C.

2013-12-01

Operational ice information services rely heavily on space-borne synthetic aperture radar (SAR) data for the production of ice charts to meet their mandate of providing timely and accurate sea ice information to support safe and efficient marine operations. During the summer melt period, the usefulness of SAR data for sea ice monitoring is limited by the presence of wet snow and melt ponds on the ice surface, which can mask the signature of the underlying ice. This is a critical concern for ice services whose clients (e.g. commercial shipping, cruise tourism, resource exploration and extraction) are most active at this time of year when sea ice is at its minimum extent, concentration and thickness. As a result, there is a need to further quantify the loss of ice information in SAR data during the melt season and to identify what information can still be retrieved about ice surface conditions and melt pond evolution at this time of year. To date the majority of studies have been limited to analysis of single-polarization C-band SAR data. This study will investigate the potential complimentary and unique sea ice information that polarimetric C- and X-band SAR data can provide to supplement the information available from traditional single co-polarized C-band SAR data. A time-series of polarimetric C- and X-band SAR data was acquired over Jones Sound in the Canadian Arctic Archipelago, in the vicinity of the Grise Fiord, Nunavut. Five RADARSAT-2 Wide Fine Quad-pol images and 11 TerraSAR-X StripMap dual-pol (HH/VV) images were acquired. The time-series begins at the onset of melt in early June and extends through advanced melt conditions in late July. Over this period several ponding and drainage events and two snowfall events occurred. Field observations of sea ice properties were collected using an Ice Mass Balance (IMB) buoy, hourly photos from a time-lapse camera deployed on a coastal cliff, and manual in situ measurements of snow thickness and melt pond depth. Where available, clear-sky data from optical sensors (MODIS, Landsat-8, and WorldView) are also used to provide supplementary information on melt pond coverage and evolution. Meteorological data are available from an Environment Canada weather station in Grise Fiord. In this presentation we will discuss the sea ice information provided by each polarization and frequency and evaluate the impact of melt pond evolution on SAR backscatter. Results to date indicate that C- and X-band provide predominantly redundant information, and cross-polarized backscatter (only acquired at C-band) is often very low and near the system noise floor. Early in the melt season a thick wet snow pack is present and both frequencies provide very little ice information. This is attributed to the strong attenuation of the microwave signal by the wet snow. At this time the underlying ice is effectively obscured. During heavily ponded periods backscatter is highly variable, attributed to changing winds and thus variable melt pond surface roughness. In the final week of observations the fast ice in the region is breaking up and open water is present in some images. In these images C-band appears to provide greater contrast between the melting ice and open water than X-band. Analysis of polarimetric parameters is ongoing.

Origin, distribution and glaciological implications of Jurassic high heat production granites in the Weddell Sea rift, Antarctica

NASA Astrophysics Data System (ADS)

Leat, Phil T.; Jordan, Tom A. R. M.; Ferraccioli, Fausto; Flowerdew, Michael; R, Riley, Teal; Vaughan, Alan P. M.; Whitehouse, Martin

2013-04-01

The distribution of heat flow in Antarctic continental crust is critical to understanding ice sheet nucleation, growth and basal rheology and hydrology. We identify a group of High Heat Production granites intruded into Palaeozoic sedimentary sequences which may contribute to locally high heat flow beneath the central part of the West Antarctic Ice Sheet. Four of the granite plutons are exposed above ice sheet level at Pagano Nunatak, Pirrit Hills, Nash Hills and Whitmore Mountains. A new U-Pb zircon age from Pirrit Hills of 177.9 ± 2.3 Ma confirms earlier Rb-Sr dating that suggested an Early-Middle Jurassic age for the granites, coincident with the Karoo-Ferrar large igneous province and the first stage of Gondwana break-up. Our recently-acquired aerogeophysical data indicate that the plutons are distributed unevenly over 1000 km2 and were intruded into the actively extending, locally transcurrent, Jurassic Weddell Sea Rift [1]. In the NW part of the rift, the Pirrit Hills, Nash Hills and Whitmore Mountains granites form small isolated intrusions within weakly deformed upper crust. In the SE part of the rift, where granite intrusion was strongly structurally controlled within transtensional structures, the Pagano Nunatak granite is the only outcrop of a probably multiphase, ca 180 km long granite intrusion. The granites are weakly peraluminous, S-type and have Th and U abundances up to 61 and 19 ppm respectively. Heat production of analysed granite samples is ca. 2.9-9.1 µWm-3, toward the upper limit of values for High Heat Production granites globally. The granites are thought to have been generated during mafic underplating of the Weddell Rift during eruption of the contemporaneous Karoo-Ferrar magmatism [2]. The high Th and U abundances may be related to fractionation of the high Th-U Ferrar basaltic magmas combined with assimilation of pelitic sedimentary rocks. The granites correspond to an area of West Antarctica that may have heat flow significantly above the Antarctic average, as predicted from satellite magnetic data [3]. [1] Jordan, T.A., et al., Inland extent of the Weddell Sea Rift imaged by new aerogeophysical data, Tectonophysics (2012), 10.1016/j.tecto.2012.09.010 [2] Storey, B.C., et al., Middle Jurassic within-plate granites in West Antarctica and their bearing on the break-up of Gondwanaland. J. Geol. Soc. Lond, (1988), 145, 999-1007. [3] Fox Maule, C., et al., Heat flux anomalies in Antarctica revealed by satellite magnetic data. Science (2005), 10.1126/science.1106888

Glacier Acceleration and Thinning after Ice Shelf Collapse in the Larsen B Embayment, Antarctica

NASA Technical Reports Server (NTRS)

Scambos, T. A.; Bohlander, J. A.; Shuman, C. A.; Skvarca, P.

2004-01-01

Ice velocities derived from five Landsat 7 images acquired between January 2000 and February 2003 show a two- to six-fold increase in centerline speed of four glaciers flowing into the now-collapsed section of the Larsen B Ice Shelf. Satellite laser altimetry from ICEsat indicates the surface of Hektoria Glacier lowered by up to 38 +/- 6 m a six-month period beginning one year after the break-up in March 2002. Smaller elevation losses are observed for Crane and Jorum glaciers over a later 5-month period. Two glaciers south of the collapse area, Flask and Leppard, show little change in speed or elevation. Seasonal variations in speed preceding the large post-collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics.

Interoperability and different ways of knowing: How semantics can aid in cross-cultural understanding

NASA Astrophysics Data System (ADS)

Pulsifer, P. L.; Parsons, M. A.; Duerr, R. E.; Fox, P. A.; Khalsa, S. S.; McCusker, J. P.; McGuinness, D. L.

2012-12-01

To address interoperability, we first need to understand how human perspectives and worldviews influence the way people conceive of and describe geophysical phenomena. There is never a single, unambiguous description of a phenomenon - the terminology used is based on the relationship people have with it and what their interests are. So how can these perspectives be reconciled in a way that is not only clear to different people but also formally described so that information systems can interoperate? In this paper we explore conceptions of Arctic sea ice as a means of exploring these issues. We examine multiple conceptions of sea ice and related processes as fundamental components of the Earth system. Arctic sea ice is undergoing rapid and dramatic decline. This will have huge impact on climate and biological systems as well as on shipping, exploration, human culture, and geopolitics. Local hunters, operational shipping forecasters, global climate researchers, and others have critical needs for sea ice data and information, but they conceive of, and describe sea ice phenomena in very different ways. Our hypothesis is that formally representing these diverse conceptions in a suite of formal ontologies can help facilitate sharing of information across communities and enhance overall Arctic data interoperability. We present initial work to model operational, research, and Indigenous (Iñupiat and Yup'ik) concepts of sea ice phenomena and data. Our results illustrate important and surprising differences in how these communities describe and represent sea ice, and we describe our approach to resolving incongruities and inconsistencies. We begin by exploring an intriguing information artifact, the World Meteorological Organization "egg code". The egg code is a compact, information rich way of illustrating detailed ice conditions that has been used broadly for a century. There is much agreement on construction and content encoding, but there are important regional differences in its application. Furthermore, it is an analog encoding scheme whose meaning has evolved over time. By semantically modeling the egg code, its subtle variations, and how it connects to other data, we illustrate a mechanism for translating across data formats and representations. But there are limits to what semantically modeling the egg-code can achieve. The egg-code and common operational sea ice formats do not address community needs, notably the timing and processes of sea ice freeze-up and break-up which have profound impact on local hunting, shipping, oil exploration, and safety. We work with local experts from four very different Indigenous communities and scientific creators of sea ice forecasts to establish an understanding of concepts and terminology related to fall freeze-up and spring break up from the individually represented regions. This helps expand our conceptions of sea ice while also aiding in understanding across cultures and communities, and in passing knowledge to younger generations. This is an early step to expanding concepts of interoperability to very different ways of knowing to make data truly relevant and locally useful.

Polynya dynamics and associated atmospheric forcing at the Ronne Ice Shelf

NASA Astrophysics Data System (ADS)

Ebner, Lars; Heinemann, Günther

2014-05-01

The Ronne Ice Shelf is known as one of the most active regions of polynya developments around the Antarctic continent. Low temperatures are prevailing throughout the whole year, particularly in winter. It is generally recognized that polynya formations are primarily forced by offshore winds and secondarily by ocean currents. Many authors have addressed this issue previously at the Ross Ice Shelf and Adélie Coast and connected polynya dynamics to strong katabatic surge events. Such investigations of atmospheric dynamics and simultaneous polynya occurrence are still severely underrepresented for the southwestern part of the Weddell Sea and especially for the Ronne Ice Shelf. Due to the very flat terrain gradients of the ice shelf katabatic winds are of minor importance in that area. Other atmospheric processes must therefore play a crucial role for polynya developments at the Ronne Ice Shelf. High-resolution simulations have been carried out for the Weddell Sea region using the non-hydrostatic NWP model COSMO from the German Meteorological Service (DWD). For the austral autumn and winter (March to August) 2008 daily forecast simulations were conducted with the consideration of daily sea-ice coverage deduced from the passive microwave system AMSR-E. These simulations are used to analyze the synoptic and mesoscale atmospheric dynamics of the Weddell Sea region and find linkages to polynya occurrence at the Ronne Ice Shelf. For that reason, the relation between the surface wind speed, the synoptic pressure gradient in the free atmosphere and polynya area is investigated. Seven significant polynya events are identified for the simulation period, three in the autumn and four in the winter season. It can be shown that in almost all cases synoptic cyclones are the primary polynya forcing systems. In most cases the timely interaction of several passing cyclones in the northern and central Weddell Sea leads to maintenance of a strong synoptic pressure gradient above the Ronne Ice Shelf. This strong synoptic forcing results in a moderate to strong offshore surface wind. It turned out that these synoptic depressions lead to strong barrier winds above the northwestern Ronne Ice Shelf and along the eastern flank of the Antarctic Peninsula. The fact, that these barrier winds often appear prior or during the initial break up of sea ice at the shelf ice edge, suggest that this mesoscale wind phenomenon plays a crucial role for polynya development. Furthermore, even mesoscale cyclogenesis above the Ronne Ice Shelf and the following northeastward passage of such a system can break up sea-ice cover under large-scale stationary weather conditions.

Assessment and validation of the community radiative transfer model for ice cloud conditions

NASA Astrophysics Data System (ADS)

Yi, Bingqi; Yang, Ping; Weng, Fuzhong; Liu, Quanhua

2014-11-01

The performance of the Community Radiative Transfer Model (CRTM) under ice cloud conditions is evaluated and improved with the implementation of MODIS collection 6 ice cloud optical property model based on the use of severely roughened solid column aggregates and a modified Gamma particle size distribution. New ice cloud bulk scattering properties (namely, the extinction efficiency, single-scattering albedo, asymmetry factor, and scattering phase function) suitable for application to the CRTM are calculated by using the most up-to-date ice particle optical property library. CRTM-based simulations illustrate reasonable accuracy in comparison with the counterparts derived from a combination of the Discrete Ordinate Radiative Transfer (DISORT) model and the Line-by-line Radiative Transfer Model (LBLRTM). Furthermore, simulations of the top of the atmosphere brightness temperature with CRTM for the Crosstrack Infrared Sounder (CrIS) are carried out to further evaluate the updated CRTM ice cloud optical property look-up table.

Changes in ice dynamics along the northern Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Seehaus, Thorsten; Marinsek, Sebastian; Cook, Alison; Van Wessem, Jan-Melchior; Braun, Matthias

2017-04-01

The climatic conditions along the Antarctic Peninsula have undergone considerable changes during the last 50 years. A period of pronounced air temperature rise, increasing ocean temperatures as well as changes in the precipitation pattern have been reported by various authors. Consequently, the glacial systems showed changes including widespread retreat, surface lowering as well as variations in flow speeds. During the last decades numerous ice shelves along the Antarctic Peninsula retreated, started to break-up or disintegrated completely. The loss of the buttressing effect caused tributary glaciers to accelerate with increasing ice discharge along the Antarctic Peninsula. Quantification of the mass changes is still subject to considerable errors although numbers derived from the different methods are converging. The aim is to study the reaction of glaciers at the northern Antarctic Peninsula to the changing climatic conditions and the readjustments of tributary glaciers to ice shelf disintegration, as well as to better quantify the ice mass loss and its temporal changes. We analysed time series of various satellite sensors (ERS-1/2 SAR, ENVISAT ASAR, RADARSAT-1, ALOS PALSAR, TerraSAR-X/TanDEM-X, ASTER, Landsat) to detect changes in ice dynamics of 74 glacier basins along the northern Antarctic Peninsula (<65°). Intensity feature tracking techniques were applied on data stacks from different SAR satellites over the last 20 years to infer temporal trends in glacier surface velocities. In combination with ice thickness reconstructions and modeled climatic mass balance fields regional imbalances were calculated. Variations in ice front position were mapped based on optical and SAR satellite data sets. Along the west coast of the northern Antarctic Peninsula an increase in flow speeds by 40% between 1992 and 2014 was observed, whereas glaciers on the east side (north of former Prince-Gustav Ice Shelf) showed a strong deceleration. Nearly all former ice shelf tributaries showed similar reactions to ice shelf disintegration, with a significant acceleration and frontal retreat after ice shelf break-up and a subsequent deceleration and front stabilization. In total an ice discharge of 17.93±6.22 Gt/a was estimated for the study region in the period 2010-2014. Regional mass balance estimates indicate nearly balanced mass budgets in the period 1992-1996 and positive imbalances in more recent years (2010-2014), dominated by the clearly positive mass balances along the west coast due to high climatic mass balances. The detailed multi-mission time series analysis of glacier changes supports the interpretation of the ongoing processes in this region and allows multi temporal imbalance estimates.

Student Support using Project Adventure

NASA Astrophysics Data System (ADS)

Kawanishi, Toshimasa

University students become maladjustment at the time of entrance to school not to have friends. Project adventure is effective in the making of friend and brings up confidence with persons. General concepts of project adventure make from experimental learning cycle, full value contract and challenge by choice. This paper explains purpose of PA, practice, ice breaking, trust and initiative.

A common and optimized age scale for Antarctic ice cores

NASA Astrophysics Data System (ADS)

Parrenin, F.; Veres, D.; Landais, A.; Bazin, L.; Lemieux-Dudon, B.; Toye Mahamadou Kele, H.; Wolff, E.; Martinerie, P.

2012-04-01

Dating ice cores is a complex problem because 1) there is a age shift between the gas bubbles and the surrounding ice 2) there are many different ice cores which can be synchronized with various proxies and 3) there are many methods to date the ice and the gas bubbles, each with advantages and drawbacks. These methods fall into the following categories: 1) Ice flow (for the ice) and firn densification modelling (for the gas bubbles); 2) Comparison of ice core proxies with insolation variations (so-called orbital tuning methods); 3) Comparison of ice core proxies with other well dated archives; 4) Identification of well-dated horizons, such as tephra layers or geomagnetic anomalies. Recently, an new dating tool has been developped (DATICE, Lemieux-Dudon et al., 2010), to take into account all the different dating information into account and produce a common and optimal chronology for ice cores with estimated confidence intervals. In this talk we will review the different dating information for Antarctic ice cores and show how the DATICE tool can be applied.

CHEMICAL EVOLUTION OF A CO ICE INDUCED BY SOFT X-RAYS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ciaravella, A.; Cecchi-Pestellini, C.; Jiménez-Escobar, A.

2016-03-01

We irradiated a pure carbon monoxide ice with soft X-rays of energies up to 1.2 keV. The experiments were performed using the spherical grating monochromator beamline at the National Synchrotron Radiation Research Center in Taiwan, exploiting both monochromatic (at 0.3 and 0.55 keV) and broader energy (0.25–1.2 keV) fluxes. The infrared spectra of the irradiated ices showed the formation of a number of products such as polycarbon mono- and dioxides C{sub n}O{sub m}, and chains containing up to 10 carbon atoms. While a gentle increase in the energy absorbed by the ice sample is reflected by an increase in themore » column densities of newly born species, such correlation breaks down at very high fluxes. In this regime the production yield falls down sharply by about a factor of 100. The refractory residue obtained in the broad energy irradiation is a “compromise” between those obtained with proton irradiation of C{sub 3}O{sub 2} and CO ices in previous experiments. Finally, we discuss the possible implications for space chemistry.« less

How's the Weather?: Ice-Breaking and Fog-Lifting in Your Written Messages.

ERIC Educational Resources Information Center

Vassallo, Philip

1994-01-01

Describes two ways to combat "bad tone" and "unclear thinking" in writing. Describes "breaking the ice" as being aware of a written message's appearance--the message's readability. Explains that "fog-lifting" is accomplished by writing clearly, and by paying particular attention to the verb "to…

The role of ice dynamics in shaping vegetation in flowing waters.

PubMed

Lind, Lovisa; Nilsson, Christer; Polvi, Lina E; Weber, Christine

2014-11-01

Ice dynamics is an important factor affecting vegetation in high-altitude and high-latitude streams and rivers. During the last few decades, knowledge about ice in streams and rivers has increased significantly and a respectable body of literature is now available. Here we review the literature on how ice dynamics influence riparian and aquatic vegetation. Traditionally, plant ecologists have focused their studies on the summer period, largely ignoring the fact that processes during winter also impact vegetation dynamics. For example, the freeze-up period in early winter may result in extensive formation of underwater ice that can restructure the channel, obstruct flow, and cause flooding and thus formation of more ice. In midwinter, slow-flowing reaches develop a surface-ice cover that accumulates snow, protecting habitats under the ice from formation of underwater ice but also reducing underwater light, thus suppressing photosynthesis. Towards the end of winter, ice breaks up and moves downstream. During this transport, ice floes can jam up and cause floods and major erosion. The magnitudes of the floods and their erosive power mainly depend on the size of the watercourse, also resulting in different degrees of disturbance to the vegetation. Vegetation responds both physically and physiologically to ice dynamics. Physical action involves the erosive force of moving ice and damage caused by ground frost, whereas physiological effects - mostly cell damage - happen as a result of plants freezing into the ice. On a community level, large magnitudes of ice dynamics seem to favour species richness, but can be detrimental for individual plants. Human impacts, such as flow regulation, channelisation, agriculturalisation and water pollution have modified ice dynamics; further changes are expected as a result of current and predicted future climate change. Human impacts and climate change can both favour and disfavour riverine vegetation dynamics. Restoration of streams and rivers may mitigate some effects of anticipated climate change on ice and vegetation dynamics by, for example, slowing down flows and increasing water depth, thus reducing the potential for massive formation of underwater ice. © 2014 The Authors. Biological Reviews © 2014 Cambridge Philosophical Society.

C-band Joint Active/Passive Dual Polarization Sea Ice Detection

NASA Astrophysics Data System (ADS)

Keller, M. R.; Gifford, C. M.; Winstead, N. S.; Walton, W. C.; Dietz, J. E.

2017-12-01

A technique for synergistically-combining high-resolution SAR returns with like-frequency passive microwave emissions to detect thin (<30 cm) ice under the difficult conditions of late melt and freeze-up is presented. As the Arctic sea ice cover thins and shrinks, the algorithm offers an approach to adapting existing sensors monitoring thicker ice to provide continuing coverage. Lower resolution (10-26 km) ice detections with spaceborne radiometers and scatterometers are challenged by rapidly changing thin ice. Synthetic Aperture Radar (SAR) is high resolution (5-100m) but because of cross section ambiguities automated algorithms have had difficulty separating thin ice types from water. The radiometric emissivity of thin ice versus water at microwave frequencies is generally unambiguous in the early stages of ice growth. The method, developed using RADARSAT-2 and AMSR-E data, uses higher-ordered statistics. For the SAR, the COV (coefficient of variation, ratio of standard deviation to mean) has fewer ambiguities between ice and water than cross sections, but breaking waves still produce ice-like signatures for both polarizations. For the radiometer, the PRIC (polarization ratio ice concentration) identifies areas that are unambiguously water. Applying cumulative statistics to co-located COV levels adaptively determines an ice/water threshold. Outcomes from extensive testing with Sentinel and AMSR-2 data are shown in the results. The detection algorithm was applied to the freeze-up in the Beaufort, Chukchi, Barents, and East Siberian Seas in 2015 and 2016, spanning mid-September to early November of both years. At the end of the melt, 6 GHz PRIC values are 5-10% greater than those reported by radiometric algorithms at 19 and 37 GHz. During freeze-up, COV separates grease ice (<5 cm thick) from water. As the ice thickens, the COV is less reliable, but adding a mask based on either the PRIC or the cross-pol/co-pol SAR ratio corrects for COV deficiencies. In general, the dual-sensor detection algorithm reports 10-15% higher total ice concentrations than operational scatterometer or radiometer algorithms, mostly from ice edge and coastal areas. In conclusion, the algorithm presented combines high-resolution SAR returns with passive microwave emissions for automated ice detection at SAR resolutions.

Effects of vibration on the readability of an electronic flight instrument display

NASA Astrophysics Data System (ADS)

Viveash, Jacqueline P.; Cable, A. N.; King, S. K.; Stott, J. R.; Wright, R.

1993-12-01

An in-flight icing incident involving a BAe advanced turboprop (ATP) aircraft led to severe vibration of the airframe and a loss of aerodynamic control. During the period of vibration the pilot reported a specific pattern of image break up on the electronic flight instrument system (EFIS). Three experiments to investigate this visual effect are reported.

Late summer and fall wave climate in the Beaufort and Chukchi Seas, 2000-2014

NASA Astrophysics Data System (ADS)

Fan, Y.; Rogers, W.; Thomson, J.; Stopa, J.

2016-02-01

Jim Thomson, Applied Physics Laboratory, University of Washington, Seattle, WA According to IPCC, "warming in the Arctic, as indicated by daily maximum and minimum temperatures, has been as great as in any other part of the world." Some regions within the Arctic have warmed even more rapidly, with Alaska and western Canada's temperature rising by 3 to 4 °C (5.40 to 7.20 °F). Arctic ice is getting thinner, melting and rupturing. The polar ice cap as a whole is shrinking. Images from NASA satellites show that the area of permanent ice cover is contracting at a rate of 9 percent each decade. If this trend continues, summers in the Arctic could become ice-free by the end of the century. Arctic storms thus have the potential to create large waves in the region. Ocean waves can also penetrate remarkable distances into ice fields and impact sea-ice thermodynamics by breaking up ice floes and accelerating ice melting during the summer (Asplin et al 2012); or influencing sea-ice growth and hence the morphology of the mature ice sheet during the winter (Lange et al 1989). Waves breaking on the shore could also affect the coastlines, where melting permafrost is already making shores more vulnerable to erosion. Preliminary wave model results from four selected years suggests that the sea state of the Beaufort and Chukchi seas is controlled by the wind forcing and the amount of ice-free water available to generate surface waves. In particular, larger waves are more common in years with low or late sea ice cover. Trends in amount of wave energy impinging on the ice edge, however, are inconclusive. To better understand the potential effect of surface wave on the advance/retreat of ice edges and the coastlines. 15 years (2000 to 2014) of surface wave simulations in the Arctic Ocean using WAVEWATCH III will be conducted. Wind and ice forcing are obtained from the ERA-interim global reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). Wave energy flux arriving at the ice edges and land boundaries will be analyzed and histograms and fitted Weibull probability distribution functions will used to identify similarities and differences during the 15 year period. The potential effect of surface waves on ice advance/retreat and land erosion will be explored and discussed.

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.

Using Appreciative Intelligence for Ice-Breaking: A New Design

ERIC Educational Resources Information Center

Verma, Neena; Pathak, Anil Anand

2011-01-01

Purpose: The purpose of this paper is to highlight the importance of applying appreciative intelligence and appreciative inquiry concepts to design a possibly new model of ice-breaking, which is strengths-based and very often used in any training in general and team building training in particular. Design/methodology/approach: The design has…

Wave-ice interaction, observed and modelled

NASA Astrophysics Data System (ADS)

Gemmrich, Johannes

2017-04-01

The need for wide-spread, up-to-date sea state predictions and observations in the emerging ice-free Arctic will further increase as the region will open up to marine operations. Wave models for arctic regions have to capture the additional wave physics associated with wave-ice interactions, and different prediction schemes have to be tested against observations. Here we present examples of spatial wave field parameters obtained from TerraSAR-X StripMap swaths in the southern Beaufort Sea taken as part of the "Arctic Sea State and Boundary Layer DRI". Fetch evolution of the significant wave height and length in open waters, and dominant wave lengths and the high frequency cut-off of the wave spectrum in ice are readily extracted from the SAR (synthetic aperture radar) data. A surprising result is that wave evolution in off-ice wind conditions is more rapidly than the fetch evolution in off-land cases, suggesting seeding of the wave field within the ice-covered region.

Modeling dynamics of large tabular icebergs submerged in the ocean

NASA Astrophysics Data System (ADS)

Adcroft, A.; Stern, A. A.; Sergienko, O. V.

2017-12-01

Large tabular icebergs account for a major fraction of the ice calved from the Antarctic ice shelves, and have long lifetimes due to their size. They drift for long distances, interacting with the local ocean circulation, impacting bottom-water formation, sea-ice formation, and biological productivity in the vicinity of the icebergs. However, due to their large horizontal extent and mass, it is challenging to consistently represent large tabular icebergs in global ocean circulation models and so large tabular icebergs are not currently represented in climate models. In this study we develop a novel framework to model large tabular icebergs submerged in the ocean. In this framework, a tabular iceberg is represented by a collection of Lagrangian elements that are linked through rigid bonds. The Lagrangian elements are finite-area modifications of the point-particles used in previous studies to represent small icebergs. These elements interact with the ocean by exerting pressure on the ocean surface, and through melt water and momentum exchange. A breaking of the rigid bonds allows the model to emulate calving events (i.e. detachment of a tabular iceberg from an ice shelf), and to emulate the breaking up of tabular icebergs into smaller pieces. Idealized simulations of the calving of a tabular iceberg, subsequent drift and breakup, demonstrate the capabilities of the new framework with a promise that climate models may soon be able to represent large tabular icebergs.

Sea Ice, Clouds, Sunlight, and Albedo: The Umbrella Versus the Blanket

NASA Astrophysics Data System (ADS)

Perovich, D. K.

2017-12-01

The Arctic sea ice cover has undergone a major decline in recent years, with reductions in ice extent, ice thickness, and ice age. Understanding the feedbacks and forcing driving these changes is critical in improving predictions. The surface radiation budget plays a central role in summer ice melt and is governed by clouds and surface albedo. Clouds act as an umbrella reducing the downwelling shortwave, but also serve as a blanket increasing the downwelling longwave, with the surface albedo also determining the net balance. Using field observations from the SHEBA program, pairs of clear and cloudy days were selected for each month from May through September and the net radiation flux was calculated for different surface conditions and albedos. To explore the impact of albedo we calculated a break even albedo, where the net radiation for cloudy skies is the same as clear skies. For albedos larger than the break-even value the net radiation flux is smaller under clear skies compared to cloudy skies. Break-even albedos ranged from 0.30 in September to 0.58 in July. For snow covered or bare ice, clear skies always resulted in less radiative heat input. In contrast, leads always had, and ponds usually had, more radiative heat input under clear skies than cloudy skies. Snow covered ice had a net radiation flux that was negative or near zero under clear skies resulting in radiative cooling. We combined the albedo of individual ice types with the area of those ice types to calculate albedos averaged over a 50 km x 50 km area. The July case had the smallest areally averaged albedo of 0.50. This was less than the breakeven albedo, so cloudy skies had a smaller net radiation flux than clear skies. For the cases from the other four months, the areally averaged albedo was greater than the break-even albedo. The areally averaged net radiation flux was negative under clear skies for the May and September cases.

The Sea-Ice Floe Size Distribution

NASA Astrophysics Data System (ADS)

Stern, H. L., III; Schweiger, A. J. B.; Zhang, J.; Steele, M.

2017-12-01

The size distribution of ice floes in the polar seas affects the dynamics and thermodynamics of the ice cover and its interaction with the ocean and atmosphere. Ice-ocean models are now beginning to include the floe size distribution (FSD) in their simulations. In order to characterize seasonal changes of the FSD and provide validation data for our ice-ocean model, we calculated the FSD in the Beaufort and Chukchi seas over two spring-summer-fall seasons (2013 and 2014) using more than 250 cloud-free visible-band scenes from the MODIS sensors on NASA's Terra and Aqua satellites, identifying nearly 250,000 ice floes between 2 and 30 km in diameter. We found that the FSD follows a power-law distribution at all locations, with a seasonally varying exponent that reflects floe break-up in spring, loss of smaller floes in summer, and the return of larger floes after fall freeze-up. We extended the results to floe sizes from 10 m to 2 km at selected time/space locations using more than 50 high-resolution radar and visible-band satellite images. Our analysis used more data and applied greater statistical rigor than any previous study of the FSD. The incorporation of the FSD into our ice-ocean model resulted in reduced sea-ice thickness, mainly in the marginal ice zone, which improved the simulation of sea-ice extent and yielded an earlier ice retreat. We also examined results from 17 previous studies of the FSD, most of which report power-law FSDs but with widely varying exponents. It is difficult to reconcile the range of results due to different study areas, seasons, and methods of analysis. We review the power-law representation of the FSD in these studies and discuss some mathematical details that are important to consider in any future analysis.

Using timing of ice retreat to predict timing of fall freeze-up in the Arctic

NASA Astrophysics Data System (ADS)

Stroeve, Julienne C.; Crawford, Alex D.; Stammerjohn, Sharon

2016-06-01

Reliable forecasts of the timing of sea ice advance are needed in order to reduce risks associated with operating in the Arctic as well as planning of human and environmental emergencies. This study investigates the use of a simple statistical model relating the timing of ice retreat to the timing of ice advance, taking advantage of the inherent predictive power supplied by the seasonal ice-albedo feedback and ocean heat uptake. Results show that using the last retreat date to predict the first advance date is applicable in some regions, such as Baffin Bay and the Laptev and East Siberian seas, where a predictive skill is found even after accounting for the long-term trend in both variables. Elsewhere, in the Arctic, there is some predictive skills depending on the year (e.g., Kara and Beaufort seas), but none in regions such as the Barents and Bering seas or the Sea of Okhotsk. While there is some suggestion that the relationship is strengthening over time, this may reflect that higher correlations are expected during periods when the underlying trend is strong.

Gastrectomy - slideshow

MedlinePlus

... the small intestine, and functions to break up food into small particles that can be absorbed by the small intestine. Review Date 11/10/2016 Updated by: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. ...

Domestic Ice Breaking Simulation Model User Guide

DTIC Science & Technology

2012-04-01

Temperatures” sub-module. Notes on Ice Data Sources Selected Historical Ice Data *** D9 Historical (SIGRID Coded) NBL Waterways * D9 Waterway...numbers in NBL scheme D9 Historical Ice Data (Feet Thickness) Main Model Waterways * SIGRID code conversion to feet of ice thickness D9 Historical Ice Data...Feet Thickness) NBL Waterways * SIGRID codes Years for Ice Data ** Types of Ice Waterway Time Selected Ice and Weather Data Years DOMICE Simulation

Ice Floe Breaking in Contemporary Third Generation Operational Wave Models

NASA Astrophysics Data System (ADS)

Sévigny, C.; Baudry, J.; Gauthier, J. C.; Dumont, D.

2016-02-01

The dynamical zone observed at the edge of the consolidated ice area where are found the wave-fractured floes (i.e. marginal ice zone or MIZ) has become an important topic in ocean modeling. As both operational and climate ocean models now seek to reproduce the complex atmosphere-ice-ocean system with realistic coupling processes, many theoretical and numerical studies have focused on understanding and modeling this zone. Few attempts have been made to embed wave-ice interactions specific to the MIZ within a two-dimensional model, giving the possibility to calculate both the attenuation of surface waves by sea ice and the concomitant breaking of the sea ice-cover into smaller floes. One of the first challenges consists in improving the parameterization of wave-ice dynamics in contemporary third generation operational wave models. A simple waves-in-ice model (WIM) similar to the one proposed by Williams et al. (2013a,b) was implemented in WAVEWATCH III. This WIM considers ice floes as floating elastic plates and predicts the dimensionless attenuation coefficient by the use of a lookup-table-based, wave scattering scheme. As in Dumont et al. (2011), the different frequencies are treated individually and floe breaking occurs for a particular frequency when the expected wave amplitude exceeds the allowed strain amplitude, which considers ice floes properties and wavelength in ice field. The model is here further refined and tested in idealized two-dimensional cases, giving preliminary results of the performance and sensitivity of the parameterization to initial wave and ice conditions. The effects of the wave-ice coupling over the incident wave spectrum are analyzed as well as the resulting floe size distribution. The model gives prognostic values of the lateral extent of the marginal ice zone with maximum ice floe diameter that progressively increases with distance from the ice edge.

Carbon cycling in a high-arctic marine ecosystem - Young Sound, NE Greenland

NASA Astrophysics Data System (ADS)

Rysgaard, Søren; Nielsen, Torkel Gissel

2006-10-01

Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of ∼1.5 m topped with 0-40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice-water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August-September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7-11 g C m -2) is similar to phytoplankton production (6-10 g C m -2). Furthermore, the carbon demand of pelagic bacteria amounts to 7-12 g C m -2 yr -1. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem. In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m -2 yr -1 is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m -2 yr -1 of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m -2 yr -1 was determined. A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves ( Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters.

The Timing of Arctic Sea Ice Advance and Retreat as an Indicator of Ice-Dependent Marine Mammal Habitat

NASA Astrophysics Data System (ADS)

Stern, H. L.; Laidre, K. L.

2013-12-01

The Arctic is widely recognized as the front line of climate change. Arctic air temperature is rising at twice the global average rate, and the sea-ice cover is shrinking and thinning, with total disappearance of summer sea ice projected to occur in a matter of decades. Arctic marine mammals such as polar bears, seals, walruses, belugas, narwhals, and bowhead whales depend on the sea-ice cover as an integral part of their existence. While the downward trend in sea-ice extent in a given month is an often-used metric for quantifying physical changes in the ice cover, it is not the most relevant measure for characterizing changes in the sea-ice habitat of marine mammals. Species that depend on sea ice are behaviorally tied to the annual retreat of sea ice in the spring and advance in the fall. Changes in the timing of the spring retreat and the fall advance are more relevant to Arctic marine species than changes in the areal sea-ice coverage in a particular month of the year. Many ecologically important regions of the Arctic are essentially ice-covered in winter and ice-free in summer, and will probably remain so for a long time into the future. But the dates of sea-ice retreat in spring and advance in fall are key indicators of climate change for ice-dependent marine mammals. We use daily sea-ice concentration data derived from satellite passive microwave sensors to calculate the dates of sea-ice retreat in spring and advance in fall in 12 regions of the Arctic for each year from 1979 through 2013. The regions include the peripheral seas around the Arctic Ocean (Beaufort, Chukchi, East Siberian, Laptev, Kara, Barents), the Canadian Arctic Archipelago, and the marginal seas (Okhotsk, Bering, East Greenland, Baffin Bay, Hudson Bay). We find that in 11 of the 12 regions (all except the Bering Sea), sea ice is retreating earlier in spring and advancing later in fall. Rates of spring retreat range from -5 to -8 days/decade, and rates of fall advance range from +5 to +9 days/decade, with steeper trends in the Barents Sea. Thus the season of sparse sea-ice coverage is lengthening by about 2 weeks/decade, or 6 weeks over the period of record. The trends in all 11 regions are statistically significant. The dates of sea-ice retreat in spring and advance in fall are negatively correlated: an early spring retreat tends to be followed by a late fall advance, and vice-versa. This is a manifestation of the ice-albedo feedback: with an early sea-ice retreat, the ocean has more time to absorb heat from the sun. The extra heat is stored in the upper ocean through the summer, and must be released to the atmosphere in the fall before sea ice can begin to form, thus delaying fall freeze-up. This relationship gives some predictive power to the date of fall sea-ice advance, given the date of spring retreat. Changes have been reported in the seasonal distribution of polar bears, walruses, seals, and whales in the Arctic. We are developing metrics for potential use by the U.S. National Climate Assessment based on the timing of sea-ice advance and retreat, to be used as indicators of ice-dependent marine mammal habitat. Future work will examine connections between the phenology of Arctic marine mammals and the sea-ice indicators.

Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion

PubMed Central

Lorenz, Ralph D.; Ray, Jib; Jackson, Brian

2014-01-01

The engraved trails of rocks on the nearly flat, dry mud surface of Racetrack Playa, Death Valley National Park, have excited speculation about the movement mechanism since the 1940s. Rock movement has been variously attributed to high winds, liquid water, ice, or ice flotation, but has not been previously observed in action. We recorded the first direct scientific observation of rock movements using GPS-instrumented rocks and photography, in conjunction with a weather station and time-lapse cameras. The largest observed rock movement involved >60 rocks on December 20, 2013 and some instrumented rocks moved up to 224 m between December 2013 and January 2014 in multiple move events. In contrast with previous hypotheses of powerful winds or thick ice floating rocks off the playa surface, the process of rock movement that we have observed occurs when the thin, 3 to 6 mm, “windowpane” ice sheet covering the playa pool begins to melt in late morning sun and breaks up under light winds of ∼4–5 m/s. Floating ice panels 10 s of meters in size push multiple rocks at low speeds of 2–5 m/min. along trajectories determined by the direction and velocity of the wind as well as that of the water flowing under the ice. PMID:25162535

Implications of 36Cl exposure ages from Skye, northwest Scotland for the timing of ice stream deglaciation and deglacial ice dynamics

NASA Astrophysics Data System (ADS)

Small, David; Rinterknecht, Vincent; Austin, William E. N.; Bates, Richard; Benn, Douglas I.; Scourse, James D.; Bourlès, Didier L.; Hibbert, Fiona D.

2016-10-01

Geochronological constraints on the deglaciation of former marine based ice streams provide information on the rates and modes by which marine based ice sheets have responded to external forcing factors such as climate change. This paper presents new 36Cl cosmic ray exposure dating from boulders located on two moraines (Glen Brittle and Loch Scavaig) in southern Skye, northwest Scotland. Ages from the Glen Brittle moraines constrain deglaciation of a major marine terminating ice stream, the Barra-Donegal Ice Stream that drained the former British-Irish Ice Sheet, depending on choice of production method and scaling model this occurred 19.9 ± 1.5-17.6 ± 1.3 ka ago. We compare this timing of deglaciation to existing geochronological data and changes in a variety of potential forcing factors constrained through proxy records and numerical models to determine what deglaciation age is most consistent with existing evidence. Another small section of moraine, the Scavaig moraine, is traced offshore through multibeam swath-bathymetry and interpreted as delimiting a later stillstand/readvance stage following ice stream deglaciation. Additional cosmic ray exposure dating from the onshore portion of this moraine indicate that it was deposited 16.3 ± 1.3-15.2 ± 0.9 ka ago. When calculated using the most up-to-date scaling scheme this time of deposition is, within uncertainty, the same as the timing of a widely identified readvance, the Wester Ross Readvance, observed elsewhere in northwest Scotland. This extends the area over which this readvance has potentially occurred, reinforcing the view that it was climatically forced.

On the possibility of ice on Greenland during the Eocene-Oligocene transition

NASA Astrophysics Data System (ADS)

Langebroek, Petra M.; Nisancioglu, Kerim H.; Lunt, Daniel J.; Kathrine Pedersen, Vivi; Nele Meckler, A.; Gasson, Edward

2017-04-01

The Eocene-Oligocene transition ( 34 Ma) is one of the major climate transitions of the Cenozoic era. Atmospheric CO2 decreased from the high levels of the Greenhouse world (>1000 ppm) to values of about 600-700 ppm in the early Oligocene. High latitude temperatures dropped by several degrees, causing a large-scale expansion of the Antarctic ice sheet. Concurrently, in the Northern Hemisphere, the inception of ice caps on Greenland is suggested by indirect evidence from ice-rafted debris and changes in erosional regime. However, ice sheet models have not been able to simulate extensive ice on Greenland under the warm climate of the Eocene-Oligocene transition. We show that elevated bedrock topography is key in solving this inconsistency. During the late Eocene / early Oligocene, East Greenland bedrock elevations were likely higher than today due to tectonic and deep-Earth processes related to the break-up of the North Atlantic and the position of the Icelandic plume. When allowing for higher initial bedrock topography, we do simulate a large ice cap on Greenland under the still relatively warm climate of the early Oligocene. Ice inception takes place at high elevations in the colder regions of North and Northeast Greenland; with the size of the ice cap being strongly dependent on the climate forcing and the bedrock topography applied.

Evaluating the Duration and Continuity of Potential Climate Records From the Allan Hills Blue Ice Area, East Antarctica

NASA Astrophysics Data System (ADS)

Kehrl, Laura; Conway, Howard; Holschuh, Nicholas; Campbell, Seth; Kurbatov, Andrei V.; Spaulding, Nicole E.

2018-05-01

The current ice core record extends back 800,000 years. Geologic and glaciological evidence suggests that the Allan Hills Blue Ice Area, East Antarctica, may preserve a continuous record that extends further back in time. In this study, we use ice-penetrating radar and existing age constraints to map the internal stratigraphy and age structure of the Allan Hills Main Ice Field. The dated isochrones provide constraints for an ice flow model to estimate the age of ice near the bed. Previous drilling in the region recovered stratigraphically disturbed sections of ice up to 2.7 million years old. Our study identifies a site 5 km upstream, which likely preserves a continuous record through Marine Isotope Stage 11 with the possibility that the record extends back 1 million years. Such records would provide new insight into the past climate and glacial history of the Ross Sea Sector.

Can phenological models predict tree phenology accurately in the future? The unrevealed hurdle of endodormancy break.

PubMed

Chuine, Isabelle; Bonhomme, Marc; Legave, Jean-Michel; García de Cortázar-Atauri, Iñaki; Charrier, Guillaume; Lacointe, André; Améglio, Thierry

2016-10-01

The onset of the growing season of trees has been earlier by 2.3 days per decade during the last 40 years in temperate Europe because of global warming. The effect of temperature on plant phenology is, however, not linear because temperature has a dual effect on bud development. On one hand, low temperatures are necessary to break bud endodormancy, and, on the other hand, higher temperatures are necessary to promote bud cell growth afterward. Different process-based models have been developed in the last decades to predict the date of budbreak of woody species. They predict that global warming should delay or compromise endodormancy break at the species equatorward range limits leading to a delay or even impossibility to flower or set new leaves. These models are classically parameterized with flowering or budbreak dates only, with no information on the endodormancy break date because this information is very scarce. Here, we evaluated the efficiency of a set of phenological models to accurately predict the endodormancy break dates of three fruit trees. Our results show that models calibrated solely with budbreak dates usually do not accurately predict the endodormancy break date. Providing endodormancy break date for the model parameterization results in much more accurate prediction of this latter, with, however, a higher error than that on budbreak dates. Most importantly, we show that models not calibrated with endodormancy break dates can generate large discrepancies in forecasted budbreak dates when using climate scenarios as compared to models calibrated with endodormancy break dates. This discrepancy increases with mean annual temperature and is therefore the strongest after 2050 in the southernmost regions. Our results claim for the urgent need of massive measurements of endodormancy break dates in forest and fruit trees to yield more robust projections of phenological changes in a near future. © 2016 John Wiley & Sons Ltd.

A Chronology of Late-Glacial and Holocene Advances of Quelccaya Ice Cap, Peru, Based on 10Be and Radiocarbon Dating

NASA Astrophysics Data System (ADS)

Kelly, M. A.; Lowell, T. V.; Schaefer, J. M.

2007-12-01

The Quelccaya Ice Cap region in the southeastern Peruvian Andes (~13-14°S latitude) is a key location for the development of late-glacial and Holocene terrestrial paleoclimate records in the tropics. We present a chronology of past extents of Quelccaya Ice Cap based on ~thirty internally consistent 10Be dates of boulders on moraines and bedrock as well as twenty radiocarbon dates of organic material associated with moraines. Based on results from both dating methods, we suggest that significant advances of Quelccaya Ice Cap occurred during late-glacial time, at ~12,700-11,400 yr BP, and during Late Holocene time ~400-300 yr BP. Radiocarbon dating of organic material associated with moraines provides maximum and minimum ages for ice advances and recessions, respectively, thus providing an independent check on 10Be dates of boulders on moraines. The opportunity to use both 10Be and radiocarbon dating makes the Quelccaya Ice Cap region a potentially important low-latitude calibration site for production rates of cosmogenic nuclides. Our radiocarbon chronology provides a tighter constraint on maximum ages of late-glacial and Late Holocene ice advances. Upcoming field research will obtain organic material for radiocarbon dating to improve minimum age constrains for late-glacial and Late Holocene ice recessions.

Ice Complex permafrost of MIS5 age in the Dmitry Laptev Strait coastal region (East Siberian Arctic)

NASA Astrophysics Data System (ADS)

Wetterich, Sebastian; Tumskoy, Vladimir; Rudaya, Natalia; Kuznetsov, Vladislav; Maksimov, Fedor; Opel, Thomas; Meyer, Hanno; Andreev, Andrei A.; Schirrmeister, Lutz

2016-09-01

Ice Complex deposits (locally known as the Buchchagy Ice Complex) are exposed at both coasts of the East Siberian Dmitry Laptev Strait and preserved below the Yedoma Ice Complex that formed during MIS3 and MIS2 (Marine Isotope Stage) and lateglacial-Holocene thermokarst deposits (MIS1). Radioisotope disequilibria (230Th/U) of peaty horizons date the Buchchagy Ice Complex deposition to 126 + 16/-13 kyr and 117 + 19/-14 kyr until 98 ± 5 kyr and 89 ± 5 kyr. The deposit is characterised by poorly-sorted medium-to-coarse silts with cryogenic structures of horizontal ice bands, lens-like, and lens-like reticulated segregation ice. Two peaty horizons within the Buchchagy Ice Complex and syngenetic ice wedges (2-4 m wide, up to 10 m high) are striking. The isotopic composition (δ18O, δD) of Buchchagy ice-wedge ice indicates winter conditions colder than during the MIS3 interstadial and warmer than during MIS2 stadial, and similar atmospheric winter moisture sources as during the MIS2 stadial. Buchchagy Ice Complex pollen spectra reveal tundra-steppe vegetation and harsher summer conditions than during the MIS3 interstadial and rather similar vegetation as during the MIS2 stadial. Short-term climatic variability during MIS5 is reflected in the record. Even though the regional chronostratigraphic relationship of the Buchchagy Ice Complex to the Last Interglacial remains unclear because numerical dating is widely lacking, the present study indicates permafrost (Ice Complex) formation during MIS5 sensu lato, and its preservation afterwards. Palaeoenvironmental insights into past climate and the periglacial landscape dynamics of arctic lowlands in eastern Siberia are deduced from the record.

Field testing and adaptation of a methodology to measure "in-stream" values in the Tongue River, northern Great Plains (NGP) region

USGS Publications Warehouse

Bovee, Ken D.; Gore, James A.; Silverman, Arnold J.

1978-01-01

A comprehensive, multi-component in-stream flow methodology was developed and field tested in the Tongue River in southeastern Montana. The methodology incorporates a sensitivity for the flow requirements of a wide variety of in-stream uses, and the flexibility to adjust flows to accommodate seasonal and sub-seasonal changes in the flow requirements for different areas. In addition, the methodology provides the means to accurately determine the magnitude of the water requirement for each in-stream use. The methodology can be a powerful water management tool in that it provides the flexibility and accuracy necessary in water use negotiations and evaluation of trade-offs. In contrast to most traditional methodologies, in-stream flow requirements were determined by additive independent methodologies developed for: 1) fisheries, including spawning, rearing, and food production; 2) sediment transport; 3) the mitigation of adverse impacts of ice; and 4) evapotranspiration losses. Since each flow requirement varied in important throughout the year, the consideration of a single in-stream use as a basis for a flow recommendation is inadequate. The study shows that the base flow requirement for spawning shovelnose sturgeon was 13.0 m3/sec. During the same period of the year, the flow required to initiate the scour of sediment from pools is 18.0 m3/sec, with increased scour efficiency occurring at flows between 20.0 and 25.0 m3/sec. An over-winter flow of 2.83 m3/sec. would result in the loss of approximately 80% of the riffle areas to encroachment by surface ice. At the base flow for insect production, approximately 60% of the riffle area is lost to ice. Serious damage to the channel could be incurred from ice jams during the spring break-up period. A flow of 12.0 m3/sec. is recommended to alleviate this problem. Extensive ice jams would be expected at the base rearing and food production levels. The base rearing flow may be profoundly influenced by the loss of streamflow to transpiration. Transpiration losses to riparian vegetation ranged from 0.78 m3/sec. in April, to 1.54 m3/sec. in July, under drought conditions. Requirement for irrigation were estimated to range from 5.56 m3/sec. in May to 7.97 m3/sec. in July, under drought conditions. It was concluded that flow requirements to satisfy monthly water losses to transpiration must be added to the base fishery flows to provide adequate protection to the resources in the lower reaches of the river. Integration of the in-stream requirements for various use components shows that a base flow of at least 23.6 m3/sec. must be reserved during the month of June to initiate scour of sediment from pools, provide spawning habitat to shovelnose sturgeon, and to accommodate water losses from the system. In comparison, a base flow of 3.85 m3/sec. would be required during early February to provide fish rearing habitat and insect productivity, and to prevent excessive loss of food production areas to surface ice formation. During mid to late February, a flow of 12 m3/sec. would be needed to facilitate ice break-up and prevent ice jams from forming. Following break-up, the base flow would again be 3.85 m3/sec. until the start of spawning season.

Crustal structure and evolution of the Mawson Sea, western Wilkes Land margin, East Antarctica

USGS Publications Warehouse

Leitchenkov, G.L.; Gandyukhin, V.V.; Guseva, Yu. B.; Kazankov, A. Yu

2007-01-01

3 to 11 mm/yr. Three major unconformities are identified in the sedimentary cover of the Mawson Sea and are interpreted to be caused by break-up between Australia and Antarctica at about 81 Ma ago (WL1), the first arrival of the ice sheet to the Mawson Sea (WL3) and continental scale glaciation at about 34 Ma ago (WL4).

Global biogeography since Pangaea.

PubMed

McIntyre, Sarah R N; Lineweaver, Charles H; Groves, Colin P; Chopra, Aditya

2017-06-14

The break-up of the supercontinent Pangaea around 180 Ma has left its imprint on the global distribution of species and resulted in vicariance-driven speciation. Here, we test the idea that the molecular clock dates, for the divergences of species whose geographical ranges were divided, should agree with the palaeomagnetic dates for the continental separations. Our analysis of recently available phylogenetic divergence dates of 42 pairs of vertebrate taxa, selected for their reduced ability to disperse, demonstrates that the divergence dates in phylogenetic trees of continent-bound terrestrial and freshwater vertebrates are consistent with the palaeomagnetic dates of continental separation. © 2017 The Author(s).

WCRP's Climate and Cryosphere (CliC) Project: Climate Change and Middle and Low Latitude Glaciers

NASA Astrophysics Data System (ADS)

Dick, C. A.; Clic Project, W.

2004-12-01

The newest World Climate Research Programme (WCRP) Core Project, the Climate and Cryosphere (CliC) Project, is concerned with all aspects of the interactions between the cryosphere and climate. The cryosphere, defined as those portions of the Earth's surface where water exists in solid form, is an integral part of the climate system, both responding to, and influencing climate change. The cryosphere also provides many of the best indicators of climate variability and change. In addition to a range of direct physical indicators (e.g., snow/sea ice/glacier extent and thickness, river and lake freeze-up/break-up dates, etc.), ice cores from glaciers, ice caps and ice sheets have been shown to contain a wealth of information about past climate and environmental conditions. Ice cores are of particular value, since they often come from areas that are remote and poorly observed, yet have a major effect on the climate of the rest of the globe. General Circulation Models (GCMs) usually predict that the Earth's polar regions will warm fastest with the increasing levels of atmospheric greenhouse gases. However, models also indicate that continental interiors should warm more quickly than marine areas at non-polar latitudes. In fact, while some areas in the Arctic and Antarctic have warmed rapidly over the last few decades, it has generally been in the middle and low latitudes that the greatest effects of climate change have been observed. Particularly obvious has been the widespread retreat of glaciers. This retreat, and the warming which it implies, will have not only important scientific consequences but also socio-economic consequences in areas where glacier melt-water is an important component of the water supply. Glaciers preserve records of climate and the environment through both the isotopic composition of the water molecules, and through the chemicals 'trapped' in the snow, firn and ice layers. In polythermal (i.e., cold) glaciers where only limited melt occurs, the isotopic and chemical signals remain largely undisturbed, and ice cores can provide excellent high resolution records of past conditions. In temperate glaciers, where the ice is at its pressure melting point throughout, diffusion processes are much more rapid, and summer melt and run-off can drastically alter the chemical composition. Much of the climatic and environmental information is destroyed. This presentation will discuss the very serious concern that so many middle and low latitude glaciers are retreating and warming. The CliC Project recognizes an urgent need to recover ice cores from all non-polar glaciated regions before warming affects the glaciers and removes the information they contain. Without such information our ability to understand the climate changes that have occurred in the world's mountainous regions will be restricted, and our ability to model and predict future climate will be severely impaired.

Flexural-response of the McMurdo Ice Shelf to surface lake filling and drainage

NASA Astrophysics Data System (ADS)

Banwell, A. F.; MacAyeal, D. R.; Willis, I.; Macdonald, G. J.; Goodsell, B.

2017-12-01

Antarctic ice-shelf instability and break-up, as exhibited by the Larsen B ice shelf in 2002, remains one of the most difficult glaciological processes to observe directly. 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 previously been proposed, including the ability of surface lakes to introduce ice-shelf fractures when they fill and drain. During the austral summer of 2016/2017, we monitored the filling and draining of four surface lakes on the McMurdo Ice Shelf, Antarctica, and the effect of these processes on ice-shelf flexure. Water-depth data from pressure sensors reveal that two lakes filled to >2 m in depth and subsequently drained over multiple week timescales, which had a simultaneous effect on vertical ice deflection in the area. Differential GPS data from 12 receivers over three months show that vertical deflection varies as a function of distance from the maximum load change (i.e. at the lake centre). Using remote sensing techniques applied to both Landsat 8 and Worldview imagery, we also quantify the meltwater volume in these two lakes through the melt season, which, together with the vertical deflection data, are used to constrain key flexural parameter values in numerical models of ice-shelf flexure.

Techniques for integrating the animations, multimedia, and interactive features of NASA’s climate change website, Climate Change: NASA’s Eyes on the Earth, into the classroom to advance climate literacy and encourage interest in STEM disciplines

NASA Astrophysics Data System (ADS)

Tenenbaum, L. F.; Jackson, R.; Greene, M.

2009-12-01

I developed a variety of educational content for the "Climate Change: NASA’s Eyes on the Earth" website, notably an interactive feature for the "Key Indicators: Ice Mass Loss" link that includes photo pair images of glaciers around the world, changes in Arctic sea ice extent videos, Greenland glacial calving time lapse videos, and Antarctic ice shelf break up animations, plus news pieces and a Sea Level Quiz. I integrated these resources and other recent NASA and JPL climate and oceanography data and information into climate change components of Oceanography Lab exercises, Oceanography lectures and Introduction to Environmental Technology courses. I observed that using these Internet interactive features in the classroom greatly improved student participation, topic comprehension, scientific curiosity and interest in Earth and climate science across diverse student populations. Arctic Sea Ice Extent Summer 2007 Credit: NASA

Deglacial climate modulated by the storage and release of Arctic sea ice

NASA Astrophysics Data System (ADS)

Condron, A.; Coletti, A. J.; Bradley, R. S.

2017-12-01

Periods of abrupt climate cooling during the last deglaciation (20 - 8 kyr ago) are often attributed to glacial outburst floods slowing the Atlantic meridional overturning circulation (AMOC). Here, we present results from a series of climate model simulations showing that the episodic break-up and mobilization of thick, perennial, Arctic sea ice during this time would have released considerable volumes of freshwater directly to the Nordic Seas, where processes regulating large-scale climate occur. Massive sea ice export events to the North Atlantic are generated whenever the transport of sea ice is enhanced, either by changes in atmospheric circulation, rising sea level submerging the Bering land bridge, or glacial outburst floods draining into the Arctic Ocean from the Mackenzie River. We find that the volumes of freshwater released to the Nordic Seas are similar to, or larger than, those estimated to have come from terrestrial outburst floods, including the discharge at the onset of the Younger Dryas. Our results provide the first evidence that the storage and release of Arctic sea ice helped drive deglacial climate change by modulating the strength of the AMOC.

Break-ups Before Marriage: The End of 103 Affairs

ERIC Educational Resources Information Center

Hill, Charles T.; And Others

1976-01-01

Factors that predicted breakups before marriage, investigated as part of a two-year study of dating relationships among college students include unequal involvement in the relationship and discrepant age, educational aspirations, intelligence, and physical attractiveness. (Author/AM)

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica

PubMed Central

Buizert, Christo; Baggenstos, Daniel; Jiang, Wei; Purtschert, Roland; Petrenko, Vasilii V.; Lu, Zheng-Tian; Müller, Peter; Kuhl, Tanner; Lee, James; Severinghaus, Jeffrey P.; Brook, Edward J.

2014-01-01

We present successful 81Kr-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four ∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The 81Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) 85Kr and 39Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the ice did not experience gas loss. We estimate the error in the 81Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130–115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA 81Kr analysis requires a 40–80-kg ice sample; as sample requirements continue to decrease, 81Kr dating of ice cores is a future possibility. PMID:24753606

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica.

PubMed

Buizert, Christo; Baggenstos, Daniel; Jiang, Wei; Purtschert, Roland; Petrenko, Vasilii V; Lu, Zheng-Tian; Müller, Peter; Kuhl, Tanner; Lee, James; Severinghaus, Jeffrey P; Brook, Edward J

2014-05-13

We present successful (81)Kr-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four ∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The (81)Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) (85)Kr and (39)Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the ice did not experience gas loss. We estimate the error in the (81)Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130-115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA (81)Kr analysis requires a 40-80-kg ice sample; as sample requirements continue to decrease, (81)Kr dating of ice cores is a future possibility.

Historical trend in river ice thickness and coherence in hydroclimatological trends in Maine

USGS Publications Warehouse

Huntington, T.G.; Hodgkins, G.A.; Dudley, R.W.

2003-01-01

We analyzed long-term records of ice thickness on the Piscataquis River in central Maine and air temperature in Maine to determine whether there were temporal trends that were associated with climate warming. The trend in ice thickness was compared and correlated with regional time series of winter air temperature, heating degree days (HDD), date of river ice-out, seasonal center-of-volume date (SCVD) (date on which half of the stream runoff volume during the period 1 Jan. to 31 May has occurred), water temperature, and lake ice-out date. All of these variables except lake ice-out date showed significant temporal trends during the 20th century. Average ice thickness around 28 February decreased by about 23 cm from 1912 to 2001. Over the period 1900 to 1999, winter air temperature increased by 1.7??C and HDD decreased by about 7.5%. Final ice-out date on the Piscataquis River occurred earlier (advanced), by 0.21 days yr-1 over the period 1931 to 2002, and the SCVD advanced by 0.11 days yr-1 over the period 1903 to 2001. Ice thickness was significantly correlated (P-value < 0.01) with winter air temperature, HDD, river ice-out, and SCVD. These systematic temporal trends in multiple hydrologic indicator variables indicate a coherent response to climate forcing.

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.

Evolution of a Greenland Ice sheet Including Shelves and Regional Sea Level Variations

NASA Astrophysics Data System (ADS)

Bradley, S.; Reerink, T.; Vandewal, R.; Helsen, M.

2015-12-01

Observational evidence, including offshore moraines and marine sediment cores infer that at the Last Glacial maximum (LGM) the Greenland ice sheet (GIS) grounded out across the Davis Strait into Baffin Bay, with fast flowing ice streams extending out to the continental shelf break along the NW margin. These observations lead to a number of questions as to weather the GIS and Laurentide ice sheet (LIS) coalesced during glacial maximums, and if so, did a significant ice shelf develop across Baffin Bay and how would such a configuration impact on the relative contribution of these ice sheets to eustatic sea level (ESL). Most previous paleo ice sheet modelling simulations of the GIS recreated an ice sheet that either did not extend out onto the continental shelf or utilised a simplified marine ice parameterisation to recreate an extended GIS, and therefore did not fully include ice shelf dynamics. In this study we simulate the evolution of the GIS from 220 kyr BP to present day using IMAU-ice; a 3D thermodynamical ice sheet model which fully accounts for grounded and floating ice, calculates grounding line migration and ice shelf dynamics. There is few observational estimates of long-term (yrs) sub marine basal melting rates (mbm) for the GIS. Therefore we investigate a range of relationships to constrain the spatial and temporal parameterisation of mbm within IMAU-ice related to changes in paleo water depth, driven by changes in relative sea level and ocean temperature. We will present results of how changes in the mbm directly impacts on the ice sheet dynamics, timing and spatial extent of the GIS at the glacial maximums, but also on the rate of retreat and spatial extent at the Last interglacial (LIG) minimum. Initial results indicate that with the inclusion of ice shelf dynamics, a larger GIS is generated which is grounded out into Davis strait, up to a water depth of -750 m, but the total contribution to LIG ESL is reduced by up to 0.6 m.

Cryosphere Sensor Webs With The Autonomous Sciencecraft Experiment

NASA Astrophysics Data System (ADS)

Scharenbroich, L.; Doggett, T.; Kratz, T.; Castano, R.; Chien, S.; Davies, A. G.; Tran, D.; Mazzoni, D.

2006-12-01

Autonomous sensor-webs are being deployed as part of the Autonomous Sciencecraft Experiment [1], whereby observations using the Hyperion instrument [2] on-board Earth Observing-1 (EO-1 are triggered by either ground sensors or by near-real-time analysis of data from other space-based sensors. In the realm of cryosphere monitoring, one sensor-web has been set up pairing EO-1 with a sensor buoy [3] deployed in Sparkling Lake, one of several lakes in northern Wisconsin monitored by University of Wisconsin's Trout Lake Station. A Support Vector Machine (SVM) classifier was trained on historical thermistor chain data with manually recorded ice-in and ice-out times and used to trigger Hyperion observations of the Trout Lake area during spring thaw and winter freeze in 2005. A second sensor-web is being developed using near-real time sea ice data products, based on Department of Defense meteorological satellites, available from the National Snow and Ice Data Center (NSIDC) [4]. Once operational, this sensor web will trigger Hyperion observations of pre-defined targets in the Arctic and Antarctic where regional resolution data shows sea ice formation or break up. [1] Chien et al. (2005), An autonomous earth-observing sensor-web, IEEE Intelligent Systems, [2] Pearlman et al. (2003), Hyperion, a space-based imaging spectrometer, IEEE Trans. Geosci. Rem. Sens., 41(6), [3] Kratz, T. et al. (in press) Toward a Global Lake Ecological Observatory Network, Proceedings of the Karelian Institute, [4] Cavalieri et al. (1999) Near real-time DMSP SSM/I daily polar gridded sea ice concentrations, National Snow and Ice Data Center. Digital Media.

Toward Surface Mass Balance Modeling over Antarctic Peninsula with Improved Snow/Ice Physics within WRF

NASA Astrophysics Data System (ADS)

Villamil-Otero, G.; Zhang, J.; Yao, Y.

2017-12-01

The Antarctic Peninsula (AP) has long been the focus of climate change studies due to its rapid environmental changes such as significantly increased glacier melt and retreat, and ice-shelf break-up. Progress has been continuously made in the use of regional modeling to simulate surface mass changes over ice sheets. Most efforts, however, focus on the ice sheets of Greenland with considerable fewer studies in Antarctica. In this study the Weather Research and Forecasting (WRF) model, which has been applied to the Antarctic region for weather modeling, is adopted to capture the past and future surface mass balance changes over AP. In order to enhance the capabilities of WRF model simulating surface mass balance over the ice surface, we implement various ice and snow processes within the WRF and develop a new WRF suite (WRF-Ice). The WRF-Ice includes a thermodynamic ice sheet model that improves the representation of internal melting and refreezing processes and the thermodynamic effects over ice sheet. WRF-Ice also couples a thermodynamic sea ice model to improve the simulation of surface temperature and fluxes over sea ice. Lastly, complex snow processes are also taken into consideration including the implementation of a snowdrift model that takes into account the redistribution of blowing snow as well as the thermodynamic impact of drifting snow sublimation on the lower atmospheric boundary layer. Intensive testing of these ice and snow processes are performed to assess the capability of WRF-Ice in simulating the surface mass balance changes over AP.

Change in Ice Thaw Dates for Selected U.S. Lakes, 1905-2015

EPA Pesticide Factsheets

This figure shows the change in the ice-off date, or date of ice thawing and breakup, for 14 U.S. lakes during the period from 1905 to 2015. All of the lakes have red circles with negative numbers, which represent earlier thaw dates. Larger circles indicate larger changes. For more information: www.epa.gov/climatechange/science/indicators

Towards seasonal Arctic shipping route predictions

NASA Astrophysics Data System (ADS)

Haines, K.; Melia, N.; Hawkins, E.; Day, J. J.

2017-12-01

In our previous work [1] we showed how trans-Arctic shipping routes would become more available through the 21st century as sea ice declines, using CMIP5 models with means and stds calibrated to PIOMAS sea ice observations. Sea ice will continue to close shipping routes to open water vessels through the winter months for the foreseeable future so the availability of open sea routes will vary greatly from year to year. Here [2] we look at whether the trans-Arctic shipping season period can be predicted in seasonal forecasts, again using several climate models, and testing both perfect and imperfect knowledge of the initial sea ice conditions. We find skilful predictions of the upcoming summer shipping season can be made from as early as January, although typically forecasts may show lower skill before a May `predictability barrier'. Focussing on the northern sea route (NSR) off Siberia, the date of opening of this sea route is twice as variable as the closing date, and this carries through to reduced predictability at the start of the season. Under climate change the later freeze-up date accounts for 60% of the lengthening season, Fig1 We find that predictive skill is state dependent with predictions for high or low ice years exhibiting greater skill than for average ice years. Forecasting the exact timing of route open periods is harder (more weather dependent) under average ice conditions while in high and low ice years the season is more controlled by the initial ice conditions from spring onwards. This could be very useful information for companies planning vessel routing for the coming season. We tested this dependence on the initial ice conditions by changing the initial ice state towards climatologically average conditions and show directly that early summer sea-ice thickness information is crucial to obtain skilful forecasts of the coming shipping season. Mechanisms for this are discussed. This strongly suggests that good sea ice thickness observations should become a key component of the future Arctic observing system. Melia, N., K. Haines, and E. Hawkins (2016), Sea ice decline and 21st century trans-Arctic shipping routes, Geophys. Res. Lett., doi:10.1002/ 2016GL069315. Melia, N., K. Haines, E. Hawkins and J.J. Day, 2017, Towards seasonal Arctic shipping route predictions. Env. Res. Lett., doi:10.1088/1748-9326/aa7a60

"Ice out": the contribution of citizen scientists to our understanding of climate change

NASA Astrophysics Data System (ADS)

Patterson, R. Timothy; Swindles, Graeme T.

2016-04-01

Long-term trends in spring 'ice out' dates (1836-2013) for twelve lakes in Maine, New Brunswick and New Hampshire, in eastern North America reveal a remarkable coherency across the region (rs=0.462-0.933, p<0.01). These data have been compiled since the early 19th century, primarily by amateur citizen scientists, for a variety of purposes, including determining fishing seasons, estimating the spring opening of ferry boat routes, community contests, and general curiosity. Ice out dates correlate closely with late-winter/early-spring, March-April (MA), instrumental temperature records from across the region (rs=0.488-0.816, p<0.01). This correlation permits use of ice out dates as a proxy to extend the shorter MA instrumental record (1876-2013). Mean ice out dates trended progressively earlier during the recovery from the Little Ice Age through to the 1940s, and gradually became later again through to the late 1970s, when ice out dates had returned to values more typical of the late nineteenth century. Post-1970's ice out dates resumed trending toward earlier dates, with the twenty-first century being characterized by the earliest ice out dates on record. Spectral and wavelet time series analysis indicate that ice out is influenced by several teleconnections including the Quasi-biennial Oscillation, El Niño-Southern Oscillation, North Atlantic Oscillation, Atlantic Multidecadal Oscillation as well as a significant correlation between inland lake records and the Arctic Oscillation. The relative influence of these teleconnections is variable with notable shifts occurring after ~1870, ~1925, and ~1980-2000. The intermittent expression of these cycles in the ice out and MA instrumental record is not only influenced by absolute changes in the intensity of the various teleconnections and other climate drivers, but by phase interference between teleconnections, which periodically damps the various signals.

Review of technology for Arctic offshore oil and gas recovery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sackinger, W. M.

1980-08-01

The technical background briefing report is the first step in the preparation of a plan for engineering research oriented toward Arctic offshore oil and gas recovery. A five-year leasing schedule for the ice-prone waters of the Arctic offshore is presented, which also shows the projected dates of the lease sale for each area. The estimated peak production rates for these areas are given. There is considerable uncertainty for all these production estimates, since no exploratory drilling has yet taken place. A flow chart is presented which relates the special Arctic factors, such as ice and permafrost, to the normal petroleummore » production sequence. Some highlights from the chart and from the technical review are: (1) in many Arctic offshore locations the movement of sea ice causes major lateral forces on offshore structures, which are much greater than wave forces; (2) spray ice buildup on structures, ships and aircraft will be considerable, and must be prevented or accommodated with special designs; (3) the time available for summer exploratory drilling, and for deployment of permanent production structures, is limited by the return of the pack ice. This time may be extended by ice-breaking vessels in some cases; (4) during production, icebreaking workboats will service the offshore platforms in most areas throughout the year; (5) transportation of petroleum by icebreaking tankers from offshore tanker loading points is a highly probable situation, except in the Alaskan Beaufort; and (6) Arctic pipelines must contend with permafrost, making instrumentation necessary to detect subtle changes of the pipe before rupture occurs.« less

Domestic Ice Breaking (DOMICE) Simulation Model User Guide

DTIC Science & Technology

2013-02-01

Second, add new ice data to the variable “D9 Historical Ice Data (SIGRID Coded) NBL Waterways” (D9_historical_ice_d3), which contains the...within that “ NBL ” scheme. The interpretation of the SIGRID ice codes into ice thickness estimates is also contained within the sub- module “District 9...User Guide)  “D9 Historical Ice Data (SIGRID Coded) NBL Waterways” (see Section 5.1.1.3.2 of this User Guide)  “Historical District 1 Weekly Air

Retreat of the Coalescent Greenland and Innuitian Ice Sheets from Nares Strait

NASA Astrophysics Data System (ADS)

Jennings, A. E.; Bailey, E.; Oliver, B.; Andrews, J. T.; Prins, M. A.; Troelstra, S.; Stoner, J. S.; Reilly, B. T.; Davies-Walczak, M.; Mix, A. C.

2015-12-01

Nares Strait, which forms one of the main connections between the Arctic Ocean and Baffin Bay was blocked by coalescent Innuitian and Greenland ice sheets during the LGM. Nares Strait opened ca. 9000 cal ka BP when the connection between the two ice sheets was finally severed. Our research focuses on the events and processes leading up to the opening of the strait and the response of the glacier and marine systems to establishment of the throughflow. The study at present involves new analysis of two sediment cores: 2001LSSL-163PC from Smith Sound, at the southern end of Nares Strait, and 2001LSSL-079PC from the mouth of Petermann Fjord at the northern end of the strait. X-radiography and core photographs were studied to establish basic lithofacies and stratigraphy. Foraminiferal faunas provide insight into changes in ice margin proximity, Atlantic Water advection and sea-ice conditions and are used to develop the radiocarbon chronologies. Quantitative X-ray diffraction analysis of bulk sediments aids in determining sediment provenance and the establishment of a north to south connection. Grain size analysis allows sediment processes and sedimentary environments, such as iceberg rafting, current deposition, and sub ice-shelf deposition to be evaluated. A radiocarbon date of >50 kyr was obtained from foraminifera in an overconsolidated, gray diamicton in core 163PC. The diamicton is overlain by a red deglacial sequence of barren laminated sediments followed by gray pebbly mud. Two radiocarbon dates submitted from near the base of the pebbly mud constrain the timing of ice retreat from Smith Sound. The chronology of core 079PC indicates that it captures the opening of Nares Strait, but 4 submitted radiocarbon dates will further constrain its chronology. The goal of the work on these two cores is to lay a framework for extensive marine fieldwork to study ice sheet-ocean interactions in the Petermann Glacier in late summer 2015.

Can phenological models predict tree phenology accurately under climate change conditions?

NASA Astrophysics Data System (ADS)

Chuine, Isabelle; Bonhomme, Marc; Legave, Jean Michel; García de Cortázar-Atauri, Inaki; Charrier, Guillaume; Lacointe, André; Améglio, Thierry

2014-05-01

The onset of the growing season of trees has been globally earlier by 2.3 days/decade during the last 50 years because of global warming and this trend is predicted to continue according to climate forecast. The effect of temperature on plant phenology is however not linear because temperature has a dual effect on bud development. On one hand, low temperatures are necessary to break bud dormancy, and on the other hand higher temperatures are necessary to promote bud cells growth afterwards. Increasing phenological changes in temperate woody species have strong impacts on forest trees distribution and productivity, as well as crops cultivation areas. Accurate predictions of trees phenology are therefore a prerequisite to understand and foresee the impacts of climate change on forests and agrosystems. Different process-based models have been developed in the last two decades to predict the date of budburst or flowering of woody species. They are two main families: (1) one-phase models which consider only the ecodormancy phase and make the assumption that endodormancy is always broken before adequate climatic conditions for cell growth occur; and (2) two-phase models which consider both the endodormancy and ecodormancy phases and predict a date of dormancy break which varies from year to year. So far, one-phase models have been able to predict accurately tree bud break and flowering under historical climate. However, because they do not consider what happens prior to ecodormancy, and especially the possible negative effect of winter temperature warming on dormancy break, it seems unlikely that they can provide accurate predictions in future climate conditions. It is indeed well known that a lack of low temperature results in abnormal pattern of bud break and development in temperate fruit trees. An accurate modelling of the dormancy break date has thus become a major issue in phenology modelling. Two-phases phenological models predict that global warming should delay or compromise dormancy break at the species equatorward range limits leading to a delay or even impossibility to flower or set new leaves. These models are classically parameterized with flowering or budburst dates only, with no information on the dormancy break date because this information is very scarce. We evaluated the efficiency of a set of process-based phenological models to accurately predict the dormancy break dates of four fruit trees. Our results show that models calibrated solely with flowering or budburst dates do not accurately predict the dormancy break date. Providing dormancy break date for the model parameterization results in much more accurate simulation of this latter, with however a higher error than that on flowering or bud break dates. But most importantly, we show also that models not calibrated with dormancy break dates can generate significant differences in forecasted flowering or bud break dates when using climate scenarios. Our results claim for the urgent need of massive measurements of dormancy break dates in forest and fruit trees to yield more robust projections of phenological changes in a near future.

Obliquity-paced Pliocene West Antarctic ice sheet oscillations

USGS Publications Warehouse

Naish, T.; Powell, R.; Levy, R.; Wilson, G.; Scherer, R.; Talarico, F.; Krissek, L.; Niessen, F.; Pompilio, M.; Wilson, T.; Carter, L.; DeConto, R.; Huybers, P.; McKay, R.; Pollard, D.; Ross, J.; Winter, D.; Barrett, P.; Browne, G.; Cody, R.; Cowan, E.; Crampton, J.; Dunbar, G.; Dunbar, N.; Florindo, F.; Gebhardt, C.; Graham, I.; Hannah, M.; Hansaraj, D.; Harwood, D.; Helling, D.; Henrys, S.; Hinnov, L.; Kuhn, G.; Kyle, P.; Laufer, A.; Maffioli, P.; Magens, D.; Mandernack, K.; McIntosh, W.; Millan, C.; Morin, R.; Ohneiser, C.; Paulsen, T.; Persico, D.; Raine, I.; Reed, J.; Riesselman, C.; Sagnotti, L.; Schmitt, D.; Sjunneskog, C.; Strong, P.; Taviani, M.; Vogel, S.; Wilch, T.; Williams, T.

2009-01-01

Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages1, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles2. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch (5–3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming3. Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to 3 °C warmer than today4 and atmospheric CO2 concentration was as high as 400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model7 that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt8 under conditions of elevated CO2.

Obliquity-paced Pliocene West Antarctic ice sheet oscillations.

PubMed

Naish, T; Powell, R; Levy, R; Wilson, G; Scherer, R; Talarico, F; Krissek, L; Niessen, F; Pompilio, M; Wilson, T; Carter, L; DeConto, R; Huybers, P; McKay, R; Pollard, D; Ross, J; Winter, D; Barrett, P; Browne, G; Cody, R; Cowan, E; Crampton, J; Dunbar, G; Dunbar, N; Florindo, F; Gebhardt, C; Graham, I; Hannah, M; Hansaraj, D; Harwood, D; Helling, D; Henrys, S; Hinnov, L; Kuhn, G; Kyle, P; Läufer, A; Maffioli, P; Magens, D; Mandernack, K; McIntosh, W; Millan, C; Morin, R; Ohneiser, C; Paulsen, T; Persico, D; Raine, I; Reed, J; Riesselman, C; Sagnotti, L; Schmitt, D; Sjunneskog, C; Strong, P; Taviani, M; Vogel, S; Wilch, T; Williams, T

2009-03-19

Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch ( approximately 5-3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming. Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, approximately 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to approximately 3 degrees C warmer than today and atmospheric CO(2) concentration was as high as approximately 400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt under conditions of elevated CO(2).

Radiostratigraphy and age structure of the Greenland Ice Sheet

PubMed Central

MacGregor, Joseph A; Fahnestock, Mark A; Catania, Ginny A; Paden, John D; Prasad Gogineni, S; Young, S Keith; Rybarski, Susan C; Mabrey, Alexandria N; Wagman, Benjamin M; Morlighem, Mathieu

2015-01-01

Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet. Key Points Phase information predicts reflection slope and simplifies reflection tracing Reflections can be dated away from ice cores using a simple ice flow model Radiostratigraphy is often disrupted near the onset of fast ice flow PMID:26213664

Tidewater dynamics at Store Glacier, West Greenland from daily repeat UAV surveys

NASA Astrophysics Data System (ADS)

Ryan, Jonathan; Hubbard, Alun; Toberg, Nick; Box, Jason; Todd, Joe; Christoffersen, Poul; Neal, Snooke

2017-04-01

A significant component of the Greenland ice sheet's mass wasteage to sea level rise is attributed to the acceleration and dynamic thinning at its tidewater margins. To improve understanding of the rapid mass loss processes occurring at large tidewater glaciers, we conducted a suite of daily repeat aerial surveys across the terminus of Store Glacier, a large outlet draining the western Greenland Ice Sheet, from May to July 2014 (https://www.youtube.com/watch?v=-y8kauAVAfE). The unmanned aerial vehicles (UAVs) were equipped with digital cameras, which, in combination with onboard GPS, enabled production of high spatial resolution orthophotos and digital elevation models (DEMs) using standard structure-from-motion techniques. These data provide insight into the short-term dynamics of Store Glacier surrounding the break-up of the sea-ice mélange that occurred between 4 and 7 June. Feature tracking of the orthophotos reveals that mean speed of the terminus is 16 - 18 m per day, which was independently verified against a high temporal resolution time-series derived from an expendable/telemetric GPS deployed at the terminus. Differencing the surface area of successive orthophotos enable quantification of daily calving rates, which significantly increase just after melange break-up. Likewise, by differencing bulk freeboard volume of icebergs through time we could also constrain the magnitude and variation of submarine melt. We calculate a mean submarine melt rate of 0.18 m per day throughout the spring period with relatively little supraglacial runoff and no active meltwater plumes to stimulate fjord circulation and upwelling of deeper, warmer water masses. Finally, we relate calving rates to the zonation and depth of water-filled crevasses, which were prominent across parts of the terminus from June onwards.

Short commentary on marine productivity at Arctic shelf breaks: upwelling, advection and vertical mixing

NASA Astrophysics Data System (ADS)

Randelhoff, Achim; Sundfjord, Arild

2018-04-01

The future of Arctic marine ecosystems has received increasing attention in recent years as the extent of the sea ice cover is dwindling. Although the Pacific and Atlantic inflows both import huge quantities of nutrients and plankton, they feed into the Arctic Ocean in quite diverse regions. The strongly stratified Pacific sector has a historically heavy ice cover, a shallow shelf and dominant upwelling-favourable winds, while the Atlantic sector is weakly stratified, with a dynamic ice edge and a complex bathymetry. We argue that shelf break upwelling is likely not a universal but rather a regional, albeit recurring, feature of the new Arctic. It is the regional oceanography that decides its importance through a range of diverse factors such as stratification, bathymetry and wind forcing. Teasing apart their individual contributions in different regions can only be achieved by spatially resolved time series and dedicated modelling efforts. The Northern Barents Sea shelf is an example of a region where shelf break upwelling likely does not play a dominant role, in contrast to the shallower shelves north of Alaska where ample evidence for its importance has already accumulated. Still, other factors can contribute to marked future increases in biological productivity along the Arctic shelf break. A warming inflow of nutrient-rich Atlantic Water feeds plankton at the same time as it melts the sea ice, permitting increased photosynthesis. Concurrent changes in sea ice cover and zooplankton communities advected with the boundary currents make for a complex mosaic of regulating factors that do not allow for Arctic-wide generalizations.

The Role of Basal Channels in Ice Shelf Calving.

NASA Astrophysics Data System (ADS)

Dow, C. F.; Lee, W. S.; Greenbaum, J. S.; Greene, C. A.; Blankenship, D. D.; Poinar, K.; Forrest, A.; Young, D. A.; Zappa, C. J.

2017-12-01

Increased rates of ice shelf break-up drives acceleration of grounded glacial ice into the ocean, resulting in sea-level rise. Ice shelves are vulnerable to thinning, which make them more susceptible to calving. Here, we examine basal channels under three ice shelves that locally thin the ice and drive formation of transverse ice shelf fractures. The basal channels also cause surface depressions due to hydrostatic buoyancy effects and can draw in surface water to form rivers. These rivers exacerbate thinning by surface melting and hydraulic loading, and can accelerate rifting when they flow into the transverse fractures. Our investigation focuses on Nansen Ice Shelf in the Ross Sea Embayment, East Antarctica. We use ice-sounding radar and single-beam laser altimeter data from two aerogeophysical campaigns conducted in 2011 and 2014, ice surface DEM reconstruction, and satellite imagery analysis, to examine the role of a substantial basal channel in the stability of this ice shelf. Nansen Ice Shelf calved two large icebergs totaling 214 km2 in area in April 2016. The transverse fracture that eventually rifted to form these icebergs initiated directly over the basal channel in 1987. In years when surface water formed on Nansen Ice Shelf, a river flowed into the transverse fracture. In November 2016, we identified a new fracture over the basal channel during in-situ data collection. We compare the Nansen Ice Shelf fractures with those at other vulnerable ice-shelf systems, including Petermann Glacier in Greenland and Totten Glacier in East Antarctica, to evaluate the role that basal channels may play in simultaneous basal and surface weakening and their consequent effect on ice-shelf rifting and stability.

Continued rapid glacier recession following the 1995 collapse of the Prince Gustav Ice Shelf on the Antarctic Peninsula (Invited)

NASA Astrophysics Data System (ADS)

Glasser, N. F.; Scambos, T. A.

2009-12-01

We use optical satellite imagery (ASTER and Landsat) to document changes in the Prince Gustav Ice Shelf (PGIS) and its tributary glaciers before and after its 1995 collapse. Interpretation of a pre-collapse Landsat 4-5 TM image acquired in February 1988 shows that the ice shelf was fed primarily by Sjogren Glacier from the Antarctic Peninsula and by Rhoss Glacier from James Ross Island (JRI). In 1988, the PGIS contained numerous structural discontinuities (rifts and crevasses), which collectively indicate that ice-shelf break-up had commenced at least seven years before collapse. Meltwater ponds and streams were also common across its surface. After the ice shelf collapsed, Rhoss Glacier became a tidewater glacier and has since experienced rapid and continued recession. Between January 2001 and December 2006 (six to eleven years after the collapse of the PGIS), the front of Rhoss Glacier receded a total of 13.6 km. We conclude that where tributary glaciers become tidewater glaciers they react to ice-shelf removal by rapid and continued recession and that the response time of glaciers on the Antarctic Peninsula to ice-shelf removal is measured on annual to decadal timescales. This rapid recession, coupled with previously documented tributary glacier thinning and acceleration, indicates that Antarctic Peninsula glaciers are extremely sensitive to ice-shelf collapse.

Dry ice blasting

NASA Astrophysics Data System (ADS)

Lonergan, Jeffrey M.

1992-04-01

As legal and societal pressures against the use of hazardous waste generating materials has increased, so has the motivation to find safe, effective, and permanent replacements. Dry ice blasting is a technology which uses CO2 pellets as a blasting medium. The use of CO2 for cleaning and stripping operations offers potential for significant environmental, safety, and productivity improvements over grit blasting, plastic media blasting, and chemical solvent cleaning. Because CO2 pellets break up and sublime upon impact, there is no expended media to dispose of. Unlike grit or plastic media blasting which produce large quantities of expended media, the only waste produced by CO2 blasting is the material removed. The quantity of hazardous waste produced, and thus the cost of hazardous waste disposal is significantly reduced.

Earth Observation taken by the Expedition 19 crew

NASA Image and Video Library

2009-04-23

ISS019-E-010556 (23 April 2009) --- A circle in thin ice in Lake Baikal, Russia is featured in this image photographed by an Expedition 19 crewmember on the International Space Station. Late in April 2009, astronauts aboard the station observed a strange circular area of thinned ice (dark in color, with a diameter of about 4.4 kilometers) in the southern end of Lake Baikal in southern Siberia. Lake Baikal is unique in many regards. It is the largest (by volume) and deepest (1,637 meters at the deepest point) fresh water lake on Earth and, as a World Heritage Site, is considered one of Russia?s environmental jewels. The lake?s long, thin and deep profile results from its location in the Baikal Rift valley in Siberia. According to scientists, it is also one of the world?s oldest lakes (25-30 million years old); it contains up to 7 kilometers of sediment deposited on the bottom, and is home to an amazing array of plants and animals, many being found only in Lake Baikal. The lake?s biodiversity includes fresh water seals and several species of fish that are not found elsewhere on Earth. Siberia is remote and cold; ice cover can persist into June. This detailed image shows a circle of thin ice, which is the focal point for ice break up in the very southern end of the lake. While the origin of the circles is unknown, the peculiar pattern suggests convection in the lake?s water column. Ice cover changes rapidly at this time of year. Within a day, the ice can melt almost completely, and then freeze again overnight. Throughout April, the circles are persistent ? they appear when ice cover forms, and then disappear as ice melts. The pattern and appearance suggests that the ice is quite thin.

The electrolytical processes in dirty ices: implications for origin and chemistry of minor bodies and related objects.

PubMed

Drobyshevski, E M; Chesnakov, V A; Sinitsyn, V V

1995-01-01

Many moonlike bodies (M approximately or = 1 Moon) beyond the Martian orbit contain large amounts of dirty ice (approximately 50%) forming thick mantle with the solid phase thermal convection. When a body moves through the inter- or nearplanetary magnetized plasma, electric current is generated in the body and its environment. The current passing through a dirty ice containing up to 10% of organic admixtures produces a lot of electrochemical effects which have a profound impact on its composition. At this stage one can hardly say something definite concerning changes experienced by organics. The changes must occur inevitably and can be of a rather unexpected and far-reaching nature, so deserving a close study. Another obvious effect is a volumetric electrolysis of ice containing alien inclusions. The electrolysis products accumulate in ice in the form of a solid solution which is capable of detonation at 15-20 wt.% of 2H2 + O2. If M > or = 1 Moon (Galilean satellites, Titan), the body loses in explosion a part of its mass in the form of vapor and ice fragments (=short-period comet nuclei), whereas if M < or = 0.2 Moon, the body breaks up totally (the Main Belt asteroids origin approximately 3.9 Byr ago). 2H2 + O2 containing cometary nuclei are capable of burning or suffer new explosions when receiving an additional energy. The combustion in the sublimation products containing also light organics and 2H2 + O2 explains unexpected energetics and nearnuclear chemistry of Comet P/Halley (e.g. great abundances of negative and positive ions, atomic carbon, CO over CO2, origin of CHON particles etc) and its distant outbursts correlated, possibly, with the Solar activity. Thus the electrochemical processes in the dirty ice with organics, along with its subsequent thermal, radiative etc. processing, open up new potentials for explanation and prediction of quite unexpected discoveries.

Long-term trends in a Dimictic Lake

USGS Publications Warehouse

Robertson, Dale M.; Hsieh, Yi-Fang; Lathrop, Richard C; Wu, Chin H; Magee, Madeline; Hamilton, David P.

2016-01-01

 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 abrupt changes in air temperature and wind speed. Average summer hypolimnetic temperature and fall turnover date exhibit significant differences between the third period and the first two periods. Changes in ice cover (ice-on and ice-off dates, ice cover duration, and maximum ice thickness) exhibit an abrupt change after 1994, which was related in part to the warm El Niño winter of 1997–1998. Under-ice water temperature, freeze-over water temperature, hypolimnetic temperature, fall turnover date, and stratification duration demonstrate a significant difference in the third period (1994–2014), when air temperature was warmest and wind speeds decreased rather abruptly. The trends in ice cover and water temperature demonstrate responses to both long-term and abrupt changes in meteorological conditions that can be complemented with numerical modeling to better understand how these variables will respond in a future climate.

The transition from winter to early spring in the eastern Weddell Sea, Antarctica: Plankton biomass and composition in relation to hydrography and nutrients

NASA Astrophysics Data System (ADS)

Scharek, Renate; Smetacek, Victor; Fahrbach, Eberhard; Gordon, Louis I.; Rohardt, Gerd; Moore, Stanley

1994-08-01

Hydrography and nutrient distribution in relation to plankton biomass and composition were studied during two transects (October and December) that crossed the ice-covered eastern Weddell Sea (approximately along the Greenwich Meridian) from the ice edge at 58°S to the continental margin at 70°30'S in 1986. Whereas the winter situation still prevailed under the intact ice cover during the October transect, extensive melting was underway by December. Despite the very low levels of plankton biomass encountered under sea ice in late winter (as low at 0.02 μg chlorophyll α 1 -1), distinct differences, particularly in diatom abundance and species composition, were present between the northern, eastward-flowing and southern, westward-flowing limbs of the Weddell Gyre. On the basis of species composition and physiological state of diatom assemblages, the higher biomass of the northern limb is attributed to entrainment of plankton-rich water from the ice-free Circumpolar Current rather than to in situ growth. The pelagic community characteristic of the region under the pack ice throughout the study was dominated by nanoflagellates, ciliates and heterotrophic dinoflagellates. Biomass of the latter groups ranged between 12 and 119% of that of autotrophs, and microscopic observations suggested that grazing pressure was heavy. This winter and early spring community resembled the regenerating communities of nutrient-limited waters. Break-up and melt of the ice cover in early December occurred simultaneously over an extensive area yet did not elicit biomass build-up, not even at the northern ice edge where favorable growth conditions appeared to prevail. Apparently most of the diatoms sinking into the water from the rich stocks developing in melting ice are grazed by protozoa and krill, hence do not contribute to water column blooms in this region. This situation contrasts with those reported from the western Weddell and Ross Sea ice edges where blooms of ice diatoms were observed in sharply defined melt-water zones adjoining closed ice pack. The role of melting sea ice in initiating blooms will hence differ in accordance with regional hydrography.

Adapting to a Warmer Ocean—Seasonal Shift of Baleen Whale Movements over Three Decades

PubMed Central

Ramp, Christian; Delarue, Julien; Palsbøll, Per J.; Sears, Richard; Hammond, Philip S.

2015-01-01

Global warming poses particular challenges to migratory species, which face changes to the multiple environments occupied during migration. For many species, the timing of migration between summer and winter grounds and also within-season movements are crucial to maximise exploitation of temporarily abundant prey resources in feeding areas, themselves adapting to the warming planet. We investigated the temporal variation in the occurrence of fin (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) in a North Atlantic summer feeding ground, the Gulf of St. Lawrence (Canada), from 1984 to 2010 using a long-term study of individually identifiable animals. These two sympatric species both shifted their date of arrival at a previously undocumented rate of more than 1day per year earlier over the study period thus maintaining the approximate 2-week difference in arrival of the two species and enabling the maintenance of temporal niche separation. However, the departure date of both species also shifted earlier but at different rates resulting in increasing temporal overlap over the study period indicating that this separation may be starting to erode. Our analysis revealed that the trend in arrival was strongly related to earlier ice break-up and rising sea surface temperature, likely triggering earlier primary production. The observed changes in phenology in response to ocean warming are a remarkable example of phenotypic plasticity and may partly explain how baleen whales were able to survive a number of changes in climate over the last several million years. However, it is questionable whether the observed rate of change in timing can be maintained. Substantial modification to the distribution or annual life cycle of these species might be required to keep up with the ongoing warming of the oceans. PMID:25785462

Adapting to a warmer ocean--seasonal shift of baleen whale movements over three decades.

PubMed

Ramp, Christian; Delarue, Julien; Palsbøll, Per J; Sears, Richard; Hammond, Philip S

2015-01-01

Global warming poses particular challenges to migratory species, which face changes to the multiple environments occupied during migration. For many species, the timing of migration between summer and winter grounds and also within-season movements are crucial to maximise exploitation of temporarily abundant prey resources in feeding areas, themselves adapting to the warming planet. We investigated the temporal variation in the occurrence of fin (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) in a North Atlantic summer feeding ground, the Gulf of St. Lawrence (Canada), from 1984 to 2010 using a long-term study of individually identifiable animals. These two sympatric species both shifted their date of arrival at a previously undocumented rate of more than 1 day per year earlier over the study period thus maintaining the approximate 2-week difference in arrival of the two species and enabling the maintenance of temporal niche separation. However, the departure date of both species also shifted earlier but at different rates resulting in increasing temporal overlap over the study period indicating that this separation may be starting to erode. Our analysis revealed that the trend in arrival was strongly related to earlier ice break-up and rising sea surface temperature, likely triggering earlier primary production. The observed changes in phenology in response to ocean warming are a remarkable example of phenotypic plasticity and may partly explain how baleen whales were able to survive a number of changes in climate over the last several million years. However, it is questionable whether the observed rate of change in timing can be maintained. Substantial modification to the distribution or annual life cycle of these species might be required to keep up with the ongoing warming of the oceans.

IceChrono v1: a probabilistic model to compute a common and optimal chronology for several ice cores

NASA Astrophysics Data System (ADS)

Parrenin, Frédéric

2015-04-01

Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores is essential to interpret the paleo records that they contain, but it is a complicated problem since it involves different dating methods. Here I present IceChrono v1, a new probabilistic model to combine different kinds of chronological information to obtain a common and optimized chronology for several ice cores, as well as its uncertainty. It is based on the inversion of three quantities: the surface accumulation rate, the Lock-In Depth (LID) of air bubbles and the vertical thinning function. The chronological information used are: models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice and gas dated horizons, ice and gas dated depth intervals, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air), stratigraphic links in between ice cores (ice-ice, air-air or mix ice-air and air-ice links). The optimization problem is formulated as a least squares problems, that is, all densities of probabilities are assumed gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono is similar in scope to the Datice model, but has differences from the mathematical, numerical and programming point of views. I apply IceChrono on an AICC2012-like experiment and I find similar results than Datice within a few centuries, which is a confirmation of both IceChrono and Datice codes. IceChrono v1 is freely available under the GPL v3 open source license.

Flooding on Russia's Lena River

NASA Technical Reports Server (NTRS)

2002-01-01

Nearly every year in the late spring, ice blocks the flow of water at the mouth of the Lena River in northeastern Russia and gives rise to floods across the Siberian plains. This year's floods can be seen in this image taken on June 2, 2002, by the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument aboard the Terra satellite. The river runs down the left side of the image, and its delta is shrouded in ice (red) at the top of the image. Normally, the river would resemble a thin black line in MODIS imagery. The river, which is Russia's longest, flows 2,641 miles (4,250 kilometers) south to north through Siberia and into the Laptev Sea. In the winter, the river becomes nearly frozen. In the spring, however, water upstream thaws earlier than water at the mouth of the river. As the southern end of the river begins to melt, blocks of ice travel downstream to the still frozen delta, pile up, and often obstruct the flow of water. Flooding doesn't always occur on the same parts of the river. The floods hit further south last year. If the flooding grows severe enough, explosive charges are typically used to break up the ice jams. In these false-color images land areas are a dull, light green or tan, and water is black. Clouds appear pink, and ice comes across as bright red. Image courtesy Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC

Ice-flow reorganization in West Antarctica 2.5 kyr ago dated using radar-derived englacial flow velocities

NASA Astrophysics Data System (ADS)

Kingslake, Jonathan; Martín, Carlos; Arthern, Robert J.; Corr, Hugh F. J.; King, Edward C.

2016-09-01

We date a recent ice-flow reorganization of an ice divide in the Weddell Sea Sector, West Antarctica, using a novel combination of inverse methods and ice-penetrating radars. We invert for two-dimensional ice flow within an ice divide from data collected with a phase-sensitive ice-penetrating radar while accounting for the effect of firn on radar propagation and ice flow. By comparing isochronal layers simulated using radar-derived flow velocities with internal layers observed with an impulse radar, we show that the divide's internal structure is not in a steady state but underwent a disturbance, potentially implying a regional ice-flow reorganization, 2.5 (1.8-2.9) kyr B.P. Our data are consistent with slow ice flow in this location before the reorganization and the ice divide subsequently remaining stationary. These findings increase our knowledge of the glacial history of a region that lacks dated constraints on late-Holocene ice-sheet retreat and provides a key target for models that reconstruct and predict ice-sheet behavior.

Floe-size distributions in laboratory ice broken by waves

NASA Astrophysics Data System (ADS)

Herman, Agnieszka; Evers, Karl-Ulrich; Reimer, Nils

2018-02-01

This paper presents the analysis of floe-size distribution (FSD) data obtained in laboratory experiments of ice breaking by waves. The experiments, performed at the Large Ice Model Basin (LIMB) of the Hamburg Ship Model Basin (Hamburgische Schiffbau-Versuchsanstalt, HSVA), consisted of a number of tests in which an initially continuous, uniform ice sheet was broken by regular waves with prescribed characteristics. The floes' characteristics (surface area; minor and major axis, and orientation of equivalent ellipse) were obtained from digital images of the ice sheets after five tests. The analysis shows that although the floe sizes cover a wide range of values (up to 5 orders of magnitude in the case of floe surface area), their probability density functions (PDFs) do not have heavy tails, but exhibit a clear cut-off at large floe sizes. Moreover, the PDFs have a maximum that can be attributed to wave-induced flexural strain, producing preferred floe sizes. It is demonstrated that the observed FSD data can be described by theoretical PDFs expressed as a weighted sum of two components, a tapered power law and a Gaussian, reflecting multiple fracture mechanisms contributing to the FSD as it evolves in time. The results are discussed in the context of theoretical and numerical research on fragmentation of sea ice and other brittle materials.

75 FR 9256 - Notice of Buy American Waiver Under the American Recovery and Reinvestment Act of 2009

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-01

... ice wedge located on the hull. An ice wedge is a projection at the front of a vessel below the water line that moves ice to the sides as the bow breaks and pushes it down. This particular hull form... particular vessel: [[Page 9257

Ice-Breaking as a Useful Teaching Policy for Both Genders

ERIC Educational Resources Information Center

Yeganehpour, Parisa

2017-01-01

These days focus of interest in English learning changes to productive skills, in Turkey. This research study assesses the teachers' point of view about using ice-breakers for adult Turkish EFL learners in upper-intermediate level. It also anticipates finding valuable information with applying ice-breaker activities as a useful teaching policy…

Tidal Impacts on Oceanographic and Sea-ice Processes in the Southern Ocean

NASA Astrophysics Data System (ADS)

Padman, L.; Muench, R. D.; Howard, S.; Mueller, R.

2008-12-01

We review recent field and modeling results that demonstrate the importance of tides in establishing the oceanographic and sea-ice conditions in the boundary regions of the Southern Ocean. The tidal component dominates the total oceanic kinetic energy throughout much of the circum-Antarctic seas. This domination is especially pronounced over the continental slope and shelf including the sub-ice-shelf cavities. Tides provide most of the energy that forces diapycnal mixing under ice shelves and thereby contributes to basal melting. The resulting Ice Shelf Water is a significant component of the Antarctic Bottom Water (AABW) filling much of the deep global ocean. Tides exert significant divergent forcing on sea ice along glacial ice fronts and coastal regions, contributing to creation and maintenance of the coastal polynyas where much of the High Salinity Shelf Water component of AABW is formed. Additional tidally forced ice divergence along the shelf break and upper slope significantly impacts area-averaged ice growth and upper-ocean salinity. Tidally forced cross- slope advection, and mixing by the benthic stress associated with tidal currents along the shelf break and upper slope, strongly influence the paths, volume fluxes and hydrographic properties of benthic outflows of dense water leaving the continental shelf. These outflows provide primary source waters for the AABW. These results confirm that general ocean circulation and coupled ocean/ice/atmosphere climate models must incorporate the impacts of tides.

The Svalbard-Barents Sea ice-sheet - Historical, current and future perspectives

NASA Astrophysics Data System (ADS)

Ingólfsson, Ólafur; Landvik, Jon Y.

2013-03-01

The history of research on the Late Quaternary Svalbard-Barents Sea ice sheet mirrors the developments of ideas and the shifts of paradigms in glacial theory over the past 150 years. Since the onset of scientific research there in the early 19th Century, Svalbard has been a natural laboratory where ideas and concepts have been tested, and played an important (but rarely acknowledged) role in the break-through of the Ice Age theory in the 1870's. The history of how the scientific perception of the Svalbard-Barents sea ice sheet developed in the mid-20th Century also tells a story of how a combination of fairly scattered and often contradictory observational data, and through both deductive and inductive reasoning, could outline a major ice sheet that had left but few tangible fingerprints. Since the 1980's, with increased terrestrial stratigraphical data, ever more marine geological evidence and better chronological control of glacial events, our perception of the Svalbard-Barents Sea ice sheet has changed. The first reconstructions depicted it as a static, concentric, single-domed ice sheet, with ice flowing from an ice divide over the central northern Barents Sea that expanded and declined in response to large-scale, Late Quaternary climate fluctuations, and which was more or less in tune with other major Northern Hemisphere ice sheets. We now increasingly perceive it as a very dynamic, multidomed ice sheet, controlled by climate fluctuations, relative sea-level change, as well as subglacial topography, substrate properties and basal temperature. In this respect, the Svalbard-Barents Sea ice sheet will increasingly hold the key for understanding the dynamics and processes of how marine-based ice sheets build-up and decay.

Proving and Improving Wave Models in the Arctic Ocean and its MIZ

DTIC Science & Technology

2015-09-30

in the central Arctic Ocean (Hunkins, 1966); in the Antarctic MIZ, Weddell Sea, slightly larger values were reported ranging from 1.6 × 10-2 m2 s-1...unprecedented spatial resolution. Such vast fields of pancake ice have traditionally only been associated with the advancing Antarctic MIZ, and, on a smaller...achieved in an MIZ dominated by large waves. Data on the break-up of a large tabular iceberg by swell, measured in Baffin Bay, were published

Seasonal Changes of Arctic Sea Ice Physical Properties Observed During N-ICE2015: An Overview

NASA Astrophysics Data System (ADS)

Gerland, S.; Spreen, G.; Granskog, M. A.; Divine, D.; Ehn, J. K.; Eltoft, T.; Gallet, J. C.; Haapala, J. J.; Hudson, S. R.; Hughes, N. E.; Itkin, P.; King, J.; Krumpen, T.; Kustov, V. Y.; Liston, G. E.; Mundy, C. J.; Nicolaus, M.; Pavlov, A.; Polashenski, C.; Provost, C.; Richter-Menge, J.; Rösel, A.; Sennechael, N.; Shestov, A.; Taskjelle, T.; Wilkinson, J.; Steen, H.

2015-12-01

Arctic sea ice is changing, and for improving the understanding of the cryosphere, data is needed to describe the status and processes controlling current seasonal sea ice growth, change and decay. We present preliminary results from in-situ observations on sea ice in the Arctic Basin north of Svalbard from January to June 2015. Over that time, the Norwegian research vessel «Lance» was moored to in total four ice floes, drifting with the sea ice and allowing an international group of scientists to conduct detailed research. Each drift lasted until the ship reached the marginal ice zone and ice started to break up, before moving further north and starting the next drift. The ship stayed within the area approximately 80°-83° N and 5°-25° E. While the expedition covered measurements in the atmosphere, the snow and sea ice system, and in the ocean, as well as biological studies, in this presentation we focus on physics of snow and sea ice. Different ice types could be investigated: young ice in refrozen leads, first year ice, and old ice. Snow surveys included regular snow pits with standardized measurements of physical properties and sampling. Snow and ice thickness were measured at stake fields, along transects with electromagnetics, and in drillholes. For quantifying ice physical properties and texture, ice cores were obtained regularly and analyzed. Optical properties of snow and ice were measured both with fixed installed radiometers, and from mobile systems, a sledge and an ROV. For six weeks, the surface topography was scanned with a ground LIDAR system. Spatial scales of surveys ranged from spot measurements to regional surveys from helicopter (ice thickness, photography) during two months of the expedition, and by means of an array of autonomous buoys in the region. Other regional information was obtained from SAR satellite imagery and from satellite based radar altimetry. The analysis of the data collected has started, and first results will be presented.

SHOCK AND VIBRATION COMPUTER PROGRAMS. REVIEWS AND SUMMARIES

DTIC Science & Technology

1975-01-01

hurricanes , special for- mulas nay have to be conaidered. Ice Ice load la usually specified by the thickness of the ice and by the ice- breaking force...Vibration Institute 5401 Katrine Downers Grove, Illinois 60515 Attn: Dr. Ronald. L. Eshleman, Director Critical Speeds ot a Rptor-Bearlng System...Instruction manual, and exanples. Contact: The Vibration Institute 5401 Katrine Downers Grove, 111. 60515 KOUTIMi MACHINSW 477 Attn; Dr. Ronald L

Casual Dating Dissolution: A Typology.

ERIC Educational Resources Information Center

Loyer-Carlson, Vicki L.; Walker, Alexis J.

Although there are many typologies of relationship development and love, it is frequently assumed that all break-ups are alike. This longitudinal study examined persons' cognitions regarding early relationship interactions and/or observations which caused them to think about the viability of the relationship. The role of causal attributions in the…

Subaqueous ice-contact fans: Depositional systems characterised by highly aggradational supercritical flow conditions

NASA Astrophysics Data System (ADS)

Lang, Joerg; Winsemann, Jutta

2015-04-01

Subaqueous ice-contact fans are deposited by high-energy plane-wall jets from subglacial conduits into standing water bodies. Highly aggradational conditions during flow expansion and deceleration allow for the preservation of bedforms related to supercritical flows, which are commonly considered rare in the depositional record. We present field examples from gravelly and sandy subaqueous ice-contact fan successions, which indicate that deposition by supercritical flows might be considered as a characteristic feature of these depositional systems. The studied successions were deposited in deep ice-dammed lakes, which formed along the margins of the Middle Pleistocene Scandinavian ice sheets across Northern Germany. The gravel-rich subaqueous fan deposits are dominated by large scour-fills (up to 25 m wide and 3 m) deep and deposits of turbulent hyperconcentrated flows, which are partly attributed to supercritical flow conditions (Winsemann et al., 2009). Scours (up to 4.5 m wide and 0.9 m deep) infilled by gravelly backsets are observed above laterally extensive erosional surfaces and are interpreted as deposits of cyclic steps. Laterally discontinuous beds of low-angle cross-stratified gravel are interpreted as antidune deposits. Downflow and up-section the gravel-rich deposits pass into sand-rich successions, which include deposits of chutes-and-pools, breaking antidunes, stationary antidunes and humpback dunes (Lang and Winsemann, 2013). Deposits of chutes-and-pools and breaking antidunes are characterised by scour-fills (up to 4 m wide and 1.2 m deep) comprising backsets or gently dipping sigmoidal foresets. Stationary antidune deposits consist of laterally extensive sinusoidal waveforms with long wavelengths (1-12 m) and low amplitudes (0.1-0.5 m), which formed under quasi-steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation. Humpback dunes are characterised by divergent sigmoidal foresets and are interpreted as bedforms related to transcritical flow conditions. Deposits of aggrading stationary antidunes and humpback dunes represent a characteristic facies association of the distal zone of flow transition. Downflow the succession passes into deposits of large 3D dunes and climbing ripples. The large-scale lateral and vertical successions of bedforms are interpreted as representing the temporal and spatial evolution of the supercritical meltwater jets, which was affected by hydraulic jumps. Small-scale facies changes and the formation of individual bedforms are interpreted as controlled by fluctuating discharge, pulsating unstable flows and bed topography. References: Lang, J., Winsemann, J. (2013) Lateral and vertical facies relationships of bedforms deposited by aggrading supercritical flows: from cyclic steps to humpback dunes. Sedimentary Geology 296, 36-54. Winsemann, J., Hornung, J.J., Meinsen, J., Asprion, U., Polom, U., Brandes, C., Bussmann, M., Weber, C., (2009) Anatomy of a subaqueous ice-contact fan and delta complex, Middle Pleistocene, North-west Germany, Sedimentology 56, 1041-1076.

ARC-1979-A79-7087

NASA Image and Video Library

1979-07-09

P-21758 BW Range: 246,000 kilometers (152,000 miles) This picture by Voyager 2 is the first close look ever obtained of Jupiter's satellite, Europa. The linear crack-like features had been seen from a much greater distance by Voyager 1 but this image provides a resolution of about four kilometers (2.5 miles). The complicated linear features appear even more like cracks or huge fractures in these images. Also seen are somewhat darker mottled regions which appear to have a slightly pitted appearance, perhaps due to small scale craters. No large craters (more than five kilometers in diameter) are easily identifiable in the Europa photographs to date, suggesting that this satellite has a young surface relative to Ganymede and Callisto, although not perhaps as young as Io's. Various models for Europa's structure will be tested during analysis of these images, including the possibility that the surface is a thin ice crust overlying water or softer ice and that the fracture systems seen are breaks in that crust. Resurfacing mechanisms such as production of fresh ice or snow along the cracks and cold glacier-like flows are being considered as possibilities for removing evidence of impact events. Europa thus appears to truly be a satellite with many properties intermediate between Ganymede and Io.

Water survey of Canada: Application for use of ERTS-A for retransmission of water resources data

NASA Technical Reports Server (NTRS)

Halliday, R. A. (Principal Investigator); Reid, I. A.

1974-01-01

The author has identified the following significant results. Water resources data were retransmitted from nine data collection platforms (DCP) located in remote regions of Canada. The DCPs located in the Arctic operated in temperatures lower than -40 C and the DCP antennas have survived wind speeds of greater than 80 kph and snow loads of a depth of one metre. Ice-out indicators were installed at a few DCP sites. The purpose of these indicators was to enable the detection of the movement of ice out of river channel during spring break-up. The suitability of satellite retransmission as a means of obtaining data from remote areas of Canada continues to be demonstrated. A modest expansion of the DCP network is planned.

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.

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.

QCM Thermo-Gravimetric Analysis (QTGA) Comparisons

NASA Technical Reports Server (NTRS)

Rosecrans, Glenn; Meadows, George

2004-01-01

The ASTM E-1559 apparatus has been used for years at NASA/Goddard Space Flight Center (GSFC) to determine in situ outgassing rate information, as well as pertinent in situ TML and multiple VCM values. The apparatus also affords the opportunity to experimentally compute the evaporation rates of molecular species that are reemitted as the Quartz Crystal Microbalances (QCMs) are gradually warmed up at some controlled temperature. Typically the molecular mass that accumulates onto the test QCMs are a compilation of species that are outgassing from the sample due to their respective activation energies and the desorption processes that the sample undergoes at various tested temperatures. It has been speculated that if there is too much molecular buildup of condensed water vapor (ice) onto the QCM crystal that a significantly higher temperature would be needed to break these "ice" bonds. ASTM E-1559 data plots will be used to demonstrate the thermogravimetric effects of water and other miscible molecular species with various water/ice thicknesses and at different evaporation rates.

SIPEX 2012: Extreme sea-ice and atmospheric conditions off East Antarctica

NASA Astrophysics Data System (ADS)

Heil, P.; Stammerjohn, S.; Reid, P.; Massom, R. A.; Hutchings, J. K.

2016-09-01

In 2012, Antarctic sea-ice coverage was marked by weak annual-mean climate anomalies that consisted of opposing anomalies early and late in the year (some setting new records) which were interspersed by near-average conditions for most of the austral autumn and winter. Here, we investigate the ocean-ice-atmosphere system off East Antarctica, prior to and during the Sea Ice Physics and Ecosystems eXperiment [SIPEX] 2012, by exploring relationships between atmospheric and oceanic forcing together with the sea-ice and snow characteristics. During August and September 2012, just prior to SIPEX 2012, atmospheric circulation over the Southern Ocean was near-average, setting up the ocean-ice-atmosphere system for near-average conditions. However, below-average surface pressure and temperature as well as strengthened circumpolar winds prevailed during June and July 2012. This led to a new record (19.48×106 km2) in maximum Antarctic sea-ice extent recorded in late September. In contrast to the weak circum-Antarctic conditions, the East Antarctic sector (including the SIPEX 2012 region) experienced positive sea-ice extent and concentration anomalies during most of 2012, coincident with negative atmospheric pressure and sea-surface temperature anomalies. Heavily deformed sea ice appeared to be associated with intensified wind stress due to increased cyclonicity as well as an increased influx of sea ice from the east. This increased westward ice flux is likely linked to the break-up of nearly 80% of the Mertz Glacier Tongue in 2010, which strongly modified the coastal configuration and hence the width of the westward coastal current. Combined with favourable atmospheric conditions the associated changed coastal configuration allowed more sea ice to remain within the coastal current at the expense of a reduced northward flow in the region around 141°-145°E. In addition a westward propagating positive anomaly of sea-ice extent from the western Ross Sea during austral winter 2012 has been identified to have fed into the westward current of the SIPEX 2012 region. A pair of large grounded icebergs appears to have modified the local stress state as well as the structure of the ice pack upstream and also towards the Dalton Glacier Tongue. Together with the increased influx of sea ice into the regions, this contributed to the difficulties in navigating the SIPEX 2012 region.

Possible Effects of Climate Warming on Selected Populations of Polar Bears (Ursus maritimus) in the Canadian Arctic

NASA Technical Reports Server (NTRS)

Parkinson, Claire L.; Stirling Ian

2006-01-01

Polar bears are dependent on sea ice for survival. Climate warming in the Arctic has caused significant declines in coverage and thickness of sea ice in the polar basin and progressively earlier breakup in some areas. In four populations of polar bears in the eastern Canadian Arctic (including Western Hudson Bay), Inuit hunters report more bears near settlements during the open water period in recent years. These observations have been interpreted as evidence of increasing population size, resulting in increases in hunting quotas. However, long-term data on the population size and condition of polar bears in Western Hudson Bay, and population and harvest data from Baffin Bay, make it clear that those two populations at least are declining, not increasing. While the details vary in different arctic regions, analysis of passive-microwave satellite imagery, beginning in the late 1970s, indicates that the sea ice is breaking up at progressively earlier dates, so that bears must fast for longer periods during the open water season. Thus, at least part of the explanation for the appearance of more bears in coastal communities is likely that they are searching for alternative food sources because their stored body fat depots are being exhausted. We hypothesize that, if the climate continues to warm as projected by the IPCC, then polar bears in all five populations discussed in this paper will be stressed and are likely to decline in numbers, probably significantly so. As these populations decline, there will likely also be continuing, possibly increasing, numbers of problem interactions between bears and humans as the bears seek alternate food sources. Taken together, the data reported in this paper suggest that a precautionary approach be taken to the harvesting of polar bears and that the potential effects of climate warming be incorporated into planning for the management and conservation of this species throughout the Arctic.

NASA Spacecraft Images One of Earth Iceberg Incubators

NASA Image and Video Library

2012-04-13

Acquired by NASA Terra spacecraft, this image shows the west coast of Greenland, one of Earth premiere incubators for icebergs -- large blocks of land ice that break off from glaciers or ice shelves and float in the ocean.

Symmetry breaking in occupation number based slave-particle methods

NASA Astrophysics Data System (ADS)

Georgescu, Alexandru B.; Ismail-Beigi, Sohrab

2017-10-01

We describe a theoretical approach to finding spontaneously symmetry-broken electronic phases due to strong electronic interactions when using recently developed slave-particle (slave-boson) approaches based on occupation numbers. We describe why, to date, spontaneous symmetry breaking has proven difficult to achieve in such approaches. We then provide a total energy based approach for introducing auxiliary symmetry-breaking fields into the solution of the slave-particle problem that leads to lowered total energies for symmetry-broken phases. We point out that not all slave-particle approaches yield energy lowering: the slave-particle model being used must explicitly describe the degrees of freedom that break symmetry. Finally, our total energy approach permits us to greatly simplify the formalism used to achieve a self-consistent solution between spinon and slave modes while increasing the numerical stability and greatly speeding up the calculations.

Buried glacier ice in southern Iceland and its wider significance

NASA Astrophysics Data System (ADS)

Everest, Jeremy; Bradwell, Tom

2003-06-01

Geo-electrical resistivity surveys have been carried out at recently deglaciated sites in front of three glaciers in southern Iceland: Skeiðarájökull, Hrútárjökull, and Virkisjökull. The results show the presence of old glacier ice beneath debris mantles of various thickness. We conclude that buried glacier ice has survived for at least 50 years at Virkisjökull and Hrútárjökull, and probably for over 200 years at Skeiðarájökull. Additional data from a further site have identified a discontinuous ice core within 18th-century jökulhlaup deposits. Photographic and lichenometric evidence show that the overlying debris has been relatively stable, and hence melting of the ice at all four sites is proceeding slowly due to the heat-shielding properties of the overburden. The geomorphic implications are pertinent when considering the potential longevity of buried ice. The possible implications for dating techniques, such as lichenometry, radiocarbon dating and cosmogenic surface-exposure dating are also important, as long-term readjustments of surface forms may lead to dating inaccuracy. Finally, it is recognised that landscape development in areas of stagnant ice topography may post-date initial deglaciation by a considerable degree.

Dating a tropical ice core by time-frequency analysis of ion concentration depth profiles

NASA Astrophysics Data System (ADS)

Gay, M.; De Angelis, M.; Lacoume, J.-L.

2014-09-01

Ice core dating is a key parameter for the interpretation of the ice archives. However, the relationship between ice depth and ice age generally cannot be easily established and requires the combination of numerous investigations and/or modelling efforts. This paper presents a new approach to ice core dating based on time-frequency analysis of chemical profiles at a site where seasonal patterns may be significantly distorted by sporadic events of regional importance, specifically at the summit area of Nevado Illimani (6350 m a.s.l.), located in the eastern Bolivian Andes (16°37' S, 67°46' W). We used ion concentration depth profiles collected along a 100 m deep ice core. The results of Fourier time-frequency and wavelet transforms were first compared. Both methods were applied to a nitrate concentration depth profile. The resulting chronologies were checked by comparison with the multi-proxy year-by-year dating published by de Angelis et al. (2003) and with volcanic tie points. With this first experiment, we demonstrated the efficiency of Fourier time-frequency analysis when tracking the nitrate natural variability. In addition, we were able to show spectrum aliasing due to under-sampling below 70 m. In this article, we propose a method of de-aliasing which significantly improves the core dating in comparison with annual layer manual counting. Fourier time-frequency analysis was applied to concentration depth profiles of seven other ions, providing information on the suitability of each of them for the dating of tropical Andean ice cores.

Rapid Environmental Change Drives Increased Land Use by an Arctic Marine Predator.

PubMed

Atwood, Todd C; Peacock, Elizabeth; McKinney, Melissa A; Lillie, Kate; Wilson, Ryan; Douglas, David C; Miller, Susanne; Terletzky, Pat

2016-01-01

In the Arctic Ocean's southern Beaufort Sea (SB), the length of the sea ice melt season (i.e., period between the onset of sea ice break-up in summer and freeze-up in fall) has increased substantially since the late 1990s. Historically, polar bears (Ursus maritimus) of the SB have mostly remained on the sea ice year-round (except for those that came ashore to den), but recent changes in the extent and phenology of sea ice habitat have coincided with evidence that use of terrestrial habitat is increasing. We characterized the spatial behavior of polar bears spending summer and fall on land along Alaska's north coast to better understand the nexus between rapid environmental change and increased use of terrestrial habitat. We found that the percentage of radiocollared adult females from the SB subpopulation coming ashore has tripled over 15 years. Moreover, we detected trends of earlier arrival on shore, increased length of stay, and later departure back to sea ice, all of which were related to declines in the availability of sea ice habitat over the continental shelf and changes to sea ice phenology. Since the late 1990s, the mean duration of the open-water season in the SB increased by 36 days, and the mean length of stay on shore increased by 31 days. While on shore, the distribution of polar bears was influenced by the availability of scavenge subsidies in the form of subsistence-harvested bowhead whale (Balaena mysticetus) remains aggregated at sites along the coast. The declining spatio-temporal availability of sea ice habitat and increased availability of human-provisioned resources are likely to result in increased use of land. Increased residency on land is cause for concern given that, while there, bears may be exposed to a greater array of risk factors including those associated with increased human activities.

Rapid Environmental Change Drives Increased Land Use by an Arctic Marine Predator

PubMed Central

Atwood, Todd C.; Peacock, Elizabeth; McKinney, Melissa A.; Lillie, Kate; Wilson, Ryan; Douglas, David C.; Miller, Susanne; Terletzky, Pat

2016-01-01

In the Arctic Ocean’s southern Beaufort Sea (SB), the length of the sea ice melt season (i.e., period between the onset of sea ice break-up in summer and freeze-up in fall) has increased substantially since the late 1990s. Historically, polar bears (Ursus maritimus) of the SB have mostly remained on the sea ice year-round (except for those that came ashore to den), but recent changes in the extent and phenology of sea ice habitat have coincided with evidence that use of terrestrial habitat is increasing. We characterized the spatial behavior of polar bears spending summer and fall on land along Alaska’s north coast to better understand the nexus between rapid environmental change and increased use of terrestrial habitat. We found that the percentage of radiocollared adult females from the SB subpopulation coming ashore has tripled over 15 years. Moreover, we detected trends of earlier arrival on shore, increased length of stay, and later departure back to sea ice, all of which were related to declines in the availability of sea ice habitat over the continental shelf and changes to sea ice phenology. Since the late 1990s, the mean duration of the open-water season in the SB increased by 36 days, and the mean length of stay on shore increased by 31 days. While on shore, the distribution of polar bears was influenced by the availability of scavenge subsidies in the form of subsistence-harvested bowhead whale (Balaena mysticetus) remains aggregated at sites along the coast. The declining spatio-temporal availability of sea ice habitat and increased availability of human-provisioned resources are likely to result in increased use of land. Increased residency on land is cause for concern given that, while there, bears may be exposed to a greater array of risk factors including those associated with increased human activities. PMID:27249673

Rapid environmental change drives increased land use by an Arctic marine predator

USGS Publications Warehouse

Atwood, Todd C.; Peacock, Elizabeth; McKinney, Melissa A.; Lillie, Kate; Wilson, Ryan R.; Douglas, David C.; Miller, Susanne; Terletzky, Pat

2016-01-01

In the Arctic Ocean’s southern Beaufort Sea (SB), the length of the sea ice melt season (i.e., period between the onset of sea ice break-up in summer and freeze-up in fall) has increased substantially since the late 1990s. Historically, polar bears (Ursus maritimus) of the SB have mostly remained on the sea ice year-round (except for those that came ashore to den), but recent changes in the extent and phenology of sea ice habitat have coincided with evidence that use of terrestrial habitat is increasing. We characterized the spatial behavior of polar bears spending summer and fall on land along Alaska’s north coast to better understand the nexus between rapid environmental change and increased use of terrestrial habitat. We found that the percentage of radiocollared adult females from the SB subpopulation coming ashore has tripled over 15 years. Moreover, we detected trends of earlier arrival on shore, increased length of stay, and later departure back to sea ice, all of which were related to declines in the availability of sea ice habitat over the continental shelf and changes to sea ice phenology. Since the late 1990s, the mean duration of the open-water season in the SB increased by 36 days, and the mean length of stay on shore increased by 31 days. While on shore, the distribution of polar bears was influenced by the availability of scavenge subsidies in the form of subsistence-harvested bowhead whale (Balaena mysticetus) remains aggregated at sites along the coast. The declining spatio-temporal availability of sea ice habitat and increased availability of human-provisioned resources are likely to result in increased use of land. Increased residency on land is cause for concern given that, while there, bears may be exposed to a greater array of risk factors including those associated with increased human activities.

Direct observations of ice seasonality reveal changes in climate over the past 320–570 years

USGS Publications Warehouse

Sharma, Sapna; Magnuson, John J.; Batt, Ryan D.; Winslow, Luke; Korhonen, Johanna; Yasuyuki Aono,

2016-01-01

Lake and river ice seasonality (dates of ice freeze and breakup) responds sensitively to climatic change and variability. We analyzed climate-related changes using direct human observations of ice freeze dates (1443–2014) for Lake Suwa, Japan, and of ice breakup dates (1693–2013) for Torne River, Finland. We found a rich array of changes in ice seasonality of two inland waters from geographically distant regions: namely a shift towards later ice formation for Suwa and earlier spring melt for Torne, increasing frequencies of years with warm extremes, changing inter-annual variability, waning of dominant inter-decadal quasi-periodic dynamics, and stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution. Although local factors, including human population growth, land use change, and water management influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems, suggesting that global processes including climate change and variability are driving the long-term changes in ice seasonality.

Direct observations of ice seasonality reveal changes in climate over the past 320–570 years

PubMed Central

Sharma, Sapna; Magnuson, John J.; Batt, Ryan D.; Winslow, Luke A.; Korhonen, Johanna; Aono, Yasuyuki

2016-01-01

Lake and river ice seasonality (dates of ice freeze and breakup) responds sensitively to climatic change and variability. We analyzed climate-related changes using direct human observations of ice freeze dates (1443–2014) for Lake Suwa, Japan, and of ice breakup dates (1693–2013) for Torne River, Finland. We found a rich array of changes in ice seasonality of two inland waters from geographically distant regions: namely a shift towards later ice formation for Suwa and earlier spring melt for Torne, increasing frequencies of years with warm extremes, changing inter-annual variability, waning of dominant inter-decadal quasi-periodic dynamics, and stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution. Although local factors, including human population growth, land use change, and water management influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems, suggesting that global processes including climate change and variability are driving the long-term changes in ice seasonality. PMID:27113125

The Connemara Fan: a major glacial grounding line fan west of Ireland

NASA Astrophysics Data System (ADS)

McCarron, Stephen; Praeg, Daniel; Monteys, Xavier; Scott, Gill

2014-05-01

Glacigenic topography on the mid-shelf (~130-350 m water depth) west of Galway, Ireland appears to have the morphological form, internal architecture and sediments associated with a large glacial grounding-line fan. Seismic data collected in 2009 and 2012 (during the GLAMAR and GATEWAYS 1 campaigns) reveal that the broad, arcuate ridges of the 'Olex moraine' form the landward part of a fan system which prograded beyond the mid-shelf break (defining the outer margin of the 'Clare Platform') westwards into the Porcupine Seabight. The topography is comparable to larger shelf-edge trough-mouth fans found further north along the same margin, however no discernible 'trough' has been identified on the Clare Platform. The ridge and fan topographic assemblage is renamed the 'Connemara Fan' in its entirety, based on its genetic relations and geographic location due west of Connemara, western Ireland. A macrofossil recovered from within a debris flow on the outer fan slope comprised of remobilised plumites dates to ~ 20 ka Cal B.P., indicating sediment reworking downslope following deglacial sediment input to at least that time. The Connemara Fan is the most southerly glacigenic fan identified along the north-east Atlantic margin. Its identification also adds to our knowledge of possibly multiple generations of ice sheets feeding onto the Irish shelf from west-central Ireland and the occurrence of ice sheet geometries and dynamics that evacuated ice, melt-water and sediment (ice streams?) westwards across the Clare Platform during past glaciations.

In situ cosmogenic radiocarbon production and 2-D ice flow line modeling for an Antarctic blue ice area

NASA Astrophysics Data System (ADS)

Buizert, Christo; Petrenko, Vasilii V.; Kavanaugh, Jeffrey L.; Cuffey, Kurt M.; Lifton, Nathaniel A.; Brook, Edward J.; Severinghaus, Jeffrey P.

2012-06-01

Radiocarbon measurements at ice margin sites and blue ice areas can potentially be used for ice dating, ablation rate estimates and paleoclimatic reconstructions. Part of the measured signal comes from in situ cosmogenic 14C production in ice, and this component must be well understood before useful information can be extracted from 14C data. We combine cosmic ray scaling and production estimates with a two-dimensional ice flow line model to study cosmogenic 14C production at Taylor Glacier, Antarctica. We find (1) that 14C production through thermal neutron capture by nitrogen in air bubbles is negligible; (2) that including ice flow patterns caused by basal topography can lead to a surface 14C activity that differs by up to 25% from the activity calculated using an ablation-only approximation, which is used in all prior work; and (3) that at high ablation margin sites, solar modulation of the cosmic ray flux may change the strength of the dominant spallogenic production by up to 10%. As part of this effort we model two-dimensional ice flow along the central flow line of Taylor Glacier. We present two methods for parameterizing vertical strain rates, and assess which method is more reliable for Taylor Glacier. Finally, we present a sensitivity study from which we conclude that uncertainties in published cosmogenic production rates are the largest source of potential error. The results presented here can inform ongoing and future 14C and ice flow studies at ice margin sites, including important paleoclimatic applications such as the reconstruction of paleoatmospheric 14C content of methane.

Relating modes of extension to the spatial and temporal distribution of major sediment unconformities at passive margins

NASA Astrophysics Data System (ADS)

Andrés-Martínez, Miguel; Pérez-Gussinyé, Marta; Armitage, John; Morgan, Jason P.

2017-04-01

Rifting is a regional process which results in thinning of the crust over hundreds of kilometres. However, basins where deposition takes place could have different subsidence histories due to local graben-bounding fault kinetics. A change in the rift dynamics often results in a displacement of the basin depocenters, with subsequent erosion of old sediments and later deposition, creating an unconformity. Unconformities of regional character are typically studied to unveil the overall rift deformation history, and major ones separating syn- and post-kinematic sediments are often associated with break-up of the continental crust. However, evolution of the basement deformation is typically challenging to study since reflection images are usually diffuse at these depths and boreholes are typically scarce, which complicates the dating of the sediments overlying the basement. Consequently, relating the deformation styles and rift evolution to unconformities is not straight forward. We use numerical models in order to approach the meaning of regional unconformities and to study the sedimentation patterns under different modes of extension. Our models solve 2D Stokes flow for rocks treated as non-Newtonian bodies, together with heat conservation equation. Viscosities and densities depend on temperatures. Elasticity and plasticity are plugged-in in the mechanical formulation. We also use strain softening to simulate faulting and shear zones. The top boundary is a free-surface so that tectonics result in topography. Additionally, we update this topography every time step using a sediment transport model, and we store information about depositional times, paleo-depths and erosional events. These models allow for the recovery of the basement deformation during rift evolution simultaneously to the recovery of sedimentation history. Here, we run models with different crustal rheologies to reproduce different extensional modes. This allows us to contrast sedimentation patterns and unconformities under variable kinetic scenarios, from regional to faulted-block scales. We find that unconformities are generally associated to a change in the locus of extension. In models with intermediate-strength crust, sequential faulting takes place, so that only one fault is active at a time and occur in the hanging wall of the previous fault, resulting in asymmetric conjugate margins. In this case a major unconformity separates syn- and post-kinematic sediments. Both syn- and post-kinematic sediments young oceanwards and the unconformity dates the time in which extension abandons the area in favour of new faults forming oceanwards. Models with weaker crusts display extension along a wide region, with overprinting of different faulting phases. Eventually, deformation localizes in a narrow region due to cooling, and crustal break-up occurs. In this case, a first set of unconformities separates different phases of faulting inside the syn-kinematic sediments, and later unconformities separate syn-kinematic and post-kinematic sediments, dating the time at which extension localizes. We also find that unconformities date the crustal break-up only when they develop in the vicinity of the break-up locus. This stresses on that terms such as syn- and post-rift sediments and break-up unconformity should be handled carefully when seismic interpretation is done, and also provides support for unconformities as rifting story-tellers.

Seismic Events and Tidal Forces near the Grounding Line of Beardmore Glacier, Antarctica

NASA Astrophysics Data System (ADS)

Cooley, J.; Winberry, J. P.; Conway, H.; Koutnik, M. R.

2016-12-01

Ice shelves are floating extensions of large ice sheets. Weakening or break-up of these ice shelves allow ice upstream to move off the continent at increased rates, contributing to sea level rise. One prominent mechanism by which shelves are weakened is through crevasse formation. Icequakes are small magnitude seismic events that occur within a volume of ice which reveal areas where crevasses on an ice shelf might form, providing insight into ice shelf stability. The processes that drive these crevassing events are not well-understood, but past research on icequakes near the grounding line has found a correlation with tide. During high tide, there is a large mass of water pushing against the ice shelf, compressing it. As the tide falls, so does this pressure, allowing the ice shelf to stretch. This creates an enormous amount of stress, released as crevasses, near the grounding line. Preliminary examination of data taken over a three week period in the austral summer of 2013/14 at Beardmore Glacier also reveals a tidal correlation, but with rising tide playing a bigger role than previously thought. I aim to find a pattern in the physical locations of events which separates those that occur during rising tide from those that occur during falling tide, to take steps in understanding what constraint rising tide could have on the creation of crevasses. Research methods involve programming scripts to automate counting of events, locating the epicenters with beamforming, calculating the local magnitudes of the events, and utilizing processed GPS data to correlate the events to ocean tide.

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.

[Radiocarbon dating of pollen and spores in wedge ice from Iamal and Kolyma].

PubMed

Vasil'chuk, A K

2004-01-01

Radiocarbon dating of pollen concentrate from late Pleistocene syngenetic wedge ice was carried out using acceleration mass spectrometry (AMS) in Seyakha and Bizon sections. Comparison of the obtained dating with palynological analysis and AMS radiocarbon dating previously obtained for other organic fractions of the same samples allowed us to evaluate accuracy of dating of different fractions. Quantitative tests for data evaluation were considered in terms of possible autochthonous or allochthonous accumulation of the material on the basis of pre-Pleistocene pollen content in these samples. Paleoecological information content of pollen spectra from late Pleistocene syngenetic wedge ice was evaluated.

Ice Shelves and Landfast Ice on the Antarctic Perimeter: Revised Scope of Work

NASA Technical Reports Server (NTRS)

Scambos, Ted

2002-01-01

Ice shelves respond quickly and profoundly to a warming climate. Within a decade after mean summertime temperature reaches approx. O C and persistent melt pending is observed, a rapid retreat and disintegration occurs. This link was documented for ice shelves in the Antarctic Peninsula region (the Larsen 'A', 'B' and Wilkins Ice shelves) by the results of a previous grant under ADRO-1. Modeling of ice flow and the effects of meltwater indicated that melt pending accelerates shelf breakup by increasing fracture penetration. SAR data supplemented an AVHRR- and SSM/I-based image analysis of extent and surface characteristic changes. This funded grant is a revised, scaled-down version of an earlier proposal under the ADRO-2 NRA. The overall objective remains the same: we propose to build on the previous study by examining other ice shelves of the Antarctic and incorporate an examination of the climate-related characteristics of landfast ice. The study now considers just a few shelf and fast ice areas for study, and is funded for two years. The study regions are the northeastern Ross Ice Shelf, the Larsen 'B' and 'C' shelves, fast ice and floating shelf ice in the Pine Island Glacier area, and fast ice along the Wilkes Land coast. Further, rather than investigating a host of shelf and fast ice processes, we will home in on developing a series of characteristics associated with climate change over shelf and fast ice areas. Melt pending and break-up are the end stages of a response to a warming climate that may begin with increased melt event frequency (which changes both albedo and emissivity temporarily), changing firn backscatter (due to percolation features), and possibly increased rifting of the shelf surface. Fast ice may show some of these same processes on a seasonal timescale, providing insight into shelf evolution.

Marital satisfaction and break-ups differ across on-line and off-line meeting venues

PubMed Central

Cacioppo, John T.; Cacioppo, Stephanie; Gonzaga, Gian C.; Ogburn, Elizabeth L.; VanderWeele, Tyler J.

2013-01-01

Marital discord is costly to children, families, and communities. The advent of the Internet, social networking, and on-line dating has affected how people meet future spouses, but little is known about the prevalence or outcomes of these marriages or the demographics of those involved. We addressed these questions in a nationally representative sample of 19,131 respondents who married between 2005 and 2012. Results indicate that more than one-third of marriages in America now begin on-line. In addition, marriages that began on-line, when compared with those that began through traditional off-line venues, were slightly less likely to result in a marital break-up (separation or divorce) and were associated with slightly higher marital satisfaction among those respondents who remained married. Demographic differences were identified between respondents who met their spouse through on-line vs. traditional off-line venues, but the findings for marital break-up and marital satisfaction remained significant after statistically controlling for these differences. These data suggest that the Internet may be altering the dynamics and outcomes of marriage itself. PMID:23733955

Emergent Dead Vegetation and Paired Cosmogenic Isotope Constraints on Ice Cap Activity, Baffin Island, Arctic Canada

NASA Astrophysics Data System (ADS)

Pendleton, S.; Miller, G. H.

2014-12-01

Recent summer warming has now raised the equilibrium line above almost all ice caps on Baffin Island, resulting in surface lowering and marginal recession everywhere. As cold-based ice recedes it frequently exposes in situ tundra plants that were living at the time ice expanded across the site. Radiocarbon dates for each plant records when cold summers dropped regional snowline below the site, killing the plants, and snowline remained below the site until the collection date. The kill dates also represent the last time that the climate was warm enough to expose the sampling location. Seventy-six vegetation samples collected in 2013 from the Penny Ice Cap region have been dated, with significant age populations at ~0.5, 1.8, 2.3, and 3.6 ka. The absence of ages around ~1, 2, 3, 4.5, and 5.5 ka suggest periods of either no snowline depression or stability. Sixteen vegetation samples returned ages of >45 ka (2 revisited sites from 2010, 14 new). It is postulated that these radiocarbon dead samples were last exposed during the last interglaciation (~120 ka), the last time climate was as warm as present. In addition to plant collections, bedrock exposures at the ice margins were sampled for 26Al/10Be cosmogenic nuclide dating. Seven samples from and around the Penny Ice cap have returned maximum exposure ages from ~ 0.6-0.9 ma and total histories of ~0.6-1.5 ma. In general, samples from the larger Penny Ice Cap exhibited lower amounts of exposure (~20% of total history) than those samples from smaller, localized ice caps (~55%). Radiocarbon dead sites north of the Penny Ice cap experienced significantly more exposure over their lifetimes than their counterparts east of the Penny Ice cap, suggesting significant differences in local and regional land ice fluctuations over the last 2 million years. Utilizing both the method of in situ moss and 26Al/10Be dating provides new insight into both the recent activity and long-term evolution of ice on Baffin Island. In particular these new data help to shed light on how late Holocene coolings affect both large and small ice bodies and how this behavior is represented in the longer-term burial/exposure record contained within the rock surface.

Landforms, sediments and dates to constrain rates and style of marine-influenced ice sheet decay; the BRITICE-CHRONO project.

NASA Astrophysics Data System (ADS)

Clark, Chris

2014-05-01

Uncertainty exists regarding the future mass of the Antarctic and Greenland ice sheets and how they will respond to forcings from sea level, and atmospheric and ocean temperatures. If we want to know more about the mechanisms and rate of change of shrinking ice sheets, then why not examine an ice sheet that has fully disappeared and track its retreat through time? If achieved in enough detail such information on ice retreat could be a data-rich playground for improving the next breed of numerical ice sheet models to be used in ice and sea level forecasting. We regard that the last British-Irish Ice Sheet is a good target for this work, on account of its small size, density of information and with its numerous researchers already investigating it. Geomorphological mapping across the British Isles and the surrounding continental shelf has revealed the nature and distribution of glacial landforms. Here we demonstrate how such data have been used to build a pattern of ice margin retreat. The BRITICE-CHRONO consortium of Quaternary scientists and glaciologists, are now working on a project running from 2012 - 2017 to produce an ice sheet wide database of geochronometric dates to constrain and then understand ice margin retreat. This is being achieved by focusing on 8 transects running from the continental shelf edge to a short distance (10s km) onshore and acquiring marine and terrestrial samples for geochronometric dating. The project includes funding for 587 radiocarbon, 140 OSL and 158 TCN samples for surface exposure dating; with sampling accomplished by two research cruises and 16 fieldwork campaigns. Results will reveal the timing and rate of change of ice margin recession for each transect, and combined with existing landform and dating databases, will be used to build an ice sheet-wide empirical reconstruction of retreat. Simulations using two numerical ice sheet models, fitted against the margin data, will help us understand the nature and significance of sea-level rise and ocean/atmosphere forcing on influencing the rate of retreat and ice sheet demise and the effect that bed topography has in controlling this.

Gas exchange in the ice zone: the role of small waves and big animals

NASA Astrophysics Data System (ADS)

Loose, B.; Takahashi, A.; Bigdeli, A.

2016-12-01

The balance of air-sea gas exchange and net biological carbon fixation determine the transport and transformation of carbon dioxide and methane in the ocean. Air-sea gas exchange is mostly driven by upper ocean physics, but biology can also play a role. In the open ocean, gas exchange increases proportionate to the square of wind speed. When sea ice is present, this dependence breaks down in part because breaking waves and air bubble entrainment are damped out by interactions between sea ice and the wave field. At the same time, sea ice motions, formation, melt, and even sea ice-associated organisms can act to introduce turbulence and air bubbles into the upper ocean, thereby enhancing air-sea gas exchange. We take advantage of the knowledge advances of upper ocean physics including bubble dynamics to formulate a model for air-sea gas exchange in the sea ice zone. Here, we use the model to examine the role of small-scale waves and diving animals that trap air for insulation, including penguins, seals and polar bears. We compare these processes to existing parameterizations of wave and bubble dynamics in the open ocean, to observe how sea ice both mitigates and locally enhances air-sea gas transfer.

Invasive Species Science Update (No. 6)

Treesearch

Paula Fornwalt

2013-01-01

The sixth issue of the Rocky Mountain Research Station's (RMRS) Invasive Species Science Update is now complete. Published approximately once per year, this newsletter keeps managers and other users up-to-date with recently completed and ongoing research by RMRS scientists, and covers breaking news related to invasive species issues. The newsletter is produced by...

Flirting, Dating, and Breaking up within New Media Environments

ERIC Educational Resources Information Center

Meenagh, Joni

2015-01-01

Although romantic and sexual relationships are an important aspect of young people's lives, research on how young people negotiate their love/sex relationships is lacking. New media environments provide a new context within which young people negotiate their love/sex relationships; however, what is negotiated is often not all that different from…

Glacio-isostasy and Glacial Ice Load at Law Dome, Wilkes Land, East Antarctica

NASA Astrophysics Data System (ADS)

Goodwin, Ian D.; Zweck, Christopher

2000-05-01

The Holocene sea-level high stand or "marine limit" in Wilkes Land, East Antarctica, reached ˜30 m above present sea level at a few dispersed sites. The most detailed marine limit data have been recorded for the Windmill Islands and Budd Coast at the margin of the Law Dome ice cap, a dome of the East Antarctic Ice Sheet (EAIS). Relative sea-level lowering of 30 m and the associated emergence of the Windmill Islands have occurred since 6900 14C (corr.) yr B.P. Numerical modeling of the Earth's rheology is used to determine the glacio-isostatic component of the observed relative sea-level lowering. Glaciological evidence suggests that most of EAIS thickening occurred around its margin, with expansion onto the continental shelf. Consequently, a regional ice history for the last glacial maximum (LGM) was applied in the glacio-isostatic modeling to test whether the observed relative sea-level lowering was primarily produced by regional ice-sheet changes. The results of the modeling indicate that the postglacial (13,000 to 8000 14C yr B.P) removal of an ice load of between 770 and 1000 m from around the margin of the Law Dome and adjacent EAIS have produced the observed relative sea-level lowering. Such an additional ice load would have been associated with a 40- to 65-km expansion of the Law Dome to near the continental shelf break, together with a few hundred meters of ice thickening on the adjoining coastal slope of the EAIS up to 2000 m elevation. Whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes, the glacio-isostatic response at the Windmill Islands results from a combination of regional and, to a lesser extent, Antarctic-wide effects. The correspondence between the Holocene relative sea-level lowering interpreted at the margin of the Law Dome and the lowering interpreted along the remainder of the Wilkes Land and Oates Land coasts (105°-160° E) suggests that a similar ice load of up to 1000 m existed along the EAIS margin between Wilkes Land and Oates Land.

Passive Acoustic Thermometry Using Low-Frequency Deep Water Noise

DTIC Science & Technology

2015-09-30

where potential ice noise sources contributing to the coherent arrivals shown in C-D are located (18b). In the low-frequency band used in this...seismic activity (e.g. along major undersea fault lines) or ice -breaking noise in the Polar Regions (19-22). Ice - generated ambient noise near the...using geodesic paths to obtain a simple estimate of the geographical area from where ice -generated ambient noise is likely to emanate for each site

The evolution of a coupled ice shelf-ocean system under different climate states

NASA Astrophysics Data System (ADS)

Grosfeld, Klaus; Sandhäger, Henner

2004-07-01

Based on a new approach for coupled applications of an ice shelf model and an ocean general circulation model, we investigate the evolution of an ice shelf-ocean system and its sensitivity to changed climatic boundary conditions. Combining established 3D models into a coupled model system enabled us to study the reaction and feedbacks of each component to changes at their interface, the ice shelf base. After calculating the dynamics for prescribed initial ice shelf and bathymetric geometries, the basal mass balance determines the system evolution. In order to explore possible developments for given boundary conditions, an idealized geometry has been chosen, reflecting basic features of the Filchner-Ronne Ice Shelf, Antarctica. The model system is found to be especially sensitive in regions where high ablation or accretion rates occur. Ice Shelf Water formation as well as the build up of a marine ice body, resulting from accretion of marine ice, is simulated, indicating strong interaction processes. To improve consistency between modeled and observed ice shelf behavior, we incorporate the typical cycle of steady ice front advance and sudden retreat due to tabular iceberg calving in our time-dependent simulations. Our basic hypothesis is that iceberg break off is associated with abrupt crack propagation along elongated anomalies of the inherent stress field of the ice body. This new concept yields glaciologically plausible results and represents an auspicious basis for the development of a thorough calving criterion. Experiments under different climatic conditions (ocean warming of 0.2 and 0.5 °C and doubled surface accumulation rates) show the coupled model system to be sensitive especially to ocean warming. Increased basal melt rates of 100% for the 0.5 °C ocean warming scenario and an asymmetric development of ice shelf thicknesses suggest a high vulnerability of ice shelf regions, which represent pivotal areas between the Antarctic Ice Sheet and the Southern Ocean.

Chlorine-containing salts as water ice nucleating particles on Mars

NASA Astrophysics Data System (ADS)

Santiago-Materese, D. L.; Iraci, L. T.; Clapham, M. E.; Chuang, P. Y.

2018-03-01

Water ice cloud formation on Mars largely is expected to occur on the most efficient ice nucleating particle available. Salts have been observed on the Martian surface and have been known to facilitate water cloud formation on Earth. We examined heterogeneous ice nucleation onto sodium chloride and sodium perchlorate substrates under Martian atmospheric conditions, in the range of 150 to 180 K and 10-7 to 10-5 Torr water partial pressure. Sub-155 K data for the critical saturation ratio (Scrit) suggests an exponential model best describes the temperature-dependence of nucleation onset of water ice for all substrates tested. While sodium chloride does not facilitate water ice nucleation more easily than bare silicon, sodium perchlorate does support depositional nucleation at lower saturation levels than other substrates shown and is comparable to smectite-rich clay in its ability to support cloud initiation. Perchlorates could nucleate water ice at partial pressures up to 40% lower than other substrates examined to date under Martian atmospheric conditions. These findings suggest air masses on Mars containing uplifted salts such as perchlorates could form water ice clouds at lower saturation ratios than in air masses absent similar particles.

Developing A Model for Lake Ice Phenology Using Satellite Remote Sensing Observations

NASA Astrophysics Data System (ADS)

Skoglund, S. K.; Weathers, K. C.; Norouzi, H.; Prakash, S.; Ewing, H. A.

2017-12-01

Many northern temperate freshwater lakes are freezing over later and thawing earlier. This shift in timing, and the resulting shorter duration of seasonal ice cover, is expected to impact ecological processes, negatively affecting aquatic species and the quality of water we drink. Long-term, direct observations have been used to analyze changes in ice phenology, but those data are sparse relative to the number of lakes affected. Here we develop a model to utilize remote sensing data in approximating the dates of ice-on and ice-off for many years over a variety of lakes. Day and night surface temperatures from MODIS (Moderate Resolution Imaging Spectroradiometer) Aqua and Terra (MYD11A1 and MOD11A1 data products) for 2002-2017 were utilized in combination with observed ice-on and ice-off dates of Lake Auburn, Maine, to determine the ability of MODIS data to match ground-based observations. A moving average served to interpolate MODIS temperature data to fill data gaps from cloudy days. The nighttime data were used for ice-off, and the daytime measurements were used for ice-on predictions to avoid fluctuations between day and night ice/water status. The 0˚C intercepts of those data were used to mark approximate days of ice-on or ice-off. This revealed that approximations for ice-off dates were satisfactory (average ±8.2 days) for Lake Auburn as well as for Lake Sunapee, New Hampshire (average ±8.1 days), while approximations for Lake Auburn ice-on were less accurate and showed consistently earlier-than-observed ice-on dates (average -33.8 days). The comparison of observed and remotely sensed Lake Auburn ice cover duration showed relative agreement with a correlation coefficient of 0.46. Other remote sensing observations, such as the new GOES-R satellite, and further exploration of the ice formation process can improve ice-on approximation methods. The model shows promise for estimating ice-on, ice-off, and ice cover duration for northern temperate lakes.

Oceanographic Controls on the Variability of Ice-Shelf Basal Melting and Circulation of Glacial Meltwater in the Amundsen Sea Embayment, Antarctica

NASA Astrophysics Data System (ADS)

Kimura, Satoshi; Jenkins, Adrian; Regan, Heather; Holland, Paul R.; Assmann, Karen M.; Whitt, Daniel B.; Van Wessem, Melchoir; van de Berg, Willem Jan; Reijmer, Carleen H.; Dutrieux, Pierre

2017-12-01

Ice shelves in the Amundsen Sea Embayment have thinned, accelerating the seaward flow of ice sheets upstream over recent decades. This imbalance is caused by an increase in the ocean-driven melting of the ice shelves. Observations and models show that the ocean heat content reaching the ice shelves is sensitive to the depth of thermocline, which separates the cool, fresh surface waters from warm, salty waters. Yet the processes controlling the variability of thermocline depth remain poorly constrained. Here we quantify the oceanic conditions and ocean-driven melting of Cosgrove, Pine Island Glacier (PIG), Thwaites, Crosson, and Dotson ice shelves in the Amundsen Sea Embayment from 1991 to 2014 using a general circulation model. Ice-shelf melting is coupled to variability in the wind field and the sea-ice motions over the continental shelf break and associated onshore advection of warm waters in deep troughs. The layer of warm, salty waters at the calving front of PIG and Thwaites is thicker in austral spring (June-October) than in austral summer (December-March), whereas the seasonal cycle at the calving front of Dotson is reversed. Furthermore, the ocean-driven melting in PIG is enhanced by an asymmetric response to changes in ocean heat transport anomalies at the continental shelf break: melting responds more rapidly to increases in ocean heat transport than to decreases. This asymmetry is caused by the inland deepening of bathymetry and the glacial meltwater circulation around the ice shelf.

Subannual layer variability in Greenland firn cores

NASA Astrophysics Data System (ADS)

Kjær, Helle Astrid; Vallelonga, Paul; Vinther, Bo; Winstrup, Mai; Simonsen, Marius; Maffezzoli, Niccoló; Jensen, Camilla Marie

2017-04-01

Ice cores are used to infer information about the past and modern techniques allow for high resolution (< cm) continuous flow analysis (CFA) of the ice. Such analysis is often used to inform on annual layers to constrain dating of ice cores, but can also be extended to provide information on sub-annual deposition patterns. In this study we use available high resolution data from multiple shallow cores around Greenland to investigate the seasonality and trends in the most often continuously measured components sodium, insoluble dust, calcium, ammonium and conductivity (or acidity) from 1800 AD to today. We evaluate the similarities and differences between the records and discuss the causes from different sources and transport to deposition and post-deposition effects over differences in measurement set up. Further we add to the array of cores already published with measurements from the newly drilled ReCAP ice core from a coastal ice cap in eastern Greenland and from a shallow core drilled at the high accumulation site at the Greenland South Dome.

Late glacial ice advances in the Strait of Magellan, Southern Chile

NASA Astrophysics Data System (ADS)

Mcculloch, Robert D.; Bentley, Michael J.

During the last glacial cycle low gradient glaciers repeatedly drained north-eastward into the Strait of Magellan and dammed extensive proglacial lakes in the central section of the strait. This paper focuses on the two most recent glacial advances in the strait, culminating over 150 and 80 km from the present ice limits. The timing of the first of the two advances has, up to now, been ambiguous and depended on the interpretation of anomously older dates of 16,590-15,800 yr BP for deglaciation at Puerto del Hambre. Here, we show there is evidence from seismic data and truncated shorelines that the Puerto del Hambre basin has been tectonically displaced and that the dates do not represent minimums for deglaciation. Several other dates show that the advance occurred sometime before 14,260 yr BP. The timing of the second advance has been investigated using a refined tephrochronology for the region, which has also enabled a palaeoshoreline and glaciolacustrine sediments to be linked to a moraine limit. 14C dating of peat and a key tephra layer, above and below the glaciolacustrine deposits, respectively suggest that the advance culminated in the Strait of Magellan between 12,010 and 10,050 yr BP.

The importance of independent chronology in integrating records of past climate change for the 60-8 ka INTIMATE time interval

NASA Astrophysics Data System (ADS)

Brauer, Achim; Hajdas, Irka; Blockley, Simon P. E.; Bronk Ramsey, Christopher; Christl, Marcus; Ivy-Ochs, Susan; Moseley, Gina E.; Nowaczyk, Norbert N.; Rasmussen, Sune O.; Roberts, Helen M.; Spötl, Christoph; Staff, Richard A.; Svensson, Anders

2014-12-01

This paper provides a brief overview of the most common dating techniques applied in palaeoclimate and palaeoenvironmental studies including four radiometric and isotopic dating methods (radiocarbon, 230Th disequilibrium, luminescence, cosmogenic nuclides) and two incremental methods based on layer counting (ice layer, varves). For each method, concise background information about the fundamental principles and methodological approaches is provided. We concentrate on the time interval of focus for the INTIMATE (Integrating Ice core, MArine and TErrestrial records) community (60-8 ka). This dating guide addresses palaeoclimatologists who aim at interpretation of their often regional and local proxy time series in a wider spatial context and, therefore, have to rely on correlation with proxy records obtained from different archives from various regions. For this reason, we especially emphasise scientific approaches for harmonising chronologies for sophisticated and robust proxy data integration. In this respect, up-to-date age modelling techniques are presented as well as tools for linking records by age equivalence including tephrochronology, cosmogenic 10Be and palaeomagnetic variations. Finally, to avoid inadequate documentation of chronologies and assure reliable correlation of proxy time series, this paper provides recommendations for minimum standards of uncertainty and age datum reporting.

Implications of a electroweak triplet scalar leptoquark on the ultra-high energy neutrino events at IceCube

NASA Astrophysics Data System (ADS)

Mileo, Nicolas; de la Puente, Alejandro; Szynkman, Alejandro

2016-11-01

We study the production of scalar leptoquarks at IceCube, in particular, a particle transforming as a triplet under the weak interaction. The existence of electroweak-triplet scalars is highly motivated by models of grand unification and also within radiative seesaw models for neutrino mass generation. In our framework, we extend the Standard Model by a single colored electroweak-triplet scalar leptoquark and analyze its implications on the excess of ultra-high energy neutrino events observed by the IceCube collaboration. We consider only couplings between the leptoquark to first generation of quarks and first and second generations of leptons, and carry out a statistical analysis to determine the parameters that best describe the IceCube data as well as set 95% CL upper bounds. We analyze whether this study is still consistent with most up-to-date LHC data and various low energy observables.

Multiyear ice transport and small scale sea ice deformation near the Alaska coast measured by air-deployable Ice Trackers

NASA Astrophysics Data System (ADS)

Mahoney, A. R.; Kasper, J.; Winsor, P.

2015-12-01

Highly complex patterns of ice motion and deformation were captured by fifteen satellite-telemetered GPS buoys (known as Ice Trackers) deployed near Barrow, Alaska, in spring 2015. Two pentagonal clusters of buoys were deployed on pack ice by helicopter in the Beaufort Sea between 20 and 80 km offshore. During deployment, ice motion in the study region was effectively zero, but two days later the buoys captured a rapid transport event in which multiyear ice from the Beaufort Sea was flushed into the Chukchi Sea. During this event, westward ice motion began in the Chukchi Sea and propagated eastward. This created new openings in the ice and led to rapid elongation of the clusters as the westernmost buoys accelerated away from their neighbors to the east. The buoys tracked ice velocities of over 1.5 ms-1, with fastest motion occurring closest to the coast indicating strong current shear. Three days later, ice motion reversed and the two clusters became intermingled, rendering divergence calculations based on the area enclosed by clusters invalid. The data show no detectable difference in velocity between first year and multiyear ice floes, but Lagrangian timeseries of SAR imagery centered on each buoy show that first year ice underwent significant small-scale deformation during the event. The five remaining buoys were deployed by local residents on prominent ridges embedded in the landfast ice within 16 km of Barrow in order to track the fate of such features after they detached from the coast. Break-up of the landfast ice took place over a period of several days and, although the buoys each initially followed a similar eastward trajectory around Point Barrow into the Beaufort Sea, they rapidly dispersed over an area more than 50 km across. With rapid environmental and socio-economic change in the Arctic, understanding the complexity of nearshore ice motion is increasingly important for predict future changes in the ice and the tracking ice-related hazards contaminants entrained in the ice. This work demonstrates the ability of low-cost easily-deployable Ice Trackers to generate to generate data of both scientific and operational value.

Structural Continuum Modeling of Space Shuttle External Tank Foam Insulation

NASA Technical Reports Server (NTRS)

Steeve, Brian; Ayala, Sam; Purlee, T. Eric; Shaw, Phillip

2006-01-01

This document is a viewgraph presentation reporting on work in modeling the foam insulation of the Space Shuttle External Tank. An analytical understanding of foam mechanics is required to design against structural failure. The Space Shuttle External Tank is covered primarily with closed cell foam to: Prevent ice, Protect structure from ascent aerodynamic and engine plume heating, and Delay break-up during re-entry. It is important that the foam does not shed unacceptable debris during ascent environment. Therefore a modeling of the foam insulation was undertaken.

Glacial-Geomorphological Evidence for Past Ice Cover in the Western Amundsen Sea Embayment of Antarctica

NASA Astrophysics Data System (ADS)

Roberts, S. J.; Johnson, J.; Ireland, L.; Rood, D. H.; Schaefer, J. M.; Whitehouse, P. L.; Pollard, D.

2016-12-01

Reliable model predictions of the future evolution of the West Antarctic Ice Sheet in the Amundsen Sea Embayment of Antarctica are currently hindered by a lack of data on the regional thinning history, particularly to the west of Thwaites Glacier. Our project will fill this critical gap by acquiring glacial-geological data, in particular, a high density of cosmogenic exposure ages that record ice sheet changes in the western Amundsen Sea Embayment over the past 20,000 years. In 2015/6, during the first of two field seasons in the region, we collected glacial-geomorphological evidence and cosmogenic surface exposure dating samples to constrain past ice cover of nunataks around Mt Murphy, which are adjacent to the Pope Glacier. The presence of abundant rounded granite and gneiss cobbles perched on bedrock ridges and terraces up to 885 m asl, as well as extensive striated bedrock above this height, indicate that ice was much thicker in the past. We also present preliminary results from a novel study on Turtle Rock, a key site for understanding past fluctuations of Pope Glacier. We used an unmanned aerial vehicle (UAV) to map the geomorphology of selected areas in greater detail than is currently possible from high-resolution satellite imagery, and ground-truthed the data by measuring the size, orientation and lithological composition of erratic cobbles and boulders. Combined with surface exposure dating, we will use these datasets to determine whether there were multiple phases of ice overriding, and the timing of thinning of Pope Glacier since the Last Glacial Maximum.

Seasonal Ice Zone Reconnaissance Surveys Coordination

DTIC Science & Technology

2013-09-30

of SIZRS are covered in separate reports. Our long-term goal is to track and understand the interplay among the ice, atmosphere, and ocean...OMB control number. 1. REPORT DATE 30 SEP 2013 2. REPORT TYPE 3. DATES COVERED 00-00-2013 to 00-00-2013 4. TITLE AND SUBTITLE Seasonal Ice Zone...sensing resources include MODIS visible and IR imagery, NSIDC ice extent charts based on a composite of passive microwave products (http://nsidc.org

First Younger Dryas moraines in Greenland

NASA Astrophysics Data System (ADS)

Funder, Svend; Larsen, Nicolaj K.; Linge, Henriette; Möller, Per; Schomacker, Anders; Fabel, Derek; Kjær, Kurt H.; Xu, Sheng

2016-04-01

Over the Greenland ice sheet the Younger Dryas (YD) cold climate oscillation (12.9-11.7 kaBP) began with up to 10°C drop in temperatures and ended with up to 12°C abrupt warming. In the light of the present warming and melting of the ice sheet, and its importance for future climate change, the ice sheet's response to these dramatic changes in the past is of great interest. However, even though much effort has gone into charting YD ice margin behaviour around Greenland in recent years, no clear-cut signal of response to the oscillation has been uncovered. Here we show evidence to suggest that three major outlets from a local ice cap at Greenland's north coast advanced and retreated synchronously during YD. The evidence comprises OSL (optically stimulated luminescence) dates from a marine transgression of the coastal valleys that preceded the advance, and exposure ages from boulders on the moraines, formed by glaciers that overrode the marine sediment. The OSL ages suggest a maximum age of 12.4 ±0.6 kaBP for the marine incursion, and 10 exposure ages on boulders from the three moraines provide an average minimum age of 12.5 ±0.7 kaBP for the moraines, implying that the moraines were formed within the interval 11.8-13.0 kaBP. Elsewhere in Greenland evidence for readvance has been recorded in two areas. Most notably, in the East Greenland fjord zone outlet glaciers over a stretch of 800 km coast advanced through the fjords. In Scoresby Sund, where the moraines form a wide belt, an extensive 14C and exposure dating programme has shown that the readvance here probably culminated before YD, while cessation of moraine formation and rapid retreat from the moraine belt did not commence until c. 11.5 kaBP, but no moraines have so far been dated to YD. Readvance is also seen in Disko Bugt, the largest ice sheet outlet in West Greenland. However, here the advance and retreat of the ice stream took place in mid YD times, and lasted only a few hundred years, while YD in general was characterised by large scale, more than 200 km, retreat on the shelf. Therefore, although readvance and retreat occurred in both areas, the readvance was apparently not triggered by the initial YD cooling nor was the retreat caused by the abrupt warming at the end. At all other sites with a record that run through or into YD - Southeast Greenland, South Greenland, northern West Greenland - the ice margins were apparently retreating through YD, leaving the north coast as the only area with evidence for a climatically conditioned YD readvance/retreat. The apparent mismatch between ice core temperatures and ice margin behaviour is generally seen as a function of reduced AMOC (Atlantic Meridional Overturning Circulation), inducing both higher seasonality with very cold winters and warm summers, and also occurrence of warm subsurface water to melt the ice sheet margin along some coasts. Therefore the ice margin response to the cold oscillation was to some extent determined by the nearness to the North Atlantic - with North Greenland being the farthest away. Although this may explain why glaciers advanced in North Greenland, while they melted in more southerly parts, it still leaves the question with a bearing on the future: why don't we see any ice margin response neither to the initial YD cooling, nor to the abrupt warming at the end?

Moisture transport and Atmospheric circulation in the Arctic

NASA Astrophysics Data System (ADS)

Woods, Cian; Caballero, Rodrigo

2013-04-01

Cyclones are an important feature of the Mid-Latitudes and Arctic Climates. They are a main transporter of warm moist energy from the sub tropics to the poles. The Arctic Winter is dominated by highly stable conditions for most of the season due to a low level temperature inversion caused by a radiation deficit at the surface. This temperature inversion is a ubiquitous feature of the Arctic Winter Climate and can persist for up to weeks at a time. The inversion can be destroyed during the passage of a cyclone advecting moisture and warming the surface. In the absence of an inversion, and in the presence of this warm moist air mass, clouds can form quite readily and as such influence the radiative processes and energy budget of the Arctic. Wind stress caused by a passing cyclones also has the tendency to cause break-up of the ice sheet by induced rotation, deformation and divergence at the surface. For these reasons, we wish to understand the mechanisms of warm moisture advection into the Arctic from lower latitudes and how these mechanisms are controlled. The body of work in this area has been growing and gaining momentum in recent years (Stramler et al. 2011; Morrison et al. 2012; Screen et al. 2011). However, there has been no in depth analysis of the underlying dynamics to date. Improving our understanding of Arctic dynamics becomes increasingly important in the context of climate change. Many models agree that a northward shift of the storm track is likely in the future, which could have large impacts in the Arctic, particularly the sea ice. A climatology of six-day forward and backward trajectories starting from multiple heights around 70 N is constructed using the 22 year ECMWF reanalysis dataset (ERA-INT). The data is 6 hourly with a horizontal resolution of 1 degree on 16 pressure levels. Our methodology here is inspired by previous studies examining flow patterns through cyclones in the mid-latitudes. We apply these earlier mid-latitude methods in the Arctic. We investigate an Arctic trajectory dataset and provide a phenomenological/descriptive analysis of these trajectories, including key meteorological variables carried along trajectories. The trajectory climatology is linked to a previously established cyclone climatology dataset from Hanley and Caballero (2011). We associate trajectories and the meteorological variables they are carrying to cyclones in this dataset. A climatology of 'Arctic-influencing' cyclones is constructed from the cyclone dataset. The resilience of the polar vortex and its effect on circulation, via blocking and breaking, is examined in relation to our trajectory climatology.

The last glaciation of Bear Peninsula, central Amundsen Sea Embayment of Antarctica: Constraints on timing and duration revealed by in situ cosmogenic 14C and 10Be dating

NASA Astrophysics Data System (ADS)

Johnson, Joanne S.; Smith, James A.; Schaefer, Joerg M.; Young, Nicolás E.; Goehring, Brent M.; Hillenbrand, Claus-Dieter; Lamp, Jennifer L.; Finkel, Robert C.; Gohl, Karsten

2017-12-01

Ice streams in the Pine Island-Thwaites region of West Antarctica currently dominate contributions to sea level rise from the Antarctic ice sheet. Predictions of future ice-mass loss from this area rely on physical models that are validated with geological constraints on past extent, thickness and timing of ice cover. However, terrestrial records of ice sheet history from the region remain sparse, resulting in significant model uncertainties. We report glacial-geological evidence for the duration and timing of the last glaciation of Hunt Bluff, in the central Amundsen Sea Embayment. A multi-nuclide approach was used, measuring cosmogenic 10Be and in situ14C in bedrock surfaces and a perched erratic cobble. Bedrock 10Be ages (118-144 ka) reflect multiple periods of exposure and ice-cover, not continuous exposure since the last interglacial as had previously been hypothesized. In situ14C dating suggests that the last glaciation of Hunt Bluff did not start until 21.1 ± 5.8 ka - probably during the Last Glacial Maximum - and finished by 9.6 ± 0.9 ka, at the same time as ice sheet retreat from the continental shelf was complete. Thickening of ice at Hunt Bluff most likely post-dated the maximum extent of grounded ice on the outer continental shelf. Flow re-organisation provides a possible explanation for this, with the date for onset of ice-cover at Hunt Bluff providing a minimum age for the timing of convergence of the Dotson and Getz tributaries to form a single palaeo-ice stream. This is the first time that timing of onset of ice cover has been constrained in the Amundsen Sea Embayment.

Correlating Ice Cores from Quelccaya Ice Cap with Chronology from Little Ice Age Glacial Extents

NASA Astrophysics Data System (ADS)

Stroup, J. S.; Kelly, M. A.; Lowell, T. V.

2010-12-01

Proxy records indicate Southern Hemisphere climatic changes during the Little Ice Age (LIA; ~1300-1850 AD). In particular, records of change in and around the tropical latitudes require attention because these areas are sensitive to climatic change and record the dynamic interplay between hemispheres (Oerlemans, 2005). Despite this significance, relatively few records exist for the southern tropics. Here we present a reconstruction of glacial fluctuations of Quelccaya Ice Cap (QIC), Peruvian Andes, from pre-LIA up to the present day. In the Qori Kalis valley, extensive sets of moraines exist beginning with the 1963 AD ice margin (Thompson et al., 2006) and getting progressively older down valley. Several of these older moraines can be traced and are continuous with moraines in the Challpa Cocha valley. These moraines have been dated at <1050-1350-AD (Mercer and Palacios, 1977) and interpreted to have been deposited during the Little Ice Age. We present a new suite of surface exposure and radiocarbon dates collected in 2008 and 2009 that constrain the ages of these moraines. Preliminary 10Be ages of boulder surfaces atop the moraines range from ~350-1370 AD. Maximum and minimum-limiting radiocarbon ages bracketing the moraines are ~0-1800 AD. The chronology of past ice cap extents are correlated with ice core records from QIC which show an accumulation increase during ~1500-1700 AD and an accumulation decrease during ~1720-1860 AD (Thompson et al., 1985; 1986; 2006). In addition, other proxy records from Peru and the tropics are correlated with the records at QIC as a means to understand climate conditions during the LIA. This work forms the basis for future modeling of the glacial system during the LIA at QIC and for modeling of past temperature and precipitation regimes at high altitude in the tropics.

Arctic landfast sea ice

NASA Astrophysics Data System (ADS)

Konig, Christof S.

Landfast ice is sea ice which forms and remains fixed along a coast, where it is attached either to the shore, or held between shoals or grounded icebergs. Landfast ice fundamentally modifies the momentum exchange between atmosphere and ocean, as compared to pack ice. It thus affects the heat and freshwater exchange between air and ocean and impacts on the location of ocean upwelling and downwelling zones. Further, the landfast ice edge is essential for numerous Arctic mammals and Inupiat who depend on them for their subsistence. The current generation of sea ice models is not capable of reproducing certain aspects of landfast ice formation, maintenance, and disintegration even when the spatial resolution would be sufficient to resolve such features. In my work I develop a new ice model that permits the existence of landfast sea ice even in the presence of offshore winds, as is observed in mature. Based on viscous-plastic as well as elastic-viscous-plastic ice dynamics I add tensile strength to the ice rheology and re-derive the equations as well as numerical methods to solve them. Through numerical experiments on simplified domains, the effects of those changes are demonstrated. It is found that the modifications enable landfast ice modeling, as desired. The elastic-viscous-plastic rheology leads to initial velocity fluctuations within the landfast ice that weaken the ice sheet and break it up much faster than theoretically predicted. Solving the viscous-plastic rheology using an implicit numerical method avoids those waves and comes much closer to theoretical predictions. Improvements in landfast ice modeling can only verified in comparison to observed data. I have extracted landfast sea ice data of several decades from several sources to create a landfast sea ice climatology that can be used for that purpose. Statistical analysis of the data shows several factors that significantly influence landfast ice distribution: distance from the coastline, ocean depth, as well as the strength of offshore winds during nine out of the twelve months each year. Additionally, I identify regions where landfast ice appearance has been increasing or decreasing over the observed time span.

Dating of 30m ice cores drilled by Japanese Antarctic Research Expedition and environmental change study

NASA Astrophysics Data System (ADS)

Motoyama, H.; Suzuki, T.; Fukui, K.; Ohno, H.; Hoshina, Y.; Hirabayashi, M.; Fujita, S.

2017-12-01

1. Introduction It is possible to reveal the past climate and environmental change from the ice core drilled in polar ice sheet and glaciers. The 54th Japanese Antarctic Research Expedition conducted several shallow core drillings up to 30 m depth in the inland and coastal areas of the East Antarctic ice sheet. Ice core sample was cut out at a thickness of about 5 cm in the cold room of the National Institute of Polar Research, and analyzed ion, water isotope, dust and so one. We also conducted dielectric profile measurement (DEP measurement). The age as a key layer of large-scale volcanic explosion was based on Sigl et al. (Nature Climate Change, 2014). 2. Inland ice core Ice cores were collected at the NDF site (77°47'14"S, 39°03'34"E, 3754 m.a.s.l.) and S80 site (80°00'00"S, 40°30'04"E, 3622 m.a.s.l.). Dating of ice core was done as follows. Calculate water equivalent from core density. Accumulate water equivalent from the surface. Approximate the relation of depth - cumulative water equivalent by a quartic equation. We determined the key layer with nssSO42 - peak corresponding to several large volcanic explosions. The accumulation rate was kept constant between the key layers. As a result, NDF was estimated to be around 1360 AD and S80 was estimated to be around 1400 AD in the deepest ice core. 3. Coastal ice core An ice core was collected at coastal H15 sites (69°04'10"S, 40°44'51"E, 1030 m.a.s.l.). Dating of ice core was done as follows. Calculate water equivalent from ice core density. Accumulate water equivalent from the surface. Approximate the relation of depth - cumulative water equivalent by a quartic equation. Basically we decided to summer (December) and winter (June) due to the seasonal change of the water isotope (δD or δ18O). In addition to the seasonal change of isotope, confirm the following. Maximum of SO42- / Na +, which is earlier in time than the maximum of water isotope. Maximum of MSA at about the same time as the maximum of the water isotope. Na+ is maximal immediately after the local maximum of the water isotope. The deepest age was estimated to be around 1940 AD. 4. Example of results In the inland area, the annual average surface mass balance decreased from 1450 to 1850 AD, but it has increased since 1850 AD. The annual mass balance of coastal H15 is consistent with the result of snow stake measurement.

Extensive MIS 3 glaciation in southernmost Patagonia revealed by cosmogenic nuclide dating of outwash sediments

NASA Astrophysics Data System (ADS)

Darvill, Christopher M.; Bentley, Michael J.; Stokes, Chris R.; Hein, Andrew S.; Rodés, Ángel

2015-11-01

The timing and extent of former glacial advances can demonstrate leads and lags during periods of climatic change and their forcing, but this requires robust glacial chronologies. In parts of southernmost Patagonia, dating pre-global Last Glacial Maximum (gLGM) ice limits has proven difficult due to post-deposition processes affecting the build-up of cosmogenic nuclides in moraine boulders. Here we provide ages for the Río Cullen and San Sebastián glacial limits of the former Bahía Inútil-San Sebastián (BI-SSb) ice lobe on Tierra del Fuego (53-54°S), previously hypothesised to represent advances during Marine Isotope Stages (MIS) 12 and 10, respectively. Our approach uses cosmogenic 10Be and 26Al exposure dating, but targets glacial outwash associated with these limits and uses depth-profiles and surface cobble samples, thereby accounting for surface deflation and inheritance. The data reveal that the limits formed more recently than previously thought, giving ages of 45.6 ka (+139.9/-14.3) for the Río Cullen, and 30.1 ka (+45.6/-23.1) for the San Sebastián limits. These dates indicate extensive glaciation in southern Patagonia during MIS 3, prior to the well-constrained, but much less extensive MIS 2 (gLGM) limit. This suggests the pattern of ice advances in the region was different to northern Patagonia, with the terrestrial limits relating to the last glacial cycle, rather than progressively less extensive glaciations over hundreds of thousands of years. However, the dates are consistent with MIS 3 glaciation elsewhere in the southern mid-latitudes, and the combination of cooler summers and warmer winters with increased precipitation, may have caused extensive glaciation prior to the gLGM.

Invasive Species Science Update (No. 8)

Treesearch

Dean Pearson; Yvette Ortega; Jack Butler

2015-01-01

Invasive Species Science Updates are designed to keep managers and other users up-to-date with recently completed and ongoing research by RMRS scientists, as well as highlight breaking news related to invasive species issues. The newsletter is produced by the RMRS Invasive Species Working Group (ISWG), which is a core group of scientists who volunteer to coordinate...

Invasive Species Science Update (No. 7)

Treesearch

Dean Pearson; Yvette Ortega; Jack Butler

2014-01-01

Invasive Species Science Updates are designed to keep managers and other users up-to-date with recently completed and ongoing research by RMRS scientists, as well as highlight breaking news related to invasive species issues. The newsletter is produced by the RMRS Invasive Species Working Group (ISWG), which is a core group of scientists who volunteer to coordinate...

Invasive Species Science Update (No. 9)

Treesearch

Justin Runyon

2017-01-01

This newsletter is designed to keep managers and other users up-to-date with recently completed and ongoing research by RMRS scientists, as well as to highlight breaking news related to invasive species issues. The newsletter is produced by the RMRS Invasive Species Working Group (ISWG), a core group of scientists who volunteer to disseminate RMRS invasive species...

Late mid-Holocene sea-level oscillation: A possible cause

NASA Astrophysics Data System (ADS)

Scott, D. B.; Collins, E. S.

Sea level oscillated between 5500 and 3500 years ago at Murrells Inlet, South Carolina, Chezzetcook and Baie Verte, Nova Scotia and Montmagny, Quebec. The oscillation is well constrained by foraminiferal marsh zonations in three locations and by diatoms in the fourth one. The implications are: (1) there was a eustatic sea-level oscillation of about 2-10 m in the late mid-Holocene on the southeast coast of North America (South Carolina to Quebec) that is not predicted by present geophysical models of relative sea-level change; (2) this oscillation coincides with oceanographic cooling on the east coast of Canada that we associate with melting ice; and (3) this sea- level oscillation/climatic event coincides exactly with the end of pyramid building in Egypt which is suggested to have resulted from a climate change (i.e. drought, cooling). This sea-level/climatic change is a prime example of feedback where climatic warming in the mid-Holocene promoted ice melt in the Arctic which subsequently caused climatic cooling by opening up Arctic channels releasing cold water into the Inner Labrador Current that continued to intensify until 4000 years ago. This sea-level event may also be the best way of measuring when the final ice melted since most estimates of the ages of the last melting are based on end moraine dates in the Arctic which may not coincide with when the last ice actually melted out, since there is no way of dating the final ice positions.

Great Lakes Demonstration 2

DTIC Science & Technology

2012-06-01

A-8 Figure A-12. Laser fluorometer...District Response Advisory Team DRMM Dynamic Risk Management Model EPA Environmental Protection Agency FL Laser fluorometer FOSC Federal On-Scene...this tactic. During this evolution the Hollyhock experimented applying its ice-breaking capabilities to cut channels and pockets into the ice for oil

Downslope flow across the Ross Sea shelf break (Antarctica)

NASA Astrophysics Data System (ADS)

Bergamasco, A.; Budillon, G.; Carniel, S.; Defendi, V.; Meloni, R.; Paschini, E.; Sclavo, M.; Spezie, G.

2003-12-01

The analysis of some high-resolution hydrological data sets acquired during the 1997, 1998, 2001 and 2003 austral summers across the Ross Sea continental shelf break are here presented. The main focus of these cruises carried out in the framework of the Italian National Antarctic Program was the investigation of the downslope flow of the dense waters originated inside the Ross Sea. Such dense waters, flow near the bottom and, reaching the continental shelf break, ventilate the deep ocean. Two Antarctic continental shelf mechanisms can originate dense and deep waters. The former mechanism involves the formation, along the Victoria Land coasts, of a dense and saline water mass, the High Salinity Shelf Water (HSSW). The HSSW formation is linked to the rejection of salt into the water column as sea ice freezes, especially during winter, in the polynya areas, where the ice is continuously pushed offshore by the strong katabatic winds. The latter one is responsible of the formation of a supercold water mass, the Ice Shelf Water (ISW). The salt supplied by the HSSW recirculated below the Ross Ice Shelf, the latent heat of melting and the heat sink provided by the Ross Ice Shelf give rise to plumes of ISW, characterized by temperatures below the sea-surface freezing point. The dense shelf waters migrate to the continental shelf-break, spill over the shelf edge and descend the continental slope as a shelf-break gravity current, subject to friction and possibly enhanced by topographic channelling. Friction, in particular, breaks the constraint of potential vorticity conservation, counteracting the geostrophic tendency for along slope flow. The density-driven downslope motion or cascading entrains ambient water, namely the lower layer of the CDW, reaches a depth where density is the same and spreads off-slope. In fact, the cascading event is inhibited by friction without entrainment. The downslope processes are important for the ocean and climate system because they play a crucial role in the formation of oceanic deep water responsible for ocean/continental shelf exchange of organic carbon, suspended material and dissolved gases around Antarctica. In this context, this work presents the analysis of the 1997, 2001 and 2003 high-resolution surveys carried out in the western Ross Sea near Cape Adare, where the HSSW flows down the continental slope. The second study area was investigated during the 1998 survey of the Italian National Programme for Antarctic Research of the CLIMA Project, in order to follow the ISW overflow path at the shelf break in the central Ross Sea. A 3D primitive equation model was also implemented as a first step in the construction of a high-resolution process study model to explore the dynamical constraints involved in the downslope motion.

Brinicles as a case of inverse chemical gardens.

PubMed

Cartwright, Julyan H E; Escribano, Bruno; González, Diego L; Sainz-Díaz, C Ignacio; Tuval, Idan

2013-06-25

Brinicles are hollow tubes of ice from centimeters to meters in length that form under floating sea ice in the polar oceans when dense, cold brine drains downward from sea ice to seawater close to its freezing point. When this extremely cold brine leaves the ice, it freezes the water it comes into contact with: a hollow tube of ice-a brinicle-growing downward around the plume of descending brine. We show that brinicles can be understood as a form of the self-assembled tubular precipitation structures termed chemical gardens, which are plantlike structures formed on placing together a soluble metal salt, often in the form of a seed crystal, and an aqueous solution of one of many anions, often silicate. On one hand, in the case of classical chemical gardens, an osmotic pressure difference across a semipermeable precipitation membrane that filters solutions by rejecting the solute leads to an inflow of water and to its rupture. The internal solution, generally being lighter than the external solution, flows up through the break, and as it does so, a tube grows upward by precipitation around the jet of internal solution. Such chemical-garden tubes can grow to many centimeters in length. In the case of brinicles, on the other hand, in floating sea ice we have porous ice in a mushy layer that filters out water, by freezing it, and allows concentrated brine through. Again there is an osmotic pressure difference leading to a continuing ingress of seawater in a siphon pump mechanism that is sustained as long as the ice continues to freeze. Because the brine that is pumped out is denser than the seawater and descends rather than rises, a brinicle is a downward-growing tube of ice, an inverse chemical garden.

Foehn and temperature-based melt patterns over the Larsen C Ice Shelf as simulated by the MAR regional climate model

NASA Astrophysics Data System (ADS)

Datta, R.; Tedesco, M.; Agosta, C.; Fettweis, X.; Kuipers Munneke, P.; van den Broeke, M. R.

2017-12-01

Surface melting has been implicated in the collapse of Antarctic Peninsula ice shelves, most dramatically in the Larsen A (1995) and Larsen B (2002) ice shelves. In July of this year, a rift in the remaining Larsen C ice shelf broke away one of the largest icebergs ever recorded. Ice-shelf retreat is likely related to strong atmospheric warming in this area, by means of hydrofracturing and possibly by the warming atmosphere itself. According the hydrofracture mechanism, meltwater produced during anomalously warm summers infiltrates and deepens pre-existent crevasses, leading to the eventual break-up of the ice shelf. In addition to region-wide warming, melting in the East Antarctic Peninsula can be caused by frequent intrusions of westerly foehn winds. The remaining Larsen C ice shelf, as well as glaciers previously feeding to the former Larsen B ice shelf, are therefore vulnerable to both (a) the atmospheric circulation patterns that influence foehn wind frequency and intensity and (b) regional interannual temperature trends. We discuss spatial patterns of meltwater production in the northeast basin of the Antarctic Peninsula as modeled by the Modèle Atmosphérique Régionale (MAR) at a 10km resolution between 2001 and 2014. The timeseries associated with these patterns are used to identify interannual changes in the frequency of foehn-induced melt, and compare foehn-induced melting to melt associated with regional warming. Melt occurrence in MAR is evaluated against multiple satellite datasets and near-surface automatic weather station data from three sites. Finally, we discuss the seasonal depth to which meltwater percolates into the snowpack (as modeled by MAR) because of the potential influence of meltwater on both warming and densification of the ice shelf.

Experimental Measurement of Frozen and Partially Melted Water Droplet Impact Dynamics

NASA Technical Reports Server (NTRS)

Palacios, Jose; Yan, Sihong; Tan, Jason; Kreeger, Richard E.

2014-01-01

High-speed video of single frozen water droplets impacting a surface was acquired. The droplets diameter ranged from 0.4 mm to 0.9 mm and impacted at velocities ranging from 140 m/sec to 309 m/sec. The techniques used to freeze the droplets and launch the particles against the surfaces is described in this paper. High-speed video was used to quantify the ice accretion area to the surface for varying impact angles (30 deg, 45 deg, 60 deg), impacting velocities, and break-up angles. An oxygen /acetylene cross-flow flame used to ensure partial melting of the traveling frozen droplets is also discussed. A linear relationship between impact angle and ice accretion is identified for fully frozen particles. The slope of the relationship is affected by impact speed. Perpendicular impacts, i.e. 30 deg, exhibited small differences in ice accretion for varying velocities, while an increase of 60% in velocity from 161 m/sec to 259 m/sec, provided an increase on ice accretion area of 96% at an impact angle of 60 deg. The increase accretion area highlights the importance of impact angle and velocity on the ice accretion process of ice crystals. It was experimentally observed that partial melting was not required for ice accretion at the tested velocities when high impact angles were used (45 and 60 deg). Partially melted droplets doubled the ice accretion areas on the impacting surface when 0.0023 Joules were applied to the particle. The partially melted state of the droplets and a method to quantify the percentage increase in ice accretion area is also described in the paper.

Photographer: JPL P-21758 BW Range: 246,000 kilometers (152,000 miles) This picture by Voyager 2 is

NASA Technical Reports Server (NTRS)

1979-01-01

Photographer: JPL P-21758 BW Range: 246,000 kilometers (152,000 miles) This picture by Voyager 2 is the first close look ever obtained of Jupiter's satellite, Europa. The linear crack-like features had been seen from a much greater distance by Voyager 1 but this image provides a resolution of about four kilometers (2.5 miles). The complicated linear features appear even more like cracks or huge fractures in these images. Also seen are somewhat darker mottled regions which appear to have a slightly pitted appearance, perhaps due to small scale craters. No large craters (more than five kilometers in diameter) are easily identifiable in the Europa photographs to date, suggesting that this satellite has a young surface relative to Ganymede and Callisto, although not perhaps as young as Io's. Various models for Europa's structure will be tested during analysis of these images, including the possibility that the surface is a thin ice crust overlying water or softer ice and that the fracture systems seen are breaks in that crust. Resurfacing mechanisms such as production of fresh ice or snow along the cracks and cold glacier-like flows are being considered as possibilities for removing evidence of impact events. Europa thus appears to truly be a satellite with many properties intermediate between Ganymede and Io.

Europa Linear Features from 246,000 kilometers

NASA Technical Reports Server (NTRS)

1979-01-01

The first close look ever obtained of Jupiter's satellite, Europa, was taken today, July 9, by Voyager 2 as the spacecraft approached the planet. The linear crack-like features had been seen from a much greater distance last March by Voyager 1. This picture was made at a range of 246,000 kilometers (152,000 miles) and provides a resolution of about four kilometers (2.5 miles). The complicated linear features appear even more like cracks or huge fractures in these images. Also seen are somewhat darker mottled regions which appear to have a slightly pitted appearance, perhaps due to small scale craters. No large craters (more than five kilometers in diameter) are easily identifiable in the Europa photographs to date, suggesting that this satellite has a young surface relative to Ganymede and Callisto, although not perhaps as young as Io's. Various models for Europa's structure will be tested during analysis of these images, including the possibility that the surface is a thin ice crust overlying water or softer ice and that the fracture systems seen are breaks in that crust. Resurfacing mechanisms such as production of fresh ice or snow along the cracks and cold glacier-like flows are being considered as possibilities for removing evidence of impact events. Europa thus appears to truly be a satellite with many properties intermediate between Ganymede and Io.

East Antarctic ice-sheet dynamics between 5.2 and 0 Ma from a high-resolution terrigenous particle size record, ODP Site 1165, Prydz Bay-Cooperation Sea

USGS Publications Warehouse

Passchier, S.

2007-01-01

This paper discusses a 5.2-0 Ma high-resolution terrigenous particle size record recovered from a sediment drift off East Antarctica. The particle size properties of Hole 1165B are interpreted in the context of previously acquired data on a continental shelf to slope transect drilled by ODP Leg 188 in Prydz Bay and the Cooperation Sea. The new data indicate that the Lambert ice stream stayed predominantly landward of the shelf break in the early Pliocene (5.2-3.5 Ma) with periods of ice sheet recession on land. The middle Pliocene (3.5-3.1 Ma) is characterized as major ice expansion during glacials with deposition of laminated clays from meltwater plumes on the continental rise, alternating with periods of ice recession. A change in sedimentary facies and a decrease in sedimentation rates occurred at ~3.1 Ma indicating a more retreated Lambert Glacier. Between 2.5 and 1 Ma the ice stream was generally stable and had become cold-based with ice flow in a glacial trough extending to the shelf break. Three-four large pulses of coarse-grained glacigenic debris mark the record at ~1 Ma. These are interpreted as extensive calving due to decoupling of the marine terminus from its bed in response to Northern Hemisphere deglaciations and associated sea level rises.

The deglacial history of NW Alexander Island, Antarctica, from surface exposure dating

NASA Astrophysics Data System (ADS)

Johnson, Joanne S.; Everest, Jeremy D.; Leat, Philip T.; Golledge, Nicholas R.; Rood, Dylan H.; Stuart, Finlay M.

2012-03-01

Recent changes along the margins of the Antarctic Peninsula, such as the collapse of the Wilkins Ice Shelf, have highlighted the effects of climatic warming on the Antarctic Peninsula Ice Sheet (APIS). However, such changes must be viewed in a long-term (millennial-scale) context if we are to understand their significance for future stability of the Antarctic ice sheets. To address this, we present nine new cosmogenic 10Be exposure ages from sites on NW Alexander Island and Rothschild Island (adjacent to the Wilkins Ice Shelf) that provide constraints on the timing of thinning of the Alexander Island ice cap since the last glacial maximum. All but one of the 10Be ages are in the range 10.2-21.7 ka, showing a general trend of progressive ice-sheet thinning since at least 22 ka until 10 ka. The data also provide a minimum estimate (490 m) for ice-cap thickness on NW Alexander Island at the last glacial maximum. Cosmogenic 3He ages from a rare occurrence of mantle xenoliths on Rothschild Island yield variable ages up to 46 ka, probably reflecting exhumation by periglacial processes.

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.

Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics

NASA Astrophysics Data System (ADS)

Greenwood, Sarah L.; Clark, Chris D.

2009-12-01

The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel - Irish Sea Basin in driving such asymmetry, since rapid collapse would sever the ties between the British and Irish Ice Sheets and drive flow configuration changes in response. Enhanced calving and flow acceleration in response to rising relative sea level is speculated to have undermined the integrity of the ice stream system, precipitating its collapse and driving the reconstructed pattern of ice sheet evolution.

Alaska shorefast ice: Interfacing geophysics with local sea ice knowledge and use

NASA Astrophysics Data System (ADS)

Druckenmiller, Matthew L.

This thesis interfaces geophysical techniques with local and traditional knowledge (LTK) of indigenous ice experts to track and evaluate coastal sea ice conditions over annual and inter-annual timescales. A novel approach is presented for consulting LTK alongside a systematic study of where, when, and how the community of Barrow, Alaska uses the ice cover. The goal of this research is to improve our understanding of and abilities to monitor the processes that govern the state and dynamics of shorefast sea ice in the Chukchi Sea and use of ice by the community. Shorefast ice stability and community strategies for safe hunting provide a framework for data collection and knowledge sharing that reveals how nuanced observations by Inupiat ice experts relate to identifying hazards. In particular, shorefast ice break-out events represent a significant threat to the lives of hunters. Fault tree analysis (FTA) is used to combine local and time-specific observations of ice conditions by both geophysical instruments and local experts, and to evaluate how ice features, atmospheric and oceanic forces, and local to regional processes interact to cause break-out events. Each year, the Barrow community builds trails across shorefast ice for use during the spring whaling season. In collaboration with hunters, a systematic multi-year survey (2007--2011) was performed to map these trails and measure ice thickness along them. Relationships between ice conditions and hunter strategies that guide trail placement and risk assessment are explored. In addition, trail surveys provide a meaningful and consistent approach to monitoring the thickness distribution of shorefast ice, while establishing a baseline for assessing future environmental change and potential impacts to the community. Coastal communities in the region have proven highly adaptive in their ability to safely and successfully hunt from sea ice over the last 30 years as significant changes have been observed in the ice zone north of Alaska. This research further illustrates how Barrow's whaling community copes with year-to-year variability and significant intra-seasonal changes in ice conditions. Hence, arctic communities that have coped with such short-term variability may be more adaptive to future environmental change than communities located in less dynamic environments.

Complex astrophysical experiments relating to jets, solar loops, and water ice dusty plasma

NASA Astrophysics Data System (ADS)

Bellan, P. M.; Zhai, X.; Chai, K. B.; Ha, B. N.

2015-10-01

> Recent results of three astrophysically relevant experiments at Caltech are summarized. In the first experiment magnetohydrodynamically driven plasma jets simulate astrophysical jets that undergo a kink instability. Lateral acceleration of the kinking jet spawns a Rayleigh-Taylor instability, which in turn spawns a magnetic reconnection. Particle heating and a burst of waves are observed in association with the reconnection. The second experiment uses a slightly different setup to produce an expanding arched plasma loop which is similar to a solar corona loop. It is shown that the plasma in this loop results from jets originating from the electrodes. The possibility of a transition from slow to fast expansion as a result of the expanding loop breaking free of an externally imposed strapping magnetic field is investigated. The third and completely different experiment creates a weakly ionized plasma with liquid nitrogen cooled electrodes. Water vapour injected into this plasma forms water ice grains that in general are ellipsoidal and not spheroidal. The water ice grains can become quite long (up to several hundred microns) and self-organize so that they are evenly spaced and vertically aligned.

Towards an Ice-Free Arctic Ocean in Summertime

NASA Astrophysics Data System (ADS)

Gascard, Jean Claude

2014-05-01

Dividing the Arctic Ocean in two parts, the so-called Atlantic versus the Pacific sector, two distinct modes of variability appear for characterizing the Arctic sea-ice extent from 70°N up to 80°N in both sectors. The Atlantic sector seasonal sea-ice extent is characterized by a longer time scale than the Pacific sector with a break up melting season starting in May and reaching a peak in June-July, one month earlier than the Pacific sector of the Arctic Ocean revealing a faster time evolution and a larger spatial amplitude than the Atlantic sector. During recent years like 2007, sea-ice extent with sea-ice concentration above 15% retreated from 4 millions km2 to about 1 million km2 in the Arctic Pacific sector between 70° and 80°N except for 2012 when most of sea-ice melted away in this region. That explained most of the differences between the two extreme years 2007 and 2012. In the Atlantic sector, Arctic sea-ice retreated from 2 millions km2 to nearly 0 during recent years including 2007 and 2012. The Atlantic inflow North of Svalbard and Franz Josef Land is more likely responsible for a northward retreat of the ice edge in that region. The important factor is not only that the Arctic summer sea-ice minimum extent decreased by 3 or 4 millions km2 over the past 10 years but also that the melting period was steadily increasing by one to two days every year during that period. An important factor concerns the strength of the freezing that can be quantified in terms of Freezing Degree Days FDD accumulated during the winter-spring season and the strength of the melting (MDD) that can be accumulated during the summer season. FDD and MDD have been calculated for the past 30 years all over the Arctic Ocean using ERA Interim Reanalysis surface temperature at 2m height in the atmosphere. It is clear that FDD decreased significantly by more than 2000 FDD between 1980 and 2012 which is equivalent to the sensible heat flux corresponding to more than a meter of sea-ice thickness. During the same period MDD increased steadily mainly due to an increase of the melting period rather than an increase in summer temperatures. Due to uncertainties in sea-ice thickness distribution, an estimated 66% up to 75% of sea-ice mass or volume melted away during recent summers compare to previous 20 or 30 years. How long would it take to melt away the 1/4 or 1/3 of Arctic sea-ice left in summer? A root mean square extrapolation based on the last 10 years summer sea-ice minimum extent would lead to an ice-free Arctic Ocean by 2035.

Breaking Off of Large Ice Masses From Hanging Glaciers

NASA Astrophysics Data System (ADS)

Pralong, A.; Funk, M.

In order to reduce damage to settlements or other installations (roads, railway, etc) and avoid loss of life, a forecast of the final failure time of ice masses is required. At present, the most promising approach for such a prediction is based on the regularity by which certain large ice masses accelerate prior to the instant of collapse. The lim- itation of this forecast lies in short-term irregularities and in the difficulties to obtain sufficiently accurate data. A better physical understanding of the breaking off process is required, in order to improve the forecasting method. Previous analyze has shown that a stepwise crack extension coupling with a viscous flow leads to the observed acceleration function. We propose another approach by considering a local damage evolution law (gener- alized Kachanow's law) coupled with Glen's flow law to simulate the spatial evolu- tion of damage in polycristalline ice, using a finite element computational model. The present study focuses on the transition from a diffuse to a localised damage reparti- tion occurring during the damage evolution. The influence of inhomogeneous initial conditions (inhomogeneity of the mechanical properties of ice, damage inhomogene- ity) and inhomogeneous boundary conditions on the damage repartition are especially investigated.

Yellow River Icicle Hazard Dynamic Monitoring Using UAV Aerial Remote Sensing Technology

NASA Astrophysics Data System (ADS)

Wang, H. B.; Wang, G. H.; Tang, X. M.; Li, C. H.

2014-02-01

Monitoring the response of Yellow River icicle hazard change requires accurate and repeatable topographic surveys. A new method based on unmanned aerial vehicle (UAV) aerial remote sensing technology is proposed for real-time data processing in Yellow River icicle hazard dynamic monitoring. The monitoring area is located in the Yellow River ice intensive care area in southern BaoTou of Inner Mongolia autonomous region. Monitoring time is from the 20th February to 30th March in 2013. Using the proposed video data processing method, automatic extraction covering area of 7.8 km2 of video key frame image 1832 frames took 34.786 seconds. The stitching and correcting time was 122.34 seconds and the accuracy was better than 0.5 m. Through the comparison of precise processing of sequence video stitching image, the method determines the change of the Yellow River ice and locates accurate positioning of ice bar, improving the traditional visual method by more than 100 times. The results provide accurate aid decision information for the Yellow River ice prevention headquarters. Finally, the effect of dam break is repeatedly monitored and ice break five meter accuracy is calculated through accurate monitoring and evaluation analysis.

Influence of temperature fluctuations on equilibrium
ice sheet volume

NASA Astrophysics Data System (ADS)

Bøgeholm Mikkelsen, Troels; Grinsted, Aslak; Ditlevsen, Peter

2018-01-01

Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing temperatures. The surface mass balance (SMB) of the Greenland Ice Sheet (GrIS) has a nonlinear response to warming. Cold and warm anomalies of equal size do not cancel out and it is therefore important to consider the effect of interannual fluctuations in temperature. We find that the steady-state volume of an ice sheet is biased toward larger size if interannual temperature fluctuations are not taken into account in numerical modeling of the ice sheet. We illustrate this in a simple ice sheet model and find that the equilibrium ice volume is approximately 1 m SLE (meters sea level equivalent) smaller when the simple model is forced with fluctuating temperatures as opposed to a stable climate. It is therefore important to consider the effect of interannual temperature fluctuations when designing long experiments such as paleo-spin-ups. We show how the magnitude of the potential bias can be quantified statistically. For recent simulations of the Greenland Ice Sheet, we estimate the bias to be 30 Gt yr-1 (24-59 Gt yr-1, 95 % credibility) for a warming of 3 °C above preindustrial values, or 13 % (10-25, 95 % credibility) of the present-day rate of ice loss. Models of the Greenland Ice Sheet show a collapse threshold beyond which the ice sheet becomes unsustainable. The proximity of the threshold will be underestimated if temperature fluctuations are not taken into account. We estimate the bias to be 0.12 °C (0.10-0.18 °C, 95 % credibility) for a recent estimate of the threshold. In light of our findings it is important to gauge the extent to which this increased variability will influence the mass balance of the ice sheets.

Arctic sea ice variability during the last deglaciation: a biomarker approach

NASA Astrophysics Data System (ADS)

Müller, J.; Stein, R. H.

2014-12-01

The last transition from full glacial to current interglacial conditions was accompanied by distinct short-term climate fluctuations caused by changes in the global ocean circulation system. Most palaeoceanographic studies focus on the documentation of the behaviour of the Atlantic Meridional Overturning Circulation (AMOC) during the last deglaciation in response to freshwater forcing events. In this respect, the role of Arctic sea ice remained relatively unconsidered - primarily because of the difficulty of its reconstruction. Here we present new proxy data on late glacial (including the Last Glacial Maximum; LGM) and deglacial sea ice variability in the Arctic Ocean and its main gateway - the Fram Strait - and how these changes in sea ice coverage contributed to AMOC perturbations observed during Heinrich Event 1 and the Younger Dryas. Recurrent short-term advances and retreats of sea ice in Fram Strait, prior and during the LGM, are in line with a variable (or intermittent) North Atlantic heat flow along the eastern corridor of the Nordic Seas. Possibly in direct response to the initial freshwater discharge from melting continental ice-sheets, a permanent sea ice cover established only at about 19 ka BP (i.e. post-LGM) and lasted until 17.6 ka BP, when an abrupt break-up of this thick ice cover and a sudden discharge of huge amounts of sea ice and icebergs through Fram Strait coincided with the weakening of the AMOC during Heinrich Event 1. Similarly, another sea ice maximum at about 12.8 ka BP is associated with the slowdown of the AMOC during the Younger Dryas. The new data sets clearly highlight the important role of Arctic sea ice for the re-organisation of the oceanographic setting in the North Atlantic during the last deglaciation. Further studies and sensitivity experiments to identify crucial driving (and feedback) mechanisms within the High Latitude ice-ocean-atmosphere system will contribute the understanding of rapid climate changes.

The Seasonal Evolution of Sea Ice Floe Size Distribution

DTIC Science & Technology

2013-09-30

the summer breakup of the ice cover . Large-scale, lower resolution imagery from MODIS and other platforms will also be analyzed to determine changes...control number. 1. REPORT DATE 30 SEP 2013 2. REPORT TYPE 3. DATES COVERED 00-00-2013 to 00-00-2013 4. TITLE AND SUBTITLE The Seasonal Evolution...appearance and morphology of the Arctic sea ice cover over and annual cycle. These photos were taken over the pack ice near SHEBA in May (left) and

The Seasonal Evolution of Sea Ice Floe Size Distribution

DTIC Science & Technology

2014-09-30

summer breakup of the ice cover . Large-scale, lower resolution imagery from MODIS and other platforms will also be analyzed to determine changes in floe...number. 1. REPORT DATE 30 SEP 2014 2. REPORT TYPE 3. DATES COVERED 00-00-2014 to 00-00-2014 4. TITLE AND SUBTITLE The Seasonal Evolution of Sea...morphology of the Arctic sea ice cover over and annual cycle. These photos were taken over the pack ice near SHEBA in May (left) and August (right

BRITICE-CHRONO: Constraining rates and style of marine-influenced ice sheet decay to provide a data-rich playground for ice sheet modellers

NASA Astrophysics Data System (ADS)

Clark, Chris

2014-05-01

Uncertainty exists regarding the fate of the Antarctic and Greenland ice sheets and how they will respond to forcings from sea level and atmospheric and ocean temperatures. If we want to know more about the mechanisms and rate of change of shrinking ice sheets, then why not examine an ice sheet that has fully disappeared and track its retreat through time? If achieved in enough detail such information could become a data-rich playground for improving the next breed of numerical ice sheet models to be used in ice and sea level forecasting. We regard that the last British-Irish Ice Sheet is a good target for this work, on account of its small size, density of information and with its numerous researchers already investigating it. BRITICE-CHRONO is a large (>45 researchers) NERC-funded consortium project comprising Quaternary scientists and glaciologists who will search the seafloor around Britain and Ireland and parts of the landmass in order to find and extract samples of sand, rock and organic matter that can be dated (OSL; Cosmogenic; 14C) to reveal the timing and rate of change of the collapsing British-Irish Ice Sheet. The purpose is to produce a high resolution dataset on the demise on an ice sheet - from the continental shelf edge and across the marine to terrestrial transition. Some 800 new date assessments will be added to those that already exist. This poster reports on the hypotheses that underpin the work. Data on retreat will be collected by focusing on 8 transects running from the continental shelf edge to a short distance (10s km) onshore and acquiring marine and terrestrial samples for geochronometric dating. The project includes funding for 587 radiocarbon, 140 OSL and 158 TCN samples for surface exposure dating; with sampling accomplished by two research cruises and 16 fieldwork campaigns. Results will reveal the timing and rate of change of ice margin recession for each transect, and combined with existing landform and dating databases, will be used to build an ice sheet-wide empirical reconstruction of retreat incorporating Bayesian analysis to assess uncertainty. We invite and encourage ice sheet modellers to use our data for modelling experiments and in particular to explore the role of bed topography in modulating ice retreat.

Controlled formation of cyclopentane hydrate suspensions via capillary-driven jet break-up

NASA Astrophysics Data System (ADS)

Geri, Michela; McKinley, Gareth

2017-11-01

Clathrate hydrates are crystalline compounds that form when a lattice of hydrogen-bonded water molecules is filled by guest molecules sequestered from an adjacent gas or liquid phase. Being able to rapidly produce and transport synthetic hydrates is of great interest given their significant potential as a clean energy source and safe option for hydrogen storage. We propose a new method to rapidly produce cyclopentane hydrate suspensions at ambient pressure with tunable particle size distribution by taking advantage of the Rayleigh-Plateau instability to form a mono-disperse stream of droplets during the controlled break-up of a water jet. The droplets are immediately frozen into ice particles through immersion in a subcooled reservoir and converted into hydrates with a dramatic reduction in the nucleation induction time. By measuring the evolution of the rheological properties with time, we monitor the process of hydrates formation via surface crystallization and agglomeration with different droplet size distributions. This new method enables us to gain new insights into hydrate formation and transport which was previously hindered by uncontrolled droplet formation and hydrate nucleation processes. MITei Chevron Fellowship.

Evolution of a Greenland Ice sheet Including Shelves and Regional Sea Level Variations

NASA Astrophysics Data System (ADS)

Bradley, Sarah; Reerink, Thomas; van de Wal, Roderik S. W.; Helsen, Michiel; Goelzer, Heiko

2016-04-01

Observational evidence, including offshore moraines and marine sediment cores infer that at the Last Glacial maximum (LGM) the Greenland ice sheet (GIS) grounded out across the Davis Strait into Baffin Bay, with fast flowing ice streams extending out to the continental shelf break along the NW margin. These observations lead to a number of questions as to weather the GIS and Laurentide ice sheet (LIS) coalesced during glacial maximums, and if so, did a significant ice shelf develop across Baffin Bay and how would such a configuration impact on the relative contribution of these ice sheets to eustatic sea level (ESL). Most previous paleo ice sheet modelling simulations of the GIS recreated an ice sheet that either did not extend out onto the continental shelf or utilised a simplified marine ice parameterisation to recreate an extended GIS, and therefore did not fully include ice shelf dynamics. In this study we simulate the evolution of the GIS from 220 kyr BP to present day using IMAU-ice; a 3D thermodynamical ice sheet model which fully accounts for grounded and floating ice, calculates grounding line migration and ice shelf dynamics. As there are few observational estimates of the long-term (yrs) sub marine basal melting rates (mbm) for the GIS, we developed a mbm parameterization within IMAU-ice controlled primarily by changes in paleo water depth. We also investigate the influence of the LIS on the GIS evolution by including relative sea level forcing's derived from a Glacial Isostatic Adjustment model. We will present results of how changes in the mbm directly impacts on the ice sheet dynamics, timing and spatial extent of the GIS at the glacial maximums, but also on the rate of retreat and spatial extent at the Last interglacial (LIG) minimum. Results indicate that with the inclusion of ice shelf dynamics, a larger GIS is generated which is grounded out into Davis strait, up to a water depth of -750 m, but significantly reduces the GIS contribution to Last interglacial ESL.

Polynyas and Ice Production Evolution in the Ross Sea (PIPERS)

NASA Astrophysics Data System (ADS)

Ackley, S. F.

2017-12-01

One focus of the PIPERS cruise into the Ross Sea ice cover during April-June 2017 was the Terra Nova Bay (TNB) polynya where joint measurements of air-ice-ocean wave interaction were conducted over twelve days. In Terra Nova Bay, measurements were made in three katabatic wind events each with sustained winds over 35 ms-1 and air temperatures below -15C. Near shore, intense wave fields with wave amplitudes of over 2m and 7-9 sec periods built and large amounts of frazil ice crystals grew. The frazil ice gathered initially into short and narrow plumes that eventually were added laterally to create longer and wider streaks or bands. Breaking waves within these wider streaks were dampened which appeared to enhance the development of pancake ice. Eventually, the open water areas between the streaks sealed off, developing a complete ice cover of 100 percent concentration (80-90 percent pancakes, 20-10 percent frazil) over a wide front (30km). The pancakes continued to grow in diameter and thickness as waves alternately contracted and expanded the ice cover, with the thicker larger floes further diminishing the wave field and lateral motion between pancakes until the initial pancake ice growth ceased. The equilibrium thickness of the ice was 20-30cm in the pancake ice. While the waves had died off however, katabatic wind velocities were sustained and resulted in a wide area of concentrated, rafted, pancake ice that was rapidly advected downstream until the end of the katabatic event. High resolution TerraSar-X radar satellite imagery showed the length of the ice area produced in one single event extended over 300km or ten times the length of the open water area during one polynya event. The TNB polynya is therefore an "ice factory" where frazil ice is manufactured into pancake ice floes that are then pushed out of the assembly area and advected, rafted (and occasionally piled up into "dragon skin" ice), until the katabatic wind dies off at the coastal source.

Do physical maturity and birth date predict talent in male youth ice hockey players?

PubMed

Sherar, Lauren B; Baxter-Jones, Adam D G; Faulkner, Robert A; Russell, Keith W

2007-06-01

The aim of this study was to examine the relationships among biological maturity, physical size, relative age (i.e. birth date), and selection into a male Canadian provincial age-banded ice hockey team. In 2003, 619 male ice hockey players aged 14-15 years attended Saskatchewan provincial team selection camps, 281 of whom participated in the present study. Data from 93 age-matched controls were obtained from the Saskatchewan Pediatric Bone Mineral Accrual Study (1991-1997). During the initial selection camps, birth dates, heights, sitting heights, and body masses were recorded. Age at peak height velocity, an indicator of biological maturity, was determined in the controls and predicted in the ice hockey players. Data were analysed using one-way analysis of variance, logistic regression, and a Kolmogorov-Smirnov test. The ice hockey players selected for the final team were taller, heavier, and more mature (P < 0.05) than both the unselected players and the age-matched controls. Furthermore, age at peak height velocity predicted (P < 0.05) being selected at the first and second selection camps. The birth dates of those players selected for the team were positively skewed, with the majority of those selected being born in the months January to June. In conclusion, team selectors appear to preferentially select early maturing male ice hockey players who have birth dates early in the selection year.

Chronicling ice shelf history in the sediments left behind

NASA Astrophysics Data System (ADS)

Rosenheim, B. E.; Subt, C.; Shevenell, A.; Guitard, M.; Vadman, K. J.; DeCesare, M.; Wellner, J. S.; Bart, P. J.; Lee, J. I.; Domack, E. W.; Yoo, K. C.; Hayes, J. M.

2017-12-01

Collapsing and retreating ice shelves leave unmistakable sediment sequences on the Antarctic margin. These sequences tell unequivocal stories of collapse or retreat through a typical progression of sub-ice shelf diamicton (marking the past positions of grounding lines), sequentially overlain by a granulated facies from beneath the ice shelf, ice rafted debris from the calving line, and finally open marine sediment. The timelines to these stories, however, are troublesome. Difficulties in chronicling these stories recorded in sediment have betrayed their importance to our understanding of a warming world in many cases. The difficulties involve the concerted lack of preservation/production of calcium carbonate tests from the water column above and admixture of relict organic material from older sources of carbon. Here, we summarize our advances in the last decade of overcoming difficulties associated with the paucity of carbonate and creating chronologies of ice shelf retreat into the deglacial history of Antarctica by exploiting the range of thermochemical stability in organic matter (Ramped PyrOx) from these sediment sequences. We describe our success in comparing Ramped PyrOx 14C dates with foraminiferal dates, the relationship between sediment facies and radiocarbon age spectrum, and our ability to push limits of dating sediments deposited underneath ice shelves. With attention to the caveats of recent dating developments, we summarize expectations that geologist should have when coring the Antarctic margins to discern deglacial history. Perhaps most important among these expectations is the ability to design coring expeditions without regard to our ability to date calcium carbonate microfossils within the cores, in essence removing suspense of knowing whether cores taken from crucial paleo ice channels and other bathymetric features will ultimately yield a robust chronology for its sedimentary sequence.

Lateglacial retreat chronology of the Scandinavian Ice Sheet in Finnmark, northern Norway, reconstructed from surface exposure dating of major end moraines

NASA Astrophysics Data System (ADS)

Romundset, Anders; Akçar, Naki; Fredin, Ola; Tikhomirov, Dmitry; Reber, Regina; Vockenhuber, Christof; Christl, Marcus; Schlüchter, Christian

2017-12-01

We report results from a comprehensive surface exposure dating campaign in eastern Finnmark, located in the northernmost part of Norway and close to the Norwegian-Russian border. This is a palaeo-glaciologically important region as it sits near the proposed border-zone between the former Scandinavian and Barents Sea Ice Sheets. However, until now the deglaciation history has few direct dates onshore and the chronology of ice front retreat is instead found by correlating ice-marginal deposits with isostatically raised shorelines and marine sediment cores. We measured the content of 10Be (N = 22) and 36Cl (N = 17) from boulders located at the crest of major moraine ridges at four localities; Kjæs, Kongsfjorden, Vardø and Kirkenes. These are key localities of existing regional reconstructions of ice recession in this area. Despite some spread in age results from each locality due to methodological challenges associated with surface exposure dating, the large numbers of samples from each site except Kjæs still allow for obtaining clusters of similar ages which are used for arriving at a likely chronology of ice front retreat. Our results show that the Kongsfjorden and Vardø moraines were deposited 14.3 ± 1.7 ka and 13.6 ± 1.4 ka, respectively, and thus point to a Older Dryas age of the proposed 'Outer Porsanger' deglaciation sub-stage. Moraine ridges belonging to the 'Main' sub-stage near Kirkenes were dated to 11.9 ± 1.2 ka, corresponding well with the ice retreat chronology farther west in northern Norway and suggesting that the maximum Younger Dryas ice sheet extent was attained in the late Younger Dryas along a more than 500 km long stretch in northernmost Scandinavia.

Low Force Penetration of Icy Regolith

NASA Technical Reports Server (NTRS)

Mantovani, J. G.; Galloway, G. M.; Zacny, K.

2016-01-01

A percussive cone penetrometer measures the strength of granular material by using percussion to deliver mechanical energy into the material. A percussive cone penetrometer was used in this study to penetrate a regolith ice mixture by breaking up ice and decompacting the regolith. As compared to a static cone penetrometer, percussion allows low reaction forces to push a penetrometer probe tip more easily into dry regolith in a low gravity environment from a planetary surface rover or a landed spacecraft. A percussive cone penetrates icy regolith at ice concentrations that a static cone cannot penetrate. In this study, the percussive penetrator was able to penetrate material under 65 N of down-force which could not be penetrated using a static cone under full body weight. This paper discusses using a percussive cone penetrometer to discern changes in the concentration of water-ice in a mixture of lunar regolith simulant and ice to a depth of one meter. The rate of penetration was found to be a function of the ice content and was not significantly affected by the down-force. The test results demonstrate that this method may be ideal for a small platform in a reduced gravity environment. However, there are some cases where the system may not be able to penetrate the icy regolith, and there is some risk of the probe tip becoming stuck so that it cannot be retracted. It is also shown that a percussive cone penetrometer could be used to prospect for water ice in regolith at concentrations as high as 8 by weight.

Development of an improved model for runback water on aircraft surfaces

NASA Technical Reports Server (NTRS)

Al-Khalil, Kamel M.; Keith, Theo G., Jr.; De Witt, Kenneth J.

1992-01-01

A computer simulation for 'running wet' and evaporative aircraft anti-icing systems is developed. The model is based on the analysis of the liquid water film which forms in the regions of direct impingement and, then, breaks up near the impingement limits into rivulets. The wetness factor distribution resulting from the film breakup and the rivulet configuration on the surface are predicted using a stability analysis theory and the laws of mass energy conservation. The solid structure is modeled as a multiple layer wall. The anti-icing system modeled is of the thermal type utilizing hot air and/or electrical heating elements embedded within the wall layers. Experimental observations revealing some of the basic physics of the water flow on the surface are presented. Detailed qualitative documentation of the tests are given. Several numerical examples are considered, and the effect of some of the involved parameters on the system performance are investigated.

Volcanic ash layers in blue ice fields (Beardmore Glacier Area, Antarctica): Iridium enrichments

NASA Technical Reports Server (NTRS)

Koeberl, Christian

1988-01-01

Dust bands on blue ice fields in Antarctica have been studied and have been identified to originate from two main sources: bedrock debris scraped up from the ground by the glacial movement (these bands are found predominantly at fractures and shear zones in the ice near moraines), and volcanic debris deposited on and incorporated in the ice by large-scale eruptions of Antarctic (or sub-Antractic) volcanoes. Ice core studies have revealed that most of the dust layers in the ice cores are volcanic (tephra) deposits which may be related to some specific volcanic eruptions. These eruptions have to be related to some specific volcanic eruptions. These eruptions have to be relatively recent (a few thousand years old) since ice cores usually incorporate younger ice. In contrast, dust bands on bare blue ice fields are much older, up to a few hundred thousand years, which may be inferred from the rather high terrestrial age of meteorites found on the ice and from dating the ice using the uranium series method. Also for the volcanic ash layers found on blue ice fields correlations between some specific volcanoes (late Cenozoic) and the volcanic debris have been inferred, mainly using chemical arguments. During a recent field expedition samples of several dust bands found on blue ice fields at the Lewis Cliff Ice Tongue were taken. These dust band samples were divided for age determination using the uranium series method, and chemical investigations to determine the source and origin of the dust bands. The investigations have shown that most of the dust bands found at the Ice Tongue are of volcanic origin and, for chemical and petrological reasons, may be correlated with Cenozoic volcanoes in the Melbourne volcanic province, Northern Victoria Land, which is at least 1500 km away. Major and trace element data have been obtained and have been used for identification and correlation purposes. Recently, some additional trace elements were determined in some of the dust band samples, including Ir. Iridium determinations were made using INAA, with synthetical and natural (meteorite) standards. These findings are discussed.

SEASAT economic assessment. Volume 6: Arctic operations case study and generalization. [economic benefits of SEASAT satellites to oil exploration in the Arctic

NASA Technical Reports Server (NTRS)

1975-01-01

The hypothetical development and transportation of Arctic oil and other resources by ice breaking super tanker fleets to the continental East Coast are discussed. The utilization of SEASAT ice mapping data is shown to contribute to a more effective transportation operation through the Arctic ice by reducing transportation costs as a consequence of reduced transit time per voyage.

Strong-Isospin-Breaking Correction to the Muon Anomalous Magnetic Moment from Lattice QCD at the Physical Point

NASA Astrophysics Data System (ADS)

Chakraborty, B.; Davies, C. T. H.; Detar, C.; El-Khadra, A. X.; Gámiz, E.; Gottlieb, Steven; Hatton, D.; Koponen, J.; Kronfeld, A. S.; Laiho, J.; Lepage, G. P.; Liu, Yuzhi; MacKenzie, P. B.; McNeile, C.; Neil, E. T.; Simone, J. N.; Sugar, R.; Toussaint, D.; van de Water, R. S.; Vaquero, A.; Fermilab Lattice, Hpqcd,; Milc Collaborations

2018-04-01

All lattice-QCD calculations of the hadronic-vacuum-polarization contribution to the muon's anomalous magnetic moment to date have been performed with degenerate up- and down-quark masses. Here we calculate directly the strong-isospin-breaking correction to aμHVP for the first time with physical values of mu and md and dynamical u , d , s , and c quarks, thereby removing this important source of systematic uncertainty. We obtain a relative shift to be applied to lattice-QCD results obtained with degenerate light-quark masses of δ aμHVP ,mu≠md=+1.5 (7 )% , in agreement with estimates from phenomenology.

Strong-Isospin-Breaking Correction to the Muon Anomalous Magnetic Moment from Lattice QCD at the Physical Point

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakraborty, B.; Davies, C. T. H.; DeTar, C.

All lattice-QCD calculations of the hadronic-vacuum-polarization contribution to the muon’s anomalous magnetic moment to date have been performed with degenerate up- and down-quark masses. Here we calculate directly the strong-isospin-breaking correction tomore » $${a}_{{\\mu}}^{\\mathrm{HVP}}$$ for the first time with physical values of $${m}_{u}$$ and $${m}_{d}$$ and dynamical $u$, $d$, $s$, and $c$ quarks, thereby removing this important source of systematic uncertainty. We obtain a relative shift to be applied to lattice-QCD results obtained with degenerate light-quark masses of $${\\delta}{a}_{{\\mu}}^{\\mathrm{HVP},{m}_{u}{\

Strong-Isospin-Breaking Correction to the Muon Anomalous Magnetic Moment from Lattice QCD at the Physical Point

DOE PAGES

Chakraborty, B.; Davies, C. T. H.; DeTar, C.; ...

2018-04-12

All lattice-QCD calculations of the hadronic-vacuum-polarization contribution to the muon’s anomalous magnetic moment to date have been performed with degenerate up- and down-quark masses. Here we calculate directly the strong-isospin-breaking correction tomore » $${a}_{{\\mu}}^{\\mathrm{HVP}}$$ for the first time with physical values of $${m}_{u}$$ and $${m}_{d}$$ and dynamical $u$, $d$, $s$, and $c$ quarks, thereby removing this important source of systematic uncertainty. We obtain a relative shift to be applied to lattice-QCD results obtained with degenerate light-quark masses of $${\\delta}{a}_{{\\mu}}^{\\mathrm{HVP},{m}_{u}{\

Regional Climate Model Performance in Simulating Intra-seasonal and Interannual Variability of Indian Summer Monsoon

NASA Astrophysics Data System (ADS)

Bhatla, R.; Ghosh, Soumik; Mall, R. K.; Sinha, P.; Sarkar, Abhijit

2018-05-01

Establishment of Indian summer monsoon (ISM) rainfall passes through the different phases and is not uniformly distributed over the Indian subcontinent. This enhancement and reduction in daily rainfall anomaly over the Indian core monsoon region during peak monsoon season (i.e., July and August) are commonly termed as `active' and `break' phases of monsoon. The purpose of this study is to analyze REGional Climate Model (RegCM) results obtained using the most suitable convective parameterization scheme (CPS) to determine active/break phases of ISM. The model-simulated daily outgoing longwave radiation (OLR), mean sea level pressure (MSLP), and the wind at 850 hPa of spatial resolution of 0.5°× 0.5° are compared with NOAA, NCEP, and EIN15 data, respectively over the South-Asia Co-Ordinated Regional Climate Downscaling EXperiment (CORDEX) region. 25 years (1986-2010) composites of OLR, MSLP, and the wind at 850 hPa are considered from start to the dates of active/break phase and up to the end dates of active/break spell of monsoon. A negative/positive anomaly of OLR with active/break phase is found in simulations with CPSs Emanuel and Mix99 (Grell over land; Emanuel over ocean) over the core monsoon region as well as over Monsoon Convergence Zone (MCZ) of India. The appearance of monsoon trough during active phase over the core monsoon zone and its shifting towards the Himalayan foothills during break phase are also depicted well. Because of multi-cloud function over oceanic region and single cloud function over the land mass, the Mix99 CPSs perform well in simulating the synoptic features during the phases of monsoon.

Diminishing sea ice in the western Arctic Ocean

USGS Publications Warehouse

Stone, R.S.; Belchansky, G.I.; Drobot, Sheldon; Douglas, David C.; Levinson, D.H.; Waple, A.M.

2004-01-01

Since the advent of satellite passive microwave radiometry (1978), variations in sea ice extent and concentration have been carefully monitored from space. An estimated 7.4% decrease in sea ice extent has occurred in the last 25 yr (Johannessen et al. 2004), with recent record minima (e.g., Maslanik et al. 1999; Serreze et al. 2003) accounting for much of the decline. Comparisons between the time series of Arctic sea ice melt dynamics and snowmelt dates at the NOAA–CMDL Barrow Observatory (BRW) reveal intriguing correlations.Melt-onset dates over sea ice (Drobot and Anderson 2001) were cross correlated with the melt-date time series from BRW, and a prominent region of high correlation between snowmelt onset over sea ice and the BRW record of melt dates was approximately aligned with the climatological center of the Beaufort Sea Anticyclone (BSA). The BSA induces anticyclonic ice motion in the region, effectively forcing the Beaufort gyre. A weak gyre caused by a breakdown of the BSA diminishes transport of multiyear ice into this region (Drobot and Maslanik 2003). Similarly, the annual snow cycle at BRW varies with the position and intensity of the BSA (Stone et al. 2002, their Fig. 6). Thus, variations in the BSA appear to have far-reaching effects on the annual accumulation and subsequent melt of snow over a large region of the western Arctic.A dramatic increase in melt season duration (Belchansky et al. 2004) was also observed within the same region of high correlation between onset of melt over the ice pack and snowmelt at BRW (Fig. 5.7). By inference, this suggests linkages between factors that modulate the annual cycle of snow on land and processes that influence melting of snow and ice in the western Arctic Ocean.

Surface Exposure Dating of Glaciated Landscapes in Washington Land, Northwest Greenland

NASA Astrophysics Data System (ADS)

Reusche, M.; Ceperley, E. G.; Marcott, S. A.; Brook, E.; Mix, A. C.

2016-12-01

The timing and rate of sea-level contribution from the Greenland ice sheet (GIS) and its outlet glaciers through the 21st century is uncertain. Given the long response time of ice sheets, characterizing the sensitivity of the GIS to both atmospheric and oceanic forcings in the past plays a vital role in forecasting future GIS changes. Our terrestrial-based study is primarily focused along the margins of the marine-terminating Petermann Glacier of northwestern Greenland, and is part of a larger multidisciplinary research effort with oceanographers, geophysicists, and atmospheric scientists that aims to better understand Petermann's response to past perturbations in climate and the primary mechanisms that drive those changes. In order to more accurately determine the ice sheet history of the northwestern sector of the GIS, rock samples from erratic boulders on moraines and from across an expansive ice free region (Washington Land) adjacent to Nares Strait were collected for surface exposure dating with 10Be. The project goal is to apply exposure histories from these glacial erratics to determine the timing and rate of GIS retreat since the last glacial maximum from Nares Strait up to the relatively `fresh' moraines that front the present GIS and Petermann Glacier margins nearly 70 km away. Moraine chronologies will also be constructed from these presumably late Holocene moraines, which serve as unique evidence of pre-Little Ice Age (LIA) Neoglaciation that are often obliterated from the landscape due to the large extent of the LIA advance across much of Greenland. Preliminary exposure ages and results will be presented and discussed within the context of the ice-ocean-atmosphere system of northwestern Greenland and compared to ongoing and prior work.

Survival and First-Year Growth of Hardwoods Planted in Saturated Soils

Treesearch

F. T. Bonner

1966-01-01

Up to 16 weeks of soil saturation from the time of planting did not significantly affect survival, date of bud-break, or initiation of height growth of sycamore, sweetgum, and Nuttall oak seedlings. But when soil temperatures were rapidly increasing in mid-April, saturation for more than 10 to 12 weeks did severely reduce height, root, and stem-diameter growth....

High Arctic sea ice conditions influence marine birds wintering in Low Arctic regions

NASA Astrophysics Data System (ADS)

McFarlane Tranquilla, Laura; Hedd, April; Burke, Chantelle; Montevecchi, William A.; Regular, Paul M.; Robertson, Gregory J.; Stapleton, Leslie Ann; Wilhelm, Sabina I.; Fifield, David A.; Buren, Alejandro D.

2010-09-01

Ocean climate change is having profound biological effects in polar regions. Such change can also have far-reaching downstream effects in sub-polar regions. This study documents an environmental relationship between High Arctic sea ice changes and mortality events of marine birds in Low Arctic coastal regions. During April 2007 and March 2009, hundreds of beached seabird carcasses and moribund seabirds were found along the east and northeast coasts of Newfoundland, Canada. These seabird "wrecks" (i.e. dead birds on beaches) coincided with a period of strong, persistent onshore winds and heavily-accumulated sea ice that blocked bays and trapped seabirds near beaches. Ninety-two percent of wreck seabirds were Thick-billed Murres ( Uria lomvia). Body condition and demographic patterns of wreck murres were compared to Thick-billed Murres shot in the Newfoundland murre hunt. Average body and pectoral masses of wreck carcasses were 34% and 40% lighter (respectively) than shot murres, indicating that wreck birds had starved. The acute nature of each wreck suggested that starvation and associated hypothermia occurred within 2-3 days. In 2007, first-winter murres (77%) dominated the wreck. In 2009, there were more adults (78%), mostly females (66%). These results suggest that spatial and temporal segregation in ages and sexes can play a role in differential survival when stochastic weather conditions affect discrete areas where these groups aggregate. In wreck years, southward movement of Arctic sea ice to Low Arctic latitudes was later and blocked bays longer than in most other years. These inshore conditions corresponded with recent climate-driven changes in High Arctic ice break-up and ice extent; coupled with local weather conditions, these ice conditions appeared to be the key environmental features that precipitated the ice-associated seabird wrecks in the Low Arctic region.

Changes in ice dynamics along the northern Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Seehaus, T.; Braun, M.; Cook, A.; Marinsek, S.

2016-12-01

The climatic conditions along the Antarctic Peninsula have undergone considerable changes during the last 50 years. Numerous ice shelves along the Antarctic Peninsula retreated, started to break-up or disintegrated. The loss of the buttressing effect caused tributary glaciers to accelerate with increasing ice discharge along the Antarctic Peninsula. The aim is to study the reaction of glaciers at the northern Antarctic Peninsula to the changing climatic conditions and the readjustments of tributary glaciers to ice shelf disintegration, as well as to better quantify the ice mass loss and its temporal changes.We analysed time series of various SAR satellite sensors to detect changes in ice flow speed and surface elevation. Intensity feature tracking techniques were applied on data stacks from different SAR satellites over the last 20 years to infer changes in glacier surface velocities. High resolution bi-static TanDEM-X data was used to derive digital elevation models by differential SAR interferometry. In combination with ASTER and SPOT stereo images, changes in surface elevations were determined. Altimeter data from ICESat, CryoSat-2 and NASA operation IceBridge ATM were used for vertical referencing and quality assessment of the digital elevation models. Along the west coast of the northern Antarctic Peninsula an increase in flow speeds by 40% between 1992 and 2014 was observed, whereas glaciers on the east side (north of former Prince-Gustav Ice Shelf) showed a strong deceleration. In total an ice discharge of 17.93±6.22 Gt/a was estimated for 74 glaciers on the Antarctic Peninsula north of 65°S. Most of the former ice shelf tributaries showed similar reactions to ice shelf disintegration. At the Sjögren-Inlet a total ice mass loss of -37.5±8.2 Gt and a contribution to sea level rise of 20.9±5.2 Gt were found in the period 1993-2014. The average surface lowering rate in the period 2012-2014 amounts to -2.2 m/a. At Dinsmoor-Bombardier-Edgeworth glacier system the results show an increase in surface velocity from 0.9 m/d in 1996 up to 8.8 m/d in 1999 close to the terminus. Subsequently, surface velocities decreased to 1.5 m/d in 2014. The changes in flow speeds are coinciding with changes in front position. The surface elevation changed by at least -130±15 m between 1995 and 2014 and -40.7±3.9 Gt of ice were discharged.

Measured and Modelled Tidal Circulation Under Ice Covered Van Mijenforden

NASA Astrophysics Data System (ADS)

Nilsen, F.

The observation and model area Van Mijenfjorden is situated at the west coast of Spits- bergen. An area of 533 km2 makes it the second largest fjord on Spitsbergen and the distance from the head to the mouth of the fjord is approximately 70 km. An 8.5km long and 1km wide island, Akseløya, is lying across the fjord mouth and blocking exchanges between the fjord and the coastal water masses outside. The sound Aksel- sundet on the northern side of the island is 1km wide and has a sill at 34m depth. On the southern side an islet, Mariaholmen, is between two sounds that are 200m wide and 2m deep, and 500m wide and 12m deep. Strong tidal currents exist in these sounds. Van Mijenfjorden has special ice conditions in that Akseløya almost closes the fjord, and comparatively little ice comes in from west. On the other hand, there are periods with fast ice in the fjord inside Akseløya longer than in other places, as the sea waves have little chance to break up fast ice here, or delay ice formation in autumn/winter. Van Mijenfjorden is often separated into two basins by a sill at 30m depth. The inner basin is typical 5km wide and has a maximum depth of 80m, while the outer basin is on average 10 km wide and has a maximum depth of 115m. Hydrographic measurements have been conducted since 1958 and up to the present. Through the last decade, The University Courses on Svalbard (UNIS) has used this fjord as a laboratory for their student excursions, in connection to courses in air-ice- ocean interaction and master programs, and build up an oceanographic data base. In this work, focus is put on the wintertime situation and the circulation under an ice covered fjord. Measurements show a mean cyclonic circulation pattern in the outer basin with tidal oscillation (mainly M2) superposed on this mean vector. A three- dimensional sigma layered numerical model called Bergen Ocean Model (BOM) was used to simulate the circulation in Van Mijenfjorden with only tidal forcing. The four most pronounced tidal components were used to force the model area outside Ak- seløya. The calculated cyclonic circulation pattern fits the measurements, proving that the fjord circulation is controlled by tides in periods when the ice cover shade the fjord water masses from direct wind forcing.

Earth observations taken during STS-81 mission

NASA Image and Video Library

1997-01-13

STS081-715-004 (12-22 Jan. 1997) --- As photographed with a 70mm camera aboard the Space Shuttle Atlantis, this scene features the Volga River and Volgograd under snow. Contrast in brightness shows up many features in this near-vertical view of the great bend of the Volga River's dark, open strip of water, center. The Volga flows south into the view from top right, then southeast from the center to the bottom. Volgograd appears as the gray zone along the left (west) side of the open water. Presumably the ice-free part of the river opposite Volgograd relates to the slightly warmer water which is spilled from prominent, ice-covered Lake Volgograd (top right). The wide patterns of swirls, center to lower right, are numerous meander bends on the Volga's floodplain (up to 20 miles wide), highlighted by snow. The main course of the Volga is once again ice covered in this floodplain belt. The Volga-Don Canal can be seen leaving the river just south of the bend, exiting the view center left. This canal, with others in the Moscow region, allows barge traffic to move through the Russian heartland, from the Black Sea to the Baltic at Leningrad. The long parallel lines in threes and fours are lines of trees used as wind breaks. They stretch across Russia for hundreds of miles.

Towards breaking the spatial resolution barriers: An optical flow and super-resolution approach for sea ice motion estimation

NASA Astrophysics Data System (ADS)

Petrou, Zisis I.; Xian, Yang; Tian, YingLi

2018-04-01

Estimation of sea ice motion at fine scales is important for a number of regional and local level applications, including modeling of sea ice distribution, ocean-atmosphere and climate dynamics, as well as safe navigation and sea operations. In this study, we propose an optical flow and super-resolution approach to accurately estimate motion from remote sensing images at a higher spatial resolution than the original data. First, an external example learning-based super-resolution method is applied on the original images to generate higher resolution versions. Then, an optical flow approach is applied on the higher resolution images, identifying sparse correspondences and interpolating them to extract a dense motion vector field with continuous values and subpixel accuracies. Our proposed approach is successfully evaluated on passive microwave, optical, and Synthetic Aperture Radar data, proving appropriate for multi-sensor applications and different spatial resolutions. The approach estimates motion with similar or higher accuracy than the original data, while increasing the spatial resolution of up to eight times. In addition, the adopted optical flow component outperforms a state-of-the-art pattern matching method. Overall, the proposed approach results in accurate motion vectors with unprecedented spatial resolutions of up to 1.5 km for passive microwave data covering the entire Arctic and 20 m for radar data, and proves promising for numerous scientific and operational applications.

Antarctic icebergs distributions 1992-2014

NASA Astrophysics Data System (ADS)

Tournadre, J.; Bouhier, N.; Girard-Ardhuin, F.; Rémy, F.

2016-01-01

Basal melting of floating ice shelves and iceberg calving constitute the two almost equal paths of freshwater flux between the Antarctic ice cap and the Southern Ocean. The largest icebergs (>100 km2) transport most of the ice volume but their basal melting is small compared to their breaking into smaller icebergs that constitute thus the major vector of freshwater. The archives of nine altimeters have been processed to create a database of small icebergs (<8 km2) within open water containing the positions, sizes, and volumes spanning the 1992-2014 period. The intercalibrated monthly ice volumes from the different altimeters have been merged in a homogeneous 23 year climatology. The iceberg size distribution, covering the 0.1-10,000 km2 range, estimated by combining small and large icebergs size measurements follows well a power law of slope -1.52 ± 0.32 close to the -3/2 laws observed and modeled for brittle fragmentation. The global volume of ice and its distribution between the ocean basins present a very strong interannual variability only partially explained by the number of large icebergs. Indeed, vast zones of the Southern Ocean free of large icebergs are largely populated by small iceberg drifting over thousands of kilometers. The correlation between the global small and large icebergs volumes shows that small icebergs are mainly generated by large ones breaking. Drifting and trapping by sea ice can transport small icebergs for long period and distances. Small icebergs act as an ice diffuse process along large icebergs trajectories while sea ice trapping acts as a buffer delaying melting.

Identification & Characterization of Fungal Ice Nucleation Proteins

NASA Astrophysics Data System (ADS)

Scheel, Jan Frederik; Kunert, Anna Theresa; Kampf, Christopher Johannes; Mauri, Sergio; Weidner, Tobias; Pöschl, Ulrich; Fröhlich-Nowoisky, Janine

2016-04-01

Freezing of water at relatively warm subfreezing temperatures is dependent on ice nucleation catalysis facilitated by ice nuclei (IN). These IN can be of various origins and although extensive research was done and progress was achieved, the nature and mechanisms leading to an effective IN are to date still poorly understood. Some of the most important processes of our geosphere like the water cycle are highly dependent on effective ice nucleation at temperatures between -2°C - -8°C, a temperature range which is almost exclusively covered by biological IN (BioIN). BioIN are usually macromolecular structures of biological polymers. Sugars as well as proteins have been reported to serve as IN and the best characterized BioIN are ice nucleation proteins (IN-P) from gram negative bacteria. Fungal strains from Fusarium spp. were described to be effective IN at subfreezing temperatures up to -2°C already 25 years ago and more and more fungal species are described to serve as efficient IN. Fungal IN are also thought to be proteins or at least contain a proteinaceous compound, but to date the fungal IN-P primary structure as well as their coding genetic elements of all IN active fungi are unknown. The aim of this study is a.) to identify the proteins and their coding genetic elements from IN active fungi (F. acuminatum, F. avenaceum, M. alpina) and b.) to characterize the mechanisms by which fungal IN serve as effective IN. We designed an interdisciplinary approach using biological, analytical and physical methods to identify fungal IN-P and describe their biological, chemical, and physical properties.

A first assessment of Sentinel-3 SAR altimetry over ice sheets

NASA Astrophysics Data System (ADS)

McMillan, M.; Muir, A. S.; Shepherd, A.

2017-12-01

The first Sentinel-3 satellite was launched in 2016 and carries onboard a Ku-band Synthetic Aperture Radar (SAR) altimeter. With coverage up to a latitude of 81.5 degrees and a repeat period of 27 days, it offers the opportunity to measure surface topography and elevation change across much of the Antarctic and Greenland Ice Sheets, therefore continuing the existing 25 year radar altimeter record. The global operation of Sentinel-3 in SAR mode differs from all past Ku-band instruments; for the first time SAR measurements are routinely acquired across the interiors of the ice sheets; however unlike CryoSat-2 it does not carry an interferometer to aid signal retrieval in regions of complex coastal terrain. In view of these differences and the novel characteristics of the Sentinel-3 system, assessments of the performance of the instrument are required, to evaluate the satellite's utility for monitoring Earth's Polar regions. Here, we analyse data acquired during the first year of routine operations, to assess the performance of the Sentinel-3 SAR altimeter to date. We focus both on inland ice sheet regions, where Sentinel-3 provides the first operational SAR altimeter measurements, and also on coastal areas with more complex topography. We investigate SAR waveforms and retrieved elevations in both regions, and through comparison to measurements from earlier missions examine the impact of the different modes of operation. We also conduct a high level evaluation of the data, by comparing it to reference airborne altimetry, to provide an assessment of Sentinel-3 performance to date over ice sheets.

Uranium series dating of Allan Hills ice

NASA Technical Reports Server (NTRS)

Fireman, E. L.

1986-01-01

Uranium-238 decay series nuclides dissolved in Antarctic ice samples were measured in areas of both high and low concentrations of volcanic glass shards. Ice from the Allan Hills site (high shard content) had high Ra-226, Th-230 and U-234 activities but similarly low U-238 activities in comparison with Antarctic ice samples without shards. The Ra-226, Th-230 and U-234 excesses were found to be proportional to the shard content, while the U-238 decay series results were consistent with the assumption that alpha decay products recoiled into the ice from the shards. Through this method of uranium series dating, it was learned that the Allen Hills Cul de Sac ice is approximately 325,000 years old.

Ice Engineering: Ice Jams, Winter 2002-2003

DTIC Science & Technology

2004-07-01

located between Caribou and Fort Fairfield, and from Presque Isle and Washburn (NWS 2003i). Of the seven, four were reported in December and three...the towns of Washburn and Presque Isle ) was estimated to be one-quarter of a mile long in December. This jam remained in place until 21 April 2003...then appeared to break in half, sending the downstream floe of ice southeast through the town of Presque Isle while the most upstream section of

South Greenland, North Atlantic Ocean

NASA Technical Reports Server (NTRS)

1992-01-01

This spectacular north looking view of south Greenland (62.0N, 46.0W) shows numerous indentations along the coastline, many of which contain small settlements. These indentations are fiords carved by glaciers of the last ice age. Even today, ice in the center of Greenland is as much as 10,000 ft. thick and great rivers of ice continuously flow toward the sea, where they melt or break off as icebergs - some of which may be seen floating offshore.

South Greenland, North Atlantic Ocean

NASA Image and Video Library

1992-04-02

This spectacular north looking view of south Greenland (62.0N, 46.0W) shows numerous indentations along the coastline, many of which contain small settlements. These indentations are fiords carved by glaciers of the last ice age. Even today, ice in the center of Greenland is as much as 10,000 ft. thick and great rivers of ice continuously flow toward the sea, where they melt or break off as icebergs - some of which may be seen floating offshore.

Tree ring and ice core time scales around the Santorini eruption

NASA Astrophysics Data System (ADS)

Löfroth, Elin; Muscheler, Raimund; Aldahan, Ala; Possnert, Göran; Berggren, Ann-Marie

2010-05-01

When studying cosmogenic radionuclides in ice core and tree ring archives around the Santorini eruption a ~20 year discrepancy was found between the records (Muscheler 2009). In this study a new 10Be dataset from the NGRIP ice core is presented. It has a resolution of 7 years and spans the period 3752-3244 BP (1803-1295 BC). The NGRIP 10Be record and the previously published 10Be GRIP record were compared to the IntCal datasets to further investigate the discrepancy between the ice core and tree ring chronologies. By modelling the 14C production rate based on atmospheric 14C records a comparison could be made to the 10Be flux which is assumed to represent the 10Be production rate. This showed a time shift of ~23 years between the records. The sensitivity of the results to changes in important model parameters was evaluated. Uncertainties in the carbon cycle model cannot explain a substantial part of the timing differences. Potential influences of climate and atmospheric processes on the 10Be deposition were studied using δ18O from the respective cores and GISP2 ice core ion data. The comparison to δ18O revealed a small but significant correlation between 10Be flux and δ18O when the 14C-derived production signal was removed from the 10Be curves. The ion data, as proxies for atmospheric circulation changes, did not show any correlations to the 10Be record or the 10Be/14C difference. When including possible data uncertainties there is still a minimum discrepancy of ~10 years between the 10Be ice core and the 14C tree ring record. Due to lack of alternative explanations it is concluded that the ice core and/or the tree ring chronologies contains unaccounted errors in this range. This also reconciles the radiocarbon 1627-1600 BC (Friedrich et al., 2006) and ice core 1642±5 BC (Vinther et al., 2006) datings of the Santorini eruption. Friedrich, W.L., Kromer, B., Friedrich, M., Heinemeier, J., Pfeiffer, T., & Talamo, S., 2006: Santorini eruption radiocarbon dated to 1627-1600 BC. Science 312, 548-548. Muscheler, 2009: 14C and 10Be around 1650 cal BC. In Warburton, D.A., (ed.): Time's Up! Dating the Minoan Eruption of Santorini: acts of the Minoan Eruption Chronology Workshop, Sandbjerg November 2007: Monographs of the Danish Institute at Athens. Aarhus University Press, Aarhus. 298 pp. Vinther, B.M., Clausen, H.B., Johnsen, S.J., Rasmussen, S.O., Andersen, K.K., Buchardt, S.L., Dahl-Jensen, D., Seierstad, I.K., Siggaard-Andersen, M.L., Steffensen, J.P., Svensson, A., Olsen, J., & Heinemeier, J., 2006: A synchronized dating of three Greenland ice cores throughout the Holocene. Journal of Geophysical Research-Atmospheres 111, 11.

Modeling of Ice Flow and Internal Layers Along a Flow Line Through Swiss Camp in West Greenland

NASA Technical Reports Server (NTRS)

Wang, W. L.; Zwally, H. Jay; Abdalati, W.; Luo, S.; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

An anisotropic ice flow line model is applied to a flow line through Swiss Camp (69.57 N, 49.28 W) in West Greenland to estimate the dates of internal layers detected by Radio-Echo Sounding measurements. The effect of an anisotropic ice fabric on ice flow is incorporated into the steady state flow line model. The stress-strain rate relationship for anisotropic ice is characterized by an enhancement factor based on the laboratory observations of ice deformation under combined compression and shear stresses. By using present-day data of accumulation rate, surface temperature, surface elevation and ice thickness along the flow line as model inputs, a very close agreement is found between the isochrones generated from the model and the observed internal layers with confirmed dates. The results indicate that this part of Greenland ice sheet is primarily in steady state.

Modeling the evolution of the Laurentide Ice Sheet from MIS 3 to the Last Glacial Maximum: an approach using sea level modeling and ice flow dynamics

NASA Astrophysics Data System (ADS)

Weisenberg, J.; Pico, T.; Birch, L.; Mitrovica, J. X.

2017-12-01

The history of the Laurentide Ice Sheet since the Last Glacial Maximum ( 26 ka; LGM) is constrained by geological evidence of ice margin retreat in addition to relative sea-level (RSL) records in both the near and far field. Nonetheless, few observations exist constraining the ice sheet's extent across the glacial build-up phase preceding the LGM. Recent work correcting RSL records along the U.S. mid-Atlantic dated to mid-MIS 3 (50-35 ka) for glacial-isostatic adjustment (GIA) infer that the Laurentide Ice Sheet grew by more than three-fold in the 15 ky leading into the LGM. Here we test the plausibility of a late and extremely rapid glaciation by driving a high-resolution ice sheet model, based on a nonlinear diffusion equation for the ice thickness. We initialize this model at 44 ka with the mid-MIS 3 ice sheet configuration proposed by Pico et al. (2017), GIA-corrected basal topography, and mass balance representative of mid-MIS 3 conditions. These simulations predict rapid growth of the eastern Laurentide Ice Sheet, with rates consistent with achieving LGM ice volumes within 15 ky. We use these simulations to refine the initial ice configuration and present an improved and higher resolution model for North American ice cover during mid-MIS 3. In addition we show that assumptions of ice loads during the glacial phase, and the associated reconstructions of GIA-corrected basal topography, produce a bias that can underpredict ice growth rates in the late stages of the glaciation, which has important consequences for our understanding of the speed limit for ice growth on glacial timescales.

IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores

NASA Astrophysics Data System (ADS)

Parrenin, F.; Bazin, L.; Capron, E.; Landais, A.; Lemieux-Dudon, B.; Masson-Delmotte, V.

2015-05-01

Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age-scale uncertainty are essential to interpret the climate and environmental records that they contain. It is, however, a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the lock-in depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice- and air-dated horizons, ice and air depth intervals with known durations, depth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 (Antarctic ice core chronology) for four Antarctic ice cores and one Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono1 are demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono1 and Datice codes. We also test new functionalities with respect to the original version of Datice: observations as ice intervals with known durations, correlated observations, observations as air intervals with known durations and observations as mixed ice-air stratigraphic links. IceChrono1 is freely available under the General Public License v3 open source license.

Breaking the ice and forging links: the importance of socializing in research.

PubMed

Stobbe, Miranda; Mishra, Tarun; Macintyre, Geoff

2013-01-01

When meeting someone for the first time-whether another PhD student, or the Founding Editor-in-chief of PLOS Computational Biology-nothing breaks the ice like eating pancakes or having drinks together. A social atmosphere provides a relaxed, informal environment where people can connect, share ideas, and form collaborations. Being able to build a network and thrive in a social environment is crucial to a successful scientific career. This article highlights the importance of bringing people together who speak the same scientific language in an informal setting. Using examples of events held by Regional Student Groups of the ISCB's Student Council, this article shows that socializing is much more than simply sharing a drink.

Atmospheric and oceanic forcing of Weddell Sea ice motion

NASA Astrophysics Data System (ADS)

Kottmeier, C.; Sellmann, Lutz

1996-09-01

The data from sea ice buoys, which were deployed during the Winter Weddell Sea Project 1986, the Winter Weddell Gyre Studies 1989 and 1992, the Ice Station Weddell in 1992, the Antarctic Zone Flux Experiment in 1994, and several ship cruises in Austral summers, are uniformly reanalyzed by the same objective methods. Geostrophic winds are derived after matching of the buoy pressure data with the surface pressure fields of the European Centre for Medium Range Weather Forecasts. The ratio between ice drift and geostrophic wind speeds is reduced when winds and currents oppose each other, when the atmospheric surface layer is stably stratified, and when the ice is under pressure near coasts. Over the continental shelves, the spatial inhomogeneity of tidal and inertial motion effectively controls the variability of divergence for periods below 36 hours. Far from coasts, speed ratios, which presumably reflect internal stress variations in the ice cover, are independent of drift divergence on the spatial scale of 100 km. To study basin-scale ice dynamics, all ice drift data are related to the geostrophic winds based on the complex linear model [Thorndike and Colony, 1982] for daily averaged data. The composite patterns of mean ice motion, geostrophic winds, and geostrophic surface currents document cyclonic basin-wide circulations. Geostrophic ocean currents are generally small in the Weddell Sea. Significant features are the coastal current near the southeastern coasts and the bands of larger velocities of ≈6 cm s-1 following the northward and eastward orientation of the continental shelf breaks in the western and northwestern Weddell Sea. In the southwestern Weddell Sea the mean ice drift speed is reduced to less than 0.5% of the geostrophic wind speed and increases rather continuously to 1.5% in the northern, central, and eastern Weddell Sea. The linear model accounts for less than 50% of the total variance of drift speeds in the southwestern Weddell Sea and up to 80% in the northern and eastern Weddell Sea.

Spawning of Massive Antarctic Iceberg Captured by NASA

NASA Image and Video Library

2017-07-14

Between July 10 and 12, 2017, the Larsen C Ice Shelf in West Antarctica calved one of the largest icebergs in history (named "A-68"), weighing approximately one trillion tons. The rift in the ice shelf that spawned the iceberg has been present on the shelf since at least the beginning of the Landsat era (approximately the 1970s), but remained relatively dormant until around 2012, when it was observed actively moving through a suture zone in the ice shelf (Jansen et al., 2015). Suture zones are wide bands of ice that extend from glacier grounding lines (the boundary between a floating ice shelf and ice resting on bedrock) to the sea comprised of a frozen mixture of glacial ice and sea water, traditionally considered to be stabilizing features in ice shelves. When the Antarctic entered its annual dark period in late April, scientists knew the rift only had a few more miles to go before it completely calved the large iceberg. However, due to the lack of sunlight during the Antarctic winter, visible imagery is generally not available each year between May and August. This frame is from an animation that shows the ice shelf as imaged by the NASA/NOAA satellite Suomi NPP, which features the VIIRS (Visible Infrared Imaging Radiometer Suite) instrument. VIIRS has a day/night panchromatic band capable of collecting nighttime imagery of Earth with a spatial resolution of 2,460 feet (750 meters). An image from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra satellite shows the last cloud-free, daytime image of the ice shelf on April 6; the MODIS thermal imagery band is shown on April 29. The images from May 9 to July 14 show available cloud-free imagery from Suomi NPP. Luckily, despite several cloudy days leading up to the break, the weather mostly cleared on July 11, allowing scientists to see the newly formed iceberg on July 12. The animation is available at https://photojournal.jpl.nasa.gov/catalog/PIA21785

Discrete-Element bonded-particle Sea Ice model DESIgn, version 1.3a - model description and implementation

NASA Astrophysics Data System (ADS)

Herman, Agnieszka

2016-04-01

This paper presents theoretical foundations, numerical implementation and examples of application of the two-dimensional Discrete-Element bonded-particle Sea Ice model - DESIgn. In the model, sea ice is represented as an assemblage of objects of two types: disk-shaped "grains" and semi-elastic bonds connecting them. Grains move on the sea surface under the influence of forces from the atmosphere and the ocean, as well as interactions with surrounding grains through direct contact (Hertzian contact mechanics) and/or through bonds. The model has an experimental option of taking into account quasi-three-dimensional effects related to the space- and time-varying curvature of the sea surface, thus enabling simulation of ice breaking due to stresses resulting from bending moments associated with surface waves. Examples of the model's application to simple sea ice deformation and breaking problems are presented, with an analysis of the influence of the basic model parameters ("microscopic" properties of grains and bonds) on the large-scale response of the modeled material. The model is written as a toolbox suitable for usage with the open-source numerical library LIGGGHTS. The code, together with full technical documentation and example input files, is freely available with this paper and on the Internet.

IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores

NASA Astrophysics Data System (ADS)

Parrenin, Frédéric; Bazin, Lucie; Capron, Emilie; Landais, Amaëlle; Lemieux-Dudon, Bénédicte; Masson-Delmotte, Valérie

2016-04-01

Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age scale uncertainty are essential to interpret the climate and environmental records that they contain. It is however a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the Lock-In Depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are: models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice and air dated horizons, ice and air depth intervals with known durations, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 chronology for 4 Antarctic ice cores and 1 Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono is demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono and Datice codes. We also test new functionalities with respect to the original version of Datice: observations as ice intervals with known durations, correlated observations, observations as gas intervals with known durations and observations as mixed ice-air stratigraphic links. IceChrono1 is freely available under the GPL v3 open source license.

Consequences of Dating for Post-Divorce Maternal Well-Being

PubMed Central

Langlais, Michael R.; Anderson, Edward R.; Greene, Shannon M.

2016-01-01

Repartnering has been linked to health benefits for mothers, yet few studies have examined relationship quality in this context. According to the divorce-stress-adaptation perspective, relationship quality may influence the relationship between maternal well-being and dating after divorce. The current study examines the consequences of dating, relationship quality, and dating transitions (breaking up and dating new partners) on maternal well-being (negative affect and life satisfaction). Using monthly surveys completed by mothers over a two-year period after filing for divorce, we examined changes in intercepts and slopes of dating status and transitions for maternal well-being while also testing the effects of relationship quality. Mothers entering high-quality relationships were likely to report boosts in well-being at relationship initiation compared to single mothers and mothers entering low-quality relationships. Mothers entering lower-quality relationships were likely to report lower levels of well-being than single mothers. Dating transitions were associated with increases in well-being. Implications for maternal adjustment are discussed. PMID:27746511

Holocene relative sea level changes in Greenland: a review

NASA Astrophysics Data System (ADS)

Bennike, O.

2010-12-01

During the Holocene marked relative sea-level changes have taken place in the ice-free parts of Greenland. Already in 1776 it was reported that Thule winter houses and Norse ruins were partly inundated by the sea, and in 1962 the first emergence curve from Greenland was published. This has been followed by reconstruction of many other emergence curves. During the last ice age, large volumes of water were stored in the ice sheets. When the ice melted global sea level rose. In Greenland the ice sheet shrank in size, and the following emergence of the land surpassed the global sea level rise. Raised beach ridges, deltas and marine deposits are widespread in Greenland, and the uppermost form the marine limit, above which fresh-looking till deposits and perched boulders can be found. The marine limit has been mapped at numerous sites in Greenland, and the highest is at about 140 metres above the present sea level. In general, the marine limit is highest in those areas that were released from the largest load of ice. In other Arctic regions, well-constrained sea level curves have been constructed from dated drift-wood samples or whale bones from raised beaches. However, both driftwood and whale bones are rare in Greenland, and most curves have been developed from dated shells of bivalves. In the past years, isolation basins have increasingly been used to reconstruct sea level changes after the last deglaciation. Isolation basins are formed when the threshold of marine basins are lifted up above sea level. The use of this method requires that a series of lakes can be sampled at different elevations below the marine limit. Sampling of marine basins in shallow waters has also shown that many lakes have been inundated by the sea, and by dating the transgression horizons in the sediment sequences and by determining the depth of the sill, it is possible to work out curves for relative sea level rises during the past millennia. The global sea level has been fairly stable during the late Holocene, and the relative sea level rise seen in Greenland may be due to growth of the ice sheet, or related to the decay of the Laurentide ice sheet in North America. New shore-line displacement curves are presented for different parts of Greenland, and their implications with respect to the history of the Greenland ice sheet will be discussed. Comparisons between sea level data and curves based on geophysical modelling often show poor match, and it appears that the models have underestimated the rate and magnitude of ice load changes.

Lacustrine Records of Holocene Mountain Glacier Fluctuations from Western Greenland

NASA Astrophysics Data System (ADS)

Schweinsberg, A.; Briner, J. P.; Bennike, O.

2014-12-01

Recent studies have focused on documenting fluctuations of the Greenland Ice Sheet margin throughout the Holocene but few data exist that constrain past changes of local glaciers independent of the ice sheet. Our research combines proglacial lake sediment analysis with cosmogenic 10Be dating of Holocene moraines and radiocarbon dating of ice-cap-killed vegetation with an overall objective to use this multi-proxy approach to generate a detailed record of the coupled climate-glacier system through the Holocene. Here, we present lacustrine records of mountain glacier variability from continuous pro-glacial lake sediment sequences recovered from two glaciated catchments in northeastern Nuussuaq, western Greenland. We use radiocarbon-dated sediments from Sikuiui and Pauiaivik lakes to reconstruct the timing of advance and retreat of local glaciers. Sediments were characterized with magnetic susceptibility (MS), gamma density, Itrax XRF and visible reflectance spectroscopy at 0.2 cm intervals and sediment organic matter at 0.5 cm intervals. Basal radiocarbon ages provide minimum-age constraints on deglaciation from Sikuiui and Pauiaivik lakes of ~9.6 and 8.7 ka, respectively. Organic-rich gyttja from deglaciation until ~5.0 ka in Pauiaivik Lake suggests minimal glacial extent there while slightly elevated MS values from ~9.0 - 7.0 ka in Sikuiui Lake may reflect early Holocene glacial advances. Minerogenic sediment input gradually increases starting at ~5.0 ka in Pauiaivik Lake, which we interpret as the onset of Neoglaciation in the catchment. Furthermore, a distinct episode of enhanced glacial activity from ~4.0 - 2.2 ka in Sikuiui Lake may be correlative to a period of persistent snowline lowering evidenced by radiocarbon dates of ice-killed vegetation from nearby ice cap margins. Results from these lacustrine records and our ice-killed vegetation dataset suggest a middle Holocene onset of Neoglaciation ~5.0 - 4.0 ka in this region. We are supplementing these records with cosmogenic 10Be exposure dating to further constrain the timing of deglaciation. In addition, these sedimentary archives will continue to be compared to radiocarbon dates of ice-killed vegetation along adjacent ice cap margins to determine if times of persistent snowline lowering are correlative to periods of glacier advance.

The breakup of large tabular icebergs - direct observations and theoretical considerations

NASA Astrophysics Data System (ADS)

Wadhams, P.

2013-12-01

Peter Wadhams and Till Wagner Dept. of Applied Mathematics and Theoretical Physics (DAMTP), University of Cambridge. We review the factors governing the stability, dynamics and decay of icebergs and describe areas where current models are inadequate. These include questions such as draft changes in capsizing icebergs; iceberg trajectory modelling; the melt rate of the ice underside and ways of reducing it; and wave-induced flexure and its role in the break-up of tabular icebergs. In July 2012 the authors worked on a very large (42 sq km) tabular iceberg in Baffin Bay, which had calved from the Petermann Glacier in NW Greenland. We measured incoming swell spectrum and the iceberg response; also the role of buoyancy forces due to erosion of a waterline wave cut and the creation of an underwater ram. The iceberg broke up while we were on it, allowing an instrumental measurement of the calving event. The experiments were included in the BBC-2 film 'Operation Iceberg' shown on Nov 1 2012 and repeated on Nov 18. We conclude that two processes interacted in the break-up event: increased bending stress due to buoyancy of underwater rams; and direct flexural strain due to incidence of ocean swell. Implications for icebergs in the open sea are estimated.

Glacimarine Sedimentary Processes and Facies on the Polar North Atlantic Margins

NASA Astrophysics Data System (ADS)

Dowdeswell, J. A.; Elverhfi, A.; Spielhagen, R.

Major contrasts in the glaciological, oceanic and atmospheric parameters affecting the Polar North Atlantic, both over space between its eastern and western margins, and through time from full glacial to interglacial conditions, have lead to the deposition of a wide variety of sedimentary facies in these ice-influenced seas. The dynamics of the glaciers and ice sheets on the hinterlands surrounding the Polar North Atlantic have exterted a major influence on the processes, rates and patterns of sedimentation on the continental margins of the Norwegian and Greenland seas over the Late Cenozoic. The western margin is influenced by the cold East Greenland Current and the Svalbard margin by the northernmost extent of the warm North Atlantic Drift and the passage of relatively warm cyclonic air masses. In the fjords of Spitsbergen and the northwestern Barents Sea, glacial meltwater is dominant in delivering sediments. In the fjords of East Greenland the large numbers of icebergs produced from fast-flowing outlets of the Greenland Ice Sheet play a more significant role in sedimentation. During full glacials, sediments are delivered to the shelf break from fast-flowing ice streams, which drain huge basins within the parent ice sheet. Large prograding fans located on the continental slope offshore of these ice streams are made up of stacked debris flows. Large-scale mass failures, turbidity currents, and gas-escape structures also rework debris in continental slope and shelf settings. Even during interglacials, both the margins and the deep ocean basins beyond them retain a glacimarine overprint derived from debris in far-travelled icebergs and sea ice. Under full glacial conditions, the glacier influence is correspondingly stronger, and this is reflected in the glacial and glacimarine facies deposited at these times.

Rapid Access Ice Drill: A New Tool for Exploration of the Deep Antarctic Ice Sheets and Subglacial Geology

NASA Astrophysics Data System (ADS)

Goodge, J. W.; Severinghaus, J. P.

2014-12-01

The Rapid Access Ice Drill (RAID) will penetrate the Antarctic ice sheets in order to core through deep ice, the glacial bed, and into bedrock below. This new technology will provide a critical first look at the interface between major ice caps and their subglacial geology. Currently in construction, RAID is a mobile drilling system capable of making several long boreholes in a single field season in Antarctica. RAID is interdisciplinary and will allow access to polar paleoclimate records in ice >1 Ma, direct observation at the base of the ice sheets, and recovery of rock cores from the ice-covered East Antarctic craton. RAID uses a diamond rock-coring system as in mineral exploration. Threaded drill-pipe with hardened metal bits will cut through ice using reverse circulation of Estisol for pressure-compensation, maintenance of temperature, and removal of ice cuttings. Near the bottom of the ice sheet, a wireline bottom-hole assembly will enable diamond coring of ice, the glacial bed, and bedrock below. Once complete, boreholes will be kept open with fluid, capped, and made available for future down-hole measurement of thermal gradient, heat flow, ice chronology, and ice deformation. RAID will also sample for extremophile microorganisms. RAID is designed to penetrate up to 3,300 meters of ice and take sample cores in less than 200 hours. This rapid performance will allow completion of a borehole in about 10 days before moving to the next drilling site. RAID is unique because it can provide fast borehole access through thick ice; take short ice cores for paleoclimate study; sample the glacial bed to determine ice-flow conditions; take cores of subglacial bedrock for age dating and crustal history; and create boreholes for use as an observatory in the ice sheets. Together, the rapid drilling capability and mobility of the drilling system, along with ice-penetrating imaging methods, will provide a unique 3D picture of the interior Antarctic ice sheets.

Strong-Isospin-Breaking Correction to the Muon Anomalous Magnetic Moment from Lattice QCD at the Physical Point.

PubMed

Chakraborty, B; Davies, C T H; DeTar, C; El-Khadra, A X; Gámiz, E; Gottlieb, Steven; Hatton, D; Koponen, J; Kronfeld, A S; Laiho, J; Lepage, G P; Liu, Yuzhi; Mackenzie, P B; McNeile, C; Neil, E T; Simone, J N; Sugar, R; Toussaint, D; Van de Water, R S; Vaquero, A

2018-04-13

All lattice-QCD calculations of the hadronic-vacuum-polarization contribution to the muon's anomalous magnetic moment to date have been performed with degenerate up- and down-quark masses. Here we calculate directly the strong-isospin-breaking correction to a_{μ}^{HVP} for the first time with physical values of m_{u} and m_{d} and dynamical u, d, s, and c quarks, thereby removing this important source of systematic uncertainty. We obtain a relative shift to be applied to lattice-QCD results obtained with degenerate light-quark masses of δa_{μ}^{HVP,m_{u}≠m_{d}}=+1.5(7)%, in agreement with estimates from phenomenology.

Satellite observation of lake ice as a climate indicator - Initial results from statewide monitoring in Wisconsin

NASA Technical Reports Server (NTRS)

Wynne, Randolph H.; Lillesand, Thomas M.

1993-01-01

The research reported herein focused on the general hypothesis that satellite remote sensing of large-area, long-term trends in lake ice phenology (formation and breakup) is a robust, integrated measure of regional and global climate change. To validate this hypothesis, we explored the use of data from the Advanced Very High Resolution Radiometer (AVHRR) to discriminate the presence and extent of lake ice during the winter of 1990-1991 on the 45 lakes and reservoirs in Wisconsin with a surface area 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= -0.87) of the date so derived with local surface-based temperature measurements. These results suggest the potential of using current and archival satellite data to monitor changes in the date of lake ice breakup as a means of detecting regional 'signals' of greenhouse warming.

Fossils harbor climate clues and fuel debate over glacier stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

At the edge of the Ross Ice Shelf near McMurdo Station in Antarctica, scientists have discovered fossils of well preserved wood and a mixture of microscopic marine organisms, dating from the Eocene epoch. This discovery promises significant clues to the onset of glaciation in Antarctica. Geologists believe that this discovery may shed light on Antarctica's link to world climate and help predict future climatic change. Debate centers around when glaciation first became extensive, 15 or 20 million years ago, and whether or not the ice sheet was dynamic and responsive to small fluctuations in climate or stable and able tomore » lock up massive amounts of the world's water. 7 refs.« less

A Prospective Study of Adolescents’ Sexual Partnerships on Emerging Adults’ Relationship Satisfaction and Intimate Partner Aggression

PubMed Central

Longmore, Monica A.; Manning, Wendy D.; Copp, Jennifer E.; Giordano, Peggy C.

2016-01-01

We examined whether the influence of adolescents’ sexual partnerships, both dating and casual, carried over to affect emerging adults’ relationship satisfaction and experiences of intimate partner aggression. Analyses of longitudinal data from the Toledo Adolescent Relationships Study (n = 294) showed that net of control variables (delinquency, depression, family violence, relational and sociodemographic characteristics), adolescents’ number of dating, but not casual, sexual partners led to greater odds of intimate partner aggression during emerging adulthood. Further, relationship churning (breaking-up and getting back together) and sexual non-exclusivity during emerging adulthood mediated the influence of adolescents’ number of dating sexual partnerships on intimate partner aggression. The positive effect of dating sexual partnerships on intimate partner aggression was stronger for women compared with men. These findings confirm the long reach of adolescent experiences into emerging adulthood. PMID:28546885

Duration of the Arctic sea ice melt season: Regional and interannual variability, 1979-2001

USGS Publications Warehouse

Belchansky, G.I.; Douglas, David C.; Platonov, Nikita G.

2004-01-01

Melt onset dates, freeze onset dates, and melt season duration were estimated over Arctic sea ice, 1979–2001, using passive microwave satellite imagery and surface air temperature data. Sea ice melt duration for the entire Northern Hemisphere varied from a 104-day minimum in 1983 and 1996 to a 124-day maximum in 1989. Ranges in melt duration were highest in peripheral seas, numbering 32, 42, 44, and 51 days in the Laptev, Barents-Kara, East Siberian, and Chukchi Seas, respectively. In the Arctic Ocean, average melt duration varied from a 75-day minimum in 1987 to a 103-day maximum in 1989. On average, melt onset in annual ice began 10.6 days earlier than perennial ice, and freeze onset in perennial ice commenced 18.4 days earlier than annual ice. Average annual melt dates, freeze dates, and melt durations in annual ice were significantly correlated with seasonal strength of the Arctic Oscillation (AO). Following high-index AO winters (January–March), spring melt tended to be earlier and autumn freeze later, leading to longer melt season durations. The largest increases in melt duration were observed in the eastern Siberian Arctic, coincident with cyclonic low pressure and ice motion anomalies associated with high-index AO phases. Following a positive AO shift in 1989, mean annual melt duration increased 2–3 weeks in the northern East Siberian and Chukchi Seas. Decreasing correlations between consecutive-year maps of melt onset in annual ice during 1979–2001 indicated increasing spatial variability and unpredictability in melt distributions from one year to the next. Despite recent declines in the winter AO index, recent melt distributions did not show evidence of reestablishing spatial patterns similar to those observed during the 1979–88 low-index AO period. Recent freeze distributions have become increasingly similar to those observed during 1979–88, suggesting a recurrent spatial pattern of freeze chronology under low-index AO conditions.

Cambrian palaeomagnetic data confirm a Natal Embayment location for the Ellsworth-Whitmore Mountains, Antarctica, in Gondwana reconstructions

NASA Astrophysics Data System (ADS)

Randall, Darren E.; Mac Niocaill, Conall

2004-04-01

The Ellsworth-Whitmore Mountains (EWM) are one of five terranes that form West Antarctica. Constraining the positions of these terranes in pre-break up Gondwana is crucial to understanding the history of the palaeo-Pacific Gondwana margin. We report the results of a detailed palaeomagnetic investigation of the EWM, which comprises some 150 sites in six formations, ranging in age from Cambrian to Permian. Five of the studied units yield only viscous remnant magnetizations of recent age, or unstable natural remanent magnetizations. The remaining unit, the mid-late Cambrian Frazier Ridge Formation, yielded stable magnetizations at 16 of 35 sites. This component passes a fold test at the 95 per cent confidence level, indicating that it pre-dates Permian deformation, and we argue that it is of primary origin. The resulting palaeopole (9°N 293°E A95= 5.1°) is in good agreement with two previously published palaeopoles from similarly aged rocks in the EWM. Collectively these data indicate that the EWM were located in the Natal Embayment prior to Gondwana break-up, and underwent 90° of anticlockwise rotation during break-up. All three studies, however, yield inclinations that are slightly too shallow when compared with coeval Gondwana reference poles.

A Search for Neutrino Emission from Fast Radio Bursts with Six Years of IceCube Data

NASA Astrophysics Data System (ADS)

Aartsen, M. G.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Samarai, I. Al; Altmann, D.; Andeen, K.; Anderson, T.; Ansseau, I.; Anton, G.; Argüelles, C.; Auffenberg, J.; Axani, S.; Bagherpour, H.; Bai, X.; Barron, J. P.; Barwick, S. W.; Baum, V.; Bay, R.; Beatty, J. J.; Becker Tjus, J.; Becker, K.-H.; BenZvi, S.; Berley, D.; Bernardini, E.; Besson, D. Z.; Binder, G.; Bindig, D.; Blaufuss, E.; Blot, S.; Bohm, C.; Börner, M.; Bos, F.; Böser, S.; Botner, O.; Bourbeau, E.; Bourbeau, J.; Bradascio, F.; Braun, J.; Brenzke, M.; Bretz, H.-P.; Bron, S.; Brostean-Kaiser, J.; Burgman, A.; Busse, R. S.; Carver, T.; Cheung, E.; Chirkin, D.; Christov, A.; Clark, K.; Classen, L.; Collin, G. H.; Conrad, J. M.; Coppin, P.; Correa, P.; Cowen, D. F.; Cross, R.; Dave, P.; Day, M.; de André, J. P. A. M.; De Clercq, C.; DeLaunay, J. J.; Dembinski, H.; De Ridder, S.; Desiati, P.; de Vries, K. D.; de Wasseige, G.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; di Lorenzo, V.; Dujmovic, H.; Dumm, J. P.; Dunkman, M.; Dvorak, E.; Eberhardt, B.; Ehrhardt, T.; Eichmann, B.; Eller, P.; Evenson, P. A.; Fahey, S.; Fazely, A. R.; Felde, J.; Filimonov, K.; Finley, C.; Flis, S.; Franckowiak, A.; Friedman, E.; Fritz, A.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Ghorbani, K.; Giang, W.; Glauch, T.; Glüsenkamp, T.; Goldschmidt, A.; Gonzalez, J. G.; Grant, D.; Griffith, Z.; Haack, C.; Hallgren, A.; Halzen, F.; Hanson, K.; Hebecker, D.; Heereman, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hignight, J.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Hoinka, T.; Hokanson-Fasig, B.; Hoshina, K.; Huang, F.; Huber, M.; Hultqvist, K.; Hünnefeld, M.; Hussain, R.; In, S.; Iovine, N.; Ishihara, A.; Jacobi, E.; Japaridze, G. S.; Jeong, M.; Jero, K.; Jones, B. J. P.; Kalaczynski, P.; Kang, W.; Kappes, A.; Kappesser, D.; Karg, T.; Karle, A.; Katz, U.; Kauer, M.; Keivani, A.; Kelley, J. L.; Kheirandish, A.; Kim, J.; Kim, M.; Kintscher, T.; Kiryluk, J.; Kittler, T.; Klein, S. R.; Koirala, R.; Kolanoski, H.; Köpke, L.; Kopper, C.; Kopper, S.; Koschinsky, J. P.; Koskinen, D. J.; Kowalski, M.; Krings, K.; Kroll, M.; Krückl, G.; Kunwar, S.; Kurahashi, N.; Kuwabara, T.; Kyriacou, A.; Labare, M.; Lanfranchi, J. L.; Larson, M. J.; Lauber, F.; Leonard, K.; Lesiak-Bzdak, M.; Leuermann, M.; Liu, Q. R.; Lozano Mariscal, C. J.; Lu, L.; Lünemann, J.; Luszczak, W.; Madsen, J.; Maggi, G.; Mahn, K. B. M.; Mancina, S.; Maruyama, R.; Mase, K.; Maunu, R.; Meagher, K.; Medici, M.; Meier, M.; Menne, T.; Merino, G.; Meures, T.; Miarecki, S.; Micallef, J.; Momenté, G.; Montaruli, T.; Moore, R. W.; Moulai, M.; Nahnhauer, R.; Nakarmi, P.; Naumann, U.; Neer, G.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke Pollmann, A.; Olivas, A.; O’Murchadha, A.; O’Sullivan, E.; Palczewski, T.; Pandya, H.; Pankova, D. V.; Peiffer, P.; Pepper, J. A.; Pérez de los Heros, C.; Pieloth, D.; Pinat, E.; Plum, M.; Price, P. B.; Przybylski, G. T.; Raab, C.; Rädel, L.; Rameez, M.; Rauch, L.; Rawlins, K.; Rea, I. C.; Reimann, R.; Relethford, B.; Relich, M.; Resconi, E.; Rhode, W.; Richman, M.; Robertson, S.; Rongen, M.; Rott, C.; Ruhe, T.; Ryckbosch, D.; Rysewyk, D.; Safa, I.; Sälzer, T.; Sanchez Herrera, S. E.; Sandrock, A.; Sandroos, J.; Santander, M.; Sarkar, S.; Sarkar, S.; Satalecka, K.; Schlunder, P.; Schmidt, T.; Schneider, A.; Schoenen, S.; Schöneberg, S.; Schumacher, L.; Sclafani, S.; Seckel, D.; Seunarine, S.; Soedingrekso, J.; Soldin, D.; Song, M.; Spiczak, G. M.; Spiering, C.; Stachurska, J.; Stamatikos, M.; Stanev, T.; Stasik, A.; Stein, R.; Stettner, J.; Steuer, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strotjohann, N. L.; Stuttard, T.; Sullivan, G. W.; Sutherland, M.; Taboada, I.; Tatar, J.; Tenholt, F.; Ter-Antonyan, S.; Terliuk, A.; Tilav, S.; Toale, P. A.; Tobin, M. N.; Tönnis, C.; Toscano, S.; Tosi, D.; Tselengidou, M.; Tung, C. F.; Turcati, A.; Turley, C. F.; Ty, B.; Unger, E.; Usner, M.; Vandenbroucke, J.; Van Driessche, W.; van Eijk, D.; van Eijndhoven, N.; Vanheule, S.; van Santen, J.; Vogel, E.; Vraeghe, M.; Walck, C.; Wallace, A.; Wallraff, M.; Wandler, F. D.; Wandkowsky, N.; Waza, A.; Weaver, C.; Weiss, M. J.; Wendt, C.; Werthebach, J.; Westerhoff, S.; Whelan, B. J.; Wiebe, K.; Wiebusch, C. H.; Wille, L.; Williams, D. R.; Wills, L.; Wolf, M.; Wood, J.; Wood, T. R.; Woolsey, E.; Woschnagg, K.; Xu, D. L.; Xu, X. W.; Xu, Y.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Yuan, T.; IceCube Collaboration

2018-04-01

We present a search for coincidence between IceCube TeV neutrinos and fast radio bursts (FRBs). During the search period from 2010 May 31 to 2016 May 12, a total of 29 FRBs with 13 unique locations have been detected in the whole sky. An unbinned maximum likelihood method was used to search for spatial and temporal coincidence between neutrinos and FRBs in expanding time windows, in both the northern and southern hemispheres. No significant correlation was found in six years of IceCube data. Therefore, we set upper limits on neutrino fluence emitted by FRBs as a function of time window duration. We set the most stringent limit obtained to date on neutrino fluence from FRBs with an E ‑2 energy spectrum assumed, which is 0.0021 GeV cm‑2 per burst for emission timescales up to ∼102 s from the northern hemisphere stacking search.

Ramped PyrOx 14C With a Twist: Improving Radiocarbon Chronologies on Highly Detrital Marginal Antarctic Sediments

NASA Astrophysics Data System (ADS)

Subt, C.; Yoon, H.; Yoo, K. C.; Lee, J. I.; Domack, E. W.; Rosenheim, B. E.

2016-02-01

Highly detrital sediments can be difficult to date when the detritus includes material similar to that from which dates are sought. For radiocarbon dating, samples with a high degree of pre-aged detrital carbon contamination necessitate measurement of a very small portion of the sample to remove that contamination from the targeted component, even when using advanced techniques such as Ramped PyrOx (RP) 14C dating. Here we present three case studies of alternative RP approaches, producing accurate and precise chronologies for highly detrital sediments near the Larsen C ice shelf, near the Drygalski Ice Tongue in Ross Sea, and in Lapeyrère Bay, Anvers Island. For sediments where the proportion of organic carbon that was modern at the time of deposition is too small for a traditional AMS analysis after RP treatment, we have developed an innovative multiple RP analyses approach to minimize the cost in precision from using smaller temperature intervals, while maximizing the benefit in accuracy. Resulting sub ice-shelf chronologies show vastly improved dates down-core, significantly younger than the equivalent 14C chronology from the bulk acid insoluble organic (AIO) carbon with increasing ages down-core. By comparison, bulk AIO 14C dates in the study areas are not only older, but are subject to age reversals and nearly constant ages that make sedimentation rates impossible to resolve. Using our new approaches, we can reduce pre-aged carbon contamination in Lapeyrère Bay, and date sediments within layers of siliceous mud and ooze in the Ross Sea, and near the Larsen C ice shelf. Improved accuracy for 14C dates of highly detrital sediments can sometimes require the incorporation of a larger blank correction to account for multiple analyses, decreasing the precision. Application of this method refines ages of hard-to-date sediments, removing limits on what to include in a regional approach to chronicle ice shelf collapse.

77 FR 75066 - Special Conditions: Airbus, A350-900 Series Airplane; Flight Envelope Protection (Icing and Non...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-19

... Protection (Icing and Non-Icing Conditions); High Incidence Protection and Alpha-Floor Systems AGENCY... or unusual design features associated with flight envelope protection in icing and non- icing... establish a level of safety equivalent to that established by the existing airworthiness standards. DATES...

Low Force Icy Regolith Penetration Technology

NASA Technical Reports Server (NTRS)

Metzger, P. T.; Galloway, G. M.; Mantovani, J. G.; Zacny, K.; Zacny, Kris; Craft, Jack

2011-01-01

Recent data from the Moon, including LCROSS data, indicate large quantities of water ice and other volatiles frozen into the soil in the permanently shadowed craters near the poles. If verified and exploited, these volatiles will revolutionize spaceflight as an inexpensive source of propellants and other consumables outside Earth's gravity well. This report discusses a preliminary investigation of a method to insert a sensor through such a soiVice mixture to verify the presence, nature, and concentration of the ice. It uses percussion to deliver mechanical energy into the frozen mixture, breaking up the ice and decompacting the soil so that only low reaction forces are required from a rover or spacecraft to push the sensor downward. The tests demonstrate that this method may be ideal for a small platform in lunar gravity. However, there are some cases where the system may not be able to penetrate the icy soil, and there is some risk ofthe sensor becoming stuck so that it cannot be retracted, so further work is needed. A companion project (ISDS for Water Detection on the Lunar Surface) has performed preliminary investigation of a dielectric/thermal sensor for use with this system.

Simulation of the Greenland Ice Sheet over two glacial-interglacial cycles: investigating a sub-ice-shelf melt parameterization and relative sea level forcing in an ice-sheet-ice-shelf model

NASA Astrophysics Data System (ADS)

Bradley, Sarah L.; Reerink, Thomas J.; van de Wal, Roderik S. W.; Helsen, Michiel M.

2018-05-01

Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM) the Greenland ice sheet (GrIS) expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS) and Innuitian Ice Sheet (IIS), it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial-interglacial cycles (240 ka BP to the present day) using the ice-sheet-ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL) forcing generated by a glacial isostatic adjustment (GIA) model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG) and LGM the ice sheet added 1.46 and -2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (˜ 1.26 m) than most previous studies whereas the contribution to the LIG highstand is lower (˜ 0.7 m). The spatial and temporal behaviour of the northern margin was highly variable in all simulations, controlled by the sub-ice-shelf melting which was dictated by the RSL forcing and the glacial history of the IIS and LIS. In contrast, the southwestern part of the ice sheet was insensitive to these forcings, with a uniform response in all simulations controlled by the surface air temperature, derived from ice cores.

Retrieving Arctic Sea Fog Geometrical Thickness and Inversion Characteristics from Surface and Radiosonde Observations.

NASA Astrophysics Data System (ADS)

Gilson, Gaëlle; Jiskoot, Hester

2017-04-01

Arctic sea fog hasn't been extensively studied despite its importance for environmental impact such as on traffic safety and on glacier ablation in coastal Arctic regions. Understanding fog processes can improve nowcasting of environmental impact in such remote regions where few observational data exist. To understand fog's physical, macrophysical and radiative properties, it is important to determine accurate Arctic fog climatology. Our previous study suggested that fog peaks in July over East Greenland and associates with sea ice break-up and a sea breeze with wind speeds between 1-4 m/s. The goal of this study is to understand Arctic coastal fog macrophysical properties and quantify its vertical extent. Radiosonde profiles were extracted from the Integrated Global Radiosonde Archive (IGRA) between 1980-2012, coincident with manual and automated fog observations at three synoptic weather stations along the coast of East Greenland. A new method using air mass saturation ratio and thermodynamic stability was developed to derive fog top height from IGRA radiosonde profiles. Soundings were classified into nine categories, based on surface and low-level saturation ratio, inversion type, and the fog top height relative to the inversion base. Results show that Arctic coastal fog mainly occurs under thermodynamically stable conditions characterized by deep and strong low-level inversions. Fog thickness is commonly about 100-400 m, often reaching the top of the boundary layer. Fog top height is greater at northern stations, where daily fog duration is also longer and often lasts throughout the day. Fog thickness is likely correlated to sea ice concentration density during sea ice break-up. Overall, it is hypothesized that our sounding classes represent development or dissipation stages of advection fog, or stratus lowering and fog lifting processes. With a new automated method, it is planned to retrieve fog height from IGRA data over Arctic terrain around the entire North Atlantic region. These results will serve as a basis for the incorporation of fog and temperature inversions into glacier surface energy balance models and can aid in improving the parameterization of fog for nowcasting methods for aviation applications.

Dating an 800,000 year Antarctic ice core record using the isotopic composition of trapped air

NASA Astrophysics Data System (ADS)

Dreyfus, Gabrielle Boissier

Here we measure the isotopic composition of air trapped in the European Project for Ice Coring in Antarctica Dome C (EDC) ice core, and use this geochemical information to improve the ice core agescale and our understanding of air enclosure processes. A first result is the detection of a flow anomaly in the bottom 500m of the EDC ice core using the delta18O of atmospheric oxygen (noted delta18Oatm). By tuning the measured delta18Oatm to the orbital precession signal, we correct the EDC agescale over 400-800 ka for flow-induced distortions in the duration of events. Uncertainty in delta 18Oatm phasing with respect to precession limits the accuracy of the tuned agescale to +/-6 ka. We use this improved agescale to date two 10Be peaks detected in the EDC ice core and associated with the Matuyama-Brunhes geomagnetic boundary. While the ice age of the "precursor" event agrees within uncertainty with the age of radioisotopically dated lavas, the volcanic age for the younger reversal is approximately 10 ka older than the mid-point of the 10 Be peak in the ice. Since 80% of the lavas recording the Matuyama-Brunhes reversal are located in the Central Pacific, the observed age difference may indicate that the magnetic field orientation at this location changed prior to the dipole intensity minimum recorded by the ice core 10Be, as suggested by recent geodynamo modeling. A particular challenge for ice core dating is accurately accounting for the age difference between the trapped air and surrounding ice. This gas age - ice age difference (noted Deltaage) depends on the age of the ice at the bottom of the firn. delta15N of N2 is constant in the atmosphere over the timescales considered here, so any deviation from atmospheric composition reflects fractionation processes in the firn. We show that delta15N is positively correlated with the ice deuterium content, a proxy for temperature, over the entire EDC record, and propose an accumulation-permeability-convection mechanism. While temporal resolution and noise in the available data limit our ability to constrain glacial Deltaage, these data suggest that delta15N may be used as a gas-phase climate proxy at EDC.

Advances in river ice hydrology 1999-2003

NASA Astrophysics Data System (ADS)

Morse, Brian; Hicks, Faye

2005-01-01

In the period 1999 to 2003, river ice has continued to have important socio-economic impacts in Canada and other Nordic countries. Concurrently, there have been many important advances in all areas of Canadian research into river ice engineering and hydrology. For example: (1) River ice processes were highlighted in two special journal issues (Canadian Journal of Civil Engineering in 2003 and Hydrological Processes in 2002) and at five conferences (Canadian Committee on River Ice Processes and the Environment in 1999, 2001 and 2003, and International Association of Hydraulic Research in 2000 and 2002). (2) A number of workers have clearly advanced our understanding of river ice processes by bringing together disparate information in comprehensive review articles. (3) There have been significant advances in river ice modelling. For example, both one-dimensional (e.g. RIVICE, RIVJAM, ICEJAM, HEC-RAS, etc.) and two-dimensional (2-D; www.river2d.ca) public-domain ice-jam models are now available. Work is ongoing to improve RIVER2D, and a commercial 2-D ice-process model is being developed. (4) The 1999-2003 period is notable for the number of distinctly hydrological and ecological studies. On the quantitative side, many are making efforts to determine streamflow during the winter period. On the ecological side, some new publications have addressed the link to water quality (temperature, dissolved oxygen, nutrients and pollutants), and others have dealt with sediment transport and geomorphology (particularly as it relates to break-up), stream ecology (plants, food cycle, etc.) and fish habitat.There is the growing recognition, that these types of study require collaborative efforts. In our view, the main areas requiring further work are: (1) to interface geomorphological and habitat models with quantitative river ice hydrodynamic models; (2) to develop a manager's toolbox (database management, remote sensing, forecasting, intervention methodologies, etc.) to enable agencies to intervene better at the time of ice-jam-induced floods; and (3) finalize ice-jam prevention methods on the St Lawrence River to safeguard its $2 billion commercial navigation industry. Copyright

Cabled observatories: Connecting coastal communities to local ocean data

NASA Astrophysics Data System (ADS)

Pelz, M.; Hoeberechts, M.; Brown, J. C. K.; McLean, M. A.; Ewing, N.; Moran, K.

2015-12-01

Coastal communities are facing a wide range of rapid changes due to anthropogenic and natural environmental influences. Communities are under pressure to adapt to effects of climate change, including altered shorelines, changes in availability of seafood, and in northern regions, changes to the extent, formation and break-up of land-fast and sea-ice. Access to up-to-date scientific data and basic climate literacy are essential tools to enable community members to make informed decisions about their own coast. Ocean Networks Canada (ONC) operates the world-leading NEPTUNE and VENUS cabled ocean observatories off the west coast of British Columbia (BC). ONC also operates smaller, coastal community observatories which provide data for both scientific and educational initiatives.The first Arctic community observatory, deployed in 2012, is located in Cambridge Bay, Nunavut. Real-time data flowing from the platform are collected by a range of instruments, including a conductivity-temperature-depth sensor (CTD), hydrophone, video camera, and an ice profiler. There is also a meteorological station and time lapse camera on the dock. Five additional community observatories are being installed over the next year along the coast of BC. Indigenous communities, including the Inuit population in Cambridge Bay and First Nations on BC's north and central coast, are key partners and collaborators of this initiative.Benefits to communities from cabled observatory ocean monitoring can only be achieved if the data collected are relevant to community members and contribute to research priorities identified within the community. The data must be easily accessible and complement existing environmental monitoring initiatives. Community members must possess knowledge and tools to analyze and interpret the data for their purposes. For these reasons, community involvement is critical to the project, including the design of user interfaces for data access, development of educational programs, and long-term planning.Here we describe Ocean Networks Canada's community initiatives including collaboration with Indigenous knowledge holders and local experts, programs in community schools to foster K-12 climate literacy and post-secondary programs targeted to community members.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagos, Samson M.; Feng, Zhe; Burleyson, Casey D.

Regional cloud permitting model simulations of cloud populations observed during the 2011 ARM Madden Julian Oscillation Investigation Experiment/ Dynamics of Madden-Julian Experiment (AMIE/DYNAMO) field campaign are evaluated against radar and ship-based measurements. Sensitivity of model simulated surface rain rate statistics to parameters and parameterization of hydrometeor sizes in five commonly used WRF microphysics schemes are examined. It is shown that at 2 km grid spacing, the model generally overestimates rain rate from large and deep convective cores. Sensitivity runs involving variation of parameters that affect rain drop or ice particle size distribution (more aggressive break-up process etc) generally reduce themore » bias in rain-rate and boundary layer temperature statistics as the smaller particles become more vulnerable to evaporation. Furthermore significant improvement in the convective rain-rate statistics is observed when the horizontal grid-spacing is reduced to 1 km and 0.5 km, while it is worsened when run at 4 km grid spacing as increased turbulence enhances evaporation. The results suggest modulation of evaporation processes, through parameterization of turbulent mixing and break-up of hydrometeors may provide a potential avenue for correcting cloud statistics and associated boundary layer temperature biases in regional and global cloud permitting model simulations.« less

Breaking the Ice and Forging Links: The Importance of Socializing in Research

PubMed Central

Stobbe, Miranda; Mishra, Tarun; Macintyre, Geoff

2013-01-01

When meeting someone for the first time—whether another PhD student, or the Founding Editor-in-chief of PLOS Computational Biology—nothing breaks the ice like eating pancakes or having drinks together. A social atmosphere provides a relaxed, informal environment where people can connect, share ideas, and form collaborations. Being able to build a network and thrive in a social environment is crucial to a successful scientific career. This article highlights the importance of bringing people together who speak the same scientific language in an informal setting. Using examples of events held by Regional Student Groups of the ISCB's Student Council, this article shows that socializing is much more than simply sharing a drink. PMID:24282392

Sensitivity of glacier mass balance and equilibrium line altitude to climatic change on King George Island, Antarctic Peninsula.

NASA Astrophysics Data System (ADS)

Falk, Ulrike; Lopez, Damian; Silva-Busso, Adrian

2017-04-01

The South Shetland Islands are located at the northern tip of the Antarctic Peninsula which is among the fastest warming regions on Earth. Surface air temperature increases (ca. 3 K in 50 years) are concurrent with retreating glacier fronts, an increase in melt areas, ice surface lowering and rapid break-up and disintegration of ice shelves. Observed surface air temperature lapse rates show a high variability during winter months (standard deviations up to ±1.0 K/100 m), and a distinct spatial heterogeneity reflecting the impact of synoptic weather patterns especially during winter glacial mass accumulation periods. The increased mesocyclonic activity during the winter time in the study area results in intensified advection of warm, moist air with high temperatures and rain, and leads to melt conditions on the ice cap, fixating surface air temperatures to the melting point. The impact on winter accumulation results in even more negative mass balance estimates. Six years of glaciological measurements on mass balance stake transects are used with a glacier melt model to assess changes in melt water input to the coastal waters, glacier surface mass balance and the equilibrium line altitude. The average equilibrium line altitude (ELA) calculated from own glaciological observations for KGI over the time period 2010 - 2015 amounts to ELA=330±100 m. Published studies suggest rather stable condition slightly negative glacier mass balance until the mid 80's with an ELA of approx. 150 m. The calculated accumulation area ratio suggests rather dramatic changes in extension of the inland ice cap for the South Shetland Islands until an equilibrium with concurrent climate conditions is reached.

Multi-millennia simulation of Greenland deglaciation from the Max-Plank-Institute Model (MPI-ISM) 2xCO2 simulation

NASA Astrophysics Data System (ADS)

Cabot, Vincent; Vizcaino, Miren; Mikolajewicz, Uwe

2016-04-01

Long-term ice sheet and climate coupled simulations are of great interest since they assess how the Greenland Ice Sheet (GrIS) will respond to global warming and how GrIS changes will impact on the climate system. We have run the Max-Plank-Institute Earth System Model coupled with an Ice Sheet Model (SICOPOLIS) over a time period of 10500 years under two times CO2 forcing. This is a coupled atmosphere (ECHAM5T31), ocean (MPI-OM), dynamic vegetation (LPJ), and ice sheet (SICOPOLIS, 10 km horizontal resolution) model. Given the multi-millennia simulation, the horizontal spatial resolution of the atmospheric component is relatively coarse (3.75°). A time-saving technique (asynchronous coupling) is used once the global climate reaches quasi-equilibrium. In our doubling-CO2 simulation, the GrIS is expected to break up into two pieces (one ice cap in the far north on one ice sheet in the south and east) after 3000 years. During the first 500 simulation years, the GrIS climate and surface mass balance (SMB) are mainly affected by the greenhouse effect-forced climate change. After the simulated year 500, the global climate reaches quasi-equilibrium. Henceforth Greenland climate change is mainly due to ice sheet decay. GrIS albedo reduction enhances melt and acts as a powerful feedback for deglaciation. Due to increased cloudiness in the Arctic region as a result of global climate change, summer incoming shortwave radiation is substantially reduced over Greenland, reducing deglaciation rates. At the end of the simulation, Greenland becomes green with forest growing over the newly deglaciated regions. References: Helsen, M. M., van de Berg, W. J., van de Wal, R. S. W., van den Broeke, M. R., and Oerlemans, J. (2013), Coupled regional climate-ice-sheet simulation shows limited Greenland ice loss during the Eemian, Climate of the Past, 9, 1773-1788, doi: 10.5194/cp-9-1773-2013 Helsen, M. M., van de Wal, R. S. W., van den Broeke, M. R., van de Berg, W. J., and Oerlemans, J. (2015), Coupling of climate models and ice sheet models by the surface mass balance gradients: application to the Greenland Ice Sheet, The Cryosphere, 6, 255-272, doi: 10.5194/tc-6-255-2012 Robinson, A., Calov, R., and Ganopolski, A. (2011), Greenland ice sheet model parameters constrained using simulations of the Eemian Interglacial, Climate of the Past, 7, 381-396, doi: 10.5194/cp-7-381-2011 Vizcaino, M., Mikolajewicz, U., Ziemen, F., Rodehacke, C. B., Greve, R., and van den Broeke, M. R. (2015), Coupled simulations of Greenland Ice Sheet and climate change up to A.D. 2300, Geophysical Research Letters, 42, doi: 10.1002/2014GL061142

Elemental depletions in Antarctic micrometeorites and Arctic cosmic spherules: Comparison and relationships

NASA Technical Reports Server (NTRS)

Presper, T.; Kurat, G.; Koeberl, C.; Palme, H.; Maurette, Michel

1993-01-01

Antarctic micrometeorites (MM's) and Arctic cosmic spherules (CS's) have bulk compositions comparable to those of chondritic meteorites. However, abundance of Na, Ca, Mn, Ni, Co, and S are commonly lower in MM's and CS's as compared to chondrites. Our SEM, EMP, and INAA studies suggest that these elemental depletions in unmelted MM's are likely to be due to leaching of soluble components from the MM's in the upper atmosphere and the melt ice water. Depletions in CS's appear to be mainly due to volatilization during melting in the atmosphere or to sampling bias during aggregate formation or parent rock break-up.

Relationship power, control, and dating violence among Latina girls.

PubMed

Lopez, Vera; Chesney-Lind, Meda; Foley, Julia

2012-06-01

We drew on the theory of gender and power and grounded theory methodology to explore how 18 Latina girls conceptualized power and control within their heterosexual dating relationships. Our findings indicate that boys/men used a number of strategies to control girls, including: regulating appearances and behaviors; cheating and threatening to cheat; and physical and sexual violence. Girls used a variety of strategies to resist these attempts to control them, including: lying, flirting, and cheating; reactive violence; breaking up; and maintaining emotional distance. Girls attempted to subvert boys' attempts to control them; however, these attempts were not always successful given the constraints of gender that adolescent females must negotiate.

A Detailed Geophysical Investigation of the Grounding of Henry Ice Rise, with Implications for Holocene Ice-Sheet Extent.

NASA Astrophysics Data System (ADS)

Wearing, M.; Kingslake, J.

2017-12-01

It is generally assumed that since the Last Glacial Maximum the West Antarctic Ice Sheet (WAIS) has experienced monotonic retreat of the grounding line (GL). However, recent studies have cast doubt on this assumption, suggesting that the retreat of the WAIS grounding line may have been followed by a significant advance during the Holocene in the Weddell and Ross Sea sectors. Constraining this evolution is important as reconstructions of past ice-sheet extent are used to spin-up predictive ice-sheet models and correct mass-balance observations for glacial isostatic adjustment. Here we examine in detail the formation of the Henry Ice Rise (HIR), which ice-sheet model simulations suggest played a key role in Holocene ice-mass changes in the Weddell Sea sector. Observations from a high-resolution ground-based, ice-penetrating radar survey are best explained if the ice rise formed when the Ronne Ice Shelf grounded on a submarine high, underwent a period of ice-rumple flow, before the GL migrated outwards to form the present-day ice rise. We constrain the relative chronology of this evolution by comparing the alignment and intersection of isochronal internal layers, relic crevasses, surface features and investigating the dynamic processes leading to their complex structure. We also draw analogies between HIR and the neighbouring Doake Ice Rumples. The date of formation is estimated using vertical velocities derived with a phase-sensitive radio-echo sounder (pRES). Ice-sheet models suggest that the formation of the HIR and other ice rises may have halted and reversed large-scale GL retreat. Hence the small-scale dynamics of these crucial regions could have wide-reaching consequences for future ice-sheet mass changes and constraining their formation and evolution further would be beneficial. One stringent test of our geophysics-based conclusions would be to drill to the bed of HIR to sample the ice for isotopic analysis and the bed for radiocarbon analysis.

Assessing the Global Climate Response to Freshwater Forcing from the Antarctic Ice Sheet Under Future Climate Scenarios

NASA Astrophysics Data System (ADS)

Rogstad, S.; Condron, A.; DeConto, R.; Pollard, D.

2017-12-01

Observational evidence indicates that the West Antarctic Ice Sheet (WAIS) is losing mass at an accelerating rate. Impacts to global climate resulting from changing ocean circulation patterns due to increased freshwater runoff from Antarctica in the future could have significant implications for global heat transport, but to-date this topic has not been investigated using complex numerical models with realistic freshwater forcing. Here, we present results from a high resolution fully coupled ocean-atmosphere model (CESM 1.2) forced with runoff from Antarctica prescribed from a high resolution regional ice sheet-ice shelf model. Results from the regional simulations indicate a potential freshwater contribution from Antarctica of up to 1 m equivalent sea level rise by the end of the century under RCP 8.5 indicating that a substantial input of freshwater into the Southern Ocean is possible. Our high resolution global simulations were performed under IPCC future climate scenarios RCP 4.5 and 8.5. We will present results showing the impact of WAIS collapse on global ocean circulation, sea ice, air temperature, and salinity in order to assess the potential for abrupt climate change triggered by WAIS collapse.

Toward an integrated ice core chronology using relative and orbital tie-points

NASA Astrophysics Data System (ADS)

Bazin, L.; Landais, A.; Lemieux-Dudon, B.; Toyé Mahamadou Kele, H.; Blunier, T.; Capron, E.; Chappellaz, J.; Fischer, H.; Leuenberger, M.; Lipenkov, V.; Loutre, M.-F.; Martinerie, P.; Parrenin, F.; Prié, F.; Raynaud, D.; Veres, D.; Wolff, E.

2012-04-01

Precise ice cores chronologies are essential to better understand the mechanisms linking climate change to orbital and greenhouse gases concentration forcing. A tool for ice core dating (DATICE [developed by Lemieux-Dudon et al., 2010] permits to generate a common time-scale integrating relative and absolute dating constraints on different ice cores, using an inverse method. Nevertheless, this method has only been applied for a 4-ice cores scenario and for the 0-50 kyr time period. Here, we present the bases for an extension of this work back to 800 ka using (1) a compilation of published and new relative and orbital tie-points obtained from measurements of air trapped in ice cores and (2) an adaptation of the DATICE inputs to 5 ice cores for the last 800 ka. We first present new measurements of δ18Oatm and δO2/N2 on the Talos Dome and EPICA Dome C (EDC) ice cores with a particular focus on Marine Isotopic Stages (MIS) 5, and 11. Then, we show two tie-points compilations. The first one is based on new and published CH4 and δ18Oatm measurements on 5 ice cores (NorthGRIP, EPICA Dronning Maud Land, EDC, Talos Dome and Vostok) in order to produce a table of relative gas tie-points over the last 400 ka. The second one is based on new and published records of δO2/N2, δ18Oatm and air content to provide a table of orbital tie-points over the last 800 ka. Finally, we integrate the different dating constraints presented above in the DATICE tool adapted to 5 ice cores to cover the last 800 ka and show how these constraints compare with the established gas chronologies of each ice core.

Visual-Stratigraphic Dating of the GISP2 Ice Core: Basis, Reproducibility, and Application

NASA Technical Reports Server (NTRS)

Alley, R. B.; Shuman, C. A.; Meese, D. A.; Gow, A. J.; Taylor, K. C.; Cuffey, K. M.; Fitzpatrick, J. J.; Grootes, P. M.; Zielinski, G. A.; Ram, M.;

Visual-stratigraphic dating of the GISP2 ice core: Basis, reproducibility, and application

NASA Astrophysics Data System (ADS)

Alley, R. B.; Shuman, C. A.; Meese, D. A.; Gow, A. J.; Taylor, K. C.; Cuffey, K. M.; Fitzpatrick, J. J.; Grootes, P. M.; Zielinski, G. A.; Ram, M.; Spinelli, G.; Elder, B.

1997-11-01

Annual layers are visible in the Greenland Ice Sheet Project 2 ice core from central Greenland, allowing rapid dating of the core. Changes in bubble and grain structure caused by near-surface, primarily summertime formation of hoar complexes provide the main visible annual marker in the Holocene, and changes in "cloudiness" of the ice correlated with dustiness mark Wisconsinan annual cycles; both markers are evident and have been intercalibrated in early Holocene ice. Layer counts are reproducible between different workers and for one worker at different times, with 1% error over century-length times in the Holocene. Reproducibility is typically 5% in Wisconsinan ice-age ice and decreases with increasing age and depth. Cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50,000 years. Visible observations are not greatly degraded by "brittle ice" or many other core-quality problems, allowing construction of long, consistently sampled time series. High accuracy requires careful study of the core by dedicated observers.

Rapid coupling between ice volume and polar temperature over the past 150,000 years.

PubMed

Grant, K M; Rohling, E J; Bar-Matthews, M; Ayalon, A; Medina-Elizalde, M; Ramsey, C Bronk; Satow, C; Roberts, A P

2012-11-29

Current global warming necessitates a detailed understanding of the relationships between climate and global ice volume. Highly resolved and continuous sea-level records are essential for quantifying ice-volume changes. However, an unbiased study of the timing of past ice-volume changes, relative to polar climate change, has so far been impossible because available sea-level records either were dated by using orbital tuning or ice-core timescales, or were discontinuous in time. Here we present an independent dating of a continuous, high-resolution sea-level record in millennial-scale detail throughout the past 150,000 years. We find that the timing of ice-volume fluctuations agrees well with that of variations in Antarctic climate and especially Greenland climate. Amplitudes of ice-volume fluctuations more closely match Antarctic (rather than Greenland) climate changes. Polar climate and ice-volume changes, and their rates of change, are found to covary within centennial response times. Finally, rates of sea-level rise reached at least 1.2 m per century during all major episodes of ice-volume reduction.

Geochronology of Tropical Alpine Glaciations From the Cordillera Huayhuash, Peru

NASA Astrophysics Data System (ADS)

Hall, S. R.; Farber, D. L.; Rodbell, D. T.; Finkel, R. C.; Ramage, J. M.; Smith, J. A.; Mark, B. G.; Seltzer, G. O.

2004-12-01

The Cordillera Huayhuash of the Central Peruvian Andes (10.3° S, 76.9° W) is an ideal range to study regional climate signals and variations in paleo-ice volumes. Located between the Cordillera Blanca to the north and the Junin region to the south, the range trends nearly north-south with modern glaciers confined to the high peaks (>4800 m). Cross-cutting relationships, geomorphology, and correlation with surface exposure dated moraines in the nearby Cordillera Blanca suggest the region preserves a rich record of tropical glaciation. In order to determine the glacial chronology we mapped and dated glacial features of the Jahuacocha valley (which drains the western side of the range) and two eastern drainages, the Mitococha valley, and the Carhuacocha valley. At each locality we used ASTER data, aerial photographs, and GPS to map glacial features both within main valleys and tributaries. We sampled quartz-bearing erratics on moraine crests as well as ice-polished bedrock surfaces for exposure age dating using in situ produced cosmogenic 10Be and 26Al. In the Jahuacocha valley, the greatest ice extent reached an elevation of ˜4090m and moraine crest boulders yield and age of ˜11.2 ±0.6 ka suggesting a significant late Glacial ice advance or stillstand. A younger cluster of moraines exists ˜1 km up-valley at an elevation of ˜4100m. These moraines, dated at ˜8.0 ±1.0 ka, suggest an early Holocene advance. In the Mitococha valley, a young moraine and polished bedrock dated at ˜0.2 ka and ˜11.4 ±0.4 ka respectively span the late Glacial through recent. The late Glacial features of this eastern drainage occur at an elevation of ˜4100m while the recent events occur at an elevation of ˜4380m. Our preliminary results suggest that all three valleys experienced a very similar glacial history with minor differences likely due to the variations in valley morphology. Comparing the chronology of glaciation in the Cordillaera Huayhuash with that in regions to the south and north will provide a means of evaluating the degree of synchroneity of glaciation and climate change across 5° of latitude in the tropics.

Comparison of Passive Microwave-Derived Early Melt Onset Records on Arctic Sea Ice

NASA Technical Reports Server (NTRS)

Bliss, Angela C.; Miller, Jeffrey A.; Meier, Walter N.

2017-01-01

Two long records of melt onset (MO) on Arctic sea ice from passive microwave brightness temperatures (Tbs) obtained by a series of satellite-borne instruments are compared. The Passive Microwave (PMW) method and Advanced Horizontal Range Algorithm (AHRA) detect the increase in emissivity that occurs when liquid water develops around snow grains at the onset of early melting on sea ice. The timing of MO on Arctic sea ice influences the amount of solar radiation absorbed by the ice-ocean system throughout the melt season by reducing surface albedos in the early spring. This work presents a thorough comparison of these two methods for the time series of MO dates from 1979through 2012. The methods are first compared using the published data as a baseline comparison of the publically available data products. A second comparison is performed on adjusted MO dates we produced to remove known differences in inter-sensor calibration of Tbs and masking techniques used to develop the original MO date products. These adjustments result in a more consistent set of input Tbs for the algorithms. Tests of significance indicate that the trends in the time series of annual mean MO dates for the PMW and AHRA are statistically different for the majority of the Arctic Ocean including the Laptev, E. Siberian, Chukchi, Beaufort, and central Arctic regions with mean differences as large as 38.3 days in the Barents Sea. Trend agreement improves for our more consistent MO dates for nearly all regions. Mean differences remain large, primarily due to differing sensitivity of in-algorithm thresholds and larger uncertainties in thin-ice regions.

Reassessment of the Upper Fremont Glacier Ice-Core Chronologies by Synchronizing of Ice-Core-Water Isotopes to a Nearby Tree-Ring Chronology.

PubMed

Chellman, Nathan; McConnell, Joseph R; Arienzo, Monica; Pederson, Gregory T; Aarons, Sarah M; Csank, Adam

2017-04-18

The Upper Fremont Glacier (UFG), Wyoming, is one of the few continental glaciers in the contiguous United States known to preserve environmental and climate records spanning recent centuries. A pair of ice cores taken from UFG have been studied extensively to document changes in climate and industrial pollution (most notably, mid-19th century increases in mercury pollution). Fundamental to these studies is the chronology used to map ice-core depth to age. Here, we present a revised chronology for the UFG ice cores based on new measurements and using a novel dating approach of synchronizing continuous water isotope measurements to a nearby tree-ring chronology. While consistent with the few unambiguous age controls underpinning the previous UFG chronologies, the new interpretation suggests a very different time scale for the UFG cores with changes of up to 80 years. Mercury increases previously associated with the mid-19th century Gold Rush now coincide with early-20th century industrial emissions, aligning the UFG record with other North American mercury records from ice and lake sediment cores. Additionally, new UFG records of industrial pollutants parallel changes documented in ice cores from southern Greenland, further validating the new UFG chronologies while documenting the extent of late 19th and early 20th century pollution in remote North America.

Reassessment of the Upper Fremont Glacier ice-core chronologies by synchronizing of ice-core-water isotopes to a nearby tree-ring chronology

USGS Publications Warehouse

Chellman, Nathan J.; McConnell, Joseph R.; Arienzo, Monica; Pederson, Gregory T.; Aarons, Sarah; Csank, Adam

2017-01-01

The Upper Fremont Glacier (UFG), Wyoming, is one of the few continental glaciers in the contiguous United States known to preserve environmental and climate records spanning recent centuries. A pair of ice cores taken from UFG have been studied extensively to document changes in climate and industrial pollution (most notably, mid-19th century increases in mercury pollution). Fundamental to these studies is the chronology used to map ice-core depth to age. Here, we present a revised chronology for the UFG ice cores based on new measurements and using a novel dating approach of synchronizing continuous water isotope measurements to a nearby tree-ring chronology. While consistent with the few unambiguous age controls underpinning the previous UFG chronologies, the new interpretation suggests a very different time scale for the UFG cores with changes of up to 80 years. Mercury increases previously associated with the mid-19th century Gold Rush now coincide with early-20th century industrial emissions, aligning the UFG record with other North American mercury records from ice and lake sediment cores. Additionally, new UFG records of industrial pollutants parallel changes documented in ice cores from southern Greenland, further validating the new UFG chronologies while documenting the extent of late 19th and early 20th century pollution in remote North America.

Sea-ice indicators of polar bear habitat

NASA Astrophysics Data System (ADS)

Stern, Harry L.; Laidre, Kristin L.

2016-09-01

Nineteen subpopulations of polar bears (Ursus maritimus) are found throughout the circumpolar Arctic, and in all regions they depend on sea ice as a platform for traveling, hunting, and breeding. Therefore polar bear phenology - the cycle of biological events - is linked to the timing of sea-ice retreat in spring and advance in fall. We analyzed the dates of sea-ice retreat and advance in all 19 polar bear subpopulation regions from 1979 to 2014, using daily sea-ice concentration data from satellite passive microwave instruments. We define the dates of sea-ice retreat and advance in a region as the dates when the area of sea ice drops below a certain threshold (retreat) on its way to the summer minimum or rises above the threshold (advance) on its way to the winter maximum. The threshold is chosen to be halfway between the historical (1979-2014) mean September and mean March sea-ice areas. In all 19 regions there is a trend toward earlier sea-ice retreat and later sea-ice advance. Trends generally range from -3 to -9 days decade-1 in spring and from +3 to +9 days decade-1 in fall, with larger trends in the Barents Sea and central Arctic Basin. The trends are not sensitive to the threshold. We also calculated the number of days per year that the sea-ice area exceeded the threshold (termed ice-covered days) and the average sea-ice concentration from 1 June through 31 October. The number of ice-covered days is declining in all regions at the rate of -7 to -19 days decade-1, with larger trends in the Barents Sea and central Arctic Basin. The June-October sea-ice concentration is declining in all regions at rates ranging from -1 to -9 percent decade-1. These sea-ice metrics (or indicators of habitat change) were designed to be useful for management agencies and for comparative purposes among subpopulations. We recommend that the National Climate Assessment include the timing of sea-ice retreat and advance in future reports.

Latest Pleistocene and Holocene Glacier Fluctuations in southernmost Patagonia

NASA Astrophysics Data System (ADS)

Menounos, B.; Maurer, M.; Clague, J. J.; osborn, G.; Ponce, F.; Davis, P. T.; Rabassa, J.; Coronato, A.; Marr, R.

2011-12-01

Summer insolation has been proposed to explain long-term glacier fluctuations during the Holocene. If correct, the record of glacier fluctuations at high latitudes in the Southern Hemisphere should differ from that in the Northern Hemisphere. Testing this insolation hypothesis has been hampered by dating uncertainties of many Holocene glacier chronologies from Patagonia. We report on our ongoing research aimed at developing a regional glacier chronology at the southern end of the Andes north and west of Ushuaia, Argentina. We have found evidence for an advance of cirque glaciers at the end of the Pleistocene; one or locally two closely spaced moraines extend up to 2 km beyond Little Ice Age moraines. Radiocarbon dating of terrestrial macrofossils recovered from basal sediments behind two of these moraines yielded ages of 10,320 ± 25 and 10,330 ± 30 14C yr BP. These moraines may record glacier advances coeval with the Antarctic Cold Reversal; surface exposure dating of these moraines is currently in progress to test this hypothesis. We find no evidence of Holocene moraines older than 6800 14C yr BP, based on the distribution of Hudson tephra of that age. At some sites, there is evidence for an early Neoglacial advance of glaciers slightly beyond (< 0.5 km) Little Ice Age limits. Terrestrial macrofossils at the upper contact of basal till from one site yielded an age of 4505 ± 30 14C yr BP; this age overlaps the most probable age range of early Neoglacial ice expansion in southern Patagonia reported by Porter (2000) and the age of plants killed by expansion of the Quelccaya Ice Cap in Peru. We have documented multiple wood mats with stumps in growth position separated by till units in a 100 m section of the northeast lateral moraine at Stoppani Glacier (54.78 S, 68.98 W), 50 km west of Ushuaia. Ten radiocarbon ages on these wood mats range in age from 3510 ± 15 to 135 ± 15 14C yr BP. The mats decrease in age up-section; many overlap with published age ranges for Neoglacial advances in western Canada. Taken together, these data: a) do not support the summer insolation hypothesis for Holocene glacier fluctuations in southernmost Patagonia; b) confirm paleobotanical evidence for a warm, dry early Holocene; and c) suggest that many Neoglacial advances in southernmost Patagonia and western North America were synchronous.

Upper ocean stratification and sea ice growth rates during the summer-fall transition, as revealed by Elephant seal foraging in the Adélie Depression, East Antarctica

NASA Astrophysics Data System (ADS)

Williams, G. D.; Hindell, M.; Houssais, M.-N.; Tamura, T.; Field, I. C.

2010-11-01

Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140-148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine-rejection in the local coastal polynyas. In 2005 two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for nearly two weeks at the onset of sea ice growth. One of the seals migrated north thereafter and the other headed west, possibly utilising the Antarctic Slope Front current near the continental shelf break. In 2010, after that years calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and occupied the Commonwealth Bay polynya from March through April. Here we present unique observations of the regional oceanography during the summer-fall transition, in particular (a) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (b) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (c) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth (7.5-12.5 cm s-1). Heat and freshwater budgets to 200-300 m are used to estimate the ocean heat content, heat flux and sea ice growth rates. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer-fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep seasonal mixed layer and chlorophyll maximum that is a reported feature of this location.

Upper ocean stratification and sea ice growth rates during the summer-fall transition, as revealed by Elephant seal foraging in the Adélie Depression, East Antarctica

NASA Astrophysics Data System (ADS)

Williams, G. D.; Hindell, M.; Houssais, M.-N.; Tamura, T.; Field, I. C.

2011-03-01

Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140-148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine rejection in the local coastal polynyas. In 2005, two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for several weeks from the end of February. One of the seals migrated west to the Dibble Ice Tongue, apparently utilising the Antarctic Slope Front current near the continental shelf break. In 2010, immediately after that year's calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and sampled the Commonwealth Bay polynya from March through April. Here we present observations of the regional oceanography during the summer-fall transition, in particular (i) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (ii) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (iii) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth. Heat and freshwater budgets to 200-300 m are used to estimate the ocean heat content (400→50 MJ m-2), flux (50-200 W m-2 loss) and sea ice growth rates (maximum of 7.5-12.5 cm day-1). Mean seal-derived sea ice growth rates were within the range of satellite-derived estimates from 1992-2007 using ERA-Interim data. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer/fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep seasonal mixed layer and chlorophyll maximum that is a reported feature of this location.

Monitoring Snow on ice as Critical Habitat for Ringed Seals

NASA Astrophysics Data System (ADS)

Kelly, B. P.; Moran, J.; Douglas, D. C.; Nghiem, S. V.

2007-12-01

Ringed seals are the primary prey of polar bears, and they are found in all seasonally ice covered seas of the northern hemisphere as well as in several freshwater lakes. The presence of snow covered sea ice is essential for successful ringed seal reproduction. Ringed seals abrade holes in the ice allowing them to surface and breathe under the snow cover. Where snow accumulates to sufficient depths, ringed seals excavate subnivean lairs above breathing holes. They rest, give birth, and nurse their young in those lairs. Temperatures within the lairs remain within a few degrees of freezing, well within the zone of thermal neutrality for newborn ringed seals, even at ambient temperatures of -30° C. High rates of seal mortality have been recorded when early snow melt caused lairs to collapse exposing newborn seals to predators and to subsequent extreme cold events. As melt onset dates come earlier in the Arctic Ocean, ringed seal populations (and the polar bears that depend upon them) will be increasingly challenged. We determined dates of lair abandonment by ringed seals fitted with radio transmitters in the Beaufort Sea (n = 60). We compared abandonment dates to melt onset dates measured in the field, as well as estimated dates derived from active (Ku-band backscatter) and passive (SSM/I) microwave satellite imagery. Date of snow melt significantly improved models of environmental influences on the timing of lair abandonment. We used an algorithm based on multi-channel means and variances of passive microwave data to detect melt onset dates. Those melt onset dates predicted the date of lair abandonment ± 3 days (r 2 = 0.982, p = 0.001). The predictive power of passive microwave proxies combined with their historical record suggest they could serve to monitor critical changes to ringed seal habitat.

An Imminent Revolution in Modeling Interactions of Ice Sheets With Climate

NASA Astrophysics Data System (ADS)

Hughes, T.

2008-12-01

Modeling continental ice sheets was inaugurated by meteorologists William Budd and Uwe Radok, with mathematician Richard Jenssen, in 1971. Their model calculated the thermal and mechanical regime using measured surface accumulation rates, temperatures, and elevations, and bed topography. This top-down approach delivered a basal thermal regime of temperatures or melting rates for an assumed basal geothermal heat flux. When Philippe Huybrechts and others incorporated time, largely unknownpast surface conditions had a major effect on present basal thermal conditions. This approach produced ice-sheet models with only a slow response to external forcing, whereas the glacial geological record and climate records from ice and ocean cores show that ice sheets can have rapid changes in size and shape independent of external forcing. These top-down models were wholly inadequate for reconstructing former ice sheets at the LGM for CLIMAP in 1981. Ice-sheet areas,elevations, and volumes provided the albedo, surface topography, and sea-surface area as input to climate models. A bottom-up model based on dated glacial geology was developed to provide the areal extent and basal thermal regime of ice sheets at the LGM. Basal thermal conditions determined ice-bed coupling and therefore the elevation of ice sheets. High convex ice surfaces for slow sheet flow lower about 20 percent when a frozen bed becomes thawed. As further basal melting drowns bedrock bumps that "pin" basal ice, the ice surface becomes concave in fast stream flow that ends as low floating ice shelves at marine ice margins. A revolution in modeling interactions between glaciation, climate, and sea level is driven by new Greenland and Antarctic data from Earth-orbiting satellites, airborne and surface traverses, and deep drilling. We anticipate continuous data acquisition of surface albedo, accumulation/ablation rates, elevations, velocities, and temperatures over a whole ice sheet, mapping basal thermal conditions by radar, seismic, and magnetic profiling, and direct measurement of basal conditions by deep drilling and coring into the ice and the bed. These data allow calculating the geothermal heat flux and mapping flow of basal meltwater from geothermal sources to sinks at the termini of ice streams, which discharge up to 90 percent of the ice. James Fastook has a preliminary solution of the full momentum equation needed to model ice streams. Douglas MacAyeal has pioneered modeling catastrophic ice-shelf disintegration that releases "armadas" of icebergs into the world ocean, to extract heat from ocean surface water and thereby reduce the critical ocean-to-atmosphere heat exchange that drives global climate. Ice sheets are the only component of Earth's climate machine that can destroy itself-- swiftly--and thereby radically and rapidly alter global climate and sea level.

Spatial variability and trends of seasonal snowmelt processes over Antarctic sea ice observed by satellite scatterometers

NASA Astrophysics Data System (ADS)

Arndt, S.; Haas, C.

2017-12-01

Snow is one of the key drivers determining the seasonal energy and mass budgets of sea ice in the Southern Ocean. Here, we analyze radar backscatter time series from the European Remote Sensing Satellites (ERS)-1 and-2 scatterometers, from the Quick Scatterometer (QSCAT), and from the Advanced Scatterometer (ASCAT) in order to observe the regional and inter-annual variability of Antarctic snowmelt processes from 1992 to 2014. On perennial ice, seasonal backscatter changes show two different snowmelt stages: A weak backscatter rise indicating the initial warming and metamorphosis of the snowpack (pre-melt), followed by a rapid rise indicating the onset of internal snowmelt and thaw-freeze cycles (snowmelt). In contrast, similar seasonal backscatter cycles are absent on seasonal ice, preventing the periodic retrieval of spring/summer transitions. This may be due to the dominance of ice bottom melt over snowmelt, leading to flooding and ice disintegration before strong snowmelt sets in. Resulting snowmelt onset dates on perennial sea ice show the expected latitudinal gradient from early melt onsets (mid-November) in the northern Weddell Sea towards late (end-December) or even absent snowmelt conditions further south. This result is likely related to seasonal variations in solar shortwave radiation (absorption). In addition, observations with different microwave frequencies allow to detect changing snow properties at different depths. We show that short wavelengths of passive microwave observations indicate earlier pre-melt and snowmelt onset dates than longer wavelength scatterometer observations, in response to earlier warming of upper snow layers compared to lower snow layers. Similarly, pre-melt and snowmelt onset dates retrieved from Ku-Band radars were earlier by an average of 11 and 23 days, respectively, than those retrieved from C-Band. This time difference was used to correct melt onset dates retrieved from Ku-Band to compile a consistent time series from 1992 to 2014. The subsequent regression analysis showed that no significant temporal trend in the retrieved snowmelt onset dates can be observed, but strong inter-annual variability. This absence of any notable changes in snowmelt behavior is in line with the small observed temporal changes of the Antarctic sea ice cover and atmospheric warming

An up-to-date quality-controlled surface mass balance data set for the 90°-180°E Antarctica sector and 1950-2005 period

NASA Astrophysics Data System (ADS)

Magand, O.; Genthon, C.; Fily, M.; Krinner, G.; Picard, G.; Frezzotti, M.; Ekaykin, A. A.

2007-06-01

On the basis of thousands of surface mass balance (SMB) field measurements over the entire Antarctic ice sheet it is currently estimated that more than 2 Gt of ice accumulate each year at the surface of Antarctica. However, these estimates suffer from large uncertainties. Various problems affect Antarctic SMB measurements, in particular, limited or unwarranted spatial and temporal representativeness, measurement inaccuracy, and lack of quality control. We define quality criteria on the basis of (1) an up-to-date review and quality rating of the various SMB measurement methods and (2) essential information (location, dates of measurements, time period covered by the SMB values, and primary data sources) related to each SMB data. We apply these criteria to available SMB values from Queen Mary to Victoria lands (90°-180°E Antarctic sector) from the early 1950s to present. This results in a new set of observed SMB values for the 1950-2005 time period with strong reduction in density and coverage but also expectedly reduced inaccuracies and uncertainties compared to other compilations. The quality-controlled SMB data set also contains new results from recent field campaigns (International Trans-Antarctic Scientific Expedition (ITASE), Russian Antarctic Expedition (RAE), and Australian National Antarctic Research Expeditions (ANARE) projects) which comply with the defined quality criteria. A comparative evaluation of climate model results against the quality-controlled updated SMB data set and other widely used ones illustrates that such Antarctic SMB studies are significantly affected by the quality of field SMB values used as reference.

A method to precisely measure Ar isotopes and Xe/Kr ratios in air trapped in ice cores for simultaneous ice core dating and mean ocean temperature reconstruction

NASA Astrophysics Data System (ADS)

Yan, Y.; Ng, J.; Higgins, J. A.; Kurbatov, A.; Clifford, H.; Spaulding, N. E.; Mayewski, P. A.; Brook, E.; Bender, M. L.; Severinghaus, J. P.

2017-12-01

Antarctic efforts are underway to find and retrieve ice cores older than 800 thousand years (kyr) by both shallow drilling in "blue ice" areas and classic deep ice coring. Ice stratigraphy at "blue ice" sites is typically disordered, and the high cost of deep drilling mandates rapid reconnaissance drilling (e.g. RAID) with very small sample size. Both approaches therefore require methods of absolute dating on a single piece of ice without stratigraphic context. Here we present a dating method modified from Bender et al. (2008; PNAS) to precisely measure the isotopic composition of argon (36Ar, 38Ar, and 40Ar) in air bubbles trapped in the ice, which changes over time in a known way. Our method has an analytical uncertainty of 110 kyr (1σ) or 10% of the age of the sample, whichever is greater. We measured Ar isotopes from the Allan Hills blue ice areas, East Antarctica, where 1 Ma ice was previously found by Higgins et al. (2015; PNAS). Results show ice as old as 2.7±0.3 million years, but the ice column is stratigraphically disturbed. Hence Allan Hills ice core records should be viewed as a series of "climate snapshots" rather than a continuum. Xenon-to-krypton (Xe/Kr) ratios are also measured in the same aliquot of extracted gas to reconstruct mean ocean temperature (Shackleton et al., 2016; Fall AGU). Preliminary mean ocean temperature in ice older than 1 Ma ranges from -0.3 to -1.2 deg. colder than present with an uncertainty of 0.24 deg., which agrees well with other Pleistocene ocean temperature records (e.g. Rohling et al., 2014; Nature and Elderfield et al., 2012; Science). The observed range is 40% of the glacial-interglacial variability in the 100-kyr climate cycles ( 2 deg.), close to the 50% reduction in the glacial-interglacial δ18O amplitude across the Mid-Pleistocene Transition. Finally, Xe/Kr ratios are found to correlate positively with δD of the ice, implying a coupling between the global ocean temperature and Antarctic temperature throughout the Pleistocene.

10Be dating of late-glacial moraines near the Cordillera Vilcanota and the Quelccaya Ice Cap, Peru

NASA Astrophysics Data System (ADS)

Kelly, M. A.; Thompson, L. G.

2004-12-01

The surface exposure method, based on the measurement of cosmogenic 10Be produced in quartz, is applied to determine the age of deposition of glacial moraines near the Cordillera Vilcanota and the Quelccaya Ice Cap (about 13° S, 70° W) in southeastern Peru. These data are useful for examining the timing of past glaciation in the tropical Andes and for comparison with chronologies of glaciation at higher latitudes. The preliminary data set consists of more than ten surface exposure ages. Samples used for dating are from the surfaces of boulders on a set of prominent moraines about four kilometers away from the present ice margins. The age of the moraine set was previously bracketed by radiocarbon dating of peat associated with the glacial deposits. Based on radiocarbon ages, these moraines were formed during the late-glacial period, just prior to the last glacial-interglacial transition. The surface exposure dating method enables the direct dating of the moraines. Surface exposure dates are cross-checked with the previously existing radiocarbon dates and provide a means to improve the chronology of past glaciation in the tropical Andes.

Identification and correlation of crypto-tephra horizons within Marine Isotope Stages 5e to 4 of the NGRIP ice-core - culmination of the SMART research project

NASA Astrophysics Data System (ADS)

Meara, R. H.; Davies, S. M.; Abbott, P. M.; Pearce, N. J.; Austin, W. E.; Bigler, M.; Steffensen, J. P.; Svensson, A.

2012-12-01

The NERC-funded SMART (Synchronising MARine and ice-core records using Tephrochronology) project has focused on dating, correlating and synchronising palaeo climatic events during the last interglacial-glacial transition by developing a regional tephrochronological framework for the North Atlantic region. The NGRIP ice-core within the Greenland ice sheet is the focus of this work and here we report on the tephra horizons identified to date. A suite of c. 1,000 ice samples (c. 173 m) were subsampled, chosen for their relation to a) known tephra horizons in marine and terrestrial proxy records, b) prominent sulphate peaks and c) rapid climate transitions. To date, 10 new tephra horizons have been identified, ranging in age from 71,430 - 121,865 years b2k which add to the NGRIP tephras identified previously by Abbott et al. Individual tephra shards within each horizon have been geochemically characterised using both EMPA and LA-ICP-MS techniques. The tephras are typically basaltic in composition and show predominantly Icelandic compositions with sources identified as the Grimsvötn, Hekla-Katla and Veidivötn volcanic systems. Together with the work on the GRIP ice-core, a comprehensive suite of tephras now provides a detailed tephrochronological framework for the Greenland ice-sheet (Abbott et al. 2012). At present, four of the identified tephra horizons are candidates for correlation with known crypto-tephra horizons from marine records. These potential correlations present a robust means for dating and testing phase relationships and climate-forcing mechanisms associated with dramatic climate transitions during MIS stages 5e - 4.

Reconstructing the history of major Greenland glaciers since the Little Ice Age

NASA Astrophysics Data System (ADS)

Csatho, B. M.; Schenk, A. F.; van der Veen, C. J.; Stearns, L.; Babonis, G. S.

2008-12-01

The Greenland Ice Sheet may have been responsible for rapid sea level rise during the last interglacial period and recent studies indicate that it is likely to make a faster contribution to sea-level rise than previously believed. Rapid thinning and velocity increase has been observed on most major outlet glaciers with terminus retreat that might lead to increased discharge from the interior and consequent further thinning and retreat. Potentially, such behavior could have serious implications for global sea level. However, the current thinning may simply be a manifestation of longer-term behavior of the ice sheet as it responds to the general warming following the Little Ice Age (LIA). Although Greenland outlet glaciers have been comprehensively monitored since the 1980s, studies of long-term changes mostly rely on records of the calving front position. Such records can be misleading because the glacier terminus, particularly if it is afloat, can either advance or retreat as ice further upstream thins and accelerates. To assess whether recent trends deviate from longer-term behavior, we examined three rapidly thinning and retreating outlet glaciers, Jakobshavn Isbrae in west, Kangerdlussuaq Glacier in east and Petermann Glacier in northwest Greenland. Glacier surface and trimline elevations, as well as terminus positions were measured using historical photographs and declassified satellite imagery acquired between the 1940s and 1985. These results were combined with data from historical records, ground surveys, airborne laser altimetry, satellite observations and field mapping of lateral moraines and trimlines, to reconstruct the history of changes since the (LIA) up to the present. We identified several episodes of rapid thinning and ice shelf break-up, including thinning episodes that occurred when the calving front was stationary. Coastal weather station data are used to assess the influence of air temperatures and intensity of surface melting, and to isolate glacier changes likely associated with changes in glacier dynamics. We also examined the potential influence of geologic control, including the effect of increased heat flux and high rates of subglacial melt suggested by geophysical data.

76 FR 1362 - Safety Zone; Ice Conditions for the Baltimore Captain of Port Zone

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-10

...-AA00 Safety Zone; Ice Conditions for the Baltimore Captain of Port Zone AGENCY: Coast Guard, DHS... protect mariners from the hazards associated with ice in the navigable waterways. DATES: This rule is... necessary to protect persons and vessels against the hazards associated with ice on navigable waters. Such...

78 FR 12595 - Safety Zone for Ice Conditions; Baltimore Captain of the Port Zone

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-25

... 1625-AA00 Safety Zone for Ice Conditions; Baltimore Captain of the Port Zone AGENCY: Coast Guard, DHS... protect mariners from the hazards associated with ice in the navigable waterways. DATES: This rule has... vessels against the hazards associated with ice on navigable waters. Such hazards include vessels becoming...

Sea ice effects in a spectral wave model: principles and practical implementation

NASA Astrophysics Data System (ADS)

Boutin, G.; Ardhuin, F.; Girard-Ardhuin, F.; Dumont, D.; Sévigny, C.

2016-12-01

Numerical wave models have their largest errors around sea ice, and their accuracy is generally unknown in the ice as very few data are available. This is largely because they do not, or in a coarse way, take into account the interactions of waves and sea ice, and because the necessary information about sea ice properties is not readily available. Recent progress have expanded our knowledge of wave scattering by sea ice as well as several dissipation processes, highlighting the need to include ice thickness and information on the ice floes size. Starting from a consistent representation of energy and dispersion in the presence of sea ice, we have redefined a set of self-consistent dissipation and scattering parameterizations for the WAVEWATCH III model which is expected to apply to a variety of ice conditions with the exception of forming ice. In our model the ice is treated as a single layer that can be fractured in many floes expected to be equivalent to circular floes with a power law distribution of diameters that is defined from the maximum diameter Dmax and a fragility parameter. This layer of ice induces a dissipation of the wave energy through basal friction (Stopa et al. The Cryosphere, 2016) and secondary creep associated with ice flexure (Cole et al. 1998), in addition to an energy-conserving scattering modeled following Kohout and Meylan (2006). The ice thickness and concentration are taken uniform over a model grid cell, and are typically provided by model products or satellite data, and are not affected by the waves. The wave model results are used to update Dmax by a probabilistic evaluation of ice break-up by the waves. This process introduces an interesting feedback on the wave scattering and dissipation. The combination of dissipation and scattering leads to spatial patterns in the wave height and directional spreading of the wave field that can be easily tested with in situ or remote sensing data (Sutherland and Gascard GRL 2016, Ardhuin et al. GRL 2016). In particular our model assumes that wave dissipation in unbroken ice is dominated by creep, which then vanishes once the ice is broken, reproducing the wave attenuation observed by Collins et al. (GRL 2015). Consistent with the low directional spread in most SAR imagery, scattering does not appear as the main factor for the attenuation of dominant swells with periods 12 to 25 s.

Reliable radiocarbon evidence for the maximum extent of the West Antarctic Ice Sheet in the easternmost Amundsen Sea Embayment during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Hillenbrand, C. D.; Klages, J. P.; Kuhn, G.; Smith, J.; Graham, A. G. C.; Gohl, K.; Wacker, L.

2016-02-01

We present the first age control and sedimentological data for the upper part of a stratified seismic unit that is unusually thick ( 6-9 m) for the outer shelf of the ASE and overlies an acoustically transparent unit. The transparent unit probably consists of soft till deposited during the last advance of grounded ice onto the outer shelf. We mapped subtle mega-scale glacial lineations (MSGL) on the seafloor and suggest that these are probably the expressions of bedforms originally moulded into the surface of the underlying till layer. We note that the lineations are less distinct when compared to MSGLs recorded in bathymetric data collected further upstream and suggest that this is because of the blanketing influence of the thick overlying drape. The uppermost part (≤ 3 m) of the stratified drape was sampled by two of our sediment cores and contains sufficient amounts of calcareous foraminifera throughout to establish reliable age models by radiocarbon dating. In combination with facies analysis of the recovered sediments the obtained radiocarbon dates suggest deposition of the draping unit in a sub-ice shelf/sub-sea ice to seasonal-open marine environment that existed on the outer shelf from well before (>45 ka BP) the Last Glacial Maximum until today. This indicates the maximum extent of grounded ice at the LGM must have been situated south of the two core locations, where a well-defined grounding-zone wedge (`GZWa') was deposited. The third sediment core was recovered from the toe of this wedge and retrieved grounding-line proximal glaciogenic debris flow sediments that were deposited by 14 cal. ka BP. Our new data therefore provide direct evidence for 1) the maximum extent of grounded ice in the easternmost ASE at the LGM (=GZWa), 2) the existence of a large shelf area seawards the wedge that was not covered by grounded ice during that time, and 3) landward grounding line retreat from GZWa prior to 14 cal. ka BP. This knowledge will help to improve LGM ice sheet reconstructions and to quantify precisely the volume of LGM ice-sheet build-up in Antarctica. Our study also alludes to the possibility that refugia for Antarctic shelf benthos may have existed in the ASE during the last glacial period.

Episodic Neoglacial snowline descent and glacier expansion on Svalbard reconstructed from the 14C ages of ice-entombed plants

NASA Astrophysics Data System (ADS)

Miller, Gifford H.; Landvik, Jon Y.; Lehman, Scott J.; Southon, John R.

2017-01-01

The response of the Northern Hemisphere cryosphere to the monotonic decline in summer insolation and variable radiative forcing during the Holocene has been one of irregular expansion culminating in the Little Ice Age, when most glaciers attained their maximum late Holocene dimensions. Although periods of intervening still-stand or ice-retreat can be reconstructed by direct dating of ice-recessional features, defining times of Neoglacial ice growth has been limited to indirect proxies preserved in distal archives. Here we report 45 precise radiocarbon dates on in situ plants emerging from beneath receding glaciers on Svalbard that directly date the onset of snowline descent and glacier expansion, entombing the plants. Persistent snowline lowering occurred between 4.0 and 3.4 ka, but with little additional persistent lowering until early in the first millennium AD. Populations of individual 14C calendar age results and their aggregate calendar age probabilities define discrete episodes of vegetation kill and snowline lowering 240-340 AD, 410-540 AD and 670-750 AD, each with a lower snowline than the preceding episode, followed by additional snowline lowering between 1000 and 1220 AD, and between 1300 and 1450 AD. Snowline changes after 1450 AD, including the maximum ice extent of the Little Ice Age are not resolved by our collections, although snowlines remained lower than their 1450 AD level until the onset of modern warming. A time-distance diagram derived from a 250-m-long transect of dated ice-killed plants documents ice-margin advances ∼750, ∼1100 and after ∼1500 AD, concordant with distributed vegetation kill ages seen in the aggregate data set, supporting our central thesis that vegetation kill ages provide direct evidence of snowline lowering and cryospheric expansion. The mid- to late-Holocene history of snowline lowering on Svalbard is similar to ELA reconstructions of Norwegian and Svalbard cirque glaciers, and consistent with a cryospheric response to the secular decline of regional summertime insolation and stepped changes in nearby surface ocean environments. The widespread exposure of entombed plants dating from the first millennium AD suggests that Svalbard's average summer temperatures of the past century now exceed those of any century since at least 700 AD, including medieval times.

Deciphering sub-micron ice particles on Enceladus surface

NASA Astrophysics Data System (ADS)

Scipioni, F.; Schenk, P.; Tosi, F.; D'Aversa, E.; Clark, R.; Combe, J.-Ph.; Ore, C. M. Dalle

2017-07-01

The surface of Saturn's moon Enceladus is composed primarily by pure water ice. The Cassini spacecraft has observed present-day geologic activity at the moon's South Polar Region, related with the formation and feeding of Saturn's E-ring. Plumes of micron-sized particles, composed of water ice and other non-ice contaminants (e.g., CO2, NH3, CH4), erupt from four terrain's fractures named Tiger Stripes. Some of this material falls back on Enceladus' surface to form deposits that extend to the North at ∼40°W and ∼220°W, with the highest concentration found at the South Pole. In this work we analyzed VIMS-IR data to identify plumes deposits across Enceladus' surface through the variation in band depth of the main water ice spectral features. To characterize the global variation of water ice band depths across Enceladus, the entire surface was sampled with an angular resolution of 1° in both latitude and longitude, and for each angular bin we averaged the value of all spectral indices as retrieved by VIMS. The position of the plumes' deposits predicted by theoretical models display a good match with water ice band depths' maps on the trailing hemisphere, whereas they diverge significantly on the leading side. Space weathering processes acting on Enceladus' surface ionize and break up water ice molecules, resulting in the formation of particles smaller than one micron. We also mapped the spectral indices for sub-micron particles and we compared the results with the plumes deposits models. Again, a satisfactory match is observed on the trailing hemisphere only. Finally, we investigated the variation of the depth of the water ice absorption bands as a function of the phase angle. In the visible range, some terrains surrounding the Tiger Stripes show a decrease in albedo when the phase angle is smaller than 10°. This unusual effect cannot be confirmed by near infrared data, since observations with a phase angle lower than 10° are not available. For phase angle values greater than 10°, the depth of the water ice features remains quite constant within a broad range of phase angle values.

Historical Carbon Dioxide Record from the Siple Station Ice Core (1734-1983)

DOE Data Explorer

Neftel, A. [Physics Institute, University of Bern, Bern, Switzerland; Friedli, H. [Physics Institute, University of Bern, Bern, Switzerland; Moor, E. [Physics Institute, University of Bern, Bern, Switzerland; Lotscher, H. [Physics Institute, University of Bern, Bern, Switzerland; Oeschger, H. [Physics Institute, University of Bern, Bern, Switzerland; Siegenthaler, U. [Physics Institute, University of Bern, Bern, Switzerland; Stauffer, B. [Physics Institute, University of Bern, Bern, Switzerland

1994-09-01

Determinations of ancient atmospheric CO2 concentrations for Siple Station, located in West Antarctica, were derived from measurements of air occluded in a 200-m core drilled at Siple Station in the Antarctic summer of 1983-84. The core was drilled by the Polar Ice Coring Office in Nebraska and the Physics Institute at the University of Bern. The ice could be dated with an accuracy of approximately ±2 years to a depth of 144 m (which corresponds to the year 1834) by counting seasonal variations in electrical conductivity. Below that depth, the core was dated by extrapolation (Friedli et al. 1986). The gases from ice samples were extracted by a dry-extraction system, in which bubbles were crushed mechanically to release the trapped gases, and then analyzed for CO2 by infrared laser absorption spectroscopy or by gas chromatography (Neftel et al. 1985). After the ice samples were crushed, the gas expanded over a cold trap, condensing the water vapor at -80°C in the absorption cell. The analytical system was calibrated for each ice sample measurement with a standard mixture of CO2 in nitrogen and oxygen. For further details on the experimental and dating procedures, see Neftel et al. (1985), Friedli et al. (1986), and Schwander and Stauffer (1984).

Changing pattern of ice flow and mass balance for glaciers discharging into the Larsen A and B embayments, Antarctic Peninsula, 2011 to 2016

NASA Astrophysics Data System (ADS)

Rott, Helmut; Abdel Jaber, Wael; Wuite, Jan; Scheiblauer, Stefan; Floricioiu, Dana; Melchior van Wessem, Jan; Nagler, Thomas; Miranda, Nuno; van den Broeke, Michiel R.

2018-04-01

We analysed volume change and mass balance of outlet glaciers on the northern Antarctic Peninsula over the periods 2011 to 2013 and 2013 to 2016, using high-resolution topographic data from the bistatic interferometric radar satellite mission TanDEM-X. Complementary to the geodetic method that applies DEM differencing, we computed the net mass balance of the main outlet glaciers using the mass budget method, accounting for the difference between the surface mass balance (SMB) and the discharge of ice into an ocean or ice shelf. The SMB values are based on output of the regional climate model RACMO version 2.3p2. To study glacier flow and retrieve ice discharge we generated time series of ice velocity from data from different satellite radar sensors, with radar images of the satellites TerraSAR-X and TanDEM-X as the main source. The study area comprises tributaries to the Larsen A, Larsen Inlet and Prince Gustav Channel embayments (region A), the glaciers calving into the Larsen B embayment (region B) and the glaciers draining into the remnant part of the Larsen B ice shelf in Scar Inlet (region C). The glaciers of region A, where the buttressing ice shelf disintegrated in 1995, and of region B (ice shelf break-up in 2002) show continuing losses in ice mass, with significant reduction of losses after 2013. The mass balance numbers for the grounded glacier area of region A are -3.98 ± 0.33 Gt a-1 from 2011 to 2013 and -2.38 ± 0.18 Gt a-1 from 2013 to 2016. The corresponding numbers for region B are -5.75 ± 0.45 and -2.32 ± 0.25 Gt a-1. The mass balance in region C during the two periods was slightly negative, at -0.54 ± 0.38 Gt a-1 and -0.58 ± 0.25 Gt a-1. The main share in the overall mass losses of the region was contributed by two glaciers: Drygalski Glacier contributing 61 % to the mass deficit of region A, and Hektoria and Green glaciers accounting for 67 % to the mass deficit of region B. Hektoria and Green glaciers accelerated significantly in 2010-2011, triggering elevation losses up to 19.5 m a-1 on the lower terminus during the period 2011 to 2013 and resulting in a mass balance of -3.88 Gt a-1. Slowdown of calving velocities and reduced calving fluxes in 2013 to 2016 coincided with years in which ice mélange and sea ice cover persisted in proglacial fjords and bays during summer.

Periglacial process and Pleistocene environment in northern China

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo Xudong; Liu Dongsheng; Yan Fuhua

1991-03-01

In the present time, five kinds of periglacial phenomena have been defined: ice wedges, periglacial involutions, congelifolds, congeliturbations, and loess dunes. From the stratigraphical and geochronological data, the periglacial process is divided into six stages. (1) Guanting periglacial stage, characterized by the congeliturbative deposits that have developed in early Pleistocene Guanting loess-like formation. Paleomagnetic dating gives 2.43 Ma B.P. (2) Yanchi periglacial stage, characterized by the congelifold that has developed in middle Pleistocene Yanchi Lishi loess formation. Paleomagnetic dating gives 0.50 Ma B.P. (3) Zhaitang periglacial stage (II), characterized by the periglacial involutions that have developed in lower middle Pleistocenemore » Lishi loess formation. Paleomagnetic dating gives 0.30 Ma B.P. (4) Zhaitang periglacial state (I), characterized by the ice (soil) wedge that has developed in upper-middle Pleistocene Lishi loess formation. Paleomagnetic dating gives 0.20 Ma B.P. (5) Qiansangyu periglacial stage (II), characterized by the ice (sand) wedges that has developed in late Pleistocene Malan loess formation. Paleomagnetic dating gives 0.13 Ma B.P. (6) Qiansangyu periglacial stage (I), characterized by the ice (soil) wedge that has developed in late Pleistocene Malan loess-like formation. Thermoluminescent dating gives 0.018 Ma B.P. Spore-pollen composition analysis shows that the savannah steppe environment prevailed in northern China during Pleistocene periglacial periods. These fossilized periglacial phenomena indicate a rather arid and windy periglacial environment with a mean annual temperature estimated some 12-15C colder than that in the present.« less

Changes in Arctic Sea Ice Floe Size Distribution in the Marginal Ice Zone in a Thickness and Floe Size Distribution Model

NASA Astrophysics Data System (ADS)

Zhang, J.; Stern, H. L., III; Hwang, P. B.; Schweiger, A. J. B.; Stark, M.; Steele, M.

2015-12-01

To better describe the state of sea ice in the marginal ice zone (MIZ) with floes of varying thicknesses and sizes, both an ice thickness distribution (ITD) and a floe size distribution (FSD) are needed. We have developed a FSD theory [Zhang et al., 2015] that is coupled to the ITD theory of Thorndike et al. [1975] in order to explicitly simulate the evolution of FSD and ITD jointly. The FSD theory includes a FSD function and a FSD conservation equation in parallel with the ITD equation. The FSD equation takes into account changes in FSD due to ice advection, thermodynamic growth, and lateral melting. It also includes changes in FSD because of mechanical redistribution of floe size due to ice opening, ridging and, particularly, ice fragmentation induced by stochastic ocean surface waves. The floe size redistribution due to ice fragmentation is based on the assumption that wave-induced breakup is a random process such that when an ice floe is broken, floes of any smaller sizes have an equal opportunity to form, without being either favored or excluded. It is also based on the assumption that floes of larger sizes are easier to break because they are subject to larger flexure-induced stresses and strains than smaller floes that are easier to ride with waves with little bending; larger floes also have higher areal coverages and therefore higher probabilities to break. These assumptions with corresponding formulations ensure that the simulated FSD follows a power law as observed by satellites and airborne surveys. The FSD theory has been tested in the Pan-arctic Ice/Ocean Modeling and Assimilation System (PIOMAS). The existing PIOMAS has 12 categories each for ice thickness, ice enthalpy, and snow depth. With the implementation of the FSD theory, PIOMAS is able to represent 12 categories of floe sizes ranging from 0.1 m to ~3000 m. It is found that the simulated 12-category FSD agrees reasonably well with FSD derived from SAR and MODIS images. In this study, we will examine PIOMAS-estimated variability and changes in Arctic FSD over the period 1979-present. Thorndike, A. S., D. A. Rothrock, G. A. Maykut, and R. Colony, The thickness distribution of sea ice. J. Geophys. Res., 80, 1975. Zhang, J., A. Schweiger, M. Steele, and H. Stern, Sea ice floe size distribution in the marginal ice zone: Theory and numerical experiments, J. Geophys. Res., 120, 2015.

The Effective Business Practices of Mexican Drug Trafficking Organizations (DTOs)

DTIC Science & Technology

2013-06-01

perspective, such as previous release dates of the iPhone or changes in supporting platforms such as iTunes . Through this type of analysis, which breaks down...For example, Apple’s iPod/ iTunes business model encompassed two main activities: provide customers with an easy way to browse, purchase, and listen to...two separate activities, each with different customers, value, and infrastructure, in order to make up its iPod/ iTunes business model. This is

The interaction of radio frequency electromagnetic fields with atmospheric water droplets and applications to aircraft ice prevention. Thesis

NASA Technical Reports Server (NTRS)

Hansman, R. J., Jr.

1982-01-01

The feasibility of computerized simulation of the physics of advanced microwave anti-icing systems, which preheat impinging supercooled water droplets prior to impact, was investigated. Theoretical and experimental work performed to create a physically realistic simulation is described. The behavior of the absorption cross section for melting ice particles was measured by a resonant cavity technique and found to agree with theoretical predictions. Values of the dielectric parameters of supercooled water were measured by a similar technique at lambda = 2.82 cm down to -17 C. The hydrodynamic behavior of accelerated water droplets was studied photograhically in a wind tunnel. Droplets were found to initially deform as oblate spheroids and to eventually become unstable and break up in Bessel function modes for large values of acceleration or droplet size. This confirms the theory as to the maximum stable droplet size in the atmosphere. A computer code which predicts droplet trajectories in an arbitrary flow field was written and confirmed experimentally. The results were consolidated into a simulation to study the heating by electromagnetic fields of droplets impinging onto an object such as an airfoil. It was determined that there is sufficient time to heat droplets prior to impact for typical parameter values. Design curves for such a system are presented.

Subsurface North Atlantic warming as a trigger of rapid cooling events: evidences from the Early Pleistocene (MIS 31-19)

NASA Astrophysics Data System (ADS)

Hernández-Almeida, I.; Sierro, F.-J.; Cacho, I.; Flores, J.-A.

2014-10-01

Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt IRD events during cold periods of the Early Pleistocene. We used Mg / Ca-based temperatures of deep-dwelling (Neogloboquadrina pachyderma sinistral) planktonic foraminifera and paired Mg / Ca-δ18O measurements to estimate the subsurface temperatures and δ18O of seawater at Site U1314. Carbon isotopes on benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and δ18O of seawater suggest increased temperatures and salinities during ice-rafting, likely due to enhanced northward subsurface transport of subtropical waters during periods of AMOC reduction. Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of ice-rafted detritus (IRD). Warm waters accumulated at subsurface would result in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. Release of heat and salt stored at subsurface would help to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during the MIS3.

What Models and Satellites Tell Us (and Don't Tell Us) About Arctic Sea Ice Melt Season Length

NASA Astrophysics Data System (ADS)

Ahlert, A.; Jahn, A.

2017-12-01

Melt season length—the difference between the sea ice melt onset date and the sea ice freeze onset date—plays an important role in the radiation balance of the Arctic and the predictability of the sea ice cover. However, there are multiple possible definitions for sea ice melt and freeze onset in climate models, and none of them exactly correspond to the remote sensing definition. Using the CESM Large Ensemble model simulations, we show how this mismatch between model and remote sensing definitions of melt and freeze onset limits the utility of melt season remote sensing data for bias detection in models. It also opens up new questions about the precise physical meaning of the melt season remote sensing data. Despite these challenges, we find that the increase in melt season length in the CESM is not as large as that derived from remote sensing data, even when we account for internal variability and different definitions. At the same time, we find that the CESM ensemble members that have the largest trend in sea ice extent over the period 1979-2014 also have the largest melt season trend, driven primarily by the trend towards later freeze onsets. This might be an indication that an underestimation of the melt season length trend is one factor contributing to the generally underestimated sea ice loss within the CESM, and potentially climate models in general.

The Impact of Clouds and Hazes in Substellar Atmospheres

NASA Astrophysics Data System (ADS)

Morley, Caroline; Fortney, Jonathan J.; Marley, Mark S.

2016-01-01

The formation of clouds significantly alters the spectra of cool substellar atmospheres from terrestrial planets to brown dwarfs. In cool planets like Earth and Jupiter, volatile species like water and ammonia condense to form ice clouds. In hot planets and brown dwarfs, iron and silicates instead condense, forming dusty clouds. Irradiated methane-rich planets may have substantial hydrocarbon hazes. During my thesis, I have studied the impact of clouds and hazes in a variety of substellar objects. First, I present results for cool brown dwarfs including clouds previously neglected in model atmospheres. Model spectra that include sulfide and salt clouds can match the spectra of T dwarf atmospheres; water ice clouds will alter the spectra of the newest and coldest brown dwarfs, the Y dwarfs. These sulfide/salt and ice clouds potentially drive spectroscopic variability in these cool objects, and this variability should be distinguishable from variability caused by hot spots.Next, I present results for small, cool exoplanets between the size of Earth and Neptune, so-called super Earths. They likely have sulfide and salt clouds and also have photochemical hazes caused by stellar irradiation. Vast resources have been dedicated to characterizing the handful of super Earths accessible to current telescopes, yet of the planets smaller than Neptune studied to date, all have radii in the near-infrared consistent with being constant in wavelength, likely showing that these small planets are consistently enshrouded in thick hazes and clouds. Very thick, lofted clouds of salts or sulfides in high metallicity (1000× solar) atmospheres create featureless transmission spectra in the near-infrared. Photochemical hazes with a range of particle sizes also create featureless transmission spectra at lower metallicities. I show that despite these challenges, there are promising avenues for understanding this class of small planets: by observing the thermal emission and reflectivity of small planets, we can break the degeneracies and better constrain the atmospheric compositions. These observations may provide rich diagnostics of molecules and clouds in small planets, in contrast to the limited success to date.

Reduced Duration of Ice Cover in Swedish Lakes and Rivers

NASA Astrophysics Data System (ADS)

AghaKouchak, A.; Hallerback, S. A. M.; Stensen, K.; David, G.; Persson, M.

2016-12-01

The worlds freshwater systems are one of the most altered ecosystems on earth. Climate change introduces additional stresses on such systems, and this study presents an example of such change in an investigation of ice cover duration in Swedish lakes and rivers. In situ observations from over 750 lakes and rivers in Sweden were analyzed, with some records dating back to the beginning of the 18th century. Results show that ice duration significantly decreased over the last century. Change in ice duration is affected by later freeze as well as (more dominantly) earlier breakup dates. Additionally, since the late 1980's there has been an increase of extreme events, meaning years with extremely short duration of ice cover. The affect of temperature on the system was also examined. Using 113 years of temperature data, we empirically show how temperature changes affect the ice duration in lakes at different latitudes as well as dependent on lake area, volume and depth.

Online sea ice data platform: www.seaiceportal.de

NASA Astrophysics Data System (ADS)

Nicolaus, Marcel; Asseng, Jölund; Bartsch, Annekathrin; Bräuer, Benny; Fritzsch, Bernadette; Grosfeld, Klaus; Hendricks, Stefan; Hiller, Wolfgang; Heygster, Georg; Krumpen, Thomas; Melsheimer, Christian; Ricker, Robert; Treffeisen, Renate; Weigelt, Marietta; Nicolaus, Anja; Lemke, Peter

2016-04-01

There is an increasing public interest in sea ice information from both Polar Regions, which requires up-to-date background information and data sets at different levels for various target groups. In order to serve this interest and need, seaiceportal.de (originally: meereisportal.de) was developed as a comprehensive German knowledge platform on sea ice and its snow cover in the Arctic and Antarctic. It was launched in April 2013. Since then, the content and selection of data sets increased and the data portal received increasing attention, also from the international science community. Meanwhile, we are providing near-real time and archive data of many key parameters of sea ice and its snow cover. The data sets result from measurements acquired by various platforms as well as numerical simulations. Satellite observations of sea ice concentration, freeboard, thickness and drift are available as gridded data sets. Sea ice and snow temperatures and thickness as well as atmospheric parameters are available from autonomous platforms (buoys). Additional ship observations, ice station measurements, and mooring time series are compiled as data collections over the last decade. In parallel, we are continuously extending our meta-data and uncertainty information for all data sets. In addition to the data portal, seaiceportal.de provides general comprehensive background information on sea ice and snow as well as expert statements on recent observations and developments. This content is mostly in German in order to complement the various existing international sites for the German speaking public. We will present the portal, its content and function, but we are also asking for direct user feedback.

Breaking the Ice: Potential U.S.-Russian Maritime Conflict in the Arctic

DTIC Science & Technology

2012-12-01

meanwhile, has been involved in several altercations involving Russian commercial fishing vessels poaching in the U.S.-claimed waters of the Bering...with an asterisk (*) indicating that this score is higher than it would be if the impact of a particular variable on a country were considered in...political, and military impact of the melting Arctic ice cap, including articles by Arctic experts and scholars, think tank reports, academic theses

Polar Bears Across the Arctic Face Shorter Sea Ice Season

NASA Image and Video Library

2017-12-08

Polar bears already face shorter ice seasons - limiting prime hunting and breeding opportunities. Nineteen separate polar bear subpopulations live throughout the Arctic, spending their winters and springs roaming on sea ice and hunting. The bears have evolved mainly to eat seals, which provide necessary fats and nutrients in the harsh Arctic environment. Polar bears can't outswim their prey, so instead they perch on the ice as a platform and ambush seals at breathing holes or break through the ice to access their dens. The total number of ice-covered days declined at the rate of seven to 19 days per decade between 1979 and 2014. The decline was even greater in the Barents Sea and the Arctic basin. Sea ice concentration during the summer months — an important measure because summertime is when some subpopulations are forced to fast on land — also declined in all regions, by 1 percent to 9 percent per decade. Read more: go.nasa.gov/2cIZSSc Photo credit: Mario Hoppmann

26. Photocopy of photograph taken by W. Terry Averbeck, date ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

26. Photocopy of photograph taken by W. Terry Averbeck, date unknown. VIEW, LOOKING NORTHWEST, OF SECOND STREET BETWEEN SCOTT AND COURT STREETS, SHOWING PORTIONS OF THE ICE STORAGE BUILDING AND ORIGINAL SHIPPING AREA, NOW USED AS BAGGING/CRUSHING AREA (8x10' enlargement from 4x5' negative) - Champion Ice Manufacturing & Cold Storage Company, 40 East Second Street, Covington, Kenton County, KY

Glacial terminations and the Last Interglacial in the Okhotsk Sea; Their implication to global climatic changes

NASA Astrophysics Data System (ADS)

Gorbarenko, Sergey; Velivetskaya, Tatyana; Malakhov, Mikhail; Bosin, Aleksandr

2017-05-01

Paleoclimate data from the Okhotsk Sea (OS) over Terminations II and I (TII, TI), and the Last and Present Interglacial (LIG, PIG) periods were compiled in order to examine Northern Hemisphere climate and sea level changes. Based on records of four AMS 14C-dated OS cores over TI-PIG, it is argued that the OS productivity/climate, IRD (ice-rafted debris), and benthic foraminiferal oxygen isotope (δ18Obf) proxies provide representative and in-phase evidence of the Northern Hemisphere climate and continental ice sheet changes consistent with the LR 04 δ18Obf curve. Chronologies for two central OS cores over TII-LIG-cooling event 23 (C23) were constructed by correlating OS productivity proxies with well-dated δ18O records of Chinese speleothems because OS environment is modulated by East Asian Monsoon; and, as well as correlating measured magnetic paleointensity excursions with those in the dated PISO-1500 paleointensity stack. Results show several OS climatic and environment states, including TII coeval with Asian Weak Monsoon Interval (WMI) II since 136 ka, LIG with a sharp two-step transition (130.2-129 ka) and demise at С25 (116.5 ka), and last glaciation with coolings at C24 (111 ka) and C23. The OS productivity and IRD records demonstrate certain climate amelioration in the middle of WMI-II, and two insignificant cooling events inside the LIG marked by C27 (126 ka) and C26 (120.6 ka). OS δ18Obf records of both cores demonstrate a gradual trend of lighter values since around 131.5 ka BP, continuing from the onset of LIG (129 ka) to minimum values at 126 ka BP (C27), then nearly constant values until 121.5 ka, followed by a slight increase up to 120.6 ka (C26), and a subsequent strong increase up to 116.5 ka (C25). The magnitude of OS δ18Obf oscillations is 1.35‰, which is less than those in the N. Atlantic. It may therefore be suggested that this OS index probably tracks changes in continental ice sheet volume and sea level.

Single-particle characterization of ice-nucleating particles and ice particles residuals sampled by three different techniques

NASA Astrophysics Data System (ADS)

Kandler, Konrad; Worringen, Annette; Benker, Nathalie; Dirsch, Thomas; Mertes, Stephan; Schenk, Ludwig; Kästner, Udo; Frank, Fabian; Nillius, Björn; Bundke, Ulrich; Rose, Diana; Curtius, Joachim; Kupiszewski, Piotr; Weingartner, Ernest; Vochezer, Paul; Schneider, Johannes; Schmidt, Susan; Weinbruch, Stephan; Ebert, Martin

2015-04-01

During January/February 2013, at the High Alpine Research Station Jungfraujoch a measurement campaign was carried out, which was centered on atmospheric ice-nucleating particles (INP) and ice particle residuals (IPR). Three different techniques for separation of INP and IPR from the non-ice-active particles are compared. The Ice Selective Inlet (ISI) and the Ice Counterflow Virtual Impactor (Ice-CVI) sample ice particles from mixed phase clouds and allow for the analysis of the residuals. The combination of the Fast Ice Nucleus Chamber (FINCH) and the Ice Nuclei Pumped Counterflow Virtual Impactor (IN-PCVI) provides ice-activating conditions to aerosol particles and extracts the activated INP for analysis. Collected particles were analyzed by scanning electron microscopy and energy-dispersive X-ray microanalysis to determine size, chemical composition and mixing state. All INP/IPR-separating techniques had considerable abundances (median 20 - 70 %) of instrumental contamination artifacts (ISI: Si-O spheres, probably calibration aerosol; Ice-CVI: Al-O particles; FINCH+IN-PCVI: steel particles). Also, potential sampling artifacts (e.g., pure soluble material) occurred with a median abundance of < 20 %. While these could be explained as IPR by ice break-up, for INP their IN-ability pathway is less clear. After removal of the contamination artifacts, silicates and Ca-rich particles, carbonaceous material and metal oxides were the major INP/IPR particle types separated by all three techniques. Soot was a minor contributor. Lead was detected in less than 10 % of the particles, of which the majority were internal mixtures with other particle types. Sea-salt and sulfates were identified by all three methods as INP/IPR. Most samples showed a maximum of the INP/IPR size distribution at 400 nm geometric diameter. In a few cases, a second super-micron maximum was identified. Soot/carbonaceous material and metal oxides were present mainly in the submicron range. ISI and FINCH yielded silicates and Ca-rich particles mainly with diameters above 1 µm, while the Ice-CVI also separated many submicron IPR. As strictly parallel sampling could not be performed, a part of the discrepancies between the different techniques may result from variations in meteorological conditions and subsequent INP/IPR composition. The observed differences in the particle group abundances as well as in the mixing state of INP/IPR express the need for further studies to better understand the influence of the separating techniques on the INP/IPR chemical composition.

Decadal shifts in autumn migration timing by Pacific Arctic beluga whales are related to delayed annual sea ice formation.

PubMed

Hauser, Donna D W; Laidre, Kristin L; Stafford, Kathleen M; Stern, Harry L; Suydam, Robert S; Richard, Pierre R

2017-06-01

Migrations are often influenced by seasonal environmental gradients that are increasingly being altered by climate change. The consequences of rapid changes in Arctic sea ice have the potential to affect migrations of a number of marine species whose timing is temporally matched to seasonal sea ice cover. This topic has not been investigated for Pacific Arctic beluga whales (Delphinapterus leucas) that follow matrilineally maintained autumn migrations in the waters around Alaska and Russia. For the sympatric Eastern Chukchi Sea ('Chukchi') and Eastern Beaufort Sea ('Beaufort') beluga populations, we examined changes in autumn migration timing as related to delayed regional sea ice freeze-up since the 1990s, using two independent data sources (satellite telemetry data and passive acoustics) for both populations. We compared dates of migration between 'early' (1993-2002) and 'late' (2004-2012) tagging periods. During the late tagging period, Chukchi belugas had significantly delayed migrations (by 2 to >4 weeks, depending on location) from the Beaufort and Chukchi seas. Spatial analyses also revealed that departure from Beaufort Sea foraging regions by Chukchi whales was postponed in the late period. Chukchi beluga autumn migration timing occurred significantly later as regional sea ice freeze-up timing became later in the Beaufort, Chukchi, and Bering seas. In contrast, Beaufort belugas did not shift migration timing between periods, nor was migration timing related to freeze-up timing, other than for southward migration at the Bering Strait. Passive acoustic data from 2008 to 2014 provided independent and supplementary support for delayed migration from the Beaufort Sea (4 day yr -1 ) by Chukchi belugas. Here, we report the first phenological study examining beluga whale migrations within the context of their rapidly transforming Pacific Arctic ecosystem, suggesting flexible responses that may enable their persistence yet also complicate predictions of how belugas may fare in the future. © 2016 John Wiley & Sons Ltd.

Fram-2014/2015: A 400 Day Investigation of the Arctic's Oldest Sediments over the Alpha Ridge with a Research Hovercraft

NASA Astrophysics Data System (ADS)

Hall, J. K.; Kristoffersen, Y.

2014-12-01

The thickest multi-year ice in the Arctic covers a secret. Four short cores raised from the Alpha Ridge in the 1970s and 1980s from drift stations T-3 and CESAR showed ages between 45 and 76 my. The reason for these old ages became clear when examination of legacy seismic data from T-3 showed that in some places up to 500 m of sediments had been removed within an area of some 200 by 600 km, presumably by an impact of asteroid fragments. To investigate the impact area, the authors conceived an innovative research platform in 2007. Named the R/H SABVABAA, this 12m by 6m hovercraft has been home-based in Svalbard since June 2008. During the following 6 years the craft and its evolving innovative light-weight equipment have made 18 trips to the summer ice pack, traveling some 4410 km over ice during some six months of scientific investigations. An opportunity to get a lift to this area, some 1500 km from Svalbard, came in a 2011 invitation to join AWI's icebreaker POLARSTERN in its ARK-XXVIII/4 expedition departing Tromsö August 5, 2014. The 400 day drift will be the first wintering over, ever, of a mobile research platform with geophysical, geological, and oceanographic capabilities. The Arctic ice pack continually moves due to winds and currents. While at the main camp, observations will consist of marine geophysics (seismic profiling with four element CHIRP, a 20 in³ airgun with single hydrophone, as well as 12 kHz bathymetry and 200 kHz sounding of the deep scattering layer), marine geology (coring with a hydrostatically-boosted 3 or 6 m corer; bottom photography; and two rock dredges), and oceanography. Deployed away from the camp, four sonobuoys will allow 3-D seismic acquisition. Access to the depths below the ice is via a hydraulic capstan winch, with 6500 m of Kevlar aramid fiber rope with 2.8 ton breaking strength. Ice thickness monitoring of the local 100 km² will be made with the craft's EM-31 probe when away from the camp, moving to choice locations for taking cores, and deformation of the ice pack monitored by 5 remote GPS data loggers. A meteorological station including radiation flux measurements will be operated. Several cameras will be used to observe under-ice conditions (ice formation, biology) as well as time-lapse local ice movement. The talk will summarize the operations up to the time of the GEBCO 2014 Science Day at the AGU Fall Meeting.

Online Sea Ice Knowledge and Data Platform: www.seaiceportal.de

NASA Astrophysics Data System (ADS)

Treffeisen, R. E.; Nicolaus, M.; Bartsch, A.; Fritzsch, B.; Grosfeld, K.; Haas, C.; Hendricks, S.; Heygster, G.; Hiller, W.; Krumpen, T.; Melsheimer, C.; Nicolaus, A.; Ricker, R.; Weigelt, M.

2016-12-01

There is an increasing public interest in sea ice information from both Polar Regions, which requires up-to-date background information and data sets at different levels for various target groups. In order to serve this interest and need, seaiceportal.de (originally: meereisportal.de) was developed as a comprehensive German knowledge platform on sea ice and its snow cover in the Arctic and Antarctic. It was launched in April 2013. Since then, the content and selection of data sets increased and the data portal received increasing attention, also from the international science community. Meanwhile, we are providing near-real time and archived data of many key parameters of sea ice and its snow cover. The data sets result from measurements acquired by various platforms as well as numerical simulations. Satellite observations (e.g., AMSR2, CryoSat-2 and SMOS) of sea ice concentration, freeboard, thickness and drift are available as gridded data sets. Sea ice and snow temperatures and thickness as well as atmospheric parameters are available from autonomous ice-tethered platforms (buoys). Additional ship observations, ice station measurements, and mooring time series are compiled as data collections over the last decade. In parallel, we are continuously extending our meta-data and uncertainty information for all data sets. In addition to the data portal, seaiceportal.de provides general comprehensive background information on sea ice and snow as well as expert statements on recent observations and developments. This content is mostly in German in order to complement the various existing international sites for the German speaking public. We will present the portal, its content and function, but we are also asking for direct user feedback and are open for potential new partners.

A Late-Glacial sedimentary sequence at KIlkeel, Northern Ireland: implications for the glaciation of the Irish Sea Basin

NASA Astrophysics Data System (ADS)

Merritt, Jon; Roberson, Sam; Cooper, Mark

2017-04-01

This paper re-evaluates the nature and timing of a Late-Glacial ice sheet re-advance in the north western sector of the Irish Sea basin. The sedimentary archive in the region records the collapse of the Irish Sea Ice Stream, a major outlet glacier of the British-Irish Ice Sheet. The region documents the interplay between southerly flowing Scottish ice, ice flowing southeast from Lough Neagh and locally sourced Mournes ice. We present the results of sedimentological analysis of a glacigenic sequence exposed in a modern cliff section 3 km long between Derryoge and Kilkeel, Co. Down, Northern Ireland. The interaction between an advancing ice-sheet outlet lobe and rapidly changing sea levels are examined using facies analysis and micromorphology. The section is composed of four lithofacies associations (LAs). These are, from the base, a laminated, fossiliferous and deformed silt (LA1) at least 4.5 m thick that contains lenses of diamicton and discontinuous rafts of sandy gravel. Marine shells form the axis of a fold hinge, part of a lightly tectonised channel fill within the raft. LA1 is overlain by a sandy diamict (LA2) up to 14 m thick containing mainly local clasts with some of northern provenance. Within LA2 are wide channel structures infilled by laminated clayey silts (LA2b). These form deposits up to 14 m thick and contain small-scale folds, discrete shear zones and ball-and-pillow structures. LA2b forms a lithofacies association with LA2, consisting of a lower subfacies of sheared and deformed silts, overlain by sandy diamicton, capped by a striated boulder pavement. These are interpreted to represent retreat/advance cycles of a marine terminating ice margin. Up to five such cycles are identified. LA2 is widely punctuated by fissures and conduits infilled by loose sands and gravels. These are inferred to be emplaced by subglacial meltwater during the final stages of ice sheet advance. Covering both LA2 and LA2b, LA3 is a unit of glaciofluvial outwash, composed of cross-trough stratified sandy gravels, with flame structures indicative of syn-depositional loading. The entire sequence is capped by loose interbedded sands and gravels (LA4) representing a Late-Glacial raised beach. Evidence of a marine terminating ice margin provides support for high relative sea levels in the north western sector of the Irish Sea during deglaciation. Forthcoming dates from shells with the rafted subaqueous fan deposits underlying LF2 provide the opportunity to constrain either: a) sea-level rise prior to the onset of Irish Sea Basin glaciation, or, b) Late-Glacial sea level rise following deglaciation of the Irish Sea and prior to the re-advance of local ice masses.

What Lies Below a Martian Ice Cap

NASA Technical Reports Server (NTRS)

2008-01-01

[figure removed for brevity, see original site] Click on image for larger annotated version

This image (top) taken by the Shallow Radar instrument on NASA's Mars Reconnaissance Orbiter reveals the layers of ice, sand and dust that make up the north polar ice cap on Mars. It is the most detailed look to date at the insides of this ice cap. The colored map below the radar picture shows the topography of the corresponding Martian terrain (red and white represent higher ground, and green and yellow lower).

The radar image reveals four never-before-seen thick layers of ice and dust separated by layers of nearly pure ice. According to scientists, these thick ice-free layers represent approximately one-million-year-long cycles of climate change on Mars caused by variations in the planet's tilted axis and its eccentric orbit around the sun. Adding up the entire stack of ice gives an estimated age for the north polar ice cap of about 4 million years a finding that agrees with previous theoretical estimates. The ice cap is about 2 kilometers (1.2 miles) thick.

The radar picture also shows that the boundary between the ice layers and the surface of Mars underneath is relatively flat (bottom white line on the right). This implies that the surface of Mars is not sagging, or bending, under the weight of the ice cap and this, in turn, suggests that the planet's lithosphere, a combination of the crust and the strong parts of the upper mantle, is thicker than previously thought.

A thicker lithosphere on Mars means that temperatures increase more gradually with depth toward the interior. Temperatures warm enough for water to be liquid are therefore deeper than previously thought. Likewise, if liquid water does exist in aquifers below the surface of Mars, and if there are any organisms living in that water, they would have to be located deeper in the planet.

The topography data are from Mars Orbiter Laser Altimeter, which was flown on NASA's Mars Global Surveyor mission.

NPLD stands for the north polar layered deposits.

BU stands for basal unit, an ice-sand deposit that lies beneath parts of the north polar layered deposits.

The Shallow Radar instrument was provided by the Italian Space Agency. Its operations are led by the University of Rome and its data are analyzed by a joint U.S.-Italian science team. JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington.

Late-glacial and Holocene history of changes in Quelccaya Ice Cap, Peru

NASA Astrophysics Data System (ADS)

Kelly, M. A.; Lowell, T. V.; Schaefer, J. M.; Finkel, R. C.

2008-12-01

Quelccaya Ice Cap in the southeastern Peruvian Andes (~13-14° S latitude) is an icon for climate change. Its rapidly receding outlet, Qori Kalis Glacier, has been monitored since the 1970's. Cores from Quelccaya Ice Cap provide high-resolution information about temperature and precipitation during the past 1,500 years. We extend the understanding of past changes in Quelccaya Ice Cap based on mapping and dating of glacial moraines and associated deposits. Our results include fifty 10Be ages of moraines and bedrock as well as twenty-nine 14C ages of organic material associated with moraines. These results form the basis of a chronology of changes in Quelccaya Ice Cap from ~16,000 yr BP to late Holocene time. Results from 10Be and 14C dating indicate that Quelccaya Ice Cap experienced a significant advance at 12,700-11,400 yr BP. Subsequent to this advance, the ice margin deposited at least three recessional moraine sets. Quelccaya Ice Cap receded to near its present-day margin by ~10,000 yr BP. Neoglacial advances began by ~3,000 yr BP and culminated with a maximum advance during the Little Ice Age. This chronology fits well with prior work which indicates a restricted Quelccaya Ice Cap during middle Holocene time. Moreover, the overlap between moraine and ice core data for the last 1,500 years provides a unique opportunity to assess the influences of temperature and precipitation on past ice cap extents.

Final Laurentide ice-sheet deglaciation and Holocene climate-sea level change

USGS Publications Warehouse

Ullman, David J.; Carlson, Anders E.; Hostetler, Steven W.; Clark, Peter U.; Cuzzone, Joshua; Milne, Glenn A.; Winsor, Kelsey; Caffee, Marc A.

2016-01-01

Despite elevated summer insolation forcing during the early Holocene, global ice sheets retained nearly half of their volume from the Last Glacial Maximum, as indicated by deglacial records of global mean sea level (GMSL). Partitioning the GMSL rise among potential sources requires accurate dating of ice-sheet extent to estimate ice-sheet volume. Here, we date the final retreat of the Laurentide Ice Sheet with 10Be surface exposure ages for the Labrador Dome, the largest of the remnant Laurentide ice domes during the Holocene. We show that the Labrador Dome deposited moraines during North Atlantic cold events at ∼10.3 ka, 9.3 ka and 8.2 ka, suggesting that these regional climate events helped stabilize the retreating Labrador Dome in the early Holocene. After Hudson Bay became seasonally ice free at ∼8.2 ka, the majority of Laurentide ice-sheet melted abruptly within a few centuries. We demonstrate through high-resolution regional climate model simulations that the thermal properties of a seasonally ice-free Hudson Bay would have increased Laurentide ice-sheet ablation and thus contributed to the subsequent rapid Labrador Dome retreat. Finally, our new 10Be chronology indicates full Laurentide ice-sheet had completely deglaciated by 6.7 ± 0.4 ka, which re quires that Antarctic ice sheets contributed 3.6–6.5 m to GMSL rise since 6.3–7.1 ka.

40 CFR 60.4200 - Am I subject to this subpart?

Code of Federal Regulations, 2012 CFR

2012-07-01

... stationary compression ignition (CI) internal combustion engines (ICE) and other persons as specified in... commences is the date the engine is ordered by the owner or operator. (1) Manufacturers of stationary CI ICE... model year, for fire pump engines. (2) Owners and operators of stationary CI ICE that commence...

40 CFR 60.4200 - Am I subject to this subpart?

Code of Federal Regulations, 2014 CFR

2014-07-01

... stationary compression ignition (CI) internal combustion engines (ICE) and other persons as specified in... commences is the date the engine is ordered by the owner or operator. (1) Manufacturers of stationary CI ICE... model year, for fire pump engines. (2) Owners and operators of stationary CI ICE that commence...

40 CFR 60.4200 - Am I subject to this subpart?

Code of Federal Regulations, 2010 CFR

2010-07-01

... stationary compression ignition (CI) internal combustion engines (ICE) as specified in paragraphs (a)(1... date the engine is ordered by the owner or operator. (1) Manufacturers of stationary CI ICE with a..., for fire pump engines. (2) Owners and operators of stationary CI ICE that commence construction after...

40 CFR 60.4200 - Am I subject to this subpart?

Code of Federal Regulations, 2013 CFR

2013-07-01

... stationary compression ignition (CI) internal combustion engines (ICE) and other persons as specified in... commences is the date the engine is ordered by the owner or operator. (1) Manufacturers of stationary CI ICE... model year, for fire pump engines. (2) Owners and operators of stationary CI ICE that commence...

40 CFR 60.4200 - Am I subject to this subpart?

Code of Federal Regulations, 2011 CFR

2011-07-01

... stationary compression ignition (CI) internal combustion engines (ICE) as specified in paragraphs (a)(1... date the engine is ordered by the owner or operator. (1) Manufacturers of stationary CI ICE with a..., for fire pump engines. (2) Owners and operators of stationary CI ICE that commence construction after...

Breaking the Ice--And Winter's Spell--At Twin Buttes.

ERIC Educational Resources Information Center

Keown, Duane

1979-01-01

During the month of February, eighth and ninth graders at a university school in Wyoming participate in a winter lake study. Descriptions are given of various measurement techniques related to water quality studies. (SA)

Analysis and Prediction of Ice Shedding for a Full-Scale Heated Tail Rotor

NASA Technical Reports Server (NTRS)

Kreeger, Richard E.; Work, Andrew; Douglass, Rebekah; Gazella, Matthew; Koster, Zakery; Turk, Jodi

2016-01-01

When helicopters are to fly in icing conditions, it is necessary to consider the possibility of ice shed from the rotor blades. In 2013, a series of tests were conducted on a heated tail rotor at NASA Glenn's Icing Research Tunnel (IRT). The tests produced several shed events that were captured on camera. Three of these shed events were captured at a sufficiently high frame rate to obtain multiple images of the shed ice in flight that had a sufficiently long section of shed ice for analysis. Analysis of these shed events is presented and compared to an analytical Shedding Trajectory Model (STM). The STM is developed and assumes that the ice breaks off instantly as it reaches the end of the blade, while frictional and viscous forces are used as parameters to fit the STM. The trajectory of each shed is compared to that predicted by the STM, where the STM provides information of the shed group of ice as a whole. The limitations of the model's underlying assumptions are discussed in comparison to experimental shed events.

A stacking ensemble learning framework for annual river ice breakup dates

NASA Astrophysics Data System (ADS)

Sun, Wei; Trevor, Bernard

2018-06-01

River ice breakup dates (BDs) are not merely a proxy indicator of climate variability and change, but a direct concern in the management of local ice-caused flooding. A framework of stacking ensemble learning for annual river ice BDs was developed, which included two-level components: member and combining models. The member models described the relations between BD and their affecting indicators; the combining models linked the predicted BD by each member models with the observed BD. Especially, Bayesian regularization back-propagation artificial neural network (BRANN), and adaptive neuro fuzzy inference systems (ANFIS) were employed as both member and combining models. The candidate combining models also included the simple average methods (SAM). The input variables for member models were selected by a hybrid filter and wrapper method. The performances of these models were examined using the leave-one-out cross validation. As the largest unregulated river in Alberta, Canada with ice jams frequently occurring in the vicinity of Fort McMurray, the Athabasca River at Fort McMurray was selected as the study area. The breakup dates and candidate affecting indicators in 1980-2015 were collected. The results showed that, the BRANN member models generally outperformed the ANFIS member models in terms of better performances and simpler structures. The difference between the R and MI rankings of inputs in the optimal member models may imply that the linear correlation based filter method would be feasible to generate a range of candidate inputs for further screening through other wrapper or embedded IVS methods. The SAM and BRANN combining models generally outperformed all member models. The optimal SAM combining model combined two BRANN member models and improved upon them in terms of average squared errors by 14.6% and 18.1% respectively. In this study, for the first time, the stacking ensemble learning was applied to forecasting of river ice breakup dates, which appeared promising for other river ice forecasting problems.

Surface energy balance measurements and modeling on the ice cap of King George Island, West Antarctica

NASA Astrophysics Data System (ADS)

Falk, U.; Braun, M.; Sala, H.; Menz, G.

2012-04-01

The Antarctic Peninsula is amongst the fastest warming places on Earth and further temperature increase is to be expected. It has undergone rapid environmental changes in the past decades. Exceptional rates of surface air temperature increases (2.5K in 50 years) are concurrent with retreating glacier fronts, an increase in melt areas, surface lowering and rapid retreat, break-up and disintegration of ice shelves. The South Shetland Islands are located on the northern tip of the Peninsula and are especially vulnerable to climate change due to their maritime climate. For King George Island we have compiled a unique data set comprising direct measurements of evaporation and sensible heat flux by eddy covariance on the Warszawa Icefield for the austral summers November 2010 to March 2011 and January to February 2012 in combination with a fully equipped automated weather station measuring long- and short-wave radiation components, profiles of temperature, humidity and wind velocities as well as glacier ice temperatures in profile. The combination with the eddy covariance data allows for analysis of variability and seasonality of surface energy balance components on a glacier for an entire year. Repeat measurements of surface lowering at different locations on King George Island are used for analysis of multi-sensor satellite data to identify melt patterns and bare ice areas during summer. In combination with long-term time series of weather data, these data give indication of the sensitivity of the inland ice cap to the ongoing changes. This research is part of the ESF project IMCOAST funded by BMBF. Field work was carried out at the Dallmann laboratory (Jubany, King George Island) in cooperation of the Instituto Antartico Argentino (Argentina) and the Alfred-Wegener Institute (German).

The sensitivity of the Greenland Ice Sheet to glacial-interglacial oceanic forcing

NASA Astrophysics Data System (ADS)

Tabone, Ilaria; Blasco, Javier; Robinson, Alexander; Alvarez-Solas, Jorge; Montoya, Marisa

2018-04-01

Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has experienced a gradually accelerating mass loss, in part due to the observed speed-up of several of Greenland's marine-terminating glaciers. Recent studies directly attribute this to warming North Atlantic temperatures, which have triggered melting of the outlet glaciers of the GrIS, grounding-line retreat and enhanced ice discharge into the ocean, contributing to an acceleration of sea-level rise. Reconstructions suggest that the influence of the ocean has been of primary importance in the past as well. This was the case not only in interglacial periods, when warmer climates led to a rapid retreat of the GrIS to land above sea level, but also in glacial periods, when the GrIS expanded as far as the continental shelf break and was thus more directly exposed to oceanic changes. However, the GrIS response to palaeo-oceanic variations has yet to be investigated in detail from a mechanistic modelling perspective. In this work, the evolution of the GrIS over the past two glacial cycles is studied using a three-dimensional hybrid ice-sheet-shelf model. We assess the effect of the variation of oceanic temperatures on the GrIS evolution on glacial-interglacial timescales through changes in submarine melting. The results show a very high sensitivity of the GrIS to changing oceanic conditions. Oceanic forcing is found to be a primary driver of GrIS expansion in glacial times and of retreat in interglacial periods. If switched off, palaeo-atmospheric variations alone are not able to yield a reliable glacial configuration of the GrIS. This work therefore suggests that considering the ocean as an active forcing should become standard practice in palaeo-ice-sheet modelling.

Fathoms Below: Propagation of Deep Water-driven Fractures and Implications for Surface Expression and Temporally-varying Activity at Europa

NASA Astrophysics Data System (ADS)

Walker, C. C.; Craft, K.; Schmidt, B. E.

2015-12-01

The fracture and failure of Europa's icy shell are not only observable scars of variable stress and activity throughout its evolution, they also serve key as mechanisms in the interaction of surface and subsurface material, and thus crucial aspects of the study of crustal overturn and ice shell habitability. Galileo images, our best and only reasonable-resolution views of Europa until the Europa Multiple Flyby Mission arrives in the coming decades, illustrates a single snapshot in time in Europa's history from which we deduce many temporally-based hypotheses. One of those hypotheses, which we investigate here, is that sub-surface water-both in the form of Great Lake-sized perched water pockets in the near-surface and the larger global ocean below-drives the deformation, fracture, and failure of the surface. Using Galileo's snapshot in time, we use a 2D/3D hydraulic fracturing model to investigate the propagation of vertical fractures upward into the ice shell, motion of water within and between fractures, and the subsequent break-up of ice over shallow water, forming the chaos regions and other smaller surface features. We will present results from a cohesive fragmentation model to determine the time over which chaos formation occurs, and use a fracking model to determine the time interval required to allow water to escape from basal fractures in the ice shell. In determining the style, energy, and timescale of these processes, we constrain temporal variability in observable activity and topography at the surface. Finally, we compare these results to similar settings on Earth-Antarctica-where we have much higher resolution imagery and observations to better understand how sub-surface water can affect ice surface morphology, which most certainly have implications for future flyby and surface lander exploration.

Ice-Cliff Failure via Retrogressive Slumping

NASA Astrophysics Data System (ADS)

Parizek, B. R.; Christianson, K.; Alley, R. B.; Voytenko, D.; Vankova, I.; Dixon, T. H.; Holland, D.

2016-12-01

The magnitude and rate of future sea-level rise from warming-induced ice-sheet shrinkage remain notably uncertain. Removal of most of an ice sheet by surface melting alone requires centuries to millennia. Oceanic warming may accelerate loss by removing buttressing ice shelves and thereby speeding flow of non-floating ice into the ocean, but, until recently, modeled timescales for major dynamic ice-sheet shrinkage were centuries or longer. Beyond certain thresholds, however, observations show that warming removes floating ice shelves, leaving grounded ice cliffs from which icebergs break off directly. Cliffs higher than some limit experience rapid structural failure. Recent parameterization of this process in a comprehensive ice-flow model produced much faster sea-level rise from future rapid warming than in previous modeling studies, through formation and retreat of tall ice cliffs. Fully physical representations of this process are not yet available, however. Here, we use modeling guided by terrestrial radar data from Helheim Glacier, Greenland to show that cliffs will fail by slumping and trigger rapid retreat at a threshold height that, in crevassed ice with surface melting, may be only slightly above the 100-m maximum observed today, but may be roughly twice that (180-275 m) in mechanically-competent ice under well-drained or low-melt conditions.

Can glacial shearing of sediment reset the signal used for luminescence dating?

NASA Astrophysics Data System (ADS)

Bateman, Mark D.; Swift, Darrel A.; Piotrowski, Jan A.; Rhodes, Edward J.; Damsgaard, Anders

2018-04-01

Understanding the geomorphology left by waxing and waning of former glaciers and ice sheets during the late Quaternary has been the focus of much research. This has been hampered by the difficulty in dating such features. Luminescence has the potential to be applied to glacial sediments but requires signal resetting prior to burial in order to provide accurate ages. This paper explores the possibility that, rather than relying on light to reset the luminescence signal, glacial processes underneath ice might cause resetting. Experiments were conducted on a ring-shear machine set up to replicate subglacial conditions and simulate the shearing that can occur within subglacial sediments. Luminescence measurement at the single grain level indicates that a number (albeit small) of zero-dosed grains were produced and that these increased in abundance with distance travelled within the shearing zone. Observed changes in grain shape characteristics with increasing shear distance indicate the presence of localised high pressure grain-to-grain stresses caused by grain bridges. This appears to explain why some grains became zeroed whilst others retained their palaeodose. Based on the observed experimental trend, it is thought that localised grain stress is a viable luminescence resetting mechanism. As such relatively short shearing distances might be sufficient to reset a small proportion of the luminescence signal within subglacial sediments. Dating of previously avoided subglacial sediments may therefore be possible.

Ergovaline Stability in Tall Fescue Based on Sample Handling and Storage Methods

NASA Astrophysics Data System (ADS)

Lea, Krista; Smith, Lori; Gaskill, Cynthia; Coleman, Robert; Smith, S.

2014-09-01

Ergovaline is an ergot alkaloid produced by the endophyte Neotyphodium coenophialum (Morgan-Jones and Gams) found in tall fescue (Schedonorus arundinacea (Schreb.) Dumort.) and blamed for a multitude of livestock disorders. Ergovaline is known to be unstable and affected by many variables. The objective of this study was to determine the effect of sample handling and storage on the stability of ergovaline in tall fescue samples. Fresh tall fescue was collected from a horse farm in central Kentucky at three harvest dates and transported on ice to the University of Kentucky Veterinary Diagnostic Laboratory. Plant material was frozen in liquid nitrogen, milled and mixed before being allocated into different sub-samples. Three sub-samples were assigned to each of 14 sample handling or storage treatments. Sample handling included increased heat and UV light to simulate transportation in a vehicle and on ice in a cooler per standard transportation recommendations. Storage conditions included storage at 22oC, 5oC and -20oC for up to 28 days. Each sub-sample was then analyzed for ergovaline concentration using HPLC with fluorescence detection and this experiment was repeated for each harvest date. Sub-samples exposed to UV light and heat lost a significant fraction of ergovaline in 2 hours, while sub-samples stored on ice in a cooler showed no change in ergovaline in 2 hours. All sub-samples stored at 22oC, 5oC and -20oC lost a significant fraction of ergovaline in the first 24 hours of storage. There was little change in ergovaline in the freezer (-20oC) after the first 24 hours up to 28 days of storage but intermittent losses were observed at 22oC and 5oC. To obtain results that most closely represent levels in the field, all samples should be transported on ice to the laboratory immediately after harvest for same day analysis. If immediate testing is not possible, samples should be stored at -20oC until analysis.

Worldwide Emerging Environmental Issues Affecting the U.S. Military. April 2008 Report

DTIC Science & Technology

2008-04-01

Arctic faster, harder - Polar bears may be at even greater risk http://www.wwf.ca/NewsAndFacts/NewsRoom/default.asp?section=archive&page=display&ID =1586...Derek Smith, professor of infectious disease informatics at Cambridge University’s Department of Zoology , and colleagues at Los Alamos National...ice shelves are breaking off or cracking at a higher rate than feared, noted polar ice researchers who accompanied Canadian Rangers on a patrol

Paleolimnology of the McMurdo Dry Valleys, Antarctica

NASA Technical Reports Server (NTRS)

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

1994-01-01

The McMurdo Dry Valleys presently contain more than 20 permanent lakes and ponds, which vary markedly in character. All, with the exception of a hypersaline pond, have a perennial ice-cover. The dry valley lakes, and lakes in other ice-free regions of continental Antarctica, are unique on this planet in that they consistently maintain a thick year-round ice cover (2.8-6.0 m) over liquid water. The persistent ice covers minimize wind-generated currents and reduce light penetration, as well as restricting sediment deposition into a lake and the exchange of atmospheric gases between the water column and the atmosphere. From a paleolimnological perspective, the dry valley lakes offer an important record of catchment and environmental changes. These lakes are also modern-day equivalents of periglacial lakes that were common during glacial periods at temperate latitudes. The present lakes are mostly remnants of larger glacial lakes that occupied the valleys in the past, perhaps up to 4.6 Ma ago. Two of the valleys contain evidence of being filled with large glacial lakes within the last 10000 years. Repeated drying and filling events since then have left a characteristic impression on the salt profiles of some lakes creating a unique paleo-indicator within the water column. These events are also marked in the sediments by the concentration and dilution of certain chemical constituents, particularly salts, and are also corroborated by carbonate speciation and oxygen isotope analysis. Stratigraphic analysis of dry valley lake sediments is made difficult by the occurrence of an 'old carbon' reservoir creating spurious radiocarbon dates, and by the high degree of spatial variability in lake sedimentation. From a biological perspective, the lakes are relatively simple, containing various taxa of planktonic and benthic microorganisms, but no higher forms of life, which is an advantage to paleolimnologists because there is no bioturbation in the sediments. Useful biological paleo-indicators found in the sediments include cyanobacterial filament sheaths, diatom frustules and other eukaryotic algal cells, protozoan cysts, photosynthetic pigments, and minerals (e.g. carbonates) associated with microbial activity. Future work will benefit from fully characterizing the connection between the ice covers, environmental conditions, and paleo-indicators, thereby allowing refinement of inferences made concerning the paleoenvironment. New dating techniques need to be tested in this environment to overcome the problems associated with radiocarbon dating. The establishment of a detailed and focused paleolimnological campaign is proposed.

Paleolimnology of the McMurdo Dry Valleys, Antarctica.

PubMed

Doran, P T; Wharton, R A; Lyons, W B

1994-01-01

The McMurdo Dry Valleys presently contain more than 20 permanent lakes and ponds, which vary markedly in character. All, with the exception of a hypersaline pond, have a perennial ice-cover. The dry valley lakes, and lakes in other ice-free regions of continental Antarctica, are unique on this planet in that they consistently maintain a thick year-round ice cover (2.8-6.0 m) over liquid water. The persistent ice covers minimize wind-generated currents and reduce light penetration, as well as restricting sediment deposition into a lake and the exchange of atmospheric gases between the water column and the atmosphere. From a paleolimnological perspective, the dry valley lakes offer an important record of catchment and environmental changes. These lakes are also modern-day equivalents of periglacial lakes that were common during glacial periods at temperate latitudes. The present lakes are mostly remnants of larger glacial lakes that occupied the valleys in the past, perhaps up to 4.6 Ma ago. Two of the valleys contain evidence of being filled with large glacial lakes within the last 10000 years. Repeated drying and filling events since then have left a characteristic impression on the salt profiles of some lakes creating a unique paleo-indicator within the water column. These events are also marked in the sediments by the concentration and dilution of certain chemical constituents, particularly salts, and are also corroborated by carbonate speciation and oxygen isotope analysis. Stratigraphic analysis of dry valley lake sediments is made difficult by the occurrence of an 'old carbon' reservoir creating spurious radiocarbon dates, and by the high degree of spatial variability in lake sedimentation. From a biological perspective, the lakes are relatively simple, containing various taxa of planktonic and benthic microorganisms, but no higher forms of life, which is an advantage to paleolimnologists because there is no bioturbation in the sediments. Useful biological paleo-indicators found in the sediments include cyanobacterial filament sheaths, diatom frustules and other eukaryotic algal cells, protozoan cysts, photosynthetic pigments, and minerals (e.g. carbonates) associated with microbial activity. Future work will benefit from fully characterizing the connection between the ice covers, environmental conditions, and paleo-indicators, thereby allowing refinement of inferences made concerning the paleoenvironment. New dating techniques need to be tested in this environment to overcome the problems associated with radiocarbon dating. The establishment of a detailed and focused paleolimnological campaign is proposed.

The rise and fall of an ancient Adélie penguin `supercolony' at Cape Adare, Antarctica

NASA Astrophysics Data System (ADS)

Emslie, Steven D.; McKenzie, Ashley; Patterson, William P.

2018-04-01

We report new discoveries and radiocarbon dates on active and abandoned Adélie penguin (Pygoscelis adeliae) colonies at Cape Adare, Antarctica. This colony, first established at approximately 2000 BP (calendar years before present, i.e. 1950), is currently the largest for this species with approximately 338 000 breeding pairs, most located on low-lying Ridley Beach. We hypothesize that this colony first formed after fast ice began blocking open-water access by breeding penguins to the Scott Coast in the southern Ross Sea during a cooling period also at approximately 2000 BP. Our results suggest that the new colony at Cape Adare continued to grow, expanding to a large upper terrace above Ridley Beach, until it exceeded approximately 500 000 breeding pairs (a `supercolony') by approximately 1200 BP. The high marine productivity associated with the Ross Sea polynya and continental shelf break supported this growth, but the colony collapsed to its present size for unknown reasons after approximately 1200 BP. Ridley Beach will probably be abandoned in the near future due to rising sea level in this region. We predict that penguins will retreat to higher elevations at Cape Adare and that the Scott Coast will be reoccupied by breeding penguins as fast ice continues to dissipate earlier each summer, restoring open-water access to beaches there.

The rise and fall of an ancient Adélie penguin 'supercolony' at Cape Adare, Antarctica.

PubMed

Emslie, Steven D; McKenzie, Ashley; Patterson, William P

2018-04-01

We report new discoveries and radiocarbon dates on active and abandoned Adélie penguin ( Pygoscelis adeliae ) colonies at Cape Adare, Antarctica. This colony, first established at approximately 2000 BP (calendar years before present, i.e. 1950), is currently the largest for this species with approximately 338 000 breeding pairs, most located on low-lying Ridley Beach. We hypothesize that this colony first formed after fast ice began blocking open-water access by breeding penguins to the Scott Coast in the southern Ross Sea during a cooling period also at approximately 2000 BP. Our results suggest that the new colony at Cape Adare continued to grow, expanding to a large upper terrace above Ridley Beach, until it exceeded approximately 500 000 breeding pairs (a 'supercolony') by approximately 1200 BP. The high marine productivity associated with the Ross Sea polynya and continental shelf break supported this growth, but the colony collapsed to its present size for unknown reasons after approximately 1200 BP. Ridley Beach will probably be abandoned in the near future due to rising sea level in this region. We predict that penguins will retreat to higher elevations at Cape Adare and that the Scott Coast will be reoccupied by breeding penguins as fast ice continues to dissipate earlier each summer, restoring open-water access to beaches there.

The rise and fall of an ancient Adélie penguin ‘supercolony’ at Cape Adare, Antarctica

PubMed Central

McKenzie, Ashley; Patterson, William P.

2018-01-01

We report new discoveries and radiocarbon dates on active and abandoned Adélie penguin (Pygoscelis adeliae) colonies at Cape Adare, Antarctica. This colony, first established at approximately 2000 BP (calendar years before present, i.e. 1950), is currently the largest for this species with approximately 338 000 breeding pairs, most located on low-lying Ridley Beach. We hypothesize that this colony first formed after fast ice began blocking open-water access by breeding penguins to the Scott Coast in the southern Ross Sea during a cooling period also at approximately 2000 BP. Our results suggest that the new colony at Cape Adare continued to grow, expanding to a large upper terrace above Ridley Beach, until it exceeded approximately 500 000 breeding pairs (a ‘supercolony’) by approximately 1200 BP. The high marine productivity associated with the Ross Sea polynya and continental shelf break supported this growth, but the colony collapsed to its present size for unknown reasons after approximately 1200 BP. Ridley Beach will probably be abandoned in the near future due to rising sea level in this region. We predict that penguins will retreat to higher elevations at Cape Adare and that the Scott Coast will be reoccupied by breeding penguins as fast ice continues to dissipate earlier each summer, restoring open-water access to beaches there. PMID:29765656

Ocean processes at the Antarctic continental slope

PubMed Central

Heywood, Karen J.; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D.; Queste, Bastien Y.; Stevens, David P.; Wadley, Martin; Thompson, Andrew F.; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K.; Smith, Walker

2014-01-01

The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean–atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system. PMID:24891389

Ocean processes at the Antarctic continental slope.

PubMed

Heywood, Karen J; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D; Queste, Bastien Y; Stevens, David P; Wadley, Martin; Thompson, Andrew F; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K; Smith, Walker

2014-07-13

The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean-atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system.

Prebiotic hydrocarbon synthesis in impacting reduced astrophysical icy mixtures

DOE PAGES

Koziol, Lucas; Goldman, Nir

2015-04-21

We present results of prebiotic organic synthesis in shock-compressed reducing mixtures of simple ices from quantum molecular dynamics simulations extended to close to chemical equilibrium timescales. Given the relative abundance of carbon in reduced forms in astrophysical ices as well as the tendency of these mixtures to form complex hydrocarbons under the presence of external stimuli, it is possible that cometary impacts on a planetary surface could have yielded a larger array of prebiotic organic compounds than previously investigated. We find that the high pressures and temperatures due to shock compression yield a large assortment of carbon- and nitrogen-bonded extendedmore » structures that are highly reactive with short molecular lifetimes. Expansion and cooling causes these materials to break apart and form a wide variety of stable, potentially life-building compounds, including long-chain linear and branched hydrocarbons, large heterocyclic compounds, and a variety of different amines and exotic amino acids. Lastly, our results help provide a bottom-up understanding of hydrocarbon impact synthesis on the early Earth and its role in producing life-building molecules from simple starting materials.« less

Prebiotic hydrocarbon synthesis in impacting reduced astrophysical icy mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koziol, Lucas; Goldman, Nir

We present results of prebiotic organic synthesis in shock-compressed reducing mixtures of simple ices from quantum molecular dynamics simulations extended to close to chemical equilibrium timescales. Given the relative abundance of carbon in reduced forms in astrophysical ices as well as the tendency of these mixtures to form complex hydrocarbons under the presence of external stimuli, it is possible that cometary impacts on a planetary surface could have yielded a larger array of prebiotic organic compounds than previously investigated. We find that the high pressures and temperatures due to shock compression yield a large assortment of carbon- and nitrogen-bonded extendedmore » structures that are highly reactive with short molecular lifetimes. Expansion and cooling causes these materials to break apart and form a wide variety of stable, potentially life-building compounds, including long-chain linear and branched hydrocarbons, large heterocyclic compounds, and a variety of different amines and exotic amino acids. Lastly, our results help provide a bottom-up understanding of hydrocarbon impact synthesis on the early Earth and its role in producing life-building molecules from simple starting materials.« less

Numerical Simulation of Thin Film Breakup on Nonwettable Surfaces

NASA Astrophysics Data System (ADS)

Suzzi, N.; Croce, G.

2017-01-01

When a continuous film flows on a nonwettable substrate surface, it may break up, with the consequent formation of a dry-patch. The actual shape of the resulting water layer is of great interest in several engineering applications, from in-flight icing simulation to finned dehumidifier behavior modeling. Here, a 2D numerical solver for the prediction of film flow behavior is presented. The effect of the contact line is introduced via the disjoining pressure terms, and both gravity and shear are included in the formulation. The code is validated with literature experimental data for the case of a stationary dry-patch on an inclined plane. Detailed numerical results are compared with literature simplified model prediction. Numerical simulation are then performed in order to predict the threshold value of the film thickness allowing for film breakup and to analyze the dependence of the dynamic contact angle on film velocity and position along the contact line. Those informations will be useful in order to efficiently predict more complex configuration involving multiple breakups on arbitrarily curved substrate surfaces (as those involved in in-flight icing phenomena on aircraft).

Extensive Ice Fractures in the Beaufort Sea

NASA Image and Video Library

2017-12-08

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this view of extensive sea-ice fracturing off the northern coast of Alaska. The event began in late-January and spread west toward Banks Island throughout February and March 2013. Visualizations of the Arctic often give the impression that the ice cap is a continuous sheet of stationary, floating ice. In fact, it is a collection of smaller pieces that constantly shift, crack, and grind against one another as they are jostled by winds and ocean currents. Especially during the summer—but even during the height of winter—cracks—or leads—open up between pieces of ice. That was what was happening on the left side of the animation (seen here: bit.ly/10kE7sh) in late January. A high-pressure weather system was parked over the region, producing warmer temperatures and winds that flowed in a southwesterly direction. That fueled the Beaufort Gyre, a wind-driven ocean current that flows clockwise. The gyre was the key force pulling pieces of ice west past Point Barrow, the northern nub of Alaska that protrudes into the Beaufort Sea. “A fracturing event in this area is not unusual because the Beaufort Gyre tends to push ice away from Banks Island and the Canadian Archipelago,” explained Walt Meier of the National Snow & Ice Data Center (NSIDC). “Point Barrow can act like a ‘pin point’ where the ice catches and fractures to the north and east.” In February, however, a series of storms passing over central Alaska exacerbated the fracturing. Strong westerly winds prompted several large pieces of ice to break away in an arc-shaped wave that moved progressively east. By the end of February, large pieces of ice had fractured all the way to the western coast of Banks Island, a distance of about 1,000 kilometers (600 miles). The data used to create the animation came from the longwave infrared (thermal) portion of the electromagnetic spectrum, so the animation illustrates how much heat the surface was emitting as VIIRS surveyed the area. Cooler areas (sea ice) appear white, while warmer areas (open water) are dark. The light gray plume near the cracks is warmer, moister air escaping from the ocean and blowing downwind. Clouds do not show up well in the VIIRS thermal band, so the storms that fueled the fracturing are not readily visible. While fracturing events are common, few events sprawl across such a large area or produce cracks as long and wide as those seen here. The age of the sea ice in this area was one of the key reasons this event became so widespread. “The region is covered almost completely by seasonal or first-year ice—ice that has formed since last September,” said Meier. “This ice is thinner and weaker than the older, multi-year ice, so it responds more readily to winds and is more easily broken up.” NASA Earth Observatory images by Jesse Allen using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership. Suomi NPP is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense. Caption by Adam Voiland. Instrument: Suomi NPP - VIIRS For more info go to: earthobservatory.nasa.gov/IOTD/view.php?id=80752 Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Extensive Ice Fractures in the Beaufort Sea [detail

NASA Image and Video Library

2017-12-08

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this view of extensive sea-ice fracturing off the northern coast of Alaska. The event began in late-January and spread west toward Banks Island throughout February and March 2013. Visualizations of the Arctic often give the impression that the ice cap is a continuous sheet of stationary, floating ice. In fact, it is a collection of smaller pieces that constantly shift, crack, and grind against one another as they are jostled by winds and ocean currents. Especially during the summer—but even during the height of winter—cracks—or leads—open up between pieces of ice. That was what was happening on the left side of the animation (seen here: bit.ly/10kE7sh) in late January. A high-pressure weather system was parked over the region, producing warmer temperatures and winds that flowed in a southwesterly direction. That fueled the Beaufort Gyre, a wind-driven ocean current that flows clockwise. The gyre was the key force pulling pieces of ice west past Point Barrow, the northern nub of Alaska that protrudes into the Beaufort Sea. “A fracturing event in this area is not unusual because the Beaufort Gyre tends to push ice away from Banks Island and the Canadian Archipelago,” explained Walt Meier of the National Snow & Ice Data Center (NSIDC). “Point Barrow can act like a ‘pin point’ where the ice catches and fractures to the north and east.” In February, however, a series of storms passing over central Alaska exacerbated the fracturing. Strong westerly winds prompted several large pieces of ice to break away in an arc-shaped wave that moved progressively east. By the end of February, large pieces of ice had fractured all the way to the western coast of Banks Island, a distance of about 1,000 kilometers (600 miles). The data used to create the animation came from the longwave infrared (thermal) portion of the electromagnetic spectrum, so the animation illustrates how much heat the surface was emitting as VIIRS surveyed the area. Cooler areas (sea ice) appear white, while warmer areas (open water) are dark. The light gray plume near the cracks is warmer, moister air escaping from the ocean and blowing downwind. Clouds do not show up well in the VIIRS thermal band, so the storms that fueled the fracturing are not readily visible. While fracturing events are common, few events sprawl across such a large area or produce cracks as long and wide as those seen here. The age of the sea ice in this area was one of the key reasons this event became so widespread. “The region is covered almost completely by seasonal or first-year ice—ice that has formed since last September,” said Meier. “This ice is thinner and weaker than the older, multi-year ice, so it responds more readily to winds and is more easily broken up.” NASA Earth Observatory images by Jesse Allen using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership. Suomi NPP is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense. Caption by Adam Voiland. Instrument: Suomi NPP - VIIRS For more info go to: earthobservatory.nasa.gov/IOTD/view.php?id=80752 Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Extensive Ice Fractures in the Beaufort Sea [annotated

NASA Image and Video Library

2017-12-08

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this view of extensive sea-ice fracturing off the northern coast of Alaska. The event began in late-January and spread west toward Banks Island throughout February and March 2013. Visualizations of the Arctic often give the impression that the ice cap is a continuous sheet of stationary, floating ice. In fact, it is a collection of smaller pieces that constantly shift, crack, and grind against one another as they are jostled by winds and ocean currents. Especially during the summer—but even during the height of winter—cracks—or leads—open up between pieces of ice. That was what was happening on the left side of the animation (seen here: bit.ly/10kE7sh) in late January. A high-pressure weather system was parked over the region, producing warmer temperatures and winds that flowed in a southwesterly direction. That fueled the Beaufort Gyre, a wind-driven ocean current that flows clockwise. The gyre was the key force pulling pieces of ice west past Point Barrow, the northern nub of Alaska that protrudes into the Beaufort Sea. “A fracturing event in this area is not unusual because the Beaufort Gyre tends to push ice away from Banks Island and the Canadian Archipelago,” explained Walt Meier of the National Snow & Ice Data Center (NSIDC). “Point Barrow can act like a ‘pin point’ where the ice catches and fractures to the north and east.” In February, however, a series of storms passing over central Alaska exacerbated the fracturing. Strong westerly winds prompted several large pieces of ice to break away in an arc-shaped wave that moved progressively east. By the end of February, large pieces of ice had fractured all the way to the western coast of Banks Island, a distance of about 1,000 kilometers (600 miles). The data used to create the animation came from the longwave infrared (thermal) portion of the electromagnetic spectrum, so the animation illustrates how much heat the surface was emitting as VIIRS surveyed the area. Cooler areas (sea ice) appear white, while warmer areas (open water) are dark. The light gray plume near the cracks is warmer, moister air escaping from the ocean and blowing downwind. Clouds do not show up well in the VIIRS thermal band, so the storms that fueled the fracturing are not readily visible. While fracturing events are common, few events sprawl across such a large area or produce cracks as long and wide as those seen here. The age of the sea ice in this area was one of the key reasons this event became so widespread. “The region is covered almost completely by seasonal or first-year ice—ice that has formed since last September,” said Meier. “This ice is thinner and weaker than the older, multi-year ice, so it responds more readily to winds and is more easily broken up.” NASA Earth Observatory images by Jesse Allen using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership. Suomi NPP is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense. Caption by Adam Voiland. Instrument: Suomi NPP - VIIRS For more info go to: earthobservatory.nasa.gov/IOTD/view.php?id=80752 Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Ecology of southern ocean pack ice.

PubMed

Brierley, Andrew S; Thomas, David N

2002-01-01

Around Antarctica the annual five-fold growth and decay of sea ice is the most prominent physical process and has a profound impact on marine life there. In winter the pack ice canopy extends to cover almost 20 million square kilometres--some 8% of the southern hemisphere and an area larger than the Antarctic continent itself (13.2 million square kilometres)--and is one of the largest, most dynamic ecosystems on earth. Biological activity is associated with all physical components of the sea-ice system: the sea-ice surface; the internal sea-ice matrix and brine channel system; the underside of sea ice and the waters in the vicinity of sea ice that are modified by the presence of sea ice. Microbial and microalgal communities proliferate on and within sea ice and are grazed by a wide range of proto- and macrozooplankton that inhabit the sea ice in large concentrations. Grazing organisms also exploit biogenic material released from the sea ice at ice break-up or melt. Although rates of primary production in the underlying water column are often low because of shading by sea-ice cover, sea ice itself forms a substratum that provides standing stocks of bacteria, algae and grazers significantly higher than those in ice-free areas. Decay of sea ice in summer releases particulate and dissolved organic matter to the water column, playing a major role in biogeochemical cycling as well as seeding water column phytoplankton blooms. Numerous zooplankton species graze sea-ice algae, benefiting additionally because the overlying sea-ice ceiling provides a refuge from surface predators. Sea ice is an important nursery habitat for Antarctic krill, the pivotal species in the Southern Ocean marine ecosystem. Some deep-water fish migrate to shallow depths beneath sea ice to exploit the elevated concentrations of some zooplankton there. The increased secondary production associated with pack ice and the sea-ice edge is exploited by many higher predators, with seals, seabirds and whales aggregating there. As a result, much of the Southern Ocean pelagic whaling was concentrated at the edge of the marginal ice zone. The extent and duration of sea ice fluctuate periodically under the influence of global climatic phenomena including the El Niño Southern Oscillation. Life cycles of some associated species may reflect this periodicity. With evidence for climatic warming in some regions of Antarctica, there is concern that ecosystem change may be induced by changes in sea-ice extent. The relative abundance of krill and salps appears to change interannually with sea-ice extent, and in warm years, when salps proliferate, krill are scarce and dependent predators suffer severely. Further research on the Southern Ocean sea-ice system is required, not only to further our basic understanding of the ecology, but also to provide ecosystem managers with the information necessary for the development of strategies in response to short- and medium-term environmental changes in Antarctica. Technological advances are delivering new sampling platforms such as autonomous underwater vehicles that are improving vastly our ability to sample the Antarctic under sea-ice environment. Data from such platforms will enhance greatly our understanding of the globally important Southern Ocean sea-ice ecosystem.

Towards seasonal Arctic shipping route predictions

NASA Astrophysics Data System (ADS)

Melia, N.; Haines, K.; Hawkins, E.; Day, J. J.

2017-08-01

The continuing decline in Arctic sea-ice will likely lead to increased human activity and opportunities for shipping in the region, suggesting that seasonal predictions of route openings will become ever more important. Here we present results from a set of ‘perfect model’ experiments to assess the predictability characteristics of the opening of Arctic sea routes. We find skilful predictions of the upcoming summer shipping season can be made from as early as January, although typically forecasts show lower skill before a May ‘predictability barrier’. We demonstrate that in forecasts started from January, predictions of route opening date are twice as uncertain as predicting the closing date and that the Arctic shipping season is becoming longer due to climate change, with later closing dates mostly responsible. We find that predictive skill is state dependent with predictions for high or low ice years exhibiting greater skill than medium ice years. Forecasting the fastest open water route through the Arctic is accurate to within 200 km when predicted from July, a six-fold increase in accuracy compared to forecasts initialised from the previous November, which are typically no better than climatology. Finally we find that initialisation of accurate summer sea-ice thickness information is crucial to obtain skilful forecasts, further motivating investment into sea-ice thickness observations, climate models, and assimilation systems.

Matching conjugate volcanic rifted margins: 40Ar/ 39Ar chrono-stratigraphy of pre- and syn-rift bimodal flood volcanism in Ethiopia and Yemen

NASA Astrophysics Data System (ADS)

Ukstins, Ingrid A.; Renne, Paul R.; Wolfenden, Ellen; Baker, Joel; Ayalew, Dereje; Menzies, Martin

2002-05-01

40Ar/ 39Ar dating of mineral separates and whole-rock samples of rhyolitic ignimbrites and basaltic lavas from the pre- and syn-rift flood volcanic units of northern Ethiopia provides a temporal link between the Ethiopian and Yemen conjugate rifted volcanic margins. Sixteen new 40Ar/ 39Ar dates confirm that basaltic flood volcanism in Ethiopia was contemporaneous with flood volcanism on the conjugate margin in Yemen. The new data also establish that flood volcanism initiated prior to 30.9 Ma in Ethiopia and may predate initiation of similar magmatic activity in Yemen by ˜0.2-2.0 Myr. Rhyolitic volcanism in Ethiopia commenced at 30.2 Ma, contemporaneous with the first rhyolitic ignimbrite unit in Yemen at ˜30 Ma. Accurate and precise 40Ar/ 39Ar dates on initial rhyolitic ignimbrite eruptions suggest that silicic flood volcanism in Afro-Arabia post-dates the Oligocene Oi2 global cooling event, ruling out a causative link between these explosive silicic eruptions (with individual volumes ≥200 km 3) and climatic cooling which produced the first major expansion of the Antarctic ice sheets. Ethiopian volcanism shows a progressive and systematic younging from north to south along the escarpment and parallel to the rifted margin, from pre-rift flood volcanics in the north to syn-rift northern Main Ethiopian Rift volcanism in the south. A dramatic decrease in volcanic activity in Ethiopia between 25 and 20 Ma correlates with a prominent break-up unconformity in Yemen (26-19 Ma), both of which mark the transition from pre- to syn-rift volcanism (˜25-26 Ma) triggered by the separation of Africa and Arabia. The architecture of the Ethiopian margin is characterized by accumulation and preservation of syn-rift volcanism, while the Yemen margin was shaped by denudational unloading and magmatic starvation as the Arabian plate rifted away from the Afar plume. A second magmatic hiatus and angular unconformity in the northern Main Ethiopian Rift is evident at 10.6-3.2 Ma, and is also observed throughout the Arabian plate in Jordanian, Saudi Arabian and Yemeni intraplate volcanic fields and is possibly linked to tectonic re-organization and initiation of sea floor spreading in the Gulf of Aden and the Red Sea at 10 and 5 Ma, respectively.

Propeller torque load and propeller shaft torque response correlation during ice-propeller interaction

NASA Astrophysics Data System (ADS)

Polić, Dražen; Ehlers, Sören; Æsøy, Vilmar

2017-03-01

Ships use propulsion machinery systems to create directional thrust. Sailing in ice-covered waters involves the breaking of ice pieces and their submergence as the ship hull advances. Sometimes, submerged ice pieces interact with the propeller and cause irregular fluctuations of the torque load. As a result, the propeller and engine dynamics become imbalanced, and energy propagates through the propulsion machinery system until equilibrium is reached. In such imbalanced situations, the measured propeller shaft torque response is not equal to the propeller torque. Therefore, in this work, the overall system response is simulated under the ice-related torque load using the Bond graph model. The energy difference between the propeller and propeller shaft is estimated and related to their corresponding mechanical energy. Additionally, the mechanical energy is distributed among modes. Based on the distribution, kinetic and potential energy are important for the correlation between propeller torque and propeller shaft response.

FDC Mentor-Mentee Mixer Breaks the Ice Between Investigators and Trainees | Poster

Cancer.gov

The Frederick Diversity Committee’s mentor-mentee mixer gave research trainees, senior investigators, scientists, and administrative staff a chance to meet and mingle over refreshments and games following the Spring Research Festival.

2016 Climate Trends Continue to Break Records

NASA Image and Video Library

2017-12-08

Two key climate change indicators -- global surface temperatures and Arctic sea ice extent -- have broken numerous records through the first half of 2016, according to NASA analyses of ground-based observations and satellite data. Each of the first six months of 2016 set a record as the warmest respective month globally in the modern temperature record, which dates to 1880, according to scientists at NASA's Goddard Institute for Space Studies (GISS) in New York. The six-month period from January to June was also the planet's warmest half-year on record, with an average temperature 1.3 degrees Celsius (2.4 degrees Fahrenheit) warmer than the late nineteenth century. Read more: go.nasa.gov/29SQngq Credit: NASA/Goddard NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Surface water mass composition changes captured by cores of Arctic land-fast sea ice

NASA Astrophysics Data System (ADS)

Smith, I. J.; Eicken, H.; Mahoney, A. R.; Van Hale, R.; Gough, A. J.; Fukamachi, Y.; Jones, J.

2016-04-01

In the Arctic, land-fast sea ice growth can be influenced by fresher water from rivers and residual summer melt. This paper examines a method to reconstruct changes in water masses using oxygen isotope measurements of sea ice cores. To determine changes in sea water isotope composition over the course of the ice growth period, the output of a sea ice thermodynamic model (driven with reanalysis data, observations of snow depth, and freeze-up dates) is used along with sea ice oxygen isotope measurements and an isotopic fractionation model. Direct measurements of sea ice growth rates are used to validate the output of the sea ice growth model. It is shown that for sea ice formed during the 2011/2012 ice growth season at Barrow, Alaska, large changes in isotopic composition of the ocean waters were captured by the sea ice isotopic composition. Salinity anomalies in the ocean were also tracked by moored instruments. These data indicate episodic advection of meteoric water, having both lower salinity and lower oxygen isotopic composition, during the winter sea ice growth season. Such advection of meteoric water during winter is surprising, as no surface meltwater and no local river discharge should be occurring at this time of year in that area. How accurately changes in water masses as indicated by oxygen isotope composition can be reconstructed using oxygen isotope analysis of sea ice cores is addressed, along with methods/strategies that could be used to further optimize the results. The method described will be useful for winter detection of meteoric water presence in Arctic fast ice regions, which is important for climate studies in a rapidly changing Arctic. Land-fast sea ice effective fractionation coefficients were derived, with a range of +1.82‰ to +2.52‰. Those derived effective fractionation coefficients will be useful for future water mass component proportion calculations. In particular, the equations given can be used to inform choices made when engaging in end member determination for working out the component proportions of water masses.

A customer value analysis of Taiwan ice cream market: a means-end chain approach across consumption situations.

PubMed

Chen, Yan-Kwang; Tsai, Pei-Shan; Chiu, Fei-Rung

2015-01-01

In the highly competitive market, it is increasingly hard for ice cream stores to develop creative marketing strategies to retain existing customers and attract new ones. This study applies the means-end chain approach to identify the customer value, consequences, and attributes of ice cream and to suggest useful information for ice cream sellers to develop differential marketing strategies across various consumption situations (i.e. on a date, gathering with friends, craving for ice cream). This study conducted one-on-one in-depth interviews with participants. The interview content was subsequently analyzed and coded to produce an implication matrix and a hierarchical value map, which was further used to determine customers' value perceptions. The results indicate the terminal values of the highest strength comprised economy, pleasure, and efficiency. Pleasure was emphasized among consumers who were on a date or gathering with friends, whereas satisfaction was emphasized among consumers who craved ice cream. Based on the results, the study also provides suggestions to the industry and future researchers.

Aragonite undersaturation in the Arctic Ocean: effects of ocean acidification and sea ice melt.

PubMed

Yamamoto-Kawai, Michiyo; McLaughlin, Fiona A; Carmack, Eddy C; Nishino, Shigeto; Shimada, Koji

2009-11-20

The increase in anthropogenic carbon dioxide emissions and attendant increase in ocean acidification and sea ice melt act together to decrease the saturation state of calcium carbonate in the Canada Basin of the Arctic Ocean. In 2008, surface waters were undersaturated with respect to aragonite, a relatively soluble form of calcium carbonate found in plankton and invertebrates. Undersaturation was found to be a direct consequence of the recent extensive melting of sea ice in the Canada Basin. In addition, the retreat of the ice edge well past the shelf-break has produced conditions favorable to enhanced upwelling of subsurface, aragonite-undersaturated water onto the Arctic continental shelf. Undersaturation will affect both planktonic and benthic calcifying biota and therefore the composition of the Arctic ecosystem.

Sea ice cover variability and river run-off in the western Laptev Sea (Arctic Ocean) since the last 18 ka

NASA Astrophysics Data System (ADS)

Hörner, T.; Stein, R.; Fahl, K.; Birgel, D.

2015-12-01

Multi-proxy biomarker measurements were performed on two sediment cores (PS51/154, PS51/159) with the objective reconstructing sea ice cover (IP25, brassicasterol, dinosterol) and river-runoff (campesterol, β-sitosterol) in the western Laptev Sea over the last 18 ka with unprecedented temporal resolution. The sea ice cover varies distinctly during the whole time period. The absence of IP25 during 18 and 16 ka indicate that the western Laptev Sea was mostly covered with permanent sea ice (pack ice). However, a period of temporary break-up of the permanent ice coverage occurred at c. 17.2 ka (presence of IP25). Very little river-runoff occurred during this interval. Decreasing terrigenous (riverine) input and synchronous increase of marine produced organic matter around 16 ka until 7.5 ka indicate the gradual establishment of a marine environment in the western Laptev Sea related to the onset of the post-glacial transgression of the shelf. Strong river run-off and reduced sea ice cover characterized the time interval between 15.2 and 12.9 ka, including the Bølling/Allerød warm period (14.7 - 12.9 ka). Moreover, the DIP25 Index (ratio of HBI-dienes and IP25) might document the presence of Atlantic derived water at the western Laptev Sea shelf area. A sudden return to severe sea ice conditions occurred during the Younger Dryas (12.9 - 11.6 ka). This abrupt climate change was observed in the whole circum-Arctic realm (Chukchi Sea, Bering Sea, Fram Strait and Laptev Sea). At the onset of the Younger Dryas, a distinct alteration of the ecosystem (deep drop in terrigenous and phytoplankton biomarkers) may document the entry of a giant freshwater plume, possibly relating to the Lake Agassiz outburst at 13 ka. IP25 concentrations increase and higher values of the PIP25 Index during the last 7 ka reflect a cooling of the Laptev Sea spring season. Moreover, a short-term variability of c. 1.5 thousand years occurred during the last 12 ka, most probably following Bond Cycles.

On Wave-Ice Interaction in the Arctic Marginal Ice Zone: Dispersion, Attenuation, and Ice Response

DTIC Science & Technology

2016-06-01

PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 2. REPORT TYPE1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 6. AUTHOR(S) 8. PERFORMING...schemes and contributes to a change of wave height (and direction) analogous to shoaling and refraction. A method for jointly measuring dispersion and...46 APPENDEX B: WAVE HEIGHTS MEASURED IN ARTIC ICE

Radiocarbon chronology of the last deglaciation in the Baffin Bay reveals asynchronous melting of Arctic and Laurentide ice sheets

NASA Astrophysics Data System (ADS)

Jackson, Rebecca; Kucera, Michal; Vogt, Christoph; Wacker, Lukas

2016-04-01

The transition from the last ice age into the Holocene interglacial was characterised by rapid retreat of North American ice sheets, discharging large quantities of meltwater into the Labrador Sea. Whereas the meltwater chronology of the Laurentide Ice Sheet is well documented, the deglacial history of the American Arctic ice sheets (Inuit Ice sheet and northern Greenland Ice Sheet) draining into the Labrador Sea via the Baffin Bay is less well constrained. Here we present the first high-resolution radiocarbon-dated deglacial records from the Canadian and Greenland margins of the central Baffin Bay. Sedimentological and geochemical data confirm the presence during Termination I of two events of enhanced delivery of detrital carbonate (Baffin Bay Detrital Carbonate Events) dated to 14.2-13.7 ka BP and 12.7-11 ka BP. The events are synchronous across the Baffin Bay and their mineralogical signature indicates a common source of detrital carbonate from the Canadian Arctic, with a synchronous clastic source proximal to Greenland. The events postdate Heinrich layers and their onset is not linked to Greenland temperature change. This indicates that the deglaciation of American Arctic ice sheets and associated meltwater discharge were decoupled from the dominant North Atlantic climate mode.

Rapid changes in ice core gas records - Part 1: On the accuracy of methane synchronisation of ice cores

NASA Astrophysics Data System (ADS)

Köhler, P.

2010-08-01

Methane synchronisation is a concept to align ice core records during rapid climate changes of the Dansgaard/Oeschger (D/O) events onto a common age scale. However, atmospheric gases are recorded in ice cores with a log-normal-shaped age distribution probability density function, whose exact shape depends mainly on the accumulation rate on the drilling site. This age distribution effectively shifts the mid-transition points of rapid changes in CH4 measured in situ in ice by about 58% of the width of the age distribution with respect to the atmospheric signal. A minimum dating uncertainty, or artefact, in the CH4 synchronisation is therefore embedded in the concept itself, which was not accounted for in previous error estimates. This synchronisation artefact between Greenland and Antarctic ice cores is for GRIP and Byrd less than 40 years, well within the dating uncertainty of CH4, and therefore does not calls the overall concept of the bipolar seesaw into question. However, if the EPICA Dome C ice core is aligned via CH4 to NGRIP this synchronisation artefact is in the most recent unified ice core age scale (Lemieux-Dudon et al., 2010) for LGM climate conditions of the order of three centuries and might need consideration in future gas chronologies.

DISINTEGRATING ASTEROID P/2013 R3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jewitt, David; Li, Jing; Agarwal, Jessica

Splitting of the nuclei of comets into multiple components has been frequently observed but, to date, no main-belt asteroid has been observed to break up. Using the Hubble Space Telescope, we find that main-belt asteroid P/2013 R3 consists of 10 or more distinct components, the largest up to 200 m in radius (assumed geometric albedo of 0.05) each of which produces a coma and comet-like dust tail. A diffuse debris cloud with total mass ∼2 × 10{sup 8} kg further envelopes the entire system. The velocity dispersion among the components, ΔV ∼ 0.2-0.5 m s{sup –1}, is comparable to the gravitational escape speeds ofmore » the largest members, while their extrapolated plane-of-sky motions suggest a break up between 2013 February and September. The broadband optical colors are those of a C-type asteroid. We find no spectral evidence for gaseous emission, placing model-dependent upper limits to the water production rate ≤1 kg s{sup –1}. Breakup may be due to a rotationally induced structural failure of the precursor body.« less

Little ice bodies, huge ice lands, and the up-going of the big water body

NASA Astrophysics Data System (ADS)

Ultee, E.; Bassis, J. N.

2017-12-01

Ice moving out of the huge ice lands causes the big water body to go up. That can cause bad things to happen in places close to the big water body - the land might even disappear! If that happens, people living close to the big water body might lose their homes. Knowing how much ice will come out of the huge ice lands, and when, can help the world plan for the up-going of the big water body. We study the huge ice land closest to us. All around the edge of that huge ice land, there are smaller ice bodies that control how much ice makes it into the big water body. Most ways of studying the huge ice land with computers struggle to tell the computer about those little ice bodies, but we have found a new way. We will talk about our way of studying little ice bodies and how their moving brings about up-going of the big water.

Heavy metals in Antarctic ice from Law Dome: Initial results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, S.; Boutron, C.F.; Edwards, R.

1998-08-01

Pb, Cd, Cu, and Zn have been measured using ultraclean procedures in eight sections taken from two well-dated ice cores from Law Dome, an independent small size ice cap with high accumulation rate situated in the coastal area of East Antarctica. Seven sections were dated from the 1830s to 1940s and one was dated from three millennia ago. The data show that there are strong seasonal variations in the concentrations of Pb and Cd, with values {approximately} two- to four-fold higher in winter than in spring-summer. Evaluation of the contributions from the different sources suggests that contribution from sea saltmore » spray is relatively important, especially for Cd. Contribution from marine biogenic emissions could also be very significant. The importance of marine contributions is consistent with strong intrusions of marine air masses at this coastal site, especially during wintertime.« less

New cetacean ΔR values for Arctic North America and their implications for marine-mammal-based palaeoenvironmental reconstructions

NASA Astrophysics Data System (ADS)

Furze, Mark F. A.; Pieńkowski, Anna J.; Coulthard, Roy D.

2014-05-01

Radiocarbon-dated marine mammal remains from emergent Arctic coastlines have frequently been used to reconstruct Holocene sea-ice histories. The use of such reconstructions has hitherto been complicated by uncertain marine reservoir corrections precluding meaningful intercomparisons with data reported in calibrated or sidereal years. Based on an exhaustive compilation of previously published marine mammal radiocarbon dates (both live-harvested materials and subfossils) from the Canadian Arctic Archipelago (CAA), new, statistically-derived δ13C and ΔR values are provided. Average δ13C values are: -16.1 ± 1.1‰ (bone collagen; n = 193) for bowhead (Balaena mysticetus); -14.4 ± 0.5‰ (n = 44; dentine) for beluga (Delphinapterus leucas); -14.8 ± 1.9‰ (teeth and tusks; n = 18) and -18.0 ± 4.7‰ (n = 9; bone collagen) for walrus (Odobenus rosmarus). ΔR values are 170 ± 95 14C years for bowhead (n = 23) and 240 ± 60 14C years for beluga (n = 12). Scarce data preclude calculation of meaningful, statistically robust walrus ΔR. Using the new ΔR values, an expanded and revised database of calibrated bowhead dates (651 dates; many used in previous CAA sea-ice reconstructions) shows pronounced late Quaternary spatio-temporal fluctuations in bone abundance. Though broadly resembling earlier bowhead subfossil frequency data, analysis of the new expanded database suggests early- and mid-Holocene increases in whale abundance to be of longer duration and lower amplitude than previously considered. A more even and persistent spread of infrequent low-abundance remains during “whale free” intervals is also seen. The dominance of three eastern regions (Prince Regent Inlet & Gulf of Boothia; Admiralty Inlet; Berlinguet Inlet/Bernier Bay) in the CAA data, collectively contributing up to 88% of all subfossil remains in the mid-Holocene, is notable. An analysis of calibrated regional sea-level index points suggests that severance of the Admiralty Inlet-Gulf of Boothia marine channel due to isostatically-driven regression may have played a significant role in enhanced whale mortality during this interval. Comparisons between the newly calibrated bowhead data and other regional sea-ice proxy data further highlight spatial and temporal discrepancies, potentially due to regional asynchronicities and variable sensitivities in proxy response to climate and oceanographic forcing. However, the limited number of deglacial-postglacial marine records continues to hamper extensive intercomparisons between marine mammal and other proxy datasets. Nevertheless, an examination of assumptions inherent in linking bowhead subfossil frequencies, population densities, and sea-ice thickness and distribution, shows that such relationships are highly complex. Factors such as broad sea-ice preferences, variable mortality rates and causes, long distance carcass transport, variable coastline and basin/channel geometries, and changing emergence rates all complicate the correlation of whale bone abundance to sea-ice histories.

Ice-dammed lateral lake and epishelf lake insights into Holocene dynamics of Marguerite Trough Ice Stream and George VI Ice Shelf, Alexander Island, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Davies, Bethan J.; Hambrey, Michael J.; Glasser, Neil F.; Holt, Tom; Rodés, Angél; Smellie, John L.; Carrivick, Jonathan L.; Blockley, Simon P. E.

2017-12-01

We present new data regarding the past dynamics of Marguerite Trough Ice Stream, George VI Ice Shelf and valley glaciers from Ablation Point Massif on Alexander Island, Antarctic Peninsula. This ice-free oasis preserves a geological record of ice stream lateral moraines, ice-dammed lakes, ice-shelf moraines and valley glacier moraines, which we dated using cosmogenic nuclide ages. We provide one of the first detailed sediment-landform assemblage descriptions of epishelf lake shorelines. Marguerite Trough Ice Stream imprinted lateral moraines against eastern Alexander Island at 120 m at Ablation Point Massif. During deglaciation, lateral lakes formed in the Ablation and Moutonnée valleys, dammed against the ice stream in George VI Sound. Exposure ages from boulders on these shorelines yielded ages of 13.9 to 9.7 ka. Following recession of the ice stream, George VI Ice Shelf formed in George VI Sound. An epishelf lake formed at 15-20 m asl in Ablation and Moutonnée valleys, dated from 9.4 to 4.6 ka, suggesting that the lake was stable and persistent for some 5000 years. Lake-level lowering occurred after this, with the lake level at 12 m at 3.1 ± 0.4 ka and at 5 m asl today. A readvance of the valley glaciers on Alexander Island at 4.4 ± 0.7 ka is recorded by valley glacier moraines overlying epishelf lake sediments. We speculate that the glacier readvance, which occurred during a period of warmth, may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of George VI Ice Shelf.

High-resolution record of the deglaciation of the British-Irish Ice Sheet from North Atlantic deep-sea sediments.

NASA Astrophysics Data System (ADS)

Tarlati, S.; Benetti, S.; Callard, L.; O'Cofaigh, C.; Dunlop, P.; Chiverrell, R. C.; Fabel, D.; Moreton, S.; Clark, C.

2016-12-01

During the last glacial maximum the British-Irish Ice Sheet (BIIS) covered the majority of Ireland and Britain. Recent studies have described the BIIS as largely marine-based and highly dynamic with several advances and retreats recorded on the continental shelf. The focus of this study is the more recent sediment record from the Donegal Barra Fan (DBF), the largest sediment depocentre formed by the ice streaming of the western BIIS onto the North Atlantic continental margin. In this project, well-preserved, glacially-derived, deep-water sediments from 3 cores, up to 6.7 m long and retrieved from the DBF, are used to investigate and chronologically constrain the pattern of deglaciation of the BIIS. Deep-water sediments can record continuous sedimentation through time, avoiding hiatuses and erosional surfaces characteristic of a glacial environment and allow a detailed reconstruction of deglacial processes. Five lithofacies have been identified using sedimentology, x-rays, physical properties and grain size analysis. They include bioturbated foraminifera-bearing muds, interpreted as hemipelagic and contouritic deposits from interglacial periods. Chaotic and laminated muds, ice-rafted debris (IRD)-rich layers and laminated mud to sand couplets are characteristic of the glacial period including ice-sheet maximum extent and the beginning of retreat. These represent downslope mass movements, plumites from meltwater alongside melting icebergs and turbidites. Radiocarbon dates from foraminifera suggest that the deglacial sedimentary sequence is up to 5m thick. The IRD concentration and abundance of the foraminifera Neogloboquadrina pachyderma sinistral indicate a minimum of 3 different calving events during deglaciation and a marked Younger Dryas cooling and ice calving period. Additionally the δ 18O record will be used to investigate the record of climatic changes in the region and x-ray fluorescence will be used to assess sediment provenance during deglaciation.

Changing characteristics of arctic pressure ridges

NASA Astrophysics Data System (ADS)

Wadhams, Peter; Toberg, Nick

2012-04-01

The advent of multibeam sonar permits us to obtain full three-dimensional maps of the underside of sea ice. In particular this enables us to distinguish the morphological characteristics of first-year (FY) and multi-year (MY) pressure ridges in a statistically valid way, whereas in the past only a small number of ridges could be mapped laboriously by drilling. In this study pressure ridge distributions from two parts of the Arctic Ocean are compared, in both the cases using mainly data collected by the submarine “Tireless” in March 2007 during two specific grid surveys, in the Beaufort Sea at about 75° N, 140° W (N of Prudhoe Bay), and north of Ellesmere Island at about 83° 20‧ N, 64° W. In the Beaufort Sea the ice was mainly FY, and later melted or broke up as this area became ice-free during the subsequent summer. N of Ellesmere Island the ice was mainly MY. Ridge depth and spacing distributions were derived for each region using the boat's upward looking sonar, combined with distributions of shapes of the ridges encountered, using the Kongsberg EM3002 multibeam sonar. The differing shapes of FY and MY ridges are consistent with two later high-resolution multibeam studies of specific ridges by AUV. FY ridges are found to fit the normal triangular shape template in cross-section (with a range of slope angles averaging 27°) with a relatively constant along-crest depth, and often a structure of small ice blocks can be distinguished. MY ridges, however, are often split into a number of independent solid, smooth blocks of large size, giving an irregular ridge profile which may be seemingly without linearity. Our hypothesis for this difference is that during its long lifetime an MY ridge is subjected to several episodes of crack opening; new cracks in the Arctic pack often run in straight lines across the ridges and undeformed ice alike. Such a crack will open somewhat before refreezing, interpolating a stretch of thin ice into the structure, and breaking up the continuity and linearity of the ridge crest. Many such episodes over a number of years can cause the ridge to become simply a series of blocks. This has implications for ridge strength and for permeability to spilled oil. As the percentage of MY ice in the Arctic diminishes, Arctic ridging will be more and more dominated by FY ridges, and we discuss the implications of this change of character of the ice underside in the light of the statistics that we have generated for the two types of ridge.

Prediction of sea ice thickness cluster in the Northern Hemisphere

NASA Astrophysics Data System (ADS)

Fuckar, Neven-Stjepan; Guemas, Virginie; Johnson, Nathaniel; Doblas-Reyes, Francisco

2016-04-01

Sea ice thickness (SIT) has a potential to contain substantial climate memory and predictability in the northern hemisphere (NH) sea ice system. We use 5-member NH SIT, reconstructed with an ocean-sea-ice general circulation model (NEMOv3.3 with LIM2) with a simple data assimilation routine, to determine NH SIT modes of variability disentangled from the long-term climate change. Specifically, we apply the K-means cluster analysis - one of nonhierarchical clustering methods that partition data into modes or clusters based on their distances in the physical - to determine optimal number of NH SIT clusters (K=3) and their historical variability. To examine prediction skill of NH SIT clusters in EC-Earth2.3, a state-of-the-art coupled climate forecast system, we use 5-member ocean and sea ice initial conditions (IC) from the same ocean-sea-ice historical reconstruction and atmospheric IC from ERA-Interim reanalysis. We focus on May 1st and Nov 1st start dates from 1979 to 2010. Common skill metrics of probability forecast, such as rank probability skill core and ROC (relative operating characteristics - hit rate versus false alarm rate) and reliability diagrams show that our dynamical model predominately perform better than the 1st order Marko chain forecast (that beats climatological forecast) over the first forecast year. On average May 1st start dates initially have lower skill than Nov 1st start dates, but their skill is degraded at slower rate than skill of forecast started on Nov 1st.

Habitat selection and seasonal movements of young bearded seals (Erignathus barbatus) in the Bering Sea

PubMed Central

2018-01-01

The first year of life is typically the most critical to a pinniped’s survival, especially for Arctic phocids which are weaned at only a few weeks of age and left to locate and capture prey on their own. Their seasonal movements and habitat selection are therefore important factors in their survival. During a cooperative effort between scientists and subsistence hunters in October 2004, 2005, and 2006, 13 female and 13 male young (i.e., age <2) bearded seals (Erignathus barbatus) were tagged with satellite-linked dive recorders (SDRs) in Kotzebue Sound, Alaska. Shortly after being released, most seals moved south with the advancing sea-ice through the Bering Strait and into the Bering Sea where they spent the winter and early spring. The SDRs of 17 (8 female and 9 male) seals provided frequent high-quality positions in the Bering Sea; their data were used in our analysis. To investigate habitat selection, we simulated 20 tracks per seal by randomly selecting from the pooled distributions of the absolute bearings and swim speeds of the tagged seals. For each point in the observed and simulated tracks, we obtained the depth, sea-ice concentration, and the distances to sea-ice, open water, the shelf break and coastline. Using logistic regression with a stepwise model selection procedure, we compared the simulated tracks to those of the tagged seals and obtained a model for describing habitat selection. The regression coefficients indicated that the bearded seals in our study selected locations near the ice edge. In contrast, aerial surveys of the bearded seal population, predominantly composed of adults, indicated higher abundances in areas farther north and in heavier pack ice. We hypothesize that this discrepancy is the result of behavioral differences related to age. Ice concentration was also shown to be a statistically significant variable in our model. All else being equal, areas of higher ice concentration are selected for up to about 80%. The effects of sex and bathymetry were not statistically significant. The close association of young bearded seals to the ice edge in the Bering Sea is important given the likely effects of climate warming on the extent of sea-ice and subsequent changes in ice edge habitat. PMID:29489846

Ground ice conditions in Salluit, Northern Quebec

NASA Astrophysics Data System (ADS)

Allard, M.; Fortier, R.; Calmels, F.; Gagnon, O.; L'Hérault, E.

2011-12-01

Salluit in Northern Québec (ca. 1300 inhabitants) faces difficult ground ice conditions for its development. The village is located in a U-shaped valley, along a fjord that was deglaciated around 8000 cal BP. The post-glacial marine limit is at the current elevation of 150 m ASL. Among the mapped surficial geology units, three contain particularly ice-rich permafrost: marine clays, till and silty colluviums. A diamond drill was used to extract 10 permafrost cores down to 23 m deep. In addition, 18 shallow cores (to 5 m deep) were extracted with a portable drill. All the frozen cores were shipped to Québec city where ground ice contents were measured and cryostructures were imaged by CT-Scanning. Water contents, grain-size and pore water salinity were measured. Refraction seismic profiles were run to measure the depth to bedrock. GPR and electrical resistivity surveys helped to map ice-rich areas. Three cone penetration tests (CPT) were run in the frozen clays to depths ranging from 8 to 21 m. Maximum clay thickness is ca. 50 m deep near the shoreline. The cone penetration tests and all the cores in clays revealed large amounts of both segregated and aggradational ice (volumetric contents up to 93% over thicknesses of one meter) to depths varying between 2.5 and 4 m, below which the ice content decreases and the salinity increases (values measured up to 42 gr/L between 4.5 and 6 m deep). Chunks of organic matter buried below the actual active layer base indicate past cryoturbations under a somewhat warmer climate, most probably associated with intense frost boil action, as widely observed today. The stony till has developed large quantities of segregation ice which can be seen in larger concentrations and as thicker lenses under boulders and in matrix rich (≥ 50% sand and silt) parts of the glacial sediment. As digging for a sewage pond was undertaken in winter 2008 by blasting, the clast-influenced cryostructure of the till could be observed in cuts and in large chunks of permafrost. Volumetric ice contents between 30 and 70% were measured in the till. In addition, low lying areas where till thickness exceeds ca 5 m contain polygons with ice wedges up to 2 m wide. Colluviums on slopes laid by sheet flow have been accumulating on two sectors of the study area, the source material being eroded clay at higher elevations; these slope sediments contain alternating layers of buried organics (C-14 date of 2300 BP at base of the sequence), silt and lenses of aggradational ice. Although the surface geophysical methods (electrical resistivity,GPR) were essential for mapping ice rich permafrost, the detailed appraisal of ground ice conditions was made truly possible by drilling and extracting intact cores. The use of the Cat-scan method proved very efficient for the precise and rapid measurement of ground ice contents and for imaging cryostructures on a large number of samples, thus providing exact information on permafrost composition and for interpreting permafrost history. The Salluit study also involves climate monitoring, thermal analysis and modeling, and intense community consultations.

Megajoule Dense Plasma Focus Solid Target Experiments

NASA Astrophysics Data System (ADS)

Podpaly, Y. A.; Falabella, S.; Link, A.; Povilus, A.; Higginson, D. P.; Shaw, B. H.; Cooper, C. M.; Chapman, S.; Bennett, N.; Sipe, N.; Olson, R.; Schmidt, A. E.

2016-10-01

Dense plasma focus (DPF) devices are plasma sources that can produce significant neutron yields from beam into gas interactions. Yield increases, up to approximately a factor of five, have been observed previously on DPFs using solid targets, such as CD2 and D2O ice. In this work, we report on deuterium solid-target experiments at the Gemini DPF. A rotatable target holder and baffle arrangement were installed in the Gemini device which allowed four targets to be deployed sequentially without breaking vacuum. Solid targets of titanium deuteride were installed and systematically studied at a variety of fill pressures, bias voltages, and target positions. Target holder design, experimental results, and comparison to simulations will be presented. Prepared by LLNL under Contract DE-AC52-07NA27344.

Release of liquid water from the Space Shuttle

NASA Technical Reports Server (NTRS)

Pike, C. P.; Knecht, D. J.; Viereck, R. A.; Murad, E.; Kofsky, I. L.; Bagian, J. P.; Buchli, J. F.

1990-01-01

Groundbased and onboard video images of a sunlit Shuttle Orbiter water dump are interpreted as showing that the continuous 1-mm-diameter liquid stream quickly breaks up in near-vacuum to form ice/snow particles of two characteristic sizes. Discrete large droplets are most evident in the close-in photographs, and unresolved submicron 'fog' from recondensation of overexpanded evaporated water appears to dominate the ground-telescope photographs of the 2.5 km long optically detectable trail. The mean diameter of the smaller particles was estimated from the spatial distribution of visible radiance using a model of their energy balance, (small) surface roughening as they sublime, and Mie scattering of pre-dawn sunlight. The results are consistent with those from recent space-tank simulations.

Detection of an oxygen atmosphere on Jupiter's moon Europa.

PubMed

Hall, D T; Strobel, D F; Feldman, P D; McGrath, M A; Weaver, H A

1995-02-23

Europa, the second large satellite out from Jupiter, is roughly the size of Earth's Moon, but unlike the Moon, it has water ice on its surface. There have been suggestions that an oxygen atmosphere should accumulate around such a body, through reactions which break up the water molecules and form molecular hydrogen and oxygen. The lighter H2 molecules would escape from Europa relatively easily, leaving behind an atmosphere rich in oxygen. Here we report the detection of atomic oxygen emission from Europa, which we interpret as being produced by the simultaneous dissociation and excitation of atmospheric O2 by electrons from Jupiter's magnetosphere. Europa's molecular oxygen atmosphere is very tenuous, with a surface pressure about 10(-11) that of the Earth's atmosphere at sea level.

The Relationship Between Arctic Sea Ice Albedo and the Geophysical Parameters of the Ice Cover

NASA Astrophysics Data System (ADS)

Riihelä, A.

2015-12-01

The Arctic sea ice cover is thinning and retreating. Remote sensing observations have also shown that the mean albedo of the remaining ice cover is decreasing on decadal time scales, albeit with significant annual variability (Riihelä et al., 2013, Pistone et al., 2014). Attribution of the albedo decrease between its different drivers, such as decreasing ice concentration and enhanced surface melt of the ice, remains an important research question for the forecasting of future conditions of the ice cover. A necessary step towards this goal is understanding the relationships between Arctic sea ice albedo and the geophysical parameters of the ice cover. Particularly the question of the relationship between sea ice albedo and ice age is both interesting and not widely studied. The recent changes in the Arctic sea ice zone have led to a substantial decrease of its multi-year sea ice, as old ice melts and is replaced by first-year ice during the next freezing season. It is generally known that younger sea ice tends to have a lower albedo than older ice because of several reasons, such as wetter snow cover and enhanced melt ponding. However, the quantitative correlation between sea ice age and sea ice albedo has not been extensively studied to date, excepting in-situ measurement based studies which are, by necessity, focused on a limited area of the Arctic Ocean (Perovich and Polashenski, 2012).In this study, I analyze the dependencies of Arctic sea ice albedo relative to the geophysical parameters of the ice field. I use remote sensing datasets such as the CM SAF CLARA-A1 (Karlsson et al., 2013) and the NASA MeaSUREs (Anderson et al., 2014) as data sources for the analysis. The studied period is 1982-2009. The datasets are spatiotemporally collocated and analysed. The changes in sea ice albedo as a function of sea ice age are presented for the whole Arctic Ocean and for potentially interesting marginal sea cases. This allows us to see if the the albedo of the older sea ice in the central parts of the Arctic Ocean is resistant to the decreasing overall trend.A similar analysis is also extended to ice concentration, melt season length and other appropriate parameters describing the surface conditions. The results of the analyses are summed up to provide an assessment of the relative impact strengths of the ice field parameters on the albedo.

Post-Industrial Revolution changes in large-scale atmospheric pollution of the northern hemisphere by heavy metals as documented in central Greenland snow and ice

NASA Astrophysics Data System (ADS)

Candelone, Jean-Pierre; Hong, Sungmin; Pellone, Christian; Boutron, Claude F.

1995-08-01

Pb, Zn, Cd and Cu have been measured using ultraclean procedures in various sections of a 70.3-m snow/ice core covering the past 220 years (including the Industrial Revolution) drilled at Summit, central Greenland. These time series are the first reliable ones ever published for Zn, Cd, and Cu; for Pb they are the first verification of the pioneering data published more than two decades ago by C. Patterson and his coworkers [Murozumi et al., 1969]. For all four heavy metals, concentrations are found to have markedly increased up until the 1960s and 1970s before decreasing significantly during the following few decades. The timing and the amplitude of the observed changes differ significantly however from one metal to another. Comparison with concentration values obtained by analyzing ancient Holocene ice dated 7760 years B.P., that is, before humans started to impact on the atmosphere, show that no detectable increase occurred for Zn, Cd, and Cu before the Industrial Revolution. On the other hand, Pb concentrations were already one order of magnitude above natural values in late 18th century ice. Cumulative deposition of heavy metals to the whole Greenland ice cap since the Industrial Revolution ranges from 3200 t for Pb to 60 t for Cd.

Evolution of ice sheets in the early Quaternary of the central North Sea: 2.58 Ma to 0.78 Ma

NASA Astrophysics Data System (ADS)

Lamb, R.; Huuse, M.; Stewart, M.; Brocklehurst, S. H.

2016-12-01

Integration of chronostratigraphic proxies with 3D seismic and well-log data has allowed for a basin-wide re-interpretation of the onset of glaciation in the central North Sea during the Quaternary. Mapping of seismic geomorphology, calculations of water depth and sediment accumulation rates, and other basin analysis techniques unravel the evolution of the North Sea basin during the early Pleistocene, a period of dramatic global cooling and rapid 41 kyr glacial-interglacial cycles, identifying a system which is increasingly dominated by large, continental-scale ice sheets. Prior to this study continental-scale ice sheets were generally not considered able to grow in a 41 kyr cycle and the earliest date for such an ice sheet in the North Sea was identified at the onset of tunnel valley formation in the Elsterian (0.48 Ma; MIS 12) which forms a large regional-scale glacial unconformity. At the onset of the Pleistocene at 2.58 Ma the North Sea basin was an elongate `mega-fjord' with water depths of up to 350 m, infilling rapidly as the European river systems deposited a large clinoform complex in the southern end of the basin. This period corresponds to the preservation of large scale ice-berg scouring on clinoform topsets, suggesting the presence of marine-terminating ice sheets with repeated calving events. As the Pleistocene progressed and global climate became increasingly colder the North Sea became smaller and shallower due to the continual infill of the basin. At 1.72 Ma the basin reached a critical point between the cold climate and the shallowing of the basin and the first evidence for grounded glaciation in the form of mega-scale glacial lineations is seen at this level. Between 1.72 and 0.48 Ma there is evidence for ice-streaming in the form of multiple MSGL flow sets re-occupying the central North Sea, as well as a large glaciotectonic complex. The glacial geomorphological evidence presented pushes back the date of grounded glaciation in the central North Sea by over one million years relative to the existing models. This raises important questions about the completeness of glaciation histories of Europe and other high and mid latitude land areas that can only be addressed by in depth scrutiny of their adjacent offshore sedimentary records.

Different modes of continental break-up triggered by a sole mantle plume: a 2D and 3D numerical study

NASA Astrophysics Data System (ADS)

Beniest, Anouk; Koptev, Alexander; Leroy, Sylvie; Burov, Evgueni

2017-04-01

We used 2D and 3D numerical models to investigate the impact of a single mantle plume on continental rifting and breakup processes. We varied the thermo-rheological structure of the continental lithosphere, its geometry and the initial plume position. Based on the results of our 2D experiments, three continental break-up modes can be distinguished: A) 'central' continental break-up, the break-up center is located directly above the original mantle anomaly position, B) 'shifted' break-up, the break-up center is 50 to 200 km displaced from the initial plume location and C) 'distant' break-up, due to convection and/or slab-subduction/delamination, the break-up center is considerably shifted (300 to 800 km) from the primary plume position. Our 3D model, with a laterally homogeneous initial setup also results in continental break-up with the axis of continental break-up hundreds of kilometers shifted from the original plume location. The model results show that the classical, 'central' view of mantle plume induced continental break-up is not the only mode of break-up. When considering a diversity of break-up styles, it is possible to explain a variety of observed geophysical and geological features. For example, the mantle material glued to the base of the lithosphere at shallower depths corresponds geometrically and location-wise to high-velocity/high-density bodies observed on seismic data below the thinned continental lithosphere and the transition zone of the South Atlantic domain. During migration, products of partial melting of the mantle material can move vertically to (shallow) lower crustal levels. They might resemble high density bodies observed at lower crustal levels inside continental crust with similar geometries observed with gravity modelling. Also, topographic variation form in the very early stages of rifting on the first impingement of upwelled plume material. These variations remain visible, as the final position of the spreading center is shifted from the point of impingement and can be interpreted as aborted rifts, observed along passive margins. Our modelling demonstrates that both simple and perfectly symmetric preliminary settings as well as complex initial setups can result in a variety of break-up systems.

Subsurface North Atlantic warming as a trigger of rapid cooling events: evidence from the early Pleistocene (MIS 31-19)

NASA Astrophysics Data System (ADS)

Hernández-Almeida, I.; Sierro, F.-J.; Cacho, I.; Flores, J.-A.

2015-04-01

Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt ice-rafted detritus (IRD) events during cold periods of the early Pleistocene. We used paired Mg / Ca and δ18O measurements of Neogloboquadrina pachyderma (sinistral - sin.), deep-dwelling planktonic foraminifera, to estimate the subsurface temperatures and seawater δ18O from a sediment core from Gardar Drift, in the subpolar North Atlantic. Carbon isotopes of benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and seawater δ18O suggest increased subsurface temperatures and salinities during ice-rafting, likely due to northward subsurface transport of subtropical waters during periods of weaker Atlantic Meridional Overturning Circulation (AMOC). Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of IRD. Subsurface accumulation of warm waters would have resulted in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. The release of heat stored at the subsurface to the atmosphere would have helped to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during Marine Isotope Stage (MIS) 3.

Preservation of ancient ice at Pavonis and Arsia Mons: Tropical mountain glacier deposits on Mars

NASA Astrophysics Data System (ADS)

Head, James W.; Weiss, David K.

2014-11-01

Large tropical mountain glacier (TMG) deposits on the northwest flanks of the Tharsis Montes and Olympus Mons volcanoes are interpreted to be the record of ancient climates characteristic of Mars several hundred million years ago when planetary spin-axis obliquity was ~45°. During this era, polar volatiles (predominantly H2O) were mobilized and transferred equatorward, undergoing adiabatic cooling on the Tharsis volcano flanks, and precipitating snow and ice to form cold-based tropical mountain glaciers up to several kilometers in thickness. Subsequent climate change resulted in retreat, sublimation and collapse of the tropical mountain glaciers, leaving the three typical facies observed today: (1) concentric ridges, the ridged facies, interpreted as drop moraines; (2) knobby facies, interpreted as debris-dominated sublimation residue; and (3) the smooth facies, interpreted as remnant alpine glacial deposits. Ring-mold craters (RMCs) are distinctive features formed by impacts into debris-covered ice. We describe a set of relatively fresh ring-mold craters superposed on the Arsia and Pavonis Mons TMG deposits; we interpret these to indicate that the impact events penetrated a veneer of sublimation lag and excavated buried remnant glacial ice, despite the lack of detection of buried ice by orbital radar instruments. The diameter distribution of the RMCs suggest that the remnant ice lies at a depth of at least 16 m. The TMG deposit ages suggest that these ice deposits date from a period in the range of 125-220 million years before the present; the remnant ice may thus preserve records of the ancient atmospheric gas content and microbiota, as is common in terrestrial glacial ice. Preservation of this ice and the lack of any associated fluvial features suggest that the post-glacial climate has been cold, and related surface temperatures have not been sufficient to bring the buried deposits to the melting point of water.

Pyroelectricity of water ice.

PubMed

Wang, Hanfu; Bell, Richard C; Iedema, Martin J; Schenter, Gregory K; Wu, Kai; Cowin, James P

2008-05-22

Water ice usually is thought to have zero pyroelectricity by symmetry. However, biasing it with ions breaks the symmetry because of the induced partial dipole alignment. This unmasks a large pyroelectricity. Ions were soft-landed upon 1 mum films of water ice at temperatures greater than 160 K. When cooled below 140-150 K, the dipole alignment locks in. Work function measurements of these films then show high and reversible pyroelectric activity from 30 to 150 K. For an initial approximately 10 V induced by the deposited ions at 160 K, the observed bias below 150 K varies approximately as 10 Vx(T/150 K)2. This implies that water has pyroelectric coefficients as large as that of many commercial pyroelectrics, such as lead zirconate titanate (PZT). The pyroelectricity of water ice, not previously reported, is in reasonable agreement with that predicted using harmonic analysis of a model system of SPC ice. The pyroelectricity is observed in crystalline and compact amorphous ice, deuterated or not. This implies that for water ice between 0 and 150 K (such as astrophysical ices), temperature changes can induce strong electric fields (approximately 10 MV/m) that can influence their chemistry, ion trajectories, or binding.

Pack ice along the Kamchatka Peninsula, Russia as seen from STS-60

NASA Image and Video Library

1994-02-09

STS060-73-038 (3-11 Feb 1994) --- Pack ice is documented in this photograph along the coast of the Kamchatka Peninsula of Russia in Zaliv Ozernoj. Newly formed ice continually breaks away from the land and takes the form imposed by coastal currents. Detailed photographs of the ice provide information to scientists in both Russia and the united States about the location and fluctuation of ice edges, and how this new sea ice interacts with ocean and littoral currents. This information results in better ice warnings to shipping traffic and provides data points for long-range climate change research for both the Mission-To-Planet Earth and the Russian Priroda ("Nature") monitoring and assessment programs that are respectively coordinated by NASA and the Russian Academy of Sciences. This photography of ice development in the North Pacific, North Atlantic, the Southern Ocean, the Baltic and North Seas, and the Great Lakes is of great interest to the international scientific community. NASA scientists feel high-resolution analog and digital photography from the Space Shuttle and future craft can be a particularly important component in satisfying their data needs on both an operational and a long-term research basis.

HiRISE observations of gas sublimation-driven activity in Mars' southern polar regions: III. Models of processes involving translucent ice

USGS Publications Warehouse

Portyankina, G.; Markiewicz, W.J.; Thomas, N.; Hansen, C.J.; Milazzo, M.

2010-01-01

Enigmatic surface features, known as 'spiders', found at high southern martian latitudes, are probably caused by sublimation-driven erosion under the seasonal carbon dioxide ice cap. The Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) has imaged this terrain in unprecedented details throughout southern spring. It has been postulated [Kieffer, H.H., Titus, T.N., Mullins, K.F., Christensen, P.R., 2000. J. Geophys. Res. 105, 9653-9700] that translucent CO2 slab ice traps gas sublimating at the ice surface boundary. Wherever the pressure is released the escaping gas jet entrains loose surface material and carries it to the top of the ice where it is carried downslope and/or downwind and deposited in a fan shape. Here we model two stages of this scenario: first, the cleaning of CO2 slab ice from dust, and then, the breaking of the slab ice plate under the pressure built below it by subliming ice. Our modeling results and analysis of HiRISE images support the gas jet hypothesis and show that outbursts happen very early in spring. ?? 2009 Elsevier Inc. All rights reserved.

Break-the-ice Demos.

ERIC Educational Resources Information Center

Smith, Jack L.

1989-01-01

Discusses the advantages of opening class sessions with demonstrations. Describes 11 demonstrations, including cloud formation, lather expansion, singing glassware, a flickering filament, balancing a fork and spoon, spinning an egg, television distortion, a roll race, a vortex generator, a suspended egg, and flight magic. (YP)

Atmospheric Profiles, Clouds, and the Evolution of Sea Ice Cover in the Beaufort and Chukchi Seas Atmospheric Observations and Modeling as Part of the Seasonal Ice Zone Reconnaissance Surveys

DTIC Science & Technology

2013-09-30

Cover in the Beaufort and Chukchi Seas Atmospheric Observations and Modeling as Part of the Seasonal Ice Zone Reconnaissance Surveys Axel...how changes in sea ice and sea surface conditions in the SIZ affect changes in cloud properties and cover . • Determine the role additional atmospheric...REPORT TYPE 3. DATES COVERED 00-00-2013 to 00-00-2013 4. TITLE AND SUBTITLE Atmospheric Profiles, Clouds, and the Evolution of Sea Ice Cover in the

Fate of the key Arctic copepod Calanus glacialis in a changing environment

NASA Astrophysics Data System (ADS)

Daase, M.; Søreide, J.; Freese, D.; Boissonnot, L.; Hatlebakk, M. K.; Graeve, M.; Niehoff, B.

2016-02-01

High latitude marine ecosystems experience strong seasonality in incoming light and thus primary production and food availability. Herbivorous calanoid copepods of the genus Calanus may comprise up to 90% of the mesozooplankton biomass in Arctic seas. They are able to build up large lipid deposits during the short, but productive summer and to survive food shortage in winter by entering a dormant state, referred to as diapause. The ongoing reduction in sea ice thickness and extent will significantly change the underwater light climate and thus the timing, quantity and quality of the primary producers in the Arctic with possible consequences for the grazers. Up to date we have very limited knowledge on the overwintering ecology and physiology of Calanus spp., and their ability to respond to external cues like light and food while in diapause. In the research project "Climate effects on planktonic food quality and trophic transfer in Arctic marginal ice zones (CLEOPATRA II)" we combined extensive field and experimental work to investigate the winter ecology and physiology of Calanus glacialis, endemic to the Arctic. This relatively large and lipid-rich copepod prefer seasonal ice covered shelf seas and thus have evolved somewhat different physiological adaptation and behavior than its sibling species in the deeper oceanic realms, C. finmarchicus in the North Atlantic and C. hyperboreus in the Arctic Ocean. Key project results will be presented which all add up to the conclusion that the oldest overwintering stages of C. glacialis do not enter a true diapause in winter, and thus this species is able to respond to rapid changes in its surrounding physical and biological environment.

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-pulse radar measurements of ice thickness. The radar data was relayed by a NOAA satellite to a ground station where NOAA analyzed it and created picture maps, such as the one shown at lower left, showing where icebreakers can cut paths easily or where shipping can move through thin ice without the aid of icebreakers. The ice charts were then relayed directly to the wheelhouses of ships operating on the Lakes. Following up the success of the Great Lakes program, the icewarn team applied its system in another demonstration, this one a similarly successful application designed to aid Arctic coast shipping along the Alaskan North Slope. Further improvement of the ice-monitoring system is planned. Although aircraft-mounted radar is effective, satellites could provide more frequent data. After the launch this year of Seasat, an ocean-monitoring satellite, NASA will conduct tests to determine the ice-mapping capability and accuracy of satellite radar images.

Marine evidence of a deconvolving Antarctic Ice Sheet during post-LGM retreat of the Ross Sea sector

NASA Astrophysics Data System (ADS)

Prothro, L. O.; Yokoyama, Y.; Simkins, L. M.; Anderson, J. B.; Majewski, W.; Yamane, M.; Ohkouchi, N.

2017-12-01

Predictive models of ice sheet and sea level change are dependent on observational data of ice-sheet behavior for model testing and tuning. The geologic record contains a wealth of information about ice-sheet dynamics, with fewer logistical, spatial, and temporal limitations than are involved in data acquisition along contemporary ice margins. However, past ice-sheet behavior is still largely uncertain or contested due to issues with obtaining meaningful radiocarbon dates. We minimize bias from glacially-reworked carbon and limitations from unknown geomorphic context and uncertainty in sediment facies identification by using careful sedimentary analyses within a geomorphic framework, as well as selection of appropriate dating methods. Our study area, the Ross Sea sector of Antarctica, is the primary drainage outlet for 25% of the continent's grounded ice. During the Last Glacial Maximum, the low-profile, marine-based West Antarctic Ice Sheet (WAIS) and the steeper profile, largely land-based East Antarctic Ice Sheet (EAIS) converged in the Ross Sea to flow out to or near the continental shelf edge. Geomorphic and sedimentary data reveal that during their subsequent retreat to form the Ross Sea Embayment, the two ice sheets behaved differently, with the WAIS rapidly retreating tens of kilometers followed by extended pauses, while the EAIS retreated steadily, with shorter (decadal- to century-long) pauses. This behavior leads us to believe that the two ice sheets may have contributed diachronously to sea level. By acquiring accurate timing of grounding line retreat, we are able to calculate volumes of ice lost throughout deglaciation, as well as associated sea level contributions. In addition, we attempt to rectify the contradicting marine and terrestrial interpretations of retreat patterns from the Ross Sea continental shelf.

Late glacial and Holocene history of the Greenland Ice Sheet margin, Nunatarssuaq, Northwestern Greenland

NASA Astrophysics Data System (ADS)

Farnsworth, L. B.; Kelly, M. A.; Axford, Y.; Bromley, G. R.; Osterberg, E. C.; Howley, J. A.; Zimmerman, S. R. H.; Jackson, M. S.; Lasher, G. E.; McFarlin, J. M.

2015-12-01

Defining the late glacial and Holocene fluctuations of the Greenland Ice Sheet (GrIS) margin, particularly during periods that were as warm or warmer than present, provides a longer-term perspective on present ice margin fluctuations and informs how the GrIS may respond to future climate conditions. We focus on mapping and dating past GrIS extents in the Nunatarssuaq region of northwestern Greenland. During the summer of 2014, we conducted geomorphic mapping and collected rock samples for 10Be surface exposure dating as well as subfossil plant samples for 14C dating. We also obtained sediment cores from an ice-proximal lake. Preliminary 10Be ages of boulders deposited during deglaciation of the GrIS subsequent to the Last Glacial Maximum range from ~30-15 ka. The apparently older ages of some samples indicate the presence of 10Be inherited from prior periods of exposure. These ages suggest deglaciation occurred by ~15 ka however further data are needed to test this hypothesis. Subfossil plants exposed at the GrIS margin on shear planes date to ~ 4.6-4.8 cal. ka BP and indicate less extensive ice during middle Holocene time. Additional radiocarbon ages from in situ subfossil plants on a nunatak date to ~3.1 cal. ka BP. Geomorphic mapping of glacial landforms near Nordsø, a large proglacial lake, including grounding lines, moraines, paleo-shorelines, and deltas, indicate the existence of a higher lake level that resulted from a more extensive GrIS margin likely during Holocene time. A fresh drift limit, characterized by unweathered, lichen-free clasts approximately 30-50 m distal to the modern GrIS margin, is estimated to be late Holocene in age. 10Be dating of samples from these geomorphic features is in progress. Radiocarbon ages of subfossil plants exposed by recent retreat of the GrIS margin suggest that the GrIS was at or behind its present location at AD ~1650-1800 and ~1816-1889. Results thus far indicate that the GrIS margin in northwestern Greenland responded sensitively to Holocene climate changes. Ongoing research will improve the chronological constraints on these fluctuations.

Low-latitude ice cores and freshwater availability

NASA Astrophysics Data System (ADS)

Kehrwald, Natalie Marie

2009-12-01

Recent retreat of Tibetan Plateau glaciers affects at least half a billion people. Himalayan glaciers seasonally release meltwater into tributaries of the Indus, Ganges, and Brahmaputra Rivers and supply freshwater necessary to support agricultural and economic practices. Tibetan Plateau glaciers are retreating more rapidly than mountain glaciers elsewhere in the world, and this retreat is accelerating. The Naimona'nyi (30°27'N; 81°91'E, 6050 m a.s.l), Guliya (35°17'N; 81°29'E, 6710 m a.s.l.) and Dasuopu (28°23'N; 85°43'E, 7200 m a.s.l.) ice cores place this recent retreat into a longer time perspective through quantifying climate parameters such as past temperature, aridity, and atmospheric chemistry. Naimona'nyi has not accumulated mass since at least 1950, as evidenced by the virtual lack of radiogenic isotopes (36Cl, 3 H, and beta radioactivity) present in the ice core. These isotopes were produced by U.S. and Soviet atmospheric thermonuclear bomb tests conducted in the 1950s and 1960s and provide independent dating horizons for the ice cores. Lead-210 dates imply that the uppermost preserved glacial ice on Naimona'nyi formed during the 1940s. While this is the highest documented glacial thinning in the world other glaciers at elevations similar to that of Naimona'nyi, such as Kilimanjaro (3°4'S; 37°21'E, 5893 m a.s.l.), are also losing mass at their summits. The global scope of high-elevation glacial thinning suggests that ablation on the Earth's highest ice fields may be more prevalent as global mean temperatures continue to increase. Glacial thinning has not been taken into account in future projections of regional freshwater availability, and the net mass loss indicates that Himalayan glaciers currently store less freshwater than assumed in models. The acceleration of Tibetan Plateau glacial retreat has been hypothesized to be due in part to deposition of black carbon (BC) from biomass burning on to ice fields, thereby lowering the reflectivity of the glacier surface and melting the upper ice. The application of a novel technique of measuring and radiocarbon-dating ultra-small samples (< 100mug) of the BC and total organic carbon (TOC) fractions of Naimona'nyi demonstrates a decrease (˜12 to 14 ka versus ˜7 ka) in the composite age of BC in the upper 40 m and lowest 20 m of the 137 m ice core, suggesting the incorporation of radiocarbon-dead BC. Precambrian black shale in the Lesser Himalaya provide a natural source material which may be operationally defined as black carbon and which may incorporate radiocarbon-dead sediments into the bulk 14C measurements, yet as the mean 14C age is ˜10 ka, modern BC from biomass burning must also be incorporated into the ice core record. While the uppermost sample (5 m) contains 38% BC, 210 Pb dates show that this depth corresponds to an age before 1850 AD, or before the regional Industrial Revolution. As BC is a hydrophobic substance, the BC is unlikely to have migrated through the firn and glacial ice. Therefore, the high-elevation thinning on Naimona'nyi appears to be a response to increased temperatures rather than primarily driven by changes in surface albedo. This technique was applied to the annually-dated ice core from the accumulating summit of the Quleccaya ice cap, Peru (13'56'S; 70°50'W; 5670 m a.s.l.). A marked increase in modern BC and TOC was measured since 1880 AD. No increase in radiocarbon-dead (> 60,000 ka) BC or TOC was noted, suggesting that the source of the carbon was from biomass burning, with a possible contribution of Amazon slash and burn clearing, rather than the input of fossil fuel combustion. The age of the BC and TOC is thousands of years older than the age of the surrounding ice, and should not be used to date the ice core. Although Naimona'nyi provides challenges for constructing an ice core chronology due to its lack of independent horizons such as volcanic activity, methane gas measurements, 14C dates, 3H, 36Cl, or beta radioactivity, the oxygen isotopic record can be correlated with the neighboring Dasuopu and Guliya ice cores. Naimona'nyi contains a pronounced positive ˜10‰ shift in delta18O in the basal 37 m of the core which mimics similar isotopic shifts in regional speleothems, lacustrian sediments, and planktonic foraminifera proxy records. This distinct shift is attributed to amplified monsoon intensity caused by increased summer insolation at 30°N. This correlation between regional proxy records results in a basal age of ˜8.6 ka for Naimona'nyi, suggesting that the ice field grew as a response to tropical rather than polar climate forcings.

Mass Balance of Multiyear Sea Ice in the Southern Beaufort Sea

DTIC Science & Technology

2013-09-30

model of MY ice circulation, which is shown in Figure 1. In this model , we consider the Beaufort Sea to consist of four zones defined by mean drift...Arctic Regional Climate Model Simulation Project 3 International Arctic Buoy Program 4 Sea ice Experiment - Dynamic Nature of the Arctic 5Cold...2 Table 2: Datasets compiled to date Geophysical data type Source Time period acquired Buoy tracks IABP 12 hrly position data 1978-2012 Ice

Planetary Analogs in Antarctica: Icy Satellites

NASA Technical Reports Server (NTRS)

Malin, M. C.

1985-01-01

As part of a study to provide semi-quantitative techniques to date past Antarctic glaciations, sponsored by the Antarctic Research Program, field observations pertinent to other planets were also acquired. The extremely diverse surface conditions, marked by extreme cold and large amounts of ice, provide potential terrain and process analogs to the icy satellites of Jupiter and Saturn. Thin ice tectonic features and explosion craters (on sea ice) and deformation features on thicker ice (glaciers) are specifically addressed.

Visible and Thermal Imaging of Sea Ice and Open Water from Coast Guard Arctic Domain Awareness Flights

DTIC Science & Technology

2012-09-30

to better predict the seasonal evolution of the ice cover . APPROACH The Coast Guard Arctic Domain Awareness (ADA) flights based out of Kodiak...does not display a currently valid OMB control number. 1. REPORT DATE 2012 2. REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE...satellite remote sensing data ( MODIS and SSMI) for flight planning before flights and during and after flights for inclusion in the SIZRS-DC database

Mass Balance of the Northern Antarctic Peninsula and its Ongoing Response to Ice Shelf Loss

NASA Astrophysics Data System (ADS)

Scambos, T. A.; Berthier, E.; Haran, T. M.; Shuman, C. A.; Cook, A. J.; Bohlander, J. A.

2012-12-01

An assessment of the most rapidly changing areas of the Antarctic Peninsula (north of 66°S) shows that ice mass loss for the region is dominated by areas affected by eastern-Peninsula ice shelf losses in the past 20 years. Little if any of the mass loss is compensated by increased snowfall in the northwestern or far northern areas. We combined satellite stereo-image DEM differencing and ICESat-derived along-track elevation changes to measure ice mass loss for the Antarctic Peninsula north of 66°S between 2001-2010, focusing on the ICESat-1 period of operation (2003-2009). This mapping includes all ice drainages affected by recent ice shelf loss in the northeastern Peninsula (Prince Gustav, Larsen Inlet, Larsen A, and Larsen B) as well as James Ross Island, Vega Island, Anvers Island, Brabant Island and the adjacent west-flowing glaciers. Polaris Glacier (feeding the Larsen Inlet, which collapsed in 1986) is an exception, and may have stabilized. Our method uses ASTER and SPOT-5 stereo-image DEMs to determine dh/dt for elevations below 800 m; at higher elevations ICESat along-track elevation differencing is used. To adjust along-track path offsets between its 2003-2009 campaigns, we use a recent DEM of the Peninsula to establish and correct for cross-track slope (Cook et al., 2012, doi:10.5194/essdd-5-365-2012; http://nsidc.org/data/nsidc-0516.html) . We reduce the effect of possible seasonal variations in elevation by using only integer-year repeats of the ICESat tracks for comparison. Mass losses are dominated by the major glaciers that had flowed into the Prince Gustav (Boydell, Sjorgren, Röhss), Larsen A (Edgeworth, Bombardier, Dinsmoor, Drygalski), and Larsen B (Hektoria, Jorum, and Crane) embayments. The pattern of mass loss emphasizes the significant and multi-decadal response to ice shelf loss. Areas with shelf losses occurring 30 to 100s of years ago seem to be relatively stable or losing mass only slowly (western glaciers, northernmost areas). The remnant of the Larsen B, Scar Inlet Ice Shelf, shows signs of imminent break-up, and its feeder glaciers (Flask and Leppard) are already increasing in speed as the ice shelf remnant decreases in area.

Characterization of icebergs and floating sea ice in the Yung Sund fjord in Greenland from satellite radar and optical images.

NASA Astrophysics Data System (ADS)

Guillaso, Stephane; Gay, Michel; Gervaise, Cedric

2017-04-01

At the Zackenberg site, sea ice starts to move between June and September resulting in icebergs flowing freely on the sea. Splitting into smaller parts, they reduce in size. Icebergs represent a risk for maritime transport and needs to be studied. In order to determine iceberg density per surface unit, size distribution, and movement of icebergs, we need to observe, detect, range and track them. The use of SAR images is particularly well adapted in regions where cloud cover is very present. We focused our study on the Yung Sund fjord in Greenland, where lots of icebergs and sea ice are generated during the summer. In the beginning of July, sea ice breaks up first, followed by icebergs created by the different glaciers based in the ocean. During our investigation, we noticed that the iceberg and sea ice were drifting very fast and thus, we needed to adapt our methodology. To achieve our goal, we collected all remote sensing data available in the region, principally Sentinel 1/2 and LandSAT 8 during one ice free season (from July 1st 2016 to September 30th, 2016). We developed an original approach in order to detect, characterize and track icebergs and sea ice independently from data. The iceberg detection was made using a watershed technique. The advantage of this technique is that it can be applied to both optical and radar images. For the latter, calibrated intensity is transformed into an image using a scaling function, in order to make ice brighter. Land data is masked using a topographic map. When data is segmented, a statistical test derived from the CFAR approach is performed to isolate an iceberg and floating sea ice from the ocean. Finally, a method, such SIFT or BRISK is used to identify and track the different segmented object. These approaches give a representation of the object and make the tracking easier and independent of the scale and rotation, which can occur because icebergs are dependent on ocean currents and wind. Finally, to fill in the gap between acquisition, mainly due to cloud cover or no image available, we use an ocean current and wind models to estimate the position of some icebergs. The used models are constrained using observation data.

78 FR 32700 - Hours of Service of Drivers: U.S. Department of Energy (DOE); Application for Exemption

Federal Register 2010, 2011, 2012, 2013, 2014

2013-05-31

...) an exemption from the minimum 30-minute rest break provision of the Agency's hours-of-service (HOS... minutes or more of ``attendance time'' to meet the HOS rest break requirements providing they do not perform any other work during the break. DATES: This exemption is effective from July 1, 2013 through June...

Temperature under the Tongue: A paleotemperature record of the Drygalksi Ice Tongue with improved chronology of ice retreat

NASA Astrophysics Data System (ADS)

Subt, C.; Rosenheim, B. E.; Lee, J. I.; Yoo, K. C.; Browne, I. M.; Shevenell, A.

2017-12-01

The Ross Embayment is among the most well-studied regions in Antarctica. Despite the relative abundance of data, the style and forcing of deglaciation of the Ross Sea sector following the Last Glacial Maximum (LGM; 23-19 ka) is challenging due to the region's considerable size, complex geometry, and the difficulties in dating Antarctic glaciomarine sedimentary sequences. Ross Sea sediments indicate a dynamic glacial retreat in the western Ross Sea, whereas regional glacial systems may have retreated and advanced multiple times during the last deglaciation. Two marine sediment cores collected near the Drygalski Ice Tongue in the western Ross Sea during 2012 and 2015 Korea Polar Research Institute (KOPRI) expeditions reveal a sequence of alternating diatomaceous muds and oozes interbedded with diamict, which suggest dynamic post-LGM grounded ice retreat in the Ross Sea. Dynamic retreat is hypothesized to have been driven by rising sea levels and warmer ocean waters on the continental shelf, thus a record of upper ocean temperatures should reflect this. Here we present the first post-LGM upper ocean temperature record from the Ross Sea, developed using the TEX86 (tetraether index of lipids consisting of 86 carbons) paleothermometer. To overcome the difficulties of dating these sediments using traditional methods, we apply specialized Ramped PyrOx 14C dating for sediments with high proportions of relict carbon . This technique is particularly well-suited for the post-LGM retreat sedimentary sequences from Antarctic margins because it allows for separation of autochthonous and relict material for dating. By combining organic paleothermometry and state-of-the-art chronologic techniques, we gain a more thorough understanding of upper ocean temperatures in the Ross Sea during the last deglaciation, and their implications for ice retreat.

International Workshop on Antarctic Meteorites

NASA Technical Reports Server (NTRS)

Annexstad, J. O.; Schultz, L.; Waenke, H.

1986-01-01

Topics addressed include: meteorite concentration mechanisms; meteorites and the Antarctic ice sheet; iron meteorites; iodine overabundance in meteorites; entrainment, transport, and concentration of meteorites in polar ice sheets; weathering of stony meteorites; cosmic ray records; radiocarbon dating; element distribution and noble gas isotopic abundances in lunar meteorites; thermoanalytical characterization; trace elements; thermoluminescence; parent sources; and meteorite ablation and fusion spherules in Antarctic ice.

Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation

USGS Publications Warehouse

Jakobsson, Martin; Nilsson, Johan; Anderson, Leif G.; Backman, Jan; Bjork, Goran; Cronin, Thomas M.; Kirchner, Nina; Koshurnikov, Andrey; Mayer, Larry; Noormets, Riko; O'Regan, Matthew; Stranne, Christian; Ananiev, Roman; Macho, Natalia Barrientos; Cherniykh, Dennis; Coxall, Helen; Eriksson, Bjorn; Floden, Tom; Gemery, Laura; Gustafsson, Orjan; Jerram, Kevin; Johansson, Carina; Khortov, Alexey; Mohammad, Rezwan; Semiletov, Igor

2016-01-01

The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (~140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

The Milankovitch Signature of the air Content Along the EPICA DC Ice Record: a Tool Towards an Absolute Dating and Implication for ice Flow Modeling

NASA Astrophysics Data System (ADS)

Raynaud, D.; Duval, P.; Lemieux-Dudon, B.; Lipenkov, V.; Parrenin, F.

2006-12-01

Air content of polar ice, V, depends primarily on air pressure, temperature and pore volume at close-off prevailing at the site of ice formation. Here we present the recently measured V record of the EPICA DC (EDC) Antarctic ice core covering the last 650,000 years. The first 440,000 years remarkably displays the fundamental Milankovitch orbital frequencies. The 100 kyr period, corresponding to the eccentricity of the Earth's orbit and found in the V record, likely reflects essentially the pressure/elevation signature of V. But most of the variations observed in the V record cannot be explained neither by air pressure nor by temperature changes, and then should reflect properties influencing the porosity at close-off other than temperature. A wavelet analysis indicates a dominant period around 41 kyr, the period characteristic of the obliquity variations of the Earth's axis. We propose that the local insolation, via the solar radiation absorbed by the snow, leaves its imprint on the snow structure, then affects the snow-firn transition, and therefore is one of the controlling factors for the porosity at close-off. Such mechanism could account for the observed anti-correlation between local insolation and V. We estimate the variations of the absorbed solar flux in the near-surface snow layers on the basis of a simple albedo model (Lemieux-Dudon et al., this session). We compare the dating of the ice obtained using the local insolation signal deduced from the V record with a chronology based on ice flow modelling. We discuss the glaciological implications of the comparison between the two chronologies, as well as the potential of local insolation markers for approaching an absolute dating of ice core. The latest results covering the period 440-650 kyr BP will also be presented.

A Web-Based Toolkit to Provide Evidence-Based Resources About Crystal Methamphetamine for the Australian Community: Collaborative Development of Cracks in the Ice.

PubMed

Champion, Katrina Elizabeth; Chapman, Cath; Newton, Nicola Clare; Brierley, Mary-Ellen; Stapinski, Lexine; Kay-Lambkin, Frances; Nagle, Jack; Teesson, Maree

2018-03-20

The use of crystal methamphetamine (ice) and the associated harms for individuals, families, and communities across Australia has been the subject of growing concern in recent years. The provision of easily accessible, evidence-based, and up-to-date information and resources about crystal methamphetamine for the community is a critical component of an effective public health response. This paper aims to describe the codevelopment process of the Web-based Cracks in the Ice Community Toolkit, which was developed to improve access to evidence-based information and resources about crystal methamphetamine for the Australian community. Development of the Cracks in the Ice Community Toolkit was conducted in collaboration with community members across Australia and with experts working in the addiction field. The iterative process involved the following: (1) consultation with end users, including community members, crystal methamphetamine users, families and friends of someone using crystal methamphetamine, health professionals, and teachers (n=451) via a cross-sectional Web-based survey to understand information needs; (2) content and Web development; and (3) user testing of a beta version of the Web-based toolkit among end users (n=41) and experts (n=10) to evaluate the toolkit's acceptability, relevance, and appeal. Initial end user consultation indicated that the most commonly endorsed reasons for visiting a website about crystal methamphetamine were "to get information for myself" (185/451, 41.0%) and "to find out how to help a friend or a family member" (136/451, 30.2%). Community consultation also revealed the need for simple information about crystal methamphetamine, including what it is, its effects, and when and where to seek help or support. Feedback on a beta version of the toolkit was positive in terms of content, readability, layout, look, and feel. Commonly identified areas for improvement related to increasing the level of engagement and personal connection, improving the ease of navigation, and balancing a "low prevalence of use, yet high impact" message. A total of 9138 users visited the website in the 3 months immediately post launch, and over 25,000 hard-copy Cracks in the Ice booklets and flyers were distributed across Australia. Of these resources, 60.93% (15,525/25,480) were distributed to relevant organizations and mailing list subscribers, and 39.07% (9955/25,480) were ordered directly by individuals, services, and community groups via the Cracks in the Ice website. The codevelopment process resulted in an engaging Web-based resource for the Australian community to access up-to-date and evidence-based resources about crystal methamphetamine. The Cracks in the Ice Community Toolkit provides much-needed information and support for individuals, families, and communities. ©Katrina Elizabeth Champion, Cath Chapman, Nicola Clare Newton, Mary-Ellen Brierley, Lexine Stapinski, Frances Kay-Lambkin, Jack Nagle, Maree Teesson. Originally published in JMIR Mental Health (http://mental.jmir.org), 20.03.2018.

The interaction between sea ice and salinity-dominated ocean circulation: implications for halocline stability and rapid changes of sea-ice cover

NASA Astrophysics Data System (ADS)

Jensen, M. F.; Nilsson, J.; Nisancioglu, K. H.

2016-02-01

In this study, we develop a simple conceptual model to examine how interactions between sea ice and oceanic heat and freshwater transports affect the stability of an upper-ocean halocline in a semi-enclosed basin. The model represents a sea-ice covered and salinity stratified ocean, and consists of a sea-ice component and a two-layer ocean; a cold, fresh surface layer above a warmer, more saline layer. The sea-ice thickness depends on the atmospheric energy fluxes as well as the ocean heat flux. We introduce a thickness-dependent sea-ice export. Whether sea ice stabilizes or destabilizes against a freshwater perturbation is shown to depend on the representation of the vertical mixing. In a system where the vertical diffusivity is constant, the sea ice acts as a positive feedback on a freshwater perturbation. If the vertical diffusivity is derived from a constant mixing energy constraint, the sea ice acts as a negative feedback. However, both representations lead to a circulation that breaks down when the freshwater input at the surface is small. As a consequence, we get rapid changes in sea ice. In addition to low freshwater forcing, increasing deep-ocean temperatures promote instability and the disappearance of sea ice. Generally, the unstable state is reached before the vertical density difference disappears, and small changes in temperature and freshwater inputs can provoke abrupt changes in sea ice.

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.

Comprehensive Examination of Bottom Ash, Soil Dust, and Direct Emissions and Aging of Laboratory Biomass Burning as Potential Sources of Ice Nucleating Particles

NASA Astrophysics Data System (ADS)

Polen, M.; Jahl, L.; Jahn, L.; Somers, J.; Sullivan, R. C.

2017-12-01

Recent laboratory and field studies have found that biomass burning can produce ice nucleating particles (INP) with varying efficiencies depending on fuel and burn conditions. Few studies have examined the ice nucleating potential of bottom ash, which has the potential to be lofted during intense burning events. To date, no publications have examined the impact of atmospheric aging or lofted soil particles on INP emitted from biomass burning. This study investigated each of these aspects through laboratory biomass fuel combustion studies. We burned a number of grasses from different locations, and collected filter samples of fresh and photochemically aged biomass burning aerosol, as well as bottom ash collected after the burn. Some burns included soil that the grasses grew in to test for the importance of soil dust to INP emissions lofting during intense fires. The composition and mixing state of the aerosol was determined using a suite of online and offline single-particle techniques. Our findings suggest that bottom ash is a relatively weak INP, but all samples froze consistently at -20 °C < T < -25 °C. We also found that oxidation of the biomass burning aerosol typically enhances ice nucleating activity over fresh, unaged particles, increasing the ice active site surface density by up to a factor of 3 at T = -25 °C. Lastly, the presence of soil dust can greatly enhance INP concentrations for biomass burning events with an increase in the freezing temperature spectrum by > 3 °C. Detailed analysis of these samples aims to provide a clearer understanding of what components of biomass burning increase the ambient concentrations of ice nucleation active particles, and how their ice nucleation properties evolve during atmospheric aging.

Ice Cores Dating With a New Inverse Method Taking Account of the Flow Modeling Errors

NASA Astrophysics Data System (ADS)

Lemieux-Dudon, B.; Parrenin, F.; Blayo, E.

2007-12-01

Deep ice cores extracted from Antarctica or Greenland recorded a wide range of past climatic events. In order to contribute to the Quaternary climate system understanding, the calculation of an accurate depth-age relationship is a crucial point. Up to now ice chronologies for deep ice cores estimated with inverse approaches are based on quite simplified ice-flow models that fail to reproduce flow irregularities and consequently to respect all available set of age markers. We describe in this paper, a new inverse method that takes into account the model uncertainty in order to circumvent the restrictions linked to the use of simplified flow models. This method uses first guesses on two flow physical entities, the ice thinning function and the accumulation rate and then identifies correction functions on both flow entities. We highlight two major benefits brought by this new method: first of all the ability to respect large set of observations and as a consequence, the feasibility to estimate a synchronized common ice chronology for several cores at the same time. This inverse approach relies on a bayesian framework. To respect the positive constraint on the searched correction functions, we assume lognormal probability distribution on one hand for the background errors, but also for one particular set of the observation errors. We test this new inversion method on three cores simultaneously (the two EPICA cores : DC and DML and the Vostok core) and we assimilate more than 150 observations (e.g.: age markers, stratigraphic links,...). We analyze the sensitivity of the solution with respect to the background information, especially the prior error covariance matrix. The confidence intervals based on the posterior covariance matrix calculation, are estimated on the correction functions and for the first time on the overall output chronologies.

Improved age constraints for the retreat of the Irish Sea Ice Stream

NASA Astrophysics Data System (ADS)

Smedley, Rachel; Chiverrell, Richard; Duller, Geoff; Scourse, James; Small, David; Fabel, Derek; Burke, Matthew; Clarke, Chris; McCarroll, Danny; McCarron, Stephen; O'Cofaigh, Colm; Roberts, David

2016-04-01

BRITICE-CHRONO is a large (> 45 researchers) consortium project working to provide an extensive geochronological dataset constraining the rate of retreat of a number of ice streams of the British-Irish Ice Sheet following the Last Glacial Maximum. When complete, the large empirical dataset produced by BRITICE-CHRONO will be integrated into model simulations to better understand the behaviour of the British-Irish Ice Sheet in response to past climate change, and provide an analogue for contemporary ice sheets. A major feature of the British-Irish Ice Sheet was the dynamic Irish Sea Ice Stream, which drained a large proportion of the ice sheet and extended to the proposed southern limit of glaciation upon the Isles of Scilly (Scourse, 1991). This study will focus on a large suite of terrestrial samples that were collected along a transect of the Irish Sea basin, covering the line of ice retreat from the Isles of Scilly (50°N) in the south, to the Isle of Man (54°N) in the north; a distance of 500 km. Ages are determined for both the eastern and western margins of the Irish Sea using single-grain luminescence dating (39 samples) and terrestrial cosmogenic nuclide dating (10 samples). A Bayesian sequence model is then used in combination with the prior information determined for deglaciation to integrate the geochronological datasets, and assess retreat rates for the Irish Sea Ice Stream. Scourse, J.D., 1991. Late Pleistocene stratigraphy and palaeobotany of the Isles of Scilly. Philosophical Transactions of the Royal Society of London B334, 405 - 448.

Surface rupture and slip distribution of the Denali and Totschunda faults in the 3 November 2002 M 7.9 earthquake, Alaska

USGS Publications Warehouse

Haeussler, Peter J.; Schwartz, David P.; Dawson, Timothy E.; Stenner, Heidi D.; Lienkaemper, James J.; Sherrod, Brian; Cinti, Francesca R.; Montone, Paola; Craw, Patricia; Crone, Anthony J.; Personius, Stephen F.

2004-01-01

The 3 November 2002 Denali fault, Alaska, earthquake resulted in 341 km of surface rupture on the Susitna Glacier, Denali, and Totschunda faults. The rupture proceeded from west to east and began with a 48-km-long break on the previously unknown Susitna Glacier thrust fault. Slip on this thrust averaged about 4 m (Crone et al., 2004). Next came the principal surface break, along 226 km of the Denali fault, with average right-lateral offsets of 4.5–5.1 m and a maximum offset of 8.8 m near its eastern end. The Denali fault trace is commonly left stepping and north side up. About 99 km of the fault ruptured through glacier ice, where the trace orientation was commonly influenced by local ice fabric. Finally, slip transferred southeastward onto the Totschunda fault and continued for another 66 km where dextral offsets average 1.6–1.8 m. The transition from the Denali fault to the Totschunda fault occurs over a complex 25-km-long transfer zone of right-slip and normal fault traces. Three methods of calculating average surface slip all yield a moment magnitude of Mw 7.8, in very good agreement with the seismologically determined magnitude of M 7.9. A comparison of strong-motion inversions for moment release with our slip distribution shows they have a similar pattern. The locations of the two largest pulses of moment release correlate with the locations of increasing steps in the average values of observed slip. This suggests that slip-distribution data can be used to infer moment release along other active fault traces.

Under-estimated wave contribution to coastal sea-level rise

NASA Astrophysics Data System (ADS)

Melet, Angélique; Meyssignac, Benoit; Almar, Rafael; Le Cozannet, Gonéri

2018-03-01

Coastal communities are threatened by sea-level changes operating at various spatial scales; global to regional variations are associated with glacier and ice sheet loss and ocean thermal expansion, while smaller coastal-scale variations are also related to atmospheric surges, tides and waves. Here, using 23 years (1993-2015) of global coastal sea-level observations, we examine the contribution of these latter processes to long-term sea-level rise, which, to date, have been relatively less explored. It is found that wave contributions can strongly dampen or enhance the effects of thermal expansion and land ice loss on coastal water-level changes at interannual-to-multidecadal timescales. Along the US West Coast, for example, negative wave-induced trends dominate, leading to negative net water-level trends. Accurate estimates of past, present and future coastal sea-level rise therefore need to consider low-frequency contributions of wave set-up and swash.

Amphiphilic nanoparticles suppress droplet break-up in a concentrated emulsion flowing through a narrow constriction

PubMed Central

Gai, Ya; Kim, Minkyu; Pan, Ming; Tang, Sindy K. Y.

2017-01-01

This paper describes the break-up behavior of a concentrated emulsion comprising drops stabilized by amphiphilic silica nanoparticles flowing in a tapered microchannel. Such geometry is often used in serial droplet interrogation and sorting processes in droplet microfluidics applications. When exposed to high viscous stresses, drops can undergo break-up and compromise their physical integrity. As these drops are used as micro-reactors, such compromise leads to a loss in the accuracy of droplet-based assays. Here, we show droplet break-up is suppressed by replacing the fluoro-surfactant similar to the one commonly used in current droplet microfluidics applications with amphiphilic nanoparticles as droplet stabilizer. We identify parameters that influence the break-up of these drops and demonstrate that break-up probability increases with increasing capillary number and confinement, decreasing nanoparticle size, and is insensitive to viscosity ratio within the range tested. Practically, our results reveal two key advantages of nanoparticles with direct applications to droplet microfluidics. First, replacing surfactants with nanoparticles suppresses break-up and increases the throughput of the serial interrogation process to 3 times higher than that in surfactant system under similar flow conditions. Second, the insensitivity of break-up to droplet viscosity makes it possible to process samples having different composition and viscosities without having to change the channel and droplet geometry in order to maintain the same degree of break-up and corresponding assay accuracy. PMID:28652887

Past collapse and late Holocene reestablishment of the Petermann Ice Tongue, Northwest Greenland

NASA Astrophysics Data System (ADS)

Reilly, B. T.; Stoner, J. S.; Mix, A. C.; Jakobsson, M.; Jennings, A. E.; Walczak, M.; Dyke, L. M.

2017-12-01

Petermann Glacier, Northwest Greenland, has been a stable outlet glacier of the Greenland Ice Sheet on historical timescales. Yet, anomalous calving events in 2010 and 2012 and oceanographic studies over the last decade indicate that Petermann Glacier and its ice tongue are especially sensitive to ice-ocean interactions, leading many to speculate on its future stability. To place these observations in the context of a longer timeframe and better understand the sensitivity of Petermann Glacier to future climate change, a 2015 international and interdisciplinary expedition of the Icebreaker Oden collected a suite of sediment cores from Petermann Fjord, spanning the mid to late Holocene and forming a transect from beneath the modern ice tongue to the mouth of the fjord (25 - 80 km from the modern grounding line). We characterize the stratigraphy ( 5.5 - 6.5 m at piston core sites) using a combination of X-ray fluorescence (XRF) scanning geochemistry, computed tomography (CT) scanning, and particle-size specific magnetic measurements on these cores and nearby terrestrial samples. Age-depth modeling, based on radiocarbon dated benthic foraminifera, is in progress with reservoir age corrections assessed using paleomagnetic comparisons to regional and global records. We observe changes in the composition and spatial pattern of ice rafted debris (IRD) and sediment fabric that reveal a dynamic history. Following early Holocene deglaciation of the region, a paleo-ice tongue broke up and an extended period of seasonally open marine conditions ensued through the middle Holocene. This ice-tongue collapse was followed by a large increase in the relative abundance of Petermann sourced IRD of non-local granitic composition. This granitic IRD component steadily declined through the middle Holocene, reaching negligible contributions when the ice tongue was reestablished in the late Holocene. Regional paleoenvironmental studies suggest warmer oceanographic and atmospheric conditions around Northwest Greenland in the middle Holocene, offering an opportunity to study the sensitivity of one of Greenland's major outlet glaciers to environmental forcing.

Porphyry Cu indicator minerals in till as an exploration tool: Example from the giant pebble porphyry Cu-Au-Mo deposit, Alaska, USA

USGS Publications Warehouse

Kelley, Karen D.; Eppinger, Robert G.; Lang, J.; Smith, Steven M.; Fey, David L.

2011-01-01

Porphyry Cu indicator minerals are mineral species in clastic sediments that indicate the presence of mineralization and hydrothermal alteration associated with porphyry Cu and associated skarn deposits. Porphyry Cu indicator minerals recovered from shallow till samples near the giant Pebble Cu-Au-Mo porphyry deposit in SW Alaska, USA, include apatite, andradite garnet, Mn-epidote, visible gold, jarosite, pyrite, and cinnabar. Sulphide minerals other than pyrite are absent from till, most likely due to the oxidation of the till. The distribution of till samples with abundant apatite and cinnabar suggest sources other than the Pebble deposit. With three exceptions, all till samples up-ice of the Pebble deposit contain 40grains/10kg) are in close proximity to smaller porphyry and skarn occurrences in the region. The distribution of Mn-epidote closely mimics the distribution of garnet in the till samples and further supports the interpretation that these minerals most likely reflect skarns associated with the porphyry deposits. All but two till samples, including those up-ice from the deposit, contain some gold grains. However, tills immediately west and down-ice of Pebble contain more abundant gold grains, and the overall number of grains decreases in the down-ice direction. Furthermore, all samples in the immediate vicinity of Pebble contain more than 65% pristine and modified grains compared to mostly re-shaped grains in distal samples. The pristine gold in till reflects short transport distances and/or liberation of gold during in-situ weathering of transported chalcopyrite grains. Jarosite is also abundant (1-2 500 grains/10kg) in samples adjacent to and up to 7 km down-ice from the deposit. Most jarosite grains are rounded and preliminary Ar/Ar dates suggest the jarosite formed prior to glaciation and it implies that a supergene cap existed over Pebble West. Assuming this interpretation is accurate, it suggests a shallow level of erosion of the Pebble deposit by glacial processes. Overall the results of this study indicate that porphyry Cu indicator minerals in till samples may be useful in the exploration for porphyry deposits in SW Alaska.

Linking two thousand years of European historical records with environmental change recorded in a high Alpine ice core

NASA Astrophysics Data System (ADS)

Bohleber, Pascal; Spaulding, Nicole; Mayewski, Paul; Kurbatov, Andrei; Hoffmann, Helene; Erhardt, Tobias; Fischer, Hubertus; More, Alexander; Loveluck, Christopher; Luongo, Matthew; Kabala, Jakub; McCormick, Michael

2016-04-01

Its extraordinary network of historical and archaeological records makes Europe exceptionally promising for investigating environmental change and human response over the last two thousand years. Among natural proxy archives, ice core records offer a wide range of environmental reconstructions including natural and human source histories of the chemistry of the atmosphere. To link these robust environmental records with historical evidence of past civilizations remains a great challenge, however. In central Europe the unique target for a comparison for environmental change recorded in ice cores and human activity is the small firn saddle of Colle Gnifetti (4550 m above sea level on the Italian-Swiss border). Its exceptionally low net accumulation make Colle Gnifetti (CG) the only feasible site in the Alps for retrieving a long-term ice core record beyond the last century. However, at CG rapid annual layer thinning eventually limits conventional cm-resolution analysis to multi-annual signals and hampers dating by annual layer counting beyond a few hundred years. Thereby, a crucial gap is introduced to the sub-seasonal time scale of events typically recorded in written archives. In our ongoing project we pioneer correlating the CG environmental ice core archive with a unique compilation of European historical records provided through the Harvard Initiative for the Science of the Human Past and the Digital Atlas of Roman and Medieval Civilization. For this purpose, state-of-the-art glacio-chemical analysis was performed on a newly recovered CG ice core, including continuous flow analysis chemistry and stable isotopes. A crucial contribution comes from the application of LA-ICP-MS (laser ablation ion coupled plasma mass spectrometry) to meter long sections of frozen ice samples, developed and operated by the University of Maine's Climate Change Institute, offering glacio-chemical records up to 100 μm in resolution. The new methods significantly improves sampling resolution and allows detection of annual layers even in highly compressed old sections of CG ice cores: A breakthrough not only for extending the ice core dating over the last two millennia but also for bridging the gap in time scales to historical records. Here we present first results from our ongoing efforts in bringing together ice core time series with historical evidence, focusing on the time period from 1 to 1400 C.E. Based on a thorough consideration of the glaciological constraints at CG we explore various ice core proxy signals for their significance to correlate with events recorded in human writing, such as dust storms, volcanic events, climate-induced crop failures and starvation as well as metal production levels. Distinct dust layers are frequently found in CG ice cores, representative for meteorological conditions that transported sand from the Sahara to Europe. At the same time, Saharan dust events were also frequently recorded by ancient and medieval observers as "blood rain". Ultimately we work towards using past extreme climate events from medieval Europe recorded as written evidence to constrain the ice core age scale and, vice versa, to investigate the response of human societies to environmental change recorded in the CG glacier archive.

Seafloor Control on Sea Ice

NASA Technical Reports Server (NTRS)

Nghiem, S. V.; Clemente-Colon, P.; Rigor, I. G.; Hall, D. K.; Neumann, G.

2011-01-01

The seafloor has a profound role in Arctic sea ice formation and seasonal evolution. Ocean bathymetry controls the distribution and mixing of warm and cold waters, which may originate from different sources, thereby dictating the pattern of sea ice on the ocean surface. Sea ice dynamics, forced by surface winds, are also guided by seafloor features in preferential directions. Here, satellite mapping of sea ice together with buoy measurements are used to reveal the bathymetric control on sea ice growth and dynamics. Bathymetric effects on sea ice formation are clearly observed in the conformation between sea ice patterns and bathymetric characteristics in the peripheral seas. Beyond local features, bathymetric control appears over extensive ice-prone regions across the Arctic Ocean. The large-scale conformation between bathymetry and patterns of different synoptic sea ice classes, including seasonal and perennial sea ice, is identified. An implication of the bathymetric influence is that the maximum extent of the total sea ice cover is relatively stable, as observed by scatterometer data in the decade of the 2000s, while the minimum ice extent has decreased drastically. Because of the geologic control, the sea ice cover can expand only as far as it reaches the seashore, the continental shelf break, or other pronounced bathymetric features in the peripheral seas. Since the seafloor does not change significantly for decades or centuries, sea ice patterns can be recurrent around certain bathymetric features, which, once identified, may help improve short-term forecast and seasonal outlook of the sea ice cover. Moreover, the seafloor can indirectly influence cloud cover by its control on sea ice distribution, which differentially modulates the latent heat flux through ice covered and open water areas.

Ice dynamics of Heinrich events: Insights and implications

NASA Astrophysics Data System (ADS)

Alley, R. B.; Parizek, B. R.; Anandakrishnan, S.

2017-12-01

Physical understanding of ice flow provides important constraints on Heinrich (H) events, which in turn provide lessons for ice dynamics and future sea-level change. Iceberg-rafted debris (IRD), the defining feature of H events, is a complex indicator; however, in cold climates with extensive marine-ending ice, increased IRD flux records ice-shelf loss. Ice shelves fed primarily by inflow from grounded ice experience net basal melting, giving sub-ice-sedimentation rather than open-ocean IRD. Ice-shelf loss has been observed recently in response to atmospheric warming increasing surface meltwater that wedged open crevasses (Larsen B), but also by break-off following thinning from warming of waters reaching the grounding line (Jakobshavn). The H events consistently occurred during cold times resulting from reduced North Atlantic overturning circulation ("conveyor"), but as argued by Marcott et al. (PNAS 2011), this was accompanied by delayed warming at grounding-line depths of the Hudson Strait ice stream, the source of the Heinrich layers, implicating oceanic control. As shown in a rich literature, additional considerations involving thermal state of the ice-stream bed, isostasy and probably other processes influenced why some reduced-conveyor events triggered H-events while others did not. Ice shelves, including the inferred Hudson Strait ice shelf, typically exist in high-salinity, cold waters produced by brine rejection from sea-ice formation, which are the coldest abundant waters in the world ocean. Thus, almost any change in air or ocean temperature, winds or currents can remove ice shelves, because "replacement" water masses are typically warmer. And, because ice shelves almost invariably slow flow of non-floating ice into the ocean, climatic perturbations to regions with ice shelves typically lead to sea-level rise, with important implications.

Ross Ice Shelf airstream driven by polar vortex cyclone

NASA Astrophysics Data System (ADS)

Schultz, Colin

2012-07-01

The powerful air and ocean currents that flow in and above the Southern Ocean, circling in the Southern Hemisphere's high latitudes, form a barrier to mixing between Antarctica and the rest of the planet. Particularly during the austral winter, strong westerly winds isolate the Antarctic continent from heat, energy, and mass exchange, bolstering the scale of the annual polar ozone depletion and driving the continent's record-breaking low temperatures. Pushing through this wall of high winds, the Ross Ice Shelf airstream (RAS) is responsible for a sizable amount of mass and energy exchange from the Antarctic inland areas to lower latitudes. Sitting due south of New Zealand, the roughly 470,000-square-kilometer Ross Ice Shelf is the continent's largest ice shelf and a hub of activity for Antarctic research. A highly variable lower atmospheric air current, RAS draws air from the inland Antarctic Plateau over the Ross Ice Shelf and past the Ross Sea. Drawing on modeled wind patterns for 2001-2005, Seefeldt and Cassano identify the primary drivers of RAS.

Precisely dated multidecadally resolved Asian summer monsoon dynamics 113.5-86.6 thousand years ago

NASA Astrophysics Data System (ADS)

Jiang, Xiuyang; Wang, Xiaoyan; He, Yaoqi; Hu, Hsun-Ming; Li, Zhizhong; Spötl, Christoph; Shen, Chuan-Chou

2016-07-01

We present a new 230Th-dated absolute chronology of Asian summer monsoon (ASM) variability from 113.5 to 86.6 kyr BP (before 1950 AD). This integrated multidecadally resolved record, based on 1435 oxygen isotope data and 46 230Th dates with 2-sigma errors as low as ±0.3 kyr from three stalagmites collected in Sanxing Cave, southwestern China, can be a new reference for calibrating paleoclimate proxy sequences. The Sanxing δ18O record follows the 23 kyr precessional cycle of insolation and is punctuated by prominent millennial-scale oscillations of the Chinese Interstadials (CIS) 25 to 22, corresponding to Greenland Interstadials (GIS) 25 to 22. The onset of CIS 25, 24, 23 and 22 is dated to 113.1 ± 0.4, 108.1 ± 0.3, 103.7 ± 0.3 and 91.4 ± 0.6 kyr BP in the Sanxing record, respectively. The end of CIS 24 and CIS 22 is constrained to 105.5 ± 0.4 and 87.7 ± 0.3 kyr BP, respectively. A centennial-scale precursor event at 104.1 ± 0.3 kyr BP preceding CIS 23 is clearly registered. These events in the Sanxing record are synchronous with those identified in stalagmites from the European Alps (NALPS), except for the onset of GIS 25 and the end of GIS 22, and differ by up to 2.3 kyr from the corresponding ones in Greenland ice core records. The high degree of similarity of the δ18O records between Sanxing Cave and Greenland supports a Northern Hemisphere forcing of the ASM. The anti-phase relationship of δ18O records between Sanxing stalagmites and Antarctic ice cores suggests an additional ASM linkage to the Southern Hemisphere.

Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier [Sub-ice shelf sediments record 20 th century retreat history of Pine Island Glacier

DOE PAGES

Smith, J. A.; Andersen, T. J.; Shortt, M.; ...

2016-11-23

The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreatmore » is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Furthermore our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.« less

Little Ice Age Fluctuations of Quelccaya Ice Cap, Peru

NASA Astrophysics Data System (ADS)

Stroup, J. S.; Kelly, M. A.; Lowell, T.

2009-12-01

A record of the past extents of Quelccaya Ice Cap (QIC) provides valuable information about tropical climate change from late glacial to recent time. Here, we examine the timing and regional significance of fluctuations of QIC during the Little Ice Age (LIA; ~1300-1850 AD). One prominent set of moraines, known as the Huancane I moraines, is located ~1 km from the present-day western ice cap margin and provides a near-continuous outline of the most recent advance of QIC. This moraine set was radiocarbon dated (~298 ± 134 and 831 ± 87 yr BP) by Mercer and Palacios (1977) and presented as some of the first evidence for cooling in the tropics during the Little Ice Age. Recent field investigations in the QIC region focused on refining the chronology of the Huancane I moraines. In 2008, new stratigraphic sections exposed by local lake-flooding events revealed multiple layers of peat within the Huancane I moraines. In both 2008 and 2009, samples were obtained for 10Be dating of boulders on Huancane I moraines. A combination of radiocarbon and 10Be ages indicate that the Huancane I moraines were deposited by ice cap expansion after ~3800 yr BP and likely by multiple advances at approximately 1000, 600, 400, and 200 yr BP. Radiocarbon and 10Be chronologies of the Huancane I moraines are compared with the Quelccaya ice core records (Thompson et al., 1985; 1986; 2006). Accumulation data from the ice core records are interpreted to indicate a significant wet period at ~1500-1700 AD followed by a significant drought at ~1720-1860 AD. We examine ice marginal fluctuations during these times to determine influence of such events on the ice cap extent.

Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier [Sub-ice shelf sediments record 20 th century retreat history of Pine Island Glacier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, J. A.; Andersen, T. J.; Shortt, M.

The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreatmore » is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Furthermore our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.« less

Critical porosity of gas enclosure in polar firn independent of climate

NASA Astrophysics Data System (ADS)

Florian Schaller, Christoph; Freitag, Johannes; Eisen, Olaf

2017-11-01

In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. Within the porous firn, bubbles are sealed continuously until the respective horizontal layer reaches a critical porosity. Present-day firn air models use a postulated temperature dependence of this value as the only parameter to adjust to the surrounding conditions of individual sites. However, no direct measurements of the firn microstructure could confirm these assumptions. Here we show that the critical porosity is a climate-independent constant by providing an extensive data set of micrometer-resolution 3-D X-ray computer tomographic measurements for ice cores representing different extremes of the temperature and accumulation ranges. We demonstrate why indirect measurements suggest a climatic dependence and substantiate our observations by applying percolation theory as a theoretical framework for bubble trapping. The incorporation of our results significantly influences the dating of trace gas records, changing gas-age-ice-age differences by up to more than 1000 years. This may further help resolve inconsistencies, such as differences between East Antarctic δ15N records (as a proxy for firn height) and model results. We expect our findings to be the basis for improved firn air and densification models, leading to lower dating uncertainties. The reduced coupling of proxies and surrounding conditions may allow for more sophisticated reinterpretations of trace gas records in terms of paleoclimatic changes and will benefit the development of new proxies, such as the air content as a marker of local insolation.

34 CFR 682.605 - Determining the date of a student's withdrawal.

Code of Federal Regulations, 2014 CFR

2014-07-01

... next scheduled term following a summer break, which includes any summer term or terms in which classes... student who does not return from a summer break, the school must follow the procedures in § 668.22(b) or...

Using Melting Ice to Teach Radiometric Dating.

ERIC Educational Resources Information Center

Wise, Donald Underkofler

1990-01-01

Presented is an activity in which a mystery setting is used to motivate students to construct their own decay curves of melting ice used as an analogy to radioactive decay. Procedures, materials, apparatus, discussion topics, presentation, and thermodynamics are discussed. (CW)

Debris-Covered Glaciers in Antarctica: Analogs for Viscous-Flow Features on Mars

NASA Astrophysics Data System (ADS)

Marchant, D. R.; Phillips, W. M.; Schaefer, J.; Fastook, J.; Landis, G.

2007-12-01

The McMurdo Dry Valleys (MDV) are generally classified as a hyper-arid, cold-polar desert. Subtle variations in climate parameters throughout the region result in considerable differences in the distribution, origin, and morphology of buried ice. In the coastal thaw zone, near-surface buried ice experiences seasonal melt and may have formed where pore water from surface snowmelt freezes underground (segregation ice). Characteristic landforms associated with this type of buried ice include thermokarst, shallow planar slides, and solifluction. In contrast, in the coldest and driest regions of the MDV, the stable upland zone, there is insufficient meltwater to produce extensive segregation ice. Rather, widespread buried ice in this zone is typically glacier ice. Temperature data indicate that ice remains frozen in this zone if buried beneath ~15 cm of debris. The Mullins-valley debris-covered glacier, which lies within the stable upland zone, contains ancient glacier ice beneath a thin layer of sublimation till. Four independent dating techniques confirm that the glacier age ranges from ~10 ka near the valley head, to >8 Ma at its diffuse terminus in central Beacon Valley. The dating methods include cosmogenic-nuclide analyses of surface boulders; horizontal ice-flow velocities as determined from synthetic aperture radar interferometry; 40Ar/39Ar analyses of in-situ ash fall in relict polygon troughs at the till surface; and numerical ice-flow models. Age results so derived are in accord with measured variations in ancient community DNA extracted from pristine ice samples along the length of the glacier. Multi- channel seismic and ground-penetrating radar surveys demonstrate that the ice is relatively clean and that it averages from ~45 m to ~150 m thick. Morphologic comparisons of the Mullins Valley debris-covered glacier are used to shed light on the origin and modification of near-surface ice on Mars.

Mesozoic paleogeography and paleoclimates - A discussion of the diverse greenhouse and hothouse conditions of an alien world

NASA Astrophysics Data System (ADS)

Holz, Michael

2015-08-01

The Mesozoic was the time of the break-up of Pangaea, with profound consequences not only for the paleocontinental configuration, but also for paleoclimates and for the evolution of life. Cool greenhouse conditions alternated with warm greenhouse and even hothouse conditions, with global average temperatures around 6-9 °C warmer than the present ones. There are only sparse and controversial evidence for polar ice; meanwhile, extensive evaporitic and desertic deposits are well described. Global sea levels were mainly high, and the content of atmospheric O2 was varying between 15 and 25%. These conditions make the Mesozoic Earth an alien world compared to present-day conditions. Degassing from volcanism linked to the rifting process of Pangaea and methane emissions from reptilian biotas were climate-controlling factors because they enhanced atmospheric CO2 concentrations up to 16 times compared to present-day levels. The continental break-up modified paleopositions and shoreline configurations of the landmasses, generating huge epicontinental seas and altering profoundly the oceanic circulation. The Mesozoic was also a time of important impact events as probable triggers for "impact winters"; and for the Era at least nine huge (diameter > 20 km) impact structures are known. This paper presents an abridged but updated overview of the Mesozoic paleogeographic and paleoclimatic variations, characterizing each period and sub-period in terms of paleoclimatic state and main tectonic and climatic events, and provides a brief geologic, stratigraphic, paleoclimatic and taphonomic characterization of dinosaur occurrences as recorded in the Brazilian continental basins.

Breaking Ice 2: A rift system on the Ross Ice Shelf as an analog for tidal tectonics on icy moons

NASA Astrophysics Data System (ADS)

Brunt, K. M.; Hurford, T., Jr.; Schmerr, N. C.; Sauber, J. M.; MacAyeal, D. R.

2016-12-01

Ice shelves are the floating regions of the polar ice sheets. Outside of the influence of the narrow region of their grounding zone, they are fully hydrostatic and strongly influenced by the ocean tides. Recent observational and modeling studies have assessed the effect of tides on ice shelves, including: the tidal influence on the ice-shelf surface height, which changes by as much as 6 to 7 m on the southern extreme of the Ronne-Filchner Ice Shelf; the tidal modulation of the ice-shelf horizontal flow velocities, which changes the mean ice-flow rate by as much as two fold on the Ross Ice Shelf; and the tidal contribution to fracture and rift propagation, which eventually leads to iceberg calving. Here, we present the analysis of 16 days of continuous GPS data from a rift system near the front of the Ross Ice Shelf. While the GPS sites were installed for a different scientific investigation, and not optimized to assess tidal rifting mechanics, they provide a first-order sense of the tidal evolution of the rift system. These analyses can be used as a terrestrial analog for tidal activity on icy satellites, such as Europa and Enceladus, moons of Jupiter and Saturn, respectively. Using remote sensing and modeling of the Ross Ice Shelf rift system, we can investigate the geological processes observed on icy satellites and advance modeling efforts of their tidal-tectonic evolution.

Impacts of projected sea ice changes on trans-Arctic navigation

NASA Astrophysics Data System (ADS)

Stephenson, S. R.; Smith, L. C.

2012-12-01

Reduced Arctic sea ice continues to be a palpable signal of global change. Record lows in September sea ice extent from 2007 - 2011 have fueled speculation that trans-Arctic navigation routes may become physically viable in the 21st century. General Circulation Models project a nearly ice-free Arctic Ocean in summer by mid-century; however, how reduced sea ice will realistically impact navigation is not well understood. Using the ATAM (Arctic Transportation Accessibility Model) we present simulations of 21st-century trans-Arctic voyages as a function of climatic (ice) conditions and vessel class. Simulations are based on sea ice projections for three climatic forcing scenarios (RCP 4.5, 6.0, and 8.5 W/m^2) representing present-day and mid-century conditions, assuming Polar Class 6 (PC6) and open-water vessels (OW) with medium and no ice-breaking capability, respectively. Optimal least-cost routes (minimizing travel time while avoiding ice impassible to a given vessel class) between the North Atlantic and the Bering Strait were calculated for summer months of each time window. While Arctic navigation depends on other factors besides sea ice including economics, infrastructure, bathymetry, current, and weather, these projections should be useful for strategic planning by governments, regulatory and environmental agencies, and the global maritime industry to assess potential changes in the spatial and temporal ranges of Arctic marine operations.

Persistent Ice on Lake Superior

NASA Image and Video Library

2017-12-08

Though North America is a full month into astronomical spring, the Great Lakes have been slow to give up on winter. As of April 22, 2014, the Great Lakes were 33.9 percent ice covered. The lake they call Superior dominated the pack. In the early afternoon on April 20, 2014, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image of Lake Superior, which straddles the United States–Canada border. At the time Aqua passed over, the lake was 63.5 percent ice covered, according to the NOAA Great Lakes Environmental Research Lab (GLERL). Averaged across Lake Superior, ice was 22.6 centimeters (8.9 inches) thick; it was as much as twice that thickness in some locations. GLERL researcher George Leshkevich affirmed that ice cover this spring is significantly above normal. For comparison, Lake Superior had 3.6 percent ice cover on April 20, 2013; in 2012, ice was completely gone by April 12. In the last winter that ice cover grew so thick on Lake Superior (2009), it reached 93.7 percent on March 2 but was down to 6.7 percent by April 21. Average water temperatures on all of the Great Lakes have been rising over the past 30 to 40 years and ice cover has generally been shrinking. (Lake Superior ice was down about 79 percent since the 1970s.) But chilled by persistent polar air masses throughout the 2013-14 winter, ice cover reached 88.4 percent on February 13 and 92.2 percent on March 6, 2014, the second highest level in four decades of record-keeping. Air temperatures in the Great Lakes region were well below normal for March, and the cool pattern is being reinforced along the coasts because the water is absorbing less sunlight and warming less than in typical spring conditions. The graph below, based on data from Environment Canada, shows the 2014 conditions for all of the Great Lakes in mid-April compared to the past 33 years. Lake Superior ice cover got as high as 95.3 percent on March 19. By April 22, it was reported at 59.9 percent; Lake Huron was nearly 30.4 percent. News outlets noted that as many as 70 ships have been backed up in Lakes Michigan, Huron, and Erie, waiting for passage into ports on Lake Superior. The U.S. Coast Guard has been grouping ships together into small convoys after they pass through locks at Sault Ste. Marie, in order to maximize ice-breaking efficiency and to protect ships from damage. Superior is the world’s largest freshwater lake by area (82,100 square kilometers or 31,700 square miles) and the third largest by volume. The waters average 147 meters (483 feet) in depth, and the basin is believed to hold about 10 percent of the world’s liquid fresh water. NASA image courtesy Jeff Schmaltz LANCE/EOSDIS MODIS Rapid Response Team, GSFC. Caption by Mike Carlowicz. Read more: earthobservatory.nasa.gov/IOTD/view.php?id=83541&eocn... Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

The little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap.

PubMed

Thompson, L G; Mosley-Thompson, E; Dansgaard, W; Grootes, P M

1986-10-17

The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that the Little Ice Age (about A.D. 1500 to 1900) stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event.

A summary of ERTS data applications in Alaska

NASA Technical Reports Server (NTRS)

Miller, J. M.; Belon, A. E.

1974-01-01

ERTS has proven to be an exceedingly useful tool for the preparation of urgently needed resource surveys in Alaska. For this reason the wide utilization of ERTS data by federal, state and industrial agencies in Alaska is increasingly directed toward the solution of operational problems in resource inventories, environmental surveys, and land use planning. Examples of some applications are discussed in connection with surveys of potential agricultural lands; mapping of predicted archaeological sites; permafrost terrain and aufeis mapping; snow melt enhancement from Prudhoe Bay roads; geologic interpretations correlated ith possible new petroleum fields, with earthquake activity, and with plate tectonic motion along the Denali fault system; hydrology in monitoring surging glaciers and the break-up characteristics of the Chena River watershed; sea-ice morphology correlated with marine mammal distribution; and coastal sediment plume circulation patterns.

Research on the Test of Transmission Line Galloping

NASA Astrophysics Data System (ADS)

Zhang, Lichun; Li, Qing; lv, Zhongbin; Ji, Kunpeng; Liu, Bin

2018-03-01

The load of iced transmission line and the load generated by galloping after the conductor are covered by ice all may cause severe circuit faults, such as tripping, conductor breaking, armor clamp damage and even tower collapse, thus severely threatening running safety of power system. The generation and development processes of galloping of power transmission line is very complicated, and numerous factors may influence the galloping excitation, such as environmental factors, terrain factors and structural parameters of power transmission line; in which, the ice covering of conductor is one of necessary factors causing galloping. Therefore, researches on ice covering increasing test of different types of conductors under different meteorological conditions have been conducted in large-sized multi-functional phytotron, thus obtaining the relation curve of ice covering increasing of conductor along with time under different conditions, and analyzing factors influencing increasing of ice covering. The research result shows that under the same ice covering conditions, the increasing of ice covering of conductor with small diameter is relatively rapid; both environmental temperature and wind speed have obvious influence on increasing of ice covering of conductor, and the environmental temperature will decide the type of ice covering of conductor surface. Meanwhile, after wind tunnel tests targeting conductors with different ice covering shapes, pneumatic stability loss characteristics of conductors with different ice shapes have been obtained. Research results have important scientific reference value for revealing the mechanism of galloping of iced power transmission line, and have relatively high engineering practicability value for promoting realization of early warning system for galloping of iced power transmission line.

Continuous earlywood vessels chronologies in floodplain ring-porous species can improve dendrohydrological reconstructions of spring high flows and flood levels

NASA Astrophysics Data System (ADS)

Kames, S.; Tardif, J. C.; Bergeron, Y.

2016-03-01

Plants respond to environmental stimuli through changes in growth and development. Characteristics of wood cells such as the cross-sectional area of vessel elements (hereafter referred to as vessels) may store information about environmental factors present at the time of vessel differentiation. The analysis of vessel characteristics therefore offers a different time resolution than annual ring width because vessels in tree rings differentiate within days to a few weeks. Little research has been conducted on the sensitivity of earlywood vessels in ring-porous species in response to flooding. The general objectives of this study were to determine the plasticity of earlywood vessel to high flows and spring flooding in floodplain black ash (Fraxinus nigra Marsh.) trees and to assess the utility of developing continuous earlywood vessel chronologies in dendrohydrological reconstruction. In contrast, most dendrohydrological studies until now have mainly used vessel anomalies (flood rings) as discrete variables to identify exceptional flood events. The study area is located in the boreal region of northwestern Québec. Vessel and ring-width chronologies were generated from F. nigra trees growing on the floodplain of Lake Duparquet. Spring discharge had among all hydro-climatic variables the strongest impact on vessel formation and this signal was coherent spatially and in the frequency domain. The mean vessel area chronology was significantly and negatively correlated to discharge and both the linearity and the strength of this association were unique. In floodplain F. nigra trees, spring flooding promoted the formation of more abundant but smaller earlywood vessels. Earlywood vessels chronologies were also significantly associated with other hydrological indicators like Lake Duparquet's ice break-up date and both ice-scar frequency and height chronologies. These significant relationships stress the utility of developing continuous vessels chronologies for hydrological reconstructions prior to instrumental data. Continuous earlywood vessel chronologies may also be useful in determining the impact of altered hydrological regime in floodplain habitat regulated by spring floods. Future research should involve quantifying the impact of high flows and flooding on other cell constituents and also determining the plasticity and utility of continuous anatomical series in floodplain diffuse-porous species.

Dirac strings and magnetic monopoles in the spin ice Dy2Ti2O7.

PubMed

Morris, D J P; Tennant, D A; Grigera, S A; Klemke, B; Castelnovo, C; Moessner, R; Czternasty, C; Meissner, M; Rule, K C; Hoffmann, J-U; Kiefer, K; Gerischer, S; Slobinsky, D; Perry, R S

2009-10-16

Sources of magnetic fields-magnetic monopoles-have so far proven elusive as elementary particles. Condensed-matter physicists have recently proposed several scenarios of emergent quasiparticles resembling monopoles. A particularly simple proposition pertains to spin ice on the highly frustrated pyrochlore lattice. The spin-ice state is argued to be well described by networks of aligned dipoles resembling solenoidal tubes-classical, and observable, versions of a Dirac string. Where these tubes end, the resulting defects look like magnetic monopoles. We demonstrated, by diffuse neutron scattering, the presence of such strings in the spin ice dysprosium titanate (Dy2Ti2O7). This is achieved by applying a symmetry-breaking magnetic field with which we can manipulate the density and orientation of the strings. In turn, heat capacity is described by a gas of magnetic monopoles interacting via a magnetic Coulomb interaction.

Dating High Arctic Holocene relative sea level changes using juvenile articulated marine shells in raised beaches

NASA Astrophysics Data System (ADS)

Long, Antony J.; Strzelecki, Mateusz C.; Lloyd, Jerry M.; Bryant, Charlotte L.

2012-08-01

High Arctic raised beaches provide evidence for changes in relative sea-level (RSL), sea-ice extent, storminess, and variations in sediment supply. In many High Arctic areas, driftwood and whale bone are usually the preferred targets for radiocarbon dating, with marine shells a third choice because of their often large age and height uncertainties with respect to former sea level. Here we detail a new approach to sampling marine shells that reduces these problems by targeting juvenile, articulated specimens of Astarte borealis that are washed onto the beach under storm conditions and become incorporated into the beach crest. Radiocarbon dates from articulated valves of A. borealis from eight raised beaches from Billefjorden, Svalbard, provide a chronology for Holocene beach ridge formation and RSL change that compares favourably to the most precise records developed from elsewhere in Svalbard using driftwood or whale bone. We demonstrate the value of this new approach by comparing our record with previously published RSL data from eastern Svalbard to test different models of Late Weichselian ice load in this region. We find support for a major ice dome centred south and east of Kong Karls Land but no evidence for a significant ice dome located over easternmost Spitsbergen or southern Hinlopen Strait as proposed from recent marine geophysical survey. The approach is potentially applicable elsewhere in Svalbard and the High Arctic to address questions of RSL change and beach ridge chronology, and hence wider questions regarding palaeoclimate and ice load history.

Spatiotemporal Variation of Arctic Nearshore Fish Communities in Barrow, AK

NASA Astrophysics Data System (ADS)

Boswell, K. M.; Barton, M. B.; Lemoine, N. P.; Heintz, R.; Vollenweider, J.; Norcross, B.; Sousa, L.

2016-02-01

Climate change, oil and gas development, and increased transportation opportunities associated with retreating sea ice cover are likely to affect the processes underlying community development. Unfortunately, there is a paucity of information that prohibits establishing a baseline from which to examine biological and ecological changes. To address these concerns, we developed an intensive field sampling program using weekly beach seining for the six weeks following land-fast ice break-up during the summers of 2013-2015 (183 beach seine hauls totaling 37,303 fish) in three distinct water masses near Pt. Barrow, Alaska to examine how fish communities develop in the Arctic nearshore. Preliminary analyses indicate that inter-annual variability in temperature and salinity influence species composition observed in late summer, but it is unclear which factors operate on smaller temporal scales. We applied multivariate variance partitioning to quantify variation in community structure on multiple spatial and temporal scales during the summer season and identified several physicochemical parameters as important spatiotemporal drivers in structuring nearshore fish communities. Understanding how these drivers affect nearshore communities on the seasonal scale is an integral step to predict how these ecologically important ecosystems may shift in the face of Arctic climate change and continued development.

Simulation of water vapor condensation on LOX droplet surface using liquid nitrogen

NASA Technical Reports Server (NTRS)

Powell, Eugene A.

1988-01-01

The formation of ice or water layers on liquid oxygen (LOX) droplets in the Space Shuttle Main Engine (SSME) environment was investigated. Formulation of such ice/water layers is indicated by phase-equilibrium considerations under conditions of high partial pressure of water vapor (steam) and low LOX droplet temperature prevailing in the SSME preburner or main chamber. An experimental investigation was begun using liquid nitrogen as a LOX simulant. A monodisperse liquid nitrogen droplet generator was developed which uses an acoustic driver to force the stream of liquid emerging from a capillary tube to break up into a stream of regularly space uniformly sized spherical droplets. The atmospheric pressure liquid nitrogen in the droplet generator reservoir was cooled below its boiling point to prevent two phase flow from occurring in the capillary tube. An existing steam chamber was modified for injection of liquid nitrogen droplets into atmospheric pressure superheated steam. The droplets were imaged using a stroboscopic video system and a laser shadowgraphy system. Several tests were conducted in which liquid nitrogen droplets were injected into the steam chamber. Under conditions of periodic droplet formation, images of 600 micron diameter liquid nitrogen droplets were obtained with the stroboscopic video systems.

Spontaneous De-Icing Phenomena on Extremely Cold Surfaces

NASA Astrophysics Data System (ADS)

Song, Dong; Choi, Chang-Hwan

2017-11-01

Freezing of droplets on cold surfaces is universal phenomenon, while the mechanisms are still inadequately understood. Here we report spontaneous de-icing phenomena of an impacting droplet which occur on extreme cold surfaces. When a droplet impacts on cold surfaces lower than -80°, it takes more than two times longer for the droplet to freeze than the ones at -50°. Moreover, the frozen droplet below -80° breaks up into several large parts spontaneously in the end. When a droplet impacts on the extreme cold surfaces, evaporation and condensation occur immediately as the droplet approaches the substrate. A thick layer of frost forms between the droplet and substrate, decreasing the contact area of the droplet with substrate. It leads to impede the heat transfer and hence extends the freezing time significantly. On the extremely cold substrate, the droplet freezes from the center to the edge area, in contrast to a typical case freezing from the bottom to the top. This novel from-center-to-edge freezing process changes the internal tension of the frozen droplet and results in the instantaneous breakup and release eventually, which can be taken advantage of for effective deicing mechanisms.

Observed platelet ice distributions in Antarctic sea ice: An index for ocean-ice shelf heat flux

NASA Astrophysics Data System (ADS)

Langhorne, P. J.; Hughes, K. G.; Gough, A. J.; Smith, I. J.; Williams, M. J. M.; Robinson, N. J.; Stevens, C. L.; Rack, W.; Price, D.; Leonard, G. H.; Mahoney, A. R.; Haas, C.; Haskell, T. G.

2015-07-01

Antarctic sea ice that has been affected by supercooled Ice Shelf Water (ISW) has a unique crystallographic structure and is called platelet ice. In this paper we synthesize platelet ice observations to construct a continent-wide map of the winter presence of ISW at the ocean surface. The observations demonstrate that, in some regions of coastal Antarctica, supercooled ISW drives a negative oceanic heat flux of -30 Wm-2 that persists for several months during winter, significantly affecting sea ice thickness. In other regions, particularly where the thinning of ice shelves is believed to be greatest, platelet ice is not observed. Our new data set includes the longest ice-ocean record for Antarctica, which dates back to 1902 near the McMurdo Ice Shelf. These historical data indicate that, over the past 100 years, any change in the volume of very cold surface outflow from this ice shelf is less than the uncertainties in the measurements.

Dendrochronology and late Holocene history of Bering piedmont glacier, Alaska

USGS Publications Warehouse

Wiles, G.C.; Post, A.; Muller, E.H.; Molnia, B.F.

1999-01-01

Fluctuations of the piedmont lobe of Bering Glacier and its sublobe Steller Glacier over the past two millennia are reconstructed using 34 radiocarbon dates and tree-ring data from 16 sites across the glaciers' forelands. The general sequence of glacial activity is consistent with well-dated fluctuations of tidewater and land-terminating glaciers elsewhere along the Gulf of Alaska. Extensive forested areas along 25 km of the Bering ice margin were inundated by glacio-lacustrine and glacio-fluvial sediments during a probable ice advance shortly before 500 cal yr A.D. Regrowth of forests followed the retreating ice as early as the 7th century A.D., with frequent interruptions of tree growth due to outwash aggradation. Forests overrun by ice and buried in outwash indicate readvance about 1080 cal yr A.D. Retreat followed, with ice-free conditions maintained along the distal portions of the forefield until the early 17th century after which the ice advanced to within a few kilometers of its outer Neoglacial moraine. Ice reached this position after the mid-17th century and prior to 200 yr ago. Since the early 20th century, glacial retreat has been punctuated by periodic surges. The record from forests overrun by the nonsurging Steller Lobe shows that this western ice margin was advancing by 1250 A.D., reaching near its outer moraine after 1420 cal yr A.D. Since the late 19th century, the lobe has dominantly retreated.

School Personnel's Bystander Action in Situations of Dating Violence, Sexual Violence, and Sexual Harassment Among High School Teens: A Qualitative Analysis.

PubMed

Edwards, Katie M; Rodenhizer, Kara Anne; Eckstein, Robert P

2017-04-01

We examined school personnel's engagement in bystander action in situations of teen dating violence (DV), sexual violence (SV), and sexual harassment (SH). We conducted focus groups with 22 school personnel from three high schools in New Hampshire. School personnel identified their own barriers to intervening in situations of teen DV, SV, and SH (e.g., not having the time or ability to intervene). School personnel also discussed the ways in which they intervened before (e.g., talking with teens about healthy relationships), during (e.g., breaking up fights between dating partners) and after (e.g., comforting victims) instances of teen DV, SV, and SH. These data can be used to support the development of bystander training for school personnel as one component of comprehensive DV, SV, and SH prevention for teens. In addition, these data provide information that can be used to develop measures that assess school personnel bystander action barriers and behaviors in instances of teen DV, SV, and SH.

Where is the 1-million-year-old ice at Dome A?

NASA Astrophysics Data System (ADS)

Zhao, Liyun; Moore, John C.; Sun, Bo; Tang, Xueyuan; Guo, Xiaoran

2018-05-01

Ice fabric influences the rheology of ice, and hence the age-depth profile at ice core drilling sites. To investigate the age-depth profile to be expected of the ongoing deep ice coring at Kunlun station, Dome A, we use the depth-varying anisotropic fabric suggested by the recent polarimetric measurements around Dome A along with prescribed fabrics ranging from isotropic through girdle to single maximum in a three-dimensional, thermo-mechanically coupled full-Stokes model of a 70 × 70 km2 domain around Kunlun station. This model allows for the simulation of the near basal ice temperature and age, and ice flow around the location of the Chinese deep ice coring site. Ice fabrics and geothermal heat flux strongly affect the vertical advection and basal temperature which consequently control the age profile. Constraining modeled age-depth profiles with dated radar isochrones to 2/3 ice depth, the surface vertical velocity, and also the spatial variability of a radar isochrones dated to 153.3 ka BP, limits the age of the deep ice at Kunlun to between 649 and 831 ka, a much smaller range than previously inferred. The simple interpretation of the polarimetric radar fabric data that we use produces best fits with a geothermal heat flux of 55 mW m-2. A heat flux of 50 mW m-2 is too low to fit the deeper radar layers, and 60 mW m-2 leads to unrealistic surface velocities. The modeled basal temperature at Kunlun reaches the pressure melting point with a basal melting rate of 2.2-2.7 mm a-1. Using the spatial distribution of basal temperatures and the best fit fabric suggests that within 400 m of Kunlun station, 1-million-year-old ice may be found 200 m above the bed, and that there are large regions where even older ice is well above the bedrock within 5-6 km of the Kunlun station.

Age and origin of ice-rich Yedoma silts at Duvanny Yar, northeast Siberia: a record of Beringian environmental change since the last interglacial

NASA Astrophysics Data System (ADS)

Murton, J.; Edwards, M. E.; Murton, D.; Bateman, M.; Haile, J.

2010-12-01

Silty Yedoma deposits at the important Beringian site of Duvanny Yar (68o,37’ N; 159o08’ E) in northeast Siberia, have been interpreted before as both loess and nival deposits. The yedoma deposits form a stratigraphic unit more than 30 m thick that comprises sandy silts which are generally massive and rich in ground ice and organic material. The ground ice includes pore ice, segregated ice and wedge ice (both syngenetic and epigenetic), and much of it accumulated more or less coevally with deposition of the silt and upward growth of permafrost. Organic material includes pervasive rootlets of former steppe-tundra vegetation (e.g. grasses), vertebrate bones (e.g. mammoth, bison, horse), pollen, insect remains, and plant macrofossils. A number of cryoturbated organic horizons within the silts are interpreted as incipient palaeosols. The sedimentary properties of the silts (particle size and magnetic susceptibility) and the palaeocological characteristics of the contained organic material are both consistent with deposition of silts primarily as loess and loess-sand intergrades, sedimentologically similar to known aeolian deposits in northwest Europe (e.g. Pegwell Bay, UK). Deposition primarily by snow meltwater is unlikely because the nearest uplands where snow could have accumulated and hillslopes could have provided runoff sites are many kilometers distant. The remnants of the original landsurface—prior to thermokarst activity during the late-glacial and Holocene—indicate an essentially flat landscape during dust deposition. Radiocarbon dating of mainly in situ rootlets indicates a complete record of dust deposition during the Last Glacial Maximum (LGM), potentially one of the best terrestrial records of LGM palaeoenvironments. Older radiocarbon dates suggest at least two periods of soil formation between the LGM and about 40,000 radiocarbon years BP (within Marine Isotope Stage 3). Optical dating is currently being undertaken to constrain the ages of older dust deposits and palaeosols. U-series dating of wood contained within thaw-lake deposits at the base of the sequence provides an age from the Last Interglacial. Overall, dating of the yedoma sequence constrains interpretation of ancient soil DNA contained within the silts and provides a basis for reconstructing LGM palaeo-wind conditions associated with the Siberian high-pressure cell.

A glimpse beneath Antarctic sea ice: observation of platelet-layer thickness and ice-volume fraction with multi-frequency EM

NASA Astrophysics Data System (ADS)

Hendricks, S.; Hoppmann, M.; Hunkeler, P. A.; Kalscheuer, T.; Gerdes, R.

2015-12-01

In Antarctica, ice crystals (platelets) form and grow in supercooled waters below ice shelves. These platelets rise and accumulate beneath nearby sea ice to form a several meter thick sub-ice platelet layer. This special ice type is a unique habitat, influences sea-ice mass and energy balance, and its volume can be interpreted as an indicator for ice - ocean interactions. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In the present study, we applied a lateral constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the ice-shelf influenced fast-ice regime of Atka Bay, eastern Weddell Sea. We adapted the inversion algorithm to incorporate a sensor specific signal bias, and confirmed the reliability of the algorithm by performing a sensitivity study using synthetic data. We inverted the field data for sea-ice and sub-ice platelet-layer thickness and electrical conductivity, and calculated ice-volume fractions from platelet-layer conductivities using Archie's Law. The thickness results agreed well with drill-hole validation datasets within the uncertainty range, and the ice-volume fraction also yielded plausible results. Our findings imply that multi-frequency EM induction sounding is a suitable approach to efficiently map sea-ice and platelet-layer properties. However, we emphasize that the successful application of this technique requires a break with traditional EM sensor calibration strategies due to the need of absolute calibration with respect to a physical forward model.

Role of CO2-forced Antarctic shelf freshening on local shelf warming in an eddying global climate model

NASA Astrophysics Data System (ADS)

Goddard, P.; Dufour, C.; Yin, J.; Griffies, S. M.; Winton, M.

2017-12-01

Ocean warming near the Antarctic ice shelves has critical implications for future ice sheet mass loss and global sea level rise. A global climate model (GFDL CM2.6) with an eddying ocean is used to quantify and better understand the mechanisms contributing to ocean warming on the Antarctic continental shelf in an idealized 2xCO2 experiment. The results indicate that the simulated shelf region warming varies in magnitude at different locations. Relatively large warm anomalies occur both in the upper 100 m and at depth, which are controlled by different mechanisms. Here, we focus on the deep shelf warming and its relationship to shelf freshening. Under CO2-forcing, enhanced runoff from Antarctica, more regional precipitation, and reduction of sea ice contribute to the shelf freshening. The freshening increases the lateral density gradient of the Antarctic Slope Front, which can limit along-isopycnal onshore transport of heat from the Circumpolar Deep Water across the shelf break. Thus, the magnitude and location of the freshening anomalies govern the magnitude and location of onshore heat transport and deep warm anomalies. Additionally, the freshening increases vertical stratification on the shelf. The enhanced stratification reduces vertical mixing of heat associated with diffusion and gravitational instabilities, further contributing to the build-up of temperature anomalies at depth. Freshening is a crucial driver of the magnitude and location of the warming; however, other drivers influence the warming such as CO2-forced weakening of the easterly wind stress and associated shoaling of isotherms. Understanding the relative role of freshening in the inhomogeneous ocean warming of the Antarctic continental shelf would lead to better projections of future ice sheet mass loss, especially near the most vulnerable calving fronts.

Calibration And Validation Of CryoSat-2 Low Resolution Mode Data

NASA Astrophysics Data System (ADS)

Naeije, M.; Schrama, E.; Scharroo, R.

2011-02-01

Running ahead of the continuously growing need for operational use of sea level products, TUDelft started off the Radar Altimeter Database System RADS many years ago. This system attends to a global international sea- level service. It supports, on one hand, science, like studies on ocean circulation, El Nio, sea level change, and ice topography, and on the other hand (offshore) operations, like delivery of ocean current information, wind and wave statistics, ice detection and ice classification. At present, the database is used by a large scientific community throughout the world, and is daily maintained and developed by Altimetrics LLC, TUDelft and NOAA. It contains all historic altimeter data, and now has to be up- dated with the data from ESAs ice mission CryoSat-2, which was launched successfully in April 2010. These new data are important to augment the data set and by that to improve the estimates of sea level change and its contributors. For this the data have to be validated and calibrated, necessary corrections added and improved (including modelling of corrections that are not directly available from the CryoSat-2 platform), and the orbit ac- curacy verified and if possible the orbits brushed up. Subsequently, value-added ocean and ice products need to be developed in synergy with all the other satellite altimeter data. During the commissioning phase we primarily looked at the sanity of the available level-1b and level-2 Low Resolution Mode (LRM) data. Here, for the 2011 CryoSat Validation Workshop, we present the results of our calibration and validation of LRM L2 data by internal comparison of CryoSat-2 and external comparison with other satellites. We have established a range bias of 3.77 (measurement range too long) and a timing bias of 8.2ms (measurement range too late).

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. 

Seasonal-Scale Dating of a Shallow Ice Core From Greenland Using Oxygen Isotope Matching Between Data and Simulation

NASA Astrophysics Data System (ADS)

Furukawa, Ryoto; Uemura, Ryu; Fujita, Koji; Sjolte, Jesper; Yoshimura, Kei; Matoba, Sumito; Iizuka, Yoshinori

2017-10-01

A precise age scale based on annual layer counting is essential for investigating past environmental changes from ice core records. However, subannual scale dating is hampered by the irregular intraannual variabilities of oxygen isotope (δ18O) records. Here we propose a dating method based on matching the δ18O variations between ice core records and records simulated by isotope-enabled climate models. We applied this method to a new δ18O record from an ice core obtained from a dome site in southeast Greenland. The close similarity between the δ18O records from the ice core and models enables correlation and the production of a precise age scale, with an accuracy of a few months. A missing δ18O minimum in the 1995/1996 winter is an example of an indistinct δ18O seasonal cycle. Our analysis suggests that the missing δ18O minimum is likely caused by a combination of warm air temperature, weak moisture transport, and cool ocean temperature. Based on the age scale, the average accumulation rate from 1960 to 2014 is reconstructed as 1.02 m yr-1 in water equivalent. The annual accumulation rate shows an increasing trend with a slope of 3.6 mm yr-1, which is mainly caused by the increase in the autumn accumulation rate of 2.6 mm yr-1. This increase is likely linked to the enhanced hydrological cycle caused by the decrease in Arctic sea ice area. Unlike the strong seasonality of precipitation amount in the ERA reanalysis data in the southeast dome region, our reconstructed accumulation rate suggests a weak seasonality.

Historical record of European emissions of heavy metals to the atmosphere since the 1650s from alpine snow/ice cores drilled near Monte Rosa.

PubMed

Barbante, Carlo; Schwikowski, Margit; Döring, Thomas; Gäggeler, Heinz W; Schotterer, Ulrich; Tobler, Leo; van de Velde, Katja; Ferrari, Christophe; Cozzi, Giulio; Turetta, Andrea; Rosman, Kevin; Bolshov, Michael; Capodaglio, Gabriele; Cescon, Paolo; Boutron, Claude

2004-08-01

Cr, Cu, Zn, Co, Ni, Mo, Rh, Pd, Ag, Cd, Sb, Pt, Au, and U have been determined in clean room conditions by inductively coupled plasma sector field mass spectrometry and other analytical techniques, in various sections of two dated snow/ice cores from the high-altitude (4450 m asl) glacier saddle Colle Gnifetti, Monte Rosa massif, located in the Swiss-Italian Alps. These cores cover a 350-year time period, from 1650 to 1994. The results show highly enhanced concentrations for most metals in snow/ice dated from the second half of the 20th century, compared with concentrations in ancient ice dated from the 17th and 18th centuries. The highest increase factors from the pre-1700 period to the post-1970 period are observed for Cd (36), Zn (19), Bi (15), Cu (11), and Ni (9), confirming the importance of atmospheric pollution by heavy metals in Europe. Metal concentrations observed in Colle Gnifetti snow around 1980 appear to be quantitatively related to metal emissions from Italy, Switzerland, Germany, France, Belgium, and Austria at that time, making it possible to reconstruct past changes in metal emission in these countries during the last centuries.

Lake Generated Microseisms at Yellowstone Lake as a Record of Ice Phenology

NASA Astrophysics Data System (ADS)

Mohd Mokhdhari, A. A.; Koper, K. D.; Burlacu, R.

2017-12-01

It has recently been shown that wave action in lakes produces microseisms, which generate noise peaks in the period range of 0.8-1.2 s as recorded by nearby seismic stations. Such noise peaks have been observed at seven seismic stations (H17A, LKWY, B208, B944, YTP, YLA, and YLT) located within 2 km of the Yellowstone Lake shoreline. Initial work using 2016 data shows that the variations in the microseism signals at Yellowstone Lake correspond with the freezing and thawing of lake ice: the seismic noise occurs more frequently in the spring, summer, and fall, and less commonly in the winter. If this can be confirmed, then lake-generated microseisms could provide a consistent measure of the freezing and melting dates of high-latitude lakes in remote areas. The seismic data would then be useful in assessing the effects of climate change on the ice phenology of those lakes. In this work, we analyze continuous seismic data recorded by the seven seismic stations around Yellowstone Lake for the years of 1995 to 2016. We generate probability distribution functions of power spectral density for each station to observe the broad elevation of energy near a period of 1 s. The time dependence of this 1-s seismic noise energy is analyzed by extracting the power spectral density at 1 s from every processed hour. The seismic observations are compared to direct measurements of the dates of ice-out and freeze-up as reported by rangers at Yellowstone National Park. We examine how accurate the seismic data are in recording the freezing and melting of Yellowstone Lake, and how the accuracy changes as a function of the number of stations used. We also examine how sensitive the results are to the particular range of periods that are analyzed.

Windscapes and olfactory foraging in a large carnivore

PubMed Central

Togunov, Ron R.; Derocher, Andrew E.; Lunn, Nicholas J.

2017-01-01

The theoretical optimal olfactory search strategy is to move cross-wind. Empirical evidence supporting wind-associated directionality among carnivores, however, is sparse. We examined satellite-linked telemetry movement data of adult female polar bears (Ursus maritimus) from Hudson Bay, Canada, in relation to modelled winds, in an effort to understand olfactory search for prey. In our results, the predicted cross-wind movement occurred most frequently at night during winter, the time when most hunting occurs, while downwind movement dominated during fast winds, which impede olfaction. Migration during sea ice freeze-up and break-up was also correlated with wind. A lack of orientation during summer, a period with few food resources, likely reflected reduced cross-wind search. Our findings represent the first quantitative description of anemotaxis, orientation to wind, for cross-wind search in a large carnivore. The methods are widely applicable to olfactory predators and their prey. We suggest windscapes be included as a habitat feature in habitat selection models for olfactory animals when evaluating what is considered available habitat. PMID:28402340

The tephrostratigraphy of Mt. Berlin volcano, Antarctica: Integrating blue ice tephra and ice core tephra records

NASA Astrophysics Data System (ADS)

Iverson, N. A.; Dunbar, N. W.; McIntosh, W. C.; Kurbatov, A.

2016-12-01

Reconstructing volcanic activity in Antarctica is difficult because of the limited outcrop exposure. However, ice is an excellent medium for sampling tephra, allowing for a more complete eruptive record than can be found in other depositional environments. Furthermore, because of low ambient temperature, glass shards trapped in ice remain unaltered and unhydrated. Mt. Berlin is an ice covered volcano in Marie Byrd Land, Antarctica, and, because of heavy glaciation, eruptive records on the volcano itself are sparse. Here, we present the integration of two different records of Mt. Berlin volcanism: the blue ice record found at Mt. Moulton (Dunbar et al., 2008) and the ice core record from the WAIS Divide ice core. Tephra from Mt. Berlin are also found in other ice and marine core records, and these have been correlated and integrated into the combined volcanic record. The Mt. Moulton blue ice area is located 30 km from Mt. Berlin and hosts a fabulous tephra record spanning the last 500 ka. A total of 36 tephra from Mt. Berlin were sampled in stratigraphic order and nine were directly dated by 40Ar/39Ar dating method. Twenty five tephra from WAIS Divide have been analyzed and are geochemically similar to Mt. Berlin with ice core ages dating back to 70 ka. The two tephra records were integrated using their respective timescales. In locations where the Mt. Moulton record does not have precise chronology, the δ18O records from Mt. Moulton (Popp, 2008) and WAIS (WAIS, 2015) were used to integrate the stratigraphy. In total 61 tephra from both ice sections provide an excellent record of the magmatic evolution of Mt. Berlin over the past 500 ka. EMP analyses on glass shards show a gradual change in Fe and S over time. Most of the other major elements remain relatively unchanged. The trend in Fe and S could be produced by progressive tapping of a single, stratified magma chamber, but the long duration of volcanism makes this unlikely. We instead favor small batches of progressively more primitive melts being generated over time. Thirty nine of the tephra have been erupted within the past 100 ka with the majority (25) of them being erupted between 40 ka and 20 ka. The resolution in eruptive frequency is unparalleled and provides many stratigraphic markers that can be correlated throughout West Antarctica, which are useful in climate research.

Hard Break-Up of Two-Nucleons and QCD Dynamics of NN Interaction

NASA Astrophysics Data System (ADS)

Sargsian, Misak; Granados, Carlos

2009-05-01

We investigate hard photodisintegration of two nucleons from ^3He nucleus within the framework of hard rescattering model (HRM). In HRM a quark of one nucleon knocked-out by incoming photon rescatters with a quark of the other nucleon leading to the production of two nucleons with high relative momentum. HRM allows to express the amplitude of two-nucleon break-up reaction through the convolution of photon-quark scattering, NN hard scattering amplitude and nuclear spectral function which can be calculated using nonrelativistic ^3He wave function. HRM predicts several specific features for hard break-up reaction. First, the cross section will approximately scale as s-11. Also one predicts comparable or larger cross section for pp break up as compared to that of pn break-up, which is opposite to what is observed in low energy kinematics. Another result is the prediction of different spectator momentum dependencies of pp and pn break-up cross sections. This is due to the fact that same-helicity pp-component is strongly suppressed in the ground state wave function of ^3He. Due to this suppression HRM predicts significantly different asymmetries for the cross section of polarization transfer NN break-up reactions for circularly polarized photons. For the pp break-up this asymmetry is predicted to be zero while for the pn it is close to 23.

Timing and east-west correlation of south Swedish ice marginal lines during the Late Weichselian

NASA Astrophysics Data System (ADS)

Lundqvist, Jan; Wohlfarth, Barbara

2000-01-01

The retreat of the Late Weichselian ice sheet over the southern part of Sweden is marked along the southwest coast by distinct marginal moraine ridges. Their timing can directly and indirectly be assessed based on a number of radiocarbon dates and pollen stratigraphic investigations on lake sediment sequences adjacent to the ice marginal lines. Along the southeastern side of the peninsula, the ice recession has been reconstructed based on a combination of clay-varve chronology, pollen and radiocarbon stratigraphy. A morphological correlation of ice marginal lines between the west and east coast is problematic since the distinct west-coast moraines cannot be followed through the central part of the peninsula towards the east coast. This paper is an attempt to reconstruct an age-equivalent west-east extension of the ice-recession lines on the basis of existing data sets. For our correlation we use calibrated radiocarbon ages for ice marginal deposits on the west coast and compare these with a partly radiocarbon-dated clay-varve chronology on the east coast. We conclude that the two oldest moraines on the west coast formed at ˜18,000-16,000 and ˜15,400-14,500 cal yr BP, respectively. During the following rapid deglaciation, which may have coincided with the beginning of the Bølling pollen zone, large parts of southernmost Sweden became ice free, except for higher elevated areas, where stagnant ice remained for another 400-500 yr. A best guess is that the formation of the next younger ice marginal lines may have occurred at ˜14,400-14,200, ˜14,200 and ˜13,400 cal yr BP and during the Younger Dryas cold event.

Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier.

PubMed

Smith, J A; Andersen, T J; Shortt, M; Gaffney, A M; Truffer, M; Stanton, T P; Bindschadler, R; Dutrieux, P; Jenkins, A; Hillenbrand, C-D; Ehrmann, W; Corr, H F J; Farley, N; Crowhurst, S; Vaughan, D G

2017-01-05

The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line-which marks the boundary between grounded ice and floating ice shelf-is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Thus our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.

Sea ice and oceanic processes on the Ross Sea continental shelf

NASA Astrophysics Data System (ADS)

Jacobs, S. S.; Comiso, J. C.

1989-12-01

We have investigated the spatial and temporal variability of Antarctic sea ice concentrations on the Ross Sea continental shelf, in relation to oceanic and atmospheric forcing. Sea ice data were derived from Nimbus 7 scanning multichannel microwave radiometer (SMMR) brightness temperatures from 1979-1986. Ice cover over the shelf was persistently lower than above the adjacent deep ocean, averaging 86% during winter with little month-to-month or interannual variability. The large spring Ross Sea polynya on the western shelf results in a longer period of summer insolation, greater surface layer heat storage, and later ice formation in that region the following autumn. Newly identified Pennell and Ross Passage polynyas near the continental shelf break appear to be maintained in part by divergence above a submarine bank and by upwelling of warmer water near the slope front. Warmer subsurface water enters the shelf region year-round and will retard ice growth and enhance heat flux to the atmosphere when entrained in the strong winter vertical circulation. Temperatures at 125-m depth on a mooring near the Ross Ice Shelf during July 1984 averaged 0.15°C above freezing, sufficient to support a vertical heat flux above 100 W/m2. Monthly average subsurface ocean temperatures along the Ross Ice Shelf lag the air temperature cycle and begin to rise several weeks before spring ice breakout. The coarse SMMR resolution and dynamic ice shelf coastlines can compromise the use of microwave sea ice data near continental boundaries.

Automatic detection of Floating Ice at Antarctic Continental Margin from Remotely Sensed Image with Object-oriented Matching

NASA Astrophysics Data System (ADS)

Zhao, Z.

2011-12-01

Changes in ice sheet and floating ices around that have great significance for global change research. In the context of global warming, rapidly changing of Antarctic continental margin, caving of ice shelves, movement of iceberg are all closely related to climate change and ocean circulation. Using automatic change detection technology to rapid positioning the melting Region of Polar ice sheet and the location of ice drift would not only strong support for Global Change Research but also lay the foundation for establishing early warning mechanism for melting of the polar ice and Ice displacement. This paper proposed an automatic change detection method using object-based segmentation technology. The process includes three parts: ice extraction using image segmentation, object-baed ice tracking, change detection based on similarity matching. An approach based on similarity matching of eigenvector is proposed in this paper, which used area, perimeter, Hausdorff distance, contour, shape and other information of each ice-object. Different time of LANDSAT ETM+ data, Chinese environment disaster satellite HJ1B date, MODIS 1B date are used to detect changes of Floating ice at Antarctic continental margin respectively. We select different time of ETM+ data(January 7, 2003 and January 16, 2003) with the area around Antarctic continental margin near the Lazarev Bay, which is from 70.27454853 degrees south latitude, longitude 12.38573410 degrees to 71.44474167 degrees south latitude, longitude 10.39252222 degrees,included 11628 sq km of Antarctic continental margin area, as a sample. Then we can obtain the area of floating ices reduced 371km2, and the number of them reduced 402 during the time. In addition, the changes of all the floating ices around the margin region of Antarctic within 1200 km are detected using MODIS 1B data. During the time from January 1, 2008 to January 7, 2008, the floating ice area decreased by 21644732 km2, and the number of them reduced by 83080. The results show that the object-based information extraction algorithm can obtain more precise details of a single object, while the change detection method based on similarity matching can effectively tracking the change of floating ice.

Dykes as Tracers of Continental Break-up: Argon Geochronology of Mesozoic Flood Basalts of Western Dronning Maud Land, Antarctica

NASA Astrophysics Data System (ADS)

Fazel, A.; Kelley, S. P.; Leat, P. T.; Hawkesworth, C.

2003-04-01

The British Antarctic Survey MAMOG Project (Magmatism as A Monitor Of Gondwana break up processes) is investigating the mantle processes that resulted in the eruption of the Karoo-Dronning Maud Land CFB suite and its importance in our understanding of the initial stages of Gondwana break-up. One of the problems of understanding the 180Ma continental flood basalts is knowing their precise age. Since they are erupted through more ancient (1000Ma) rocks we have to use the Ar-Ar dating technique to determine whether they are related to the continental break-up or are part of some older event. In addition, we have analysed the chemistry of the dykes and can relate them to several chemical types, the challenge is to test if dykes with similar chemistry all erupted at the same time. It has been suggested that many of the Jurassic dykes in western DML fed the CFB suite that is higher in the volcanic pile. We have found dykes of different ages in the Kirwanveggen and Ahlmannryggen regions of western DML. Although more work needs to be done, we now have mounting evidence to suggest that episodes of chemically similar magmatism in DML stretched from 1000-180Ma with some events separated by hundreds of millions of years implying a lithospheric mantle control on magma composition. The precise ages for the dykes are slightly younger than the accepted ages for the South African Karoo province. In addition to determining the ages of dyke intrusions, a high spatial resolution UV laser has been used to measure argon loss from diorite host rocks adjacent to the dykes. Progressive heating of the country rock during magma emplacement causes argon loss. Thermal modelling of the dykes will allow us to differentiate between various heat loss mechanisms and give an indication of the style, volume and rapidity of magma flow through the dyke. The UV results have shown that some of the dykes were active for long periods probably feeding the surface lava eruptions.

Extent and timing of paleoglaciation in the Kanas Valley, Altai Mountains, China, based on remote sensing, field investigations and multiple dating methods

NASA Astrophysics Data System (ADS)

Zhang, Wei; Harbor, Jon; Cui, Zhijiu; Liu, Liang; Liu, Beibei; Fu, Yanjing; Shi, Yuanhuang; Gribenski, Natacha; Blomdin, Robin; Stroeven, Arjen; Caffee, Marc; Jansson, Krister

2014-05-01

Reconstructions of the timing and extent of past glaciation provide key constraints for paleoclimate and numerical modeling of past glacier behavior. As part of the multinational Central Asian Paleoglaciology Project we are reconstructing the timing and extent of past glaciation along and across a series of mountain ranges in central Asia using consistent methods for mapping, field investigations and numerical dating. Here we report on new findings for the Kanas Valley in northwest China, a large glaciated valley system on the south side of the Altai Mountains. Previous studies have concluded that the Kanas Valley has been shaped by a series of major glacial advances that produced overdeepened basins, a U-shaped valley cross profile, and extensive glacial and glaciofluvial deposits. Existing Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) dating results suggest major glaciation in the Kanas Valley during Marine Oxygen Isotope Stages (MIS) 3, 5, and 6, but very limited MIS 2 glaciation. Limited MIS 2 glaciation has also been suggested for other parts of central Asia, and this contrasts with extensive MIS 2 glaciation in Europe and North America. Field studies in 2013 provided new evidence for the highest elevation extent of glaciation in the Kanas Valley in the vicinity of the 20-km long Lake Kanas, with the upper limit of distinct erratics on the valley sidewalls indicating past ice thicknesses here up to 1000 m. Upper limits of erratics extending from Lake Kanas to the mapped maximum down-valley extent of glaciation suggest an ice surface slope of 1.8 degrees for the lower half of the paleoglacier in the Kanas Valley, assuming that all the erratics were deposited at the same time. Systematic sampling of glacial erratics, basal till, terminal moraines, glacially eroded bedrock, and glaciofluvial deposits provided material that is being used for cosmogenic radionuclide, OSL and ESR dating of the glacial chronology, and for dating intercomparisons.

The Antarctica component of postglacial rebound model ICE-6G_C (VM5a) based on GPS positioning, exposure age dating of ice thicknesses, and relative sea level histories

NASA Astrophysics Data System (ADS)

Argus, Donald F.; Peltier, W. R.; Drummond, R.; Moore, Angelyn W.

2014-07-01

A new model of the deglaciation history of Antarctica over the past 25 kyr has been developed, which we refer to herein as ICE-6G_C (VM5a). This revision of its predecessor ICE-5G (VM2) has been constrained to fit all available geological and geodetic observations, consisting of: (1) the present day uplift rates at 42 sites estimated from GPS measurements, (2) ice thickness change at 62 locations estimated from exposure-age dating, (3) Holocene relative sea level histories from 12 locations estimated on the basis of radiocarbon dating and (4) age of the onset of marine sedimentation at nine locations along the Antarctic shelf also estimated on the basis of 14C dating. Our new model fits the totality of these data well. An additional nine GPS-determined site velocities are also estimated for locations known to be influenced by modern ice loss from the Pine Island Bay and Northern Antarctic Peninsula regions. At the 42 locations not influenced by modern ice loss, the quality of the fit of postglacial rebound model ICE-6G_C (VM5A) is characterized by a weighted root mean square residual of 0.9 mm yr-1. The Southern Antarctic Peninsula is inferred to be rising at 2 mm yr-1, requiring there to be less Holocene ice loss there than in the prior model ICE-5G (VM2). The East Antarctica coast is rising at approximately 1 mm yr-1, requiring ice loss from this region to have been small since Last Glacial Maximum. The Ellsworth Mountains, at the base of the Antarctic Peninsula, are inferred to be rising at 5-8 mm yr-1, indicating large ice loss from this area during deglaciation that is poorly sampled by geological data. Horizontal deformation of the Antarctic Plate is minor with two exceptions. First, O'Higgins, at the tip of the Antarctic Peninsula, is moving southeast at a significant 2 mm yr-1 relative to the Antarctic Plate. Secondly, the margins of the Ronne and Ross Ice Shelves are moving horizontally away from the shelf centres at an approximate rate of 0.8 mm yr-1, in viscous response to the early Holocene unloading of ice from the current locations of the ice shelf centers. ICE-6G_C (VM5A) fits the horizontal observations well (wrms residual speed of 0.7 mm yr-1), there being no need to invoke any influence of lateral variation in mantle viscosity. ICE-6G_C (VM5A) differs in several respects from the recently published W12A model of Whitehouse et al. First, the upper-mantle viscosity in VM5a is 5 × 1020 Pa s, half that in W12A. The VM5a profile, which is identical to that inferred on the basis of the Fennoscandian relaxation spectrum, North American relative sea level histories and Earth rotation constraints, when coupled with the revised ICE-6G_C deglaciation history, fits all of the available constraints. Secondly, the net contribution of Antarctica ice loss to global sea level rise is 13.6 m, 2/3 greater than the 8 m in W12A. Thirdly, ice loss occurs quickly from 12 to 5 ka, and the contribution to global sea level rise during Meltwater Pulse 1B (11.5 ka) is large (5 m), consistent with sedimentation constraints from cores from the Antarctica ice shelf. Fourthly, in ICE-6G_C there is no ice gain in the East Antarctica interior, as there is in W12A. Finally, the new model of Antarctic deglaciation reconciles the global constraint upon the global mass loss during deglaciation provided by the Barbados record of relative sea level history when coupled with the Northern Hemisphere counterpart of this new model.

Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation

PubMed Central

Jakobsson, Martin; Nilsson, Johan; Anderson, Leif; Backman, Jan; Björk, Göran; Cronin, Thomas M.; Kirchner, Nina; Koshurnikov, Andrey; Mayer, Larry; Noormets, Riko; O'Regan, Matthew; Stranne, Christian; Ananiev, Roman; Barrientos Macho, Natalia; Cherniykh, Denis; Coxall, Helen; Eriksson, Björn; Flodén, Tom; Gemery, Laura; Gustafsson, Örjan; Jerram, Kevin; Johansson, Carina; Khortov, Alexey; Mohammad, Rezwan; Semiletov, Igor

2016-01-01

The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (∼140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening. PMID:26778247

Evaluating an Ice-Storage System in a Deregulated Environment.

ERIC Educational Resources Information Center

Staniewicz, Theodore J.; Watson, Joseph J.

2001-01-01

Examines the difficulties the electric industry's deregulation created for St. Joseph's University's (Philadelphia) development of a thermal ice-storage system as part of its HVAC design and the school's solution. A monthly equipment summary sheet with year-to-date figures is provided. (GR)