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Sample records for 19-m ice cover

  1. Effect of ice cover on hydropower production

    SciTech Connect

    Yapa, P.D.; Shen H.T.

    1984-09-01

    For hydropower developments in northern regions, the annual occurrence of river ice cover presents various problems of operation and management. The existence of an ice cover can lead to a substantial loss in power production. This loss in power due to the presence of ice cover, however, can be minimized with appropriate ice control measures. In this technical note, a quantitative analysis of power loss is carried out for the St. Lawrence Power Project. Major factors that affect the magnitude of power loss are examined to provide some information for future ice-related hydropower operations. The St. Lawrence River, which conveys water from the Great Lakes Basin to the Atlantic Ocean, has been utilized for hydroelectric power production since the early 1900's. The St. Lawrence Seaway and Power Project, constructed in 1954-58, developed the hydropower potential of the upper St. Lawrence River. The Moses-Saunders Power Dam is located about 100 miles downstream of the outlet of Lake Ontario. Since the development of this power project, the regulation of flow through the dam in relation to the ice conditions has been an important element in its winter operation. The existence of an ice cover reduces the power production capability of the river significantly.

  2. Tides of global ice-covered oceans

    NASA Astrophysics Data System (ADS)

    Wunsch, Carl

    2016-08-01

    The tides of an ice-covered ocean are examined using a Cartesian representation of the elastic and fluid equations. Although unconstrained by any observations, the ocean tides of a Neoproterozoic "snowball" Earth could have been significantly larger than they are today. Time-mean tidal-residual circulations would then have been set up that are competitive with the circulation driven by geothermal heating. In any realistic configuration, the snowball Earth would have had an ice cover that is in the thin shell limit, but by permitting the ice thickness to become large, more interesting ice tidal response can be found, ones conceivably of application to bodies in the outer Solar System or hypothetical exoplanets. Little can be said concerning a reduction in tidal dissipation necessary to avoid a crisis in the history of the lunar orbit.

  3. Modal Behavior of Hemispheric Sea Ice Covers

    NASA Technical Reports Server (NTRS)

    Gloersen, Per; Huang, Norden; Shen, Zheng

    1998-01-01

    Recent papers have described 18-year trends and annual oscillations in the Arctic and Antarctic sea ice extents, areas, and enclosed open water areas based on a newly-formulated 18.2-year ice concentration time series. This time series includes data for the entire Arctic and Antarctic ice covers, as well as for previously defined subregions consisting of 5 sectors in the Antarctic and 9 regions in the Arctic. It was obtained by fine-tuning the sea ice algorithm tie points individually for each of the four sensors used to acquire the data. In this paper, we extend these analyses to an examination of the intrinsic modes of these time series, obtained by means of Empirical Mode Decomposition, with emphasis on periodicities greater than the annual cycle. Quasibiennial and quasiquadrennial oscillations observed with a different technique and reported earlier for the first 8.8 years of this time series were also observed in the present series. However, the intrinsic modes were not monochromatic; they feature frequency as well as amplitude modulation within their respective frequency bands. Modal periods of up to 18 years are observed, with important implications for the trend analyses published earlier. These results are compared with the oscillations in the Length-of-Day and North Atlantic Oscillation parameters similarly determined for the same 18.2-year period.

  4. Modeling ocean wave propagation under sea ice covers

    NASA Astrophysics Data System (ADS)

    Zhao, Xin; Shen, Hayley H.; Cheng, Sukun

    2015-02-01

    Operational ocean wave models need to work globally, yet current ocean wave models can only treat ice-covered regions crudely. The purpose of this paper is to provide a brief overview of ice effects on wave propagation and different research methodology used in studying these effects. Based on its proximity to land or sea, sea ice can be classified as: landfast ice zone, shear zone, and the marginal ice zone. All ice covers attenuate wave energy. Only long swells can penetrate deep into an ice cover. Being closest to open water, wave propagation in the marginal ice zone is the most complex to model. The physical appearance of sea ice in the marginal ice zone varies. Grease ice, pancake ice, brash ice, floe aggregates, and continuous ice sheet may be found in this zone at different times and locations. These types of ice are formed under different thermal-mechanical forcing. There are three classic models that describe wave propagation through an idealized ice cover: mass loading, thin elastic plate, and viscous layer models. From physical arguments we may conjecture that mass loading model is suitable for disjoint aggregates of ice floes much smaller than the wavelength, thin elastic plate model is suitable for a continuous ice sheet, and the viscous layer model is suitable for grease ice. For different sea ice types we may need different wave ice interaction models. A recently proposed viscoelastic model is able to synthesize all three classic models into one. Under suitable limiting conditions it converges to the three previous models. The complete theoretical framework for evaluating wave propagation through various ice covers need to be implemented in the operational ocean wave models. In this review, we introduce the sea ice types, previous wave ice interaction models, wave attenuation mechanisms, the methods to calculate wave reflection and transmission between different ice covers, and the effect of ice floe breaking on shaping the sea ice morphology

  5. Ice-covered water volcanism on Ganymede

    NASA Technical Reports Server (NTRS)

    Allison, M. Lee; Clifford, Stephen M.

    1987-01-01

    Eruption of liquid H2O magmas along extensional fractures and graben-bounding normal faults may have played a critical role in the development of Ganymede's grooved terrain. The resurfacing potential of a water magma is dependent on a variety of factors, including the areal extent of the source region, the rate of discharge, the thickness of the flow, and the time that it takes the flow to completely freeze to its base. In this paper the thermal evolution of such a flow is considered in detail. The minimum unfrozen lifetime of a 5-m flow is approximately 12.5 days while a 10-m flow would survive for at least 50 days. Heating resulting from frictional head loss could reasonably extend these lifetimes by 50 percent or more. With a discharge rate of the order of 1-10 cu km/d, an individual volcanic water flow could flood an area of about 10,000 sq km before freezing. As the flow solidifies, its volume will increase, thus lifting and arching its protective ice cover. Extensional fractures may then develop in the ice subparallel to the graben walls. These fractures could result in grooves directly, given a sufficiently thick (1 km) flow, or they may simply act to concentrate various tectonic forces that could initiate groove-producing faults.

  6. Quantifying surface roughness over debris covered ice

    NASA Astrophysics Data System (ADS)

    Quincey, Duncan; Rounce, David; Ross, Andrew

    2016-04-01

    Aerodynamic roughness length (z0) remains a major uncertainty when determining turbulent heat fluxes over glacier surfaces, and can vary by an order of magnitude even within a small area and through the melt season. Defining z0 over debris-covered ice is particularly complex, because the surface may comprise clasts of greatly varying size, and the broader-scale surface relief can be similarly heterogeneous. Several recent studies have used Structure from Motion to data model debris-covered surfaces at the centimetric scale and calculate z0 based on measurements of surface microtopography. However, few have validated these measurements with independent vertical wind profile measurements, or considered how the measurements vary over a range of different surface types or scales of analysis. Here, we present the results of a field investigation conducted on the debris covered Khumbu Glacier during the post-monsoon season of 2015. We focus on two sites. The first is characterised by gravels and cobbles supported by a fine sandy matrix. The second comprises cobbles and boulders separated by voids. Vertical profiles of wind speed measured over both sites enable us to derive measurements of aerodynamic roughness that are similar in magnitude, with z0 at the second site exceeding that at the first by < 1 cm. During our observation period, snow covered the second site for three days, but the impact on z0 is small, implying that roughness is predominantly determined by major rock size obstacles rather than the general form of the surface. To complement these aerodynamic measurements we also conducted a Structure from Motion survey across each patch and calculated z0 using microtopographic methods published in a range of recent studies. We compare the outputs of each of these algorithms with each other and with the aerodynamic measurements, assess how they perform over a range of scales, and evaluate the validity of using microtopographic methods where aerodynamic measurements

  7. Seasonal change of antarctic sea ice cover.

    PubMed

    Gordon, A L; Taylor, H W

    1975-01-31

    The winter expansion of the sea ice surrounding Antarctica and the subsequent retreat of the ice in summer may be linked with the wind stress acting on the Southern Ocean in conjunction with the heat exchange in open water regions within the ice fields. PMID:17814267

  8. The structure of internal stresses in the uncompacted ice cover

    SciTech Connect

    Sukhorukov, K.K.

    1995-12-31

    Interactions between engineering structures and sea ice cover are associated with an inhomogeneous space/time field of internal stresses. Field measurements (e.g., Coon, 1989; Tucker, 1992) have revealed considerable local stresses depending on the regional stress field and ice structure. These stresses appear in different time and space scales and depend on rheologic properties of the ice. To estimate properly the stressed state a knowledge of a connection between internal stress components in various regions of the ice cover is necessary. To develop reliable algorithms for estimates of ice action on engineering structures new experimental data are required to take into account both microscale (comparable with local ice inhomogeneities) and small-scale (kilometers) inhomogeneities of the ice cover. Studies of compacted ice (concentration N is nearly 1) are mostly important. This paper deals with the small-scale spatial distribution of internal stresses in the interaction zone between the ice covers of various concentrations and icebergs. The experimental conditions model a situation of the interaction between a wide structure and the ice cover. Field data on a drifting ice were collected during the Russian-US experiment in Antarctica WEDDELL-I in 1992.

  9. A rapidly declining perennial sea ice cover in the Arctic

    NASA Astrophysics Data System (ADS)

    Comiso, Josefino C.

    2002-10-01

    The perennial sea ice cover in the Arctic is shown to be declining at -9% per decade using satellite data from 1978 to 2000. A sustained decline at this rate would mean the disappearance of the multiyear ice cover during this century and drastic changes in the Arctic climate system. An apparent increase in the fraction of second year ice in the 1990s is also inferred suggesting an overall thinning of the ice cover. Surface ice temperatures derived from satellite data are negatively correlated with perennial ice area and are shown to be increasing at the rate of 1.2 K per decade. The latter implies longer melt periods and therefore decreasing ice volume in the more recent years.

  10. A Rapidly Declining Arctic Perennial Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.; Koblinsky, Chester J. (Technical Monitor)

    2002-01-01

    The perennial sea ice cover in the Arctic is shown to be declining at -8.9 plus or minus 2.0% per decade, using 22 years of satellite data. A sustained decline at this rate would mean the disappearance of the multiyear ice cover during this century and drastic changes in the seasonal characteristics of the Arctic ice cover. An apparent increase in the fraction of second year ice in the 1990s is also inferred suggesting an overall thinning of the ice cover while co-registered satellite surface temperatures show a warming trend of 0.8 plus or minus 0.6 K per decade in summer and a good correlation with the perennial ice data.

  11. Satellite Evidence for an Arctic Sea Ice Cover in Transformation.

    PubMed

    Johannessen; Shalina; Miles

    1999-12-01

    Recent research using microwave satellite remote sensing data has established that there has been a reduction of about 3 percent per decade in the areal extent of the Arctic sea ice cover since 1978, although it is unknown whether the nature of the perennial ice pack has changed. These data were used to quantify changes in the ice cover's composition, revealing a substantial reduction of about 14 percent in the area of multiyear ice in winter during the period from 1978 to 1998. There also appears to be a strong correlation between the area of multiyear ice and the spatially averaged thickness of the perennial ice pack, which suggests that the satellite-derived areal decreases represent substantial rather than only peripheral changes. If this apparent transformation continues, it may lead to a markedly different ice regime in the Arctic, altering heat and mass exchanges as well as ocean stratification. PMID:10583953

  12. A Digital Low Dispersion Spectral Library Covering the 3500-7500 Å Region Using the SAAO Radcliffe 1.9 m Telescope's Cassegrain Spectrograph

    NASA Astrophysics Data System (ADS)

    James, David J.

    2013-09-01

    We have created a digital spectral library, using low resolution optical spectra, of photometric and spectral standard stars. The data were acquired using the Cassegrain spectrograph installed on the 1.9 m Radcliffe telescope at the South African Astronomical Observatory. The library consists of optical wavelength (sime3500-7500 Å) spectra for main sequence and giant stars encompassing those most commonly observed in the Galaxy, namely the late-B, A, F, G, K, and early- to mid-M stars. We intend that our standard star spectra will be especially useful for spectral classification of stars in the field and Galactic clusters alike and will have high pedagogic value when included into representative "Introductory Astronomy" or "Stellar Astronomy" curricula for undergraduate astronomy major and minor programs. We exploit the spectral library in order to derive spectral types for 76 optically and X-ray selected members of the young open cluster NGC 6475. Comparison of spectral type, optical and infrared photometric data to theoretical colors derived from spectral type show that the reddening of the cluster is EBV = 0.068 ± 0.012 (1σ = 0.058), a vector consistent with earlier surveys. Our analysis also highlights the utility of such spectra in rejecting cluster nonmembers, thereby allowing the creation of a clean sample of bona fide cluster members for follow-up science observations.

  13. Exploring Ice-Covered Waters with an Autonomous Underwater Vehicle

    NASA Astrophysics Data System (ADS)

    Hamilton, A.; Forrest, A.; Laval, B.

    2009-12-01

    Reductions in lake- and sea-ice extent and ice-shelf collapse in both the Arctic and Antarctic are exposing underlying waters to significant increases in light and heat penetration, altering water mass properties and current dynamics. These physical changes likely drive rapid biological evolution and succession in associated marine ecosystems, influencing the biogeochemical transformation of matter and energy in previously ice-covered waters. However the unaltered, or pristine state of waters covered by thick (>3m) or moving ice is poorly understood, as these environments are largely inaccessible to investigation from the surface. Advancement of autonomous underwater vehicle (AUV) technology now allows these vehicles to be utilized as platforms for polar oceanographic research, permitting exploration of previously uncharted ice-covered waters. UBC-Gavia, a 2.5 m long AUV operated out of the University of British Columbia, has been involved in several under-ice (both lake and sea) missions making it one of the few such vehicles to be successfully deployed under-ice. Results of three under-ice case studies are presented in this work: Pavilion Lake, Canada - an ice-covered temperate lake; Lake Thingvallavatn, Iceland - a subarctic lake experiencing spring ice break-up; and Joliffe Bay, Lincoln Sea, Canadian High Arctic - a near shore multi- and first-year sea ice environment. The focus of each of these case studies was to examine physical processes in the water column under ice (e.g. radiatively driven convection) using a Conductivity-Temperature-Depth (CTD) profiler mounted on the front of the vehicle. In addition, various engineering lessons were acquired in order to adapt the vehicle for deployment, operation and recovery in ice-covered waters. The next phase of research will also be presented; a planned deployment of UBC-Gavia near the McMurdo Ice Shelf in Antarctica, to map under ice structure, ice thickness and convective processes in the water column. These

  14. Seasonal Evolution of Snow Cover on Antarctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Maksym, T.; Leonard, K. C.; Trujillo, E.; White, S.; Wilkinson, J.; Stammerjohn, S. E.; Mei, J.

    2015-12-01

    Snow cover on Antarctic sea ice plays a key role in the evolution of ice thickness, its estimation from space-borne altimeters, and structuring of sea ice ecosystems. Yet until recently, there have been very few continuous observations of the seasonal evolution of snow cover on Antarctic sea ice. We present observations of the seasonal evolution of the snow cover from ice mass balance buoys (IMBs) deployed between 2009 and 2013 in the Weddell, Bellingshausen, and Amundsen Seas and the East Antarctic sector. In addition, automatic weather stations that provided direct observations of precipitation, accumulation, and blowing snow were deployed alongside IMBs in October, 2012 in the East Antarctic during the Sea Ice Physics and Ecosystem eXperiment II (SIPEX II), and in July and August, 2013 in the Weddell Sea during the Antarctic Winter Ecosystem and Climate Study (AWECS). These buoys show markedly different snow accumulation regimes in each sector, although accumulation is also strongly controlled by the local morphology of the ice cover through snow erosion and deposition during blowing snow and precipitations events. Comparisons of snow accumulation from these buoys with estimates from atmospheric reanalysis and the direct measurements of precipitation and blowing snow show that precipitation is generally not a good estimator of snow accumulation. Improved treatment of blowing snow is needed if sea ice models are to accurately simulate Antarctic snow and sea ice mass balance. In summer, melting of the snow pack is relatively modest in most cases. Nevertheless, it appears to play an important role in governing sea ice hydrology and sea ice surface properties, and hence may play an important role in modulating sea ice primary productivity.

  15. 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

  16. Evaporation of ice in planetary atmospheres - Ice-covered rivers on Mars

    NASA Technical Reports Server (NTRS)

    Wallace, D.; Sagan, C.

    1979-01-01

    The existence of ice covered rivers on Mars is considered. It is noted that the evaporation rate of water ice on the surface of a planet with an atmosphere involves an equilibrium between solar heating and radiative and evaporative cooling of the ice layer. It is determined that even with a mean Martian insolation rate above the ice of approximately 10 to the -8th g per sq cm/sec, a flowing channel of liquid water will be covered by ice which evaporates sufficiently slowly that the water below can flow for hundreds of kilometers even with modest discharges. Evaporation rates are calculated for a range of frictional velocities, atmospheric pressures, and insolations and it is suggested that some subset of observed Martian channels may have formed as ice-choked rivers. Finally, the exobiological implications of ice covered channels or lakes on Mars are discussed.

  17. Microwave remote sensing of the Southern Ocean ice cover

    NASA Astrophysics Data System (ADS)

    Comiso, Josefino C.; Grenfell, Thomas C.; Lange, Manfred; Lohanick, Alan W.; Moore, Richard K.; Wadhams, Peter

    The Southern Ocean sea ice cover grows dramatically to about 20 × 106 km2 in the spring and breaks up abruptly to about 4 × 106 km2 in the summer (e.g., Zwally et al. [1983b]). This makes it one of the most seasonally variable climate parameters on the surface of the globe. Compared to the Northern Hemisphere, the ice cover in the Southern Ocean is about 20% greater at its maximum extent [Comiso and Zwally, 1984; Gloersen and Campbell, 1988]. By virtue of its size alone, the impact of the Southern Ocean ice cover on the regional and global climate can be considerable, since sea ice drastically changes surface albedo and roughness and insulates the ocean from the atmosphere. Seasonal and interannual variations in the spatial distribution of sea ice also cause the redistribution of salts, which, in turn, cause changes in the vertical stratification of the ocean. Compared to the Arctic, the environmental geographical background for sea ice in the Antarctic is also very different. Land surrounds most of the southern limits of the Arctic ice cover, whereas in the Antarctic, there is no corresponding land boundary in the north. The Southern Ocean ice cover is more divergent since it is more vulnerable to dynamic forcing than its Arctic counterpart. Accurate estimation of the percentage of open water is important because heat and salinity fluxes increase considerably even with just small increases in the fraction of open water or new ice [Maykut, 1978; Allison, 1981]. These fluxes are, in turn, closely linked with bottom water formation, ocean circulation, and momentum exchange between the ocean and the atmosphere. Oceanic heat flux is also believed to be a major determinant of ice growth rate [Bagriantsev et. al., 1989].

  18. Large Decadal Decline of the Arctic Multiyear Ice Cover

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2011-01-01

    The perennial ice area was drastically reduced to 38% of its climatological average in 2007 but recovered somewhat in 2008, 2009 and 2010 with the areas being 10%, 24%, and 11% higher than in 2007, respectively. However, the trends in the extent and area remain strongly negative at -12.2% and -13.5 %/decade, respectively. The thick component of the perennial ice, called multiyear ice, as detected by satellite data in the winters of 1979 to 2011 was studied and results reveal that the multiyear ice extent and area are declining at an even more rapid rate of -15.1% and -17.2 % per decade, respectively, with record low value in 2008 followed by higher values in 2009, 2010 and 2011. Such high rate in the decline of the thick component of the Arctic ice cover means a reduction in average ice thickness and an even more vulnerable perennial ice cover. The decline of the multiyear ice area from 2007 to 2008 was not as strong as that of the perennial ice area from 2006 to 2007 suggesting a strong role of second year ice melt in the latter. The sea ice cover is shown to be strongly correlated with surface temperature which is increasing at about three times global average in the Arctic but appears weakly correlated with the AO which controls the dynamics of the region. An 8 to 9-year cycle is apparent in the multiyear ice record which could explain in part the slight recovery in the last three years.

  19. Large Decadal Decline of the Arctic Multiyear Ice Cover

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2012-01-01

    The perennial ice area was drastically reduced to 38% of its climatological average in 2007 but recovered slightly in 2008, 2009, and 2010 with the areas being 10%, 24%, and 11% higher than in 2007, respectively. However, trends in extent and area remained strongly negative at -12.2% and -13.5% decade (sup -1), respectively. The thick component of the perennial ice, called multiyear ice, as detected by satellite data during the winters of 1979-2011 was studied, and results reveal that the multiyear ice extent and area are declining at an even more rapid rate of -15.1% and -17.2% decade(sup -1), respectively, with a record low value in 2008 followed by higher values in 2009, 2010, and 2011. Such a high rate in the decline of the thick component of the Arctic ice cover means a reduction in the average ice thickness and an even more vulnerable perennial ice cover. The decline of the multiyear ice area from 2007 to 2008 was not as strong as that of the perennial ice area from 2006 to 2007, suggesting a strong role of second-year ice melt in the latter. The sea ice cover is shown to be strongly correlated with surface temperature, which is increasing at about 3 times the global average in the Arctic but appears weakly correlated with the Arctic Oscillation (AO), which controls the atmospheric circulation in the region. An 8-9-yr cycle is apparent in the multiyear ice record, which could explain, in part, the slight recovery in the last 3 yr.

  20. Cladoceran zooplankton abundance under clear and snow-covered ice

    USGS Publications Warehouse

    DeBates, T.J.; Chipps, S.R.; Ward, M.C.; Werlin, K.B.; Lorenzen, P.B.

    2003-01-01

    We described the distribution of cladoceran zooplankton under the ice in a natural, glacial lake. Local light availability apparently altered the spatial distribution of cladocerans. Light levels measured under snow-covered areas (0.178 lux) were an order of magnitude less than those measured at the same depth under clear ice (1.750 lux). Cladoceran density under snow-covered areas was significantly higher (Bosmina spp.=3.34/L; Daphnia spp.=0.61/L) than cladoceran abundance under clear ice (Bosmina spp.=0.91/L; Daphnia spp.=0.19/L).

  1. Perspectives on the Arctic's shrinking sea-ice cover.

    PubMed

    Serreze, Mark C; Holland, Marika M; Stroeve, Julienne

    2007-03-16

    Linear trends in arctic sea-ice extent over the period 1979 to 2006 are negative in every month. This ice loss is best viewed as a combination of strong natural variability in the coupled ice-ocean-atmosphere system and a growing radiative forcing associated with rising concentrations of atmospheric greenhouse gases, the latter supported by evidence of qualitative consistency between observed trends and those simulated by climate models over the same period. Although the large scatter between individual model simulations leads to much uncertainty as to when a seasonally ice-free Arctic Ocean might be realized, this transition to a new arctic state may be rapid once the ice thins to a more vulnerable state. Loss of the ice cover is expected to affect the Arctic's freshwater system and surface energy budget and could be manifested in middle latitudes as altered patterns of atmospheric circulation and precipitation. PMID:17363664

  2. Abrupt Decline in the Arctic Winter Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2007-01-01

    Maximum ice extents in the Arctic in 2005 and 2006 have been observed to be significantly lower (by about 6%) than the average of those of previous years starting in 1979. Since the winter maxima had been relatively stable with the trend being only about -1.5% per decade (compared to about -10% per decade for the perennial ice area), this is a significant development since signals from greenhouse warming are expected to be most prominent in winter. Negative ice anomalies are shown to be dominant in 2005 and 2006 especially in the Arctic basin and correlated with winds and surface temperature anomalies during the same period. Progressively increasing winter temperatures in the central Arctic starting in 1997 is observed with significantly higher rates of increase in 2005 and 2006. The Atlantic Oscillation (AO) indices correlate weakly with the sea ice and surface temperature anomaly data but may explain the recent shift in the perennial ice cover towards the western region. Results suggest that the trend in winter ice is finally in the process of catching up with that of the summer ice cover.

  3. Measurement of flow under ice covers in North America

    USGS Publications Warehouse

    Walker, J.F.; Wang, D.

    1997-01-01

    A substantial proportion of natural streams in the United States and Canada are affected by ice cover during the winter. To substantiate the currently used procedures for measuring streamflow during the winter, the U.S. Geological Survey (USGS) and Water Survey of Canada (WSC) began independent, coordinated programs for research and development related to the measurement of streamflow under an ice cover. Detailed measurements of vertical velocity profiles under ice covers in field settings were collected by each agency in accordance with standardized guidelines. The data were then compiled into a joint database. This paper presents a description of the two measurement programs, describes the structure and format of the joint database, and provides preliminary summaries of the data. Ongoing research efforts by the USGS and WSC are described briefly to give examples of the use of the joint database.

  4. Variability and Anomalous Trends in the Global Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2012-01-01

    The advent of satellite data came fortuitously at a time when the global sea ice cover has been changing rapidly and new techniques are needed to accurately assess the true state and characteristics of the global sea ice cover. The extent of the sea ice in the Northern Hemisphere has been declining by about -4% per decade for the period 1979 to 2011 but for the period from 1996 to 2010, the rate of decline became even more negative at -8% per decade, indicating an acceleration in the decline. More intriguing is the drastically declining perennial sea ice area, which is the ice that survives the summer melt and observed to be retreating at the rate of -14% per decade during the 1979 to 2012 period. Although a slight recovery occurred in the last three years from an abrupt decline in 2007, the perennial ice extent was almost as low as in 2007 in 2011. The multiyear ice, which is the thick component of the perennial ice and regarded as the mainstay of the Arctic sea ice cover is declining at an even higher rate of -19% per decade. The more rapid decline of the extent of this thicker ice type means that the volume of the ice is also declining making the survival of the Arctic ice in summer highly questionable. The slight recovery in 2008, 2009 and 2010 for the perennial ice in summer was likely associated with an apparent cycle in the time series with a period of about 8 years. Results of analysis of concurrent MODIS and AMSR-E data in summer also provide some evidence of more extensive summer melt and meltponding in 2007 and 2011 than in other years. Meanwhile, the Antarctic sea ice cover, as observed by the same set of satellite data, is showing an unexpected and counter intuitive increase of about 1 % per decade over the same period. Although a strong decline in ice extent is apparent in the Bellingshausen/ Amundsen Seas region, such decline is more than compensated by increases in the extent of the sea ice cover in the Ross Sea region. The results of analysis of

  5. Modelling Lake Ice and the Future of the Arctic Lake Ice Cover

    NASA Astrophysics Data System (ADS)

    Brown, L.; Derksen, C.; Duguay, C. R.; Samuelsson, P.

    2014-12-01

    Lake ice cover is a robust indicator of climate variability and change. Recent studies have demonstrated that ice break-up dates, in particular, have been occurring earlier in many parts of the Northern Hemisphere over the last 50 years in response to warmer climatic conditions in the winter and spring seasons. It is important to compare the observed impacts of variability and trends in air temperature and precipitation over the last five decades, with projected trends from climate models in order to quantify future changes in the timing and duration of ice cover (and ice thickness) on Arctic lakes. The Canadian Lake Ice Model (CLIMo) was used to simulate both the contemporary and future lake ice conditions throughout the Arctic. The contemporary climate simulations were driven by both ECMWF ERA-Interim and ERA-40 reanalysis data (1958 - 2011). The future simulations were driven by CORDEX scenarios (Arc-44, 1951-2100), which were produced by the Rossby Centre regional atmospheric model (RCA4) and the Canadian Centre for Climate Modelling and Analysis Canadian Regional Climate Model (CanRCM4). An ensemble of simulated lake ice data was created from five regional model output scenarios using the RCP8.5 emission scenario for the future climate conditions. The 30-year mean ice break-up, freeze-up, and thickness was compared between the scenarios for the entire Arctic region for 1981 - 2010 and 2071 - 2100 to examine the possible changes to the ice cover regimes. Results suggest a mean pan-Arctic reduction in ice cover duration ranging from 42 - 57 days, and a reduction in ice thickness ranging from 0.4 m to 0.7 m, depending on the snow conditions and lake depth used in the simulation. These projected changes could have an important feedback effect on energy, water, and biogeochemical cycling throughout the pan-Arctic region.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  7. Ocean wave transmission and reflection by viscoelastic ice covers

    NASA Astrophysics Data System (ADS)

    Zhao, Xin; Shen, Hayley H.

    2015-08-01

    Modeling ice covers as viscoelastic continua, Zhao and Shen, (2013) applied a two-mode approximate method to determine the transmission and reflection between two different ice covers. This approximate solution considered only two modes of the dispersion relation. In addition, the horizontal boundary conditions were simplified by matching mean values over the interfaces. In this study, we employ a variational method (Fox and Squire, (1990)) to calculate the wave transmission and reflection from two connecting viscoelastic ice covers of different properties. The variational approach minimizes the overall error function at the interface of two ice covers, hence is more rigorous than the previous approximate method that minimized the difference between mean values at the interface. The effect of additional travelling and evanescent modes are also investigated. We compare results from different matching methods, as well as the effects of including additional modes. From this study, we find that additional modes do not always improve the results for our model. For all cases tested, two modes appear to be sufficient. These two modes represent the open-water-like and the elastic-pressure wave-like behavior. The two-mode approximate method and the variational method have similar results except at very short wave periods.

  8. NASA IceBridge: Scientific Insights from Airborne Surveys of the Polar Sea Ice Covers

    NASA Astrophysics Data System (ADS)

    Richter-Menge, J.; Farrell, S. L.

    2015-12-01

    The NASA Operation IceBridge (OIB) airborne sea ice surveys are designed to continue a valuable series of sea ice thickness measurements by bridging the gap between NASA's Ice, Cloud and Land Elevation Satellite (ICESat), which operated from 2003 to 2009, and ICESat-2, which is scheduled for launch in 2017. Initiated in 2009, OIB has conducted campaigns over the western Arctic Ocean (March/April) and Southern Oceans (October/November) on an annual basis when the thickness of sea ice cover is nearing its maximum. More recently, a series of Arctic surveys have also collected observations in the late summer, at the end of the melt season. The Airborne Topographic Mapper (ATM) laser altimeter is one of OIB's primary sensors, in combination with the Digital Mapping System digital camera, a Ku-band radar altimeter, a frequency-modulated continuous-wave (FMCW) snow radar, and a KT-19 infrared radiation pyrometer. Data from the campaigns are available to the research community at: http://nsidc.org/data/icebridge/. This presentation will summarize the spatial and temporal extent of the OIB campaigns and their complementary role in linking in situ and satellite measurements, advancing observations of sea ice processes across all length scales. Key scientific insights gained on the state of the sea ice cover will be highlighted, including snow depth, ice thickness, surface roughness and morphology, and melt pond evolution.

  9. Regional Changes in the Sea Ice Cover and Ice Production in the Antarctic

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2011-01-01

    Coastal polynyas around the Antarctic continent have been regarded as sea ice factories because of high ice production rates in these regions. The observation of a positive trend in the extent of Antarctic sea ice during the satellite era has been intriguing in light of the observed rapid decline of the ice extent in the Arctic. The results of analysis of the time series of passive microwave data indicate large regional variability with the trends being strongly positive in the Ross Sea, strongly negative in the Bellingshausen/Amundsen Seas and close to zero in the other regions. The atmospheric circulation in the Antarctic is controlled mainly by the Southern Annular Mode (SAM) and the marginal ice zone around the continent shows an alternating pattern of advance and retreat suggesting the presence of a propagating wave (called Antarctic Circumpolar Wave) around the circumpolar region. The results of analysis of the passive microwave data suggest that the positive trend in the Antarctic sea ice cover could be caused primarily by enhanced ice production in the Ross Sea that may be associated with more persistent and larger coastal polynyas in the region. Over the Ross Sea shelf, analysis of sea ice drift data from 1992 to 2008 yields a positive rate-of-increase in the net ice export of about 30,000 km2 per year. For a characteristic ice thickness of 0.6 m, this yields a volume transport of about 20 km3/year, which is almost identical, within error bars, to our estimate of the trend in ice production. In addition to the possibility of changes in SAM, modeling studies have also indicated that the ozone hole may have a role in that it causes the deepening of the lows in the western Antarctic region thereby causing strong winds to occur offthe Ross-ice shelf.

  10. Evaporation of ice in planetary atmospheres: Ice-covered rivers on Mars

    NASA Technical Reports Server (NTRS)

    Wallace, D.; Sagan, C.

    1978-01-01

    The evaporation rate of water ice on the surface of a planet with an atmosphere involves an equilibrium between solar heating and radiative and evaporative cooling of the ice layer. The thickness of the ice is governed principally by the solar flux which penetrates the ice layer and then is conducted back to the surface. Evaporation from the surface is governed by wind and free convection. In the absence of wind, eddy diffusion is caused by the lower density of water vapor in comparison to the density of the Martian atmosphere. For mean martian insolations, the evaporation rate above the ice is approximately 10 to the minus 8th power gm/sq cm/s. Evaporation rates are calculated for a wide range of frictional velocities, atmospheric pressures, and insolations and it seems clear that at least some subset of observed Martian channels may have formed as ice-chocked rivers. Typical equilibrium thicknesses of such ice covers are approximately 10m to 30 m; typical surface temperatures are 210 to 235 K.

  11. Nature and History of Cenozoic Polar Ice Covers: The Case of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Spielhagen, R.; Thiede, J.

    2009-04-01

    The nature of the modern climate System is characterized by steep temperature gradients between the tropical and polar climatic zones and finds its most spectacular expression in the formation of ice caps in high Northern and Southern latitudes. While polar regions of Planet Earth have been glaciated repeatedly in the long course of their geological history, the Cenozoic transition from a „greenhouse" to an „icehouse" has in fact produced a unique climatic scenario with bipolar glacation, different from all previous glacial events. The Greenland ice sheet is a remainder of the Northern Hemisphere last glacial maximum ice sheets and represents hence a spectacular anomaly. Geological records from Tertiary and Quaternary terrestrial and oceanic sections have documented the presence of ice caps and sea ice covers both on the Southern as well on the Northern hemisphere since Eocene times, aqpprox. 45 Mio. years ago. While this was well known in the case of Antarctica already for some time, previous ideas about the origin of Northern hemisphere glaciation during Pliocene times (approx. 2-3 Mio. years ago) have been superceded by the dramatic findings of coarse, terrigenous ice rafted detritus in Eocene sediments from Lomonosov Ridge (close to the North Pole) apparently slightly older than the oldest Antarctic records of ice rafting.The histories of the onset of Cenozoic glaciation in high Northern and Southern latitudes remain enigmatic and are presently subjects of international geological drilling projects, with prospects to reveal some of their secrets over the coming decades. By virtue of the physical porperties of ice and the processes controlling the dynamics of the turn-over of the ice-sheets only young records of glacial ice caps on Antarctica and on Greemnland have been preserved, on Greenland with ice probably not older than a few hundred thousand years, on Antarctica potentially as old as 1.5-2 Mio. years. Deep-sea cores with their records od ice

  12. Phytoplankton spring bloom beneath heavily snow-covered arctic sea ice during the N-ICE2015 cruise

    NASA Astrophysics Data System (ADS)

    Assmy, Philipp; Fernández-Méndez, Mar; Olsen, Lasse M.; Kauko, Hanna; Duarte, Pedro; Mundy, Christopher J.; Hop, Haakon; Fransson, Agneta; Chierici, Melissa; Gerland, Sebastian; Granskog, Mats A.; Hudson, Stephen R.; Roesel, Anja; Meyer, Amelie; Hughes, Nick; Steen, Harald

    2016-04-01

    The arctic icescape is rapidly transforming from a thick multi-year ice cover to a thinner and largely seasonal first-year ice cover with significant consequences for Arctic primary production. Recent studies have reported extensive phytoplankton blooms beneath ponded sea ice during summer, indicating that satellite-based arctic net primary production estimates may be significantly underestimated. We studied phytoplankton seasonal dynamics under changing sea-ice and snow conditions in the drifting pack-ice north of Svalbard from 11 January to 24 June 2015 during the Norwegian Young Sea ICE cruise (N-ICE2015). N-ICE2015 provided a unique time-series of under-ice bloom dynamics during the winter-spring transition in the high Arctic pack-ice ecosystem. Phytoplankton productivity stayed low throughout winter and early spring. By late May a large under-ice bloom (>300 mg Chl a m-2) dominated by Phaeocystis pouchetii developed over the Yermak plateau underneath 1.1 - 1.3 m thick sea ice and 0.3 - 0.5 m thick snow cover. The circulation characteristics over the plateau indicate that the bloom developed in situ and was not advected. The high lead activity, characteristic for the area, apparently provided enough open or thin ice covered area for sufficient light to penetrate into the underlying water column and initiate and sustain the bloom, despite the thick snow cover. Our observation of a spring under-ice phytoplankton bloom extends the spatial and temporal scale of under-ice blooms and indicates that these phenomena might become increasingly important in the future Arctic under changing sea-ice but also snow dynamics.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  15. Impacts of the Variability of Ice Types on the Decline of the Arctic Perennial Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2005-01-01

    The observed rapid decline in the Arctic perennial ice cover is one of the most remarkable signal of change in the Arctic region. Updated data now show an even higher rate of decline of 9.8% per decade than the previous report of 8.9% per decade mainly because of abnormally low values in the last 4 years. To gain insights into this decline, the variability of the second year ice, which is the relatively thin component of the perennial ice cover, and other ice types is studied. The perennial ice cover in the 1990s was observed to be highly variable which might have led to higher production of second year ice and may in part explain the observed ice thinning during the period and triggered further decline. The passive microwave signature of second year ice is also studied and results show that while the signature is different from that of the older multiyear ice, it is surprisingly more similar to that of first year ice. This in part explains why previous estimates of the area of multiyear ice during the winter period are considerably lower than the area of the perennial ice cover during the preceding summer. Four distinct clusters representing radiometrically different types have been identified using multi-channel cluster analysis of passive microwave data. Data from two of these clusters, postulated to come from second year and older multiyear ice regions are also shown to have average thicknesses of 2.4 and 4.1 m, respectively, indicating that the passive microwave data may contain some ice thickness information that can be utilized for mass balance studies. The yearly anomaly maps indicate high gains of first year ice cover in the Arctic during the last decade which means higher production of second year ice and fraction of this type in the declining perennial ice cover. While not the only cause, the rapid decline in the perennial ice cover is in part caused by the increasing fractional component of the thinner second year ice cover that is very vulnerable to

  16. Physical and Radiative Characteristic and Long-term Variability of the Okhotsk Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Nishio, Fumihiko; Comiso, Josefino C.; Gersten, Robert; Nakayama, Masashige; Ukita, Jinro; Gasiewski, Al; Stanko, Boba; Naoki, Kazuhiro

    2008-01-01

    Much of what we know about the large scale characteristics of the Okhotsk Sea ice cover has been provided by ice concentration maps derived from passive microwave data. To understand what satellite data represent in a highly divergent and rapidly changing environment like the Okhotsk Sea, we take advantage of concurrent satellite, aircraft, and ship data acquired on 7 February and characterized the sea ice cover at different scales from meters to hundreds of kilometers. Through comparative analysis of surface features using co-registered data from visible, infrared and microwave channels we evaluated the general radiative and physical characteristics of the ice cover as well as quantify the distribution of different ice types in the region. Ice concentration maps from AMSR-E using the standard sets of channels, and also only the 89 GHz channel for optimal resolution, are compared with aircraft and high resolution visible data and while the standard set provides consistent results, the 89 GHz provides the means to observe mesoscale patterns and some unique features of the ice cover. Analysis of MODIS data reveals that thick ice types represents about 37% of the ice cover indicating that young and new ice types represent a large fraction of the ice cover that averages about 90% ice concentration according to passive microwave data. These results are used to interpret historical data that indicate that the Okhotsk Sea ice extent and area are declining at a rapid rate of about -9% and -12 % per decade, respectively.

  17. A Lightweight Vertical Rosette for Deployment in Ice Covered Water

    NASA Astrophysics Data System (ADS)

    Smethie, W. M.; Chayes, D. N.; Perry, R. S.; Schlosser, P.

    2009-12-01

    Although remote sensing technology provides measurement capability for a number of water properties, there are important substances for which this technology does not currently exist and the only way to measure these substances is to collect water samples and return the samples to the lab. In the Arctic Ocean water samples are difficult to obtain from ships because of the extensive ice cover and thick pressure ridges. However, the ice provides a landing platform for aircraft, which can rapidly cover long distances. Aircraft have been used for sampling the Arctic Ocean for the past half-century using bottles and internally recording CTDs attached to a cable and lowered through leads or holes drilled in the ice. The routine CTD/rosette technology used for sampling from ships measures profiles of temperature, salinity, oxygen as well as other substances in situ, displays the data in real time for choosing depths to obtain water samples and the water samples are then collected with the rosette. These systems are too heavy and bulky to deploy from aircraft. We have developed a lightweight modular CTD/rosette system that is deployed through a 12-inch diameter hole drilled in the ice. The modules are connected together physically and electrically with the water bottle modules, which contain four 4-liter bottles each, stacked on top of the CTD module. The CTD traces are displayed on a laptop computer and the bottles are tripped using modified Seabird controllers and a melt-lanyard tripping mechanism. We have used this system for several years with Twin Otter fixed wing aircraft as part of the Switchyard Project, sampling a line of stations annually in the heavily ice covered region between Alert and the North Pole. Casts are carried out in a tent connected to the airplane using a lightweight winch mounted in the airplane. At the completion of a cast, the water modules are placed in a cooler with bags of snow to provide thermal stability at about 0°C and the end caps

  18. Geometric effects of an inhomogeneous sea ice cover on the under ice light field

    NASA Astrophysics Data System (ADS)

    Katlein, Christian; Perovich, Donald; Nicolaus, Marcel

    2016-02-01

    Light measurements in the ocean provide crucial information about the energy fluxes in the climate and ecosystem. Currently radiative transfer problems are usually considered in horizontally homogeneous layers although it is known to be a crude assumption in many cases. In this paper, we examine the effects of a horizontally inhomogeneous sea ice layer on the light field in the water underneath. We implemented a three dimensional model, capable to simulate the light field underneath arbitrary surface geometries using ray optics. The results show clear effects of the measurement geometry on measured fluxes obtained with different sensor types, which need to be taken into account for the correct interpretation of the data. Radiance sensors are able to better sense the spatial variability of ice optical properties as compared to irradiance sensors. Furthermore we show that the determination of the light extinction coefficient of water from vertical profiles is complicated under a horizontally inhomogeneous ice cover. This uncertainty in optical properties of the water, as well as the measurement geometry also limits the possibility to correct light measurements taken at depth for the influence of water in between the sea ice and the sensor.

  19. Physical and Radiative Characteristics and Long Term Variability of the Okhotsk Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Nishio, Fumihiko; Comiso, Josefino C.; Gersten, Robert; Nakayama, Masashige; Ukita, Jinro; Gasiewski, Al; Stanko, Boba; Naoki, Kazuhiro

    2007-01-01

    Much of what we know about the large scale characteristics of the Okhotsk Sea ice cover comes from ice concentration maps derived from passive microwave data. To understand what these satellite data represents in a highly divergent and rapidly changing environment like the Okhotsk Sea, we analyzed concurrent satellite, aircraft, and ship data and characterized the sea ice cover at different scales from meters to tens of kilometers. Through comparative analysis of surface features using co-registered data from visible, infrared and microwave channels we evaluated how the general radiative and physical characteristics of the ice cover changes as well as quantify the distribution of different ice types in the region. Ice concentration maps from AMSR-E using the standard sets of channels, and also only the 89 GHz channel for optimal resolution, are compared with aircraft and high resolution visible data and while the standard set provides consistent results, the 89 GHz provides the means to observe mesoscale patterns and some unique features of the ice cover. Analysis of MODIS data reveals that thick ice types represents about 37% of the ice cover indicating that young and new ice represent a large fraction of the lice cover that averages about 90% ice concentration, according to passive microwave data. A rapid decline of -9% and -12 % per decade is observed suggesting warming signals but further studies are required because of aforementioned characteristics and because the length of the ice season is decreasing by only 2 to 4 days per decade.

  20. Stress-strain state of ice cover during aircraft takeoff and landing

    NASA Astrophysics Data System (ADS)

    Pogorelova, A. V.; Kozin, V. M.; Matyushina, A. A.

    2015-09-01

    We consider the linear unsteady motion of an IL-76TD aircraft on ice. Water is treated as an ideal incompressible liquid, and the liquid motion is considered potential. Ice cover is modeled by an initially unstressed uniform isotropic elastic plate, and the load exerted by the aircraft on the ice cover with consideration of the wing lift is modeled by regions of distributed pressure of variable intensity, arranged under the aircraft landing gear. The effect of the thickness and elastic modulus of the ice plate, takeoff and landing regimes on stress-strain state of the ice cover used as a runway.

  1. Is Ice-Rafted Sediment in a North Pole Marine Record Evidence for Perennial Sea-ice Cover?

    NASA Technical Reports Server (NTRS)

    Tremblay, L.B.; Schmidt, G.A.; Pfirman, S.; Newton, R.; DeRepentigny, P.

    2015-01-01

    Ice-rafted sediments of Eurasian and North American origin are found consistently in the upper part (13 Ma BP to present) of the Arctic Coring Expedition (ACEX) ocean core from the Lomonosov Ridge, near the North Pole (approximately 88 degrees N). Based on modern sea-ice drift trajectories and speeds, this has been taken as evidence of the presence of a perennial sea-ice cover in the Arctic Ocean from the middle Miocene onwards. However, other high latitude land and marine records indicate a long-term trend towards cooling broken by periods of extensive warming suggestive of a seasonally ice-free Arctic between the Miocene and the present. We use a coupled sea-ice slab-ocean model including sediment transport tracers to map the spatial distribution of ice-rafted deposits in the Arctic Ocean. We use 6 hourly wind forcing and surface heat fluxes for two different climates: one with a perennial sea-ice cover similar to that of the present day and one with seasonally ice-free conditions, similar to that simulated in future projections. Model results confirm that in the present-day climate, sea ice takes more than 1 year to transport sediment from all its peripheral seas to the North Pole. However, in a warmer climate, sea-ice speeds are significantly faster (for the same wind forcing) and can deposit sediments of Laptev, East Siberian and perhaps also Beaufort Sea origin at the North Pole. This is primarily because of the fact that sea-ice interactions are much weaker with a thinner ice cover and there is less resistance to drift. We conclude that the presence of ice-rafted sediment of Eurasian and North American origin at the North Pole does not imply a perennial sea-ice cover in the Arctic Ocean, reconciling the ACEX ocean core data with other land and marine records.

  2. 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.

  3. 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

  4. Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation

    NASA Astrophysics Data System (ADS)

    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.

  5. Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation.

    PubMed

    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

  6. Reconstructing past sea ice cover of the Northern Hemisphere from dinocyst assemblages: status of the approach

    NASA Astrophysics Data System (ADS)

    de Vernal, Anne; Rochon, André; Fréchette, Bianca; Henry, Maryse; Radi, Taoufik; Solignac, Sandrine

    2013-11-01

    Dinocysts occur in a wide range of environmental conditions, including polar areas. We review here their use for the reconstruction of paleo sea ice cover in such environments. In the Arctic Ocean and subarctic seas characterized by dense sea ice cover, Islandinium minutum, Islandinium? cezare, Echinidinium karaense, Polykrikos sp. var. Arctic, Spiniferites elongatus-frigidus and Impagidinium pallidum are common and often occur with more cosmopolitan taxa such as Operculodinium centrocarpum sensu Wall & Dale, cyst of Pentapharsodinium dalei and Brigantedinium spp. Canonical correspondence analyses conducted on dinocyst assemblages illustrate relationships with sea surface parameters such as salinity, temperature, and sea ice cover. The application of the modern analogue technique permits quantitative reconstruction of past sea ice cover, which is expressed in terms of seasonal extent of sea ice cover (months per year with more than 50% of sea ice concentration) or mean annual sea ice concentration (in tenths). The accuracy of reconstructions or root mean square error of prediction (RMSEP) is ±1.1 over 10, which corresponds to perennial sea ice. Such an error is close to the interannual variability (standard deviation) of observed sea ice cover. Mismatch between the time interval of instrumental data used as reference (1953-2000) and the time interval represented by dinocyst populations in surface sediment samples, which may cover decades if not centuries, is another source of error. Despite uncertainties, dinocyst assemblages are useful for making quantitative reconstruction of seasonal sea ice cover.

  7. High-resolution wave forecasting system for the seasonally ice-covered Baltic Sea

    NASA Astrophysics Data System (ADS)

    Tuomi, Laura; Lehtiranta, Jonni

    2016-04-01

    When forecasting surface waves in seasonally ice-covered seas, the inclusion of ice conditions in the modelling is important. The ice cover affects the propagation and also changes the fetch over which the waves grow. In wave models the ice conditions are often still given as a boundary condition and handled by excluding areas where the ice concentration exceeds a certain threshold value. The ice data used are typically based on satellite analysis or expert analysis of local Ice Services who combine data from different sources. This type of data is sufficiently accurate to evaluate the near-real time ice concentrations, but when making forecasts it is also important to account for the possible changes in ice conditions. For example in a case of a high wind situation, there can be rapid changes in the ice field, when the wind and waves may push the ice towards shores and cause fragmentation of ice field. To enhance handling of ice conditions in the Baltic Sea wave forecasts, utilisation of ice model data was studied. Ice concentration, thickness produced by FMI's operational ice model HELMI were used to provide ice data to wave model as follows: Wave model grid points where the ice concentration was more than or equal to 70% and the ice thickness more than1 cm, were excluded from calculations. Ice concentrations smaller than that were taken into account as additional grid obstructions by decreasing the wave energy passed from one grid cell to another. A challenge in evaluating wave forecast accuracy in partly ice covered areas it that there's typically no wave buoy data available, since the buoys have to be recovered well before the sea area freezes. To evaluate the accuracy of wave forecast in partially ice covered areas, significant wave heights from altimeter's ERS2, Envisat, Jason-1 and Jason-2 were extracted from Ifremer database. Results showed that the more frequent update of the ice data was found to improve the wave forecast especially during high wind

  8. Observation of Sea Ice Surface Thermal States Under Cloud Cover

    NASA Technical Reports Server (NTRS)

    Nghiem, S. V.; Perovich, D. K.; Gow, A. J.; Kwok, R.; Barber, D. G.; Comiso, J. C.; Zukor, Dorothy J. (Technical Monitor)

    2001-01-01

    Clouds interfere with the distribution of short-wave and long-wave radiations over sea ice, and thereby strongly affect the surface energy balance in polar regions. To evaluate the overall effects of clouds on climatic feedback processes in the atmosphere-ice-ocean system, the challenge is to observe sea ice surface thermal states under both clear sky and cloudy conditions. From laboratory experiments, we show that C-band radar (transparent to clouds) backscatter is very sensitive to the surface temperature of first-year sea ice. The effect of sea ice surface temperature on the magnitude of backscatter change depends on the thermal regimes of sea ice thermodynamic states. For the temperature range above the mirabilite (Na2SO4.10H20) crystallization point (-8.2 C), C-band data show sea ice backscatter changes by 8-10 dB for incident angles from 20 to 35 deg at both horizontal and vertical polarizations. For temperatures below the mirabilite point but above the crystallization point of MgCl2.8H2O (-18.0 C), relatively strong backwater changes between 4-6 dB are observed. These backscatter changes correspond to approximately 8 C change in temperature for both cases. The backscattering mechanism is related to the temperature which determines the thermodynamic distribution of brine volume in the sea ice surface layer. The backscatter is positively correlated to temperature and the process is reversible with thermodynamic variations such as diurnal insolation effects. From two different dates in May 1993 with clear and overcast conditions determined by the Advanced Very High Resolution Radiometer (AVHRR), concurrent Earth Resources Satellite 1 (ERS-1) C-band ice observed with increases in backscatter over first-year sea ice, and verified by increases in in-situ sea ice surface temperatures measured at the Collaborative-Interdisciplinary Cryosphere Experiment (C-ICE) site.

  9. Impact of snow cover on CO2 dynamics in Antarctic pack ice

    NASA Astrophysics Data System (ADS)

    Geilfus, N.-X.; Tison, J.-L.; Ackley, S. F.; Rysgaard, S.; Miller, L. A.; Delille, B.

    2014-06-01

    Temporal evolution of pCO2 profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows that the CO2 system in the ice was primarily controlled by physical and thermodynamic processes. During the survey, a succession of warming and cold events strongly influenced the physical, chemical and thermodynamic properties of the ice cover. Two sampling sites with contrasting characteristics of ice and snow thickness were sampled: one had little snow accumulation (from 8 to 25 cm) and larger temperature and salinity variations than the second site, where the snow cover was up to 38 cm thick and therefore better insulated the underlying sea ice. We confirm that each cooling/warming event was associated with an increase/decrease in the brine salinity, total alkalinity (TA), total dissolved inorganic carbon (TCO2), and in situ brine and bulk ice CO2 partial pressures (pCO2). Thicker snow covers muted these changes, suggesting that snow influences changes in the sea ice carbonate system through its impact on the temperature and salinity of the sea ice cover. During this survey, pCO2 was undersaturated with respect to the atmosphere both in situ, in the bulk ice (from 10 to 193 μatm), and in the brine (from 65 to 293 μatm), and the ice acted as a sink for atmospheric CO2 (up to 2.9 mmol m-2 d-1), despite the underlying supersaturated seawater (up to 462 μatm).

  10. Correlation and Trend Studies of the Sea Ice Cover and Surface Temperatures in the Arctic

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    Co-registered and continuous satellite data of sea ice concentrations and surface ice temperatures from 1981 to 1999 are analyzed to evaluate relationships between these two critical climate parameters and what they reveal in tandem about the changing Arctic environment. During the 18-year period, the actual Arctic ice area is shown to be declining at a rate of 3.1 +/- 0.4 % /decade while the surface ice temperature has been increasing at 0.4 +/- 0.2 K /decade. Yearly anomaly maps also show that the ice concentration anomalies are predominantly positive in the 1980s and negative in the 1990s while surface temperature anomalies were mainly negative in the 1980s and positive in the 1990s. The yearly ice concentration and surface temperature anomalies are shown to be highly correlated indicating a strong link especially in the seasonal region and around the periphery of the perennial ice cover. The surface temperature data are also especially useful in providing the real spatial scope of each warming (or cooling) phenomenon that usually extends beyond the boundaries of the sea ice cover. Studies of the temporal variability of the summer ice minimum also reveal that the perennial ice cover has been declining at the rate of 6.6% /decade while the summer surface ice temperature has been increasing at the rate of 1.3 K /decade. Moreover, high year-to-year fluctuations in the minimum ice cover in the 1990s may have caused reductions in average thickness of the Arctic sea ice cover.

  11. Is ice-rafted sediment in a North Pole marine record evidence for perennial sea-ice cover?

    PubMed

    Tremblay, L B; Schmidt, G A; Pfirman, S; Newton, R; DeRepentigny, P

    2015-10-13

    Ice-rafted sediments of Eurasian and North American origin are found consistently in the upper part (13 Ma BP to present) of the Arctic Coring Expedition (ACEX) ocean core from the Lomonosov Ridge, near the North Pole (≈88° N). Based on modern sea-ice drift trajectories and speeds, this has been taken as evidence of the presence of a perennial sea-ice cover in the Arctic Ocean from the middle Miocene onwards (Krylov et al. 2008 Paleoceanography 23, PA1S06. (doi:10.1029/2007PA001497); Darby 2008 Paleoceanography 23, PA1S07. (doi:10.1029/2007PA001479)). However, other high latitude land and marine records indicate a long-term trend towards cooling broken by periods of extensive warming suggestive of a seasonally ice-free Arctic between the Miocene and the present (Polyak et al. 2010 Quaternary Science Reviews 29, 1757-1778. (doi:10.1016/j.quascirev.2010.02.010)). We use a coupled sea-ice slab-ocean model including sediment transport tracers to map the spatial distribution of ice-rafted deposits in the Arctic Ocean. We use 6 hourly wind forcing and surface heat fluxes for two different climates: one with a perennial sea-ice cover similar to that of the present day and one with seasonally ice-free conditions, similar to that simulated in future projections. Model results confirm that in the present-day climate, sea ice takes more than 1 year to transport sediment from all its peripheral seas to the North Pole. However, in a warmer climate, sea-ice speeds are significantly faster (for the same wind forcing) and can deposit sediments of Laptev, East Siberian and perhaps also Beaufort Sea origin at the North Pole. This is primarily because of the fact that sea-ice interactions are much weaker with a thinner ice cover and there is less resistance to drift. We conclude that the presence of ice-rafted sediment of Eurasian and North American origin at the North Pole does not imply a perennial sea-ice cover in the Arctic Ocean, reconciling the ACEX ocean core data with

  12. Ice cover affects the growth of a stream-dwelling fish.

    PubMed

    Watz, Johan; Bergman, Eva; Piccolo, John J; Greenberg, Larry

    2016-05-01

    Protection provided by shelter is important for survival and affects the time and energy budgets of animals. It has been suggested that in fresh waters at high latitudes and altitudes, surface ice during winter functions as overhead cover for fish, reducing the predation risk from terrestrial piscivores. We simulated ice cover by suspending plastic sheeting over five 30-m-long stream sections in a boreal forest stream and examined its effects on the growth and habitat use of brown trout (Salmo trutta) during winter. Trout that spent the winter under the artificial ice cover grew more than those in the control (uncovered) sections. Moreover, tracking of trout tagged with passive integrated transponders showed that in the absence of the artificial ice cover, habitat use during the day was restricted to the stream edges, often under undercut banks, whereas under the simulated ice cover condition, trout used the entire width of the stream. These results indicate that the presence of surface ice cover may improve the energetic status and broaden habitat use of stream fish during winter. It is therefore likely that reductions in the duration and extent of ice cover due to climate change will alter time and energy budgets, with potentially negative effects on fish production. PMID:26787075

  13. Constraining GRACE-derived cryosphere-attributed signal to irregularly shaped ice-covered areas

    NASA Astrophysics Data System (ADS)

    Colgan, W.; Luthcke, S.; Abdalati, W.; Citterio, M.

    2013-12-01

    We use a Monte Carlo approach to invert a spherical harmonic representation of cryosphere-attributed mass change in order to infer the most likely underlying mass changes within irregularly shaped ice-covered areas at nominal 26 km resolution. By inverting a spherical harmonic representation through the incorporation of additional fractional ice coverage information, this approach seeks to eliminate signal leakage between non-ice-covered and ice-covered areas. The spherical harmonic representation suggests a Greenland mass loss of 251 ± 25 Gt a-1 over the December 2003 to December 2010 period. The inversion suggests 218 ± 20 Gt a-1 was due to the ice sheet proper, and 34 ± 5 Gt a-1 (or ~14%) was due to Greenland peripheral glaciers and ice caps (GrPGICs). This mass loss from GrPGICs exceeds that inferred from all ice masses on both Ellesmere and Devon islands combined. This partition therefore highlights that GRACE-derived "Greenland" mass loss cannot be taken as synonymous with "Greenland ice sheet" mass loss when making comparisons with estimates of ice sheet mass balance derived from techniques that sample only the ice sheet proper.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  15. Comparison of measurements and theory for backscatter from bare and snow-covered saline ice

    NASA Technical Reports Server (NTRS)

    Bredow, Jonathan W.; Gogineni, Sivaprasad

    1990-01-01

    C-band radar backscatter measurements were made on artificially grown sea ice during the winters of 1987-1988 and 1988-1989. These measurements were made on smooth, rough, and snow-covered saline ice. The measured sigma-deg(theta) of smooth saline ice (rms height less than 0.05 cm) disagreed with small perturbation method (SPM) surface scattering predictions. Using physical parameters of the ice in a simple layer model, it us shown that this discrepancy can be explained by scattering from beneath the surface. A thin (7-cm) dry snow cover had a significant influence on backscatter from the smooth ice sheet. This influence was due to scattering from particles within the snow, and can be predicted by a commonly used empirical layer model for snow. The results of backscatter measurements of a moderately rough saline ice sheet were found to agree with SPM predictions.

  16. Experimental study and mathematical modelling of flashover on extra-high voltage insulators covered with ice

    NASA Astrophysics Data System (ADS)

    Farzaneh-Dehkordi, J.; Zhang, J.; Farzaneh, M.

    2004-12-01

    Using a test method developed at the high-voltage laboratory of the NSERC/Hydro-Quebec/UQAC Industrial Chair on Atmospheric Icing of Power Network Equipment (CIGELE), the relation between the minimum flashover voltage VMF and the insulator dry arcing distance for standard porcelain station post insulators, as typically used in Hydro-Quebec substations, was investigated under icing conditions. The experimental results show that, under wet-grown ice, known as the most dangerous type of ice for power transmission systems, the VMF increases nonlinearly with an increase in insulator length. Based on these results, an improved mathematical model for predicting the critical flashover voltage versus length of ice-covered insulators is presented. This model is helpful for understanding the flashover phenomenon on ice-covered insulators and presents a powerful tool for choosing the proper length of outdoor insulators in cold climate regions. Copyright

  17. THE STRUCTURE OF SURFACE H{sub 2}O LAYERS OF ICE-COVERED PLANETS WITH HIGH-PRESSURE ICE

    SciTech Connect

    Ueta, S.; Sasaki, T. E-mail: takanori@geo.titech.ac.jp

    2013-10-01

    Many extrasolar (bound) terrestrial planets and free-floating (unbound) planets have been discovered. While the existence of bound and unbound terrestrial planets with liquid water is an important question, of particular importance is the question of these planets' habitability. Even for a globally ice-covered planet, geothermal heat from the planetary interior may melt the interior ice, creating an internal ocean covered by an ice shell. In this paper, we discuss the conditions that terrestrial planets must satisfy for such an internal ocean to exist on the timescale of planetary evolution. The question is addressed in terms of planetary mass, distance from a central star, water abundance, and abundance of radiogenic heat sources. In addition, we investigate the structure of the surface H{sub 2}O layers of ice-covered planets by considering the effects of ice under high pressure (high-pressure ice). As a fiducial case, a 1 M{sub ⊕} planet at 1 AU from its central star and with 0.6-25 times the H{sub 2}O mass of the Earth could have an internal ocean. We find that high-pressure ice layers may appear between the internal ocean and the rock portion on a planet with an H{sub 2}O mass over 25 times that of the Earth. The planetary mass and abundance of surface water strongly restrict the conditions under which an extrasolar terrestrial planet may have an internal ocean with no high-pressure ice under the ocean. Such high-pressure ice layers underlying the internal ocean are likely to affect the habitability of the planet.

  18. Modeling photosynthesis in sea ice-covered waters

    NASA Astrophysics Data System (ADS)

    Long, Matthew C.; Lindsay, Keith; Holland, Marika M.

    2015-09-01

    The lower trophic levels of marine ecosystems play a critical role in the Earth System mediating fluxes of carbon to the ocean interior. Many of the functional relationships describing biological rate processes, such as primary productivity, in marine ecosystem models are nonlinear functions of environmental state variables. As a result of nonlinearity, rate processes computed from mean fields at coarse resolution will differ from similar computations that incorporate small-scale heterogeneity. Here we examine how subgrid-scale variability in sea ice thickness impacts simulated net primary productivity (NPP) in a 1°×1° configuration of the Community Earth System Model (CESM). CESM simulates a subgrid-scale ice thickness distribution and computes shortwave penetration independently for each ice thickness category. However, the default model formulation uses grid-cell mean irradiance to compute NPP. We demonstrate that accounting for subgrid-scale shortwave heterogeneity by computing light limitation terms under each ice category then averaging the result is a more accurate invocation of the photosynthesis equations. Moreover, this change delays seasonal bloom onset and increases interannual variability in NPP in the sea ice zone in the model. The new treatment reduces annual production by about 32% in the Arctic and 19% in the Antarctic. Our results highlight the importance of considering heterogeneity in physical fields when integrating nonlinear biogeochemical reactions.

  19. Impact of ice cover in the Arctic on ocean-atmosphere turbulent heat fluxes

    NASA Astrophysics Data System (ADS)

    Selivanova, J. V.; Tilinina, N. D.; Gulev, S. K.; Dobrolubov, S. A.

    2016-01-01

    The impact of spatiotemporal variability of the ice-covered area in the Arctic on the value and interannual dynamics of turbulent heat fluxes on the ocean-atmosphere border is considered. An expected inverse dependence of the heat fluxes integrated over the Arctic area and the area of ice is not detected. The largest interannual oscillations of heat fluxes from the ocean to the atmosphere are timed to the varying position of the ice edge and, to a lesser extent, are connected with total area of ice. The role of the marginal ice zone in oceanic heat transfer is analyzed. In particular, it is shown that while moving along the marginal zone from the ice-free surface to the surface with an ice concentration of 0.8, latent and sensible heat fluxes are reduced by a factor of 2.5-3.

  20. Hydrocarbons in the snow-ice cover of different areas of the White Sea

    NASA Astrophysics Data System (ADS)

    Nemirovskaya, I. A.

    2014-05-01

    The data on the content of hydrocarbons (HC) are presented and compared to the contents of organic carbon, lipids, and particulate matter in the snow-ice cover of the coastal areas of Dvina and Kandalaksha bays of the White Sea (2008-2012). The accumulation of HC in the snow-ice cover depends on the degree of atmosphere contamination, the conditions of the ice formation, and the intensity of the biogeochemical processes at the ice-water interface. Because of this, the aquatic area of Arkhangelsk is characterized by the highest HC concentrations in the snow and in the upper layer of ice. The peculiarities of the formation of the snow-ice cover in Rugozero bight of Kandalaksha Bay cause the concentrating of HC in different layers of ice. The decrease of the concentration of HC in the show-ice cover of the White Sea compared to earlier studies resulted from the recession of industrial activities during the recent years.

  1. Global Changes in the Sea Ice Cover and Associated Surface Temperature Changes

    NASA Astrophysics Data System (ADS)

    Comiso, Josefino C.

    2016-06-01

    The trends in the sea ice cover in the two hemispheres have been observed to be asymmetric with the rate of change in the Arctic being negative at -3.8 % per decade while that of the Antarctic is positive at 1.7 % per decade. These observations are confirmed in this study through analyses of a more robust data set that has been enhanced for better consistency and updated for improved statistics. With reports of anthropogenic global warming such phenomenon appears physically counter intuitive but trend studies of surface temperature over the same time period show the occurrence of a similar asymmetry. Satellite surface temperature data show that while global warming is strong and dominant in the Arctic, it is relatively minor in the Antarctic with the trends in sea ice covered areas and surrounding ice free regions observed to be even negative. A strong correlation of ice extent with surface temperature is observed, especially during the growth season, and the observed trends in the sea ice cover are coherent with the trends in surface temperature. The trend of global averages of the ice cover is negative but modest and is consistent and compatible with the positive but modest trend in global surface temperature. A continuation of the trend would mean the disappearance of summer ice by the end of the century but modelling projections indicate that the summer ice could be salvaged if anthropogenic greenhouse gases in the atmosphere are kept constant at the current level.

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  3. NET ATMOSPHERIC INPUTS OF PCBS TO THE ICE COVER ON LAKE HURON

    EPA Science Inventory

    This report describes the first measurements of the net atmospheric deposition of PCBs to the ice cover of a body of water. The net deposition of PCBs includes the wet, dry, and vapor deposition, less any evaporation. The measurements were made on ice cores collected from the fro...

  4. Passive microwave characteristics of the Bering Sea ice cover during Marginal Ice Zone Experiment (MIZEX) West

    NASA Technical Reports Server (NTRS)

    Cavalieri, D. J.; Gloersen, P.; Wilheit, T. T.; Calhoon, C.

    1984-01-01

    Passive microwave measurements of the Bering Sea were made with the NASA CV-990 airborne laboratory during February. Microwave data were obtained with imaging and dual-polarized, fixed-beam radiometers in a range of frequencies from 10 to 183 GHz. The high resolution imagery at 92 GHz provides a particularly good description of the marginal ice zone delineating regions of open water, ice compactness, and ice-edge structure. Analysis of the fixed-beam data shows that spectral differences increase with a decrease in ice thickness. Polarization at 18 and 37 GHz distinguishes among new, young, and first-year sea ice types.

  5. Large Scale Characteristics and Variability of the Global Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    More than two decades of satellite passive microwave data are used to study and evaluate the large scale characteristics and the changing state of the sea ice cover in both the Northern and Southern Hemispheres. Satellite data provide day/night almost continuous observation of global sea ice cover thereby enabling quantitative variability studies at various time scales. Despite coarse sensor resolution, spatial detail is provided through the use of sea ice concentrations which are derived using an algorithm that determines the fraction of ice and open water within each satellite footprint. Large seasonal fluctuations in the extent are apparent with those of the Southern Hemisphere having larger amplitudes but less symmetrical seasonal distribution than those of the Northern Hemisphere. The large scale interannual variability of the ice cover has been evaluated globally as well as regionally and in the Northern Hemisphere, the yearly anomaly maps show a predominance of positive values in the 1980s and negative values in the 1990s. Regression analysis show that the ice extent and ice area are on a decline at the rate of -2.0 +/- 0.5% and -3.1 +/- 0.3% per decade, respectively, in the Northern Hemisphere but there are regions like the Bering Sea with positive trends. What is intriguing, however, is that the perennial sea ice cover has been declining at a much faster rate than for the entire hemisphere, i.e., 6.7 +/- 2.4% and 8.3 +/- 2.4 % per decade for ice extent and ice area, respectively. The perennial ice cover consists mainly of thick multiyear ice floes, and its persistent decline would mean a reduction in the average thickness of sea ice and a change in the overall characteristics of the Arctic sea ice cover. Furthermore, the yearly anomaly patterns are coherent with those of surface temperatures derived from 19 years of thermal infrared AVHRR data. The latter also shows that in consolidated ice regions, the average temperature during summer minima has been

  6. Deformation of the Arctic Ocean Sea Ice Cover Between November 1996 and April 1997: A Survey

    NASA Technical Reports Server (NTRS)

    Kwok, R.

    2000-01-01

    Quasi-linear features of the scale of kilometers to hundreds of kilometers can be observed in the high-resolution deformation fields of the sea ice cover produced by the RADARSAT Geophysical Processor System.

  7. Oscillations of a cylindrical body submerged in a fluid with ice cover

    NASA Astrophysics Data System (ADS)

    Tkacheva, L. A.

    2015-11-01

    The linear plane problem of oscillations of an elliptic cylinder in an ideal incompressible fluid of finite depth in the presence of an ice cover of finite length is solved. The ice cover is modeled by an elastic plate of constant thickness. The hydrodynamic loads acting on the body are determined as functions of the oscillation frequency and the positions of the cylinder and plate.

  8. Diurnal Wind Regimes and Lapse-Rate Variability Over Clean and Debris-Covered Ice

    NASA Astrophysics Data System (ADS)

    Flowers, G. E.; Young, E.

    2015-12-01

    Near-surface winds and air temperature play an important role in the surface energy balance of glaciers and ice sheets, and can be highly variable in space and time. The increasing fraction of debris-covered ice observed in many retreating alpine glacier environments motivates the study of these variables, and the processes that control them, over both clean and debris-covered ice. We use meteorological data collected in the ablation zone of a ~ 5km-long valley glacier in Yukon, Canada, to analyze the diurnal variability of temperature and wind regimes over debris-covered and debris-free ice. Our data reveal pronounced diurnal cycles in temperature lapse rates, wind speeds, and wind directions. Common to both clean and debris-covered areas are: (1) a shallowing of lapse rates in the early morning from 6:00 to 9:00 and a steepening of lapse rates during the day from 9:00 to 16:00, (2) nearly identical lapse rates regardless of surface type between 15:00 and 19:00, and (3) a persistent diurnal wind regime in which up-valley winds occur from late morning to evening, peaking at 16:00-17:00, and relatively weaker down-valley winds occur overnight. Significant differences between the clean-ice and debris-covered sites are also evident in the data, namely: (1) much steeper night-time lapse rates over debris-covered ice than clean ice, (2) the occurrence of steepest lapse rates overnight for debris-covered ice and in late afternoon (around 16:00) for clean ice, and (3) a more pronounced diurnal cycle in windspeed over debris-covered ice than clean ice, despite all stations exhibiting evidence of the diurnal changes in wind direction. The patterns described above conform to a model of weak katabatic flow at night and relatively stronger up-valley winds during the day, peaking in late afternoon. Though absolute temperatures over clean and debris-covered ice are markedly different during the day, lapse rates over both surfaces evolve similarly through the day to achieve steep

  9. Water quality observations of ice-covered, stagnant, eutrophic water bodies and analysis of influence of ice-covered period on water quality

    NASA Astrophysics Data System (ADS)

    sugihara, K.; Nakatsugawa, M.

    2013-12-01

    The water quality characteristics of ice-covered, stagnant, eutrophic water bodies have not been clarified because of insufficient observations. It has been pointed out that climate change has been shortening the duration of ice-cover; however, the influence of climate change on water quality has not been clarified. This study clarifies the water quality characteristics of stagnant, eutrophic water bodies that freeze in winter, based on our surveys and simulations, and examines how climate change may influence those characteristics. We made fixed-point observation using self-registering equipment and vertical water sampling. Self-registering equipment measured water temperature and dissolved oxygen(DO).vertical water sampling analyzed biological oxygen demand(BOD), total nitrogen(T-N), nitrate nitrogen(NO3-N), nitrite nitrogen(NO2-N), ammonium nitrogen(NH4-N), total phosphorus(TP), orthophosphoric phosphorus(PO4-P) and chlorophyll-a(Chl-a). The survey found that climate-change-related increases in water temperature were suppressed by ice covering the water area, which also blocked oxygen supply. It was also clarified that the bottom sediment consumed oxygen and turned the water layers anaerobic beginning from the bottom layer, and that nutrient salts eluted from the bottom sediment. The eluted nutrient salts were stored in the water body until the ice melted. The ice-covered period of water bodies has been shortening, a finding based on the analysis of weather and water quality data from 1998 to 2008. Climate change was surveyed as having caused decreases in nutrient salts concentration because of the shortened ice-covered period. However, BOD in spring showed a tendency to increase because of the proliferation of phytoplankton that was promoted by the climate-change-related increase in water temperature. To forecast the water quality by using these findings, particularly the influence of climate change, we constructed a water quality simulation model that

  10. Assessing, understanding, and conveying the state of the Arctic sea ice cover

    NASA Astrophysics Data System (ADS)

    Perovich, D. K.; Richter-Menge, J. A.; Rigor, I.; Parkinson, C. L.; Weatherly, J. W.; Nghiem, S. V.; Proshutinsky, A.; Overland, J. E.

    2003-12-01

    Recent studies indicate that the Arctic sea ice cover is undergoing significant climate-induced changes, affecting both its extent and thickness. Satellite-derived estimates of Arctic sea ice extent suggest a reduction of about 3% per decade since 1978. Ice thickness data from submarines suggest a net thinning of the sea ice cover since 1958. Changes (including oscillatory changes) in atmospheric circulation and the thermohaline properties of the upper ocean have also been observed. These changes impact not only the Arctic, but the global climate system and are likely accelerated by such processes as the ice-albedo feedback. It is important to continue and expand long-term observations of these changes to (a) improve the fundamental understanding of the role of the sea ice cover in the global climate system and (b) use the changes in the sea ice cover as an early indicator of climate change. This is a formidable task that spans a range of temporal and spatial scales. Fortunately, there are numerous tools that can be brought to bear on this task, including satellite remote sensing, autonomous buoys, ocean moorings, field campaigns and numerical models. We suggest the integrated and coordinated use of these tools during the International Polar Year to monitor the state of the Arctic sea ice cover and investigate its governing processes. For example, satellite remote sensing provides the large-scale snapshots of such basic parameters as ice distribution, melt zone, and cloud fraction at intervals of half a day to a week. Buoys and moorings can contribute high temporal resolution and can measure parameters currently unavailable from space including ice thickness, internal ice temperature, and ocean temperature and salinity. Field campaigns can be used to explore, in detail, the processes that govern the ice cover. Numerical models can be used to assess the character of the changes in the ice cover and predict their impacts on the rest of the climate system. This work

  11. On the sea-ice cover of the Nordic Seas in an idealized MITgcm-setup

    NASA Astrophysics Data System (ADS)

    Jensen, Mari F.; Spall, Michael A.; Nisancioglu, Kerim H.

    2016-04-01

    Changes in the sea-ice cover of the Nordic Seas have been proposed to play a key role for the dramatic temperature excursions associated with the Dansgaard-Oeschger events during the last glacial. However, with its proximity to the warm Atlantic water, how a sea-ice cover can persist in the Nordic Seas is not well understood. In this study, we apply an eddy-resolving configuration of the Massachusetts Institute of Technology general circulation model with an idealized topography to study the presence of sea ice in a Nordic Seas-like domain. The sea-surface temperatures are restored toward cold, atmospheric temperatures, and as a result, sea ice is present in the interior of the domain. However, the warm, cyclonic boundary current prevents sea ice from being formed along the boundaries. Preliminary results suggest that freshwater inputs at the margins can introduce sea ice in the warm, cyclonic boundary. In addition, a reduction in the meridional heat transport and a shift in the vertical location of the warm inflowing water is observed when freshwater is introduced. The magnitude and location of the freshwater input will be studied, along with changes in the temperature of the inflowing warm water. Results suggest a threshold value in the freshwater forcing for when sea ice is present in the boundaries, and a sea-ice cover which is sensitive to the temperature of the inflowing, warm water.

  12. Comparison of wave propagation through ice covers in calm and storm conditions

    NASA Astrophysics Data System (ADS)

    Li, Jingkai; Kohout, Alison L.; Shen, Hayley H.

    2015-07-01

    Motivated by a dramatic reduction in Arctic sea ice cover, interest in the field of wave-ice interaction has accelerated over the past few years. Recent observations have identified that large waves (>3 m) have a linear attenuation rate, rather than the previously assumed exponential rate that is found for small waves. This suggests that waves penetrate further into the ice cover than previously expected. To explore this further we tested two exponentially decaying wave models. Contributions from nonlinear and wind generation source terms enabled both models to reproduce the observed regime shift. Essentially, the accumulation of nonlinear and wind energy contributions to long (and thus higher amplitude) waves can offset the ice damping, thus reducing the apparent attenuation. This study highlights the relevance of considering frequency dependence when analyzing wave attenuation in sea ice field data.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  14. Can large scale sea ice cover changes affect precipitation patterns over California?

    NASA Astrophysics Data System (ADS)

    Cvijanovic, I.; Bonfils, C.; Lucas, D. D.; Santer, B. D.; Chiang, J. C. H.

    2015-12-01

    Pronounced Arctic sea ice loss since the beginning of the satellite era has intensified the interest into whether these high latitude changes can significantly influence the weather and climate far from the Arctic. Current attempts to demonstrate statistically significant remote responses to sea ice changes have been hindered by factors such as large high latitude variability, relatively short observational datasets, and model limitations in adequately representing current sea ice changes. In this study, we sample uncertainty in sea ice physics parameters and variability in atmospheric initial conditions to obtain an ensemble of simulations with substantially different states of Arctic and Antarctic sea ice cover. This large ensemble isolates a robust, statistically significant climate change response arising from changes in sea ice cover only. Our results show a significant link between Arctic and Antarctic sea ice cover changes and precipitation across the tropical Atlantic and Pacific basins, the Sahel, and the west coast of the United States. For example, large Arctic sea ice decline leads to a northward shift of the tropical convergence zone, increased subsidence over the southwest United States and a geopotential anomaly over the North Pacific; with all of these factors resulting in significant drying over California. We conclude that high-latitude sea ice cover changes are an important driver of low-latitude precipitation. Consequently, reliable predictions of future precipitation changes over areas such as California (and the Sahel) will strongly depend on our ability to adequately simulate both Arctic and Antarctic sea ice changes. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and is released as LLNL-ABS-675694.

  15. Extreme ecological response of a seabird community to unprecedented sea ice cover.

    PubMed

    Barbraud, Christophe; Delord, Karine; Weimerskirch, Henri

    2015-05-01

    Climate change has been predicted to reduce Antarctic sea ice but, instead, sea ice surrounding Antarctica has expanded over the past 30 years, albeit with contrasted regional changes. Here we report a recent extreme event in sea ice conditions in East Antarctica and investigate its consequences on a seabird community. In early 2014, the Dumont d'Urville Sea experienced the highest magnitude sea ice cover (76.8%) event on record (1982-2013: range 11.3-65.3%; mean±95% confidence interval: 27.7% (23.1-32.2%)). Catastrophic effects were detected in the breeding output of all sympatric seabird species, with a total failure for two species. These results provide a new view crucial to predictive models of species abundance and distribution as to how extreme sea ice events might impact an entire community of top predators in polar marine ecosystems in a context of expanding sea ice in eastern Antarctica. PMID:26064653

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

    EPA Science Inventory

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

  17. Impacts of the variability of second-year ice types on the decline of the Arctic perennial sea-ice cover

    NASA Astrophysics Data System (ADS)

    Comiso, Josefino C.

    The observed rapid decline in the Arctic perennial ice cover is one of the most remarkable signals of change in the Arctic region. Updated data now show an even higher rate of decline of 9.8% decade -1 (1978-2005) than the previous report of 8.9% decade -1 (1978-2000). To gain insights into this decline, the variability of the second-year ice, which is the relatively thin component of the perennial ice cover, is studied. The perennial ice cover in the 1990s was observed to be highly variable, leading to relatively high production of second-year ice that may in part explain the observed ice thinning during the period and have triggered further decline. The microwave signature of second-year ice is shown to be different from that of the older multi-year ice types and, surprisingly, more similar to that of first-year ice. This in part explains why previous estimates of the area of multi-year ice during the winter period are considerably lower than the area of the perennial ice cover during the preceding summer. Analysis of multichannel cluster maps in conjunction with submarine ice-draft data indicates ability to detect regions covered primarily by second-year ice and hence to infer ice-thickness information from the microwave data. The periodic increase of second-year ice in the 1990s was apparently followed by continuous decline due in part to anomolously warm temperatures during the latter period that shortened the ice season and kept first-year ice from getting thick enough to survive the summer and become second year ice.

  18. Estimation of composite hydraulic resistance in ice-covered alluvial streams

    NASA Astrophysics Data System (ADS)

    Ghareh Aghaji Zare, Soheil; Moore, Stephanie A.; Rennie, Colin D.; Seidou, Ousmane; Ahmari, Habib; Malenchak, Jarrod

    2016-02-01

    Formation, propagation, and recession of ice cover introduce a dynamic boundary layer to the top of rivers during northern winters. Ice cover affects water velocity magnitude and distribution, water level and consequently conveyance capacity of the river. In this research, total resistance, i.e., "composite resistance," is studied for a 4 month period including stable ice cover, breakup, and open water stages in Lower Nelson River (LNR), northern Manitoba, Canada. Flow and ice characteristics such as water velocity and depth and ice thickness and condition were measured continuously using acoustic techniques. An Acoustic Doppler Current Profiler (ADCP) and Shallow Water Ice Profiling Sonar (SWIPS) were installed simultaneously on a bottom mount and deployed for this purpose. Total resistance to the flow and boundary roughness are estimated using measured bulk hydraulic parameters. A novel method is developed to calculate composite resistance directly from measured under ice velocity profiles. The results of this method are compared to the measured total resistance and to the calculated composite resistance using formulae available in literature. The new technique is demonstrated to compare favorably to measured total resistance and to outperform previously available methods.

  19. Influence of high latitude ice cover on the marine Intertropical Convergence Zone

    NASA Astrophysics Data System (ADS)

    Chiang, John C. H.; Bitz, Cecilia M.

    2005-10-01

    We investigate the causes for a strong high latitude imposed ice (land or sea) influence on the marine Intertropical Convergence Zone (ITCZ) in the Community Climate Model version 3 coupled to a 50-m slab ocean. The marine ITCZ in all the ocean basins shift meridionally away from the hemisphere with an imposed added ice cover, altering the global Hadley circulation with an increased tropical subsidence in the hemisphere with imposed ice and uplift in the other. The effect appears to be independent of the longitudinal position of imposed ice. The anomalous ice induces a rapid cooling and drying of the air and surface over the entire high- and midlatitudes; subsequent progression of cold anomalies occurs in the Pacific and Atlantic northeasterly trade regions, where a wind-evaporation-sea surface temperature (SST) feedback initiates progression of a cold SST ‘front’ towards the ITCZ latitudes. Once the cooler SST reaches the ITCZ latitude, the ITCZ shifts southwards, aided by positive feedbacks associated with the displacement. The ITCZ displacement transports moisture away from the colder and drier hemisphere into the other hemisphere, resulting in a pronounced hemispheric asymmetric response in anomalous specific humidity; we speculate that the atmospheric humidity plays a central role in the hemispheric asymmetric nature of the climate response to high latitude ice cover anomalies. From an energy balance viewpoint, the increased outgoing radiative flux at the latitudes of the imposed ice is compensated by an increased radiative energy flux at the tropical latitudes occupied by the displaced ITCZ, and subsequently transported by the altered Hadley and eddy circulations to the imposed ice latitudes. The situation investigated here may be applicable to past climates like the Last Glacial Maximum where hemispheric asymmetric changes to ice cover occurred. Major caveats to the conclusions drawn include omission of interactive sea ice physics and ocean dynamical

  20. Ground penetrating radar detection of subsnow liquid overflow on ice-covered lakes in interior Alaska

    NASA Astrophysics Data System (ADS)

    Gusmeroli, A.; Grosse, G.

    2012-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Gusmeroli, A.; Grosse, G.

    2012-12-01

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

  2. Spatial Distribution of Trends and Seasonality in the Hemispheric Sea Ice Covers

    NASA Technical Reports Server (NTRS)

    Gloersen, P.; Parkinson, C. L.; Cavalieri, D. J.; Cosmiso, J. C.; Zwally, H. J.

    1998-01-01

    We extend earlier analyses of a 9-year sea ice data set that described the local seasonal and trend variations in each of the hemispheric sea ice covers to the recently merged 18.2-year sea ice record from four satellite instruments. The seasonal cycle characteristics remain essentially the same as for the shorter time series, but the local trends are markedly different, in some cases reversing sign. The sign reversal reflects the lack of a consistent long-term trend and could be the result of localized long-term oscillations in the hemispheric sea ice covers. By combining the separate hemispheric sea ice records into a global one, we have shown that there are statistically significant net decreases in the sea ice coverage on a global scale. The change in the global sea ice extent, is -0.01 +/- 0.003 x 10(exp 6) sq km per decade. The decrease in the areal coverage of the sea ice is only slightly smaller, so that the difference in the two, the open water within the packs, has no statistically significant change.

  3. Satellite SAR remote sensing of Great Lakes ice cover using RADARSAT data

    SciTech Connect

    Leshkevich, G.A.

    1997-06-01

    During winter months, cloud cover over the Laurentian Great Lakes impairs the use of satellite imagery from passive sensors operating in the visible, near infrared, and thermal infrared spectra for ice cover monitoring and analysis. The all-weather, day/night viewing capability of satellite Synthetic Aperture Radar (SAR) makes it a unique and valuable tool for Great Lakes ice identification and mapping providing that data analysis techniques and capability for using SAR data in an operational setting are developed. RADARSAT, an operational satellite carrying a SAR operating at 5.3 GHz (C-Band) with a horizontal polarization, was successfully launched in 1995. This study explores algorithms for Great Lakes ice cover classification and mapping using RADARSAT SAR data. Preliminary analysis of a ScanSAR Narrow scene of western Lake Superior using a supervised (level slicing) classification technique indicates that different ice types in the ice cover can be identified and mapped and that wind has a strong influence on the backscatter from open water. However, further research needs to be conducted on the repeatability and automation of classification and interpretation from scene to scene. During the 1997 winter season, an experiment is planned to acquire shipborne polarimetric backscatter data using the Jet Propulsion Laboratory (JPL) C-band scatterometer together with surface-based ice physical characterization measurements and environmental parameters coincident with RADARSAT overpass.

  4. Sea ice cover in Isfjorden and Hornsund 2000-2014 by using remote sensing

    NASA Astrophysics Data System (ADS)

    Muckenhuber, S.; Nilsen, F.; Korosov, A.; Sandven, S.

    2015-07-01

    A satellite database including 16 555 satellite images and ice charts displaying the area of Isfjorden, Hornsund and the Svalbard region has been established with focus on the time period 2000-2014. 3319 manual interpretations of sea ice conditions have been conducted, resulting in two time series dividing the area of Isfjorden and Hornsund into "Fast ice", "Drift ice" and open "Water". The maximum fast ice coverage of Isfjorden is > 40 % in the periods 2000-2005 and 2009-2011 and stays < 30 % in 2006-2008 and 2012-2014. Fast ice cover in Hornsund reaches > 40 % in all considered years, except for 2012 and 2014, where the maximum stays < 20 %. The mean seasonal cycles of fast ice in Isfjorden and Hornsund show monthly averaged values of less than 1 % between July and November and maxima in March (Isfjorden, 35.7 %) and April (Hornsund, 42.1 %) respectively. A significant reduction of the monthly averaged fast ice coverage is found when comparing the time periods 2000-2005 and 2006-2014. The seasonal maximum decreases from 57.5 to 23.2 % in Isfjorden and from 52.6 to 35.2 % in Hornsund. A new concept, called "days of fast ice coverage" (DFI), is introduced for quantification of the interannual variation of fast ice cover, allowing for comparison between different fjords and winter seasons. Considering the time period from 1 March until end of sea ice season, the mean DFI values for 2000-2014 are 33.1 ± 18.2 DFI (Isfjorden) and 42.9 ± 18.2 DFI (Hornsund). A distinct shift to lower DFI values is observed in 2006. Calculating a mean before and after 2006 yields a decrease from 50 to 22 DFI for Isfjorden and from 56 to 34 DFI for Hornsund.

  5. Influence of ice and snow covers on the UV exposure of terrestrial microbial communities: dosimetric studies.

    PubMed

    Cockell, Charles S; Rettberg, Petra; Horneck, Gerda; Wynn-Williams, David D; Scherer, Kerstin; Gugg-Helminger, Anton

    2002-08-01

    Bacillus subtilis spore biological dosimeters and electronic dosimeters were used to investigate the exposure of terrestrial microbial communities in micro-habitats covered by snow and ice in Antarctica. The melting of snow covers of between 5- and 15-cm thickness, depending on age and heterogeneity, could increase B. subtilis spore inactivation by up to an order of magnitude, a relative increase twice that caused by a 50% ozone depletion. Within the snow-pack at depths of less than approximately 3 cm snow algae could receive two to three times the DNA-weighted irradiance they would receive on bare ground. At the edge of the snow-pack, warming of low albedo soils resulted in the formation of overhangs that provided transient UV protection to thawed and growing microbial communities on the soils underneath. In shallow aquatic habitats, thin layers of heterogeneous ice of a few millimetres thickness were found to reduce DNA-weighted irradiances by up to 55% compared to full-sky values with equivalent DNA-weighted diffuse attenuation coefficients (K(DNA)) of >200 m(-1). A 2-mm snow-encrusted ice cover on a pond was equivalent to 10 cm of ice on a perennially ice covered lake. Ice covers also had the effect of stabilizing the UV exposure, which was often subject to rapid variations of up to 33% of the mean value caused by wind-rippling of the water surface. These data show that changing ice and snow covers cause relative changes in microbial UV exposure at least as great as those caused by changing ozone column abundance. PMID:12208033

  6. A Small Diameter Rosette for Sampling Ice Covered Waters

    NASA Astrophysics Data System (ADS)

    Chayes, D. N.; Smethie, W. M.; Perry, R. S.; Schlosser, P.; Friedrich, R.

    2011-12-01

    A gas tight, small diameter, lightweight rosette, supporting equipment and an effective operational protocol has been developed for aircraft supported sampling of sea water across the Lincoln Sea. The system incorporates a commercial off the shelf CTD electronics (SBE19+ sensor package and SBE33 deck unit) to provide real-time measurement data at the surface. We designed and developed modular water sample units and custom electronics to decode the bottle firing commands and close the sample bottles. For a typical station, we land a ski-equipped deHaviland Twin Otter (DHC-6) aircraft on a suitable piece of sea-ice, drill a 12" diameter hole through the ice next to the cargo door and set up a tent to provide a reasonable working environment over the hole. A small winch with 0.1" diameter single conductor cable is mounted in the aircraft by the cargo door and a tripod supports a sheave above the hole. The CTD module is connected to the end of the wire and the water sampling modules are stacked on top as the system is lowered. For most stations, three sample modules are used to provide 12 four (4) liter sample bottles. Data collected during the down-cast is used to formulate the sampling plan which is executed on the up-cast. The system is powered by a 3,700 Watt, 120VAC gasoline generator. After collection, the sample modules are stored in passively temperature stabilized ice chests during the flight back to the logistics facility at Alert where a broad range of samples are drawn and stored for future analysis. The transport mechanism has a good track record of maintaining water samples within about two degrees of the original collection temperature which minimizes out-gassing. The system has been successfully deployed during a field program each spring starting in 2004 along a transect between the north end of Ellesmere Island (Alert, Nunavut) and the North Pole. During the eight field programs we have taken 48 stations with twelve bottles at most stations (eight at

  7. Northern Hemisphere sea-ice cover during the Holocene - proxy data reconstruction and modelling

    NASA Astrophysics Data System (ADS)

    Seidenkrantz, M. S.; de Vernal, A.; Goosse, H.; Solignac, S.; Van Nieuwenhove, N.; Macias-Fauria, M.; Klein, F.; Pearce, C.; Belt, S. T.; Caissie, B.; Cronin, T. M.; Stein, R. H.; Sha, L.; DeNinno, L. H.

    2014-12-01

    A strikingly fast decrease of Arctic sea-ice cover has been recorded for the instrumental period and attributed to anthropogenic climate change, but little is known about natural sea-ice variability. Hence, there is a need for longer sea-ice time series to establish a baseline for natural Arctic sea-ice variability. We compiled 119 proxy-based sea-ice reconstructions from the Arctic Ocean and subarctic marginal seas to evaluate the stability/variability of sea-ice cover during the Holocene. The reconstructions are primarily based on published data combined with some yet-unpublished records of biological (diatoms, dinocysts, foraminifera, ostracods), sedimentological (IRD), and biogeochemical (IP25, PIP25) sea-ice indicators. Each indicator and record has been interpreted independently. We present all data as long-term annual means (months of sea ice per year). Sea-ice reconstructions are grouped into these classes: perennial (11-12 month/yr), dense (6-10 m/yr), common (1-6 m/yr), occasional (0.1-1 m/yr), rare (almost never) and absent (never). Further, reconstructions are made for the time slices 0-2 cal. ka (BP), 2-4 ka, 4-6 ka, 6±0.5 ka, 6-8 ka and 8-10 ka. Our study shows that winter sea ice was present during the entire Holocene, but summer sea ice may have been somewhat reduced in some areas during the Holocene Climate Optimum (10-6 ka), with variations between basins. In the Nordic Seas and N Atlantic minimum sea-ice conditions are seen 10-6 ka, whereas in the eastern Labrador Sea minimum sea-ice occurred 6-4 ka. Since ~4 ka sea-ice cover has increased, especially in the most recent millennia. Changes are subtle, however, but nonetheless consistent. The Pacific sector of the Arctic (Bering, Chukchi, Beaufort, Laptev, Okhotsk seas) show less variability during the Holocene, though it is noted that these records have poorer age control and resolution than those from the Atlantic sector. Our proxy data interpretations have been used to constrain model output

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  9. Peculiarities of hydrocarbon distribution in the snow-ice cover of different regions of the white sea

    NASA Astrophysics Data System (ADS)

    Nemirovskaya, I. A.

    2014-03-01

    This paper presents data on the content of hydrocarbons (HCs) in the snow-ice cover of the coastal regions of the Dvina and Kandalaksha gulfs, White Sea, in 2008-2012 in comparison with the content of organic carbon, lipids, and the suspension. The accumulation of HCs in the snow-ice cover depends on the degree of pollution of the atmosphere, formation conditions of ice, and intensity of biogeochemical processes at the ice-water boundary. Thus, the highest concentrations in the water basin of Arkhangelsk are identified in snow and in the upper part of the ice. The peculiarities of formation of the snow-ice cover in Rugozero Bay of the Kandalaksha Gulf leads to the concentration of HCs in different snow and ice layers. The decreased HC content in the snow-ice cover of the White Sea, in comparison with previous studies, is caused by recession of industrial production in recent years.

  10. Application of SLAR for monitoring Great Lakes total ice cover. [for winter ship navigation

    NASA Technical Reports Server (NTRS)

    Jirberg, R. J.; Schertler, R. J.; Gedney, R. T.; Mark, H.

    1973-01-01

    A series of X-band SLAR images is presented showing the development and disintegration of the entire ice cover on Lake Erie during the winter of 1972-1973. Simultaneous ground truth observations and ERTS-1 photography establish accurate correlations of radar responses with ice conditions. The all-weather, broad areal mapping capability of SLAR is seen to be the means for obtaining the repeated coverage needed for winter navigation on the Great Lakes.

  11. Reemergence of sea ice cover anomalies and the role of the sea ice-albedo feedback in CCSM simulations

    NASA Astrophysics Data System (ADS)

    Deweaver, E. T.

    2008-12-01

    The dramatic sea ice decline of 2007 and lack of recovery in 2008 raise the question of a "tipping point" for Arctic sea ice, beyond which the transition to a seasonal sea ice state becomes abrupt and irreversible. The tipping point is essentially a "memory catastrophe", in which a dramatic loss of sea ice in one summer is "remembered" in reduced ice thickness over the winter season and leads to a comparably dramatic loss the following summer. The dominant contributor to this memory is presumably the sea ice - albedo feedback (SIAF), in which excess insolation absorbed due to low summer ice cover leads to a shorter ice growth season and hence thinner ice. While these dynamics are clearly important, they are difficult to quantify given the lack of long-term observations in the Arctic and the suddenness of the recent loss. Alternatively, we attempt to quantify the contribution of the SIAF to the year-to-year memory of sea ice cover anomalies in simulations of the NCAR Community Climate System Model (CCSM) under 20th century conditions. Lagged autocorrelation plots of sea ice area anomalies show that anomalies in one year tend to "reemerge" in the following year. Further experiments using a slab ocean model (SOM) are used to assess the contribution of oceanic processes to the year-to-year reemergence. This contribution is substantial, particularly in the winter season, and includes memory due to the standard mixed layer reemergence mechanism and low-frequency ocean heat transport anomalies. The contribution of the SIAF to persistence in the SOM experiment is determined through additional experiments in which the SIAF is disabled by fixing surface albedo to its climatological value regardless of sea ice concentration anomalies. SIAF causes a 50% increase in the magnitude of the anomalies but a relatively small increase in their persistence. Persistence is not dramatically increased because the enhancement of shortwave flux anomalies by SIAF is compensated by stronger

  12. Yearlong, Daily Assessments of Bio-Optical Distributions under Perennial Ice Cover in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Laney, S. R.; Toole, J. M.; Krishfield, R. A.

    2013-12-01

    Over the past three years eight Ice-Tethered Profilers have been outfitted with a new bio-optical sensor suite and have been deployed under perennial ice cover in the Arctic Ocean. This sensor suite enables the measurement of chlorophyll (a proxy for algal biomass), colored dissolved organic matter concentration, and particular backscatter intensities throughout the entire upper 750 m of the under-ice water column. An irradiance sensor additionally provides concurrent measurements of the light field underneath ice cover during times of the year that receive insolation. Two of these profilers have operated for a full year, returning multiple daily profiles of these basic biogeochemical optical properties with sub-meter vertical resolution. These observations provide unprecedented insight into the basic optical seasonality of the pelagic ocean environment under perennial ice cover, including the timing of important biogeochemical events in the Arctic such as periods of high under-ice productivity and the subsequent export of organic matter to the deep ocean.

  13. The influence of supraglacial debris cover variability on de-icing processes - examples from Svalbard

    NASA Astrophysics Data System (ADS)

    Lukas, Sven; Benn, Douglas I.; Boston, Clare M.; Hawkins, Jack; Lehane, Niall E.; Lovell, Harold; Rooke, Michael

    2014-05-01

    Extensive supraglacial debris covers are widespread near the margins of many cold-based and polythermal surging and non-surging glaciers in Svalbard. Despite their importance for current glacier dynamics and a detailed understanding of how they will affect the de-icing of ice-marginal areas, little work has been carried out to shed light on the sedimentary processes operating in these debris covers. We here present data from five different forelands in Svalbard. In all five cases, surfaces within the debris cover can be regarded as stable where debris cover thickness exceeds that of the active layer; vegetation development and absence of buried ice exposures at the surface support this conclusion, although test pits and geophysical investigations have revealed the presence of buried ice at greater depths (> 1-3 m). These findings imply that even seemingly stable surfaces at present will be subject to change by de-icing in the future. Factors and processes that contribute towards a switch from temporarily stable to unstable conditions have been identified as: 1. The proximity to englacial or supraglacial meltwater channels. These channels enlarge due to thermo-erosion, which can lead to the eventual collapse of tunnel roofs and the sudden generation of linear instabilities in the system. Along such channels, ablation is enhanced compared to adjacent debris-covered ice, and continued thermo-erosion continuously exposes new areas of buried ice at the surface. This works in conjunction with 2. Debris flows that occur on all sloping ground and transfer material from stable to less stable (sloping) locations within the debris cover and eventually into supraglacial channels, from where material is then removed from the system. Several generations of debris flows have been identified in all five debris covers, strongly suggesting that these processes are episodic and that the loci of these processes switch. This in turn indicates that transfer of material by debris flows

  14. Modeling surface energy fluxes and thermal dynamics of a seasonally ice-covered hydroelectric reservoir.

    PubMed

    Wang, Weifeng; Roulet, Nigel T; Strachan, Ian B; Tremblay, Alain

    2016-04-15

    The thermal dynamics of human created northern reservoirs (e.g., water temperatures and ice cover dynamics) influence carbon processing and air-water gas exchange. Here, we developed a process-based one-dimensional model (Snow, Ice, WAater, and Sediment: SIWAS) to simulate a full year's surface energy fluxes and thermal dynamics for a moderately large (>500km(2)) boreal hydroelectric reservoir in northern Quebec, Canada. There is a lack of climate and weather data for most of the Canadian boreal so we designed SIWAS with a minimum of inputs and with a daily time step. The modeled surface energy fluxes were consistent with six years of observations from eddy covariance measurements taken in the middle of the reservoir. The simulated water temperature profiles agreed well with observations from over 100 sites across the reservoir. The model successfully captured the observed annual trend of ice cover timing, although the model overestimated the length of ice cover period (15days). Sensitivity analysis revealed that air temperature significantly affects the ice cover duration, water and sediment temperatures, but that dissolved organic carbon concentrations have little effect on the heat fluxes, and water and sediment temperatures. We conclude that the SIWAS model is capable of simulating surface energy fluxes and thermal dynamics for boreal reservoirs in regions where high temporal resolution climate data are not available. SIWAS is suitable for integration into biogeochemical models for simulating a reservoir's carbon cycle. PMID:26849343

  15. Sea ice cover in Isfjorden and Hornsund, Svalbard (2000-2014) from remote sensing data

    NASA Astrophysics Data System (ADS)

    Muckenhuber, S.; Nilsen, F.; Korosov, A.; Sandven, S.

    2016-01-01

    A satellite database including 16 555 satellite images and ice charts displaying the area of Isfjorden, Hornsund, and the Svalbard region has been established with focus on the time period 2000-2014. 3319 manual interpretations of sea ice conditions have been conducted, resulting in two time series dividing the area of Isfjorden and Hornsund into "fast ice" (sea ice attached to the coastline), "drift ice", and "open water". The maximum fast ice coverage of Isfjorden is > 40 % in the periods 2000-2005 and 2009-2011 and stays < 30 % in 2006-2008 and 2012-2014. Fast ice cover in Hornsund reaches > 40 % in all considered years, except for 2012 and 2014, where the maximum stays < 20 %. The mean seasonal cycles of fast ice in Isfjorden and Hornsund show monthly averaged values of less than 1 % between July and November and maxima in March (Isfjorden, 35.7 %) and April (Hornsund, 42.1 %), respectively. A significant reduction of the monthly averaged fast ice coverage is found when comparing the time periods 2000-2005 and 2006-2014. The seasonal maximum decreases from 57.5 to 23.2 % in Isfjorden and from 52.6 to 35.2 % in Hornsund. A new index, called "days of fast ice" (DFI), is introduced for quantification of the interannual variation of fast ice cover, allowing for comparison between different fjords and winter seasons. Considering the time period from 1 March until end of the sea ice season, the mean DFI values for 2000-2014 are 33.1 ± 18.2 DFI (Isfjorden) and 42.9 ± 18.2 DFI (Hornsund). A distinct shift to lower DFI values is observed in 2006. Calculating a mean before and after 2006 yields a decrease from 50 to 22 DFI for Isfjorden and from 56 to 34 DFI for Hornsund. Fast ice coverage generally correlates well with remote-sensing sea surface temperature and in situ air temperature. An increase of autumn ocean heat content is observed during the last few years when the DFI values decrease. The presented sea ice time series can be utilized for various climate effect

  16. Sea ice cover in Isfjorden and Hornsund, Svalbard (2000-2014) from remote sensing data

    NASA Astrophysics Data System (ADS)

    Muckenhuber, Stefan; Nilsen, Frank; Korosov, Anton; Sandven, Stein

    2016-04-01

    A satellite database including 16 555 satellite images and ice charts displaying the area of Isfjorden, Hornsund and the Svalbard region has been established with focus on the time period 2000-2014. 3319 manual interpretations of sea ice conditions have been conducted, resulting in two time series dividing the area of Isfjorden and Hornsund into "Fast ice" (sea ice attached to the coastline), "Drift ice" and "Open water". The maximum fast ice coverage of Isfjorden is > 40 % in the periods 2000-2005 and 2009-2011 and stays < 30 % in 2006-2008 and 2012-2014. Fast ice cover in Hornsund reaches > 40 % in all considered years, except for 2012 and 2014, where the maximum stays < 20 %. The mean seasonal cycles of fast ice in Isfjorden and Hornsund show monthly averaged values of less than 1 % between July and November and maxima in March (Isfjorden, 35.7 %) and April (Hornsund, 42.1 %) respectively. A significant reduction of the monthly averaged fast ice coverage is found when comparing the time periods 2000-2005 and 2006-2014. The seasonal maximum decreases from 57.5 to 23.2 % in Isfjorden and from 52.6 to 35.2 % in Hornsund. A new index, called "days of fast ice" (DFI), is introduced for quantification of the interannual variation of fast ice cover, allowing for comparison between different fjords and winter seasons. Considering the time period from 1 March until end of the sea ice season, the mean DFI values for 2000-2014 are 33.1 ± 18.2 DFI (Isfjorden) and 42.9 ± 18.2 DFI (Hornsund). A distinct shift to lower DFI values is observed in 2006. Calculating a mean before and after 2006 yields a decrease from 50 to 22 DFI for Isfjorden and from 56 to 34 DFI for Hornsund. Fast ice coverage generally correlates well with remote-sensing sea surface temperature and in-situ air temperature. An increase of autumn ocean heat content is observed during the last few years when the DFI values decrease. The presented sea ice time series can be utilised for various climate effect

  17. Interannual and Regional Variability of Southern Ocean Snow on Sea Ice and its Correspondence with Sea Ice Cover and Atmospheric Circulation Patterns

    NASA Technical Reports Server (NTRS)

    Markus, T.; Cavalieri, D. J.

    2006-01-01

    Snow depth on sea ice plays a critical role in the heat exchange between ocean and atmosphere because of its thermal insulation property. Furthermore, a heavy snow load on the relatively thin Southern Ocean sea-ice cover submerges the ice floes below sea level, causing snow-to-ice conversion. Snowfall is also an important freshwater source into the weakly stratified ocean. Snow depth on sea-ice information can be used as an indirect measure of solid precipitation. Satellite passive microwave data are used to investigate the interannual and regional variability of the snow cover on sea ice. In this study we make use of 12 years (1992-2003) of Special Sensor Microwave/Imager (SSM/I) radiances to calculate average monthly snow depth on the Antarctic sea-ice cover. The results show a slight increase in snow depth and a partial eastward propagation of maximum snow depths, which may be related to the Antarctic Circumpolar Wave.

  18. Impact Studies of a 2 C Global Warming on the Arctic Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2004-01-01

    The possible impact of an increase in global temperatures of about 2 C, as may be caused by a doubling of atmospheric CO2, is studied using historical satellite records of surface temperatures and sea ice from late 1970s to 2003. Updated satellite data indicate that the perennial ice continued to decline at an even faster rate of 9.2 % per decade than previously reported while concurrently, the surface temperatures have steadily been going up in most places except for some parts of northern Russia. Surface temperature is shown to be highly correlated with sea ice concentration in the seasonal sea ice regions. Results of regression analysis indicates that for every 1 C increase in temperature, the perennial ice area decreases by about 1.48 x 10(exp 6) square kilometers with the correlation coefficient being significant but only -0.57. Arctic warming is estimated to be about 0.46 C per decade on average in the Arctic but is shown to be off center with respect to the North Pole, and is prominent mainly in the Western Arctic and North America. The length of melt has been increasing by 13 days per decade over sea ice covered areas suggesting a thinning in the ice cover. The length of melt also increased by 5 days per decade over Greenland, 7 days per decade over the permafrost areas of North America but practically no change in Eurasia. Statistically derived projections indicate that the perennial sea ice cover would decline considerably in 2025, 2035, and 2060 when temperatures are predicted by models to reach the 2 C global increase.

  19. Atmospheric impacts of changing sea ice cover in CO2 induced global warming

    NASA Astrophysics Data System (ADS)

    Cvijanovic, I.; Caldeira, K.

    2013-12-01

    Changes in sea ice cover have important consequences for both Earth's energy budget and atmospheric dynamics. Sea ice amplifies the effects of applied radiative forcing, insulates ocean from atmosphere and induces changes in the meridional temperature gradients thus affecting atmospheric motion in several ways. In this study, we partition and evaluate the effect of changing sea ice cover in global warming using sets of simulations with active and suppressed sea ice response. In particular, we investigate the effect of CO2 induced sea ice changes on global circulation response and extratropical precipitation extremes. Importantly, our setup employs the Atmospheric General Circulation Model coupled to a mixed layer ocean, thus enabling the atmosphere-surface ocean interactions and global atmospheric teleconnections from remote areas. Mid-latitude circulation patterns are found to be most strongly affected by the sea ice changes. In the standard, 'active' ice setup, westerly winds weaken in response to CO2-induced warming. In contrast, in the absence of sea ice response, westerly winds strengthen with global warming. These contrasting wind responses further affect the atmospheric weather patterns and extreme precipitation event development. We identify two opposing roles of sea ice decline on extreme events: (i) a dominant warming effect leads to an increase in the number and strength of extreme events; (ii) a decrease in the pole to equator gradient (a consequence of sea ice loss) acts to temper the development of precipitation extremes due to a decreased midlatitude dry static energy transport.This leads to the conclusion that for the same global temperature increase, the magnitude and frequency of mid-latitude precipitation extremes is smaller when sea ice loss is enabled than when it is suppressed. In general, in the absence of sea ice feedbacks, we find up to 35% less global warming (depending on the simulation type). This is not only due to the smaller high

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

    PubMed

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

    2016-01-01

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

  1. An Ultra Wide-Band Radar Altimeter for Ice Sheet Surface Elevation and Snow Cover Over Sea Ice Measurement

    NASA Astrophysics Data System (ADS)

    Patel, A. E.; Gogineni, P. S.; Leuschen, C.; Rodriguez-Morales, F.; Panzer, B.

    2010-12-01

    The Ice sheets of Greenland and Antarctica are losing mass at a rapid rate and there has been significant decrease in sea ice volume over the last few years. CryoSat-II with optimized radar altimeter for ice-sheet and sea ice surface elevation measurements is launched. We developed ultra wide-band FM-CW radar that operates over the frequency range from 13-17 GHz for airborne measurements. The radar is designed to provide high-resolution surface-elevation data and also map near surface layers in polar firn with high precision. It is designed to generate an ultra linear transmit chirp using a fast settling PLL with a reference signal from Direct Digital Synthesizer (DDS). The pulse length of the transmit chirp is 240-us and pulse repetition frequency is 2-KHz. The peak transmit power of the system is 100-mW, radiated using horn antennas. The radar was deployed in Greenland and Antarctica in 2009-10 as a part of Operation Ice Bridge campaign to collect data in conjunction with other instruments including Airborne Topographic Mapper (ATM) and Digital Mapping System Camera (DMS). The radar also collected data under the Cryosat-II path. This paper will provide an overview of the Ku-Band radar design along with results from the 2009-2010 field campaigns. The data collected over polar firn shows near surface internal layers down to a depth of about 15-m with a resolution of 15-cm. When flying over sea ice the radar provides snow cover thickness data to a depth of about 0.5-m. Even over highly crevassed areas, such as outlet glaciers, the radar is able to detect large surface elevation changes of a few tens of meters with high resolution.

  2. Atlantic water in Svalbard fjords: variability and effects on local sea ice cover

    NASA Astrophysics Data System (ADS)

    Sundfjord, Arild; Albretsen, Jon; Kasajima, Yoshie; Prominska, Agnieszka; Nilsen, Frank; Beszczynska-Möller, Agnieszka; Muckenhuber, Stefan; Isaksen, Ketil; Cottier, Finlo; Gerland, Sebasitan; Kohler, Jack

    2016-04-01

    Atlantic Water entering the Arctic fjords of western Svalbard transport large amounts of heat, sufficient to influence the local sea ice cover as well as contributing to glacier front melting. Recent measurement campaigns, including moorings and high-resolution surveys, spanning years with very different Atlantic Water inflow, were conducted in two fjords with different characteristics; Hornsund and Kongsfjorden. The data collected reveal a strong coupling between ocean-fjord exchanges and local sea ice cover. Possible triggering mechanisms for exchange events such as wind episodes, internal waves, and density differences are explored. Results from fine-resolution coupled ocean-sea ice model simulations complement the analysis of Atlantic Water exchange mechanisms and allow us to quantify the extent to which glacial runoff forces local circulation.

  3. The Rapidly Diminishing Arctic ice Cover and its Potential Impact on Navy Operational Considerations

    NASA Astrophysics Data System (ADS)

    Muench, R. D.; Conlon, D.; Lamb, D.

    2001-12-01

    Observations made from U.S. Navy Fleet submarines during the 1990s have revealed a dramatic decrease in thickness, when compared to historical values, of the central Arctic Ocean pack ice cover. Estimates of this decrease have been as high as 40%. Remote sensing observations have shown a coincident decrease in the areal extent of the pack. The areal decrease has been especially apparent during winter. The overall loss of ice appears to have accelerated over the past decade, raising the possibility that the Northwest Passage and the Northern Sea Route may become seasonally navigable on a regular basis in the coming decade. The ice loss has been most evident in the peripheral seas and continental shelf areas. For example, during winter 2000-2001 the Bering Sea was effectively ice-free, with strong and immediate impacts on the surrounding indigenous populations. Lessening of the peripheral pack ice cover will presumably, lead to accelerated development of the resource-rich regions that surround the deep, central Arctic Ocean basin. This raises potential issues with respect to national security and commercial interests, and has implicit strategic concerns for the Navy. The timeline for a significantly navigable Arctic may extend decades into the future; however, operational requirements must be identified in the nearer term to ensure that the necessary capabilities exist when future Arctic missions do present themselves. A first step is to improve the understanding of the coupled atmosphere/ice/ocean system. Current environmental measurement and prediction, including Arctic weather and ice prediction, shallow water acoustic performance prediction, dynamic ocean environmental changes and data to support navigation is inadequate to support sustained naval operations in the Arctic. A new focus on data collection is required in order to measure, map, monitor and model Arctic weather, ice and oceanographic conditions.

  4. FECAL INDICATOR BACTERIA PERSISTENCE UNDER NATURAL CONDITIONS IN AN ICE-COVERED RIVER

    EPA Science Inventory

    Total coliform (TC), fecal coliform (FC), and fecal streptococcus (FS) survival characteristics, under natural conditions at 0C in an ice-covered river, were examined during February and March 1975. The membrane filter (MF) technique was used throughout the study, and the multipl...

  5. IDENTIFICATION OF FECAL INDICATOR BACTERIA ISOLATES FROM AN ICE-COVERED RIVER

    EPA Science Inventory

    The membrane filter technique was used to enumerate the total coliform (TC), fecal coliform (FC), and fecal streptococcus (FS) populations at seven sample stations on an ice-covered river downstream from a major source of domestic pollution. From each membrane filter population (...

  6. New Evidence Supporting an Ice-covered Lake in Gusev Crater

    NASA Technical Reports Server (NTRS)

    Grin, E. A.; Fike, D.; Cabrol, N. A.

    2002-01-01

    The morphology and setting of a groove in Gusev strongly supports the hypothesis of a lateral channel generated by meltwater flowing against an ice covered lake margin. The size of the groove and the slope of the bed independent of the topography of the crater are consistent with modest discharges. Additional information is contained in the original extended abstract.

  7. Temporal variatiions of Sea ice cover in the Baltic Sea derived from operational sea ice products used in NWP.

    NASA Astrophysics Data System (ADS)

    Lange, Martin; Paul, Gerhard; Potthast, Roland

    2014-05-01

    Sea ice cover is a crucial parameter for surface fluxes of heat and moisture over water areas. The isolating effect and the much higher albedo strongly reduces the turbulent exchange of heat and moisture from the surface to the atmosphere and allows for cold and dry air mass flow with strong impact on the stability of the whole boundary layer and consequently cloud formation as well as precipitation in the downstream regions. Numerical weather centers as, ECMWF, MetoFrance or DWD use external products to initialize SST and sea ice cover in their NWP models. To the knowledge of the author there are mainly two global sea ice products well established with operational availability, one from NOAA NCEP that combines measurements with satellite data, and the other from OSI-SAF derived from SSMI/S sensors. The latter one is used in the Ostia product. DWD additionally uses a regional product for the Baltic Sea provided by the national center for shipping and hydrografie which combines observations from ships (and icebreakers) for the German part of the Baltic Sea and model analysis from the hydrodynamic HIROMB model of the Swedish meteorological service for the rest of the domain. The temporal evolution of the three different products are compared for a cold period in Februar 2012. Goods and bads will be presented and suggestions for a harmonization of strong day to day jumps over large areas are suggested.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  9. SIMPL Laser Altimeter Measurements of Lake Erie Ice Cover: a Pathfinder for ICESat-2

    NASA Astrophysics Data System (ADS)

    Harding, D. J.; Dabney, P.; Valett, S. R.; Kelly, A.

    2010-12-01

    NASA’s ICESat-2 missions, scheduled for launch in 2015, will make measurements of ice sheet elevation change, sea ice thickness change and vegetation height using a micro-pulse, multi-beam laser altimeter employing single photon ranging at 532 nm (green). Lake Erie ice and snow cover data acquired in February 2009 by the Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) provides pathfinder information enabling improved understanding of this next-generation altimeter measurement approach. SIMPL is an airborne, multi-beam laser altimeter developed through the NASA Earth Science Technology Office Instrument Incubator Program with a focus on cryopshere remote sensing. SIMPL operates at 532 nm and 1064 nm using a micropulse laser, achieving a ranging precision of 8 cm per single photon, and acquires reflected energy parallel and perpendicular to the transmit pulse polarization plane. Approximately 30,000 single photon returns per second are acquired from snow and ice at the nominal flight altitude of 8,000 ft. The resulting two-color information on surface and volume scattering properties enables differentiation of open water and ice types with varying optical properties. For open water, SIMPL data documents laser pulse penetration at 532 nm in the water column, relative to the surface defined by the 1064 nm data. And increasing amount of perpendicularly polarized light with depth relative to the parallel polarization, indicating an increasing fraction of multiply scattered photons, provides a measure of water column optical depth. The observed ice cover types (skim, nias, new grey ice, new grey-white ice) represent the early stages of sea ice formation. Differences in surface roughness and transparency of the ice types are indicated by the 532 nm and 1064 nm perpendicular/parallel depolarization ratio measures of the degree of multiple scattering. The understanding of laser pulse interactions with water, ice and snow using this first-of-its-kind data set

  10. Changes in atmospheric circulation and ocean ice cover over the North Atlantic during the last 41,000 years

    SciTech Connect

    Mayewski, P.A.; Meeker, L.D.; Whitlow, S.; Twickler, M.S.; Morrison, M.C. ); Bloomfield, P. ); Alley, R.B. ); Gow, A.J.; Meese, D.A. ); Grootes, P.M. )

    1994-03-25

    High-resolution, continuous multivariate chemical records from a central Greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41,000 years. These chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to Greenland [defined here as the polar circulation index (PC)] and in the extent of ocean ice cover. Massive iceberg discharge events previously defined from the marine record are correlated with notable expansion of ocean ice cover and increases in PCI. During stadials without discharge events, ocean ice cover appears to reach some common maximum level. The massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling.

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

    PubMed

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

    2012-02-01

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

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

    EPA Science Inventory

    Abstract

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

  13. Extreme ecological response of a seabird community to unprecedented sea ice cover

    PubMed Central

    Barbraud, Christophe; Delord, Karine; Weimerskirch, Henri

    2015-01-01

    Climate change has been predicted to reduce Antarctic sea ice but, instead, sea ice surrounding Antarctica has expanded over the past 30 years, albeit with contrasted regional changes. Here we report a recent extreme event in sea ice conditions in East Antarctica and investigate its consequences on a seabird community. In early 2014, the Dumont d'Urville Sea experienced the highest magnitude sea ice cover (76.8%) event on record (1982–2013: range 11.3–65.3%; mean±95% confidence interval: 27.7% (23.1–32.2%)). Catastrophic effects were detected in the breeding output of all sympatric seabird species, with a total failure for two species. These results provide a new view crucial to predictive models of species abundance and distribution as to how extreme sea ice events might impact an entire community of top predators in polar marine ecosystems in a context of expanding sea ice in eastern Antarctica. PMID:26064653

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

    USGS Publications Warehouse

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

    1998-01-01

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

  15. Trends in annual minimum exposed snow and ice cover in High Mountain Asia from MODIS

    NASA Astrophysics Data System (ADS)

    Rittger, Karl; Brodzik, Mary J.; Painter, Thomas H.; Racoviteanu, Adina; Armstrong, Richard; Dozier, Jeff

    2016-04-01

    Though a relatively short record on climatological scales, data from the Moderate Resolution Imaging Spectroradiometer (MODIS) from 2000-2014 can be used to evaluate changes in the cryosphere and provide a robust baseline for future observations from space. We use the MODIS Snow Covered Area and Grain size (MODSCAG) algorithm, based on spectral mixture analysis, to estimate daily fractional snow and ice cover and the MODICE Persistent Ice (MODICE) algorithm to estimate the annual minimum snow and ice fraction (fSCA) for each year from 2000 to 2014 in High Mountain Asia. We have found that MODSCAG performs better than other algorithms, such as the Normalized Difference Index (NDSI), at detecting snow. We use MODICE because it minimizes false positives (compared to maximum extents), for example, when bright soils or clouds are incorrectly classified as snow, a common problem with optical satellite snow mapping. We analyze changes in area using the annual MODICE maps of minimum snow and ice cover for over 15,000 individual glaciers as defined by the Randolph Glacier Inventory (RGI) Version 5, focusing on the Amu Darya, Syr Darya, Upper Indus, Ganges, and Brahmaputra River basins. For each glacier with an area of at least 1 km2 as defined by RGI, we sum the total minimum snow and ice covered area for each year from 2000 to 2014 and estimate the trends in area loss or gain. We find the largest loss in annual minimum snow and ice extent for 2000-2014 in the Brahmaputra and Ganges with 57% and 40%, respectively, of analyzed glaciers with significant losses (p-value<0.05). In the Upper Indus River basin, we see both gains and losses in minimum snow and ice extent, but more glaciers with losses than gains. Our analysis shows that a smaller proportion of glaciers in the Amu Darya and Syr Darya are experiencing significant changes in minimum snow and ice extent (3.5% and 12.2%), possibly because more of the glaciers in this region are smaller than 1 km2 than in the Indus

  16. The influence of sea ice cover on air-sea gas exchange estimated with radon-222 profiles

    NASA Astrophysics Data System (ADS)

    Rutgers van der Loeff, Michiel M.; Cassar, Nicolas; Nicolaus, Marcel; Rabe, Benjamin; Stimac, Ingrid

    2014-05-01

    Air-sea gas exchange plays a key role in the cycling of greenhouse and other biogeochemically important gases. Although air-sea gas transfer is expected to change as a consequence of the rapid decline in summer Arctic sea ice cover, little is known about the effect of sea ice cover on gas exchange fluxes, especially in the marginal ice zone. During the Polarstern expedition ARK-XXVI/3 (TransArc, August/September 2011) to the central Arctic Ocean, we compared 222Rn/226Ra ratios in the upper 50 m of 14 ice-covered and 4 ice-free stations. At three of the ice-free stations, we find 222Rn-based gas transfer coefficients in good agreement with expectation based on published relationships between gas transfer and wind speed over open water when accounting for wind history from wind reanalysis data. We hypothesize that the low gas transfer rate at the fourth station results from reduced fetch due to the proximity of the ice edge, or lateral exchange across the front at the ice edge by restratification. No significant radon deficit could be observed at the ice-covered stations. At these stations, the average gas transfer velocity was less than 0.1 m/d (97.5% confidence), compared to 0.5-2.2 m/d expected for open water. Our results show that air-sea gas exchange in an ice-covered ocean is reduced by at least an order of magnitude compared to open water. In contrast to previous studies, we show that in partially ice-covered regions, gas exchange is lower than expected based on a linear scaling to percent ice cover.

  17. Estimation of Greenland's Ice Cover Melting Area Using the Atmospheric Infrared Sounder (AIRS)

    NASA Astrophysics Data System (ADS)

    Imbiriba, B.; Desouza-Machado, S. G.; Hannon, S.; Strow, L. L.

    2012-12-01

    Using the Atmospheric Infrared Sounder (AIRS), we are able to detect the melting of Greenland's ice cover for the July 12, 2012 warming event and estimate the corresponding fractional melted area. We collect all of AIRS' overpasses above Greenland, using the reflected solar radiation to avoid cloudy scenes. We perform a retrieval of the skin surface temperature in order to classify a scene as likely frozen (skin temperature well below the freezing point), likely melted (skin temperature well above freezing point), or thawing. Using empirical snow and water emissivity data we retrieve an effective scene snow/water fraction. For this day we estimate that 90% of the ice cover exhibits some thawing and that 53% of the ice cover area was effectivelly covered with liquid water. For contrast we also look at July 8, 2012, and verify that most of the island, 68%, was frozen at that date. We also see a correlation of the thawing area with the solar angle as the day progresses.

  18. Changes in sea-ice cover and temperature in the Western Ross Sea during the Holocene

    NASA Astrophysics Data System (ADS)

    Fleury, Sophie; Kim, Jung-Hyun; Gal, Jong-Ku; Mezgec, Karin; Belt, Simon; Smik, Lukas; Stenni, Barbara; Melis, Romana; Crosta, Xavier; Shin, Kyung-Hoon

    2016-04-01

    Although changes in sea-ice cover contribute to global climatic variations, they are poorly constrained for periods earlier than the last decades. More records are especially required around Antarctica, where the formation of Antarctic Bottom Waters participates to global thermohaline circulation. However, this region provided only a few marine sediment cores spanning the entire Holocene, especially because of generally low sedimentation rates. This study focuses on marine sediment core ANTA99-CJ5 (73°49'S; 175°39'E), located in the open sea ice zone (OSIZ) of the western Ross Sea. We analyzed several lipid biomarkers: highly branched isoprenoids (HBIs), sterols, diols and GDGTs. The combination of several biomarkers and the comparison of these results with a diatom record previously published on the same core enabled us to trace past changes in temperatures as well as in sea-ice condition over the last 11,600 years.

  19. Ice Prevention on Aircraft by Means of Impregnated Leather Covers, Special Report

    NASA Technical Reports Server (NTRS)

    Clay, William C.

    1935-01-01

    The National Advisory Committee for Aeronautics is testing the effectiveness of a method to prevent the formation of ice on airplanes. The system makes use of a leather cover that is attached to the leading edge of the wing. A small tube, attached to the inner surface of the leather, distributes to the leading edge a solution that permeates throughout the leather and inhibits the formation of ice on the surface. About 25 pounds of the liquid per hour would be sufficient to prevent ice from forming on a wing of 50-foot span. The additional gross weight of the system will not be excessive. The tests are not yet completed but the method is thought to be practicable for the wing and it may also be adaptable to the propeller.

  20. Integration and Visualization of Multiple Sensors in Generating the NOAA Operational Snow and Ice Cover Products

    NASA Astrophysics Data System (ADS)

    Li, M.; Helfrich, S.

    2011-12-01

    Global snow and ice cover is a key component in the climate and hydrologic system as well as daily weather forecasting. The National Oceanic and Atmospheric Administration (NOAA) has produced a daily northern hemisphere snow and ice cover chart since 1997 through the Interactive Multisensor Snow and Ice Mapping System (IMS). The IMS integrates and visualizes a wide variety of satellite data, as well as derived snow/ice products and surface observations, to provide meteorologists with the ability to interactively prepare the daily northern hemisphere snow and ice cover chart. These products are presently used as operational inputs into several weather prediction models and are applied in climate monitoring. The IMS is currently on its second version (released in 2004) and scheduled to be upgraded to the third version (V3) in 2013. The IMS V3 will have nearly 40 external inputs as data sources processed by the IMS, which fall into five data formats: binary image, HDF file, GeoTIFF image, Shapefile image and ASCII file. With the exception of the GeoTIFF and Shapefile files, which are used directly by IMS, all other types of data are pre-processed to ENVI image file format and "sectorized" for different areas around the northern hemisphere. The IMS V3 will generate daily snow and ice cover maps in five formats: ASCII, ENVI, GeoTIFF, GIF and GRIB2 and three resolutions: 24km, 4km and 1km. In this presentation, the methods are discussed for accessing and processing satellite data, model results and surface reports. All input data with varying formats and resolutions are processed to a fixed projection. The visualization methodology for IMS are provided for five different resolutions of 48km, 24km, 8km, 4km, 2km and 1km. This work will facilitate the future enhancement of IMS, provide users with an understanding of the software architecture, provide a prospectus on future data sources, and help to preserve the integrity of the long-standing satellite-derived snow and ice

  1. Modelling changes in the dielectric and scattering properties of young snow-covered sea ice at GHz frequencies

    NASA Technical Reports Server (NTRS)

    Drinkwater, Mark R.; Crocker, G. B.

    1988-01-01

    Observations of the physical properties of the snow cover and underlying young fast ice in Resolute Passage, Canada, were made during the winter of 1982. Detailed measurements of snow density and ice and snow temperatures, salinities, and brine volumes were made over a period of 46 d, beginning when the ice was 0.4 m thick and about 9 d old. The recorded values are used in a theoretical mixture model to predict the dielectric properties of the snow cover over the microwave frequency range. The results of this analysis are then used to investigate the effects of the snow properties on the radar backscatter signatures of young sea ice. The results show that backscatter is a function of the incidence angle and can change significantly over short periods of time during the early evolutionary phase of ice and snow-cover development. This has important consequences for the identification of young ice forms from SAR or SLAR images.

  2. Improved identification of clouds and ice/snow covered surfaces in SCIAMACHY observations

    NASA Astrophysics Data System (ADS)

    Krijger, J. M.; Tol, P.; Istomina, L. G.; Schlundt, C.; Schrijver, H.; Aben, I.

    2011-10-01

    In the ultra-violet, visible and near infra-red wavelength range the presence of clouds can strongly affect the satellite-based passive remote sensing observation of constituents in the troposphere, because clouds effectively shield the lower part of the atmosphere. Therefore, cloud detection algorithms are of crucial importance in satellite remote sensing. However, the detection of clouds over snow/ice surfaces is particularly difficult in the visible wavelengths as both clouds an snow/ice are both white and highly reflective. The SCIAMACHY Polarisation Measurement Devices (PMD) Identification of Clouds and Ice/snow method (SPICI) uses the SCIAMACHY measurements in the wavelength range between 450 nm and 1.6 μm to make a distinction between clouds and ice/snow covered surfaces, specifically developed to identify cloud-free SCIAMACHY observations. For this purpose the on-board SCIAMACHY PMDs are used because they provide higher spatial resolution compared to the main spectrometer measurements. In this paper we expand on the original SPICI algorithm (Krijger et al., 2005a) to also adequately detect clouds over snow-covered forests which is inherently difficult because of the similar spectral characteristics. Furthermore the SCIAMACHY measurements suffer from degradation with time. This must be corrected for adequate performance of SPICI over the full SCIAMACHY time range. Such a correction is described here. Finally the performance of the new SPICI algorithm is compared with various other datasets, such as from FRESCO, MICROS and AATSR, focusing on the algorithm improvements.

  3. Light reflection from a sea-ice cover during the onset of summer melt

    NASA Astrophysics Data System (ADS)

    Perovich, Donald K.; Govoni, John W.

    1992-12-01

    A knowledge of the reflection of light from a sea ice cover is important for both the interpretation of remote sensing imagery at visible and near-infrared wavelengths and for climatological studies involving the energy balance of the polar regions. Spectral measurements of albedo, bidirectional reflectance function (BDRF), and polarized reflectance were made for sea ice conditions found during the onset of melt in the Canadian Arctic. The wavelength region studied was from the ultraviolet to the near infrared (370 - 1000 nm). Results for five surface types are presented: (1) dry snow, (2) dry snow with a glazed surface, (3) bare ice, (4) blue ice, and (5) a melt pond. Results indicate that spectral albedos decrease at all wavelengths as the melt season progresses and the surface conditions evolve from (1) through (5), and that the decrease is most pronounced at longer wavelengths. Reflectance data suggest that (1) at most angles reflectance has the same spectral shape as albedo, (2) at 30 degree(s) elevation reflectance is for the most part azimuthally isotropic and (3) at 60 degree(s) elevation a significant specular component was evident at 0 degree(s) azimuth, especially for the bare ice case.

  4. Automated mapping of persistent ice and snow cover across the western U.S. with Landsat

    NASA Astrophysics Data System (ADS)

    Selkowitz, David J.; Forster, Richard R.

    2016-07-01

    We implemented an automated approach for mapping persistent ice and snow cover (PISC) across the conterminous western U.S. using all available Landsat TM and ETM+ scenes acquired during the late summer/early fall period between 2010 and 2014. Two separate validation approaches indicate this dataset provides a more accurate representation of glacial ice and perennial snow cover for the region than either the U.S. glacier database derived from US Geological Survey (USGS) Digital Raster Graphics (DRG) maps (based on aerial photography primarily from the 1960s-1980s) or the National Land Cover Database 2011 perennial ice and snow cover class. Our 2010-2014 Landsat-derived dataset indicates 28% less glacier and perennial snow cover than the USGS DRG dataset. There are larger differences between the datasets in some regions, such as the Rocky Mountains of Northwest Wyoming and Southwest Montana, where the Landsat dataset indicates 54% less PISC area. Analysis of Landsat scenes from 1987-1988 and 2008-2010 for three regions using a more conventional, semi-automated approach indicates substantial decreases in glaciers and perennial snow cover that correlate with differences between PISC mapped by the USGS DRG dataset and the automated Landsat-derived dataset. This suggests that most of the differences in PISC between the USGS DRG and the Landsat-derived dataset can be attributed to decreases in PISC, as opposed to differences between mapping techniques. While the dataset produced by the automated Landsat mapping approach is not designed to serve as a conventional glacier inventory that provides glacier outlines and attribute information, it allows for an updated estimate of PISC for the conterminous U.S. as well as for smaller regions. Additionally, the new dataset highlights areas where decreases in PISC have been most significant over the past 25-50 years.

  5. Tree rings, solar radiation and ice cover of the Barents sea

    NASA Astrophysics Data System (ADS)

    Kasatkina, Elena; Shumilov, Oleg; Timonen, Mauri; Kanatjev, Alexandr

    2015-04-01

    Intercomparisons of the Kola Peninsula tree-ring records, ice cover of the Barents sea and sea and surface temperatures have been made. Tree-ring series over the last 100 years showed a highly significant correlation with the sea surface temperatures and ice cover (r=-0.57, p<0.05). It should be noted that the correlation between the tree-ring widths and local temperatures was not so high. We suppose that a possible reason seems to be the prevailing influence of solar irradiance and their UV components on tree growth in the Kola North. It is known that solar variability and fluctuations of solar irradiance in the UV band of the spectrum has increased over the last decades. In addition, there are frequent cases of total ozone content depletions (or so-called ozone mini-holes) resulting in increased UV-B. The recent studies demonstrate that many boreal and subarctic plants have increased susceptibility to UV-B radiation. An indirect confirmation of the hypothesis proposed is a close relationship between solar total irradiance and global sea surface temperature (Reid, 2000). The results of spectral MTM-analysis also revealed periodicities close to the solar cycles in the ice cover and tree-ring records. These results confirm the above-mentioned interpretation.

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

    PubMed

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

    2007-03-01

    The effect of the heat interaction between a water column and sediments on the formation, development, and duration of existence of anaerobic zones in ice-covered lakes is estimated based on observational data from five frozen lakes located in northwestern Russia and North America. A simple one-dimensional model that describes the formation and development of the dissolved oxygen deficit in shallow ice-covered lakes is suggested. The model reproduces the main features of dissolved oxygen dynamics during the ice-covered period; that is, the vertical structure, the thickness, and the rate of increase of the anaerobic zone in bottom layers. The model was verified against observational data. The results from the verification show that the model adequately describes the dissolved oxygen dynamics in winter. The consumption rates of DO by bacterial plankton and by bottom sediments, which depend on the heat transfer through the water-sediment interface, are calculated. The results obtained allow the appearance of potentially dangerous anaerobic zones in shallow lakes and in separate lake areas, which result from thermal regime changes, to be predicted. PMID:17115190

  7. Trends and variability in summer sea ice cover in the Canadian Arctic based on the Canadian Ice Service Digital Archive, 1960-2008 and 1968-2008

    NASA Astrophysics Data System (ADS)

    Tivy, Adrienne; Howell, Stephen E. L.; Alt, Bea; McCourt, Steve; Chagnon, Richard; Crocker, Greg; Carrieres, Tom; Yackel, John J.

    2011-03-01

    The Canadian Ice Service Digital Archive (CISDA) is a compilation of weekly ice charts covering Canadian waters from the early 1960s to present. The main sources of uncertainty in the database are reviewed and the data are validated for use in climate studies before trends and variability in summer averaged sea ice cover are investigated. These data revealed that between 1968 and 2008, summer sea ice cover has decreased by 11.3% ± 2.6% decade-1 in Hudson Bay, 2.9% ± 1.2% decade-1 in the Canadian Arctic Archipelago (CAA), 8.9% ± 3.1% decade-1 in Baffin Bay, and 5.2% ± 2.4% decade-1 in the Beaufort Sea with no significant reductions in multiyear ice. Reductions in sea ice cover are linked to increases in early summer surface air temperature (SAT); significant increases in SAT were observed in every season and they are consistently greater than the pan-Arctic change by up to ˜0.2°C decade-1. Within the CAA and Baffin Bay, the El Niño-Southern Oscillation index correlates well with multiyear ice coverage (positive) and first-year ice coverage (negative) suggesting that El Niño episodes precede summers with more multiyear ice and less first-year ice. Extending the trend calculations back to 1960 along the major shipping routes revealed significant decreases in summer sea ice coverage ranging between 11% and 15% decade-1 along the route through Hudson Bay and 6% and 10% decade-1 along the southern route of the Northwest Passage, the latter is linked to increases in SAT. Between 1960 and 2008, no significant trends were found along the northern western Parry Channel route of the Northwest Passage.

  8. Tracking and responding to a changing Arctic sea-ice cover: How ice users can help the scientific community design better observing systems (Louis Agassiz Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Eicken, Hajo

    2010-05-01

    The Arctic sea-ice cover is undergoing a major transformation, with substantial reductions in summer ice extent reflecting changes in ice thickness, age, and circulation. These changes are impacting Arctic ecosystems and a range of human activities. Anticipating and responding to such impacts, exacerbated by increasing economic activity in parts of the Arctic, requires a foundation of environmental observations and model predictions. Recent increases in industrial activities such as shipping and resource development in parts of the Arctic have further highlighted the need for an integrated observing system. In the case of a changing sea-ice cover, how would one best design and optimize such a system? One of the challenges is to meet the information needs of the scientific community in furthering fundamental understanding of the Arctic system, as well as those of key stakeholders and society, helping them to prepare for and respond to Arctic change. This presentation focuses on how the concept of sea-ice system services, i.e., the uses and benefits (or harm) derived from sea ice, may help guide the implementation of an effective observing system. Principal service categories are (1) sea ice as climate regulator, marine hazard, and coastal buffer; (2) transportation and use of ice as a platform; (3) cultural services obtained from the "icescape"; and (4) support of food webs and biological diversity by sea ice. An analysis of the different ice services provided to different user groups can help prioritize different types of observations and determine optimal measurement strategies. Moreover, the focus on different uses of the ice cover may also help synthesize fundamental and applied research to help Arctic communities adapt in a changing environment. Alaska has experienced some of the most substantial changes in sea-ice conditions throughout the Arctic over the past three decades and is used to illustrate the concepts discussed above. Specifically, we have examined

  9. Historic cartographic evidence for Holocene changes in the Antarctic ice cover

    NASA Astrophysics Data System (ADS)

    Weihaupt, John G.

    1984-04-01

    Roughly 125,000 years ago, the earth underwent a climatic warming trend [Bergen and Van Couvering, 1979] called the Sangamon. This occurred more than 1 million years after the commencement of the Pleistocene time of great glacial advances which brought ice sheets of continental proportions to North America, northern Europe, and Siberia. That interglacial warming trend is the most pronounced climatic warming that we know during the period of the Ice Ages [Mitchell, 1977]. The Sangamon was followed, however, by a time of lower worldwide temperatures when the glaciers advanced once more and until a new warming trend commenced some 20,000-30,000 years ago. Earth's glaciers and ice sheets then began to retreat again, and about 10,000 years ago the last vestiges of these northern continental ice sheets withdrew as the latest warm interglacial, the Holocene, began. The Holocene continues today. Earth's atmospheric and oceanic temperatures rose in this time, well after Neanderthal and Cro-Magnon men lived in Asia and in Europe. The Holocene warming has been synchronous in both hemispheres and led to a worldwide climatic optimum, called the Hypsithermal interval, between 9,000 and 2,500 years ago [Deevey, 1957]. The Hypsithermal interval was the warmest part of the Holocene to date, and it largely preceded the Bronze Age, which commenced about 3,000 years ago. While the continental ice sheets of North America, Europe, and Asia disintegrated with the approach of the Holocene, the great ice sheets that cover Greenland and Antartica remained stable and largely unchanged at least since the warm Sangamon interglacial of 125,000 years ago.

  10. Last glacial-interglacial sea-ice cover in the SW Atlantic and its potential role in global deglaciation

    NASA Astrophysics Data System (ADS)

    Allen, Claire S.; Pike, Jennifer; Pudsey, Carol J.

    2011-09-01

    Sea-ice growth and decay in Antarctica is one of the biggest seasonal changes on Earth, expanding ice cover from 4 × 10 6 km 2 to a maximum of 19 × 10 6 km 2 during the austral winter. Analyses of six marine sediment cores from the Scotia Sea, SW Atlantic, yield records of sea-ice migration across the basin since the Lateglacial. The cores span nearly ten degrees of latitude from the modern seasonal sea-ice zone to the modern Polar Front. Surface sediments in the cores comprise predominantly diatomaceous oozes and muddy diatom oozes that reflect Holocene conditions. The cores exhibit similar down-core stratigraphies with decreasing diatom concentrations and increasing magnetic susceptibility from modern through to the Last Glacial Maximum (LGM). Sediments in all cores contain sea-ice diatoms that preserve a signal of changing sea-ice cover and permit reconstruction of past sea-ice dynamics. The sea-ice records presented here are the first to document the position of both the summer and winter sea-ice cover at the Last Glacial Maximum (LGM) in the Scotia Sea. Comparison of the LGM and Holocene sea-ice conditions shows that the average winter sea-ice extent was at least 5° further north at the LGM. Average summer sea-ice extent was south of the most southerly core site at the LGM, and suggests that sea-ice expanded from approximately ˜61°S to ˜52°S each season. Our data also suggest that the average summer sea-ice position at the LGM was not the maximum extent of summer sea-ice during the last glacial. Instead, the sediments contain evidence of a pre-LGM maximum extent of summer sea-ice between ˜30 ka and 22 ka that extended to ˜59°S, close to the modern average winter sea-ice limit. Based on our reconstruction we propose that the timing of the maximum extent of summer sea-ice and subsequent retreat by 22 ka, could be insolation controlled and that the strong links between sea-ice and bottom water formation provide a potential mechanism by which Southern

  11. Monitoring Inland Ice Cover under All-weather Conditions with the Combined Use of Microwave and GOES-R Observations

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Key, J. R.; Wang, X.

    2010-12-01

    The cryosphere exists at all latitudes and in about one hundred countries. Not only does the cryosphere play a significant role in climate, but also it has profound socio-economic value, especially over inland water, including lakes and rivers, due to its role in water resources and its impact on transportation, fisheries, hunting, herding, and agriculture. A number of ice characterization algorithms have been improved and/or developed for the next generation Geostationary Operational Environmental Satellite (GOES-R) Advanced Baseline Imager (ABI), including ice identification, ice concentration, ice thickness and age, and ice motion. These products will play an important role in monitoring ice cover over inland water considering its high spatial, temporal, and spectral resolution. However, the effectiveness of such products is constrained by cloud cover. Lake ice products from microwave observations are less affected by clouds, but their quality is hindered by coarse spatial and temporal resolution as well as contamination by the land surface. Optimization of all-weather ice products from microwave observations, and ice products with higher spatial and temporal resolutions from GOES-R enables us to monitor the ice characteristics over the inland water surfaces, e.g., the Great Lakes, effectively in real time under all-weather conditions, and improves the products that are being developed for ABI. The combined used of both products provides accurate, timely information on ice characteristics over inland water surfaces to meet the needs of transportation and winter weather forecasting. An overview of the ice cover, concentration, and motion products for both GOES-R and microwave observation will be given, and case studies of combining both products for monitoring ice characteristics over inland water will be presented.

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

    PubMed

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

    2016-01-01

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

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

    PubMed Central

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

    2016-01-01

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

  14. Soliton-like structures on a liquid surface under an ice cover

    NASA Astrophysics Data System (ADS)

    Il'ichev, A. T.; Tomashpolskii, V. Ya.

    2015-02-01

    For a complete system of equations describing wave propagation in a fluid of finite depth under an ice cover, we prove the existence of soliton-like solutions corresponding to a family of solitary waves of surface level depression. The ice cover is modeled as a Kirchhoff-Love elastic plate and has a significant thickness such that the plate inertia is taken into account in the model formulation. The family of solitary waves is parameterized by the wave propagation velocity, and its existence is proved for velocities that bifurcate from the characteristic velocity of linear waves and are rather close to this velocity. In turn, the solitary waves bifurcate from the rest state and are located in its neighborhood. In other words, we prove the existence of small-amplitude solitary waves of water-ice interface level depression. The proof uses the projection of the sought system of equations onto the center manifold (whose dimensionality is two in this case) and a further analysis of a finite-dimensional reduced dynamical system on the center manifold.

  15. Sea Ice SAR Signature Dependence on Thaw and Refreeze Event in the Snow Cover

    NASA Astrophysics Data System (ADS)

    Hudier, E. J.; Tolszczuk-Leclerc, S.

    2010-12-01

    As a result of the dependence of microwaves on the dielectric properties of the material they interfere with, the microwave signature of sea ice changes dramatically with the seasons as well as overnight when the snow layer is at the freezing point While pure ice and dry snow do not cause significant scattering and can be considered transparent throughout the winter season, the presence of liquid water, later on at spring, on air-ice or air-snow interfaces or within the snow cover turns the snow layer into an opaque medium and makes the air-snow interface the main contributor of the microwave backscattered to the SAR antenna. The availability of liquid water in the snow is the result of a shift in the thermodynamic balance of the snow layer and sea ice sheet. At spring, with the irradiance and air temperature increasing, the snow media quickly becomes isothermal. The snow layer is then a tri-phasic medium in which water changes state to balance radiations (short and long waves) and conductive heat fluxes variations. As a consequence, the surface layer of the snow cover is subject to a diurnal cycle of thaw during day time and refreeze at night which translates into a parallel diurnal cycle on snow wetness content. This cycle is of major relevance to microwave remote sensing applications and specifically to sea ice morphological features extraction. Using the output of a thermodynamic model of an isothermal snow cover forced by incoming L↓ and outgoing L↑ long-wave radiations, incident S↓ and reflected S↑ short-wave radiations and a turbulent atmospheric heat flux Qatm, an evaluation of the volume and surface components of a backscattered SAR is computed as a function of the SAR incident angle. We observe that when heat fluxes (irradiative and conductive) are positive, liquid water available in the top layer of the snow cover turns the air-snow interface into a specular reflector. Conversely, with wetness decreasing overnight, more energy can penetrate the

  16. Evolution of sea ice drift, deformation and fracturing during the last decades and their role on the decline of the Arctic sea ice cover

    NASA Astrophysics Data System (ADS)

    Weiss, J.; Rampal, P.; Marsan, D.

    2009-04-01

    Using buoy data from the International Arctic Buoy Program, we found that the sea ice mean speed over the Arctic has substantially increased over the last 29 years (+17% per decade for winter; +8.5% for summer). We check that these trends were not affected by temporal or spatial sampling bias. A strong seasonal dependence of the mean speed is also revealed, with a maximum in October and a minimum in April, i.e. out of phase, lagging by 6 months with respect to the sea ice extent seasonal variability. The sea ice mean strain rate, deduced from the dispersion of buoys trajectories, also increased significantly over the period (+51% per decade for winter; +52% for summer). We check that these increases in both sea ice mean speed and deformation rate are unlikely a consequence of a stronger atmospheric forcing, as the mean wind speed over the Arctic did not increase significantly over the period. Instead, they suggest that sea ice kinematics plays a fundamental role in the albedo feedback loop and sea ice decline: increasing deformation means stronger fracturing, hence more lead opening and therefore a decreasing albedo. This accelerates sea ice thinning in summer and delays refreezing in early winter, therefore decreasing the mechanical strength of the cover and allowing even more fracturing and larger drifting speed and deformation, and possibly a faster export of sea ice through the Fram Strait. The September minimum sea ice extent of 2007 might be a good illustration of this interplay between sea ice deformation and sea ice shrinking, as we found that for both winter 2006-2007 and summer 2007, exceptionally large deformation rates affected the Arctic sea ice cover, in agreement with a much faster than expected drift of the polar schooner Tara during its journey along the transpolar current.

  17. 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, Mari F.; Nilsson, Johan; Nisancioglu, Kerim H.

    2016-02-01

    Changes in the sea ice cover of the Nordic Seas have been proposed to play a key role for the dramatic temperature excursions associated with the Dansgaard-Oeschger events during the last glacial. 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 Nordic Seas, and consists of a sea ice component and a two-layer ocean. 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 diapycnal flow. In a system where the diapycnal flow increases with density differences, the sea ice acts as a positive feedback on a freshwater perturbation. If the diapycnal flow decreases with density differences, 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 the temperature of the deep ocean do not need to increase as much as previously thought to provoke abrupt changes in sea ice.

  18. Into the Deep Black Sea: The Icefin Modular AUV for Ice-Covered Ocean Exploration

    NASA Astrophysics Data System (ADS)

    Meister, M. R.; Schmidt, B. E.; West, M. E.; Walker, C. C.; Buffo, J.; Spears, A.

    2015-12-01

    The Icefin autonomous underwater vehicle (AUV) was designed to enable long-range oceanographic exploration of physical and biological ocean environments in ice-covered regions. The vehicle is capable of surveying under-ice geometry, ice and ice-ocean interface properties, as well as water column conditions beneath the ice interface. It was developed with both cryospheric and planetary-analog exploration in mind. The first Icefin prototype was successfully operated in Antarctica in Austral summer 2014. The vehicle was deployed through a borehole in the McMurdo Ice Shelf near Black Island and successfully collected sonar, imaging, video and water column data down to 450 m depth. Icefin was developed using a modular design. Each module is designed to perform specific tasks, dependent on the mission objective. Vehicle control and data systems can be stably developed, and power modules added or subtracted for mission flexibility. Multiple sensor bays can be developed in parallel to serve multiple science objectives. This design enables the vehicle to have greater depth capability as well as improved operational simplicity compared to larger vehicles with equivalent capabilities. As opposed to those vehicles that require greater logistics and associated costs, Icefin can be deployed through boreholes drilled in the ice. Thus, Icefin satisfies the demands of achieving sub-ice missions while maintaining a small form factor and easy deployment necessary for repeated, low-logistical impact field programs. The current Icefin prototype is 10.5 inches in diameter by 10 feet long and weighs 240 pounds. It is comprised of two thruster modules with hovering capabilities, an oceanographic sensing module, main control module and a forward-sensing module for obstacle avoidance. The oceanographic sensing module is fitted with a side scan sonar (SSS), CT sensor, altimetry profiler and Doplar Velocity Log (DVL) with current profiling. Icefin is depth-rated to 1500 m and is equipped with

  19. Data sets for snow cover monitoring and modelling from the National Snow and Ice Data Center

    NASA Astrophysics Data System (ADS)

    Holm, M.; Daniels, K.; Scott, D.; McLean, B.; Weaver, R.

    2003-04-01

    A wide range of snow cover monitoring and modelling data sets are pending or are currently available from the National Snow and Ice Data Center (NSIDC). In-situ observations support validation experiments that enhance the accuracy of remote sensing data. In addition, remote sensing data are available in near-real time, providing coarse-resolution snow monitoring capability. Time series data beginning in 1966 are valuable for modelling efforts. NSIDC holdings include SMMR and SSM/I snow cover data, MODIS snow cover extent products, in-situ and satellite data collected for NASA's recent Cold Land Processes Experiment, and soon-to-be-released ASMR-E passive microwave products. The AMSR-E and MODIS sensors are part of NASA's Earth Observing System flying on the Terra and Aqua satellites Characteristics of these NSIDC-held data sets, appropriateness of products for specific applications, and data set access and availability will be presented.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  1. Transient atmospheres on Charon and water-ice covered KBOs resulting from comet impacts

    NASA Astrophysics Data System (ADS)

    Stern, S. Alan; Gladstone, Randall; Zangari, Amanda; Fleming, Thadeus; Goldstein, David

    2015-01-01

    Evidence from stellar occultation datasets and Charon's H2O-ice dominated surface composition has long suggested a lack of any current atmosphere around this satellite planet. However, impacts from both Kuiper Belt and Oort Cloud comets must from time to time import N2, CH4, and other cometary super-volatiles that can create temporary atmospheres around Charon. Here we estimate the frequency of such cometary impacts on Charon and the imported mass of super-volatiles from each such impact. We then examine the characteristics of such transient atmospheric events, including their column densities, mean molecular weights, scale heights, and loss timescales. We then report on the detectability of such a transient atmosphere by New Horizons, and discuss the generalized case of cometary impact-created transient atmospheres on other satellites of Pluto and water-ice covered KBOs across the Kuiper Belt.

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

    PubMed

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

    2014-01-01

    In winter 2009/10, a sudden under-ice bloom of heterotrophic bacteria occurred in the seasonally ice-covered, temperate, deep, oligotrophic Lake Stechlin (Germany). Extraordinarily high bacterial abundance and biomass were fueled by the breakdown of a massive bloom of Aphanizomenon flos-aquae after ice formation. A reduction in light resulting from snow coverage exerted a pronounced physiological stress on the cyanobacteria. Consequently, these were rapidly colonized, leading to a sudden proliferation of attached and subsequently of free-living heterotrophic bacteria. Total bacterial protein production reached 201 µg C L(-1) d(-1), ca. five times higher than spring-peak values that year. Fluorescence in situ hybridization and denaturing gradient gel electrophoresis at high temporal resolution showed pronounced changes in bacterial community structure coinciding with changes in the physiology of the cyanobacteria. Pyrosequencing of 16S rRNA genes revealed that during breakdown of the cyanobacterial population, the diversity of attached and free-living bacterial communities were reduced to a few dominant families. Some of these were not detectable during the early stages of the cyanobacterial bloom indicating that only specific, well adapted bacterial communities can colonize senescent cyanobacteria. Our study suggests that in winter, unlike commonly postulated, carbon rather than temperature is the limiting factor for bacterial growth. Frequent phytoplankton blooms in ice-covered systems highlight the need for year-round studies of aquatic ecosystems including the winter season to correctly understand element and energy cycling through aquatic food webs, particularly the microbial loop. On a global scale, such knowledge is required to determine climate change induced alterations in carbon budgets in polar and temperate aquatic systems. PMID:25419654

  3. Massive Regime Shifts and High Activity of Heterotrophic Bacteria in an Ice-Covered Lake

    PubMed Central

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

    2014-01-01

    In winter 2009/10, a sudden under-ice bloom of heterotrophic bacteria occurred in the seasonally ice-covered, temperate, deep, oligotrophic Lake Stechlin (Germany). Extraordinarily high bacterial abundance and biomass were fueled by the breakdown of a massive bloom of Aphanizomenon flos-aquae after ice formation. A reduction in light resulting from snow coverage exerted a pronounced physiological stress on the cyanobacteria. Consequently, these were rapidly colonized, leading to a sudden proliferation of attached and subsequently of free-living heterotrophic bacteria. Total bacterial protein production reached 201 µg C L−1 d−1, ca. five times higher than spring-peak values that year. Fluorescence in situ hybridization and denaturing gradient gel electrophoresis at high temporal resolution showed pronounced changes in bacterial community structure coinciding with changes in the physiology of the cyanobacteria. Pyrosequencing of 16S rRNA genes revealed that during breakdown of the cyanobacterial population, the diversity of attached and free-living bacterial communities were reduced to a few dominant families. Some of these were not detectable during the early stages of the cyanobacterial bloom indicating that only specific, well adapted bacterial communities can colonize senescent cyanobacteria. Our study suggests that in winter, unlike commonly postulated, carbon rather than temperature is the limiting factor for bacterial growth. Frequent phytoplankton blooms in ice-covered systems highlight the need for year-round studies of aquatic ecosystems including the winter season to correctly understand element and energy cycling through aquatic food webs, particularly the microbial loop. On a global scale, such knowledge is required to determine climate change induced alterations in carbon budgets in polar and temperate aquatic systems. PMID:25419654

  4. Sea ice in the Baltic Sea - revisiting BASIS ice, a historical data set covering the period 1960/1961-1978/1979

    NASA Astrophysics Data System (ADS)

    Löptien, U.; Dietze, H.

    2014-12-01

    The Baltic Sea is a seasonally ice-covered, marginal sea in central northern Europe. It is an essential waterway connecting highly industrialised countries. Because ship traffic is intermittently hindered by sea ice, the local weather services have been monitoring sea ice conditions for decades. In the present study we revisit a historical monitoring data set, covering the winters 1960/1961 to 1978/1979. This data set, dubbed Data Bank for Baltic Sea Ice and Sea Surface Temperatures (BASIS) ice, is based on hand-drawn maps that were collected and then digitised in 1981 in a joint project of the Finnish Institute of Marine Research (today the Finnish Meteorological Institute (FMI)) and the Swedish Meteorological and Hydrological Institute (SMHI). BASIS ice was designed for storage on punch cards and all ice information is encoded by five digits. This makes the data hard to access. Here we present a post-processed product based on the original five-digit code. Specifically, we convert to standard ice quantities (including information on ice types), which we distribute in the current and free Network Common Data Format (NetCDF). Our post-processed data set will help to assess numerical ice models and provide easy-to-access unique historical reference material for sea ice in the Baltic Sea. In addition we provide statistics showcasing the data quality. The website http://www.baltic-ocean.org hosts the post-processed data and the conversion code. The data are also archived at the Data Publisher for Earth & Environmental Science, PANGAEA (doi:10.1594/PANGAEA.832353).

  5. Sea ice in the Baltic Sea - revisiting BASIS ice, a~historical data set covering the period 1960/1961-1978/1979

    NASA Astrophysics Data System (ADS)

    Löptien, U.; Dietze, H.

    2014-06-01

    The Baltic Sea is a seasonally ice-covered, marginal sea, situated in central northern Europe. It is an essential waterway connecting highly industrialised countries. Because ship traffic is intermittently hindered by sea ice, the local weather services have been monitoring sea ice conditions for decades. In the present study we revisit a historical monitoring data set, covering the winters 1960/1961. This data set, dubbed Data Bank for Baltic Sea Ice and Sea Surface Temperatures (BASIS) ice, is based on hand-drawn maps that were collected and then digitised 1981 in a joint project of the Finnish Institute of Marine Research (today Finish Meteorological Institute (FMI)) and the Swedish Meteorological and Hydrological Institute (SMHI). BASIS ice was designed for storage on punch cards and all ice information is encoded by five digits. This makes the data hard to access. Here we present a post-processed product based on the original five-digit code. Specifically, we convert to standard ice quantities (including information on ice types), which we distribute in the current and free Network Common Data Format (NetCDF). Our post-processed data set will help to assess numerical ice models and provide easy-to-access unique historical reference material for sea ice in the Baltic Sea. In addition we provide statistics showcasing the data quality. The website www.baltic-ocean.org hosts the post-prossed data and the conversion code. The data are also archived at the Data Publisher for Earth & Environmental Science PANGEA (doi:10.1594/PANGEA.832353).

  6. Water wave scattering by a nearly circular cylinder submerged beneath an ice-cover

    NASA Astrophysics Data System (ADS)

    Chakraborty, Rumpa; Mandal, Birendra Nath

    2015-03-01

    Assuming linear theory, the two-dimensional problem of water wave scattering by a horizontal nearly circular cylinder submerged in infinitely deep water with an ice cover modeled as a thin-elastic plate floating on water, is investigated here. The cross-section of the nearly circular cylinder is taken as r= a( 1+δC( θ)), where a is the radius of the corresponding circular cross-section of the cylinder, δ is a measure of small departure of the cross-section of the cylinder from its circularity and C( θ) is the shape function. Using a simplified perturbation technique the problem is reduced to two independent boundary value problems up to first order in δ. The first one corresponds to water wave scattering by a circular cylinder submerged in water with an ice-cover, while the second problem describes wave radiation by a submerged circular cylinder and involves first order correction to the reflection and transmission coefficients. The corrections are obtained in terms of integrals involving the shape function. Assuming a general Fourier expansion of the shape function, these corrections are evaluated approximately. It is well known that normally incident wave trains experience no reflection by a circular cylinder submerged in infinitely deep water with an ice cover. It is shown here that the reflection coefficient also vanishes up to first order for some particular choice of the shape function representing a nearly circular cylinder. For these cases, full transmission occurs, only change is in its phase which is depicted graphically against the wave number in a number of figures and appropriate conclusions are drawn.

  7. Simulation of the interannual variability of the wind-driven Arctic sea-ice cover during 1958-1998

    NASA Astrophysics Data System (ADS)

    Arfeuille, G.; Mysak, L. A.; Tremblay, L.-B.

    A thermodynamic-dynamic sea-ice model based on a granular material rheology developed by Tremblay and Mysak is used to study the interannual variability of the Arctic sea-ice cover during the 41-year period 1958-98. Monthly wind stress forcing derived from the National Centers for Environmental Prediction (NCEP) Reanalysis data is used to produce the year-to-year variations in the sea-ice circulation and thickness. We focus on analyzing the variability of the sea-ice volume in the Arctic Basin and the subsequent changes in sea-ice export into the Greenland Sea via Fram Strait. The relative contributions of the Fram Strait sea-ice thickness and velocity anomalies to the sea-ice export anomalies are first investigated, and the former is shown to be particularly important during several large export events. The sea-ice export anomalies for these events are next linked to prior sea-ice volume anomalies in the Arctic Basin. The origin and evolution of the sea-ice volume anomalies are then related to the sea-ice circulation and atmospheric forcing patterns in the Arctic. Large sea-ice export anomalies are generally preceded by large volume anomalies formed along the East Siberian coast due to anomalous winds which occur when the Arctic High is centered closer than usual to this coastal area. When the center of this High relocates over the Beaufort Sea and the Icelandic Low extends far into the Arctic Basin, the ice volume anomalies are transported to the Fram Strait region via the Transpolar Drift Stream. Finally, the link between the sea-ice export and the North Atlantic Oscillation (NAO) index is briefly discussed. The overall results from this study show that the Arctic Basin and its ice volume anomalies must be considered in order to fully understand the export through Fram Strait.

  8. Results of the US contribution to the joint US/USSR Bering Sea experiment. [atmospheric circulation and sea ice cover

    NASA Technical Reports Server (NTRS)

    Campbell, W. J.; Chang, T. C.; Fowler, M. G.; Gloersen, P.; Kuhn, P. M.; Ramseier, R. O.; Ross, D. B.; Stambach, G.; Webster, W. J., Jr.; Wilheit, T. T.

    1974-01-01

    The atmospheric circulation which occurred during the Bering Sea Experiment, 15 February to 10 March 1973, in and around the experiment area is analyzed and related to the macroscale morphology and dynamics of the sea ice cover. The ice cover was very complex in structure, being made up of five ice types, and underwent strong dynamic activity. Synoptic analyses show that an optimum variety of weather situations occurred during the experiment: an initial strong anticyclonic period (6 days), followed by a period of strong cyclonic activity (6 days), followed by weak anticyclonic activity (3 days), and finally a period of weak cyclonic activity (4 days). The data of the mesoscale test areas observed on the four sea ice option flights, and ship weather, and drift data give a detailed description of mesoscale ice dynamics which correlates well with the macroscale view: anticyclonic activity advects the ice southward with strong ice divergence and a regular lead and polynya pattern; cyclonic activity advects the ice northward with ice convergence, or slight divergence, and a random lead and polynya pattern.

  9. (abstract) A Polarimetric Model for Effects of Brine Infiltrated Snow Cover and Frost Flowers on Sea Ice Backscatter

    NASA Technical Reports Server (NTRS)

    Nghiem, S. V.; Kwok, R.; Yueh, S. H.

    1995-01-01

    A polarimetric scattering model is developed to study effects of snow cover and frost flowers with brine infiltration on thin sea ice. Leads containing thin sea ice in the Artic icepack are important to heat exchange with the atmosphere and salt flux into the upper ocean. Surface characteristics of thin sea ice in leads are dominated by the formation of frost flowers with high salinity. In many cases, the thin sea ice layer is covered by snow, which wicks up brine from sea ice due to capillary force. Snow and frost flowers have a significant impact on polarimetric signatures of thin ice, which needs to be studied for accessing the retrieval of geophysical parameters such as ice thickness. Frost flowers or snow layer is modeled with a heterogeneous mixture consisting of randomly oriented ellipsoids and brine infiltration in an air background. Ice crystals are characterized with three different axial lengths to depict the nonspherical shape. Under the covering multispecies medium, the columinar sea-ice layer is an inhomogeneous anisotropic medium composed of ellipsoidal brine inclusions preferentially oriented in the vertical direction in an ice background. The underlying medium is homogeneous sea water. This configuration is described with layered inhomogeneous media containing multiple species of scatterers. The species are allowed to have different size, shape, and permittivity. The strong permittivity fluctuation theory is extended to account for the multispecies in the derivation of effective permittivities with distributions of scatterer orientations characterized by Eulerian rotation angles. Polarimetric backscattering coefficients are obtained consistently with the same physical description used in the effective permittivity calculation. The mulitspecies model allows the inclusion of high-permittivity species to study effects of brine infiltrated snow cover and frost flowers on thin ice. The results suggest that the frost cover with a rough interface

  10. Comparison of simulated spectral bidirectional reflectance function of snow-covered austral summer sea ice with measurements

    NASA Astrophysics Data System (ADS)

    Li, S.; Zhou, X.

    2003-12-01

    The bidirectional reflectance distribution function (BRDF) is an important geophysical variable that provides patterns of surface directional reflectance due to direct beam incidence. Information of BRF is required to derive surface albedo from remote sensing data sets. Also, albedo under various conditions can be evaluated by integration of BRFs. Knowledge of BRF of snow covered sea ice surface is especially important because sea ice exerts a strong positive feedback effect on the surface energy budget, and snow covered sea ice exhibits a strong anisotropic pattern when the solar incidence angle is large. However, it is difficult to obtain a complete data set of snow-covered sea ice surface BRDF through field measurement because of the general paucity of clear sky conditions and the narrow range of solar incidence angles that occur during measurement. The information gap can be filled through validation of the modeled results from radiative transfer simulations. We performed a simulation of snow covered sea ice surface BRF using a multi-layered azimuth- and zenith-dependent plane parallel radiative transfer code. Combined with Mie scattering algorithm, the code takes the measured snow grain sizes, densities and thicknesses of individual layers as input, and generates snow-covered sea ice surface spectral BRF as output. The simulated surface spectral BRF is then compared with measurements. The discrepancies between the model simulation and measurements are analyzed and causes inferred.

  11. A laboratory study of ion-induced erosion of ice-covered carbon grains

    NASA Astrophysics Data System (ADS)

    Sabri, T.; Baratta, G. A.; Jäger, C.; Palumbo, M. E.; Henning, T.; Strazzulla, G.; Wendler, E.

    2015-03-01

    Context. It has been confirmed that solid carbon dioxide (CO2) is abundantly present along the line of sight to quiescent clouds and star-forming regions via space IR observations with ISO-SWS and Spitzer Space Telescope. Since CO2 has low abundance in the gas-phase, the assumption is that it is synthesized on grains after energetic processing of icy mantles and surface reactions. Aims: The role of solid carbon is investigated as a reservoir for molecule formation and structural modifications of the material with and without an ice layer upon ion bombardment. Methods: A gas-phase condensation technique was used to prepare a layer of 13C amorphous grains. These grains were covered with H2O and O2 ice and finally bombarded with 200 keV protons. The formation of new molecular species was analyzed using IR spectroscopy. The formation cross sections of solid 13CO and 13CO2 were determined from the increase in the column density as a function of the fluence. In addition, bare carbon grains were bombarded with a comparable fluence of protons to study the processing of the grains without ice layer. Imaging techniques such as transmission electron microscopy were used to monitor the changes in the structure. Results: CO and CO2 were formed efficiently at the interface between ice and solid carbon grains at the expense of solid carbon, leading to strong grain erosion. Given the initial thickness of our C-samples (about 120 nm), this resulted in an erosion of about 50% after 200 keV proton bombardment with 6.76 × 1016 ions/cm2. The column density of CO and CO2 follows an exponential trend as a function of the irradiation fluence. The asymptotic values obtained when O2 ice is deposited on top of the carbon grains are about one order of magnitude higher than the values obtained when H2O ice is deposited on the solid carbon layer. The carbon grains were strongly graphitized upon ion bombardment in a surface layer. Less graphitization accompanied by the formation of fullerene

  12. A lightweight vertical rosette for deployment in ice-covered waters

    NASA Astrophysics Data System (ADS)

    Smethie, William M., Jr.; Chayes, Dale; Perry, Richard; Schlosser, Peter

    2011-04-01

    A lightweight modular rosette system has been developed that can be launched and recovered from aircraft in ice-covered waters through a 12 in. diameter hole in the ice. The small diameter is achieved by the modular design, in which a CTD module is attached to the end of a conducting cable and water bottle modules (four 4-L bottles per module) are positioned vertically above it. A novel tripping mechanism based on melting a link of monofilament line is used to close the water bottles at the desired depths. After launching the rosette, the cast proceeds like a normal rosette cast with the traces of temperature, salinity, oxygen and other desired sensors being displayed on a computer screen during the down and up casts and tripping the bottles electronically at the desired depths on the up cast. A Seabird 19+ CTD and Seabird 43 oxygen sensor are mounted in the CTD module and data acquisition and bottle tripping are controlled using a Seabird 33 deck unit and Seabird's SeaSave software run on a laptop computer. Deployment and recovery are done in a heated tent attached to the aircraft to prevent the water from freezing. After recovery the bottle modules are placed in coolers with bags of snow to stabilize the cooler temperature close to 0 °C, which is within ±1.8 °C of the in situ temperature, and the modules are transported back to a base camp for subsampling and sample processing. This system has been used to collect over 250 water samples in the ice-covered Lincoln Sea and the quality of the samples for dissolved gases and other constituents has been excellent.

  13. Coupling of climate change and biotic UV exposure through changing snow-ice covers in terrestrial habitats.

    PubMed

    Cockell, Charles S; Córdoba-Jabonero, Carmen

    2004-01-01

    During the spring, when ozone depletion at the polar regions is at its maximum and consequently the environmental UV exposure is potentially high, many terrestrial communities are covered in snow and heterogeneous snow-encrusted ice that form near the edges of snowpack. Using field measurements and a theoretical radiative transfer model, we calculated the thicknesses of these covers that are necessary to reduce DNA-weighted dose to levels equal to or lower than those received later in the season in the absence of covers when there is no ozone depletion. This depth is approximately 4 cm for a 60% depletion of the ozone column, suggesting that even thin snow-ice covers are enough to completely cancel the biological effects of ozone depletion. Loss of snow-ice covers during early summer can be rapid. The maximum rate of retreat of snow cover measured during November at Mars Oasis, Antarctica (71.9 degrees S, 68.2 degrees W), was 44.1 cm/day, with a mean retreat of 15.4 cm/day. Climate warming might increase UV-radiation damage by melting UV-protecting terrestrial snow-ice covers earlier in the season, when ozone depletion is more severe. Conversely, climate cooling could increase UV-protection afforded to terrestrial communities by increasing the extent of snow and ice covers. Even if anthropogenic ozone depletion is eventually reversed, these data suggest the importance of climate forcing in determining UV exposures of terrestrial microbial communities in snow- and ice-covered environments. PMID:14974712

  14. Trends in the Sea Ice Cover Using Enhanced and Compatible AMSR-E, SSM/I and SMMR Data

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.; Nishio, Fumihiko

    2007-01-01

    Arguably, the most remarkable manifestation of change in the polar regions is the rapid decline (of about -10 %/decade) in the Arctic perennial ice cover. Changes in the global sea ice cover, however, are more modest, being slightly positive in the Southern Hemisphere and slightly negative in the Northern Hemisphere, the significance of which has not been adequately assessed because of unknown errors in the satellite historical data. We take advantage of the recent and more accurate AMSR-E data to evaluate the true seasonal and interannual variability of the sea ice cover, assess the accuracy of historical data, and determine the real trend. Consistently derived ice concentrations from AMSR-E, SSM/I, and SMMR data were analyzed and a slight bias is observed between AMSR-E and SSM/I data mainly because of differences in resolution. Analysis of the combine SMMR, SSM/I and AMSR-E data set, with the bias corrected, shows that the trends in extent and area of sea ice in the Arctic region is -3.4 +/- 0.2 and -4.0 +/- 0.2 % per decade, respectively, while the corresponding values for the Antarctic region is 0.9 +/- 0.2 and 1.7 .+/- 0.3 % per decade. The higher resolution of the AMSR-E provides an improved determination of the location of the ice edge while the SSM/I data show an ice edge about 6 to 12 km further away from the ice pack. Although the current record of AMSR-E is less than 5 years, the data can be utilized in combination with historical data for more accurate determination of the variability and trends in the ice cover.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  17. Microwave brightness temperatures of laboratory-grown undeformed first-year ice with an evolving snow cover

    SciTech Connect

    Lohanick, A.W. )

    1993-03-15

    A laboratory experiment was performed to study a case in which a snow cover introduced on an established saline ice sheet resulted in physical processes that significantly affected the microwave brightness temperature over a period of a few weeks. Saline ice was grown to a thickness of 240 mm in an outdoor pool at ambient air temperatures. Precipitation was allowed by use of a movable roof. Brightness temperatures were measured at 10 and 85 GHz before and for several weeks after one snowfall. During the same period, the vertical temperature profile and crystallography of the snow column, as well as ice structure and salinity at the original ice surface, were monitored. The 10-GHz brightness temperature dropped by as much as 100 K from bare ice values during the first few days after the snow fell, because of a saline slush layer which formed at the bottom of the snow. The saline water in the slush layer apparently was forced up through the unbroken ice by the added snow load. The slush layer eventually froze into an added highly emissive frazil ice layer which raised the 10-GHz brightness temperature to above its bare ice values. The frazil ice layer was similar to superimposed frazil ice observed on freezing leads in high-latitude ice packs. The 85-GHz brightness temperature did not change from bare ice values soon after the snowfall but dropped by about 40 K over the following 20 days. We use a simple dielectric model to qualitatively test the dependence of 10-GHz brightness temperature on relevant physical conditions at the bottom of the snow. At 85 GHz the snow layer was optically thick, and the brightness temperature drop was probably the result of increased volume scatter from the growing snow grains. 24 refs., 7 figs.

  18. Divergent patterns of recent sea ice cover across the Bering, Chukchi, and Beaufort seas of the Pacific Arctic Region

    NASA Astrophysics Data System (ADS)

    Frey, Karen E.; Moore, G. W. K.; Cooper, Lee W.; Grebmeier, Jacqueline M.

    2015-08-01

    Over the past three decades of the observed satellite record, there have been significant changes in sea ice cover across the Bering, Chukchi, and Beaufort seas of the Pacific Arctic Region (PAR). Satellite data reveal that patterns in sea ice cover have been spatially heterogeneous, with significant declines in the Chukchi and Beaufort seas, yet more complex multi-year variability in the Bering Sea south of St. Lawrence Island. These patterns in the Chukchi and Beaufort seas have intensified since 2000, indicating a regime shift in sea ice cover across the northern portion of the PAR. In particular, satellite data over 1979-2012 reveal localized decreases in sea ice presence of up to -1.64 days/year (Canada Basin) and -1.24 days/year (Beaufort Sea), which accelerated to up to -6.57 days/year (Canada Basin) and -12.84 days/year (Beaufort Sea) over the 2000-2012 time period. In contrast, sea ice in the Bering Sea shows more complex multi-year variability with localized increases in sea ice presence of up to +8.41 days/year since 2000. The observed increases in sea ice cover since 2000 in the southern Bering Sea shelf region are observed in wintertime, whereas sea ice losses in the Canada Basin and Beaufort Sea have occurred during summer. We further compare sea ice variability across the region with the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR) wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs. wind-driven processes. Results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover, those in the Beaufort Sea are primarily wind driven, those offshore in the Canada Basin are primarily thermally driven, and those in the Bering Sea are influenced by elements of both. Sea ice variability (and its drivers) across the PAR provides critical insight into the forcing effects of recent shifts in climate and its likely

  19. Distribution of fish and macrozooplankton in ice-covered and open-water areas of the eastern Bering Sea

    NASA Astrophysics Data System (ADS)

    De Robertis, Alex; Cokelet, Edward D.

    2012-06-01

    The eastern Bering Sea shelf is a productive ecosystem with extensive commercial fisheries. Although the area is well-studied during summer months, little is known about the abundance and distribution of fish and macrozooplankton during periods of seasonal ice cover. The use of an icebreaker during the Bering Sea Ecosystem Study (BEST) provided a platform for spring acoustic surveys of fish and zooplankton in ice-covered areas for the first time. Icebreaker measurements were complemented with observations from conventional vessels during spring and summer. In spring, very little backscatter from fish (dominated by walleye pollock, Theragra chalcogramma) was observed in the ice-covered northern areas where near-bottom waters were cold (<˜0.5 °C), including areas where walleye pollock are abundant in summer. The majority of fish were observed within 40 km (and often slightly inside) the ice edge over similar seafloor depths as in summer. Together, these observations suggest that pollock, a dominant component of the ecosystem, shift their distribution to a more restricted geographic area in spring, following the ice edge southeast along the bathymetry, away from areas of cold water and extensive ice cover, then reoccupying these areas in summer. In contrast, acoustic backscatter attributed to zooplankton (likely dominated by euphausiids) was more evenly distributed, and less restricted by water temperature and ice cover. The implications of this seasonal shift in fish distribution are uncertain, but this may affect predator-prey interactions by reducing overlap of pollock with euphausiids, an important prey source, while increasing overlap of adult and juvenile pollock and potentially increasing cannibalism.

  20. Wave motion in an ice covered ocean due to small oscillations of a submerged thin vertical plate

    NASA Astrophysics Data System (ADS)

    Maiti, Paramita; Rakshit, Puspendu; Banerjea, Sudeshna

    2015-12-01

    In this paper we study the problem of generation of surface waves produced by small oscillation of a thin vertical plate submerged in deep ice covered ocean. Two particular problems are considered here viz, the problem of wave generation due to a) rolling of the plate and b) presence of a line source in front of a fixed vertical plate. The amplitude of radiated waves at large distances from the plate, for both problems, is obtained by a suitable application of Green's integral theorem. These are then studied graphically for various values of the ice cover parameter.

  1. Origin, Evolution, and Preservation of Cold Based Debris Covered Glaciers: Quantifying Sublimation Rates of Ancient Buried Ice in Antarctica

    NASA Astrophysics Data System (ADS)

    Kowalewski, D. E.; Marchant, D. R.

    2007-12-01

    Growing interest in our planet's climate history has placed a premium on acquiring detailed records of past climate change. Of considerable interest are archives of ancient atmosphere trapped within the debris-covered alpine glaciers of the western Dry Valleys region of Antarctica. The Mullins Valley debris-covered glacier (~8 km in length) is sourced from local snowfall at the steep headwall of the valley. The first 1.2 km of this glacier is generally free of overlying debris except for isolated cobbles and boulders. Thereafter, the ice surface is covered with a thin, continuous sheet of dolerite-rich rubble. Factors that influence the origin and modification of this ice include atmospheric temperature and relative humidity, precipitation, incoming solar radiance, surface albedo, till texture, winds, surface roughness, salts, and secondary ice lenses. We applied a diffusion model to track vapor flux within a sublimation till overlying the Mullins Valley debris-covered glacier, purportedly the world's oldest debris-covered alpine glacier. As input, we used meteorological data from HOBO data loggers that captured climate change and till temperatures. Results show that vapor flows into and out of the sublimation till at rates dependent on the non-linear variation of soil temperature with depth. Sublimation rates along the Mullins Glacier varied as a function of till thickness, local climate (using a calculated regional lapse rate of 0.88°C per 100 m), and till texture. Ice loss during the study interval (November 27, 2006 to December 24, 2006) ranged from as high as 2.12 mm for exposed glacier ice in the upper ablation zone, to as low as 0.01 mm for buried ice beneath till >50 cm in thickness. Averaged over the entire ablation zone (6.7 km2), this yields a net ice-surface lowering of 0.32 mm during the study interval. Numerical modeling suggests that a modest ice accumulation rate at the headwall of ~1 cm a-1 appears sufficient to maintain current ice volumes

  2. Multi-Decadal Comparison between Clean-Ice and Debris-Covered Glaciers in the Eastern Himalaya

    NASA Astrophysics Data System (ADS)

    Maurer, J. M.; Rupper, S.

    2014-12-01

    Himalayan glaciers are important natural resources and climatic indicators. Many of these glaciers have debris-covered ablation zones, while others are mostly clean ice. Regarding glacier dynamics, it is expected that debris-covered glaciers will respond differently to atmospheric warming compared to clean ice glaciers. In the Bhutanese Himalaya, there are (1) north flowing clean-ice glaciers with high velocities, likely with large amounts of basal sliding, and (2) south flowing debris-covered glaciers with slow velocities, thermokarst features, and influenced more by the Indian Summer Monsoon. This region, therefore, is ideal for comparing the dynamical response of clean-ice versus debris-covered glaciers to climatic change. In particular, previous studies have suggested the north flowing glaciers are likely adjusting more dynamically (i.e. retreating) in response to climate variations, while the south flowing glaciers are likely experiencing downwasting, with stagnant termini locations. We test this hypothesis by assessing glacier changes over three decades in the Bhutan region using a newly-developed workflow to extract DEMs and orthorectified imagery from both 1976 historical spy satellite images and 2006 ASTER images. DEM differencing for both debris-covered and clean glaciers allows for quantification of glacier surface elevation changes, while orthorectified imagery allows for measuring changes in glacier termini. The same stereo-matching, denoising, and georeferencing methodology is used on both datasets to ensure consistency, while the three decade timespan allows for a better signal to noise ratio compared to studies performed on shorter timescales. The results of these analyses highlight the similarities and differences in the decadal response of clean-ice and debris-covered glaciers to climatic change, and provide insights into the complex dynamics of debris-covered glaciers in the monsoonal Himalayas.

  3. Correlations between Inter-Annual Variations in Arctic Sea Ice Extent, Greenland Surface Melt, and Boreal Snow Cover

    NASA Technical Reports Server (NTRS)

    Markus, Thorstena; Stroeve, Julienne C.; Armstrong, Richard L.

    2004-01-01

    Intensification of global warming in recent decades has caused a rise of interest in year-to-year and decadal-scale climate variability in the Arctic. This is because the Arctic is believed to be one of the most sensitive and vulnerable regions to climatic changes. For over two decades satellite passive microwave observations have been utilized to continuously monitor the Arctic environment. Derived parameters include sea ice cover, snow cover and snow water equivalent over land, and Greenland melt extent and length of melt season. Most studies have primarily concentrated on trends and variations of individual variables. In this study we investigated how variations in sea ice cover, Greenland surface melt, and boreal snow cover are correlated. This was done on hemispheric as well as on regional scales. Latest results will be presented including data from the summer of 2004.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  5. Highly Active Microbial Communities in the Ice and Snow Cover of High Mountain Lakes

    PubMed Central

    Felip, M.; Sattler, B.; Psenner, R.; Catalan, J.

    1995-01-01

    An exploratory study carried out in Pyrenean and Alpine lakes shows that a rich, active microbial community lives in the slush layers of the winter cover of such lakes in spite of the low temperature and the seasonal occurrence of the habitat. Bacteria were very diverse in morphology, with filaments reaching up to 100 (mu)m long; flagellates, both autotrophic (chrysophytes, cryptophytes, dinoflagellates, and volvocales) and heterotrophic, and ciliates were abundant, reaching biovolume values up to 2.7 x 10(sup6) (mu)m(sup3) ml(sup-1). Species composition was very variable, with dominance depending on date and depth. Although many species were typical of lake plankton communities, some were restricted to the slush, for instance the predatory ciliates Dileptus sp. and Lacrymaria sp., and others were restricted to the surface pools, such as the snow algae Chlamydomonas nivalis. Microbial biomasses and usually bacterial and algal activities were greater in the slush layers than in the lake water. Photosynthesis rate in the upper cover layers reached values up to 0.5 (mu)g of C liter(sup-1) h(sup-1), and high bacterial activities up to 226 pmol of leucine incorporated liter(sup-1) h(sup-1) and 25 pmol of thymidine incorporated liter(sup-1) h(sup-1) were measured. For most species, lake water flooding the ice and snow cover could provide an inoculum. Differential growth depending on the environmental conditions (nutrients, organic matter, light) of a particular slush layer could provide dominance of different groups or species. However, there was no obvious colonizing mechanism for those species not appearing either in plankton or in communities on top of the snowpack. PMID:16535056

  6. Highly active microbial communities in the ice and snow cover of high mountain lakes.

    PubMed

    Felip, M; Sattler, B; Psenner, R; Catalan, J

    1995-06-01

    An exploratory study carried out in Pyrenean and Alpine lakes shows that a rich, active microbial community lives in the slush layers of the winter cover of such lakes in spite of the low temperature and the seasonal occurrence of the habitat. Bacteria were very diverse in morphology, with filaments reaching up to 100 (mu)m long; flagellates, both autotrophic (chrysophytes, cryptophytes, dinoflagellates, and volvocales) and heterotrophic, and ciliates were abundant, reaching biovolume values up to 2.7 x 10(sup6) (mu)m(sup3) ml(sup-1). Species composition was very variable, with dominance depending on date and depth. Although many species were typical of lake plankton communities, some were restricted to the slush, for instance the predatory ciliates Dileptus sp. and Lacrymaria sp., and others were restricted to the surface pools, such as the snow algae Chlamydomonas nivalis. Microbial biomasses and usually bacterial and algal activities were greater in the slush layers than in the lake water. Photosynthesis rate in the upper cover layers reached values up to 0.5 (mu)g of C liter(sup-1) h(sup-1), and high bacterial activities up to 226 pmol of leucine incorporated liter(sup-1) h(sup-1) and 25 pmol of thymidine incorporated liter(sup-1) h(sup-1) were measured. For most species, lake water flooding the ice and snow cover could provide an inoculum. Differential growth depending on the environmental conditions (nutrients, organic matter, light) of a particular slush layer could provide dominance of different groups or species. However, there was no obvious colonizing mechanism for those species not appearing either in plankton or in communities on top of the snowpack. PMID:16535056

  7. Elastic parabolic equation and normal mode solutions for seismo-acoustic propagation in underwater environments with ice covers.

    PubMed

    Collis, Jon M; Frank, Scott D; Metzler, Adam M; Preston, Kimberly S

    2016-05-01

    Sound propagation predictions for ice-covered ocean acoustic environments do not match observational data: received levels in nature are less than expected, suggesting that the effects of the ice are substantial. Effects due to elasticity in overlying ice can be significant enough that low-shear approximations, such as effective complex density treatments, may not be appropriate. Building on recent elastic seafloor modeling developments, a range-dependent parabolic equation solution that treats the ice as an elastic medium is presented. The solution is benchmarked against a derived elastic normal mode solution for range-independent underwater acoustic propagation. Results from both solutions accurately predict plate flexural modes that propagate in the ice layer, as well as Scholte interface waves that propagate at the boundary between the water and the seafloor. The parabolic equation solution is used to model a scenario with range-dependent ice thickness and a water sound speed profile similar to those observed during the 2009 Ice Exercise (ICEX) in the Beaufort Sea. PMID:27250161

  8. Fecal indicator bacteria persistence under natural conditions in an ice-covered river.

    PubMed

    Davenport, C V; Sparrow, E B; Gordon, R C

    1976-10-01

    Total coliform (TC), fecal coliform (FC), and fecal streptococcus (FS) survival characteristics, under natural conditions at 0 degrees C in an ice-covered river, were examined during February and March 1975. The membrane filter (MF) technique was used throughout the study, and the multiple-tube (MPN) method was used in parallel on three preselected days for comparative recovery of these bacteria. Survival was studied at seven sample stations downstream from all domestic pollution sources in a 317-km reach of the river having 7.1 days mean flow time (range of 6.0 to 9.1 days). The mean indicator bacteria densities decreased continuously at successive stations in this reach and, after adjustment for dilution, the most rapid die-off was found to occur during the first 1.9 days, followed by a slower decrease. After 7.1 days, the relative survival was TC less than FC less than FS, with 8.4%, 15.7%, and 32.8% of the initial populations remaining viable, respectively. These rates are higher than previously reported and suggest that the highest survival rates for these bacteria in receiving streams can be expected at 0 degree C under ice cover. Additionally, the FC-FS ratio was greater than 5 at all stations, indicating that this ratio may be useable for determining the source of fecal pollution in receiving streams for greater than 7 days flow time at low water temperatures. The MPN and MF methods gave comparable results for the TC and FS at all seven sample stations, with both the direct and verified MF counts within the 95% confidence limits of the respective MPNs in most samples, but generally lower than the MPN index. Although FC recovery on membrane filters was comparable results at stations near the pollution source. However, the results became more comparable with increasing flow time. The results of this study indicate that heat shock is a major factor in suppression of the FC counts on the membrane filters at 44.5 degree C. Heat shock may be minimized by extended

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  10. Formation of lobate debris aprons on Mars: Assessment of regional ice sheet collapse and debris-cover armoring

    NASA Astrophysics Data System (ADS)

    Fastook, James L.; Head, James W.; Marchant, David R.

    2014-01-01

    Lobate debris aprons (LDA) are lobate-shaped aprons surrounding scarps and isolated massifs that are concentrated in the vicinity of the northern Dichotomy Boundary on Mars. LDAs have been interpreted as (1) ice-cemented talus aprons undergoing viscous flow, (2) local debris-covered alpine-like glaciers, or (3) remnants of the collapse of a regional retreating ice sheet. We investigate the plausibility that LDAs are remnants of a more extensive regional ice sheet by modeling this process. We find that as a regional ice sheet collapses, the surface drops below cliff and massif bedrock margins, exposing bedrock and regolith, and initiating debris deposition on the surface of a cold-based glacier. Reduced sublimation due to debris-cover armoring of the proto-LDA surface produces a surface slope and consequent ice flow that carries the armoring debris away from the rock outcrops. As collapse and ice retreat continue the debris train eventually reaches the substrate surface at the front of the glacier, leaving the entire LDA armored by debris cover. Using a simplified ice flow model we are able to characterize the temperature and sublimation rate that would be necessary to produce LDAs with a wide range of specified lateral extents and thicknesses. We then apply this method to a database of documented LDA parameters (height, lateral extent) from the Dichotomy Boundary region, and assess the implications for predicted climate conditions during their formation and the range of formation times implied by the model. We find that for the population examined here, typical temperatures are in the range of -85 to -40 °C and typical sublimation rates lie in the range of 6-14 mm/a. Lobate debris apron formation times (from the point of bedrock exposure to complete debris cover) cluster near 400-500 ka. These results show that LDA length and thickness characteristics are consistent with climate conditions and a formation scenario typical of the collapse of a regional retreating

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

    PubMed

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

    2016-06-01

    Mid-winter limnological surveys of Lake Erie captured extremes in ice extent ranging from expansive ice cover in 2010 and 2011 to nearly ice-free waters in 2012. Consistent with a warming climate, ice cover on the Great Lakes is in decline, thus the ice-free condition encountered may foreshadow the lakes future winter state. Here, we show that pronounced changes in annual ice cover are accompanied by equally important shifts in phytoplankton and bacterial community structure. Expansive ice cover supported phytoplankton blooms of filamentous diatoms. By comparison, ice free conditions promoted the growth of smaller sized cells that attained lower total biomass. We propose that isothermal mixing and elevated turbidity in the absence of ice cover resulted in light limitation of the phytoplankton during winter. Additional insights into microbial community dynamics were gleaned from short 16S rRNA tag (Itag) Illumina sequencing. UniFrac analysis of Itag sequences showed clear separation of microbial communities related to presence or absence of ice cover. Whereas the ecological implications of the changing bacterial community are unclear at this time, it is likely that the observed shift from a phytoplankton community dominated by filamentous diatoms to smaller cells will have far reaching ecosystem effects including food web disruptions. PMID:25712272

  12. Aircraft and satellite passive microwave observations of the Bering Sea ice cover during MIZEX West

    NASA Technical Reports Server (NTRS)

    Cavalieri, D. J.; Gloersen, P.; Wilheit, T. T., Jr.

    1986-01-01

    Passive microwave measurements of the Bering Sea were made with the NASA CV-990 airborne laboratory during February. Microwave data were obtained with imaging and dual-polarized, fixed-beam radiometers in a range of frequencies from 10 to 183 GHz. The high resolution imagery at 92 GHz provides a particularly good description of the marginal ice zone delineating regions of open water, ice compactness, and ice-edge structure. Analysis of the fixed-beam data shows that spectral differences increase with a decrease in ice thickness. Polarization at 18 and 37 GHz distinguishes among new, young, and first-year ice types.

  13. Sea-ice information co-management: Planning for sustainable multiple uses of ice-covered seas in a rapidly changing Arctic

    NASA Astrophysics Data System (ADS)

    Eicken, H.; Lovecraft, A. L.

    2012-12-01

    A thinner, less extensive and more mobile summer sea-ice cover is a major element and driver of Arctic Ocean change. Declining summer sea ice presents Arctic stakeholders with substantial challenges and opportunities from the perspective of sustainable ocean use and derivation of sea-ice or ecosystem services. Sea-ice use by people and wildlife as well as its role as a major environmental hazard focuses the interests and concerns of indigenous hunters and Arctic coastal communities, resource managers and the maritime industry. In particular, rapid sea-ice change and intensifying offshore industrial activities have raised fundamental questions as to how best to plan for and manage multiple and increasingly overlapping ocean and sea ice uses. The western North American Arctic - a region that has seen some of the greatest changes in ice and ocean conditions in the past three decades anywhere in the North - is the focus of our study. Specifically, we examine the important role that relevant and actionable sea-ice information can play in allowing stakeholders to evaluate risks and reconcile overlapping and potentially competing interests. Our work in coastal Alaska suggests that important prerequisites to address such challenges are common values, complementary bodies of expertise (e.g., local or indigenous knowledge, engineering expertise, environmental science) and a forum for the implementation and evaluation of a sea-ice data and information framework. Alongside the International Polar Year 2007-08 and an associated boost in Arctic Ocean observation programs and platforms, there has been a movement towards new governance bodies that have these qualities and can play a central role in guiding the design and optimization of Arctic observing systems. To help further the development of such forums an evaluation of the density and spatial distribution of institutions, i.e., rule sets that govern ocean use, as well as the use of scenario planning and analysis can serve as

  14. Dynamic Coupling of Iron, Manganese, and Phosphorus Behavior in Water and Sediment of Shallow Ice-Covered Eutrophic Lakes.

    PubMed

    Schroth, Andrew W; Giles, Courtney D; Isles, Peter D F; Xu, Yaoyang; Perzan, Zachary; Druschel, Gregory K

    2015-08-18

    Decreasing duration and occurrence of northern hemisphere ice cover due to recent climate warming is well-documented; however, biogeochemical dynamics underneath the ice are poorly understood. We couple time-series analyses of water column and sediment water interface (SWI) geochemistry with hydrodynamic data to develop a holistic model of iron (Fe), manganese (Mn), and phosphorus (P) behavior underneath the ice of a shallow eutrophic freshwater bay. During periods of persistent subfreezing temperatures, a highly reactive pool of dissolved and colloidal Fe, Mn, and P develops over time in surface sediments and bottom waters due to reductive dissolution of Fe/Mn(oxy)hydroxides below the SWI. Redox dynamics are driven by benthic O2 consumption, limited air-water exchange of oxygen due to ice cover, and minimal circulation. During thaw events, the concentration, distribution and size partitioning of all species changes, with the highest concentrations of P and "truly dissolved" Fe near the water column surface, and a relatively well-mixed "truly dissolved" Mn and "colloidal" Fe profile due to the influx of geochemically distinct river water and increased circulation. The partitioning and flux of trace metals and phosphorus beneath the ice is dynamic, and heavily influenced by climate-dependent physical processes that vary in both time and space. PMID:26206098

  15. Axisymmetric circulation driven by marginal heating in ice-covered lakes

    NASA Astrophysics Data System (ADS)

    Kirillin, G. B.; Forrest, A. L.; Graves, K. E.; Fischer, A.; Engelhardt, C.; Laval, B. E.

    2015-04-01

    Below the temperature of maximum density (TMD) in freshwater lakes, heating at the lateral margins produces gravity currents along the bottom slope, akin to katabatic winds in the atmosphere and currents on continental shelves. We describe axisymmetric basin-scale circulation driven by heat flux at the shorelines in polar Lake Kilpisjärvi. A dense underflow originating near the shore converges toward the lake center, where it produces warm upwelling and return flow across the bulk of lake water column. The return flow, being subject to Coriolis force, creates a lake-wide anticyclonic gyre with velocities of 2-4 cm s-1. While warm underflows are common on ice-covered lakes, the key finding is the basin-scale anticyclonic gyre with warm upwelling in the core. This circulation mechanism provides a key to understanding transport processes in (semi) enclosed basins subject to negative buoyancy flux due to heating (or cooling at temperatures above TMD) at their lateral boundaries.

  16. Numerical simulation of 2D buoyant jets in ice-covered and temperature-stratified water

    NASA Astrophysics Data System (ADS)

    Gu, Ruochuan

    A two-dimensional (2D) unsteady simulation model is applied to the problem of a submerged warm water discharge into a stratified lake or reservoir with an ice cover. Numerical simulations and analyses are conducted to gain insight into large-scale convective recirculation and flow processes in a cold waterbody induced by a buoyant jet. Jet behaviors under various discharge temperatures are captured by directly modeling flow and thermal fields. Flow structures and processes are described by the simulated spatial and temporal distributions of velocity and temperature in various regions: deflection, recirculation, attachment, and impingement. Some peculiar hydrothermal and dynamic features, e.g. reversal of buoyancy due to the dilution of a warm jet by entraining cold ambient water, are identified and examined. Simulation results show that buoyancy is the most important factor controlling jet behavior and mixing processes. The inflow boundary is treated as a liquid wall from which the jet is offset. Similarity and difference in effects of boundaries perpendicular and parallel to flow, and of buoyancy on jet attachment and impingement, are discussed. Symmetric flow configuration is used to de-emphasize the Coanda effect caused by offset.

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

    PubMed

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

    2011-09-01

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

  18. Turbulent nitrate fluxes in the Amundsen Gulf during ice-covered conditions

    NASA Astrophysics Data System (ADS)

    Bourgault, D.; Hamel, C.; Cyr, F.; Tremblay, J.-É.; Galbraith, P. S.; Dumont, D.; Gratton, Y.

    2011-08-01

    Turbulence and nitrate measurements collected in the Amundsen Gulf during ice-covered conditions in fall 2007 are combined to provide mean vertical profiles of eddy diffusivity $\\overline{K and diffusive nitrate fluxes $\\overline{F. The mean diffusivity (with 95% confidence intervals) was maximum near the uppermost sampling depth (10 m) with $\\overline{Kmax = 3(2, 5) × 10-3 m2 s-1 and decreased exponentially to a depth of ˜50 m, below which it was roughly constant at the background value $\\overline{Kb = 3(2, 5) × 10-6 m2 s-1. The nitracline, centered around 62 m depth, was subject to an eddy diffusivity close to the background value $\\overline{Kb and the mean diffusive nitrate flux across the nitracline was $\\overline{Fnit = 0.5(0.3, 0.8) mmol m-2 d-1. These observations are compared with other regions and the role of vertical mixing on primary production in the Amundsen Gulf is discussed.

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

    NASA Astrophysics Data System (ADS)

    Leppäranta, Matti; Arvola, Lauri

    2014-05-01

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

  20. The impact of organochlorines cycling in the cryosphere on global distributions and fate--2. Land ice and temporary snow cover.

    PubMed

    Hofmann, Lorenz; Stemmler, Irene; Lammel, Gerhard

    2012-03-01

    Global fate and transport of γ-HCH and DDT was studied using a global multicompartment chemistry-transport model, MPI-MCTM, with and without inclusion of land ice (in Antarctica and Greenland) or snow cover (dynamic). MPI-MCTM is based on coupled ocean and atmosphere general circulation models. After a decade of simulation 4.2% γ-HCH and 2.3% DDT are stored in land ice and snow. Neglection of land ice and snow in modelling would underestimate the total environmental residence time, τ(ov), of γ-HCH and overestimate τ(ov) for DDT, both on the order of 1% and depending on actual compartmental distribution. Volatilisation of DDT from boreal, seasonally snow covered land is enhanced throughout the year, while volatilisation of γ-HCH is only enhanced during the snow-free season. Including land ice and snow cover in modelling matters in particular for the Arctic, where higher burdens are predicted to be stored. PMID:22054697

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  2. New high-resolution aerosol proxy data from the Greenland NEEM ice core covering the last 128,000 years

    NASA Astrophysics Data System (ADS)

    Schüpbach, Simon; Bigler, Matthias; Gfeller, Gideon; Fischer, Hubertus

    2014-05-01

    High-resolution multicomponent continuous flow analysis (CFA) measurements have been performed over the entire depth of the NEEM ice core in three field seasons 2009-2011. Only in the brittle ice section, covering an age of approx. 4,000-8,000 years, continuous measurements could not be performed due to the bad ice quality which hampered such analyses. On all the other ice, continuous records of tracers for sea salt aerosol (sodium), mineral dust aerosol (calcium), inorganic and biogenic nitrogen compounds (nitrate and ammonium), hydrogen peroxide, and electrolytic conductivity were recorded. Data evaluation and quality control of the raw data of the 2.5 km long ice core have recently been finalised, resulting in the final multi-proxy CFA dataset of the NEEM ice core presented here. It covers the last 128,000 years including the entire (stratigraphically folded) Eemian warm period in Greenland. Our chemical CFA measurements are performed in a nominal resolution of 0.5 mm, allowing for the resolution of seasonal cycles over the top 1500 m of the ice core. Thus, seasonality of aerosol tracers can be studied as far back as the early Holocene, and to a certain extent even further back in time. The lower part of the ice core, however, including the last glacial period as well as the Eemian ice section, is subject to such strong thinning of the ice that no unambiguous seasonal cycles can be resolved any more. Nevertheless, long-term glacial-interglacial and stadial-interstadial changes on the one side and the peculiarities of the first Greenland Eemian aerosol record in comparison to the Holocene on the other can be investigated in highest resolution. Here, the new NEEM aerosol proxy records are presented and compared to NGRIP and GRIP CFA records focussed on the early Holocene and last glacial period. Thanks to the particularly high resolution we can furthermore closely investigate the timing and phasing of fast climate transitions such as Termination I and Dansgaard

  3. Field and Satellite Observations of the Formation and Distribution of Arctic Atmospheric Bromine Above a Rejuvenated Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Nghiem, Son V.; Rigor, Ignatius G.; Richter, Andreas; Burrows, John P.; Shepson, Paul B.; Bottenheim, Jan; Barber, David G.; Steffen, Alexandra; Latonas, Jeff; Wang, Feiyue; Stern, Gary; Clemente-Colon, Pablo; Martin, Seelye; Hall, Dorothy K.; Kaleschke, Lars; Tackett, Philip; Neumann, Gregory; Asplin, Matthew G.

    2012-01-01

    Recent drastic reduction of the older perennial sea ice in the Arctic Ocean has resulted in a vast expansion of younger and saltier seasonal sea ice. This increase in the salinity of the overall ice cover could impact tropospheric chemical processes. Springtime perennial ice extent in 2008 and 2009 broke the half-century record minimum in 2007 by about one million km2. In both years seasonal ice was dominant across the Beaufort Sea extending to the Amundsen Gulf, where significant field and satellite observations of sea ice, temperature, and atmospheric chemicals have been made. Measurements at the site of the Canadian Coast Guard Ship Amundsen ice breaker in the Amundsen Gulf showed events of increased bromine monoxide (BrO), coupled with decreases of ozone (O3) and gaseous elemental mercury (GEM), during cold periods in March 2008. The timing of the main event of BrO, O3, and GEM changes was found to be consistent with BrO observed by satellites over an extensive area around the site. Furthermore, satellite sensors detected a doubling of atmospheric BrO in a vortex associated with a spiral rising air pattern. In spring 2009, excessive and widespread bromine explosions occurred in the same region while the regional air temperature was low and the extent of perennial ice was significantly reduced compared to the case in 2008. Using satellite observations together with a Rising-Air-Parcel model, we discover a topographic control on BrO distribution such that the Alaskan North Slope and the Canadian Shield region were exposed to elevated BrO, whereas the surrounding mountains isolated the Alaskan interior from bromine intrusion.

  4. Field and satellite observations of the formation and distribution of Arctic atmospheric bromine above a rejuvenated sea ice cover

    NASA Astrophysics Data System (ADS)

    Nghiem, Son V.; Rigor, Ignatius G.; Richter, Andreas; Burrows, John P.; Shepson, Paul B.; Bottenheim, Jan; Barber, David G.; Steffen, Alexandra; Latonas, Jeff; Wang, Feiyue; Stern, Gary; Clemente-Colón, Pablo; Martin, Seelye; Hall, Dorothy K.; Kaleschke, Lars; Tackett, Philip; Neumann, Gregory; Asplin, Matthew G.

    2012-09-01

    Recent drastic reduction of the older perennial sea ice in the Arctic Ocean has resulted in a vast expansion of younger and saltier seasonal sea ice. This increase in the salinity of the overall ice cover could impact tropospheric chemical processes. Springtime perennial ice extent in 2008 and 2009 broke the half-century record minimum in 2007 by about one million km2. In both years seasonal ice was dominant across the Beaufort Sea extending to the Amundsen Gulf, where significant field and satellite observations of sea ice, temperature, and atmospheric chemicals have been made. Measurements at the site of the Canadian Coast Guard Ship Amundsen ice breaker in the Amundsen Gulf showed events of increased bromine monoxide (BrO), coupled with decreases of ozone (O3) and gaseous elemental mercury (GEM), during cold periods in March 2008. The timing of the main event of BrO, O3, and GEM changes was found to be consistent with BrO observed by satellites over an extensive area around the site. Furthermore, satellite sensors detected a doubling of atmospheric BrO in a vortex associated with a spiral rising air pattern. In spring 2009, excessive and widespread bromine explosions occurred in the same region while the regional air temperature was low and the extent of perennial ice was significantly reduced compared to the case in 2008. Using satellite observations together with a Rising-Air-Parcel model, we discover a topographic control on BrO distribution such that the Alaskan North Slope and the Canadian Shield region were exposed to elevated BrO, whereas the surrounding mountains isolated the Alaskan interior from bromine intrusion.

  5. Radar-based observatiions of variable thickness debris cover on martian ice masses: evidence of debris transfer by flowing ice on Mars

    NASA Astrophysics Data System (ADS)

    Souness, Colin; Brough, Stephen; Woodward, John; Hubbard, Bryn; Davis, Joel; Grindrod, Peter

    2016-04-01

    The mid-latitudes of Mars host a wide range of ice-based landforms, many of which display surface morphologies indicative of viscous flow of that ice. Despite being shrouded beneath a layer of rocky debris, these viscous flow features (VFFs) are thought to have similarities with terrestrial glaciers. Until recently most studies that focussed on the origin, structure and role of these martian VFFs were restricted to observations made from satellite imagery. Little data have been available to gain a clearer picture of VFF internal structure, which has impeded our collective ability to infer many particulars of VFF growth and flow, including the extent to which these ice flows have interacted with, and potentially helped shape, the martian landscape. However, the Shallow Radar (SHARAD) system mounted on the Mars Reconnaissance Orbiter (MRO) can, in some cases, provide a valuable insight into what lies beneath the surface of these ice masses. We present a SHARAD-based study of glacial systems on Mars which reveals pronounced heterogeneity in the thickness of their observed superficial debris covers. The surface debris layers in question appear to thicken in a down-slope direction. Radar data indicates that in the lower reaches of each studied glacial catchment, ice surface debris cover exceeds 10 m in thickness. The observed flow-parallel a-symmetry in debris thickness atop these martian glaciers is similar to that recorded on many terrestrial glaciers, indicating that cumulative down-flow debris mass transfer such as occurs within glacierised catchments on Earth may also currently operate, or have operated, on Mars. This suggests that glaciers on Mars have played a substantial role in redistributing lithic material from mountainous catchments to lower-lying areas, potentially throughout the glacial regions of Mars' mid-latitudes, thus making an important processual contribution to the evolution of Mars' contemporary landscape.

  6. Pyroclastic density current dynamics and associated hazards at ice-covered volcanoes

    NASA Astrophysics Data System (ADS)

    Dufek, J.; Cowlyn, J.; Kennedy, B.; McAdams, J.

    2015-12-01

    Understanding the processes by which pyroclastic density currents (PDCs) are emplaced is crucial for volcanic hazard prediction and assessment. Snow and ice can facilitate PDC generation by lowering the coefficient of friction and by causing secondary hydrovolcanic explosions, promoting remobilisation of proximally deposited material. Where PDCs travel over snow or ice, the reduction in surface roughness and addition of steam and meltwater signficantly changes the flow dynamics, affecting PDC velocities and runout distances. Additionally, meltwater generated during transit and after the flow has come to rest presents an immediate secondary lahar hazard that can impact areas many tens of kilometers beyond the intial PDC. This, together with the fact that deposits emplaced on ice are rarely preserved means that PDCs over ice have been little studied despite the prevalence of summit ice at many tall stratovolcanoes. At Ruapehu volcano in the North Island of New Zealand, a monolithologic welded PDC deposit with unusually rounded clasts provides textural evidence for having been transported over glacial ice. Here, we present the results of high-resolution multiphase numerical PDC modeling coupled with experimentaly determined rates of water and steam production for the Ruapehu deposits in order to assess the effect of ice on the Ruapehu PDC. The results suggest that the presence of ice significantly modified the PDC dynamics, with implications for assessing the PDC and associated lahar hazards at Ruapehu and other glaciated volcanoes worldwide.

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

    PubMed

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

    2016-01-01

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

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

    PubMed Central

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

    2015-01-01

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

  9. Remote Sensing of Snow-covered Sea Ice with Ultra-wideband Airborne Radars

    NASA Astrophysics Data System (ADS)

    Yan, S.; Gogineni, P. S.; Gomez-Garcia, D.; Leuschen, C.; Hale, R.; Rodriguez-Morales, F.; Paden, J. D.; Li, J.

    2015-12-01

    The extent and thickness of sea ice and snow play a critical role in the Earth's climate system. Both sea ice and snow have high albedo and control the heat exchange between the atmosphere and ocean and atmosphere and land. In terms of hydrology, the presence of sea ice and snow modulates the flow and the salinity of ocean water. This in turn can modify the weather patterns around the globe. Understanding the formation, coverage and the properties of sea ice and snow are important for both short-term and long-term climate modeling. The advancements in high-frequency electronics and digital signal processing enabled the development of ultra-wideband radars by the Center for Remote Sensing of Ice Sheets (CReSIS) for airborne measurements of snow and ice properties over large areas. CReSIS recently developed and deployed two ultra-wideband airborne radars, namely the Multichannel Coherent Radar Depth Sounder/Imager (MCoRDS/I) and the Snow Radar. The MCoRDS/I is designed to operate over the frequency range of 180-450 MHz for sounding land ice and imaging its ice-bed interface. We also took advantage of the deployment to explore the potential of UWB MCoRDS/I in sounding sea ice and collected data on flight lines flown as part of NASA Operation IceBridge mission during Spring 2015. Preliminary results show we sounded sea ice under favorable conditions. We will perform detailed processing and analysis of data over the next few months and we will compare results obtained are compared with existing altimetry-derived data products. The new snow radar, on the other hand, operating from 2 to 18 GHz, was deployed on the NRL Twin Otter aircraft in Barrow, AK. It was shown to have a vertical resolution of down to 1.5 cm which opens up the potential for thin snow measurement on both sea ice and land. Both of these new radars will be further optimized for future airborne missions to demonstrate their capabilities for sea ice and snow measurements. We will also show new technical

  10. Impact of aerosol emission controls on future Arctic sea ice cover

    NASA Astrophysics Data System (ADS)

    Gagné, M.-È.; Gillett, N. P.; Fyfe, J. C.

    2015-10-01

    We examine the response of Arctic sea ice to projected aerosol and aerosol precursor emission changes under the Representative Concentration Pathway (RCP) scenarios in simulations of the Canadian Earth System Model. The overall decrease in aerosol loading causes a warming, largest over the Arctic, which leads to an annual mean reduction in sea ice extent of approximately 1 million km2 over the 21st century in all RCP scenarios. This accounts for approximately 25% of the simulated reduction in sea ice extent in RCP 4.5, and 40% of the reduction in RCP 2.5. In RCP 4.5, the Arctic ocean is projected to become ice-free during summertime in 2045, but it does not become ice-free until 2057 in simulations with aerosol precursor emissions held fixed at 2000 values. Thus, while reductions in aerosol emissions have significant health and environmental benefits, their substantial contribution to projected Arctic climate change should not be overlooked.

  11. Modeling thermal structure, ice cover regime and sensitivity to climate change of two regulated lakes - a Norwegian case study

    NASA Astrophysics Data System (ADS)

    Gebre, Solomon; Boissy, Thibault; Alfredsen, Knut

    2013-04-01

    A great number of river and lakes in Norway and the Nordic region at large are regulated for water management such as hydropower production. Such regulations have the potential to alter the thermal and hydrological regimes in the lakes and rivers downstream impacting on river environment and ecology. Anticipated changes as a result of climate change in meteorological forcing data such as air temperature and precipitation cause changes in the water balance, water temperature and ice cover duration in the reservoirs. This may necessitate changes in operational rules as part of an adaptation strategy for the future. In this study, a one dimensional (1D) lake thermodynamic and ice cover model (MyLake) has been modified to take into account the effect of dynamic outflows in reservoirs and applied to two small but relatively deep regulated lakes (reservoirs) in Norway (Follsjøen and Tesse). The objective was to assess climate change impacts on the seasonal thermal characteristics, the withdrawal temperatures, and the reservoir ice cover dynamics with current operational regimes. The model solves the vertical energy balance on a daily time-step driven by meteorological and hydrological forcings: 2m air temperature, precipitation, 2m relative humidity, 10m wind speed, cloud cover, air pressure, solar insolation, inflow volume, inflow temperature and reservoir outflows. Model calibration with multi-seasonal data of temperature profiles showed that the model performed well in simulating the vertical water temperature profiles for the two study reservoirs. The withdrawal temperatures were also simulated reasonably well. The comparison between observed and simulated lake ice phenology (which were available only for one of the reservoirs - Tesse) was also reasonable taking into account the uncertainty in the observational data. After model testing and calibration, the model was then used to simulate expected changes in the future (2080s) due to climate change by considering

  12. Arctic layer salinity controls heat loss from deep Atlantic layer in seasonally ice-covered areas of the Barents Sea

    NASA Astrophysics Data System (ADS)

    Lind, Sigrid; Ingvaldsen, Randi B.; Furevik, Tore

    2016-05-01

    In the seasonally ice-covered northern Barents Sea an intermediate layer of cold and relatively fresh Arctic Water at ~25-110 m depth isolates the sea surface and ice cover from a layer of warm and saline Atlantic Water below, a situation that resembles the cold halocline layer in the Eurasian Basin. The upward heat flux from the Atlantic layer is of major concern. What causes variations in the heat flux and how is the Arctic layer maintained? Using observations, we found that interannual variability in Arctic layer salinity determines the heat flux from the Atlantic layer through its control of stratification and vertical mixing. A relatively fresh Arctic layer effectively suppresses the upward heat flux, while a more saline Arctic layer enhances the heat flux. The corresponding upward salt flux causes a positive feedback. The Arctic layer salinity and the water column structures have been remarkably stable during 1970-2011.

  13. The perennially ice covered lakes of the cold and rainless deserts of the Antarctic, and by extension, Mars: implications for finding Martian life

    NASA Astrophysics Data System (ADS)

    Wilson, A. T.

    2008-08-01

    The salt geochemistry of Mars is predicted as an extrapolation of the salt geochemistry of the Dry (ice-free) Valleys in Antarctica. It is hard to escape the implication that there must be calcium/magnesium brine lakes in the enclosed drainage basins associated with the Northern Ice Cap. Because of the extreme cold these lakes will have acquired an ice cover. At the interface between the ice cover and the brine, one may find a thin layer of relatively fresh water. This might be the best and easiest place to look for Martian life.

  14. Evolution of Martian polar landscapes - Interplay of long-term variations in perennial ice cover and dust storm intensity

    NASA Technical Reports Server (NTRS)

    Cutts, J. A.; Blasius, K. R.; Roberts, W. J.

    1979-01-01

    The discovery of a new type of Martian polar terrain, called undulating plain, is reported and the evolution of the plains and other areas of the Martian polar region is discussed in terms of the trapping of dust by the perennial ice cover. High-resolution Viking Orbiter 2 observations of the north polar terrain reveal perennially ice-covered surfaces with low relief, wavelike, regularly spaced, parallel ridges and troughs (undulating plains) occupying areas of the polar terrain previously thought to be flat, and associated with troughs of considerable local relief which exhibit at least partial annual melting. It is proposed that the wavelike topography of the undulating plains originates from long-term periodic variations in cyclical dust precipitation at the margin of a growing or receding perennial polar cap in response to changes in insolation. The troughs are proposed to originate from areas of steep slope in the undulating terrain which have lost their perennial ice cover and have become incapable of trapping dust. The polar landscape thus appears to record the migrations, expansions and contractions of the Martian polar cap.

  15. Evidence of form II RubisCO (cbbM) in a perennially ice-covered Antarctic lake.

    PubMed

    Kong, Weidong; Dolhi, Jenna M; Chiuchiolo, Amy; Priscu, John; Morgan-Kiss, Rachael M

    2012-11-01

    The permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica, harbor microbially dominated food webs. These organisms are adapted to a variety of unusual environmental extremes, including low temperature, low light, and permanently stratified water columns with strong chemo- and oxy-clines. Owing to the low light levels during summer caused by thick ice cover as well as 6 months of darkness during the polar winter, chemolithoautotrophic microorganisms could play a key role in the production of new carbon for the lake ecosystems. We used clone library sequencing and real-time quantitative PCR of the gene encoding form II Ribulose 1, 5-bisphosphate carboxylase/oxygenase to determine spatial and seasonal changes in the chemolithoautotrophic community in Lake Bonney, a 40-m-deep lake covered by c. 4 m of permanent ice. Our results revealed that chemolithoautotrophs harboring the cbbM gene are restricted to layers just above the chemo- and oxi-cline (≤ 15 m) in the west lobe of Lake Bonney (WLB). Our data reveal that the WLB is inhabited by a unique chemolithoautotrophic community that resides in the suboxic layers of the lake where there are ample sources of alternative electron sources such as ammonium, reduced iron and reduced biogenic sulfur species. PMID:22703237

  16. Walrus areas of use in the Chukchi Sea during sparse sea ice cover

    USGS Publications Warehouse

    Jay, Chadwick V.; Fischbach, Anthony S.; Kochnev, Anatoly A.

    2012-01-01

    The Pacific walrus Odobenus rosmarus divergens feeds on benthic invertebrates on the continental shelf of the Chukchi and Bering Seas and rests on sea ice between foraging trips. With climate warming, ice-free periods in the Chukchi Sea have increased and are projected to increase further in frequency and duration. We radio-tracked walruses to estimate areas of walrus foraging and occupancy in the Chukchi Sea from June to November of 2008 to 2011, years when sea ice was sparse over the continental shelf in comparison to historical records. The earlier and more extensive sea ice retreat in June to September, and delayed freeze-up of sea ice in October to November, created conditions for walruses to arrive earlier and stay later in the Chukchi Sea than in the past. The lack of sea ice over the continental shelf from September to October caused walruses to forage in nearshore areas instead of offshore areas as in the past. Walruses did not frequent the deep waters of the Arctic Basin when sea ice retreated off the shelf. Walruses foraged in most areas they occupied, and areas of concentrated foraging generally corresponded to regions of high benthic biomass, such as in the northeastern (Hanna Shoal) and southwestern Chukchi Sea. A notable exception was the occurrence of concentrated foraging in a nearshore area of northwestern Alaska that is apparently depauperate in walrus prey. With increasing sea ice loss, it is likely that walruses will increase their use of coastal haul-outs and nearshore foraging areas, with consequences to the population that are yet to be understood.

  17. Wintertime water dynamics and moonlight disruption of the acoustic backscatter diurnal signal in an ice-covered Northeast Greenland fjord

    NASA Astrophysics Data System (ADS)

    Petrusevich, Vladislav; Dmitrenko, Igor; Kirillov, Sergey; Rysgaard, Søren; Falk-Petersen, Stig; Barber, David; Ehn, Jens

    2016-04-01

    Six and a half month time series of acoustic backscatter and velocity from three ice-tethered Acoustic Doppler Current Profilers deployed in the Young Sound fjord in Northeast Greenland were used to analyse the acoustic signal. During period of civil polar night below the land-fast ice, the acoustic data suggest a systematic diel vertical migration (DVM) of backscatters likely comprised of zooplankton. The acoustic backscatter and vertical velocity data were also arranged in a form of actograms. Results show that the acoustic signal pattern typical to DVM in Young Sound persists throughout the entire winter including the period of civil polar night. However, polynya-enhanced estuarine-like cell circulation that occurred during winter disrupted the DVM signal favouring zooplankton to occupy the near-surface water layer. This suggests that zooplankton avoided spending additional energy crossing the interface with a relatively strong velocity gradient comprised by fjord inflow in the intermediate layer and outflow in the subsurface layer. Instead the zooplankton tended to favour remaining in the upper 40 m layer where also the relatively warmer water temperatures associated with upward heat flux during enhanced estuarine-like circulation could be energetically favourable. Furthermore, our data show moonlight disruption of DVM in the subsurface layer and weaker intensity of vertical migration beneath snow covered land-fast ice during polar night. Using existing models for lunar illuminance and light transmission through sea ice and snow cover we estimated under ice illuminance and compared it with known light sensitivity for Arctic zooplankton species.

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

    USGS Publications Warehouse

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

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  20. Sensitivity of Greenland Ice Sheet surface mass balance to perturbations in sea surface temperature and sea ice cover: a study with the regional climate model MAR

    NASA Astrophysics Data System (ADS)

    Noël, B.; Fettweis, X.; van de Berg, W. J.; van den Broeke, M. R.; Erpicum, M.

    2014-10-01

    During recent summers (2007-2012), several surface melt records were broken over the Greenland Ice Sheet (GrIS). The extreme summer melt resulted in part from a persistent negative phase of the North Atlantic Oscillation (NAO), favoring warmer atmospheric conditions than normal over the GrIS. Simultaneously, large anomalies in sea ice cover (SIC) and sea surface temperature (SST) were observed in the North Atlantic, suggesting a possible connection. To assess the direct impact of 2007-2012 SIC and SST anomalies on GrIS surface mass balance (SMB), a set of sensitivity experiments was carried out with the regional climate model MAR forced by ERA-Interim. These simulations suggest that perturbations in SST and SIC in the seas surrounding Greenland do not considerably impact GrIS SMB, as a result of the katabatic wind blocking effect. These offshore-directed winds prevent oceanic near-surface air, influenced by SIC and SST anomalies, from penetrating far inland. Therefore, the ice sheet SMB response is restricted to coastal regions, where katabatic winds cease. A topic for further investigation is how anomalies in SIC and SST might have indirectly affected the surface melt by changing the general circulation in the North Atlantic region, hence favoring more frequent warm air advection towards the GrIS.

  1. Vertical distribution and diel vertical migration of krill beneath snow-covered ice and in ice-free waters

    PubMed Central

    Vestheim, Hege; Røstad, Anders; Klevjer, Thor A.; Solberg, Ingrid; Kaartvedt, Stein

    2014-01-01

    A bottom mounted upward looking Simrad EK60 120-kHz echo sounder was used to study scattering layers (SLs) and individuals of the krill Meganyctiphanes norvegica. The mooring was situated at 150-m depth in the Oslofjord, connected with an onshore cable for power and transmission of digitized data. Records spanned 5 months from late autumn to spring. A current meter and CTD was associated with the acoustic mooring and a shore-based webcam monitored ice conditions in the fjord. The continuous measurements were supplemented with intermittent krill sampling campaigns and their physical and biological environment. The krill carried out diel vertical migration (DVM) throughout the winter, regardless of the distribution of potential prey. The fjord froze over in mid-winter and the daytime distribution of a mid-water SL of krill immediately became shallower associated with snow fall after freezing, likely related to reduction of light intensities. Still, a fraction of the population always descended all the way to the bottom, so that the krill population by day seemed to inhabit waters with light levels spanning up to six orders of magnitude. Deep-living krill ascended in synchrony with the rest of the population in the afternoon, but individuals consistently reappeared in near-bottom waters already <1 h after the ascent. Thereafter, the krill appeared to undertake asynchronous migrations, with some krill always being present in near-bottom waters even though the entire population appeared to undertake DVM. PMID:24616550

  2. Vertical distribution and diel vertical migration of krill beneath snow-covered ice and in ice-free waters.

    PubMed

    Vestheim, Hege; Røstad, Anders; Klevjer, Thor A; Solberg, Ingrid; Kaartvedt, Stein

    2014-03-01

    A bottom mounted upward looking Simrad EK60 120-kHz echo sounder was used to study scattering layers (SLs) and individuals of the krill Meganyctiphanes norvegica. The mooring was situated at 150-m depth in the Oslofjord, connected with an onshore cable for power and transmission of digitized data. Records spanned 5 months from late autumn to spring. A current meter and CTD was associated with the acoustic mooring and a shore-based webcam monitored ice conditions in the fjord. The continuous measurements were supplemented with intermittent krill sampling campaigns and their physical and biological environment. The krill carried out diel vertical migration (DVM) throughout the winter, regardless of the distribution of potential prey. The fjord froze over in mid-winter and the daytime distribution of a mid-water SL of krill immediately became shallower associated with snow fall after freezing, likely related to reduction of light intensities. Still, a fraction of the population always descended all the way to the bottom, so that the krill population by day seemed to inhabit waters with light levels spanning up to six orders of magnitude. Deep-living krill ascended in synchrony with the rest of the population in the afternoon, but individuals consistently reappeared in near-bottom waters already <1 h after the ascent. Thereafter, the krill appeared to undertake asynchronous migrations, with some krill always being present in near-bottom waters even though the entire population appeared to undertake DVM. PMID:24616550

  3. Historical Response of Ice Cover on Large Lakes of Northern Canada, Derived from Smmr and Ssm/i (1979-2015)

    NASA Astrophysics Data System (ADS)

    Kang, K.; Duguay, C. R.

    2015-12-01

    Lakes that form a seasonal ice cover are a significant part of the terrestrial landscape. Ice cover presence/absence (and extent) on large northern lakes influences both regional climate and weather events (e.g. thermal moderation and lake-effect snowfall). Ice phenology parameters such as freeze-onset (FO)/melt-onset (MO), ice-on/ice-off dates, and ice cover duration (ICD) are useful climate data records as they are sensitive to variability and changes in air temperature and, to a lesser extent, on ice snow depth. Given the poor spatial/temporal coverage of ground-based lake ice observations in many northern countries, remote sensing has been assuming a greater role in observing lake ice phenology, and for investigating the response and role of ice cover in lake-atmosphere interactions. Spaceborne passive microwave instruments operating since the late 1970s present an invaluable data source for assessing the response of ice cover on large northern lakes to climate. The primary objective of this study was to develop new ice phenology retrieval algorithms (H-pol) from SSM/I 19.35 GHz brightness temperature measurements (1987-2015), and 18.00 GHz TB data (1979-1987) from SMMR over four large northern lakes in Canada: Great Bear Lake (GBL) and Great Slave Lake (GSL) in the Mackenzie River Basin as well as Lake Nettiling, and Lake Amadjuak on Baffin Island in the eastern Canadian Arctic. The second objective consisted of analyzing trends in the derived ice phenology time series (SMMR and SSM/I combined). From the preliminary analysis (1979-2013), FO and ice-on dates were found to occur later on both GBL (6 d decade-1 and 4 d decade-1) and GSL (4 d decade-1 and 2 d decade-1). Trends in MO are positive (later) by 4 d decade-1 in GSL while ice-off date and ICD show negative trends (earlier ice-off and shorter ICD) of -2 d decade-1 and -3 d decade-1, respectively, for both GBL and GSL.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    USGS Publications Warehouse

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

    2016-01-01

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

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

    PubMed

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

    2013-01-01

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

  7. Peculiarities of stochastic regime of Arctic ice cover time evolution over 1987-2014 from microwave satellite sounding on the basis of NASA team 2 algorithm

    NASA Astrophysics Data System (ADS)

    Raev, M. D.; Sharkov, E. A.; Tikhonov, V. V.; Repina, I. A.; Komarova, N. Yu.

    2015-12-01

    The GLOBAL-RT database (DB) is composed of long-term radio heat multichannel observation data received from DMSP F08-F17 satellites; it is permanently supplemented with new data on the Earth's exploration from the space department of the Space Research Institute, Russian Academy of Sciences. Arctic ice-cover areas for regions higher than 60° N latitude were calculated using the DB polar version and NASA Team 2 algorithm, which is widely used in foreign scientific literature. According to the analysis of variability of Arctic ice cover during 1987-2014, 2 months were selected when the Arctic ice cover was maximal (February) and minimal (September), and the average ice cover area was calculated for these months. Confidence intervals of the average values are in the 95-98% limits. Several approximations are derived for the time dependences of the ice-cover maximum and minimum over the period under study. Regression dependences were calculated for polynomials from the first degree (linear) to sextic. It was ascertained that the minimal root-mean-square error of deviation from the approximated curve sharply decreased for the biquadratic polynomial and then varied insignificantly: from 0.5593 for the polynomial of third degree to 0.4560 for the biquadratic polynomial. Hence, the commonly used strictly linear regression with a negative time gradient for the September Arctic ice cover minimum over 30 years should be considered incorrect.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  9. Quantitative and qualitative constraints on hind-casting the formation of multiyear lake-ice covers at Lake El'gygytgyn

    NASA Astrophysics Data System (ADS)

    Nolan, M.

    2013-06-01

    Analysis of the 3.6 Ma, 318 m long sediment core from Lake El'gygytgyn suggests that the lake was covered by ice for millennia at a time for much of its history and therefore this paper uses a suite of existing, simple, empirical degree-day models of lake-ice growth and decay to place quantitative constraints on air temperatures needed to maintain a permanent ice cover on the lake. We also provide an overview of the modern climatological and physical processes that relate to lake-ice growth and decay as a basis for evaluating past climate and environmental conditions. Our modeling results indicate that modern annual mean air temperature would only have to be reduced by 3.3 °C ± 0.9 °C to initiate a multiyear ice cover and a temperature reduction of at least 5.5 °C ± 1.0 °C is likely needed to completely eliminate direct air-water exchange of oxygen, conditions that have been inferred at Lake El'gygytgyn from the analysis of sediment cores. Once formed, a temperature reduction of only 1-3 °C relative to modern may be all that is required to maintain multiyear ice. We also found that formation of multiyear ice covers requires that positive degree days are reduced by about half the modern mean, from about +608 to +322. A multiyear ice cover can persist even with summer temperatures sufficient for a two-month long thawing period, including a month above +4 °C. Thus, it is likely that many summer biological processes and some lake-water warming and mixing may still occur beneath multiyear ice-covers even if air-water exchange of oxygen is severely restricted.

  10. Snow cover and short-term synoptic events drive biogeochemical dynamics in winter Weddell Sea pack ice (AWECS cruise - June to August 2013)

    NASA Astrophysics Data System (ADS)

    Tison, Jean-Louis; Delille, Bruno; Dieckmann, Gherard; de Jong, Jeroen; Janssens, Julie; Rintala, Janne; Luhtanen, Annemari; Gussone, Niklaus; Uhlig, Christiane; Nomura, Daïki; Schoemann, Véronique; Zhou, Jiayun; Carnat, Gauthier; Fripiat, François

    2014-05-01

    This paper presents the preliminary results of an integrated multidisciplinary study of pack ice biogeochemistry in the Weddell Sea during the winter 2013 (June-August). The sea ice biogeochemistry group was one of the components of the AWECS (Antarctic Winter Ecosystem and Climate Study) cruise (Polarstern ANTXXIX-6). A total of 12 stations were carried out by the sea ice biogeochemistry group, which collected a suite of variables in the fields of physics, inorganic chemistry, gas content and composition, microbiology, biogeochemistry, trace metals and the carbonate system in order to give the best possible description of the sea ice cover and its interactions at interfaces. Samples were collected in the atmosphere above (gas fluxes), in the snow cover, in the bulk ice (ice cores), in the brines (sackholes) and in the sea water below (0m, 1m, 30 m). Here we present the results of basic physico-chemical (T° , bulk ice salinity, brine volumes, brine salinity, Rayleigh numbers) and biological (Chla) measurements in order to give an overview of the general status of the Weddell Sea winter pack ice encountered, and discuss how it controls climate relevant biogeochemical processes. Our results from the first set of 9 stations, mainly sampled along the Greenwich meridian and the easternmost part of the Weddell Sea definitively refute the view of a biogeochemically 'frozen' sea ice during the Winter. This has already been demonstrated for the Spring and Summer, but we now see that sea ice sustains considerable biological stocks and activities throughout the Winter, despite the reduced amount of available PAR radiation. Accretion of the snow cover appears to play an essential role in driving biogeochemical activity, through warming from insulation, thus favouring brine transport, be it through potential convection, surface brine migration (brine tubes) or flooding. This results in a 'widening' of the internal autumn layer (quite frequent in this rafting-dominated sea ice

  11. Influence of sea ice cover on high latitude precipitation: Inferences from precipitation isotope measurements and a 2D model

    NASA Astrophysics Data System (ADS)

    Posmentier, E. S.; Faiia, A.; Feng, X.; Michel, F. A.

    2009-12-01

    The most widely cited climate feedback in the Arctic region is ice cover. Warming climate reduces the sea ice extent, which causes a lower surface albedo, resulting in more absorbed insolation and further warming - a positive feedback. Conversely, warming is also likely to result in increased Arctic evaporation and precipitation, leading to increased snow cover and a higher Arctic terrestrial albedo, which would cause cooling - a negative feedback. The balance between these feedbacks must be understood and quantified in order to predict climate response to influences such as increased greenhouse gases. Here, we use measurements of high latitude precipitation isotopes and a 2D model to investigate interannual variability in the contributions of subtropical and Arctic vapor sources to Arctic precipitation. In a previous study, we used isotopic ratios alone to investigate the sources of moisture to the Arctic. We found significant positive relationships between ice area and the d-excess of precipitation on both interannual and seasonal timescales, an expected result under the assumption that sea ice prevents evaporation from the sea surface and consequently reduces the contribution of Arctic moisture with low d-excess values to Arctic precipitation. In this work, we go a step further with an attempt to estimate the influence of sea ice cover on Arctic evaporation using a 2D model and constraining it with high latitude isotopic measurements. The 2D model is a vertical-meridional mass conservation model for H2O, HDO, and H218O with prescribed atmospheric circulation and temperatures. For each isotope, the rates of surface evaporation, sublimation, precipitation, and reevaporation of falling hydrometeors are calculated, and values of the humidity and isotopic concentrations of both vapor and hydrometeors are computed interdependently with the four process rates.. The model fractionation associated with the four processes is based primarily on the work of Jouzel and

  12. Variations in the Arctic's multiyear sea ice cover: A neural network analysis of SMMR-SSM/I data, 1979-2004

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.; Eremeev, V.A.; Platonov, N.G.

    2005-01-01

    A 26-year (1979-2004) observational record of January multiyear sea ice distributions, derived from neural network analysis of SMMR-SSM/I passive microwave satellite data, reveals dense and persistent cover in the central Arctic basin surrounded by expansive regions of highly fluctuating interannual cover. Following a decade of quasi equilibrium, precipitous declines in multiyear ice area commenced in 1989 when the Arctic Oscillation shifted to a pronounced positive phase. Although extensive survival of first-year ice during autumn 1996 fully replenished the area of multiyear ice, a subsequent and accelerated decline returned the depletion to record lows. The most dramatic multiyear sea ice declines occurred in the East Siberian, Chukchi, and Beaufort Seas. Copyright 2005 by the American Geophysical Union.

  13. Variations in the Arctic's multiyear sea ice cover: A neural network analysis of SMMR-SSM/I data, 1979-2004

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.; Eremeev, V.A.; Platonov, N.G.

    2005-01-01

    A 26-year (1979-2004) observational record of January multiyear sea ice distributions, derived from neural network analysis of SMMR-SSM/I passive microwave satellite data, reveals dense and persistent cover in the central Arctic basin surrounded by expansive regions of highly fluctuating interannual cover. Following a decade of quasi equilibrium, precipitous declines in multiyear ice area commenced in 1989 when the Arctic Oscillation shifted to a pronounced positive phase. Although extensive survival of first-year ice during autumn 1996 fully replenished the area of multiyear ice, a subsequent and accelerated decline returned the depletion to record lows. The most dramatic multiyear sea ice declines occurred in the East Siberian, Chukchi, and Beaufort Seas.

  14. Drilling and operational sounds from an oil production island in the ice-covered Beaufort Sea

    NASA Astrophysics Data System (ADS)

    Blackwell, Susanna B.; Greene, Charles R.; Richardson, W. John

    2004-11-01

    Recordings of sounds underwater and in air, and of iceborne vibrations, were obtained at Northstar Island, an artificial gravel island in the Beaufort Sea near Prudhoe Bay (Alaska). The aim was to document the levels, characteristics, and range dependence of sounds and vibrations produced by drilling and oil production during the winter, when the island was surrounded by shore-fast ice. Drilling produced the highest underwater broadband (10-10 000 Hz) levels (maximum=124 dB re: 1 μPa at 1 km), and mainly affected 700-1400 Hz frequencies. In contrast, drilling did not increase broadband levels in air or ice relative to levels during other island activities. Production did not increase broadband levels for any of the sensors. In all media, broadband levels decreased by ~20 dB/tenfold change in distance. Background levels underwater were reached by 9.4 km during drilling and 3-4 km without. In the air and ice, background levels were reached 5-10 km and 2-10 km from Northstar, respectively, depending on the wind but irrespective of drilling. A comparison of the recorded sounds with harbor and ringed seal audiograms showed that Northstar sounds were probably audible to seals, at least intermittently, out to ~1.5 km in water and ~5 km in air. .

  15. Drilling and operational sounds from an oil production island in the ice-covered Beaufort sea.

    PubMed

    Blackwell, Susanna B; Greene, Charles R; Richardson, W John

    2004-11-01

    Recordings of sounds underwater and in air, and of iceborne vibrations, were obtained at Northstar Island, an artificial gravel island in the Beaufort Sea near Prudhoe Bay (Alaska). The aim was to document the levels, characteristics, and range dependence of sounds and vibrations produced by drilling and oil production during the winter, when the island was surrounded by shore-fast ice. Drilling produced the highest underwater broadband (10-10,000 Hz) levels (maximum= 124 dB re: 1 microPa at 1 km), and mainly affected 700-1400 Hz frequencies. In contrast, drilling did not increase broadband levels in air or ice relative to levels during other island activities. Production did not increase broadband levels for any of the sensors. In all media, broadband levels decreased by approximately 20 dB/tenfold change in distance. Background levels underwater were reached by 9.4 km during drilling and 3-4 km without. In the air and ice, background levels were reached 5-10 km and 2-10 km from Northstar, respectively, depending on the wind but irrespective of drilling. A comparison of the recorded sounds with harbor and ringed seal audiograms showed that Northstar sounds were probably audible to seals, at least intermittently, out to approximately 1.5 km in water and approximately 5 km in air. PMID:15603166

  16. Lake temperature and ice cover regimes in the Alaskan Subarctic and Arctic: Integrated monitoring, remote sensing, and modeling

    USGS Publications Warehouse

    Arp, C.D.; Jones, Benjamin M.; Whitman, Matthew; Larsen, A.; Urban, F.E.

    2010-01-01

    Lake surface regimes are fundamental attributes of lake ecosystems and their interaction with the land and atmosphere. High latitudes may be particularly sensitive to climate change, however, adequate baselines for these lakes are often lacking. In this study, we couple monitoring, remote sensing, and modeling techniques to generate baseline datasets of lake surface temperature and ice cover in the Alaskan Subarctic and Arctic. No detectable trends were observed during this study period, but a number of interesting patterns were noted among lakes and between regions. The largest Arctic lake was relatively unresponsive to air temperature, while the largest Subarctic lake was very responsive likely because it is fed by glacial runoff. Mean late summer water temperatures were higher than air temperatures with differences ranging from 1.7 to 5.4°C in Subarctic lakes and from 2.4 to 3.2°C in Arctic lakes. The warmest mean summer water temperature in both regions was in 2004, with the exception of Subarctic glacially fed lake that was highest in 2005. Ice-out timing had high coherence within regions and years, typically occurring in late May in Subarctic and in early-July in Arctic lakes. Ice-on timing was more dependent on lake size and depth, often varying among lakes within a region. Such analyses provide an important baseline of lake surface regimes at a time when there is increasing interest in high-latitude water ecosystems and resources during an uncertain climate future.

  17. 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).

  18. Hg Stable Isotope Time Trend in Ringed Seals Registers Decreasing Sea Ice Cover in the Alaskan Arctic.

    PubMed

    Masbou, Jérémy; Point, David; Sonke, Jeroen E; Frappart, Frédéric; Perrot, Vincent; Amouroux, David; Richard, Pierre; Becker, Paul R

    2015-08-01

    Decadal time trends of mercury (Hg) concentrations in Arctic biota suggest that anthropogenic Hg is not the single dominant factor modulating Hg exposure to Arctic wildlife. Here, we present Hg speciation (monomethyl-Hg) and stable isotopic composition (C, N, Hg) of 53 Alaskan ringed seal liver samples covering a period of 14 years (1988-2002). In vivo metabolic effects and foraging ecology explain most of the observed 1.6 ‰ variation in liver δ(202)Hg, but not Δ(199)Hg. Ringed seal habitat use and migration were the most likely factors explaining Δ(199)Hg variations. Average Δ(199)Hg in ringed seal liver samples from Barrow increased significantly from +0.38 ± 0.08‰ (±SE, n = 5) in 1988 to +0.59 ± 0.07‰ (±SE, n = 7) in 2002 (4.1 ± 1.2% per year, p < 0.001). Δ(199)Hg in marine biological tissues is thought to reflect marine Hg photochemistry before biouptake and bioaccumulation. A spatiotemporal analysis of sea ice cover that accounts for the habitat of ringed seals suggests that the observed increase in Δ(199)Hg may have been caused by the progressive summer sea ice disappearance between 1988 and 2002. While changes in seal liver Δ(199)Hg values suggests a mild sea ice control on marine MMHg breakdown, the effect is not large enough to induce measurable HgT changes in biota. This suggests that Hg trends in biota in the context of a warming Arctic are likely controlled by other processes. PMID:26132925

  19. Sensitivity of sea-ice cover and ocean properties to wind-stress and radiative forcings from 1500 to 2000

    NASA Astrophysics Data System (ADS)

    Sedlacek, Jan

    In this thesis we investigate the sensitivity of the Arctic and Antarctic sea-ice cover and global ocean properties to wind-stress and radiative forcings from 1500 to 2000. In a first step, the conversion of the granular sea-ice model (GRAN) (Tremblay and Mysak, 1997) from Cartesian to spherical coordinates is presented. The GRAN is coupled to the Earth System Climate Model of the University of Victoria as an application. The sea-ice thickness and drift in the Arctic Ocean agree well with observations. The sea-ice volume and area fluxes through Fram Strait show good correlations with observations, although the simulated area flux has a smaller mean value as compared to the observations. To further validate the model, the results of thermodynamic component are compared with the Surface Heat Budget of the Arctic Ocean (SHEBA) datasets which were collected between autumn 1997 and autumn 1998. The simulated growth rate is larger and the melt rate is smaller than observed. The larger growth rate is caused by thinner ice at the beginning of the SHEBA period and the absence of internal heat storage, while the lower summer melt is due to smaller-than-observed surface melt. The simulated surface and bottom melt contribute equal parts to the overall melt. In a second step, the model is used to investigate which forcings had a dominant effect on the sea-ice cover in both polar regions during the Little Ice Age (LIA), defined as the period between 1500 and 1850, and the industrial period (1850--2000). Three different reconstructed wind-stress fields which take into account the North Atlantic Oscillation, one general circulation model wind-stress field, and three different radiative forcings are used (i.e., volcanic activity, insolation changes, greenhouse gas changes). The annual surface air temperature anomalies for the Northern Hemisphere, which are used as model validation, show good agreement with reconstructed temperature anomalies, i.e., cooling during the LIA and

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    USGS Publications Warehouse

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

    2001-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    PubMed

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

    2008-12-15

    In January 2003, a helicopter crashed on the 5 m thick perennial ice cover of Lake Fryxell (McMurdo Dry Valleys, East Antarctica), spilling approximately 730 l of aviation diesel fuel (JP5-AN8 mixture). The molecular composition of the initial fuel was analyzed by solid phase microextraction (SPME) gas chromatography-mass spectrometry (GC-MS), then compared to the composition of the contaminated ice, water, and sediments collected a year after the spill. Evaporation is the major agent of diesel weathering in meltpool waters and in the ice. This process is facilitated by the light non-aqueous phase liquid properties of the aviation diesel and by the net upward movement of the ice as a result of ablation. In contrast, in sediment-bearing ice, biodegradation by both alkane- and aromatic-degraders was the prominent attenuation mechanism. The composition of the diesel contaminant in the ice was also affected by the differential solubility of its constituents, some ice containing water-washed diesel and some ice containing exclusively relatively soluble low molecular weight aromatic hydrocarbons such as alkylbenzene and naphthalene homologues. The extent of evaporation, water washing and biodegradation between sites and at different depths in the ice are evaluated on the basis of molecular ratios and the results of JP5-AN8 diesel evaporation experiment at 4 degrees C. Immediate spread of the aviation diesel was enhanced where the presence of aeolian sediments induced formations of meltpools. However, in absence of melt pools, slow spreading of the diesel is possible through the porous ice and the ice cover aquifer. PMID:18804261

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

    PubMed Central

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

    2013-01-01

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

  6. A grid-based Model for Backwasting at supraglacial Ice Cliffs on a debris-covered Glacier

    NASA Astrophysics Data System (ADS)

    Buri, P.; Steiner, J. F.; Pellicciotti, F.; Miles, E. S.; Immerzeel, W.

    2014-12-01

    In the Himalaya, debris-covered glaciers cover significant portions of the glacierised area. Their behaviour is not entirely understood, but they seem to experience strong mass losses in direct contradiction with the insulating effect of debris. A characteristic most debris-covered glaciers share is the appearance of cliffs and lakes on their surface. These supraglacial features play a role in surface evolution, dynamics and downwasting of debris-covered glaciers but their actual effects have not been quantified at the glacier scale. Numerous measurements of radiative fluxes at the cliff surface, detailed survey of cliffs geometry and ablation have been conducted on the debris-covered Lirung Glacier, Nepalese Himalayas. We used four 20cm-resolution DEMs obtained from UAV flights to represent the glacier surface to a very detailed degree. As the debris remains stable on slopes up to 30°, ice cliffs show inclinations above this threshold and were clearly represented in the DEMs. Direct measurements and a point-scale cliff-backwasting model have showed that melt patterns over a single cliff are highly variable across and along the ice surface due to non-uniform geometry, varying inclination, aspect and terrain view factors. Variability in observed ablation was large also among cliffs. We therefore developed an energy balance model with a gridded representation of the cliff to understand the melt behaviour at the cliff scale. Previous models assumed the cliff to be a plane with a constant slope and aspect, and extrapolation of melt rates to the glacier scale based on this assumption might be erroneous. Using a grid-based approach allows representation of real inclined areas of the cliff. The detailed surface from the UAV-DEM was taken as initial condition for the model. The model was in close agreement with ablation measurements at numerous stakes located on 3 cliffs. Results show very high variability both along the cliffs' elevation and extension. These cannot be

  7. Sensitivity of Asian and African climate to variations in seasonal insolation, glacial ice cover, sea surface temperature, and Asian orography

    NASA Technical Reports Server (NTRS)

    Demenocal, Peter B.; Rind, David

    1993-01-01

    A general circulation model was used to investigate the sensitivity of Asian and African climate to prescribed changes in boundary conditions with the objective of identifying the relative importance of individual high-latitude glacial boundary conditions on seasonal climate and providing a physical basis for interpreting the paleoclimate record. The circulation model is described and results are presented. Insolation forcing increased summer Asian monsoon winds, while increased high-latitude ice cover strengthened winter Asian trade winds causing decreased precipitation. These factors had little effect on African climate. Cooler North Atlantic sea surface temperatures enhanced winter trade winds over North Africa, southern Asian climate was relatively unaffected. Reducing Asian orography enhanced Asian winter circulation while decreasing the summer monsoon. These model results suggest that African and southern Asian climate respond differently to separate elements of high-latitude climate variability.

  8. Scattering of surface waves by the edge of a small undulation on a porous bed in an ocean with ice-cover

    NASA Astrophysics Data System (ADS)

    Mohapatra, Smrutiranjan

    2014-06-01

    Scattering of surface waves by the edge of a small undulation on a porous bed in an ocean of finite depth, where the free surface has an ice-cover being modelled as an elastic plate of very small thickness, is investigated within the framework of linearized water wave theory. The effect of surface tension at the surface below the ice-cover is neglected. There exists only one wave number propagating at just below the ice-cover. A perturbation analysis is employed to solve the boundary value problem governed by Laplace's equation by a method based on Green's integral theorem with the introduction of appropriate Green's function and thereby evaluating the reflection and transmission coefficients approximately up to first order. A patch of sinusoidal ripples is considered as an example and the related coefficients are determined.

  9. Sea surface height and dynamic topography of the ice-covered oceans from CryoSat-2: 2011-2014

    NASA Astrophysics Data System (ADS)

    Kwok, Ron; Morison, James

    2016-01-01

    We examine 4 years (2011-2014) of sea surface heights (SSH) from CryoSat-2 (CS-2) over the ice-covered Arctic and Southern Oceans. Results are from a procedure that identifies and determines the heights of sea surface returns. Along 25 km segments of satellite ground tracks, variability in the retrieved SSHs is between ˜2 and 3 cm (standard deviation) in the Arctic and is slightly higher (˜3 cm) in the summer and the Southern Ocean. Average sea surface tilts (along these 25 km segments) are 0.01 ± 3.8 cm/10 km in the Arctic, and slightly lower (0.01 ± 2.0 cm/10 km) in the Southern Ocean. Intra-seasonal variability of CS-2 dynamic ocean topography (DOT) in the ice-covered Arctic is nearly twice as high as that of the Southern Ocean. In the Arctic, we find a correlation of 0.92 between 3 years of DOT and dynamic heights (DH) from hydrographic stations. Further, correlation of 4 years of area-averaged CS-2 DOT near the North Pole with time-variable ocean-bottom pressure from a pressure gauge and from GRACE, yields coefficients of 0.83 and 0.77, with corresponding differences of <3 cm (RMS). These comparisons contrast the length scale of baroclinic and barotropic features and reveal the smaller amplitude barotropic signals in the Arctic Ocean. Broadly, the mean DOT from CS-2 for both poles compares well with those from the ICESat campaigns and the DOT2008A and DTU13MDT fields. Short length scale topographic variations, due to oceanographic signals and geoid residuals, are especially prominent in the Arctic Basin but less so in the Southern Ocean.

  10. Consequences of future increased Arctic runoff on Arctic Ocean stratification, circulation, and sea ice cover

    NASA Astrophysics Data System (ADS)

    Nummelin, Aleksi; Ilicak, Mehmet; Li, Camille; Smedsrud, Lars H.

    2016-01-01

    The Arctic Ocean has important freshwater sources including river runoff, low evaporation, and exchange with the Pacific Ocean. In the future, we expect even larger freshwater input as the global hydrological cycle accelerates, increasing high-latitude precipitation, and river runoff. Previous modeling studies show some robust responses to high-latitude freshwater perturbations, including a strengthening of Arctic stratification and a weakening of the large-scale ocean circulation; some idealized modeling studies also document a stronger cyclonic circulation within the Arctic Ocean itself. With the broad range of scales and processes involved, the overall effect of increasing runoff requires an understanding of both the local processes and the broader linkages between the Arctic and surrounding oceans. Here we adopt a more comprehensive modeling approach by increasing river runoff to the Arctic Ocean in a coupled ice-ocean general circulation model, and show contrasting responses in the polar and subpolar regions. Within the Arctic, the stratification strengthens, the halocline and Atlantic Water layer warm, and the cyclonic circulation spins up, in agreement with previous work. In the subpolar North Atlantic, the model simulates a colder and fresher water column with weaker barotropic circulation. In contrast to the estuarine circulation theory, the volume exchange between the Arctic Ocean and the surrounding oceans does not increase with increasing runoff. While these results are robust in our model, we require experiments with other model systems and more complete observational syntheses to better constrain the sensitivity of the climate system to high-latitude freshwater perturbations.

  11. The Arctic Cone Exploration Structure: A mobile offshore drilling unit for heavy ice cover

    SciTech Connect

    Byrd, R.C.; Boaz, I.B.; Coleman, R.K.; Sauve, E.R.; Weiss, R.T.; White, R.M.

    1984-05-01

    This paper reports on the results of a rig development program which began in 1981 to design a mobile drilling unit which could operate beyond the 50 ft depth contour in the most exposed ice conditions. The Arctic Cone Exploration Structure (ACES) project has produced the design of what is likely to be the prototype for heavy-duty, bottom-founded mobile rigs for arctic offshore drilling. The current ACES rig design has focused on developing the drilling capability for the water depth range of 50 to 110 ft. Approximately 68% of tracts made available during the recent OCS Sale 71 fell within this depth range. The latest phase of the ACES rig design was sponsored by Exxon Company, U.S.A.; Shell Oil Company; and Standard Oil Company of California/Chevron. An earlier conceptual design phase of the program included three additional U.S. oil and gas companies. Brian Watt Associates, Inc. (BWA) of Houston, Texas, was the prime contractor for the design. Zapata Off-Shore Company of Houston was responsible for the drilling related systems. The objective of this paper is to show the level of effort which has gone into the development of the ACES mobile rig design. The results of that effort are presented, including the design criteria and performance objectives used.

  12. Affects of Changes in Sea Ice Cover on Bowhead Whales and Subsistence Whaling in the Western Arctic

    NASA Astrophysics Data System (ADS)

    Moore, S.; Suydam, R.; Overland, J.; Laidre, K.; George, J.; Demaster, D.

    2004-12-01

    Global warming may disproportionately affect Arctic marine mammals and disrupt traditional subsistence hunting activities. Based upon analyses of a 24-year time series (1979-2002) of satellite-derived sea ice cover, we identified significant positive trends in the amount of open-water in three large and five small-scale regions in the western Arctic, including habitats where bowhead whales (Balaena mysticetus) feed or are suspected to feed. Bowheads are the only mysticete whale endemic to the Arctic and a cultural keystone species for Native peoples from northwestern Alaska and Chukotka, Russia. While copepods (Calanus spp.) are a mainstay of the bowhead diet, prey sampling conducted in the offshore region of northern Chukotka and stomach contents from whales harvested offshore of the northern Alaskan coast indicate that euphausiids (Thysanoessa spp.) advected from the Bering Sea are also common prey in autumn. Early departure of sea ice has been posited to control availability of zooplankton in the southeastern Bering Sea and in the Cape Bathurst polynya in the southeastern Canadian Beaufort Sea, with maximum secondary production associated with a late phytoplankton bloom in insolatoin-stratified open water. While it is unclear if declining sea-ice has directly affected production or advection of bowhead prey, an extension of the open-water season increases opportunities for Native subsistence whaling in autumn. Therefore, bowhead whales may provide a nexus for simultaneous exploration of the effects sea ice reduction on pagophillic marine mammals and on the social systems of the subsistence hunting community in the western Arctic. The NOAA/Alaska Fisheries Science Center and NSB/Department of Wildlife Management will investigate bowhead whale stock identity, seasonal distribution and subsistence use patterns during the International Polar Year, as an extension of research planned for 2005-06. This research is in response to recommendations from the Scientific

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed

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

    2014-06-01

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

  15. Transport of marine fish larvae to Saroma-ko Lagoon (Hokkaido, Japan) in relation to the availability of zooplankton prey under the winter ice cover

    NASA Astrophysics Data System (ADS)

    Fortier, Martin; Fortier, Louis

    1997-02-01

    To assess the importance of ice-covered Saroma-ko Lagoon as a winter nursery area for young fish spawned offshore, we monitored the recruitment of marine fish larvae from the Sea of Okhotsk to the lagoon as well as the availability of larval fish prey under the ice cover from 24 February to 23 March 1992. Sand lance ( Ammodytes sp.) and walleye pollock ( Theragra chalcogramma) larvae recruited to the lagoon on flood tide whereas snake prickleback ( Lumpenus sagitta) larvae were exported to the Sea of Okhotsk on ebb. Before the ice breakup, ice microalgae made up the bulk of the microalgal biomass in the lagoon. The production and release of ice algae did not trigger the maturation of the late copepodite stages of copepods, and the proportion of adult females in the copepod assemblage remained low. The production of copepod nauplii (the main prey of fish larvae) under the ice was probably insufficient to insure suitable feeding and growth of fish larvae entering the lagoon in winter. Sand lance larvae, the most abundant species to colonize the lagoon in February-March, had to survive for nearly two months at low food abundance. Based on our results, the importance of Saroma-ko Lagoon as a winter nursery area for fish larvae appears negligible.

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

    USGS Publications Warehouse

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

    1996-01-01

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

  17. Separating snow, clean and debris covered ice in the Upper Indus Basin, Hindukush-Karakoram-Himalayas, using Landsat images between 1998 and 2002

    NASA Astrophysics Data System (ADS)

    Khan, Asif; Naz, Bibi S.; Bowling, Laura C.

    2015-02-01

    The Hindukush Karakoram Himalayan mountains contain some of the largest glaciers of the world, and supply melt water from perennial snow and glaciers to the Upper Indus Basin (UIB) upstream of Tarbela dam, which constitutes greater than 80% of the annual flows, and caters to the needs of millions of people in the Indus Basin. It is therefore important to study the response of perennial snow and glaciers in the UIB under changing climatic conditions, using improved hydrological modeling, glacier mass balance, and observations of glacier responses. However, the available glacier inventories and datasets only provide total perennial-snow and glacier cover areas, despite the fact that snow, clean ice and debris covered ice have different melt rates and densities. This distinction is vital for improved hydrological modeling and mass balance studies. This study, therefore, presents a separated perennial snow and glacier inventory (perennial snow-cover on steep slopes, perennial snow-covered ice, clean and debris covered ice) based on a semi-automated method that combines Landsat images and surface slope information in a supervised maximum likelihood classification to map distinct glacier zones, followed by manual post processing. The accuracy of the presented inventory falls well within the accuracy limits of available snow and glacier inventory products. For the entire UIB, estimates of perennial and/or seasonal snow on steep slopes, snow-covered ice, clean and debris covered ice zones are 7238 ± 724, 5226 ± 522, 4695 ± 469 and 2126 ± 212 km2 respectively. Thus total snow and glacier cover is 19,285 ± 1928 km2, out of which 12,075 ± 1207 km2 is glacier cover (excluding steep slope snow-cover). Equilibrium Line Altitude (ELA) estimates based on the Snow Line Elevation (SLE) in various watersheds range between 4800 and 5500 m, while the Accumulation Area Ratio (AAR) ranges between 7% and 80%. 0 °C isotherms during peak ablation months (July and August) range

  18. Species interactions and response time to climate change: ice-cover and terrestrial run-off shaping Arctic char and brown trout competitive asymmetries

    NASA Astrophysics Data System (ADS)

    Finstad, A. G.; Palm Helland, I.; Jonsson, B.; Forseth, T.; Foldvik, A.; Hessen, D. O.; Hendrichsen, D. K.; Berg, O. K.; Ulvan, E.; Ugedal, O.

    2011-12-01

    There has been a growing recognition that single species responses to climate change often mainly are driven by interaction with other organisms and single species studies therefore not are sufficient to recognize and project ecological climate change impacts. Here, we study how performance, relative abundance and the distribution of two common Arctic and sub-Arctic freshwater fishes (brown trout and Arctic char) are driven by competitive interactions. The interactions are modified both by direct climatic effects on temperature and ice-cover, and indirectly through climate forcing of terrestrial vegetation pattern and associated carbon and nutrient run-off. We first use laboratory studies to show that Arctic char, which is the world's most northernmost distributed freshwater fish, outperform trout under low light levels and also have comparable higher growth efficiency. Corresponding to this, a combination of time series and time-for-space analyses show that ice-cover duration and carbon and nutrient load mediated by catchment vegetation properties strongly affected the outcome of the competition and likely drive the species distribution pattern through competitive exclusion. In brief, while shorter ice-cover period and decreased carbon load favored brown trout, increased ice-cover period and increased carbon load favored Arctic char. Length of ice-covered period and export of allochthonous material from catchments are major, but contrasting, climatic drivers of competitive interaction between these two freshwater lake top-predators. While projected climate change lead to decreased ice-cover, corresponding increase in forest and shrub cover amplify carbon and nutrient run-off. Although a likely outcome of future Arctic and sub-arctic climate scenarios are retractions of the Arctic char distribution area caused by competitive exclusion, the main drivers will act on different time scales. While ice-cover will change instantaneously with increasing temperature

  19. Ancient ice

    NASA Astrophysics Data System (ADS)

    2009-11-01

    Simon Belt, Guillaume Massé and colleagues rammed their way through sheets of ice, spotting some polar bears on the way, in their attempt to reconstruct Arctic sea-ice records covering thousands of years.

  20. Pros and Cons of Physical/Empirical SAR Altimetry Retracking in Seasonally Ice-Covered Waters in Preparation for Sentinel-3

    NASA Astrophysics Data System (ADS)

    Jain, Maulik; Andersen, Ole Baltazar; Stenseng, Lars

    2015-12-01

    An investigation is performed into the retrieval of sea surface heights in the Arctic Ocean to evaluate the determination of seasonal sea level in the Arctic Ocean from satellite altimetry. Physical retrackers assume a uniform probability density function for the wave height within the footprint which is frequently compromised in the Arctic Ocean due to the presence of seasonal sea ice and the period of initial freezing of the ocean. Preliminary investigations highlight the pros of the empirical retrackers for seasonal sea ice covered regions as it does not assume anything about physical properties and the pros of a physical retracker for either permanent near fully ice covered or open ocean. Comparison with tide gauge data is performed in this study to highlight the pros and cons of physical and empirical retracking in the Arctic Ocean.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  2. Stabilization of Global Temperature and Polar Sea-ice cover via seeding of Maritime Clouds

    NASA Astrophysics Data System (ADS)

    Chen, Jack; Gadian, Alan; Latham, John; Launder, Brian; Neukermans, Armand; Rasch, Phil; Salter, Stephen

    2010-05-01

    The marine cloud albedo enhancement (cloud whitening) geoengineering technique (Latham1990, 2002, Bower et al. 2006, Latham et al. 2008, Salter et al. 2008, Rasch et al. 2009) involves seeding maritime stratocumulus clouds with seawater droplets of size (at creation) around 1 micrometer, causing the droplet number concentration to increase within the clouds, thereby enhancing their albedo and possibly longevity. GCM modeling indicates that (subject to satisfactory resolution of specified scientific and technological problems) the technique could produce a globally averaged negative forcing of up to about -4W/m2, adequate to hold the Earth's average temperature constant as the atmospheric carbon dioxide concentration increases to twice the current value. This idea is being examined using GCM modeling, LES cloud modeling, technological development (practical and theoretical), and analysis of data from the recent, extensive VOCALS field study of marine stratocumulus clouds. We are also formulating plans for a possible limited-area field test of the technique. Recent general circulation model computations using a fully coupled ocean-atmosphere model indicate that increasing cloud reflectivity by seeding maritime boundary layer clouds may compensate for some effects on climate of increasing greenhouse gas concentrations. The chosen seeding strategy (one of many possible scenarios), when employed in an atmosphere where the CO2 concentration is doubled, can restore global averages of temperature, precipitation and polar sea-ice to present day values, but not simultaneously. The response varies nonlinearly with the extent of seeding, and geoengineering generates local changes to important climatic features. Our computations suggest that for the specimen cases examined there is no appreciable reduction of rainfall over land, as a consequence of seeding. This result is in agreement with one separate study but not another. Much further work is required to explain these

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  4. Sea Ice

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.; Cavalieri, Donald J.

    2005-01-01

    Sea ice covers vast areas of the polar oceans, with ice extent in the Northern Hemisphere ranging from approximately 7 x 10(exp 6) sq km in September to approximately 15 x 10(exp 6) sq km in March and ice extent in the Southern Hemisphere ranging from approximately 3 x 10(exp 6) sq km in February to approximately 18 x 10(exp 6) sq km in September. These ice covers have major impacts on the atmosphere, oceans, and ecosystems of the polar regions, and so as changes occur in them there are potential widespread consequences. Satellite data reveal considerable interannual variability in both polar sea ice covers, and many studies suggest possible connections between the ice and various oscillations within the climate system, such as the Arctic Oscillation, North Atlantic Oscillation, and Antarctic Oscillation, or Southern Annular Mode. Nonetheless, statistically significant long-term trends are also apparent, including overall trends of decreased ice coverage in the Arctic and increased ice coverage in the Antarctic from late 1978 through the end of 2003, with the Antarctic ice increases following marked decreases in the Antarctic ice during the 1970s. For a detailed picture of the seasonally varying ice cover at the start of the 21st century, this chapter includes ice concentration maps for each month of 2001 for both the Arctic and the Antarctic, as well as an overview of what the satellite record has revealed about the two polar ice covers from the 1970s through 2003.

  5. High-resolution record of last post-glacial variations of sea-ice cover and river discharge in the western Laptev Sea (Arctic Ocean)

    NASA Astrophysics Data System (ADS)

    Stein, R. H.; Hörner, T.; Fahl, K.

    2014-12-01

    Here, we provide a high-resolution reconstruction of sea-ice cover variations in the western Laptev Sea, a crucial area in terms of sea-ice production in the Arctic Ocean and a region characterized by huge river discharge. Furthermore, the shallow Laptev Sea was strongly influenced by the post-glacial sea-level rise that should also be reflected in the sedimentary records. The sea Ice Proxy IP25 (Highly-branched mono-isoprenoid produced by sea-ice algae; Belt et al., 2007) was measured in two sediment cores from the western Laptev Sea (PS51/154, PS51/159) that offer a high-resolution composite record over the last 18 ka. In addition, sterols are applied as indicator for marine productivity (brassicasterol, dinosterol) and input of terrigenous organic matter by river discharge into the ocean (campesterol, ß-sitosterol). The sea-ice cover varies distinctly during the whole time period and shows a general increase in the Late Holocene. A maximum in IP25 concentration can be found during the Younger Dryas. This sharp increase can be observed in the whole circumarctic realm (Chukchi Sea, Bering Sea, Fram Strait and Laptev Sea). Interestingly, there is no correlation between elevated numbers of ice-rafted debris (IRD) interpreted as local ice-cap expansions (Taldenkova et al. 2010), and sea ice cover distribution. The transgression and flooding of the shelf sea that occurred over the last 16 ka in this region, is reflected by decreasing terrigenous (riverine) input, reflected in the strong decrease in sterol (ß-sitosterol and campesterol) concentrations. ReferencesBelt, S.T., Massé, G., Rowland, S.J., Poulin, M., Michel, C., LeBlanc, B., 2007. A novel chemical fossil of palaeo sea ice: IP25. Organic Geochemistry 38 (1), 16e27. Taldenkova, E., Bauch, H.A., Gottschalk, J., Nikolaev, S., Rostovtseva, Yu., Pogodina, I., Ya, Ovsepyan, Kandiano, E., 2010. History of ice-rafting and water mass evolution at the northern Siberian continental margin (Laptev Sea) during Late

  6. Post-glacial variations of sea ice cover and river discharge in the western Laptev Sea (Arctic Ocean) - a high-resolution study over the last 18 ka

    NASA Astrophysics Data System (ADS)

    Hörner, Tanja; Stein, Ruediger; Fahl, Kirsten

    2015-04-01

    Here, we provide a high-resolution reconstruction of sea-ice cover variations in the western Laptev Sea, a crucial area in terms of sea-ice production in the Arctic Ocean and a region characterized by huge river discharge. Furthermore, the shallow Laptev Sea was strongly influenced by the post-glacial sea-level rise that should also be reflected in the sedimentary records. The sea Ice Proxy IP25 (Highly-branched mono-isoprenoid produced by sea-ice algae; Belt et al., 2007) was measured in two sediment cores from the western Laptev Sea (PS51/154, PS51/159) that offer a high-resolution composite record over the last 18 ka. In addition, sterols are applied as indicator for marine productivity (brassicasterol, dinosterol) and input of terrigenous organic matter by river discharge into the ocean (campesterol, ß-sitosterol). The sea-ice cover varies distinctly during the whole time period and shows a general increase in the Late Holocene. A maximum in IP25 concentration can be found during the Younger Dryas. This sharp increase can be observed in the whole circumarctic realm (Chukchi Sea, Bering Sea, Fram Strait and Laptev Sea). Interestingly, there is no correlation between elevated numbers of ice-rafted debris (IRD) interpreted as local ice-cap expansions (Taldenkova et al. 2010), and sea ice cover distribution. The transgression and flooding of the shelf sea that occurred over the last 16 ka in this region, is reflected by decreasing terrigenous (riverine) input, reflected in the strong decrease in sterol (ß-sitosterol and campesterol) concentrations. References Belt, S.T., Massé, G., Rowland, S.J., Poulin, M., Michel, C., LeBlanc, B., 2007. A novel chemical fossil of palaeo sea ice: IP25. Organic Geochemistry 38 (1), 16e27. Taldenkova, E., Bauch, H.A., Gottschalk, J., Nikolaev, S., Rostovtseva, Yu., Pogodina, I., Ya, Ovsepyan, Kandiano, E., 2010. History of ice-rafting and water mass evolution at the northern Siberian continental margin (Laptev Sea) during Late

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  8. Trends in Sea Ice Cover, Sea Surface Temperature, and Chlorophyll Biomass Across a Marine Distributed Biological Observatory in the Pacific Arctic Region

    NASA Astrophysics Data System (ADS)

    Frey, K. E.; Grebmeier, J. M.; Cooper, L. W.; Wood, C.; Panday, P. K.

    2011-12-01

    The northern Bering and Chukchi Seas in the Pacific Arctic Region (PAR) are among the most productive marine ecosystems in the world and act as important carbon sinks, particularly during May and June when seasonal sea ice-associated phytoplankton blooms occur throughout the region. Recent dramatic shifts in seasonal sea ice cover across the PAR should have profound consequences for this seasonal phytoplankton production as well as the intimately linked higher trophic levels. In order to investigate ecosystem responses to these observed recent shifts in sea ice cover, the development of a prototype Distributed Biological Observatory (DBO) is now underway in the PAR. The DBO is being developed as an internationally-coordinated change detection array that allows for consistent sampling and monitoring at five spatially explicit biologically productive locations across a latitudinal gradient: (1) DBO-SLP (south of St. Lawrence Island (SLI)), (2) DBO-NBS (north of SLI), (3) DBO-SCS (southern Chukchi Sea), (4) DBO-CCS (central Chukchi Sea), and (5) DBO-BCA (Barrow Canyon Arc). Standardized measurements at many of the DBO sites were made by multiple research cruises during the 2010 and 2011 pilot years, and will be expanded with the development of the DBO in coming years. In order to provide longer-term context for the changes occurring across the PAR, we utilize multi-sensor satellite data to investigate recent trends in sea ice cover, chlorophyll biomass, and sea surface temperatures for each of the five DBO sites, as well as a sixth long-term observational site in the Bering Strait. Satellite observations show that over the past three decades, trends in sea ice cover in the PAR have been heterogeneous, with significant declines in the Chukchi Sea, slight declines in the Bering Strait region, but increases in the northern Bering Sea south of SLI. Declines in the persistence of seasonal sea ice cover in the Chukchi Sea and Bering Strait region are due to both earlier sea

  9. Modelling the feedbacks between mass balance, ice flow and debris transport to predict the response to climate change of debris-covered glaciers in the Himalaya

    NASA Astrophysics Data System (ADS)

    Rowan, Ann V.; Egholm, David L.; Quincey, Duncan J.; Glasser, Neil F.

    2015-11-01

    Many Himalayan glaciers are characterised in their lower reaches by a rock debris layer. This debris insulates the glacier surface from atmospheric warming and complicates the response to climate change compared to glaciers with clean-ice surfaces. Debris-covered glaciers can persist well below the altitude that would be sustainable for clean-ice glaciers, resulting in much longer timescales of mass loss and meltwater production. The properties and evolution of supraglacial debris present a considerable challenge to understanding future glacier change. Existing approaches to predicting variations in glacier volume and meltwater production rely on numerical models that represent the processes governing glaciers with clean-ice surfaces, and yield conflicting results. We developed a numerical model that couples the flow of ice and debris and includes important feedbacks between debris accumulation and glacier mass balance. To investigate the impact of debris transport on the response of a glacier to recent and future climate change, we applied this model to a large debris-covered Himalayan glacier-Khumbu Glacier in Nepal. Our results demonstrate that supraglacial debris prolongs the response of the glacier to warming and causes lowering of the glacier surface in situ, concealing the magnitude of mass loss when compared with estimates based on glacierised area. Since the Little Ice Age, Khumbu Glacier has lost 34% of its volume while its area has reduced by only 6%. We predict a decrease in glacier volume of 8-10% by AD2100, accompanied by dynamic and physical detachment of the debris-covered tongue from the active glacier within the next 150 yr. This detachment will accelerate rates of glacier decay, and similar changes are likely for other debris-covered glaciers in the Himalaya.

  10. Interannual variations in atmospheric mass over liquid water oceans, continents, and sea-ice-covered arctic regions and their possible impacts on the boreal winter climate

    NASA Astrophysics Data System (ADS)

    Guan, Zhaoyong; Zhang, Qian; Li, Minggang

    2015-12-01

    Using reanalysis data from National Centers for Environmental Prediction/National Center for Atmospheric Research, ERA-interim, and Hadley Centre Sea Ice and Sea Surface Temperature for the period of 1979-2012, the variations in atmospheric mass (AM) over liquid water oceans, continents, and sea-ice-covered Arctic regions during boreal winter are investigated. It is found that AM may migrate in a compensatory manner among these three types of surfaces on interannual time scales. There are two pairs of strong antiphase relations. One lies in a zonal orientation between the Eurasian continent and the midlatitude Pacific (referred to as Eurasian continent/Pacific antiphase relation) and exhibits a teleconnection pattern characterized by two strong correlation centers, one over Eurasia and one over the North Pacific. The other antiphase AM relation, referred to as ocean/ice-covered Arctic antiphase relation (OIAR), exhibits a meridional orientation between the ice-covered Arctic and liquid water oceans, including the Atlantic and Pacific. In the context of the OIAR, two teleconnection patterns are observed. One features three strong correlation centers, one each over the Mediterranean, Arctic, and North Pacific, and corresponds to AM fluctuations over liquid water oceans. The other is characterized by three strong correlation centers over the Mediterranean, the Arctic, and East Asia, and corresponds to AM fluctuations over the ice-covered Arctic. These teleconnections are the results of thermal contrasts among the three types of surfaces. Rossby waves and vertical circulations play important roles in the formation of these teleconnections. Interestingly, these teleconnections may have significant and widespread influences on the winter climate in the Northern Hemisphere, especially in regions near the Mediterranean, the northern Eurasia, parts of North America, and East Asia.

  11. Assessing the potential impacts of declining Arctic sea ice cover on the photochemical degradation of dissolved organic matter in the Chukchi and Beaufort Seas

    NASA Astrophysics Data System (ADS)

    Logvinova, Christie L.; Frey, Karen E.; Mann, Paul J.; Stubbins, Aron; Spencer, Robert G. M.

    2015-11-01

    A warming and shifting climate in the Arctic has led to significant declines in sea ice over the last several decades. Although these changes in sea ice cover are well documented, large uncertainties remain in how associated increases in solar radiation transmitted to the underlying ocean water column will impact heating, biological, and biogeochemical processes in the Arctic Ocean. In this study, six under-ice marine, two ice-free marine, and two ice-free terrestrially influenced water samples were irradiated using a solar simulator for 72 h (representing ~10 days of ambient sunlight) to investigate dissolved organic matter (DOM) dynamics from the Chukchi and Beaufort Seas. Solar irradiation caused chromophoric DOM (CDOM) light absorption at 254 nm to decrease by 48 to 63%. An overall loss in total DOM fluorescence intensity was also observed at the end of all experiments, and each of six components identified by parallel factor (PARAFAC) analysis was shown to be photoreactive in at least one experiment. Fluorescent DOM (FDOM) also indicated that the majority of DOM in under-ice and ice-free marine waters was likely algal-derived. Measurable changes in dissolved organic carbon (DOC) were only observed for sites influenced by riverine runoff. Losses of CDOM absorbance at shorter wavelengths suggest that the beneficial UV protection currently received by marine organisms may decline with the increased light transmittance associated with sea ice melt ponding and overall reductions of sea ice. Our FDOM analyses demonstrate that DOM irrespective of source was susceptible to photobleaching. Additionally, our findings suggest that photodegradation of CDOM in under-ice waters is not currently a significant source of carbon dioxide (CO2) (i.e., we did not observe systematic DOC loss). However, increases in primary production and terrestrial freshwater export expected under future climate change scenarios may cause an increase in CDOM quantity and shift in quality

  12. Modern seasonal variability of central Arctic Ocean sea-ice cover: Reconstruction based on biomarker ("IP25" and "PIP25") data from sediment trap samples

    NASA Astrophysics Data System (ADS)

    Fahl, K.; Stein, R.

    2012-04-01

    During the Polarstern 1995 Expedition, a long-term mooring system with two cone-shaped multi-sampling traps was deployed at the dominantly ice-covered western slope of the southern Lomonosov Ridge (81°04.5'N, 138°54.0'E, 1712 m water depth). One trap was installed at 150 m below the sea surface, the other at 150 m above the bottom at 1550 m depth; material was collected in 20 time intervals between September 1995 and August 1996. For background data see Fahl and Nöthig (2007). Here, we present new biomarker data recording the seasonal variability of sea-ice cover. This type of data representing modern seasonal variability of the sea-ice biomarker proxies, was not available so far from the central Arctic Ocean but may help significantly the interpretation of these proxies to be used in sedimentary records for reconstruction of paleo-sea-ice distributions. In this study, we have focused on the novel sea ice proxy "IP25", a direct proxy for sea ice coverage (Belt et al., 2007). Furthermore, we used the phytoplankton-IP25 index ("PIP25" Index), a further development of the IP25 index, based on the coupling of the environmental information carried by IP25 (sea ice) and brassicasterol (open-water phytoplankton productivity) (Müller et al., 2011). The interval November 1995 to June 1996 is characterized by the absence of the sea-ice proxy IP25 (except very minor values for January and April), suggesting a predominantly permanent sea-ice cover at the trap location. During July/August 1996, maximum fluxes of the diatom-specific fatty acids and brassicasterol as well as maximum contents of biogenic opal (Fahl and Nöthig, 2007) indicate increased primary productivity. The marine organic matter (here POC, brassicasterol, and fatty acids) and the IP25 values decrease systematically from 150 to 1550m depth, indicating the typical biogeochemical degradation with increasing water depth. Due to the coincidence of maximum abundances of sea-ice proxies and open-ocean primary

  13. Post-glacial variability of sea ice cover, river run-off and biological production in the western Laptev Sea (Arctic Ocean) - A high-resolution biomarker study

    NASA Astrophysics Data System (ADS)

    Hörner, T.; Stein, R.; Fahl, K.; Birgel, D.

    2016-07-01

    Multi-proxy biomarker measurements were applied on two sediment cores (PS51/154, PS51/159) to reconstruct sea ice cover (IP25), biological production (brassicasterol, dinosterol) and river run-off (campesterol, β-sitosterol) in the western Laptev Sea over the last ∼17 ka with unprecedented temporal resolution. The absence of IP25 from 17.2 to 15.5 ka, in combination with minimum concentration of phytoplankton biomarkers, suggests that the western Laptev Sea shelf was mostly covered with permanent sea ice. Very minor river run-off and restricted biological production occurred during this cold interval. From ∼16 ka until 7.5 ka, a long-term decrease of terrigenous (riverine) organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western Laptev Sea, caused by the onset of the post-glacial transgression. Intensified 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). Prominent peaks of the DIP25 Index coinciding with maximum abundances of subpolar foraminifers, are interpreted as pulses of Atlantic water inflow on the western Laptev Sea shelf. After the warm period, a sudden return to severe sea ice conditions with strongest ice-coverage between 11.9 and 11 ka coincided with the Younger Dryas (12.9-11.6 ka). At the onset of the Younger Dryas, a distinct alteration of the ecosystem (reflected in a distinct drop in terrigenous and phytoplankton biomarkers) was detected. During the last 7 ka, the sea ice proxies reflect a cooling of the Laptev Sea spring/summer season. This cooling trend was superimposed by a short-term variability in sea ice coverage, probably representing Bond cycles (1500 ± 500 ka) that are related to solar activity changes. Hence, atmospheric circulation changes were apparently able to affect the sea ice conditions on the Laptev Sea shelf under modern sea level

  14. From the Sun to the Ice - Then Where? A Bi-polar, Integrated View of the Role of Polar Snow and Floating Ice Covers in the Earth's Heat Budget During IPY 2007/08

    NASA Astrophysics Data System (ADS)

    Eicken, H.; Grenfell, T.; Jeffries, M.; Perovich, D.; Sturm, M.

    2003-12-01

    The polar regions play a key role in the disposition of energy and in particular solar radiation in the earth's climate system. With the largest seasonal variations in surface albedo occurring over the polar oceans and with substantial changes in the extent and nature of the snow and ice covers in recent decades, the polar regions are a critical link between top-of-the atmosphere radiative fluxes and solar energy absorbed by the earth system. While recent studies have greatly improved our knowledge of the heat budget of the polar oceans, we are still far from understanding a number of fundamental questions related to the role of snow and ice in the global radiation budget and their importance for albedo feedback processes. For example, currently albedo parameterizations in large-scale sea ice and climate models are only partially successful in taking into account the physical processes driving seasonal and interannual albedo changes. In fact, the majority of models employ different albedo parameterizations for northern and southern hemisphere snow and sea ice. This is dictated by the strong contrasts in snow and ice melt processes in Arctic and Antarctic, which in of themselves are not all that well understood. Our own research in the Western Arctic and in the southern Ross Sea indicates that snow may play a crucial, currently underestimated role in governing these processes and hence the nature and magnitude of ice-albedo feedback processes. Here, we propose that an integrated, bi-polar examination of the interaction between snow and floating ice covers (sea and lake ice), coupled with a global-scale analysis of the role of polar ice masses in affecting the earth's radiation budget would provide an interesting and scientifically significant cryospheric thread within the framework of the IPY 2007/08. This work would also address other important aspects such as large-scale cloud radiative forcing over ice surfaces and spatio-temporal partitioning of the radiation

  15. 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.

  16. In situ and satellite-derived ablation season temperature and surface characteristics of clean and debris-covered ice at Matanuska glacier, Alaska

    NASA Astrophysics Data System (ADS)

    Casey, K.

    2012-12-01

    Outside of the ice sheets and the Himalayas, Alaska contains one of the largest masses of ice on Earth. The rapid loss of ice in Alaska in recent decades is the subject of intense investigation (Berthier et al., 2010). An under quantified factor in the understanding of ice mass loss is the role in which different surface glacier dust and debris types and thicknesses play on the ablation process. Ground-based measurements of surface temperature of several glacier debris types were collected in July 2012 at Matanuska glacier in Alaska. Wet, dry, moderately covered and cleaner ice sites were observed over a two week period. Temperatures were recorded every 20 minutes. Significant diurnal and debris type temperature variability were observed. Satellite-based shortwave and thermal infrared analysis of debris covered ice is used to estimate surface debris mineralogy. Thermal satellite data is further used to derive entire glacier surface temperatures. Terminal glacier in situ temperature observations are compared with satellite derived surface temperatures. In situ measurements are also evaluated with respect to Foster et al. (2012) physically based method for estimating surface glacier debris thickness. E. Berthier, E. Schiefer, G.K.C. Clarke, B. Menounos, F. Rémy, 2010, Contribution of Alaskan glaciers to sea-level rise derived from satellite imagery, Nature Geoscience, 3, 92-95. L.A. Foster, B.W. Brock, M.E.J. Cutler, F. Diotri, 2012, Instruments and Methods: A physically based method for estimating supraglacial debris thickness from thermal band remote-sensing data, Journal of Glaciology, 58, 210, 677-691.

  17. Laser-Induced Fluorescence Emission (L.I.F.E.): In Situ Nondestructive Detection of Microbial Life in the Ice Covers of Antarctic Lakes

    NASA Astrophysics Data System (ADS)

    Storrie-Lombardi, Michael C.; Sattler, Birgit

    2009-09-01

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

  18. Seasonal sea ice cover as principal driver of spatial and temporal variation in depth extension and annual production of kelp in Greenland

    PubMed Central

    Krause-Jensen, Dorte; Marbà, Núria; Olesen, Birgit; Sejr, Mikael K; Christensen, Peter Bondo; Rodrigues, João; Renaud, Paul E; Balsby, Thorsten JS; Rysgaard, Søren

    2012-01-01

    We studied the depth distribution and production of kelp along the Greenland coast spanning Arctic to sub-Arctic conditions from 78 °N to 64 °N. This covers a wide range of sea ice conditions and water temperatures, with those presently realized in the south likely to move northwards in a warmer future. Kelp forests occurred along the entire latitudinal range, and their depth extension and production increased southwards presumably in response to longer annual ice-free periods and higher water temperature. The depth limit of 10% kelp cover was 9–14 m at the northernmost sites (77–78 °N) with only 94–133 ice-free days per year, but extended to depths of 21–33 m further south (73 °N–64 °N) where >160 days per year were ice-free, and annual production of Saccharina longicruris and S. latissima, measured as the size of the annual blade, ranged up to sevenfold among sites. The duration of the open-water period, which integrates light and temperature conditions on an annual basis, was the best predictor (relative to summer water temperature) of kelp production along the latitude gradient, explaining up to 92% of the variation in depth extension and 80% of the variation in kelp production. In a decadal time series from a high Arctic site (74 °N), inter-annual variation in sea ice cover also explained a major part (up to 47%) of the variation in kelp production. Both spatial and temporal data sets thereby support the prediction that northern kelps will play a larger role in the coastal marine ecosystem in a warmer future as the length of the open-water period increases. As kelps increase carbon-flow and habitat diversity, an expansion of kelp forests may exert cascading effects on the coastal Arctic ecosystem.

  19. Copepods in ice-covered seas—Distribution, adaptations to seasonally limited food, metabolism, growth patterns and life cycle strategies in polar seas

    NASA Astrophysics Data System (ADS)

    Conover, R. J.; Huntley, M.

    1991-07-01

    While a seasonal ice cover limits light penetration into both polar seas for up to ten months a year, its presence is not entirely negative. The mixed layer under sea ice will generally be shallower than in open water at the same latitude and season. Ice forms a substrate on which primary production can be concentrated, a condition which contrasts with the generally dilute nutritional conditions which prevail in the remaining ocean. The combination of a shallow, generally stable mixed layer with a close proximity to abundant food make the under-ice zone a suitable nursery for both pelagic and benthic species, an upside-down benthos for opportunistic substrate browsers, and a rich feeding environment for species often considered to be neritic in temperate environments. Where the ice cover is not continuous there may be a retreating ice edge that facilitates the seasonal production of phytoplankton primarily through increased stability from the melt water. Ice edge blooms similarly encourage secondary production by pelagic animals. Pseudocalanus acuspes, which may be the most abundant and productive copepod in north polar latitudes, initiates growth at the start of the "spring bloom" of epontic algae, reaching sexual maturity at breakup or slightly before. In the Southern Hemisphere, the small neritic copepod Paralabidocera antarctica and adult krill have been observed to utilize ice algae. Calanus hyperboreus breeds in the dark season at depth and its buoyant eggs, slowly developing on the ascent, reach the under-ice layer in April as nauplii ready to benefit from the primary production there. On the other hand, C. glacialis may initiate ontogenetic migrations and reproduction in response to increased erosion of ice algae due to solar warming and melting at the ice-water interface. While the same species in a phytoplankton bloom near the ice edge reproduces actively, those under still-consolidated ice nearby can have immature gonads. Diel migration and diel feeding

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

    PubMed

    Storrie-Lombardi, Michael C; Sattler, Birgit

    2009-09-01

    Laser-induced fluorescence emission (L.I.F.E.) images were obtained in situ following 532 nm excitation of cryoconite assemblages in the ice covers of annual and perennially frozen Antarctic lakes during the 2008 Tawani International Expedition to Schirmacher Oasis and Lake Untersee in Dronning Maud Land, Antarctica. Laser targeting of a single millimeter-scale cryoconite results in multiple neighboring excitation events secondary to ice/air interface reflection and refraction in the bubbles surrounding the primary target. Laser excitation at 532 nm of cyanobacteria-dominated assemblages produced red and infrared autofluorescence activity attributed to the presence of phycoerythrin photosynthetic pigments. The method avoids destruction of individual target organisms and does not require the disruption of either the structure of the microbial community or the surrounding ice matrix. L.I.F.E. survey strategies described may be of interest for orbital monitoring of photosynthetic primary productivity in polar and alpine glaciers, ice sheets, snow, and lake ice of Earth's cryosphere. The findings open up the possibility of searching from either a rover or from orbit for signs of life in the polar regions of Mars and the frozen regions of exoplanets in neighboring star systems. PMID:19778277

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    operational agencies, and the requirements of the operational user community to better characterize river-ice (and glacier temporary lakes) dynamics in flood forecasting models at the basin scale. This paper presents recent results on the development and evaluation of EO-based lake ice cover and LST products for future NWP/RCM experiments, and comparison with output from numerical lake models using Great Bear Lake (GBL) and Great Slave Lake (GSL), Canada, as test sites. Lake ice cover fraction estimates derived from Radarsat-1 imagery using the iterative region-growing using semantics as the core algorithm of the MAGIC (MAp Guided Ice-Classification) software are comparable to those determined through visual interpretation by expert ice analysts. Mean daily LST estimates from MODIS (Terra/Aqua satellites) are shown to be overall in good agreement with LSTs estimated with two lake models, with larger differences during the ice cover season than the open water season. Implications of these results in advancing our understanding of ice thermodynamics and the open-water thermal regime of the two large lakes, and for improving lake schemes currently used in NWP models and RCMs are also discussed.

  2. The Bering Sea ice cover during March 1979: Comparison of surface and satellite data with the Nimbus-7 SMMR

    NASA Technical Reports Server (NTRS)

    Martin, S.; Cavalieri, D. J.; Gloersen, P.; Mcnutt, S. L.

    1982-01-01

    During March 1979, field operations were carried out in the Marginal Ice Zone (MIZ) of the Bering Sea. The field measurements which included oceanographic, meteorological and sea ice observations were made nearly coincident with a number of Nimbus-7 and Tiros-N satellite observations. The results of a comparison between surface and aircraft observations, and images from the Tiros-N satellite, with ice concentrations derived from the microwave radiances of the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) are given. Following a brief discussion of the field operations, including a summary of the meteorological conditions during the experiment, the satellite data is described with emphasis on the Nimbus-7 SMMR and the physical basis of the algorithm used to retrieve ice concentrations.

  3. Pliocene-Pleistocene changes in Arctic sea-ice cover: New biomarker records from Fram Strait/Yermak Plateau (ODP Sites 911 and 912)

    NASA Astrophysics Data System (ADS)

    Stein, Ruediger; Fahl, Kirsten

    2013-04-01

    Recently, a novel and promising biomarker proxy for reconstruction of Arctic sea-ice conditions was developed and is based on the determination of a highly branched isoprenoid with 25 carbons (IP25; Belt et al., 2007). Following this pioneer IP25 study by Belt and colleagues, several IP25 studies of marine surface sediments and sediment cores as well as sediment trap samples from northpolar areas were carried out successfully and allowed detailed reconstruction of modern and late Quaternary sea ice variability in these regions (e.g., Massé et al., 2008; Müller et al., 2009, 2011; Vare et al., 2009; Belt et al., 2010; Fahl and Stein, 2012; for review see Stein et al., 2012). Here, we present new (low-resolution) biomarker records from Ocean Drilling Program (ODP) Sites 911 and 912, representing the Pliocene-Pleistocene time interval (including the interval of major intensification of Northern Hemisphere Glaciation near 2.7 Ma). These data indicate that sea ice of variable extent was present in the Fram Strait/southern Yermak Plateau area during most of the time period under investigation. In general, an increase in sea-ice cover seems to correlate with phases of extended late Pliocene-Pleistocene continental ice-sheets. At ODP Site 912, a significant increase in sea-ice extension occurred near 1.2 Ma (Stein and Fahl, 2012). Furthermore, our data support the idea that a combination of IP25 and open water, phytoplankton biomarker data ("PIP25 index"; Müller et al., 2011) may give more reliable and quantitative estimates of past sea-ice cover (at least for the study area). This study reveals that the novel IP25/PIP25 biomarker approach has potential for semi-quantitative paleo-sea ice studies covering the entire Quaternary and motivate to carry out further detailed high-resolution research on ODP/IODP material using this proxy. References Belt, S.T., Massé, G., Rowland, S.J., Poulin, M., Michel, C., LeBlanc, B., 2007. A novel chemical fossil of palaeo sea ice: IP25

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  5. 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).

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

    NASA Astrophysics Data System (ADS)

    Nolan, M.

    2012-04-01

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

  7. Formation of Ice-Rich Lobate Debris Aprons Through Regional Icesheet Collapse and Debris-Cover Armoring

    NASA Astrophysics Data System (ADS)

    Fastook, J. L.; Head, J. W.; Marchant, D. R.

    2011-03-01

    We use a flowband model to assess development of lobate debris apron sublimation lag thickness and lateral extent beneath scarps. We obtain estimates of the climate in place as the LDAs were forming during collapse of a larger, regional ice sheet.

  8. Metric remote sensing experiments in preparation for Spacelab flights. [alpine geomorphology and ice and/or snow cover

    NASA Technical Reports Server (NTRS)

    Galibert, G.

    1978-01-01

    Aerial and ground photographs of Wallis mountains and of Dolomiti di Cortina d'Ampezzo in Italy were made using spectrozonal emulsions and optical multichannel filters. A metric camera was used in the perspective of the first Spacelab flight aboard the space shuttle. Elementary forms of alpine geomorphology and ice or snow phenomena are detectable on these metric scenes.

  9. CHARACTERIZATION OF PM-10 EMISSIONS FROM ANTISKID MATERIALS APPLIED TO ICE- AND SNOW-COVERED ROADWAYS - PHASE II

    EPA Science Inventory

    The report gives results of field sampling on 47th Street in Kansas City, MO, during February and March 1993 to quantify the PM-10 emissions associated with the use of rock salt (NaCl) for ice and snow control. A baseline test was conducted in September 1993. The emissions were d...

  10. Variations of Winter Climate in Association with the Interannual Variability of Atmospheric Mass over Water Oceans, Continents, and Sea Ice-Covered Arctic Region

    NASA Astrophysics Data System (ADS)

    Guan, Z.; Zhang, Q.; Li, M.

    2015-12-01

    Using reanalysis data from NCEP/NCAR, ERA-interim, and HadISST for period 1979-2012, variations of atmospheric mass (AM) over water oceans, continents, and sea-ice-covered arctic region during boreal winter are investigated. It is found that the AM may migrate compensatively among these three types of surfaces on interannual time scales. There are two pairs of strong anti-phase relations. The one is in zonal between Eurasian continent and mid-latitude Pacific (referred to as EPAR), which is a teleconnection pattern characterizing with two strong correlation centers respectively over Eurasia and North Pacific. The other anti-phase relation of AM, referred to as OIAR, is found in meridional between ice-covered Arctic and water oceans including Atlantic and Pacific. In the context of OIAR, two teleconnection patterns are found. One is MANP, which merges as three strong correlation centers respectively over the Mediterranean, Arctic, and North Pacific when AM fluctuates over water oceans. Another is MAEA, which characterizes with three strong correlation centers respectively around the Mediterranean, Arctic, and East Asia when AM fluctuates over the ice-covered Arctic. The MAEA looks largely different from MANP in anomalous surface air pressure over the northwest Pacific. These teleconnections including MANP, MAEA, and EPAR are resulted from thermal contrasts among the three types of surfaces. Rossby waves and vertical circulations play important roles in forming these teleconnection patterns. Interestingly, these teleconnections may significantly influence the winter climate widely in the Northern Hemisphere, especially in regions around the Mediterranean, the northern part of Eurasia, parts of North America, and East Asia.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  12. The permanent ice cover of Lake Bonney, Antarctica: The influence of thickness and sediment distribution on photosynthetically available radiation and chlorophyll-a distribution in the underlying water column

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    The thick permanent ice cover on the lakes of the McMurdo Dry Valleys, Antarctica, inhibits spatial lake sampling due to logistical constraints of penetrating the ice cover. To date most sampling of these lakes has been made at only a few sites with the assumption that there is a spatial homogeneity of the physical and biogeochemical properties of the ice cover and the water column at any given depth. To test this underlying assumption, an autonomous underwater vehicle (AUV) was deployed in Lake Bonney, Taylor Valley. Measurements were obtained over the course of 2 years in a 100 × 100 m horizontal sampling grid (at a 0.2 m vertical resolution). Additionally, the AUV measured the ice thickness (in water equivalent) and collected images looking up through the ice, which were used to quantify sediment distribution on the surface and within the ice. Satellite imagery was used to map sediment distribution on the surface of the ice. We present results of the spatial investigation of the sediment distribution on the ice cover and its effects on biological processes, with particular emphasis on photosynthetically active radiation (PAR). The surface sediment is a secondary controller of the ice cover thickness, which in turn controls the depth-integrated PAR in the water column. Our data revealed that depth-integrated PAR was negatively correlated with depth-integrated chlorophyll-a (r = 0.88, p < 0.001, n = 83), which appears to be related to short-term photoadaptation of phytoplanktonic communities to spatial and temporal variation in PAR within the water column.

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

    USGS Publications Warehouse

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

    1997-01-01

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

  14. Modeling the Seasonal Ice Zone from the Air: use of repeat aerial hydrographic surveys to constrain a regional ice-ocean model in an area of rapidly evolving ice cover

    NASA Astrophysics Data System (ADS)

    Dewey, S.; Morison, J.; Zhang, J.

    2015-12-01

    The Seasonal Ice Zone of the Beaufort Sea is the area of ocean north of Alaska over which sea ice melts and reforms annually. It contains the more narrow, near-edge marginal ice zone (MIZ). Seasonal Ice Zone Reconnaissance Surveys (SIZRS) measure hydrography along two meridional sections using Air eXpendable CTDs (AXCTDs) and Air eXpendable Current Profilers (AXCPs). These surveys take place aboard U.S. Coast Guard Arctic Domain Awareness flights of opportunity during each melt season (June-October) starting in 2012. The Marginal Ice Zone Modeling and Assimilation System (MIZMAS) is a high-resolution regional ice-ocean model with daily, three-dimensional output encompassing the SIZRS survey area. Direct comparison of the SIZRS data with MIZMAS output as well as with several regional climatologies can constrain the ice-ocean model and help to explain recent changes in subsurface heat content and salinity. For example, observed freshening relative to climatology has been used as a reference to which MIZMAS surface salinity values can be relaxed. MIZMAS may in turn shed light on the physical mechanisms driving the observed freshening. In addition, use of MIZMAS surface fluxes to drive a one-dimensional mixed layer model gives results close to observations when the model is initialized with SIZRS profiles. Because SIZRS observations range in time from the onset of melt to the onset of Fall freeze-up, the comparison of the one-dimensional model with MIZMAS illustrates the relative roles of local and regional processes in forming near-surface temperature maxima and salinity minima. The SIZRS observations and one-dimensional model are used to constrain MIZMAS estimations of stored subsurface heat while establishing the physical drivers of these temperature and salinity changes.

  15. Links between ocean properties, ice cover, and plankton dynamics on interannual time scales in the Canadian Arctic Archipelago

    NASA Astrophysics Data System (ADS)

    Hamilton, James M.; Collins, Kate; Prinsenberg, Simon J.

    2013-10-01

    A decade of instrumented mooring data from Barrow Strait in the eastern Canadian Arctic Archipelago reveals connections between sea ice, water characteristics, and zooplankton dynamics on interannual time scales. On the North side of the Strait, the timing of breakup is positively related to the timing of freezeup in the previous year and negatively related to spring water temperature. This suggests that an early freezeup insulates the ocean from a cold autumn atmosphere, allowing heat to be retained until spring when it contributes to early sea ice erosion. There is also a very strong negative association between the timing of freezeup and late summer salinity, suggesting that monitoring of salinity in real time could be used to predict freezeup. A zooplankton biomass index derived from acoustic Doppler current profiler echo intensity data is used to demonstrate that on the North side there are also strong connections between early summer water temperature and the start, length, and productivity of the zooplankton growth season. On the South side of the Strait where currents are stronger, the relationships seen on the North side were not observed. But here integrated zooplankton biomass index and measured currents are used to identify interannual variability in the zooplankton biomass being delivered downstream into Lancaster Sound. Also on the South side, two yearlong records of daily fluorescence profiles reveal a large difference in the phytoplankton biomass being delivered downstream between years and demonstrate a strong relationship between the timing of the spring phytoplankton bloom and that of breakup.

  16. Stable-isotope studies on ice cores and snow pits in Dronning Maud Land, Antarctica, covering the past 2000 years

    NASA Astrophysics Data System (ADS)

    Oerter, H.; Kipfstuhl, S.; Wilhelms, F.

    2012-12-01

    During the past 15 years various ice cores were drilled at and upstream of Kohnen station (75.0017 S, 0.0678 E, 2882 m a.s.l.) Dronning Maud Land, East Antarctica, supplemented by snow pit studies. These data sets of stable-isotope data (18O, D, deuterium excess d) are available over various time periods displaying centennial and strong decadal variations. 5 ice cores are used to create staked profiles of the deviation of the 18O content from the mean of the period 1259-1816 (an interval well defined by 2 unique volcanic events) for the time slices of the past 2000 and 200 years. For the past 50 years data from various shallow firn cores and snow pits in the area will be presented. The used reference period for the short term studies is 1961-1990. δ18O values may be converted to temperature with the local gradient of 0.77 δ18O-‰/°C. The Common Era follows the Roman period which is characterised by isotope values or temperatures, respectively, higher than observed in the 2000 years afterwards until today. The so-called medieval optimum around 1050-1250 is recognisable. The so-called Little Ice Age, which is attributed to the period 1650-1850 in the Northern hemisphere, is not clearly displayed. Overall, a slight cooling (0.008 δ18O-‰/100a) is evident within the Common Era until 1900. In the time slice of the past 200 years the coldest period occurred between 1875 and 1900. During the 20th century the isotope content and thus the air temperature have been increasing (0.88 δ18O-‰/100a) and reached values in the first decade of the 21st century clearly higher than around 1800 and before. The 1940ies formed the coldest decade in the 20th century, another relative minimum appeared in the 1980ies. The time series with shallow firn cores and snow pits stop at 2008 CE. For the past 50 years it is not possible to determine a trend unambiguously. This is due to the decadal variations and the shortness of the time series from single pits and shallow cores. However

  17. Stress tolerance and stress-induced injury in crop plants measured by chlorophyll fluorescence in vivo: chilling, freezing, ice cover, heat, and high light.

    PubMed

    Smillie, R M; Hetherington, S E

    1983-08-01

    The proposition is examined that measurements of chlorophyll fluorescence in vivo can be used to monitor cellular injury caused by environmental stresses rapidly and nondestructively and to determine the relative stress tolerances of different species. Stress responses of leaf tissue were measured by F(R), the maximal rate of the induced rise in chlorophyll fluorescence. The time taken for F(R) to decrease by 50% in leaves at 0 degrees C was used as a measure of chilling tolerance. This value was 4.3 hours for chilling-sensitive cucumber. In contrast, F(R) decreased very slowly in cucumber leaves at 10 degrees C or in chilling-tolerant cabbage leaves at 0 degrees C. Long-term changes in F(R) of barley, wheat, and rye leaves kept at 0 degrees C were different in frost-hardened and unhardened material and in the latter appeared to be correlated to plant frost tolerance. To simulate damage caused by a thick ice cover, wheat leaves were placed at 0 degrees C under N(2). Kharkov wheat, a variety tolerant of ice encapsulation, showed a slower decrease in F(R) than Gatcher, a spring wheat. Relative heat tolerance was also indicated by the decrease in F(R) in heated leaves while changes in vivo resulting from photoinhibition, ultraviolet radiation, and photobleaching can also be measured. PMID:16663118

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    DOE PAGESBeta

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

    2016-04-15

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

  20. Number and phylogenetic affiliation of bacteria assimilating dimethylsulfoniopropionate and leucine in the ice-covered coastal Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Vila-Costa, Maria; Simó, Rafel; Alonso-Sáez, Laura; Pedrós-Alió, Carlos

    2008-12-01

    The ability of bacteria to assimilate sulfur from dimethylsulfoniopropionate (DMSP) was examined in the western Arctic Ocean by combining microautoradiography and fluorescence in situ hybridization (FISH). Assimilation of leucine was also measured for comparative purposes since leucine is considered a universal substrate for bacteria, which use it for protein synthesis. Samples were collected at 3 m depth, through a hole in the ice, in the CASES (Canadian Arctic Shelf Ecosystem Study) overwintering station in Franklin Bay (eastern Beaufort Sea) in March and May 2004 to compare two contrasting situations: winter and early spring. FISH counts indicated that the bacterial assemblage consisted of α- (up to 60% of the EUB positive cells), β- (up to 10%) and γ-proteobacteria (around 20%), and Bacteroidetes (up to 60%). The β-proteobacteria were not active with any of the two substrates tested. The remaining groups were much less efficient at assimilating DMSP-sulfur (5% of the cells) than leucine (20-35%) both in winter and in spring. Only the Roseobacter group of α-proteobacteria showed a similar assimilation of both substrates.

  1. Exploring the Habitability of Ice-covered Waterworlds: The Deep-Sea Hydrothermal System of the Aurora Mount at Gakkel Ridge, Arctic Ocean (82°54' N, 6°15W, 3900 m)

    NASA Astrophysics Data System (ADS)

    Boetius, A.; Bach, W.; Borowski, C.; Diehl, A.; German, C. R.; Kaul, N. E.; Koehler, J.; Marcon, Y.; Mertens, C.; Molari, M.; Schlindwein, V. S. N.; Tuerke, A.; Wegener, G.

    2014-12-01

    The geographic remoteness of the ultraslow Gakkel Ridge in the ice-covered Arctic Ocean raises many questions about the nature and biogeography of its habitats. In 2001, the two-ice-breaker mission AMORE (RV POLARSTERN and USCGC HEALY) detected hydrothermal plumes and evidence for seafloor venting associated with volcanic ridges rising from the rift valley floor of 4.2 km depth (Edmonds et al., 2003; Michael et al., 2003). The AURORA expedition in July 2014 (RV POLARSTERN Cruise PS86) targeted this "Aurora" field at the SW limit of Gakkel Ridge, to investigate its habitats, communities and their energy sources. No robots can yet be deployed through ice-cover to explore such deep habitats and ice-breaking research vessels cannot hold position in the thick multiyear ice. Instead, we estimated ice-drift to predict suitable start positions, then attached POLARSTERN to a matching ice floe, to achieve the bottom trajectories that we required for targeted exploration. The Aurora mount is volcanic in origin formed from mounded pillow basalts overlain by about a meter of sediment and cut through by steep cliffs revealing basalt pillows in outcrop and in talus piles. We identified persistent plume activity in the water column above the mount at 3100-3600 m (800-300 m off-bottom of its top) characterized by anomalies in turbidity, Eh, methane, temperature, density, and elevated microbial chemoautotrophic activity. Using a towed camera-, and multisensor- platform (OFOS) we located active venting as the source of this plume together with inactive chimneys and associated craters on the SW flank of Mt.Aurora. Its dominantly filter-feeding fauna is apparently sustained by venting of energy-rich fluids and microbial transfer of this geofuel into nutrition. This communication presents first results of our recent fieldwork and experimental investigations in Summer 2014 to explore deep-sea ecosystems in ice-covered oceans.

  2. The current evolution of complex high mountain debris-covered glacier systems and its relation with ground ice nature and distribution: the case of Rognes and Pierre Ronde area (Mont-Blanc range, France).

    NASA Astrophysics Data System (ADS)

    Bosson, Jean-Baptiste; Lambiel, Christophe

    2014-05-01

    The current climate forcing, through negative glacier mass balance and rockfall intensification, is leading to the rapid burring of many small glacier systems. When the debris mantle exceeds some centimeters of thickness, the climate control on ice melt is mitigated and delayed. As well, debris-covered glaciers respond to climate forcing in a complex way. This situation is emphasised in high mountain environments, where topo-climatic conditions, such as cold temperatures, amount of solid precipitation, duration of snow cover, nebulosity or shadow effect of rockwalls, limit the influence of rising air temperatures in the ground. Beside, due to Holocene climate history, glacier-permafrost interactions are not rare within the periglacial belt. Glacier recurrence may have removed and assimilated former ice-cemented sediments, the negative mass balance may have led to the formation of ice-cored rock glaciers and neopermafrost may have formed recently under cold climate conditions. Hence, in addition to sedimentary ice, high mountain debris-covered glacier systems can contain interstitial magmatic ice. Especially because of their position at the top of alpine cascade systems and of the amount of water and (unconsolidated) sediment involved, it is important to understand and anticipate the evolution of these complex landforms. Due to the continuous and thick debris mantle and to the common existence of dead ice in deglaciated areas, the current extent of debris-covered glacier can be difficult to point out. Thus, the whole system, according to Little Ice Age (LIA) extent, has sometimes to be investigated to understand the current response of glacier systems to the climate warming. In this context, two neighbouring sites, Rognes and Pierre Ronde systems (45°51'38''N, 6°48'40''E; 2600-3100m a.s.l), have been studied since 2011. These sites are almost completely debris-covered and only few ice outcrops in the upper slopes still witness the existence of former glaciers

  3. Life and death of ice cliffs and lakes on debris covered glaciers - insights from a new dataset from the Nepalese Himalaya

    NASA Astrophysics Data System (ADS)

    Steiner, Jakob; Buri, Pascal; Miles, Evan; Ragettli, Silvan; Pellicciotti, Francesca

    2016-04-01

    Numerous studies suggest that supraglacial ice cliffs and lakes could be one contributing factor to relatively high overall ablation rates on debris covered glaciers. While some studies have quantified backwasting rates, developments over the larger scale have not yet been assessed. Field work and earlier studies during three seasons in the Langtang catchment in the Nepalese Himalaya has given some insights into how these landforms develop, from initial emergence to persistence and disappearance. From 6 sets of concurrent high-resolution satellite imagery and DEMs between 2006 and 2015 and an additional image from 1974, we assembled an extensive dataset of these landforms on all glaciers in the catchment, including nearly 4000 individual lakes and cliffs. We show that ice cliffs appear in combination with lakes or without and there are lakes that are not bordered by a cliff. Numbers vary strongly between seasons, especially as lakes show strong seasonal variability. There are furthermore different types of cliff forms - circular, lateral and longitudinal - that give an indication of their formation process. Circular cliffs form with either collapsing subglacial channels or overdeepenings caused by water accumulating on the surface, while lateral cliffs are likely associated with underlying crevasses. Some of the cliff and lake systems remain at the same location on-glacier over a number of years, while most move with the whole glacier body down valley. From the DEMs determine preferential slopes and expositions of the cliffs in the catchment which have been shown to be essential aspects in explaining the backwasting process. In combination with field observations from one glacier, where most of these types were present, we can infer development processes of a number of systems over the whole catchment. It is also apparent that densities of these landforms vary greatly over the glacier surface, which can be explained with velocities or underlying bed topography in

  4. The Role of Terrestrial Inputs of Organic Matter in Arctic Lagoons: Comparative Studies from Open-Water and Ice-Covered Periods

    NASA Astrophysics Data System (ADS)

    Dunton, K. H.; McClelland, J. W.; Connelly, T.; Linn, S.; Khosh, M.

    2012-12-01

    Coastal ecosystems of the Arctic receive extraordinarily large quantities of terrestrial organic matter through river discharge and shoreline erosion. This organic matter, both in dissolved and particulate form, may provide an important carbon and energy subsidy that supports and maintains heterotrophic activity and food webs in coastal waters, especially in the lagoons. Recent food web studies using stable isotopes confirm the significant assimilation of terrestrial organic matter, based on the depletion in both 13C and 15N content of invertebrate and vertebrate consumers collected in eastern Beaufort Sea lagoons vs. offshore waters. Our current work specifically focuses on a set of 12 field sites along the eastern Alaskan Beaufort Sea coast, from Barter Island to Demarcation Bay. To examine linkages between biological communities and organic matter inputs from land, we compared sites ranging from lagoons to open coastal systems that receive differing amounts of freshwater runoff and also differ markedly in their exchange characteristics with shelf waters. Our temporal and spatial effort included field sampling during the ice covered period in a number of lagoons characterized by differences in their exchange characteristics with the nearshore shelf. Our preliminary chemical and biological measurements, the first of their kind in arctic coastal lagoons, reveal that lagoon benthos can become hypersaline (43) and net heterotrophic (values to 30% oxygen saturation) during winter, before rebounding during the period of ice break-up to net autotrophic (>100% saturation) under continued hypersaline conditions. Measurements of water and sediment chemistry, benthic and water column community characteristics, and natural abundance isotopic tracers promise to reveal the dynamic nature of these productive lagoon ecosystems under different hydrologic conditions. The possible role of terrestrially derived carbon to arctic estuarine food webs is especially important in view of

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  6. Prognostic relevance of circulating CK19 mRNA in advanced malignant biliary tract diseases

    PubMed Central

    Leelawat, Kawin; Narong, Siriluck; Udomchaiprasertkul, Wandee; Wannaprasert, Jerasak; Treepongkaruna, Sa-ard; Subwongcharoen, Somboon; Ratanashu-ek, Tawee

    2012-01-01

    AIM: To determine the role of circulating tumor cells (CTCs) in prediction of the overall survival of patients with advanced malignant biliary tract obstruction. METHODS: We investigated the prognostic value of CTCs by examining two markers, cytokeratin (CK) 19 and human telomerase reverse transcriptase (hTERT) mRNA, in 40 patients diagnosed with advanced malignant biliary tract diseases. Quantitative real-time reverse transcription polymerase chain reaction was used to detect CK19 and hTERT mRNA in the peripheral blood of these patients. Overall survival was analyzed using the Kaplan-Meier method and Cox regression modeling. RESULTS: Positive CK19 and hTERT mRNA expression was detected in 45% and 60%, respectively, of the 40 patients. Univariable analysis indicated that positive CK19 mRNA expression was significantly associated with worse overall survival (P = 0.009). Multivariable analysis determined that positive CK19 mRNA expression, patient’s age and serum bilirubin were each independently associated with overall survival. CONCLUSION: CK19 mRNA expression levels in peripheral blood appear to provide a valuable marker to predict the overall survival of patients with advanced malignant biliary tract obstruction. PMID:22253524

  7. Area and Elevation Changes of a Debris-Covered Glacier and a Clean-Ice Glacier Between 1952-2013 Using Aerial Images and Structure-from-Motion

    NASA Astrophysics Data System (ADS)

    Lardeux, P.; Glasser, N. F.; Holt, T.; Irvine-Fynn, T. D.; Hubbard, B. P.

    2015-12-01

    Since 1952, the clean-ice Glacier Blanc has retreated twice as fast as the adjacent debris-covered Glacier Noir. Located in the French Alps and separated by only 1 km, both glaciers experience the same climatic conditions, making them ideal to evaluate the impact of debris cover on glacier evolution. We used aerial photographs from 16 acquisitions from 1952 to 2013 to reconstruct and analyze glacier elevation changes using Structure-from-Motion (SfM) techniques. Here, we present the process of developing sub-metric resolution digital elevation models (DEMs) from these aerial photographs. By combining 16 DEMs, we produced a dataset of elevation changes of Glacier Noir and Glacier Blanc, including time-series analysis of lateral and longitudinal profiles, glacier hypsometry and mass balance variation. Our preliminary results indicate that Glacier Noir and Glacier Blanc have both thinned to a similar magnitude, ≤ 20 m, despite a 1 km retreat for Glacier Blanc and only 500 m for Glacier Noir. However, these elevation change reconstructions are hampered by large uncertainties, principally due to the lack of independent camera calibration on the historical imagery. Initial attempts using posteriori correction grids have proven to significantly increase the accuracy of these data. We will present some of the uncertainties and solutions linked to the use of SfM on such a large scale and on such an old dataset. This study demonstrates how SfM can be used to investigate long-term trends in environmental change, allowing glacier monitoring to be up-scaled. It also highlights the need for on-going validation of methods to increase the accuracy and precision of SfM in glaciology. This work is not only advancing our understanding of the role of the debris layer, but will also aid glacial geology more generally with, for example, detailed geomorphological analysis of proglacial terrain and Quaternary sciences with quick and accurate reconstruction of a glacial paleo-environment.

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

    PubMed

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

    2015-03-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

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

    PubMed Central

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

    2015-01-01

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

  11. Satellite observations of the ice cover of the Kuril Basin region of the Okhotsk Sea and its relation to the regional oceanography

    NASA Technical Reports Server (NTRS)

    Wakatsuchi, Masaaki; Martin, Seelye

    1990-01-01

    For the period 1978-1982, this paper examines the nature of the sea ice which forms over the Kuril Basin of the Okhotsk Sea and describes the impact of this ice on the regional oceanography. The oceanographic behavior during the heavy ice season associated with the cold 1979 winter is compared with the behavior during the lighter ice years of 1980 and 1982. Examination of the oceanography in the Okhotsk and the adjacent Pacific shows that the early summer water column structure depends on the heat loss from the Okhotsk during the preceding ice season, the total amount of Okhotsk ice formation, and, specifically, the amount of the ice formation in the Kuril Basin. Following the 1979 ice season, the upper 200-300 m of the Kuril Basin waters were cooler, less saline, and richer in oxygen than for the other years. This modification appears to be a process local to the Kuril Basin, driven by eddy-induced mixing, local cooling, and ice melting.

  12. Combined influence of PDO and ENSO on northern Andean glaciers: a case study on the Cotopaxi ice-covered volcano, Ecuador

    NASA Astrophysics Data System (ADS)

    Veettil, Bijeesh Kozhikkodan; Leandro Bayer Maier, Éder; Bremer, Ulisses Franz; de Souza, Sergio Florencio

    2014-12-01

    This paper describes the application of remote sensing in monitoring the fluctuations in one of the mountain glaciers in the Ecuadorean Andes during the past few decades using ASTER, EO-1 ALI, Landsat MSS, TM and ETM + images. Satellite images were used to calculate the snow line altitudes (SLAs) during the period 1979-2013. Cotopaxi ice covered volcano was studied as representative of Ecuadorian glaciers in the eastern cordillera. Precipitation and air temperature data from various gauging stations within the range of 30 km from the study site and monthly discharge and water level data from a gauging station were also utilized in this study. Anomalies in precipitation and temperature were found to be slightly different in the Cotopaxi region compared to nearby Antizana in the same cordillera and Chimborazo region in the western cordillera. An attempt to correlate the El Niño—southern oscillation phenomenon with the glacier fluctuations in Ecuadorian Andes was done successfully. Cold and warm regimes of Pacific Decadal Oscillation is also considered. The calculated glacier fluctuations obtained were similar to that performed on the nearby Antizana 15 in the eastern cordillera during 1995-2002. Precipitation and temperature anomalies were similar with Antizana 15. It is evident from the research that SLAs were highly fluctuated between the period of occurrence of El Niño and La Niña events. It is also seen that the glacier fluctuations show a negative mass balance trend in during the warm regime of Pacific Decadal Oscillation during the past three decades. Glaciated areas were advanced during the La Nina events in the cold regime of PDO during 1998-2002.

  13. Diversity and Expression of RubisCO Genes in a Perennially Ice-Covered Antarctic Lake during the Polar Night Transition

    PubMed Central

    Kong, Weidong; Ream, David C.; Priscu, John C.

    2012-01-01

    The autotrophic communities in the lakes of the McMurdo Dry Valleys, Antarctica, have generated interest since the early 1960s owing to low light transmission through the permanent ice covers, a strongly bimodal seasonal light cycle, constant cold water temperatures, and geographical isolation. Previous work has shown that autotrophic carbon fixation in these lakes provides an important source of organic matter to this polar desert. Lake Bonney has two lobes separated by a shallow sill and is one of several chemically stratified lakes in the dry valleys that support year-round biological activity. As part of an International Polar Year initiative, we monitored the diversity and abundance of major isoforms of RubisCO in Lake Bonney by using a combined sequencing and quantitative PCR approach during the transition from summer to polar winter. Form ID RubisCO genes related to a stramenopile, a haptophyte, and a cryptophyte were identified, while primers specific for form IA/B RubisCO detected a diverse autotrophic community of chlorophytes, cyanobacteria, and chemoautotrophic proteobacteria. Form ID RubisCO dominated phytoplankton communities in both lobes of the lake and closely matched depth profiles for photosynthesis and chlorophyll. Our results indicate a coupling between light availability, photosynthesis, and rbcL mRNA levels in deep phytoplankton populations. Regulatory control of rbcL in phytoplankton living in nutrient-deprived shallow depths does not appear to be solely light dependent. The distinct water chemistries of the east and west lobes have resulted in depth- and lobe-dependent variability in RubisCO diversity, which plays a role in transcriptional activity of the key gene responsible for carbon fixation. PMID:22492447

  14. Hydroacoustic detection of large winter aggregations of Arctic cod (Boreogadus saida) at depth in ice-covered Franklin Bay (Beaufort Sea)

    NASA Astrophysics Data System (ADS)

    Benoit, Delphine; Simard, Yvan; Fortier, Louis

    2008-06-01

    In the Canadian Arctic, the large biomass of Arctic cod that must exist to explain consumption by predators has eluded detection. From December 2003 to May 2004, acoustic estimates of Arctic cod biomass at a 225-m-deep station in central Franklin Bay (southeastern Beaufort Sea) increased progressively by 2 orders of magnitude, reaching maximum values of 2.7 and 55 kg m-2 in April. During accumulation in Franklin Bay, the fish occupied the lower part of the Pacific halocline (140 m to bottom), where the temperature-salinity signature (-1.4 to 0.3°C; 33 to 34.8 practical salinity units) corresponded to slope waters. Currents at 200 m along the western slope of Amundsen Gulf headed SSE in early winter, suggesting the passive advection of Arctic cod from Amundsen Gulf into Franklin Bay. Retention in Franklin Bay against the general circulation resulted from the fish keeping at depth to reduce predation by diving seals and/or to benefit from relatively warm temperatures in the lower halocline. Extrapolating a standing biomass of 11.23 kg m-2 at the station in April to the whole of Franklin Bay, the availability of polar cod would amply satisfy the requirements of predators. Dense accumulations of Arctic cod in embayments in winter likely play an important role in structuring the ecosystem of the Beaufort Sea. Understanding how climate change and the reduction of the sea ice cover will affect the stability of the oceanographic/behavioral accumulation process requires further research and modeling.

  15. Ice electrode electrolytic cell

    DOEpatents

    Glenn, D.F.; Suciu, D.F.; Harris, T.L.; Ingram, J.C.

    1993-04-06

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  16. Ice electrode electrolytic cell

    DOEpatents

    Glenn, David F.; Suciu, Dan F.; Harris, Taryl L.; Ingram, Jani C.

    1993-01-01

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  17. Ice electrode electrolytic cell

    SciTech Connect

    Glenn, D.F.; Suciu, D.F.; Harris, T.L.; Ingram, J.C.

    1992-12-31

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  18. The role of sea ice dynamics in global climate change

    NASA Technical Reports Server (NTRS)

    Hibler, William D., III

    1992-01-01

    The topics covered include the following: general characteristics of sea ice drift; sea ice rheology; ice thickness distribution; sea ice thermodynamic models; equilibrium thermodynamic models; effect of internal brine pockets and snow cover; model simulations of Arctic Sea ice; and sensitivity of sea ice models to climate change.

  19. Multi-year Arctic Sea Ice

    NASA Video Gallery

    The most visible change in the Arctic region in recent years has been the rapid decline of the perennial ice cover. The perennial ice is the portion of the sea ice floating on the surface of the oc...

  20. Crustal and upper-mantle structure beneath ice-covered regions in Antarctica from S-wave receiver functions and implications for heat flow

    NASA Astrophysics Data System (ADS)

    Ramirez, C.; Nyblade, A.; Hansen, S. E.; Wiens, D. A.; Anandakrishnan, S.; Aster, R. C.; Huerta, A. D.; Shore, P.; Wilson, T.

    2016-03-01

    S-wave receiver functions (SRFs) are used to investigate crustal and upper-mantle structure beneath several ice-covered areas of Antarctica. Moho S-to-P (Sp) arrivals are observed at ˜6-8 s in SRF stacks for stations in the Gamburtsev Mountains (GAM) and Vostok Highlands (VHIG), ˜5-6 s for stations in the Transantarctic Mountains (TAM) and the Wilkes Basin (WILK), and ˜3-4 s for stations in the West Antarctic Rift System (WARS) and the Marie Byrd Land Dome (MBLD). A grid search is used to model the Moho Sp conversion time with Rayleigh wave phase velocities from 18 to 30 s period to estimate crustal thickness and mean crustal shear wave velocity. The Moho depths obtained are between 43 and 58 km for GAM, 36 and 47 km for VHIG, 39 and 46 km for WILK, 39 and 45 km for TAM, 19 and 29 km for WARS and 20 and 35 km for MBLD. SRF stacks for GAM, VHIG, WILK and TAM show little evidence of Sp arrivals coming from upper-mantle depths. SRF stacks for WARS and MBLD show Sp energy arriving from upper-mantle depths but arrival amplitudes do not rise above bootstrapped uncertainty bounds. The age and thickness of the crust is used as a heat flow proxy through comparison with other similar terrains where heat flow has been measured. Crustal structure in GAM, VHIG and WILK is similar to Precambrian terrains in other continents where heat flow ranges from ˜41 to 58 mW m-2, suggesting that heat flow across those areas of East Antarctica is not elevated. For the WARS, we use the Cretaceous Newfoundland-Iberia rifted margins and the Mesozoic-Tertiary North Sea rift as tectonic analogues. The low-to-moderate heat flow reported for the Newfoundland-Iberia margins (40-65 mW m-2) and North Sea rift (60-85 mW m-2) suggest that heat flow across the WARS also may not be elevated. However, the possibility of high heat flow associated with localized Cenozoic extension or Cenozoic-recent magmatic activity in some parts of the WARS cannot be ruled out.

  1. Reconstruction of sea-ice cover and primary production on the East Greenland Shelf (73°N) during the last 5200 years

    NASA Astrophysics Data System (ADS)

    Kolling, Henriette Marie; Stein, Rüdiger; Fahl, Kirsten; Perner, Kerstin; Moros, Matthias

    2016-04-01

    Over the last decades the extent and thickness of Arctic sea ice has changed dramatically and much more rapidly than predicted by climate models. Thus, high-resolution sea-ice reconstructions from pre-anthropogenic times are useful and needed in order to better understand the processes controlling the natural sea-ice variability. Here, we present the first high-resolution biomarker (IP25, sterols) approach over the last 5.2 ka from the East Greenland Shelf (for background about the biomarker approach see Belt et al., 2007; Müller et al., 2009, 2011). This area is highly sensitive to sea-ice changes, as it underlies the pathway of the East Greenland Current, the main exporter of Arctic freshwater and sea ice that affects the environmental conditions on the East Greenland Shelf and deep-water formation/ convection in the Northern North Atlantic. After rather stable sea-ice conditions in the mid-Holocene we found a strong increase in sea ice, cumulating around 1.5 ka and associated with the Neoglacial cooling. The general trend especially during the last 1ka is interrupted by several short-lived events such as the prominent Medieval Warm Period and Little Ice Age, characterized by minimum and maximum sea-ice extent, respectively. Using a spectral analysis, we could identify several cyclicites, e.g. a 45-year cyclicity for cold events. A comparison to similar records from the eastern Fram Strait revealed a slight time lag in the onset of the Neoglacial, but also suggesting the direct link of the East Greenland Shelf area to the Arctic sea-ice/freahwater outflow. A comparison of the biomarker data with a new foraminiferal record obtained from the same site (Perner et al., 2015) suggests that IP25 and foraminifera assemblages are probably controlled by rather different processes within the oceanographic systems, such as the sea-ice conditions and, for the foraminifera, water-mass changes and nutrient supply. References: Belt. S.T., Massé, G., Rowland, S.J., Poulin, M

  2. State of the Earth’s cryosphere at the beginning of the 21st century : glaciers, global snow cover, floating ice, and permafrost and periglacial environments: Chapter A in Satellite image atlas of glaciers of the world

    USGS Publications Warehouse

    Williams, Richard S., Jr.; Ferrigno, Jane G.

    2012-01-01

    This chapter is the tenth in a series of 11 book-length chapters, collectively referred to as “this volume,” in the series U.S. Geological Survey Professional Paper 1386, Satellite Image Atlas of Glaciers of the World. In the other 10 chapters, each of which concerns a specific glacierized region of Earth, the authors used remotely sensed images, primarily from the Landsat 1, 2, and 3 series of spacecraft, in order to analyze that glacierized region and to monitor changes in its glaciers. Landsat images, acquired primarily during the period 1972 through 1981, were used by an international team of glaciologists and other scientists to study the various glacierized regions and (or) to discuss related glaciological topics. In each glacierized region, the present distribution of glaciers within its geographic area is compared, wherever possible, with historical information about their past areal extent. The atlas provides an accurate regional inventory of the areal extent of glacier ice on our planet during the 1970s as part of an expanding international scientific effort to measure global environmental change on the Earth’s surface. However, this chapter differs from the other 10 in its discussion of observed changes in all four elements of the Earth’s cryosphere (glaciers, snow cover, floating ice, and permafrost) in the context of documented changes in all components of the Earth System. Human impact on the planet at the beginning of the 21st century is pervasive. The focus of Chapter A is on changes in the cryosphere and the importance of long-term monitoring by a variety of sensors carried on Earth-orbiting satellites or by a ground-based network of observatories in the case of permafrost. The chapter consists of five parts. The first part provides an introduction to the Earth System, including the interrelationships of the geosphere (cryosphere, hydrosphere, lithosphere, and atmosphere), the biosphere, climate processes, biogeochemical cycles, and the

  3. Top Sounder Ice Penetration

    NASA Astrophysics Data System (ADS)

    Porter, D. L.; Goemmer, S. A.; Sweeney, J. H.

    2014-12-01

    Ice draft measurements are made as part of normal operations for all US Navy submarines operating in the Arctic Ocean. The submarine ice draft data are unique in providing high resolution measurements over long transects of the ice covered ocean. The data has been used to document a multidecadal drop in ice thickness, and for validating and improving numerical sea-ice models. A submarine upward-looking sonar draft measurement is made by a sonar transducer mounted in the sail or deck of the submarine. An acoustic beam is transmitted upward through the water column, reflecting off the bottom of the sea ice and returning to the transducer. Ice thickness is estimated as the difference between the ship's depth (measured by pressure) and the acoustic range to the bottom of the ice estimated from the travel time of the sonar pulse. Digital recording systems can provide the return off the water-ice interface as well as returns that have penetrated the ice. Typically, only the first return from the ice hull is analyzed. Information regarding ice flow interstitial layers provides ice age information and may possibly be derived with the entire return signal. The approach being investigated is similar to that used in measuring bottom sediment layers and will involve measuring the echo level from the first interface, solving the reflection loss from that transmission, and employing reflection loss versus impedance mismatch to ascertain ice structure information.

  4. Arctic Sea Ice from March to August 2016

    NASA Video Gallery

    In this animation, the daily Arctic sea ice and seasonal land cover change progress through time, from the prior sea ice maximum March 24, 2016, through Aug. 13, 2016. The Arctic sea ice cover like...

  5. MODIS Snow and Ice Production

    NASA Technical Reports Server (NTRS)

    Hall, Dorthoy K.; Hoser, Paul (Technical Monitor)

    2002-01-01

    Daily, global snow cover maps, and sea ice cover and sea ice surface temperature (IST) maps are derived from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS), are available at no cost through the National Snow and Ice Data Center (NSIDC). Included on this CD-ROM are samples of the MODIS snow and ice products. In addition, an animation, done by the Scientific Visualization studio at Goddard Space Flight Center, is also included.

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  7. Schedule-dependent therapeutic efficacy of L19mTNF-α and melphalan combined with gemcitabine

    PubMed Central

    Mortara, Lorenzo; Orecchia, Paola; Castellani, Patrizia; Borsi, Laura; Carnemolla, Barbara; Balza, Enrica

    2013-01-01

    Abstract L19-tumor necrosis factor alpha (L19mTNF-α; L), a fusion protein consisting of mouse TNFα and the human antibody fragment L19 directed to the extra domain-B (ED-B) of fibronectin, is able to selectively target tumor vasculature and to exert a long-lasting therapeutic activity in combination with melphalan (M) in syngeneic mouse tumor models. We have studied the antitumor activity of single L19mTNF-α treatment in combination with melphalan and gemcitabine (G) using different administration protocols in two histologically different murine tumor models: WEHI-164 fibrosarcoma and K7M2 osteosarcoma. All responding mice showed significant reduction in myeloid-derived suppressor cells (MDSCs) and an increase in CD4+ and CD8+ T cells in the tumor infiltrates, as well as significant reduction in regulatory T cells (Treg) at the level of draining lymph nodes. What is important is that all cured mice rejected tumor challenge up to 1 year after therapy. Targeted delivery of L19mTNF-α synergistically increases the antitumor activity of melphalan and gemcitabine, but optimal administration schedules are required. This study provides information for designing clinical studies using L19mTNF-α in combination with chemotherapeutic drugs. Targeted delivery of L19mTNF-α synergistically increases the antitumor activity of melphalan and gemcitabine, but optimal administration schedule requires a pretreatment with L19mTNF-α otherwise an antagonistic effect could occur. This study provides information for designing clinical studies using L19mTNF-α in combination with chemotherapeutic drugs. PMID:24156020

  8. Seismic tremor signals from Bárðarbunga, Grímsvötn and other glacier covered volcanoes in Iceland's Vatnajökull ice cap

    NASA Astrophysics Data System (ADS)

    Vogfjörd, Kristin S.; Eibl, Eva; Bean, Chris; Roberts, Matthew; Ófeigsson, Benedikt; Jóhannesson, Tómas

    2016-04-01

    Many of Iceland's most active volcanoes, like Grímsvötn and Bárðarbunga are located under glaciers giving rise to a range of volcanic hazards having both local and cross-border effects on humans, infrastructures and aviation. Volcanic eruptions under ice can lead to explosive hydromagmatic volcanism and generate small to catastrophic subglacial floods that may take hours to days to emerge from the glacier edge. Unrest in subglacial hydrothermal systems and the draining of subglacial meltwater can also lead to flood hazards. These processes and magma-ice interactions in general, generate seismic tremor signals that are commonly observed on seismic systems during volcanic unrest and/or eruptions. The tremor signals exhibit certain characteristics in frequency content, amplitude and behavior with time, but their characteristics overlap. Ability to discriminate between the different processes in real-time or near-real time can support early eruption and flood warnings and help mitigate their detrimental effects. One of the goals set forth in the FUTUREVOLC volcano supersite project was in fact to understand and discriminate between the different types of seismic tremor recorded at subglacial volcanoes. In that pursuit, the seismic network was expanded into the Vatnajökull glacier with four permanent stations on rock and in the ice, in addition to three seismic arrays installed at the ice margin, to enable location and possible tracking of the tremor sources. To track subglacial floods with better resolution three GPS receivers were also installed on the ice, one in an ice cauldron above the Skaftárkatlar geothermal melting area and two down glacier, above the track of the expected subglacial flood. During FUTUREVOLC this infrastructure has recorded all the types of process expected: Magmatic dyke intrusion and propagation from Bárðarbunga, subaerial fissure eruption of that magma at Holuhraun, two subglacial floods, one small and one large, draining from the

  9. Use of Synthetic Aperture Radar (SAR) to Identify and Characterize Overwintering Areas of Fish in Ice-Covered Arctic RIvers: A Demonstration with Broad Whitefish and their Habitats in the Sagavanirktok River, Alaska

    SciTech Connect

    Brown, Richard S.; Duguay, Claude R.; Mueller, Robert P.; Moulton, Larry; Doucette, Peter J.; Tagestad, Jerry D.

    2010-12-01

    In northern climates, locating overwintering fish can be very challenging due to thick ice cover. Areas near the coast of the Beaufort Sea provide valuable overwintering habitat for both resident and anadromous fish species; identifying and understanding their use of overwintering areas is of special interest. Synthetic aperture radar (SAR) imagery from two spaceborne satellites was examined as an alternative to radiotelemetry for identifying anadromous fish overwintering. The presence of water and ice were sampled at 162 sites and fish were sampled at 16 of these sites. From SAR imagery alone, we successfully identified large pools inhabited by overwintering fish in the ice-covered Sagavanirktok River. In addition, the imagery was able to identify all of the larger pools (mean minimum length of 138m (range 15-470 m; SD=131)) of water located by field sampling. The effectiveness of SAR to identify these pools varied from 31% to 100%, depending on imagery polarization, the incidence angle range, and the orbit. Horizontal transmit–vertical receive (HV) polarization appeared best. The accuracy of SAR was also assessed at a finer pixel-by-pixel (30-m x30-m) scale. The best correspondence at this finer scale was obtained with an image having HV polarization. The levels of agreement ranged from 54% to 69%. The presence of broad whitefish (the only anadromous species present) was associated with salinity and pool size (estimated with SAR imagery); fish were more likely to be found in larger pools with low salinity. This research illustrates that SAR imaging has great potential for identifying under-ice overwintering areas of riverine fish. These techniques should allow managers to identify critical overwintering areas with relatively more ease and lower cost than traditional techniques.

  10. Sky cover

    NASA Astrophysics Data System (ADS)

    Gerth, Jordan J.

    analysis. Results include discussion about how the blended sky cover analysis correlates with the cloud ice, cloud water, rain, snow, and other analysis fields from the High-Resolution Rapid Refresh (HRRR). The intent is to suggest a reasonable operational and scientific definition for sky cover and demonstrate an observational method that can bring consistency to analyses and forecasts of sky cover.

  11. A record-breaking low ice cover over the Great Lakes during winter 2011/2012: combined effects of a strong positive NAO and La Niña

    NASA Astrophysics Data System (ADS)

    Bai, Xuezhi; Wang, Jia; Austin, Jay; Schwab, David J.; Assel, Raymond; Clites, Anne; Bratton, John F.; Colton, Marie; Lenters, John; Lofgren, Brent; Wohlleben, Trudy; Helfrich, Sean; Vanderploeg, Henry; Luo, Lin; Leshkevich, George

    2015-03-01

    A record-breaking low ice cover occurred in the North American Great Lakes during winter 2011/2012, in conjunction with a strong positive Arctic Oscillation/North Atlantic Oscillation (+AO/NAO) and a La Niña event. Large-scale atmosphere circulation in the Pacific/North America (PNA) region reflected a combined signal of La Niña and +NAO. Surface heat flux analysis shows that sensible heat flux contributed most to the net surface heat flux anomaly. Surface air temperature is the dominant factor governing the interannual variability of Great Lakes ice cover. Neither La Niña nor +NAO alone can be responsible for the extreme warmth; the typical mid-latitude response to La Niña events is a negative PNA pattern, which does not have a significant impact on Great Lakes winter climate; the positive phase of NAO is usually associated with moderate warming. When the two occurred simultaneously, the combined effects of La Niña and +NAO resulted in a negative East Pacific pattern with a negative center over Alaska/Western Canada, a positive center in the eastern North Pacific (north of Hawaii), and an enhanced positive center over the eastern and southern United States. The overall pattern prohibited the movement of the Arctic air mass into mid-latitudes and enhanced southerly flow and warm advection from the Gulf of Mexico over the eastern United States and Great Lakes region, leading to the record-breaking low ice cover. It is another climatic pattern that can induce extreme warming in the Great Lakes region in addition to strong El Niño events. A very similar event occurred in the winter of 1999/2000. This extreme warm winter and spring in 2012 had significant impacts on the physical environment, as well as counterintuitive effects on phytoplankton abundance.

  12. 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.

  13. Loss of sea ice in the Arctic.

    PubMed

    Perovich, Donald K; Richter-Menge, Jacqueline A

    2009-01-01

    The Arctic sea ice cover is in decline. The areal extent of the ice cover has been decreasing for the past few decades at an accelerating rate. Evidence also points to a decrease in sea ice thickness and a reduction in the amount of thicker perennial sea ice. A general global warming trend has made the ice cover more vulnerable to natural fluctuations in atmospheric and oceanic forcing. The observed reduction in Arctic sea ice is a consequence of both thermodynamic and dynamic processes, including such factors as preconditioning of the ice cover, overall warming trends, changes in cloud coverage, shifts in atmospheric circulation patterns, increased export of older ice out of the Arctic, advection of ocean heat from the Pacific and North Atlantic, enhanced solar heating of the ocean, and the ice-albedo feedback. The diminishing Arctic sea ice is creating social, political, economic, and ecological challenges. PMID:21141043

  14. Estimating ice albedo from fine debris cover quantified by a semi-automatic method: the case study of Forni Glacier, Italian Alps

    NASA Astrophysics Data System (ADS)

    Azzoni, Roberto Sergio; Senese, Antonella; Zerboni, Andrea; Maugeri, Maurizio; Smiraglia, Claudio; Diolaiuti, Guglielmina Adele

    2016-03-01

    In spite of the quite abundant literature focusing on fine debris deposition over glacier accumulation areas, less attention has been paid to the glacier melting surface. Accordingly, we proposed a novel method based on semi-automatic image analysis to estimate ice albedo from fine debris coverage (d). Our procedure was tested on the surface of a wide Alpine valley glacier (the Forni Glacier, Italy), in summer 2011, 2012 and 2013, acquiring parallel data sets of in situ measurements of ice albedo and high-resolution surface images. Analysis of 51 images yielded d values ranging from 0.01 to 0.63 and albedo was found to vary from 0.06 to 0.32. The estimated d values are in a linear relation with the natural logarithm of measured ice albedo (R = -0.84). The robustness of our approach in evaluating d was analyzed through five sensitivity tests, and we found that it is largely replicable. On the Forni Glacier, we also quantified a mean debris coverage rate (Cr) equal to 6 g m-2 per day during the ablation season of 2013, thus supporting previous studies that describe ongoing darkening phenomena at Alpine debris-free glaciers surface. In addition to debris coverage, we also considered the impact of water (both from melt and rainfall) as a factor that tunes albedo: meltwater occurs during the central hours of the day, decreasing the albedo due to its lower reflectivity; instead, rainfall causes a subsequent mean daily albedo increase slightly higher than 20 %, although it is short-lasting (from 1 to 4 days).

  15. Using nuclear magnetic resonance and transient electromagnetics to characterise water distribution beneath an ice covered volcanic crater: the case of Sherman Crater Mt. Baker Washington.

    USGS Publications Warehouse

    Irons, Trevor P.; Martin, Kathryn; Finn, Carol A.; Bloss, Benjamin; Horton, Robert J.

    2014-01-01

    Surface and laboratory Nuclear Magnetic Resonance (NMR) measurements combined with transient electromagnetic (TEM) data are powerful tools for subsurface water detection. Surface NMR (sNMR) and TEM soundings, laboratory NMR, complex resistivity, and X-Ray Diffraction (XRD) analysis were all conducted to characterise the distribution of water within Sherman Crater on Mt. Baker, WA. Clay rich rocks, particularly if water saturated, can weaken volcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-travelled, destructive debris flows. Detecting the presence and volume of shallow groundwater is critical for evaluating these landslide hazards. The TEM data identified a low resistivity layer (<10 ohm-m), under 60 m of glacial ice related to water saturated clays. The TEM struggles to resolve the presence or absence of a plausible thin layer of bulk liquid water on top of the clay. The sNMR measurements did not produce any observable signal, indicating the lack of substantial accumulated bulk water below the ice. Laboratory analysis on a sample from the crater wall that likely represented the clays beneath the ice confirmed that the controlling factor for the lack of sNMR signal was the fine-grained nature of the media. The laboratory measurements further indicated that small pores in clays detected by the XRD contain as much as 50% water, establishing an upper bound on the water content in the clay layer. Forward modelling of geologic scenarios revealed that bulk water layers as thin as ½ m between the ice and clay layer would have been detectable using sNMR. The instrumentation conditions which would allow for sNMR detection of the clay layer are investigated. Using current instrumentation the combined analysis of the TEM and sNMR data allow for valuable characterisation of the groundwater system in the crater. The sNMR is able to reduce the uncertainty of the TEM in regards to the presence of a bulk water layer, a valuable

  16. An integrated approach to the remote sensing of floating ice

    NASA Technical Reports Server (NTRS)

    Campbell, W. J.; Ramseier, R. O.; Weeks, W. F.; Gloersen, P.

    1976-01-01

    Review article on remote sensing applications to glaciology. Ice parameters sensed include: ice cover vs open water, ice thickness, distribution and morphology of ice formations, vertical resolution of ice thickness, ice salinity (percolation and drainage of brine; flushing of ice body with fresh water), first-year ice and multiyear ice, ice growth rate and surface heat flux, divergence of ice packs, snow cover masking ice, behavior of ice shelves, icebergs, lake ice and river ice; time changes. Sensing techniques discussed include: satellite photographic surveys, thermal IR, passive and active microwave studies, microwave radiometry, microwave scatterometry, side-looking radar, and synthetic aperture radar. Remote sensing of large aquatic mammals and operational ice forecasting are also discussed.

  17. Ice age paleotopography

    SciTech Connect

    Peltier, W.R. )

    1994-07-08

    A gravitationally self-consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the Last Glacial Maximum (LGM). The results show that LGM ice volume was approximately 35 percent lower than suggested by the CLIMAP reconstruction and the maximum heights of the main Laurentian and Fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level. Use of these Ice Age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the CLIMAP data set.

  18. Climate Data Records (CDRs) for Ice Motion and Ice Age

    NASA Astrophysics Data System (ADS)

    Tschudi, M. A.; Fowler, C.; Maslanik, J. A.; Stroeve, J. C.

    2011-12-01

    Climate Data Records (CDRs) for remotely-sensed Arctic sea ice motion and sea ice age are under development by our group at the University of Colorado, Boulder. The ice motion product, archived at NSIDC, has a considerable history of use, while sea ice age is a relatively new product. Our technique to estimate sea ice motion utilizes images from SSM/I, as well as SMMR and the series of AVHRR sensors to estimate the daily motion of ice parcels. This method is augmented by incorporating ice motion observations from the network of drifting buoys deployed as part of the International Arctic Buoy Program. Our technique to calculate ice age relies on following the actual age of the ice for each ice parcel, categorizing the parcel as first-year ice, second-year, ice, etc. based on how many summer melt seasons the ice parcel survives. Both of these research-grade products have been interpolated onto 25x25 km grid points spanning the entire Arctic Ocean using the Equal-Area Scalable Earth (EASE) grid. Datasets generated from this program have shown that the Arctic ice cover has experienced a significant (> 70%) decline in multiyear ice over the last 20 years, leaving a younger ice cover in 2011. By comparing ice age derived by the Lagrangian tracking method to ice thickness estimated by Ice, Cloud and land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) data, it is observed that ice age is linearly related to ice thickness, up to an age of 10 years. Therefore, the shift in dominance of multiyear ice to first-year ice relates to a significant thinning of the ice. This thinning is estimated to correspond to a 40% reduction in ice volume in the last 20 years. An ancillary dataset (APP-X) produced by the University of Wisconsin, Madison has been combined with the ice motion product to monitor the properties of the sea ice parcels tracked by the ice motion product. This dataset includes ice surface and 2-meter air temperature, albedo, downwelling shortwave

  19. Arctic Sea ice model sensitivities.

    SciTech Connect

    Peterson, Kara J.; Bochev, Pavel Blagoveston; Paskaleva, Biliana Stefanova

    2010-12-01

    Arctic sea ice is an important component of the global climate system and, due to feedback effects, the Arctic ice cover is changing rapidly. Predictive mathematical models are of paramount importance for accurate estimates of the future ice trajectory. However, the sea ice components of Global Climate Models (GCMs) vary significantly in their prediction of the future state of Arctic sea ice and have generally underestimated the rate of decline in minimum sea ice extent seen over the past thirty years. One of the contributing factors to this variability is the sensitivity of the sea ice state to internal model parameters. A new sea ice model that holds some promise for improving sea ice predictions incorporates an anisotropic elastic-decohesive rheology and dynamics solved using the material-point method (MPM), which combines Lagrangian particles for advection with a background grid for gradient computations. We evaluate the variability of this MPM sea ice code and compare it with the Los Alamos National Laboratory CICE code for a single year simulation of the Arctic basin using consistent ocean and atmospheric forcing. Sensitivities of ice volume, ice area, ice extent, root mean square (RMS) ice speed, central Arctic ice thickness,and central Arctic ice speed with respect to ten different dynamic and thermodynamic parameters are evaluated both individually and in combination using the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA). We find similar responses for the two codes and some interesting seasonal variability in the strength of the parameters on the solution.

  20. Thickness of tropical ice and photosynthesis on a snowball Earth

    NASA Technical Reports Server (NTRS)

    McKay, C. P.

    2000-01-01

    On a completely ice-covered "snowball" Earth the thickness of ice in the tropical regions would be limited by the sunlight penetrating into the ice cover and by the latent heat flux generated by freezing at the ice bottom--the freezing rate would balance the sublimation rate from the top of the ice cover. Heat transfer models of the perennially ice-covered Antarctic dry valley lakes applied to the snowball Earth indicate that the tropical ice cover would have a thickness of 10 m or less with a corresponding transmissivity of > 0.1%. This light level is adequate for photosynthesis and could explain the survival of the eukaryotic algae.

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

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

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

  2. Prospecting for Martian Ice

    NASA Technical Reports Server (NTRS)

    McBride, S. A.; Allen, C. C.; Bell, M. S.

    2005-01-01

    During high Martian obliquity, ice is stable to lower latitudes than predicted by models of present conditions and observed by the Gamma Ray Spectrometer (approx. 60 deg N). An ice-rich layer deposited at mid-latitudes could persist to the present day; ablation of the top 1 m of ice leaving a thin insulating cover could account for lack of its detection by GRS. The presence of an ice-layer in the mid-latitudes is suggested by a network of polygons, interpreted as ice-wedge cracks. This study focuses on an exceptional concentration of polygons in Western Utopia (section of Casius quadrangle, roughly 40 deg - 50 deg N, 255 deg - 300 deg W). We attempt to determine the thickness and age of this ice layer through crater-polygons relations.

  3. Enhanced Sea Ice Concentration and Ice Temperature Algorithms for AMSR

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.; Manning, Will; Gersten, Robert

    1998-01-01

    Accurate quantification of sea ice concentration and ice temperature from satellite passive microwave data is important because they provide the only long term, spatially detailed and consistent data set needed to study the climatology of the polar regions. Sea ice concentration data are used to derive large-scale daily ice extents that are utilized in trend analysis of the global sea ice cover. They are also used to quantify the amount of open water and thin ice in polynya and divergence regions which together with ice temperatures are in turn needed to estimate vertical heat and salinity fluxes in these regions. Sea ice concentrations have been derived from the NASA Team and Bootstrap algorithms while a separate technique for deriving ice temperature has been reported. An integrated technique that will utilizes most of the channels of AMSR (Advanced Microwave Scanning Radiometer) has been developed. The technique uses data from the 6 GHz and 37 GHz channels at vertical polarization obtain an initial estimate of sea ice concentration and ice temperature. The derived ice temperature is then utilized to estimate the emissivities for the corresponding observations at all the other channels. A procedure for calculating the ice concentration similar to the Bootstrap technique is then used but with variables being emissivities instead of brightness temperatures to minimizes errors associated with spatial changes in ice temperatures within the ice pack. Comparative studies of ice concentration results with those from other algorithms, including the original Bootstrap algorithm and those from high resolution satellite visible and infrared data will be presented. Also, results from a simulation study that demonstrates the effectiveness of the technique in correcting for spatial variations in ice temperatures will be shown. The ice temperature results are likewise compared with satellite infrared and buoy data with the latter adjusted to account for the effects of the snow

  4. Ices on the surface of Triton

    NASA Technical Reports Server (NTRS)

    Cruikshank, Dale P.; Roush, Ted L.; Owen, Tobias C.; Geballe, Thomas R.; De Bergh, Catherine; Schmitt, Bernard; Brown, Robert H.; Bartholomew, Mary J.

    1993-01-01

    The near-infrared spectrum of Triton reveals ices of nitrogen, methane, carbon monoxide, and carbon dioxide, of which nitrogen is the dominant component. Carbon dioxide ice may be spatially segregated from the other more volatile ices, covering about 10 percent of Triton's surface. The absence of ices of other hydrocarbons and nitriles challenges existing models of methane and nitrogen photochemistry on Triton.

  5. Ices on the surface of Triton

    NASA Astrophysics Data System (ADS)

    Cruikshank, D. P.; Roush, T. L.; Owen, T. C.; Geballe, T. R.; de Bergh, C.; Schmitt, B.; Brown, R. H.; Bartholomew, M. J.

    1993-08-01

    The near-infrared spectrum of Triton reveals ices of nitrogen, methane, carbon monoxide, and carbon dioxide, of which nitrogen is the dominant component. Carbon dioxide ice may be spatially segregated from the other more volatile ices, covering about 10 percent of Triton's surface. The absence of ices of other hydrocarbons and nitriles challenges existing models of methane and nitrogen photochemistry on Triton.

  6. The connexin46 mutant, Cx46T19M, causes loss of gap junction function and alters hemi-channel gating.

    PubMed

    Tong, Jun-Jie; Minogue, Peter J; Kobeszko, Matthew; Beyer, Eric C; Berthoud, Viviana M; Ebihara, Lisa

    2015-02-01

    An N-terminal mutant of connexin46 (T19M) alters a highly conserved threonine and has been linked to autosomal dominant cataracts. To study the cellular and functional consequences of substitution of this amino acid, T19M was expressed in Xenopus oocytes and in HeLa cells. Unlike wild-type Cx46, T19M did not induce intercellular conductances in Xenopus oocytes. In transfected HeLa cells, T19M was largely localized within the cytoplasm, with drastically reduced formation of gap junction plaques. Expression of rat T19M was cytotoxic, as evidenced by an almost complete loss of viable cells expressing the mutant protein by 48-72 h following transfection. When incubated in medium containing physiological concentrations of divalent cations, T19M-expressing cells showed increased uptake of DAPI as compared with cells expressing wild-type Cx46, suggesting aberrant connexin hemi-channel activity. Time-lapse and dye uptake studies suggested that T19M hemi-channels had reduced sensitivity to Ca(2+). Whole cell patch clamp studies of single transfected HeLa cells demonstrated that rat T19M formed functional hemi-channels with altered voltage-dependent gating. These data suggest that T19M causes cataracts by loss of gap junctional channel function and abnormally increased hemi-channel activity. Furthermore, they implicate this conserved threonine in both gap junction plaque formation and channel/hemi-channel gating in Cx46. PMID:25404239

  7. A Systems-Level Perspective on Engine Ice Accretion

    NASA Technical Reports Server (NTRS)

    May, Ryan David; Guo, Ten-Huei; Simon, Donald L.

    2012-01-01

    Talk covers: (1) Problem of Engine Power Loss;(2) Modeling Engine Icing Effects; (3) Simulation of Engine Rollback; (4) Icing/Engine Control System Interaction; (5) Detection of Ice Accretion; (6) Potential Mitigation Strategies.

  8. Determining the ice seasons severity during 1982-2015 using the ice extents sum as a new characteristic

    NASA Astrophysics Data System (ADS)

    Rjazin, Jevgeni; Pärn, Ove

    2016-04-01

    Sea ice is a key climate factor and it restricts considerably the winter navigation in sever seasons on the Baltic Sea. So determining ice conditions severity and describing ice cover behaviour at severe seasons interests scientists, engineers and navigation managers. The present study is carried out to determine the ice seasons severity degree basing on the ice seasons 1982 to 2015. A new integrative characteristic is introduced to describe the ice season severity. It is the sum of ice extents of the ice season id est the daily ice extents of the season are summed. The commonly used procedure to determine the ice season severity degree by the maximal ice extent is in this research compared to the new characteristic values. The remote sensing data on the ice concentrations on the Baltic Sea published in the European Copernicus Programme are used to obtain the severity characteristic values. The ice extents are calculated on these ice concentration data. Both the maximal ice extent of the season and a newly introduced characteristic - the ice extents sum are used to classify the winters with respect of severity. The most severe winter of the reviewed period is 1986/87. Also the ice seasons 1981/82, 1984/85, 1985/86, 1995/96 and 2002/03 are classified as severe. Only three seasons of this list are severe by both the criteria. They are 1984/85, 1985/86 and 1986/87. We interpret this coincidence as the evidence of enough-during extensive ice cover in these three seasons. In several winters, for example 2010/11 ice cover extended enough for some time, but did not endure. At few other ice seasons as 2002/03 the Baltic Sea was ice-covered in moderate extent, but the ice cover stayed long time. At 11 winters the ice extents sum differed considerably (> 10%) from the maximal ice extent. These winters yield one third of the studied ice seasons. The maximal ice extent of the season is simple to use and enables to reconstruct the ice cover history and to predict maximal ice

  9. AMSR2 Daily Arctic Sea Ice - 2014

    NASA Video Gallery

    In this animation, the daily Arctic sea ice and seasonal land cover change progress through time, from March 21, 2014 through the 3rd of August, 2014. Over the water, Arctic sea ice changes from da...

  10. Arctic Cyclone Breaks Up Sea Ice

    NASA Video Gallery

    A powerful storm wreaked havoc on the Arctic sea ice cover in August 2012. This visualization shows the strength and direction of the winds and their impact on the ice: the red vectors represent th...

  11. An ice lithography instrument

    NASA Astrophysics Data System (ADS)

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.

    2011-06-01

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines.

  12. An ice lithography instrument

    SciTech Connect

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.

    2011-06-15

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines.

  13. An ice lithography instrument.

    PubMed

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J A

    2011-06-01

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines. PMID:21721733

  14. An ice lithography instrument

    PubMed Central

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.

    2011-01-01

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines. PMID:21721733

  15. The importance of large scale sea ice drift and ice type distribution on ice extent in the Weddell Sea

    NASA Astrophysics Data System (ADS)

    Schwegmann, S.; Haas, C.; Timmermann, R.; Gerdes, R.; Lemke, P.

    2009-12-01

    In austral winter large parts of Antarctic Seas are covered by sea ice. This modifies the exchange of heat, mass and momentum between ocean and atmosphere. The knowledge of ice extent and its variability is necessary for an adequate simulation of those fluxes and thus for climate modelling. The goal of this study is the observation of interannual and seasonal ice extent variations and their underlying causes. Variability is analysed by using monthly means of microwave and scatterometer satellite data. Results are correlated with ice drift variations calculated from a Finite Element Sea ice-Ocean Model (FESOM) and with satellite derived sea ice drift products to determine the dependency of ice extent on sea ice drift. An additional cause for changing ice extent could be the variability of ice type distribution, i.e. the contribution of first and second year ice to the total ice covered area. These ice types are determined on monthly time scales from scatterometer satellite data. Ice class distribution and sea ice drift variability are compared with the characteristics and variability of the Southern Annular Mode (SAM) to evaluate the relative importance of different sea ice parameters for shaping Weddell Sea ice extent and its variability.

  16. Sea ice-albedo climate feedback mechanism

    SciTech Connect

    Schramm, J.L.; Curry, J.A.; Ebert, E.E.

    1995-02-01

    The sea ice-albedo feedback mechanism over the Arctic Ocean multiyear sea ice is investigated by conducting a series of experiments using several one-dimensional models of the coupled sea ice-atmosphere system. In its simplest form, ice-albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature, further decreasing the area cover of snow and ice. It is shown that the sea ice-albedo feedback can operate even in multiyear pack ice, without the disappearance of this ice, associated with internal processes occurring within the multiyear ice pack (e.g., duration of the snow cover, ice thickness, ice distribution, lead fraction, and melt pond characteristics). The strength of the ice-albedo feedback mechanism is compared for several different thermodynamic sea ice models: a new model that includes ice thickness distribution., the Ebert and Curry model, the Mayjut and Untersteiner model, and the Semtner level-3 and level-0 models. The climate forcing is chosen to be a perturbation of the surface heat flux, and cloud and water vapor feedbacks are inoperative so that the effects of the sea ice-albedo feedback mechanism can be isolated. The inclusion of melt ponds significantly strengthens the ice-albedo feedback, while the ice thickness distribution decreases the strength of the modeled sea ice-albedo feedback. It is emphasized that accurately modeling present-day sea ice thickness is not adequate for a sea ice parameterization; the correct physical processes must be included so that the sea ice parameterization yields correct sensitivities to external forcing. 22 refs., 6 figs., 1 tab.

  17. Sea ice radiative forcing, sea ice area, and climate sensitivity

    NASA Astrophysics Data System (ADS)

    Caldeira, Ken; Cvijanovic, Ivana

    2014-05-01

    Changes in sea ice cover affect climate sensitivity by modifying albedo and surface heat flux exchange, which in turn affect the absorbed solar radiation at the surface as well as cloud cover, atmospheric water content and poleward atmospheric heat transport. Here, we use a configuration of the Community Earth System Model 1.0.4 with a slab ocean model and a thermodynamic-dynamic sea ice model to investigate the overall net effect of feedbacks associated with the sea ice loss. We analyze the strength of the overall sea ice feedback in terms of two factors: the sensitivity of sea ice area to changes in temperature, and the sensitivity of sea ice radiative forcing to changes in sea ice area. In this model configuration, sea ice area decreases by ~3 × 1012 m2 per K of global warming, while the effective global radiative forcing per square meter of sea ice loss is ~0.1 × 10-12 W m-2. The product of these two terms (~0.3 W m-2 K-1) approximately equals the difference in climate feedback parameter found in simulations with sea ice response (1.05 W m-2 K-1) and simulations without sea ice response (1.31 W m-2 K-1 or 1.35 W m-2 K-1, depending on the method used to disable changes in sea ice cover). Thus, we find that in our model simulations, sea ice response accounts for about 20% to 22% of the climate sensitivity to an imposed change in radiative forcing. In our model, the additional radiative forcing resulting from a loss of all sea ice in the 'pre-industrial' state is comparable to but somewhat less than the radiative forcing from a doubling of atmospheric CO2 content.

  18. Sea Ice Radiative Forcing, Sea Ice Area, and Climate Sensitivity

    NASA Astrophysics Data System (ADS)

    Caldeira, K.; Cvijanovic, I.

    2014-12-01

    Changes in sea ice cover affect climate sensitivity by modifying albedo and surface heat flux exchange, which in turn affect the absorbed solar radiation at the surface as well as cloud cover, atmospheric water content and poleward atmospheric heat transport. Here, we use a configuration of the Community Earth System Model 1.0.4 with a slab ocean model and a thermodynamic-dynamic sea ice model to investigate the overall net effect of feedbacks associated with the sea ice loss. We analyze the strength of the overall sea ice feedback in terms of two factors: the sensitivity of sea ice area to changes in temperature, and the sensitivity of sea ice radiative forcing to changes in sea ice area. In this model configuration, sea ice area decreases by ~3 × 1012 m2 per K of global warming, while the effective global radiative forcing per unit area of sea ice loss is ~0.1 × 10-12 W m-2. The product of these two terms (~0.3 W m-2 K-1) approximately equals the difference in climate feedback parameter found in simulations with sea ice response (1.05 W m-2 K-1) and simulations without sea ice response (1.31 W m-2 K-1 or 1.35 W m-2 K-1, depending on the method used to disable the changes in sea ice cover). Thus, we find that in our model simulations, sea ice response accounts for about 20% to 22% of the climate sensitivity to an imposed change in radiative forcing. In our model, the additional radiative forcing resulting from a loss of all sea-ice in the "pre-industrial" state is comparable to but somewhat less than the radiative forcing from a doubling of atmospheric CO2 content.

  19. Spin-phonon coupling in BaFe{sub 12}O{sub 19} M-type hexaferrite

    SciTech Connect

    Silva Júnior, Flávio M.; Paschoal, Carlos W. A.

    2014-12-28

    The spin-phonon coupling in magnetic materials is due to the modulation of the exchange integral by lattice vibrations. BaFe{sub 12}O{sub 19} M-type hexaferrite, which is the most used magnetic material as permanent magnet, transforms into ferrimagnet at high temperatures, but no spin-phonon coupling was previously observed at this transition. In this letter, we investigated the temperature-dependent Raman spectra of polycrystalline BaFe{sub 12}O{sub 19} M-type hexaferrite from room temperature up to 780 K to probe spin-phonon coupling at the ferrimagnetic transition. An anomaly was observed in the position of the phonon attributed to the Fe{sup (4)}O{sub 6}, Fe{sup (5)}O{sub 6}, and Fe{sup (1)}O{sub 6} octahedra, evidencing the presence of a spin-phonon coupling in BaM in the ferrimagnetic transition at 720 K. The results also confirmed the spin-phonon coupling is different for each phonon even when they couple with the same spin configuration.

  20. Modeling Commercial Turbofan Engine Icing Risk With Ice Crystal Ingestion

    NASA Technical Reports Server (NTRS)

    Jorgenson, Philip C. E.; Veres, Joseph P.

    2013-01-01

    The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that have been attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was degraded engine performance, and one or more of the following: loss of thrust control (roll back), compressor surge or stall, and flameout of the combustor. As ice crystals are ingested into the fan and low pressure compression system, the increase in air temperature causes a portion of the ice crystals to melt. It is hypothesized that this allows the ice-water mixture to cover the metal surfaces of the compressor stationary components which leads to ice accretion through evaporative cooling. Ice accretion causes a blockage which subsequently results in the deterioration in performance of the compressor and engine. The focus of this research is to apply an engine icing computational tool to simulate the flow through a turbofan engine and assess the risk of ice accretion. The tool is comprised of an engine system thermodynamic cycle code, a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor flow path, without modeling the actual ice accretion. A commercial turbofan engine which has previously experienced icing events during operation in a high altitude ice crystal environment has been tested in the Propulsion Systems Laboratory (PSL) altitude test facility at NASA Glenn Research Center. The PSL has the capability to produce a continuous ice cloud which are ingested by the engine during operation over a range of altitude conditions. The PSL test results confirmed that there was ice accretion in the engine due to ice crystal ingestion, at the same simulated altitude operating conditions as experienced previously in

  1. The Influence of Platelet Ice and Snow on Antarctic Land-fast Sea Ice

    NASA Astrophysics Data System (ADS)

    Hoppmann, M.; Nicolaus, M.

    2011-12-01

    Sea ice fastened to coasts, icebergs and ice shelves is of crucial importance for climate- and ecosystems. Near Antarctic ice shelves, this land-fast sea ice exhibits two unique characteristics that distinguish it from most other sea ice: a sub-ice layer of ice platelets and a highly stratified and thick snow cover. Ice platelets are flat, plate-like ice crystals forming and growing in a layer of super-cooled water which originates from ice shelf cavities. During growth, heat is lost to the super-cooled ocean rather than conducted to the atmosphere. The crystals accumulate beneath the solid sea-ice cover, forming a layer of loose platelets and eventually becoming incorporated into the sea-ice fabric as platelet ice. Considering the fact that the amount of platelet ice contributes between 10 and 60% to the mass of the land-fast sea ice around Antarctica, very little is known about its spatial and temporal variability. A thick and partly multi-year snow cover develops on top of the Antarctic fast ice, ultimately altering the sea-ice surface and affecting the sea-ice thermodynamics and mass balance. It typically leads to snow-ice formation, surface flooding, and the development of superimposed ice from snow melt water. In order to investigate the role of platelet ice and snow for Antarctic fast ice, we have initiated a regular observation program on the land-fast sea ice of Atka Bay as part of the international Antarctic Fast Ice Network (AFIN). We performed manual measurements of sea-ice and snow thicknesses from June to December 2010 and 2011. Additionally, a mass balance buoy and an automatic weather station were deployed in 2011 and ice cores were taken. Our measurements will reveal insight into the spatial and temporal variability of sea-ice and snow thickness distributions on Atka Bay fast ice. First results show that sea-ice thickness is lowest in the eastern part of the Bay, where a thick snow cover leads to extensive surface flooding. In the West, dynamic

  2. Arctic Sea Ice Minimum, 2015

    NASA Video Gallery

    This animation shows the evolution of the Arctic sea ice cover from its wintertime maximum extent, which was reached on Feb. 25, 2015, and was the lowest on record, to its apparent yearly minimum, ...

  3. Dynamics of Arctic sea ice discussed at workshop

    NASA Astrophysics Data System (ADS)

    Overland, James; Ukita, Jinro

    Sea ice is an interesting geophysical material: it behaves as a large-scale hardening plastic. Consider the impact of the sea-ice covers mechanical behavior on the energy and momentum exchange within the complex atmosphere-ice-ocean system. Sea ice acts as an insulator between the relatively warm ocean water and the cold polar atmosphere. Sea ice cover interacts with the atmosphere by regulating air-sea fluxes, changing surface albedo, and influencing the long-wave radiative balance.

  4. Global ice sheet modeling

    SciTech Connect

    Hughes, T.J.; Fastook, J.L.

    1994-05-01

    The University of Maine conducted this study for Pacific Northwest Laboratory (PNL) as part of a global climate modeling task for site characterization of the potential nuclear waste respository site at Yucca Mountain, NV. The purpose of the study was to develop a global ice sheet dynamics model that will forecast the three-dimensional configuration of global ice sheets for specific climate change scenarios. The objective of the third (final) year of the work was to produce ice sheet data for glaciation scenarios covering the next 100,000 years. This was accomplished using both the map-plane and flowband solutions of our time-dependent, finite-element gridpoint model. The theory and equations used to develop the ice sheet models are presented. Three future scenarios were simulated by the model and results are discussed.

  5. Ice sheets and nitrogen

    PubMed Central

    Wolff, Eric W.

    2013-01-01

    Snow and ice play their most important role in the nitrogen cycle as a barrier to land–atmosphere and ocean–atmosphere exchanges that would otherwise occur. The inventory of nitrogen compounds in the polar ice sheets is approximately 260 Tg N, dominated by nitrate in the much larger Antarctic ice sheet. Ice cores help to inform us about the natural variability of the nitrogen cycle at global and regional scale, and about the extent of disturbance in recent decades. Nitrous oxide concentrations have risen about 20 per cent in the last 200 years and are now almost certainly higher than at any time in the last 800 000 years. Nitrate concentrations recorded in Greenland ice rose by a factor of 2–3, particularly between the 1950s and 1980s, reflecting a major change in NOx emissions reaching the background atmosphere. Increases in ice cores drilled at lower latitudes can be used to validate or constrain regional emission inventories. Background ammonium concentrations in Greenland ice show no significant recent trend, although the record is very noisy, being dominated by spikes of input from biomass burning events. Neither nitrate nor ammonium shows significant recent trends in Antarctica, although their natural variations are of biogeochemical and atmospheric chemical interest. Finally, it has been found that photolysis of nitrate in the snowpack leads to significant re-emissions of NOx that can strongly impact the regional atmosphere in snow-covered areas. PMID:23713125

  6. The Great Ice Age

    USGS Publications Warehouse

    Ray, Louis L.

    1992-01-01

    The Great Ice Age, a recent chapter in the Earth's history, was a period of recurring widespread glaciations. During the Pleistocene Epoch of the geologic time scale, which began about a million or more years ago, mountain glaciers formed on all continents, the icecaps of Antarctica and Greenland were more extensive and thicker than today, and vast glaciers, in places as much as several thousand feet thick, spread across northern North America and Eurasia. So extensive were these glaciers that almost a third of the present land surface of the Earth was intermittently covered by ice. Even today remnants of the great glaciers cover almost a tenth of the land, indicating that conditions somewhat similar to those which produced the Great Ice Age are still operating in polar and subpolar climates.

  7. Sea ice/climate studies

    NASA Technical Reports Server (NTRS)

    Parkinson, C. L.

    1988-01-01

    The objectives were to determine and analyze the annual cycle of sea ice extents in the Arctic Ocean and peripheral seas and bays over the period 1973 to 1986, looking in particular for any long term trends; to examine the relationship between local sea ice covers and the surrounding atmosphere and ocean; and to examine sea ice as a potential early indicator of climate change. The work involves creating regional and hemispheric time series of sea ice variables from satellite passive microwave data and analyzing these through various intercomparisons amongst themselves and with oceanographic and atmospheric fields.

  8. Over Ice

    NASA Video Gallery

    All about NASA's IceBridge P-3B plane and its IceBridge retrofit. Upgraded with 21st century "special modifications", the aircraft is less a cold war relic and more like the Space Agency's Millenni...

  9. Thickness of ice on perennially frozen lakes.

    PubMed

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

    1985-02-14

    The dry valleys of southern Victoria Land, constituting the largest ice-free expanse in the Antarctic, contain numerous lakes whose perennial ice cover is the cause of some unique physical and biological properties. Although the depth, temperature and salinity of the liquid water varies considerably from lake to lake, the thickness of the ice cover is remarkably consistent, ranging from 3.5 to 6 m, which is determined primarily by the balance between conduction of energy out of the ice and the release of latent heat at the ice-water interface and is also affected by the transmission and absorption of sunlight. In the steady state, the release of latent heat at the ice bottom is controlled by ablation from the ice surface. Here we present a simple energy-balance model, using the measured ablation rate of 30 cm yr-1, which can explain the observed ice thickness. PMID:11539028

  10. Thickness of ice on perennially frozen lakes

    USGS Publications Warehouse

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

    1985-01-01

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

  11. Role of ice dynamics in anomalous ice conditions in the Beaufort Sea during 2006 and 2007

    NASA Astrophysics Data System (ADS)

    Hutchings, J. K.; Rigor, I. G.

    2012-05-01

    A new record minimum in summer sea ice extent was set in 2007 and an unusual polynya formed in the Beaufort Sea ice cover during the summer of 2006. Using a combination of visual observations from cruises, ice drift, and satellite passive microwave sea ice concentration, we show that ice dynamics during preceding years included events that preconditioned the Beaufort ice pack for the unusual patterns of opening observed in both summers. Intrusions of first year ice from the Chukchi Sea to the Northern Beaufort, and increased pole-ward ice transport from the western Arctic during summer has led to reduced replenishment of multiyear ice, older than five years, in the western Beaufort, resulting in a younger, thinner ice pack in most of the Beaufort. We find ice younger than five years melts out completely by the end of summer, south of 76N. The 2006 unusual polynya was bounded to the south by an ice tongue composed of sea ice older than 5 years, and formed when first year and second year ice melted between 76N and the older ice to the south. In this paper we demonstrate that a recent shift in ice circulation patterns in the western Arctic preconditions the Beaufort ice pack for increased seasonal ice zone extent.

  12. Sparse ice: Geophysical, biological and Indigenous knowledge perspectives on a habitat for ice-associated fauna

    NASA Astrophysics Data System (ADS)

    Lee, O. A.; Eicken, H.; Weyapuk, W., Jr.; Adams, B.; Mohoney, A. R.

    2015-12-01

    The significance of highly dispersed, remnant Arctic sea ice as a platform for marine mammals and indigenous hunters in spring and summer may have increased disproportionately with changes in the ice cover. As dispersed remnant ice becomes more common in the future it will be increasingly important to understand its ecological role for upper trophic levels such as marine mammals and its role for supporting primary productivity of ice-associated algae. Potential sparse ice habitat at sea ice concentrations below 15% is difficult to detect using remote sensing data alone. A combination of high resolution satellite imagery (including Synthetic Aperture Radar), data from the Barrow sea ice radar, and local observations from indigenous sea ice experts was used to detect sparse sea ice in the Alaska Arctic. Traditional knowledge on sea ice use by marine mammals was used to delimit the scales where sparse ice could still be used as habitat for seals and walrus. Potential sparse ice habitat was quantified with respect to overall spatial extent, size of ice floes, and density of floes. Sparse ice persistence offshore did not prevent the occurrence of large coastal walrus haul outs, but the lack of sparse ice and early sea ice retreat coincided with local observations of ringed seal pup mortality. Observations from indigenous hunters will continue to be an important source of information for validating remote sensing detections of sparse ice, and improving understanding of marine mammal adaptations to sea ice change.

  13. Scrambled Ice

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This complex area on the side of Europa which faces away from Jupiter shows several types of features which are formed by disruptions of Europa's icy crust. North is to the top of the image, taken by NASA's Galileo spacecraft, and the Sun illuminates the surface from the left. The prominent wide, dark bands are up to 20 kilometers (12 miles) wide and over 50 kilometers (30 miles) long. They are believed to have formed when Europa's icy crust fractured, separated and filled in with darker, 'dirtier' ice or slush from below. A relatively rare type of feature on Europa is the 15-kilometer-diameter (9.3-mile) impact crater in the lower left corner. The small number of impact craters on Europa's surface is an indication of its relatively young age. A region of chaotic terrain south of this impact crater contains crustal plates which have broken apart and rafted into new positions. Some of these 'ice rafts' are nearly 1 kilometer (about half a mile) across. Other regions of chaotic terrain are visible and indicate heating and disruption of Europa's icy crust from below. The youngest features in this scene are the long, narrow cracks in the ice which cut across all other features. One of these cracks is about 30 kilometers (18 miles) to the right of the impact crater and extends for hundreds of miles from the top to the bottom of the image.

    The image, centered near 23 degrees south latitude and 179 degrees longitude, covers an area about 240 by 215 kilometers (150 by 130 miles) across. The finest details that can be discerned in this picture are about 460 meters (500 yards) across. The image was taken as Galileo flew by Europa on March 29, 1998. The image was taken by the onboard solid state imaging system camera from an altitude of 23,000 kilometers (14,000 miles).

    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech

  14. Primary Production in Antarctic Sea Ice

    NASA Technical Reports Server (NTRS)

    Arrigo, Kevin R.; Worthen, Denise L.; Lizotte, Michael P.; Dixon, Paul; Dieckmann, Gerhard

    1997-01-01

    A numerical model shows that in Antarctic sea ice, increased flooding in regions with thick snow cover enhances primary production in the infiltration (surface) layer. Productivity in the freeboard (sea level) layer is also determined by sea ice porosity, which varies with temperature. Spatial and temporal variation in snow thickness and the proportion of first-year ice thus determine regional differences in sea ice primary production. Model results show that of the 40 tera-grams of carbon produced annually in the Antarctic ice pack, 75 percent was associated with first-year ice and nearly 50 percent was produced in the Weddell Sea.

  15. Cyclic steps on ice

    NASA Astrophysics Data System (ADS)

    Yokokawa, M.; Izumi, N.; Naito, K.; Parker, G.; Yamada, T.; Greve, R.

    2016-05-01

    Boundary waves often form at the interface between ice and fluid flowing adjacent to it, such as ripples under river ice covers, and steps on the bed of supraglacial meltwater channels. They may also be formed by wind, such as the megadunes on the Antarctic ice sheet. Spiral troughs on the polar ice caps of Mars have been interpreted to be cyclic steps formed by katabatic wind blowing over ice. Cyclic steps are relatives of upstream-migrating antidunes. Cyclic step formation on ice is not only a mechanical but also a thermodynamic process. There have been very few studies on the formation of either cyclic steps or upstream-migrating antidunes on ice. In this study, we performed flume experiments to reproduce cyclic steps on ice by flowing water, and found that trains of steps form when the Froude number is larger than unity. The features of those steps allow them to be identified as ice-bed analogs of cyclic steps in alluvial and bedrock rivers. We performed a linear stability analysis and obtained a physical explanation of the formation of upstream-migrating antidunes, i.e., precursors of cyclic steps. We compared the results of experiments with the predictions of the analysis and found the observed steps fall in the range where the analysis predicts interfacial instability. We also found that short antidune-like undulations formed as a precursor to the appearance of well-defined steps. This fact suggests that such antidune-like undulations correspond to the instability predicted by the analysis and are precursors of cyclic steps.

  16. Ice crystal ingestion by turbofans

    NASA Astrophysics Data System (ADS)

    Rios Pabon, Manuel A.

    proposed and built in this Thesis, called DBDAIS, with a complete description of the anti-ice cycle. Contrary to existing ice protection systems, which either heat the aircraft surfaces, or mechanically remove the accreted ice, the DBDAIS employs non-thermal plasma discharges to prevent ice accretion. A new apparatus that mimics inflight icing based on combining the liquid sprays of liquid nitrogen and water was designed and fabricated, named LNITA. The apparatus produces ice similar to glaze ice and rime ice, the two characteristic types of ice from inflight icing, at the cost of 1% of similar tests in icing wind tunnels. Nineteen experiments of the DBDAIS were performed in the LNITA. The results from the experiments point to 32 kV and 4 kHz being adequate to prevent ice accretion, with a power consumption of 1 W/cm2. This compares favorably to existing ice protection systems, which typically run at 10 W/cm2, and to the power consumption of a typical electric stove burner at maximum power, which is 5 W/cm2. To complete this Thesis, a design and development project is proposed to implement the DBDAIS in Unmanned Aircraft Systems (UAS), with the selection of standard FAA inflight icing conditions, the run of 240 LEWICE simulations, and an analysis of the run results. The computational results lead to the design of a wing boot covering the airfoil from 20% of the lower pressure surface to 4% of the upper suction surface as the optimal protection for a UAS.

  17. Recent summer sea ice thickness surveys in Fram Strait and associated ice volume fluxes

    NASA Astrophysics Data System (ADS)

    Krumpen, T.; Gerdes, R.; Haas, C.; Hendricks, S.; Herber, A.; Selyuzhenok, V.; Smedsrud, L.; Spreen, G.

    2016-03-01

    Fram Strait is the main gateway for sea ice export out of the Arctic Ocean, and therefore observations there give insight into the composition and properties of Arctic sea ice in general and how it varies over time. A data set of ground-based and airborne electromagnetic ice thickness measurements collected during summer between 2001 and 2012 is presented here, including long transects well into the southern part of the Transpolar Drift obtained using fixed-wing aircrafts. The primary source of the surveyed sea ice leaving Fram Strait is the Laptev Sea and its age has decreased from 3 to 2 years between 1990 and 2012. The thickness data consistently also show a general thinning of sea ice for the last decade, with a decrease in modal thickness of second year and multiyear ice, and a decrease in mean thickness and fraction of ice thicker than 3 m. Local melting in the strait was investigated in two surveys performed in the downstream direction, showing a decrease in sea ice thickness of 0.19 m degree-1 latitude south of 81° N. Further north variability in ice thickness is more related to differences in age and deformation. The thickness observations were combined with ice area export estimates to calculate summer volume fluxes of sea ice. While satellite data show that monthly ice area export had positive trends since 1980 (10.9 × 103 km2 decade-1), the summer (July and August) ice area export is low with high uncertainties. The average volume export amounts to 16.78 km3. Naturally, the volume flux estimates are limited to the period when airborne thickness surveys are available. Nevertheless, we could show that the combination of satellite data and airborne observations can be used to determine volume fluxes through Fram Strait and as such, can be used to bridge the lack of satellite-based sea ice thickness information in summer.

  18. The Role of Snow and Ice in the Climate System

    ScienceCinema

    Barry, Roger G.

    2009-09-01

    Global snow and ice cover (the 'cryosphere') plays a major role in global climate and hydrology through a range of complex interactions and feedbacks, the best known of which is the ice - albedo feedback. Snow and ice cover undergo marked seasonal and long term changes in extent and thickness. The perennial elements - the major ice sheets and permafrost - play a role in present-day regional and local climate and hydrology, but the large seasonal variations in snow cover and sea ice are of importance on continental to hemispheric scales. The characteristics of these variations, especially in the Northern Hemisphere, and evidence for recent trends in snow and ice extent are discussed.

  19. The Role of Snow and Ice in the Climate System

    SciTech Connect

    Barry, Roger G.

    2007-12-19

    Global snow and ice cover (the 'cryosphere') plays a major role in global climate and hydrology through a range of complex interactions and feedbacks, the best known of which is the ice - albedo feedback. Snow and ice cover undergo marked seasonal and long term changes in extent and thickness. The perennial elements - the major ice sheets and permafrost - play a role in present-day regional and local climate and hydrology, but the large seasonal variations in snow cover and sea ice are of importance on continental to hemispheric scales. The characteristics of these variations, especially in the Northern Hemisphere, and evidence for recent trends in snow and ice extent are discussed.

  20. The life cycle of Ice Sails

    NASA Astrophysics Data System (ADS)

    Evatt, Geoff; Mayer, Christoph; Abrahams, I. d.; Nicholson, Lindsey; Mallinson, Amy; Heil, Matthias

    2016-04-01

    The Karakoram mountain region is host to many debris-covered glaciers. A notable feature from a sub-set of mainly larger glaciers with flat tongues, is the phenomenon of `Ice Sails'. These Ice Sails are clean ice structures that protrude out of the surrounding debris-covered glacier. They can be up to 20 meters in height, with widths of up to 90 meters, and generally have flat-sided faces. They appear to grow out of areas of glacier with thin debris coverage, then persist for decades as the glacier flows downstream, before declining back into the glacier several kilometres later. Here we aim to define and categorise these ice structures, and then explain their growth, persistence and decay. In particular, we show that their growth is due to the melt rate of inclined clean-ice being smaller than that of the surrounding flat thinly-debris-covered ice, allowing these structures to appear to grow out of the debris layer. But as the glacier flows downstream, this debris thickness slowly thickens, causing the corresponding melt-rate of the underlying ice to decline. Eventually, the melt-rate of the debris-covered ice becomes lower than that of the Ice Sail's melt-rate, at which point the decaying process of the Ice Sail commences. We develop a model to quantify this process, and in so doing, draw out the key parameters that govern the existence of Ice Sails.

  1. Significance of Matrix Metalloproteinase 9 Expression as Supporting Marker to Cytokeratin 19 mRNA in Sentinel Lymph Nodes in Breast Cancer Patients

    PubMed Central

    Murawski, Marek; Woźniak, Marta; Duś-Szachniewicz, Kamila; Kołodziej, Paweł; Rzeszutko, Marta; Ziółkowski, Piotr

    2016-01-01

    One-step nucleic acid amplification (OSNA) detects and quantifies, with the use of a polymerase chain reaction, the presence of cytokeratin 19 mRNA in sentinel lymph nodes. The main advantage of the OSNA assay is the avoidance of second surgery in case of positive sentinel lymph node diagnosis. The objective of this study was to evaluate the significance of matrix metalloproteinase 9 expression by immunohistochemistry as supporting marker to cytokeratin 19 mRNA in sentinel lymph nodes in breast cancer patients and to relate this expression with clinicopathological data. This study was conducted on fresh sentinel lymph nodes obtained from 40 patients with tumors classified as carcinoma of no special type. The presence of metastatic cells in the slices of lymph nodes was evaluated by immunohistochemistry using antibodies for CK19 and MMP-9. Expression of CK19 and MMP-9 in lymph nodes was also confirmed by means of Western blot analysis. Results indicated that the strongest correlation with CK19 mRNA was displayed by MMP-9, CK19 (by immunohistochemistry, IHC), and nodal metastases (p < 0.001). Higher histological grading also positively correlated with CK19 mRNA, however that correlation was less significant. Since MMP-9 shows very strong correlation with CK19 mRNA in breast carcinoma of no special type metastases, expression of MMP-9 in sentinel lymph nodes should be considered as useful method whenever OSNA analysis is not available. PMID:27110764

  2. Layered kagome spin ice

    NASA Astrophysics Data System (ADS)

    Hamp, James; Dutton, Sian; Mourigal, Martin; Mukherjee, Paromita; Paddison, Joseph; Ong, Harapan; Castelnovo, Claudio

    Spin ice materials provide a rare instance of emergent gauge symmetry and fractionalisation in three dimensions: the effective degrees of freedom of the system are emergent magnetic monopoles, and the extensively many `ice rule' ground states are those devoid of monopole excitations. Two-dimensional (kagome) analogues of spin ice have also been shown to display a similarly rich behaviour. In kagome ice however the ground-state `ice rule' condition implies the presence everywhere of magnetic charges. As temperature is lowered, an Ising transition occurs to a charge-ordered state, which can be mapped to a dimer covering of the dual honeycomb lattice. A second transition, of Kosterlitz-Thouless or three-state Potts type, occurs to a spin-ordered state at yet lower temperatures, due to small residual energy differences between charge-ordered states. Inspired by recent experimental capabilities in growing spin ice samples with selective (layered) substitution of non-magnetic ions, in this work we investigate the fate of the two ordering transitions when individual kagome layers are brought together to form a three-dimensional pyrochlore structure coupled by long range dipolar interactions. We also consider the response to substitutional disorder and applied magnetic fields.

  3. ICESat: Ice, Cloud and Land Elevation Satellite

    NASA Technical Reports Server (NTRS)

    Zwally, Jay; Shuman, Christopher

    2002-01-01

    Ice exists in the natural environment in many forms. The Earth dynamic ice features shows that at high elevations and/or high latitudes,snow that falls to the ground can gradually build up tu form thick consolidated ice masses called glaciers. Glaciers flow downhill under the force of gravity and can extend into areas that are too warm to support year-round snow cover. The snow line, called the equilibrium line on a glacier or ice sheet, separates the ice areas that melt on the surface and become show free in summer (net ablation zone) from the ice area that remain snow covered during the entire year (net accumulation zone). Snow near the surface of a glacier that is gradually being compressed into solid ice is called firm.

  4. Summer Arctic Sea Ice Retreat: May - August 2013

    NASA Video Gallery

    The melting of sea ice in the Arctic is well on its way toward its annual "minimum," that time when the floating ice cap covers less of the Arctic Ocean than at any other period during the year. 20...

  5. 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.

  6. Sea ice terminology

    SciTech Connect

    Not Available

    1980-09-01

    A group of definitions of terms related to sea ice is presented, as well as a graphic representation of late winter ice zonation of the Beaufort Sea Coast. Terms included in the definition list are belt, bergy bit, bight, brash ice, calving, close pack ice, compacting, compact pack ice, concentration, consolidated pack ice, crack, diffuse ice edge, fast ice, fast-ice boundary, fast-ice edge, first-year ice, flaw, flaw lead, floe, flooded ice, fractured, fractured zone, fracturing, glacier, grey ice, grey-white ice, growler, hummock, iceberg, iceberg tongue, ice blink, ice boundary, ice cake, ice edge, ice foot, ice free, ice island, ice shelf, large fracture, lead, medium fracture, multiyear ice, nilas, old ice, open pack ice, open water, pack ice, polar ice, polynya, puddle, rafted ice, rafting, ram, ridge, rotten ice, second-year ice, shearing, shore lead, shore polynya, small fracture, strip, tabular berg, thaw holes, very close pack ice, very open pack ice, water sky, young coastal ice, and young ice.

  7. Arctic Perennial and Winter Multiyear Ice on a Precipitous Decline

    NASA Astrophysics Data System (ADS)

    Comiso, J. C.

    2008-12-01

    Knowledge about the state of the Arctic perennial and multiyear ice cover is important because they are the mainstay of the Arctic sea ice cover. Perennial ice is ice that survives the summer and consists mainly of second year and the older multiyear ice types. The rapid rate of decline in the perennial ice cover has been reported and examined previously and with the precipitous decline in 2007 and again in 2008, the Arctic Ocean has become an intense area of climate change result. The perennial ice area in 2007 was observed to be 27% less than the previous record low established in 2005 and was 38% less than climatological average. The sea surface temperature (SST) in the Arctic has also been on the rise at about 0.7 per decade with the SST at the Chukchi Sea region being observed by satellite data to be anomalously higher than average by about 5 oC. This is an indication that ice-albedo feedback effects in the region are already being observed and that a recovery of the perennial ice cover in the foreseeable future may not be possible. To gain insight into the state of the multiyear ice cover, we take advantage of the large contrast in the emissivity of first year and multiyear ice in winter and assess the variability and trend of the older multiyear ice type. The contrast is largest in February when the ice is cold and dry and the technique and is most pronounced between first year and the older multiyear (3 years or older) ice types. The retrieved area of winter multiyear ice is about 2 million km2 less than that of the perennial ice area observed during the previous summer indicating that only the older and thicker types of multiyear ice are included. The trend of the retrieved multiyear ice cover for the period 1979 to 2007 is observed to be about -14%/decade which indicates a significantly faster decline than the perennial ice cover. This suggests that the thicker component of the perennial ice cover is declining even more rapidly that the perennial ice. The

  8. Sea ice, erosion, and vulnerability of Arctic coasts

    NASA Astrophysics Data System (ADS)

    Barnhart, Katherine; Overeem, Irina; Kay, Jennifer; Anderson, Robert

    2015-04-01

    Coasts form the dynamic interface between the terrestrial and oceanic systems. In the Arctic, and in much of the world, the coast is a zone of relatively high population, infrastructure, biodiversity, and ecosystem services. A significant difference between Arctic and temperate coasts is the presence of sea ice. Sea ice influences Arctic coasts in two main ways: (1) the length of the sea ice-free season controls the length of time over which nearshore water can interact with the land, and (2) the location of the sea ice edge controls the fetch over which storm winds can blow over open water, resulting in changes in nearshore water level and wave field. The resulting nearshore hydrodynamic environment impacts all aspects of the coastal system. We first combine satellite records of sea ice with a simple model for wind-driven storm surge and waves to estimate how changes in the length and character of the sea ice-free season have impacted the nearshore hydrodynamic environment along Alaska's Beaufort Sea Coast for the period 1979-2012. This region has experienced some of the greatest changes in both sea ice cover and coastal erosion rates in the Arctic and is anticipated to experience significant change in the future. The median length of the 2012 open-water season along this stretch of coast, in comparison to 1979, expanded by 1.9 x. At the same time, coastal erosion rates increased from 8.7 m yr-1 to 19 m yr-1. At Drew Point, winds from the northwest result in increased water levels at the coast and control the process of submarine notch incision, the rate-limiting step of coastal retreat. When open-water conditions exist, the distance to the sea ice edge exerts control on the water level and wave field through its control on fetch. We find that the extreme values of water-level setup at Drew Point have increased consistently with increasing fetch. We then extend our analysis of the length of the open water season to the entire Arctic using both satellite

  9. Solar radiation interactions with seasonal sea ice

    NASA Astrophysics Data System (ADS)

    Ehn, Jens Kristian

    Presently, the Arctic Ocean is undergoing an escalating reduction in sea ice and a transition towards a seasonal sea ice environment. This warrants detailed investigations into improving our understanding of the seasonal evolution of sea ice and snow covers, and their representation in climate models. The interaction of solar radiation with sea ice is an important process influencing the energy balance and biological activity in polar seas, and consequently plays a key role in the earth's climate system. This thesis focuses on characterization of the optical properties---and the underlying physical properties that determine them---of seasonal sea ice during the fall freeze-up and the spring melt periods. Both periods display high spatial heterogeneity and rapid temporal changes in sea ice properties, and are therefore poorly understood. Field data were collected in Amundsen Gulf/Franklin Bay (FB), southern-eastern Beaufort Sea, in Oct.-Nov. 2003 and Apr. 2004 and in Button Bay (BB), western Hudson Bay, in Mar.-May 2005 to address (1) the temporal and spatial evolution of surface albedo and transmittance, (2) how radiative transfer in sea ice is controlled by its physical nature, and (3) the characteristics of the bottom ice algae community and its effect on the optical properties. The fall study showed the importance of surface features such as dry or slushy bare ice, frost flowers and snow cover in determining the surface albedo. Ice thickness was also important, however, mostly because surface features were associated with thickness. For example, nilas (<10 cm thick) was typically not covered by a snow layer as snow grains were dissolved or merged with the salty and warm brine skim layer on the surface, while surface conditions on thicker ice types were cold and dry enough to support a snow cover. In general, the surface albedo increased exponentially with an ice thickness increase, however, variability within ice thickness types were very large. It is apparent

  10. Covering Politics.

    ERIC Educational Resources Information Center

    Gruber, Ryan; Wind, Andrew; Trevidi, Neema

    2000-01-01

    Presents four articles considering: (1) the media's role in the coverage of politics; (2) the influence of photography particularly in terms of the president; (3) an event where an Iowa student had a chance to work with professionals while covering politics; and (4) considering scholastic reporters covering national candidates as they learn and…

  11. Thickness of tropical ice and photosynthesis on a snowball Earth.

    PubMed

    McKay, C P

    2000-07-15

    On a completely ice-covered "snowball" Earth the thickness of ice in the tropical regions would be limited by the sunlight penetrating into the ice cover and by the latent heat flux generated by freezing at the ice bottom--the freezing rate would balance the sublimation rate from the top of the ice cover. Heat transfer models of the perennially ice-covered Antarctic dry valley lakes applied to the snowball Earth indicate that the tropical ice cover would have a thickness of 10 m or less with a corresponding transmissivity of > 0.1%. This light level is adequate for photosynthesis and could explain the survival of the eukaryotic algae. PMID:11543492

  12. Arctic sea ice decline and ice export in the CMIP5 historical simulations

    NASA Astrophysics Data System (ADS)

    Langehaug, H. R.; Geyer, F.; Smedsrud, L. H.; Gao, Y.

    2013-11-01

    Arctic sea ice properties and Fram Strait ice export from six CMIP5 Global Climate and Earth System Models are evaluated and investigated for the period 1957-2005. Over the last decades most ensemble members simulate a decreasing September sea ice area and a slow, general thinning of the sea ice cover. While the different ensemble members both under- and overestimate the decline in observed September sea ice area, none of the members reproduce the observed thinning. This study is a first attempt to evaluate the Fram Strait ice area export in the CMIP5 models, and the role it has played for Arctic sea ice area and thickness. Five of the six models evaluated reproduce the seasonal cycle and the inter-annual variance of the ice area export in the Fram Strait reasonably well. The simulated southward export of sea ice in the Fram Strait constitutes a major fraction of the Arctic sea ice in these five models; 10-18% of the sea ice covered Arctic Basin is annually exported. For the same models the year-to-year variability in Fram Strait ice volume export carries 35% of the year-to-year variability in the Arctic Basin sea ice volume. We have found low but significant correlations on inter-annual timescales between the Fram Strait ice export, both in terms of area and volume, and the Arctic Basin sea ice thickness. All six models show that an increase in ice area export leads a decrease in the sea ice thickness. This inverse relationship also holds when considering the long-term trends; the larger the increase in Fram Strait ice area export, the larger the thinning of the Arctic Basin sea ice cover and the larger the loss in the September sea ice area. The different ensemble members show both negative and positive ice export trends. Focusing on the model with the largest number of ensemble members (10), we have been able to quantify the effect of the ice area export on the Arctic Basin sea ice for this particular model. For this model an increase of the ice area export

  13. Components of the ice age circulation

    NASA Technical Reports Server (NTRS)

    Rind, D.

    1987-01-01

    The effects of ice age boundary conditions on atmospheric dynamics and regional climate patterns are investigated using four GCM simulations. Particular consideration is given to sea surface temperature-sea ice distribution, the appearance of land ice, and the increased elevation of land ice. It is observed that the ice-age sea surface temperature stabilizes the atmosphere over the oceans, increases the frequency of storm tracking through central North America, and amplifies transient eddy energy without increasing baroclinic generation. It is detected that low-elevation ice generates low pressure over eastern North America and southern Europe in winter, while increasing cloud cover and cooling the land in summer. Elevation of the ice sheets cools the land in winter, further intensifies storms off northeastern North America, induces subsidence warming downstream of the European ice sheets in summer, and increases the transient and stationary eddy energy through increased baroclinicity.

  14. ROV dives under Great Lakes ice

    USGS Publications Warehouse

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

    1989-01-01

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

  15. PSL Icing Facility Upgrade Overview

    NASA Technical Reports Server (NTRS)

    Griffin, Thomas A.; Dicki, Dennis J.; Lizanich, Paul J.

    2014-01-01

    The NASA Glenn Research Center Propulsion Systems Lab (PSL) was recently upgraded to perform engine inlet ice crystal testing in an altitude environment. The system installed 10 spray bars in the inlet plenum for ice crystal generation using 222 spray nozzles. As an altitude test chamber, the PSL is capable of simulating icing events at altitude in a groundtest facility. The system was designed to operate at altitudes from 4,000 to 40,000 ft at Mach numbers up to 0.8M and inlet total temperatures from -60 to +15 degF. This paper and presentation will be part of a series of presentations on PSL Icing and will cover the development of the icing capability through design, developmental testing, installation, initial calibration, and validation engine testing. Information will be presented on the design criteria and process, spray bar developmental testing at Cox and Co., system capabilities, and initial calibration and engine validation test. The PSL icing system was designed to provide NASA and the icing community with a facility that could be used for research studies of engine icing by duplicating in-flight events in a controlled ground-test facility. With the system and the altitude chamber we can produce flight conditions and cloud environments to simulate those encountered in flight. The icing system can be controlled to set various cloud uniformities, droplet median volumetric diameter (MVD), and icing water content (IWC) through a wide variety of conditions. The PSL chamber can set altitudes, Mach numbers, and temperatures of interest to the icing community and also has the instrumentation capability of measuring engine performance during icing testing. PSL last year completed the calibration and initial engine validation of the facility utilizing a Honeywell ALF502-R5 engine and has duplicated in-flight roll back conditions experienced during flight testing. This paper will summarize the modifications and buildup of the facility to accomplish these tests.

  16. Recent progress in snow and ice research

    SciTech Connect

    Richter-menge, J.A.; Colbeck, S.C.; Jezek, K.C. )

    1991-01-01

    A review of snow and ice research in 1987-1990 is presented, focusing on the effects of layers in seasonal snow covers, ice mechanics on fresh water and sea ice, and remote sensig of polar ice sheets. These topics provide useful examples of general needs in snow and ice research applicable to most areas, such as better representation in models of detailed processes, controlled laboratory experiments to quantify processes, and field studies to provide the appropriate context for interpretation of processes from remote sensing.

  17. Ice-Binding Proteins and Their Function.

    PubMed

    Bar Dolev, Maya; Braslavsky, Ido; Davies, Peter L

    2016-06-01

    Ice-binding proteins (IBPs) are a diverse class of proteins that assist organism survival in the presence of ice in cold climates. They have different origins in many organisms, including bacteria, fungi, algae, diatoms, plants, insects, and fish. This review covers the gamut of IBP structures and functions and the common features they use to bind ice. We discuss mechanisms by which IBPs adsorb to ice and interfere with its growth, evidence for their irreversible association with ice, and methods for enhancing the activity of IBPs. The applications of IBPs in the food industry, in cryopreservation, and in other technologies are vast, and we chart out some possibilities. PMID:27145844

  18. Arctic Summer Ice Processes

    NASA Technical Reports Server (NTRS)

    Holt, Benjamin

    1999-01-01

    The primary objective of this study is to estimate the flux of heat and freshwater resulting from sea ice melt in the polar seas. The approach taken is to examine the decay of sea ice in the summer months primarily through the use of spaceborne Synthetic Aperture Radar (SAR) imagery. The improved understanding of the dynamics of the melt process can be usefully combined with ice thermodynamic and upper ocean models to form more complete models of ice melt. Models indicate that more heat is absorbed in the upper ocean when the ice cover is composed of smaller rather than larger floes and when there is more open water. Over the course of the summer, floes disintegrate by physical forcing and heating, melting into smaller and smaller sizes. By measuring the change in distribution of floes together with open water over a summer period, we can make estimates of the amount of heating by region and time. In a climatic sense, these studies are intended to improve the understanding of the Arctic heat budget which can then be eventually incorporated into improved global climate models. This work has two focus areas. The first is examining the detailed effect of storms on floe size and open water. A strong Arctic low pressure storm has been shown to loosen up the pack ice, increase the open water concentration well into the pack ice, and change the distribution of floes toward fewer and smaller floes. This suggests episodic melting and the increased importance of horizontal (lateral) melt during storms. The second focus area is related to an extensive ship-based experiment that recently took place in the Arctic called Surface Heat Budget of the Arctic (SHEBA). An icebreaker was placed purposely into the older pack ice north of Alaska in September 1997. The ship served as the base for experimenters who deployed extensive instrumentation to measure the atmosphere, ocean, and ice during a one-year period. My experiment will be to derive similar measurements (floe size, open

  19. 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

  20. Ice detector

    NASA Technical Reports Server (NTRS)

    Weinstein, Leonard M. (Inventor)

    1988-01-01

    An ice detector is provided for the determination of the thickness of ice on the outer surface on an object (e.g., aircraft) independently of temperature or the composition of the ice. First capacitive gauge, second capacitive gauge, and temperature gauge are embedded in embedding material located within a hollowed out portion of the outer surface. This embedding material is flush with the outer surface to prevent undesirable drag. The first capacitive gauge, second capacitive gauge, and the temperature gauge are respectively connected to first capacitive measuring circuit, second capacitive measuring circuit, and temperature measuring circuit. The geometry of the first and second capacitive gauges is such that the ratio of the voltage outputs of the first and second capacitance measuring circuits is proportional to the thickness of ice, regardless of ice temperature or composition. This ratio is determined by offset and dividing circuit.

  1. A coupled ice-ocean model of upwelling in the marginal ice zone

    NASA Technical Reports Server (NTRS)

    Roed, L. P.; Obrien, J. J.

    1983-01-01

    A dynamical coupled ice-ocean numerical model for the marginal ice zone (MIZ) is suggested and used to study upwelling dynamics in the MIZ. The nonlinear sea ice model has a variable ice concentration and includes internal ice stress. The model is forced by stresses on the air/ocean and air/ice surfaces. The main coupling between the ice and the ocean is in the form of an interfacial stress on the ice/ocean interface. The ocean model is a linear reduced gravity model. The wind stress exerted by the atmosphere on the ocean is proportional to the fraction of open water, while the interfacial stress ice/ocean is proportional to the concentration of ice. A new mechanism for ice edge upwelling is suggested based on a geostrophic equilibrium solution for the sea ice medium. The upwelling reported in previous models invoking a stationary ice cover is shown to be replaced by a weak downwelling due to the ice motion. Most of the upwelling dynamics can be understood by analysis of the divergence of the across ice edge upper ocean transport. On the basis of numerical model, an analytical model is suggested that reproduces most of the upwelling dynamics of the more complex numerical model.

  2. 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.

  3. Arctic Sea Ice Predictability and the Sea Ice Prediction Network

    NASA Astrophysics Data System (ADS)

    Wiggins, H. V.; Stroeve, J. C.

    2014-12-01

    Drastic reductions in Arctic sea ice cover have increased the demand for Arctic sea ice predictions by a range of stakeholders, including local communities, resource managers, industry and the public. The science of sea-ice prediction has been challenged to keep up with these developments. Efforts such as the SEARCH Sea Ice Outlook (SIO; http://www.arcus.org/sipn/sea-ice-outlook) and the Sea Ice for Walrus Outlook have provided a forum for the international sea-ice prediction and observing community to explore and compare different approaches. The SIO, originally organized by the Study of Environmental Change (SEARCH), is now managed by the new Sea Ice Prediction Network (SIPN), which is building a collaborative network of scientists and stakeholders to improve arctic sea ice prediction. The SIO synthesizes predictions from a variety of methods, including heuristic and from a statistical and/or dynamical model. In a recent study, SIO data from 2008 to 2013 were analyzed. The analysis revealed that in some years the predictions were very successful, in other years they were not. Years that were anomalous compared to the long-term trend have proven more difficult to predict, regardless of which method was employed. This year, in response to feedback from users and contributors to the SIO, several enhancements have been made to the SIO reports. One is to encourage contributors to provide spatial probability maps of sea ice cover in September and the first day each location becomes ice-free; these are an example of subseasonal to seasonal, local-scale predictions. Another enhancement is a separate analysis of the modeling contributions. In the June 2014 SIO report, 10 of 28 outlooks were produced from models that explicitly simulate sea ice from dynamic-thermodynamic sea ice models. Half of the models included fully-coupled (atmosphere, ice, and ocean) models that additionally employ data assimilation. Both of these subsets (models and coupled models with data

  4. On the relationship of sea ice thickness and sea ice classes in Fram Strait and north of Svalbard

    NASA Astrophysics Data System (ADS)

    Renner, A.; Dumont, M.; Gerland, S.; Beckers, J.; Granskog, M.; Goodwin, H.; Haas, C.

    2011-12-01

    In this poster, we present results from sea ice thickness surveys conducted during several scientific cruises in 2010 and 2011 in the region north of Svalbard and along 79° N in Fram Strait using a helicopter-borne electromagnetic device (EM-bird) in combination with aerial photography. A camera was mounted in the helicopter looking downwards at the EM-bird and the sea ice underneath and photos were taken every five seconds. A method based on discriminant analysis was developed to retrieve the fractions of the different ice types from the aerial photos. These fractions of open water, ice, thin ice, melt ponds and submerged ice were then combined with the ice thickness simultaneously measured by the EM-bird. The combination of ice thickness and ice type information provides insight into the characteristics of the different ice regimes and changes within these regimes. For example in Fram Strait in late summer 2010, the modal ice thickness was 1.2 m with the exception of a flight over the fast ice off the east coast of Greenland. There, the modal thickness was 2.9 m for a wide section of heavily ridged ice in front of the smoother, 1 m thick, level fast ice. As usual for the season, the sea ice was largely covered by melt ponds. However, the photo analyses show no significant difference between the fraction of melt ponds over ridged and level fast ice for this summer. The ice was thinner than expected, indicating the export of younger ice from the inner Arctic Ocean than in previous years. While the sea ice in Fram Strait is dominated by ice exported from the north, the ice cover north of Svalbard consists mostly of first-year ice. In summer 2010, this was visible in a narrower thickness distribution than in Fram Strait and a different distribution of the ice class fractions from the photographs.

  5. Satellite Remote Sensing: Passive-Microwave Measurements of Sea Ice

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.; Zukor, Dorothy J. (Technical Monitor)

    2001-01-01

    Satellite passive-microwave measurements of sea ice have provided global or near-global sea ice data for most of the period since the launch of the Nimbus 5 satellite in December 1972, and have done so with horizontal resolutions on the order of 25-50 km and a frequency of every few days. These data have been used to calculate sea ice concentrations (percent areal coverages), sea ice extents, the length of the sea ice season, sea ice temperatures, and sea ice velocities, and to determine the timing of the seasonal onset of melt as well as aspects of the ice-type composition of the sea ice cover. In each case, the calculations are based on the microwave emission characteristics of sea ice and the important contrasts between the microwave emissions of sea ice and those of the surrounding liquid-water medium.

  6. Determination of the age distribution of sea ice from Lagrangian observations of ice motion

    SciTech Connect

    Kwok, R.; Cunningham, G.F.; Rothrock, D.A.; Stern, H.L.

    1995-03-01

    A procedure for monitoring the local age distribution of the Arctic sea ice cover is presented. The age distribution specifies the area covered by ice in different age classes. In the authors` approach, a regular array of grid points is defined initially on the first image of a long time series, and an ice tracker finds the positions of those points in all subsequent images of the series. These Lagrangian points mark the corners of a set of cells that move and deform with the ice cover. The area of each cell changes with each new image or time step. A positive change indicates that ice in a new age class was formed in the cell. A negative change is assumed to have ridged the youngest ice in the cell, reducing its area. The ice in each cell ages as it progresses through the time series. The area of multiyear ice in each cell is computed using an ice classification algorithm. Any area that is not accounted for by the young ice or multiyear ice is assigned to a category of older first-year ice. They thus have a fine age resolution in the young end of the age distribution, and coarse resolution for older ice. The age distribution of the young ice can be converted to a thickness distribution using a simple empirical relation between accumulated freezing-degree days and ice thickness, or using a more complicated thermodynamic model. They describe a general scheme for implementing this procedure for the Arctic Ocean from fall freeze-up until the onset of melt in the spring. The concept is illustrated with a time series of five ERS-1 SAR images spanning a period of 12 days. Such a scheme could be implemented with RADARSAT SAR imagery to provide basin-wide ice age and thickness information.

  7. Sea Ice Mapping using Unmanned Aerial Systems

    NASA Astrophysics Data System (ADS)

    Solbø, S.; Storvold, R.

    2011-12-01

    Mapping of sea ice extent and sea ice features is an important task in climate research. Since the arctic coastal and oceanic areas have a high probability of cloud coverage, aerial platforms are superior to satellite measurements for high-resolution optical measurements. However, routine observations of sea ice conditions present a variety of problems using conventional piloted aircrafts. Specially, the availability of suitable aircrafts for lease does not cover the demand in major parts of the arctic. With the recent advances in unmanned aerial systems (UAS), there is a high possibility of establishing routine, cost effective aerial observations of sea ice conditions in the near future. Unmanned aerial systems can carry a wide variety of sensors useful for characterizing sea-ice features. For instance, the CryoWing UAS, a system initially designed for measurements of the cryosphere, can be equipped with digital cameras, surface thermometers and laser altimeters for measuring freeboard of ice flows. In this work we will present results from recent CryoWing sea ice flights on Svalbard, Norway. The emphasis will be on data processing for stitching together images acquired with the non-stabilized camera payload, to form high-resolution mosaics covering large spatial areas. These data are being employed to map ice conditions; including ice and lead features and melt ponds. These high-resolution mosaics are also well suited for sea-ice mechanics, classification studies and for validation of satellite sea-ice products.

  8. Formation of frazil ice in leads and polynyas

    NASA Astrophysics Data System (ADS)

    Radia, N. V.; Feltham, D. L.; Morales Maqueda, M.

    2011-12-01

    Areas of open ocean within the sea ice cover, known as leads and polynyas, expose ocean water directly to the cold atmosphere. In winter, these are re- gions of high sea ice production, and they play an important role in the mass balance of sea ice and the salt budget of the ocean. Sea ice formation is a complex process which starts with frazil ice crystals which grow and form pancake ice, and eventually consolidate and turn into a layer of solid sea ice. This study will look at all three phases, concentrating on the first. Frazil ice are millimetre-sized crystals of ice which form in supercooled, turbulent water. They initially form through a process of seeding, and then grow and multiply through secondary nucleation, which is where smaller crystals break off from larger ones to create new nucleii for further growth. The increase in volume of frazil ice will continue to occur until there is no longer supercooling in the water. The crystals eventually precipitate to the surface and pile up to form pancake ice. The presence of pancakes at the surface dampens the effects of waves and turbulence, which allows them to consolidate into a solid layer of ice. The ice then mostly grows through congelation ice forming beneath the layer of ice. Desalination of the sea ice cover due to brine drainage is modelled. The model consists of conservation equation for mass and heat, with an imposed momentum budget. Simulations appear to be realistic.

  9. Optical properties of melting first-year Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Light, Bonnie; Perovich, Donald K.; Webster, Melinda A.; Polashenski, Christopher; Dadic, Ruzica

    2015-11-01

    The albedo and transmittance of melting, first-year Arctic sea ice were measured during two cruises of the Impacts of Climate on the Eco-Systems and Chemistry of the Arctic Pacific Environment (ICESCAPE) project during the summers of 2010 and 2011. Spectral measurements were made for both bare and ponded ice types at a total of 19 ice stations in the Chukchi and Beaufort Seas. These data, along with irradiance profiles taken within boreholes, laboratory measurements of the optical properties of core samples, ice physical property observations, and radiative transfer model simulations are employed to describe representative optical properties for melting first-year Arctic sea ice. Ponded ice was found to transmit roughly 4.4 times more total energy into the ocean, relative to nearby bare ice. The ubiquitous surface-scattering layer and drained layer present on bare, melting sea ice are responsible for its relatively high albedo and relatively low transmittance. Light transmittance through ponded ice depends on the physical thickness of the ice and the magnitude of the scattering coefficient in the ice interior. Bare ice reflects nearly three-quarters of the incident sunlight, enhancing its resiliency to absorption by solar insolation. In contrast, ponded ice absorbs or transmits to the ocean more than three-quarters of the incident sunlight. Characterization of the heat balance of a summertime ice cover is largely dictated by its pond coverage, and light transmittance through ponded ice shows strong contrast between first-year and multiyear Arctic ice covers.

  10. Collaborative Project. Understanding the effects of tides and eddies on the ocean dynamics, sea ice cover and decadal/centennial climate prediction using the Regional Arctic Climate Model (RACM)

    SciTech Connect

    Hutchings, Jennifer; Joseph, Renu

    2013-09-14

    The goal of this project is to develop an eddy resolving ocean model (POP) with tides coupled to a sea ice model (CICE) within the Regional Arctic System Model (RASM) to investigate the importance of ocean tides and mesoscale eddies in arctic climate simulations and quantify biases associated with these processes and how their relative contribution may improve decadal to centennial arctic climate predictions. Ocean, sea ice and coupled arctic climate response to these small scale processes will be evaluated with regard to their influence on mass, momentum and property exchange between oceans, shelf-basin, ice-ocean, and ocean-atmosphere. The project will facilitate the future routine inclusion of polar tides and eddies in Earth System Models when computing power allows. As such, the proposed research addresses the science in support of the BER’s Climate and Environmental Sciences Division Long Term Measure as it will improve the ocean and sea ice model components as well as the fully coupled RASM and Community Earth System Model (CESM) and it will make them more accurate and computationally efficient.

  11. Passive microwave in situ observations of winter Weddell Sea ice

    NASA Technical Reports Server (NTRS)

    Comiso, J. C.; Grenfell, T. C.; Bell, D. L.; Lange, M. A.; Ackley, S. F.

    1989-01-01

    Results are presented on the microwave radiative characteristics of Antarctic sea ice measured during the 1986 Winter Weddell Sea Project with a set of portable radiometers. Radiometer measurements at 6, 10, 18, 37, and 90 GHz in vertical and horizontal polarizations were supplemented by near-simultaneous measurements of the ice physical characteristics (including ice thickness, salinity, temperature, snow cover, and density) made during two cruises, lasting 3 months each. Measurements were obtained on various types of sea ice over a large portion of the Weddell-Sea ice cover, including four transects across the entire ice pack. Data analysis shows a large variability in the multispectral microwave emissivities of different ice types, especially at 90 GHz, demonstrating a strong potential of the use of the 90-GHz channel, in combination with lower-frequency channels, for detailed characterizations of the ice cover.

  12. Atmospheric icing severity: Quantification and mapping

    NASA Astrophysics Data System (ADS)

    Lamraoui, Fayçal; Fortin, Guy; Benoit, Robert; Perron, Jean; Masson, Christian

    2013-07-01

    Atmospheric icing became a primary concern due to the significant impact and hazardous conditions of its accretion on structures. The objective of this study is to provide a map of icing events over 32 years (1979 to 2010) that describes the severity of winter icing. This information will prove useful to prevent damages and economical losses due to icing events by documenting the risk factor. To validate the icing climatology method, two case studies involving two topographically contrasting sites were selected: a simple terrain site which is the airport of Bagotville, near Saguenay (Canada) and a complex terrain site located in Mt Bélair, near Quebec City (Canada). Ice accumulation calculated by the use of reanalysis data was quantified using ice accretion on a cylinder model. Comparison between measurement and the model over Bagotville revealed insignificant differences in ice accumulation less than 0.3 mm, and in duration of icing events less than 0.2 day. On the other hand, during winter months, the calculation that showed a maximum of 60 mm in January 1999 over Mt Bélair site also had an underestimation of ice accumulation that varies from 5 mm to 16 mm. The horizontal resolution of NARR imposes a challenge on the calculation of icing events over complex terrains, especially during the months of November and March when air temperature is near freezing point. Taking into account the liquid water content, the duration of icing events and the classes of icing events as weighting factors, the icing severity index based on reanalysis data was introduced to assess the severity level of icing events, covering the north-east of Quebec including Quebec City, Sept-Iles, the east of Saguenay, the lower St Lawrence River and the Gaspe region. Consequently, an icing severity index mapping that represents the climatology of in-cloud atmospheric icing was produced.

  13. Large-Scale Surveys of Snow Depth on Arctic Sea Ice from Operation IceBridge

    NASA Technical Reports Server (NTRS)

    Kurtz, Nathan T.; Farrell, Sinead L.

    2011-01-01

    We show the first results of a large ]scale survey of snow depth on Arctic sea ice from NASA fs Operation IceBridge snow radar system for the 2009 season and compare the data to climatological snow depth values established over the 1954.1991 time period. For multiyear ice, the mean radar derived snow depth is 33.1 cm and the corresponding mean climatological snow depth is 33.4 cm. The small mean difference suggests consistency between contemporary estimates of snow depth with the historical climatology for the multiyear ice region of the Arctic. A 16.5 cm mean difference (climatology minus radar) is observed for first year ice areas suggesting that the increasingly seasonal sea ice cover of the Arctic Ocean has led to an overall loss of snow as the region has transitioned away from a dominantly multiyear ice cover.

  14. Dry Ice Etches Terrain

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1

    Every year seasonal carbon dioxide ice, known to us as 'dry ice,' covers the poles of Mars. In the south polar region this ice is translucent, allowing sunlight to pass through and warm the surface below. The ice then sublimes (evaporates) from the bottom of the ice layer, and carves channels in the surface.

    The channels take on many forms. In the subimage shown here (figure 1) the gas from the dry ice has etched wide shallow channels. This region is relatively flat, which may be the reason these channels have a different morphology than the 'spiders' seen in more hummocky terrain.

    Observation Geometry Image PSP_003364_0945 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 15-Apr-2007. The complete image is centered at -85.4 degrees latitude, 104.0 degrees East longitude. The range to the target site was 251.5 km (157.2 miles). At this distance the image scale is 25.2 cm/pixel (with 1 x 1 binning) so objects 75 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel . The image was taken at a local Mars time of 06:57 PM and the scene is illuminated from the west with a solar incidence angle of 75 degrees, thus the sun was about 15 degrees above the horizon. At a solar longitude of 219.6 degrees, the season on Mars is Northern Autumn.

  15. Mapping and Assessing Variability in the Antarctic Marginal Ice Zone, the Pack Ice and Coastal Polynyas

    NASA Astrophysics Data System (ADS)

    Stroeve, Julienne; Jenouvrier, Stephanie

    2016-04-01

    Sea ice variability within the marginal ice zone (MIZ) and polynyas plays an important role for phytoplankton productivity and krill abundance. Therefore mapping their spatial extent, seasonal and interannual variability is essential for understanding how current and future changes in these biological active regions may impact the Antarctic marine ecosystem. Knowledge of the distribution of different ice types to the total Antarctic sea ice cover may also help to shed light on the factors contributing towards recent expansion of the Antarctic ice cover in some regions and contraction in others. The long-term passive microwave satellite data record provides the longest and most consistent data record for assessing different ice types. However, estimates of the amount of MIZ, consolidated pack ice and polynyas depends strongly on what sea ice algorithm is used. This study uses two popular passive microwave sea ice algorithms, the NASA Team and Bootstrap to evaluate the distribution and variability in the MIZ, the consolidated pack ice and coastal polynyas. Results reveal the NASA Team algorithm has on average twice the MIZ and half the consolidated pack ice area as the Bootstrap algorithm. Polynya area is also larger in the NASA Team algorithm, and the timing of maximum polynya area may differ by as much as 5 months between algorithms. These differences lead to different relationships between sea ice characteristics and biological processes, as illustrated here with the breeding success of an Antarctic seabird.

  16. A toy model of sea ice growth

    NASA Technical Reports Server (NTRS)

    Thorndike, Alan S.

    1992-01-01

    My purpose here is to present a simplified treatment of the growth of sea ice. By ignoring many details, it is possible to obtain several results that help to clarify the ways in which the sea ice cover will respond to climate change. Three models are discussed. The first deals with the growth of sea ice during the cold season. The second describes the cycle of growth and melting for perennial ice. The third model extends the second to account for the possibility that the ice melts away entirely in the summer. In each case, the objective is to understand what physical processes are most important, what ice properties determine the ice behavior, and to which climate variables the system is most sensitive.

  17. Cover Crops

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cover crops are great tools to improve soil quality and health, and great tools to increase carbon sequestration. They are nutrient management tools that can help scavenge nitrate, cycle nitrogen to the following crop, mine NO3 from groundwater, and increase nitrogen use efficiency of cropping syste...

  18. Wall Covering

    NASA Technical Reports Server (NTRS)

    1978-01-01

    The attractive wall covering shown below is one of 132 styles in the Mirror Magic II line offered by The General Tire & Rubber Company, Akron, Ohio. The material is metallized plastic fabric, a spinoff from space programs. Wall coverings are one of many consumer applications of aluminized plastic film technology developed for NASA by a firm later bought by King-Seeley Thermos Company, Winchester, Massachusetts, which now produces the material. The original NASA use was in the Echo 1 passive communications satellite, a "space baloon" made of aluminized mylar; the high reflectivity of the metallized coating enabled relay of communications signals from one Earth station to another by "bouncing" them off the satellite. The reflectivity feature also made the material an extremely efficient insulator and it was subsequently widely used in the Apollo program for such purposes as temperature control of spacecraft components and insulation of tanks for fuels that must be maintained at very low temperatures. I Used as a wall covering, the aluminized material offers extra insulation, reflects light and I resists cracking. In addition to General Tire, King-Seeley also supplies wall covering material to Columbus Coated Fabrics Division of Borden, Incorporated, Columbus, Ohio, among others.

  19. Climate science: A great Arctic ice shelf

    NASA Astrophysics Data System (ADS)

    Domack, Eugene

    2016-02-01

    Newly mapped features on the floor of the Arctic Ocean suggest that the Arctic basin was once covered by a one-kilometre-thick, flowing ice shelf derived from large ice sheets in eastern Siberia, Arctic Canada and the Barents Sea.

  20. Approaching the 2015 Arctic Sea Ice Minimum

    NASA Video Gallery

    As the sun sets over the Arctic, the end of this year’s melt season is quickly approaching and the sea ice cover has already shrunk to the fourth lowest in the satellite record. With possibly some ...

  1. Evidence for a former large ice sheet in the Orville Coast- Ronne Ice Shelf area, Antarctica.

    USGS Publications Warehouse

    Carrara, P.

    1981-01-01

    The Orville Coast area of the Antarctic Peninsula was extensively glacierized in the past. Striations, polished rock surfaces, and erratics on nunatak summits indicate that this area was covered by a broad regional ice sheet whose grounded ice margin was on the continental shelf, in the present-day Ronne Ice Shelf area. If the glacial history of Antarctica has been controlled by eustatic sea-level changes, the destruction of this ice sheet would have been contemporaneous with that of the Ross Sea ice sheet due to the world-wide rise of eustatic sea-level at the end of the Wisconsin glaciation. -Author

  2. Ice streams in the Laurentide Ice Sheet: a new mapping inventory

    NASA Astrophysics Data System (ADS)

    Margold, Martin; Stokes, Chris R.; Clark, Chris D.

    2014-05-01

    Rapidly-flowing ice streams dominate the drainage of continental ice sheets and are a key component of their mass balance. Due to their potential impact on sea level, their activity in the Antarctic and Greenland Ice Sheets has undergone detailed scrutiny in recent decades. However, these observations only cover a fraction of their 'life-span' and the subglacial processes that facilitate their rapid flow are very difficult to observe. To circumvent these problems, numerous workers have highlighted the potential of investigating palaeo-ice streams tracks, preserved in the landform and sedimentary record of former ice sheets. As such, it is becoming increasingly important to know where and when palaeo-ice streams operated. We present a new examination of ice streams in the North American Laurentide Ice Sheet (LIS), which was the largest of the ephemeral Pleistocene ice sheets and where numerous ice streams have been hypothesised. We compile previously-published evidence of ice stream activity and complement it with new mapping to generate the most complete and consistent inventory to date. Our map identifies close to three times as many ice streams (117 in total) compared to previous inventories, and categorises them according to the evidence they left behind, with some locations more speculative than others. We note that LIS ice streams span a broad range of size and shapes. The majority of large ice streams, thought to have operated during the Last Glacial Maximum, are comparable in size and shape to modern Antarctic ice streams, but we note a group of ice streams with low length-to-width ratios that do not have modern-day analogues and might be unique to deglacial conditions in which they operated. This study of Laurentide ice streams considerably refines our understanding of LIS dynamics, but there is a clear requirement for improved dating of ice stream activity.

  3. Characterizing Arctic sea ice topography using high-resolution IceBridge data

    NASA Astrophysics Data System (ADS)

    Petty, Alek A.; Tsamados, Michel C.; Kurtz, Nathan T.; Farrell, Sinead L.; Newman, Thomas; Harbeck, Jeremy P.; Feltham, Daniel L.; Richter-Menge, Jackie A.

    2016-05-01

    We present an analysis of Arctic sea ice topography using high-resolution, three-dimensional surface elevation data from the Airborne Topographic Mapper, flown as part of NASA's Operation IceBridge mission. Surface features in the sea ice cover are detected using a newly developed surface feature picking algorithm. We derive information regarding the height, volume and geometry of surface features from 2009 to 2014 within the Beaufort/Chukchi and Central Arctic regions. The results are delineated by ice type to estimate the topographic variability across first-year and multi-year ice regimes. The results demonstrate that Arctic sea ice topography exhibits significant spatial variability, mainly driven by the increased surface feature height and volume (per unit area) of the multi-year ice that dominates the Central Arctic region. The multi-year ice topography exhibits greater interannual variability compared to the first-year ice regimes, which dominates the total ice topography variability across both regions. The ice topography also shows a clear coastal dependency, with the feature height and volume increasing as a function of proximity to the nearest coastline, especially north of Greenland and the Canadian Archipelago. A strong correlation between ice topography and ice thickness (from the IceBridge sea ice product) is found, using a square-root relationship. The results allude to the importance of ice deformation variability in the total sea ice mass balance, and provide crucial information regarding the tail of the ice thickness distribution across the western Arctic. Future research priorities associated with this new data set are presented and discussed, especially in relation to calculations of atmospheric form drag.

  4. 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

  5. Observational Evidence of a Hemispheric-wide Ice-ocean Albedo Feedback Effect on Antarctic Sea-ice Decay

    NASA Technical Reports Server (NTRS)

    Nihashi, Sohey; Cavalieri, Donald J.

    2007-01-01

    The effect of ice-ocean albedo feedback (a kind of ice-albedo feedback) on sea-ice decay is demonstrated over the Antarctic sea-ice zone from an analysis of satellite-derived hemispheric sea ice concentration and European Centre for Medium-Range Weather Forecasts (ERA-40) atmospheric data for the period 1979-2001. Sea ice concentration in December (time of most active melt) correlates better with the meridional component of the wind-forced ice drift (MID) in November (beginning of the melt season) than the MID in December. This 1 month lagged correlation is observed in most of the Antarctic sea-ice covered ocean. Daily time series of ice , concentration show that the ice concentration anomaly increases toward the time of maximum sea-ice melt. These findings can be explained by the following positive feedback effect: once ice concentration decreases (increases) at the beginning of the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration by the oceanic heat. Results obtained fi-om a simple ice-ocean coupled model also support our interpretation of the observational results. This positive feedback mechanism explains in part the large interannual variability of the sea-ice cover in summer.

  6. Snow and ice products from Suomi NPP VIIRS

    NASA Astrophysics Data System (ADS)

    Key, Jeffrey R.; Mahoney, Robert; Liu, Yinghui; Romanov, Peter; Tschudi, Mark; Appel, Igor; Maslanik, James; Baldwin, Dan; Wang, Xuanji; Meade, Paul

    2013-12-01

    Visible Infrared Imager Radiometer Suite (VIIRS) instrument was launched in October 2011 on the satellite now known as the Suomi National Polar-orbiting Partnership. VIIRS was designed to improve upon the capabilities of the operational Advanced Very High Resolution Radiometer and provide observation continuity with NASA's Earth Observing System's Moderate Resolution Imaging Spectroradiometer (MODIS). VIIRS snow and ice products include sea ice surface temperature, sea ice concentration, sea ice characterization, a binary snow map, and fractional snow cover. Validation results with these "provisional" level maturity products show that ice surface temperature has a root-mean-square error of 0.6-1.0 K when compared to aircraft data and a similar MODIS product, the measurement accuracy and precision of ice concentration are approximately 5% and 15% when compared to passive microwave retrievals, and the accuracy of the binary snow cover (snow/no-snow) maps is generally above 90% when compared to station data. The ice surface temperature and snow cover products meet their accuracy requirements with respect to the Joint Polar Satellite System Level 1 Requirements Document. Sea Ice Characterization, which consists of two age categories, has not been observed to meet the 70% accuracy requirements of ice classification. Given their current performance, the ice surface temperature, snow cover, and sea ice concentration products should be useful for both research and operational applications, while improvements to the sea ice characterization product are needed before it can be used for these applications.

  7. Influence of ice thickness and surface properties on light transmission through Arctic sea ice.

    NASA Astrophysics Data System (ADS)

    Katlein, Christian; Arndt, Stefanie; Nicolaus, Marcel; Jakuba, Michael V.; Laney, Samuel; Elliott, Stephen; Whitcomb, Louis L.; McFarland, Christopher J.; Suman, Stefano; Gerdes, Rüdiger; Boetius, Antje; German, Christopher R.

    2015-04-01

    The observed changes in physical properties of sea ice such as decreased thickness and increased melt pond cover severely impact the energy balance of Arctic sea ice. Increased light transmission leads to increased deposition of solar energy and thus plays a crucial role for sea-ice-melt as well as for the amount and timing of under-ice primary production. Recent developments in underwater technology provide new opportunities to undertake challenging research at the largely inaccessible underside of sea ice. We measured spectral under-ice radiance and irradiance onboard the new Nereid Under-Ice (Nereid-UI) underwater robotic vehicle, during a cruise of the R/V Polarstern to 83°N 6°W in the Arctic Ocean in July 2014. Nereid-UI is a next generation hybrid remotely operated vehicle (H-ROV) designed for both remotely-piloted and autonomous surveys underneath fixed and moving sea ice. Here we present results from the first comprehensive scientific dive of Nereid-UI employing its interdisciplinary sensor suite. We combine under-ice optical measurements with three dimensional under-ice topography (multibeam sonar) and aerial images of the surface conditions. We investigate the influence of spatially varying ice-thickness and surface properties on the spatial variability of light transmittance on floe scale. Our results indicate that surface properties dominate the spatial distribution of the under-ice light field, while sea ice-thickness and snow-depth are most important for mean light levels.

  8. Sea ice motions in the central arctic ice central arctic pack ice as inferred from AVHRR imagery

    NASA Technical Reports Server (NTRS)

    Emery, William; Maslanik, James; Fowler, Charles

    1993-01-01

    Synoptic observations of ice motion in the Arctic Basin are currently limited to those acquired by drifting buoys and, more recently, radar data from ERS-1. Buoys are not uniformly distributed throughout the Arctic, and SAR coverage is limited regionally and temporally due to the data volume, swath width, processing requirements, and power needs of the SAR. Additional ice-motion observations that can map ice responses simultaneously over large portions of the Arctic on daily to weekly time intervals are thus needed to augment the SAR and buoy data and to provide an intermediate-scale measure of ice drift suitable for climatological analyses and ice modeling. Merging the remotely-sensed ice motions with SAR, AVHRR, OLS, and SSM/I imagery permits studies of ice processes over a range of space and time scales. A medium-resolution passive microwave sensor might be ideal for this purpose, but no such satellite will be available in the near future. Combinations of existing data types are thus likely to be our best bet for generating motion fields with a coverage and resolution best suited to climate studies. Principal objectives of this project are to: (1) demonstrate whether sufficient ice features and ice motion existed within the consolidated ice pack to permit motion tracking using AVHRR imagery; (2) determine the limits imposed on AVHRR mapping by cloud cover; and (3) test the applicability of AVHRR-derived motions in studies of ice-atmosphere interactions.

  9. Sea ice pCO2 dynamics and air-ice CO2 fluxes during the Sea Ice Mass Balance in the Antarctic (SIMBA) experiment - Bellingshausen Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Geilfus, N.-X.; Tison, J.-L.; Ackley, S. F.; Galley, R. J.; Rysgaard, S.; Miller, L. A.; Delille, B.

    2014-12-01

    Temporal evolution of pCO2 profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows physical and thermodynamic processes controls the CO2 system in the ice. During the survey, cyclical warming and cooling strongly influenced the physical, chemical, and thermodynamic properties of the ice cover. Two sampling sites with contrasting characteristics of ice and snow thickness were sampled: one had little snow accumulation (from 8 to 25 cm) and larger temperature and salinity variations than the second site, where the snow cover was up to 38 cm thick and therefore better insulated the underlying sea ice. We show that each cooling/warming event was associated with an increase/decrease in the brine salinity, total alkalinity (TA), total dissolved inorganic carbon (TCO2), and in situ brine and bulk ice CO2 partial pressures (pCO2). Thicker snow covers reduced the amplitude of these changes: snow cover influences the sea ice carbonate system by modulating the temperature and therefore the salinity of the sea ice cover. Results indicate that pCO2 was undersaturated with respect to the atmosphere both in the in situ bulk ice (from 10 to 193 μatm) and brine (from 65 to 293 μatm), causing the sea ice to act as a sink for atmospheric CO2 (up to 2.9 mmol m-2 d-1), despite supersaturation of the underlying seawater (up to 462 μatm).

  10. Variability and Trends in Sea Ice Extent and Ice Production in the Ross Sea

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino; Kwok, Ronald; Martin, Seelye; Gordon, Arnold L.

    2011-01-01

    Salt release during sea ice formation in the Ross Sea coastal regions is regarded as a primary forcing for the regional generation of Antarctic Bottom Water. Passive microwave data from November 1978 through 2008 are used to examine the detailed seasonal and interannual characteristics of the sea ice cover of the Ross Sea and the adjacent Bellingshausen and Amundsen seas. For this period the sea ice extent in the Ross Sea shows the greatest increase of all the Antarctic seas. Variability in the ice cover in these regions is linked to changes in the Southern Annular Mode and secondarily to the Antarctic Circumpolar Wave. Over the Ross Sea shelf, analysis of sea ice drift data from 1992 to 2008 yields a positive rate of increase in the net ice export of about 30,000 sq km/yr. For a characteristic ice thickness of 0.6 m, this yields a volume transport of about 20 cu km/yr, which is almost identical, within error bars, to our estimate of the trend in ice production. The increase in brine rejection in the Ross Shelf Polynya associated with the estimated increase with the ice production, however, is not consistent with the reported Ross Sea salinity decrease. The locally generated sea ice enhancement of Ross Sea salinity may be offset by an increase of relatively low salinity of the water advected into the region from the Amundsen Sea, a consequence of increased precipitation and regional glacial ice melt.

  11. Operation IceBridge: Sea Ice Interlude

    NASA Video Gallery

    Sea ice comes in an array of shapes and sizes and has its own ephemeral beauty. Operation IceBridge studies sea ice at both poles, and also runs across interesting formations en route to other targ...

  12. Controls on Arctic sea ice from first-year and multi-year survival rates

    SciTech Connect

    Hunke, Jes

    2009-01-01

    The recent decrease in Arctic sea ice cover has transpired with a significant loss of multi year ice. The transition to an Arctic that is populated by thinner first year sea ice has important implications for future trends in area and volume. Here we develop a reduced model for Arctic sea ice with which we investigate how the survivability of first year and multi year ice control the mean state, variability, and trends in ice area and volume.

  13. The strength anisotropia of sea ice

    SciTech Connect

    Evdokimov, G.N.; Rogachko, S.I.

    1994-12-31

    The hydraulic-engineering structure calculations of sea ice formation force require the sea ice strength data. The strength characteristics values and the types of sea ice formations in view of water depth define the type and the design of future structures in each particular region of supposed construction. The most objective information on the sea ice physical and technical properties can be obtained by field investigations ad the existing methods of their calculations refer to a great number of errors. The accumulated bank of data on studying the sea ice formation strength properties show one that ice as a natural material is of great crystalline structure variety. The level ice fields have a number of particularities. The crystal sizes increase in ice thickness. The crystals consist of fresh-water thin plates 0.5--0.6 mm in thickness oriented by pickle-water interlayers. Difference in thickness of the sea ice cover structure is one of the main causes of the changes strength characteristics layer. Besides that the sea ice strength depends upon the destroying force direction in reference to crystal orientation which characterizes the sea ice anisotropia as a material.

  14. Breakup of Pack Ice, Antarctic Ice Shelf

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Breakup of Pack Ice along the periphery of the Antarctic Ice Shelf (53.5S, 3.0E) produced this mosaic of ice floes off the Antarctic Ice Shelf. Strong offshore winds, probably associated with strong katabatic downdrafts from the interior of the continent, are seen peeling off the edges of the ice shelf into long filamets of sea ice, icebergs, bergy bits and growlers to flow northward into the South Atlantic Ocean. 53.5S, 3.0E

  15. Sea ice transports in the Weddell Sea

    NASA Astrophysics Data System (ADS)

    Harms, Sabine; Fahrbach, Eberhard; Strass, Volker H.

    2001-05-01

    Time series of sea ice draft in the Weddell Sea are evaluated together with hydrographic observations, satellite passive microwave data, and ice drift for estimation of the freshwater fluxes into and out of the Weddell Sea. Ice draft is measured with moored upward looking sonars since 1990 along two transects across the Weddell Gyre. One transect, extending from the tip of the Antarctic Peninsula to Kapp Norvegia, was sampled between 1990 and 1994 and covers the flow into and out of the southern Weddell Sea. The other transect, sampled since 1996 and extending from the Antarctic continent northward along the Greenwich meridian, covers the exchange of water masses between the eastern and the western Weddell Sea. In order to relate results obtained during the different time periods, empirical relationships are established between the length of the sea ice season, derived from the satellite passive microwave data and defined as the number of days per year with the sea ice concentration exceeding 15%, and (1) the annual mean ice draft and (2) the annual mean ice volume transport. By using these empirical relationships, estimates of annual mean ice drafts and ice volume transports are derived at all mooring sites for the period February 1979 through February 1999. Wind and current force a westward ice transport in the coastal areas of the eastern Weddell Sea and a northward ice transport in the west. During the 2-year period 1991/1992 the mean ice volume export from the Weddell Sea is (50 ± 19) × 103 m3 s-1. This freshwater export is representative for a longer-term (20-year) mean and exceeds the average amount of freshwater gained by precipitation and ice shelf melt by about 19×103 m3 s-1, yielding an upper bound for the formation rate of newly ventilated bottom water in the Weddell Sea of 2.6 Sv.

  16. Controls on Arctic sea ice from first-year and multi-year ice survival rates

    NASA Astrophysics Data System (ADS)

    Armour, K.; Bitz, C. M.; Hunke, E. C.; Thompson, L.

    2009-12-01

    The recent decrease in Arctic sea ice cover has transpired with a significant loss of multi-year (MY) ice. The transition to an Arctic that is populated by thinner first-year (FY) sea ice has important implications for future trends in area and volume. We develop a reduced model for Arctic sea ice with which we investigate how the survivability of FY and MY ice control various aspects of the sea-ice system. We demonstrate that Arctic sea-ice area and volume behave approximately as first-order autoregressive processes, which allows for a simple interpretation of September sea-ice in which its mean state, variability, and sensitivity to climate forcing can be described naturally in terms of the average survival rates of FY and MY ice. This model, used in concert with a sea-ice simulation that traces FY and MY ice areas to estimate the survival rates, reveals that small trends in the ice survival rates explain the decline in total Arctic ice area, and the relatively larger loss of MY ice area, over the period 1979-2006. Additionally, our model allows for a calculation of the persistence time scales of September area and volume anomalies. A relatively short memory time scale for ice area (~ 1 year) implies that Arctic ice area is nearly in equilibrium with long-term climate forcing at all times, and therefore observed trends in area are a clear indication of a changing climate. A longer memory time scale for ice volume (~ 5 years) suggests that volume can be out of equilibrium with climate forcing for long periods of time, and therefore trends in ice volume are difficult to distinguish from its natural variability. With our reduced model, we demonstrate the connection between memory time scale and sensitivity to climate forcing, and discuss the implications that a changing memory time scale has on the trajectory of ice area and volume in a warming climate. Our findings indicate that it is unlikely that a “tipping point” in September ice area and volume will be

  17. An ice-ocean coupled model for the Northern Hemisphere

    NASA Technical Reports Server (NTRS)

    Cheng, Abe; Preller, Ruth

    1992-01-01

    The Hibler ice model has been modified and adapted to a domain that includes most of the sea ice-covered areas in the Northern Hemisphere. This model, joined with the Cox ocean model, is developed as an enhancement to the U.S. Navy's sea ice forecasting, PIPS, and is termed PIPS2.0. Generally, the modeled ice edge is consistent with the Navy-NOAA Joint Ice Center weekly analysis, and the modeled ice thickness distribution agrees with submarine sonar data in the central Arctic basin.

  18. Dependences of Generator Parameters on Pulsed Power Ice Breaking

    NASA Astrophysics Data System (ADS)

    Ihara, Satoshi; Kominato, Yuichi; Fukuda, Kazuyuki; Yamabe, Chobei; Ushio, Shuki

    In this research, investigation on breaking of ice using a pulsed power generator as a navigation of ice-breaker at ice-covered ocean, was described. In these experiments, pulsed arc discharge was formed by Marx generator. In order to investigate the dependence of input energy required for ice breaking on circuit parameters of generator, the capacitance of generator was changed. The input energy for ice-breaking was calculated from waveforms of electric power. It was found that the input energy for ice-breaking decreased as the peak power increased with decrease of the capacitance of generator.

  19. Ice-dependent winter survival of juvenile Atlantic salmon

    PubMed Central

    Hedger, R D; Næsje, T F; Fiske, P; Ugedal, O; Finstad, A G; Thorstad, E B

    2013-01-01

    Changes in snow and ice conditions are some of the most distinctive impacts of global warming in cold temperate and Arctic regions, altering the environment during a critical period for survival for most animals. Laboratories studies have suggested that reduced ice cover may reduce the survival of stream dwelling fishes in Northern environments. This, however, has not been empirically investigated in natural populations in large rivers. Here, we examine how the winter survival of juvenile Atlantic salmon in a large natural river, the River Alta (Norway, 70°N), is affected by the presence or absence of surface ice. Apparent survival rates for size classes corresponding to parr and presmolts were estimated using capture-mark-recapture and Cormack-Jolly-Seber models for an ice-covered and an ice-free site. Apparent survival (Φ) in the ice-covered site was greater than in the ice-free site, but did not depend on size class (0.64 for both parr and presmolt). In contrast, apparent survival in the ice-free site was lower for larger individuals (0.33) than smaller individuals (0.45). The over-winter decline in storage energy was greater for the ice-free site than the ice-covered site, suggesting that environmental conditions in the ice-free site caused a strong depletion in energy reserves likely affecting survival. Our findings highlight the importance of surface ice for the winter survival of juvenile fish, thus, underpinning that climate change, by reducing ice cover, may have a negative effect on the survival of fish adapted to ice-covered habitats during winter. PMID:23532172

  20. Drag coefficients for winter Antarctic pack ice

    NASA Technical Reports Server (NTRS)

    Wamser, Christian; Martinson, Douglas G.

    1993-01-01

    Air-ice and ice-water drag coefficients referenced to 10-m-height winds for winter Antarctic pack ice based on measurements made from R/V Polarstern during the Winter Weddell Sea Project, 1986 (WWSP-86), and from R/V Akademik Fedorov during the Winter Weddell Gyre Study, 1989 (WWGS-89), are presented. The optimal values of the air-ice drag coefficients, made from turbulent flux measurements, are (1.79 +/- 0.06) x 10 exp -3 for WWSP-86 and (1.45 +/- 0.09) x 10 exp -3 for WWGS-89. A single ice-water drag coefficient for both WWSP-86 and WWGS-89, estimated from periods of ice drift throught to represent free-drift conditions, is (1.13 +/- 0.26) x 10 exp -3, and the ice-water turning angle is 18 +/- 18 deg. It is suggested that for a typical Antarctic winter pack ice cover, the ice cover reduces the momentum flux from the atmosphere to the ocean by about 33 percent.

  1. Correlation of Cyfra 21-1 levels in saliva and serum with CK19 mRNA expression in oral squamous cell carcinoma.

    PubMed

    Malhotra, Rewa; Urs, Aadithya B; Chakravarti, Anita; Kumar, Suman; Gupta, V K; Mahajan, Bhawna

    2016-07-01

    Oral squamous cell carcinoma (OSCC) accounts for 90 % of malignant lesions of oral cavity. The study assessed the potential of Cyfra 21-1 as a tumor marker in OSCC. The study included 50 patients of OSCC to evaluate levels of Cyfra 21-1 in serum and saliva by electrochemiluminescent immunoassay (ECLIA) and CK19 messenger RNA (mRNA) expression in tissue by florescent quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR) along with healthy individuals as control. The salivary and serum Cyfra 21-1 levels in patients of OSCC were significantly higher compared to controls (p value < 0.01). There was a 2.75-fold increase in CK19 mRNA expression in OSCC cases compared to controls. A significant positive correlation was found between serum and salivary Cyfra 21-1, serum Cyfra 21-1, and CK19 mRNA expression and between salivary Cyfra 21-1 and CK19 mRNA expression. Among these, correlation between serum and salivary Cyfra 21-1 was highly significant. Salivary and serum Cyfra 21-1 showed significantly elevated levels in grade II OSCC compared to grade I histopathologically. Elevated levels of salivary Cyfra 21-1 were associated with recurrence in OSCC patients. Reverse operating curve constructed using 3 ng/ml as a cutoff for serum Cyfra 21-1 revealed the sensitivity and specificity to be 88 and 78.2 %, respectively. Using a cutoff value of 8.5 ng/ml for salivary Cyfra 21-1, the sensitivity was found to be 93.8 % and specificity 84.3 %. We advocate salivary Cyfra 21-1 as a better diagnostic marker over serum Cyfra 21-1 as well as a potential marker in the prognosis of OSCC. PMID:26779624

  2. Variability of Arctic Sea Ice as Determined from Satellite Observations

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    1999-01-01

    The compiled, quality-controlled satellite multichannel passive-microwave record of polar sea ice now spans over 18 years, from November 1978 through December 1996, and is revealing considerable information about the Arctic sea ice cover and its variability. The information includes data on ice concentrations (percent areal coverages of ice), ice extents, ice melt, ice velocities, the seasonal cycle of the ice, the interannual variability of the ice, the frequency of ice coverage, and the length of the sea ice season. The data reveal marked regional and interannual variabilities, as well as some statistically significant trends. For the north polar ice cover as a whole, maximum ice extents varied over a range of 14,700,000 - 15,900,000 sq km, while individual regions experienced much greater percent variations, for instance, with the Greenland Sea having a range of 740,000 - 1,110,000 sq km in its yearly maximum ice coverage. In spite of the large variations from year to year and region to region, overall the Arctic ice extents showed a statistically significant, 2.80% / decade negative trend over the 18.2-year period. Ice season lengths, which vary from only a few weeks near the ice margins to the full year in the large region of perennial ice coverage, also experienced interannual variability, along with spatially coherent overall trends. Linear least squares trends show the sea ice season to have lengthened in much of the Bering Sea, Baffin Bay, the Davis Strait, and the Labrador Sea, but to have shortened over a much larger area, including the Sea of Okhotsk, the Greenland Sea, the Barents Sea, and the southeastern Arctic.

  3. Environmental predictors of ice seal presence in the Bering Sea.

    PubMed

    Miksis-Olds, Jennifer L; Madden, Laura E

    2014-01-01

    Ice seals overwintering in the Bering Sea are challenged with foraging, finding mates, and maintaining breathing holes in a dark and ice covered environment. Due to the difficulty of studying these species in their natural environment, very little is known about how the seals navigate under ice. Here we identify specific environmental parameters, including components of the ambient background sound, that are predictive of ice seal presence in the Bering Sea. Multi-year mooring deployments provided synoptic time series of acoustic and oceanographic parameters from which environmental parameters predictive of species presence were identified through a series of mixed models. Ice cover and 10 kHz sound level were significant predictors of seal presence, with 40 kHz sound and prey presence (combined with ice cover) as potential predictors as well. Ice seal presence showed a strong positive correlation with ice cover and a negative association with 10 kHz environmental sound. On average, there was a 20-30 dB difference between sound levels during solid ice conditions compared to open water or melting conditions, providing a salient acoustic gradient between open water and solid ice conditions by which ice seals could orient. By constantly assessing the acoustic environment associated with the seasonal ice movement in the Bering Sea, it is possible that ice seals could utilize aspects of the soundscape to gauge their safe distance to open water or the ice edge by orienting in the direction of higher sound levels indicative of open water, especially in the frequency range above 1 kHz. In rapidly changing Arctic and sub-Arctic environments, the seasonal ice conditions and soundscapes are likely to change which may impact the ability of animals using ice presence and cues to successfully function during the winter breeding season. PMID:25229453

  4. Environmental Predictors of Ice Seal Presence in the Bering Sea

    PubMed Central

    Miksis-Olds, Jennifer L.

    2014-01-01

    Ice seals overwintering in the Bering Sea are challenged with foraging, finding mates, and maintaining breathing holes in a dark and ice covered environment. Due to the difficulty of studying these species in their natural environment, very little is known about how the seals navigate under ice. Here we identify specific environmental parameters, including components of the ambient background sound, that are predictive of ice seal presence in the Bering Sea. Multi-year mooring deployments provided synoptic time series of acoustic and oceanographic parameters from which environmental parameters predictive of species presence were identified through a series of mixed models. Ice cover and 10 kHz sound level were significant predictors of seal presence, with 40 kHz sound and prey presence (combined with ice cover) as potential predictors as well. Ice seal presence showed a strong positive correlation with ice cover and a negative association with 10 kHz environmental sound. On average, there was a 20–30 dB difference between sound levels during solid ice conditions compared to open water or melting conditions, providing a salient acoustic gradient between open water and solid ice conditions by which ice seals could orient. By constantly assessing the acoustic environment associated with the seasonal ice movement in the Bering Sea, it is possible that ice seals could utilize aspects of the soundscape to gauge their safe distance to open water or the ice edge by orienting in the direction of higher sound levels indicative of open water, especially in the frequency range above 1 kHz. In rapidly changing Arctic and sub-Arctic environments, the seasonal ice conditions and soundscapes are likely to change which may impact the ability of animals using ice presence and cues to successfully function during the winter breeding season. PMID:25229453

  5. Sedimentary record of ice divide migration and ice streams in the Keewatin core region of the Laurentide Ice Sheet

    NASA Astrophysics Data System (ADS)

    Hodder, Tyler J.; Ross, Martin; Menzies, John

    2016-06-01

    The Aberdeen Lake region of central mainland Nunavut is a former core region of the Laurentide Ice Sheet that is characterized by streamlined glacial landforms classified into multiple crosscutting flow sets and near continuous till blanket. The presence of widespread till near the centre of the Keewatin Ice Dome raises questions about its origin. Detailed drillcore logging revealed a complex stratigraphy consisting of at least 6 till units, variably preserved across the study area. Till provenance analysis indicates deposition by near opposite-trending ice flow phases, interpreted as evidence of reconfiguration of the Keewatin Ice Divide. At the surface, large north-northwesterly aligned landforms are present across the study area. The till stratigraphy within these landforms indicates the same NNW ice flow phase is responsible for considerable till production. This ice flow phase is also correlated to a long regional dispersal train of erratics toward the Gulf of Boothia. The production of an extensive, thick (~ 12 m), till sheet during the NNW-trending ice flow phase occurred far from the ice margin at a time of extensive ice cover of mainland Nunavut, likely from an east-west oriented ice divide. A deglacial westerly trending ice flow phase formed small drumlins atop the larger NNW streamlined till ridges and deposited a surficial till unit that is too thin to mask the NNW flow set across the study area. It is proposed that the Boothia paleo-ice stream catchment area propagated deep into the Laurentide Ice Sheet and contributed to significant till production in this core region of the Keewatin Sector prior to the westerly ice flow shift. The apparent relationship between till thickness and the size of the associated or correlated drumlins, flow sets, and dispersal trains indicates complex erosion/deposition interplay is involved in the formation of streamlined subglacial landforms.

  6. Modern shelf ice, equatorial Aeolis Quadrangle, Mars

    NASA Technical Reports Server (NTRS)

    Brakenridge, G. R.

    1993-01-01

    As part of a detailed study of the geological and geomorphological evolution of Aeolis Quadrangle, I have encountered evidence suggesting that near surface ice exists at low latitudes and was formed by partial or complete freezing of an inland sea. The area of interest is centered at approximately -2 deg, 196 deg. As seen in a suite of Viking Orbiter frames obtained at a range of approximately 600 km, the plains surface at this location is very lightly cratered or uncratered, and it is thus of late Amazonian age. Extant topographic data indicate that the Amazonian plains at this location occupy a trough whose surface lies at least 1000 m below the Mars datum. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. In either case, the thin (a few meters at most) high albedo, low thermal inertia cover of aeolian materials was instrumental in allowing ice preservation, and at least the lower portions of this dust cover may be cemented by water ice. Detailed mapping using Viking stereopairs and quantitative comparisons to terrestrial shelf ice geometries are underway.

  7. Interferometric System for Measuring Thickness of Sea Ice

    NASA Technical Reports Server (NTRS)

    Hussein, Ziad; Jordan, Rolando; McDonald, Kyle; Holt, Benjamin; Huang, John; Kugo, Yasuo; Ishimaru, Akira; Jaruwatanadilok, Semsak; Akins, Torry; Gogineni, Prasad

    2006-01-01

    The cryospheric advanced sensor (CAS) is a developmental airborne (and, potentially, spaceborne) radar-based instrumentation system for measuring and mapping the thickness of sea ice. A planned future version of the system would also provide data on the thickness of snow covering sea ice. Frequent measurements of the thickness of polar ocean sea ice and its snow cover on a synoptic scale are critical to understanding global climate change and ocean circulation.

  8. On the measure of sea ice area from sea ice concentration data sets

    NASA Astrophysics Data System (ADS)

    Boccolari, Mauro; Parmiggiani, Flavio

    2015-10-01

    The measure of sea ice surface variability provides a fundamental information on the climatology of the Arctic region. Sea ice extension is conventionally measured by two parameters, i.e. Sea Ice Extent (SIE) and Sea Ice Area (SIA), both parameters being derived from Sea Ice Concentration (SIC) data sets. In this work a new parameter (CSIA) is introduced, which takes into account only the compact sea-ice, which is defined as the sea-ice having concentration at least equal the 70%. Aim of this study is to compare the performances of the two parameters, SIA and CSIA, in analyzing the trends of three monthly time-series of the whole Arctic region. The SIC data set used in this study was produced by the Institute of Environmental Physics of the University of Bremen and covers the period January 2003 - December 2014, i.e. the period in which the data set is built using the new AMSR passive microwave sensor.

  9. Coincident multiscale estimates of Arctic sea ice thickness

    NASA Astrophysics Data System (ADS)

    Gardner, Joan; Richter-Menge, Jackie; Farrell, Sinead; Brozena, John

    2012-02-01

    Recent dramatic changes in the characteristics of the Arctic sea ice cover have sparked interest and concern from a wide range of disciplines including socioeconomics, maritime safety and security, and resource management, as well as basic research science. Though driven by different priorities, common to all is the demand for an improved ability to monitor and forecast changes in the sea ice cover. Key to meeting this demand is further improvement in the quality of observations collected from remote platforms. Satellites provide an important platform for instruments designed to monitor basin-wide changes in the volume of the ice cover, a function of ice extent and thickness. Remote techniques to monitor sea ice extent in all seasons are well developed—these observations reveal a dramatic decline in summer sea ice extent since 1979, when satellite records became available. Further, they indicate that the decline has been facilitated by a dramatic decrease in the extent of perennial (i.e., multiyear) ice. Combined estimates of ice thickness derived from submarine records between 1958 and 2000, and Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry from 2003 to 2008, provide the longest-term record of sea ice thickness observations. These data suggest a decrease in the mean overall thickness of the sea ice over a region covering about 38% of the Arctic Ocean.

  10. Ice-shelf melting around Antarctica.

    PubMed

    Rignot, E; Jacobs, S; Mouginot, J; Scheuchl, B

    2013-07-19

    We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines. PMID:23765278

  11. MODIS Snow and Sea Ice Products

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Riggs, George A.; Salomonson, Vincent V.

    2004-01-01

    In this chapter, we describe the suite of Earth Observing System (EOS) Moderate-Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua snow and sea ice products. Global, daily products, developed at Goddard Space Flight Center, are archived and distributed through the National Snow and Ice Data Center at various resolutions and on different grids useful for different communities Snow products include binary snow cover, snow albedo, and in the near future, fraction of snow in a 5OO-m pixel. Sea ice products include ice extent determined with two different algorithms, and sea ice surface temperature. The algorithms used to develop these products are described. Both the snow and sea ice products, available since February 24,2000, are useful for modelers. Validation of the products is also discussed.

  12. Ice-Shelf Melting Around Antarctica

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Jacobs, S.; Mouginot, J.; Scheuchl, B.

    2013-07-01

    We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines.

  13. Interannual variability in sea-ice thickness in the pack-ice zone off Lützow-Holm Bay, East Antarctica

    NASA Astrophysics Data System (ADS)

    Sugimoto, Fuko; Tamura, Takeshi; Shimoda, Haruhito; Uto, Shotaro; Simizu, Daisuke; Tateyama, Kazutaka; Hoshino, Seita; Ozeki, Toshihiro; Fukamachi, Yasushi; Ushio, Shuki; Ohshima, Kay I.

    2016-03-01

    Under the Japanese Antarctic Research Expedition (JARE) program, sea-ice thickness has been routinely monitored off Lützow-Holm Bay (East Antarctica) during the summer (mid-December to early January) since 2000/01, using an electromagnetic induction (EM) instrument onboard the icebreaker Shirase. Analysis of these data over a 10-year period, combined with visual observations using a simplified form of the ASPeCt (Antarctic Sea ice Processes and Climate) protocol, suggests a strong interannual variability in sea-ice thickness in this region. For the repeat pack-ice observation area, where the sea-ice thickness averaged over the nine seasons is ∼1.9 m, mean thicknesses of observed sea-ice in 2010/11 and 2011/12 are exceptionally large, at ∼3.3 and ∼5.8 m, respectively. This result is strongly related to regional patterns of sea ice dynamics. Ice convergence caused by anomalous northerly winds was particularly high in 2011/12, suggesting that the extremely thick ice observed in that season resulted largely from sea-ice deformation processes (including pressure ridging). Longer-term analysis of data from the past 34 years confirms that sea-ice conditions and thickness off Lützow-Holm Bay in summer are determined mainly by the large-scale pattern of atmospheric pressure in December.

  14. Spreading of oil spilled under ice

    SciTech Connect

    Yapa, P.D.; Chowdhury, T. )

    1990-12-01

    A new set of equations is presented to describe the process of oil spreading under ice in clam waters. These equations consider the gravity (buoyancy)-inertia phase, the gravity (buoyancy)-viscous phase, and the termination of spreading during the buoyancy-surface-tension phase. The derivation considers both the constant discharge mode and the constant volume mode. Therefore, a complete description of the spreading phenomena from the time of initial spill to the termination of spreading is presented. Laboratory experiments were conducted using both real ice covers in a cold room and artificial ice covers. The experiments included different ice-cover roughnesses from smooth to rough, oils of different viscosities, and a variety of discharge conditions. The experimental data show close agreement with the theory. These equations can be used during cleanup or environmental impact assessment to estimate the area of an oil slick with respect to time.

  15. Sea Ice Concentration and Extent

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2014-01-01

    Among the most seasonal and most dynamic parameters on the surface of the Earth is sea ice which at any one time covers about 3-6% of the planet. In the Northern Hemisphere, sea ice grows in extent from about 6 x 10(exp 6) sq km to 16 x 10(exp 6) sq km, while in the Southern Hemisphere, it grows from about 3 x 10(exp 6) sq km to about 19 x 10(exp 6) sq km (Comiso, 2010; Gloersen et al., 1992). Sea ice is up to about 2-3 m thick in the Northern Hemisphere and about 1 m thick in the Southern Hemisphere (Wadhams, 2002), and compared to the average ocean depth of about 3 km, it is a relatively thin, fragile sheet that can break due to waves and winds or melt due to upwelling of warm water. Being constantly advected by winds, waves, and currents, sea ice is very dynamic and usually follows the directions of the many gyres in the polar regions. Despite its vast expanse, the sea ice cover was previously left largely unstudied and it was only in recent years that we have understood its true impact and significance as related to the Earths climate, the oceans, and marine life.

  16. Sea ice motions in the Central Arctic pack ice as inferred from AVHRR imagery

    NASA Technical Reports Server (NTRS)

    Emery, William; Maslanik, James; Fowler, Charles

    1995-01-01

    Synoptic observations of ice motion in the Arctic Basin are currently limited to those acquired by drifting buoys and, more recently, radar data from ERS-1. Buoys are not uniformly distributed throughout the Arctic, and SAR coverage is currently limited regionally and temporally due to the data volume, swath width, processing requirements, and power needs of the SAR. Additional ice-motion observations that can map ice responses simultaneously over large portions of the Arctic on daily to weekly time intervals are thus needed to augment the SAR and buoys data and to provide an intermediate-scale measure of ice drift suitable for climatological analyses and ice modeling. Principal objectives of this project were to: (1) demonstrate whether sufficient ice features and ice motion existed within the consolidated ice pack to permit motion tracking using AVHRR imagery; (2) determine the limits imposed on AVHRR mapping by cloud cover; and (3) test the applicability of AVHRR-derived motions in studies of ice-atmosphere interactions. Each of these main objectives was addressed. We conclude that AVHRR data, particularly when blended with other available observations, provide a valuable data set for studying sea ice processes. In a follow-on project, we are now extending this work to cover larger areas and to address science questions in more detail.

  17. Satellite-derived ice data sets no. 2: Arctic monthly average microwave brightness temperatures and sea ice concentrations, 1973-1976

    NASA Technical Reports Server (NTRS)

    Parkinson, C. L.; Comiso, J. C.; Zwally, H. J.

    1987-01-01

    A summary data set for four years (mid 70's) of Arctic sea ice conditions is available on magnetic tape. The data include monthly and yearly averaged Nimbus 5 electrically scanning microwave radiometer (ESMR) brightness temperatures, an ice concentration parameter derived from the brightness temperatures, monthly climatological surface air temperatures, and monthly climatological sea level pressures. All data matrices are applied to 293 by 293 grids that cover a polar stereographic map enclosing the 50 deg N latitude circle. The grid size varies from about 32 X 32 km at the poles to about 28 X 28 km at 50 deg N. The ice concentration parameter is calculated assuming that the field of view contains only open water and first-year ice with an ice emissivity of 0.92. To account for the presence of multiyear ice, a nomogram is provided relating the ice concentration parameter, the total ice concentration, and the fraction of the ice cover which is multiyear ice.

  18. Trend analysis of Arctic sea ice extent

    NASA Astrophysics Data System (ADS)

    Silva, M. E.; Barbosa, S. M.; Antunes, Luís; Rocha, Conceição

    2009-04-01

    The extent of Arctic sea ice is a fundamental parameter of Arctic climate variability. In the context of climate change, the area covered by ice in the Arctic is a particularly useful indicator of recent changes in the Arctic environment. Climate models are in near universal agreement that Arctic sea ice extent will decline through the 21st century as a consequence of global warming and many studies predict a ice free Arctic as soon as 2012. Time series of satellite passive microwave observations allow to assess the temporal changes in the extent of Arctic sea ice. Much of the analysis of the ice extent time series, as in most climate studies from observational data, have been focussed on the computation of deterministic linear trends by ordinary least squares. However, many different processes, including deterministic, unit root and long-range dependent processes can engender trend like features in a time series. Several parametric tests have been developed, mainly in econometrics, to discriminate between stationarity (no trend), deterministic trend and stochastic trends. Here, these tests are applied in the trend analysis of the sea ice extent time series available at National Snow and Ice Data Center. The parametric stationary tests, Augmented Dickey-Fuller (ADF), Phillips-Perron (PP) and the KPSS, do not support an overall deterministic trend in the time series of Arctic sea ice extent. Therefore, alternative parametrizations such as long-range dependence should be considered for characterising long-term Arctic sea ice variability.

  19. Melt ponds and marginal ice zone from new algorithm of sea ice concentration retrieval

    NASA Astrophysics Data System (ADS)

    Repina, Irina; Tikhonov, Vasiliy; Komarova, Nataliia; Raev, Mikhail; Sharkov, Evgeniy

    2016-04-01

    Studies of spatial and temporal properties of sea ice distribution in polar regions help to monitor global environmental changes and reveal their natural and anthropogenic factors, as well as make forecasts of weather, marine transportation and fishing conditions, assess perspectives of mineral mining on the continental shelf, etc. Contact methods of observation are often insufficient to meet the goals, very complicated technically and organizationally and not always safe for people involved. Remote sensing techniques are believed to be the best alternative. Its include monitoring of polar regions by means of passive microwave sensing with the aim to determine spatial distribution, types, thickness and snow cover of ice. However, the algorithms employed today to retrieve sea ice characteristics from passive microwave sensing data for different reasons give significant errors, especially in summer period and also near ice edges and in cases of open ice. A new algorithm of sea ice concentration retrieval in polar regions from satellite microwave radiometry data is discussed. Beside estimating sea ice concentration, the algorithm makes it possible to indicate ice areas with melting snow and melt ponds. Melt ponds are an important element of the Arctic climate system. Covering up to 50% of the surface of drifting ice in summer, they are characterized by low albedo values and absorb several times more incident shortwave radiation than the rest of the snow and ice cover. The change of melt ponds area in summer period 1987-2015 is investigated. The marginal ice zone (MIZ) is defined as the area where open ocean processes, including specifically ocean waves, alter significantly the dynamical properties of the sea ice cover. Ocean wave fields comprise short waves generated locally and swell propagating from the large ocean basins. Depending on factors like wind direction and ocean currents, it may consist of anything from isolated, small and large ice floes drifting over a

  20. Cover Picture.

    PubMed

    Krömer; Rios-Carreras; Fuhrmann; Musch; Wunderlin; Debaerdemaeker; Mena-Osteritz; Bäuerle

    2000-10-01

    The cover picture shows the synthesis of novel conjugated macrocycles assembled from oligothiophenes bearing terminal acetylene groups. Under pseudo-high-dilution conditions the oxidative cyclooligomerization first gives the oligothiophenediynes, the precursors to the new class of alpha-cyclo[n]thiophenes. The detailed structure of macrocycles with up to 76 ring members and cavities of up to 3 nm could be investigated by means of X-ray structure analysis, scanning tunneling microscopy, and quantum chemical calculations (see the molecular model top right). The novel rings combine the excellent electronic properties of the corresponding linearly conjugated oligomers with the possibility of complexing large organic guest molecules or other objects (the tower of the Cathedral at Ulm represents a nanometer-sized, rodlike entity), which should have new fundamental properties and applications. The background shows the image obtained by scanning electron microscopy of a self-assembled and perfectly ordered monolayer of macrocycles on a graphite surface. More on these fascinating nanometer-sized rings can be found in the communication by P. Bäuerle et al. on p. 3481 ff. PMID:11091367

  1. Observations of Recent Arctic Sea Ice Volume Loss and Its Impact on Ocean-Atmosphere Energy Exchange and Ice Production

    NASA Technical Reports Server (NTRS)

    Kurtz, N. T.; Markus, T.; Farrell, S. L.; Worthen, D. L.; Boisvert, L. N.

    2011-01-01

    Using recently developed techniques we estimate snow and sea ice thickness distributions for the Arctic basin through the combination of freeboard data from the Ice, Cloud, and land Elevation Satellite (ICESat) and a snow depth model. These data are used with meteorological data and a thermodynamic sea ice model to calculate ocean-atmosphere heat exchange and ice volume production during the 2003-2008 fall and winter seasons. The calculated heat fluxes and ice growth rates are in agreement with previous observations over multiyear ice. In this study, we calculate heat fluxes and ice growth rates for the full distribution of ice thicknesses covering the Arctic basin and determine the impact of ice thickness change on the calculated values. Thinning of the sea ice is observed which greatly increases the 2005-2007 fall period ocean-atmosphere heat fluxes compared to those observed in 2003. Although there was also a decline in sea ice thickness for the winter periods, the winter time heat flux was found to be less impacted by the observed changes in ice thickness. A large increase in the net Arctic ocean-atmosphere heat output is also observed in the fall periods due to changes in the areal coverage of sea ice. The anomalously low sea ice coverage in 2007 led to a net ocean-atmosphere heat output approximately 3 times greater than was observed in previous years and suggests that sea ice losses are now playing a role in increasing surface air temperatures in the Arctic.