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Sample records for seasonal ice zone

  1. Seasonal Ice Zone Reconnaissance Surveys Coordination and Ocean Profiles

    DTIC Science & Technology

    2015-09-30

    local formation of the fresh layer by ice melt . This may have implications for the fate of freshwater in the Beaufort Gyre as the SIZ changes. IMPACT...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Seasonal Ice Zone Reconnaissance Surveys Coordination and...for the coordination of and participation in the Seasonal Ice Zone Reconnaissance Surveys (SIZRS) program of repeated ocean, ice , and atmospheric

  2. Aircraft Surveys of the Beaufort Sea Seasonal Ice Zone

    NASA Astrophysics Data System (ADS)

    Morison, J.

    2016-02-01

    The Seasonal Ice Zone Reconnaissance Surveys (SIZRS) is a program of repeated ocean, ice, and atmospheric measurements across the Beaufort-Chukchi sea seasonal sea ice zone (SIZ) utilizing US Coast Guard Arctic Domain Awareness (ADA) flights of opportunity. The SIZ is the region between maximum winter sea ice extent and minimum summer sea ice extent. As such, it contains the full range of positions of the marginal ice zone (MIZ) where sea ice interacts with open water. The increasing size and changing air-ice-ocean properties of the SIZ are central to recent reductions in Arctic sea ice extent. The changes in the interplay among the atmosphere, ice, and ocean require a systematic SIZ observational effort of coordinated atmosphere, ice, and ocean observations covering up to interannual time-scales, Therefore, every year beginning in late Spring and continuing to early Fall, SIZRS makes monthly flights across the Beaufort Sea SIZ aboard Coast Guard C-130H aircraft from USCG Air Station Kodiak dropping Aircraft eXpendable CTDs (AXCTD) and Aircraft eXpendable Current Profilers (AXCP) for profiles of ocean temperature, salinity and shear, dropsondes for atmospheric temperature, humidity, and velocity profiles, and buoys for atmosphere and upper ocean time series. Enroute measurements include IR imaging, radiometer and lidar measurements of the sea surface and cloud tops. SIZRS also cooperates with the International Arctic Buoy Program for buoy deployments and with the NOAA Earth System Research Laboratory atmospheric chemistry sampling program on board the aircraft. Since 2012, SIZRS has found that even as SIZ extent, ice character, and atmospheric forcing varies year-to-year, the pattern of ocean freshening and radiative warming south of the ice edge is consistent. The experimental approach, observations and extensions to other projects will be discussed.

  3. Contrasts in Sea Ice Deformation and Production in the Arctic Seasonal and Perennial Ice Zones

    NASA Technical Reports Server (NTRS)

    Kwok, K.

    2006-01-01

    Four years (1997-2000) of RADARSAT Geophysical Processor System (RGPS) data are used to contrast the sea ice deformation and production regionally, and in the seasonal (SIZ) and perennial (PIZ) ice zones. Ice production is of seasonal ice in openings during the winter. Three-day estimates of these quantities are provided within Lagrangian elements initially 10 km on a side. A distinct seasonal cycle is seen in both zones with these estimates highest in the late fall and with seasonal minimums in the midwinter. Regional divergence over the winter could be up to 30%. Spatially, the highest deformation is seen in the SIZ north of coastal Alaska. Both ice deformation and production are higher in the SIZ: deformation-related ice production in the SIZ (approx.0.5 m) is 1.5-2.3 times that of the PIZ (approx.0.3 m): this is connected to ice strength and thickness. Atmospheric forcing and boundary layer structure contribute to only the seasonal and interannual variability. Seasonal ice growth in ice fractures accounts for approx.25-40% of the total ice production of the Arctic Ocean. Uncertainties in these estimates are discussed. By itself, this deformation-ice production relationship could be considered a negative feedback when thickness is perturbed. However, the overall effect on ice production in the face of increasing seasonal and thinner/weaker ice coverage could be modified by local destabilization of the water column promoting overturning of warmer water due to increased brine rejection; and the upwelling of the pynocline associated with increased occurrence of large shear motion in sea ice. Divergence is shown to be negligibly correlated to cyclonic motion in summer and winter in both ice zones.

  4. Contrasts in Sea Ice Deformation and Production in the Arctic Seasonal and Perennial Ice Zones

    NASA Technical Reports Server (NTRS)

    Kwok, K.

    2006-01-01

    Four years (1997-2000) of RADARSAT Geophysical Processor System (RGPS) data are used to contrast the sea ice deformation and production regionally, and in the seasonal (SIZ) and perennial (PIZ) ice zones. Ice production is of seasonal ice in openings during the winter. Three-day estimates of these quantities are provided within Lagrangian elements initially 10 km on a side. A distinct seasonal cycle is seen in both zones with these estimates highest in the late fall and with seasonal minimums in the midwinter. Regional divergence over the winter could be up to 30%. Spatially, the highest deformation is seen in the SIZ north of coastal Alaska. Both ice deformation and production are higher in the SIZ: deformation-related ice production in the SIZ (approx.0.5 m) is 1.5-2.3 times that of the PIZ (approx.0.3 m): this is connected to ice strength and thickness. Atmospheric forcing and boundary layer structure contribute to only the seasonal and interannual variability. Seasonal ice growth in ice fractures accounts for approx.25-40% of the total ice production of the Arctic Ocean. Uncertainties in these estimates are discussed. By itself, this deformation-ice production relationship could be considered a negative feedback when thickness is perturbed. However, the overall effect on ice production in the face of increasing seasonal and thinner/weaker ice coverage could be modified by local destabilization of the water column promoting overturning of warmer water due to increased brine rejection; and the upwelling of the pynocline associated with increased occurrence of large shear motion in sea ice. Divergence is shown to be negligibly correlated to cyclonic motion in summer and winter in both ice zones.

  5. Contrasts in Sea Ice Formation and Production in the Arctic Seasonal and Perennial Ice Zones

    NASA Technical Reports Server (NTRS)

    Kwok, R.

    2006-01-01

    Four years (1997-2000) of RADARSAT Geophysical Processor System (RGPS) data are used to contrast the sea ice deformation and production regionally, and in the seasonal (SIZ) and perennial (PIZ) ice zones. Ice production is of seasonal ice in openings during the winter. 3-day estimates of these quantities are provided within Lagrangian elements initially 10 km on a side. A distinct seasonal cycle is seen in both zones with these estimates highest in the late fall and with seasonal minimums in the mid-winter. Regional divergence over the winter could be up to 30%. Spatially, the highest deformation is in the SIZ north of coastal Alaska. Both ice deformation and production are higher in the SIZ: deformation-related ice production in the SIZ (approx.0.5 m) is 1.5-2.3 times that of the PIZ (approx.0.3 m) - this is connected to ice strength and thickness. Atmospheric forcing and boundary layer structure contribute to only the seasonal and interannual variability. Seasonal ice growth in ice fractures accounts for approx.25-40% of the total ice production of the Arctic Ocean. By itself, this deformation-ice production relationship could be considered a negative feedback when thickness is perturbed. However, the overall effect on ice production in the face of increasing seasonal and thinner/weaker ice coverage could be modified by: local destabilization of the water column promoting overturning of warmer water due to increased brine rejection; and, the upwelling of the pynocline associated with increased occurrence of large shear motion in sea ice.

  6. Contrasts in Sea Ice Formation and Production in the Arctic Seasonal and Perennial Ice Zones

    NASA Technical Reports Server (NTRS)

    Kwok, R.

    2006-01-01

    Four years (1997-2000) of RADARSAT Geophysical Processor System (RGPS) data are used to contrast the sea ice deformation and production regionally, and in the seasonal (SIZ) and perennial (PIZ) ice zones. Ice production is of seasonal ice in openings during the winter. 3-day estimates of these quantities are provided within Lagrangian elements initially 10 km on a side. A distinct seasonal cycle is seen in both zones with these estimates highest in the late fall and with seasonal minimums in the mid-winter. Regional divergence over the winter could be up to 30%. Spatially, the highest deformation is in the SIZ north of coastal Alaska. Both ice deformation and production are higher in the SIZ: deformation-related ice production in the SIZ (approx.0.5 m) is 1.5-2.3 times that of the PIZ (approx.0.3 m) - this is connected to ice strength and thickness. Atmospheric forcing and boundary layer structure contribute to only the seasonal and interannual variability. Seasonal ice growth in ice fractures accounts for approx.25-40% of the total ice production of the Arctic Ocean. By itself, this deformation-ice production relationship could be considered a negative feedback when thickness is perturbed. However, the overall effect on ice production in the face of increasing seasonal and thinner/weaker ice coverage could be modified by: local destabilization of the water column promoting overturning of warmer water due to increased brine rejection; and, the upwelling of the pynocline associated with increased occurrence of large shear motion in sea ice.

  7. A Microwave Technique for Mapping Ice Temperature in the Arctic Seasonal Sea Ice Zone

    NASA Technical Reports Server (NTRS)

    St.Germain, Karen M.; Cavalieri, Donald J.

    1997-01-01

    A technique for deriving ice temperature in the Arctic seasonal sea ice zone from passive microwave radiances has been developed. The algorithm operates on brightness temperatures derived from the Special Sensor Microwave/Imager (SSM/I) and uses ice concentration and type from a previously developed thin ice algorithm to estimate the surface emissivity. Comparisons of the microwave derived temperatures with estimates derived from infrared imagery of the Bering Strait yield a correlation coefficient of 0.93 and an RMS difference of 2.1 K when coastal and cloud contaminated pixels are removed. SSM/I temperatures were also compared with a time series of air temperature observations from Gambell on St. Lawrence Island and from Point Barrow, AK weather stations. These comparisons indicate that the relationship between the air temperature and the ice temperature depends on ice type.

  8. Characteristics of Arctic Ocean ice determined from SMMR data for 1979 - Case studies in the seasonal sea ice zone

    NASA Technical Reports Server (NTRS)

    Anderson, M. R.; Crane, R. G.; Barry, R. G.

    1985-01-01

    Sea ice data derived from the Scanning Multichannel Microwave Radiometer are examined for sections of the Arctic Ocean during early summer 1979. The temporary appearance of spuriously high multiyear ice fractions in the seasonal ice zones of the Kara and Barents Seas is a result of surface melt phenomena and the relative responses of the different channels to these effects. These spurious signatures can provide early identification of melt onset and additional information on surface characteristics.

  9. An Edge-Referenced Surface Fresh Layer in the Seasonal Ice Zone

    NASA Astrophysics Data System (ADS)

    Dewey, S.; Morison, J.

    2016-02-01

    Seasonal Ice Zone Reconnaissance Surveys (SIZRS) of the Beaufort Sea aboard U.S. Coast Guard Arctic Domain Awareness flights were made monthly from June to October, 2012 to 2015. The seasonal ice zone (SIZ), where ice melts and reforms annually, encompasses the marginal ice zone (MIZ). Thus SIZRS tracks interannual MIZ conditions, providing a regional context for smaller-scale MIZ processes. Observations with Air eXpendable CTDs (AXCTDs) reveal a salinity pattern associated with large-scale gyre circulation as well as the seasonal formation of a 20m-deep fresh layer relative to the ice edge. Repeat occupations of the SIZRS lines from 72°N to 76°N on 140°W and 150°W allow us to relate observed hydrography to atmospheric indices. Using this relationship, we separate basin-wide salinity signals from the fresh layer associated with the ice edge. While this layer extends under the ice edge as the melt season progresses, its presence is independent of year and absolute latitude north. Within this fresh layer, we correlate average salinity to distance from the ice edge. To test a formation mechanism for this layer, a 1-D Price-Weller-Pinkel (PWP) model adapted for ice-covered seas simulates mixing processes in the top 100 meters of the ocean. Surface forcing fluxes are taken from the Marginal Ice Zone Modeling and Assimilation System (MIZMAS). PWP output supports local formation of the layer by ice melt. This layer may have implications for the behavior of freshwater in the Beaufort Gyre as the local SIZ grows and persists.

  10. Aerial Surveys of the Beaufort Sea Seasonal Ice Zone in 2012-2014

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Seasonal Ice Zone Reconnaissance Surveys (SIZRS) of the Beaufort Sea aboard U.S. Coast Guard Arctic Domain Awareness flights were made monthly from May 2012 to October 2012, June 2013 to August 2013, and June 2014 to October 2014. In 2012 sea ice extent reached a record minimum and the SIZRS sampling ranged from complete ice cover to open water; in addition to its large spatial coverage, the SIZRS program extends temporal coverage of the seasonal ice zone (SIZ) beyond the traditional season for ship-based observations, and is a good set of measurements for model validation and climatological comparison. The SIZ, where ice melts and reforms annually, encompasses the marginal ice zone (MIZ). Thus SIZRS tracks interannual MIZ conditions, providing a regional context for smaller-scale MIZ processes. Observations with Air eXpendable CTDs (AXCTDs) reveal two near-surface warm layers: a locally-formed surface seasonal mixed layer and a layer of Pacific origin at 50-60m. Temperatures in the latter differ from the freezing point by up to 2°C more than climatologies. To distinguish vertical processes of mixed layer formation from Pacific advection, vertical heat and salt fluxes are quantified using a 1-D Price-Weller-Pinkel (PWP) model adapted for ice-covered seas. This PWP simulates mixing processes in the top 100m of the ocean. Surface forcing fluxes are taken from the Marginal Ice Zone Modeling and Assimilation System MIZMAS. Comparison of SIZRS observations with PWP output shows that the ocean behaves one-dimensionally above the Pacific layer of the Beaufort Gyre. Despite agreement with the MIZMAS-forced PWP, SIZRS observations remain fresher to 100m than do outputs from MIZMAS and ECCO.2. The shapes of seasonal cycles in SIZRS salinity and temperature agree with MIZMAS and ECCO.2 model outputs despite differences in the values of each. However, the seasonal change of surface albedo is not high enough resolution to accurately drive the PWP. Use of ice albedo

  11. Autonomous Observations of the Upper Ocean Stratification and Velocity Fields About the Seasonally-Retreating Marginal Ice Zone

    DTIC Science & Technology

    2015-09-30

    for the plastic-jacketed wire rope tether and end weight should the ice fracture or melt , and to provide modest protection in the event of ice ridging...Stratification and Velocity Fields About the Seasonally-Retreating Marginal Ice Zone John M. Toole MS 21/354 Clark Laboratory, WHOI Woods Hole, MA 02543...controlling the evolving thermohaline stratification, the ocean currents and air- ice -sea interactions on time scales of minutes to seasonal and longer

  12. Autonomous Observations of the Upper Ocean Stratification and Velocity Field about the Seasonally-Retreating Marginal Ice Zone

    DTIC Science & Technology

    2016-12-30

    designed to observe the seasonal evolution of the upper-ocean stratification , document the time-varying ocean currents and characterize the turbulent ice...Objectives As a contribution to the Marginal Ice Zone DRI, this research element was designed to observe the seasonal evolution of the upper...Postgraduate School doctoral candidate Shawn Gallaher (and his supervisors), the collective MIZ observations were used to quantify the evolution of the ice

  13. Acquisition of Ice Thickness and Ice Surface Characteristics In the Seasonal Ice Zone by CULPIS-X During the US Coast Guards Arctic Domain Awareness Program

    DTIC Science & Technology

    2015-09-30

    Characteristics In the Seasonal Ice Zone by CULPIS-X During the US Coast Guard’s Arctic Domain Awareness Program PI: Mark A. Tschudi University of...APPROACH The CULPIS-X (CU Laser Profiler InStrument – eXtended) package is designed to take advantage of the US Coast Guard’s (USCG) Arctic Domain

  14. A Comparison of Sea Ice Type, Sea Ice Temperature, and Snow Thickness Distributions in the Arctic Seasonal Ice Zones with the DMSP SSM/I

    NASA Technical Reports Server (NTRS)

    St.Germain, Karen; Cavalieri, Donald J.; Markus, Thorsten

    1997-01-01

    Global climate studies have shown that sea ice is a critical component in the global climate system through its effect on the ocean and atmosphere, and on the earth's radiation balance. Polar energy studies have further shown that the distribution of thin ice and open water largely controls the distribution of surface heat exchange between the ocean and atmosphere within the winter Arctic ice pack. The thickness of the ice, the depth of snow on the ice, and the temperature profile of the snow/ice composite are all important parameters in calculating surface heat fluxes. In recent years, researchers have used various combinations of DMSP SSMI channels to independently estimate the thin ice type (which is related to ice thickness), the thin ice temperature, and the depth of snow on the ice. In each case validation efforts provided encouraging results, but taken individually each algorithm gives only one piece of the information necessary to compute the energy fluxes through the ice and snow. In this paper we present a comparison of the results from each of these algorithms to provide a more comprehensive picture of the seasonal ice zone using passive microwave observations.

  15. A Comparison of Sea Ice Type, Sea Ice Temperature, and Snow Thickness Distributions in the Arctic Seasonal Ice Zones with the DMSP SSM/I

    NASA Technical Reports Server (NTRS)

    St.Germain, Karen; Cavalieri, Donald J.; Markus, Thorsten

    1997-01-01

    Global climate studies have shown that sea ice is a critical component in the global climate system through its effect on the ocean and atmosphere, and on the earth's radiation balance. Polar energy studies have further shown that the distribution of thin ice and open water largely controls the distribution of surface heat exchange between the ocean and atmosphere within the winter Arctic ice pack. The thickness of the ice, the depth of snow on the ice, and the temperature profile of the snow/ice composite are all important parameters in calculating surface heat fluxes. In recent years, researchers have used various combinations of DMSP SSMI channels to independently estimate the thin ice type (which is related to ice thickness), the thin ice temperature, and the depth of snow on the ice. In each case validation efforts provided encouraging results, but taken individually each algorithm gives only one piece of the information necessary to compute the energy fluxes through the ice and snow. In this paper we present a comparison of the results from each of these algorithms to provide a more comprehensive picture of the seasonal ice zone using passive microwave observations.

  16. Evidence for ice-ocean albedo feedback in the Arctic Ocean shifting to a seasonal ice zone.

    PubMed

    Kashiwase, Haruhiko; Ohshima, Kay I; Nihashi, Sohey; Eicken, Hajo

    2017-08-15

    Ice-albedo feedback due to the albedo contrast between water and ice is a major factor in seasonal sea ice retreat, and has received increasing attention with the Arctic Ocean shifting to a seasonal ice cover. However, quantitative evaluation of such feedbacks is still insufficient. Here we provide quantitative evidence that heat input through the open water fraction is the primary driver of seasonal and interannual variations in Arctic sea ice retreat. Analyses of satellite data (1979-2014) and a simplified ice-upper ocean coupled model reveal that divergent ice motion in the early melt season triggers large-scale feedback which subsequently amplifies summer sea ice anomalies. The magnitude of divergence controlling the feedback has doubled since 2000 due to a more mobile ice cover, which can partly explain the recent drastic ice reduction in the Arctic Ocean.

  17. The seasonal succession of zooplankton in the Southern Ocean south of Australia, part I: The seasonal ice zone

    NASA Astrophysics Data System (ADS)

    Hunt, Brian P. V.; Hosie, Graham W.

    2006-07-01

    Between November 2001 and March 2002 an Australian/Japanese collaborative study completed six passes of a transect line in the Seasonal-Ice Zone (south of 62°S) along 140°E. Zooplankton samples were collected with a NORPAC net on 22-28 November, and a Continuous Plankton Recorder on 10-15 January, 11-12 February, 19-22 February, 25-26 February, and 10-11 March. Zooplankton densities were lowest on 22-28 November (ave=61 individuals (ind) m -3), when almost the entire transect was covered by sea ice. By 10-15 January sea surface temperature had increased by ˜2 °C across the transect line, and the study area was ice-free. Total zooplankton abundance had increased to maximum levels for the season (ave=1301 ind m -3; max=1979 ind m -3), dominated by a "Peak Community" comprising Oithona similis, Ctenocalanus citer, Clausocalanus laticeps, foraminiferans, Limacina spp., appendicularians, Rhincalanus gigas and large calanoid copepodites (C1-3). Total densities declined on each subsequent transect, returning to an average of 169 ind m -3 on 10-11 March. The seasonal density decline was due to the decline in densities of "Peak Community" taxa, but coincided with the rise of Euphausia superba larvae into the surface waters, increased densities of Salpa thompsoni, and an increased contribution of C4 to adult stages to the populations of Calanoides acutus, Calanus propinquus and Calanus simillimus. The seasonal community succession appeared to be influenced by the low sea ice extent and southward projection of the ACC in this region. The relatively warm ACC waters, together with low krill biomass, favoured high densities of small grazers during the January/February bloom conditions. The persistence of relatively warm surface waters in March and the seasonal decrease in chlorophyll a biomass provided favorable conditions for salps, which were able to penetrate south of the Southern Boundary.

  18. Variability of the fauna within drifting sea ice floes in the seasonal ice zone of the Southern Ocean during the austral summer

    NASA Astrophysics Data System (ADS)

    Ojima, Motoha; Takahashi, Kunio T.; Iida, Takahiro; Moteki, Masato; Miyazaki, Naho; Tanimura, Atsushi; Odate, Tsuneo

    2017-06-01

    Sea ice covering the seasonal ice zone in the Southern Ocean contains micro-organisms (sea ice biota). Studies of sea ice biota have mostly been conducted on the land-fast ice and large ice floes, despite most sea ice in the Southern Ocean being seasonal and drifting ice types. We sampled 17 drifting sea ice floes in the marginal ice zone off Adélie Land, East Antarctica, in January 2013 and 2014. We found high densities of copepods such as Harpacticoida species (18,787 ± 50,647 inds.m-3), Paralabidocera antarctica (1773 ± 6370) and their nauplii (69,943 ± 149,607), as well as foraminiferans (193,869 ± 408,721) within ice. Variability in the animal assemblages among the different ice floes was observed. Cluster analysis of samples based on the assemblage of sea ice fauna revealed two major groups, which were divided by the year of the sampling, and were dominated by harpacticoid nauplii and foraminiferans, respectively. Sea ice trajectory and drifting duration estimated from satellite data were different for both years, although the origin of the sea ice was in the same bay. This study suggests that the variability of fauna among sea ice floes may reflect the continuance period of ice formation and the trajectory from where they originated.

  19. The role of atmospheric synoptic conditions in the Beaufort and Chukchi seasonal ice zone

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Schweiger, A. J. B.

    2015-12-01

    How atmosphere and sea ice interact depends on the prevailing weather. Synoptic activities transport energy and moisture into the Arctic and modify the structure of the atmosphere, cloud conditions, and the surface energy budget over sea ice. The structure of the atmosphere, such as temperature inversions and specific humidity inversions are critical for the life cycle of Arctic clouds. Cloud radiative heating is an important component of the Arctic surface energy budget. The differences in the structure of the atmosphere, clouds, and the radiation balance at the surface under different synoptic conditions will determine which processes will govern the interaction between the atmosphere and clouds. In this study, dominant synoptic types over the Beaufort and Chukchi seasonal ice zone (BCSIZ) are identified using the ERA-Interim reanalysis data sets and a k-mean clustering synoptic classification algorithm. The synoptic classification algorithm categorizes individual weather events in the atmospheric reanalysis into four synoptic types with distinct signatures in baroclinicity and temperature advection. The typical structure of the atmosphere in ERA-Interim is determined for each synoptic type. In particular the structure of the summer atmosphere across the ice edge along 150°W and 140°W longitude will be the analyzed and evaluated with observations obtained from the Seasonal Ice Zone Reconnaissance Survey (SIZRS). Cloud conditions and cloud radiative forcings at the surface under different synoptic conditions are determined using satellite observations, from MODIS, CloudSat, and Calipso, and modeled clouds in reanalysis. The influence of synoptic conditions on the structure of atmosphere and cloud through heat and moisture transport is explored and the consequent effects on the surface energy budget in BCSIZ are assessed.

  20. Sedimentation and particle dynamics in the seasonal ice zone of the Barents Sea

    NASA Astrophysics Data System (ADS)

    Maiti, Kanchan; Carroll, JoLynn; Benitez-Nelson, Claudia R.

    2010-01-01

    The Barents Sea seasonal ice zone (SIZ) is one of the most dynamic areas in the world ocean. This biologically productive area undergoes extreme intra- and inter-annual variabilities in sea ice and water mass transport properties. Here, we investigate seafloor burial processes in three regions of the SIZ with different ice-cover frequencies: predominantly open water (POW), marginally ice-covered (MIC), and predominantly ice-covered (PIC) with approximately 0, 10 and 50% sea ice cover, respectively, in 2002-2003. Down-core sediment profiles of the radionuclides 234Th, 210Pb, and 137Cs, along with sediment carbon, nitrogen and phosphorus concentrations are examined in two to three cores from each region. Sedimentation rates and velocities using 210Pb ex (excess 210Pb) profiles and assuming negligible mixing below a surface mixed layer are relatively uniform throughout the study area, averaging 558 ± 154 g m - 2 y - 1 and 1.1 ± 0.4 mm y - 1 ( n = 7). These sedimentation velocities are confirmed using 137Cs (1.0 ± 0.4 mm y - 1 , n = 7). 234Th ex (excess 234Th) derived bioturbation rates are positively correlated with number of benthic individuals per 0.5 m 2 ( R2 = 0.83) and exhibit a pattern of higher rates in the MIC (14.5 ± 2.1 cm - 2 y - 1) relative to both the POW (6.3 ± 2.2 cm - 2 y - 1) and PIC (5.3 ± 1.2 cm - 2 y - 1) ( p < 0.01). 234Th ex inventories are also significantly higher ( p = 0.026) within the MIC, while both 210Pb ex and 137Cs sediment inventories are more regionally uniform. Furthermore, organic carbon (C org) and total nitrogen (N tot) concentrations are relatively high in both the MIC and PIC compared to POW. For this limited data set, higher bioturbation rate coefficients and higher 234Th ex sediment inventories in the MIC relative to the other sampled regions, suggest that the MIC exhibits a greater predominance of marine versus terrestrial sediment sources that support enhanced scavenging and benthic biological activity. These results

  1. The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink

    PubMed Central

    Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf

    2015-01-01

    Reduced surface–deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface–subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring–summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall–winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink. PMID:26382319

  2. The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink.

    PubMed

    Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf

    2015-09-18

    Reduced surface-deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface-subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring-summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall-winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink.

  3. The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink

    NASA Astrophysics Data System (ADS)

    Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf

    2015-09-01

    Reduced surface-deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface-subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring-summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall-winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink.

  4. Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

    NASA Astrophysics Data System (ADS)

    Roden, Nicholas P.; Tilbrook, Bronte; Trull, Thomas W.; Virtue, Patti; Williams, Guy D.

    2016-12-01

    The carbon cycle of the seasonally ice covered region of the southwest Indian Ocean sector of East Antarctica (30°-80°E, 60°-69°S) was investigated during austral summer (January-March 2006). Large variability in the drivers and timing of carbon cycling dynamics were observed and indicated that the study site was a weak net source of carbon dioxide (CO2) to the atmosphere of 0.8 ± 1.6 g C m-2 during the ice-free period, with narrow bands of CO2 uptake observed near the continental margin and north of the Southern Antarctic Circumpolar Current Front. Continuous surface measurements of dissolved oxygen and the fugacity of CO2 were combined with net community production estimates from oxygen/argon ratios to show that surface heat gain and photosynthesis were responsible for the majority of observed surface water variability. On seasonal timescales, winter sea-ice cover reduced the flux of CO2 to the atmosphere in the study area, followed by biologically driven drawdown of CO2 as the ice retreated in spring-summer highlighting the important role that sea-ice formation and retreat has on the biogeochemical cycling of the region.

  5. Two decades of surface salinity changes in the Seasonal Ice Zone near 140°E off Antarctica

    NASA Astrophysics Data System (ADS)

    Morrow, R.; Kestenare, E.

    2016-12-01

    We have analysed the seasonal and interannual changes in surface salinity (SSS) in the Seasonal Ice Zone (SIZ) along 140°E based on the 22-year time series of surface salinity observations from 1993-2015 from the R.V Astrolabe's thermosalinograph observations as part of the SURVOSTRAL programme. This analysis complements the full-depth analyses of the SIZ freshening based on 9 CTD sections by Aoki et al (2013), providing more detailed information on the seasonal and interannual SSS variations. The seasonal SSS structure is available through the 6-month heating cycle from October to March. The gradual heating and desalination of the AASW is evident in the northern SIZ from October to March. In December and January, there are distinct signatures of very cold, high salinity waters on the shelf associated with Modified Shelf Waters. We also examine the SSS changes along the shelf between 140°E and the Mertz Glacier, including observations obtained over the D'Urville Trough and the Adélie Depression, for the period from 2003 to 2012. The extended time series allows us to observe the interannual SSS variations at 140°E before and after the major Mertz Glacier calving event in Feb 2010. Periods with higher sea-ice cover in November lead to more ice melt in the surface waters in the following summer. This is particularly noted for the period after the Mertz Glacier calving, when sea-ice cover increased significantly downstream (particularly in Nov 2011 & 2013), leading to low salinity across all regions - on the shelf and offshore. Lagrangian analyses based on modelled currents help us identify the variations in the source regions for the waters observed along the SURVOSTRAL line at 140°E, and their modification by sea-ice cover and melt.

  6. 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.

  7. The dependence of Arctic cloud on the synoptic conditions in the Beaufort and Chukchi seasonal ice zone

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Schweiger, A. J. B.

    2016-12-01

    How atmosphere and sea ice interact depends on the prevailing weather. Synoptic activities transport energy and moisture into the Arctic and modify the structure of the atmosphere, cloud conditions, and the surface energy budget over sea ice. The structure of the atmosphere, such as temperature inversions and specific humidity inversions are critical for the life cycle of Arctic clouds. Cloud radiative heating is an important component of the Arctic surface energy budget. The differences in the structure of the atmosphere, clouds, and the radiation balance at the surface under different synoptic conditions will determine which processes will govern the interaction between the atmosphere and clouds. In this study, dominant synoptic states over the Beaufort and Chukchi seasonal ice zone (BCSIZ) are identified using the ERA-Interim reanalysis data sets and a k-mean clustering synoptic classification algorithm. The synoptic classification algorithm categorizes individual weather events in the atmospheric reanalysis into four synoptic states with distinct signatures in baroclinicity and temperature advection. Using the CloudSat/Calipso joint cloud mask, the cloud conditions of the four synoptic states in the BCSIZ are examined. The cloud fraction of the four states are significantly different at different levels, which are associated with differences in the lower tropospheric static stability and the abundance of moisture, especially in the middle and lower atmosphere. These differences are also captured by the ERA-Interim although the ERA-Interim greatly overestimates the low-level cloud fraction and underestimates cloud fraction higher up, which is partly due to the limitation of the joint CloudSat/Calipso cloud mask below 1 km. In addition, the seasonal cycle and horizontal distribution of cloud fraction and cloud radiative heating at surface are examined for the four synoptic states using the joint CloudSat/Calipso retrievals. Two versions of joint Cloud

  8. Atmospheric Profiles, Clouds and the Evolution of Sea Ice Cover in the Beaufort and Chukchi Seas: Atmospheric Observations and Modeling as Part of the Seasonal Ice Zone Reconnaissance Surveys

    DTIC Science & Technology

    2017-06-04

    Evolution of Sea Ice Sb. GRANT NUMBER N000 1 4-1 2- 1-0232 Sc. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Sd. PROJECT NUMBER Axel Schweiger Se. TASK NUMBER...Clouds, and the Evolution of Sea Ice Cover in the Beaufort and Chukchi Seas: Atmospheric Observations and Modeling as Part of the Seasonal Ice Zone...concentrations and ocean temperatures. These changes in turn will affect the evolution of the SIZ. An appropriate representation ofthis feedback loop in

  9. Autonomous Observations of the Upper Ocean Stratification and Velocity Field about the Seasonality Retreating Marginal Ice Zone

    DTIC Science & Technology

    2016-12-30

    From - To) 12/30/2016 final 01-Nov-2011to 30-Sep-201 6 4. TITLE AND SUBTITLE Sa. CONTRACT NUMBER Autonomous observations of the upper ocean ...designed to observe the seasonal evolution of the upper- ocean stratification. document the time-varying ocean currents and characterize the turbulent ice... ocean exchanges of heat, salt and momentum as the sea ice cover retreats poleward in spring/summer using Ice-Tethered Profilers with Velocity. A

  10. Spatial distribution of micro- and meso-zooplankton in the seasonal ice zone of east Antarctica during 1983-1995

    NASA Astrophysics Data System (ADS)

    Ojima, Motoha; Takahashi, Kunio T.; Tanimura, Atsushi; Odate, Tsuneo; Fukuchi, Mitsuo

    2015-09-01

    Historically, most studies about the geographic distribution of zooplankton in the Southern Ocean have been focused on the macro-sized zooplankton (2-20 mm), such as the Antarctic krill and larger-sized copepods. On the other hand, despite the high abundance and biomass, the distribution patterns of micro- (20-200 μm) and meso-sized (200 μm-2 mm) zooplankton communities are little understood. In this study, we investigated the distribution patterns of larger micro-zooplankton (100-200 μm) and meso-zooplankton communities in the seasonal ice zone in the Cosmonaut Sea near Syowa Station and examined the effects of environmental factors and water properties on these communities. The investigation was based on samples collected with 100 μm mesh nets, which are appropriate to estimate the quantitative abundance and community structure of micro- and meso-zooplankton species between 1983 and 1995. Cluster analysis of the samples revealed that the distribution of macro-zooplankton species was influenced by the temperature and salinity of ocean fronts. Among the meso-zooplankton, cyclopoid and small calanoid copepods tended to be ubiquitously distributed. However, among the micro-zooplankton, the distributions of foraminiferans and tintinnids were associated with sea ice extent. The distribution of micro- and meso-zooplankton communities could be used to estimate the impact of environmental changes on the marine ecosystem in the Southern Ocean.

  11. Observing Physical and Biological Drivers of pH and O2 in a Seasonal Ice Zone in the Ross Sea Using Profiling Float Data

    NASA Astrophysics Data System (ADS)

    Briggs, E.; Martz, T. R.; Talley, L. D.; Mazloff, M. R.

    2015-12-01

    Ice cover has strong influence over gas exchange, vertical stability, and biological production which are critical to understanding the Southern Ocean's central role in oceanic biogeochemical cycling and heat and carbon uptake under a changing climate. However the relative influence of physical versus biological processes in this hard-to-study region is poorly understood due to limited observations. Here we present new findings from a profiling float equipped with biogeochemical sensors in the seasonal ice zone of the Ross Sea capturing, for the first time, under-ice pH profile data over a two year timespan from 2014 to the present. The relative influence of physical (e.g. vertical mixing and air-sea gas exchange) and biological (e.g. production and respiration) drivers of pH and O2 within the mixed layer are explored during the phases of ice formation, ice cover, and ice melt over the two seasonal cycles. During the austral fall just prior to and during ice formation, O2 increases as expected due to surface-layer undersaturation and enhanced gas exchange. A small increase in pH is also observed during this phase, but without a biological signal in accompanying profiling float chlorophyll data, which goes against common reasoning from both a biological and physical standpoint. During the phase of ice cover, gas exchange is inhibited and a clear respiration signal is observed in pH and O2 data from which respiration rates are calculated. In the austral spring, ice melt gives rise to substantial ice edge phytoplankton blooms indicated by O2 supersaturation and corresponding increase in pH and large chlorophyll signal. The influence of the duration of ice cover and mixed layer depth on the magnitude of the ice edge blooms is explored between the two seasonal cycles.

  12. Atmospheric Profiles, Clouds, and the Evolution of Sea Ice Cover in the Beaufort and Chukchi Seas Atmospheric Observations and Modeling as Part of the Seasonal Ice Zone Reconnaissance Surveys

    DTIC Science & Technology

    2012-09-30

    Meric Srokosz, Alex West, Richard Wood, Axel Schweiger (2012), Assessment of Possibility and Impact of Rapid Climate Change in the Arctic Rep., 62 pp, UK MetOffice, Hadley Centre ...Ice Cover in the Beaufort and Chukchi Seas Atmospheric Observations and Modeling as Part of the Seasonal Ice Zone Reconnaissance Surveys Axel ...email: axel @apl.washington.edu Ron Lindsay Applied Physics Laboratory, University of Washington Jinlun Zhang Applied Physics Laboratory

  13. Picophytoplankton during the ice-free season in five temperate-zone rivers

    PubMed Central

    Contant, Jacinthe; Pick, Frances R.

    2013-01-01

    Although picophytoplankton (PP) (0.2–2 µm) are ubiquitous in lakes and oceans, their importance in rivers has rarely been studied. We examined PP assemblages during the ice-free period in five rivers of a temperate region varying in trophic state (9–107 µg/L total phosphorus) and water discharge (1–87 m3/s). In these rivers, PP abundance reached concentrations as high as those observed in lakes and oceans (∼104–105 cells/mL). The highest density of PP (4.9 × 105 cells/mL) was observed in the most eutrophic river when the water temperature (28°C) and total phosphorus (293 µg/L) were highest. For the most part, PP abundance was dominated by non-phycoerythrin-containing cyanobacteria; phycocyanin-rich cells accounted for ∼75% of PP abundance in all the rivers. In multiple regression analyses, water temperature and nitrate concentrations explained about half of the variation in PP abundance across the rivers. Discharge had no effect on PP abundance or biomass, whereas it had a significant negative effect on total algal biomass among the rivers. The PP contribution to total chlorophyll-a averaged 27% (ranging 16–46%) and did not decline with increasing nutrients as found in lakes and oceans. The PP biomass from microscopic enumerations reached a maximum of 9% of total phytoplankton biomass, comparable with that observed in lakes. The results of this study demonstrate the importance of including picophytoplankton when analysing phytoplankton communities in rivers. PMID:23641118

  14. Picophytoplankton during the ice-free season in five temperate-zone rivers.

    PubMed

    Contant, Jacinthe; Pick, Frances R

    2013-05-01

    Although picophytoplankton (PP) (0.2-2 µm) are ubiquitous in lakes and oceans, their importance in rivers has rarely been studied. We examined PP assemblages during the ice-free period in five rivers of a temperate region varying in trophic state (9-107 µg/L total phosphorus) and water discharge (1-87 m(3)/s). In these rivers, PP abundance reached concentrations as high as those observed in lakes and oceans (∼10(4)-10(5) cells/mL). The highest density of PP (4.9 × 10(5) cells/mL) was observed in the most eutrophic river when the water temperature (28°C) and total phosphorus (293 µg/L) were highest. For the most part, PP abundance was dominated by non-phycoerythrin-containing cyanobacteria; phycocyanin-rich cells accounted for ∼75% of PP abundance in all the rivers. In multiple regression analyses, water temperature and nitrate concentrations explained about half of the variation in PP abundance across the rivers. Discharge had no effect on PP abundance or biomass, whereas it had a significant negative effect on total algal biomass among the rivers. The PP contribution to total chlorophyll-a averaged 27% (ranging 16-46%) and did not decline with increasing nutrients as found in lakes and oceans. The PP biomass from microscopic enumerations reached a maximum of 9% of total phytoplankton biomass, comparable with that observed in lakes. The results of this study demonstrate the importance of including picophytoplankton when analysing phytoplankton communities in rivers.

  15. Color Reveals Translucent Seasonal Ice

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1

    In a region near the south pole of Mars translucent carbon dioxide ice covers the ground seasonally. For the first time we can 'see' the translucent ice by the affect it has on the appearance of the surface below.

    Dark fans of dust (figure 1) from the surface drape over the top of the seasonal ice. The surface would be the same color as the dust except that the seasonal ice affecting its appearance. Bright bluish streaks are frost that has re-crystallized from the atmosphere.

    Sunlight can penetrate through the seasonal layer of translucent ice to warm the ground below. That causes the seasonal ice layer to sublime (evaporate) from the bottom rather than the top.

    Observation Geometry Image PSP_002942_0935 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 13-Mar-2007. The complete image is centered at -86.4 degrees latitude, 99.2 degrees East longitude. The range to the target site was 245.4 km (153.4 miles). At this distance the image scale is 49.1 cm/pixel (with 2 x 2 binning) so objects 147 cm across are resolved. The image shown here has been map-projected to 50 cm/pixel . The image was taken at a local Mars time of 06:41 PM and the scene is illuminated from the west with a solar incidence angle of 82 degrees, thus the sun was about 8 degrees above the horizon. At a solar longitude of 199.6 degrees, the season on Mars is Northern Autumn.

  16. Color Reveals Translucent Seasonal Ice

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1

    In a region near the south pole of Mars translucent carbon dioxide ice covers the ground seasonally. For the first time we can 'see' the translucent ice by the affect it has on the appearance of the surface below.

    Dark fans of dust (figure 1) from the surface drape over the top of the seasonal ice. The surface would be the same color as the dust except that the seasonal ice affecting its appearance. Bright bluish streaks are frost that has re-crystallized from the atmosphere.

    Sunlight can penetrate through the seasonal layer of translucent ice to warm the ground below. That causes the seasonal ice layer to sublime (evaporate) from the bottom rather than the top.

    Observation Geometry Image PSP_002942_0935 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 13-Mar-2007. The complete image is centered at -86.4 degrees latitude, 99.2 degrees East longitude. The range to the target site was 245.4 km (153.4 miles). At this distance the image scale is 49.1 cm/pixel (with 2 x 2 binning) so objects 147 cm across are resolved. The image shown here has been map-projected to 50 cm/pixel . The image was taken at a local Mars time of 06:41 PM and the scene is illuminated from the west with a solar incidence angle of 82 degrees, thus the sun was about 8 degrees above the horizon. At a solar longitude of 199.6 degrees, the season on Mars is Northern Autumn.

  17. The Seasonal Evolution of Sea Ice Floe Size Distribution

    DTIC Science & Technology

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. “The Seasonal Evolution of Sea Ice Floe Size Distribution...This work was motivated by the desire to improve the understanding of processes governing the evolution of the marginal ice zone that forms...seasonally in the southern Beaufort and Chukchi Seas region. OBJECTIVES The objective of this work was to determine the seasonal evolution of the

  18. Autonomous Observations of the Upper Ocean Stratification and Velocity Fields About the Seasonally-Retreating Marginal Ice Zone. Acquisition of Ice-Tethered Profilers with Velocity (ITP-V) Instruments as a Contribution to the Marginal Ice Zone DRI

    DTIC Science & Technology

    2012-09-30

    ice -ocean interactions in the polar oceans ( Arctic and Southern Ocean). Particular areas of focus include ice -ocean exchanges of momentum, heat and...the manuscript of Cole et al., 2012 (Ekman veering, internal waves, and turbulent fluxes observed under Arctic sea- ice , J. Phys. Oceanogr., in...Observed ocean velocity was primarily directed to the right of ice velocity and spiraled clockwise while decaying with depth through the surface mixed

  19. Physical and biological control of protistan community composition, distribution and abundance in the seasonal ice zone of the Southern Ocean between 30 and 80°E

    NASA Astrophysics Data System (ADS)

    Davidson, Andrew T.; Scott, Fiona J.; Nash, Geraldine V.; Wright, Simon W.; Raymond, Ben

    2010-05-01

    Protists are critical components of the Antarctic marine ecosystem as they comprise most of the living carbon and are the base of the Antarctic food web. They are also key determinants of vertical carbon flux and mediate draw-down of atmospheric CO 2 by the ocean. The community composition, abundance and distribution of marine protists (phytoplankton and protozoa) was studied during the Baseline Research on Oceanography, Krill and the Environment-West (BROKE-West) survey, in the seasonal ice zone during the 2005-2006 austral summer between 30°E and 80°E. Light and electron microscopy were used to determine the protistan composition and abundance in samples obtained at 30 sites from surface waters and at 26 sites from the depth of the maximum in situ chlorophyll fluorescence (Chl max). Cluster analysis was used to identify 5 groups of sample sites at the surface and 5 at the Chl max that were of similar protist composition and abundance. The physical characteristics, taxonomic composition, indicator taxa, and taxonomic diversity were determined for each group. In the southwest, a bloom of colonial Phaeocystis antarctica dominated the protistan community composition and biomass amongst the receding ice, but this was replaced by the flagellate life stage/s of this haptophyte in waters to the north. In the southeast, a diatom bloom had the highest diversity of protist taxa observed during the survey and centric diatoms dominated the biomass. Outside these blooms, grazing by krill probably reduced the composition and abundance of large diatoms and autotrophic dinoflagellates in coastal to mid-inshore waters. Only in offshore waters did large diatoms and dinoflagellates increase in abundance and diversity, despite low concentrations of iron and silicate at many of these sites. This increase was probably due to reduced top-down control by krill and other large zooplankton. Large diatoms dominated in offshore waters, despite other coincident studies showing that the

  20. Marginal Ice Zone: Biogeochemical Sampling with Gliders

    DTIC Science & Technology

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Marginal Ice Zone: Biogeochemical Sampling with Gliders...under the ice and in the marginal ice zone. The project specific goals are to develop biogeochemical and optical proxies for glider optics; to use the...water, in the marginal ice zone, and under the ice ; to use glider optical measurements to compute fields of rates of photosynthetic carbon fixation

  1. Marginal Ice Zone: Biogeochemical Sampling with Gliders

    DTIC Science & Technology

    2014-09-30

    Figure 3. Map of 2014 IBRV Araon Arctic cruise study area, indicating CTD, XCTD, sea- ice caps , and helicopter...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Marginal Ice Zone: Biogeochemical Sampling with Gliders...distribution of phytoplankton and particulate organic carbon in the Arctic under the ice and in the marginal ice zone, as well as to understand feedbacks

  2. Wave-ice Interaction and the Marginal Ice Zone

    DTIC Science & Technology

    2015-09-30

    concentrations at the time. Any ice present appeared to be fragments of deformed ice (ridges), as most of the level ice had melted . Figure 1: Final...the buoys had approached the edge of the melting pack ice , from late August, when the vast floes had already fragmented due to dynamics and...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Wave- ice interaction and the Marginal Ice Zone Prof

  3. Bacterial biomass and production in pack ice of Antarctic marginal ice edge zones

    NASA Astrophysics Data System (ADS)

    Kottmeier, Steven T.; Sullivan, Cornelius W.

    1990-08-01

    Bacterial biomass and production in pack ice is little known even though the pack accounts for the majority of the 20 million square kilometer Antarctic sea ice habitat. On three cruises in marginal ice edge zones, spring 1983 (AMERIEZ I), autumn 1986 (AMERIEZ II), and late winter 1985 (Wintercruise I), considerable bacterial biomass and production was found throughout ice floes up to 2.22 m thick. We hypothesize that bacteria accumulate in pack ice as a result of both physical and biological processes. During the formation and growth of ice, physical processes act to concentrate and accumulate bacteria within the ice matrix. This is followed by in situ growth along physiochemical gradients found in several sea ice microhabitats. Bacterial biomass and production in ice were equal to that present in several meters of underlying seawater during all seasons. Among microhabitats, highest bacterial production and most rapid rates of growth ( >1 d -1) were found in saline ponds on the surface of floes and porewater in the interior of floes. Bacterial carbon production ranged from 2% of primary production in surface brash to 45-221% of primary production in surface ponds and porewater. Bacterial growth and microalgal photosynthetic metabolism in pack ice appear to be coupled in a fashion similar to that described for fast ice. The presence of substantial numbers of active, feeding protozoans and metazoans in pack ice suggests, albeit indirectly, that bacterial production supports microheterotrophs of the microbial loop, which in turn may support organisms at higher trophic levels. Bacterial growth in pack ice may be important to the potential for primary production. Thus ice bacteria may provide remineralized inorganic nutrients necessary for continued microalgal growth in localized microhabitats within the ice or they may compete with algae for nutrients. Upon release from melting ice, actively growing bacteria also contribute to microbial biomass in seawater. From these

  4. The Seasonality of Antarctic Sea Ice Trends

    NASA Astrophysics Data System (ADS)

    Holland, P.

    2014-12-01

    Unlike the strong decline in Arctic sea ice, Antarctic sea ice is experiencing a weak overall increase in area that is the residual of opposing regional trends. This study considers the seasonal pattern of these trends. In addition to traditional ice concentration and ice area, temporal rates of change of these quantities are investigated ("intensification" and "expansion," respectively). This is crucial to the attribution of the Antarctic sea ice trends, since changes in wind or thermal forcing directly affect ice areal change, rather than ice area itself. The study shows that diverse regional trends all contribute significantly to the overall Antarctic sea-ice increase. In contrast to the widely-held view of a 'south Pacific dipole', trends in the Weddell and Amundsen-Bellingshausen regions are found to best compensate in magnitude and seasonality. Perhaps most importantly, the largest concentration trends, in autumn, are actually caused by intensification trends during spring. Autumn intensification trends directly oppose autumn concentration trends in most places, seemingly as a result of ice and ocean feedbacks. Further study of changes during the spring melting season is therefore required to unravel the Antarctic sea ice increase.

  5. Waves and Fetch in the Marginal Ice Zone

    DTIC Science & Technology

    2014-09-30

    arctic Marginal Ice Zone (MIZ) by improving basic understanding of the interaction between waves, sea ice, and open water (i.e., fetch). OBJECTIVES...secondary objective is to develop a surface wave climatology of the arctic ocean and the relation to the seasonal MIZ. APPROACH The technical approach is...Letters 10.1002/2014GL059983 Figure 3. Scaling of waves in the Arctic Ocean, using nondimensional wave energy versus nondimensional fetch. There are

  6. Granular flow in the marginal ice zone.

    PubMed

    Feltham, Daniel L

    2005-07-15

    The region of sea ice near the edge of the sea ice pack is known as the marginal ice zone (MIZ), and its dynamics are complicated by ocean wave interaction with the ice cover, strong gradients in the atmosphere and ocean and variations in sea ice rheology. This paper focuses on the role of sea ice rheology in determining the dynamics of the MIZ. Here, sea ice is treated as a granular material with a composite rheology describing collisional ice floe interaction and plastic interaction. The collisional component of sea ice rheology depends upon the granular temperature, a measure of the kinetic energy of flow fluctuations. A simplified model of the MIZ is introduced consisting of the along and across momentum balance of the sea ice and the balance equation of fluctuation kinetic energy. The steady solution of these equations is found to leading order using elementary methods. This reveals a concentrated region of rapid ice flow parallel to the ice edge, which is in accordance with field observations, and previously called the ice jet. Previous explanations of the ice jet relied upon the existence of ocean currents beneath the ice cover. We show that an ice jet results as a natural consequence of the granular nature of sea ice.

  7. 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

  8. Spatially mapped reductions in the length of the Arctic sea ice season

    PubMed Central

    Parkinson, Claire L

    2014-01-01

    Satellite data are used to determine the number of days having sea ice coverage in each year 1979–2013 and to map the trends in these ice-season lengths. Over the majority of the Arctic seasonal sea ice zone, the ice season shortened at an average rate of at least 5 days/decade between 1979 and 2013, and in a small area in the northeastern Barents Sea the rate of shortening reached over 65 days/decade. The only substantial non-coastal area with lengthening sea ice seasons is the Bering Sea, where the ice season lengthened by 5–15 days/decade. Over the Arctic as a whole, the area with ice seasons shortened by at least 5 days/decade is 12.4 × 106 km2, while the area with ice seasons lengthened by at least 5 days/decade is only 1.1 × 106 km2. The contrast is even greater, percentage-wise, for higher rates. Key Points Sea ice seasons have shortened by at least 5 days/decade over most of the Arctic Across 1.9 million km2 ice seasons have shortened by at least 25 days/decade Counter to most of the Arctic ice seasons have lengthened in the Bering Sea PMID:25821265

  9. Variability in the Antarctic Marginal Ice Zone and Pack Ice in Observations and NCAR CESM

    NASA Astrophysics Data System (ADS)

    Stroeve, J. C.; Campbell, G. G.; Holland, M. M.; Landrum, L.

    2015-12-01

    Sea ice around Antarctica reached another record high extent in September 2014, recording a maximum extent of more than 20 million km2 for the first time since the modern satellite data record began in October 1978. This follows previous record maxima in 2012 and 2013, resulting in an overall increase in Antarctic September sea ice extent of 1.3% per decade since 1979. Several explanations have been put forward to explain the increasing trends, such as anomalous short-term wind patterns that both grow and spread out the ice, and freshening of the surface ocean layer from increased melting of floating ice from the continent. These positive trends in Antarctic sea ice are at odds with climate model forecasts that suggest the sea ice should be declining in response to increasing greenhouse gases and stratospheric ozone depletion. While the reasons for the increases in total extent remain poorly understood, it is likely that these changes are not just impacting the total ice extent, but also the distribution of pack ice, the marginal ice zone (MIZ) and polynyas, with important ramifications for phytoplankton productivity that in turn impact zooplankton, fish, sea birds and marine mammals. This study evaluates changes in the distribution of the pack ice, polynyas and the marginal ice zone around Antarctica from two sea ice algorithms, the NASA Team and the Bootstrap. These results are further compared with climate model simulations from the CESM large ensemble output. Seasonal analysis of the different ice types using NASA Team and Bootstrap shows that during ice advance, the ice advances as pack ice, with a seasonal peak in September (broader peak for Bootstrap), and as the pack ice begins to retreat, it first converts to a wide area of MIZ, that reaches its peak around November (NASA Team) or December (Bootstrap). CESM also shows a similar seasonal cycle, with a peak in the pack ice in August, and a December/January peak in the MIZ. Seasonal variability and trends are

  10. Atmospheric Profiles, Clouds, and the Evolution of Sea Ice Cover in the Beaufort and Chukchi Seas: Atmospheric Observations and Modeling as Part of the SeasonalIce Zone Reconnaissance Surveys

    DTIC Science & Technology

    2015-09-30

    record will more distinctively define the mean states of the synoptic conditions and reduce the ambiguity during classification. Future work will include... conditions in the SIZ affect changes in cloud properties and cover, 2 • develop novel instrumentation including low cost, expendable, air-deployed micro...ice, and ocean in the SIZ of the Beaufort and Chukchi seas (BCSIZ). Seasonally changing surface conditions are expected to provide a present day

  11. 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.

  12. Marginal Ice Zone: Biogeochemical Sampling with Gliders

    DTIC Science & Technology

    2013-09-30

    nutrient rich waters into the euphotic zone in supporting these blooms. 4. Evaluate the potential role of phytoplankton pigment absorption on the...vertical gradient of heating under the ice and apply a light and chlorophyll primary productivity model to estimate and compare phytoplankton ...melt and phytoplankton optical properties under Arctic ice. The project specific goals are to build collaboration with Arctic biogeochemists at

  13. Moving to a Seasonally Ice Covered Arctic.

    NASA Astrophysics Data System (ADS)

    Postlethwaite, Clare; Luneva, Maria

    2013-04-01

    The area of seasonal sea ice that forms each year is increasing. This study investigates how this will affect the brine that subsequently enters the ocean and how it contributes to the formation of the halocline or is transported from the Arctic Shelf Seas to the deep Arctic Ocean. Two idealised experiments were carried out using ocean/sea ice models NEMO-SHELF/LIM2 on a 3km resolution domain of a section of the Arctic continental shelf and slope, where dense water cascades have been observed. The model used hybrid vertical coordinates that are able to resolve dense flows down the continental slope, temperature and salinity from climatology for initial conditions and liquid boundary conditions. The model was forced with surface fluxes according to the CORE formulation using the DFS4 database. When ice forms and brine is rejected, a passive tracer, with concentration proportional to the brine was introduced in the surface layer. This brine tracer allows us to track the penetration of newly formed waters and their pathways. The heavy, salty and cold water mixes with adjacent waters and penetrates to different layers, depending on the density of the newly formed water masses. Each model idealised run was initialised with an ice cover to approximate summer ice conditions in: (a) the early 1980's when the region was nearly 100% ice covered and (b) the late 2000's when the region was ice free. All the other forcing fields were identical between runs. The experiments initialised with no summer ice cover formed more ice over the freezing season and 40% more entered the model ocean. The concentration of brine tracer was 6-fold higher to a depth of 840m. The locations where brine can cascade off the continental shelf correspond well to the locations, where cascades have been observed. A 40% increased salt flux from increased seasonal sea ice leads to more brine reaching the sea bed in these model simulations. More brine is also transported down the continental slope and into

  14. Upper Ocean Evolution Across the Beaufort Sea Marginal Ice Zone

    NASA Astrophysics Data System (ADS)

    Lee, C.; Rainville, L.; Gobat, J. I.; Perry, M. J.; Freitag, L. E.; Webster, S.

    2016-12-01

    The observed reduction of Arctic summertime sea ice extent and expansion of the marginal ice zone (MIZ) have profound impacts on the balance of processes controlling sea ice evolution, including the introduction of several positive feedback mechanisms that may act to accelerate melting. Examples of such feedbacks include increased upper ocean warming though absorption of solar radiation, elevated internal wave energy and mixing that may entrain heat stored in subsurface watermasses (e.g., the relatively warm Pacific Summer and Atlantic waters), and elevated surface wave energy that acts to deform and fracture sea ice. Spatial and temporal variability in ice properties and open water fraction impact these processes. To investigate how upper ocean structure varies with changing ice cover, how the balance of processes shift as a function of ice fraction and distance from open water, and how these processes impact sea ice evolution, a network of autonomous platforms sampled the atmosphere-ice-ocean system in the Beaufort, beginning in spring, well before the start of melt, and ending with the autumn freeze-up. Four long-endurance autonomous Seagliders occupied sections that extended from open water, through the marginal ice zone, deep into the pack during summer 2014 in the Beaufort Sea. Gliders penetrated up to 200 km into the ice pack, under complete ice cover for up to 10 consecutive days. Sections reveal strong fronts where cold, ice-covered waters meet waters that have been exposed to solar warming, and O(10 km) scale eddies near the ice edge. In the pack, Pacific Summer Water and a deep chlorophyll maximum form distinct layers at roughly 60 m and 80 m, respectively, which become increasingly diffuse late in the season as they progress through the MIZ and into open water. Stratification just above the Pacific Summer Water rapidly weakens near the ice edge and temperature variance increases, likely due to mixing or energetic vertical exchange associated with strong

  15. 36 CFR 13.1304 - Ice fall hazard zones.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 36 Parks, Forests, and Public Property 1 2010-07-01 2010-07-01 false Ice fall hazard zones. 13.1304 Section 13.1304 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... Provisions § 13.1304 Ice fall hazard zones. Entering an ice fall hazard zone is prohibited. These zones...

  16. 36 CFR 13.1304 - Ice fall hazard zones.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 36 Parks, Forests, and Public Property 1 2014-07-01 2014-07-01 false Ice fall hazard zones. 13.1304 Section 13.1304 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... Provisions § 13.1304 Ice fall hazard zones. Entering an ice fall hazard zone is prohibited. These zones will...

  17. 36 CFR 13.1304 - Ice fall hazard zones.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 36 Parks, Forests, and Public Property 1 2013-07-01 2013-07-01 false Ice fall hazard zones. 13.1304 Section 13.1304 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... Provisions § 13.1304 Ice fall hazard zones. Entering an ice fall hazard zone is prohibited. These zones will...

  18. 36 CFR 13.1304 - Ice fall hazard zones.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 36 Parks, Forests, and Public Property 1 2011-07-01 2011-07-01 false Ice fall hazard zones. 13.1304 Section 13.1304 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... Provisions § 13.1304 Ice fall hazard zones. Entering an ice fall hazard zone is prohibited. These zones will...

  19. 36 CFR 13.1304 - Ice fall hazard zones.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 36 Parks, Forests, and Public Property 1 2012-07-01 2012-07-01 false Ice fall hazard zones. 13.1304 Section 13.1304 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... Provisions § 13.1304 Ice fall hazard zones. Entering an ice fall hazard zone is prohibited. These zones will...

  20. Modeling Wave-Ice Interactions in the Marginal Ice Zone

    NASA Astrophysics Data System (ADS)

    Orzech, Mark; Shi, Fengyan; Bateman, Sam; Veeramony, Jay; Calantoni, Joe

    2015-04-01

    The small-scale (O(m)) interactions between waves and ice floes in the marginal ice zone (MIZ) are investigated with a coupled model system. Waves are simulated with the non-hydrostatic finite-volume model NHWAVE (Ma et al., 2012) and ice floes are represented as bonded collections of smaller particles with the discrete element system LIGGGHTS (Kloss et al., 2012). The physics of fluid and ice are recreated as authentically as possible, to allow the coupled system to supplement and/or substitute for more costly and demanding field experiments. The presentation will first describe the development and validation of the coupled system, then discuss the results of a series of virtual experiments in which ice floe and wave characteristics are varied to examine their effects on energy dissipation, MIZ floe size distribution, and ice pack retreat rates. Although Wadhams et al. (1986) suggest that only a small portion (roughly 10%) of wave energy entering the MIZ is reflected, dissipation mechanisms for the remaining energy have yet to be delineated or measured. The virtual experiments are designed to focus on specific properties and processes - such as floe size and shape, collision and fracturing events, and variations in wave climate - and measure their relative roles the transfer of energy and momentum from waves to ice. Questions to be examined include: How is energy dissipated by ice floe collisions, fracturing, and drag, and how significant is the wave attenuation associated with each process? Do specific wave/floe length scale ratios cause greater wave attenuation? How does ice material strength affect the rate of wave energy loss? The coupled system will ultimately be used to test and improve upon wave-ice parameterizations for large-scale climate models. References: >Kloss, C., C. Goniva, A. Hager, S. Amberger, and S. Pirker (2012). Models, algorithms and validation for opensource DEM and CFD-DEM. Progress in Computational Fluid Dynamics 12(2/3), 140-152. >Ma, G

  1. Spatially Mapped Reductions in the Length of the Arctic Sea Ice Season

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    2014-01-01

    Satellite data are used to determine the number of days having sea ice coverage in each year 1979-2013 and to map the trends in these ice-season lengths. Over the majority of the Arctic seasonal sea ice zone, the ice season shortened at an average rate of at least 5 days/decade between 1979 and 2013, and in a small area in the northeastern Barents Sea the rate of shortening reached over 65 days/decade. The only substantial non-coastal area with lengthening sea ice seasons is the Bering Sea, where the ice season lengthened by 5-15 days/decade. Over the Arctic as a whole, the area with ice seasons shortened by at least 5 days/decade is 12.4 × 10(exp 6) square kilimeters, while the area with ice seasons lengthened by at least 5 days/decade is only 1.1 × 10(exp 6) square kilometers. The contrast is even greater, percentage-wise, for higher rates.

  2. Spatially mapped reductions in the length of the Arctic sea ice season.

    PubMed

    Parkinson, Claire L

    2014-06-28

    Satellite data are used to determine the number of days having sea ice coverage in each year 1979-2013 and to map the trends in these ice-season lengths. Over the majority of the Arctic seasonal sea ice zone, the ice season shortened at an average rate of at least 5 days/decade between 1979 and 2013, and in a small area in the northeastern Barents Sea the rate of shortening reached over 65 days/decade. The only substantial non-coastal area with lengthening sea ice seasons is the Bering Sea, where the ice season lengthened by 5-15 days/decade. Over the Arctic as a whole, the area with ice seasons shortened by at least 5 days/decade is 12.4 × 10(6) km(2), while the area with ice seasons lengthened by at least 5 days/decade is only 1.1 × 10(6) km(2). The contrast is even greater, percentage-wise, for higher rates.

  3. Ocean circulation: its effects on seasonal sea-ice simulations.

    PubMed

    Hibler, W D; Bryan, K

    1984-05-04

    A diagnostic ice-ocean model of the Arctic, Greenland, and Norwegian seas is constructed and used to examine the role of ocean circulation in seasonal sea-ice simulations. The model includes lateral ice motion and three-dimensional ocean circulation. The ocean portion of the model is weakly forced by observed temperature and salinity data. Simulation results show that including modeled ocean circulation in seasonal sea-ice simulations substantially improves the predicted ice drift and ice margin location. Simulations that do not include lateral ocean movment predict a much less realistic ice edge.

  4. 46 CFR 42.30-10 - Southern Winter Seasonal Zone.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... BY SEA Zones, Areas, and Seasonal Periods § 42.30-10 Southern Winter Seasonal Zone. (a) The northern boundary of the Southern Winter Seasonal Zone is the rhumb line from the east coast of the American...) Valparaiso is to be considered as being on the boundary line of the Summer and the Winter Seasonal Zones....

  5. 46 CFR 42.30-10 - Southern Winter Seasonal Zone.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... BY SEA Zones, Areas, and Seasonal Periods § 42.30-10 Southern Winter Seasonal Zone. (a) The northern boundary of the Southern Winter Seasonal Zone is the rhumb line from the east coast of the American...) Valparaiso is to be considered as being on the boundary line of the Summer and the Winter Seasonal Zones....

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  7. Atmospheric Profiles, Clouds, and the Evolution of Sea Ice Cover in the Beaufort and Chukchi Seas Atmospheric Observations and Modeling as Part of the Seasonal Ice Zone Reconnaissance Surveys

    DTIC Science & Technology

    2013-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Atmospheric Profiles, Clouds , and the Evolution of Sea Ice...sea ice retreats further, changes in lower atmospheric temperature, humidity, winds, and clouds are likely to result from changed sea ice...how changes in sea ice and sea surface conditions in the SIZ affect changes in cloud properties and cover. • Determine the role additional atmospheric

  8. Change and Variability in East Antarctic Sea Ice Seasonality, 1979/80–2009/10

    PubMed Central

    Massom, Robert; Reid, Philip; Stammerjohn, Sharon; Raymond, Ben; Fraser, Alexander; Ushio, Shuki

    2013-01-01

    Recent analyses have shown that significant changes have occurred in patterns of sea ice seasonality in West Antarctica since 1979, with wide-ranging climatic, biological and biogeochemical consequences. Here, we provide the first detailed report on long-term change and variability in annual timings of sea ice advance, retreat and resultant ice season duration in East Antarctica. These were calculated from satellite-derived ice concentration data for the period 1979/80 to 2009/10. The pattern of change in sea ice seasonality off East Antarctica comprises mixed signals on regional to local scales, with pockets of strongly positive and negative trends occurring in near juxtaposition in certain regions e.g., Prydz Bay. This pattern strongly reflects change and variability in different elements of the marine “icescape”, including fast ice, polynyas and the marginal ice zone. A trend towards shorter sea-ice duration (of 1 to 3 days per annum) occurs in fairly isolated pockets in the outer pack from∼95–110°E, and in various near-coastal areas that include an area of particularly strong and persistent change near Australia's Davis Station and between the Amery and West Ice Shelves. These areas are largely associated with coastal polynyas that are important as sites of enhanced sea ice production/melt. Areas of positive trend in ice season duration are more extensive, and include an extensive zone from 160–170°E (i.e., the western Ross Sea sector) and the near-coastal zone between 40–100°E. The East Antarctic pattern is considerably more complex than the well-documented trends in West Antarctica e.g., in the Antarctic Peninsula-Bellingshausen Sea and western Ross Sea sectors. PMID:23705008

  9. Change and variability in East antarctic sea ice seasonality, 1979/80-2009/10.

    PubMed

    Massom, Robert; Reid, Philip; Stammerjohn, Sharon; Raymond, Ben; Fraser, Alexander; Ushio, Shuki

    2013-01-01

    Recent analyses have shown that significant changes have occurred in patterns of sea ice seasonality in West Antarctica since 1979, with wide-ranging climatic, biological and biogeochemical consequences. Here, we provide the first detailed report on long-term change and variability in annual timings of sea ice advance, retreat and resultant ice season duration in East Antarctica. These were calculated from satellite-derived ice concentration data for the period 1979/80 to 2009/10. The pattern of change in sea ice seasonality off East Antarctica comprises mixed signals on regional to local scales, with pockets of strongly positive and negative trends occurring in near juxtaposition in certain regions e.g., Prydz Bay. This pattern strongly reflects change and variability in different elements of the marine "icescape", including fast ice, polynyas and the marginal ice zone. A trend towards shorter sea-ice duration (of 1 to 3 days per annum) occurs in fairly isolated pockets in the outer pack from∼95-110°E, and in various near-coastal areas that include an area of particularly strong and persistent change near Australia's Davis Station and between the Amery and West Ice Shelves. These areas are largely associated with coastal polynyas that are important as sites of enhanced sea ice production/melt. Areas of positive trend in ice season duration are more extensive, and include an extensive zone from 160-170°E (i.e., the western Ross Sea sector) and the near-coastal zone between 40-100°E. The East Antarctic pattern is considerably more complex than the well-documented trends in West Antarctica e.g., in the Antarctic Peninsula-Bellingshausen Sea and western Ross Sea sectors.

  10. On Wave-Ice Interaction in the Arctic Marginal Ice Zone: Dispersion, Attenuation, and Ice Response

    DTIC Science & Technology

    2016-06-01

    Ice Interaction in the Arctic Marginal Ice Zone: Dispersion, Attenuation, and Ice Response ClarenCe O. COllins iii ASEE Postdoctoral Fellow Ocean ...Dynamics and Prediction Branch Oceanography Division W. eriCk rOgers Ocean Dynamics and Prediction Branch Oceanography Division aleksey MarChenkO The...focus of this report, is quite distinct from the Antarctic. In simple terms, the Arctic is ocean surrounded by land and the Antarctic is land surrounded

  11. Wave-Ice Interactions in the Marginal Ice Zone

    NASA Astrophysics Data System (ADS)

    Perrie, W.; Shen, H.; Hu, Y.; He, Y.; Li, S.

    2016-02-01

    WAVEWATCHIII (WW3) ocean wave is the 3rd generation operational state-of-the-art forecast model for many operational marine forecast offices, internationally. In this study, WW3 is adapted for wave scattering in the marginal ice zone (MIZ) following Masson and LeBlond (1989, JFM), Perrie and Hu (1996, JPO) and Meylan and Masson (2006, Ocean Modell.), and correcting errors in earlier formulations. Presently, no practical methodology has been developed to directly incorporate an accurate wave attenuation scattering model for the MIZ, in a model like WW3. By comparison, Squire et al. (2014) developed a phase resolved scattering model which can simulate ice floes. The theory of how to include scattering into ocean wave models was developed by Masson and LeBlond (1989), Meylan et al. (1997), and Meylan and Masson (2006); and Perrie and Hu (1996) made an implementation in an earlier 2nd generation wave model. One limitation on their method is that they used rigid floes, whereas ice floe flexure can be a dominant factor in some situations in the MIZ, for large floes, (Meylan and Squire, 1994; 1996). However, Perrie and Hu (1996) were able to predict some of the features observed in measurements such as the roll over effect and the strong dependence of wave scattering on wave period. Moreover, the change from rigid to flexural ice floes is feasible in this formulation. We update and optimize this model approach for wave-ice attenuation and scattering, with implementation in WW3. The resulting model system is validated with in situ and satellite remotely sensed MIZ data, collected during recent field experiments. These include some of: (b) a storm in the Greenland Sea in February 2012, (b) ice motion data from the MIZ off Antarctica, collected by Kohout et al. (2014, Nature) to estimate ocean wave attenuation, (c) a Sea State experiment in the Beaufort Sea during October 2015.

  12. Mechanisms driving the seasonality of air-sea CO2 flux in the ice-free zone of the Southern Ocean and how these might evolve: A 1D vertical biogeochemical model approach.

    NASA Astrophysics Data System (ADS)

    Lancelot, C.; Pasquer, B.; Metzl, N.; Goosse, H.

    2015-12-01

    The biogeochemical SWAMCO-3 model is used to understand mechanisms governing the seasonality of air-sea CO2 exchanges in the ice-free Southern Ocean. The model explicitly details the dynamics of three Phytoplankton Functional Types (PFTs) of importance for C, N, P, Si, Fe cycling and air-sea CO2 exchange in this area. These are the diatoms, the pico-nanophytoplankton and the coccolithophores whose growth regulation by light, temperature and nutrients has been obtained from phenomenological observations available for these PFTs. The performance of the SWAMCO-3 model coupled to a vertical one-dimensional physical model is assessed at the location of the time-series station KERFIX (around 51°S-68°E). The model was able to reproduce a mean seasonal cycle based on years where a maximum of chemical and biological observations are available. Ocean fCO2 in equilibrium with the atmosphere are simulated both in winter associated with surface layer replenishment in DIC due to deep vertical mixing and in late summer as a consequence of the warming effect on the carbonate system. A clear under-saturation is simulated in summer driven by primary production. Model scenarios cancelling biological activity or only coccolithophores allowed, by comparison with the standard simulation, untangling the respective role of physical and biological processes in driving the sign and magnitude of air-sea CO2 exchanges. First, we show that coccolithophores are repressing the ocean C uptake, but only marginally (5%). Second, the model highlights the role of diatoms on the presence of a CO2 sink in summer. Altogether, this results in a weak annual air-sea CO2 flux (-0.9 mol m-2 y-1 or -0.1 Pg C y-1 for the ice-free zone south of 50°S), whose variability seems more related to the thermodynamical processes. We then speculate how global warming might influence the latter mechanisms and alter air-sea CO2 exchanges in this region.

  13. SIPEX--Exploring the Antarctic Sea Ice Zone

    ERIC Educational Resources Information Center

    Zicus, Sandra; Dobson, Jane; Worby, Anthony

    2008-01-01

    Sea ice in the polar regions plays a key role in both regulating global climate and maintaining marine ecosystems. The international Sea Ice Physics and Ecosystem eXperiment (SIPEX) explored the sea ice zone around Antarctica in September and October 2007, investigating relationships between the physical sea ice environment and the structure of…

  14. SIPEX--Exploring the Antarctic Sea Ice Zone

    ERIC Educational Resources Information Center

    Zicus, Sandra; Dobson, Jane; Worby, Anthony

    2008-01-01

    Sea ice in the polar regions plays a key role in both regulating global climate and maintaining marine ecosystems. The international Sea Ice Physics and Ecosystem eXperiment (SIPEX) explored the sea ice zone around Antarctica in September and October 2007, investigating relationships between the physical sea ice environment and the structure of…

  15. Towards Resolving the Paradox of Antarctic Sea Ice: A New Integrated Framework for Observing the Antarctic Marginal Ice Zone

    NASA Astrophysics Data System (ADS)

    Williams, G. D.

    2014-12-01

    Antarctic sea ice distribution, a canary in the coal mine for climate change in the Southern Hemisphere, is controlled by the marginal ice zone (MIZ). The MIZ is the dynamic outer part of the sea-ice zone, where it interacts with the high-energy open ocean and is strongly affected by waves and storms. As an interface between ocean and atmosphere with extreme vertical and horizontal temperature gradients and large variations in mechanical properties, the MIZ is a complex system that evolves with, and impacts upon, the advancing/receding ice edge. More than a zone, it is a migratory transition in 'phase space' that biannually passes across the entire Antarctic SIZ. During the advance phase of sea-ice seasonality, and under freezing conditions, wave-induced pancake-ice formation can lead to rapid ice-edge advance. During the retreat phase, the dynamic break-up and modification of sea ice by passing storms, winds and waves greatly modifies the floe-size distribution within the MIZ, to create smaller floes that melt more rapidly and accelerate sea-ice retreat as spring progresses. Inspired by the current Arctic MIZ efforts, new fieldwork is proposed to resolve the key characteristics of the Antarctic MIZ and the processes controlling its extent. Combining new autonomous observation technology with ship-based techniques, integrated experiments are being designed to advance our understanding of the MIZ and its role in driving seasonal sea ice advance and retreat around Antarctica. The proposed project provides a unique opportunity to develop an observational, analytical, and science-policy framework for coordinated monitoring of sea ice in both the northern and southern hemispheres, with implications for forecasting, monitoring, and prediction that are essential with increasingly dynamic and variable polar climate systems.

  16. 46 CFR 42.07-15 - Zones and seasonal areas.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... BY SEA Control, Enforcement, and Rights of Appeal § 42.07-15 Zones and seasonal areas. (a) A vessel... regarding the zones and seasonal areas described in subpart 42.30. (b) A port located on the boundary...

  17. 46 CFR 42.07-15 - Zones and seasonal areas.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... BY SEA Control, Enforcement, and Rights of Appeal § 42.07-15 Zones and seasonal areas. (a) A vessel... regarding the zones and seasonal areas described in subpart 42.30. (b) A port located on the boundary...

  18. Seasonal variations of storm zones on Mars

    NASA Astrophysics Data System (ADS)

    Hollingsworth, J. L.; Haberle, R. M.; Schaeffer, J.

    1997-05-01

    Using the NASA Ames Mars general circulation model, an annual cycle simulation has been performed corresponding to a low atmospheric dust loading. Surface pressure time series near the Viking Lander 2 location have been analyzed using singular spectrum analysis (SSA) and autoregressive models to isolate statistically significant spectral power. Also, circulation statistics have been separated using band-pass time filtering and analyzed for coherent spatial patterns. During northern autumn, winter and spring seasons, localized `storm zones' can occur which are particularly strong within the lowlands of Arcadia, Acidalia and Utopia. During early northern spring, the transient eddy activity is stronger than that found during any other season. With weakening baroclinicity accompanying seasonal transition toward midspring, the eddies become less vigorous and the associated storm `belt' shifts into higher latitudes. Since transient baroclinic eddies are active agents in the transport of heat, momentum and moisture in middle latitudes, variations in the storm zones during the seasonal cycle will have important implications for Mars' regional climate.

  19. 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

  20. Waves and Fetch in the Marginal Ice Zone

    DTIC Science & Technology

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Waves and fetch in the Marginal Ice Zone Jim Thomson...Marginal Ice Zone (MIZ) by improving basic understanding of the interaction between waves, sea ice , and open water (i.e., fetch). OBJECTIVES The...to use Surface Wave Instrument Floats with Tracking (SWIFT) buoys to measure waves, winds, and turbulence at the air-sea- ice interface (Thomson

  1. Wave-Ice interaction in the Marginal Ice Zone: Toward a Wave-Ocean-Ice Coupled Modeling System

    DTIC Science & Technology

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Wave- Ice interaction in the Marginal Ice Zone: Toward a...Wave-Ocean- Ice Coupled Modeling System W. E. Rogers Naval Research Laboratory, Code 7322 Stennis Space Center, MS 39529 phone: (228) 688-4727...scattering of waves by interaction with ice in the Marginal Ice Zone (MIZ). The wave model physics developed here will later be part of an operational

  2. Impact of sea ice initialization on sea ice and atmosphere prediction skill on seasonal timescales

    NASA Astrophysics Data System (ADS)

    Guemas, V.; Chevallier, M.; Déqué, M.; Bellprat, O.; Doblas-Reyes, F.

    2016-04-01

    We present a robust assessment of the impact of sea ice initialization from reconstructions of the real state on the sea ice and atmosphere prediction skill. We ran two ensemble seasonal prediction experiments from 1979 to 2012 : one using realistic sea ice initial conditions and another where sea ice is initialized from a climatology, with two forecast systems. During the melting season in the Arctic Ocean, sea ice forecasts become skilful with sea ice initialization until 3-5 months ahead, thanks to the memory held by sea ice thickness. During the freezing season in both the Arctic and Antarctic Oceans, sea ice forecasts are skilful for 7 and 2 months, respectively, with negligible differences between the two experiments, the memory being held by the ocean heat content. A weak impact on the atmosphere prediction skill is obtained.

  3. Remote sensing of the Fram Strait marginal ice zone

    USGS Publications Warehouse

    Shuchman, R.A.; Burns, B.A.; Johannessen, O.M.; Josberger, E.G.; Campbell, W.J.; Manley, T.O.; Lannelongue, N.

    1987-01-01

    Sequential remote sensing images of the Fram Strait marginal ice zone played a key role in elucidating the complex interactions of the atmosphere, ocean, and sea ice. Analysis of a subset of these images covering a 1-week period provided quantitative data on the mesoscale ice morphology, including ice edge positions, ice concentrations, floe size distribution, and ice kinematics. The analysis showed that, under light to moderate wind conditions, the morphology of the marginal ice zone reflects the underlying ocean circulation. High-resolution radar observations showed the location and size of ocean eddies near the ice edge. Ice kinematics from sequential radar images revealed an ocean eddy beneath the interior pack ice that was verified by in situ oceanographic measurements.

  4. CO2, CH4, and N2O in the Open Ocean, Sea-ice Zone, and Polynya of the Southern Ocean Observed during Austral Summer Season from 2009 to 2013

    NASA Astrophysics Data System (ADS)

    Rhee, T. S.; Park, K.; Hahm, D.; Jeon, H.; Park, K.; Kwon, Y.; Shin, H.; Lee, S.; Lee, K. E.

    2013-12-01

    Korean ice-breaking research vessel Araon has been at sea since 2010 carrying out a variety of research activities. During these periods we measured CO2, CH4, and N2O at sea below and above the sea surface to estimate sink or source strengths of the ocean in the characteristic provinces at high latitude. The ocean plays a wide range of role in the budget of these gases in the atmosphere: as a sink for CO2 and a source for CH4 and N2O. High latitude of the Southern Ocean is particularly important as the change in the cryosphere can impact the ecological and physical settings that govern the content and flux of these dissolved gases in seawater. We have visited the Amundsen Sea during the austral summer in 2010/2011 and 2012, and the Ross Sea in 2013 in order to investigate the impact of the change in the cryospheric environments. In addition we had opportunity to survey the Pacific sector of the Southern Ocean in 2009 onboard R/V Polarstern. In the open ocean, CO2 in the seawater was mostly undersaturated, CH4 was in equilibrium or slightly undersaturated, and N2O was supersaturated with respect to that in the marine boundary layer. These features were not observed in the sea-ice zone; CO2 in the seawater was slightly supersaturated in 2011, but not in 2012 and 2013, while dissolved CH4 was undersaturated and N2O was supersaturated for three years. In the polynya of the Amundsen Sea and the Ross Sea, CO2 and CH4 were undersaturated in the seawater while N2O was supersaturated with respect to that in the atmosphere. Based on these 4-year observations during austral summer season, high latitude of the southern ocean contributes as a strong sink for atmospheric CO2 whilst as a strong source for N2O. In the case of CH4, the Southern Ocean acted as a sink of the atmospheric CH4, which differs from the role of the ocean in the global scale.

  5. Environment at the Grounding Zone of the Whillans Ice Stream-Ross Ice Shelf, West Antarctica

    NASA Astrophysics Data System (ADS)

    Hodson, T. O.; Powell, R. D.; Mikucki, J.; Scherer, R. P.; Tulaczyk, S. M.; Coenen, J. J.; Puttkammer, R.; Branecky, C.

    2015-12-01

    Grounding zones where grounded ice sheets transition to floating ice shelves, are the primary gateways through which the Antarctic Ice Sheet loses mass to the ocean. In these environments, ice, ocean, meltwater and sediment meet and interact, influencing both the ice sheet and ocean circulation beneath the ice shelf. Here, we report on conditions near the grounding zone of the Whillans Ice Stream, which feeds into the Ross Ice Shelf. Cameras and instruments lowered through an access borehole to the ocean cavity beneath the ice shelf found a 10m-thick water column comprising an upper layer of colder ice shelf water formed from mixing between meltwater with the lower layer of warmer higher salinity shelf water. This style of stratification is typical of large ice shelves, but it was uncertain whether it existed so near the grounding zone, where stronger tidal currents and/or strong subglacial stream discharges could mix the water column. Salinity and temperature of the water suggest it formed from sea ice production in the Western Ross Sea, with minimal modification beneath the ice shelf. This source region is distinct from waters previously observed at the nearby J-9 borehole, illustrating the importance of the sub-ice shelf bathymetry in steering circulation between the ocean and the grounding zone. Preliminary data suggest an active exchange of heat and nutrients between the grounding zone and the open ocean, despite being separated by 600km. Thus life found near the grounding line is probably not an isolated oasis, but may instead be part of a much broader ecosystem that spans the ice shelf. Although sea ice formation presently maintains water in the sub-ice shelf cavity near the surface freezing point, buffering many larger ice shelves from gradual ocean warming, these findings suggest that even grounding zones of extensive ice shelves may respond quickly to abrupt changes in ocean circulation, such as that observed in the Amundsen Sea.

  6. Skillful regional prediction of Arctic sea ice on seasonal timescales

    NASA Astrophysics Data System (ADS)

    Bushuk, Mitchell; Msadek, Rym; Winton, Michael; Vecchi, Gabriel A.; Gudgel, Rich; Rosati, Anthony; Yang, Xiaosong

    2017-05-01

    Recent Arctic sea ice seasonal prediction efforts and forecast skill assessments have primarily focused on pan-Arctic sea ice extent (SIE). In this work, we move toward stakeholder-relevant spatial scales, investigating the regional forecast skill of Arctic sea ice in a Geophysical Fluid Dynamics Laboratory (GFDL) seasonal prediction system. Using a suite of retrospective initialized forecasts spanning 1981-2015 made with a coupled atmosphere-ocean-sea ice-land model, we show that predictions of detrended regional SIE are skillful at lead times up to 11 months. Regional prediction skill is highly region and target month dependent and generically exceeds the skill of an anomaly persistence forecast. We show for the first time that initializing the ocean subsurface in a seasonal prediction system can yield significant regional skill for winter SIE. Similarly, as suggested by previous work, we find that sea ice thickness initial conditions provide a crucial source of skill for regional summer SIE.

  7. Seasonal Ice Zone Reconnaissance Surveys Coordination

    DTIC Science & Technology

    2016-03-30

    Activity Ocean Profile Measurements During the SIZRS Morison Ocean expendable probes AXCTD & AXCP for T, S, V, internal waves/mixing Clouds and...aircraft), cloud top/base heights UpTempO buoys for understanding and prediction…. Steele UpTempO buoy drops for SLP, SST, SSS, & surface velocity...pattern in previous years. The appearance of warm near-surface water in the developing open water regions at the south end of the section is also

  8. Seasonal Ice Zone Reconnaissance Surveys Coordination

    DTIC Science & Technology

    2013-09-30

    NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) University of Washington,Applied Physics Lab , Polar Science Center,1013...equipment.) RESULTS The scientific results are described in the report for the various scince components of SIZRS including for this PI “Ocean

  9. Seasonal Ice Zone Reconnaissance Surveys Coordination

    DTIC Science & Technology

    2014-09-30

    core elements (Table 1) are aircraft expendable CTD (AXCTD) vertical profiles of ocean temperature and salinity plus aircraft expendable current...profiler (AXCP) ocean velocity shear (Morison), UpTempO buoy measurements of sea surface temperature (SST), sea level atmospheric pressure (SLP), and...flights farther into the Arctic Ocean and on two lines of longitude (150°W and 140 °W) on consecutive days. These include lines of about 5 stations across

  10. 76 FR 1362 - Safety Zone; Ice Conditions for the Baltimore Captain of Port Zone

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-10

    ... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone; Ice Conditions for the Baltimore Captain of.... This safety zone is necessary to protect mariners from the hazards associated with ice in the navigable... necessary to protect persons and vessels against the hazards associated with ice on navigable waters. Such...

  11. 78 FR 12595 - Safety Zone for Ice Conditions; Baltimore Captain of the Port Zone

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-02-25

    ... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone for Ice Conditions; Baltimore Captain of the.... This safety zone is necessary to protect mariners from the hazards associated with ice in the navigable... vessels against the hazards associated with ice on navigable waters. Such hazards include vessels becoming...

  12. Selected physical, biological and biogeochemical implications of a rapidly changing Arctic Marginal Ice Zone

    NASA Astrophysics Data System (ADS)

    Barber, David G.; Hop, Haakon; Mundy, Christopher J.; Else, Brent; Dmitrenko, Igor A.; Tremblay, Jean-Eric; Ehn, Jens K.; Assmy, Philipp; Daase, Malin; Candlish, Lauren M.; Rysgaard, Søren

    2015-12-01

    The Marginal Ice Zone (MIZ) of the Arctic Ocean is changing rapidly due to a warming Arctic climate with commensurate reductions in sea ice extent and thickness. This Pan-Arctic review summarizes the main changes in the Arctic ocean-sea ice-atmosphere (OSA) interface, with implications for primary- and secondary producers in the ice and the underlying water column. Changes in the Arctic MIZ were interpreted for the period 1979-2010, based on best-fit regressions for each month. Trends of increasingly open water were statistically significant for each month, with quadratic fit for August-November, illustrating particularly strong seasonal feedbacks in sea-ice formation and decay. Geographic interpretations of physical and biological changes were based on comparison of regions with significant changes in sea ice: (1) The Pacific Sector of the Arctic Ocean including the Canada Basin and the Beaufort, Chukchi and East Siberian seas; (2) The Canadian Arctic Archipelago; (3) Baffin Bay and Hudson Bay; and (4) the Barents and Kara seas. Changes in ice conditions in the Barents sea/Kara sea region appear to be primarily forced by ocean heat fluxes during winter, whereas changes in the other sectors appear to be more summer-autumn related and primarily atmospherically forced. Effects of seasonal and regional changes in OSA-system with regard to increased open water were summarized for photosynthetically available radiation, nutrient delivery to the euphotic zone, primary production of ice algae and phytoplankton, ice-associated fauna and zooplankton, and gas exchange of CO2. Changes in the physical factors varied amongst regions, and showed direct effects on organisms linked to sea ice. Zooplankton species appear to be more flexible and likely able to adapt to variability in the onset of primary production. The major changes identified for the ice-associated ecosystem are with regard to production timing and abundance or biomass of ice flora and fauna, which are related to

  13. Skill improvement of dynamical seasonal Arctic sea ice forecasts

    NASA Astrophysics Data System (ADS)

    Krikken, Folmer; Schmeits, Maurice; Vlot, Willem; Guemas, Virginie; Hazeleger, Wilco

    2016-05-01

    We explore the error and improve the skill of the outcome from dynamical seasonal Arctic sea ice reforecasts using different bias correction and ensemble calibration methods. These reforecasts consist of a five-member ensemble from 1979 to 2012 using the general circulation model EC-Earth. The raw model reforecasts show large biases in Arctic sea ice area, mainly due to a differently simulated seasonal cycle and long term trend compared to observations. This translates very quickly (1-3 months) into large biases. We find that (heteroscedastic) extended logistic regressions are viable ensemble calibration methods, as the forecast skill is improved compared to standard bias correction methods. Analysis of regional skill of Arctic sea ice shows that the Northeast Passage and the Kara and Barents Sea are most predictable. These results show the importance of reducing model error and the potential for ensemble calibration in improving skill of seasonal forecasts of Arctic sea ice.

  14. Antarctic Sea ice variations and seasonal air temperature relationships

    NASA Technical Reports Server (NTRS)

    Weatherly, John W.; Walsh, John E.; Zwally, H. J.

    1991-01-01

    Data through 1987 are used to determine the regional and seasonal dependencies of recent trends of Antarctic temperature and sea ice. Lead-lag relationships involving regional sea ice and air temperature are systematically evaluated, with an eye toward the ice-temperature feedbacks that may influence climatic change. Over the 1958-1087 period the temperature trends are positive in all seasons. For the 15 years (l973-l987) for which ice data are available, the trends are predominantly positive only in winter and summer, and are most strongly positive over the Antarctic Peninsula. The spatially aggregated trend of temperature for this latter period is small but positive, while the corresponding trend of ice coverage is small but negative. Lag correlations between seasonal anomalies of the two variables are generally stronger with ice lagging the summer temperatures and with ice leading the winter temperatures. The implication is that summer temperatures predispose the near-surface waters to above-or below-normal ice coverage in the following fall and winter.

  15. Wave effects on ocean-ice interaction in the marginal ice zone

    NASA Technical Reports Server (NTRS)

    Liu, Antony K.; Hakkinen, Sirpa; Peng, Chih Y.

    1993-01-01

    The effects of wave train on ice-ocean interaction in the marginal ice zone are studied through numerical modeling. A coupled two-dimensional ice-ocean model has been developed to include wave effects and wind stress for the predictions of ice edge dynamics. The sea ice model is coupled to the reduced-gravity ocean model through interfacial stresses. The main dynamic balance in the ice momentum is between water-ice stress, wind stress, and wave radiation stresses. By considering the exchange of momentum between waves and ice pack through radiation stress for decaying waves, a parametric study of the effects of wave stress and wind stress on ice edge dynamics has been performed. The numerical results show significant effects from wave action. The ice edge is sharper, and ice edge meanders form in the marginal ice zone owing to forcing by wave action and refraction of swell system after a couple of days. Upwelling at the ice edge and eddy formation can be enhanced by the nonlinear effects of wave action; wave action sharpens the ice edge and can produce ice meandering, which enhances local Ekman pumping and pycnocline anomalies. The resulting ice concentration, pycnocline changes, and flow velocity field are shown to be consistent with previous observations.

  16. Mapping and assessing variability in the Antarctic marginal ice zone, pack ice and coastal polynyas in two sea ice algorithms with implications on breeding success of snow petrels

    NASA Astrophysics Data System (ADS)

    Stroeve, Julienne C.; Jenouvrier, Stephanie; Campbell, G. Garrett; Barbraud, Christophe; Delord, Karine

    2016-08-01

    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 as well as seasonal and interannual variability is essential for understanding how current and future changes in these biologically active regions may impact the Antarctic marine ecosystem. Knowledge of the distribution of MIZ, consolidated pack ice and coastal polynyas in 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 record for assessing the proportion of the sea ice cover that is covered by each of these ice categories. However, estimates of the amount of MIZ, consolidated pack ice and polynyas depend strongly on which sea ice algorithm is used. This study uses two popular passive microwave sea ice algorithms, the NASA Team and Bootstrap, and applies the same thresholds to the sea ice concentrations to evaluate the distribution and variability in the MIZ, the consolidated pack ice and coastal polynyas. Results reveal that the seasonal cycle in the MIZ and pack ice is generally similar between both algorithms, yet the NASA Team algorithm has on average twice the MIZ and half the consolidated pack ice area as the Bootstrap algorithm. Trends also differ, with the Bootstrap algorithm suggesting statistically significant trends towards increased pack ice area and no statistically significant trends in the MIZ. The NASA Team algorithm on the other hand indicates statistically significant positive trends in the MIZ during spring. Potential coastal polynya area and amount of broken ice within the consolidated ice pack are also larger in the NASA Team algorithm. The timing of maximum polynya area may differ by as much as 5 months between algorithms. These

  17. Norwegian remote sensing experiment in a marginal ice zone

    USGS Publications Warehouse

    Farrelly, B.; Johannessen, J.A.; Svendsen, E.; Kloster, K.; Horjen, I.; Matzler, C.; Crawford, J.; Harrington, R.; Jones, L.; Swift, C.; Delnore, V.E.; Cavalieri, D.; Gloersen, P.; Hsiao, S.V.; Shemdin, O.H.; Thompson, T.W.; Ramseier, R.O.; Johannessen, O.M.; Campbell, W.J.

    1983-01-01

    The Norwegian Remote Sensing Experiment in the marginal ice zone north of Svalbard took place in fall 1979. Coordinated passive and active microwave measurements were obtained from shipborne, airborne, and satellite instruments together with in situ observations. The obtained spectra of emissivity (frequency range, 5 to 100 gigahertz) should improve identification of ice types and estimates of ice concentration. Mesoscale features along the ice edge were revealed by a 1.215-gigahertz synthetic aperture radar. Ice edge location by the Nimbus 7 scanning multichannel microwave radiometer was shown to be accurate to within 10 kilometers.

  18. Investigation of Ice Dynamics in the Marginal Ice Zone.

    DTIC Science & Technology

    2014-09-26

    far met on two accasiond discussing mainly on MIZEX-83 data and modeling problems. This research project has already been partially producing six...consequence that an ocean dynamics model for the ice margin problems should have an advanced ice dynamics model coupled with it. Such modeling work has...already written for processing MIZEX-83 data. 4. Modeling A final’manuscript was preparedof one-dimenglonal modeling studies of ice drift in the

  19. The 2013 Arctic Field Season of the NRL Sea-Ice Measurement Program

    NASA Astrophysics Data System (ADS)

    Gardner, J. M.; Brozena, J. M.; Ball, D.; Hagen, R. A.; Liang, R.; Stoudt, C.

    2013-12-01

    The U.S. Naval Research Laboratory (NRL) is conducting a five year study of the changing Arctic with a particular focus on ice thickness and distribution variability with the intent of optimizing state-of-the-art computer models which are currently used to predict sea ice changes. An important part of our study is to calibrate/validate CryoSat2 ice thickness data prior to its incorporation into new ice forecast models. NRL Code 7420 collected coincident data with the CryoSat2 satellite in 2011 and 2012 using a LiDAR (Riegl Q560) to measure combined snow and ice thickness and a 10 GHz pulse-limited precision radar altimeter to measure sea-ice freeboard. This field season, LiDAR data was collected using the Riegl Q680 which permitted higher density operation and data collection. Concident radar data was collected using an improved version of the NRL 10 GHz pulse limited radar that was used for the 2012 fieldwork. 8 coincident tracks of CryoSat2 satellite data were collected. Additionally a series of grids (7 total) of adjacent tracks were flown coincident with Cryosat2 satellite overpass. These grids cover the approximate satellite footprint of the satellite on the ice as it passes overhead. Data from these grids are shown here and will be used to examine the relationship of the tracked satellite waveform data to the actual surface across the footprint. We also coordinated with the Seasonal Ice Zone Observing Network (SIZONet) group who conducted surface based ice thickness surveys using a Geonics EM-31 along hunter trails on the landfast ice near Barrow as well as on drifting ice offshore during helicopter landings. On two sorties, a twin otter carrying the NRL LiDAR and radar altimeter flew in tandem with the helicopter carrying the EM-31 to achieve synchronous data acquisition. Data from these flights are shown here along with a digital elevation map.

  20. Mechanism of seasonal Arctic sea ice evolution and Arctic amplification

    NASA Astrophysics Data System (ADS)

    Kim, Kwang-Yul; Hamlington, Benjamin D.; Na, Hanna; Kim, Jinju

    2016-09-01

    Sea ice loss is proposed as a primary reason for the Arctic amplification, although the physical mechanism of the Arctic amplification and its connection with sea ice melting is still in debate. In the present study, monthly ERA-Interim reanalysis data are analyzed via cyclostationary empirical orthogonal function analysis to understand the seasonal mechanism of sea ice loss in the Arctic Ocean and the Arctic amplification. While sea ice loss is widespread over much of the perimeter of the Arctic Ocean in summer, sea ice remains thin in winter only in the Barents-Kara seas. Excessive turbulent heat flux through the sea surface exposed to air due to sea ice reduction warms the atmospheric column. Warmer air increases the downward longwave radiation and subsequently surface air temperature, which facilitates sea surface remains to be free of ice. This positive feedback mechanism is not clearly observed in the Laptev, East Siberian, Chukchi, and Beaufort seas, since sea ice refreezes in late fall (November) before excessive turbulent heat flux is available for warming the atmospheric column in winter. A detailed seasonal heat budget is presented in order to understand specific differences between the Barents-Kara seas and Laptev, East Siberian, Chukchi, and Beaufort seas.

  1. Wave climate in the Arctic 1992-2014: seasonality, trends, and wave-ice influence

    NASA Astrophysics Data System (ADS)

    Girard-Ardhuin, Fanny; Stopa, Justin; Ardhuin, Fabrice

    2016-04-01

    The diminishing sea ice has direct implications on the wave field which is mainly dependent on the ice-free area and wind. Over the past decade, the Arctic sea ice has diminished which directly impacts the wave field. This study characterizes the wave climate in the Arctic using detailed sea state information from a wave hindcast and merged altimeter dataset spanning 1992-2014. The waves are driven by winds from the Climate Forecast System Reanalysis. Ice concentrations derived from satellites with a grid spacing of 12.5 km are sufficiently able to resolve important features in the marginal ice zone. Before implementation, suitable wind forcing is identified and the validity and consistency of the wave hindcast is verified with altimeters. The seasonal ice advance and retreat largely dictates the waves and creates distinct features in the wind-waves and swells. The Nordic-Greenland Sea is dominated by swells from the North Atlantic while the coastal regions and semi-enclosed seas of the Kara, Laptev, Chukchi, and Beaufort have a more equal proportion of wind-waves and swells. Trends in the altimeters and model are in agreement and show increasing wave activities in the Baffin Bay, Beaufort, Chukchi, Laptev, and Kara Seas due to the loss of sea ice. In the Nordic-Greenland Sea, there is a decreasing trend related to changes in the wind field by North Atlantic Oscillation. The waves also influence the sea ice. Two distinctly different wave-ice environments are identified and selected events demonstrate the importance of waves in the marginal ice zone. The crux of the research identifies the need for continued study and improvement of wave-ice interaction.

  2. Seasonal precipitation timing and ice core records

    SciTech Connect

    Steig, E.J.; Grootes, P.M.; Stuiver, M. )

    1994-12-16

    This is a commentary on global circulation model experiments of moisture source changes in Greenland, urging caution in how they are applied because they have important implications for paleoclimate reconstruction from ice cores. The work comes from preliminary find is of a ice core (GISP2) of the authors. The authors conclude that at present anomalies in Greenland ice core records should not be interpreted solely in terms of source region variations. The combined use of oxygen 18, D and ionic species in the new Summit, Greenland cores should make it possible to answer empirically some of the questions raised by the GCM experiments as to the interpretation of oxygen 18 records in terms of temperature. 4 refs., 1 fig.

  3. Seasonal Greenland Ice Sheet ice flow variations in regions of differing bed and surface topography

    NASA Astrophysics Data System (ADS)

    Sole, A. J.; Livingstone, S. J.; Rippin, D. M.; Hill, J.; McMillan, M.; Quincey, D. J.

    2015-12-01

    The contribution of the Greenland Ice Sheet (GrIS) to future sea-level rise is uncertain. Observations reveal the important role of basal water in controlling ice-flow to the ice sheet margin. In Greenland, drainage of large volumes of surface meltwater to the ice sheet bed through moulins and hydrofracture beneath surface lakes dominates the subglacial hydrological system and provides an efficient means of moving mass and heat through the ice sheet. Ice surface and bed topography influence where meltwater can access the bed, and the nature of its subsequent flow beneath the ice. However, no systematic investigation into the influence of topographic variability on Greenland hydrology and dynamics exists. Thus, physical processes controlling storage and drainage of surface and basal meltwater, and the way these affect ice flow are not comprehensively understood. This presents a critical obstacle in efforts to predict the future evolution of the GrIS. Here we present high-resolution satellite mapping of the ice-surface drainage network (e.g. lakes, channels and moulins) and measurements of seasonal variations in ice flow in south west Greenland. The region is comprised of three distinct subglacial terrains which vary in terms of the amplitude and wavelength and thus the degree to which basal topography is reflected in the ice sheet surface. We find that the distribution of surface hydrological features is related to the transfer of bed topography to the ice sheet surface. For example, in areas of thinner ice and high bed relief, moulins occur more frequently and are more uniformly dispersed, indicating a more distributed influx of surface-derived meltwater to the ice sheet bed. We investigate the implications of such spatial variations in surface hydrology on seasonal ice flow rates.

  4. Multi-system seasonal predictions of Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Merryfield, W. J.; Lee, W.-S.; Wang, W.; Chen, M.; Kumar, A.

    2013-04-01

    The utility of multi-system, coupled model-based seasonal predictions of Arctic sea ice area and extent is investigated for combined predictions from the Climate Forecast System version 2 (CFSv2) and Canadian Seasonal to Interannual Prediction System (CanSIPS) operational seasonal forecasting systems, which are among the first to have sea ice as a prognostic variable. Forecast skills for predictions of total anomalies and departures from long-term linear trends are examined both for the individual systems and the combined forecasts, and are compared against simple predictions such as damped anomaly persistence. Results indicate that the tendency for climate forecasts based on combined output from multiple prediction systems to outperform any one system, demonstrated previously for global variables such as temperature and precipitation, is realized for predictions of Arctic sea ice as well.

  5. 46 CFR 42.30-5 - Northern Winter Seasonal Zones and area.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    .... Excluded from this zone are the North Atlantic Winter Seasonal Zone I and the Baltic Sea bounded by the... FOREIGN VOYAGES BY SEA Zones, Areas, and Seasonal Periods § 42.30-5 Northern Winter Seasonal Zones...

  6. 46 CFR 42.30-5 - Northern Winter Seasonal Zones and area.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    .... Excluded from this zone are the North Atlantic Winter Seasonal Zone I and the Baltic Sea bounded by the... FOREIGN VOYAGES BY SEA Zones, Areas, and Seasonal Periods § 42.30-5 Northern Winter Seasonal Zones...

  7. 46 CFR 42.30-5 - Northern Winter Seasonal Zones and area.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    .... Excluded from this zone are the North Atlantic Winter Seasonal Zone I and the Baltic Sea bounded by the... FOREIGN VOYAGES BY SEA Zones, Areas, and Seasonal Periods § 42.30-5 Northern Winter Seasonal Zones...

  8. Zooplankton data report: the Marginal Ice Zone Experiment MIZEX, 1984

    SciTech Connect

    Smith, S.L.; Lane, P.V.Z.; Schwarting, E.M.

    1986-03-01

    The Marginal Ice Zone Experiment (MIZEX 84) concentrated on atmospheric, oceanic, and ice interactions in the Fram Strait region of the Greenland Sea, specifically the effect of the retreating ice margin on the productivity in the area and the use of zooplanktonic species as indicators of Arctic and North Atlantic water masses. The data in this report are the quantitative analyses of zooplankton collected while aboard the research vessel Polarstern.

  9. Seasonal ice flow patterns as indicators of subglacial hydrology on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Moon, T. A.; Fahnestock, M. A.; Scambos, T.; Joughin, I.; van den Broeke, M.; Klinger, M. J.

    2015-12-01

    Improvements in satellite coverage of the Greenland Ice Sheet have supported a substantial increase in the spatial and temporal resolution of surface velocity measurements. Previously, with seasonal TerraSAR-X satellite measurements of marine-terminating glaciers across the western and southeastern coasts, we identified three dominant and distinct seasonal velocity patterns. Two patterns likely indicate differences in the development of the subglacial hydrologic system, one suggesting development of efficient subglacial drainage during the summer melt season and the other without. Using this framework, we are now taking advantage of a new velocity record we created from Landsat 8 OLI imagery, which allows for better sampling across space and time, to examine local and regional variations in ice sheet surface velocity. Readily measurable, ice velocity holds strong potential as a proxy for understanding changes in subglacial hydrology, which is much more difficult to observe. We investigate seasonal velocity behavior from glacier termini toward the ice sheet interior and among separate glacier systems across the Greenland Ice Sheet as a way to understand changes in ice motion and ice sheet hydrology.

  10. 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.

  11. Wave-Ice Interaction and the Marginal Ice Zone

    DTIC Science & Technology

    2013-09-30

    primarily during the summer ice breakup of 2014. WORK COMPLETED Activity during the second year continued to focus on the design and build of wave...buoys for the 2014 field experiment, in collaboration with the British Antarctic Survey, Cambridge. Dr Doble travelled to Cambridge on nine...icebreakers Louis St Laurent (one buoy deployed on ice as part of a multi-buoy array) and the Araon ( two buoys, deployed into open water). The buoys

  12. Regional seasonal forecasts of the Arctic sea ice in two coupled climate models

    NASA Astrophysics Data System (ADS)

    Chevallier, Matthieu; Guémas, Virginie; Salas y Mélia, David; Doblas-Reyes, Francisco

    2015-04-01

    The predictive capabilities of two state-of-the-art coupled atmosphere-ocean global climate models (CNRM-CM5.1 and EC-Earth v2.3) in seasonal forecasting of the Arctic sea ice will be presented with a focus on regional skill. 5-month hindcasts of September sea ice area in the Arctic peripherial seas (Barents-Kara seas, Laptev-East Siberian seas, Chukchi sea and Beaufort sea) and March sea ice area in the marginal ice zones (Barents, Greenland, Labrador, Bering and Okhotsk sea) have been produced over the period 1990-2009. Systems mainly differ with respect to the initialization strategy, the ensemble generation techniques and the sea ice components. Predictive skill, assessed in terms of actual and potential predictability, is comparable in the two systems for both summer and winter hindcasts. Most interestingly, the multi-model prediction is often better than individual predictions in several sub-basins, including the Barents sea in the winter and most shelf seas in the summer. Systematic biases are also reduced using the multi-model predictions. Results from this study show that a regional zoom of global seasonal forecasts could be useful for operational needs. This study also show that the multi-model approach may be the step forward in producing accurate and reliable seasonal forecasts based on coupled global climate models.

  13. Deterministic multi-zone ice accretion modeling

    NASA Technical Reports Server (NTRS)

    Yamaguchi, K.; Hansman, R. John, Jr.; Kazmierczak, Michael

    1991-01-01

    The focus here is on a deterministic model of the surface roughness transition behavior of glaze ice. The initial smooth/rough transition location, bead formation, and the propagation of the transition location are analyzed. Based on the hypothesis that the smooth/rough transition location coincides with the laminar/turbulent boundary layer transition location, a multizone model is implemented in the LEWICE code. In order to verify the effectiveness of the model, ice accretion predictions for simple cylinders calculated by the multizone LEWICE are compared to experimental ice shapes. The glaze ice shapes are found to be sensitive to the laminar surface roughness and bead thickness parameters controlling the transition location, while the ice shapes are found to be insensitive to the turbulent surface roughness.

  14. Seismic exploration noise reduction in the Marginal Ice Zone.

    PubMed

    Tollefsen, Dag; Sagen, Hanne

    2014-07-01

    A sonobuoy field was deployed in the Marginal Ice Zone of the Fram Strait in June 2011 to study the spatial variability of ambient noise. High noise levels observed at 10-200 Hz are attributed to distant (1400 km range) seismic exploration. The noise levels decreased with range into the ice cover; the reduction is fitted by a spreading loss model with a frequency-dependent attenuation factor less than for under-ice interior Arctic propagation. Numerical modeling predicts transmission loss of the same order as the observed noise level reduction and indicates a significant loss contribution from under-ice interaction.

  15. Identification of paleo Arctic winter sea ice limits and the marginal ice zone: Optimised biomarker-based reconstructions of late Quaternary Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Belt, Simon T.; Cabedo-Sanz, Patricia; Smik, Lukas; Navarro-Rodriguez, Alba; Berben, Sarah M. P.; Knies, Jochen; Husum, Katrine

    2015-12-01

    Analysis of >100 surface sediments from across the Barents Sea has shown that the relative abundances of the mono-unsaturated sea ice diatom-derived biomarker IP25 and a tri-unsaturated highly branched isoprenoid (HBI) lipid (HBI III) are characteristic of the overlying surface oceanographic conditions, most notably, the location of the seasonal sea ice edge. Thus, while IP25 is generally limited to locations experiencing seasonal sea ice, with higher abundances found for locations with longer periods of ice cover, HBI III is found in sediments from all sampling locations, but is significantly enhanced in sediments within the vicinity of the retreating sea ice edge or marginal ice zone (MIZ). The response of HBI III to this well-defined sea ice scenario also appears to be more selective than that of the more generic phytoplankton biomarker, brassicasterol. The potential for the combined analysis of IP25 and HBI III to provide more detailed assessments of past sea ice conditions than IP25 alone has been investigated by quantifying both biomarkers in three marine downcore records from locations with contrasting modern sea ice settings. For sediment cores from the western Barents Sea (intermittent seasonal sea ice) and the northern Norwegian Sea (ice-free), high IP25 and low HBI III during the Younger Dryas (ca. 12.9-11.9 cal. kyr BP) is consistent with extensive sea cover, with relatively short periods of ice-free conditions resulting from late summer retreat. Towards the end of the YD (ca. 11.9-11.5 cal. kyr BP), a general amelioration of conditions resulted in a near winter maximum ice edge scenario for both locations, although this was somewhat variable, and the eventual transition to predominantly ice-free conditions was later for the western Barents Sea site (ca. 9.9 cal. kyr BP) compared to NW Norway (ca. 11.5 cal. kyr BP). For both locations, coeval elevated HBI III (but absent IP25) potentially provides further evidence for increased Atlantic Water inflow

  16. 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.

  17. Understanding the Sea Ice Zone: Scientists and Communities Partnering to Archive, Analyze and Disseminate Local Ice Observations

    NASA Astrophysics Data System (ADS)

    Collins, J. A.; Oldenburg, J.; Liu, M.; Pulsifer, P. L.; Kaufman, M.; Eicken, H.; Parsons, M. A.

    2012-12-01

    Knowledge of sea ice is critical to the hunting, whaling, and cultural activities of many Indigenous communities in Northern and Western Alaska. Experienced hunters have monitored seasonal changes of the sea ice over many years, giving them a unique expertise in assessing the current state of the sea ice as well as any anomalies in seasonal sea ice conditions. The Seasonal Ice Zone Observing Network (SIZONet), in collaboration with the Exchange for Local Observations and Knowledge of the Arctic (ELOKA), has developed an online application for collecting, storing, and analyzing sea ice observations contributed by local experts from coastal Alaskan communities. Here we present the current iteration of the application, outline future plans and discuss how the development process and resulting system have improved our collective understanding of sea ice processes and changes. The SIZONet application design is based on the needs of the research scientists responsible for entering observation data into the database, the needs of local sea ice experts contributing their observations and knowledge, and the information needs of Alaska coastal communities. Entry forms provide a variety of input methods, including menus, check boxes, and free text input. Input options strive to balance flexibility in capturing concepts and details with the need for analytical consistency. Currently, research staff at the University of Alaska Fairbanks use the application to enter observations received via written or electronic communications from local sea ice experts. Observation data include current weather conditions, snow and ice quantity and quality, and wildlife sighted or taken. Future plans call for direct use of the SIZONet interface by local sea ice experts as well as students, both as contributors to the data collection and as users seeking meaning in the data. This functionality is currently available to a limited number of community members as we extend the application to support

  18. Autonomous Investigations of Marginal Ice Zone Processes- Changing Feedbacks and Observational Challenges

    NASA Astrophysics Data System (ADS)

    Lee, C.

    2014-12-01

    The observed reduction of Arctic summertime sea ice extent and expansion of the marginal ice zone (MIZ) has profound impacts on the balance of processes controlling sea ice evolution, including the introduction of several positive feedback mechanisms that may act to accelerate melting. Examples of such feedbacks include increased upper ocean warming though absorption of solar radiation, elevated internal wave energy and mixing that may entrain heat stored in subsurface watermasses (e.g. the relatively warm Pacific Summer (PSW) and Atlantic (AW) waters) and elevated surface wave energy that acts to deform and fracture sea ice, all of which grow in importance with increasing open water extent. Investigations of MIZ dynamics must resolve the short spatial and temporal scales associated with the processes that govern the exchange of momentum, heat and freshwater near the atmosphere-ice-ocean interface while also achieving the spatial scope and temporal persistence required to characterize how the balance of processes shifts as a function of evolving open water fraction and open water fetch to the south. The recent Office of Naval Research (ONR) Marginal Ice Zone program provides an example of how autonomous platforms can be applied to provide high-resolution measurements that extend from open water, through the MIZ and deep into ice-covered regions while providing persistence to quantify evolution over an entire summertime melt season. This talk will provide an overview of the strategy developed by the ONR MIZ team and highlight early results from the 2014 field program.

  19. Autonomous Investigations of Marginal Ice Zone Processes- Changing Feedbacks and Observational Challenges

    NASA Astrophysics Data System (ADS)

    Lee, Craig; Doble, Martin; Maslowski, Wieslaw; Stanton, Tim; Timmermans, Mary-Louise; Thomson, Jim; Wilkinson, Jeremy

    2015-04-01

    The observed reduction of Arctic summertime sea ice extent and expansion of the marginal ice zone (MIZ) have profound impacts on the balance of processes controlling sea ice evolution, including the introduction of several positive feedback mechanisms that may act to accelerate melting. Examples of such feedbacks include increased upper ocean warming though absorption of solar radiation, elevated internal wave energy and mixing that may entrain heat stored in subsurface watermasses (e.g. the relatively warm Pacific Summer (PSW) and Atlantic (AW) waters) and elevated surface wave energy that acts to deform and fracture sea ice, all of which grow in importance with increasing open water extent. Investigations of MIZ dynamics must resolve the short spatial and temporal scales associated with the processes that govern the exchange of momentum, heat and freshwater near the atmosphere-ice-ocean interface while also achieving the spatial scope and temporal persistence required to characterize how the balance of processes shifts as a function of evolving open water fraction and open water fetch to the south. The recent Office of Naval Research (ONR) Marginal Ice Zone program employed an integrated system of autonomous platforms to provide high-resolution measurements that extend from open water, through the MIZ and deep into ice-covered regions while providing persistence to quantify evolution over an entire summertime melt season. This presentation will provide an overview of the strategy developed by the ONR MIZ team and present early results from the 2014 field program.

  20. Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica.

    PubMed

    Khazendar, Ala; Rignot, Eric; Schroeder, Dustin M; Seroussi, Helene; Schodlok, Michael P; Scheuchl, Bernd; Mouginot, Jeremie; Sutterley, Tyler C; Velicogna, Isabella

    2016-10-25

    Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300-490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica.

  1. Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica

    NASA Astrophysics Data System (ADS)

    Khazendar, Ala; Rignot, Eric; Schroeder, Dustin M.; Seroussi, Helene; Schodlok, Michael P.; Scheuchl, Bernd; Mouginot, Jeremie; Sutterley, Tyler C.; Velicogna, Isabella

    2016-10-01

    Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300-490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica.

  2. Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica

    PubMed Central

    Khazendar, Ala; Rignot, Eric; Schroeder, Dustin M.; Seroussi, Helene; Schodlok, Michael P.; Scheuchl, Bernd; Mouginot, Jeremie; Sutterley, Tyler C.; Velicogna, Isabella

    2016-01-01

    Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300–490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica. PMID:27780191

  3. Arctic sea ice a major determinant in Mandt's black guillemot movement and distribution during non-breeding season

    USGS Publications Warehouse

    Divoky, G.J.; Douglas, David C.; Stenhouse, I. J.

    2016-01-01

    Mandt's black guillemot (Cepphus grylle mandtii) is one of the few seabirds associated in all seasons with Arctic sea ice, a habitat that is changing rapidly. Recent decreases in summer ice have reduced breeding success and colony size of this species in Arctic Alaska. Little is known about the species' movements and distribution during the nine month non-breeding period (September–May), when changes in sea ice extent and composition are also occurring and predicted to continue. To examine bird movements and the seasonal role of sea ice to non-breeding Mandt's black guillemots, we deployed and recovered (n = 45) geolocators on individuals at a breeding colony in Arctic Alaska during 2011–2015. Black guillemots moved north to the marginal ice zone (MIZ) in the Beaufort and Chukchi seas immediately after breeding, moved south to the Bering Sea during freeze-up in December, and wintered in the Bering Sea January–April. Most birds occupied the MIZ in regions averaging 30–60% sea ice concentration, with little seasonal variation. Birds regularly roosted on ice in all seasons averaging 5 h d−1, primarily at night. By using the MIZ, with its roosting opportunities and associated prey, black guillemots can remain in the Arctic during winter when littoral waters are completely covered by ice.

  4. Arctic sea ice a major determinant in Mandt's black guillemot movement and distribution during non-breeding season.

    PubMed

    Divoky, G J; Douglas, D C; Stenhouse, I J

    2016-09-01

    Mandt's black guillemot (Cepphus grylle mandtii) is one of the few seabirds associated in all seasons with Arctic sea ice, a habitat that is changing rapidly. Recent decreases in summer ice have reduced breeding success and colony size of this species in Arctic Alaska. Little is known about the species' movements and distribution during the nine month non-breeding period (September-May), when changes in sea ice extent and composition are also occurring and predicted to continue. To examine bird movements and the seasonal role of sea ice to non-breeding Mandt's black guillemots, we deployed and recovered (n = 45) geolocators on individuals at a breeding colony in Arctic Alaska during 2011-2015. Black guillemots moved north to the marginal ice zone (MIZ) in the Beaufort and Chukchi seas immediately after breeding, moved south to the Bering Sea during freeze-up in December, and wintered in the Bering Sea January-April. Most birds occupied the MIZ in regions averaging 30-60% sea ice concentration, with little seasonal variation. Birds regularly roosted on ice in all seasons averaging 5 h d(-1), primarily at night. By using the MIZ, with its roosting opportunities and associated prey, black guillemots can remain in the Arctic during winter when littoral waters are completely covered by ice. © 2016 The Author(s).

  5. Sea ice melting in the marginal ice zone.

    USGS Publications Warehouse

    Josberger, E.G.

    1983-01-01

    The heat and salt flux boundary conditions together with the freezing curve relationship are a necessary component of any ice- sea water thermodynamic model. A neutral two-layer oceanic planetary boundary layer model that incorporates these boundary conditions is used. The results are discussed. -from Author

  6. Quantifying model uncertainty in seasonal Arctic sea-ice forecasts

    NASA Astrophysics Data System (ADS)

    Blanchard-Wrigglesworth, Edward; Barthélemy, Antoine; Chevallier, Matthieu; Cullather, Richard; Fučkar, Neven; Massonnet, François; Posey, Pamela; Wang, Wanqiu; Zhang, Jinlun; Ardilouze, Constantin; Bitz, Cecilia; Vernieres, Guillaume; Wallcraft, Alan; Wang, Muyin

    2017-04-01

    Dynamical model forecasts in the Sea Ice Outlook (SIO) of September Arctic sea-ice extent over the last decade have shown lower skill than that found in both idealized model experiments and hindcasts of previous decades. Additionally, it is unclear how different model physics, initial conditions or post-processing techniques contribute to SIO forecast uncertainty. In this work, we have produced a seasonal forecast of 2015 Arctic summer sea ice using SIO dynamical models initialized with identical sea-ice thickness in the central Arctic. Our goals are to calculate the relative contribution of model uncertainty and irreducible error growth to forecast uncertainty and assess the importance of post-processing, and to contrast pan-Arctic forecast uncertainty with regional forecast uncertainty. We find that prior to forecast post-processing, model uncertainty is the main contributor to forecast uncertainty, whereas after forecast post-processing forecast uncertainty is reduced overall, model uncertainty is reduced by an order of magnitude, and irreducible error growth becomes the main contributor to forecast uncertainty. While all models generally agree in their post-processed forecasts of September sea-ice volume and extent, this is not the case for sea-ice concentration. Additionally, forecast uncertainty of sea-ice thickness grows at a much higher rate along Arctic coastlines relative to the central Arctic ocean. Potential ways of offering spatial forecast information based on the timescale over which the forecast signal beats the noise are also explored.

  7. Marginal Ice Zone Processes Observed from Unmanned Aerial Systems

    NASA Astrophysics Data System (ADS)

    Zappa, C. J.

    2015-12-01

    Recent years have seen extreme changes in the Arctic. Marginal ice zones (MIZ), or areas where the "ice-albedo feedback" driven by solar warming is highest and ice melt is extensive, may provide insights into the extent of these changes. Furthermore, MIZ play a central role in setting the air-sea CO2 balance making them a critical component of the global carbon cycle. Incomplete understanding of how the sea-ice modulates gas fluxes renders it difficult to estimate the carbon budget in MIZ. Here, we investigate the turbulent mechanisms driving mixing and gas exchange in leads, polynyas and in the presence of ice floes using both field and laboratory measurements. Measurements from unmanned aerial systems (UAS) in the marginal ice zone were made during 2 experiments: 1) North of Oliktok Point AK in the Beaufort Sea were made during the Marginal Ice Zone Ocean and Ice Observations and Processes EXperiment (MIZOPEX) in July-August 2013 and 2) Fram Strait and Greenland Sea northwest of Ny-Ålesund, Svalbard, Norway during the Air-Sea-Ice Physics and Biogeochemistry Experiment (ASIPBEX) April - May 2015. We developed a number of new payloads that include: i) hyperspectral imaging spectrometers to measure VNIR (400-1000 nm) and NIR (900-1700 nm) spectral radiance; ii) net longwave and net shortwave radiation for ice-ocean albedo studies; iii) air-sea-ice turbulent fluxes as well as wave height, ice freeboard, and surface roughness with a LIDAR; and iv) drone-deployed micro-drifters (DDµD) deployed from the UAS that telemeter temperature, pressure, and RH as it descends through the atmosphere and temperature and salinity of the upper meter of the ocean once it lands on the ocean's surface. Visible and IR imagery of melting ice floes clearly defines the scale of the ice floes. The IR imagery show distinct cooling of the skin sea surface temperature (SST) as well as an intricate circulation and mixing pattern that depends on the surface current, wind speed, and near

  8. A meteorological experiment in the melting zone of the Greenland ice sheet

    SciTech Connect

    Oerlemans, J. ); Vugts, H.F. )

    1993-03-01

    Preliminary results are described from a glaciometeorological experiment carried out in the margin (melting zone) of the Greenland ice sheet in the summers of 1990 and 1991. This work was initiated within the framework of a Dutch research program on land ice and sea level change. Seven meteostations were operated along a transect running from the tundra well onto the ice sheet. At the ice edge, humidity, temperature, and wind profiles were obtained with a tethered balloon. On the ice sheet, 90 km from the edge, a boundary-layer research unit, including a sound detecting and ranging system (SODAR) and a radio acoustic sounding system (RASS), was established. Although focusing on the relation between surface energy balance, glacier mass balance, and ice flow, the experiment has also delivered a unique dataset on the dynamics of the atmospheric boundary layer around the warm tundra-cold ice sheet transition. Unexpected behavior was found for the surface albedo during the melt season. Lowest values are not found close to the ice edge, which is usual for glaciers, but higher on the ice sheet. Meltwater accumulation due to inefficient surface drainage was found to be the cause for this. The wind regime is dominated by katabatic flow from the ice sheet. The katabatic layer is typically 100-200 m thick. Close to the ice edge, the flow exhibits a very regular daily rhythm, with maximum wind speed in the afternoon. Farther on the ice sheet, the regime changes, and wind speed reaches maximum values in late night/early morning.

  9. Effects of Wind and Sea Ice Drift on the Seasonal Variation of Warm Circumpolar Deep Water in the Amundsen Sea

    NASA Astrophysics Data System (ADS)

    Kim, T. W.; Wahlin, A.; Ha, H. K.; Lee, S.; Lee, J. H.

    2014-12-01

    We examined the effect of wind and sea ice on seasonal variation in the thickness of circumpolar deep water, to better understand the processes causing mass loss in the West Antarctic ice sheet (WAIS). Spatial and temporal variation of the layer of warm and salty circumpolar deep water (CDW) at the center of the Amundsen Shelf was measured during two oceanographic surveys and a two-year mooring deployment. A hydrographic transect from the deep ocean, across the shelf break, and into the Dotson Trough shows a local elevation of the warm deep water layer at the shelf break. On the shelf, the water flows south-east along the trough. The thickness of the warm layer displays seasonal variation with maximum thickness in austral summer and minimum thickness in austral winter. The variation in warm layer thickness gives rise to a seasonal variation of the modified CDW heat content. In order to investigate the effects of wind and sea ice drift on the heat content, ocean surface stress was calculated using the ERA interim reanalysis wind data and observed sea ice velocity and concentration from satellites. The Ekman pumping velocity was calculated from the ocean surface stress field. The Ekman pumping at the shelf break, where the warm layer is elevated, shows a strong seasonal variation coinciding with the mooring data. The average wind field is eastward north of the shelf break and westward south of the shelf break during all seasons. The main effect of a layer of sea ice (between the wind and the water) is to reduce the surface stress which can intensify the horizontal gradient of surface stress at the marginal ice zone. This creates a divergence of the Ekman transport and a positive Ekman pumping at the marginal ice zone, if the wind direction is eastward. From February to April, a marginal ice zone close to the shelf break gives rise to a positive Ekman pumping that may explain the seasonal signal seen in the mooring data. At northern boundaries of coastal polynya

  10. Polar Bears Across the Arctic Face Shorter Sea Ice Season

    NASA Image and Video Library

    2017-09-28

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

  11. Large and rapid melt-induced velocity changes in the ablation zone of the Greenland Ice Sheet.

    PubMed

    van de Wal, R S W; Boot, W; van den Broeke, M R; Smeets, C J P P; Reijmer, C H; Donker, J J A; Oerlemans, J

    2008-07-04

    Continuous Global Positioning System observations reveal rapid and large ice velocity fluctuations in the western ablation zone of the Greenland Ice Sheet. Within days, ice velocity reacts to increased meltwater production and increases by a factor of 4. Such a response is much stronger and much faster than previously reported. Over a longer period of 17 years, annual ice velocities have decreased slightly, which suggests that the englacial hydraulic system adjusts constantly to the variable meltwater input, which results in a more or less constant ice flux over the years. The positive-feedback mechanism between melt rate and ice velocity appears to be a seasonal process that may have only a limited effect on the response of the ice sheet to climate warming over the next decades.

  12. Sea ice drift and deformation in the coastal boundary zone

    NASA Astrophysics Data System (ADS)

    Oikkonen, Annu; Haapala, Jari; Lensu, Mikko; Karvonen, Juha

    2016-10-01

    Small-scale sea ice deformation was studied in the coastal boundary zone (CBZ). Sequences of coastal radar images from the northern Baltic Sea (13 February to 13 May 2011) were used and trajectories of identifiable objects calculated. Average drift velocities in CBZ are small (<0.01 m/s), and events of high drift speeds are short and local. Deformations follow power law scaling but with an exponent of greater magnitude than in the Arctic. We discovered a connection between air temperature and sea ice deformation on a short time scale. During warm days, the mean deformation rate was significantly higher in all length scales than during cold days. This cannot be explained by changes in ice thickness or concentration, which suggests that the ice pack strength responds to air temperature faster than previously assumed. However, we cannot quantify how much this response is enhanced by lower ice thickness compared to the Arctic.

  13. Grounding zone heterogeneity around the Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

    Marsh, Oliver; Floricioiu, Dana; Rack, Wolfgang

    2017-04-01

    Grounding lines are most accurately mapped by identifying patterns of differential vertical movement from SAR interferometry. The apparent grounding line position at the upstream limit of flexure and the width of the flexure zone are influenced by satellite acquisition time relative to the tides, even for steep bedrock slopes. Here we identify and interpret spatial variations in flexure around the Ross Ice Shelf using a suite of TerraSAR-X interferograms. A small change in grounding line position can indicate short-term dynamic variability in ice thickness or the onset of ocean-induced instability, though neither are observed here. Nevertheless, interferograms also contain information about the stiffness of ice, its time-dependent response to tides and basal characteristics at the ice shelf boundary. Using flexure zone width, we estimate ice stiffness and link it to variations in thickness and rheology. Surface profiles across the grounding line from ICESat laser altimetry are re-interpreted and used to clarify the process of buoyancy-induced bending. Observations match well to theoretical models predicting an ice-shelf bump of variable amplitude and wavelength downstream of the transition. A deviation from hydrostatic balance is particularly clear at the steep, fast-flowing outlet glaciers of the Transantarctic Mountains (Mulock / Beardmore) but is also found in non-moving areas such as the Kamb Ice Stream. This deviation can lead to a positive bias of up to 15% of ice thickness and may cause significant miscalculation of ice shelf basal melt rates and errors in 'flux gate' type mass balance calculations. Here, cross-sections through the grounding line are modelled analytically in 1D from fundamental glaciological parameters using the new grounding line locations, leading to much improved estimates of ice thickness from ICESat surface profiles. Thickness is validated using airborne ground penetrating radar data where available.

  14. Coupled ice-ocean dynamics in the marginal ice zones Upwelling/downwelling and eddy generation

    NASA Technical Reports Server (NTRS)

    Hakkinen, S.

    1986-01-01

    This study is aimed at modeling mesoscale processes such as upwelling/downwelling and ice edge eddies in the marginal ice zones. A two-dimensional coupled ice-ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model through interfacial stresses. The parameters of the ocean model were chosen so that the dynamics would be nonlinear. The model was tested by studying the dynamics of upwelling. Wings parallel to the ice edge with the ice on the right produce upwelling because the air-ice momentum flux is much greater than air-ocean momentum flux; thus the Ekman transport is greater than the ice than in the open water. The stability of the upwelling and downwelling jets is discussed. The downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence. The constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling/downwelling regions, i.e., wind-forced vortices. Steepening and strengthening of vortices are provided by the nonlinear terms. When forcing is time-varying, the advection terms will also redistribute the vorticity. The wind reversals will separate the vortices from the ice edge, so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice.

  15. 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

  16. Small-scale sea ice deformation during N-ICE2015: From compact pack ice to marginal ice zone

    NASA Astrophysics Data System (ADS)

    Oikkonen, Annu; Haapala, Jari; Lensu, Mikko; Karvonen, Juha; Itkin, Polona

    2017-06-01

    We studied small-scale (50 m to 5 km) sea ice deformation from ship radar images recorded during the N-ICE2015 campaign. The campaign consisted of four consecutive drifting ice stations (Floes 1-4) north of Svalbard, with a total duration of nearly 5 months. Deformation was calculated using 5 different time intervals from 10 min to 24 h, and the deformation rate was found to depend strongly on the time scale. Floes 1-3 had a mean deformation rate within the range of 0.06-0.07 h-1 with the interval of 10 min, and 0.03-0.04 h-1 with the interval of 1 h. Floe 4 represented marginal ice zone (MIZ) with very high deformation rate, 0.14/0.08 h-1 with the interval of 10 min/1 h. Deep in the ice pack, high deformation rates occurred only with high wind and drift speed, while in MIZ they were found also during calm conditions. The deformation rates were found to follow power law scaling with respect to length and time scale even on this small scale and in small domain (15 km × 15 km). The length scale dependence of deformation rate depends on the time scale: the power law scaling exponent β of the whole study period decreases from 0.82 to 0.52 with the time interval increasing from 10 min to 24 h. Ship radar images reveal the importance of the deformation history of the ice pack, since the deformation events were initialized along the lines of previous damages.

  17. Formation processes of floe size distribution in the marginal ice zone (Invited)

    NASA Astrophysics Data System (ADS)

    Toyota, T.; Kohout, A.; Fraser, A.

    2013-12-01

    Since the marginal ice zone (MIZ) is the outer sea ice zone, its behavior is key to the understanding of the variability of sea ice extent associated with climate change. Especially for the melting processes in MIZ, where relatively small ice floes are dominant, floe size distribution (FSD) is an important parameter because smaller ice floes are subject to stronger lateral melting due to their larger cumulative perimeters. As the MIZ is characterized by vigorous interaction between sea ice and waves, breakup of sea ice due to flexural forcing and collisions is considered to play an essential role in the determination of FSD there. However, the available data have been very limited so far. Analysis of the observations of ice floes with a heli-borne video camera, focusing on the floe size ranging from 2 m to 100 m, in the Sea of Okhotsk, the Weddell Sea and off East Antarctica, revealed that while FSD is basically scale-invariant, a regime shift occurs at a size of about a few tens of meters, irrespective of the study region. It was also shown 1) that the floe size at which regime shift occurs slightly increases from 20 to 40 m with ice thickness, consistent with the theory of the flexural failure of sea ice; and 2) that to explain the scale invariance in FSD for smaller floes, a fragility of sea ice which is relevant to the strength of sea ice relative to waves can be a useful physical parameter to be correlated with the fractal dimension. Thus these results confirm the importance of wave-ice interaction to the formation of FSD. Based on this, a possible mechanism of the melting process was hypothesized that in the melting season sea ice extent retreats keeping the FSD relative to the ice edge nearly constant. As a next step and to confirm and further investigate this result, we planned to conduct the concurrent measurements of FSD, wave activities, and ice thickness off East Antarctica during the Sea Ice Physics and Ecosystem Experiment 2 (SIPEX2) in September to

  18. DRI Technical Program: Emerging Dynamics of the Marginal Ice Zone Ice, Ocean and Atmosphere Interactions in the Arctic Marginal Ice Zone. Year 3 Annual Report

    DTIC Science & Technology

    2014-09-30

    and Atmosphere Interactions in the Arctic Marginal...ice mass balance buoys (IMBs), wave buoys (WBs), and Automatic Weather Stations (AWS) in the region north of Alaska. The now deployed arrays have a... Arctic Marginal Ice Zone. Year 3 Annual Report 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e

  19. Arctic sea ice trends, variability and implications for seasonal ice forecasting

    PubMed Central

    Serreze, Mark C.; Stroeve, Julienne

    2015-01-01

    September Arctic sea ice extent over the period of satellite observations has a strong downward trend, accompanied by pronounced interannual variability with a detrended 1 year lag autocorrelation of essentially zero. We argue that through a combination of thinning and associated processes related to a warming climate (a stronger albedo feedback, a longer melt season, the lack of especially cold winters) the downward trend itself is steepening. The lack of autocorrelation manifests both the inherent large variability in summer atmospheric circulation patterns and that oceanic heat loss in winter acts as a negative (stabilizing) feedback, albeit insufficient to counter the steepening trend. These findings have implications for seasonal ice forecasting. In particular, while advances in observing sea ice thickness and assimilating thickness into coupled forecast systems have improved forecast skill, there remains an inherent limit to predictability owing to the largely chaotic nature of atmospheric variability. PMID:26032315

  20. Arctic sea ice trends, variability and implications for seasonal ice forecasting.

    PubMed

    Serreze, Mark C; Stroeve, Julienne

    2015-07-13

    September Arctic sea ice extent over the period of satellite observations has a strong downward trend, accompanied by pronounced interannual variability with a detrended 1 year lag autocorrelation of essentially zero. We argue that through a combination of thinning and associated processes related to a warming climate (a stronger albedo feedback, a longer melt season, the lack of especially cold winters) the downward trend itself is steepening. The lack of autocorrelation manifests both the inherent large variability in summer atmospheric circulation patterns and that oceanic heat loss in winter acts as a negative (stabilizing) feedback, albeit insufficient to counter the steepening trend. These findings have implications for seasonal ice forecasting. In particular, while advances in observing sea ice thickness and assimilating thickness into coupled forecast systems have improved forecast skill, there remains an inherent limit to predictability owing to the largely chaotic nature of atmospheric variability. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  1. Anomalous snow accumulation over the southeast region of the Greenland ice sheet during 2002-2003 snow season

    NASA Technical Reports Server (NTRS)

    Nghiem, S. V.; Steffen, K.; Huff, R.; Neumann, G.

    2005-01-01

    Our objective is to determine seasonal snow accumulation in the percolation zone of the Greenland ice sheet on the daily-weekly basis over the large scale. Our approach utilizes data from the Greenland Climate Network (GC-Net) and from the SeaWinds Scatterometer on the QuikSCAT satellite (QSCAT) to measure snow accumulation (SA) in the percolation zone of the Greenland ice sheet. GC-Net measurements provide crucial in-situ data to facilitate the interpretation of QSCAT backscatter signature for the development of an algorithm to map SA.

  2. Fire season climatic zones of mainland Alaska.

    Treesearch

    William M. Trigg

    1971-01-01

    Calculated values of precipitation effectiveness index and temperature efficiency index for 48 weather observation stations on the Alaska mainland are used to delineate areas that have different climatic subclassifications during the wildfire season of April through September. The paper outlines procedures, provides maps showing step- by- step analysis along with the...

  3. Trends in the Length of the Southern Ocean Sea Ice Season: 1979-1999

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.; Zukor, Dorothy J. (Technical Monitor)

    2001-01-01

    Satellite data can be used to observe the sea ice distribution around the continent of Antarctica on a daily basis and hence to determine how many days a year have sea ice at each location. This has been done for each of the 21 years 1979-1999. Mapping the trends in these data over the 21-year period reveals a detailed pattern of changes in the length of the sea ice season around Antarctica. Most of the Ross Sea ice cover has undergone a lengthening of the sea ice season, whereas most of the Amundsen Sea ice cover and almost the entire Bellingshausen Sea ice cover have undergone a shortening of the sea ice season. Results around the rest of the continent, including in the Weddell Sea, are more mixed, but overall, more of the Southern Ocean experienced a lengthening of the sea ice season than a shortening. For instance, the area experiencing a lengthening of the sea ice season by at least 1 day per year is 5.8 x 10(exp 6) sq km, whereas the area experiencing a shortening of the sea ice season by at least 1 day per year is less than half that, at 2.8 x 10(exp 6) sq km. This contrasts sharply with what is happened over the same period in the Arctic, where, overall, there has been some depletion of the ice cover, including shortened sea ice seasons and decreased ice extents.

  4. Formation processes of sea ice floe size distribution in the interior pack and its relationship to the marginal ice zone off East Antarctica

    NASA Astrophysics Data System (ADS)

    Toyota, Takenobu; Kohout, Alison; Fraser, Alexander D.

    2016-09-01

    To understand the behavior of the Seasonal Ice Zone (SIZ), which is composed of sea-ice floes of various sizes, knowledge of the floe size distribution (FSD) is important. In particular, FSD in the Marginal Ice Zone (MIZ), controlled by wave-ice interaction, plays an important role in determining the retreating rates of sea-ice extent on a global scale because the cumulative perimeter of floes enhances melting. To improve the understanding of wave-ice interaction and subsequent effects on FSD in the MIZ, FSD measurements were conducted off East Antarctica during the second Sea Ice Physics and Ecosystems eXperiment (SIPEX-2) in late winter 2012. Since logistical reasons limited helicopter operations to two interior ice regions, FSD in the interior ice region was determined using a combination of heli-photos and MODIS satellite visible images. The possible effect of wave-ice interaction in the MIZ was examined by comparison with past results obtained in the same MIZ, with our analysis showing: (1) FSD in the interior ice region is basically scale invariant for both small- (<100 m) and large- (>1 km) scale regimes; (2) although fractal dimensions are quite different between these two regimes, they are both rather close to that in the MIZ; and (3) for floes <100 m in diameter, a regime shift which appeared at 20-40 m in the MIZ is absent. These results indicate that one role of wave-ice interaction is to modulate the FSD that already exists in the interior ice region, rather than directly determine it. The possibilities of floe-floe collisions and storm-induced lead formation are considered as possible formation processes of FSD in the interior pack.

  5. 46 CFR 42.30-5 - Northern Winter Seasonal Zones and area.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... FOREIGN VOYAGES BY SEA Zones, Areas, and Seasonal Periods § 42.30-5 Northern Winter Seasonal Zones and.... Excluded from this zone are the North Atlantic Winter Seasonal Zone I and the Baltic Sea bounded by the.... Summer: April 1 to October 31. (b) North Atlantic Winter Seasonal Area. (1) The boundary of the...

  6. 46 CFR 42.30-5 - Northern Winter Seasonal Zones and area.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... FOREIGN VOYAGES BY SEA Zones, Areas, and Seasonal Periods § 42.30-5 Northern Winter Seasonal Zones and.... Excluded from this zone are the North Atlantic Winter Seasonal Zone I and the Baltic Sea bounded by the.... Summer: April 1 to October 31. (b) North Atlantic Winter Seasonal Area. (1) The boundary of the...

  7. The 2012 Arctic Field Season of the NRL Sea-Ice Measurement Program

    NASA Astrophysics Data System (ADS)

    Gardner, J. M.; Brozena, J. M.; Hagen, R. A.; Liang, R.; Ball, D.

    2012-12-01

    The U.S. Naval Research Laboratory (NRL) is beginning a five year study of the changing Arctic with a particular focus on ice thickness and distribution variability with the intent of optimizing state-of-the-art computer models which are currently used to predict sea ice changes. An important part of our study is to calibrate/validate CryoSat2 ice thickness data prior to its incorporation into new ice forecast models. NRL Code 7420 collected coincident data with the CryoSat2 satellite in both 2011 and 2012 using a LiDAR (Riegl Q560) to measure combined snow and ice thickness and a 10 GHz pulse-limited precision radar altimeter to measure sea-ice freeboard. These measurements were coordinated with the Seasonal Ice Zone Observing Network (SIZONet) group who conducted surface based ice thickness surveys using a Geonics EM-31 along hunter trails on the landfast ice near Barrow as well as on drifting ice offshore during helicopter landings. On two sorties, a twin otter carrying the NRL LiDAR and radar altimeter flew in tandem with the helicopter carrying the EM-31 to achieve synchronous data acquisition. Data from these flights are shown here along with a digital elevation map. The LiDAR and radar altimeter were also flown on grid patterns over the ice that were synchronous with 5 Cryosat2 satellite passes. These grids were intended to cover roughly 10 km long segments of Cryosat2 tracks with widths similar to the footprint of the satellite (~2 km). Reduction of these grids is challenging because of ice drift which can be many hundreds of meters over the 1-2 hours collection period of each grid. Relocation of the individual scanning LiDAR tracks is done by means of tie-points observed in the overlapping swaths. Data from these grids are shown here and will be used to examine the relationship of the tracked satellite waveform data to the actual surface across the footprint.

  8. Ocean-ice interaction in the marginal ice zone using synthetic aperture radar imagery

    NASA Technical Reports Server (NTRS)

    Liu, Antony K.; Peng, Chich Y.; Weingartner, Thomas J.

    1994-01-01

    Ocean-ice interaction processes in the marginal ice zone (MIZ) by wind, waves, and mesoscale features, such as up/downwelling and eddies are studied using Earth Remote-Sensing Satellite (ERS) 1 synthetic aperture radar (SAR) images and an ocean-ice interaction model. A sequence of seven SAR images of the MIZ in the Chukchi Sea with 3 or 6 days interval are investigated for ice edge advance/retreat. Simultaneous current measurements from the northeast Chukchi Sea, as well as the Barrow wind record, are used to interpret the MIZ dynamics. SAR spectra of waves in ice and ocean waves in the Bering and Chukchi Sea are compared for the study of wave propagation and dominant SAR imaging mechanism. By using the SAR-observed ice edge configuration and wind and wave field in the Chukchi Sea as inputs, a numerical simulation has been performed with the ocean-ice interaction model. After 3 days of wind and wave forcing the resulting ice edge configuration, eddy formation, and flow velocity field are shown to be consistent with SAR observations.

  9. Bulk heat transfer coefficient in the ice-upper ocean system in the ice melt season derived from concentration-temperature relationship

    NASA Astrophysics Data System (ADS)

    Nihashi, Sohey; Ohshima, Kay I.

    2008-06-01

    The bulk heat transfer coefficient in the ice-upper ocean system (Kb) in the ice melt season is estimated by a new method at 18 areas that cover much of the Antarctic seasonal ice zone. The method is based on a model in which ice melting is caused only by heat input through open water and is treated in a bulk fashion in the ice-upper ocean system. Kb is estimated by fitting a convergent curve derived from the model to an observed ice concentration-temperature plot (CT-plot). Estimated Kb is 1.15 ± 0.72 × 10-4 m s-1 on average. If Kb can be expressed by the product of the heat transfer coefficient (ch) and the friction velocity (uτ), ch is 0.0113 ± 0.0055. This value is about two times larger than that estimated at the ice bottom. The relationship between Kb and the geostrophic wind speed (Uw), which is roughly proportional to uτ, shows a significant positive correlation, as expected. Further, Kb seems more likely to be proportional to the square or cube of Uw rather than a linear relationship. Since Kb estimated from our method is associated with ice melting in a bulk fashion in the ice-upper ocean system, this relationship likely indicates both the mixing process of heat in the upper ocean (proportional to uτ3) and the local heat transfer process at the ice-ocean interface (proportional to uτ).

  10. Radar measurements of melt zones on the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Jezek, Kenneth C.; Gogineni, Prasad; Shanableh, M.

    1994-01-01

    Surface-based microwave radar measurements were performed at a location on the western flank of the Greenland Ice Sheet. Here, firn metamorphasis is dominated by seasonal melt, which leads to marked contrasts in the vertical structure of winter and summer firn. This snow regime is also one of the brightest radar targets on Earth with an average backscatter coefficient of 0 dB at 5.3 GHz and an incidence angle of 25 deg. By combining detailed observations of firn physical properties with ranging radar measurements we find that the glaciological mechanism associated with this strong electromagnetic response is summer ice lens formation within the previous winter's snow pack. This observation has important implications for monitoring and understanding changes in ice sheet volume using spaceborne microwave sensors.

  11. Artic ice and drilling structures

    SciTech Connect

    Sodhl, D.S.

    1985-04-01

    The sea ice in the southern Beaufort Sea is examined and subdivided into three zones: the fast ice zone, the seasonal pack-ice zone, an the polar pack ice zone. Each zone requires its own type of system. Existing floating drilling systems include ice-strengthened drill ships, conical drilling systems, and floating ice platforms in deep-water land-fast ice. The development of hydrocarbon resources in the Arctic presents great challenges to engineers, since the structures are required to operate safely under various conditions. Significant progress has yet to be made in understanding the behavior of ice.

  12. Wind stress measurements over rough ice during the 1984 Marginal Ice Zone Experiment

    NASA Astrophysics Data System (ADS)

    Anderson, R. J.

    1987-06-01

    The indirect dissipation method has been used to estimate momentum fluxes from a ship working in the outer marginal ice zone of the East Greenland Sea during the 1984 Marginal Ice Zone Experiment. These indirect measurements have been compared with direct eddy correlation measurements whenever the ship was moored to an ice floe and a sonic anemometer could be deployed. Neutral drag coefficients referenced to 10 m have been grouped in categories for various ice types and concentrations during 4- to 11-m/s winds. There is a gradual increase in the neutral drag coefficient with ice concentration and a doubling of the value in 70-90% concentration from 2.7 ± 0.3 × 10-3 (mean plus or minus standard deviation) for a mixture of brash, small, and medium floes with rafted edges to 5.3 ± 0.5 × 10-3 over very rough cakes and brash with many sharp vertical edges. Drag coefficients in this region of multiyear floes with larger roughness features are typically higher than most values obtained over ice and reported in the literature and up to 5 times larger than open ocean values for similar wind speeds. The drag coefficient is determined primarily by floe size, roughness, and concentration.

  13. Atmospheric boundary layer modification in the marginal ice zone

    NASA Technical Reports Server (NTRS)

    Bennett, Theodore J., Jr.; Hunkins, Kenneth

    1986-01-01

    A case study of the Andreas et al. (1984) data on atmospheric boundary layer modification in the marginal ice zone is made. The model is a two-dimensional, multilevel, linear model with turbulence, lateral and vertical advection, and radiation. Good agreement between observed and modeled temperature cross sections is obtained. In contrast to the hypothesis of Andreas et al., the air flow is found to be stable to secondary circulations. Adiabatic lifting and, at long fetches, cloud top longwave cooling, not an air-to-surface heat flux, dominate the cooling of the boundary layer. The accumulation with fetch over the ice of changes in the surface wind field is shown to have a large effect on estimates of the surface wind stress. It is speculated that the Andreas et al. estimates of the drag coefficient over the compact sea ice are too high.

  14. Seasonal circulation under the eastern Ross Ice Shelf, Antarctia

    SciTech Connect

    Hellmer, H.H.; Jacobs, S.S.

    1995-06-15

    An annual cycle of shelf water temperatures and salinities measured at depth near the eastern Ross Ice Shelf front is used to force a two-dimensional thermohaline circulation model adapted to different subice paths in the vicinity of Roosevelt Island. These paths were assumed to have constant water column thicknesses of 160, 200, and 240 m and lengths of 460-800 km. Additional simulations with the longer cavity included a 80-m thick interior water column in order to approximate conditions closer to the grounding line. Model results were compared with other long-term measurements that showed outflow from beneath the ice shelf. Shelf water flowing into the cavity west of Roosevelt Island appears to follow a cyclonic route around the island. The ice shelf base loses mass at a rate of 18-27 cm yr{sup {minus}1}, with seasonal forcing increasing the spatial and temporal variability of circulation and property distributions in the larger cavities. Shallow cavities reduce the influence of shelf water variability with increasing length. Introducing a transient shelf water temperature rise of 0.01{degrees}C yr {sup {minus}1} for 100 years increases the melt rate by 4-5 times. However, this increase is smaller if salinity also decreases over the same period of time, as might be expected from the added meltwater component. 42 refs., 9 figs.

  15. SAR Monitoring of Waves in Pancake Ice in the Marginal Ice Zone

    NASA Astrophysics Data System (ADS)

    De Carolis, Giacomo; Laurenza, Lucia Maria

    2016-08-01

    Frazil and pancake ice (FPI) is becoming an important component of the marginal ice zone (MIZ) owing to the dramatic changes occurring in the Arctic seas. This paper deals with the capability of synthetic aperture radars (SAR) to capture the changes suffered by ocean waves traveling in FPI fields, in order to relate them to the thickness of the ice layer crossed. We took advantage of the long-term ERS SAR acquisitions over polar oceans to carry out quantitative SAR spectral analysis for the Odden Ice Tongue (OIT), which developed in the Eastern Greenland Sea in the winter/spring 1997. A sea ice model, specifically developed to predict FPI distribution in the OIT, ran for that period to provide daily ice thicknesses and concentrations over 25 Km spatial scale. In situ samplings and wave ocean spectra collected within FPI fields during an oceanographic campaign for ice-ocean physics study carried on the R/V Jan Mayen were also available. To demonstrate the feasibility of the method, SAR inversion results were compared to the wave spectra collected by a directional wave buoy deployed on different FPI locations. Finally, wave attenuation rates computed over the ERS2 SAR image acquired on March 11, were compared with those collected in the Weddell Sea using an array of wave buoys.

  16. Toward Process Resolving Modeling of the Arctic Marginal Ice Zone

    NASA Astrophysics Data System (ADS)

    Maslowski, W.; Osinski, R.; DiMaggio, D.; Roberts, A.; Clement Kinney, J. L.

    2016-02-01

    The Regional Arctic System Model (RASM) has been developed to better understand the past and present operation of Arctic System at process scale and to predict its change at time scales from days to decades. It is a limited-area, fully coupled ice-ocean-atmosphere-land model that includes the Weather Research and Forecasting (WRF) model, the LANL Parallel Ocean Program (POP) and Community Ice Model (CICE) and the Variable Infiltration Capacity (VIC) land hydrology model, as well as a streamflow routing (RVIC) model to transport the freshwater flux from the land surface to the Arctic Ocean. All RASM components are coupled at high frequency (currently at 20-minute intervals) to allow realistic representation of inertial interactions among the model components. The model domain covers the entire Northern Hemisphere marine cryosphere, terrestrial drainage to the Arctic Ocean and its major inflow and outflow pathways, with optimal extension into the North Pacific / Atlantic to model the passage of cyclones into the Arctic. By default RASM is configured at an eddy-permitting resolution of 1/12° (or 9km) for the ice-ocean and 50 km for the atmosphere-land model components. In addition, we have recently developed, analyzed and will present results from a 1/48° (or 2.4km) grid configuration for the ice-ocean model components. Model results are presented from both fully coupled and a subset of RASM, where the atmospheric and land components are replaced with prescribed realistic atmospheric reanalysis data. Selected physical processes and resulting feedbacks in the Arctic marginal ice zone (MIZ) will be discussed to emphasize the need for high model resolution and fine-tuning of many present parameterizations of sub-grid physical processes when changing model spatial resolution. We also investigate sensitivity of simulated sea ice states to scale dependence of model parameters controlling ocean and sea ice dynamics, thermodynamics, and their coupling.

  17. Stratospheric Impact on the Onset of the Mesospheric Ice Season

    NASA Astrophysics Data System (ADS)

    Fiedler, J.; Baumgarten, G.; Berger, U.; Gabriel, A.; Latteck, R.; Luebken, F. J.

    2014-12-01

    Mesospheric ice layers, observed as noctilucent clouds (NLC) from ground, are the visible manifestation of extreme conditions in the polar summer mesopause region. Temperatures fall very low so that water vapor can freeze condence, which at 69°N usually occurs beginning of June. However, in 2013 the ALOMAR RMR lidar observed the first NLC on 21 May and the clouds reoccured during the following days. These were the earliest detections since 20 years and indicated an about 10 days earlier onset of the mesospheric ice season. This is supported by the colocated MAARSY radar which showed the occurrence rates of polar mesospheric summer echoes (PMSE) increasing faster than usual.The exceptional case was accompanied by ˜6 K lower temperatures and higher water vapor mixing ratios at NLC altitudes above ALOMAR from end of April until beginning of June as measured by the MLS instrument onboard the AURA satellite. Using MERRA reanalysis data we will show that the zonal mean temperature as well as the dynamic conditions in the Arctic middle atmosphere deviated in spring 2013 significantly from the mean conditions of the last 20 years. The planetary wave activity in the high latitude stratosphere was enhanced from 20 April to beginning of May. The colder and wetter upper mesosphere in May 2013 is attributed to this unusual late planetary wave activity in the stratosphere, introducing a strong upwelling in the mesosphere, lower temperatures and an upward transport of water vapor, which finally resulted into earlier existence conditions for mesospheric ice particles. For the southern hemisphere a high correlation between winter/summer transition in the stratosphere and onset of mesospheric ice is known as intra-hemispheric coupling. We regard the processes in the Arctic middle atmosphere in spring 2013 as a first evidence for intra-hemispheric coupling in the northern hemisphere, extending from the stratosphere into the mesopause region.

  18. Observations of the PCB distribution within and in-between ice, snow, ice-rafted debris, ice-interstitial water, and seawater in the Barents Sea marginal ice zone and the North Pole area.

    PubMed

    Gustafsson, O; Andersson, P; Axelman, J; Bucheli, T D; Kömp, P; McLachlan, M S; Sobek, A; Thörngren, J-O

    2005-04-15

    To evaluate the two hypotheses of locally elevated exposure of persistent organic pollutants (POPs) in ice-associated microenvironments and ice as a key carrier for long-range transport of POPs to the Arctic marginal ice zone (MIZ), dissolved and particulate polychlorinated biphenyls (PCBs) were analyzed in ice, snow, ice-interstitial water (IIW), seawater in the melt layer underlying the ice, and in ice-rafted sediment (IRS) from the Barents Sea MIZ to the high Arctic in the summer of 2001. Ultra-clean sampling equipment and protocols were specially developed for this expedition, including construction of a permanent clean room facility and a stainless steel seawater intake system on the I/B ODEN as well as two mobile 370 l ice-melting systems. Similar concentrations were found in several ice-associated compartments. For instance, the concentration of one of the most abundant congeners, PCB 52, was typically on the order of 0.1-0.3 pg l(-1) in the dissolved (melted) phase of the ice, snow, IIW, and underlying seawater while its particulate organic-carbon (POC) normalized concentrations were around 1-3 ng gPOC(-1) in the ice, snow, IIW, and IRS. The solid-water distribution of PCBs in ice was well correlated with and predictable from K(ow) (ice log K(oc)-log K(ow) regressions: p<0.05, r2=0.78-0.98, n=9), indicating near-equilibrium partitioning of PCBs within each local ice system. These results do generally not evidence the existence of physical microenvironments with locally elevated POP exposures. However, there were some indications that the ice-associated system had harbored local environments with higher exposure levels earlier/before the melting/vegetative season, as a few samples had PCB concentrations elevated by factors of 5-10 relative to the typical values, and the elevated levels were predominantly found at the station where melting had putatively progressed the least. The very low PCB concentrations and absence of any significant concentration

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

    PubMed Central

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

    2013-01-01

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

  20. Ku band airborne radar altimeter observations of marginal sea ice during the 1984 Marginal Ice Zone Experiment

    NASA Technical Reports Server (NTRS)

    Drinkwater, Mark R.

    1991-01-01

    Pulse-limited, airborne radar data taken in June and July 1984 with a 13.8-GHz altimeter over the Fram Strait marginal ice zone are analyzed with the aid of large-format aerial photography, airborne synthetic aperture radar data, and surface observations. Variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the Marginal Ice Zone Experiment. Results indicate that the wide-beam altimeter is a flexible instrument, capable of identifying the ice edge with a high degree of accuracy, calculating the ice concentration, and discriminating a number of different ice classes. This suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited. When fused with SSM/I, AVHRR and ERS-1 synthetic aperture radar imagery, future ERS-1 altimeter data are expected to provide some missing pieces to the sea ice geophysics puzzle.

  1. Seasonal Variability in Vadose zone biodegradation at a crude oil pipeline rupture site

    USGS Publications Warehouse

    Sihota, Natasha J.; Trost, Jared J.; Bekins, Barbara; Berg, Andrew M.; Delin, Geoffrey N.; Mason, Brent E.; Warren, Ean; Mayer, K. Ulrich

    2016-01-01

    Understanding seasonal changes in natural attenuation processes is critical for evaluating source-zone longevity and informing management decisions. The seasonal variations of natural attenuation were investigated through measurements of surficial CO2 effluxes, shallow soil CO2 radiocarbon contents, subsurface gas concentrations, soil temperature, and volumetric water contents during a 2-yr period. Surficial CO2 effluxes varied seasonally, with peak values of total soil respiration (TSR) occurring in the late spring and summer. Efflux and radiocarbon data indicated that the fractional contributions of natural soil respiration (NSR) and contaminant soil respiration (CSR) to TSR varied seasonally. The NSR dominated in the spring and summer, and CSR dominated in the fall and winter. Subsurface gas concentrations also varied seasonally, with peak values of CO2 and CH4 occurring in the fall and winter. Vadose zone temperatures and subsurface CO2 concentrations revealed a correlation between contaminant respiration and temperature. A time lag of 5 to 7 mo between peak subsurface CO2 concentrations and peak surface efflux is consistent with travel-time estimates for subsurface gas migration. Periods of frozen soils coincided with depressed surface CO2 effluxes and elevated CO2 concentrations, pointing to the temporary presence of an ice layer that inhibited gas transport. Quantitative reactive transport simulations demonstrated aspects of the conceptual model developed from field measurements. Overall, results indicated that source-zone natural attenuation (SZNA) rates and gas transport processes varied seasonally and that the average annual SZNA rate estimated from periodic surface efflux measurements is 60% lower than rates determined from measurements during the summer.

  2. Seasonal Variation in Basal Shear Stress Beneath the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Joughin, I.; Alley, R. B.; Behn, M. D.; Das, S. B.; Flowers, G. E.

    2015-12-01

    Over the last decade, it has been well established that in the ablation zone of the Greenland Ice Sheet, surface melt water makes its way to the bed and seasonally modulates ice-flow speed. With a conventional sliding law, the basal shear stress is proportional to the nonlinear product of the sliding speed and the effective pressure (difference between ice overburden and water pressure). Thus, when seasonal surface melting raises subglacial water pressure, it lowers the effective pressure, requiring additional sliding to restore the basal shear stress to maintain an overall force balance. This variation need not be uniform, however, and the basal hydrological system may produce variability at different spatial scales. To examine variability at scales of a few ice thicknesses, we use control-method inverse techniques to determine the basal shear stress using a shallow-shelf, ice-flow model constrained by speckle-tracked velocities measured over 11 and 22-day intervals. We begin by determining a reference basal shear stress estimated for a typical winter velocity field (typically over a 30-by-50 km region). We then determine the corresponding estimates for the region during periods of enhanced summer flow. In general, we find that relative to the winter data, summer basal shear stress tends to increase in areas of steep surface slope (high driving stress) and decrease, despite elevated speeds, in low slope regions, which often correspond to the basins where supraglacial lakes form. Computing the ratio of summer to winter effective pressure indicates little seasonal change in effective pressure for areas of high basal shear stress and a summer decrease in low-slope regions. This pattern is consistent with surface and bed slopes that drive water away from areas of high slopes and stress concentration (e.g., where ice flows over bedrock bumps) toward weak, low-slope regions of the bed. The net result is that, during the summer delivery of water to the bed, basal shear

  3. Recent Trends in the Arctic Navigable Ice Season and Links to Atmospheric Circulation

    NASA Astrophysics Data System (ADS)

    Maslanik, J.; Drobot, S.

    2002-12-01

    One of the potential effects of Arctic climate warming is an increase in the navigable ice season, perhaps resulting in development of the Arctic as a major shipping route. The distance from western North American ports to Europe through the Northwest Passage (NWP) or the Northern Sea Route (NSR) is typically 20 to 60 percent shorter than travel through the Panama Canal, while travel between Europe and the Far East may be reduced by as much as three weeks compared to transport through the Suez Canal. An increase in the navigable ice season would also improve commercial opportunities within the Arctic region, such as mineral and oil exploration and tourism, which could potentially expand the economic base of Arctic residents and companies, but which would also have negative environmental impacts. Utilizing daily passive-microwave derived sea ice concentrations, trends and variability in the Arctic navigable ice season are examined from 1979 through 2001. Trend analyses suggest large increases in the length of the navigable ice season in the Kara and Barents seas, the Sea of Okhotsk, and the Beaufort Sea, with decreases in the length of the navigable ice season in the Bering Sea. Interannual variations in the navigable ice season largely are governed by fluctuations in low-frequency atmospheric circulation, although the specific annular modes affecting the length of the navigable ice season vary by region. In the Beaufort and East Siberian seas, variations in the North Atlantic Oscillation/Arctic Oscillation control the navigable ice season, while variations in the East Pacific anomaly play an important role in controlling the navigable ice season in the Kara and Barents seas. In Hudson Bay, the Canadian Arctic Archipelago, and Baffin Bay, interannual variations in the navigable ice season are strongly related to the Pacific Decadal Oscillation.

  4. Seasonal Changes in Mars' North Polar Ice Cap

    NASA Technical Reports Server (NTRS)

    1997-01-01

    These images, which seem to have been taken while NASA's Hubble Space Telescope (HST) was looking directly down on the Martian North Pole, were actually created by assembling mosaics of three sets of images taken by HST in October, 1996 and in January and March, 1997 and projecting them to appear as they would if seen from above the pole. This first mosaic is a view which could not actually be seen in nature because at this season a portion of the pole would have actually been in shadow; the last view, taken near the summer solstice, would correspond to the Midnight Sun on Earth with the pole fully illuminated all day. The resulting polar maps begin at 50 degrees N latitude and are oriented with 0 degrees longitude at the 12 o'clock position. This series of pictures captures the seasonal retreat of Mars' north polar cap.

    October 1996 (early spring in the Northern hemisphere): In this map, assembled from images obtained between Oct. 8 and 15, the cap extends down to 60 degrees N latitude, nearly it's maximum winter extent. (The notches are areas where Hubble data were not available). A thin, comma-shaped cloud of dust can be seen as a salmon-colored crescent at the 7 o'clock position. The cap is actually fairly circular about the geographic pole at this season; the bluish 'knobs' where the cap seems to extend further are actually clouds that occurred near the edges of the three separate sets of images used to make the mosaic.

    January 1997 (mid-spring): Increased warming as spring progresses in the northern hemisphere has sublimated the carbon dioxide ice and frost below 70 degrees north latitude. The faint darker circle inside the cap boundary marks the location of circumpolar sand dunes (see March '97 map); these dark dunes are warmed more by solar heating than are the brighter surroundings, so the surface frost sublimates from the dunes earlier than from the neighboring areas. Particularly evident is the marked hexagonal shape of the polar cap at this season

  5. Seasonal Changes in Mars' North Polar Ice Cap

    NASA Technical Reports Server (NTRS)

    1997-01-01

    These images, which seem to have been taken while NASA's Hubble Space Telescope (HST) was looking directly down on the Martian North Pole, were actually created by assembling mosaics of three sets of images taken by HST in October, 1996 and in January and March, 1997 and projecting them to appear as they would if seen from above the pole. This first mosaic is a view which could not actually be seen in nature because at this season a portion of the pole would have actually been in shadow; the last view, taken near the summer solstice, would correspond to the Midnight Sun on Earth with the pole fully illuminated all day. The resulting polar maps begin at 50 degrees N latitude and are oriented with 0 degrees longitude at the 12 o'clock position. This series of pictures captures the seasonal retreat of Mars' north polar cap.

    October 1996 (early spring in the Northern hemisphere): In this map, assembled from images obtained between Oct. 8 and 15, the cap extends down to 60 degrees N latitude, nearly it's maximum winter extent. (The notches are areas where Hubble data were not available). A thin, comma-shaped cloud of dust can be seen as a salmon-colored crescent at the 7 o'clock position. The cap is actually fairly circular about the geographic pole at this season; the bluish 'knobs' where the cap seems to extend further are actually clouds that occurred near the edges of the three separate sets of images used to make the mosaic.

    January 1997 (mid-spring): Increased warming as spring progresses in the northern hemisphere has sublimated the carbon dioxide ice and frost below 70 degrees north latitude. The faint darker circle inside the cap boundary marks the location of circumpolar sand dunes (see March '97 map); these dark dunes are warmed more by solar heating than are the brighter surroundings, so the surface frost sublimates from the dunes earlier than from the neighboring areas. Particularly evident is the marked hexagonal shape of the polar cap at this season

  6. Ice surface temperatures: seasonal cycle and daily variability from in-situ and satellite observations

    NASA Astrophysics Data System (ADS)

    Madsen, Kristine S.; Dybkjær, Gorm; Høyer, Jacob L.; Nielsen-Englyst, Pia; Rasmussen, Till A. S.; Tonboe, Rasmus T.

    2016-04-01

    Surface temperature is an important parameter for understanding the climate system, including the Polar Regions. Yet, in-situ temperature measurements over ice- and snow covered regions are sparse and unevenly distributed, and atmospheric circulation models estimating surface temperature may have large biases. To change this picture, we will analyse the seasonal cycle and daily variability of in-situ and satellite observations, and give an example of how to utilize the data in a sea ice model. We have compiled a data set of in-situ surface and 2 m air temperature observations over land ice, snow, sea ice, and from the marginal ice zone. 2523 time series of varying length from 14 data providers, with a total of more than 13 million observations, have been quality controlled and gathered in a uniform format. An overview of this data set will be presented. In addition, IST satellite observations have been processed from the Metop/AVHRR sensor and a merged analysis product has been constructed based upon the Metop/AVHRR, IASI and Modis IST observations. The satellite and in-situ observations of IST are analysed in parallel, to characterize the IST variability on diurnal and seasonal scales and its spatial patterns. The in-situ data are used to estimate sampling effects within the satellite observations and the good coverage of the satellite observations are used to complete the geographical variability. As an example of the application of satellite IST data, results will be shown from a coupled HYCOM-CICE ocean and sea ice model run, where the IST products have been ingested. The impact of using IST in models will be assessed. This work is a part of the EUSTACE project under Horizon 2020, where the ice surface temperatures form an important piece of the puzzle of creating an observationally based record of surface temperatures for all corners of the Earth, and of the ESA GlobTemperature project which aims at applying surface temperatures in models in order to

  7. The Expansion of the Marginal Ice Zone in the Pacific Arctic

    NASA Astrophysics Data System (ADS)

    Hutchings, J. K.; Martini, K. I.; Perovich, D. K.; Rigor, I. G.; Petty, A.; Farrell, S. L.; Gens, R.; Barker, E.

    2014-12-01

    Since 2007 the Beaufort and Chukchi Seas have experienced persistently low summer minimum ice extents and the Marginal Ice Zone has grown in latitudinal extent. Here we describe the dynamic preconditioning of the ice pack for enhanced ice-albedo feedback that has facilitated this change. Enhanced meridional drift transported sea ice from the Pacific Arctic into the Transpolar Drift, preconditioning the ice loss in 2007. Since then mechanical weakening of the ice pack has led to enhanced opening and shear along the southern sector of the Beaufort Gyre, which preconditions further ice loss in subsequent summers. To determine the fate of Arctic sea ice the relationship between this dynamic preconditioning and the magnitude of positive feedbacks to summer ice loss due to ice-albedo feedback, wave-ice interaction and oceanic heat flux to the ice must all be quantified.

  8. Modeling the seasonal variability of a coupled Arctic ice-ocean system

    NASA Technical Reports Server (NTRS)

    Hakkinen, Sirpa; Mellor, George L.

    1992-01-01

    The seasonal variability of the ice-ocean system in the Arctic Basin and the Norwegian, Greenland, and Barents Seas was modeled using a three-dimensional coupled ice-ocean model developed at Princeton University. The snow-ice model uses a three-level thermodynamic scheme similar to Semtner's (1976), but is extended to include the effect of leads. It is shown that simulations using the climatological monthly forcing fields produce a realistic seasonal variability of the ice cover. The ice thickness had a considerable sensitivity to the choice of the long-wave back radiation scheme, but these effects can be reduced through dynamical factors.

  9. Shallow methylmercury production in the marginal sea ice zone of the central Arctic Ocean.

    PubMed

    Heimbürger, Lars-Eric; Sonke, Jeroen E; Cossa, Daniel; Point, David; Lagane, Christelle; Laffont, Laure; Galfond, Benjamin T; Nicolaus, Marcel; Rabe, Benjamin; van der Loeff, Michiel Rutgers

    2015-05-20

    Methylmercury (MeHg) is a neurotoxic compound that threatens wildlife and human health across the Arctic region. Though much is known about the source and dynamics of its inorganic mercury (Hg) precursor, the exact origin of the high MeHg concentrations in Arctic biota remains uncertain. Arctic coastal sediments, coastal marine waters and surface snow are known sites for MeHg production. Observations on marine Hg dynamics, however, have been restricted to the Canadian Archipelago and the Beaufort Sea (<79 °N). Here we present the first central Arctic Ocean (79-90 °N) profiles for total mercury (tHg) and MeHg. We find elevated tHg and MeHg concentrations in the marginal sea ice zone (81-85 °N). Similar to other open ocean basins, Arctic MeHg concentration maxima also occur in the pycnocline waters, but at much shallower depths (150-200 m). The shallow MeHg maxima just below the productive surface layer possibly result in enhanced biological uptake at the base of the Arctic marine food web and may explain the elevated MeHg concentrations in Arctic biota. We suggest that Arctic warming, through thinning sea ice, extension of the seasonal sea ice zone, intensified surface ocean stratification and shifts in plankton ecodynamics, will likely lead to higher marine MeHg production.

  10. Shallow methylmercury production in the marginal sea ice zone of the central Arctic Ocean

    PubMed Central

    Heimbürger, Lars-Eric; Sonke, Jeroen E.; Cossa, Daniel; Point, David; Lagane, Christelle; Laffont, Laure; Galfond, Benjamin T.; Nicolaus, Marcel; Rabe, Benjamin; van der Loeff, Michiel Rutgers

    2015-01-01

    Methylmercury (MeHg) is a neurotoxic compound that threatens wildlife and human health across the Arctic region. Though much is known about the source and dynamics of its inorganic mercury (Hg) precursor, the exact origin of the high MeHg concentrations in Arctic biota remains uncertain. Arctic coastal sediments, coastal marine waters and surface snow are known sites for MeHg production. Observations on marine Hg dynamics, however, have been restricted to the Canadian Archipelago and the Beaufort Sea (<79°N). Here we present the first central Arctic Ocean (79–90°N) profiles for total mercury (tHg) and MeHg. We find elevated tHg and MeHg concentrations in the marginal sea ice zone (81–85°N). Similar to other open ocean basins, Arctic MeHg concentration maxima also occur in the pycnocline waters, but at much shallower depths (150–200 m). The shallow MeHg maxima just below the productive surface layer possibly result in enhanced biological uptake at the base of the Arctic marine food web and may explain the elevated MeHg concentrations in Arctic biota. We suggest that Arctic warming, through thinning sea ice, extension of the seasonal sea ice zone, intensified surface ocean stratification and shifts in plankton ecodynamics, will likely lead to higher marine MeHg production. PMID:25993348

  11. Influence of ice load variations on shallow magma storage zones: Application to Katla volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Albino, F.; Pinel, V.; Sigmundsson, F.

    2009-12-01

    As a consequence of climate warming, many volcanoes are currently located under retreating ice caps. The resulting unloading can modify the eruptive activity as proven by observed correlation between deglaciation periods and eruptive activity in the past. Unloading can modify melt generation in the mantle, or modify magma storage conditions at shallow depth. Here we investigate how ice load variations at the Earth's surface act on shallow magma chambers. Numerical calculations are carried out in axisymmetric geometry for an elliptical chamber embedded in an elastic medium, taking magma compressibility into account. For variable chamber shape, size and depth, we quantify how unloading events induce magmatic pressure change as well as variation of the threshold pressure required for dyke initiation at the chamber wall. Influence on eruption likelihood is determined by the interplay between these two parameters. We evaluate the triggering effect of these surface events on onset of eruptions and find it depends strongly on the surface load location and magnitude, and the shape, depth and size of the magma chamber. We apply this model to Katla volcano, Iceland, which is covered by the Mýrdalsjökull ice cap. Ice load variations include long term thinning, as well as an annual load cycle, with up to 6 meters change in snow thickness from winter to summer. As the seasonal snow load is reduced, a pressure decrease of the same order of magnitude as the load is induced within the magma storage zone. The threshold pressure for failure is modified at the same time. Our model predicts that, in case of a spherical or horizontally elongated magma chamber, eruptions are more likely when the seasonal snow cover is smallest. This triggering effect is small, around few kPa, but appears consistent with the fact that all the nine last major historical eruptions at Katla occurred during the summer period. A long-term ice thinning due to global warming is also occurring, mainly at the

  12. Influence of timing of sea ice retreat on phytoplankton size during marginal ice zone bloom period on the Chukchi and Bering shelves

    NASA Astrophysics Data System (ADS)

    Fujiwara, A.; Hirawake, T.; Suzuki, K.; Eisner, L.; Imai, I.; Nishino, S.; Kikuchi, T.; Saitoh, S.-I.

    2016-01-01

    The size structure and biomass of a phytoplankton community during the spring bloom period can affect the energy use of higher-trophic-level organisms through the predator-prey body size relationships. The timing of the sea ice retreat (TSR) also plays a crucial role in the seasonally ice-covered marine ecosystem, because it is tightly coupled with the timing of the spring bloom. Thus, it is important to monitor the temporal and spatial distributions of a phytoplankton community size structure. Prior to this study, an ocean colour algorithm was developed to derive phytoplankton size index FL, which is defined as the ratio of chlorophyll a (chl a) derived from cells larger than 5 µm to the total chl a, using satellite remote sensing for the Chukchi and Bering shelves. Using this method, we analysed the pixel-by-pixel relationships between FL during the marginal ice zone (MIZ) bloom period and TSR over the period of 1998-2013. The influences of the TSR on the sea surface temperature (SST) and changes in ocean heat content (ΔOHC) during the MIZ bloom period were also investigated. A significant negative relationship between FL and the TSR was widely found in the shelf region during the MIZ bloom season. However, we found a significant positive (negative) relationship between the SST (ΔOHC) and TSR. Specifically, an earlier sea ice retreat was associated with the dominance of larger phytoplankton during a colder and weakly stratified MIZ bloom season, suggesting that the duration of the nitrate supply, which is important for the growth of large-sized phytoplankton in this region (i.e. diatoms), can change according to the TSR. In addition, under-ice phytoplankton blooms are likely to occur in years with late ice retreat, because sufficient light for phytoplankton growth can pass through the ice and penetrate into the water columns as a result of an increase in solar radiation toward the summer solstice

  13. Influence of timing of sea ice retreat on phytoplankton size during marginal ice zone bloom period in the Chukchi and Bering shelves

    NASA Astrophysics Data System (ADS)

    Fujiwara, A.; Hirawake, T.; Suzuki, K.; Eisner, L.; Imai, I.; Nishino, S.; Kikuchi, T.; Saitoh, S. I.

    2015-08-01

    Timing of sea ice retreat (TSR) as well as cell size of primary producers (i.e., phytoplankton) plays crucial roles in seasonally ice-covered marine ecosystem. Thus, it is important to monitor the temporal and spatial distribution of phytoplankton community size structure. Prior to this study, an ocean color algorithm has been developed to derive phytoplankton size index FL, which is defined as the ratio of chlorophyll a derived from the cells larger than 5 μm to the total chl a using satellite remote sensing for the Chukchi and Bering shelves. Using this method, we analyzed pixel-by-pixel relationships between FL during marginal ice zone (MIZ) bloom period and TSR over a period of 1998-2013. The influence of TSR on sea surface temperature (SST) and changes in ocean heat content (ΔOHC) during the MIZ bloom period were also investigated. A significant negative relationship between FL and TSR was widely found in the shelf region during MIZ bloom season. On the other hand, we found a significant positive (negative) relationship between SST (ΔOHC) and TSR. That is, earlier sea-ice retreat was associated with a dominance of larger phytoplankton during a colder and weakly stratified MIZ bloom season, suggesting that duration of nitrate supply, which is important for large-sized phytoplankton growth in this region (i.e., diatoms), can change according to TSR. In addition, under-ice phytoplankton blooms are likely to occur in years with late ice retreat, because sufficient light for phytoplankton growth can pass through the ice and penetrate into the water columns due to an increase in solar radiation toward the summer solstice. Moreover, we found not only the length of ice-free season but also annual median of FL positively correlated with annual net primary production (APP). Thus, both phytoplankton community composition and growing season are important for APP in the study area. Our findings showed quantitative relationship between the inter-annual variability of FL

  14. Grounding-zone wedges and lateral moraines of palaeo-ice streams

    NASA Astrophysics Data System (ADS)

    Batchelor, C.; Dowdeswell, J. A.

    2016-12-01

    The landforms that are preserved at the beds of former marine-terminating ice streams provide information about ice-sheet dynamics and the processes that are operating beneath contemporary ice streams. Sedimentary landforms, including grounding-zone wedges (GZWs), can build up during still-stands or re-advances of the frontal grounding zone of ice streams. Significant sedimentary depocentres, termed ice-stream lateral moraines (ISLMs), can also be formed at ice-stream lateral margins. We present an inventory of GZWs and ISLMs that is compiled from available studies and independent analysis of seismic-reflection and swath-bathymetric data. We discuss the geomorphic and acoustic characteristics of these landforms and their implications for ice dynamics. GZWs indicate episodic ice stream retreat and probably form mainly where floating ice shelves constrain vertical accommodation space beyond the grounding zone. Many GZWs occur at vertical or lateral pinning points, where cross-shelf troughs either shallow or constrict, which encourage grounding-zone stability through increasing basal and lateral drag and reducing mass flow across the grounding zone. We identify two different types of ISLMs. Lateral shear-moraines form subglacially in the shear zone between ice streams and slower-flowing ice. They are up to 3.5 km wide and 60 m thick, and maintain a relatively constant width, thickness and cross-sectional shape along their length. Lateral marginal-moraines form at the lateral boundary between ice streams and seafloor terrain that was free of grounded ice. They are up to 50 km wide and 300 m thick, and exhibit a seaward increase in width and thickness. Lateral marginal-moraines have a similar volume and acoustic character to GZWs. However, whereas GZWs are formed by the ice-flow parallel delivery of sediment to the grounding zone, lateral marginal-moraines are produced when sediment is delivered to the ice-stream lateral margin at an oblique angle to the ice

  15. Prospects for improved seasonal Arctic sea ice predictions from multivariate data assimilation

    NASA Astrophysics Data System (ADS)

    Massonnet, François; Fichefet, Thierry; Goosse, Hugues

    2015-04-01

    Predicting the summer Arctic sea ice conditions a few months in advance has become a challenging priority. Seasonal prediction is partly an initial condition problem; therefore, a good knowledge of the initial sea ice state is necessary to hopefully produce reliable forecasts. Most of the intrinsic memory of sea ice lies in its thickness, but consistent and homogeneous observational networks of sea ice thickness are still limited in space and time. To overcome this problem, we constrain the ocean-sea ice model NEMO-LIM3 with gridded sea ice concentration retrievals from satellite observations using the ensemble Kalman filter. No sea ice thickness products are assimilated. However, thanks to the multivariate formalism of the data assimilation method used, sea ice thickness is globally updated in a consistent way whenever observations of concentration are available. We compare in this paper the skill of 27 pairs of initialized and uninitialized seasonal Arctic sea ice hindcasts spanning 1983-2009, driven by the same atmospheric forcing as to isolate the pure role of initial conditions on the prediction skill. The results exhibit the interest of multivariate sea ice initialization for the seasonal predictions of the September ice concentration and are particularly encouraging for hindcasts in the 2000s. In line with previous studies showing the interest of data assimilation for sea ice thickness reconstruction, our results thus show that sea ice data assimilation is also a promising tool for short-term prediction, and that current seasonal sea ice forecast systems could gain predictive skill from a more realistic sea ice initialization.

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

    USGS Publications Warehouse

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

    2016-01-01

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

  17. Direct observations of ice seasonality reveal changes in climate over the past 320-570 years

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    PubMed Central

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

    2016-01-01

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

  19. A numerical model of the atmospheric boundary layer over a marginal ice zone

    NASA Astrophysics Data System (ADS)

    Kantha, Lakshmi H.; Mellor, George L.

    1989-04-01

    A two-dimensional, multilevel model for simulating changes in the atmospheric boundary layer across a marginal ice zone is described and applied to off-ice, on-ice, and along-ice edge wind conditions. The model incorporates a second-moment closure for parameterizing the intensification and suppression of turbulent mixing in the boundary layer due to stratification effects. For off-ice winds, as the atmospheric boundary layer passes from cold smooth ice onto warm open water, the onset of intense convection raises the inversion. Over the transition zone of rough rafted ice with open leads, the shear stress on the ice cover increases significantly before dropping down to the downstream values over water. Such nonmonotonic surface stress could be the cause of divergence of sea ice near the ice edge in a marginal ice zone. These results are in agreement with the one-layer model simulations of off-ice winds by Overland et al. (1983). For on-ice wind conditions, as the warm flow in the boundary layer encounters the cold ice conditions, the resulting stable stratification could rapidly suppress the turbulence in the boundary layer, leading to the development of a shallow inversion and an associated jet. When the wind is predominantly along the ice edge, the temperature contrast between the open water and the ice could produce a thermal front at the ice edge in the boundary layer with strong associated turbulence. More observations are needed to verify these model predictions. Nevertheless, these model results suggest that it is important to account for the changes in the characteristics of the atmospheric boundary layer across the marginal ice zone in our attempts to understand the behavior of the ice cover in these regions.

  20. Processes and imagery of first-year fast sea ice during the melt season

    NASA Technical Reports Server (NTRS)

    Holt, B.; Digby, S. A.

    1985-01-01

    In June and July 1982, a field program was conducted in the Canadian Arctic on Prince Patrick Island to study sea ice during the melt season with in situ measurements and microwave instrumentation operated near the surface and from aircraft. The objective of the program was to measure physical characteristics together with microwave backscatter and emission coefficients of sea ice during this major period of transition. The present paper is concerned with a study of both surface measurements and imagery of first-year fast ice during the melt season. The melting process observed in first-year fast ice was found to begin with the gradual reduction of the snow cover. For a two- to three-day period in this melt stage, a layer of superimposed ice nodules formed at the snow/ice interface as meltwater froze around ice and snow grains.

  1. Processes and imagery of first-year fast sea ice during the melt season

    NASA Technical Reports Server (NTRS)

    Holt, B.; Digby, S. A.

    1985-01-01

    In June and July 1982, a field program was conducted in the Canadian Arctic on Prince Patrick Island to study sea ice during the melt season with in situ measurements and microwave instrumentation operated near the surface and from aircraft. The objective of the program was to measure physical characteristics together with microwave backscatter and emission coefficients of sea ice during this major period of transition. The present paper is concerned with a study of both surface measurements and imagery of first-year fast ice during the melt season. The melting process observed in first-year fast ice was found to begin with the gradual reduction of the snow cover. For a two- to three-day period in this melt stage, a layer of superimposed ice nodules formed at the snow/ice interface as meltwater froze around ice and snow grains.

  2. Variations in the Sea Ice Edge and the Marginal Ice Zone on Different Spatial Scales as Observed from Different Satellite Sensor

    NASA Technical Reports Server (NTRS)

    Markus, Thorsten; Henrichs, John

    2006-01-01

    and volume scattering characteristics. The Canadian RADARSAT C-band SAR provides data that cover the Arctic Ocean and the MIZ every 3 days. A change-point detection approach was utilized to obtain an ice edge estimate from the RADARSAT data The Quickscat scatterometer provides ice edge information with a resolution of a few kilometers on a near-daily basis. During portions of March and April of 2003 a series of aircraft flights were conducted over the ice edge in the Bering Sea carrying the Polarimetric Scanning Radiometer (PSR), which provides spectral coverage identical with the AMSR-E instrument at a resolution of 500 meters. In this study we investigated these different data sets and analyzed differences in their definition of the sea ice edge and the marginal ice zone and how these differences as well as their individual limitations affect the monitoring of the ice edge dynamics. We also examined how the nature of the sea ice edge, including its location, compactness and shape, changes over the seasons. Our approach was based on calculation of distances between ice edges derived from the satellite and aircraft data sets listed above as well as spectral coherence methods and shape parameters such as tortuosity, curvature, and fractional dimension.

  3. Radar Remote Sensing of Ice and Sea State and Air-Sea Interaction in the Marginal Ice Zone

    DTIC Science & Technology

    2014-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Radar Remote Sensing of Ice and Sea State and Air-Sea...Interaction in the Marginal Ice Zone Hans C. Graber RSMAS – Department of Ocean Sciences Center for Southeastern Tropical Advanced Remote Sensing...scattering and attenuation process of ocean waves interacting with ice . A nautical X-band radar on a vessel dedicated to science would be used to follow the

  4. Dynamics of coupled ice-ocean system in the marginal ice zone: Study of the mesoscale processes and of constitutive equations for sea ice

    NASA Technical Reports Server (NTRS)

    Hakkinen, S.

    1984-01-01

    This study is aimed at the modelling of mesoscale processed such as up/downwelling and ice edge eddies in the marginal ice zones. A 2-dimensional coupled ice-ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model (f-plane) through interfacial stresses. The constitutive equations of the sea ice are formulated on the basis of the Reiner-Rivlin theory. The internal ice stresses are important only at high ice concentrations (90-100%), otherwise the ice motion is essentially free drift, where the air-ice stress is balanced by the ice-water stress. The model was tested by studying the upwelling dynamics. Winds parallel to the ice edge with the ice on the right produce upwilling because the air-ice momentum flux is much greater that air-ocean momentum flux, and thus the Ekman transport is bigger under the ice than in the open water. The upwelling simulation was extended to include temporally varying forcing, which was chosen to vary sinusoidally with a 4 day period. This forcing resembles successive cyclone passings. In the model with a thin oceanic upper layer, ice bands were formed.

  5. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap

    USGS Publications Warehouse

    Kieffer, H.H.; Christensen, P.R.; Titus, T.N.

    2006-01-01

    The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO 2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth. ?? 2006 Nature Publishing Group.

  6. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap.

    PubMed

    Kieffer, Hugh H; Christensen, Philip R; Titus, Timothy N

    2006-08-17

    The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth.

  7. Midwater food web in the vicinity of a marginal ice zone in the western Weddell Sea

    NASA Astrophysics Data System (ADS)

    Hopkins, Thomas L.; Torres, Joseph J.

    1989-04-01

    The structure of the food web in the vicinity of a marginal ice zone was investigated in the western Weddell Sea during austral autumn 1986. The diets of 40 species of zooplankton and micronekton occurring in the epipelagic zone were examined and compared using non-hierarchical clustering procedures. Over half the species were in three clusters of predominantly small-particle (phytoplankton; protozoans) grazers. These included biomass dominants Calanoides acutus, Calanus propinquus, Metridia gerlachei and Salpa thompsoni. Six clusters contained omnivores that had diets consisting of small particles as well as a substantial fraction of metazoan food. Among these was Euphausia superba. Seven groups were carnivorous, including species of copepods (1), chaetognaths (3), and fishes (5). Copepods were the most frequent food of carnivores; however krill also were important in the diets of three fish species. Among small-particle grazers, phytoplankton occurred more frequently in guts of individuals from open water; carnivory was more in evidence in samples collected under the pack ice. Regional comparisons of material taken on this and several previous cruises indicate that, in most of the dominant species, diets remain relatively consistent with respect to major food categories. Seasonal impact on feeding dynamics appears to be great: the guts of grazing species were generally much more full (visual evidence) during summer bloom conditions than during the autumn. The following trophic sequence is suggested for grazing zooplankton species in ice-covered regions of the Antarctic: (1) Active small-particle grazing during the summer bloom period; (2) reduced ingestion rates in autumn as primary production declines and the system becomes more oligotrophic, with some species augmenting grazing with carnivory; (3) descent of zooplankton biomass species into the mesopelagic zone in late autumn-early winter with feeding largely terminated. The sequence applies to the dominant

  8. Evolution of a Canada Basin ice-ocean boundary layer and mixed layer across a developing thermodynamically forced marginal ice zone

    NASA Astrophysics Data System (ADS)

    Gallaher, Shawn G.; Stanton, Timothy P.; Shaw, William J.; Cole, Sylvia T.; Toole, John M.; Wilkinson, Jeremy P.; Maksym, Ted; Hwang, Byongjun

    2016-08-01

    A comprehensive set of autonomous, ice-ocean measurements were collected across the Canada Basin to study the summer evolution of the ice-ocean boundary layer (IOBL) and ocean mixed layer (OML). Evaluation of local heat and freshwater balances and associated turbulent forcing reveals that melt ponds (MPs) strongly influence the summer IOBL-OML evolution. Areal expansion of MPs in mid-June start the upper ocean evolution resulting in significant increases to ocean absorbed radiative flux (19 W m-2 in this study). Buoyancy provided by MP drainage shoals and freshens the IOBL resulting in a 39 MJ m-2 increase in heat storage in just 19 days (52% of the summer total). Following MP drainage, a near-surface fresh layer deepens through shear-forced mixing to form the summer mixed layer (sML). In late summer, basal melt increases due to stronger turbulent mixing in the thin sML and the expansion of open water areas due in part to wind-forced divergence of the sea ice. Thermal heterogeneities in the marginal ice zone (MIZ) upper ocean led to large ocean-to-ice heat fluxes (100-200 W m-2) and enhanced basal ice melt (3-6 cm d-1), well away from the ice edge. Calculation of the upper ocean heat budget shows that local radiative heat input accounted for at least 89% of the observed latent heat losses and heat storage (partitioned 0.77/0.23). These results suggest that the extensive area of deteriorating sea ice observed away from the ice edge during the 2014 season, termed the "thermodynamically forced MIZ," was driven primarily by local shortwave radiative forcing.

  9. Climate effects on volcanism: Influence of ice load variations on magma storage zones with application to Icelandic volcanoes.

    NASA Astrophysics Data System (ADS)

    Albino, F.; Pinel, V.; Sigmundsson, F.

    2011-12-01

    Correlations between deglaciation periods and eruptive activity in the past have been strongly suggested, especially in Iceland, where the end of the last glaciation was characterised by a large pulse in volcanic production. Present-day reduction in ice load on subglacial volcanoes due to global warming is modifying pressure conditions in magmatic systems with a potential to influence magma production as well as shallow storage. Here, we model stress induced by variation in surface loads and evaluate how the resulting pressure conditions can modulate magmatic activity. We focus on the effect on shallow storage zones and show that ice loading can modify their failure conditions in a manner that depends critically on ice retreat timing and spatial distribution, the shape and depth of magma chambers as well the compressibility of the magma. We study in particular two subglacial volcanoes in Iceland: the Katla volcano under the Mýrdalsjökull ice cap and Grímsvötn at the Vatnajökull ice cap. Numerical calculations have been carried out in axisymmetric geometry for elliptical magma chambers. An elastic model is first used to evaluate the effects of the annual load cycle, due to seasonal variation of ice mass, which indicates an annual modulation of failure conditions on magma chambers at subglacial volcanoes. Our model predicts that, in case of a spherical or horizontally elongated magma chamber, eruptions are more likely when the seasonal snow cover is smallest. This triggering effect is small, around few kPa, but appears consistent with the fact that all the nine last major historical eruptions of Katla volcano occurred in period from May - October when the annual snow load is minimum. Viscous effects are then introduced to evaluate the influence of long term ice thinning on the shallow magma storage zones.

  10. A coupled dynamic-thermodynamic model of an ice-ocean system in the marginal ice zone

    NASA Technical Reports Server (NTRS)

    Hakkinen, Sirpa

    1987-01-01

    Thermodynamics are incorporated into a coupled ice-ocean model in order to investigate wind-driven ice-ocean processes in the marginal zone. Upswelling at the ice edge which is generated by the difference in the ice-air and air-water surface stresses is found to give rise to a strong entrainment by drawing the pycnocline closer to the surface. Entrainment is shown to be negligible outside the areas affected by the ice edge upswelling. If cooling at the top is included in the model, the heat and salt exchanges are further enhanced in the upswelling areas. It is noted that new ice formation occurs in the region not affected by ice edge upswelling, and it is suggested that the high-salinity mixed layer regions (with a scale of a few Rossby radii of deformation) will overturn due to cooling, possibly contributing to the formation of deep water.

  11. Arctic Sea Ice Predictability and Prediction on Seasonal-to-Decadal Timescales

    NASA Astrophysics Data System (ADS)

    Guemas, V.; Blanchard-Wrigglesworth, E.; Chevallier, M.; Déqué, M.; Doblas-Reyes, F.; Fuckar, N. S.; Volpi, D.; Salas y Mélia, D.

    2014-12-01

    Sea ice stands as a major component of the climate system through its key impact on the water and energy budgets and it substantially impacts local and remote atmospheric and oceanic circulations. The societal and economic perspectives of Arctic sea ice prediction on seasonal-to-decadal timescales have led to increasing efforts in the development of sea ice forecast systems. An overview of the potential sources of Arctic sea ice predictability on these timescales will be given. Then, current approaches to generate ensemble sea ice reconstructions and initialize climate predictions will be described. The performances over the satellite era of the EC-Earth and CNRM-CM coupled models in predicting the Arctic sea ice cover and its spatial characteristics on seasonal timescales will finally be presented.

  12. Seasonal speedup along the western flank of the Greenland Ice Sheet.

    PubMed

    Joughin, Ian; Das, Sarah B; King, Matt A; Smith, Ben E; Howat, Ian M; Moon, Twila

    2008-05-09

    It has been widely hypothesized that a warmer climate in Greenland would increase the volume of lubricating surface meltwater reaching the ice-bedrock interface, accelerating ice flow and increasing mass loss. We have assembled a data set that provides a synoptic-scale view, spanning ice-sheet to outlet-glacier flow, with which to evaluate this hypothesis. On the ice sheet, these data reveal summer speedups (50 to 100%) consistent with, but somewhat larger than, earlier observations. The relative speedup of outlet glaciers, however, is far smaller (<15%). Furthermore, the dominant seasonal influence on Jakobshavn Isbrae's flow is the calving front's annual advance and retreat. With other effects producing outlet-glacier speedups an order of magnitude larger, seasonal melt's influence on ice flow is likely confined to those regions dominated by ice-sheet flow.

  13. An Integrative Wave Model for the Marginal Ice Zone Based on a Rheological Parameterization

    DTIC Science & Technology

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. An Integrative Wave model for the Marginal Ice Zone...people.clarkson.edu/~hhshen LONG-TERM GOALS To enhance wave forecasting models such as WAVEWATCH III (WW3) so that they can predict the marginal ice zone (MIZ...wave climate in the present and future Arctic seas. OBJECTIVES 1. To build a comprehensive wave- ice interaction mathematical framework for a

  14. Bacterial communities from Arctic seasonal sea ice are more compositionally variable than those from multi-year sea ice.

    PubMed

    Hatam, Ido; Lange, Benjamin; Beckers, Justin; Haas, Christian; Lanoil, Brian

    2016-10-01

    Arctic sea ice can be classified into two types: seasonal ice (first-year ice, FYI) and multi-year ice (MYI). Despite striking differences in the physical and chemical characteristics of FYI and MYI, and the key role sea ice bacteria play in biogeochemical cycles of the Arctic Ocean, there are a limited number of studies comparing the bacterial communities from these two ice types. Here, we compare the membership and composition of bacterial communities from FYI and MYI sampled north of Ellesmere Island, Canada. Our results show that communities from both ice types were dominated by similar class-level phylogenetic groups. However, at the operational taxonomic unit (OTU) level, communities from MYI and FYI differed in both membership and composition. Communities from MYI sites had consistent structure, with similar membership (presence/absence) and composition (OTU abundance) independent of location and year of sample. By contrast, communities from FYI were more variable. Although FYI bacterial communities from different locations and different years shared similar membership, they varied significantly in composition. Should these findings apply to sea ice across the Arctic, we predict increased compositional variability in sea ice bacterial communities resulting from the ongoing transition from predominantly MYI to FYI, which may impact nutrient dynamics in the Arctic Ocean.

  15. In Situ Measurements of an Energetic Wave Event in the Arctic Marginal Ice Zone

    DTIC Science & Technology

    2015-03-01

    Arctic Marginal Ice Zone 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK...surface wave signal, show the largest waves recorded in the Arctic region with ice cover. Comparing the measurements with a spectral wave model indicated...three phases of interaction: (1) wave blocking by ice , (2) strong attenuation of wave energy and fracturing of ice by wave forcing and (3) uninhibited

  16. Evolution of the Marginal Ice Zone: Adaptive Sampling with Autonomous Gliders

    DTIC Science & Technology

    2015-09-30

    release; distribution is unlimited. Evolution of the Marginal Ice Zone: Adaptive Sampling with Autonomous Gliders Craig M. Lee, Luc Rainville and Jason I...efforts toward understanding: • Ocean-ice-atmosphere dynamics that impact sea ice evolution . • The impacts of Arctic change on sea ice and on the...intensive field program employed a broad array of autonomous platforms to characterize the processes that govern Beaufort Sea MIZ evolution from initial

  17. Physical Oceanography Report. Helicopter-Based STD Data from MIZEX 83 (Marginal Ice Zone Experiment).

    DTIC Science & Technology

    1984-09-01

    location. The ice margin in Fram Strait between Greenland and Svalbard may be characterized as "advective", dominated by ocean currents and wind, rather...than by heat budget. In this region, sea ice from the Arctic Ocean is carried far south into the Atlantic by the cold, low-salinity East Greenland ...year. The ocean in the Greenland Sea marginal ice zone is dominated by permanent and transient frontal systems, by eddies and by upwelling along the ice

  18. Martian Seasonal CO2 Frost Indicating Decameter-Scale Variability in Buried Water Ice

    NASA Astrophysics Data System (ADS)

    Mellon, M. T.; Hansen, C. J.; Cull, S.; Arvidson, R. E.; Searls, M.

    2011-12-01

    Several new lines of evidence indicate that subsurface water ice (ground ice) on Mars is more complexly distributed, and in variable concentrations, than had been previously envisioned. Understanding the current distribution of ground ice is a fundamental part of understanding how this ice was emplaced and the recent past climate conditions under which icy deposits formed and subsequently evolved. In this work we examine the seasonal defrosting of CO2 observed by HiRISE as an indicator of decameter-scale ground-ice heterogeneity. It is well known that CO2 dry ice accumulates on the martian surface in winter. The amount of dry ice and the time it spends on the ground depends strongly on surface properties. A readily observable attribute is the "crocus date", the season (Ls) when CO2 completely sublimates, exposing the soil surface. Many factors can affect the crocus date, but perhaps most important are the properties of CO2 frost and of the surface soil. We examine HiRISE observations, spanning more than a martian year, for decameter-scale patterns of CO2 frost and the crocus date. Year-to-year repeatability of CO2 ice patterns, both in polygon troughs and decameter-size patches, along with a lack of topography nor aeolian redistribution, suggests that differences in the surface substrate is the root cause for these patterns. In addition, only CO2 slab ice (solid, non-porous dry ice) is indicated throughout the observed seasons and at all spatial scales (down to meter scale), as evidenced by albedo (HiRISE and TES) and IR spectra (CRISM). In addition, the low emissivity and high albedo of fine-grained particulate CO2 frost would result in a crocus date much earlier than even the earliest observed. We present two scenarios of substrate differences which explain the observations: (i) the ice-table depth varies away from atmospheric equilibrium, such that a thicker "dry-soil" layer occurs in disequilibrium where the CO2 ice lingers longest; and (ii) the H2O

  19. Spatial patterns in the length of the sea ice season in the Southern Ocean, 1979-1986

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    1994-01-01

    The length of the sea ice season summarizes in one number the ice coverage conditions for an individual location for an entire year. It becomes a particularly valuable variable when mapped spatially over a large area and examined for regional and interannual differences, as is done here for the Southern Ocean over the years 1979-1986, using the satellite passive microwave data of the Nimbus 7 scanning multichannel microwave radiometer. Three prominent geographic anomalies in ice season lengths occur consistently in each year of the data set, countering the general tendency toward shorter ice seasons from south to north: (1) in the Weddell Sea the tendency is toward shorter ice seasons from southwest to northeast, reflective of the cyclonic ice/atmosphere/ocean circulations in the Weddell Sea region. (2) Directly north of the Ross Ice Shelf anomalously short ice seasons occur, lasting only 245-270 days, in contrast to the perennial ice coverage at comparable latitudes in the southern Bellingshausen and Amundsen Seas and in the western Weddell Sea. The short ice season off the Ross Ice Shelf reflects the consistently early opening of the ice cover each spring, under the influence of upwelling along the continental slope and shelf and atmospheric forcing from winds blowing off the Antarctic continent. (3) In the southern Amundsen Sea, anomalously short ice seasons occur adjacent to the coast, owing to the frequent existence of coastal polynyas off the many small ice shelves bordering the sea. Least squares trends in the ice season lengths over the 1979-1986 period are highly coherent spatially, with overall trends toward shorter ice seasons in the northern Weddell and Bellingshausen seas and toward longer ice seasons in the Ross Sea, around much of East Antarctica, and in a portion of the south central Weddell Sea.

  20. Spatial patterns in the length of the sea ice season in the Southern Ocean, 1979-1986

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    1994-01-01

    The length of the sea ice season summarizes in one number the ice coverage conditions for an individual location for an entire year. It becomes a particularly valuable variable when mapped spatially over a large area and examined for regional and interannual differences, as is done here for the Southern Ocean over the years 1979-1986, using the satellite passive microwave data of the Nimbus 7 scanning multichannel microwave radiometer. Three prominent geographic anomalies in ice season lengths occur consistently in each year of the data set, countering the general tendency toward shorter ice seasons from south to north: (1) in the Weddell Sea the tendency is toward shorter ice seasons from southwest to northeast, reflective of the cyclonic ice/atmosphere/ocean circulations in the Weddell Sea region. (2) Directly north of the Ross Ice Shelf anomalously short ice seasons occur, lasting only 245-270 days, in contrast to the perennial ice coverage at comparable latitudes in the southern Bellingshausen and Amundsen Seas and in the western Weddell Sea. The short ice season off the Ross Ice Shelf reflects the consistently early opening of the ice cover each spring, under the influence of upwelling along the continental slope and shelf and atmospheric forcing from winds blowing off the Antarctic continent. (3) In the southern Amundsen Sea, anomalously short ice seasons occur adjacent to the coast, owing to the frequent existence of coastal polynyas off the many small ice shelves bordering the sea. Least squares trends in the ice season lengths over the 1979-1986 period are highly coherent spatially, with overall trends toward shorter ice seasons in the northern Weddell and Bellingshausen seas and toward longer ice seasons in the Ross Sea, around much of East Antarctica, and in a portion of the south central Weddell Sea.

  1. 36 CFR 13.912 - Kantishna area summer season firearm safety zone.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... firearm safety zone. 13.912 Section 13.912 Parks, Forests, and Public Property NATIONAL PARK SERVICE... Preserve General Provisions § 13.912 Kantishna area summer season firearm safety zone. What is prohibited? No one may fire a gun during the summer season in or across the Kantishna area firearm safety zone...

  2. 36 CFR 13.912 - Kantishna area summer season firearm safety zone.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... firearm safety zone. 13.912 Section 13.912 Parks, Forests, and Public Property NATIONAL PARK SERVICE... Preserve General Provisions § 13.912 Kantishna area summer season firearm safety zone. What is prohibited? No one may fire a gun during the summer season in or across the Kantishna area firearm safety zone...

  3. 36 CFR 13.912 - Kantishna area summer season firearm safety zone.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... firearm safety zone. 13.912 Section 13.912 Parks, Forests, and Public Property NATIONAL PARK SERVICE... Preserve General Provisions § 13.912 Kantishna area summer season firearm safety zone. What is prohibited? No one may fire a gun during the summer season in or across the Kantishna area firearm safety zone...

  4. 36 CFR 13.912 - Kantishna area summer season firearm safety zone.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... firearm safety zone. 13.912 Section 13.912 Parks, Forests, and Public Property NATIONAL PARK SERVICE... Preserve General Provisions § 13.912 Kantishna area summer season firearm safety zone. What is prohibited? No one may fire a gun during the summer season in or across the Kantishna area firearm safety zone...

  5. 36 CFR 13.912 - Kantishna area summer season firearm safety zone.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... firearm safety zone. 13.912 Section 13.912 Parks, Forests, and Public Property NATIONAL PARK SERVICE... Preserve General Provisions § 13.912 Kantishna area summer season firearm safety zone. What is prohibited? No one may fire a gun during the summer season in or across the Kantishna area firearm safety zone...

  6. 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

  7. Current trends in seasonal ice storage. [Compilation of projects

    SciTech Connect

    Gorski, A.J.

    1986-05-01

    This document is a compilation of modern research projects focused upon the use of naturally grown winter ice for summer cooling applications. Unlike older methods of ice-based cooling, in which ice was cut from rivers and lakes and transported to insulated icehouses, modern techniques grow ice directly in storage containers - by means of heat pipes, snow machines, and water sprays - at the site of application. This modern adaptation of an old idea was reinvented independently at several laboratories in the United States and Canada. Applications range from air conditioning and food storage to desalinization.

  8. A study of the dark region in the western ablation zone of the Greenland ice sheet

    NASA Astrophysics Data System (ADS)

    Wientjes, I. G. M.

    2011-10-01

    The western ablation zone of the Greenland ice sheet contains a region that is darker than the surrounding ice. This region is several tens of kilometres wide and stretched parallel to the margin of the ice sheet for more than 350 kilometres. The dark appearance implies low radiance and therefore low spectral albedos, leading to enhanced melting. An estimation of the influence of this dark region with a simple model shows that it can increase the local melt rate in this area by several tens per cent. Therefore, this dark region can significantly affect the total mass balance of the Greenland ice sheet. Satellite images reveal that the dark region is caused by outcropping layers of ice that contain more dust than the brighter surrounding ice. This dust was initially deposited in the accumulation zone of the Greenland ice sheet, transported through the ice sheet towards the margin and released in the ablation zone. Geochemical analyses of dust from the dark region and dust from brighter reference ice confirm this hypothesis and indicate a local source for the dust, probably the nearby tundra. In addition, abundant microorganisms were observed in the dark region. Part of these organisms formed granules together with the mineral dust. As the organic matter in the dust is known to have a high light absorbency, the dark region is not only caused by dust from the outcropping ice, but biological processes also contribute to the darkening of the surface. Finally, carbonaceous particles in the ice from the dark region reveal that the material is not modern, and settled on the accumulation zone during the Holocene, during periods of enhanced eolian activity. Therefore, dust fluxes towards the ice sheet in the past contribute to albedo variations in the ablation zone of the Greenland ice sheet at present and can enhance the melting of the Greenland ice sheet without external forcing.

  9. 77 FR 2017 - Safety Zone; Ice Rescue Exercise; Green Bay, Dyckesville, WI

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-01-13

    ...The Coast Guard is establishing a temporary safety zone on the waters of Green Bay near Dyckesville, Wisconsin. This zone is intended to restrict vessels and persons from a portion of Green Bay due to a large scale ice rescue exercise that will involve multiple State and Federal agencies. This temporary safety zone is necessary to protect the surrounding public and vessels from the hazards associated with the ice rescue exercise.

  10. Seasonal exposure of carbon dioxide ice on the nucleus of comet 67P/Churyumov-Gerasimenko.

    PubMed

    Filacchione, G; Raponi, A; Capaccioni, F; Ciarniello, M; Tosi, F; Capria, M T; De Sanctis, M C; Migliorini, A; Piccioni, G; Cerroni, P; Barucci, M A; Fornasier, S; Schmitt, B; Quirico, E; Erard, S; Bockelee-Morvan, D; Leyrat, C; Arnold, G; Mennella, V; Ammannito, E; Bellucci, G; Benkhoff, J; Bibring, J P; Blanco, A; Blecka, M I; Carlson, R; Carsenty, U; Colangeli, L; Combes, M; Combi, M; Crovisier, J; Drossart, P; Encrenaz, T; Federico, C; Fink, U; Fonti, S; Fulchignoni, M; Ip, W-H; Irwin, P; Jaumann, R; Kuehrt, E; Langevin, Y; Magni, G; McCord, T; Moroz, L; Mottola, S; Palomba, E; Schade, U; Stephan, K; Taylor, F; Tiphene, D; Tozzi, G P; Beck, P; Biver, N; Bonal, L; Combe, J-Ph; Despan, D; Flamini, E; Formisano, M; Frigeri, A; Grassi, D; Gudipati, M S; Kappel, D; Longobardo, A; Mancarella, F; Markus, K; Merlin, F; Orosei, R; Rinaldi, G; Cartacci, M; Cicchetti, A; Hello, Y; Henry, F; Jacquinod, S; Reess, J M; Noschese, R; Politi, R; Peter, G

    2016-12-23

    Carbon dioxide (CO2) is one of the most abundant species in cometary nuclei, but because of its high volatility, CO2 ice is generally only found beneath the surface. We report the infrared spectroscopic identification of a CO2 ice-rich surface area located in the Anhur region of comet 67P/Churyumov-Gerasimenko. Spectral modeling shows that about 0.1% of the 80- by 60-meter area is CO2 ice. This exposed ice was observed a short time after the comet exited local winter; following the increased illumination, the CO2 ice completely disappeared over about 3 weeks. We estimate the mass of the sublimated CO2 ice and the depth of the eroded surface layer. We interpret the presence of CO2 ice as the result of the extreme seasonal changes induced by the rotation and orbit of the comet.

  11. Seasonal exposure of carbon dioxide ice on the nucleus of comet 67P/Churyumov-Gerasimenko

    NASA Astrophysics Data System (ADS)

    Filacchione, G.; Raponi, A.; Capaccioni, F.; Ciarniello, M.; Tosi, F.; Capria, M. T.; De Sanctis, M. C.; Migliorini, A.; Piccioni, G.; Cerroni, P.; Barucci, M. A.; Fornasier, S.; Schmitt, B.; Quirico, E.; Erard, S.; Bockelee-Morvan, D.; Leyrat, C.; Arnold, G.; Mennella, V.; Ammannito, E.; Bellucci, G.; Benkhoff, J.; Bibring, J. P.; Blanco, A.; Blecka, M. I.; Carlson, R.; Carsenty, U.; Colangeli, L.; Combes, M.; Combi, M.; Crovisier, J.; Drossart, P.; Encrenaz, T.; Federico, C.; Fink, U.; Fonti, S.; Fulchignoni, M.; Ip, W.-H.; Irwin, P.; Jaumann, R.; Kuehrt, E.; Langevin, Y.; Magni, G.; McCord, T.; Moroz, L.; Mottola, S.; Palomba, E.; Schade, U.; Stephan, K.; Taylor, F.; Tiphene, D.; Tozzi, G. P.; Beck, P.; Biver, N.; Bonal, L.; Combe, J.-Ph.; Despan, D.; Flamini, E.; Formisano, M.; Frigeri, A.; Grassi, D.; Gudipati, M. S.; Kappel, D.; Longobardo, A.; Mancarella, F.; Markus, K.; Merlin, F.; Orosei, R.; Rinaldi, G.; Cartacci, M.; Cicchetti, A.; Hello, Y.; Henry, F.; Jacquinod, S.; Reess, J. M.; Noschese, R.; Politi, R.; Peter, G.

    2016-12-01

    Carbon dioxide (CO2) is one of the most abundant species in cometary nuclei, but because of its high volatility, CO2 ice is generally only found beneath the surface. We report the infrared spectroscopic identification of a CO2 ice-rich surface area located in the Anhur region of comet 67P/Churyumov-Gerasimenko. Spectral modeling shows that about 0.1% of the 80- by 60-meter area is CO2 ice. This exposed ice was observed a short time after the comet exited local winter; following the increased illumination, the CO2 ice completely disappeared over about 3 weeks. We estimate the mass of the sublimated CO2 ice and the depth of the eroded surface layer. We interpret the presence of CO2 ice as the result of the extreme seasonal changes induced by the rotation and orbit of the comet.

  12. Arctic sea ice loss - two distinct spatial and seasonal patterns related to the ocean state

    NASA Astrophysics Data System (ADS)

    Onarheim, Ingrid; Eldevik, Tor; Smedsrud, Lars H.; Stroeve, Julienne

    2017-04-01

    The Arctic sea ice cover has decreased dramatically in recent decades. Typically focus has been on September when decreasing trends are largest and sea ice extent is at the minimum. However, decreasing sea ice trends are now significant for all months. By examining satellite observations of sea ice concentration since 1979 and an observational-based reconstruction of sea ice extent since 1850, we assess ongoing and past change in regional sea ice variability throughout the year. We find two distinct spatial and seasonal patterns of Northern Hemisphere sea ice variability throughout the observational record: summer variability and change inside the Arctic Ocean, and winter variability and change in the seas further south. In regions with largest summer variability, the recent ice loss is typically larger in spring than fall. The enhanced ice retreat in spring appears accelerated by the ice albedo feedback, while rapid fall freeze-up may be due to the strong salinity stratification. The winter variability in the seas further south, being less stratified and more affected by convection, have larger trends in fall than spring, indicating delayed and reduced ice formation in fall. These two patterns of Northern Hemisphere sea ice variability thus appear largely affected by the ocean state.

  13. Short-term sea ice forecasts with the RASM-ESRL coupled model: A testbed for improving simulations of ocean-ice-atmosphere interactions in the marginal ice zone

    NASA Astrophysics Data System (ADS)

    Solomon, A.; Cox, C. J.; Hughes, M.; Intrieri, J. M.; Persson, O. P. G.

    2015-12-01

    The dramatic decrease of Arctic sea-ice has led to a new Arctic sea-ice paradigm and to increased commercial activity in the Arctic Ocean. NOAA's mission to provide accurate and timely sea-ice forecasts, as explicitly outlined in the National Ocean Policy and the U.S. National Strategy for the Arctic Region, needs significant improvement across a range of time scales to improve safety for human activity. Unfortunately, the sea-ice evolution in the new Arctic involves the interaction of numerous physical processes in the atmosphere, ice, and ocean, some of which are not yet understood. These include atmospheric forcing of sea-ice movement through stress and stress deformation; atmospheric forcing of sea-ice melt and formation through energy fluxes; and ocean forcing of the atmosphere through new regions of seasonal heat release. Many of these interactions involve emerging complex processes that first need to be understood and then incorporated into forecast models in order to realize the goal of useful sea-ice forecasting. The underlying hypothesis for this study is that errors in simulations of "fast" atmospheric processes significantly impact the forecast of seasonal sea-ice retreat in summer and its advance in autumn in the marginal ice zone (MIZ). We therefore focus on short-term (0-20 day) ice-floe movement, the freeze-up and melt-back processes in the MIZ, and the role of storms in modulating stress and heat fluxes. This study uses a coupled ocean-atmosphere-seaice forecast model as a testbed to investigate; whether ocean-sea ice-atmosphere coupling improves forecasts on subseasonal time scales, where systematic biases develop due to inadequate parameterizations (focusing on mixed-phase clouds and surface fluxes), how increased atmospheric resolution of synoptic features improves the forecasts, and how initialization of sea ice area and thickness and snow depth impacts the skill of the forecasts. Simulations are validated with measurements at pan-Arctic land

  14. Sudden disintegration of ice in the glacial-proglacial transition zone of the largest glacier in Austria

    NASA Astrophysics Data System (ADS)

    Kellerer-Pirklbauer, Andreas; Avian, Michael; Hirschmann, Simon; Lieb, Gerhard Karl; Seier, Gernot; Sulzer, Wolfgang; Wakonigg, Herwig

    2017-04-01

    Rapid deglaciation does not only reveal a landscape which is prone to rapid geomorphic changes and sediment reworking but also the glacier ice itself might be in a state of disintegration by ice melting, pressure relief, crevasse formation, ice collapse or changes in the glacier's hydrology. In this study we considered the sudden disintegration of glacier ice in the glacial-proglacial transition zone of Pasterze Glacier. Pasterze Glacier is a typical alpine valley glacier and covers currently some 16.5 km2 making it to the largest glacier in Austria. This glacier is an important site for alpine mass tourism in Austria related to a public high alpine road and a cable car which enable access to the glacier rather easily also for unexperienced mountaineers. Spatial focus in our research is given on two particular study areas where several ice-mass movement events occurred during the 2015- and 2016-melting seasons. The first study area is a crevasse field at the lower third of the glacier tongue. This lateral crevasse field has been substantially modified during the last two melting seasons particularly because of thermo-erosional effects of a glacial stream which changed at this site from subglacial (until 2015) to glacier-lateral revealing a several tens of meters high unstable ice cliff prone to ice falls of different magnitudes. The second study area is located at the proglacial area. At Pasterze Glacier the proglacial area is widely influenced by dead-ice bodies of various dimensions making this area prone to slow to sudden geomorphic changes caused by ice mass changes. A particular ice-mass movement event took place on 20.09.2016. Within less than one hour the surface of the proglacial area changed substantially by tilting, lateral shifting, and subsidence of the ground accompanied by complete ice disintegration of once-debris covered ice. To understand acting processes at both areas of interest and to quantify mass changes we used field observations, terrain

  15. Ocean Profile Measurements During the Seasonal Ice Zone Reconnaissance Surveys

    DTIC Science & Technology

    2014-09-30

    conjunction with UpTempO deployments on July 24 and August 14. In 2013 we began supporting our oceanography graduate student, Sarah Dewey , to work...10.1029/2009GL037525. ). PUBLICATIONS S. Dewey , J. Morison, R. Andersen, J. Zhang, and M. Steele (2014). “Aerial Surveys of the Beaufort Sea

  16. Improved measurement of ice layer density in seasonal snowpacks

    NASA Astrophysics Data System (ADS)

    Watts, T.; Rutter, N.; Toose, P.; Derksen, C.; Sandells, M.; Woodward, J.

    2015-11-01

    Ice layers in snowpacks introduce uncertainty in satellite derived estimates of snow water equivalent, have ecological impacts on plants and animals, and change the thermal and vapour transport properties of the snowpack. The microstructure and specifically the density of ice layers is poorly quantified. Here we present a new field method, for measuring the density of ice layers caused by melt or rain-on-snow events. The method was used on 87 ice layer samples in the Canadian Arctic and mid-latitudes; the mean measured ice layer density was 909 ± 18 kg m-3 with a standard deviation of 23 kg m-3, significantly higher than values typically used in the literature.

  17. Sea ice conditions and melt season duration variability within the Canadian Arctic Archipelago: 1979-2008

    NASA Astrophysics Data System (ADS)

    Howell, Stephen E. L.; Duguay, Claude R.; Markus, Thorsten

    2009-05-01

    Sea ice conditions and melt season duration within the Canadian Arctic Archipelago (CAA) were investigated from 1979-2008. The CAA is exhibiting statistically significant decreases in average September total sea ice area at -8.7% decade-1. The melt season duration within the CAA is increasing significantly at 7 days decade-1. 2008 represented the longest melt season duration within the CAA over the satellite record at 129 days. Average September multi-year ice (MYI) area is decreasing at -6.4% decade-1 but has yet to reach statistical significance as a result of increasing MYI dynamic import from the Arctic Ocean. Results also find that the Western Parry Channel (WPC) region of the Northwest Passage (NWP) will continue to be susceptible to MYI as the transition to a summer-time sea ice free Arctic continues. The processes responsible for the temporary clearing of the WPC region of the NWP in 2007 were also identified.

  18. Skillful seasonal forecasts of Arctic sea ice retreat and advance dates in a dynamical forecast system

    NASA Astrophysics Data System (ADS)

    Sigmond, M.; Reader, M. C.; Flato, G. M.; Merryfield, W. J.; Tivy, A.

    2016-12-01

    The need for skillful seasonal forecasts of Arctic sea ice is rapidly increasing. Technology to perform such forecasts with coupled atmosphere-ocean-sea ice systems has only recently become available, with previous skill evaluations mainly limited to area-integrated quantities. Here we show, based on a large set of retrospective ensemble model forecasts, that a dynamical forecast system produces skillful seasonal forecasts of local sea ice retreat and advance dates - variables that are of great interest to a wide range of end users. Advance dates can generally be skillfully predicted at longer lead times ( 5 months on average) than retreat dates ( 3 months). The skill of retreat date forecasts mainly stems from persistence of initial sea ice anomalies, whereas advance date forecasts benefit from longer time scale and more predictable variability in ocean temperatures. These results suggest that further investments in the development of dynamical seasonal forecast systems may result in significant socioeconomic benefits.

  19. The structure and effect of suture zones in the Larsen C Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    McGrath, Daniel; Steffen, Konrad; Holland, Paul R.; Scambos, Ted; Rajaram, Harihar; Abdalati, Waleed; Rignot, Eric

    2014-03-01

    Ice shelf fractures frequently terminate where they encounter suture zones, regions of material heterogeneity that form between meteoric inflows in ice shelves. This heterogeneity can consist of marine ice, meteoric ice with modified rheological properties, or the presence of fractures. Here, we use radar observations on the Larsen C Ice Shelf, Antarctica, to investigate (i) the termination of a 25 km long rift in the Churchill Peninsula suture zone, which was found to contain 60 m of accreted marine ice, and (ii) the along-flow evolution of a suture zone originating at Cole Peninsula. We determine a steady state field of basal melting/freezing rates and apply it to a flowline model to delineate the along-flow evolution of layers within the ice shelf. The thickening surface wedge of locally accumulated meteoric ice, which likely has limited lateral variation in its mechanical properties, accounts for 60% of the total ice thickness near the calving front. Thus, we infer that the lower 40% of the ice column and the material heterogeneities present there are responsible for resisting fracture propagation and thereby delaying tabular calving events, as demonstrated in the >40 year time series leading up to the 2004/2005 calving event for Larsen C. This likely represents a highly sensitive aspect of ice shelf stability, as changes in the oceanic forcing may lead to the loss of this heterogeneity.

  20. Seasonal reversal at Miryang Eoreumgol (Ice Valley), Korea: observation and monitoring

    NASA Astrophysics Data System (ADS)

    Byun, Hi-Ryong; Tanaka, Hiroshi L.; Choi, Pom-Yong; Kim, Do-Woo

    2011-12-01

    We investigate an anomalous phenomenon evident in the Miryang Eoreumgol (Ice Valley), Korea: The wind and water are cold during summer and warm during winter, and ice formation does not occur in winter but in summer. We have initiated observations and investigations into the origin of heat sources particularly with regard to the mechanism of ice formation in summer. Previous theories, e.g., concerning underground gravity currents, water evaporation, diurnal and seasonal respirations of the talus, effects of ground heat, radiation and topography, etc., are considered. After a calculation of heat sources, we propose two new concepts—a repetitious heat separation mechanism and a positive feedback mechanism of cold air generation—to demonstrate that the heat mechanism of the seasonal reversal of the ice valley may be controlled by the use of the phase change between ice and water vapor with only a small amount of additional unknown energy.

  1. Seasonal variation of upwelling in the Alaskan Beaufort Sea: Impact of sea ice cover

    NASA Astrophysics Data System (ADS)

    Schulze, Lena M.; Pickart, Robert S.

    2012-06-01

    Data from a mooring array deployed from August 2002 to September 2004 are used to characterize differences in upwelling near the shelf break in the Alaskan Beaufort Sea due to varying sea ice conditions. The record is divided into three ice seasons: open water, partial ice, and full ice. The basic response is the same in each of the seasons. Roughly 8 h after the onset of easterly winds the shelf break jet reverses, followed approximately 10 h later by upwelling of saltier water which is cold near the shelf break (Pacific Winter Water) and warm at depth (Atlantic Water). The secondary circulation at the outer shelf is, to first order, consistent with a two-dimensional Ekman balance of offshore flow in the upper layer and onshore flow at depth. There are, however, important seasonal differences in the upwelling. Overall the response is strongest in the partial ice season and weakest in the full ice season. It is believed that these differences are dictated by the degree to which wind stress is transmitted through the pack-ice, as the strength of the wind-forcing was comparable over the three seasons. An EOF-based upwelling index is constructed using information about the primary flow, secondary flow, and hydrography. The ability to predict upwelling using the wind record alone is explored, which demonstrates that 90% of easterly wind events exceeding 9.5 m s-1 drive significant upwelling. During certain periods the ice cover on the shelf became landfast, which altered the upwelling and circulation patterns near the shelf break.

  2. Quantifying the Evolution of Melt Ponds in the Marginal Ice Zone Using High Resolution Optical Imagery and Neural Networks

    NASA Astrophysics Data System (ADS)

    Ortiz, M.; Pinales, J. C.; Graber, H. C.; Wilkinson, J.; Lund, B.

    2016-02-01

    Melt ponds on sea ice play a significant and complex role on the thermodynamics in the Marginal Ice Zone (MIZ). Ponding reduces the sea ice's ability to reflect sunlight, and in consequence, exacerbates the albedo positive feedback cycle. In order to understand how melt ponds work and their effect on the heat uptake of sea ice, we must quantify ponds through their seasonal evolution first. A semi-supervised neural network three-class learning scheme using a gradient descent with momentum and adaptive learning rate backpropagation function is applied to classify melt ponds/melt areas in the Beaufort Sea region. The network uses high resolution panchromatic satellite images from the MEDEA program, which are collocated with autonomous platform arrays from the Marginal Ice Zone Program, including ice mass-balance buoys, arctic weather stations and wave buoys. The goal of the study is to capture the spatial variation of melt onset and freeze-up of the ponds within the MIZ, and gather ponding statistics such as size and concentration. The innovation of this work comes from training the neural network as the melt ponds evolve over time; making the machine learning algorithm time-dependent, which has not been previously done. We will achieve this by analyzing the image histograms through quantification of the minima and maxima intensity changes as well as linking textural variation information of the imagery. We will compare the evolution of the melt ponds against several different array sites on the sea ice to explore if there are spatial differences among the separated platforms in the MIZ.

  3. Scaling Observations of Distance Limited Waves in the Seasonally Ice-Covered Beaufort Sea

    NASA Astrophysics Data System (ADS)

    Smith, M.; Thomson, J.

    2016-02-01

    In the Beaufort Sea, surface waves are affected by rapidly changing sea ice. Sea ice retreat in recent years has left larger expanses of open water for wave generation, leading to unprecedented large waves. Using wave data from 2012, the year of lowest ice extent on record, Thomson and Rogers (Geophys. Res. Lett., 41(9), 2014) showed that wave energy flux in the Arctic Ocean scales with the open water distance to land or ice edge (i.e., the fetch). We refine their results using in situ measurements of the sea state obtained from freely-drifting SWIFT buoys during the 2014 open water season. Satellite ice products are used to derive coincident open water distances and, when applicable, local ice concentrations. We determine that the scaling of wave energy and frequency with open water distance is only appropriate when the wind and wave field are relatively stationary, such that waves can be considered limited by the open water distance. Similarly, waves generated in partial ice cover can be categorized as distance limited using a newly defined "effective fetch" corresponding to the distance between ice floes, so long as the conditions are relatively stationary. Therefore, the evolution of the wave field in the Beaufort Sea is a function of the ice cover at both the local scale, where partial ice cover reduces the effective fetch, and at the basin scale, where the hard ice edge limits the fetch in a more conventional manner.

  4. Seasonal changes in the spatial distribution of phytoplankton in small, temperate-zone lakes

    USGS Publications Warehouse

    Cloern, J.E.; Alpine, A.E.; Cole, B.E.; Heller, T.

    1992-01-01

    Sampling across two N Minnesota small lakes shows that phytoplankton patchiness is greatly enhanced during winter ice-cover relative to the open-water seasons of exposure to wind stress and rapid turbulent mixing. -Authors

  5. The ocean mixed layer under Southern Ocean sea-ice: seasonal cycle and forcing.

    NASA Astrophysics Data System (ADS)

    Violaine, P.; Sallee, J. B.; Schmidtko, S.; Roquet, F.; Charrassin, J. B.

    2016-02-01

    The mixed-layer at the surface of the ocean is the gateway for all exchanges between air and sea. A vast area of the Southern Ocean is however seasonally capped by sea-ice, which alters this gateway and the characteristic the ocean mixed-layer. The interaction between the ocean mixed-layer and sea-ice plays a key role for water-mass formation and circulation, carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the mixed layer, as well as the processes responsible for its evolution, are poorly understood due to the lack of in-situ observations and measurements. We urgently need to better understand the forcing and the characteristics of the ocean mixed-layer under sea-ice if we are to understand and predict the world's climate. In this study, we combine a range of distinct sources of observation to overcome this lack in our understanding of the Polar Regions. Working on Elephant Seal-derived data as well as ship-based observations and Argo float data, we describe the seasonal cycle of the characteristics and stability of the ocean mixed layer over the entire Southern Ocean (South of 40°S), and specifically under sea-ice. Mixed-layer budgets of heat and freshwater are used to investigate the main forcings of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget, and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity and vertical entrainment play only secondary role.Our results suggest that changes in regional sea-ice distribution or sea-ice seasonal cycle duration, as currently observed, would widely affect the buoyancy budget of the underlying mixed-layer, and impacts large-scale water-mass formation and transformation.

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

    PubMed

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

    2013-07-01

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

  7. Variations of mesoscale and large-scale sea ice morphology in the 1984 Marginal Ice Zone Experiment as observed by microwave remote sensing

    NASA Technical Reports Server (NTRS)

    Campbell, W. J.; Josberger, E. G.; Gloersen, P.; Johannessen, O. M.; Guest, P. S.

    1987-01-01

    The data acquired during the summer 1984 Marginal Ice Zone Experiment in the Fram Strait-Greenland Sea marginal ice zone, using airborne active and passive microwave sensors and the Nimbus 7 SMMR, were analyzed to compile a sequential description of the mesoscale and large-scale ice morphology variations during the period of June 6 - July 16, 1984. Throughout the experiment, the long ice edge between northwest Svalbard and central Greenland meandered; eddies were repeatedly formed, moved, and disappeared but the ice edge remained within a 100-km-wide zone. The ice pack behind this alternately diffuse and compact edge underwent rapid and pronounced variations in ice concentration over a 200-km-wide zone. The high-resolution ice concentration distributions obtained in the aircraft images agree well with the low-resolution distributions of SMMR images.

  8. Quantifying Uncertainties in the Seasonal Cycle of Arctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Lucas, D. D.; Covey, C. C.; Klein, R.; Tannahill, J.; Ivanova, D. P.

    2013-12-01

    Many climate models project that the Arctic Ocean will be free of summertime sea ice within a century when forced with representative future greenhouse gas emission scenarios. To determine whether uncertainties in sea ice physics can also lead to an ice-free Arctic, we ran present-day ensemble simulations with the Community Climate System Model (CCSM4) that varied 7 parameters in the Community Ice Code (CICE4) over expert-provided ranges. The September minimum in sea ice extent computed by the ensemble ranges from 0.5 to 7.7 million km2, the lower end of which is significantly less than current observed values and lower than the models in the Coupled Model Intercomparison Project Phase 5 (CMIP5). CCSM4 can therefore simulate a summertime Arctic that is effectively free of sea ice either by increasing greenhouse gas forcing or by keeping the forcing constant and varying CICE4 parameters within recommended ranges. We identified three key CICE4 parameters related to radiative and thermal properties of snow that drive this extreme ensemble variability. Given observational data, machine learning algorithms were also used to quantify and constrain probability distribution functions for these parameters, which can be sampled to provide probabilistic assessments of sea ice characteristics simulated by CICE4. 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 was funded by the Uncertainty Quantification Strategic Initiative Laboratory Directed Research and Development Project at LLNL under project tracking code 10-SI-013 (UCRL LLNL-ABS-641752).

  9. Seasonal Variation of Cloud Radiative Forcing Over Young Sea Ice During the N-ICE2015 Experiment

    NASA Astrophysics Data System (ADS)

    Murphy, S. Y.; Walden, V. P.; Cohen, L.; Hudson, S. R.

    2016-12-01

    There is a lack of comprehensive measurements of the seasonal variation of cloud and radiation properties over sea ice. The Norwegian Young Sea Ice experiment (N-ICE2015), conducted from January to June 2015, was the first experiment since SHEBA in 1997/1998 to measure cloud properties and all components of the surface energy balance. N-ICE2015 was also the first experiment that was focused on understanding the effects of the atmosphere specifically on thin, young sea ice near the edge of the Arctic ice pack. Here we present the variation of cloud radiative forcing (CRF) at the surface during the seasonal transition from winter to summer. Cloud macrophysical and microphysical properties were measured using a micropulse lidar and a ceilometer. Broadband radiometers were used to measure upwelling and downwelling shortwave and longwave radiative fluxes at the surface. These measurements are combined with radiative transfer calculations of clear-sky fluxes to determine cloud radiative forcing during the seasonal transition. During the winter, the CRF is determined by longwave radiation and averages about 20-30 W m-2, with a range of 0 to 60 W m-2. In spring, shortwave radiation creates a strong diurnal cycle in CRF with values ranging from about -40 to +60 W m-2, the values of which depend strongly on the cloud fraction. In summer, the CRF averages to about 50-60 W m-2 and is always positive with values ranging from 10 to 100 W m-2. Two case studies, one in winter and one in spring, will be highlighted, as well as the dependence of CRF on cloud phase.

  10. Satellite and aircraft passive microwave observations during the Marginal Ice Zone Experiment in 1984

    NASA Technical Reports Server (NTRS)

    Gloersen, Per; Campbell, William J.

    1988-01-01

    This paper compares satellite data on the marginal ice zone obtained during the Marginal Ice Zone Experiment in 1984 by Nimbus 7 with simultaneous mesoscale aircraft (in particular, the NASA CV-990 airborne laboratory) and surface observations. Total and multiyear sea ice concentrations calculated from the airborne multichannel microwave radiometer were found to agree well with similar calculations using the Nimbus SMMR data. The temperature dependence of the determination of multiyear sea-ice concentration near the melting point was found to be the same for both airborne and satellite data. It was found that low total ice concentrations and open-water storm effects near the ice edge could be reliably distinguished by means of spectral gradient ratio, using data from the 0.33-cm and the 1.55-cm radiometers.

  11. Ice sheet features identification, glacier velocity estimation, and glacier zones classification using high-resolution optical and SAR data

    NASA Astrophysics Data System (ADS)

    Thakur, Praveen K.; Dixit, Ankur; Chouksey, Arpit; Aggarwal, S. P.; Kumar, A. Senthil

    2016-05-01

    Ice sheet features, glacier velocity estimation and glacier zones or facies classification are important research activities highlighting the dynamics of ice sheets and glaciers in Polar Regions and in inland glaciers. The Cband inSAR data is of ERS 1/2 tandem pairs with one day interval for spring of 1996 and L-band PolinSAR data of ALOS-PALSAR-2 for spring of 2015 is used in glacier velocity estimation. Glacier classification is done using multi-temporal C-and L-band SAR data and also with single date full polarization and hybrid polarization data. In first part, a mean displacement of 9 cm day-1 was recorded using SAR interferometric technique using ERS 1/2 tandem data of 25-26 March 1996. Previous studies using optical data based methods has shown that Gangotri glacier moves with an average displacement of 4 cm and 6 cm day-1. As present results using ERS 1/2 data were obtained for one day interval, i.e., 25th March 05:00pm to 26th March 05:00 pm, 1996, variation in displacement may be due to presence of snow or wet snow melting over the glacier, since during this time snow melt season is in progress in Gangotri glacier area. Similarly the results of glacier velocity derived using ALOSPALSAR- 2 during 22 March - 19 April 2015 shows the mean velocity of 5.4 to 7.4 cm day-1 during 28 day time interval for full glacier and main trunk glacier respectively. This L-band data is already corrected for Faraday's rotation effects by JAXA, and tropospheric correction are also being applied to refine the results. These results are significant as it is after gap of 20 years that DInSAR methods has given glacier velocity for fast moving Himalayan glacier. RISAT-1 FRS-1 hybrid data is used to create Raney's decompositions parameters, which are further used for glacier zones classification using support vector machine based classification method. The Radarsat-2 and ALOS-PALSAR-2 fully polarized data of year 2010 and 2015 are also used for glacier classification. The identified

  12. 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.

  13. Wave Climate and Wave Mixing in the Marginal Ice Zones of Arctic Seas, Observations and Modelling

    DTIC Science & Technology

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Wave Climate and Wave Mixing in the Marginal Ice Zones of... climate is available over the entire period of existence of the marginal Arctic ice zones. Figure 1. Altimeter missions by Agency (1985-2015...to obtain the wave climate in the Arctic and its trends. Trends are obtained for mean and , as well as for their 90th and 99th percentiles, over

  14. Local Effects of Ice Floes on Skin Sea Surface Temperature in the Marginal Ice Zone from UAVs

    NASA Astrophysics Data System (ADS)

    Zappa, C. J.; Brown, S.; Emery, W. J.; Adler, J.; Wick, G. A.; Steele, M.; Palo, S. E.; Walker, G.; Maslanik, J. A.

    2013-12-01

    Recent years have seen extreme changes in the Arctic. Particularly striking are changes within the Pacific sector of the Arctic Ocean, and especially in the seas north of the Alaskan coast. These areas have experienced record warming, reduced sea ice extent, and loss of ice in areas that had been ice-covered throughout human memory. Even the oldest and thickest ice types have failed to survive through the summer melt period in areas such as the Beaufort Sea and Canada Basin, and fundamental changes in ocean conditions such as earlier phytoplankton blooms may be underway. Marginal ice zones (MIZ), or areas where the "ice-albedo feedback" driven by solar warming is highest and ice melt is extensive, may provide insights into the extent of these changes. Airborne remote sensing, in particular InfraRed (IR), offers a unique opportunity to observe physical processes at sea-ice margins. It permits monitoring the ice extent and coverage, as well as the ice and ocean temperature variability. It can also be used for derivation of surface flow field allowing investigation of turbulence and mixing at the ice-ocean interface. Here, we present measurements of visible and IR imagery of melting ice floes in the marginal ice zone north of Oliktok Point AK in the Beaufort Sea made during the Marginal Ice Zone Ocean and Ice Observations and Processes EXperiment (MIZOPEX) in July-August 2013. The visible and IR imagery were taken from the unmanned airborne vehicle (UAV) ScanEagle. The visible imagery clearly defines the scale of the ice floes. The IR imagery show distinct cooling of the skin sea surface temperature (SST) as well as a intricate circulation and mixing pattern that depends on the surface current, wind speed, and near-surface vertical temperature/salinity structure. Individual ice floes develop turbulent wakes as they drift and cause transient mixing of an influx of colder surface (fresh) melt water. The upstream side of the ice floe shows the coldest skin SST, and

  15. Basal conditions at the grounding zone of Whillans Ice Stream, West Antarctica, from ice-penetrating radar

    NASA Astrophysics Data System (ADS)

    Christianson, Knut; Jacobel, Robert W.; Horgan, Huw J.; Alley, Richard B.; Anandakrishnan, Sridhar; Holland, David M.; DallaSanta, Kevin J.

    2016-11-01

    We present a comprehensive ice-penetrating radar survey of a subglacial embayment and adjacent peninsula along the grounding zone of Whillans Ice Stream, West Antarctica. Through basal waveform and reflectivity analysis, we identify four distinct basal interfaces: (1) an ice-water-saturated till interface inland of grounding; (2) a complex interface in the grounding zone with variations in reflectivity and waveforms caused by reflections from fluting, sediment deposits, and crevasses; (3) an interface of anomalously low-reflectivity downstream of grounding in unambiguously floating areas of the embayment due to basal roughness and entrained debris; and (4) a high-reflectivity ice-seawater interface that occurs immediately seaward of grounding at the subglacial peninsula and several kilometers seaward of grounding in the embayment, occurring after basal debris and grounding zone flutes have melted off the ice bottom. Sediment deposition via basal debris melt-out occurs in both locations. The higher basal melt rate at the peninsula contributes to greater grounding line stability by enabling faster construction of a stabilizing sediment wedge. In the embayment, the low slopes of the ice bottom and bed prevent development of a strong thermohaline circulation leading to a lower basal melt rate and less rapid sediment deposition. Thus, grounding lines in subglacial embayments are more likely to lack stabilizing sediment deposits and are more prone to external forcing, whether from the ocean, the subglacial water system, or large-scale ice dynamics. Our conclusions indicate that subglacial peninsulas and embayments should be treated differently in ice sheet-ocean models if these models are to accurately simulate grounding line response to external forcing.

  16. Austral winter distributions of large tintinnid and large sarcodinid protozooplankton in the ice-edge zone of the Weddell/Scotia Seas

    NASA Astrophysics Data System (ADS)

    Gowing, Marcia M.; Garrison, David L.

    1991-07-01

    Seasonal distribution and abundance data for large sarcodinid protozooplankton (Radiolaria, Foraminifera, Acantharia and the heliozoan Sticholonche spp.) and larger tintinnid ciliates (e.g., Laackmaniella spp.) are necessary for evaluating their roles in food webs and particle fluxes. As part of the Antarctic Marine Ecosystem Research in the Ice Edge Zone (AMERIEZ) project, we sampled these large (≥ 50 μm) protozooplankton in the winter ice edge zone of the Scotia/Weddell Seas. Organisms alive at the time of capture were counted in large volume (60 1) water samples from 5 paired depths in the upper 210 m from 17 stations. Relationships between abundances and environmental factors in ice-covered, ice edge, and open waters were assessed with correlation, cluster, and multidimensional scaling analyses. Mean abundances of large tintinnids were less than 3150 per m 3, and mean abundances of the individual sarcodine groups were generally less than 1000 per m 3. The most pronounced distributional patterns were related to depth. In general, large tintinnids were more abundant in the colder waters from 0-85 m, a zone encompassed by the mixed layer and the euphotic zone. Acantharians were more abundant in this upper zone only in ice-covered waters. Radiolaria (predominantly phaeodarians) and the heliozoan Sticholonche spp. were more abundant from 115 to 210 m, a zone of warmer, more saline water. Foraminiferan distributions showed little pattern with depth. Results of the cluster analyses also suggested that depth was the most significant effect determining similarity among assemblages of large protozooplankton at the 17 stations. The few correlations between abundances of the groups and chlorophyll a probably reflect relationships more complex than grazing. Abundances of large tintinnids were higher in surface waters under the ice than at the ice edge or in open water. This could result from their feeding on algal cells released from the base of the ice or it may be a

  17. Water-ice clouds on Mars: Location and seasonal variation

    NASA Astrophysics Data System (ADS)

    Christensen, P. R.; Jaramillo, L.; Greeley, R.

    1985-04-01

    Water-ice clouds were located on Mars using Viking infrared thermal mapper (IRTM) broadband spectral observations. The IRTM instrument had 5 thermal bands centered at 7, 9, 11, 15, and 20 microns. Clouds and hazes were consistently observed in four northern hemisphere regions centered over Tharsis, Arabia, Elysium, and along the boundary between the crater uplands and the northern plains. During the northern spring and summer when the atmosphere is relatively free of dust, there is a distinct difference between the cloud abundance in the Northern and Southern Hemispheres, with clouds and hazes being rare in the south. A second important class of water-ice clouds are those observed along the boundary of the retreating north polar cap. These clouds occur at all longitudes around the cap and are generally confined to within +/- 5 deg of the cap boundary. The cloud opacities can be estimated using a delta-Eddington radiative transfer model which incorporates Mie scattering and the electrical properties of water-ice. Assuming realistic, but non-unique, values for the ice particle size and cloud temperature, the derived opacities range from near-zero to 1.

  18. Water-ice Clouds on Mars: Location and Seasonal Variation

    NASA Technical Reports Server (NTRS)

    Christensen, P. R.; Jaramillo, L.; Greeley, R.

    1985-01-01

    Water-ice clouds were located on Mars using Viking infrared thermal mapper (IRTM) broadband spectral observations. The IRTM instrument had 5 thermal bands centered at 7, 9, 11, 15, and 20 microns. Clouds and hazes were consistently observed in four northern hemisphere regions centered over Tharsis, Arabia, Elysium, and along the boundary between the crater uplands and the northern plains. During the northern spring and summer when the atmosphere is relatively free of dust, there is a distinct difference between the cloud abundance in the Northern and Southern Hemispheres, with clouds and hazes being rare in the south. A second important class of water-ice clouds are those observed along the boundary of the retreating north polar cap. These clouds occur at all longitudes around the cap and are generally confined to within +/- 5 deg of the cap boundary. The cloud opacities can be estimated using a delta-Eddington radiative transfer model which incorporates Mie scattering and the electrical properties of water-ice. Assuming realistic, but non-unique, values for the ice particle size and cloud temperature, the derived opacities range from near-zero to 1.

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

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.; Platonov, N.G.

    2004-01-01

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

  20. Seasonal sea ice predictions for the Arctic based on assimilation of remotely sensed observations

    NASA Astrophysics Data System (ADS)

    Kauker, F.; Kaminski, T.; Ricker, R.; Toudal-Pedersen, L.; Dybkjaer, G.; Melsheimer, C.; Eastwood, S.; Sumata, H.; Karcher, M.; Gerdes, R.

    2015-10-01

    The recent thinning and shrinking of the Arctic sea ice cover has increased the interest in seasonal sea ice forecasts. Typical tools for such forecasts are numerical models of the coupled ocean sea ice system such as the North Atlantic/Arctic Ocean Sea Ice Model (NAOSIM). The model uses as input the initial state of the system and the atmospheric boundary condition over the forecasting period. This study investigates the potential of remotely sensed ice thickness observations in constraining the initial model state. For this purpose it employs a variational assimilation system around NAOSIM and the Alfred Wegener Institute's CryoSat-2 ice thickness product in conjunction with the University of Bremen's snow depth product and the OSI SAF ice concentration and sea surface temperature products. We investigate the skill of predictions of the summer ice conditions starting in March for three different years. Straightforward assimilation of the above combination of data streams results in slight improvements over some regions (especially in the Beaufort Sea) but degrades the over-all fit to independent observations. A considerable enhancement of forecast skill is demonstrated for a bias correction scheme for the CryoSat-2 ice thickness product that uses a spatially varying scaling factor.

  1. Seasonal Study of Mercury Species in the Antarctic Sea Ice Environment.

    PubMed

    Nerentorp Mastromonaco, Michelle G; Gårdfeldt, Katarina; Langer, Sarka; Dommergue, Aurélien

    2016-12-06

    Limited studies have been conducted on mercury concentrations in the polar cryosphere and the factors affecting the distribution of mercury within sea ice and snow are poorly understood. Here we present the first comprehensive seasonal study of elemental and total mercury concentrations in the Antarctic sea ice environment covering data from measurements in air, sea ice, seawater, snow, frost flowers, and brine. The average concentration of total mercury in sea ice decreased from winter (9.7 ng L(-1)) to spring (4.7 ng L(-1)) while the average elemental mercury concentration increased from winter (0.07 ng L(-1)) to summer (0.105 ng L(-1)). The opposite trends suggest potential photo- or dark oxidation/reduction processes within the ice and an eventual loss of mercury via brine drainage or gas evasion of elemental mercury. Our results indicate a seasonal variation of mercury species in the polar sea ice environment probably due to varying factors such as solar radiation, temperature, brine volume, and atmospheric deposition. This study shows that the sea ice environment is a significant interphase between the polar ocean and the atmosphere and should be accounted for when studying how climate change may affect the mercury cycle in polar regions.

  2. Thermodynamics of slush and snow-ice formation in the Antarctic sea-ice zone

    NASA Astrophysics Data System (ADS)

    Jutras, Mathilde; Vancoppenolle, Martin; Lourenço, Antonio; Vivier, Frédéric; Carnat, Gauthier; Madec, Gurvan; Rousset, Clément; Tison, Jean-Louis

    2016-09-01

    Snow over Antarctic sea ice is often flooded by brine or seawater, particularly in spring, forming slush and snow ice. Here, we evaluate the representation of the thermodynamics of slush and snow-ice formation in large-scale sea-ice models, using laboratory experiments (NaCl solutions poured into grated ice in an isolated container). Scaling analysis highlights latent heat as the main term of the energy budget. The temperature of the new sea ice immediately after flooding is found very close to the saltwater freezing point, whereas its bulk salinity is typically > 20 g / kg. Large-scale sea-ice models faithfully represent such physics, yet the uncertainty on the origin of flooding saltwater impacts the calculated new ice temperature, because of the different salinities of seawater and brine. The laboratory experiments also suggest a potential limitation to the existing physical representations of flooding: for brine fractions > 60 %, ice crystals start floating upon saltwater. Natural sea-ice observations suggest that the isolated system assumption holds for a few hours at most, after which rapid heat and salt exchanges mostly destroy the initial flooding signature on temperature and salinity. A small footprint on ice salinity remains however, natural snow ice is found 3-5 g/kg more saline than other forms of sea ice.

  3. Seasonal changes in ice sheet motion due to melt water lubrication

    NASA Astrophysics Data System (ADS)

    Hewitt, I.

    2012-12-01

    Significant temporal variability of ice flow has been observed at the melting margins of the Greenland ice sheet. Seasonal acceleration and deceleration has been partly attributed to changes in resistance at the ice-bed interface caused by subglacial routing of surface melt water, as is the case for valley glaciers. Larger quantities of melt water do not necessarily reduce resistance, however, and the overall effect of melt water lubrication on the mean annual motion of the ice sheet remains unclear. In this work, numerical models are used to explore the coupling between subglacial drainage of surface melt water and ice sheet motion. A synthetic ice sheet is forced to melt according to a prescribed seasonal cycle and the effect of this melting on the speed of the ice is calculated. The model adopts a distributed-channelized structure for the subglacial drainage system, with opening and closing of drainage space controlled by turbulent dissipation, cavitation around bedrock roughness elements, and creep closure of the ice. Subglacial water pressure is assumed to exert the main hydrological control on ice lubrication and is used to parameterize the basal sliding law for a vertically-integrated higher-order ice flow model. The model results suggest that the fastest ice velocities should be expected soon after the onset of surface melting, when runoff into moulins swamps the existing capacity of the drainage system. Periods of relatively high melting at any stage of the melt season can have the same effect, but the establishment of a more efficient drainage system can also have the effect of reducing water pressure and sliding velocities. This behaviour is in broad agreement with current observations. Comparing years with different total melting rates, the model further suggests that slow-down due to the more efficient drainage system is likely to be confined to close to the ice sheet margins (perhaps within about 20km), whereas further away from the margin a larger

  4. Observational uncertainty of Arctic sea-ice concentration significantly affects seasonal climate forecasts

    NASA Astrophysics Data System (ADS)

    Bunzel, Felix; Notz, Dirk; Baehr, Johanna; Müller, Wolfgang; Fröhlich, Kristina

    2016-04-01

    We examine how the choice of a particular satellite-retrieved sea-ice concentration dataset used for initialising seasonal climate forecasts impacts the prediction skill of Arctic sea-ice area and Northern hemispheric 2-meter air temperatures. To do so, we performed two assimilation runs with the Max Planck Institute Earth System Model (MPI-ESM) from 1979 to 2012, where atmospheric and oceanic parameters as well as sea-ice concentration were assimilated using Newtonian relaxation. The two assimilation runs differ only in the sea-ice concentration dataset used for assimilating sea ice. In the first run, we use sea-ice concentrations as derived by the NASA-Team algorithm, while in the second run we use sea-ice concentrations as derived from the Bootstrap algorithm. A major difference between these two sea-ice concentration data products involves the treatment of melt ponds. While for both products melt ponds appear as open water in the raw satellite data, the Bootstrap algorithm more strongly attempts to offset this systematic bias by synthetically increasing the retrieved ice concentration during summer months. For each year of the two assimilation runs we performed a 10-member ensemble of hindcast experiments starting on 1 May and 1 November with a hindcast length of 6 months. For hindcasts started in November, initial differences in Arctic sea-ice area and surface temperature decrease rapidly throughout the freezing period. For hindcasts started in May, initial sea-ice area differences increase over time. By the end of the melting period, this causes significant differences in 2-meter air temperature of regionally more than 3°C. Hindcast skill for surface temperatures over Europe and North America is higher with Bootstrap initialization during summer and with NASA Team initialisation during winter. This implies that the choice of the sea-ice data product and, thus, the observational uncertainty also affects forecasts of teleconnections that depend on Northern

  5. Seasonal comparisons of sea ice concentration estimates derived from SSM/I, OKEAN and RADARSAT data

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.

    2002-01-01

    The SSM/I microwave satellite radiometer and its predecessor SMMR are primary sources of information for global sea-ice and climate studies. However, comparisons of SSM/I, LANDSAT, AVHRR and ERS-1 SAR have shown substantial seasonal and regional differences in their estimates of sea ice concentration. To evaluate these differences, we compared SSM/I estimates of sea ice coverage derived with the NASA Team and Bootstrap algorithms to estimates made using RADARSAT, and OKEAN-01 satellite sensor data. The study area included the Barents, Kara Sea, Laptev Sea, and adjacent parts of the Arctic Ocean, during October 1995 through October 1999. Ice concentration estimates from spatially and temporally near-coincident imagery were calculated using independent algorithms for each sensor type. The OKEAN algorithm implemented the satellite's two-channel active (radar) and passive microwave data in a linear mixture model based on the measured values of brightness temperature and radar backscatter. The RADARSAT algorithm utilized a segmentation approach of the measured radar backscatter, and the SSM/I ice concentrations were derived at National Snow and Ice Data Center (NSIDC) using the NASA Team and Bootstrap algorithms. Seasonal and monthly differences between SSM/I, OKEAN, and RADARSAT ice concentrations were calculated and compared. Overall, total sea ice concentration estimates derived independently from near-coincident RADARSAT, OKEAN-01 and SSM/I satellite imagery demonstrated mean differences of less than 5.5 % (SD < 9.5%) during the winter period. Differences between the SSM/I NASA Team and the SSM/I Bootstrap concentrations were no more than 3.1 % (SD < 5.4%) during this period. RADARSAT and OKEAN-01 data both yielded higher total ice concentrations than the NASA Team and the Bootstrap algorithms. The Bootstrap algorithm yielded higher total ice concentrations than the NASA Team algorithm. Total ice concentrations derived from OKEAN-01 and SSM/I satellite imagery were

  6. Seasonal Evolution of Supra-glacial Lakes Across the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Sundal, A.; Shepherd, A.; Nienow, P.; Palmer, S.; Hanna, E.

    2008-12-01

    We used 268 MODIS satellite images spanning the melt seasons 2003 and 2005-2007 to investigate the seasonal evolution of supra-glacial lakes in three different regions of the Greenland ice sheet. Lake area estimates were obtained by developing an automated classification method for their identification based on 250 m resolution MODIS surface reflectance images. Our dataset reveal widespread supra-glacial lake formation and drainage across the Greenland ice sheet, with a 2-3 weeks delay in the evolution of total supra-glacial lake area in the northern study areas compared to the south-western study area. The onset of lake growth varies by up to one month inter-annually, and lakes form and drain at progressively higher altitudes during the melt season. The annual peak in total lake area is positively correlated with modelled annual runoff across all study areas. Our results indicate that, in a warmer climate, supra-glacial lakes on the surface of the Greenland ice sheet can be expected to form earlier in the melt season and at higher altitudes than is presently the case. In consequence, the area and time period over which connections between the ice sheet surface and base may be established (Das et al 2008) will increase, potentially increasing the rate of ice sheet discharge and its sea level contribution (Zwally et al 2002). Das, S., Joughin, M., Behn, M., Howat, I., King, M., Lizarralde, D., Bhatia, M., 2008. Fracture propagation to the base of the Greenland Ice Sheet during supra-glacial lake drainage, Science, 5877, p.778-781. Zwally, H.J., Abdalati, W., Herring, T., Larson, K., Saba, J., Steffen, K., 2002. Surface Melt-Induced Acceleration of Greenland Ice-Sheet Flow, Science, 297, p.218-221.

  7. The ocean mixed layer under Southern Ocean sea-ice: Seasonal cycle and forcing

    NASA Astrophysics Data System (ADS)

    Pellichero, Violaine; Sallée, Jean-Baptiste; Schmidtko, Sunke; Roquet, Fabien; Charrassin, Jean-Benoît

    2017-02-01

    The oceanic mixed layer is the gateway for the exchanges between the atmosphere and the ocean; in this layer, all hydrographic ocean properties are set for months to millennia. A vast area of the Southern Ocean is seasonally capped by sea-ice, which alters the characteristics of the ocean mixed layer. The interaction between the ocean mixed layer and sea-ice plays a key role for water mass transformation, the carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the under-ice mixed layer are poorly understood due to the sparseness of in situ observations and measurements. In this study, we combine distinct sources of observations to overcome this lack in our understanding of the polar regions. Working with elephant seal-derived, ship-based, and Argo float observations, we describe the seasonal cycle of the ocean mixed-layer characteristics and stability of the ocean mixed layer over the Southern Ocean and specifically under sea-ice. Mixed-layer heat and freshwater budgets are used to investigate the main forcing mechanisms of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity, and vertical entrainment play only secondary roles. Our results suggest that changes in regional sea-ice distribution and annual duration, as currently observed, widely affect the buoyancy budget of the underlying mixed layer, and impact large-scale water mass formation and transformation with far reaching consequences for ocean ventilation.

  8. Skill improvement of seasonal Arctic sea ice forecasts using bias-correction and ensemble calibration

    NASA Astrophysics Data System (ADS)

    Krikken, Folmer; Hazeleger, Wilco; Vlot, Willem; Schmeits, Maurice; Guemas, Virginie

    2016-04-01

    We explore the standard error and skill of dynamical seasonal sea ice forecasts of the Arctic using different bias-correction and ensemble calibration methods. The latter is often used in weather forecasting, but so far has not been applied to Arctic sea ice forecasts. We use seasonal predictions of Arctic sea ice of a 5-member ensemble forecast using the fully coupled GCM EC-Earth, with model initial states obtained by nudging towards ORAS4 and ERA-Interim. The raw model forecasts contain large biases in total sea ice area, especially during the summer months. This is mainly caused by a difference in average seasonal cycle between EC-Earth and observations, which translates directly into the forecasts yielding large biases. Further errors are introduced by the differences in long term trend between the observed sea ice, and the uninitialised EC-earth simulation. We find that extended logistic regression (ELR) and heteroscedastic extended logistic regression (HELR) both prove viable ensemble calibration methods, and improve the forecasts substantially compared to standard bias correction techniques. No clear distinction between ELR and HELR is found. Forecasts starting in May have higher skill (CRPSS > 0 up to 5 months lead time) than forecasts starting in August (2-3 months) and November (2-3 months), with trend-corrected climatology as reference. Analysis of regional skill in the Arctic shows distinct differences, where mainly the Arctic ocean and the Kara and Barents sea prove to be one of the more predictable regions with skilful forecasts starting in May up to 5-6 months lead time. Again, forecasts starting in August and November show much lower regional skill. Overall, it is still difficult to beat relative simple statistical forecasts, but by using ELR and HELR we are getting reasonably close to skilful seasonal forecasts up to 12 months lead time. These results show there is large potential, and need, for using ensemble calibration in seasonal forecasts of

  9. The influence of spatial and seasonal variability on the stability of the sea ice cover

    NASA Astrophysics Data System (ADS)

    Wagner, T. J. W.; Eisenman, I.

    2014-12-01

    Reports of ever new record lows of Arctic sea ice extent are making headlines almost continually in recent years. The change in albedo when sea ice is replaced by open water introduces an important nonlinearity to the system. It is this nonlinearity that has sparked an ongoing debate regarding the stability of the Arctic ice cover and the possibility of an Arctic `tipping point'. In previous studies, instabilities for a shrinking ice cover linked to the ice-albedo feedback have been identified in two different types of idealized models: (i) annual-mean diffusive energy balance models (EBMs) and (ii) seasonally-varying single-column models (SCMs). The incidence of instabilities in these low-order models stands in contrast with results from comprehensive climate models which have been found not to simulate any such instability. In the present study we investigate the stability of the sea ice cover from a theoretical perspective, developing a model that includes both seasonal and latitudinal variability. The model reduces to a standard EBM or SCM as limiting cases in the parameter regime, thus reconciling the two previous lines of research. The simple formulation of this model allows us to investigate the key physical processes that govern the stability of the system. Our results show that the stability of the ice cover vastly increases with the inclusion of additional degrees of freedom associated with a seasonal cycle or horizontal heat transport. The results suggest that the sea ice cover is substantially more stable than has been suggested by previous idealized modeling studies.

  10. On Impacts of Ocean Waves in Marginal Ice Zones and their Repercussions for Arctic Ice/Ocean Models (Invited)

    NASA Astrophysics Data System (ADS)

    Squire, V. A.

    2013-12-01

    , each with possibly different concentrations and randomized floes present in some FSD, the manner in which a long crested sea with its intrinsic directional spread advances through a conglomeration of dispersed multiply-scattering floes can be tracked, with the purpose of finding how the waves diminish in amplitude and whether the sea ice will be broken up. The details of how this is done are the subject of another AGU paper. My presentation will focus primarily on the ';why and how' of implanting wave-ice interactions in ice/ocean models and on recent developments to ensure that the physics used is as robust as practicable. Francis, O. P., G. G. Panteleev, and D. E. Atkinson (2011), Ocean wave conditions in the Chukchi Sea from satellite and in situ observations, Geophys. Res. Lett., 38, L24610, doi: 10.1029/ 2011GL049839. Williams, T. D., L. G. Bennetts, V. A. Squire, D. Dumont, and L. Bertino (2013a), Wave-ice interactions in the marginal ice zone. Part 1: Theoretical foundations, Ocean Model., doi: 10.1016/j.ocemod. 2013.05.010. ------ (2013b), Wave-ice interactions in the marginal ice zone. Part 2: Numerical implementation and sensitivity studies along 1D transects of the ocean surface, Ocean Model., doi: 10.1016/j.ocemod. 2013.05.011.

  11. Quantifying the seasonal “breathing” of the Antarctic ice sheet

    NASA Astrophysics Data System (ADS)

    Ligtenberg, S. R. M.; Horwath, M.; van den Broeke, M. R.; Legrésy, B.

    2012-12-01

    One way to estimate the mass balance of an ice sheet is to convert satellite observed surface elevation changes into mass changes. In order to do so, elevation and mass changes due to firn processes must be taken into account. Here, we use a firn densification model to simulate seasonal variations in depth and mass of the Antarctic firn layer, and assess their influence on surface elevation. Forced by the seasonal cycle in temperature and accumulation, a clear seasonal cycle in average firn depth of the Antarctic ice sheet (AIS) is found with an amplitude of 0.026 m, representing a volume oscillation of 340 km3. The phase of this oscillation is rather constant across the AIS: the ice sheet volume increases in austral autumn, winter and spring and quickly decreases in austral summer. Seasonal accumulation differences are the major driver of this annual ‘breathing’, with temperature fluctuations playing a secondary role. The modeled seasonal elevation signal explains ∼31% of the seasonal elevation signal derived from ENVISAT radar altimetry, with both signals having similar phase.

  12. A wave-based model for the marginal ice zone including a floe breaking parameterization

    NASA Astrophysics Data System (ADS)

    Dumont, D.; Kohout, A.; Bertino, L.

    2011-04-01

    The marginal ice zone (MIZ) is the boundary between the open ocean and ice-covered seas, where sea ice is significantly affected by the onslaught of ocean waves. Waves are responsible for the breakup of ice floes and determine the extent of the MIZ and floe size distribution. When the ice cover is highly fragmented, its behavior is qualitatively different from that of pack ice with large floes. Therefore, it is important to incorporate wave-ice interactions into sea ice-ocean models. In order to achieve this goal, two effects are considered: the role of sea ice as a dampener of wave energy and the wave-induced breakup of ice floes. These two processes act in concert to modify the incident wave spectrum and determine the main properties of the MIZ. A simple but novel parameterization for floe breaking is derived by considering alternatively ice as a flexible and rigid material and by using current estimates of ice critical flexural strain and strength. This parameterization is combined with a wave scattering model in a one-dimensional numerical framework to evaluate the floe size distribution and the extent of the MIZ. The model predicts a sharp transition between fragmented sea ice and the central pack, thus providing a natural definition for the MIZ. Reasonable values are found for the extent of the MIZ given realistic initial and boundary conditions. The numerical setting is commensurate with typical ice-ocean models, with the future implementation into two-dimensional sea ice models in mind.

  13. Deformation of subglacial till near ice-sheet grounding zones: theory and experiments

    NASA Astrophysics Data System (ADS)

    Kowal, K. N.; Worster, G.

    2015-12-01

    Large-scale ice-sheet dynamics pivot on the deformation and transport of subglacial sediment through changes in the basal sliding velocities of glaciers. Such unconsolidated, water-saturated glacigenic sediment, or till, is found to accumulate into sedimentary wedges, or till-deltas, in grounding zones separating floating ice shelves from grounded ice streams. In addition to affecting glacial slip, such sedimentation may serve to stabilise ice sheets against grounding-line retreat in response to rising sea levels. We present a fluid-mechanical explanation of the formation of these wedges in terms of the jump in hydrostatic loading and unloading of till across the grounding zone, and we compare our findings with geophysical data of sedimentary wedge formation at the modern-day grounding zone of Whillans Ice Stream, West Antarctica. We develop a theoretical model of wedge formation in which we treat both ice and till as viscous fluids spreading under gravity into an inviscid ocean and find that a similar wedge of underlying fluid accumulates around the grounding line in our series of fluid-mechanical laboratory experiments. The experiments were performed in a confined channel geometry. We extend our theory to unconfined geometries in which till deformation is resisted dominantly by vertical shear stresses and the flow of the overlying ice is resisted dominantly either by vertical shear stresses between the ice and till or by extensional stresses characteristic of floating ice shelves and shelfy streams. The former is relevant to less-lubricated, grounded ice sheets whereas the latter is relevant to well-lubricated ice streams, sliding over soft, deformable till of low viscosity and appreciable thickness. We formulate a local condition relating wedge slopes in each of the three scenarios and find a reasonable agreement with geophysical data.

  14. Notable increases in nutrient concentrations in a shallow lake during seasonal ice growth.

    PubMed

    Fang, Yang; Changyou, Li; Leppäranta, Matti; Xiaonghong, Shi; Shengnan, Zhao; Chengfu, Zhang

    2016-12-01

    Nutrients may be eliminated from ice when liquid water is freezing, resulting in enhanced concentrations in the unfrozen water. The nutrients diluted from the ice may contribute to accumulated concentrations in sediment during winter and an increased risk of algae blooms during the following spring and summer. The objective of this study was to evaluate the influence of ice cover on nitrogen (N) and phosphorus (P) concentrations in the water and sediment of a shallow lake, through an examination of Ulansuhai Lake, northern China, from the period of open water to ice season in 2011-2013. The N and P concentrations were between two and five times higher, and between two and eight times higher, than in unfrozen lakes, respectively. As the ice thickness grew, contents of total N and total P showed C-shaped profiles in the ice, and were lower in the middle layer and higher in the bottom and surface layers. Most of the nutrients were released from the ice to liquid water. The results confirm that ice can cause the nutrient concentrations in water and sediment during winter to increase dramatically, thereby significantly impacting on processes in the water environment of shallow lakes.

  15. Importance of initial conditions in seasonal predictions of Arctic sea ice extent

    NASA Astrophysics Data System (ADS)

    Msadek, R.; Vecchi, G. A.; Winton, M.; Gudgel, R. G.

    2014-07-01

    We present seasonal predictions of Arctic sea ice extent (SIE) over the 1982-2013 period using two suites of retrospective forecasts initialized from a fully coupled ocean-atmosphere-sea ice assimilation system. High skill scores are found in predicting year-to-year fluctuations of Arctic SIE, with significant correlations up to 7 month ahead for September detrended anomalies. Predictions over the recent era, which coincides with an improved observational coverage, outperform the earlier period for most target months. We find, however, a degradation of skill in September during the last decade, a period of sea ice thinning in observations. The two prediction models, Climate Model version 2.1 (CM2.1) and Forecast-oriented Low Ocean Resolution (FLOR), share very similar ocean and ice component and initialization but differ by their atmospheric component. FLOR has improved climatological atmospheric circulation and sea ice mean state, but its skill is overall similar to CM2.1 for most seasons, which suggests a key role for initial conditions in predicting seasonal SIE fluctuations.

  16. Rapid growth and seasonal persistence of efficient subglacial drainage under kilometre thick Greenland ice

    NASA Astrophysics Data System (ADS)

    Nienow, P.; Wadham, J.; Chandler, D.; Doyle, S. H.; Tedstone, A. J.; Hubbard, A., II

    2015-12-01

    The relationship between surface melt and ice motion partly determines the sensitivity of the Greenland Ice Sheet to climate, and the structure of the subglacial drainage system may be critical in controlling how changing melt-rates will impact on future ice dynamics. However, the extent to which efficient subglacial drainage develops tens of km inland from the ice margin under thick (>1km) ice remains equivocal. In particular, several numerical modelling studies suggest that under such conditions subglacial channels cannot evolve on seasonal timescales, even under extreme inputs of surface meltwater. Here, we present hydrological and ice-motion data collected in summer 2012 in the vicinity of a moulin located ~40 km from the western margin of the Greenland Ice Sheet, where ice is ~1km thick. Supraglacial discharge into the moulin was monitored from the onset of surface drainage and the tracer sulphur hexafluoride (SF6) was injected into the moulin at repeat intervals and its emergence was monitored at its proglacial river outlet. The tracer results indicate rapid evolution from a slow, inefficient drainage system to a fast, hydraulically efficient system within ~three weeks from the onset of surface drainage. Once an efficient hydrological pathway was established, it remained open - as evidenced by the fast tracer return times - even during periods of low surface melt (~0.01m/d), when discharge into the moulin was <4 m3 s-1 and ceased overnight. Ice motion in the vicinity of the moulin slowed following the establishment of the efficient drainage pathway with a clear diurnal cyclicity driven by variations in supraglacial discharge. Our results confirm that hydraulically-efficient subglacial drainage can exist 10s km from the ice sheet margin where ice is ~1km thick, that the drainage configuration can form in a matter of weeks, and that it persists even during cool periods when local surface melt rates and inputs are low.

  17. Mapping of ice layer extent and snow accumulation in the percolation zone of the Greenland ice sheet

    NASA Technical Reports Server (NTRS)

    Nghiem, S. V.; Steffen, K.; Neumann, G.; Huff, R.

    2005-01-01

    The Greenland ice sheet underwent record extensive melt in 2002 and prolonged melt in 2003. The severe melting created a significant and extensive ice layer over the Greenland ice sheet. An innovative approach is developed to detect the ice layer formation using data acquired by the SeaWinds scatterometer on the QuikSCAT satellite. QuikSCAT backscatter together with in situ data from automatic weather stations of the Greenland Climate Network are used to map the extent of ice layer formation. The results reveal areas of extensive ice layer formed by the 2002 melt, which is consistent with the maximum melt extent in 2002. Moreover, during freezing seasons, QuikSCAT data show a linear decrease in backscatter (in decibels or dB) that is related to the amount of snow accumulation in the ice layer formation region. This snow accumulation signature is caused by the attenuation of radar waves in the snow layer, accumulating since the last major melt event, whose thickness appears as an exponential function in relation to the backscatter signature. We use the Greenland Climate Network data to calibrate the QuikSCAT accumulation rate in order to estimate and map snow accumulation. QuikSCAT results capture the extreme snowfall in mid-April 2003, which deposited more than 0.5 m of snow in a day as measured by the automated weather station at the NASA South East site. Large-scale QuikSCAT results show an anomalous increase of snow accumulation over the southeast region of Greenland during the 2002-2003 freezing season.

  18. The Increase of the Ice-free Season as Further Indication of the Rapid Decline of the Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Rodrigues, J.

    2008-12-01

    The unprecedented depletion of sea ice in large sectors of the Arctic Ocean in the summer of 2007 has been the subject of many publications which highlight the spectacular disappearance of the sea ice at the time of minimum ice cover or emphasise the losses at very high latitudes. However, minimum values can be strongly affected by specific circumstances occurring in a comparatively short time interval. The unusually clear skies and the presence of a particular wind pattern over the Arctic Ocean may partly explain the record minimum attained in September 2007. In this contribution, instead of limiting ourselves to the September minimum or the March maximum, we consider the ice conditions throughout the year, opting for a less used, and hopefully more convenient approach. We chose as variables to describe the evolution of the sea ice situation in the Arctic Ocean and peripheral seas in the 1979-2007 period the length of the ice- free season (LIFS) and the inverse sea ice index (ISII). The latter is a quantity that measures the degree of absence of sea ice in a year and varies between zero (when there is a perennial ice cover) and one (when there is open water all year round). We used sea ice concentration data obtained from passive microwave satellite imagery and processed with the Bootstrap algorithm for the SMMR and SSM/I periods, and with the Enhanced NASA Team algorithm for the AMSR-E period. From a linear fit of the observed data, we found that the average LIFS in the Arctic went from 118 days in the late 1970s to 148 days in 2006, which represents an average rate of increase of 1.1 days/year. In the period 2001-2007 the LIFS increased monotonically at an average rate of 5.5 days/year, in good agreement with the general consensus that the Arctic sea ice is currently in an accelerated decline. We also found that 2007 was the longest ice- free season on record (168 days). The ISII also reached a maximum in 2007 . We also investigated what happened at the regional

  19. Identification of contrasting seasonal sea ice conditions during the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Cabedo-Sanz, P.; Belt, S. T.; Knies, J.

    2012-12-01

    The presence of the sea ice diatom biomarker IP25 in Arctic marine sediments has been used in previous studies as a proxy for past spring sea ice occurrence and as an indicator of wider palaeoenvironmental conditions for different regions of the Arctic over various timescales [e.g. 1, 2]. The current study focuses on high-resolution palaeo sea ice reconstructions for northern Norway during the last ca. 15 cal. kyr BP. Within this study, particular emphasis has been placed on the identification of the sea ice conditions during the Younger Dryas and the application of different biomarker-based proxies to both identify and quantify seasonal sea ice conditions. Firstly, the appearance of the specific sea ice diatom proxy IP25 at ca. 12.9 cal. kyr BP in a marine sediment core (JM99-1200) obtained from Andfjorden has provided an unambiguous but qualitative measure of seasonal sea ice and thus the onset of the Younger Dryas stadial. The near continuous occurrence of IP25 for the next ca. 1400 yr demonstrates seasonal sea ice during this interval, although variable abundances suggest that the recurrent conditions in the early-mid Younger Dryas (ca. 12.9 - 11.9 cal. kyr BP) changed significantly from stable to highly variable sea ice conditions at ca. 11.9 cal. kyr BP and this instability in sea ice prevailed for the subsequent ca. 400 yr. At ca. 11.5 cal. kyr BP, IP25 disappeared from the record indicating ice-free conditions that signified the beginning of the Holocene. Similarly, a high resolution record from the Kveithola Through, western Barents Sea, showed clearly higher IP25 concentrations during the Younger Dryas stadial compared to the Holocene. For both marine records, the IP25 concentrations were also combined with those of the open water phytoplankton biomarker brassicasterol to generate PBIP25 data from which more quantitative measurements of sea ice were determined. The contrasting seasonal sea ice conditions during the Younger Dryas were further verified

  20. Upper Ocean Evolution Across the Beaufort Sea Marginal Ice Zone from Autonomous Gliders

    NASA Astrophysics Data System (ADS)

    Lee, Craig; Rainville, Luc; Perry, Mary Jane

    2016-04-01

    The observed reduction of Arctic summertime sea ice extent and expansion of the marginal ice zone (MIZ) have profound impacts on the balance of processes controlling sea ice evolution, including the introduction of several positive feedback mechanisms that may act to accelerate melting. Examples of such feedbacks include increased upper ocean warming though absorption of solar radiation, elevated internal wave energy and mixing that may entrain heat stored in subsurface watermasses (e.g., the relatively warm Pacific Summer (PSW) and Atlantic (AW) waters), and elevated surface wave energy that acts to deform and fracture sea ice. Spatial and temporal variability in ice properties and open water fraction impact these processes. To investigate how upper ocean structure varies with changing ice cover, and how the balance of processes shift as a function of ice fraction and distance from open water, four long-endurance autonomous Seagliders occupied sections that extended from open water, through the marginal ice zone, deep into the pack during summer 2014 in the Beaufort Sea. Sections reveal strong fronts where cold, ice-covered waters meet waters that have been exposed to solar warming, and O(10 km) scale eddies near the ice edge. In the pack, Pacific Summer Water and a deep chlorophyll maximum form distinct layers at roughly 60 m and 80 m, respectively, which become increasingly diffuse as they progress through the MIZ and into open water. The isopynal layer between 1023 and 1024 kgm-3, just above the PSW, consistently thickens near the ice edge, likely due to mixing or energetic vertical exchange associated with strong lateral gradients in this region. This presentation will discuss the upper ocean variability, its relationship to sea ice extent, and evolution over the summer to the start of freeze up.

  1. Impact of the assimilated sea ice data product on seasonal climate predictions with MPI-ESM

    NASA Astrophysics Data System (ADS)

    Bunzel, Felix; Notz, Dirk; Baehr, Johanna; Müller, Wolfgang; Fröhlich, Kristina

    2015-04-01

    We examine the impact of choosing a particular satellite record of sea ice for the initialisation of a seasonal prediction system. Such systems have in the past usually only been initialised with data describing the state of the ocean and of the atmosphere. However, also sea ice yields a substantial source of predictability, as it plays an important role for the Earth's energy and water budget. Therefore, recent studies started to incorporate sea ice into the initialisation of seasonal forecasts. For our study, we performed two assimilation runs with MPI-ESM from 1979 to 2012, where atmospheric and oceanic parameters as well as sea ice concentration were assimilated using Newtonian relaxation. The two assimilation runs differ only in the sea ice concentration dataset used for assimilating sea ice. In the first run, sea ice concentrations as derived by the NASA-Team algorithm are used, while in the second run sea ice concentrations computed from the Bootstrap algorithm are assimilated. A major difference between the two sea ice concentration data products involves the treatment of melt ponds. While for both products melt ponds appear as open water in the raw satellite data, the Bootstrap algorithm more strongly attempts to offset this systematic bias by synthetically increasing the retrieved ice concentration during summer months. For each year of the two assimilation runs we performed a 10-member ensemble of hindcast experiments starting on 1 May. We find the anomaly correlation coefficient for Arctic sea ice area at 2-3 months lead time to be substantially larger for Bootstrap initialisation compared to NASA-Team initialisation. The root mean square error reveals that in the central Arctic the Bootstrap initialisation produces better predictions, whereas the NASA-Team initialisation outperforms the Bootstrap initialisation in the vicinity of the ice edge. We investigate causes and mechanisms behind the dependence of the obtained prediction skill on the sea ice

  2. Seasonal and diurnal variability of Mars water-ice clouds

    NASA Technical Reports Server (NTRS)

    Christensen, Philip R.; Zurek, Richard W.; Jaramillo, L. L.

    1988-01-01

    The diurnal and seasonal behavior of cloud opacity and frequency of occurrence was studied using an atlas of cloud occurrences compiled from the Viking IRTM (Infrared Thermal Mapper) data set. It was found that in some areas the behavior of water appeared to repeat in the zonal mean. However, this interpretation is complicated by both poor coverage and the variability of dust and clouds. As a result, the extent and nature of interannual variability remains unclear.

  3. Sea Ice Drift in the Arctic Ocean. Seasonal Variability and Long-Term Changes

    NASA Astrophysics Data System (ADS)

    Pavlov, V.; Pavlova, O.

    2010-12-01

    Variability in the drift of sea ice in the Arctic Ocean is an important parameter that can be used to characterise the thermodynamic processes in the Arctic. Knowledge of the features of sea ice drift in the Arctic Ocean is necessary for climate research, for an improved understanding of polar ecology and as an aid to human activity in the Arctic Ocean. Monthly mean sea ice drift velocities, computed from Advanced Very High Resolution Radiometer (AVHRR), Scanning Multichannel Microwave Radiometer (SMMR), Special Sensor Microwave/Imager (SSM/I), and International Arctic Buoy Programme (IABP) buoy data, are used to investigate the spatial and temporal variability of ice motion in the Arctic Ocean and Nordic Seas from 1979. Sea ice drift in the Arctic Ocean is characterized by strong seasonal and inter-annual variability. The results of combined statistical analysis of sea ice velocities and wind fields over the Arctic Ocean suggest that the seasonal changes of local wind are a predominant factor in the formation of the sea ice velocities annual cycle. Sea ice drift velocities mirror seasonal changes of the wind in the Arctic, reaching a maximum in December, with a minimum in June. In the central part of the Arctic Ocean and in the area near the Canadian shore the amplitude of this variation is not more than 2 cm/ sec. The maximum amplitudes are found in the Fram Strait (9-10 cm/sec), Beaufort Gyre (6-7 cm/sec) and the northern part of Barents Sea (5-6 cm/sec). Low frequency variations of sea ice drift velocities, with periods of 2.0-2.5 yrs and 5.0-6.0 yrs, are related to reorganization of the atmospheric circulation over the Arctic. There is evidence that the average sea ice velocity for the whole of the Arctic Ocean is increasing, with a positive trend for the period of last three decades. Trends of the monthly mean ice drift velocities are positive almost everywhere in the Arctic Ocean. In the Baffin Bay, Fram Strait and Barents Sea regions, sea ice velocities

  4. Investigation of seasonal melting of Greenland using GPS records reveals significant ice mass loss in 2010

    NASA Astrophysics Data System (ADS)

    Yang, Q.; Dixon, T.; Wdowinski, S.

    2011-12-01

    Greenland has experienced significant ice mass loss in the past decade. High-precision global positioning system (GPS) data from sites on the rocky margin of Greenland enable measurement of vertical motion of the coastal area, which is an indicator of nearby mass loss. In this study, seasonal melting variation of the Greenland ice sheet (GrIS) is investigated using GPS vertical displacement data. Using a cubic spline fitting model, we retrieve three variables of the seasonal melting pattern for GrIS from 1996 to 2010: date of the beginning and end of melt season, length of melt season, and amount of uplift in the melt season. Data from three long -term sites on the periphery of Greenland show anomalously large uplift in 2010, implying significant melting in 2010. Preliminary results also show an early onset of melting in 2010, about 8 days earlier than the 1996-2009 average. In 2010, Greenland experienced a warmer and drier winter as well as a very warm summer, which presumably contributed to the anomalous ice mass loss of 2010.

  5. Regional Patterns of Stress Transfer in the Ablation Zone of the Western Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Andrews, L. C.; Hoffman, M. J.; Neumann, T.; Catania, G. A.; Luethi, M. P.; Hawley, R. L.

    2016-12-01

    Current understanding of the subglacial system indicates that the seasonal evolution of ice flow is strongly controlled by the gradual upstream progression of an inefficient - efficient transition within the subglacial hydrologic system followed by the reduction of melt and a downstream collapse of the efficient system. Using a spatiotemporally dense network of GPS-derived surface velocities from the Pâkitsoq Region of the western Greenland Ice Sheet, we find that this pattern of subglacial development is complicated by heterogeneous bed topography, resulting in complex patterns of ice flow. Following low elevation melt onset, early melt season strain rate anomalies are dominated by regional extension, which then gives way to spatially expansive compression. However, once daily minimum ice velocities fall below the observed winter background velocities, an alternating spatial pattern of extension and compression prevails. This pattern of strain rate anomalies is correlated with changing basal topography and differences in the magnitude of diurnal surface ice speeds. Along subglacial ridges, diurnal variability in ice speed is large, suggestive of a mature, efficient subglacial system. In regions of subglacial lows, diurnal variability in ice velocity is relatively low, likely associated with a less developed efficient subglacial system. The observed pattern suggests that borehole observations and modeling results demonstrating the importance of longitudinal stress transfer at a single field location are likely widely applicable in our study area and other regions of the Greenland Ice Sheet with highly variable bed topography. Further, the complex pattern of ice flow and evidence of spatially extensive longitudinal stress transfer add to the body of work indicating that the bed character plays an important role in the development of the subglacial system; closely matching diurnal ice velocity patterns with subglacial models may be difficult without coupling these

  6. Peculiarities of the Bound Water and Water Ice Seasonal Variations in the Martian Surface Layer of the Regolith.

    NASA Astrophysics Data System (ADS)

    Kuzmin, R. O.; Zabalueva, E. V.; Evdokimova, N. A.; Christensen, P. H.; Mitrofanov, I. G.; Litvak, M. L.

    2008-09-01

    Introduction: The processes of the hydration/ dehydration of salt minerals within the Martian soil and the condensation/sublimation of water ice (and frost) in the surficial soil layer and on the polar cap surface play great significance in the modern water cycle on Mars and directly affect the redistribution of the water phases and forms in the system "atmosphere/regolith/polar caps" [1, 2, 3, 4, 5]. The processes are reversible in time and their intensity is strongly dependent on such time-variable climatic parameters as atmospheric and surface temperature, atmospheric water vapour content and specific features of atmospheric seasonal circulation [6, 7, 8, 9, 10]. In the work we report the study results of the seasonal variations of the chemically bound water (BW) spectral signature (based on the TES and OMEGA data), estimation and mapping of the winterand spring-time water ice increase within the Martian surface soil (based on the TES and HEND data). Analysis and results: Regional and global mapping of the BW spectral index distribution as function of the seasons was conducted by using of the 6.1 μm emission pick from the TES dataset and the 1.91 μm absorption band from reflectance spectra of the OMEGA data. The study of the seasonal redistribution of the water ice (and frost) within the thin surficial soil layer was conducted based on the TES thermal inertia (TI) data and the HEND neutrons flux mapping data. Bound water mapping: The mapping of the TES 6.1 μm BW index distributions was conducted at the time steps from 30° to 60° of Ls [11]. The mapping results show remarkable changes of the BW index values from one season to other one at notable latitudinal dependence of the index (Fig.1). At that, the higher BW index values are disposed mostly within the peripheral zone near the edge of the perennial and seasonal polar caps (cooler, wetter areas), while the lower BW index values are observed at low latitudes (warmer, drier areas). Between the Nspring (Ls=0

  7. Tracking Retreat of the North Seasonal Ice Cap on Mars: Results from the THEMIS Investigation

    NASA Technical Reports Server (NTRS)

    Ivanov, A. B.; Wagstaff, K. L.; Ttus, T. N.

    2005-01-01

    The CO2 ice caps on Mars advance and retreat with the seasons. This phenomenon was first observed by Cassini and then confirmed by numerous ground based observations in 19th and 20th centuries. With the advent of the space age observations of the seasonal ice cap were done by all orbiting spacecraft starting with Mariner 7. Viking Orbiters and more recently the Mars Global Surveyor (particularly Mars Orbiter Camera (MOC) and Thermal Emission Spectrometer (TES) instruments) have accumulated significant data on the retreat of the CO2 seasonal cap. During Mars year 2 of THEMIS operations at Mars, we planned an observational campaign in which the THEMIS instrument (onboard the Mars Odyssey spacecraft) repeatedly observed the north seasonal polar cap from midwinter to late spring. THEMIS allows simultaneous observations in both Thermal IR (12.57 m) and Visible wavelengths (0.65 m). One of the goals for this work is to initiate an interannual program for observations of the seasonal ice caps using the THEMIS instrument. The most efficient way to detect the edge between frost and bare ground is directly onboard of the spacecraft. Prior to onboard software design effort, we have developed two groundbased algorithms for automatically finding the edge of the seasonal polar cap in THEMIS IR data. The first algorithm relies on fully calibrated data and can be used for highly reliable groundbased analyses. The second method was specifically developed for processing raw, uncalibrated data in a highly efficient way. It has the potential to enable automatic, onboard detections of the seasonal cap retreat. We have experimentally confirmed that both methods produce similar results, and we have validated both methods against a model constructed from the MGS TES data from the same season.

  8. Seasonal prediction of the South Pacific Convergence Zone in the austral wet season

    NASA Astrophysics Data System (ADS)

    Charles, A. N.; Brown, J. R.; Cottrill, A.; Shelton, K. L.; Nakaegawa, T.; Kuleshov, Y.

    2014-11-01

    The position and orientation of the South Pacific Convergence Zone (SPCZ), modulated by the El Niño-Southern Oscillation (ENSO), determine many of the potentially predictable interannual variations in rainfall in the South Pacific region. In this study, the predictability of the SPCZ in austral summer is assessed using two coupled (ocean-atmosphere) global circulation model (CGCM)-based seasonal prediction systems: the Japan Meteorological Agency's Meteorological Research Institute Coupled Ocean-Atmosphere General Circulation Model (JMA/MRI-CGCM) and the Australian Bureau of Meteorology's Predictive Ocean-Atmosphere Model for Australia (POAMA-M24). Forecasts of austral summer rainfall, initialized in November are assessed over the period 1980-2010. The climatology of CGCM precipitation in the SPCZ region compares favorably to rainfall analyses over subsets of years characterizing different phases of ENSO. While the CGCMs display biases in the mean SPCZ latitudes, they reproduce interannual variability in austral summer SPCZ position indices for forecasts out to 4 months, with temporal correlations greater than 0.6. The summer latitude of the western branch of the SPCZ is predictable with correlations of the order of 0.6 for forecasts initialized as early as September, while the correlation for the eastern branch only exceeds 0.6 for forecasts initialized in November. Encouragingly, the models are able to simulate the large displacement of the SPCZ during zonal SPCZ years 1982-1983, 1991-1992, and 1997-1998.

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

    DOE PAGES

    Greene, S.; Walter Anthony, K. M.; Archer, D.; ...

    2014-12-08

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  12. Late Holocene Russian Arctic climate variability - spatial and seasonal aspects inferred from glacier and ground ice

    NASA Astrophysics Data System (ADS)

    Opel, T.; Meyer, H.; Fritzsche, D.; Laepple, T.; Alexander, D.

    2014-12-01

    The Arctic currently experiences an unprecedented warming. This dynamic response to changes in climate forcing as well as corresponding feedbacks as sea ice retreat make the Arctic a key region to study past and future climate changes. Recent Arctic-wide temperature reconstructions indicate a long-term cooling prior to the ongoing warming. However, they are based mostly on proxies that record summer information and hence are assumed to be seasonally biased towards the summer. Moreover, the Russian Arctic is significantly underrepresented in these Arctic-wide reconstructions. Here we present glacier and ground ice records from Northern Siberia that provide valuable information for a better spatial and seasonal understanding of Holocene climate variability in the Arctic. The high-resolution Akademii Nauk δ18O ice core record (Severnaya Zemlya) proves the Late Holocene cooling and the pronounced warming after 1800. It shows neither a prominent Medieval Climate Anomaly nor a Little Ice Age but gives evidence of several abrupt warming and cooling events during the last centuries, also found in ice-core records from Svalbard and Franz Josef Land. They may be related to the regional internal climate variability, i.e. atmosphere-sea ice feedbacks in the Barents and Kara seas region. Ice wedges were studied at several study sites in the Lena River Delta and the coastal permafrost lowlands of the Laptev Sea region. They are formed by the repeated filling of wintertime thermal contraction cracks by snow melt water in spring. Radiocarbon dating of organic matter enables the generation of centennial scale δ18O records that are indicative of temperatures in the cold period of the year (winter and spring). Our ice wedge records show general increasing δ18O trends over the Mid and Late Holocene and an unprecedented recent warming. Both may be related to the changes in orbital forcing during the cold season as well as in greenhouse gas concentrations over the last millennia

  13. The Annual Glaciohydrology Cycle in the Ablation Zone of the Greenland Ice Sheet: Part 2. Observed and Modeled Ice Flow

    NASA Technical Reports Server (NTRS)

    Colgan, William Terence; Rajaram, Harihar; Anderson, Robert S.; Steffen, Konrad; Zwally, H. Jay; Phillips, Thomas; Abdalati, Waleed

    2012-01-01

    Ice velocities observed in 2005/06 at three GPS stations along the Sermeq Avannarleq flowline, West Greenland, are used to characterize an observed annual velocity cycle. We attempt to reproduce this annual ice velocity cycle using a 1-D ice-flow model with longitudinal stresses coupled to a 1-D hydrology model that governs an empirical basal sliding rule. Seasonal basal sliding velocity is parameterized as a perturbation of prescribed winter sliding velocity that is proportional to the rate of change of glacier water storage. The coupled model reproduces the broad features of the annual basal sliding cycle observed along this flowline, namely a summer speed-up event followed by a fall slowdown event. We also evaluate the hypothesis that the observed annual velocity cycle is due to the annual calving cycle at the terminus. We demonstrate that the ice acceleration due to a catastrophic calving event takes an order of magnitude longer to reach CU/ETH ('Swiss') Camp (46km upstream of the terminus) than is observed. The seasonal acceleration observed at Swiss Camp is therefore unlikely to be the result of velocity perturbations propagated upstream via longitudinal coupling. Instead we interpret this velocity cycle to reflect the local history of glacier water balance.

  14. Using reanalysis data for the prediction of seasonal wind turbine power losses due to icing

    NASA Astrophysics Data System (ADS)

    Burtch, Daniel G.

    The Northern Plains region of the United States is home to a significant amount of potential wind energy. However, in winter months capturing this potential power is severely impacted by the meteorological conditions, in the form of icing. Predicting the expected loss in power production due to icing is a valuable parameter that can be used in wind turbine operations, determination of wind turbine site locations and long-term energy estimates which are used for financing purposes. Currently, losses due to icing must be estimated when developing predictions for turbine feasibility and financing studies, while icing maps, a tool commonly used in Europe, are lacking in the United States. This study uses the Modern-Era Retrospective Analysis for Research and Applications (MERRA) dataset in conjunction with turbine production data and in-situ wind measurements to investigate six methods of predicting seasonal losses (October-March) due to icing at two sites located in Petersburg, ND and Valley City, ND. The prediction of icing losses is based on temperature and relative humidity thresholds and is accomplished using six methods. Three methods use a Measure-Correlate-Predict (MCP) and flow model (WAsP) analysis for the determination of wind speeds and MERRA for temperature and relative humidity, while three methods use MERRA for all three variables. For each season from 2002 to 2010, the predicted losses due to icing are determined for a range of relative humidity thresholds and compared with observed icing losses. An optimal relative humidity is then determined and tested on all seasons from 2002 to 2013. The prediction methods are then compared to a common practice used in the wind energy industry of assuming a constant percentage loss for icing over the same time period. The three methods using MERRA data alone show severe deficiencies in the accurate determination of wind speeds which leads to a large underprediction in accurate power output. Of the three MCP

  15. An Observational and Analytical Study of Marginal Ice Zone Atmospheric Jets

    DTIC Science & Technology

    2016-12-01

    Coupled Ocean /Atmosphere Mesoscale Prediction System DRI Directed Research Initiative ECMWF European Center for medium range weather forecasting LLJ...low level jet MIZ marginal ice zone MKS Meters, Kilograms, Seconds NIC National Ice Center NOAA National Oceanic and Atmospheric Administration...Arctic Ocean ,” Scott Harper and Martin Jeffries, program managers. I would like to thank Professor Peter Guest for all of his help and guidance

  16. Using Reanalysis Data for the Prediction of Seasonal Wind Turbine Power Losses Due to Icing

    NASA Astrophysics Data System (ADS)

    Burtch, D.; Mullendore, G. L.; Delene, D. J.; Storm, B.

    2013-12-01

    The Northern Plains region of the United States is home to a significant amount of potential wind energy. However, in winter months capturing this potential power is severely impacted by the meteorological conditions, in the form of icing. Predicting the expected loss in power production due to icing is a valuable parameter that can be used in wind turbine operations, determination of wind turbine site locations and long-term energy estimates which are used for financing purposes. Currently, losses due to icing must be estimated when developing predictions for turbine feasibility and financing studies, while icing maps, a tool commonly used in Europe, are lacking in the United States. This study uses the Modern-Era Retrospective Analysis for Research and Applications (MERRA) dataset in conjunction with turbine production data to investigate various methods of predicting seasonal losses (October-March) due to icing at two wind turbine sites located 121 km apart in North Dakota. The prediction of icing losses is based on temperature and relative humidity thresholds and is accomplished using three methods. For each of the three methods, the required atmospheric variables are determined in one of two ways: using industry-specific software to correlate anemometer data in conjunction with the MERRA dataset and using only the MERRA dataset for all variables. For each season, a percentage of the total expected generated power lost due to icing is determined and compared to observed losses from the production data. An optimization is performed in order to determine the relative humidity threshold that minimizes the difference between the predicted and observed values. Eight seasons of data are used to determine an optimal relative humidity threshold, and a further three seasons of data are used to test this threshold. Preliminary results have shown that the optimized relative humidity threshold for the northern turbine is higher than the southern turbine for all methods

  17. Peculiarities of the Bound Water and Water Ice Seasonal Variations in the Martian Surface Layer of the Regolith.

    NASA Astrophysics Data System (ADS)

    Kuzmin, R. O.; Zabalueva, E. V.; Evdokimova, N. A.; Christensen, P. H.; Mitrofanov, I. G.; Litvak, M. L.

    2008-09-01

    Introduction: The processes of the hydration/ dehydration of salt minerals within the Martian soil and the condensation/sublimation of water ice (and frost) in the surficial soil layer and on the polar cap surface play great significance in the modern water cycle on Mars and directly affect the redistribution of the water phases and forms in the system "atmosphere/regolith/polar caps" [1, 2, 3, 4, 5]. The processes are reversible in time and their intensity is strongly dependent on such time-variable climatic parameters as atmospheric and surface temperature, atmospheric water vapour content and specific features of atmospheric seasonal circulation [6, 7, 8, 9, 10]. In the work we report the study results of the seasonal variations of the chemically bound water (BW) spectral signature (based on the TES and OMEGA data), estimation and mapping of the winterand spring-time water ice increase within the Martian surface soil (based on the TES and HEND data). Analysis and results: Regional and global mapping of the BW spectral index distribution as function of the seasons was conducted by using of the 6.1 μm emission pick from the TES dataset and the 1.91 μm absorption band from reflectance spectra of the OMEGA data. The study of the seasonal redistribution of the water ice (and frost) within the thin surficial soil layer was conducted based on the TES thermal inertia (TI) data and the HEND neutrons flux mapping data. Bound water mapping: The mapping of the TES 6.1 μm BW index distributions was conducted at the time steps from 30° to 60° of Ls [11]. The mapping results show remarkable changes of the BW index values from one season to other one at notable latitudinal dependence of the index (Fig.1). At that, the higher BW index values are disposed mostly within the peripheral zone near the edge of the perennial and seasonal polar caps (cooler, wetter areas), while the lower BW index values are observed at low latitudes (warmer, drier areas). Between the Nspring (Ls=0

  18. The Arctic-Subarctic sea ice system is entering a seasonal regime: Implications for future Arctic amplification.

    PubMed

    Haine, Thomas W N; Martin, Torge

    2017-07-04

    The loss of Arctic sea ice is a conspicuous example of climate change. Climate models project ice-free conditions during summer this century under realistic emission scenarios, reflecting the increase in seasonality in ice cover. To quantify the increased seasonality in the Arctic-Subarctic sea ice system, we define a non-dimensional seasonality number for sea ice extent, area, and volume from satellite data and realistic coupled climate models. We show that the Arctic-Subarctic, i.e. the northern hemisphere, sea ice now exhibits similar levels of seasonality to the Antarctic, which is in a seasonal regime without significant change since satellite observations began in 1979. Realistic climate models suggest that this transition to the seasonal regime is being accompanied by a maximum in Arctic amplification, which is the faster warming of Arctic latitudes compared to the global mean, in the 2010s. The strong link points to a peak in sea-ice-related feedbacks that occurs long before the Arctic becomes ice-free in summer.

  19. Ice-edge eddies in the Fram Strait marginal ice zone

    USGS Publications Warehouse

    Johannessen, O.M.; Johannessen, J.A.; Svendsen, E.; Shuchman, R.A.; Campbell, W.J.; Josberger, E.

    1987-01-01

    Five prominent ice-edge eddies in Fram Strait on the scale of 30 to 40 kilometers were observed over deep water within 77??N to 79??N and 5??W to 3??E. The use of remote sensing, a satellite-tracked buoy, and in situ oceanographic measurements showed the presence of eddies with orbital speeds of 30 to 40 centimeters per second and lifetimes of at least 20 days. Ice ablation measurements made within one of these ice-ocean eddies indicated that melting, which proceeded at rates of 20 to 40 centimeters per day, is an important process in determining the ice-edge position. These studies give new insight on the formation, propagation, and dissipation of ice-edge eddies.

  20. The impacts of intense moisture transport on the deep and marginal sea-ice zones of the Arctic during winter

    NASA Astrophysics Data System (ADS)

    Woods, Cian; Caballero, Rodrigo

    2015-04-01

    warming at the surface. There are an average of 14 such events that enter the polar cap each winter, driving about 50% of the seasonal variation in surface temperature over the deep Arctic. We show that, over the last 30 years, the marginal ice-zones in the Barents, Labrador and Chukchi Seas have experienced roughly a doubling in the frequency of these intense moisture intrusion events during winter. Interestingly, these are the regions that have experienced the most rapid wintertime ice loss in the Arctic, raising the question: to what extent has the recent Arctic warming been driven by local vs. interannual/remote processes?

  1. Seasonal Ice loss in the Beaufort Sea: Toward Synchronicity and Prediction

    NASA Astrophysics Data System (ADS)

    Steele, M.; Dickinson, S.; Zhang, J.; Lindsay, R. W.

    2014-12-01

    The seasonal evolution of sea ice loss in the Beaufort Sea during 1979-2012 is examined, focusing on spatial differences between eastern and western sectors. Two stages in ice loss are identified: "opening" is defined as the spring decrease in ice concentration from its winter maximum below a value of 80% areal concentration; "retreat" is the summer decrease below 15% concentration. We consider three aspects of the problem, i.e. (i) the long-term mean, (ii) long-term linear trends, and (iii) year-to-year variability. We find that in the mean, ice opening occurs earliest in the southeast Beaufort Sea (SEB), forced by atmospheric heating acting on particularly thin ice relative to the southwestern Beaufort Sea (SWB). This thin SEB ice arises from divergence forced by easterly winds in fall and spring. There is no significant long-term trend in the date of SEB ice opening, although ice opening in the SWB is in fact trending toward earlier dates. This means that spatial differences in opening dates across the Beaufort Sea have been shrinking over the past 33 years, i.e., these dates are becoming more synchronous, a situation which may impact human and marine mammal activity in the area. Synchronicity in ice retreat dates is also increasing, although with no statistical significance at this time. Finally, we find that in any given year, an increase in monthly mean easterly winds of ~ 1 m/s during spring is associated with earlier summer retreat of 9-15 days, offering predictive capability with 1-2 months lead time.

  2. Effects of Snowfall on the Thickness and Stability of Mars' Seasonal Ice Caps

    NASA Astrophysics Data System (ADS)

    Hayne, P. O.; Paige, D. A.; Aharonson, O.; Schofield, J. T.; Kass, D. M.; Kleinboehl, A.; Heavens, N. G.; Shirley, J. H.; McCleese, D. J.

    2012-12-01

    Seasonal exchange of carbon dioxide between the Martian atmosphere and ice caps is responsible for cyclical variations of ~30% in global atmospheric pressure, as well as for the growth and retreat of the seasonal ice caps. Energy balance and general circulation models have had limited success in reproducing the important aspects of this cycle, largely due to uncertainties in the radiative properties (albedo and emissivity) of the ice caps. Evidence from remote sensing by several different orbital investigations suggests that snowfall consisting primarily of solid CO2 contributes substantial material to the growing seasonal caps, strongly affecting their radiative properties. However, the mass of material deposited as snow, its spatial and temporal variation, and its effect on the energy budget, have all remained uncertain. Using data from the Mars Climate Sounder (MCS), we have quantified and mapped snow cloud formation and surface accumulation based on opacity profiles and calculated infrared cooling rates. We then compared the derived snowfall distribution to seasonal cap thicknesses derived from Mars Orbiter Laser Altimeter (MOLA) "crossover" data. Large variations in the occurrence, thickness, and timing of snow clouds are observed, with the most extensive and persistent clouds observed over the south polar residual cap (SPRC). We find a strong correlation between clouds, "cold spots" (regions of suppressed thermal emission), and seasonal cap thickness. Furthermore, some of these regions of high snow cloud activity also exhibit high solar albedo in the spring and summer. Together, these results suggest that granular deposits of CO2 snow: 1) are thicker (probably due to lower density) on average than "slab ice" formed by direct vapor deposition; 2) reduce energy loss by thermal emission during the polar night; and 3) reduce energy gain by reflecting solar radiation during spring and summer. As the snowiest place on Mars, the SPRC exhibits all of these properties

  3. Basal crevasses and suture zones in the Larsen C Ice Shelf, Antarctica: Implications for ice shelf stability in a warming climate

    NASA Astrophysics Data System (ADS)

    McGrath, Daniel J.

    Understanding ice shelf structure and processes is paramount to future predictions of sea level rise, as nearly 75% of the ice flux from the Antarctic Ice Sheet (AIS) passes through these gates. The breakup of an ice shelf removes the longitudinal back stress acting on the grounded inland ice and leads to flow acceleration, dynamic thinning and frontal retreat, processes that can be sustained for more than a decade. Increased ice discharge to the ocean contributes to global sea level rise. This dissertation investigates basal crevasses and suture zones, two key structural components of ice shelves, in order to understand how the structure of an ice shelf influences its stability in a warming climate. Ground penetrating radar, high-resolution satellite imagery and a variety of modeling approaches are utilized to assess these features on the Larsen C Ice Shelf but in a manner that considers their influence on ice shelf stability around the AIS. Basal crevasses are large-scale (~66% of ice thickness and ten's of kms in length) and abundant features that are significant structural weaknesses. The viscoplastic deformation of the ice shelf in response to the perturbed hydrostatic balance leads to the formation of both surface depressions and crevasses, hence weakening the ice shelf further. Basal crevasses increase the local ice-ocean interface by ~30%, thereby increasing basal roughness and altering ice-ocean interactions. Ice-shelf fractures frequently terminate where they encounter suture zones, regions of material heterogeneity that form at the lateral bounds of meteoric inflows to ice shelves. The termination of a 25 km-long rift in the Churchill Peninsula suture zone is investigated and found to contain ~60 m of accreted marine ice. Steady-state basal melting/freezing rates are determined for the ice shelf and applied to a flowline model to examine the along-flow evolution of ice shelf structure. The thickening surface wedge of locally accumulated meteoric ice

  4. 78 FR 38584 - Safety Zone; San Diego Symphony Summer POPS Fireworks 2013 Season, San Diego, CA

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-27

    ... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone; San Diego Symphony Summer POPS Fireworks... Symphony Summer POPS Fireworks 2013 season. This safety zone is necessary to provide for the safety of the... San Diego Symphony Summer POPS, which will include a fireworks presentation from a barge in San Diego...

  5. Marginal Ice Zone (MIZ) Program: Science and Experiment Plan

    DTIC Science & Technology

    2012-10-01

    generation of most of the thickest and oldest ice in the Arctic Ocean, adjacent to northern Greenland and along the northwestern margin of the Canadian...informed the design of the MIZ DRI. These multi-disciplinary efforts, summarized below, focused primarily on the permanent MIZs of the Greenland Sea and... Greenland Sea in successive years (1983, 1984), with a winter Greenland Sea field program to follow at a later date. _______________________UNIVERSITY OF

  6. Greenland Ice Sheet Surface Roughness and Glacier Zones from MISR, 2000-2013

    NASA Astrophysics Data System (ADS)

    Nolin, A. W.; Mar, E.

    2014-12-01

    The surface of the Greenland ice sheet is shaped by wind, melt, and glacier dynamics. Surface roughness affects the surface-atmospheric interactions (via the aerodynamic roughness length) and thus influences fluxes of sensible and latent heat at the ice sheet surface. When combined with near-infrared reflectance, surface roughness has been shown to discriminate between glacier zones. We present the first ever annual time series of Greenland ice sheet surface roughness derived from the Multi-angle Imaging SpectroRadiometer (MISR) for the years 2000-2013. Our cloud-free multi-angular measurements are calibrated using airborne LiDAR data from the Airborne Topographic Mapper (ATM). Roughness values range from 10 cm in the dry, snow-covered interior of the ice sheet to over 8 m along the crevassed margins of the ice sheet. Roughness increases from April to July as the surface melts and glaciers become more active. Our roughness maps are restricted to spring and early summer due to limited ATM data. We next employed ISODATA unsupervised clustering with MISR near-infrared reflectance and surface roughness to map glacier zones on the ice sheet for years 2000-2013. The number and locations of the ISODATA-derived glacier zones are consistent from year to year with slight shifts in boundaries depending on the extent of early summer melt. These maps of Greenland ice surface roughness and glacier zones are the result of processing several hundred thousand MISR images and are the first ever full-coverage, annual maps of this kind.

  7. Seasonal and interannual variability of pigment concentrations across a California Current frontal zone

    NASA Technical Reports Server (NTRS)

    Thomas, A. C.; Strub, P. T.

    1990-01-01

    The seasonal and interannual variability of the latitudinal position of the California Current frontal zone was investigated by examining satellite images of phytoplankton pigment from the coastal-zone color scanner for the periods 1979-1983 and 1986. The pigment concentrations associated with the zonal front were also determined. A general seasonal cycle of pigment concentrations is was established. It was found that variations in the frontal structure are controlled primarily by changes in pigment concentration north of the front. Seasonal variations were found to be minimal south of the front, where pigment concentrations remain low throughout the spring, summer, and fall.

  8. Seasonal and interannual variability of pigment concentrations across a California Current frontal zone

    NASA Technical Reports Server (NTRS)

    Thomas, A. C.; Strub, P. T.

    1990-01-01

    The seasonal and interannual variability of the latitudinal position of the California Current frontal zone was investigated by examining satellite images of phytoplankton pigment from the coastal-zone color scanner for the periods 1979-1983 and 1986. The pigment concentrations associated with the zonal front were also determined. A general seasonal cycle of pigment concentrations is was established. It was found that variations in the frontal structure are controlled primarily by changes in pigment concentration north of the front. Seasonal variations were found to be minimal south of the front, where pigment concentrations remain low throughout the spring, summer, and fall.

  9. Ice, Ocean and Atmosphere Interactions in the Arctic Marginal Ice Zone

    DTIC Science & Technology

    2015-09-30

    meteorological parameters and (d) the continuous measurement of open water fraction and floe size distribution over the network/array...27 GB when unpacked) of continuous wave data ii. 176 megabytes of ice mass balance data iii. 2.8 megabytes of meteorological data iv...September 2014. As the system is still upright the meteorological measurements as still valid. At this stage the ice is very

  10. Propagation of acoustic-gravity waves in arctic zones with elastic ice-sheets

    NASA Astrophysics Data System (ADS)

    Kadri, Usama; Abdolali, Ali; Kirby, James T.

    2017-04-01

    We present an analytical solution of the boundary value problem of propagating acoustic-gravity waves generated in the ocean by earthquakes or ice-quakes in arctic zones. At the surface, we assume elastic ice-sheets of a variable thickness, and show that the propagating acoustic-gravity modes have different mode shape than originally derived by Ref. [1] for a rigid ice-sheet settings. Computationally, we couple the ice-sheet problem with the free surface model by Ref. [2] representing shrinking ice blocks in realistic sea state, where the randomly oriented ice-sheets cause inter modal transition at the edges and multidirectional reflections. We then derive a depth-integrated equation valid for spatially slowly varying thickness of ice-sheet and water depth. Surprisingly, and unlike the free-surface setting, here it is found that the higher acoustic-gravity modes exhibit a larger contribution. These modes travel at the speed of sound in water carrying information on their source, e.g. ice-sheet motion or submarine earthquake, providing various implications for ocean monitoring and detection of quakes. In addition, we found that the propagating acoustic-gravity modes can result in orbital displacements of fluid parcels sufficiently high that may contribute to deep ocean currents and circulation, as postulated by Refs. [1, 3]. References [1] U. Kadri, 2016. Generation of Hydroacoustic Waves by an Oscillating Ice Block in Arctic Zones. Advances in Acoustics and Vibration, 2016, Article ID 8076108, 7 pages http://dx.doi.org/10.1155/2016/8076108 [2] A. Abdolali, J. T. Kirby and G. Bellotti, 2015, Depth-integrated equation for hydro-acoustic waves with bottom damping, J. Fluid Mech., 766, R1 doi:10.1017/jfm.2015.37 [3] U. Kadri, 2014. Deep ocean water transportation by acoustic?gravity waves. J. Geophys. Res. Oceans, 119, doi:10.1002/ 2014JC010234

  11. Ice Accumulation and the Apparent Seasonal Variation of GPS Stations in Alaska

    NASA Astrophysics Data System (ADS)

    Kochanski, K.; Herring, T.

    2015-12-01

    Many GPS stations in Alaska have apparent seasonal variations with amplitudes between 5 and 10mm. This motion is usually in phase with regional snowfall and has been attributed to hydrological loading (Fu et al. 2012). We studied the phase of vertical seasonal motion for fifty stations in the PBO network across Alaska and Washington State and found six stations which move two to four months out of phase with snowfall with amplitudes greater than 4mm. The mean date at which stations' seasonal movement reached peak height was October 21 with a standard deviation of 49.7 days. 59% of this variation is created by the six stations with phases furthest from the mean. These stations are also distinguished by discontinuous winter movements, including jumps of more than 10mm/day, and they have the six most asymmetric time-series in the study. Three of these stations, AB11, AB12, and AB14, are local high points on Alaska's west coast. These locations have high wind speeds and humidity and we expect that in freezing conditions they accumulate thick frost and rime. This hypothesis is supported by multipath values at the sites, which show increased signal scattering during the winter. We modelled signal delays for partially ice-covered GPS stations, and predicted that asymmetric horizontal ice growth will cause apparent vertical motion of GPS stations with a magnitude determined by ice thickness and orientation. Rime grows horizontally into the wind, so we estimated rime directions using wind records from nearby airports. We compared these results to our simulation, and predicted upwards apparent motion for the stations that was consistent with the stations' observed winter movement. The apparent vertical seasonal motion of these stations is not caused by loads but is an artefact of signal delay from ice accumulation.

  12. Air-sea exchange of carbon dioxide in the Southern Ocean and Antarctic marginal ice zone

    NASA Astrophysics Data System (ADS)

    Butterworth, Brian J.; Miller, Scott D.

    2016-07-01

    Direct carbon dioxide flux measurements using eddy covariance from an icebreaker in the high-latitude Southern Ocean and Antarctic marginal ice zone are reported. Fluxes were combined with the measured water-air carbon dioxide partial pressure difference (ΔpCO2) to compute the air-sea gas transfer velocity (k, normalized to Schmidt number 660). The open water data showed a quadratic relationship between k (cm h-1) and the neutral 10 m wind speed (U10n, m s-1), kopen = 0.245 U10n2 + 1.3, in close agreement with decades old tracer-based results and much lower than cubic relationships inferred from previous open ocean eddy covariance studies. In the marginal ice zone, the effective gas transfer velocity decreased in proportion to sea ice cover, in contrast with predictions of enhanced gas exchange in the presence of sea ice. The combined open water and marginal ice zone results affect the calculated magnitude and spatial distribution of Southern Ocean carbon flux.

  13. The Annual Glaciohydrology Cycle in the Ablation Zone of the Greenland Ice Sheet: Part 1. Hydrology Model

    NASA Technical Reports Server (NTRS)

    Colgan, William; Rajaram, Harihar; Anderson, Robert; Steffen. Konrad; Phillips, Thomas; Zwally, H. Jay; Abdalati, Waleed

    2012-01-01

    We apply a novel one-dimensional glacier hydrology model that calculates hydraulic head to the tidewater-terminating Sermeq Avannarleq flowline of the Greenland ice sheet. Within a plausible parameter space, the model achieves a quasi-steady-state annual cycle in which hydraulic head oscillates close to flotation throughout the ablation zone. Flotation is briefly achieved during the summer melt season along a approx.17 km stretch of the approx.50 km of flowline within the ablation zone. Beneath the majority of the flowline, subglacial conduit storage closes (i.e. obtains minimum radius) during the winter and opens (i.e. obtains maximum radius) during the summer. Along certain stretches of the flowline, the model predicts that subglacial conduit storage remains open throughout the year. A calculated mean glacier water residence time of approx.2.2 years implies that significant amounts of water are stored in the glacier throughout the year. We interpret this residence time as being indicative of the timescale over which the glacier hydrologic system is capable of adjusting to external surface meltwater forcings. Based on in situ ice velocity observations, we suggest that the summer speed-up event generally corresponds to conditions of increasing hydraulic head during inefficient subglacial drainage. Conversely, the slowdown during fall generally corresponds to conditions of decreasing hydraulic head during efficient subglacial drainage.

  14. Air Mass Modification in the Marginal Ice Zone.

    DTIC Science & Technology

    1985-11-01

    stability. The relationship between the drag coefficients and the exchange coefficients for heat and moisture has been discussed by Walter et al. (1984). An...over the Bering Sea, Walter et al. (1984) measured the ratio CH/CD to be 0.20 - 0.28 over rough sea ice which had a drag coefficient of CD = 3.0 * 0.6 x...34 *, . ...-• •.....- ........ ... .... . . . . -.-.. -. ,. . . 7 et al. (1984) estimate of C 4.0 x 10- is larger than the CD measured by Walter et al. (1984) and suggests that CH/CD

  15. 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.

  16. Hemispheric asymmetry in martian seasonal surface water ice from MGS TES

    NASA Astrophysics Data System (ADS)

    Bapst, Jonathan; Bandfield, Joshua L.; Wood, Stephen E.

    2015-11-01

    The Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) visible/near-infrared and thermal infrared bolometers measured planetary broadband albedo and temperature for more than three Mars years. As seasons progress on Mars, surface temperatures may fall below the frost point of volatiles in the atmosphere (namely, carbon dioxide and water). Systematic mapping of the spatial and temporal occurrence of these volatiles in the martian atmosphere, on the surface, and in the subsurface has shown their importance in understanding the climate of Mars. We examine TES daytime albedo, temperature, and atmospheric opacity data to map the latitudinal and temporal occurrence of seasonal surface water frost on Mars. We expand on previous work by looking at the behavior of water frost over the entire martian year, made possible with comprehensive, multi-year data. Interpretations of frost are based on albedo changes and the corresponding daytime temperature range. Data is considered consistent with water frost when there are significant albedo increases (>0.05 relative to frost-free seasons) and the observed temperatures are ∼170-200 K. We argue the presence of extensive water frost in the northern hemisphere, extending from the pole to ∼40°N, following seasonal temperature trends. In the north, water frost first appears near the pole at Ls = ∼160° and is last observed at Ls = ∼90°. Extensive water frost is less evident in southern hemisphere data, though both hemispheres show data that are consistent with the presence of a water ice annulus during seasonal cap retreat. Hemispherical asymmetry in the occurrence of seasonal water frost is due in part to the lower (∼40%) atmospheric water vapor abundances observed in the southern hemisphere. Our results are consistent with net transport of water vapor to the northern hemisphere. The deposition and sublimation of seasonal water frost may significantly increase the near-surface water vapor density that could

  17. Investigations of Spatial and Temporal Variability of Ocean and Ice Conditions in and Near the Marginal Ice Zone. The “Marginal Ice Zone Observations and Processes Experiment” (MIZOPEX) Final Campaign Summary

    SciTech Connect

    DeMott, P. J.; Hill, T. C.J.

    2016-02-01

    Despite the significance of the marginal ice zones of the Arctic Ocean, basic parameters such as sea surface temperature (SST) and a range of sea-ice characteristics are still insufficiently understood in these areas, and especially so during the summer melt period. The field campaigns summarized here, identified collectively as the “Marginal Ice Zone Ocean and Ice Observations and Processes Experiment” (MIZOPEX), were funded by U.S. National Aeronautic and Space Administration (NASA) with the intent of helping to address these information gaps through a targeted, intensive observation field campaign that tested and exploited unique capabilities of multiple classes of unmanned aerial systems (UASs). MIZOPEX was conceived and carried out in response to NASA’s request for research efforts that would address a key area of science while also helping to advance the application of UASs in a manner useful to NASA for assessing the relative merits of different UASs. To further exercise the potential of unmanned systems and to expand the science value of the effort, the field campaign added further challenges such as air deployment of miniaturized buoys and coordinating missions involving multiple aircraft. Specific research areas that MIZOPEX data were designed to address include relationships between ocean skin temperatures and subsurface temperatures and how these evolve over time in an Arctic environment during summer; variability in sea-ice conditions such as thickness, age, and albedo within the marginal ice zone (MIZ); interactions of SST, salinity, and ice conditions during the melt cycle; and validation of satellite-derived SST and ice concentration fields provided by satellite imagery and models.

  18. Wave observation in the marginal ice zone with the TerraSAR-X satellite

    NASA Astrophysics Data System (ADS)

    Gebhardt, Claus; Bidlot, Jean-Raymond; Gemmrich, Johannes; Lehner, Susanne; Pleskachevsky, Andrey; Rosenthal, Wolfgang

    2016-07-01

    This article investigates the penetration of ocean waves into the marginal ice zone (MIZ), observed by satellite, and likewise provides a basis for the future cross-validation of respective models. To this end, synthetic aperture radar images from the TerraSAR-X satellite (TS-X) and numerical simulations of the European Centre for Medium-Range Weather Forecasts (ECMWF) are used. The focus is an event of swell waves, developed during a storm passage in the Atlantic, penetrating deeply into the MIZ off the coast of Eastern Greenland in February 2013. The TS-X scene which is the basis for this investigation extends from the ice-free open ocean to solid ice. The variation of the peak wavelength is analysed and potential sources of variability are discussed. We find an increase in wavelength which is consistent with the spatial dispersion of deep water waves, even within the ice-covered region.

  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. Greenland Ice Sheet seasonal and spatial mass variability from model simulations and GRACE (2003-2012)

    NASA Astrophysics Data System (ADS)

    Alexander, Patrick M.; Tedesco, Marco; Schlegel, Nicole-Jeanne; Luthcke, Scott B.; Fettweis, Xavier; Larour, Eric

    2016-06-01

    Improving the ability of regional climate models (RCMs) and ice sheet models (ISMs) to simulate spatiotemporal variations in the mass of the Greenland Ice Sheet (GrIS) is crucial for prediction of future sea level rise. While several studies have examined recent trends in GrIS mass loss, studies focusing on mass variations at sub-annual and sub-basin-wide scales are still lacking. At these scales, processes responsible for mass change are less well understood and modeled, and could potentially play an important role in future GrIS mass change. Here, we examine spatiotemporal variations in mass over the GrIS derived from the Gravity Recovery and Climate Experiment (GRACE) satellites for the January 2003-December 2012 period using a "mascon" approach, with a nominal spatial resolution of 100 km, and a temporal resolution of 10 days. We compare GRACE-estimated mass variations against those simulated by the Modèle Atmosphérique Régionale (MAR) RCM and the Ice Sheet System Model (ISSM). In order to properly compare spatial and temporal variations in GrIS mass from GRACE with model outputs, we find it necessary to spatially and temporally filter model results to reproduce leakage of mass inherent in the GRACE solution. Both modeled and satellite-derived results point to a decline (of -178.9 ± 4.4 and -239.4 ± 7.7 Gt yr-1 respectively) in GrIS mass over the period examined, but the models appear to underestimate the rate of mass loss, especially in areas below 2000 m in elevation, where the majority of recent GrIS mass loss is occurring. On an ice-sheet-wide scale, the timing of the modeled seasonal cycle of cumulative mass (driven by summer mass loss) agrees with the GRACE-derived seasonal cycle, within limits of uncertainty from the GRACE solution. However, on sub-ice-sheet-wide scales, some areas exhibit significant differences in the timing of peaks in the annual cycle of mass change. At these scales, model biases, or processes not accounted for by models related

  1. Various remote sensing approaches to understanding roughness in the marginal ice zone

    NASA Astrophysics Data System (ADS)

    Gupta, Mukesh

    Multi-platform based measurement approaches to understanding complex marginal ice zone (MIZ) are suggested in this paper. Physical roughness measurements using ship- and helicopter-based laser systems combined with ship-based active microwave backscattering (C-band polarimetric coherences) and dual-polarized passive microwave emission (polarization ratio, PR and spectral gradient ratios, GR at 37 and 89 GHz) are presented to study diverse sea ice types found in the MIZ. Autocorrelation functions are investigated for different sea ice roughness types. Small-scale roughness classes were discriminated using data from a ship-based laser profiler. The polarimetric coherence parameter ρHHVH , is not found to exhibit any observable sensitivity to the surface roughness for all incidence angles. Rubble-ridges, pancake ice, snow-covered frost flowers, and dense frost flowers exhibit separable signatures using GR-H and GR-V at >70° incidence angles. This paper diagnosed changes in sea ice roughness on a spatial scale of ∼0.1-4000 m and on a temporal scale of ∼1-240 days (ice freeze-up to summer melt). The coupling of MIZ wave roughness and aerodynamic roughness in conjunction with microwave emission and backscattering are future avenues of research. Additionally, the integration of various datasets into thermodynamic evolution model of sea ice will open pathways to successful development of inversion models of MIZ behavior.

  2. Seasonal comparisons of sea ice concentration estimates derived from SSM/I, OKEAN, and RADARSAT data

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.

    2002-01-01

    The Special Sensor Microwave Imager (SSM/I) microwave satellite radiometer and its predecessor SMMR are primary sources of information for global sea ice and climate studies. However, comparisons of SSM/I, Landsat, AVHRR, and ERS-1 synthetic aperture radar (SAR) have shown substantial seasonal and regional differences in their estimates of sea ice concentration. To evaluate these differences, we compared SSM/I estimates of sea ice coverage derived with the NASA Team and Bootstrap algorithms to estimates made using RADARSAT, and OKEAN-01 satellite sensor data. The study area included the Barents Sea, Kara Sea, Laptev Sea, and adjacent parts of the Arctic Ocean, during October 1995 through October 1999. Ice concentration estimates from spatially and temporally near-coincident imagery were calculated using independent algorithms for each sensor type. The OKEAN algorithm implemented the satellite's two-channel active (radar) and passive microwave data in a linear mixture model based on the measured values of brightness temperature and radar backscatter. The RADARSAT algorithm utilized a segmentation approach of the measured radar backscatter, and the SSM/I ice concentrations were derived at National Snow and Ice Data Center (NSIDC) using the NASA Team and Bootstrap algorithms. Seasonal and monthly differences between SSM/I, OKEAN, and RADARSAT ice concentrations were calculated and compared. Overall, total sea ice concentration estimates derived independently from near-coincident RADARSAT, OKEAN-01, and SSM/I satellite imagery demonstrated mean differences of less than 5.5% (S.D. <9.5%) during the winter period. Differences between the SSM/I NASA Team and the SSM/I Bootstrap concentrations were no more than 3.1% (S.D. <5.4%) during this period. RADARSAT and OKEAN-01 data both yielded higher total ice concentrations than the NASA Team and the Bootstrap algorithms. The Bootstrap algorithm yielded higher total ice concentrations than the NASA Team algorithm. Total ice

  3. Seasonally-Active Water on Mars: Vapour, Ice, Adsorbate, and the Possibility of Liquid

    NASA Astrophysics Data System (ADS)

    Richardson, M. I.

    2002-12-01

    Seasonally-active water can be defined to include any water reservoir that communicates with other reservoirs on time scales of a year or shorter. It is the interaction of these water reservoirs, under the influence of varying solar radiation and in conjunction with surface and atmospheric temperatures, that determines the phase-stability field for water at the surface, and the distribution of water in various forms below, on, and above the surface. The atmosphere is the critical, dynamical link in this cycling system, and also (fortunately) one of the easiest to observe. Viking and Mars Global Surveyor observations paint a strongly asymmetric picture of the global seasonal water cycle, tied proximately to planetary eccentricity, and the existence of residual ice caps of different composition at the two poles. The northern summer experiences the largest water vapour columns, and is associated with sublimation from the northern residual water ice cap. The southern summer residual carbon dioxide ice cap is cold trap for water. Asymmetry in the water cycle is an unsolved problem. Possible solutions may involve the current timing of perihelion (the water cap resides at the pole experiencing the longer but cooler summer), the trapping of water ice in the northern hemisphere by tropical water ice clouds, and the bias in the annual-average, zonal-mean atmospheric circulation resulting from the zonal-mean difference in the elevation of the northern and southern hemispheres. Adsorbed and frozen water have proven harder to constrain. Recent Odyssey Gamma Ray Spectrometer results suggest substantial ground ice in the mid- and high-latitudes, but this water is likely below the seasonal skin depth for two reasons: the GRS results are best fit with such a model, and GCM models of the water cycle produce dramatically unrealistic atmospheric vapour distributions when such a very near surface, GRS-like distribution is initialized - ultimately removing the water to the northern and

  4. Seasonal and annual variations of mountain glaciers surface velocity, implications for ice dynamic. Case study: Karakorum and Pamir.

    NASA Astrophysics Data System (ADS)

    Nanni, Ugo; Scherler, Dirk; Ayoub, Francois; Malatesta, Luca; Herman, Frederic; Avouac, Jean-Philippe

    2017-04-01

    The Pamir and Karakorum regions are heavily glaciated and contain some of the largest and fastest mountain glaciers on Earth. Satellite imagery is key to constrain ice dynamics, in particular glacier surface velocities, and sub glacial processes, e.g., basal sliding or glacier erosion, in such large and remote regions. Significant velocity variations have previously been observed in this area and related to forcing by seasonal meltwater and surges mechanisms. However, the details of surges sequences, in particular their initiation and termination, and multiyear seasonal patterns are still poorly documented. Here we study 26 glaciers and quantify surface velocity variations at high temporal resolution from remote sensing. We present a processing strategy to exploit the large archives of optical satellite imagery available for the study area to obtain more than 500 velocity fields with a 16-day temporal resolution from April 2013 to July 2016. Glacier displacement is measured with a 1.5-meter resolution using sub-pixel correlation (COSI-Corr software) of Landsat-8 images. 14 out of the 26 studied glaciers show seasonal velocity variations with inter-annual variability. These glaciers typically accelerate in early spring, up to 150% of the winter velocity, starting in the ablation zone and occasionally propagating upstream. This behaviour supports a meteorological/hydrological forcing with higher velocities caused by an increase in water pressure due to melt water input during spring time. 12 out of the 26 glaciers underwent one sub-annual or multiyear surging event during the study period. The surging events do not follow a unique pattern. Velocity can increase by up 700% over a month, and with an acceleration that initiate anytime of the year. This suggests that surges are initiated by an internal process, e.g., shear heating or basal hydrology, rather than by an external seasonal forcing.

  5. Interannual and seasonal behavior of Martian residual ice-cap albedo

    NASA Astrophysics Data System (ADS)

    Byrne, S.; Zuber, M. T.; Neumann, G. A.

    2008-02-01

    The Mars Orbiter Laser Altimeter (MOLA), functioning as a high-resolution radiometer, has observed several appearances of the Martian residual ice caps. We examine these data to quantify both seasonal behavior and interannual differences. The northern residual cap (NRC) was found to be mostly stable with the exception of one, previously identified, region of strong variability. Interannual change in the extent of the NRC appears to be small and reversible on timescales of 1 or 2 years. The NRC has an elaborate seasonal evolution of albedo. Annuli of fine-grained CO 2 and water frost, which track the inner and outer edges of the seasonal CO 2 cap, cause large temporary brightenings. The NRC albedo is stable from just after solstice to Ls 150°, after which albedo decreases steadily. This late-summer darkening can be explained by shadowing within the rough topography of the NRC, leading to a lower limit on topographic relief of 80 cm. The southern residual cap (SRC) appears stable in extent. As has been previously discovered, its seasonal frost albedo behavior appears to be correlated with insolation. However, residual CO 2 appears not to share this characteristic; we use this behavioral difference to infer net deposition of CO 2 ice on the SRC during 1 out of 3 years. Uncharacteristically, the SRC abruptly darkens at Ls 320° in 1 Martian year (year beginning April 2002). Circumstantial evidence suggests atmospheric scattering by dust is responsible. The 2001 global dust-storm appears, either, to have had no effect on the polar cap albedos, or, resulted in slightly brighter ice deposits.

  6. Wave-Ice Interaction in the Marginal Ice Zone: Toward a Wave-Ocean-Ice Coupled Modeling System

    DTIC Science & Technology

    2014-09-30

    generated surface gravity waves (WAVEWATCH III®) such that it can accurately predict the attenuation and scattering of waves by interaction with ice in...generated ocean surface wave models at NCEP. Weather and Forecasting (NCEP Notes), 17, 311-333. Wang, R. and H. H. Shen, 2010: Gravity waves

  7. Acoustic Gravity Waves Generated by an Oscillating Ice Sheet in Arctic Zone

    NASA Astrophysics Data System (ADS)

    Abdolali, A.; Kadri, U.; Kirby, J. T., Jr.

    2016-12-01

    ., 2015, Depth-integrated equation for hydro-acoustic waves with bottom damping, Journal of Fluid Mechanics, 766, R1 doi:10.1017/jfm.2015.37 Kadri, U., 2016, Generation of Hydroacoustic Waves by an Oscillating Ice Block in Arctic Zones, Advances in Acoustics and Vibration. 2016. doi:10.1155/2016/8076108

  8. 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.

  9. 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

  10. Changes in lipid composition of copepods and Euphausia superba associated with diet and environmental conditions in the marginal ice zone, Bellingshausen Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Cripps, G. C.; Hill, H. J.

    1998-08-01

    The effect of varying diet and environmental conditions at the Marginal Ice Zone (MIZ) on the fatty acid and hydrocarbon compositions of five species of copepod and krill, Euphausia superba, was investigated. Zooplankton at the MIZ experienced a range of conditions, from a low algal biomass (mainly flagellates) under pack-ice to a spring bloom dominated by diatoms in the open ocean. Principal Component Analysis classified the copepods into three dietary regimes: (i) omnivores or general algal feeders under the pack ice, (ii) dinoflagellate feeders, and (iii) diatom feeders in the open ocean. This classification was supported by the distribution of the diatom marker n-heneicosahexaene ( n-C 21:6) and a general indicator of herbivory, the isoprenoid pristane. The fatty acid and hydrocarbon composition reflected dietary preferences and availability as the season progressed. Of the copepods under the pack-ice, Oithona spp. was omnivorous whereas Calanus propinquus was feeding preferentially on flagellates. Metridia gerlachei fed on flagellates in all conditions, but also included diatoms in its diet during the bloom. Calanoides acutus and Rhincalanus gigas, which passed the winter in diapause, were feeding almost exclusively on diatoms in the open ocean. Euphausia superba, which were also mainly diatom feeders in the open ocean, were feeding on the sea-ice algae (diatoms) and suspended material from the water column (dinoflagellates) under the pack-ice.

  11. Insurgency Season: The Link between the Intertropical Convergence Zone and Insurgencies in Equatorial Africa

    DTIC Science & Technology

    2008-04-23

    hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and...completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of...Convergence Zone ( ITCZ ) creates distinct wet and dry seasons throughout the region. During the wet season, widespread flooding and inclement weather dominate

  12. 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

  13. Primary production within the sea-ice zone west of the Antarctic Peninsula: I—Sea ice, summer mixed layer, and irradiance

    NASA Astrophysics Data System (ADS)

    Vernet, Maria; Martinson, Douglas; Iannuzzi, Richard; Stammerjohn, Sharon; Kozlowski, Wendy; Sines, Karie; Smith, Ray; Garibotti, Irene

    2008-09-01

    In shelf waters of the western Antarctic Peninsula (wAP), with abundant macro- and micronutrients, water-column stability has been suggested as the main factor controlling primary production; freshwater input from sea-ice melting stabilizes the upper water column by forming a shallow summer mixed layer. Retreating sea ice in the spring and summer thus defines the area of influence, the sea-ice zone (SIZ) and the marginal ice zone (MIZ). A 12-year time series (1995-2006) was analyzed to address two main questions: (1) what are the spatial and temporal patterns in primary production; and (2) to what extent and in what ways is primary production related to sea-ice dynamics. Data were collected on cruises performed during January of each year, at the height of the growth season, within the region bounded by 64°S and 64°W to the north and 68°S and 66°W to the south. Average daily integrated primary production varied by an order of magnitude, from ˜250 to ˜1100 mg C m -2 d -1, with an average cruise primary production of 745 mg C m -2 d -1. A strong onshore-offshore gradient was evident along the shelf with higher production observed inshore. Inter-annual regional production varied by a factor of 7: maximum rates were measured in 2006 (1788 mg C m -2 d -1) and minimum in 1999 (248 mg C m -2 d -1). The results support the hypothesis that primary production in the wAP shelf is related to sea-ice dynamics. To first order, shallower summer mixed-layer depths in the shelf correlated with late sea retreat and primary production. Principal component analysis showed that high primary production in January was associated with enhanced shelf production toward the coast and in the south, explaining 63% of the variability in space and time. This first mode captured the inter-annual variability in regional production. Temporal variability in primary production (time series of anomalies defined for each location) showed spatial dependence: higher primary production correlated

  14. Mars Water Ice and Carbon Dioxide Seasonal Polar Caps: GCM Modeling and Comparison with Mars Express Omega Observations

    NASA Technical Reports Server (NTRS)

    Forget, F.; Levrard, B.; Montmessin, F.; Schmitt, B.; Doute, S.; Langevin, Y.; Bibring, J. P.

    2005-01-01

    To better understand the behavior of the Mars CO2 ice seasonal polar caps, and in particular interpret the the Mars Express Omega observations of the recession of the northern seasonal cap, we present some simulations of the Martian Climate/CO2 cycle/ water cycle as modeled by the Laboratoire de Meteorologie Dynamique (LMD) global climate model.

  15. Abundant Methanol Ice toward a Massive Young Stellar Object in the Central Molecular Zone

    NASA Astrophysics Data System (ADS)

    An, Deokkeun; Sellgren, Kris; Boogert, A. C. Adwin; Ramírez, Solange V.; Pyo, Tae-Soo

    2017-07-01

    Previous radio observations revealed widespread gas-phase methanol (CH3OH) in the Central Molecular Zone (CMZ) at the Galactic center (GC), but its origin remains unclear. Here, we report the discovery of CH3OH ice toward a star in the CMZ, based on a Subaru 3.4-4.0 μm spectrum, aided by NASA/IRTF L\\prime imaging and 2-4 μm spectra. The star lies ˜8000 au away in projection from a massive young stellar object (MYSO). Its observed high CH3OH ice abundance (17 % +/- 3 % relative to H2O ice) suggests that the 3.535 μm CH3OH ice absorption likely arises in the MYSO’s extended envelope. However, it is also possible that CH3OH ice forms with a higher abundance in dense clouds within the CMZ, compared to within the disk. Either way, our result implies that gas-phase CH3OH in the CMZ can be largely produced by desorption from icy grains. The high solid CH3OH abundance confirms the prominent 15.4 μm shoulder absorption observed toward GC MYSOs arises from CO2 ice mixed with CH3OH. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  17. Mapping the grounding zone of Ross Ice Shelf using ICESat laser altimetry

    USGS Publications Warehouse

    Brunt, Kelly M.; Fricker, Helen A.; Padman, Laurie; Scambos, Ted A.; O'Neel, Shad

    2010-01-01

    We use laser altimetry from the Ice, Cloud, and land Elevation Satellite (ICESat) to map the grounding zone (GZ) of the Ross Ice Shelf, Antarctica, at 491 locations where ICESat tracks cross the grounding line (GL). Ice flexure in the GZ occurs as the ice shelf responds to short-term sea-level changes due primarily to tides. ICESat repeat-track analysis can be used to detect this region of flexure since each repeated pass is acquired at a different tidal phase; the technique provides estimates for both the landward limit of flexure and the point where the ice becomes hydrostatically balanced. We find that the ICESat-derived landward limits of tidal flexure are, in many places, offset by several km (and up to ∼60 km) from the GL mapped previously using other satellite methods. We discuss the reasons why different mapping methods lead to different GL estimates, including: instrument limitations; variability in the surface topographic structure of the GZ; and the presence of ice plains. We conclude that reliable and accurate mapping of the GL is most likely to be achieved when based on synthesis of several satellite datasets

  18. Bathymetry of Grounding Zones and Sub-Ice Shelf Cavities of the Amundsen Sea, from Operation IceBridge Gravity Inversions

    NASA Astrophysics Data System (ADS)

    Tinto, K. J.; Cochran, J. R.; Bell, R. E.

    2012-12-01

    In order to understand the observed changes in thinning and grounding line position of outlet glaciers it is essential to have accurate maps of the bathymetry of the sea floor within and around the grounding zone. This bathymetry controls the stability of the grounding line as well as access and circulation of seawater under their stabilizing ice shelves. Since 2009 Operation IceBridge has flown gridded surveys over four of the ice shelves of the Amundsen Sea embayment. We present a 3D inversion of the gravity from the region, supplemented by 2D profile models across the ice shelves to provide a self-consistent bathymetric model of the grounding zone and sub ice cavity of Pine Island, Thwaites, Dotson and Crosson ice shelves. Much attention has been paid to the largest outlet glaciers of the Amundsen Sea, and to the bathymetry beneath the floating ice in front of their grounding zones. Considerable changes have also been observed from the smaller Amundsen ice shelves, Crosson and Dotson, which flow to the east and north respectively, between Thwaites Glacier and Getz ice shelf, but little is known about their sub-ice bathymetry. The Amundsen Sea region is vulnerable to the influence of relatively warm circumpolar deep water encroaching on to the continental shelf. The influence of these waters at the grounding zone of the glaciers in the region is dictated by the depth and orientation of bathymetric features of the sea floor. The dominant geological fabric of the region is a NE-SW trending series of ridges and troughs, formed in association with the rifting of the Amundsen Sea region. The bathymetry models from OIB gravity inversions reveal the continuation of the deep (~1500 m) trough of the Kohler Glacier under Crosson Ice Shelf. At the eastern end of the trough, at the front of Crosson ice shelf, the sea floor rises to an average of ~500 m depth over a broad, 50 km wide region. Further east from here the NE-SW fabric is continued in a previously reported ridge

  19. A Regional Model for Seasonal Sea Ice Prediction in the Pacific Sector of the Arctic

    NASA Astrophysics Data System (ADS)

    Yuan, X.; Li, Y.; Chen, D.; Zhang, Q.; Li, C.; Niu, F.; Sun, Y.

    2015-12-01

    The recent results from a linear Markov model for seasonal prediction of pan-Arctic sea ice concentration (SIC) show that sea ice in the Pacific sector has the lowest predictability compared to other regions. One reason could be that the climate variability in the Atlantic sector is so dominant that other signals in the Arctic climate system do not appear in the leading modes used for model construction. This study develops a regional Markov model to improve seasonal forecasting of SIC in the Pacific sector. The model climate system consists of various combinations of the monthly mean series of SIC, sea surface temperature (SST), surface air temperature (SAT), pressure/geopotential height fields and winds at pressure levels. Multivariate empirical orthogonal functions (MEOF) and rotated MEOF are applied to each set of data to reduce the model dimensions. After a series of experiments, the final model configuration selects 23 rotated MEOF modes from a data matrix of three variables (SIC, SST and SAT). This regional model shows considerable improvement in the prediction skill in the Pacific sector in all seasons. The anomaly correlation skill increases by 0.2 at 1- to 4-month leads in the Bering Sea, and by 0.1 at 1- to 10-month leads in the Sea of Okhotsk. In general, the model performs better in summer and fall than in winter and spring. On average, the correlation skill can reach 0.6 at a 2-month (4-month) lead in the Bering Sea (the Sea of Okhotsk).

  20. Global warming related transient albedo feedback in the Arctic and its relation to the seasonality of sea ice

    NASA Astrophysics Data System (ADS)

    Andry, Olivier; Bintanja, Richard; Hazeleger, Wilco

    2015-04-01

    The Arctic is warming two to three times faster than the global average. Arctic sea ice cover is very sensitive to this warming and has reached historic minima in late summer in recent years (i.e. 2007, 2012). Considering that the Arctic Ocean is mainly ice-covered and that the albedo of sea ice is very high compared to that of open water, the change in sea ice cover is very likely to have a strong impact on the local surface albedo feedback. Here we quantify the temporal changes in surface albedo feedback in response to global warming. Usually feedbacks are evaluated as being representative and constant for long time periods, but we show here that the strength of climate feedbacks in fact varies strongly with time. For instance, time series of the amplitude of the surface albedo feedback, derived from future climate simulations (CIMP5, RCP8.5 up to year 2300) using a kernel method, peaks around the year 2100. This maximum is likely caused by an increased seasonality in sea-ice cover that is inherently associated with sea ice retreat. We demonstrate that the Arctic average surface albedo has a strong seasonal signature with a maximum in spring and a minimum in late summer/autumn. In winter when incoming solar radiation is minimal the surface albedo doesn't have an important effect on the energy balance of the climate system. The annual mean surface albedo is thus determined by the seasonality of both downwelling shortwave radiation and sea ice cover. As sea ice cover reduces the seasonal signature is modified, the transient part from maximum sea ice cover to its minimum is shortened and sharpened. The sea ice cover is reduced when downwelling shortwave radiation is maximum and thus the annual surface albedo is drastically smaller. Consequently the change in annual surface albedo with time will become larger and so will the surface albedo feedback. We conclude that a stronger seasonality in sea ice leads to a stronger surface albedo feedback, which accelerates

  1. Seasonal Variation of Carbon Metabolism in the Cambial Zone of Eucalyptus grandis

    PubMed Central

    Budzinski, Ilara G. F.; Moon, David H.; Lindén, Pernilla; Moritz, Thomas; Labate, Carlos A.

    2016-01-01

    Eucalyptus species are the most widely hardwood planted in the world. It is one of the successful examples of commercial forestry plantation in Brazil and other tropical and subtropical countries. The tree is valued for its rapid growth, adaptability and wood quality. Wood formation is the result of cumulative annual activity of the vascular cambium. This cambial activity is generally related to the alternation of cold and warm, and/or dry and rainy seasons. Efforts have focused on analysis of cambial zone in response to seasonal variations in trees from temperate zones. However, little is known about the molecular changes triggered by seasonal variations in trees from tropical countries. In this work we attempted to establish a global view of seasonal alterations in the cambial zone of Eucalyptus grandis Hill ex Maiden, emphasizing changes occurring in the carbon metabolism. Using transcripts, proteomics and metabolomics we analyzed the tissues harvested in summer-wet and winter-dry seasons. Based on proteomics analysis, 70 proteins that changed in abundance were successfully identified. Transcripts for some of these proteins were analyzed and similar expression patterns were observed. We identified 19 metabolites differentially abundant. Our results suggest a differential reconfiguration of carbon partioning in E. grandis cambial zone. During summer, pyruvate is primarily metabolized via ethanolic fermentation, possibly to regenerate NAD+ for glycolytic ATP production and cellular maintenance. However, in winter there seems to be a metabolic change and we found that some sugars were highly abundant. Our results revealed a dynamic change in E. grandis cambial zone due to seasonality and highlight the importance of glycolysis and ethanolic fermentation for energy generation and maintenance in Eucalyptus, a fast growing tree. PMID:27446160

  2. Seasonal Ice Mass-Balance Buoys: Adapting Tools to the Changing Arctic

    DTIC Science & Technology

    2011-01-01

    latitudes ( Schauer and others, 2004; Woodgate and others, 2006) and atmos- pheric circulation patterns (Hilmer and Jung, 2000; Rigor and others, 2002). The...at the bottom. A tick mark is 7 days. A number of interesting data features are labeled. Polashenski and others: Seasonal ice mass-balance buoys 23...Figure 4a–d are on the same timescale shown at the bottom, with 7 days between tick marks . In Figure 4c, we can see that snow depth begins to decline

  3. Meso- and submesoscale structures in marginal ice zone in Arctic ocean using Sentinel-1 data

    NASA Astrophysics Data System (ADS)

    Tarasenko, Anastasiia

    2016-07-01

    A marginal sea ice zone is a region where ocean currents interact with the sea ice. Recently freezed small sea ice particles (frazil) can be used as a passive tracer for the ocean surface dynamics studies. Sentinel-1 SAR images with a high spatial resolution (40 or 25 m) permit to exploit this approach of "frazil as surface current's passive tracer". A preliminary research on meso- and submesoscale structures in marginal sea ice zone was carried out using Sentinel-1 SAR data. A new dataset of mesoscale structures was created for Eastern Greenland, Barents and Kara seas for 2014-2015. The raw data was processed with SNAP (Sentinel application Platform designed by ESA). A classical method of maximum cross-correlation was tested together with a method developed based on (Kudriavtsev et al, 2014) for eddy-like structures detection. References: Kudryavtsev, Vladimir, I. Kozlov, Bertrand Chapron, and J. A. Johannessen. "Quad-polarization SAR features of ocean currents." Journal of Geophysical Research: Oceans 119, no. 9 (2014): 6046-6065.

  4. Propagation and Directional Scattering of Ocean Waves in the Marginal Ice Zone and Neighboring Seas

    DTIC Science & Technology

    2015-09-30

    the spatial and temporal variability of sea state, and improve forecasting of waves on the open ocean and in the marginal ice zone; 2. Develop an...Transition the methodology of Perrie and Hu (1996) to the state-of-the-art for operational wave forecasting , for example WW3, version 4.18. Incorporation... forecasting , specifically, WAVEWATCHIII (WW3), version 4.18. This involves incorporation of the scattering term in modern ocean wave models requires some pre

  5. Seasonal dynamics of organic carbon and metals in thermokarst lakes from the discontinuous permafrost zone of western Siberia

    NASA Astrophysics Data System (ADS)

    Manasypov, R. M.; Vorobyev, S. N.; Loiko, S. V.; Kritzkov, I. V.; Shirokova, L. S.; Shevchenko, V. P.; Kirpotin, S. N.; Kulizhsky, S. P.; Kolesnichenko, L. G.; Zemtzov, V. A.; Sinkinov, V. V.; Pokrovsky, O. S.

    2015-01-01

    Western Siberia's thermokarst (thaw) lakes extend over a territory spanning over a million km2; they are highly dynamic hydrochemical systems that receive chemical elements from the atmosphere and surrounding peat soil and vegetation, and exchange greenhouse gases with the atmosphere, delivering dissolved carbon and metals to adjacent hydrological systems. This work describes the chemical composition of ~ 130 thermokarst lakes of the size range from a few m2 to several km2, located in the discontinuous permafrost zone. Lakes were sampled during spring floods, just after the ice break (early June), the end of summer (August), the beginning of ice formation (October) and during the full freezing season in winter (February). Dissolved organic carbon (DOC) and the major and trace elements do not appreciably change their concentration with the lake size increase above 1000 m2 during all seasons. On the annual scale, the majority of dissolved elements including organic carbon increase their concentration from 30 to 500%, with a statistically significant (p < 0.05) trend from spring to winter. The maximal increase in trace element (TE) concentration occurred between spring and summer and autumn and winter. The ice formation in October included several stages: first, surface layer freezing followed by crack (fissure) formation with unfrozen water from the deeper layers spreading over the ice surface. This water was subsequently frozen and formed layered ice rich in organic matter. As a result, the DOC and metal concentrations were the highest at the beginning of the ice column and decreased from the surface to the depth. A number of elements demonstrated the accumulation, by more than a factor of 2, in the surface (0-20 cm) of the ice column relative to the rest of the ice core: Mn, Fe, Ni, Cu, Zn, As, Ba and Pb. The main consequences of discovered freeze-driven solute concentrations in thermokarst lake waters are enhanced colloidal coagulation and the removal of dissolved

  6. No signature of clear CO2 ice from the 'cryptic' regions in Mars' south seasonal polar cap.

    PubMed

    Langevin, Yves; Douté, Sylvain; Vincendon, Mathieu; Poulet, François; Bibring, Jean-Pierre; Gondet, Brigitte; Schmitt, Bernard; Forget, F

    2006-08-17

    The seasonal polar ice caps of Mars are composed mainly of CO2 ice. A region of low (< 30%) albedo has been observed within the south seasonal cap during early to mid-spring. The low temperature of this 'cryptic region' has been attributed to a clear slab of nearly pure CO2 ice, with the low albedo resulting from absorption by the underlying surface. Here we report near-infrared imaging spectroscopy of the south seasonal cap. The deep and broad CO2 absorption bands that are expected in the near-infrared with a thick transparent slab of CO2 ice are not observed. Models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a CO2 ice layer, which could be linked to atmospheric circulation patterns. The strength of the CO2 absorption increases after mid-spring, so part of the dust is either carried away or buried more deeply in the ice layer during the CO2 ice sublimation process.

  7. Identifying palaeo-ice-stream tributaries on hard beds: Mapping glacial bedforms and erosion zones in NW Scotland

    NASA Astrophysics Data System (ADS)

    Bradwell, Tom

    2013-11-01

    Ice streams are fed by tributaries that can extend deep into the heart of ice sheets. These tributaries are born at onset zones - the abrupt transitions from slow sheet flow to fast streaming flow that often occur at significant topographic steps on hard beds (bedrock-dominated beds). For this reason, tributary onset zones leave only a subtle erosional geomorphic signature in the landscape record that is rarely studied. This paper examines, in detail, the geomorphic signature of ice-sheet flow on a hard bed at the head of a palaeo-ice stream. We use field survey techniques to map glacial bedforms within an ~ 200-km2 area of hard crystalline bedrock in a landscape of ‘areal scour’ around Loch Laxford in NW Scotland. The bedrock bedforms range from plastically moulded (p-forms) and wholly abraded forms, to stoss-lee forms and plucked surfaces all on an outcrop scale (1-100 m). We devise a five-zone classification system to map (in a GIS) the presence, absence, and abundance of glacial erosional forms within 619 (500-m square) grid cells. We go on to use these erosional bedform zones, along with known glaciological relationships to interpret the spatial and altitudinal pattern of palaeo-ice sheet processes and glacier dynamics in this part of NW Scotland. Our interpretation highlights the strong vertical thermal zonation on mountains, and the spatial variations in ice rheology (softness), ice temperature and, by inference, ice velocity in troughs - intimately associated with the onset of ice streaming in tributaries. Consequently, we define the Laxfjord palaeo-ice-stream tributary - a feeder to the Minch palaeo-ice stream in NW Scotland. Finally, we suggest that this new mapping approach could be performed in other deglaciated hard-bed terrain to examine, more widely, the subtle erosional signatures preserved in areas traditionally thought to represent ice sheet ‘areal scour’.

  8. Observations of surface momentum exchange over the marginal ice zone and recommendations for its parametrisation

    NASA Astrophysics Data System (ADS)

    Elvidge, A. D.; Renfrew, I. A.; Weiss, A. I.; Brooks, I. M.; Lachlan-Cope, T. A.; King, J. C.

    2016-02-01

    Comprehensive aircraft observations are used to characterise surface roughness over the Arctic marginal ice zone (MIZ) and consequently make recommendations for the parametrisation of surface momentum exchange in the MIZ. These observations were gathered in the Barents Sea and Fram Strait from two aircraft as part of the Aerosol-Cloud Coupling And Climate Interactions in the Arctic (ACCACIA) project. They represent a doubling of the total number of such aircraft observations currently available over the Arctic MIZ. The eddy covariance method is used to derive estimates of the 10 m neutral drag coefficient (CDN10) from turbulent wind velocity measurements, and a novel method using albedo and surface temperature is employed to derive ice fraction. Peak surface roughness is found at ice fractions in the range 0.6 to 0.8 (with a mean interquartile range in CDN10 of 1.25 to 2.85 × 10-3). CDN10 as a function of ice fraction is found to be well approximated by the negatively skewed distribution provided by a leading parametrisation scheme (Lüpkes et al., 2012) tailored for sea-ice drag over the MIZ in which the two constituent components of drag - skin and form drag - are separately quantified. Current parametrisation schemes used in the weather and climate models are compared with our results and the majority are found to be physically unjustified and unrepresentative. The Lüpkes et al. (2012) scheme is recommended in a computationally simple form, with adjusted parameter settings. A good agreement holds for subsets of the data from different locations, despite differences in sea-ice conditions. Ice conditions in the Barents Sea, characterised by small, unconsolidated ice floes, are found to be associated with higher CDN10 values - especially at the higher ice fractions - than those of Fram Strait, where typically larger, smoother floes are observed. Consequently, the important influence of sea-ice morphology and floe size on surface roughness is recognised, and

  9. Loss of Arctic Snow Cover and Sea Ice Extent Across the Land-Ocean Boundary During the Melt Season

    NASA Astrophysics Data System (ADS)

    Bliss, A.; Anderson, M. R.

    2010-12-01

    Concern over the rapid changes in the Arctic cryosphere in recent years has spurred much research into the response of sea ice and snow cover to warming temperatures and the resulting climate feedbacks. However, the vast majority of Arctic climate studies do not assess the response of both continental snow cover and sea ice in concert through the data record. This study is designed to compare the monthly Northern Hemispheric continental snow cover extent data available from Rutgers University Global Snow Lab and the passive microwave derived monthly Bootstrap algorithm sea ice extent data available from the National Snow and Ice Data Center (NSIDC) in the Arctic during the melt season (March-August) over the 29-year study period 1979-2007. Since these data are stored in incompatible formats, little research has gone into studying the concurrent variations in the annual loss of continental snow cover and sea ice extent across the land-ocean boundary. However, with a creation of a snow and ice extent climate data record (CDR) incorporating different data formats, one would allow analysis of these data to investigate conditions during the melt season. As a CDR example three autonomous study regions located in Siberia, North America, and Western Russia were determined to reveal any differences in the response of snow and sea ice extents during melt. Each study domain extends from over land, northward, into an Arctic marginal sea, containing a land-ocean boundary that is roughly parallel to latitude and is subject to considerable inter-annual variability in the extent and retreat of both snow and sea ice during the warm season. Each domain area was also selected to include a minimal extent of mountainous areas where persistent snow cover throughout the year could misrepresent the seasonal northward progression of snow cover lost, relative to other land domains in the study. The results show on average, sea ice extent is lost earlier in the year, in May, than snow cover

  10. Analysis of Daily, Seasonal, and Interannual Changes in Hofsjokull Ice Cap, Iceland, using Satellite Data

    NASA Technical Reports Server (NTRS)

    Hall, D. K.; Garvin, J. B.; Williams, R. S., Jr.; Barton, J. S.; Sigurosson, O.; Smith, L. C.

    1998-01-01

    Analysis of a time series of European Remote Sensing Satellite (ERS)-1 and -2, RADARSAT ScanSAR synthetic aperture radar (SAR) and Landsat images from 1973 to 1998, shows daily to interannual changes in Hofsjokull, a 923 sq km ice cap in central Iceland. A digital elevation model of Hofsjokull was constructed using interferometry, and then SAR backscatter coefficient (d) was plotted with elevation, and air temperature along a transect across the ice cap. Most of the a' changes measured along the transect are caused by a change in the state (frozen or thawed) of the surficial snow or ice when air temperature rises above or below about -5 to O C. Seasonal (sigma)deg patterns are identified in a 4-year time series of 57 ERS-1 and -2 images. In addition, June 1997 ScanSAR images display rapid changes in brightness that are tied closely to daily meteorological events. SAR and Landsat data were also used to measure changes in the areal extent of Hofsjokull, from 1973 to 1997, and to locate (sigma)deg and reflectance boundaries that relate to the glacier facies. Late-summer 1997 (sigma)deg and reflectance boundaries agree and are coincident with the approximate location of the fim line, and the January 1998 position of the equilibrium line as determined from ERS-2 data.

  11. Analysis of Daily, Seasonal, and Interannual Changes in Hofsjokull Ice Cap, Iceland, using Satellite Data

    NASA Technical Reports Server (NTRS)

    Hall, D. K.; Garvin, J. B.; Williams, R. S., Jr.; Barton, J. S.; Sigurosson, O.; Smith, L. C.

    1998-01-01

    Analysis of a time series of European Remote Sensing Satellite (ERS)-1 and -2, RADARSAT ScanSAR synthetic aperture radar (SAR) and Landsat images from 1973 to 1998, shows daily to interannual changes in Hofsjokull, a 923 sq km ice cap in central Iceland. A digital elevation model of Hofsjokull was constructed using interferometry, and then SAR backscatter coefficient (d) was plotted with elevation, and air temperature along a transect across the ice cap. Most of the a' changes measured along the transect are caused by a change in the state (frozen or thawed) of the surficial snow or ice when air temperature rises above or below about -5 to O C. Seasonal (sigma)deg patterns are identified in a 4-year time series of 57 ERS-1 and -2 images. In addition, June 1997 ScanSAR images display rapid changes in brightness that are tied closely to daily meteorological events. SAR and Landsat data were also used to measure changes in the areal extent of Hofsjokull, from 1973 to 1997, and to locate (sigma)deg and reflectance boundaries that relate to the glacier facies. Late-summer 1997 (sigma)deg and reflectance boundaries agree and are coincident with the approximate location of the fim line, and the January 1998 position of the equilibrium line as determined from ERS-2 data.

  12. Development of statistical seasonal prediction models of Arctic Sea Ice concentration using CERES absorbed solar radiation

    NASA Astrophysics Data System (ADS)

    Kim, Yoojin; Kim, Ha-Rim; Choi, Yong-Sang; Kim, WonMoo; Kim, Hye-Sil

    2016-11-01

    Statistical seasonal prediction models for the Arctic sea ice concentration (SIC) were developed for the late summer (August-October) when the downward trend is dramatic. The absorbed solar radiation (ASR) at the top of the atmosphere in June has a significant seasonal leading role on the SIC. Based on the lagged ASR-SIC relationship, two simple statistical models were established: the Markovian stochastic and the linear regression models. Crossvalidated hindcasts of SIC from 1979 to 2014 by the two models were compared with each other and observation. The hindcasts showed general agreement between the models as they share a common predictor, ASR in June and the observed SIC was well reproduced, especially over the relatively thin-ice regions (of one- or multi-year sea ice). The robust predictability confirms the functional role of ASR in the prediction of SIC. In particular, the SIC prediction in October was quite promising probably due to the pronounced icealbedo feedback. The temporal correlation coefficients between the predicted SIC and the observed SIC were 0.79 and 0.82 by the Markovian and regression models, respectively. Small differences were observed between the two models; the regression model performed slightly better in August and September in terms of temporal correlation coefficients. Meanwhile, the prediction skills of the Markovian model in October were higher in the north of Chukchi, the East Siberian, and the Laptev Seas. A strong non-linear relationship between ASR in June and SIC in October in these areas would have increased the predictability of the Markovian model.

  13. Crevasse Extent and Lateral Shearing of the McMurdo Shear Zone, Antarctica: Implications of Ice Shelf Stability

    NASA Astrophysics Data System (ADS)

    Kaluzienski, L. M.; Hamilton, G. S.; Koons, P. O.; Enderlin, E. M.; Arcone, S. A.; Borstad, C.; Walker, B.

    2016-12-01

    Antarctica's ice shelves modulate the flow of inland ice towards the ocean. Understanding the controls on ice-shelf stability is critical for predicting the future evolution of the ice sheet. For the western sector of the Ross Ice Shelf (RIS), a potentially important region of lateral resistance is the McMurdo Shear Zone (MSZ) just downstream of Minna Bluff. Here the fast-moving Ross Ice Shelf ( 450 m/yr) shears past the slower-moving McMurdo Ice Shelf ( 200 m/yr) creating a zone of intense crevassing. An analysis of several satellite image datasets including a high-resolution digital elevation model (DEM) extracted from stereo Worldview imagery suggests that many of these flow features originate as the RIS flows past Minna Bluff. Here we present a sensitivity analysis of RIS ice flow using the Ice Sheet System Model (ISSM) (Larour et al. 2012) and the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA). In this analysis we assess the sensitivity of model flow of RIS tributary glaciers to boundary condition perturbations within the Minna Bluff/MSZ region. Perturbations include ice shelf thickness variations as well as a scalar damage variable that quantifies the loss of load-bearing surface area due to ice shelf fracture. Field observations of surface flow and strain (GPS) and crevasse distribution and geometry (GPR)in the MSZ help constrain the model simulations. Initial results point to the importance of sub-ice shelf topography and its interaction with features such as Minna Bluff in determining stress distribution on the western RIS. Larour, E.; Seroussi, H.; Morlighem, M.; Rignot, E. 2012. Continental scale, high order, high spatial resolution, ice sheet modeling using the Ice Sheet System Model (ISSM), Journal of Geophysical Research

  14. Seasonal variability and long term trends of chlorofluorocarbon mixing ratios in the unsaturated zone.

    PubMed

    Santella, Nicholas; Schlosser, Peter; Smethie, William M; Ho, David T; Stute, Martin

    2006-07-15

    To investigate processes that might affect chlorofluorocarbon (CFC) mixing ratios at the water table, a time series was obtained of unsaturated zone soil gas CFCs to depths of ca. 4 m at a site near New York City (NYC). Observed CFC 11, 12, and 113 mixing ratios were lower in winter than expected from either a local, high-resolution time series or remote atmospheric mixing ratios. A diffusion model, which includes seasonal changes in soil temperature, moisture, and CFC solubility, reproduces to first order the observed soil gas mixing ratios for CFC 11 and 12. Underestimation by the model of the seasonal cycle of CFC 11 points to changing levels of sorption to soils due to seasonal changes in temperature as an additional cause of the cycle seen in CFC 11 mixing ratios in soil air. In the case of spring recharge, low CFC mixing ratios in soil air caused by increased solubility may result in low CFC 11 concentrations in groundwater and, when dating groundwater recharged before the 1990s with CFCs, older apparent ages by up to 4 years. Attempts to observe average atmospheric CFC levels from soil gas are also significantly hindered by these seasonal fluctuations. Our results indicate the importance of considering seasonal changes in soil temperature when making precise observations of even very moderately soluble gases in the unsaturated zone and shallow groundwater.

  15. Local effects of ice floes and leads on skin sea surface temperature, mixing and gas transfer in the marginal ice zone

    NASA Astrophysics Data System (ADS)

    Zappa, Christopher; Brumer, Sophia; Brown, Scott; LeBel, Deborah; McGillis, Wade; Schlosser, Peter; Loose, Brice

    2014-05-01

    Recent years have seen extreme changes in the Arctic. Marginal ice zones (MIZ), or areas where the "ice-albedo feedback" driven by solar warming is highest and ice melt is extensive, may provide insights into the extent of these changes. Furthermore, MIZ play a central role in setting the air-sea CO2 balance making them a critical component of the global carbon cycle. Incomplete understanding of how the sea-ice modulates gas fluxes renders it difficult to estimate the carbon budget in MIZ. Here, we investigate the turbulent mechanisms driving gas exchange in leads, polynyas and in the presence of ice floes using both field and laboratory measurements. Here, we present measurements of visible and IR imagery of melting ice floes in the marginal ice zone north of Oliktok Point AK in the Beaufort Sea made during the Marginal Ice Zone Ocean and Ice Observations and Processes EXperiment (MIZOPEX) in July-August 2013. The visible and IR imagery were taken from the unmanned airborne vehicle (UAV) ScanEagle. The visible imagery clearly defines the scale of the ice floes. The IR imagery show distinct cooling of the skin sea surface temperature (SST) as well as an intricate circulation and mixing pattern that depends on the surface current, wind speed, and near-surface vertical temperature/salinity structure. Individual ice floes develop turbulent wakes as they drift and cause transient mixing of an influx of colder surface (fresh) melt water. We capture a melting and mixing event that explains the changing pattern observed in skin SST and is substantiated using laboratory experiments. The Gas Transfer through Polar Sea Ice experiment was performed at the US Army Cold Regions Research and Engineering Laboratory (Hanover, NH) under varying ice coverage, winds speed, fetch and currents. Supporting measurements were made of air and water temperature, humidity, salinity and wave height. Air-side profiling provided momentum, heat, and CO2 fluxes. Transfer velocities are also

  16. Observations of Wind-Induced Motion in the Arctic Marginal Ice Zone

    NASA Astrophysics Data System (ADS)

    Bradley, A. C.; Palo, S. E.; Zappa, C. J.; LoDolce, G.; Weibel, D.; Lawrence, D.

    2014-12-01

    The increasingly recognized importance of the Marginal Ice Zone (MIZ) in the global and Arctic climate systems necessitates study of the complex processes at work in the interactions between ice floes, the ocean, and the atmosphere. This study uses observations of surface currents and floe drift speeds to explore the hydrodynamic processes driven by interactions with surface winds surrounding isolated small floes in the Arctic summertime MIZ. The 2013 MIZOPEX campaign flew several unmanned aircraft over the MIZ north of Oliktok Point, AK. These flights had two primary missions: dropping microbuoys into areas of open water between ice floes, and imaging in both thermal and visible using airborne systems. The Air-Deployed Micro Buoys (ADMB) drifted with surface currents, providing a measure of current speeds from the GPS track. ADMB were equipped with a string of thermistors extending two meters below the surface, which measured near-surface temperature gradients. Analysis of visible aerial imagery of ice floes is used to retrieve floe drift speeds from sequential photos by using aircraft telemetry to geolocate the images. Wind speeds from NCEP reanalysis and nearby met data are compared to surface currents and floe drift speeds; surface currents are approximately 4% of wind speeds, which agree well with lab measurements. Thermal imagery from the campaign show cold wakes at the surface near ice floes in certain wind conditions. The spatial view provided by airborne measurements, when combined with subsurface temperature gradients and the relation between drift and current speeds to local wind forcing, paints a picture of the physical interaction between an isolated ice floe in the MIZ and the open water surrounding it.

  17. A snow and ice melt seasonal prediction modelling system for Alpine reservoirs

    NASA Astrophysics Data System (ADS)

    Förster, Kristian; Oesterle, Felix; Hanzer, Florian; Schöber, Johannes; Huttenlau, Matthias; Strasser, Ulrich

    2016-10-01

    The timing and the volume of snow and ice melt in Alpine catchments are crucial for management operations of reservoirs and hydropower generation. Moreover, a sustainable reservoir operation through reservoir storage and flow control as part of flood risk management is important for downstream communities. Forecast systems typically provide predictions for a few days in advance. Reservoir operators would benefit if lead times could be extended in order to optimise the reservoir management. Current seasonal prediction products such as the NCEP (National Centers for Environmental Prediction) Climate Forecast System version 2 (CFSv2) enable seasonal forecasts up to nine months in advance, with of course decreasing accuracy as lead-time increases. We present a coupled seasonal prediction modelling system that runs at monthly time steps for a small catchment in the Austrian Alps (Gepatschalm). Meteorological forecasts are obtained from the CFSv2 model. Subsequently, these data are downscaled to the Alpine Water balance And Runoff Estimation model AWARE running at monthly time step. Initial conditions are obtained using the physically based, hydro-climatological snow model AMUNDSEN that predicts hourly fields of snow water equivalent and snowmelt at a regular grid with 50 m spacing. Reservoir inflow is calculated taking into account various runs of the CFSv2 model. These simulations are compared with observed inflow volumes for the melting and accumulation period 2015.

  18. Greenland Ice Sheet delivers seasonally elevated nitrogen fluxes to the Arctic oceans

    NASA Astrophysics Data System (ADS)

    Wadham, J. L.; Hawkings, J.; Telling, J.; Chandler, D.; Alcock, J.; Lawson, E.; Monteiro, F. M.; Kaur, P.; Bagshaw, E.; Tranter, M.; Tedstone, A. J.; Nienow, P. W.

    2013-12-01

    The availability of nitrogen limits the productivity of phytoplankton over almost half of the world's oceans in the summer months. This includes many of the ocean basins around the Greenland Ice Sheet (GrIS). Here, nitrogen is widely limiting in comparison to other nutrients such as phosphorus, silica and iron, which show only local limitation. Marine waters bordering the GrIS include some of the most productive ecosystems in the world, and boast high socio-economic value via fisheries. The productivity of phytoplankton in the North Atlantic also draws down CO2 from the atmosphere and has an important regulatory effect on global climate. The GrIS has recently begun to be considered as a source of nutrients to neighbouring oceans, but detailed studies of nitrogen fluxes in exported meltwater and icebergs from large catchments are lacking. Here, we present data from a large land-terminating glacier in Western Greenland during the 2012 melt season, inferring fluxes, speciation and sources of nitrogen exported in the runoff. We present seasonal time series of the concentrations of dissolved and sediment-bound nitrogen species in meltwaters both entering the glacial drainage system via moulins and exported runoff at the ice margin. A comparison of these data indicate that dissolved nitrogen concentrations in meltwaters approximately double during transit through the supra- and subglacial drainage systems, largely via the acquisition of dissolved organic nitrogen, which is likely to be associated with microbial activity. We go on to estimate nitrogen fluxes from the GrIS and show that fluxes are of a similar order of magnitude to some of the largest Arctic rivers in summer. Glacial nitrogen fluxes increase with rising runoff volumes, and hence with the progression of the melt season. This is significant given the reported nitrogen limitation of marine phytoplankton in some coastal waters around the GrIS in mid-summer following the spring phytoplankton bloom. We discuss

  19. Transverse, supraglacially derived crevasse infillings in a Pleistocene ice-sheet margin zone (eastern Poland): Genesis and sedimentary record

    NASA Astrophysics Data System (ADS)

    Godlewska, Anna; Terpiłowski, Sławomir

    2012-08-01

    The so-called 'crevasse infillings' in the marginal zone of the Saalian ice sheet in eastern Poland are atypical relief forms for lowlands glaciated in the Pleistocene. They are located on a high of the Cretaceous/Palaeogene substratum and form isolated ridges arranged in trains parallel to the former ice-sheet margin, i.e., transverse to the movement of the ice sheet. The sedimentary succession of the crevasse infillings consists mainly of undeformed glaciodeltaic deposits. We propose a model of the crevasse infilling development in three phases against the background of ice mass dynamics: 1) ice-sheet advance over a high of the substratum — compressive ice flow that bumped against the high's slope and enrichment of the ice with debris; 2) an overriding of the substratum high by ice masses — a tensional ice-flow regime resulted in significant crevassing; and 3) ice mass stagnation — low energy, supraglacial deltaic sedimentation in isolated ponds between disintegrated ice blocks under frozen bed conditions. Considering this genesis, we suggest classifying these forms as kames instead of crevasse infillings.

  20. Radial drift of dust in protoplanetary discs: the evolution of ice lines and dead zones

    NASA Astrophysics Data System (ADS)

    Cridland, A. J.; Pudritz, Ralph E.; Birnstiel, T.

    2017-03-01

    We have developed a new model for the astrochemical structure of a viscously evolving protoplanetary disc that couples an analytic description of the disc's temperature and density profile, chemical evolution and an evolving dust distribution. We compute evolving radial distributions for a range of dust grain sizes, which depend on coagulation, fragmentation and radial drift processes. In particular, we find that the water ice line plays an important role in shaping the radial distribution of the maximum grain size because ice-coated grains are significantly less susceptible to fragmentation than their dry counterparts. This in turn has important effects on disc ionization and therefore on the location of dead zones. In comparison to a simple constant gas-to-dust ratio model for the dust as an example, we find that the new model predicts an outer dead zone edge that moves in by a factor of about 3 at 1 Myr (to 5 au) and by a factor of about 14 by 3 Myr (to 0.5 au). We show that the changing position of the dead zone and heat transition traps have important implications for the formation and trapping of planets in protoplanetary discs. Finally, we consider our results in light of recent Atacama Large Millimeter Array observations of HL Tau and TW Hya.

  1. Ice erosion of a sea-floor knickpoint at the inner edge of the stamukhi zone, Beaufort Sea, Alaska

    USGS Publications Warehouse

    Barnes, P.W.; Asbury, J.L.; Rearic, D.M.; Ross, C.R.

    1987-01-01

    In 1981 and 1982, detailed bathymetric and side-scan sonar surveys were made of an area of the sea floor north of Prudhoe Bay, Alaska, to study the changing characteristics of the seabed at the inner boundary of the stamukhi zone, the coast-parallel zone of grounded ice ridges that occurs in water depths between 15 and 50 m in the arctic. The fathograms and sonographs resolved 10-cm features and electronic navigation gave relocations accurate to about 10 m. Year after year an ice boundary develops at the inner edge of the stamukhi zone where major shear and pressure deformation occur in about the same location. Associated with this ice boundary, the bathymetry shows a pronounced break in slope - the knickpoint - on the shelf profile at about 20 m depth. The 2-3 m-high knickpoint is cut in a consolidated gravelly mud of pre-Holocene age. A well-defined gravel and cobble shoal a few meters high usually occurs at the inshore edge of the knickpoint. The sonograph mosaic shows that seaward of the knickpoint, ice gouges saturate the sea floor and are well defined; inshore the gouges are fewer in number and are poorly defined on the records. Few gouges can be traced from the seaward side of the knickpoint across the shoals to the inshore side of the knickpoint. Studies of ice gouging rates in two seabed corridors that cross the stamukhi zone reveal the highest rates of gouging seaward of the knickpoint. We believe that the knickpoint results from ice erosion at the inner boundary of the stamukhi zone. Intensified currents associated with this boundary winnow away fine sediments. Ice bulldozing and currents shape the shoals, which perch atop the knickpoint. The knickpoint helps to limit ice forces on the seabed inshore of the stamukhi zone. ?? 1987.

  2. Seasonal Deuterium Excess in a Tien Shan Ice Core: Influence of Moisture Transport and Recycling in Central Asia

    NASA Astrophysics Data System (ADS)

    Kreutz, K. J.; Wake, C. P.; Aizen, V. B.; Cecil, D.; Green, J.; Synal, H.; Introne, D. S.

    2002-12-01

    Stable water isotope (δ18O, δD) data from a high elevation (5100 masl) ice core recovered from the Tien Shan Mountains, Kyrgyzstan, display a seasonal cycle in deuterium excess (d = δD - 8*δ18O) related to changes in the regional hydrologic cycle during 1994-2000. While there is a strong correlation (r2 = 0.98) between δ18O and δD in the ice core samples, the regression slope (6.9) and mean d value (23.0) are significantly different than the global meteoric water line slope of 8 and global d value of 10. The resulting time-series ice core d profile contains distinct winter maxima and summer minima, with a yearly d amplitude of ~15-20 \\permil. Local-scale processes (i.e., sublimation, partial summer melting, snow formation temperature) that may affect d values preserved in the ice core are not consistent with the observed seasonal variability. Rather, we suggest that regional-scale hydrological conditions, including seasonal changes in moisture source, transport, and recycling in the Caspian/Aral Sea region, are responsible for the observed d variability. Examination of data from the Global Network of Isotopes in Precipitation (GNIP) indicates similar seasonal changes in southwestern Central Asian (Afghanistan and Tajikistan), likely related to moisture supply from the Mediterranean Sea during summer. The two years with the highest d values in the ice core record are 1997 and 1998, suggesting a possible link to ENSO ocean/atmosphere variability. The isotope data presented here provide a basis for interpreting centennial-scale ice core d records currently being developed from the region, and highlight the complexity of time-series isotope records from mid-latitude ice cores.

  3. Seasonal Evolution and Interannual Variability of the Local Solar Energy Absorbed by the Arctic Sea Ice-Ocean System

    NASA Technical Reports Server (NTRS)

    Perovich, Donald K.; Nghiem, Son V.; Markus, Thorsten; Schwieger, Axel

    2007-01-01

    The melt season of the Arctic sea ice cover is greatly affected by the partitioning of the incident solar radiation between reflection to the atmosphere and absorption in the ice and ocean. This partitioning exhibits a strong seasonal cycle and significant interannual variability. Data in the period 1998, 2000-2004 were analyzed in this study. Observations made during the 1997-1998 SHEBA (Surface HEat Budget of the Arctic Ocean) field experiment showed a strong seasonal dependence of the partitioning, dominated by a five-phase albedo evolution. QuikSCAT scatterometer data from the SHEBA region in 1999-2004 were used to further investigate solar partitioning in summer. The time series of scatterometer data were used to determine the onset of melt and the beginning of freezeup. This information was combined with SSM/I-derived ice concentration, TOVS-based estimates of incident solar irradiance, and SHEBA results to estimate the amount of solar energy absorbed in the ice-ocean system for these years. The average total solar energy absorbed in the ice-ocean system from April through September was 900 MJ m(sup -2). There was considerable interannual variability, with a range of 826 to 1044 MJ m(sup -2). The total amount of solar energy absorbed by the ice and ocean was strongly related to the date of melt onset, but only weakly related to the total duration of the melt season or the onset of freezeup. The timing of melt onset is significant because the incident solar energy is large and a change at this time propagates through the entire melt season, affecting the albedo every day throughout melt and freezeup.

  4. Seasonal Evolution and Interannual Variability of the Local Solar Energy Absorbed by the Arctic Sea Ice-Ocean System

    NASA Technical Reports Server (NTRS)

    Perovich, Donald K.; Nghiem, Son V.; Markus, Thorsten; Schwieger, Axel

    2007-01-01

    The melt season of the Arctic sea ice cover is greatly affected by the partitioning of the incident solar radiation between reflection to the atmosphere and absorption in the ice and ocean. This partitioning exhibits a strong seasonal cycle and significant interannual variability. Data in the period 1998, 2000-2004 were analyzed in this study. Observations made during the 1997-1998 SHEBA (Surface HEat Budget of the Arctic Ocean) field experiment showed a strong seasonal dependence of the partitioning, dominated by a five-phase albedo evolution. QuikSCAT scatterometer data from the SHEBA region in 1999-2004 were used to further investigate solar partitioning in summer. The time series of scatterometer data were used to determine the onset of melt and the beginning of freezeup. This information was combined with SSM/I-derived ice concentration, TOVS-based estimates of incident solar irradiance, and SHEBA results to estimate the amount of solar energy absorbed in the ice-ocean system for these years. The average total solar energy absorbed in the ice-ocean system from April through September was 900 MJ m(sup -2). There was considerable interannual variability, with a range of 826 to 1044 MJ m(sup -2). The total amount of solar energy absorbed by the ice and ocean was strongly related to the date of melt onset, but only weakly related to the total duration of the melt season or the onset of freezeup. The timing of melt onset is significant because the incident solar energy is large and a change at this time propagates through the entire melt season, affecting the albedo every day throughout melt and freezeup.

  5. Dissolved and particulate trace metal micronutrients under the McMurdo Sound seasonal sea ice: basal sea ice communities as a capacitor for iron

    NASA Astrophysics Data System (ADS)

    Noble, Abigail; Saito, Mak; Moran, Dawn; Allen, Andrew

    2013-10-01

    Dissolved and particulate metal concentrations are reported from three sites beneath and at the base of the McMurdo Sound seasonal sea ice in the Ross Sea of Antarctica. This dataset provided insight into Co and Mn biogeochemistry, supporting a previous hypothesis for water column mixing occurring faster than scavenging. Three observations support this: first, Mn-containing particles with Mn/Al ratios in excess of the sediment were present in the water column, implying the presence of bacterial Mn-oxidation processes. Second, dissolved and labile Co were uniform with depth beneath the sea ice after the winter season. Third, dissolved Co:PO43- ratios were consistent with previously observed Ross Sea stoichiometry, implying that over-winter scavenging was slow relative to mixing. Abundant dissolved Fe and Mn were consistent with a winter reserve concept, and particulate Al, Fe, Mn, and Co covaried, implying that these metals behaved similarly. Elevated particulate metals were observed in proximity to the nearby Islands, with particulate Fe/Al ratios similar to that of nearby sediment, consistent with a sediment resuspension source. Dissolved and particulate metals were elevated at the shallowest depths (particularly Fe) with elevated particulate P/Al and Fe/Al ratios in excess of sediments, demonstrating a sea ice biomass source. The sea ice biomass was extremely dense (chl a >9500 μg/L) and contained high abundances of particulate metals with elevated metal/Al ratios. A hypothesis for seasonal accumulation of bioactive metals at the base of the McMurdo Sound sea ice by the basal algal community is presented, analogous to a capacitor that accumulates iron during the spring and early summer. The release and transport of particulate metals accumulated at the base of the sea ice by sloughing is discussed as a potentially important mechanism in providing iron nutrition during polynya phytoplankton bloom formation and could be examined in future oceanographic expeditions.

  6. Dissolved and particulate trace metal micronutrients under the McMurdo Sound seasonal sea ice: basal sea ice communities as a capacitor for iron.

    PubMed

    Noble, Abigail E; Moran, Dawn M; Allen, Andrew E; Saito, Mak A

    2013-01-01

    Dissolved and particulate metal concentrations are reported from three sites beneath and at the base of the McMurdo Sound seasonal sea ice in the Ross Sea of Antarctica. This dataset provided insight into Co and Mn biogeochemistry, supporting a previous hypothesis for water column mixing occurring faster than scavenging. Three observations support this: first, Mn-containing particles with Mn/Al ratios in excess of the sediment were present in the water column, implying the presence of bacterial Mn-oxidation processes. Second, dissolved and labile Co were uniform with depth beneath the sea ice after the winter season. Third, dissolved Co:PO(3-) 4 ratios were consistent with previously observed Ross Sea stoichiometry, implying that over-winter scavenging was slow relative to mixing. Abundant dissolved Fe and Mn were consistent with a winter reserve concept, and particulate Al, Fe, Mn, and Co covaried, implying that these metals behaved similarly. Elevated particulate metals were observed in proximity to the nearby Islands, with particulate Fe/Al ratios similar to that of nearby sediment, consistent with a sediment resuspension source. Dissolved and particulate metals were elevated at the shallowest depths (particularly Fe) with elevated particulate P/Al and Fe/Al ratios in excess of sediments, demonstrating a sea ice biomass source. The sea ice biomass was extremely dense (chl a >9500 μg/L) and contained high abundances of particulate metals with elevated metal/Al ratios. A hypothesis for seasonal accumulation of bioactive metals at the base of the McMurdo Sound sea ice by the basal algal community is presented, analogous to a capacitor that accumulates iron during the spring and early summer. The release and transport of particulate metals accumulated at the base of the sea ice by sloughing is discussed as a potentially important mechanism in providing iron nutrition during polynya phytoplankton bloom formation and could be examined in future oceanographic

  7. Dissolved and particulate trace metal micronutrients under the McMurdo Sound seasonal sea ice: basal sea ice communities as a capacitor for iron

    PubMed Central

    Noble, Abigail E.; Moran, Dawn M.; Allen, Andrew E.; Saito, Mak A.

    2013-01-01

    Dissolved and particulate metal concentrations are reported from three sites beneath and at the base of the McMurdo Sound seasonal sea ice in the Ross Sea of Antarctica. This dataset provided insight into Co and Mn biogeochemistry, supporting a previous hypothesis for water column mixing occurring faster than scavenging. Three observations support this: first, Mn-containing particles with Mn/Al ratios in excess of the sediment were present in the water column, implying the presence of bacterial Mn-oxidation processes. Second, dissolved and labile Co were uniform with depth beneath the sea ice after the winter season. Third, dissolved Co:PO3−4 ratios were consistent with previously observed Ross Sea stoichiometry, implying that over-winter scavenging was slow relative to mixing. Abundant dissolved Fe and Mn were consistent with a winter reserve concept, and particulate Al, Fe, Mn, and Co covaried, implying that these metals behaved similarly. Elevated particulate metals were observed in proximity to the nearby Islands, with particulate Fe/Al ratios similar to that of nearby sediment, consistent with a sediment resuspension source. Dissolved and particulate metals were elevated at the shallowest depths (particularly Fe) with elevated particulate P/Al and Fe/Al ratios in excess of sediments, demonstrating a sea ice biomass source. The sea ice biomass was extremely dense (chl a >9500 μg/L) and contained high abundances of particulate metals with elevated metal/Al ratios. A hypothesis for seasonal accumulation of bioactive metals at the base of the McMurdo Sound sea ice by the basal algal community is presented, analogous to a capacitor that accumulates iron during the spring and early summer. The release and transport of particulate metals accumulated at the base of the sea ice by sloughing is discussed as a potentially important mechanism in providing iron nutrition during polynya phytoplankton bloom formation and could be examined in future oceanographic

  8. Seasonally chemical hydrology and ecological responses in frontal zone of the central southern Yellow Sea

    NASA Astrophysics Data System (ADS)

    Wei, Qin-Sheng; Li, Xian-Sen; Wang, Bao-Dong; Fu, Ming-Zhu; Ge, Ren-Feng; Yu, Zhi-Gang

    2016-06-01

    Based on annual-cycle survey data collected in 2006-2007 in the southern Yellow Sea (SYS) and analyses on the seasonally chemical hydrologic characteristics of the boundary front of the Yellow Sea Cold Water Mass (YSCWM) and Yellow Sea Warm Current (YSWC), the seasonal variations in upwelling along the frontal zone were determined, and the ecological impacts of the front were investigated. During the generation and dissipation of the YSCWM, the implied upwelling along its western front exhibited seasonal variation. The upwelling first shifted westward from the deep-water region to its westernmost point in summer then returned eastward. The intensity of the upwelling gradually increased from spring to summer and decreased in autumn. In spring, the existence of cold water west of the YSWC was not conducive to the reproduction of phytoplankton. Additionally, the front to the east of this cold water mass also made the western boundary of the phytoplankton bloom region in the central SYS more obvious, forming a prominent chlorophyll a (Chl-a) front. During the entire stratified season (summer and autumn), the upwelling in the frontal zone of the YSCWM played an essential role in maintaining the relatively high concentrations of Chl-a. In winter, the front that formed at the intersection of the YSWC and coastal cold water was also favorable for the formation of the high-Chl-a region. The distribution of anchovy biomass was closely related to the seasonal variations in the position of the frontal zone. In winter and spring, the tongue-shaped warm water and front associated with the intrusion of the YSWC into the SYS had a significant impact on anchovy. During the stratified season in summer and autumn, the development of a front near the boundary of the YSCWM was an important physical driving mechanism for the dense distribution of anchovy. This work enhanced the study of the seasonal relationships between the physical, chemical and biological processes in the frontal

  9. Linkages among geophysical facies, microbial composition, biogeochemical rates, and seasonal hydrology in the hyporheic zone

    NASA Astrophysics Data System (ADS)

    Stegen, J.

    2016-12-01

    The hyporheic zone is a critical ecosystem transition that links terrestrial, aquatic, and subsurface domains. To understand connections among physical, microbial, and biogeochemical components of the hyporheic zone, we obtained freeze cores along the Columbia River in the Hanford 300 Area and performed geologic, molecular, and microbial assays. Mud and sand content were found to be the primary drivers of microbial community attributes (in particular, of nitrite and carbon oxidizers). Microbial community analysis revealed an abundance of nitrifying Archaea (Thaumarchaea) and an absence of nitrifiying Bacteria. Network analysis revealed significant negative correlations between sand content and some statistical modules of microbial taxa, perhaps indicating the importance of pore water residence time on community composition. A similar set of microbial modules was positively correlated with total organic carbon. One such module that also positively correlated with aerobic metabolic rates was dominated by Thaumarchaea and Nitrospira, suggesting that ammonia oxidation was the dominant aerobic process. We also examined temporal changes in hyporheic microbial structure and activity through repeated sampling of attached and pore water microbes across a spatial gradient. We found that microbial communities remained distinct in river, hyporheic, and inland zones across seasonal variation in hydrologic mixing conditions. One reason was temperature-driven increases in microbial species richness in the hyporheic zone. We show that the relative importance of ecological selection and dispersal varied across environments and across geographic zones. Our results also indicated that while selection imposed short-term constraints on microbial community structure, hyporheic sediment communities did not respond to short-term hydrologic variation. Importantly, we demonstrated that the influence of selective pressures varied with phylogenetic affiliation, which may have been responsible

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  11. Seasonality of coastal zone scanner phytoplankton pigment in the offshore oceans

    NASA Technical Reports Server (NTRS)

    Banse, K.; English, D. C.

    1994-01-01

    The NASA Global Ocean Data Set of plant pigment concentrations in the upper euphotic zone is evaluated for diserning geographical and temporal patterns of seasonality in the open sea. Monthly medians of pigment concentrations for all available years are generated for fields of approximately 77,000 sq km. For the climatological year, highest and lowest medians, month of occurence of the highest median, ratio of highest to lowest medians, and absolute range between the highest and lowest medians are mapped ocean-wide between 62.5 deg N and 62.5 deg S. Seasonal cycles are depicted for 48 sites. In much of the offshore ocean, seasonality of pigment is inferred to be driven almost equally by the interaction of the abiotic environment with phytoplankton physiology and the loss of cells from grazing. Special emphasis among natural domains or provinces is given to the Subantarctic water ring, with no seasonality in its low chlorophyll concentrations in spite of strong environmental forcing, and the narrow Transition Zones, a few degrees of latitude on the equatorial sides of the Subtropical Convergences of the southern hemisphere and their homologs in the northern hemisphere, which have late winter blooms caused by nutrient injection into the upper layers.

  12. Seasonality of coastal zone scanner phytoplankton pigment in the offshore oceans

    NASA Technical Reports Server (NTRS)

    Banse, K.; English, D. C.

    1994-01-01

    The NASA Global Ocean Data Set of plant pigment concentrations in the upper euphotic zone is evaluated for diserning geographical and temporal patterns of seasonality in the open sea. Monthly medians of pigment concentrations for all available years are generated for fields of approximately 77,000 sq km. For the climatological year, highest and lowest medians, month of occurence of the highest median, ratio of highest to lowest medians, and absolute range between the highest and lowest medians are mapped ocean-wide between 62.5 deg N and 62.5 deg S. Seasonal cycles are depicted for 48 sites. In much of the offshore ocean, seasonality of pigment is inferred to be driven almost equally by the interaction of the abiotic environment with phytoplankton physiology and the loss of cells from grazing. Special emphasis among natural domains or provinces is given to the Subantarctic water ring, with no seasonality in its low chlorophyll concentrations in spite of strong environmental forcing, and the narrow Transition Zones, a few degrees of latitude on the equatorial sides of the Subtropical Convergences of the southern hemisphere and their homologs in the northern hemisphere, which have late winter blooms caused by nutrient injection into the upper layers.

  13. An Observational and Numerical Study of Marginal Ice Zone Atmospheric Jets

    NASA Astrophysics Data System (ADS)

    Price, D.; Guest, P. S.; Wang, S.; Persson, O. P. G.; Fairall, C. W.

    2016-12-01

    Low level atmospheric jets have been observed to frequently occur in marginal ice zones (MIZs), but little research has been done on the dynamics of these features. During the fall of 2015, during the ONR "Sea State" cruise in the Beaufort Sea, several atmospheric jets were detected in the atmospheric boundary layer or in the capping temperature inversion just above, using radiosondes and shipboard instrumentation. The three strongest jets had maximum wind speeds at elevations near 350 m to 400 m elevation; one of these jets had a secondary maximum wind height at 900 m. Different theories have been suggested as reasons for the existence of MIZ jets including: (1) thermal wind effects where the thermal wind opposes the geostrophic wind due to horizontal temperature changes and/or sloping inversion, (2) inertial effects due to the cut-off of surface friction, similar to nocturnal jets and (3) sea-ice and ice-sea circulations, analogous to land and sea breezes. We present the results of an analysis of the jets based on the in situ measurements, complimented by daily runs of the @COAMPS model by the Naval Research Laboratory. The analysis will consist of reconstructing the 3 dimensional jet scenarios as accurately as possible with emphasis on quantifying the ice edge and location of other surface features compared to the air movement and the vertical location of the jet with respect the atmospheric boundary layer (ABL) and capping inversions. For example, a jet resulting from horizontal temperature differences within an ABL would be expected to result in a wind max within the ABL, while a jet caused by a sloping inversion would be expected to be centered higher up, in the inversion layer. Both these characteristics were observed in different jets. These results will give insights on under what conditions these jets will form, how they can predicted and the resulting impacts on ice cover and sea state.

  14. Wave Climate and Wave Mixing in the Marginal Ice Zones of Arctic Seas, Observations and Modelling

    DTIC Science & Technology

    2013-09-30

    drag coefficient on the directional spreading of ocean waves. J. Geophys. Res., 117, doi:10.1029/2012JC007920, 7p Toffoli, A., L. Loffredo, P . Le Roy...REPORT TYPE 3. DATES COVERED 00-00-2013 to 00-00-2013 4 . TITLE AND SUBTITLE Wave Climate and Wave Mixing in the Marginal Ice Zones of Arctic Seas...developed for obtaining trends based on short ( 4 -year) segments of the altimeter records. This technique will be used to investigate wave climate

  15. A 21-Year Record of Arctic Sea Ice Extents and Their Regional, Seasonal, and Monthly Variability and Trends

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.; Cavalieri, Donald J.; Zukor, Dorothy J. (Technical Monitor)

    2001-01-01

    Satellite passive-microwave data have been used to calculate sea ice extents over the period 1979-1999 for the north polar sea ice cover as a whole and for each of nine regions. Over this 21-year time period, the trend in yearly average ice extents for the ice cover as a whole is -32,900 +/- 6,100 sq km/yr (-2.7 +/- 0.5 %/decade), indicating a reduction in sea ice coverage that has decelerated from the earlier reported value of -34,000 +/- 8,300 sq km/yr (-2.8 +/- 0.7 %/decade) for the period 1979-1996. Regionally, the reductions are greatest in the Arctic Ocean, the Kara and Barents Seas, and the Seas of Okhotsk and Japan, whereas seasonally, the reductions are greatest in summer, for which season the 1979-1999 trend in ice extents is -41,600 +/- 12,900 sq km/ yr (-4.9 +/- 1.5 %/decade). On a monthly basis, the reductions are greatest in July and September for the north polar ice cover as a whole, in September for the Arctic Ocean, in June and July for the Kara and Barents Seas, and in April for the Seas of Okhotsk and Japan. Only two of the nine regions show overall ice extent increases, those being the Bering Sea and the Gulf of St. Lawrence.For neither of these two regions is the increase statistically significant, whereas the 1079 - 1999 ice extent decreases are statistically significant at the 99% confidence level for the north polar region as a whole, the Arctic Ocean, the Seas of Okhotsk and Japan, and Hudson Bay.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  17. Changes in ice geometry and supraglacial hydrology, Sermeq Avannarleq ablation zone, West Greenland

    NASA Astrophysics Data System (ADS)

    McLamb, W. S.; Colgan, W.; Phillips, T. P.; Abdalati, W.; Steffen, K.; Motyka, R. J.; Rajaram, H.

    2010-12-01

    Our study quantifies changes in ice geometry and surface hydrology within a ~30 by 50 km study area in the ablation zone of the Sermeq (Glacier) Avannarleq over the period 1985 to 2009. To investigate changes in surface hydrology, we compare a 1985 supraglacial topography map created by the Grønlands Geologiske Undersøgelse (GGU) accompanied by the panchromatic orthomosaic from which it was generated, and a 2009 panchromatic WorldView-1image of the same region. A 1985 digital elevation model (DEM) was created by manually digitizing the GGU map contour lines and performing a spline interpolation of these values into a 100 m spatial resolution DEM. Differencing the 1985 DEM from a 2009 ASTER DEM yields a mean thinning rate of 1.23 ± 1.29 m/a in the ablation zone and a mean thickening rate of 0.09 ± 1.29 m/a in the accumulation zone. Analysis of secondary DEM attributes suggests a significant increase (p < 0.05, t = 115.8, df = 128605) in mean surface slope from 2.12° in 1985 (σ 1.91°) to 2.68° in 2009 (σ 1.88°). From manual delineations of the ice sheet margin in both the 2009 WorldView-1 imagery and the 1985 GGU map, we calculate a mean rate of marginal recession (of predominately land terminating ice) of 9.4 ± 1.3 m/a. We quantify the distribution of supraglacial rivers in the southern 1/3 of our study area by classifying the regions that contain surface water (i.e. rivers) and those which do not. The classification algorithm is based on fuzzy set theory and user defined parameters to “defuzzify” unclear membership regions based on surrounding pixel values and density. Preliminary results of the river comparison between 1985 orthomosaic and 2009 WorldView-1 image suggest that the river system has been substantially reorganized in some areas, presumably due to increased crevassing and surface melt. In other areas, the locations of major river channels are persistent over the study time period, resulting in geographic variability of perennial stream

  18. Seasonal variation of water quality in a lateral hyporheic zone with response to dam operations

    NASA Astrophysics Data System (ADS)

    Chen, X.; Chen, L.; Zhao, J.

    2015-12-01

    Aquatic environment of lateral hyporheic zone in a regulated river were investigated seasonally under fluctuated water levels induced by dam operations. Groundwater levels variations in preassembled wells and changes in electronic conductivity (EC), dissolved oxygen (DO) concentration, water temperature and pH in the hyporheic zone were examined as environmental performance indicators for the water quality. Groundwater tables in wells were highly related to the river water levels that showed a hysteresis pattern, and the lag time is associated with the distances from wells to the river bank. The distribution of DO and EC were strongly related to the water temperature, indicating that the cold water released from up-reservoir could determine the biochemistry process in the hyporheic zone. Results also showed that the hyporheic water was weakly alkaline in the study area but had a more or less uniform spatial distribution. Dam release-storage cycles were the dominant factor in changing lateral hyporheic flow and water quality.

  19. Seasonal deuterium excess in a Tien Shan ice core: Influence of moisture transport and recycling in Central Asia

    USGS Publications Warehouse

    Kreutz, K.J.; Wake, C.P.; Aizen, V.B.; DeWayne, Cecil L.; Synal, H.-A.

    2003-01-01

    Stable water isotope (??18O, ??D) data from a high elevation (5100 masl) ice core recovered from the Tien Shan Mountains, Kyrgyzstan, display a seasonal cycle in deuterium excess (d = ??D - 8*??18O) related to changes in the regional hydrologic cycle during 1994-2000. While there is a strong correlation (r2 = 0.98) between ??18O and ??D in the ice core samples, the regression slope (6.9) and mean d value (23.0) are significantly different than the global meteoric water line values. The resulting time-series ice core d profile contains distinct winter maxima and summer minima, with a yearly d amplitude of ???15-20???. Local-scale processes that may affect d values preserved in the ice core are not consistent with the observed seasonal variability. Data from Central Asian monitoring sites in the Global Network of Isotopes in Precipitation (GNIP) have similar seasonal d changes. We suggest that regional-scale hydrological conditions, including seasonal changes in moisture source, transport, and recycling in the Caspian/Aral Sea region, are responsible for the observed spatial and temporal d variability.

  20. How robust are in situ observations for validating satellite-derived albedo over the dark zone of the Greenland Ice Sheet?

    NASA Astrophysics Data System (ADS)

    Ryan, J. C.; Hubbard, A.; Irvine-Fynn, T. D.; Doyle, S. H.; Cook, J. M.; Stibal, M.; Box, J. E.

    2017-06-01

    Calibration and validation of satellite-derived ice sheet albedo data require high-quality, in situ measurements commonly acquired by up and down facing pyranometers mounted on automated weather stations (AWS). However, direct comparison between ground and satellite-derived albedo can only be justified when the measured surface is homogeneous at the length-scale of both satellite pixel and in situ footprint. Here we use digital imagery acquired by an unmanned aerial vehicle to evaluate point-to-pixel albedo comparisons across the western, ablating margin of the Greenland Ice Sheet. Our results reveal that in situ measurements overestimate albedo by up to 0.10 at the end of the melt season because the ground footprints of AWS-mounted pyranometers are insufficient to capture the spatial heterogeneity of the ice surface as it progressively ablates and darkens. Statistical analysis of 21 AWS across the entire Greenland Ice Sheet reveals that almost half suffer from this bias, including some AWS located within the wet snow zone.

  1. Revisiting the potential of melt pond fraction as a predictor for the seasonal Arctic sea ice extent minimum

    NASA Astrophysics Data System (ADS)

    LIU, J.; Song, M.; Horton, R. M.; Hu, Y.

    2015-12-01

    Seasonal sea ice prediction is challenging because of high variability in diverse atmospheric and oceanic influences, and because the Arctic climate is changing in ways without precedent for at least the past millennium. A recent modeling study that employed a prognostic melt pond model in a stand-alone sea ice model found that September Arctic sea ice extent can be accurately predicted from the melt pond fraction in May. Here we show that satellite observations do not support the model-based finding that the melt pond fraction in May has the strongest impact on September sea ice extent. Instead, we see no evidence of predictive skill in May. We find that a significantly strong relationship first emerges as the melt pond fraction is integrated from early May to late June, with a persistent strong relationship only occurring after late July. Our results highlight that late spring to mid summer melt pond information is required to improve the prediction skill of the seasonal sea ice minimum. Furthermore, satellite observations indicate a much higher percentage of melt pond formation in May than does the aforementioned model simulation, which points to the need to reconcile model simulations and observations, in order to better understand key mechanisms of melt pond formation and evolution and their influence on sea ice state.

  2. Revisiting the Potential of Melt Pond Fraction as a Predictor for the Seasonal Arctic Sea Ice Extent Minimum

    NASA Technical Reports Server (NTRS)

    Liu, Jiping; Song, Mirong; Horton, Radley M.; Hu, Yongyun

    2015-01-01

    The rapid change in Arctic sea ice in recent decades has led to a rising demand for seasonal sea ice prediction. A recent modeling study that employed a prognostic melt pond model in a stand-alone sea ice model found that September Arctic sea ice extent can be accurately predicted from the melt pond fraction in May. Here we show that satellite observations show no evidence of predictive skill in May. However, we find that a significantly strong relationship (high predictability) first emerges as the melt pond fraction is integrated from early May to late June, with a persistent strong relationship only occurring after late July. Our results highlight that late spring to mid summer melt pond information is required to improve the prediction skill of the seasonal sea ice minimum. Furthermore, satellite observations indicate a much higher percentage of melt pond formation in May than does the aforementioned model simulation, which points to the need to reconcile model simulations and observations, in order to better understand key mechanisms of melt pond formation and evolution and their influence on sea ice state.

  3. Simple energy balance model resolving the seasons and the continents - Application to the astronomical theory of the ice ages

    NASA Technical Reports Server (NTRS)

    North, G. R.; Short, D. A.; Mengel, J. G.

    1983-01-01

    An analysis is undertaken of the properties of a one-level seasonal energy balance climate model having explicit, two-dimensional land-sea geography, where land and sea surfaces are strictly distinguished by the local thermal inertia employed and transport is governed by a smooth, latitude-dependent diffusion mechanism. Solutions of the seasonal cycle for the cases of both ice feedback exclusion and inclusion yield good agreements with real data, using minimal turning of the adjustable parameters. Discontinuous icecap growth is noted for both a solar constant that is lower by a few percent and a change of orbital elements to favor cool Northern Hemisphere summers. This discontinuous sensitivity is discussed in the context of the Milankovitch theory of the ice ages, and the associated branch structure is shown to be analogous to the 'small ice cap' instability of simpler models.

  4. The seasonal appearance of ice shelf water in coastal Antarctica and its effect on sea ice growth

    NASA Astrophysics Data System (ADS)

    Mahoney, Andrew R.; Gough, Alexander J.; Langhorne, Patricia J.; Robinson, Natalie J.; Stevens, Craig L.; Williams, Michael M. J.; Haskell, Timothy G.

    2011-11-01

    In this paper we report measurements from the first year-round mooring underneath sea ice in McMurdo Sound, Antarctica, which we combine with full-depth ocean profiles to identify the incremental appearance of potentially supercooled ice shelf water (ISW). We investigate the effects of ISW on sea ice using observations of sea ice growth and crystal structure together with under-ice photography. We show that the appearance of ISW at the surface leads to a disruption in the columnar texture of the sea ice, but that persistent growth enhancement occurs only once the entire water column has cooled to the surface freezing point. In doing so, we demonstrate the possibility of inferring the presence of ISW beneath sea ice through crystallographic analysis of cores. These findings will be useful for both modeling and observing the extent of ISW-enhanced ice growth. In addition, we found that the local growth of first-year landfast sea ice only accounted for half of the observed increase in salinity over the water column, which indicates that polynyas are responsible for approximately half of the salt flux into McMurdo Sound.

  5. Response of Arctic Snow and Sea Ice Extents to Melt Season Atmospheric Forcing Across the Land-Ocean Boundary

    NASA Astrophysics Data System (ADS)

    Bliss, A. C.; Anderson, M. R.

    2011-12-01

    Little research has gone into studying the concurrent variations in the annual loss of continental snow cover and sea ice extent across the land-ocean boundary, however, the analysis of these data averaged spatially over three study regions located in North America and Eastern and Western Russia, reveals a distinct difference in the response of anomalous snow and sea ice conditions to the atmospheric forcing. This study compares the monthly continental snow cover and sea ice extent loss in the Arctic, during the melt season months (May-August) for the period 1979-2007, with regional atmospheric conditions known to influence summer melt including: mean sea level pressures, 925 hPa air temperatures, and mean 2 m U and V wind vectors from NCEP/DOE Reanalysis 2. The monthly hemispheric snow cover extent data used are from the Rutgers University Global Snow Lab and sea ice extents for this study are derived from the monthly passive microwave satellite Bootstrap algorithm sea ice concentrations available from the National Snow and Ice Data Center. Three case study years (1985, 1996, and 2007) are used to compare the direct response of monthly anomalous sea ice and snow cover areal extents to monthly mean atmospheric forcing averaged spatially over the extent of each study region. This comparison is then expanded for all summer months over the 29 year study period where the monthly persistence of sea ice and snow cover extent anomalies and changes in the sea ice and snow conditions under differing atmospheric conditions are explored further. The monthly anomalous atmospheric conditions are classified into four categories including: warmer temperatures with higher pressures, warmer temperatures with lower pressures, cooler temperatures with higher pressures, and cooler temperatures with lower pressures. Analysis of the atmospheric conditions surrounding anomalous loss of snow and ice cover over the independent study regions indicates that conditions of warmer temperatures

  6. Liriomyza Leafminer (Diptera: Agromyzidae) Parasitoid Complex in Different Agroecological Zones, Seasons, and Host Plants in Kenya.

    PubMed

    Foba, C N; Salifu, D; Lagat, Z O; Gitonga, L M; Akutse, K S; Fiaboe, K K M

    2016-04-01

    Liriomyza leafminers (Diptera: Agromyzidae) are severe pests of vegetables and ornamentals worldwide. Previous studies revealed low leafminer parasitism across different agroecological zones in Kenya. The present paper reports on the composition of leafminer parasitoids at different elevations, in different seasons, and on different host crops. Surveys were conducted monthly from January to November 2012, and nine parasitoid species were recovered. Total mean parasitism in the study sites was 31.23 ± 1.03% from a total of 20 different vegetable Liriomyza-infested crops belonging to seven families. Diglyphus isaea (Walker) (Hymenoptera: Eulophidae), Phaedrotoma scabriventris, a newly released parasitoid, and Opius dissitus Muesebeck (Hymenoptera: Braconidae) were the most abundant at all elevations, accounting for 67.3, 18.6, and 9.2% of total parasitoids, respectively. Elevation, season, and host crop significantly affected the parasitoid species present and their abundance. Diglyphus isaea was more abundant at the high- and mid-elevations at all seasons compared with the low-elevation, whereas the lower-elevation favored higher abundance of P. scabriventris and O. dissitus during the long rainy season compared with the high- and mid-elevations at all seasons. Of all the host crops surveyed, parasitoids were more abundant on tomato, local kidney bean, snow pea and French bean than other crops. The total parasitism rate observed in this study suggests a considerable improvement in leafminer parasitism compared with previous surveys in Kenya. The implications of these findings for leafminer management in vegetable and ornamental production in Kenya are discussed.

  7. Satellite Remote Sensing of the Dependence of Homogeneous Ice Nucleation on Latitude and Season

    NASA Astrophysics Data System (ADS)

    Mitchell, D. L.; Garnier, A.; Avery, M. A.; Erfani, E.

    2015-12-01

    Cirrus clouds can be thought of as belonging to one of two categories: those formed through (1) homo- and (2) heterogeneous ice nucleation (henceforth hom and het) due to the very different microphysical and radiative properties associated with these two mechanisms. Hom cirrus will form only when atmospheric ice nuclei (IN) are sufficiently low in concentration, and studies suggest that mineral dust may account for most IN globally. Hence the occurrence of hom and het cirrus is likely to depend on latitude and season as mineral dust does, making satellite remote sensing the preferred method for characterizing this occurrence. A new understanding of thermal absorption in two split-window channels renders a reinterpretation of a standard CALIPSO satellite retrieval; the effective absorption optical depth ratio or βeff. Using earlier studies and aircraft measurements in cirrus clouds, βeff is found to be tightly related to the ice particle number concentration/ice water content ratio, or N/IWC, and thresholds for hom cirrus are estimated in terms of N/IWC and βeff. When applied to cold semi-transparent cirrus clouds, we find that (1) polar cirrus (T < -38 C) occur much more often during winter than summer and (2) hom cirrus prevail at high latitudes during winter, and during spring and fall over Antarctica. The figure shows estimates of the fraction of cirrus produced by hom (where βeff > 1.15) during January and August, where green is ~ 50% and red ~ 90-100%. These high N/IWC values associated with hom cirrus occur in regions where mineral dust concentrations are predicted to be minimal. This high N/IWC condition during winter is likely to have a strong greenhouse effect that may increase high latitude temperatures by 2-5°K relative to conditions where het cirrus dominates (Storelvmo et al. 2014, Philos. Trans. A, Royal Soc.). Thus, the lack of mineral dust in the high latitudes during winter may result in a strong warming influence over these regions. Moreover

  8. Interannual and seasonal changes in the north polar ice deposits of Mars: Observations from MY 29-31 using MARCI

    NASA Astrophysics Data System (ADS)

    Calvin, W. M.; James, P. B.; Cantor, B. A.; Dixon, E. M.

    2015-05-01

    The MARCI camera on the Mars Reconnaissance Orbiter provides daily synoptic coverage that allows monitoring of seasonal cap retreat and interannual changes that occur between Mars year (MY) and over the northern summer. The northern seasonal cap evolution was observed in MY 29, 30 and 31 (12/2007-04/2012). Observation over multiple Mars years allows us to compare changes between years as well as longer-term evolution of the high albedo deposits at the poles. Significant variability in the early season is noted in all years and the retreating seasonal cap edge is extremely dynamic. Detailed coverage of the entire seasonal and residual ice caps allows a broader view of variations in the high albedo coverage and identifies numerous regions where high albedo areas are changing with time. Large areas of disappearance and reappearance of high albedo features (Gemini Scopuli) are seasonally cyclical, while smaller areas are variable on multi-year time scales (Abalso Mensae and Olympia Planitia). These seasonal and interannual changes directly bear on the surface-atmosphere exchange of dust and volatiles and understanding the current net processes of deposition and erosion of the residual ice deposits. Local and regional variation in high albedo areas reflects an interplay between frost deposition, evolution, and sublimation along with deposition and removal of dust.

  9. Pelagic ciliate communities within the Amundsen Sea polynya and adjacent sea ice zone, Antarctica

    NASA Astrophysics Data System (ADS)

    Jiang, Yong; Liu, Qian; Yang, Eun Jin; Wang, Min; Kim, Tae Wan; Cho, Kyoung-Ho; Lee, SangHoon

    2016-01-01

    Polynyas, areas of open water surrounded by sea ice, are sites of intense primary production and ecological hotspots in the Antarctic Ocean. This study determined the spatial variation in communities of pelagic ciliates in an Amundsen Sea polynya (ASP) and adjacent sea ice zones (SIZ) during austral summer from February to March 2012, and the results were compared with biotic and abiotic environmental factors. The species number, abundance and biomass were higher in the ASP than SIZ. Canonical analysis indicated that the communities in the ASP were distinct from those under the sea ice. The pelagic ciliate community structure was closely correlated with environmental variability. Several primary environmental variables, both alone and in combination, were found to affect community spatial patterns. The ciliate biomasses in the ASP and SIZ areas were both significantly correlated with total and nano-Chl a. This analysis of the ciliated microzooplankton communities associated with high primary production provides new insights into the roles of ciliates in biogeochemical cycles in high-latitude polynyas. Additionally, our findings provide detailed data on the composition, distribution, and structure of polynya ciliate communities in the Amundsen Sea.

  10. Sedimentary record of a Pleistocene ice-sheet interlobate zone (NE Poland)

    NASA Astrophysics Data System (ADS)

    Gruszka, Beata; Morawski, Wojciech; Zieliński, Tomasz

    2012-08-01

    Well developed NE-SW trending corridors of outwash in NE Poland are associated with a series of lakes with a similar direction of elongation. The glaciofluvial corridor under study consists of parallel ridges with associated channels and kames. The deposits are flanked by till and hummocky terrain. The gravel ridges are composed of sand and gravel deposits that are cross-stratified, massive or graded, and that contain cut-and-fill structures and large intra-clasts of sand and gravel. Locally the deposits show normal faults. The succession of one of the ridges is interpreted to reflect the infilling of a braided channel in a crevasse. Sedimentation took place in some phases when the ice-sheet regime changed from active to stagnant. Sandy-gravel ridges occur within this complex perpendicular to the Weichselian ice-sheet margin. The corridor is interpreted as an interlobate area in the zone between the Warmia and Mazury ice lobes. The braided-channel deposits are not comparable to typical Polish sandurs. The lithofacies characteristics show higher energy conditions, and the channels are deeper than those typical of Pleistocene lowland sandurs. The sand and gravel ridges are interpreted as interlobate eskers.

  11. Supraglacial Lakes in the Percolation Zone of the Western Greenland Ice Sheet: Formation and Development using Operation IceBridge Snow Radar and ATM (2009-2014)

    NASA Astrophysics Data System (ADS)

    Chen, C.; Howat, I. M.; de la Peña, S.

    2015-12-01

    Surface meltwater lakes on the Greenland Ice Sheet have appeared at higher elevations, extending well into the percolation zone, under recent warming, with the largest expansion occurring in the western Greenland Ice Sheet. The conditions that allow lakes to form atop firn are poorly constrained, but the formation of new lakes imply changes in the permeability of the firn at high elevations, promoting meltwater runoff. We explore the formation and evolution of new surface lakes in this region above 1500 meters, using a combination of satellite imagery and repeat Snow (2-6.5 GHz) radar echograms and LIDAR measurements from NASA's Operation IceBridge of 2009-2014. We identify conditions for surface lake formation at their farthest inland extent and suggest behaviors of persistence and lake drainage are due to differences in regional ice dynamics.

  12. Vadose Zone as a Potential Carbon Source: a Look at Seasonal Spikes in Hyporheic Zone pCO2

    NASA Astrophysics Data System (ADS)

    Brandes, J.

    2016-12-01

    Connections between soils, terrestrial streams and the atmosphere are not yet thoroughly understood as contributing factors to the global carbon budget. We collected data from an undisturbed soil column adjacent to a small stream in a forested watershed in the H. J. Andrews Experimental Forest in the Western Cascades of Oregon in the United States. Our data includes: CO2 (ppm); temperature (oC); depth below water table (m); and soil moisture (cm3/cm3) and spans approximately one year. We are analyzing the data using the gradient method and have observed distinct seasonal patterns which may support previous research describing temporal processes. We can expect to see changing soil moisture characteristics which may promote either vertical CO2 diffusion out of the surface or vertical/lateral advection into subsurface flow. We hypothesize that there is flushing of soil CO2 into the hyporheic zone during precipitation events following soil CO2 buildup.

  13. Seasonal and spatial variability of heterogeneous ice formation in stratiform clouds and its possible impact on precipitation formation

    NASA Astrophysics Data System (ADS)

    Seifert, P.; Ansmann, A.; Baars, H.; Buehl, J.; Kanitz, T.; Bohlmann, S.; Engelmann, R.; Kunz, C.

    2015-12-01

    Lidar observations of stratiform mid-level clouds were used to investigate the efficiency of heterogeneous ice nucleation as a function of cloud top temperature. The long-term lidar-based cloud datasets were collected in Germany (51°N,12°E), in southeastern China (22°N,112°E), Cape Verde (15°N,24°W), the Amazon Basin (1°N,60°W), South Africa (34°S,19°E), and southern Chile (53°S,71°W). They thus cover a variety of northern- and southern latitudinal belts from the midlatitudes to the tropics. Observations of the depolarization ratio were used to categorize the observed cloud layers into either ice-free (no depolarized signals observed) or ice-containing clouds (signals depolarized by scattering at ice crystals). Strong hemispheric and regional differences were observed in the heterogeneous ice formation efficiency at the different sites, especially in the high-temperature range between -20 and 0 °C. The fraction of ice containing clouds in this temperature range is highest at the northern-latitudinal sites of Germany and southeastern China. Over Leipzig, 50% of all clouds contain ice at -10 °C. In contrast, over southern Chile virtually no ice-containing clouds were observed between -20 and 0 °C. Seasonal differences in the ice-cloud fraction were found over Germany and the Amazon Basin. The observed regional, hemispheric and seasonal contrasts can be explained by differences in the aerosol concentration at cloud level above the different sites. Cloud vertical motion (observed with Doppler lidar), which also determine the microphysical cloud evolution, were found to be similar for all cloud layers. From combined observations of cloud radar and lidar at Leipzig it was in addition found that ice water contents of below approx. 10-6kg/m³ cannot be detected with lidar. Clouds classified as pure liquid from the lidar-only observations thus could contain ice water contents of below that threshold. Considering the hemispheric differences in heterogeneous

  14. Multi-model seasonal forecast of Arctic sea-ice: forecast uncertainty at pan-Arctic and regional scales

    NASA Astrophysics Data System (ADS)

    Blanchard-Wrigglesworth, E.; Barthélemy, A.; Chevallier, M.; Cullather, R.; Fučkar, N.; Massonnet, F.; Posey, P.; Wang, W.; Zhang, J.; Ardilouze, C.; Bitz, C. M.; Vernieres, G.; Wallcraft, A.; Wang, M.

    2016-10-01

    Dynamical model forecasts in the Sea Ice Outlook (SIO) of September Arctic sea-ice extent over the last decade have shown lower skill than that found in both idealized model experiments and hindcasts of previous decades. Additionally, it is unclear how different model physics, initial conditions or forecast post-processing (bias correction) techniques contribute to SIO forecast uncertainty. In this work, we have produced a seasonal forecast of 2015 Arctic summer sea ice using SIO dynamical models initialized with identical sea-ice thickness in the central Arctic. Our goals are to calculate the relative contribution of model uncertainty and irreducible error growth to forecast uncertainty and assess the importance of post-processing, and to contrast pan-Arctic forecast uncertainty with regional forecast uncertainty. We find that prior to forecast post-processing, model uncertainty is the main contributor to forecast uncertainty, whereas after forecast post-processing forecast uncertainty is reduced overall, model uncertainty is reduced by an order of magnitude, and irreducible error growth becomes the main contributor to forecast uncertainty. While all models generally agree in their post-processed forecasts of September sea-ice volume and extent, this is not the case for sea-ice concentration. Additionally, forecast uncertainty of sea-ice thickness grows at a much higher rate along Arctic coastlines relative to the central Arctic ocean. Potential ways of offering spatial forecast information based on the timescale over which the forecast signal beats the noise are also explored.

  15. Multi-model seasonal forecast of Arctic sea-ice: forecast uncertainty at pan-Arctic and regional scales

    NASA Astrophysics Data System (ADS)

    Blanchard-Wrigglesworth, E.; Barthélemy, A.; Chevallier, M.; Cullather, R.; Fučkar, N.; Massonnet, F.; Posey, P.; Wang, W.; Zhang, J.; Ardilouze, C.; Bitz, C. M.; Vernieres, G.; Wallcraft, A.; Wang, M.

    2017-08-01

    Dynamical model forecasts in the Sea Ice Outlook (SIO) of September Arctic sea-ice extent over the last decade have shown lower skill than that found in both idealized model experiments and hindcasts of previous decades. Additionally, it is unclear how different model physics, initial conditions or forecast post-processing (bias correction) techniques contribute to SIO forecast uncertainty. In this work, we have produced a seasonal forecast of 2015 Arctic summer sea ice using SIO dynamical models initialized with identical sea-ice thickness in the central Arctic. Our goals are to calculate the relative contribution of model uncertainty and irreducible error growth to forecast uncertainty and assess the importance of post-processing, and to contrast pan-Arctic forecast uncertainty with regional forecast uncertainty. We find that prior to forecast post-processing, model uncertainty is the main contributor to forecast uncertainty, whereas after forecast post-processing forecast uncertainty is reduced overall, model uncertainty is reduced by an order of magnitude, and irreducible error growth becomes the main contributor to forecast uncertainty. While all models generally agree in their post-processed forecasts of September sea-ice volume and extent, this is not the case for sea-ice concentration. Additionally, forecast uncertainty of sea-ice thickness grows at a much higher rate along Arctic coastlines relative to the central Arctic ocean. Potential ways of offering spatial forecast information based on the timescale over which the forecast signal beats the noise are also explored.

  16. Hydrogen isotope composition of dry season atmospheric water vapor on Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Samuels-Crow, K. E.; Galewsky, J.; Hardy, D. R.; Braun, C.

    2011-12-01

    In-situ measurements of modern meteorological conditions at Quelccaya Ice Cap's summit, including the isotopic composition of atmospheric water vapor, may aid in the interpretation of the 1500-year, annually resolved ice-core record available from the site (Thompson et al., 2003). Betweeen July 7 and July 9, 2011, we collected 11 samples of atmospheric water vapor from the summit of Quelccaya and analyzed the hydrogen isotopic composition on a Finnegan MAT-252 mass spectrometer using the method of Strong et al 2007. δD values ranged from -134% to -168%, and specific humidity ranged from 1.5 to 3 g/kg. The isotopic composition of tropical Andean ice cores has been variously interpreted in terms of simple Rayleigh distillation models, in which water evaporates from the tropical Atlantic and condenses as it moves upslope (Grootes et al., 1989; Pierrehumbert, 1999), or in terms of the condensation temperature (Thompson et al., 2003). The joint distribution of water vapor concentrations and δD values in our dataset cannot be explained by a simple upslope Rayleigh distillation model. Such a model predicts higher water-vapor concentrations and lower δD values than those measured during the sampling period. We hypothesize that the joint distribution of water vapor mixing ratio and isotopic composition can be explained by large-scale mixing of air parcels that were last saturated in the upper tropical troposphere. Such mixing necessarily leads to parcels that have higher delta values than would be expected for the simple Rayleigh distillation to the observed mixing ratio. Local effects of snow sublimation may exert additional controls over the water-vapor mixing ratio and delta values. Further monitoring during both the wet and dry seasons may clarify the relationship between large-scale water-vapor transport and the snow and ice preserved on Quelccaya. References Friedman, I. (1953) Deuterium content of natural waters and other substances, Geoch. et Cosmochim. Acta, 4

  17. Effects of thermal vapor diffusion on seasonal dynamics of water in the unsaturated zone

    USGS Publications Warehouse

    Milly, P.C.D.

    1996-01-01

    The response of water in the unsaturated zone to seasonal changes of temperature (T) is determined analytically using the theory of nonisothermal water transport in porous media, and the solutions are tested against field observations of moisture potential and bomb fallout isotopic (36Cl and3H) concentrations. Seasonally varying land surface temperatures and the resulting subsurface temperature gradients induce thermal vapor diffusion. The annual mean vertical temperature gradient is close to zero: however, the annual mean thermal vapor flux is downward, because the temperature-dependent vapor diffusion coefficient is larger, on average, during downward diffusion (occurring at high T) than during upward diffusion (low T). The annual mean thermal vapor flux is shown to decay exponentially with depth; the depth (about 1 m) at which it decays to ??-1 of its surface value is one half of the corresponding decay depth for the amplitude of seasonal temperature changes. This depth-dependent annual mean flux is effectively a source of water, which must be balanced by a flux divergence associated with other transport processes. In a relatively humid environment the liquid fluxes greatly exceed the thermal vapor fluxes, so such a balance is readily achieved without measurable effect on the dynamics of water in the unsaturated zone. However, if the mean vertical water flux through the unsaturated zone is very small (<1 mm y-1), as it may be at many locations in a desert landscape, the thermal vapor flux must be balanced mostly by a matric-potential-induced upward flux of water. This return flux may include both vapor and liquid components. Below any near-surface zone of weather- related fluctuations of matric potential, maintenance of this upward flux requires an increase with depth in the annual mean matric potential; this theoretical prediction is supported by long-term field measurements in the Chihuahuan Desert. The analysis also makes predictions, confirmed by the field

  18. Is there any seasonal variation in marine nematodes within the sediments of the intertidal zone?

    PubMed

    Yodnarasri, Supaporn; Montani, Shigeru; Tada, Kuninao; Shibanuma, Seiichiro; Yamada, Toshiro

    2008-01-01

    The sediment parameters and nematode assemblages in the intertidal zone of the Hichirippu shallow lagoon, Hokkaido, Japan, were investigated. The objectives of this study were to observe the seasonal variation in the nematodes in the sediment, and to investigate the relationships between the nematodes and environmental factors. Samples were collected bi-monthly from five stations on the tidal flat from April 2003 to February 2004. It was found that the sediment parameters (Chl a concentration, AVS, TOC and TN contents) varied throughout the 10-month study. Fifty-four species of nematodes were found in the study area. The density and biomass of the nematodes varied in accordance with the sediment temperature during the sampling period. In this study, there was a seasonal variation in the nematode assemblage found in the intertidal zone of this shallow lagoon. The important factors affecting this variation were sediment temperature, and food competition among the nematodes themselves. The seasonal variation of the nematode also showed a relationship with the Chl a concentration in the sediment during the sampling period.

  19. Near-inertial current oscillations in the vicinity of the Bering Sear marginal ice zone

    NASA Astrophysics Data System (ADS)

    Lagerloef, Gary S. E.; Muench, Robin D.

    1987-10-01

    Near-inertial current oscillations with 10-20-cm/s amplitudes were prevalent over the Bering Sea shelf during November 1982 and again in March and April 1983 and also evident at reduced amplitudes during the intervening winter. Spectral peak frequencies were consistently within ˜1% of the local inertial frequency ƒ, in contrast to the more superinertial (˜5% aboveƒ) frequencies commonly reported elsewhere. A superinertial secondary energy peak at 1.038ƒ was evident, corresponding to the first-mode wave. Amplitudes decreased with distance shoreward from the shelf break, consistent with the effects of decreasing bottom depth and increasing mixed layer depth. The oscillations were highly coherent over ˜100 km distances, similar to observations reported by Thomson and Huggett (1981) for the British Columbia coast, whereas near-inertial oscillations have been commonly reported to be uncoupled over much shorter (˜10 km) distances in other regions. Vigorous near-inertial "ringing" was associated with rapidly passing weather systems. The decline in near-inertial oscillation amplitudes during winter was partially due to a significant reduction in both cyclone frequency and occurrence of wind events causing clockwise wind shifts. The decline was enhanced by reduction in the vertical stratification needed to support inertio-gravity internal waves, as the shelf waters apparently became mixed from top to bottom. The loose, mobile sea ice in the winter marginal ice zone (MIZ) did not appear to inhibit wind generation of the inertial oscillations. The presence of sea ice appears, in fact, to have contributed to the spring increase of near-inertial current amplitudes through restratification of the water column caused by melting ice. Our observations, particularly the spatial coherency and spectral properties, were generally consistent with Kundu and Thomson's (1985) model for inertio-gravity waves generated in the wake of a translating weather front. The half wavelength

  20. Multi-frequency SAR, SSM/I and AVHRR derived geophysical information of the marginal ice zone

    NASA Technical Reports Server (NTRS)

    Shuchman, R. A.; Onstott, R. G.; Wackerman, C. C.; Russel, C. A.; Sutherland, L. L.; Johannessen, O. M.; Johannessen, J. A.; Sandven, S.; Gloerson, P.

    1991-01-01

    A description is given of the fusion of synthetic aperture radar (SAR), special sensor microwave imager (SSM/I), and NOAA Advanced Very High Resolution Radiometer (AVHRR) data to study arctic processes. These data were collected during the SIZEX/CEAREX experiments that occurred in the Greenland Sea in March of 1989. Detailed comparisons between the SAR, AVHRR, and SSM/I indicated: (1) The ice edge position was in agreement to within 25 km, (2) The SSM/I SAR total ice concentration compared favorably, however, the SSM/I significantly underpredicted the multiyear fraction, (3) Combining high resolution SAR with SSM/I can potentially map open water and new ice features in the marginal ice zone (MIZ) which cannot be mapped by the single sensors, and (4) The combination of all three sensors provides accurate ice information as well as sea surface temperature and wind speeds.

  1. Seasonal Changes in the Marine Production Cycles in Response to Changes in Arctic Sea Ice and Upper Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Spitz, Y. H.; Ashjian, C. J.; Campbell, R. G.; Steele, M.; Zhang, J.

    2011-12-01

    Significant seasonal changes in arctic sea ice have been observed in recent years, characterized by unprecedented summer melt-back. As summer sea ice extent shrinks to record low levels, the peripheral seas of the Arctic Ocean are exposed much earlier to atmospheric surface heat flux, resulting in longer and warmer summers with more oceanic heat absorption. The changing seasonality in the arctic ice/ocean system will alter the timing, magnitude, duration, and pattern of marine production cycles by disrupting key trophic linkages and feedbacks in planktonic food webs. We are using a coupled pan-arctic Biology/Ice/Ocean Modeling and Assimilation System (BIOMAS) to investigate the changes in the patterns of seasonality in the arctic physical and biological system. Focus on specific regions of the Arctic, such as the Chukchi Sea, the Beaufort Sea and the adjacent central Arctic, reveals that changes in the timing of the spring bloom, its duration and the response of the secondary producers vary regionally. The major changes are, however, characterized by an earlier phytoplankton bloom and a slight increase of the biomass. In addition, the largest response in the secondary producers is seen in the magnitude of the microzooplankton concentration as well as in the period (early summer to late fall) over which the microzooplankton is present.

  2. Dynamic response of an Arctic epishelf lake to seasonal and long-term forcing: implications for ice shelf thickness

    NASA Astrophysics Data System (ADS)

    Hamilton, Andrew K.; Laval, Bernard E.; Mueller, Derek R.; Vincent, Warwick F.; Copland, Luke

    2017-09-01

    Changes in the depth of the freshwater-seawater interface in epishelf lakes have been used to infer long-term changes in the minimum thickness of ice shelves; however, little is known about the dynamics of epishelf lakes and what other factors may influence their depth. Continuous observations collected between 2011 and 2014 in the Milne Fiord epishelf lake, in the Canadian Arctic, showed that the depth of the halocline varied seasonally by up to 3.3 m, which was comparable to interannual variability. The seasonal depth variation was controlled by the magnitude of surface meltwater inflow and the hydraulics of the inferred outflow pathway, a narrow basal channel in the Milne Ice Shelf. When seasonal variation and an episodic mixing of the halocline were accounted for, long-term records of depth indicated there was no significant change in thickness of ice along the basal channel from 1983 to 2004, followed by a period of steady thinning at 0.50 m a-1 between 2004 and 2011. Rapid thinning at 1.15 m a-1 then occurred from 2011 to 2014, corresponding to a period of warming regional air temperatures. Continued warming is expected to lead to the breakup of the ice shelf and the imminent loss of the last known epishelf lake in the Arctic.

  3. 33 CFR 165.T08-0240 - Safety Zone; Kemah Boardwalk Summer Season Fireworks, Galveston Bay, Kemah, TX.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Summer Season Fireworks, Galveston Bay, Kemah, TX. 165.T08-0240 Section 165.T08-0240 Navigation and... Areas Eighth Coast Guard District § 165.T08-0240 Safety Zone; Kemah Boardwalk Summer Season Fireworks...' radius around a fireworks barge located at approximate Latitude 29°32′57″ N, Longitude 095°00′31″ W....

  4. Seasonally asymmetric transition of the Asian monsoon in response to ice age boundary conditions

    NASA Astrophysics Data System (ADS)

    Ueda, Hiroaki; Kuroki, Harumitsu; Ohba, Masamichi; Kamae, Youichi

    2011-12-01

    Modulation of a monsoon under glacial forcing is examined using an atmosphere-ocean coupled general circulation model (AOGCM) following the specifications established by Paleoclimate Modelling Intercomparison Project phase 2 (PMIP2) to understand the air-sea-land interaction under different climate forcing. Several sensitivity experiments are performed in response to individual changes in the continental ice sheet, orbital parameters, and sea surface temperature (SST) in the Last Glacial Maximum (LGM: 21 ka) to evaluate the driving mechanisms for the anomalous seasonal evolution of the monsoon. Comparison of the model results in the LGM with the pre-industrial (PI) simulation shows that the Arabian Sea and Bay of Bengal are characterized by enhancement of pre-monsoon convection despite a drop in the SST encompassing the globe, while the rainfall is considerably suppressed in the subsequent monsoon period. In the LGM winter relative to the PI, anomalies in the meridional temperature gradient (MTG) between the Asian continents minus the tropical oceans become positive and are consistent with the intensified pre-monsoon circulation. The enhanced MTG anomalies can be explained by a decrease in the condensation heating relevant to the suppressed tropical convection as well as positive insolation anomalies in the higher latitude, showing an opposing view to a warmer future climate. It is also evident that a latitudinal gradient in the SST across the equator plays an important role in the enhancement of pre-monsoon rainfall. As for the summer, the sensitivity experiments imply that two ice sheets over the northern hemisphere cools the air temperature over the Asian continent, which is consistent with the reduction of MTG involved in the attenuated monsoon. The surplus pre-monsoon convection causes a decrease in the SST through increased heat loss from the ocean surface; in other words, negative ocean feedback is also responsible for the subsequent weakening of summer

  5. High-resolution modelling of the seasonal evolution of surface water storage on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Arnold, N. S.; Banwell, A. F.; Willis, I. C.

    2013-12-01

    Seasonal meltwater lakes on the Greenland Ice Sheet form when surface runoff is temporarily trapped in surface topographic depressions. The development of such lakes affects both the surface energy balance and dynamics of the ice sheet. Although areal extents, depths, and lifespans of lakes can be inferred from satellite imagery, such observational studies have a limited temporal resolution. Here, we adopt a modelling-based strategy to estimate the seasonal evolution of surface water storage for the ~ 3600 km2 Paakitsoq region of W. Greenland. We use a high-resolution time dependent surface mass balance model to calculate surface melt, a supraglacial water routing model to calculate lake filling and a prescribed water-volume based threshold to predict lake drainage events. The model shows good agreement between modelled lake locations and volumes and those observed in 9 Landsat 7 ETM+ images from 2001, 2002 and 2005. We use the model to investigate the lake water volume required to trigger drainage, and the impact that this threshold volume has on the proportion of meltwater that runs off the ice supraglacially, is stored in surface lakes, or enters the subglacial drainage system. Model performance is maximised with prescribed lake volume thresholds between 4000 and 7500 times the local ice thickness. For these thresholds, lakes transiently store < 40% of meltwater at the beginning of the melt season, decreasing to ~ 5 to 10% by the middle of the melt season. 40 to 50% of meltwater runs off the ice surface directly, and the remainder enters the subglacial drainage system through moulins at the bottom of drained lakes.

  6. Torpor is not the only option: seasonal variations of the thermoneutral zone in a small primate.

    PubMed

    Kobbe, Susanne; Nowack, Julia; Dausmann, Kathrin H

    2014-08-01

    The reddish-gray mouse lemur (Microcebus griseorufus) is one of only a few small mammals inhabiting the spiny forest of southwestern Madagascar. In this study we investigated the physiological adjustments which allow these small primates to persist under the challenging climatic conditions of their habitat. To this end we measured energy expenditure (metabolic rate) and body temperature of 24 naturally acclimatized mouse lemurs, kept in outdoor enclosures, during different seasons (summer, winter, and the transition period between the two seasons). Mouse lemurs displayed two main physiological strategies to compensate seasonal and diurnal fluctuations of ambient temperature. On the one hand, individuals entered hypometabolism with decreasing ambient temperature (T a) during the transition period and winter, enabling them to save up to 21 % energy per day (92 % per hour) compared with the normal resting metabolic rate at comparable T a. On the other hand, euthermic mouse lemurs also showed physiological adjustments to seasonality when resting: the lower critical temperature of the thermoneutral zone decreased from summer to winter by 7.5 °C, which allowed mouse lemurs to keep energy demands constant despite colder T as during winter. In addition, the basal metabolic rate was substantially lowered prior to the winter period, which facilitated accumulation of fat reserves. The combination of physiological modifications during euthermia in addition to hypometabolism, which can be individually adjusted according to external parameters and respective body condition, is important as it allows M. griseorufus to cope with the environmental variability of an energetically challenging habitat.

  7. Seasonal climate information preserved within West Antarctic ice cores and its relation to large-scale atmospheric circulation and regional sea ice variations

    NASA Astrophysics Data System (ADS)

    Küttel, M.; Steig, E. J.; Ding, Q.; Battisti, D. S.

    2010-12-01

    Recent evidence suggests that West Antarctica has been warming since at least the 1950s. With the instrumental record being limited to the mid-20th century, indirect information from stable isotopes (δ18O and δD, hereafter collectively δ) preserved within ice cores have commonly been used to place this warming into a long term context. Here, using a large number of δ records obtained during the International Trans-Antarctic Scientific Expedition (ITASE), past variations in West Antarctic δ are not only investigated over time but also in space. This study therefore provides an important complement to longer records from single locations as e.g. the currently being processed West Antarctic ice sheet (WAIS) Divide ice core. Although snow accumulation rates at the ITASE sites in West Antarctica are variable, they are generally high enough to allow studies on sub-annual scale over the last 50-100 years. Here, we show that variations in δ in this region are strongly related to the state of the large-scale atmospheric circulation as well as sea ice variations in the adjacent Southern Ocean, with important seasonal changes. While a strong relationship to sea ice changes in the Ross and Amundsen Sea as well as to the atmospheric circulation offshore is found during austral fall (MAM) and winter (JJA), only modest correlations are found during spring (SON) and summer (DJF). Interestingly, the correlations with the atmospheric circulation in the latter two seasons have the strongest signal over the Antarctic continent, but not offshore - an important difference to MAM and JJA. These seasonal changes are in good agreement with the seasonally varying predominant circulation: meridional with more frequent storms in the Amundsen Sea during MAM and JJA and more zonal and stable during SON and DJF. The relationship to regional temperature is similarly seasonally variable with highest correlations found during MAM and JJA. Notably, the circulation pattern found to be strongest

  8. Simulation of Arctic and North Atlantic ocean water and ice seasonal characteristics by the INMIO-CICE coupled model

    NASA Astrophysics Data System (ADS)

    Ushakov, K. V.; Grankina, T. B.; Ibrayev, R. A.; Gromov, I. V.

    2016-11-01

    The first results of simulation of the seasonal variability of the Arctic and North Atlantic ocean waters and ice by a coupled model based on a full three-dimensional ocean dynamics model INMIO4.1 and a sea-ice model CICE5.1 are considered. The coupled model can be run on massively parallel computers under control of the Compact Modelling Framework CMF2.0. The numerical experiment is performed according to the CORE-II protocol with 1948 atmospheric forcing data. Possible causes of the deviation of the model solution from the ERA-20C reanalysis and WOA09 climatology are discussed.

  9. Russian Arctic climate change in the Late Holocene - spatial and seasonal aspects from studying North Siberian glacier and ground ice

    NASA Astrophysics Data System (ADS)

    Opel, Thomas; Meyer, Hanno; Fritzsche, Diedrich; Laepple, Thomas; Dereviagin, Alexander

    2014-05-01

    The Arctic currently experiences a pronounced warming. This highly dynamic response on changes in climate forcing and corresponding feedbacks and the global impact of the Arctic water, carbon and energy balance make the Arctic a key region to study past and future climate changes. Recent proxy-based Arctic-wide temperature reconstructions for the past two millennia show a long-term cooling trend that has been reversed by the ongoing Arctic warming. However, most records are based on proxies that record summer information and the reconstructions are, thus, assumed to be seasonally biased. Moreover, there exist only a few records from the Russian Arctic. Consequently, this region is significantly underrepresented in Arctic-wide reconstructions and a comprehensive picture of Arctic climate variability is challenging. Here we present glacier and ground ice records from the Russian Arctic that are related to the research project "Eurasian Arctic Ice 4k" funded by the German Research Foundation. They add valuable information for a better spatial and seasonal understanding of Holocene climate variability in the Arctic. The high-resolution Akademii Nauk δ18O ice core record (Severnaya Zemlya) proves the Late Holocene cooling trend and the unprecedented warming after 1800. It shows neither a pronounced Medieval Climate Anomaly nor a Little Ice Age but gives evidence of several abrupt warming and cooling events in the last centuries. These are probably related to the internal variability of the Arctic climate system, i.e. atmosphere-sea ice feedbacks in the Barents and Kara seas region. Ice wedges were studied at several study sites in the Lena River Delta and the coastal permafrost lowlands of the Laptev Sea region. They are formed by the repeated filling of wintertime thermal contraction cracks by snow melt water in spring. Radiocarbon dating of organic matter enables the generation of centennial scale δ18O records that are indicative of climate conditions in the cold

  10. [Variability of vegetation growth season in different latitudinal zones of North China: a monitoring by NOAA NDVI and MSAVI].

    PubMed

    Wang, Hong; Li, Xiaobing; Han, Ruibo; Ge, Yongqin

    2006-12-01

    In this study, North China was latitudinally divided into five zones, i.e., 32 degrees - 36 degrees N (Zone I), 36 degrees - 40 degrees N (Zone II), 40 degrees - 44 degrees N (Zone III), 44 degrees - 48 degrees N (Zone IV) and 48 degrees - 52 degrees N (Zone V), and the NOAA/ AVHRR NDVI and MSAVI time-series images from 1982 to 1999 were smoothed with Savitzky-Golay filter algorithm. Based on the EOF analysis, the principal components of NDVI and MSAVI for the vegetations in different latitudinal zones of North China were extracted, the annual beginning and ending dates and the length of growth season in 1982 - 1999 were estimated, and the related parameters were linearly fitted, aimed to analyze the variability of vegetation growth season. The results showed that the beginning date of the growth season in different zones tended to be advanced, while the ending date tended to be postponed with increasing latitude. The length of the growth season was also prolonged, with the prolonging time exceeded 10 days.

  11. An ice core record of net snow accumulation and seasonal snow chemistry at Mt. Waddington, southwest British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Neff, P. D.; Steig, E. J.; Clark, D. H.; McConnell, J. R.; Pettit, E. C.; Menounos, B.

    2011-12-01

    We recovered a 141 m ice core from Combatant Col (51.39°N, 125.22°W, 3000 m asl) on the flank of Mt. Waddington, southern Coast Mountains, British Columbia, Canada. Aerosols and other impurities in the ice show unambiguous seasonal variations, allowing for annual dating of the core. Clustered melt layers, originating from summer surface heating, also aid in the dating of the core. Seasonality in water stable isotopes is preserved throughout the record, showing little evidence of diffusion at depth, and serves as an independent verification of the timescale. The annual signal of deuterium excess is especially well preserved. The record of lead deposition in the core agrees with those of ice cores from Mt. Logan and from Greenland, with a sharp drop-off in concentration in the 1970s and early 1980s, further validating the timescales. Despite significant summertime melt at this mid-latitude site, these data collectively reveal a continuous and annually resolved 36-year record of snow accumulation. We derived an accumulation time series from the Mt. Waddington ice core, after correcting for ice flow. Years of anomalously high or low snow accumulation in the core correspond with extremes in precipitation data and geopotential height anomalies from reanalysis data that make physical sense. Specifically, anomalously high accumulation years at Mt. Waddington correlate with years where "Pineapple Express" atmospheric river events bring large amounts of moisture from the tropical Pacific to western North America. The Mt. Waddington accumulation record thus reflects regional-scale climate. These results demonstrate the potential of ice core records from temperate glaciers to provide meaningful paleoclimate information. A longer core to bedrock (250-300 m) at the Mt. Waddington site could yield ice with an age of several hundred to 1000 years.

  12. Glacioclimatological study of Perennial Ice in the Fuji Ice Cave, Japan. Part I. Seasonal variation and mechanism of maintenance

    SciTech Connect

    Ohata, Tetsuo; Furukawa, Teruo; Higuchi, Keiji )

    1994-08-01

    Perennial cave ice in a cave located at Mt. Fuji in central Japan was studied to investigate the basic characteristics and the cause for existence of such ice under warm ground-level climate considering the ice cave as a thermal and hydrological system. Fuji Ice Cave is a lava tube cave 150 m in length with a collapsed part at the entrance. Measurements from 1984 to 1986 showed that the surface-level change of floor ice occurred due to freezing and melting at the surface and that melting at the bottom of the ice was negligible. The annual amplitude of change in surface level was larger near the entrance. Meterological data showed that the cold air inflow to the cave was strong in winter, but in summer the cave was maintained near 0[degrees]C with only weak inflow of warm air. The predominant wind system was from the entrance to the interior in both winter and summer, but the spatial scale of the wind system was different. Heat budget consideration of the cave showed that the largest component was the strong inflow of subzero dry air mass in winter. Cooling in winter was compensated for by summer inflow of warm air, heat transport from the surrounding ground layer, and loss of sensible heat due to cooling of the cave for the observed year. Strong inflow of cold air and weak inflow of warm air, which is extremely low compared to the ground level air, seemed to be the most important condition. Thus the thermal condition of the cave is quasi-balanced at the presence condition below 0[degrees]C with ice. It can be said that the interrelated result of the climatological and special structural conditions makes this cave very cold, and allows perennial ice to exist in the cave. Other climatological factors such as precipitation seem to be minor factors. 17 refs., 3 figs., 3 tabs.

  13. Seasonally resolved ice core records from West Antarctica indicate a sea ice source of sea-salt aerosol and a biomass burning source of ammonium

    NASA Astrophysics Data System (ADS)

    Pasteris, Daniel R.; McConnell, Joseph R.; Das, Sarah B.; Criscitiello, Alison S.; Evans, Matthew J.; Maselli, Olivia J.; Sigl, Michael; Layman, Lawrence

    2014-07-01

    The sources and transport pathways of aerosol species in Antarctica remain uncertain, partly due to limited seasonally resolved data from the harsh environment. Here, we examine the seasonal cycles of major ions in three high-accumulation West Antarctic ice cores for new information regarding the origin of aerosol species. A new method for continuous acidity measurement in ice cores is exploited to provide a comprehensive, charge-balance approach to assessing the major non-sea-salt (nss) species. The average nss-anion composition is 41% sulfate (SO42-), 36% nitrate (NO3-), 15% excess-chloride (ExCl-), and 8% methanesulfonic acid (MSA). Approximately 2% of the acid-anion content is neutralized by ammonium (NH4+), and the remainder is balanced by the acidity (Acy ≈ H+ - HCO3-). The annual cycle of NO3- shows a primary peak in summer and a secondary peak in late winter/spring that are consistent with previous air and snow studies in Antarctica. The origin of these peaks remains uncertain, however, and is an area of active research. A high correlation between NH4+ and black carbon (BC) suggests that a major source of NH4+ is midlatitude biomass burning rather than marine biomass decay, as previously assumed. The annual peak in excess chloride (ExCl-) coincides with the late-winter maximum in sea ice extent. Wintertime ExCl- is correlated with offshore sea ice concentrations and inversely correlated with temperature from nearby Byrd station. These observations suggest that the winter peak in ExCl- is an expression of fractionated sea-salt aerosol and that sea ice is therefore a major source of sea-salt aerosol in the region.

  14. Recent Changes in Arctic Sea Ice Melt Onset, Freeze-Up, and Melt Season Length

    NASA Technical Reports Server (NTRS)

    Markus, Thorsten; Stroeve, Julienne C.; Miller, Jeffrey

    2010-01-01

    In order to explore changes and trends in the timing of Arctic sea ice melt onset and freeze-up and therefore melt season length, we developed a method that obtains this information directly from satellite passive microwave data, creating a consistent data set from 1979 through present. We furthermore distinguish between early melt (the first day of the year when melt is detected) and the first day of continuous melt. A similar distinction is made for the freeze-up. Using this method we analyze trends in melt onset and freeze-up for 10 different Arctic regions. In all regions except for the Sea of Okhotsk, which shows a very slight and statistically insignificant positive trend (O.4 days/decade), trends in melt onset are negative, i.e. towards earlier melt. The trends range from -1.0day/decade for the Bering Sea to -7.3 days/decade for the East Greenland Sea. Except for the Sea of Okhotsk all areas also show a trend towards later autumn freeze onset. The Chukchi/Beaufort Seas and Laptev/East Siberian Seas observe the strongest trends with 7 days/decade. For the entire Arctic, the melt season length has increased by about 20 days over the last 30 years. Largest trends of over 1O days/decade are seen for Hudson Bay, the East Greenland Sea the Laptev/East Siberian Seas, and the Chukchi/Beaufort Seas. Those trends are statistically significant a1 the 99% level.

  15. Recent Changes in Arctic Sea Ice Melt Onset, Freeze-Up, and Melt Season Length

    NASA Technical Reports Server (NTRS)

    Markus, Thorsten; Stroeve, Julienne C.; Miller, Jeffrey

    2010-01-01

    In order to explore changes and trends in the timing of Arctic sea ice melt onset and freeze-up and therefore melt season length, we developed a method that obtains this information directly from satellite passive microwave data, creating a consistent data set from 1979 through present. We furthermore distinguish between early melt (the first day of the year when melt is detected) and the first day of continuous melt. A similar distinction is made for the freeze-up. Using this method we analyze trends in melt onset and freeze-up for 10 different Arctic regions. In all regions except for the Sea of Okhotsk, which shows a very slight and statistically insignificant positive trend (O.4 days/decade), trends in melt onset are negative, i.e. towards earlier melt. The trends range from -1.0day/decade for the Bering Sea to -7.3 days/decade for the East Greenland Sea. Except for the Sea of Okhotsk all areas also show a trend towards later autumn freeze onset. The Chukchi/Beaufort Seas and Laptev/East Siberian Seas observe the strongest trends with 7 days/decade. For the entire Arctic, the melt season length has increased by about 20 days over the last 30 years. Largest trends of over 1O days/decade are seen for Hudson Bay, the East Greenland Sea the Laptev/East Siberian Seas, and the Chukchi/Beaufort Seas. Those trends are statistically significant a1 the 99% level.

  16. Atmospheric influence on Arctic marginal ice zone position and width in the Atlantic sector, February-April 1979-2010

    NASA Astrophysics Data System (ADS)

    Strong, Courtenay

    2012-12-01

    Arctic marginal ice zone (MIZ) widths in the Atlantic sector were measured during the months of maximum sea ice extent (February-April) for years 1979-2010 using a novel method based on objective curves through idealized sea ice concentration fields that satisfied Laplace's equation. Over the record, the Labrador Sea MIZ (MIZL) had an average width of 122 km and narrowed by 28 % while moving 254 km poleward, the Greenland Sea MIZ (MIZG) had an average width of 98 km and narrowed by 43 % while moving 158 km west toward the Greenland coast, and the Barents Sea MIZ (MIZB) had an average width of 136 km and moved 259 km east toward the Eurasian coast without a trend in width. Trends in MIZ position and width were consistent with a warming Arctic and decreasing sea ice concentrations over the record. Beyond the trends, NAO-like atmospheric patterns influenced interannual variability in MIZ position and width: MIZL widened and moved southeast under anomalously strong northerly flow conducive to advection of sea ice into the Labrador Sea, MIZG widened and moved northeast under anomalously weak northerly flow conducive to diminishing the westward component of sea ice drift, and MIZB widened and moved poleward at the expense of pack ice under anomalously strong southwesterly flow conducive to enhancing oceanic heat flux into the Barents Sea. In addition, meridional flow anomalies associated with the NAO per se moved MIZB east and west by modulating sea ice concentration over the Barents Sea.

  17. Seasonal evolution of supra-glacial lakes on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    McMillan, Malcolm; Nienow, Peter; Shepherd, Andrew; Benham, Toby; Sole, Andrew

    2007-10-01

    A survey of supra-glacial lakes on the western margin of the Greenland Ice Sheet reveals a seasonally-driven hydrological system, culminating in widespread lake drainage in late summer. We used satellite imagery to study the evolution of 292 lakes across two sites totalling 22 000 km 2 in area. During 2001, the lakes combined area increased to 75 ± 5 km 2 by the beginning of July. Over the following 25 days, an area totalling 36 ± 3.5 km 2 drained from 216 lakes. At one study site, we used meteorological data and a positive degree day model to calculate the volume of water generated by melting in the lake catchments. Based on this estimate, the mean depth of filling lakes surveyed rose from 1.5 ± 0.7 m on 7th July to 3.9 ± 1.1 m on 1st August, in agreement with a value for one lake of 4.4 ± 0.9 m we have derived from airborne altimetry. During this 25 day period, we estimate that 38 ± 18 × 10 7 m 3 of water drained from the surface at this site, and that there was an average water flux of 1.3 ± 0.3 m 3 s - 1 passing through each lake that drained completely.

  18. Changes in Arctic Melt Season and Implications for Sea Ice Loss

    NASA Technical Reports Server (NTRS)

    Stroeve, J. C.; Markus, T.; Boisvert, L.; Miller, J.; Barrett, A.

    2014-01-01

    The Arctic-wide melt season has lengthened at a rate of 5 days dec-1 from 1979 to 2013, dominated by later autumn freeze-up within the Kara, Laptev, East Siberian, Chukchi and Beaufort seas between 6 and 11 days dec(exp -1). While melt onset trends are generally smaller, the timing of melt onset has a large influence on the total amount of solar energy absorbed during summer. The additional heat stored in the upper ocean of approximately 752MJ m(exp -2) during the last decade, increases sea surface temperatures by 0.5 to 1.5 C and largely explains the observed delays in autumn freeze-up within the Arctic Ocean's adjacent seas. Cumulative anomalies in total absorbed solar radiation from May through September for the most recent pentad locally exceed 300-400 MJ m(exp -2) in the Beaufort, Chukchi and East Siberian seas. This extra solar energy is equivalent to melting 0.97 to 1.3 m of ice during the summer.

  19. Evaluating Physical Processes during the Freeze-Up Season using a Coupled Sea Ice-Ocean-Atmosphere Forecast Model

    NASA Astrophysics Data System (ADS)

    Solomon, Amy; Intrieri, Janet; Persson, Ola; Cox, Christopher; Hughes, Mimi; Grachev, Andrey; Capotondi, Antonietta; de Boer, Gijs

    2017-04-01

    Improved sea ice forecasting must be based on improved model representation of coupled system processes that impact the sea ice thermodynamic and dynamic state. Pertinent coupled system processes remain uncertain and include surface energy fluxes, clouds, precipitation, boundary layer structure, momentum transfer and sea-ice dynamics, interactions between large-scale circulation and local processes, and others. In this presentation, we use a fully-coupled ocean-sea ice-atmosphere forecast system as a testbed for investigating biases in 0-10 day forecasts, with a focus on processes that determine fluxes at the ocean-ice-air interface. Model results and validation examples from an experimental, weather-scale, coupled ice-ocean-atmosphere model for 2015 and 2016 fall, sea ice freeze-up season will be presented. The model, a limited-area, fully-coupled atmosphere-ice-ocean model (named, RASM-ESRL), was developed from the larger-scale Regional Arctic System Model (RASM) architecture. RASM-ESRL includes the Weather Research and Forecasting (WRF) atmospheric model, Parallel Ocean Program (POP2) model, Community Ice Model (CICE5) and the NCAR Community Land Model. The domain is limited to the Arctic and all components are run with 10 km horizontal resolution. Components are coupled using a regionalized version of the CESM flux coupler (CPL7), which includes modifications important for resolving the sea ice pack's inertial response to transient (i.e. weather) events. The model is initialized with a GFS atmosphere, satellite-derived sea ice analyses using AMSR-2, and forced by 3-hourly GFS forecasts at the lateral boundaries. Experimental forecasts were run daily from late-July through mid-November in 2015 and 2016. These daily forecasts have been compared with observations of surface fluxes and vertical atmospheric profiles at the International Arctic Systems for Observing the Atmosphere (IASOA) stations, and with atmospheric and oceanic observations obtained within the sea

  20. The Effect of Carbon Dioxide (CO 2) Ice Cloud Condensation on the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Lincowski, Andrew; Meadows, Victoria; Robinson, Tyler D.; Crisp, David

    2016-10-01

    The currently accepted outer limit of the habitable zone (OHZ) is defined by the "maximum greenhouse" limit, where Rayleigh scattering from additional CO2 gas overwhelms greenhouse warming. However, this long-standing definition neglects the radiative effects of CO2 clouds (Kopparapu, 2013); this omission was justified based on studies using the two-stream approximation, which found CO2 clouds to be highly likely to produce a net warming. However, recent comparisons of the radiative effect of CO2 clouds using both a two-stream and multi-stream radiative transfer model (Kitzmann et al, 2013; Kitzmann, 2016) found that the warming effect was reduced when the more sophisticated multi-stream models were used. In many cases CO2 clouds caused a cooling effect, meaning that their impact on climate could not be neglected when calculating the outer edge of the habitable zone. To better understand the impact of CO2 ice clouds on the OHZ, we have integrated CO2 cloud condensation into a versatile 1-D climate model for terrestrial planets (Robinson et al, 2012) that uses the validated multi-stream SMART radiative transfer code (Meadows & Crisp, 1996; Crisp, 1997) with a simple microphysical model. We present preliminary results on the habitable zone with self-consistent CO2 clouds for a range of atmospheric masses, compositions and host star spectra, and the subsequent effect on surface temperature. In particular, we evaluate the habitable zone for TRAPPIST-1d (Gillon et al, 2016) with a variety of atmospheric compositions and masses. We present reflectance and transit spectra of these cold terrestrial planets. We identify any consequences for the OHZ in general and TRAPPIST-1d in particular. This more comprehensive treatment of the OHZ could impact our understanding of the distribution of habitable planets in the universe, and provide better constraints for statistical target selection techniques, such as the habitability index (Barnes et al, 2015), for missions like JWST

  1. The Floe Size Distribution in the Marginal Ice Zone of the Beaufort and Chukchi Seas

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    In order to support the calibration and validation of our high-resolution coupled sea ice/ocean modeling and assimilation system, which now includes a floe size distribution (FSD), we have analyzed the FSD in 256 MODIS satellite images from 2013 and 2014 in the Marginal Ice Zone (MIZ) of the Beaufort and Chukchi seas. Proper characterization of the FSD is important for modeling the MIZ. We find that the FSD (the number of floes in different size categories) obeys a power-law distribution with an exponent that varies systematically over the course of spring, summer, and fall. The exponent (or slope in log-log space) is relatively shallow in spring but becomes steeper in summer, reflecting the fact that floes break up, resulting in fewer large floes relative to the number of small floes. In late summer the slope becomes shallower again, since small floes melt more quickly than large floes. The spatial resolution of MODIS limits our analysis to floes larger than about 1 km in diameter. To investigate smaller scales, we calculated the FSD in satellite images from radar (SAR, 50-meter resolution) and optical (MEDEA, 1-meter resolution) sensors that overlap in space and time with MODIS images, to see whether the power-law FSD in the MODIS images extends to smaller scales. We present the results of those calculations, as well as comparisons between the modeled and observed FSD.

  2. Arctic Marine Biogeochemistry in a Global Ice-Ocean Ecosystem Model: A Look at Seasonal Features and Spatial Patterns

    NASA Astrophysics Data System (ADS)

    Deal, C.; Jin, M.; Elliott, S.; Jeffery, N.; Steiner, N.; Carpenter, L.; Chance, R.

    2015-12-01

    The LANL-UAF ice-ocean ecosystem model was developed to investigate how sea ice influences biogeochemical cycling in the arctic marine environment and predict how it will do so in the future. Sea ice is an integral component of arctic biogeochemical cycles. Rapidly changing sea ice conditions, such as thinning, increasing open water area and freshening impact C, N, and S cycles in multiple interacting ways. Here we discuss model results for chlorophyll, primary productivity, nutrients, and dimethyl sulfide (DMS) in the Arctic Ocean. We compare our results to observations and simulations from other Arctic biogeochemical models. Participation in several recent intercomparison studies provide context for interpretation of our own model results. Key seasonal features and spatial patterns of biogeochemical phenomena studied include pan-Arctic primary production, subsurface chlorophyll maxima, under-ice phytoplankton blooms, and relatively high seawater DMS concentrations following the retreating ice edge. Not surprisingly, in most all cases, the model's success depends on how well the physical processes (e.g., vertical mixing, melt-water stratification) realistically distribute available nutrients. Further explanations for model-model and model-observation agreement/disagreement will be presented. While the model predicted high ice primary productivity recently recorded in the Bering Sea, the model shows no indication of extremely high seawater DMS recently observed at sea ice stations north of Svalbard. Preliminary model results from a high resolution version of our model, as part of the Regional Arctic System Model - Marine Biogeochemistry (i.e., RASM-mBGC) project, will also be presented.

  3. Open-water and under-ice seasonal variations in trace element content and physicochemical associations in fluvial bed sediment.

    PubMed

    Doig, Lorne E; Carr, Meghan K; Meissner, Anna G N; Jardine, Tim D; Jones, Paul D; Bharadwaj, Lalita; Lindenschmidt, Karl-Erich

    2017-06-13

    Across the circumpolar world, intensive anthropogenic activities in the southern reaches of many large, northward-flowing rivers can cause sediment contamination in the downstream depositional environment. The influence of ice cover on concentrations of inorganic contaminants in bed sediment (i.e., sediment quality) is unknown in these rivers, where winter is the dominant season. A geomorphic response unit approach was used to select hydraulically diverse sampling sites across a northern test-case system, the Slave River and delta (Northwest Territories, Canada). Surface sediment samples (top 1 cm) were collected from 6 predefined geomorphic response units (12 sites) to assess the relationships between bed sediment physicochemistry (particle size distribution and total organic carbon content) and trace element content (mercury and 18 other trace elements) during open-water conditions. A subset of sites was resampled under-ice to assess the influence of season on these relationships and on total trace element content. Concentrations of the majority of trace elements were strongly correlated with percent fines and proxies for grain size (aluminum and iron), with similar trace element grain size/grain size proxy relationships between seasons. However, finer materials were deposited under ice with associated increases in sediment total organic carbon content and the concentrations of most trace elements investigated. The geomorphic response unit approach was effective at identifying diverse hydrological environments for sampling prior to field operations. Our data demonstrate the need for under-ice sampling to confirm year-round consistency in trace element-geochemical relationships in fluvial systems and to define the upper extremes of these relationships. Whether contaminated or not, under-ice bed sediment can represent a "worst-case" scenario in terms of trace element concentrations and exposure for sediment-associated organisms in northern fluvial systems

  4. Quantifying Seasonal Skill In Coupled Sea Ice Models Using Freeboard Measurements From Spaceborne Laser Altimeters

    DTIC Science & Technology

    2016-06-01

    satellite. Along the path, the LASER path is affected by clouds , aerosols and differing surface types...Altimeter System GSFC Goddard Space Flight Center ICESat Ice, Cloud , and land Elevation Satellite ICESat-2 Ice, Cloud , and land Elevation...Sea ice thickness trends are indicative of climatic changes within the Arctic Circle in response to global climate warming and its linkage to mid

  5. Evolution of a Western Arctic Ice Ocean Boundary Layer and Mixed Layer Across a Developing Thermodynamically Forced Marginal Ice Zone

    DTIC Science & Technology

    2016-09-01

    NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA DISSERTATION Approved for public release. Distribution is unlimited. EVOLUTION ...blank) 2. REPORT DATE September 2016 3. REPORT TYPE AND DATES COVERED Dissertation 4. TITLE AND SUBTITLE EVOLUTION OF A WESTERN ARCTIC ICE...measurements were collected across the Canada Basin to study the summer evolution of the ice-ocean boundary layer (IOBL) and ocean mixed layer (OML

  6. The Effects of Time-Dependent Winds and Ocean Eddies on Ice Motion in a Marginal Ice Zone.

    DTIC Science & Technology

    1987-12-01

    16 SUPPLEMENTARY NOTATION 17 COSA’i CODES 18 SUBJECT TERMS (Continue on revere if rWc idrn @entdi fy block number) FIELD GROUP SuB- GROUP MARGINAL ICE...cutofffro iceofequl ncntatin hatha fome toth soth Alo vidntm te igue s significant northward Ekman drift of the ice edge; the resulting signature of the

  7. Latitudinal and MLT dependence of the seasonal variation of geomagnetic field around auroral zone

    NASA Astrophysics Data System (ADS)

    Zhu, Jin; Du, Aimin; Ou, Jiaming; Xu, Wenyao

    2017-08-01

    Seasonal variation of geomagnetic field around auroral zone is analyzed in terms of geomagnetic latitude, magnetic local time (MLT) and geomagnetic condition in this study. The study uses horizontal component (H) of geomagnetic field obtained from 6 observatories located in geomagnetic latitude of 57.8°N-73.8°N along 115°E longitudinal line. The results indicate that seasonal variations of geomagnetic field around auroral zone are different combinations of annual and semiannual variations at different latitudinal ranges. Both annual and semiannual variations show distinct MLT dependency: (1) At dayside auroral latitudes (around 72°N geomagnetic latitude), geomagnetic field shows distinct annual variation under both quiet and disturbed conditions. Furthermore, the annual component is mainly contributed by data of dusk sector. (2) At nightside auroral latitudes (around 65°N), geomagnetic field shows semiannual dominated seasonal variation. Under quiet conditions the annual component is comparable to the semiannual component, while under disturbed conditions, the semiannual component is twice as much as the annual component. Under quiet conditions, the semiannual component is mainly contributed by 1300-1400 MLT, while the annual component has two peaks: one is around 1100-1300 MLT and the other is around 2000-2200 MLT. Under disturbed conditions, the semiannual component is mainly contributed by data around midnight, while the annual component is mainly contributed by dusk sector. (3) At subauroral latitudes (around 60°N), annual variation is comparable to semiannual variation under both quiet and disturbed conditions. Both annual and semiannual components show similar MLT dependencies as that of nightside auroral latitudes.

  8. Simulation of the melt season using a resolved sea ice model with snow cover and melt ponds

    NASA Astrophysics Data System (ADS)

    Skyllingstad, Eric D.; Shell, Karen M.; Collins, Lee; Polashenski, Chris

    2015-07-01

    A three-dimensional sea ice model is presented with resolved snow thickness variations and melt ponds. The model calculates heating from solar radiative transfer and simulates the formation and movement of brine/melt water through the ice system. Initialization for the model is based on observations of snow topography made during the summer melt seasons of 2009, 2010, and 2012 from a location off the coast of Barrow, AK. Experiments are conducted to examine the importance of snow properties and snow and ice thickness by comparing observed and modeled pond fraction and albedo. One key process simulated by the model is the formation of frozen layers in the ice as relatively warm fresh water grid cells freeze when cooled by adjacent, cold brine-filled grid cells. These layers prevent vertical drainage and lead to flooding of melt water commonly observed at the beginning of the melt season. Flooding persists until enough heat is absorbed to melt through the frozen layer. The resulting long-term melt pond coverage is sensitive to both the spatial variability of snow cover and the minimum snow depth. For thin snow cover, initial melting results in earlier, reduced flooding with a small change in pond fraction after drainage of the melt water. Deeper snow tends to generate a delayed, larger peak pond fraction before drainage.

  9. Role of the seasonal cycle in coupling climate and carbon cycling in the subantarctic zone

    NASA Astrophysics Data System (ADS)

    Monteiro, Pedro M. S.; Boyd, Philip; Bellerby, Richard

    2011-07-01

    Workshop on the Seasonal Cycle of the Carbon-Climate System in the Southern Ocean; Cape Town, South Africa, 23-25 August 2010; There is increasing evidence in the Southern Ocean that mesoscales and seasonal scales play an important role in the coupling of ocean carbon cycling and climate. The seasonal cycle is one of the strongest modes of variability in different components of the carbon cycle in the Southern Ocean. It is also the mode that couples climate forcing to ecosystem responses such as productivity and ultimately biogeochemical signals including carbon export. However, not only are these scales of coupling poorly understood, but also there appear to be important regional differences in the way they couple climate to carbon. With this as an overarching theme, a workshop in South Africa brought together scientists working in the Southern Ocean, the waters south of Australia, New Zealand, and South Africa. The importance of the Subantarctic Zone (SAZ) as a carbon sink made it an ideal system on which to focus the workshop.

  10. Seasonal behavioral responses of an arid-zone passerine in a hot environment.

    PubMed

    Pattinson, Nicholas B; Smit, Ben

    2017-10-01

    Many arid-zone animals have to forage under extremely hot conditions to maintain water and energy balance. The effect of high air temperatures (Tair) on the behavioral patterns of small endothermic animals-characterized by their high energy and water demands-will provide a valuable framework for understanding species vulnerability to climate warming. We determined the seasonal behavioral responses to changes in Tair in a~10-g arid-zone passerine, the rufous-eared warbler (Malcorus pectoralis), in the Karoo semi-desert, South Africa. Rufous-eared warblers showed significant temperature-dependence in their behavior in summer, but not in winter. During summer, the warblers frequently experienced Tair exceeding 40°C in the shade. For all observations <26°C compared to >36°C, the warblers showed reductions in preening (40% decrease), foraging effort (56% decrease), and foraging success (15% decrease), as well as a significant increase in time spent engaged in evaporative cooling behavior. Moreover, as Tair increased the warblers shifted increasingly off the ground and out of the full sun, into microsites in the shade (131% increase) and in shrubs (23% increase). In this regard, behavior varied seasonally, with the time spent in the shade 23% higher, and foraging effort 28% higher, in summer compared to winter across a range of moderate Tair (15-30°C). Our findings emphasize the link between behavior and temperature in small birds inhabiting hot, arid environments, as well as the importance of understanding these responses for predicting biologically meaningful responses (and hence, vulnerability) of arid-zone avian communities to climactic shifts. Copyright © 2017 Elsevier Inc. All rights reserved.

  11. Brief communication: Improved measurement of ice layer density in seasonal snowpacks

    NASA Astrophysics Data System (ADS)

    Watts, Tom; Rutter, Nick; Toose, Peter; Derksen, Chris; Sandells, Melody; Woodward, John

    2016-09-01

    The microstructure and density of ice layers in snowpacks is poorly quantified. Here we present a new field method for measuring the density of ice layers caused by melt or rain-on-snow events. The method was used on 87 ice layer samples taken from natural and artificial ice layers in the Canadian Arctic and mid-latitudes. Mean measured ice layer density was 909 ± 28 kg m-3 with a standard deviation of 23 kg m-3, significantly higher than values typically used in the literature.

  12. How well does wind speed predict air-sea gas transfer in the sea ice zone? A synthesis of radon deficit profiles in the upper water column of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Loose, B.; Kelly, R. P.; Bigdeli, A.; Williams, W.; Krishfield, R.; Rutgers van der Loeff, M.; Moran, S. B.

    2017-05-01

    We present 34 profiles of radon-deficit from the ice-ocean boundary layer of the Beaufort Sea. Including these 34, there are presently 58 published radon-deficit estimates of air-sea gas transfer velocity (k) in the Arctic Ocean; 52 of these estimates were derived from water covered by 10% sea ice or more. The average value of k collected since 2011 is 4.0 ± 1.2 m d-1. This exceeds the quadratic wind speed prediction of weighted kws = 2.85 m d-1 with mean-weighted wind speed of 6.4 m s-1. We show how ice cover changes the mixed-layer radon budget, and yields an "effective gas transfer velocity." We use these 58 estimates to statistically evaluate the suitability of a wind speed parameterization for k, when the ocean surface is ice covered. Whereas the six profiles taken from the open ocean indicate a statistically good fit to wind speed parameterizations, the same parameterizations could not reproduce k from the sea ice zone. We conclude that techniques for estimating k in the open ocean cannot be similarly applied to determine k in the presence of sea ice. The magnitude of k through gaps in the ice may reach high values as ice cover increases, possibly as a result of focused turbulence dissipation at openings in the free surface. These 58 profiles are presently the most complete set of estimates of k across seasons and variable ice cover; as dissolved tracer budgets they reflect air-sea gas exchange with no impact from air-ice gas exchange.

  13. Interactions among evaporation, ice cover, and water temperature on the world's largest lake: Seasonal feedbacks and long-term change

    NASA Astrophysics Data System (ADS)

    Lenters, J. D.; Van Cleave, K.; Blanken, P.; Hanes, J.; Hedstrom, N.; Spence, C.; Suyker, A. E.; Wang, J.

    2012-12-01

    Lake Superior, the largest freshwater lake in the world by surface area, has enormous impacts on the regional weather and climate. The lake also comprises over half of the total water volume in the Great Lakes system and is an important resource for commercial shipping, water supplies, hydropower, recreation, and aquatic ecosystems. Analysis of historical summer water temperature data and modeled evaporation rates for Lake Superior show significant increases in both parameters in recent decades, while ice cover has been decreasing at a rapid pace. A careful analysis of the long-term trends, however, shows that these changes have not been linear through time. Rather, a pronounced regime shift occurred in 1997/98 that resulted in a drop in ice duration of nearly 40 days, a 3°C increase in summer water temperature, and a near doubling of July-August evaporation rates. Linear regression analysis of data on either side of this step change shows trends which are largely insignificant and even opposite in sign from those of the step change. Using time-lagged correlation and composite analyses, interactions among ice cover, water temperature, and evaporation are explored across seasonal and interannual timescales. Contrary to what is often expected for inland water bodies, evaporation and ice cover do not show a simple, inverse relationship. Rather, seasonal feedbacks and temporal lags lead to complex interactions among multiple variables. For example, high evaporation rates in the autumn are found to be associated with more extensive ice cover during the subsequent winter months, presumably as a result of strong latent heat flux and correspondingly rapid ice onset and growth. In turn, high ice cover leads to cooler summer water temperatures and reduced evaporation rates in late summer and early fall. Thus, the overall relationship between ice cover and annual evaporation totals is often muted and complex. Quantifying these seasonal feedbacks and interactions is important

  14. Air-sea carbon dioxide exchange in the Southern Ocean and Antarctic Sea ice zone

    NASA Astrophysics Data System (ADS)

    Butterworth, Brian J.

    The Southern Ocean is an important part of the global carbon cycle, responsible for roughly half of the carbon dioxide (CO2) absorbed by the global ocean. The air-sea CO2 flux (Fc) can be expressed as the product of the water-air CO2 partial pressure difference (DeltapCO2) and the gas transfer velocity ( k), an exchange coefficient which represents the efficiency of gas exchange. Generally, Fc is negative (a sink) throughout the Southern Ocean and Antarctic sea ice zone (SIZ), but uncertainty in k has made it difficult to develop an accurate regional carbon budget. Constraining the functional dependence of k on wind speed in open water environments, and quantifying the effect of sea ice on k, will reduce uncertainty in the estimated contribution of the Southern Ocean and Antarctic SIZ to the global carbon cycle. To investigate Fc in the Southern Ocean, a ruggedized, unattended, closed-path eddy covariance (EC) system was deployed on the Antarctic research vessel Nathaniel B. Palmer for nine cruises during 18 months from January 2013 to June 2014 in the Southern Ocean and coastal Antarctica. The methods are described and results are shown for two cruises chosen for their latitudinal range, inclusion of open water and sea ice cover, and large DeltapCO2. The results indicated that ship-based unattended EC measurements in high latitudes are feasible, and recommendations for deployments in such environments were provided. Measurements of Fc and DeltapCO2 were used to compute k. The open water data showed a quadratic relationship between k (cm hr-1) and the neutral 10-m wind speed (U10n, m s -1), k=0.245 U10n 2+1.3, in close agreement with tracer-based results and much lower than previous EC studies. In the SIZ, it was found that k decreased in proportion to sea ice cover. This contrasted findings of enhanced Fc in the SIZ by previous open-path EC campaigns. Using the NBP results a net annual Southern Ocean (ocean south of 30°S) carbon flux of -1.1 PgC yr-1 was

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  16. A Comparison of the Seasonal Change of Albedo across Glaciers and Ice-Covered Lakes of the Taylor Valley, Antarctica

    NASA Astrophysics Data System (ADS)

    Gooseff, M. N.; Bergstrom, A.

    2016-12-01

    The Dry Valleys of Antarctica are a polar desert ecosystem consisting of piedmont and alpine glaciers, ice-covered lakes, and vast expanses of bare soil. The ecosystem is highly dependent on glacial melt a water source. Because average summer temperatures are close to freezing, glacier ice and lake ice are very closely linked to the energy balance. A slight increase in incoming radiation or decrease in albedo can have large effects on the timing and volume of available liquid water. However, we have yet to fully characterize the seasonal evolution of albedo in the valleys. In this study, we used a camera, gps, and short wave radiometer to characterize the albedo within and across landscape types in the Taylor Valley. These instruments were attached to a helicopter and flown on a prescribed path along the valley at approximately 300 feet above the ground surface five different times throughout the season from mid-November to mid-January, 2015-2016. We used these data to calculate the albedo of each glacier, lake, and the soil surface of the lake basins in the valley for each flight. As expected, we found that all landscape types had significantly different albedo, with the glaciers consistently the highest throughout the season and the bare soils the lowest (p-value < 0.05). We hypothesized that albedo would decrease throughout the season with snow melt and increasing sediment exposure on the glacier and lake surfaces. However, small snow events (< 3 cm) caused somewhat persistent high albedo on the lakes and glaciers. Furthermore, there was a range in albedo across glaciers and each responded to seasonal snow and melt differently. These findings highlight the importance of understanding the spatial and temporal variability in albedo and the close coupling of climate and landscape response. We can use this new understanding of landscape albedo to better predict how the Dry Valley ecosystems will respond to changing climate at the basin scale.

  17. High-resolution modelling of the seasonal evolution of surface water storage on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Arnold, N. S.; Banwell, A. F.; Willis, I. C.

    2014-07-01

    Seasonal meltwater lakes on the Greenland Ice Sheet form when surface runoff is temporarily trapped in surface topographic depressions. The development of such lakes affects both the surface energy balance and dynamics of the ice sheet. Although areal extents, depths and lifespan of lakes can be inferred from satellite imagery, such observational studies have a limited temporal resolution. Here, we adopt a modelling-based strategy to estimate the seasonal evolution of surface water storage for the ~ 3600 km2 Paakitsoq region of W. Greenland. We use a high-resolution time-dependent surface mass balance model to calculate surface melt, a supraglacial water routing model to calculate lake filling and a prescribed water-volume-based threshold to predict rapid lake drainage events. This threshold assumes that drainage will occur through a fracture if V = Fa ⋅ H, where V is lake volume, H is the local ice thickness and Fa is the potential fracture area. The model shows good agreement between modelled lake locations and volumes and those observed in nine Landsat 7 ETM images from 2001, 2002 and 2005. We use the model to investigate the lake water volume required to trigger drainage, and the impact that varying this threshold volume has on the proportion of meltwater that is stored in surface lakes and enters the subglacial drainage system. Model performance is maximised with values of Fa between 4000 and 7500 m2. For these thresholds, lakes transiently store < 40% of available meltwater at the beginning of the melt season, decreasing to ~ 5 to 10% by the middle of the melt season; over the course of a melt season, 40 to 50% of total meltwater production enters the subglacial drainage system through moulins at the bottom of drained lakes.

  18. Characterizing the seasonal cycle of upper-ocean flows under multi-year sea ice

    NASA Astrophysics Data System (ADS)

    Mensa, Jean A.; Timmermans, M.-L.

    2017-05-01

    Observations in the Arctic Ocean suggest that upper-ocean dynamics under sea ice might be significantly weaker than in the temperate oceans. In particular, observational evidence suggests that currents developing under sea ice present weak or absent submesoscale (O(1) Rossby number) dynamics, in contrast with midlatitude oceans typically characterized by more energetic dynamics at these scales. Idealized numerical model results of the upper ocean under multi-year sea ice, subject to realistic forcing, are employed to describe the evolution of the submesoscale flow field. During both summer and winter under multi-year sea ice, the simulated submesoscale flow field is typically much less energetic than in the midlatitude ice-free oceans. Rossby numbers under sea ice are generally consistent with geostrophic dynamics (Ro ∼ O(10-3)). During summer, ice melt generates a shallow mixed layer (O(1) m) which isolates the surface from deeper, warmer and saltier waters. The Ekman balance generally dominates the mixed layer, although inertial waves are present in the simulations during weakening and reversals of the ice-ocean stress. During winter, mixed-layer deepening (to about 40 m depth), is associated with convection driven by sea-ice growth, as well as ice-ocean shear-driven entrainment at the base of the mixed layer. Submesoscale activity is observed to develop only rarely, when winter convective mixing is laterally inhomogeneous (i.e., in the presence of sea-ice leads or spatially inhomogeneous sea-ice thickness) and when this coincides with weak ice-ocean shear-driven mixing. These submesoscale features are diagnosed with particular focus on their implications for ocean-to-ice heat fluxes.

  19. Antarctic sympagic meiofauna in winter: Comparing diversity, abundance and biomass between perennially and seasonally ice-covered regions

    NASA Astrophysics Data System (ADS)

    Kramer, Maike; Swadling, Kerrie M.; Meiners, Klaus M.; Kiko, Rainer; Scheltz, Annette; Nicolaus, Marcel; Werner, Iris

    2011-05-01

    This study of Antarctic sympagic meiofauna in pack ice during late winter compares communities between the perennially ice-covered western Weddell Sea and the seasonally ice-covered southern Indian Ocean. Sympagic meiofauna (proto- and metazoans >20μm) and eggs >20μm were studied in terms of diversity, abundance and carbon biomass, and with respect to vertical distribution. Metazoan meiofauna had significantly higher abundance and biomass in the western Weddell Sea (medians: 31.1×10 3 m -2 and 6.53 mg m -2, respectively) than in the southern Indian Ocean (medians: 1.0×10 3 m -2 and 0.06 mg m -2, respectively). Metazoan diversity was also significantly higher in the western Weddell Sea. Furthermore, the two regions differed significantly in terms of meiofauna community composition, as revealed through multivariate analyses. The overall diversity of sympagic meiofauna was high, and integrated abundance and biomass of total meiofauna were also high in both regions (0.6-178.6×10 3 m -2 and 0.02-89.70 mg m -2, respectively), mostly exceeding values reported earlier from the northern Weddell Sea in winter. We attribute the differences in meiofauna communities between the two regions to the older first-year ice and multi-year ice that is present in the western Weddell Sea, but not in the southern Indian Ocean. Our study indicates the significance of perennially ice-covered regions for the establishment of diverse and abundant meiofauna communities. Furthermore, it highlights the potential importance of sympagic meiofauna for the organic matter pool and trophic interactions in sea ice.

  20. Changes in the Seasonal Sea-Ice Cycle and Implications for Coastal Communities in Alaska: Community-Based Observations, Remote Sensing Data and Participatory Scenarios Analysis

    NASA Astrophysics Data System (ADS)

    Eicken, H.; Johnson, M. A.; Lee, O. A.; Kaufman, M. R.; Mueller-stoffels, M.; Lovecraft, A. L.

    2016-12-01

    While major reductions in the extent of Arctic summer sea ice have been well studied, changes in the seasonal cycle of sea ice have received less attention. Here, we discuss decadal scale changes and interannual variability in the timing of the transition seasons, spring break-up and fall freeze-up, with a focus on coastal communities in Arctic Alaska. Break-up and freeze-up determine the timing and extent of a number of human activities, ranging from ice use by Indigenous hunters to coastal shipping or resource exploration activities. The seasonal sea-ice cycle is also closely tied to the life cycle of Arctic marine organisms. Observations of ice conditions by Indigenous sea-ice experts since 2006 indicate significant interannual variability in both the character and timing of freeze-up and break-up in coastal Alaska. Based on these observations, we developed a simple algorithm to extract the timing of these events from passive microwave satellite data. Data from 1979 to 2013 show significant trends for the Chukchi and Beaufort Seas, with break-up start arriving earlier by 5-9 days per decade and freeze-up start arriving earlier by 7-14 days per decade. The observed trends and the nature of changes in winter ice, including reduced stability of coastal landfast ice, allow for projections of the ice cycle's evolution in coming years. To evaluate the implications of these observed and projected changes, we draw on a participatory scenarios project focusing on sustainable healthy communities, with a broad range of experts and citizens from northern Alaska participating in a series of three workshops. Participants identified climate and sea-ice change as one of the key drivers of community health and sustainability. Analysis of workshop products and associated data indicates that linkages between sea-ice or climate change and community health and sustainability are complicated, with shifts in the seasonal ice cycle emerging as an issue of major concern.

  1. Spatial patterns of increases and decreases in the length of the sea ice season in the north polar region, 1979-1986

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    1992-01-01

    Recently it was reported that sea ice extents in the Northern Hemisphere showed a very slight but statistically significant decrease over the 8.8-year period of the Nimbus 7 scanning multichannel microwave radiometer (SMMR) data set. In this paper the same SMMR data are used to reveal spatial patterns in increasing and decreasing sea ice coverage. Specifically, the length of the ice season is mapped for each full year of the SMMR data set (1979-1986), and the trends over the 8 years in these ice season lengths are also mapped. These trends show considerable spatial coherence, with a shortening in the sea ice season apparent in much of the eastern hemisphere of the north polar ice cover, particularly in the Sea of Okhotsk, the Barents Sea, and the Kara Sea, and a lengthening of the sea ice season apparent in much of the western hemisphere of the north polar ice cover, particularly in Davis Strait, the Labrador Sea, and the Beaufort Sea.

  2. Spatial patterns of increases and decreases in the length of the sea ice season in the north polar region, 1979-1986

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    1992-01-01

    Recently it was reported that sea ice extents in the Northern Hemisphere showed a very slight but statistically significant decrease over the 8.8-year period of the Nimbus 7 scanning multichannel microwave radiometer (SMMR) data set. In this paper the same SMMR data are used to reveal spatial patterns in increasing and decreasing sea ice coverage. Specifically, the length of the ice season is mapped for each full year of the SMMR data set (1979-1986), and the trends over the 8 years in these ice season lengths are also mapped. These trends show considerable spatial coherence, with a shortening in the sea ice season apparent in much of the eastern hemisphere of the north polar ice cover, particularly in the Sea of Okhotsk, the Barents Sea, and the Kara Sea, and a lengthening of the sea ice season apparent in much of the western hemisphere of the north polar ice cover, particularly in Davis Strait, the Labrador Sea, and the Beaufort Sea.

  3. Aircraft observations of the evolution of ice surface conditions at the onset of the melt season in the Beaufort Sea

    NASA Astrophysics Data System (ADS)

    Birnbaum, G.; Ehrlich, A.; Schwarz, P.; Lüpkes, C.; Dierking, W.; Hartmann, J.

    2012-12-01

    At the onset of the melt season in the Arctic, the energy exchange between atmosphere, sea ice, and ocean undergoes strong changes. Caused by melting of snow and formation of melt ponds and open leads the areally averaged albedo decreases dramatically and absorption of solar radiation is enhanced. To investigate these changes, the aircraft campaign MELTEX was performed from 11 May to 7 June, 2008 over the Beaufort Sea (region 69°N-74°N, 133°W-144°W). During the campaign, the sea ice cover experienced several episodes with strong on-ice warm-air advection from the Canadian Coast. Between these warm episodes, northerly flow with cold-air advection from the inner Arctic caused an interruption of melting and melt pond evolution and even a temporary refreezing. To quantify the evolution of ice surface conditions, the aircraft POLAR 5 was equipped with a digital reflex camera, broadband radiation sensors, a spectral albedometer with active horizontal stabilization, and further meteorological instruments. Images of seven flights were analyzed by means of a supervised classification employing the maximum likelihood method to derive the areal fraction of different surface classes. Areally averaged broadband and spectral albedo was derived for clear-sky conditions only to allow for a better comparison of values. On 11 May, the ice conditions were still characteristic for late winter. The maximum broadband albedo for snow covered ice was 0.82. On 26 May, already 21,6% of the sea ice surface right north of a coastal polynya consisted of wet ice (19,4%) and shallow melt ponds (2,2%). Broadband albedo measurements indicated an average value of 0.57 for melting snow and bare ice. The most enhanced stage of melting was encountered on 6 June for fast ice in Franklin and Darnley Bay, south of the Amundsen Gulf. The total fraction of melt ponds and particle-laden sea ice amounted to 45,0±16,7% with an average broadband albedo of 0.16. The average albedo of the remaining clean

  4. Prediction of Seasonal Arctic Sea Ice Extent Using the Regional Arctic System Model (RASM) - Modeling Approach and Bias Analysis

    NASA Astrophysics Data System (ADS)

    Kamal, S. M.; Maslowski, W.; Roberts, A.; Osinski, R.

    2016-12-01

    The Regional Arctic System Model (RASM) has been adapted to generate sea ice forecasts using seasonal climate forecasts from the National Centers for Environmental Prediction (NCEP) Coupled Forecast System version 2 (CFSv2) to prescribe boundary conditions required for a regional model. RASM is a fully coupled, limited-area model that includes the Weather Research and Forecasting model (WRF), the ocean (POP) and sea ice (CICE) models and the Variable Infiltration Capacity (VIC) land hydrology model with a source-to-sink routing scheme (RVIC) to export runoff to the ocean. These five components are coupled using the coupler, CPL7, which has been used in the Community Earth System Model (CESM). RASM has been developed and so far, used for hindcast simulations and their evaluation with available observations. We have configured RASM to integrate forward and to predict the minimum sea ice state in September 2016 using CFSv2 as boundary conditions. Our forecast ensemble members were initialized with CFSv2 in early June, July, and August of 2016 and ran until the end of the year. The raw ice extent forecasts from RASM were bias corrected using a simple linear regression model based on 27 years of satellite data to produce a forecast for 2016 monthly average as well as daily minimum sea ice extent and its date. We also applied 2D statistical model using satellite ice concentration maps to forecast mean September 2016 sea ice concentration maps. In this study we present the results of ensemble forecast and investigate possible reasons for model biases. In particular, the model surface energy fluxes and sea ice states during 2007, 2012, and 2016 are analyzed in more details and compared with available observations. For each of these years we evaluate the temporal and spatial distribution of radiative, latent heat and sensible heat fluxes at the surface as well as sea ice melt rate, thickness, volume, concentration and extent. Dynamic variables such as 10-meter velocity and

  5. Seasonal and Intra-Seasonal Variability of Surface Streams Over the West Greenland Ice Sheet from High Resolution Satellite Optical Data.

    NASA Astrophysics Data System (ADS)

    Brown, M. G.; Tedesco, M.

    2014-12-01

    The surface hydrology of the Greenland ice sheet plays a crucial role on surface energy and mass balance, as well as on the englacial and sub-glacial environments. The spatial distribution of these surface streams is poorly understood and their temporal variability is (to our knowledge) unknown. One of the reasons for the lack of knowledge on the temporal variability of such streams is related to the historical unavailability of satellite data that could spatially resolve the presence and associated properties of the streams. In recent years, however, multi-spectral commercial satellite data in the visible and infra-red bands have been made available to the scientific community. These newly accessible data sets are provided at spatial resolutions of the order of 1-2 meters, therefore, allowing to perform accurate spatial and temporal analysis of surface streams (and small lakes and ponds that cannot be resolved with sensors such as MODIS or LANDSAT). In this study, we report results concerning the seasonal and intra-seasonal variability of surface streams over a selected area on the west Greenland ice sheet. Using a combination of ENVI® and ArcGIS® software packages applied to multispectral high resolution imagery from World View 2 and Quickbird satellites, surface streams are identified through multiple approaches (either based on unsupervised classifications, band combinations, band ratio thresholds, or digitization) and vector maps of the surface hydrology network were created. Stream networks created during one melting season (at three different stages of the season) were compared and discussed as well as the networks mapped between two consecutive years for proximate dates.

  6. Seasonal and Intra-Seasonal Variability of Surface Streams over the West Greenland Ice Sheet from High Resolution Satellite Optical Data.

    NASA Astrophysics Data System (ADS)

    Brown, Michael G.; Tedesco, Marco

    2015-04-01

    The surface hydrology of the Greenland ice sheet plays a crucial role on surface energy and mass balance, as well as on the en-glacial and sub-glacial environments. The spatial distribution of these surface streams is poorly understood and their temporal variability is (to our knowledge) unknown. One of the reasons for the lack of knowledge on the temporal variability of such streams is related to the historical unavailability of satellite data that could spatially resolve the presence and associated properties of the streams. In recent years, however, multi-spectral commercial satellite data in the visible and infra-red bands have been made available to the scientific community. These newly accessible data sets are provided at spatial resolutions of the order of 1-2 meters, therefore, allowing to perform accurate spatial and temporal analysis of surface streams (and small lakes and ponds that cannot be resolved with sensors such as MODIS or LANDSAT). In this study, we report results concerning the seasonal and intra-seasonal variability of surface streams over a selected area on the west Greenland ice sheet. Using ArcGIS® software applied to multispectral high resolution imagery from World View 2 and Quickbird satellites, surface streams were identified through band math, threshold classifications, and morphological operations. Raster and vector maps of the surface hydrology network were created. Stream networks created during multiple melt seasons (at several different stages of the season) were compared and discussed as well as the networks mapped between consecutive years for proximate dates.

  7. Carbon dating reveals a seasonal progression in the source of particulate organic carbon exported from the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Kohler, T. J.; Žárský, J. D.; Yde, J. C.; Lamarche-Gagnon, G.; Hawkings, J. R.; Tedstone, A. J.; Wadham, J. L.; Box, J. E.; Beaton, A. D.; Stibal, M.

    2017-06-01

    Surface melt from the Greenland Ice Sheet (GrIS) collects particulate organic carbon (POC) as it drains into subglacial environments and transports it downstream where it serves as a microbial substrate. We hypothesized that older POC is entrained by meltwaters as the subglacial drainage network expands upglacier over the summer. To test this, POC samples were collected from a meltwater river exiting the GrIS over an ablation season and 14C dated. Resulting values were compared with meltwater hydrochemistry and satellite observations of the catchment area. We found that POC ages increased from 5000 to 9000 years B.P. until peak discharge and catchment size. Afterward, significant fluctuations in POC age were observed, interpreted to result from periods of high and low subglacial hydrological pressure and sediment supply and subsequent exhaustion. These observations suggest a seasonal progression in the source of POC exported from the GrIS and provide evidence for a seasonally evolving subglacial drainage system.

  8. Diurnal and Seasonal Fluctuations in Rectal Temperature, Respiration and Heart Rate of Pack Donkeys in a Tropical Savannah Zone

    PubMed Central

    AYO, Joseph O.; DZENDA, Tavershima; OLAIFA, Folashade; AKE, Stephen A.; SANI, Ismaila

    2014-01-01

    ABSTRACT The study was designed to determine diurnal and seasonal changes in basic physiologic responses of donkeys adapted to the tropical Savannah. The rectal temperature (RT), respiratory rate (RR) and heart rate (HR) of six male Nubian pack donkeys, and the dry-bulb temperature (DBT), relative humidity and heat index of the experimental site were concurrently recorded hourly, from 06:00 h to 18:00 h (GMT +1), for three days, spread 1 week apart, during the cold-dry (harmattan), hot-dry and humid (rainy) seasons, in an open grazing field. Values of the physiologic parameters recorded during the morning (06:00 h–11:00 h) were lower (P<0.001) than those obtained in the afternoon (12:00 h–15:00 h) and evening (16:00 h–18:00 h) hours in all seasons, but the robustness of the diurnal rhythm differed (P<0.05) between seasons. Many diurnal hourly DBT mean values recorded during the harmattan and hot-dry seasons fell outside the established thermoneutral zone for tropically-adapted donkeys, while those obtained during the rainy season were within the zone, indicating that the dry seasons were more thermally stressful to the donkeys than the humid season. Overall mean RT dropped (P<0.05) during the harmattan season. The RR rose, while HR dropped (P<0.001) during the hot-dry season. In conclusion, daytime and season had profound influence on RT, RR and HR of the donkeys, therefore, diurnal and seasonal variations should be taken into account during clinical evaluation before reaching conclusion on health status and fitness for work in donkeys. PMID:24834007

  9. Diurnal and seasonal fluctuations in rectal temperature, respiration and heart rate of pack donkeys in a tropical savannah zone.

    PubMed

    Ayo, Joseph O; Dzenda, Tavershima; Olaifa, Folashade; Ake, Stephen A; Sani, Ismaila

    2014-01-01

    The study was designed to determine diurnal and seasonal changes in basic physiologic responses of donkeys adapted to the tropical Savannah. The rectal temperature (RT), respiratory rate (RR) and heart rate (HR) of six male Nubian pack donkeys, and the dry-bulb temperature (DBT), relative humidity and heat index of the experimental site were concurrently recorded hourly, from 06:00 h to 18:00 h (GMT +1), for three days, spread 1 week apart, during the cold-dry (harmattan), hot-dry and humid (rainy) seasons, in an open grazing field. Values of the physiologic parameters recorded during the morning (06:00 h-11:00 h) were lower (P<0.001) than those obtained in the afternoon (12:00 h-15:00 h) and evening (16:00 h-18:00 h) hours in all seasons, but the robustness of the diurnal rhythm differed (P<0.05) between seasons. Many diurnal hourly DBT mean values recorded during the harmattan and hot-dry seasons fell outside the established thermoneutral zone for tropically-adapted donkeys, while those obtained during the rainy season were within the zone, indicating that the dry seasons were more thermally stressful to the donkeys than the humid season. Overall mean RT dropped (P<0.05) during the harmattan season. The RR rose, while HR dropped (P<0.001) during the hot-dry season. In conclusion, daytime and season had profound influence on RT, RR and HR of the donkeys, therefore, diurnal and seasonal variations should be taken into account during clinical evaluation before reaching conclusion on health status and fitness for work in donkeys.

  10. Using Seismic Noise Generated by Ocean Waves to Monitor Seasonal and Secular Changes in Antarctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Anthony, R. E.; Aster, R. C.; Thompson, D. W. J.; Reusch, D. B.

    2015-12-01

    The Earth's background seismic noise between ~1-30 seconds period is commonly dominated by microseisms that arise when oceanic wave energy and swell are converted to ground displacement as the waves crash and interact with the continental shelf. Peak power in the microseism bands at high-latitude stations typically coincides with large-scale extratropical cyclonic winter storm activity. However, due to the seasonal formation of sea ice around the continental shelves of polar regions, oceanic waves are impeded from efficiently exciting seismic energy, and annual peak microseism power thus occurs prior to the midwinter storm peak. We utilize recently collected seismic data from across the continent to show that power in three distinct microseism bands is found to be strongly anti-correlated with sea ice extent, with the shorter period signals being exceptionally sensitive to local conditions. Particular focus is given to the Antarctic Peninsula, the strongest source of microseism energy on the continent, where we note a significant increase in primary microseism power attributable to near coastal sources from 1993-2012. This increase correlates with regional sea ice loss driven by large-scale wind changes associated with strengthening of the Southern Annular Mode. Additionally, we use microseism analysis to explore changes in sea ice strength and extent relative to wave state and storminess in the Southern Oceans. Investigation of microseism seasonality, power, and decadal-scale trends in the Antarctic shows promise as a spatially integrated tool for monitoring and interpreting such sea ice strength and extent metrics through time.

  11. Sclerochronological analysis of Saxidomus gigantea: Implications for reconstructing past seasonality and sea ice extent in the Northern Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Bassett, C.; Andrus, C. F. T.

    2015-12-01

    Sclerochronological analysis of biogenic carbonates provides valuable paleoenvironmental information. Oxygen isotope analysis of bivalve shell yields information on the temperature of the water in which the organism grew. However, in coastal environments, variations in δ18Owater may complicate the interpretation of shell isotope profiles. Measuring and comparing the length of seasonal shell growth in select species of bivalves may complement isotopic analysis, together providing a more precise paleoclimate reconstruction. This project aims to determine the reliability of sclerochronological analysis of bivalves in reconstructing seasonality along the Northwest Coast of North America. To compare bivalves growing at different seasonal temperature conditions, samples of Saxidomus gigantea were collected from southern Alaska and northern British Columbia. Winter cessation lines were identified using oxygen isotope (δ18O) peaks from a profile of variation over the life of the clam, which was sampled sequentially from a section of its shell. Shell growth stops below ~4-5°C and so each winter cessation indicates temperatures lower than this threshold. Lunar-daily growth lines were counted between these winter growth cessation breaks, which quantitatively measure the length of the growing season. The resulting data were compared between habitats to assess if this is a useful method of determining the length of the growing season. If this method of assessing seasonality appears valid, it can be applied to ancient shells abundant in archaeological shell middens to make inferences about past seawater conditions and potentially indicate the presence or absence of the conditions necessary for sea ice accumulation.

  12. Simulated Annual and Seasonal Arctic Ocean and Sea-Ice Variability From a High Resolution, Coupled Ice-Ocean Model

    DTIC Science & Technology

    2001-09-01

    for their valuable insights and assistance. Without the help of Drs. Don Stark, Waldemar Walczowski , Julie McClean, and Yuxia Zhang here at the...Bert Semtner, Dr. Don Stark, Dr. Yuxia Zhang, and Dr. Waldemar Walczowski along with myself and collaborators from other institutions. The research... Walczowski and A. J. Semtner, On large scale shifts in the Arctic Ocean and sea ice conditions during 1979-1998, in press Annals Glac., 2001. Matishov

  13. Seasonal variation in freeze tolerance and ice content of the tree frog Hyla versicolor.

    PubMed

    Layne, J R; Lee, R E

    1989-02-01

    Freeze tolerance and ice content of Hyla versicolor showed pronounced variation between summer (June) and winter (December). Summer frogs survived freezing at -3 degrees C for up to 9 hr and ice accumulation up to 50% of their total body water. A time course of ice formation indicated that an equilibrium level was reached in approximately 15 hr. Thus, the lethal ice content was less than the equilibrium ice content for these conditions (63.1%). A second group was induced to enter an overwintering condition by holding them through the summer and then subjecting them to a progressive reduction in temperature and photoperiod for 2 months. These frogs survived freezing for 48 hr at -3 degrees C. Their equilibrium ice content at this temperature was significantly lower (52.5%) than comparably treated summer animals. In the winter acclimatized group, frozen frogs had substantially higher blood glucose levels than unfrozen frogs (22.7 mumol/ml vs. 1.33 mumol/ml), but glycerol levels were not elevated after freezing. Freezing frogs conditioned for overwintering at -7 degrees C resulted in a higher equilibrium ice content (62.6%), but none survived. It is evident that in preparation for overwintering, frogs reduce the amount of ice formed at a given subzero temperature, but there is little indication of a substantial change in the total amount of ice tolerated.

  14. Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China.

    PubMed

    Tang, Qiang; Bao, Yuhai; He, Xiubin; Fu, Bojie; Collins, Adrian L; Zhang, Xinbao

    2016-04-01

    Since the launch of the Three Gorges Dam on the Yangtze River, a distinctive reservoir fluctuation zone has been created and significantly modified by regular dam operations. Sediment redistribution within this artificial landscape differs substantially from that in natural fluvial riparian zones, due to a specific hydrological regime comprising steps of water impoundment with increasing magnitudes and seasonal water level fluctuation holding a range of sediment fluxes. This study reinterpreted post-dam sedimentary dynamics in the reservoir fluctuation zone by stratigraphy determination of a 345-cm long sediment core, and related it to impact of the hydrological regime. Seasonality in absolute grain-size composition of suspended sediment was applied as a methodological basis for stratigraphic differentiation. Sedimentary laminations with relatively higher proportions of sandy fractions were ascribed to sedimentation during the dry season when proximal subsurface bank erosion dominates source contributions, while stratigraphy with a lower proportion of sandy fractions is possibly contributed by sedimentation during the wet season when distal upstream surface erosion prevails. Chronology determination revealed non-linear and high annual sedimentation rates ranging from 21.7 to 152.1cm/yr. Although channel geomorphology may primarily determine the spatial extent of sedimentation, seasonal sedimentary dynamics was predominantly governed by the frequency, magnitude, and duration of flooding. Summer inundation by natural floods with enhanced sediment loads produced from upstream basins induced higher sedimentation rates than water impoundment during the dry season when distal sediment supply was limited. We thus conclude that flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone, though little impact on total sediment retention rate was detected. Ongoing reductions in flow and sediment supply under human disturbance may

  15. In situ measurements of an energetic wave event in the Arctic marginal ice zone

    NASA Astrophysics Data System (ADS)

    Collins, Clarence O.; Rogers, W. Erick; Marchenko, Aleksey; Babanin, Alexander V.

    2015-03-01

    R/V Lance serendipitously encountered an energetic wave event around 77°N, 26°E on 2 May 2010. Onboard GPS records, interpreted as the surface wave signal, show the largest waves recorded in the Arctic region with ice cover. Comparing the measurements with a spectral wave model indicated three phases of interaction: (1) wave blocking by ice, (2) strong attenuation of wave energy and fracturing of ice by wave forcing, and (3) uninhibited propagation of the peak waves and an extension of allowed waves to higher frequencies (above the peak). Wave properties during fracturing of ice cover indicated increased groupiness. Wave-ice interaction presented binary behavior: there was zero transmission in unbroken ice and total transmission in fractured ice. The fractured ice front traveled at some fraction of the wave group speed. Findings do not motivate new dissipation schemes for wave models, though they do indicate the need for two-way, wave-ice coupling.

  16. Sinking Particle Flux in the Sea Ice Zone of the Amundsen Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Kim, M.; Hwang, J.; Kim, H. J.; Kim, D.; Ducklow, H. W.; Lee, S. H.; Yang, E. J.; Lee, S.

    2014-12-01

    We have examined the flux, compositions of biogenic components, and isotopic values of sinking particles collected by a sediment trap deployed in the sea ice zone (SIZ) of the Amundsen Sea from January 2011 for one year. Major portion of the particle flux occurred during the austral summer in January and February when sea ice concentration was reduced to below 60 %. Biogenic components, dominated by opal, accounted for over 75 % during this high flux period. The dominant source of sinking particles shifted from diatoms to soft-tissued organisms, evidenced by high particulate organic carbon (POC) content (> 30 %) during the polar night. CaCO3 content and its contribution to total particle flux were low throughout the study period. Contribution of aged POC likely supplied from sediment resuspension was considerable only from October to December, evidenced by low radiocarbon content and relatively high (30-50 %) content of the non-biogenic component. When compared to POC flux inside the Amundsen Sea polynya obtained by the US Amundsen Sea Polynya International Research Expedition (ASPIRE), the POC flux integrated over the austral summer in the SIZ was virtually identical although maximum POC flux was about half that inside the Amundsen Sea polynya. This comparatively high POC flux in the SIZ may be caused by persistence of phytoplankton bloom for longer period and more efficient export of organic matter owing to the diatom-dominant plankton community. If this observation is a general phenomenon on the Amundsen shelf, the role of the SIZ compared to the polynyas need to be examined more carefully when trying to characterize the POC export in this region.

  17. Sinking particle flux in the sea ice zone of the Amundsen Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Kim, Minkyoung; Hwang, Jeomshik; Kim, Hyung J.; Kim, Dongseon; Yang, Eun J.; Ducklow, Hugh W.; Hyoung, S. La; Lee, Sang H.; Park, Jisoo; Lee, SangHoon

    2015-07-01

    We have examined the flux, biogenic composition, and isotopic values of sinking particles collected by a time-series sediment trap deployed in the sea ice zone (SIZ) of the Amundsen Sea from January 2011 for 1 year. The major portion of the particle flux occurred during the austral summer in January and February when sea ice concentration was reduced to <60%. Biogenic components, dominated by opal (~78% of the biogenic components), accounted for over 75% of particle flux during this high-flux period. The dominant source of sinking particles shifted from diatoms to soft-tissued organisms, evidenced by high particulate organic carbon (POC) content (>30%) and a low bio-Si/POC ratio (<0.5) during the austral winter. CaCO3 content and its contribution to total particle flux was low (~6%) throughout the study period. Aged POC likely supplied from sediment resuspension accounted for a considerable fraction only from October to December, which was evidenced by a low radiocarbon content and relatively high (30-50%) content of the non-biogenic components. When compared with POC flux inside the Amundsen Sea polynya obtained by the US Amundsen Sea Polynya International Research Expedition (ASPIRE), the POC flux integrated over the austral summer in the SIZ was virtually identical, although the maximum POC flux was approximately half that inside the Amundsen Sea polynya. This comparatively high POC flux integrated over the austral summer in the SIZ may be caused by phytoplankton blooms persisting over a longer periods and more efficient export of organic matter potentially owing to the diatom-dominant plankton community. If this observation is a general phenomenon on the Amundsen Shelf, the role of the SIZ, compared with the polynyas, need to be examined more carefully when trying to characterize the POC export in this region.

  18. Viable Particles from Iodine Compounds in the Antarctic Sea Ice Zone

    NASA Astrophysics Data System (ADS)

    Roscoe, H. K.; Jones, A. E.; Brough, N.; Weller, R.; Saiz-Lopez, A.; Mahajan, A. S.; Schoenhardt, A.; Burrows, J. P.; Fleming, Z.

    2015-12-01

    Aerosol particle number concentrations have been measured at Halley and Neumayer on the Antarctic coast, since 2004 and 1984 respectively. Sulphur compounds known to be implicated in particle formation and growth were independently measured: sulphate ions and methane sulphonic acid in filtered aerosol samples; and gas-phase di-methyl sulphide for limited periods. Iodine oxide, IO, was determined by a satellite sensor from 2003 to 2009, and by different ground-based sensors at Halley in 2004 and in 2007. Previous model results and mid-latitude observations show that iodine compounds consistent with the large values of IO observed may be responsible for an increase in number concentrations of small particles. Coastal Antarctica is useful for investigating correlations between particles, sulphur and iodine compounds, because of their large annual cycles together with the source of iodine compounds in sea ice. After smoothing all measured data by several days, the shapes of the annual cycles in particle concentration at Halley and at Neumayer are approximated by linear combinations of the shapes of sulphur compounds and IO, but not by sulphur compounds alone. However, there is no short-term correlation between IO and particle concentration. The apparent correlation after smoothing but not in the short term suggests that iodine compounds and particles are sourced some distance offshore. This suggests that new particles formed from iodine compounds are viable, i.e. they can last long enough to grow to the larger particles that contribute to Cloud Condensation Nuclei, rather than being adsorbed by existing particles. If so there is significant potential for climate feedback near the sea ice zone via the aerosol indirect effect.

  19. Low melt rates with seasonal variability at the base of Fimbul Ice Shelf, East Antarctica, revealed by in situ interferometric radar measurements

    NASA Astrophysics Data System (ADS)

    Langley, Kirsty; Kohler, Jack; Sinisalo, Anna; Øyan, Mats Jørgen; Hamran, Svein Erik; Hattermann, Tore; Matsuoka, Kenichi; Nøst, Ole Anders; Isaksson, Elisabeth

    2014-11-01

    Basal melt is a major cause of ice shelf thinning affecting the stability of the ice shelf and reducing its buttressing effect on the inland ice. The Fimbul ice shelf (FIS) in Dronning Maud Land (DML), East Antarctica, is fed by the fast-flowing Jutulstraumen glacier, responsible for 10% of ice discharge from the DML sector of the ice sheet. Current estimates of the basal melt rates of the FIS come from regional ocean models, autosub measurements, and satellite observations, which vary considerably. This discrepancy hampers evaluation of the stability of the Jutulstraumen catchment. Here, we present estimates of basal melt rates of the FIS using ground-based interferometric radar. We find a low average basal melt rate on the order of 1 m/yr, with the highest rates located at the ice shelf front, which extends beyond the continental shelf break. Furthermore, our results provide evidence for a significant seasonal variability.

  20. Dry season refugia of malaria-transmitting mosquitoes in a dry savannah zone of east Africa.

    PubMed

    Charlwood, J D; Vij, R; Billingsley, P F

    2000-06-01

    Dry season survival of Anopheles funestus, Anopheles gambiae and Anopheles arabiensis in the Kilombero valley a dry savannah zone of east Africa, was investigated with over 400 collections from 23 areas, covering 300 sq km of the valley. Anopheles gambiae was found only in association with humans, in forested areas of high annual rainfall, while An. funestus occurred at high densities at the valley edge where large non-moving bodies of water remained. A large population of An. arabiensis was present along the river system throughout the middle of the valley, and mosquitoes probably derived from this population were occasionally caught in villages bordering the valley. No evidence was obtained of aestivation in any mosquito species. Anopheles gambiae was the most long lived, 6.3% compared to 2.0% of the An. arabiensis and 4% of the An. funestus surviving for four or more gonotrophic cycles, the approximate duration of the extrinsic cycle of most malaria parasites. Oocysts of malaria parasites were found in 5.4% of An. funestus and 2.3% of An. arabiensis from villages. Oocyst rates in An. funestus differed significantly between areas but not between houses within areas. Anopheles funestus is the most important dry season malaria vector in the valley, and remains in foci closely associated with groups of houses. All three species survive at high densities but as otherwise hidden refugia populations.