bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors Affecting the Success Rate of External Dacryocystorhinostomy at B. P. Koirala Institute of Health Sciences, Dharan, Nepal
Authors: Pokharel Shailesh Mani , Chaudhary SK , Chaurasiya BD
Published: November 2017

IntroductionAny disturbance to the normal ouVlow of tears through the nasolacrimal passage causes overﬂow known as epiphora. The clinical symptoms of epiphora range from mild dribble to the continuous ouVlow of tears. Watering of eyes caused by the nasolacrimal drainage  obstruction  is  managed  by surgery. One of the many surgeries to treat this is external dacryocystorhinostomy.ObjectiveThe objective of this study was to evaluate the success rate of external dacryocystorhinostomy as well as factors aﬀecting it.MethodologyThis is a retrospective cross-sectional study, conducted in the Department of Ophthalmology, B. P. Koirala Institute of Health Sciences (BPKIHS), Dharan with the approval of Institutional Review Committee, BPKIHS. The medical records of patients who underwent external Dacryocystorhinostomy surgery from April 2011 to April 2016 at BPKIHS were retrospectively reviewed. Statistical analysis was performed using SPSS for windows, version 11.5 (SPSS Inc., Chicago, IL). Binary logistic regression models were used to investigate the association of the surgical outcome with various predicting variables.ResultsThe success rate of the external dacryocystorhinostomy was 78.09%. Factors studied were: age, with a range of 2-81 years; duration of symptoms with a range of 1-84 months; and gender of the patients. The intra-operative factors studied were use of silastic tube, types of ﬂap, and osteotomy size. Among these factors, the duration of symptoms and osteotomy size had signiﬁcant association with the outcome of the surgery p<0.05.ConclusionOur study yielded high success rate in patients with shorter duration of watering of eyes and larger osteotomy size during surgery. Hence, a larger osteotomy size and early intervention is recommended for better surgical outcome. Birat Journal of Health Sciences Vol.2/No.1/Issue 2/ Jan - April 2017, Page: 196-200
Correlation of Fine Needle Aspiration Cytology and Histopathology of the Neck Swellings Presenting at National Academy of Medical Sciences, Kathmandu, Nepal
Authors: Devkota Harihar , Sibakoti YC , Menyangbo S , Basnet S , Jha MK , Banstola L
Published: November 2017

IntroductionNeck masses are frequently found in clinical practice. A spectrum of pathological lesions ranging from inflammation to benign and highly malignant manifestation is observed. Fine needle aspiration cytology (FNAC) of neck masses is a quick, easy, safe and cheap technique in the diagnosis which has been a well-accepted procedure in diagnosing various swellings. Histopathology is a gold standard technique in diagnosing any swelling which also provide detail architecture, however it also requires OT setings, more manpower, expensive, time consuming, more traumatic and can sometimes become difficult.ObjectiveThe objective of our study was to evaluate the frequencies of neck swellings and how efficacy FNAC is in diagnosing neck masses by correlating the gold standard histopathological examination.MethodologyA Hospital based descriptive cross sectional prospective study was conducted in 50 patients with neck swellings presenting in the surgery OPD and admitied patient for some other reasons. FNAC and histopathological examinations were done from those lesions and were compared. The sensitivity, specificity and accuracy rates were calculated. Data entry and analysis was performed using SPSS.ResultsA total of 50 patient were subjected to both FNAC and histopathology examination (HPE). Out of 50 cases, 25 were male and 25 were female. The age ranged from 16 to 82 years. Lymph nodes 22 (44%) was the most common case, followed by thyroid 17 (34%), salivary glands 10 (20%) and soft issue 1 (2%).Among all Tubercular lymphadenitis (18%) followed by papillary carcinoma of thyroid (14%),metastatic carcinoma of lymph node, NHL, and pleomorphic adenoma 10% each. The sensitivity of FNAC in diagnosing neck masses is 90.08%, specificity is of 98.53%, and diagnostic accuracy is of 87.64%.ConclusionFNAC is a simple, fast, inexpensive, and minimally invasive technique which can be used as the first line investigation in diagnosing neck swellings.Birat Journal of Health SciencesVol.2/No.1/Issue 2/ Jan - April 2017, page: 206-210
Thermal-hydraulic analysis of research reactor core with different LEU fuel types using RELAP5
Authors: El-Sahlamy N. M.
Published: November 2017

In the current work, comparisons between the core performances when using different LEU fuels are done. The fuels tested are UA1X-A1, U3O8-Al, and U3Si2-Al fuels with 19.7 % enrichment. Calculations are done using RELAP5 code to evaluate the thermal-hydraulic performance of the IAEA benchmark 10 MW reactor. First, a reassessment of the slow reactivity insertion transient with UA1X-A1 LEU fuel to compare the results with those reported in the IAEA TECDOC [1]. Then, comparisons between the thermal-hydraulic core performances when using the three LEU fuels are done. The assessment is performed at initial power of 1.0 W. The reactor power is calculated using the RELAP5 point kinetic model. The reactivity feedback, from changes in water density and fuel temperature, is considered for all cases. From the results it is noticed that U3Si2-Al fuel gives the best fuel performance since it has the minimum value of peak fuel temperature and the minimum peak clad surface temperature, as operating parameters. Also, it gives the maximum value of the Critical Heat Flux Ratio and the lowest tendency to flow instability occurrence.
Robust observer based control for axial offset in pressurized-water nuclear reactors based on the multipoint reactor model using Lyapunov approach
Authors: Zaidabadinejad M. , Ansarifar G. R.
Published: November 2017

In nuclear reactor imbalance of axial power distribution induces xenon oscillations. These fluctuations must be maintained bounded within allowable limits. Otherwise, the nuclear power plant could become unstable. Therefore, bounded these oscillations is considered to be a restriction for the load following operation. Also, in order to design the nuclear reactor control systems, poisons concentrations, especially xenon must be accessible. But, physical measurement of these parameters is impossible. In this paper, for the first time, in order to estimate the axial xenon oscillations and ensures these oscillations are kept bounded within allowable limits during load-following operation, a robust observer based nonlinear control based on multipoint kinetics reactor model for pressurized-water nuclear reactors is presented. The reactor core is simulated based on the multi-point nuclear reactor model (neutronic and thermal-hydraulic). Simulation results are presented to demonstrate the effectiveness of the proposed observer based controller for the load-following operation.
The integrity of NSSS and containment during extended station blackout for Kuosheng BWR plant
Authors: Hsu K.-H. , Yuann Y.-R. , Lin A.
Published: November 2017

The Fukushima Daiichi accident occurring on March 11, 2011, reveals that Station Blackout (SBO) may last longer than 8 h. However, the original design may not have sufficient capacity to cope with a SBO for more than 8 h. In view of this, Taiwan Power Company has initiated several enhancements to mitigate the severity of the extended SBO. Based on the improved plant configuration, a SBO coping analysis is performed in this study to assess whether the Kuosheng BWR plant has sufficient capability to cope with SBO for 24 h with respect to maintaining the integrity of the reactor core and containment. The analyses in the Nuclear Steam Supply System (NSSS) and the containment are based on the RETRAN-3D and GOTHIC models, respectively. The flow conditions calculated by RETRAN-3D during the event are retrieved and input to the GOTHIC containment model to determine the containment pressure and temperature response. These boundary conditions include SRV flow rate, SRV flow enthalpy, and total reactor coolant system leakage flow rate.
Experimental investigation of effect of spacer on two phase turbulent mixing rate in subchannels of pressure tube type BWR
Authors: Verma S. K. , Sinha S. L. , Chandraker D. K.
Published: November 2017

Turbulent mixing rate between adjacent subchannels in a two-phase flow has been known to be strongly dependent on the flow pattern. The most important aspect of turbulent motion is that the velocity and pressure at a fixed point do not remain constant with time even in steady state but go through very irregular high frequency fluctuations. These fluctuations influence the diffusion of scalar and vector quantities. The Advanced Heavy Water Reactor (AHWR) is a vertical pressure tube type, heavy water moderated and boiling light water cooled natural circulation based reactor. The fuel bundle of AHWR contains 54 fuel rods set in three concentric rings of 12, 18 and 24 fuel rods. This fuel bundle is divided into number of imaginary interacting flow channel called subchannels. Alteration from single phase to two phase flow situation occurs in reactor rod bundle with raise in power. The two phase flow regimes like bubbly, slug-churn, and annular flow are generally encountered in reactor rod bundle. Prediction of thermal margin of the reactor has necessitated the investigation of turbulent mixing rate of coolant between these subchannels under these flow regimes. Thus, it is fundamental to estimate the effect of spacer grids on turbulent mixing between subchannels of AHWR rod bundle.
Identifying areas of low-profile ice sheet and outcrop damming in the
Antarctic ice sheet by ERS-1 satellite altimetry
Authors: Vaughan David G. , Bamber Jonathan L.
Published: November 2017

A digital elevation model (DEM) of the surface of the Antarctic ice sheet is
compared with a simple two-dimensional ice-flow model to illuminate gross
distortions (>500 m) of the ice-surface elevation. We use a DEM derived
from ERS-1 satellite altimetry, airborne data and TWERLE balloon data. This is
compared with an ice-sheet elevation model generated by applying theoretical
surface elevations, calculated for two-dimensional ice flow, to isolines of
distance from the grounding line (continentality). The model is scaled using only
one parameter, to match the measured surface elevation at Dome Argus. The model is
far from rigorous, violating continuity conditions, ignoring variations in surface
mass balance and temperature, and assuming uniform basal conditions. However, the
comparison of model and observed surface elevations is illuminating in terms of
the behaviour of the ice sheet at a continental scale. Across the ice sheet the
rms difference between modelled elevation and the DEM is around 300 m, but much of
this results from isolated areas of much greater disagreement. We ascribe these
gross differences to the effects of basal conditions. in four areas, the observed
surface is more than 500 m higher than the modelled surface. Most of these are
immediately upstream of substantial areas of rock outcrop and are caused by the
damming effect of these mountain ranges. in nine areas, the measured surface is
more than 500 m lower than predicted. Eight of these areas, in West Antarctica and
the Lambert Glacier basin, are associated with suspected areas of basal sliding.
The ninth is an area of 250 000 km2 in East Antarctica not
previously noted as having unusual flow characteristics, but for which very
few-data exist. We speculate that this area results from unusual basal conditions
resulting in a low-profile ice sheet. A low-profile ice sheet of this size with in
the East Antarctic ice sheet indicates that basal conditions are perhaps more
variable than previously thought.
First point measurements of ice-sheet thickness change in Antarctica
Authors: Hamilton Gordon S. , Whillans Ian M. , Morgan Peter J.
Published: November 2017

Ice-sheet thickening or thinning rates in Antarctica are measured using the
“coffee-can” or “submergence velocity” method. in this, repeated measurements of
the positions of firn anchors are obtained using the global positioning system
(GPS). The thickness change is (lie difference between vertical velocity so
obtained and long-term rate of snow accumulation. Minor corrections for firn
settling and downslopc motion are made. The technique avoids difficulties of
short-term fluctuations in snowfall or snow den-sification. The result for Byrd
Station is near balance, -0.004 (0.022) ma−1, and for the
Dragon, just outboard of Ice Stream B, thinning at -0.096 (0.044)
ma−1. Uncertainties with these first results are mainly
due to the short occupation times during the first GPS surveys.
Modelling the Antarctic and Northern Hemisphere ice-sheet changes with global
climate through the Glacial cycle
Authors: Budd W. F. , Coutts B. , Warner Roland C.
Published: November 2017

The future behaviour of the Antarctic ice sheet depends to some extent on its
current state of balance and its past history. The past history is primarily
influenced by global climate changes, with some small amount of local feedback,
and by sea-level changes generated primarily by the Northern Hemisphere ice-sheet
changes, again with a small amount of feedback from the Antarctic ice sheet. An
ice-sheet model which includes ice shelves has been used to model the Antarctic
region and the whole Northern Hemisphere high-latitude region through the last
ice-age cycle. For the climate forcing, the results from the global energy-balance
model of Budd and Rayner (1990) are used. These are based on the Earth's orbital
radiation changes with ice-sheet albedo feedback. Additional sensitivity studies
are carried out for the amplitudes of the derived temperature changes and for
changes in precipitation over the ice-sheets. For the Antarctic snow-accumulation
changes, the results from the Voslok ice core are used with proportional changes
over the rest of the ice sheet. For the sea-level variations, the results
generated by the Northern Hemisphere ice-sheet changes provide the primary
forcing, but account is also taken of the feedback effects from bed response under
changing ice and ocean loading and from the Antarctic changes.

The results of the modelling provide a wide range of features for comparison
with observations, such as the margins of maximum ice extent. For the Northern
Hemisphere the results indicate that the peak mean temperature shift required for
the ice-edge region is about -12°C, whereas outside the ice-sheet region this
change is smaller but over the ice sheets it is larger. For the Antarctic region
during the ice age the interior region decreases in thickness, due to lower
accumulation, while the grounding-edge region expands and thickens due to the
sea-level lowering. As a result, the derived present state of balance shows a
positive region over most of inland East Antarctica, whereas coastal regions tend
to be nearer to balance, with some slightly negative regions around some of the
large ice shelves and coastal ice streams which are still adjusting slowly to the
post-ice-age changes of sea level and accumulation rates.
Simulations of the Northern Hemisphere through the last Glacial-interglacial
cycle with a vertically integrated and a three-dimensional thermomechanical
ice-sheet model coupled to a climate model
Authors: Calov R. , Marsiat I.
Published: November 2017

We present simulations of the Northern Hemisphere land ice through the last
glacial-interglacial cycle with a vertically integrated ice-sheet model and a
three-dimensional thermomechanical ice-sheet model. Both models are coupled
asynchronously to the zonally averaged Louvain-la-Neuve climate model, which
includes simplified treatments of the atmosphere, ocean and sea ice. The
two-dimensional vertically integrated ice-sheet model, which contains no
thermomechanical coupling, was developed in spherical coordinates (Marsiat, 1994).
The three-dimensional thermomechanical ice-sheet model was developed using the
two-dimensional vertically integrated model as source.

We compare results of the vertically integrated with those of the
thermomechanical ice-sheet model. in the thermomechanical model the deformation
properties of ice depend on the temperature within the ice and the enhancement
factor; the latter is introduced to model, in a simplified approach, the different
flow properties of Pleistocene and Holocene ice due to varying dust content. The
computations with the thermomechanical model show that the growth and decay of the
Northern Hemisphere ice sheets can be modelled with a common enhancement factor
for all ice sheets. It is shown that there are model set-ups for the
thermomechanical model yielding temporal developments of the total ice volume
comparable to those of the vertically integrated model. Furthermore, we
demonstrate that for the coupled climate/cryosphere system the total ice volume
depends considerably on the enhancement factor.
Surface meltstreams on the Amery Ice Shelf, East Antarctica
Authors: Phillips Helen A.
Published: November 2017

A topographic map of a 120 km by 20 km section of the Amery Ice Shelf, East
Antarctica, mapped with the global positioning system (GPS) in the spring of 1995,
revealed two long, shallow troughs in the ice-shelf surface. Smooth features
coinciding with these troughs appeared in a synthetic aperture radar image
acquired 18 months earlier. ERS-1 altimeter waveform sequences and backscatter
measurements along repeat satellite ground tracks across the same section of the
Amery Ice Shelf, for the 1993-94 summer, exhibited a dramatic change over a 2 km
sector between 30 January and 2 February 1994. The change is consistent with the
presence of liquid water on the ice-shelf surface, located in the deeper of the
two troughs. A time series of special sensor microwave/ imager brightness
temperatures over the Lambert Glacier-Amery Ice Shelf region for the same period
has sharp maxima on 5 January and 21 January 1994. These maxima are interpreted as
the melting events leading to the meltstream observed in the altimeter data 25
days later.
Simulation of the influence of ice rheology on velocity profiles and ice-sheet
mass balance
Authors: Wang W. L. , Warner Roland C.
Published: November 2017

Assessment of the effect of the Antarctic ice sheet on sea level requires an
accurate determination of its current state of balance. This is usually done by
comparing the ice net accumulation for an area with the net outward flow of the
ice. To obtain the net outward flux to better than 20% accuracy the relationship
between the column-integrated ice flux and measurements of ice-sheet thickness and
surface velocity must be considered. That relationship is summarised by the ratio
of depth-averaged velocity
ϒ
to surface velocity γs
in areas where ice sliding can be neglected, this ratio strongly
reflects the rheological properties of the ice and depends on the shear
strain-rate profile through the ice column, which is influenced by profiles of
stress, temperature and ice-crystal fabric.

We present calculations from a flowline
model of a hypothetical large ice sheet to demonstrate how development of an
anisotropic ice-crystal fabric can influence the depth profile of horizontal
velocity. The temperature dependence of ice rheology, combined with typical
ice-sheet temperature profiles, yields a more block-like velocity profile with
increasing to
values in the range 0.89-0.96 from the isothermal rheology value of 0.8. Our
results show that the onset of enhanced shear flow with increasing shear strain,
as a consequence of anisotropy, and then a reduction of enhancement nearer the
bedrock, can modify the velocity profile, giving values typically
in the range 0.86-0.91. Smaller values than these may also occur for rougher
bedrock or thinner ice.
Simulation of the Antarctic ice sheet with a three-dimensional polythermal
ice-sheet model, in support of the EPICA project
Authors: Calov R. , Savvin A. , Greve R. , Hansen I. , Hutter K.
Published: November 2017

The three-dimensional polythermal ice-sheet model SICOPOLIS is applied to the
entire Antarctic ice sheet in support of the European Project for Ice Coring in
Antartica (EPICA). in this study, we focus on the deep ice core to be drilled in
Dronning Maud Land (Atlantic sector of East Antarctica) as part of EPICA. It has
not yel been decided where the exact drill-site will be situated. Our objective is
to support EPICA during its planning phase as well as during the actual drilling
process.

We discuss a transient simulation with a climate forcing derived from the
Vostok ice core and the SPECMAP sea-level record. This simulation shows the range
of accumulation, basal temperature, age and shear deformation to be expected in
the region of Dronning Maud Land. Based on these results, a possible coring
position is proposed, and the distribution of temperature, age, horizontal
velocity and shear deformation is shown for this column.
70 years of northern Victoria Land (Antarctica) accumulation rate
Authors: Maggi V. , Orombelli G. , Stenni Β. , Flora O. , Udisti R. , Becagli S. , Traversi R. , Vermigli S. , Petit J.-R.
Published: November 2017

Measurements of oxygen isotope ratio , major anions and
cations, insoluble dust and tritium were performed every 4-6 cm along the Hercules
Névé (northern Victoria Land, Antarctica) 22 m firn core. Concentration/depth
profiles for H2O2, methane sulphonic
acid and non-sea-salt sulphate (nssSO4
2-) were used to obtain a dating for the core by a
multiparametric method involving a normalisation procedure and a linear
combination of original profiles. This dating was compared with the
and dust records
to obtain a reliable identification of successive annual snow layers. The
time-scale obtained from the seasonally varying signals was confirmed by an
absolute date obtained from the 1965 thermonuclear atmospheric bomb test tritium
peak. Around 70 years (1926-94) of annual accumulation rate data were obtained
from the core. variations
recorded along the core may be ascribed to seasonal variations of this parameter
related to temperature variations.
Radar interferometry detection of hinge-line migration on Rutford Ice Stream
and Carlson Inlet, Antarctica
Authors: Rignot Eric
Published: November 2017

Satellite synthetic aperture radar interferometry is employed to map the
hinge-line position, or limit of tidal flexing, of Rutford Ice Stream (RIS) and
Carlson Inlet (CI), Antarctica, and detect its horizontal migration between 1992
and 1996. The hinge-line position is mapped using a model fit from an elastic-beam
theory. The rms noise of the model fit is 1-7 mm. The hinge-line position is
located with a statistical noise of 30—50 m. Using this method, we find no
hinge-line migration on RIS and CI. Only the southern flank of CI, which is
stagnant (velocity 10-20 m a−1 vs 100 m
a−1 in the main flow of CI), retreated 376 ±36 m in 4
years. The effect of changes in ocean tide is calculated to yield a 60 m advance
of the hinge-line position in our data. Hence, the detected stationarity of the
hinge-line positions suggests stable ice-thickness conditions at the hinge line,
except for the southern flank of CI which may be thinning. A comparison of the ice
discharge calculated at the grounding line of RIS (17±2 km3
ice a−1) and of CI (2.9 ±0.3
km3a−1) with mass input from the
interior regions (20 ±3 km3 ice a−1 for
RIS and 2.9 ±0.4 km3 a–1 for CI)
suggests a balanced mass budget for CI, whereas RIS may have a slightly positive
mass budget of 3±4 km3 ice a−1.
Effect of meltwater input from the Antarctic ice sheet on the thermohaline
circulation
Authors: Mikolajewicz Uwf
Published: November 2017

The potential effect of meltwater input from the Antarctic ice sheet is
studied in sensitivity experiments with an ocean general circulation model coupled
to an energy-balance model of the atmosphere. The effect is generally a reduction
of surface salinity and deep convection in The Southern Ocean, associated with
surface cooling. There is an accompanying, delayed intensification of the
overturning in the Northern Hemisphere, leading to warmer conditions over both the
North Atlantic and North Pacific With a sufficiently large meltwater pulse it is
possible to trigger switches between different steady states of the ocean's
thermohaline circulation, which differ mainly in the formation rates of North
Atlantic Deep Water. Thus a transient perturbation in the Southern Ocean can lead
to long-term climate changes in both hemispheres. The model reacts morè
sensitively to melt water input into theWeddell Sea than into the Ross
Sea.
Crystal-size and microparticle record in the ice core from Dome Summit South,
Law Dome, East Antarctica
Authors: Jun Li , Jacka T. H. , Morgan Vin
Published: November 2017

An investigation of crystal-size and microparticle variations has been
carried out for the 1196 m ice core retrieved from Dome Summit South (DSS) near
the summit of Law Dome, East Antarctica. Results show that for ice deposited
during the Holocenr (depth <1103 m), microparticle concentrations are low.
Variations of crystal size with in the Holocenc ice are due to growth with time at
a temperature-dependent rate, and recrystallisation as a consequence of the ice
flow. in the DSS ice core the highest microparticle concentration occurs close to
the depth (1133 M) at which oxygen isotope ratios exhibit the greatest negative
values, i.e. the Last Glaciol Maximum (LGM). Also at this depth, crystal size
reduces sharply from a general crystal growth trend above to near minimum core
values below. For ice originating during the LGM, the concentration of particles
is an order of magnitude greater than the mean Holocene concentration. Laboratory
annealing tests at -1 °C confirm the retarded crystal growth in the
high-microparlicle-concent ration ice.
Internal radio-echo layering at Vostok station, Antarctica, as an independent
stratigraphie control on the ice-core record
Authors: Siegert Martin J. , Hodgkinst Richard , Dowdeswell Julian A.
Published: November 2017

Antarctic radio-echo sounding (RES) data at 60 MHz have been used to
determine an independent stratigraphy for the ice core at Vostok station, based on
internal radio-echo layering. A-scope RES data allow the amplitude of reflected
electromagnetic (e/m) waves to be measured and, by accounting fur geometric
spreading and absorption losses of the e/m wave, power reflection coefficients
(PRCs) to be calculated. This information is compared with time-continuous Z-scope
RES data in order to trace continuous e/m reflectors across the ice sheet.
Internal ice-sheet horizons deeper than 800 m are caused by layers of ice that
possess distinctly different dielectric properties (i.e. acidic layers) compared
with ice above and/or below. Comparison of four PRC samples, located ~ 5 km from
Vostok station, revealed five distinct internal reflections between 1000 and 2200
m. Z-scope data from directly over the Vostok station site show the same five
prominent internal radio-echo layers. The depth-related radio-echo signals were
then compared with chemical records from the Vostok ice core, including the
H2SO4 signal, a major component of
which is derived from volcanic events. From this procedure, internal radio-echo
reflectors and Vostok ice-core acid measurements were correlated. Avery good match
was made between Z-scope and ice-core data. However, vertical offsets observed
between A-scope-derived RES layers and peaks in the chemical signal of up to 100 m
are probably due to the general Inkling of the ice-sheet layering between the core
site and the RES flight-line. We conclude that 60 MHz RES layering may be regarded
as a stratigraphy independent of palaeoclimate, and may be used to correlate other
deep Southern Hemisphere ice cores.
Limited migration of soluble ionic species in a Siple Dome, Antarctica, ice
core
Authors: Kreutz Karl J. , Mayewski Paul A. , Whitlow Sallie I. , Twickler Mark S.
Published: November 2017

High-resolution (>10 samples a−1) glaciochemical
analyses covering the last 110 years from a Siplc Dome, Antarctica, ire core
reveal limited migration of certain soluble ionic species (methane sulfonic acid,
NO3
− and Mg2+). The observed chemical
migration may be due in part to seasonal alternation between less acidic winter
(from high sea-salt concentrations) and more acidic summer (from high marine
biogenic acid concentrations) layers, common at coastal siles such as Siplc Dome.
Exact mechanisms to expla in the migration are unclear, although simple diffusion
and gravitational movement are unlikely since new peaks are formed where none
previously existed in each case. Initial migration of each species is both
shallower and earlier at Siple Dome than at other sites in Antarctica where
similar phenomena have been observed, which may be related to the relatively low
accumulation rate at Siple Dome (~13.3 cm ice a−1). Migration
appears to be limited to either the preceding or following seasonal layer for each
species, suggesting that paleoclimatic interpretations based on dala with lower
than annual resolution are not likely to be affected.
Retreat of northern margins of George VI and Wilkins Ice Shelves, Antarctic
Peninsula
Authors: Lucchitta B. K. , Rosanova C. E.
Published: November 2017

The George VI and Wilkins Ice Shelves are considered at risk of
disintegration due to a regional atmospheric warming trend on the Antarctic
Peninsula. Retreat of the northern margin of the George VI Ice Shelf has been
observed previously, but the Wilkins Ice Shelf was thought to be stable. We
investigated the positions of the northern fronts of these shelves from the
literature and looked for changes on 1974 Landsat and 1992 and 1995 European
remote-sensing satellite (ERS) synthetic aperture radar images. Our investigation
shows that the northern George VI Ice Shelf lost a total of 906
km2 between 1974 and 1992, and an additional 87
km2 by 1995. The northern margin of the Wilkins Ice Shelf
lost 796 km2 between 1990 and 1992, and another 564
km2 between 1992 and 1995. Armadas of tabular icebergs
were visible in front of this shelf in the ERS images. These two ice shelves mark
the southernmost documented conspicuous retreat of ice-shell margins.
Brine infiltration in the snow cover of sea ice in the eastern Weddell Sea,
Antarctica
Authors: Rapley M. , Lytle Victoria I.
Published: November 2017

The snow cover on Antarctic sea iee often depresses the ice below sea level,
allowing brine or seawaier to infíltrale, or flood the snowpack. This
significantly reduces the thermal insulation properties of the snow cover, and
increases the ocean/ atmosphere heat flux. The subsequent refreezing of this
saturated snow or slush layer, to form snow-ice, can account for a significant
percentage of the total ice mass in some regions. The extent of saturated snow
cannot presently be estimated from satellite remote-sensing data and, because it
is often hidden by a layer of dry snow, cannot be estimated from visual
observations. Here, we use non-parametric statistics to combine sea-ice and snow
thickness data from drillhole measurements with routine visual observations of
snow and ice characteristics to estimate the extent of brine-infiltrated snow. The
data were collected duringjuly-August 1994 from the R/V Nathaniel B.
Palmer in the eastern Weddell Sea from 60° to 68° S latitude and
from 20° wto 5° E longitude.
Antarctic Circumpolar Wave in a coupled ocean-atmosphere model
Authors: Moroi T. , Kitoh A. , Koide H.
Published: November 2017

An Antarctic Circumpolar Wave (ACW) is simulated by a global coupled
ocean-atmosphere model. Time-longitude diagrams of anomalies in sea-surface
temperature (SST) and sea-surface salinity (SSS) show that anomalies propágale
eastward, taking 20-30 years to encircle the pole. The time taken is 2-3 times
longer than indicated by observations, due to the relatively slow speed of the
modelled Antarctic Circumpolar Current (ACC). High-SSS anomalies correspond to
high-SST anomalies and high-density anomalies, and thus to low sea-surface height
anomalies, indicating that salinity IS a dominant factor for dynamics with in the
Southern Ocean and is indispensable for understanding the mechanism of the ACW.
Sea-ice formation is suppressed southward of warm, saline surface-water regions.
High sea-ice concentration anomalies correspond to thick sea-ice anomalies.
Empirical orthogonal function analyses of SSTanomalies for both model and
observation show that the dominant mode in the Southern Ocean has a spatial
pattern closely related to El Niño activity. Sea-level pressure (SLP) anomalies
propagate eastward with the ACW. High SLP anomalies in the atmosphere correspond
to low-density anomalies 111 the ocean. The ACC has clockwise geostrophic velocity
anomalies over high-density anomaly regions with upwelling. Both heat and salt are
transported from the deep layer to the surface layer by upwelling. This could
suppress sea-ice formation directly. Anomalous horizontal advection of heat and
salt by geostrophic velocity anomalies in the ACC appears to influence the
anomalies in SST, SSS and sea ice.
Spatial distribution and seasonal pattern of biogenic sulphur compounds in snow from northern Victoria Land, Antarctica
Authors: Udisti R. , Traversi R. , Becagli S. , Piccardi G.
Published: November 2017

A study of the spatial and temporal distribution of methane sulphonic aeid (MSA) and nssSO42-concentrations in snow-pit samples was performed to determine the main and secondary sources, transport effects and seasonal pattern of biogenic sulphur compounds. Four snow pits, about 3 m deep, excavated at the same time at different altitudes (870-2960 m a.s.1.) in northern Victoria Land, Antarctica, gave coherent information about the effect of altitude and seasonality on the snow chemical composition. A progressive, well-defined decreasing concentration trend is shown as altitude increases, with the biggest effect in the first 1000 m a.s.1. At higher altitudes, biogenic sources make the most important contribution to the tola! sulphate balance with respect to sea-mray input. Particular attention was paid to the relationship between MSA and nssSO42-by using MSA as a univoca] biogenic marker. The nssSO42-/MSA ratio was evaluated with respect to altitude and seasonality to determine the effect of transport mechanisms (such as long-range transport and fractionation) or non-dimethyl sulphide sources on nssSO42-snow content.
Climate change in the western Antarctic Peninsula since 1945: observations and
possible causes
Authors: King J. C. , Harangozo S. A.
Published: November 2017

Temperature records from slations on the west roast of the Antarctic
Peninsula show a very high level of interannual variability and, over the last 50
years, larger warming trends than are seen elsewhere in Antarctica. in this paper
we investigate the role of atmospheric circulation variability and sea-ice extent
variations in driving these changes. Owing to a lack of independent data, the
reliability of Antarctic atmospheric analyses produced in the 1950s and 1960s
cannot be readily established, but examination of the available data suggests that
there has been an increase in the northerly component of the circulation over the
Peninsula since the late 1950s. Few observations of sea-ice extent are available
prior to 1973, but the limited data available indicate that the ice edge to the
west of the Peninsula lay to the north of recently observed extremes during the
very cold conditions prevailing in the late 1950s. The ultimate cause of the
atmospheric-circulation changes remains to be determined and may lie outside the
Antarctic region.
Comparison of warming trends predicted over the next century around Antarctica
from two coupled models
Authors: O'Farrell Siobhan P. , Connolley William M.
Published: November 2017

This paper investigales the climate change in two atmosphere ice-ocean
coupled climate models — the UKMO and the CSIRO— in the Antarctic region over the
next century. The objectives were to sec if an enhanced level of greenhouse-gas
forcing results in a surface temperature signal above background variability, and
to see if this pattern of change resembles the change seen to date in Antarctica,
especially the warming around the Peninsula. The models show that although reduced
sea-ice compactness is responsible for regions of enhanced air-temperature
anomalies, these ice-compactness anomalies are determined by different mechanisms
in the respective models. The pattern of warming in both models does not match the
differential rates of warming seen in the observations of temperature change over
the Antarctic continent in the lait few decades. Also the level of background
ocean variability in the Drake Passage and Weddell Sea region hampers the clear
definition of a signal over the Antarctic Peninsula in the coupled models.
Although no winter enhancement in warming over the Peninsula region IS found, an
autumn anomaly is seen in one of the models. The mechanism for this feature IS
documented, and an explanation of why it does not persist throughout the winter
season is presented.
Detailed topography of Roosevelt Island and Siple Dome, West
Antarctica
Authors: Scambos Ted A. , Nereson Nadine A. , Fahnestock Mark A.
Published: November 2017

Detailed surface topography is presented for two dome features of the West
Antarctic ice sheet, Siple Dome and Roosevelt Island. Both these domes show linear
topographic features, or “scars”, on [heir flanks. Topography is determined from a
combination of existing digital elevation models (DEMs; based on satellite radar
altimctry), photoclinomctry (using advanced very high-resolution radiometer images
to quantitatively infer topographic details) and, in the case of Siple Dome,
surface global positioning system topographic profiles. The enhanced DEMs provide
heights and shapes for a variety of surface features in the vicinity of the domes,
such as scars, surface undulations, ice rises and the domes themselves.

The DEMs indicate that the scar features on both domes are high relative to
adjacent rapid-ice-llow areas. Scars and other related morphologic features on the
flanks of both domes can be interpreted as former active ice streams and stream
margins. For Siple Dome, this interpretation is confirmed by radar profiling. The
evolution of the topographic height of the scars is a combination of two
processes: initial elevation rise due to a positive mass balance at the shear
margin in the immediate aftermath of shut-down of the ice stream; and later
downslope flow as the scars become part of the dome and the dome surface velocity
field. Superimposed on these events is accumulation, which buries the original
shear margin but elevates the scar surface expression. Depending upon the timing
of shut-flown, and the relative magnitude of these processes, the height of the
scars above the current rapidly flowing surfaces may be indicative of ice-sheet
thinning since shut-down, or dome expansion across former ice-stream trunks in a
more or less steady-state ice sheet.
Climate-change indicators from archival aerial photography of the Antarctic
Peninsula
Authors: Fox A.J. , Cooper A. P. R.
Published: November 2017

Aerial photography has been used as a mapping tool in the Antarctic Peninsula
region sinre the late 1920s. Following pioneering work by Wilkins in 1928,
Ellsworth in 1934 and the British Graham Land Expedition in 1934-37, the Falkland
Islands and Dependencies Aerial Survey Expedition carried out extensive aerial
photography during the period 1955-57. Since then, many other aerial surveys have
been carried out, and the result is an archive of aerial photography that, for
some localities, spans 40 years. The production of maps both from different
generations of photographs and satellite images has revealed many changes in the
extent of ice cover with time. For example, changes in ice shelves such as the
Wordie Ice Shelf, Larsen Ice Shelf and Müller Ice Shelf, are well recorded, and
the termini of some glaciers have retreated. However, the most pervasive change is
the consistent decline in the extent of small bodies of snow and ice. This paper
shows how perennial snow or ice cover has decreased in the northern Marguerite Bay
area, at 68°S. The correlation of the change with elevation and with climate
records from Adelaide and Rothera research stations in the Antarctic Peninsula
region is examined.
Ice-front change and iceberg behaviour along Oates and George V Coasts,
Antarctica, 1912-96
Authors: Frezzotti Massimo , Cimbelli Alessandro , Ferrigno Jane G.
Published: November 2017

Ice-front change may well be a sensitive indicator of regional climate
change. We have studied the western Oates Coast from Cape Kinsey (158°50' E,
69°19' S) to Cape Hudson (153°45' Ε, 68°20' S) and the entire George V Coast, from
Cape Hudson to Point Alden (142°02' E, 66°48' S). The glaciers here drain part of
the Dome Charlie and Talos Dome areas (640 000 km2). A
comparison between various documents, dated several years apart, has allowed an
estimate of the surficial ice discharge, the ice-front fluctuation and the
iceberg-calving flux during the last 50 years. The ice-front discharge of the
studied coast has been estimated at about 90 ± 12
km3a−1 in 1989-91, 8.5
km3a−1 for western Oates Coast and 82
km3a−1 for George V Coast. From
1962-63 to 1973-74 the floating glaciers underwent a net reduction that continued
from 1973-74 to 1989-91. On the other hand, from 1989-91 to 1996 the area of
floating glaciers increased. Ninnis Glacier Tongue and the western part of Cook
Ice Shelf underwent a significant retreat after 1980 and 1947, respectively.
Satellite-image analysis of large icebergs has provided information about
ice-ocean interaction and the existence of an “iceberg trap” along George V Coast.
A first estimate of the mass balance of the drainage basin of Mertz and Ninnis
Glaciers shows a value close to zero or slightly negative.
Circulation beneath the Filchner Ice Shelf, Antarctica, and its sensitivity to
changes in the oceanic environment: a case-study
Authors: Grosfeld K. , Gerdes R.
Published: November 2017

We investigate the sensitivity of the ocean circulation in the Filchner
Trough to changes in the large-scale oceanic environment and its impact on the
mass balance of the Filchner Ice Shelf, Antarctica. Three experiments with a
three-dimensional ocean model describe (i) the current situation, (ii) a scenario
with increased ocean temperatures, and (iii) a scenario with reduced sea-ice
formation rates on the adjacent continental shelf. in the final discussion brief
results of a combined scenario with increased ocean temperatures and reduced
sea-ice formation are presented. The changes from the current situation affect the
circulation in the Filchner Trough, and melting and freezing processes beneath the
ice shelf. The latter affect the amount and properties of Ice Shelf Water (ISW), a
component of Antarctic Bottom Water. Net basal melt rates provide an overall
measure for the changes: while the control run yields 0.35 m
a−1 net melting averaged over the Filchner Ice Shelf area,
the warming scenario results in a more than twofold increase in ice-shelf mass
loss. Reduced production of High Salinity ShelfWater due to smaller sea-ice
formation rates in the second scenario leads, on the other hand, to a decrease in
basal mass loss, because the deep cavity is less well ventilated than in the
control run. ISW is cooled and the ice shelf is stabilized under this scenario,
which is arguably the more likely development in the southern Weddell
Sea.
Physical characteristics of the Antarctic sea-ice zone derived
from modelling and observations
Authors: Budd W. F. , Wu Xingren , Reid P. A.
Published: November 2017

Antarctic sea ice plays a key role in the present climate system, providing
a regulating balance between the atmosphere and ocean heat fluxes, as well
as influencing the salt fluxes and deep water formation over the continental
shelves. The severe winter environmental conditions of the Antarctic sea-ice
zone make it difficult to observe many of the physical characteristics in a
comprehensive way. The inter-relations between the variables mean that much
can be learnt from the observations of some features along with detailed
numerical modelling of the whole system and the interactions between the
variables. This study therefore aims to use numerical modelling of the
atmosphere, sea ice and surface mixed-layer ocean in the sea-ice zone,
together with observations to simulate a comprehensive range of parameters
and their variability through the annual cycle to provide a basis for
further observations and model validation for the present climate.

The model includes a coupled atmospheric general circulation model with an
interactive dynamic and thermodynamic sea-ice model and surface mixed-layer
ocean. The deep ocean and ocean surface conditions outside the sea-ice zone
are constrained to the present mean climate conditions to ensure no climatic
drift. The sca-ice model is similar to previous published versions, bill has
refined schemes for partitioning of the freezing of frazil ice within the
leads and under the ice floes, and for rafting. These perform well in both
polar regions with the same physics. The model simulates the annual cycle of
atmospheric and sea-ice features well in comparison with data from the
global atmospheric analyses, the satellite sensing of sea ice, and the
limited in situ surface observations.

The output from the model also includes: all components of the heart fluxes,
atmospheric profiles and surface temperatures for air, ice and ice-ocean
mixtures, open-water fractions, surface snow and snow-ice depths, and the
sea-ice convergence-divergence and drift. The comparison of these features
with additional observations provides a means for further validating the
model and representing the present climate more closely.
The effect of sea-ice parameterizations on the simulation of the
Arctic ice pack
Authors: Vavrus Stephen J.
Published: November 2017

A one-dimensional (1-D), thermodynamic sea-ice model with parameterized ice
dynamics is coupled to a mixed-layer ocean model and driven with prescribed
atmospheric forcings for the central Arctic. The model is used to calculate
the sensitivity of the ice pack to various parameterizations that have
traditionally been neglected or considered only implicitly in large-scale
sea-ice models. The model includes melt ponds, leads (with summertime
stratification), an ice-export term, a stability-dependent air–sea
heat-exchange coefficient, a prognostic ocean–ice heat exchange, a crude
ice-thickness distribution, and a sophisticated albedo parameterization.

The ice pack is sensitive to the partitioning of solar energy between
lateral melting and mixed-layer warming, with the most realistic simulations
occurring when the heat is nearly evenly divided between these two
processes. Conversely, ice thickness and coverage are fairly insensitive to
the amount of lateral mixing within the upper ocean, vertical mixing within
leads, and to the partitioning of mixed-layer heat content between warming
the water and melting the ice bottom. The ice concentration during summer is
strongly dependent on the assumed ice-thickness distribution: the amount of
open water during summer is less than half the size of the empirically based
distribution used here, compared with one in which ice floes are distributed
uniformly across a range of thicknesses.