bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced thermodynamic ice growth by sea-ice deformation
Authors: Heil Petra , Lytle Victoria I. , Allison Ian
Published: November 2017

Sca-icc drift and deformation were measured with an array of drifting buoys during a 1995 winter experiment off the East Antarctic continental shelf south of the Antarctic Divergence. The buoys were configured so that deformation of the icefield could be monitored on a range of spatial scales from 2 to 130 km. The mean hourly drift rate during the 3 week-long experiment was 0.21 m s−1, and the mean daily translation of the field was 17.3 km. Differential kinematic parameters calculated from the data show a very high short-term variance, indicating that high-frequency processes are dominant. Spectral analysis of the velocity data shows a major peak of the energy spectrum at the frequency of passage of synoptic weather systems, and a second peak at the inertial frequency. A major storm event occurred during the experiment. Net divergence over this phase of the experiment, as measured by a five-buoy array, is small compared to the short-period variance. This alternating divergence and convergence has a marked effect on the net ice growth. Intense freezing and rapid new ice formation occurs in the open water areas formed during divergence, and this is thickened by rafting and ridge-building during the subsequent convergence. New open water areas equivalent to 10% of the total area formed during the first phase of the experiment. A one-dimensional multilayer thermodynamic model of ice growth shows that this led to an increase of 2.8 cm in the area-averaged ice growth over a 7 day interval, which is equivalent to 40-50% of the total estimated ice growth over the region.
On simulating high-frequency variability in Antarctic sea-ice dynamics
models
Authors: Hibler III W. D. , Heil Petra , Lytle Victoria I.
Published: November 2017

Due to frequent and intense storm systems moving across the Antarctic sea
ice, ice drift and deformation fluctuate substantially. Observations of drilling
buoys show inertial power to be a substantial component of ice drift and
deformation. Because the inertial period at high latitudes is close to tidal
periods, this peak can be amplified due to resonance. in practice, the energy
dissipation by ice interaction plays a significant role in dampening out this
inertial energy. in present sea-ice dynamics models both with and without ice
interaction, this inertial motion is overdamped due to the underestimation of
coupling to the ocean boundary layer. To develop a more consistent treatment of
ice drift under fluctuating wind fields, we consider here a vertically integrated
formulation of the ice-ocean boundary-layer system that incorporates a more
realistic treatment of the upper ocean. Under steady wind conditions this model
reduces to the normal water-drag formulation used in most sea-ice dynamics models.
Simulations using this “imbedded” model are analyzed to elucidate the role of ice
interaction in the Antarctic ice-pack in modifying the high-frequency motion and
inducing deformation which in turn significantly impact ice-thickness
characteristics. The simulations demonstrate that in an interacting ice field in
the presence of kinematic waves inertial imbedding can lead to oscillations in ice
concentration of up to ~10% open water. These variations are similar in magnitude
to observed deformation fluctuations in tide-free regions.
East Antarctic seasonal sea-ice and ocean stability: a model study
Authors: Marsland Simon , Wolff Jörg-Olaf
Published: November 2017

A high-resolution primitive equation ocean model has been coupled to a
dynamic/thermodynamic sea-ice model and applied to a region of the Southern Ocean
south of Australia. The model is found to be very sensitive to the surface
fresh-water flux! A stable seasonal cycle of sea-ice advance and retreat is
simulated only for sufficient surface fresh-water fluxes. For fresh-water fluxes
below a threshold value of around 40 cm a−1 the coupled
system enters a thermal mode characterised by vertical homogeneity of the oceanic
temperature and salinity fields. Such an ocean has a surface temperature that is
too warm for a sea-ice cover to develop. Spatial and temporal variability of the
oceanic heat llux into the upper model layer iS examined for the stable
simulations. High values of this oceanic heat flux (~40Wm−2)
occur during the sea-ice formation period (March-June), with values as low as 5
wM−2 occurring in November. The source of this heat is
primarily convective, a process induced by brine rejection during ice
growth.
Global atmospheric responses to Antarctic forcing
Authors: Bromwich David H. , Chen Biao , Hines Keith M. , Cullather Richard I.
Published: November 2017

To evaluate the greatest impact that sea-ice anomalies around Antarctica
could have on the global atmosphere, 15 year seasonal cycle simulations are
conducted with the U.S. National Center for Atmospheric Research Community Climate
Model version 2.1. Sensitivity simulations are performed with the following
conditions: (1) all sea ice in the Southern Hemisphere is replaced by year-round
open water, but the permanent ice shelves are retained (NSIS); and (2) all sea ice
in the Southern Hemisphere and the major ice shelves are removed and replaced by
open water (NISH). The results are compared to a standard run (CNT) with boundary
conditions set for the present climate. The comparison shows that trains of
positive and negative anomalies in zonal-mean fields extend into the tropical
latitudes of the Northern Hemisphere. Anomalies are largest during April-October.
The additional removal of the ice shelves in NISH enhances the response, as
zonally averaged anomalies are similar in pattern to those in NSIS but are roughly
twice as large poleward of 50° S, and only slightly larger farther north.
Anomalies in the eddy fields are found in both hemispheres. in NISH, and to a
lesser degree in NSIS. these anomalies appear to be related to a delayed northern
advance over China during June of the rain front associated with the summer
monsoon. Consequently, precipitation is enhanced in middle and southern China and
decreased in northern China. Observational analyses have also found links between
Antarctic sea-ice variations and modulations of the East Asian monsoon.
Comparison between glacier ice velocities inferred from GPS and sequential
satellite images
Authors: Frezzotti MAssimo , Capra Alessandro , Vittuari Luca
Published: November 2017

Measurements derived from remote-sensing research and Held surveys have
provided new ice-velocity data for David Glacier-Drygalski Ice Tongue and
Priestley and Reeves Glaciers, Antarctica. Average surface velocities were
determined by tracking crevasses and other patterns moving with the ice in two
sequential satellite images. Velocity measurements were made for different time
intervals (1973-90, 1990-92, etc.) using images from various satellite sensors
(Landsat 1 MSS, Landsat TM, SPOT XS). in a study of the dynamics of David
Glacier-Drygalski IceTongue and Priestley and Reeves Glaciers, global positioning
system (GPS) measurements were made between 1989 and 1994. A number of points were
measured on each glacier: five points on David Glacier, three on Drygalski Ice
Tongue,two on Reeves Glacier—Nansen Ice Sheet and two on Priestley Glacier.
(lomparison of the results from GPS data and feature-tracking in areas close to
image tie-points shows that errors in measured average velocity from the
feature-tracking may be as little as +15-20 m a−1. in areas
far from tie-points, such as the outer part of Drygalski Ice Tongue, comparison of
the two types of measurements shows differences of about ± 70 m
a−1.
Regional impacts of climate change in the Arctic and Antarctic
Authors: Weller Gunter
Published: November 2017

Regional assessments of impacts due to global climate change are a high
priority in the international programs on global-change research. in the polar
regions, climate models indicate an amplification of global greenhouse warming,
but there are large differences between the results of various models, and
uncertainties about the magnitude and timing of the expected changes. Also, the
observed high-latitude climate trends over the past few decades are much more
regional and patchy than predicted by the models. As a first step in assessing
possible climate impacts, model results are compared with observations of changes
in temperature, precipitation, sea-ice extent, the permafrost regime and other
cryospheric parameters. While considerable uncertainties remain in the long-term
prediction of change, there is some agreement between model results and observed
trends by season on shorter time-scales, The warming observed over the land masses
of the Arctic over the past few decades is matched by corresponding observed
decreases in snow cover the glacier mass, balances, by thawing of the permafrost,
and to a lesser degree by reductions in sea-ice extent. in Antarctica, warming in
the Antarctic Peninsula and Ross Sea regions is associated with large decreases in
ice-shelf areas and reduced ice thicknesses on the lakes in the McMurdo Dry
Valleys. Major future impacts due to global greenhouse warming are likely to
include permafrost thawing on and and its consequences for ecosystems and humans;
changes in the productivity of marine ecosystems in the Arctic and Southern Ocean:
economic impacts on fisheries, petroleum and other human activities; and social
impacts on northern indigenous populations. Some of these impacts will have
positive ramifications, but most are likely to be detrimental. While uncertainties
exist about the future, climate change in the polar regions during the past few
decades can be shown to have had major impacts already which will become much mole
pronounced if present trends continue.
Detection of temperature and sea-ice-extent changes in the Antarctic and
Southern Ocean, 1949-96
Authors: Jacka T. H. , Budd W. F.
Published: November 2017

Surface temperature data for the occupied Antarctic stations (for the period
1959-96) and Southern Ocean island stations (1949-96), and sea-ice-extent data
(1973-96) are analyzed to provide trends over the indicated time intervals. The
mean trend (mean slope of linear regressions through the annual mean station data)
for the Antarctic stations indicates a warming of 1.2°C (100
a)−1. The slope of the linear regression fit to a
composite of the mean station anomaly data indicates a warming rate of 0.9°C (100
a)−1. For the Southern Ocean island station data, warming
rates of 1.0° and 0.7°C (100 a) −1 are indicated by the two
methods. For the sea-ice data, no significant trend is detectable over the
satellite era, 1973-96, but for the longer period commencing in the mid-1940s
there is some evidence of a decrease in sea-ice extent from whaling records
recently published.
Monitoring of atmospheric aerosol particles on the Antarctic Peninsula
Authors: Correia Alexandre , Artaxo Paulo , Maenhaut Willy
Published: November 2017

Atmospheric aerosol particles have been sampled since 1985 at the Brazilian
Antarctic station, Comandante Ferraz (62°05' S, 58°23 5'W) Stacked niter units
were used to collect particles with an aerodynamic diameter of less than 10μm. The
elemental concentration was measured by particle-induced X-ray emission, yielding
data for 23 elements: Na, Mg, Al, Si, P, S, Cl, K, Ca, K, V, Cr, Mn, Fe, Ni, Cu,
Zn Sc, Br Kb, SrZr and Pb. The detection limit was typically near 5 ng m
−3 for elements with atomic number
(z) less than 20, and Oingm for 21 <
z <.30. Principal-factor and cluster analyses
identified four sources for the Antarctic aerosol: fine and coarse sea salt, soil
dust and sulphates. The fine-mode non-sea-salt sulphate concentration showed a
clear seasonal pattern accompanying the biological cycle of algae, with minimum
during winter. Some elements, such as Ni and Pb, showed very high enriched
concentrations relative to the bulk sea-water composition. This indicates the
existence of sources of regional or long-range transported pollution.
Understanding Antarctic Peninsula precipitation distribution and variability
using a numerical weather prediction model
Authors: Turner John , Leonard Steven , Lachlan-Cope Tom , Marshall Gareth J.
Published: November 2017

Daily precipitation fields and annual means from the European Centre for
Medium-range Weather Forecasts re-analysis exercise are used to examine the
distribution and variability of precipitation across the Antarctic Peninsula. The
annual mean precipitation field from the model agrees well with the available
ice-core data and suggests that the maximum accumulation for the area is on the
western side of the barrier at about the 200 m level where the annual total is
close to 1.3 m w.e. The Peninsula is shown to be a very effective barrier to the
zonal movement of precipitating weather systems, which results in quite different
atmospheric flow regimes being responsible for significant precipitation events on
other side of the divide. Frontal depressions are the primary source of large
daily snowfall totals on both sides of the Peninsula. On the southern coast of the
Bellingshausen Sea, major snowfall events are often linked to strong northerly
flow when the atmospheric circulation is blocked. Predominantly northerly flow is
also responsible for significant snowfall on the Ronne Ice Shelf, which often
occurs in association with lee cyclogenesis events to the east of the-
Peninsula.
Interpreting recent accumulation records through an understanding of the
regional synoptic climatology: an example from the southern Antarctic
Peninsula
Authors: Marshall Garetti J. , Turner John , Miners William D.
Published: November 2017

In this study we correlate temporal features within the electrical
conductivity (acidity) traces of four shallow firn cores obtained from the
southern Antarctic Peninsula to synoptic-scale variations in the regional climate,
as depicted by a numerical weather prediction model. It is demonstrated that the
three high-acidity features present within the 1992-93 accumulation correspond to
periods of significant precipitation, a hypothesis supported by the association of
these events with strong onshore winds, ideal for transporting the biogenically
derived sources of precipitation acidity to the core sites. The longitudinal
location of depressions within the Bellingshausen Sea is shown to be the principal
factor governing the volume of precipitation that they give over the western
Peninsula. Annual accumulation in the model is ~25% lower than revealed by the
cores; although there are too many uncertainties to provide a definite reason for
the deviation, the smoothed model orography and inaccurate land-sea mask are
believed to be significant factors. It is postulated that the acidity pattern
within southern Peninsula cores may reveal an El Niño-Southern Oscillation
signal.
Recent retreat of ice cliffs, King George Island, South Shetland Islands,
Antarctic Peninsula
Authors: Park Byong-Kwon , Chang Soon-Keun , Yoon Ho Il , Chung Hosung
Published: November 2017

Comparison of aerial photos shows that the ice cliff in Marian Cove, Maxwell
Bay, southwestern King George Island, retreated approximately 250 m between 1956
and 1986, but advanced about 40 m between December 1986 and January 1989. The
advance in the late 1980s seems to be related to the cold austral winters of
1986-88. A topographic survey in January 1994 revealed that the ice cliff in
Marian Cove had again retreated around 270 m since January 1989; approximately the
same as from December 1956 to December 1986. in Potter Cove, the ice cliff
retreated approximately 400 m from 1956-89. The more pronounced retreat here may
be attributable to shallower water depths (<30m). These ice cliffs retreats
are discussed as a possible consequence of recent regional warming.
Sources and origins of aerosols reaching Antarctica as revealed by lead
concentration profiles in shallow snow
Authors: Barbante C. , Turetta C. , Gambaro A. , Capodaglio G. , Scarponi G.
Published: November 2017

Changes in the lead concentration in Antarctic snow over the past 30 years
are considered as a response of the environment to a well-documented environmental
change (decrease of lead emissions into the atmosphere). New data confirm the
recent decreasing trend of lead concentration in snow as revealed by previous
studies. Furthermore, comparing changes in the lead concentration in Antarctic
snow layers with lead emissions from different anthropic sources, we can
hypothesise that under present-day climatic conditions, lead-enriched aerosols
reaching the Atlantic and Pacific sectors of East Antarctica originate mainly in
South America and Australia, respectively.
Chemical and isotopic profiles from snow pits and shallow firn cores on
Campbell Glacier, northern Victoria Land, Antarctica
Authors: Gragnani R. , Smiraglia C. , Stenni B. , Torcini S.
Published: November 2017

The chemical (Na+, K+,
Mg2+, Ca2+,
CH3SO3
− (MSA), Cl− , NO3
− , SO4
2-) and isotopic (δl8O) composition of
snow and firn samples from Campbell Glacier, northern Victoria Land, Antarctica,
was studied to evaluate the accumulation rate of snow and to investigate the
chemical contribution from some emission sources (marine biogenic activity, sea
and crust). During the 1994-95 Italian Antarctic Expedition, snow and firn were
collected from snow pits and from cores obtained from drilling at three sites (A:
74°41'S, 164°30' E; B: 74°15' S, 164° '04' E; C: 73°45' S, 163°20' E), located ai
50 m (on the floating glacier tongue), 800 m and 1580 m a.s.l.,
respectively.

The mean concentration of sea salt decreased with increasing distance from
the coast and with altitude. Generally, the
Na+/K+ and
Na+/Ca2+ ratios were much lower than
the bulk sea-water ratios at sites B and C. The MSA showed mean concentrations
(0.27 and 0.17 ¿teq 1 at sites B and C, respectively) consistent with data
obtained from other Antarctic sites. The mean concentrations of
NO3 ranged from 2.1 μeq 1−1 (site A)
to 0.97 μeq1 1 (site C).The mean nss (non-sea-salt)
SO4
2-/SO4
2- ratio was -0.055,0.54 and 0.42 at sites A, B and C,
respectively. Moreover, the relationship between a2+,
nssCa2+, SO4
2- and nssSO4 was quite different at
sites B and C. in order to expla in the relationships between the elements and
compounds studied at these sites, chemical fractionation and/or reactions inside
air masses and différent origin of the air masses at the two sites should be
considered.

A comparison of the isotopic and chemical profiles was carried out in order
to provide a more reliable chronological scale. The chemical and
δ18O seasonal variations recorded along the firn cores
from the upper site of Campbell Glacier seem to be fairly homogeneous. This made
it possible to identify many annual cycles (14-18 years for the 7 m firn core).
Using the measured density values, the accumulation rale was also calculated for
lower and upper Campbell Glacier. It did not appear to differ between the two
sites (150-170 kg m −2a−1 at site B and
140-180 kg m−2a−1at site C) and is in
keeping with rates calculated previously for the same area.
Inorganic carbon-isotope distribution and budget in the Lake Hoare and Lake
Fryxell basins, Taylor Valley, Antarctica
Authors: Neumann Klaus , Lyons W. Berry , Des Marais David J.
Published: November 2017

One of the unusual features of Lakes Fryxell and Hnare in Taylor Valley,
southern Victoria Land, Antarctica, is their perennial ice cover. This ice cover
limits gas exchange between the atmosphere and the lake water, and causesa very
stable stratification of the lakes. We analyzed a series of water samples from
profiles of these lakes and their tributaries for δ13C of the
dissolved inorganic carbon (DIC) in order to qualify the carbon flux from the
streams into the lakes, and to investigate the carbon cycling with in the lakes.
Isotopic values in the uppermost waters (δ13C = +l.3‰ to 5.3‰
in Lake Hoare, +0.4‰ to +3.0‰ in Lake Fryxell) are close to the carbon-isotope
values encountered in the streams feeding Lake Fryxell, but distinctively heavier
than in streams feeding Lake Hoare (δ13C= — 2.3%n to 1.4%).
These ratios are much heavier than ratios found in the moat that forms around the
lakes injanuary February (δC = -10.1%). in the oxic
photic zones of the lakes, photosynthesis clearly influences the isotopic
composition, with layers of high productivity having enriched carbon-isotope
signatures δ13C= +2.7‰ to +6.1‰). in both lakes, the isotopic
values become lighter with depth, reaching minima of 3.2‰ and 4.0% in Lakes
Fryxell and Hoare, respectively. These minima are caused by the microbial
remineralization of isotopically light organic carbon. We present DIC flux
calculations that help to interpret the isotopic distribution. For example, in
Lake Hoare the higher utilization of CO2aq, and a
substantially smaller inflow of CO2 from streams cause the
heavier observed isotopic ratios. Differences in the hydrology and stream
morphologies of the tributaries also greatly influence the carbon budgets of the
basins.
Arctic and Antarctic lakes as optical indicators of global change
Authors: Evincent Warwick E. , Laurion Isabelle , Pienitz Reinhard
Published: November 2017

Lakes are a major feature of Arctic and Antarctic landscapes and are likely
to be sensitive indicators ofclimate change. New bio-optical technologies for in
situ measurements (e.g. UV-profiling) and remote sensing (e.g. light detection and
ranging) now offer a suite of options for long-term monitoring at these sites.
Certain properties of high-latitude lakes are highly responsive to changes in
climate forcing and could be targeted within a monitoring strategy based on
optical properties; these include lake levels, lake-ice dynamics, phytoplankton
biomass and chromophoric dissolved organic matter (CDOM). High-latitude lakes are
optically sensitive to changes in CDOM export from their surrounding catchments
that could result from climate effects on hydrology and vegetation. Using a new
model based on biologically weighted transparency, we show that a 20% change in
GDOM concentration (as measured by dissolved organic carbon) can have a much
greater effect on UV inhibition of phytoplankton than a similar percentage change
in stratospheric ozone. Much of this effect is due to UV-A, because the reduced
photodamaging effect per unit energy (i.e. low biological weighting) in this
waveband is offset by its higher incident flux at the lake surface relative to
UV-B and its deeper penetration into the water column. These transparency
calculations also show that small changes in CDOM in polar lakes will have a large
effect on underwater light availability for photosynthesis. The spectral
absorption and fluorescence properties of CDOM lend themselves to a variety of
optical monitoring approaches. Future research on the paleo-optics of GDOM will
allow the interpretation of current optical trends in high-latitude lakes relative
to the scales of natural variability in the past.
Antarctic non-stationary signals derived from Seasat-ERS-1 altimetry
comparison
Authors: Rémy Frédérique , Benoit Legrésy
Published: November 2017

Geographical changes in the height of the Antarctic ice sheet between 1978
and 1992 are mapped using altimeter data from Seasat and ERS-1 via an inverse
technique that allows us to take imo account the whole altimctric error budget. in
a belt between 70° and 72° S and between 150° and 80° E, a precision better than
40 cm is found for the surface elevation change, while the change in height
averaged in the along-slopc direction has a precision of around 10-20 cm, leading
to a precision better than 10% of the mass balance. These data suggest a relative
positive imbalance of around 20% in this sector for the western and high-altitude
areas, and a relative negative imbalance in some areas of lower altitude.
The possible effects of including ridge-related roughness in
air–ice drag parameterization: a sensitivity study
Authors: Tremblay L. -B. , Mysak L. A.
Published: November 2017

The effects on ice-thickness distribution of including ridge-related
roughness in the drag parameterization is investigated using a sea-ice
dynamic and thermodynamic model. A long-term integration of the sea-ice
model forced by a 5 day running mean of daily geostrophic winds and steady
but spatially varying ocean currents was performed to construct
climatological thickness fields. Compared to a constant drag coefficient
model, results that include roughness have a significantly different spatial
distribution with much thicker ice in the western Arctic. These results
match observations better than those where ice roughness was omitted.
On the improvement of sea-ice models for climate simulations:
the Sea Ice Model Intercomparison Project
Authors: Lemke Peter , Hibler W.D. , Flato G. , Harder M. , Kreyscher M.
Published: November 2017

Experiments with dynamic thermodynamic sea-ice models indicate a strong
dependence of the net freezing rate, sea-ice transport and variability on
dynamic model parameters. Although current dynamic—thermodynamic sea-ice
models show relatively good agreement with observations, an optimization
seems to be necessary, especially for the parameterizations of dynamic
processes.

Presently, only a few coupled climate models use dynamic-thermodynamic
sea-ice models. In order to promote, by means of coordinated numerical
experiments, the development of an optimal sea-ice model for climate
research, the Sea Ice Ocean Modelling Panel of the Arctic Climate System
Study (ACSYS, a project of the World Climate Research Programme has
initiated the Sea Ice Model Intercomparison Project (SIMIP). The first
results from this model hierarchy approach are presented.
Calculation of solar-energy inputs into melt
ponds
Authors: Podgorny Igor A.
Published: November 2017

The emphasis of this paper is on the partitioning of solar energy in an open
plane-parallel melt pond with a Lambertian bottom. Spectral radiative-energy
fluxes into the meltwater and underlying ice ocean layers are calculated
analytically as a function of pond-bottom spectral albedo, pond depth and
illumination condition Albedo of the pond bottom is reconstructed from data
on pond albedo and depth. Results of calculations are presented for melt
ponds of comparatively high and comparatively low reflectivity for a broad
range of pond depths and for various illumination conditions. In the 350–700
nm spectral band, spectrally averaged pond albedo and solar-energy inputs
are a function of pond-bottom albedo, pond depth and illumination condition.
In the 700–2400 nm spectral band, the partitioning of solar energy in melt
ponds depends on pond depth and illumination condition only. The effect of
uncertainty in specifying pond-bottom albedo on total energy input into the
water layer is relatively small compared to that on spectrally averaged pond
albedo and total energy input into the ice-ocean layer.
Areal distribution of the oxygen-isotope ratio in
Greenland
Authors: Zwally H. Jay , Giovinetto Mario B.
Published: November 2017

Mean values of the oxygen-isotope ratio relative to standard mean ocean
water (δ18O, in ‰) reported for 46 sites on the Greenland ice sheet are
compiled together with data on mean annual surface temperature, latitude,
δ18O elevation, and mean annual shortest distance to the open
ocean denoted by the 10% sea-ice concentration boundary. Stepwise regression
analyses, with δ18O as the dependent variable, define two robust models. In the
forward mode at the 99.9% confidence level, only temperature enters the
model. In the backward mode at the 95% confidence level, only temperature,
latitude and distance to the open ocean remain in the model. Inversions of
the models on the basis of 160 gridpoint locations 100 km apart in the area
delimited by the surface equilibrium line produce four contoured
distributions of δ18O. Two distributions are based on the bivarrate model and two
on the multivariate model. The second distribution for each model is
obtained substituting mean annual surface-temperature values obtained from
the Nimbus-7 Temperature Humidity Infrared Radiometer (THIR) database. All
four distributions are considered valid, and differences between them are
evaluated using contoured anomaly maps. It is suggested that the inversion
of the multivariate model using THIR data provides the more reliable pattern
for studies of atmospheric advection or for the derivation of ice-flow
adjustments for δ18O series obtained from deep-core or ablation-zone sites.
An assessment of the regional distribution of the oxygen-isotope
ratio in northeastern canada
Authors: Giovinetto Mario B. , Holdsworth Gerald , Fisher David A. , Waters Nigel M. , Zwally H. Jay
Published: November 2017

A compilation of mean values of the oxygen-isotope ratio relative to
standard mean ocean water (δ18O, in ‰) for 22 siIes
representative of conditions in northeastern Canada is complemented with
data on mean annual surface temperature, latitude, surface elevation, and
mean annual shortest distance to open ocean denoted by the 10% sea-ice
concentration boundary. Stepwise regression analysis is used to develop a
multivariate model suitable to inter the distribution of δ18O in
an area of complex topography and possibly mixed sourcing of advected water
vapor. The best model is produced by a run in the backward mode at the 95%
confidence level in which only temperature, latitude and distance to the
open ocean remain in the model (the correlation coefficient is 0.915, the
adjusted coefficient of determination is 0.809, the root mean square
residual is 1.62). This model is similar to the best δ18O
predictive model derived elsewhere for Greenland, suggesting a common
principal source of advected moisture.
Hemispheric snow cover and surface albedo for model
validation
Authors: Robinson David A.
Published: November 2017

Accurate information concerning snow cover, and associated impacts of snow
on regional surface albedo, needs to be available for empirical studies and
for the validation of climate models. Here, a new integrated dataset for
Northern Hemisphere lands is discussed, including files of visible and
microwave satellite-derived snow estimates and in situ station data. These
files will be used to examine snow extent, snow depth and surface albedo
over five-day intervals, and have been generated using
geographic-information system techniques. Visible and station observations
extend from 1972 to present, and microwave estimates from 1979 to present,
The 1×1° gridded files permit the strengths and weaknesses of the individual
data sources to be identified and quantified. Also included is a hemispheric
time series of snow extern derived from the visible satellite file. Of note
are the two pronounced regimes of Northern Hemisphere extent during the past
several decades. Between 1972 and 1985, 12 month running means of snow
extent fluctuated around a mean of 25.9 × 106 km2. An
abrupt transition occurred in 1986 and 1987, and since then mean annual
extern has been 24.2 × 106 km2. Recent decreases are
found from late winter to early summer.
Modeling the Antarctic ice sheet
Authors: Verbitsky Mikhail , Saltzman Barry
Published: November 2017

A three-dimensional (3-D), high-resolution, non-linearly viscous,
non-isothermal ice-sheet model is employed to calculate the “present-day”
equilibrium regime of the Antarctic ice sheet and its evolution during the
last glacial cycle. The model is augmented by an approximate formula for
ice-sheet basal temperature, based on a scaling of the thermodynamic
equation for the ice flow. Steady-state solutions for both the shape and
extent of the areas of basal melting (or freezing) are shown to be in good
agreement with those obtained from the solution of the full 3-D
thermodynamic equation. The solution for the basal temperature field of the
West Antarctic Siple Coast produces areas at the pressure-melting point
separated by strips of frozen-to-bed ice, the structure of which is
reminiscent of Ice Streams A–E. This configuration appears to be robust,
preserving its features in spite of climatic changes during the last glacial
cycle. Ice Stream C seems to be more vulnerable to stagnation, switching to
a passive mode at least once during the penultimate interglacial. We
conjecture that the peculiarities of local topography determine the unique
behavior of Ice Stream C: reduced basal stress and, consequently, relatively
weak warming due to internal friction and basal sliding is not able to
counteract the advective cooling during the periods of increased snowfall
rate.
Impact of sea-ice formation on the properties of Antarctic
bottom water
Authors: Goosse H. , Campin J. M. , Fichefet T. , Deleersnijder E.
Published: November 2017

It is generally accepted that fresh-water fluxes due to ice accretion or
melting profoundly influence the formation of Antarctic bottom water (AABW).
This is investigated by means of a global, three-dimensional ice–ocean
model. Two model runs were conducted. At the high southern latitudes, the
control experiment exhibits positive (i.e. towards the ocean) fresh-water
fluxes over the deep ocean, and large negative fluxes over the Antarctic
continental shelf, because of the intense ice-production taking place in
this region. The salinity of shelf water can increase in such a way that
deep-water formation is facilitated. The simulated net fresh-water flux over
the shelf has an annual mean value of −1 m a−1. This flux induces
a transport of salt to bottom waters, which corresponds to an increase of
their salinity estimated to be around 0.05 psu. In the second model run, the
fresh-water fluxes due to ice melting or freezing are neglected, leading to
a rearrangement of the water masses. In particular, the AABW-formation rate
decreases, which allows the influence of North Atlantic deep water (NADW) to
increase. As NADW is warmer and saltier than AABW, the bottom-water salinity
and temperature become higher.
Thermodynamic feedback processes in a single-column
sea-ice–ocean model
Authors: Holland Marika M. , Schramm Julie L. , Curry Judith A.
Published: November 2017

Due to large uncertainties in many of the parameters used to model sea ice,
it is possible that models with significantly different physical processes
can be tuned to obtain realistic present-day simulations. However, in
studies of climate change, it is the response of the model it various
perturbations that is important, in studies response can be significantly
different in sea-ice models that include or exclude various physical
feedback mechanisms. Because simplifications in sea-ice physics are
necessary for general circulation model experiments, it is important to
assess which physical processes are essential for the accurate determination
of the sensitivity of the ice pack to climate perturbations. We have
attempted to address these issues using a new coupled ice-thickness
distribution ocean mixed-layer model. The sensitivity of the model to
surface heat-flux perturbations is examined and the importance of the ice
ocean and ice-albedo feedback mechanisms in determining this sensitivity is
analyzed. We find that the ice ocean and ice-albedo feedback processes are
not mutually exclusive, and that they both significantly alter the model
response to surface heat flux perturbations.
Determination of a melt-onset date for Arctic sea-ice regions
using passive-microwave data
Authors: Anderson Mark R.
Published: November 2017

Although the formation and melt of sea ice are primarily functions of the
annual radiation cycle, atmospheric sensible-heat forcing does serve to
delay or advance the timing of such events. Additionally, if atmospheric
conditions in the Arctic were to vary due to climate change it may have
significant influence on ice conditions. Therefore, this paper investigates
a methodology to determine melt-onset dale distribution, both spatially and
temporally, in the Arctic Ocean and surrounding sea-ice covered regions.

Melt determination is made by a threshold technique using the spectral
signatures of the horizontal brightness temperatures (19 GHz horizontal
channel minus the 37 GHz horizontal channel) obtained from the Special
Sensor Microwave Imager (SSM/I) passive-microwave sensor. Passive-microwave
observations are used to identify melt because of the large increase in
emissivity that occurs when liquid water is present. Emissivity variations
are observed in the brightness temperatures due to the different scattering,
absorption and penetration depths of the snowpack from the available
satellite channels during melt. Monitoring the variations in the brightness
temperatures allows the determination of melt-onset dates.

Analysis of daily brightness temperature data allows spatial variations in
the date of the snow inch onset for sea ice to be detected. Since the data
are gridded on a daily basis, a climatology of daily melt-onset dates can be
produced for the Arctic region. From this climatology, progression of melt
can be obtained and compared inter-annually.
AVHRR-based Polar Pathfinder products for modeling
applications
Authors: Maslanik James , Fowler Charles , Key Jeffrey , Scambos Ted , Hutchinson Todd , Emery William
Published: November 2017

A suite of Arctic and Antarctic products is being prepared from Advanced
Very High Resolution Radiometer (AVHRR) and ancillary data as part of NASA’s
Polar Pathfinder effort. These products consist of twice-daily gridded
fields of clear-sky surface temperature, surface albedo and cloud fraction,
as well as daily ice velocities, for 1983–96. The products and their
production methodology are summarized here, with examples demonstrating
applications of the Pathfinder products for process studies and
modeling.
On the potential use of glacier and permafrost observations for
verification of climate models
Authors: Beniston Martin , Haeberli Wilfried , Hoelzle Martin , Taylor Alan
Published: November 2017

While the capability of global and regional climate models in reproducing
current climate has significantly improved over the past few years, the
confidence in model results for remote regions, or those where complex
orography is a dominant feature, is still relatively low. This is, in part,
linked to the lack of observational data for model verification and
intercomparison purposes.

Glacier and permafrost observations are directly related to past and present
energy flux patterns at the Earth-atmosphere interface and could be used as
a proxy for air temperature and precipitation, particularly of value in
remote mountain regions and boreal and Arctic zones where instrumental
climate records are sparse or non-existent. It is particularly important to
verify climate-model performance in these regions, as this is where most
general circulation models (GCMs) predict the greatest changes in air
temperatures in a warmer global climate.

Existing datasets from glacier and permafrost monitoring sites in remote and
high altitudes are described in this paper; the data could be used in
model-verification studies, as a means to improving model performance in
these regions.
Geometry response of glaciers to changes in spatial pattern of
mass balance
Authors: Boudreaux Andrew , Raymond Charles
Published: November 2017

The effect of the spatial pattern of mass balance on the steady-state
geometry of a glacier is examined using a Vialov -Nye glacier-flow model
based on non-linear internal deformation of the ice with no basal motion.
Surface profiles are predicted using a range of spatial variations of mass
balance that include uniform shifts that cause a change in the mean and
spatial patterns with zero mean representing changes in balance gradient and
curvature. The corresponding effect on geometry induced by the different
mass-balance patterns are described in terms of the volume and measures of
surface slope and convexity. The change in glacier volume, slope and
convexity induced by uniform changes in mass balance with non-zero mean are
more than one order of magnitude larger than corresponding changes caused by
spatial patterns of similar amplitude, but with zero mean. These results
show that the mean mass balance contains most of the mass-balance
information relevant to the dynamic changes of a glacier. An important
consequence is that the memory of a change in climate, which is controlled
by the consequent volume change, should be insensitive to the spatial
pattern other than how that affects the mean. The spatial pattern of mass
balance does induce small changes in the shape of the steady-state profile,
which indicates the spatial pattern could affect the short time-scale
response characteristics.
An improved elevation dataset for climate and ice-sheet
modelling: validation with satellite imagery
Authors: Bamber J. L. , Bindschadler R. A.
Published: November 2017

Recent studies by several groups have indicated that the performance of
general circulation models (GCMs) over the ice sheets is severely limited by
the relatively low resolution of the models at the margins, where surface
slopes are greatest. To provide accurate energy-budget estimates,
resolutions of better than 0.5° are desirable, requiring nested or multiple
gridding and accurate, high-resolution boundary conditions. Here we present
a new, high-resolution (5 km) digital elevation model for the Antarctic ice
sheet, derived from radar-altimeter data obtained from the geodetic phase of
the satellite, ERS-1. These data have been combined with the revised
ice-thickness grid reported in Bamber and
Huybrechts (1996) to produce a bed- and surface-elevation dataset
for use in regional and global climate and paleo-climaie modelling
applications. The real level of spatial detail in the datasets has been
examined with the aid of Landsat Thematic Mapper data. Imagery around Ice
Stream D, West Antarctica, shows that the revised ice-thickness grid is
accurately geolocated, and contains valuable fine-scale topographic detail
beyond that available from the cartographic version of the data (Drewry, 1983). The surface topography in
the region of the Ross Ice Shelf has been used to illustrate the level of
detail in both the vertical and horizontal resolution of (he surface
dataset. Laudsat data has also been used to examine features in the
surface-elevation data. In particular, the location of the grounding zone,
for Ice Streams D and E, derived from the two data sources shows good
agreement. The results of this validation underscore the utility of the new
datasets for high-resolution modelling, and highlight the limitations of the
Folio maps for such applications.
Areal distribution of the oxygen-isotope ratio in Antarctica: comparison of
results based on field and remotely sensed data
Authors: Zwally H. Jay , Giovinetto Mario , Craven Mike , Morgan Vin , Goodwin Ian
Published: November 2017

An updated compilation of oxygen-isotope ratio data for 562 sites in
Antarctica shows a significant increase in the number of sites and an improvement
in the representation of the coastal zone oyer previous versions. The data hase
consists of ratio values (δ18O; multi-year mean
18O/16O relative to Standard Mean
Ocean Water, in ‰) compiled as the dependent variable, together with data for the
so-called independent variables: latitude, surface elevation, mean annual surface
temperature and mean annual shortest distance to open ocean denoted by the 20%
sea-ice concentration boundary. The problem of covariation between so-called
independent variables is minimized using stepwise regression analyses. A general
model is described using all the field data, and the regional variation at
drainage-system scale is assessed by contrasting models for two physiographically
distinct regions. in addition, entity-specific models are determined using data
subsets for the conterminous grounded-ice and ice-shelf areas. Inversions of the
specific models are applied to a 100 km grid data base to produce two contoured
distributions of the ratio, one based on field data, and the other on remotely
sensed data. The difference between these produces residuals that, relative to the
summation of standard errors of the models, are small in most of the interior area
of the ice sheet, and large in several areas of mountain and coastal regions,
where interpolation and extrapolation of field data are particularly unreliable.
Remotely sensed data generally produce ratio values which are isotopically
cooler.
Effects of Amerindian Genetic Ancestry on Clinical Variables and Therapy in Patients with Rheumatoid Arthritis
Authors: Sánchez Elena , García de la Torre Ignacio , Sacnún Mónica , Goñi Mario , Berbotto Guillermo , Paira Sergio , Musuruana Jorge Luis , Graf César , Alvarellos Alejandro , Messina Osvaldo D. , Babini Alejandra , Strusberg Ingrid , Marcos Juan Carlos , Scherbarth Hugo , Spindler Alberto , Quinteros Ana , Toloza Sergio , Moreno José Luis C. , Catoggio Luis J. , Tate Guillermo , Eimon Alicia , Citera Gustavo , Pellet Antonio Catalán , Nasswetter Gustavo , Cardiel Mario H. , Miranda Pedro , Ballesteros Francisco , Esquivel-Valerio Jorge A. , Maradiaga-Ceceña Marco A. , Acevedo-Vásquez Eduardo M. , García Conrado García , Tusié-Luna Teresa , Pons-Estel Bernardo A. , Alarcón-Riquelme Marta E. ,   the GENAR Study
Published: November 2017

Objective.

To define whether Amerindian genetic ancestry correlates with clinical and therapeutic variables in admixed individuals with rheumatoid arthritis (RA) from Latin America.

Methods.

Patients with RA (n = 1347) and healthy controls (n = 1012) from Argentina, Mexico, Chile, and Peru were included. Samples were genotyped for the Immunochip v1 using the Illumina platform. Clinical data were obtained through interviews or the clinical history.

Results.

Percentage of Amerindian ancestry was comparable between cases and controls. Morning stiffness (p < 0.0001, OR 0.05), rheumatoid factor (RF; p < 0.0001, OR 0.22), radiographic changes (p < 0.0001, OR 0.05), and higher number of criteria were associated with lower Amerindian ancestry after Bonferroni correction. Higher Amerindian ancestry correlated only with weight loss (pBonferroni < 0.0001, OR 2.85). Increased Amerindian ancestry correlated with higher doses of azathioprine (p < 0.0001, OR 163.6) and sulfasalazine (p < 0.0001, OR 48.6), and inversely with methotrexate (p = 0.001, OR 0.35), leflunomide (p = 0.001, OR 0.16), and nonsteroidal antiinflammatory drugs (pBonferroni = 0.001, OR 0.37). Only the presence of RF and weight loss were modified after confounders adjustment.

Conclusion.

Amerindian ancestry protects against most major clinical criteria of RA, but regarding the association of RF with increased European ancestry, age, sex, and smoking are modifiers. Ancestry also correlates with the therapeutic profiles.